Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In the present work we study Zn+O divacancies filled up with varying amount of hydrogen atoms. Besides the structure and energy-related properties of such defects, we also investigate their capability to trap positrons taking into account positron induced forces. We show that the Zn+O divacancy may trap positrons when up to two hydrogen atoms are located inside the divacancy. The calculated properties are discussed in the context of other computational and experimental studies of ZnO.

In the present work we study theoretically hydrogen incorporated into several positions in the zirconia cubic and tetragonal lattices. These are positions in the interstitial space and in the zirconium vacancy (VZr). We examine the structure of such configurations and for VZr-related defects we also calculate selected positron characteristics in order to assess their capability of trapping positrons. It is shown that hydrogen atoms do not prefer to stay in the center of the largest interstitial space nor of VZr and they rather tend to create bonds with neighboring oxygen atoms. The positron lifetime of the VZr+1H complex is shorter than that for non-decorated VZr and positron trapping in VZr+1H complexes could, in principle, explain experimental lifetime data.

Intermetallic Fe-Al alloys are perspective materials for industrial applications at elevated temperatures. A high concentration of vacancies is a specific feature of such alloys. The equilibrium concentration of thermal vacancies in these alloys is considerably higher than in pure metals and may be as high as several at.%. Moreover, a high concentration of thermal vacancies existing at elevated temperatures can be quenched-in down to room temperature. Hence, a detailed investigation of vacancies and other vacancy-like defects in Fe-Al based alloys is necessary for a deeper understanding of the physical properties of these materials.

Quenched-in vacancies in Fe-Al alloys were investigated in this work employing three complementary techniques of positron annihilation: Doppler broadening spectroscopy performed using a variable energy slow positron beam (SPIS = slow positron implantation spectroscopy), coincidence Doppler broadening (CDB) spectroscopy and positron lifetime (LT) measurements. It was found that quenched alloys exhibit a high concentration of vacancies. Although a free positron component cannot be resolved in our LT spectra, the concentration of quenched-in vacancies can still be determined from the shortening of the positron diffusion length measured by SPIS. Hence, SPIS is a very important technique for the investigation of defect-rich materials, like quenched Fe-Al alloys.

In the present work, the concentration of quenched-in vacancies was determined in Fe-Al based alloys at various Al content ranging from 24 up to 45 at.-%. The lowest concentration of quenched-in vacancies was found in the stoichiometric Fe3Al alloy, i.e. an alloy with an Al concentration of 25 at.-%. This concentration increases with an increasing degree of non-stoichiometry with respect to Fe3Al. Hence, the concentration of quenched-in vacancies increases both in alloys with under-stoichiometric as well as in those with over-stoichiometric Al content. However, the increase in concentration is more pronounced in the Al-rich alloys, i.e. alloys containing more than 25 at.% of Al. CDB revealed that quenched-in vacancies are surrounded predominantly by Al atoms which indicates that they occupy predominantly the Fe sub-lattice.

Yttria stabilized zirconia (YSZ) has a big potential of use in a wide area of high-temperature applications. Although pure zirconia is monoclinic at room temperature and exhibits relatively poor mechanical properties, high temperature tetragonal or cubic zirconia phases with superior properties can be stabilized down to room temperature by the addition of an appropriate amount of yttria (Y2O3). The deviation from stoichiometry caused by the addition of trivalent yttrium ions leads to the formation of a high density of point defects in YSZ. These defects are believed to influence significantly not only phase stabilization itself but also material characteristics of YSZ’s important for their practical use. Hence, the detailed characterization of defects in YSZ is a very important task.
In this work we performed a thorough investigation of point defects in tetragonal and cubic YSZ single crystals. Experimental data were obtained by three complementary techniques of positron annihilation spectroscopy (PAS), namely slow positron implantation spectroscopy, positron lifetime measurements, and coincidence Doppler broadening. The interpretation of PAS data was performed with the help of state-of-the-art ab-inito theoretical calculations of positron parameters for various types of vacancy-like defects.
Present experimental data suggest that both tetragonal and cubic YSZ single crystals contain a high concentration of vacancy-like defects. Theoretical calculations showed that neither oxygen vacancies nor their neutral complexes with substitute yttrium atoms are capable of positron trapping. On the other hand, zirconium vacancies are deep positron traps and most probably responsible for positron trapping observed in YSZ single crystals. However, the calculated positron lifetime for a zirconium vacancy is apparently longer than the experimental value estimated for YSZ single crystals. We argue that this effect could be explained by hydrogen atoms trapped at zirconium vacancies. On the basis of structure relaxations, we found that zirconium vacancy – hydrogen complexes represent positron traps with the calculated lifetimes close to the experimental ones. In the vicinity of a zirconium vacancy the hydrogen atom forms an O-H bond with one of the nearest neighbour oxygen atoms. This result testifies that hydrogen is an important impurity in YSZ which strongly interacts with vacancies. Hence, the hydrogen content in YSZ materials should be considered as a very important parameter. In this work, therefore, we employed also nuclear reaction analysis for a determination of the hydrogen content in YSZ single crystals. It was found that the hydrogen content in our studied samples is in a range of 0.1-0.3 at.-%, which is sufficient for the formation of hydrogen complexes with zirconium vacancies capable of saturated positron trapping.

ZnO is a wide band gap semiconductor with a variety of applications including UV light emitting diodes and lasers, optoelectronic devices, and gas sensors. Due to a progress in crystal growth, high quality single crystals are nowadays available. However, properties which are essential for any of the applications mentioned are significantly influenced by the presence of lattice defects. A detailed characterization of lattice defects in ZnO crystals is, therefore, a key task in order to understand their physical properties. Defect studies of hydrothermally grown ZnO single crystals revealed that hydrogen is the most important impurity in ZnO crystals [1]. It was found that hydrogen is coupled with zinc vacancies in the form of vacancy-hydrogen complexes. Moreover, it has been demonstrated that a huge amount of hydrogen (30 at.-%) can be introduced into ZnO crystals by electrochemical loading [2].

Surface changes in ZnO crystals electrochemically doped with hydrogen were investigated in this work using slow positron implantation spectroscopy (SPIS) combined with atomic force microscopy (AFM) and optical microscopy (OM). It was found that hexagonally shaped pyramids were formed on the surface (Fig. 1). All these pyramids have the same crystallographic orientation as the ZnO matrix. The formation of pyramids can be explained by hydrogen-induced plastic deformation which is realized by slip in the [0001] direction. Such a picture is supported (i) by AFM where terraces of a height comparable with the c-lattice parameter were found at the base of the pyramids, and (ii) by SPIS which revealed a defected subsurface layer, being formed by the hydrogen-induced plastic deformation and exhibiting an enhanced concentration of open-volume defects.

Fig. 1 Optical microscopy image (taken using oblique light) of the surface of a ZnO crystal electrochemically loaded with hydrogen.

References
[1] G. Brauer, et al., Phys. Rev. B 79, 115212 (2009).
[2] J. Čížek, et al., J. Appl. Phys. 103, 053508 (2008).

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The visual photoreceptor rhodopsin is a proto¬typical class-I (rhodopsin-like) G protein-coupled receptor (GPCR). Photoisomerization of the covalently bound ligand 11-cis-retinal leads to restructuring of the cytosolic face of rhodopsin. The ensuing protonation of Glu-134 in the class-conserved D(E)RY motif at the C-terminal end of trans¬membrane helix-3 promotes the formation of the G-protein-activating state. Using trans¬mem¬brane segments derived from helix-3 of bovine rhodopsin, we show that lipid protein interactions play a key role in this cytosolic "proton switch". Infra¬red- and fluo¬res¬cence-spectroscopic pKa deter¬minations reveal that the D(E)RY motif is an auto¬no¬mous functional module coupling side chain neu¬trali¬za¬tion to conformation and helix positio¬ning as evidenced by side chain to lipid headgroup Foerster-re¬so¬nance-energy-transfer. Using rapid scan FTIR spectroscopy, we show that the motif is also a local protonein hydration site. This dual function renders the proton acceptor group a key residue in conformational control by positioning helix-3 at the water lipid protein interface.

As the first superconducting rf photo-injector (SRF gun) in practice, the FZD 3+1/2 cell SRF gun is successfully connected to the superconducting linac ELBE. This setting will improve the beam quality for ELBE users. It is the first example for an accelerator facility fully based on superconducting RF technology. For high average power FEL and ERL sources, the combination of SRF linac and SRF gun provides a new chance to produce beams of high average current and low emittance with relative low power consumption.
The main parameters achieved from the present SRF gun are the final electron energy of 3 MeV, 16 μA average current, and rms transverse normalized emittances of 3 mm mrad at 77 pC bunch charge. A modified 3+1/2 cell niobium cavity has been fabricated and tested, which will increase the rf gradient in the gun and thus better the beam parameters further. In this paper the status of the integration of the SRF gun with the ELBE linac will be presented, and the latest results of the beam experiments will be discussed.

At the superconducting LINAC ELBE [1] at Research Centre Dresden-Rossendorf the new facility for Gamma-induced Positron Spectroscopy (GiPS) is successfully running [2] and first measurements were done. Two AMOC (Age Momentum Correlation) spectrometers (each consisting of a barium fluoride timing detector and a high purity germanium detector for measuring the energy) and a detector setup for Coincidence Doppler Broadening Spectroscopy allow to measure standard positron techniques simultaneously.
Influences from the surroundings (e.g. randomly scattered photons) disturb the recorded energy and lifetime spectra (increase of background, several peaks in lifetime spectra). Therefore it is of great importance to avoid such disturbing influences and to get clear and corrected spectra.
Recent efforts to optimize the setup and to eliminate the negative influences of the surroundings are presented. Selected results of first measurements with GiPS show the great potential of this unique facility.

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The structure of neutron rich nitrogen nuclei has been studied by use of neutron removal reaction and inelastic scattering. Mass and charge deformations have been deduced for the first excited state of 21N, which indicates the partial persitence of the N=14 subshell closure in nitrogen isotopes. The spectroscopic information obtained on the structure of 19,20,21N confirms the results from a previous experiment.

no abstract available

The increasing age of the European NPPs and envisaged lifetime extensions up to 80 years require an improved understanding of RPV irradiation embrittlement effects connected with long term operation (LTO). Phenomena which might become important at high neutron fluences (such as late blooming effects and flux effects) must be considered adequately in the safety assessments. Therefore the project LONGLIFE was initiated within the 7th Framework Programme of the European Commission. The project aims at: i) improved knowledge on LTO phenomena relevant for European reactors; ii) assessment of prediction tools, codes, standards and surveillance guidelines. In the paper, we give an overview of the project structure and the related tasks. Furthermore we present two examples for the experimental evidence of LTO relevant phenomena: the first example is related to the flux dependence of defect cluster formation in a neutron irradiated weld material. We have found that the size of the irradiation induced defects exhibits a flux effect whereas the mechanical properties are almost independent of the flux. The second example refers to the acceleration of irradiation hardening after exceeding a threshold fluence. This effect was observed by means of both small angle neutron scattering (SANS) and tensile testing for low Cu RPV steels irradiated at a temperature of 255°C. These examples demonstrate that LTO irradiation effects have to be investigated in more detail to guarantee the applicability of the embrittlement surveillance guidelines beyond 40 years of operation.

The complexation of U(VI) with humic acid (HA) in aqueous solution has been investigated at an ionic strength of 0.1 M (NaCl) in the pH range between pH 2 and 10 at different carbonate concentrations by attenuated total reflection Fourier-transform infrared (ATR FT IR) spectroscopy. For the first time, the formation of binary and ternary U(VI) humate complexes was directly verified by in-situ spectroscopic measurements. The complex formation constants for the binary U(VI) humate complex (UO₂HA_(II)) and the for ternary U(VI) mono hydroxo humate complex (UO₂(OH)HA_(I)) as well as the ternary U(VI) dicarbonato humate complex (UO₂(CO₃)₂HA_(II) ⁴⁻) determined from the spectroscopic data amount to log β_0.1 M = 6.70 ± 0.25, log β_0.1 M = 15.14 ± 0.25 and log β_0.1 M = 24.47 ± 0.70, respectively and verify literature data.

The use of radiopharmaceuticals for molecular imaging of biochemical and physiological processes in vivo has evolved into an important diagnostic tool in modern nuclear medicine and medical research. Positron emission tomography (PET) is currently the most sophisticated molecular imaging methodology, mainly due to the unrivalled high sensitivity which allows for the studying of biochemistry in vivo on the molecular level. The most frequently used radionuclides for PET have relatively short half-lives (e. g. C-11: 20.4 min; F-18: 109.8 min) which may limit both the synthesis procedures and the time frame of PET studies. Iodine-124 (I-124, t(1/2) = 4.2 d) is an alternative long-lived PET radionuclide attracting increasing interest for long term clinical and small animal PET studies. The present review gives a survey on the use of I-124 as promising PET radionuclide for molecular imaging. The first part describes the production of I-124. The second part covers basic radiochemistry with I-124 focused on the synthesis of I-124-labeled compounds for molecular imaging purposes. The review concludes with a summary and an outlook on the future prospective of using the long-lived positron emitter I-124 in the field of organic PET chemistry and molecular imaging.

An improved labeling procedure for peptides attached to organometallic ^99mTc(III) ‘4+1’ mixed-ligand complexes in which the radiometal is coordinated by a tripodal tetradentate chelator 2,2',2''-nitrilotriethanethiol (NS₃) and a monodentate isocyanide ligand is presented. The labeling procedure was evaluated by the synthesis of [^99mTc(NS₃)(L2-RGD)]. The containing radiopharmaceutically interesting RGD-peptide cyclo[Arg-Gly-Asp-D-Tyr-Lys] was modified with 4-isocyanobutanoic acid (L2) as linker conjugated to N⁶-Lys to get the monodentate ligand L2-RGD. The structural identity of the ^99mTc-conjugate was confirmed by comparison to a Re reference compound. The Tc- and Re-conjugates had matching retention times under identical HPLC conditions. The ^99mTc-labeling was performed in a novel one-step procedure using the eluate of a ⁹⁹Mo/^99mTc generator, NS₃, the isocyanide modified peptide, SnCl₂, Na₂EDTA, mannitol and ascorbic acid in the reaction mixture. Using optimized reagents it is possible to label 50 nmol peptide with ^99mTc within 60 min at room temperature with a radiochemical yield higher than 95% and a specific activity of ~20 GBq/mmol.

Experiments on the influence of 2.5 MeV proton irradiation on self- and dopant diffusion in germanium (Ge) were performed at 600 and 570°C, respectively. Ge isotope heterostructures consisting of 20 layers were used for the self-diffusion study. Ge with boron (B) doped multilayers and samples implanted with phosphorus (P) were utilized for the investigation of irradiation mediated dopant diffusion. Self-diffusion under irradiation reveals an unusual homogenous broadening of the isotope structure. This behaviour and the enhanced diffusion of B and retarded diffusion of P under irradiation demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This discovery establishes new ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that limits Ge-based nanoelectronics.

Review of recent results on electrical doping of Ge by ion implantation and ms flash lamp annealing, overview on atomistic simulation of solid phase epitaxial recrystallization of amorphous Ge

In case of in-vessel corium retention during a severe accident in a light water reactor, weakening of the vessel wall and deterioration of the vessel steel properties can be caused both by the melting of the steel and by its physicochemical interaction with corium. The interaction behavior has been studied in medium-scale experiments with prototypic corium. The experiments yielded data for the steel corrosion rate during interaction with UO2+X - ZrO2 - FeOy melt in air and steam at different steel surface temperatures and heat fluxes from the corium to the steel. It has been observed that the corrosion rates in air and steam atmosphere are almost the same. Further, if the temperature at the interface increases beyond a certain level, corrosion intensifies. This is explained by the formation of liquid phases in the interaction zone. The available experimental data have been used to develop a correlation for the corrosion rate as a function of temperature and heat flux.

This thesis addresses the evolution of nanoscale ripple patterns on solid surfaces during low-energy ion sputtering. Particular attention is paid to the long-time regime in which the surface evolution is dominated by nonlinear processes. This is explored in simulation and experiment.
In numerical simulations, the influence of anisotropy on the evolution of the surface patterns in the anisotropic stochastic Kuramoto-Sivashinsky (KS) equation with and without damping is studied. For a strong nonlinear anisotropy, a 90 rotation of the initial ripple pattern is observed and explained by anisotropic renormalization properties of the anisotropic KS equation. This explanation is supported by comparison with analytical predictions. In contrast to the isotropic stochastic KS equation, interrupted ripple coarsening is found in the presence of low damping. This coarsening seems to be a nonlinear anisotropy effect that occurs only in a narrow range of the nonlinear anisotropy parameter.
Ex-situ atomic force microscopy (AFM) investigations of Si(100) surfaces sputtered with sub-keV Ar ions under oblique ion incidence show the formation of a periodic ripple pattern. This pattern is oriented normal to the direction of the ion beam and has a periodicity well below 100 nm. With increasing ion fluence, the ripple pattern is superposed by larger corrugations that form another quasi-periodic pattern at high fluences.
This ripple-like pattern is oriented parallel to the direction of the ion beam and has a periodicity of around one micrometer. Interrupted wavelength coarsening is observed for both patterns. A dynamic scaling analysis of the AFM images shows the appearance of anisotropic scaling at large lateral scales and high fluences. Based on comparison with the predictions of different nonlinear continuum models, the recent hydrodynamic model of ion erosion, a generalization of the anisotropic KS equation, is considered as a potentially powerful continuum description of this experiment.
In further in-situ experiments, the dependence of the dynamic scaling behavior of the sputtered Si surface on small variations of the angle of incidence is investigated by grazing incidence small angle X-ray scattering (GISAXS). A transition from strongly anisotropic to isotropic scaling is observed. This indicates the presence of at least two fixed points in the system, an anisotropic and an isotropic one. The dynamic scaling exponents of the isotropic fixed point are in reasonable agreement with those of the Kardar-Parisi-Zhang (KPZ) equation. It remains to be seen whether the hydrodynamic model is able to show such a transition from anisotropic to isotropic KPZ-like scaling.

The Rossendorf Beamline (ROBL) - located at BM20 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France - is in operation since 1998. This 6th report covers the period from January 2007 to December 2008. In these two years, 50 peerreviewed papers have been published based on experiments done at the beamline. The average citation index, which increased constantly over the years, has now reached 3.5 (RCH) and 3.0 (MRH), indicating that papers are predominately published in journals with high impact factors. Six exemplary highlight reports on the following pages should demonstrate the scientific strength and diversity of the experiments performed on the two end-stations of the beamline, dedicated to Radiochemistry (RCH) and Materials Research (MRH).
Demand for beamtime remains very high as in the previous years, with an average oversubscription rate of 1.8 for ESRF experiments. The attractiveness of our beamline is based upon the high specialization of its two end-stations. RCH is one of only two stations in Europe dedicated to x-ray absorption spectroscopy of actinides and other radionuclides. The INE beamline at ANKA provides superior experimental flexibility and extends to lower energies, including important elements like P and S. In contrast, ROBL-RCH provides a much higher photon flux, hence lower detection limits crucial for environmental samples, and a higher energy range extending to elements like Sb and I. Therefore, both beamlines are highly complementary, covering different aspects of radiochemistry research. Once the MARS beamline at SOLEIL is ready to run radionuclides (>2010), it will cover a third niche (Materials Science of actinides, including irradiated fuel) not accessible for the two other beamlines.
The Materials Research Hutch MRH has realized an increasing number of in-situ investigations in the last years. On the one hand thin film systems were characterized during magnetron sputtering. On the other hand diffraction experiments under controlled atmosphere were performed. A high variety of experimental parameters was covered by varying pressure, temperature and atmospheric compositions including highly reactive gases. Furthermore structural investigations were combined with electrical conductivity measurements. These kind of in-situ experiments are the key to monitor and understand reaction mechanism or the influence of process parameters, which are again the basis to tailor materials properties on demand. The core competences of MRH are these experimental possibilities, which make it unique among other diffraction beamlines. In fall 2007, ROBL was reviewed by an international panel on behalf of the ESRF. The very positive panel report recommended a renewal of the contract between ESRF and FZD for the next five years, and a major upgrade of critical optical components of the beamline to keep ROBL competitive for the next decade. The FZD will provide 2 Mio € from 2009 to 2011 for this upgrade, which will be performed in parallel to the major upgrade of the ESRF to minimize the downtime. According to the current plans of the ESRF, our users have to expect that ROBL will have only limited or no operation for several months from August 2011 on.
Since July 2004 the beamline is a member of the pooled facilities of ACTINET – European Network of Excellence. In the reported period, RCH has provided 27 % of its inhouse beamtime to perform 11 ACTINET experiments. The success of ACTINET within FP-6 has now led to a renewal of ACTINET within FP-7, running until end of 2011.

The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of the Forschungszentrum Dresden-Rossendorf (FZD), and contributes the largest part to its Research Program "Advanced Materials", mainly in the fields of semiconductor physics and materials research using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users.

The formation of near surface SiGe layers by means of combined high dose Ge ion implantation and flash lamp annealing will be addressed. Furthermore, we show that the formation of an undesirable facetted liquid/solid in-terface, which is well known for pulse melting in the mil-lisecond time regime, is less pronounced due to the de-creasing melting temperature of Si with increasing Ge concentration at the SiGe/Si interface. A dislocation net-work, which is observed by using transmission electron microscopy, is expected to play an important role to form these thin SiGe layers. We will demonstrate the depth profiles of Ge by Rutherford backscattering spectrometry and discuss the concerned mechanism.

To determine the coefficient of thermal expansion of trigonal langasite (La3Ga5SiO14) the two independent lattice parameters a and c are measured over a temperature range of 800 degrees C using X-ray diffraction on single crystal samples. From the given nonlinear temperature dependence the linear and quadratic thermal coefficients of expansion alpha(11), beta(11) and alpha(33), beta(33) for the two lattice parameters a and c could be deduced.

We applied proton microbeam particle-induced X-ray emission (mu-PIXE) for mapping Ca, Zr, Ba and Yb, and atomic force microscopy (AFM) for imaging the surface landscape of a dental composite which releases Ca2+ and F- for the protection of hard dental tissues. Three areas,similar to 250 x 250 mu m(2) located similar to 0.5-2 mm apart on a smooth surface specimen were mapped with 3.1 MeV protons focused to a similar to 3.0 mu m spot and at similar to 3.9 mu m pixel size sampling. The maps evidenced particles with diameters of 3.2-32 mu m (Ca), 20-60 mu m (Zr), <= 4 mu m (Ba) and 10-50 mu m (Yb). Cross-section area histograms of Ca-rich particles fitted with 2-6 Poisson functions revealed a polydisperse size distribution and substantial differences from an area to another, possibly implying large local variations of Ca2+ released in the hard tissue near a dental filling of a few millimeters in diameter. Such imbalances may lead to low local Ca2+ protection of the dental tissue!
, favoring the onset of secondary caries. Similarly, AFM images showed high zone-dependent differences in the distributions of grains with apparent diameters of 1-4 mu m, plausibly recognized as Ca- and Ba-containing particles. In a simple model based on demineralization data, lateral diffusion of Ca2+ between adjacent domains containing high- and low-area Ca-rich grains is described by exponential concentration gradients. These gradients may generate appreciable electromotive forces, which may enhance electrochemically the local tissue demineralization. Similar effects are to be expected in the protective action of F- ions released from microgranules of YbF3 and of Ba fluoroaluminosilicate glass.

We present details on the implementation of the particle-in-cell algorithm on a single GPU and a GPU cluster.

Aktuelle Grafikkarten können eine Fließkomma-Leistung von mehreren TFLOPS liefern. Sie sind daher eine interressante Plattform für preiswertes, energieeffizientes Höchstleistungsrechnen. Eine GPU-getriebene Simulations-Software für echte Physikanwendungen benötigt eine hierarchische Strukturierung der Berechnungs- und Kommunikationsaufgaben, welche weit über die einfache Meldungsübergabe im heutzutage weit verbreiteten Hochleistungsrechnen (HPC) hinausgeht. Ich werde eine GPGPU Implementierung für eine Laser Plasma Simulation präsentieren, die auch auf große Rechencluster skaliert und führe Performancewerkzeuge ein, die gleichzeitig Informationen über die Prozessausführung auf CPUs und GPUs liefern. Zuletzt werde ich vorstellen, warum ein hierarchisches Algorithmen-Design unumgänglich ist, wenn man auf stark skalierbare Simulationen abzielt und wie dies in Zukunft die Softwareentwicklung in der Wissenschaft beeinflussen wird.

A bismuth liquid metal ion sources (LMIS) is investigated with respect to the emission behaviour as a function of current and temperature, the mass spectra and the energy distribution of the individual ion species [1]. For this Bi-LMIS the sputtering yields for monomer Bi ions as well as Bi-clusters (Bi2+, Bi3+, Bi4+, Bi3++) on Si, SiO2 and Ge substrates were compared with that of Ga projectile ions applied in a mass separating focused ion beam system (CANION 31Mplus). Additionally, a self-organisation of very regular, high-amplitude dot and ripple patterns depending on the angle of incidence on (001)Ge has been found under bombardment with heavy ions of bismuth dimers and trimers. Some applications in surface modification will be presented and discussed.

[1] L. Bischoff, W. Pilz, P. Mazarov, A.D.Wieck, Comparison of bismuth emitting liquid metal ion sources, Appl. Phys. A 99 (2010)145.

This work is concerned with induction heating of a metal sheet going to be used for multiple instance melt extraction from the lower edge. The task formulation of heating the edge in first place while keeping the release of Joule’s heat along that edge as homogeneous as possible, i.e. the avoidance of end effects, is solved numerically with a parametric study. A set of factors is also physically modeled in the framework of an experimental series. Subject to variation are (i) the extension of the substrate, which simulates the extraction wheel, in both directions parallel and perpendicular to the inductor, and (ii) the protrusion depth of the edge of the sheet below the lower face of the inductor. Reasonable conformity may be stated between the calculated and the experimental results.

A multilayer quantum dot sample has been excited with a strong terahertz (THz) electric field and probed with a near-infrared (NIR) laser. First- and second-order THz optical sidebands are generated on the NIR probe beam by driving quantum dot intersublevel resonances with the THz fields. A conversion efficiency of 3×10−6 was obtained for the conversion of NIR power into sideband emission at 4 K, decreasing by a factor of 20 up to room temperature. The sideband emission wavelength can be tuned over ∼ 20 nm by selection of appropriate NIR and THz frequencies, due to the inhomogeneous broadening of the dot ensemble.

Pulses of energetic protons with energies of several MeV can be produced by focusing an ultra-short intense laser pulse onto a solid target. The protons stem from the target rear side where they gain energy in an electric field that builds up due to charge separation effects triggered by electrons that are accelerated during the interaction of the laser with the target.
In order to investigate the acceleration of protons at solid targets which is expected to be strongly correlated to the properties of the electrons that set up the electric field at the target rear side we have set up a diagnostic which allows for the simultaneous online analysis of the accelerated protons as well as electrons. Here we are going to present first experimental results that have been measured at a table-top Ti:Sapphire laser with a pulse length of 30 fs and a peak intensity exceeding 1021 W/cm². From these data fundamental parameters can be derived that allow for a testing of theoretical scaling laws for the proton acceleration mechanism.

We report g-factor measurements for the 19/2+ T1/2 = 4.5(3) µs isomer in 127 Sn and the 10+ T1/2 = 2.69(23) µs isomer in 128 Sn. The experiment was carried out on isomers which were produced and spin-aligned in relativistic heavy-ion fragmentation at GSI and were selected and separated by the GSI fragment separator (FRS). The gamma-rays of the isomer decay were detected by the RISING array. The method of time-differential perturbed angular distribution was utilized. The measured g factors, g(19/2+ ;127 Sn) = -0.17(2) and g(10+ ;128 Sn) = -0.20(4), are compared with shell model calculations. The results demonstrate the feasibility of the method for similar measurements in exotic neutron-rich nuclei.

The talk starts with a short summary of liquid metal experiments on dynamo action that have been carried out during the last decade. Its main focus, however, is on recent experiments on the magnetorotational instability (MRI). The prospects for future experiments on dynamo action, MRI, and the Tayler instability, as well as for possible combinations will also be discussed.

The magnetorotational instability (MRI) is widely believed to play a key role in cosmic structure formation by maintaining turbulence and enabling angular momentum transport in accretion disks. The helical version of MRI (HMRI) was recently shown to have a scaling behaviour that is quite different to that of the standard version of MRI. Yet both types are continuously connected. We solve this apparent paradox by showing the emergence of an exceptional spectral point at which the slow magneto-Coriolis wave and one inertial wave coalesce and exchange their branches. Further, we compare the results of the PROMISE experiment on HMRI with various numerical predictions.

Unter dem Motto „Lernen von der Natur" gibt der Vortrag einen Überblick über die radioökologische Grundlagenforschung zur Wechselwirkung bakterieller Haldenisolate mit Uran und anderen Metallen, sowie darüber, welche Möglichkeiten sich daraus ergeben, neue Materialien für technische Anwendungen zu entwickeln.

Vorgestellt werden die radioökologischen Arbeiten des Instituts mit Bakterien und deren Potenzial zur Entwicklung neuartiger Materialien für technische Anwendungen.

Bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example, intensively studied at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf, is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins prevent the uptake and any sustainable damage of the cell by toxic and/or radioactive metals. The S-layers itself form highly ordered and mono-molecular envelopes around bacterial cells. Noteworthy is their ability to self-assemble in suspension, on surfaces and at interfaces. Furthermore S-layers of different bacteria are able to fulfil different functions and thus may act as immobilization matrix for exoenzymes, as molecular sieve, as ion and molecule trap or they protect the cell from being affected by the immune defence of host organism, by other bacteria or by lytic enzymes. By using and combining these unique features of S-layer proteins, smart coatings on many different surface can be realized. Currently at the Institute of Radiochemistry, S-layer based functional coatings are under development for the production of (photo)catalytic active materials, metal selective filters or highly specific biosensors. Therefore possible applications are the elimination of pharmaceuticals and germs, the detoxification of metals, the recovery of noble metals or the detection of pharmaceuticals and other organic matter in water. Additionally, combinations of functionalities are possible using a layer-by-layer technique, offering a wide field for the development of new nanostructured biocomposites for many different applications.

The -ray strength function is an important input quantity for the determination of the photoreaction rate and the neutron capture rate for astrophysics as well as for nuclear technologies. To test model predictions, the photoabsorption cross section of 139La up to the neutron-separation energy was measured using bremsstrahlung produced at the electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf with an electron beam of 11.5 MeV kinetic energy. The experimental data were analyzed by applying Monte Carlo simulations of -ray cascades to obtain the intensities of the ground-state transitions and their branching ratios. We found a large enhancement of electric dipole strength in the energy range from 6 to 8 MeV that may be related with a pygmy dipole resonance. The present data are combined with photoneutron cross sections for 139La and compared with results of ISS-QRPA calculations.

Measurements of electrical conductivity and P-wave velocity of seven rock samples were made in the laboratory under inferred in situ conditions. The samples were collected from smectite and chlorite alteration zones in boreholes from the Krafla and Hengill, Iceland, geothermal areas. The measurements were done in the 25–250°C range, with pore pressure and confining pressure equal to inferred in situ hydrostatic and lithostatic pressures, respectively. Conductivity increases linearly with temperature over the 30–170°C range; that rise is considerably smaller above 170°C. Time-dependent effects on conductivity occur above approximately 100°C. These effects may be related to ion exchange between the clay minerals or the Stern layer, and the pore fluid. The temperature coefficient of conductivity is found to be considerably higher than attributed to pore fluid conduction alone, indicating interface conduction in an electrical double layer on the mineral-water interface in the pores. The results also show that there is no distinction in electrical conduction mechanism in the smectite and chlorite alteration zones; both are dominated by interface conductivity under in situ conditions. The sharp decrease in conductivity at the top of the chlorite alteration zone, commonly observed in resistivity surveys in high-temperature geothermal systems, is most likely due to the lower cation exchange capacity of chlorite compared to that of smectite.

The presented work is part of a joint research project performed in cooperation between the Forschungszentrum Dresden and University of Applied Sciences Zittau/Goerlitz.
The paper deals with experimental investigations concerning the influence of an impinging jet on sedimented insulation material in a building sump of the reactor containment.
To investigate the influence of an impinging jet a special test facility was designed. The test facility "Tank" was build up with acrylic glass. Thereby it is possible to use laser PIV to measure the flow field and high-speed video to analyze the jet-structure in the test facility. With help of this instrumentation the following experiments were performed:

• Experiments without air entrainment and different distances between pipe outlet and water surface in the test facility.
• Experiments with air entrainment, different distances between pipe outlet and water surface in the test facility and different flow velocities of the impinging jet.
• Experiments with a cold impinging jet and hot water in the test facility for a defined distance between pipe outlet and water surface and a defined jet velocity of the jet.

Im Vortrag werden Ergebnisse zur Temperaturabhängigkeit der Eu(III)-Sorption an Opalinuston sowie zum Einfluss kleiner organischer Moleküle auf das Sorptionsverhalten vorgestellt. Außerdem wird die Komplexierung von Am(III) mit Weinsäure, untersucht bei Raumtemperatur mit UV-vis mittels LWCC, präsentiert. Des weiteren werden die Temperaturabhängigkeit des Eu(III)-Pyromellitsäure-Komplexsystems, untersucht mit TRLFS und Mikrokalorimetrie, und strukturelle Aspekte dieses Systems, ermittelt mit FT-IR und DFT, diskutiert.

This work shows the effect of the use of moderating layers on the sodium void effect in sodium cooled, MOX fuelled fast breeder reactors. The moderating layers are consisting of either zirconium boride ZrB2 or zirconium hydride ZrH2. The two investigated ZrH2 layers (0.1mm and 0.2 mm thick) cause a strong reduction of the sodium void effect. Additionally these layers improve the fuel temperature effect and the coolant effect of the system significantly. All changes caused by the insertion of the ZrH2 layers cause a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides.

This work shows the effect of the use of moderating layers on the sodium void effect in sodium cooled fast breeder reactors. The moderating layers consisting of either boron carbide B4C or uranium-zirconium hydride UzrH cause a strong reduction of the sodium void effect. Additionally these layers improve the fuel temperature effect and the coolant effect of the system. The use of the UZrH is significantly more effective for the reduction of the sodium void effect as well as for the improvement of the fuel temperature and the coolant effect. All changes cause by the insertion of the UZrH layer cause a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides.

The electroluminescence (EL) of Er-implanted SiO2 layers containing Ge nanocrystals (NCs) was investigated and correlated with microstructural results obtained by transmission electron microscopy, Raman spectroscopy and x-ray diffraction. In case of EL, and in contrast to the behaviour of Er-doped Si-rich SiO2 known from literature it appears that there is an inverse energy transfer from Er to Ge-related oxygen deficiency centres which are located at the surface of the Ge NCs or in the transition region between the NC and the SiO2 matrix. This is indicated by the increase of the blue-violet, Ge-related EL in presence of Er, although the Ge-related photoluminescence, which was excited by UV wavelengths non-resonant to Er, decreases at the same time. The microstructural results reveal that the maximum increase of the Ge-related EL occurs when the Ge NCs are not amorphized and/or fragmented by the Er implantation but surrounded by an Er shell. Possible mechanisms for this unexpected behaviour will be discussed.

Quantum fluctuations in low-dimensional magnets give rise to a variety of exotic strongly correlated states, making those systems an extremely attractive ground for testing various theoretical concepts. In this presentation I will focus on high-field ESR studies of two spin-chain systems. The first system is copper pyrimidine dinitrate, a material containing S=1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction and exhibiting a field-induced spin gap. Signatures of three breather branches and a soliton excitation have been identified [1,2], which is in excellent agreement with predictions of the sine-Gordon quantum field theory. In addition, a field-induced crossover from the soliton-breather to the magnon state was observed in this material in higher magnetic field [3]. The second material is NiCl2-4SC(NH2)2 (DTN), a quantum spin-1 chain system with strong easy-pane anisotropy. Using high-field ESR data, a revised set of spin-Hamiltonian parameters has been obtained [4]. These values were used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data was obtained.

High-performance liquid chromatography enantioseparation of vesamicol and six novel azaspirovesamicols (amino alcohols) was accomplished on different chiral stationary phases (CSPs) by using an optical rotation based chiral detector for identification of the resolved enantiomers. The Pirkle-type column Reprosil Chiral-NR was found to be most suitable for chiral resolution in normal phase (NP) mode; all compounds could be enantioseparated successfully. Also the cellulose-based column Reprosil Chiral-OM showed appropriate separation properties by using NP conditions. The amylose-type column Reprosil Chiral-AM-RP was most suitable for enantioseparation in reversed phase (RP) mode; five out of seven compounds were resolved. This CSP showed a considerably higher capability for chiral recognition of vesamicol derivatives in RP mode than the corresponding cellulose-based column Reprosil Chiral-OM-RP. Enantioseparation with the teicoplanin aglycone-based column Reprosil Chiral-AA was successful under polar ionic mobile phase conditions.

In the present work, low energy ion beam irradiation was used for surface modification of polymethyl-methacrylate (PMMA) using silicon (Si+) as the ion species. After high doses ion implantation of Si+ in the polymer material, a characterization of the optical properties was performed using optical transmission measurements in the visible and near infra-red (IR) wavelength range. The optical absorption increase observed with the ion dose was attributed to ion beam induced structural changes in the modified material.

The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C.
SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.

Visible photo luminescence (PL) of ion implanted polymers was studied. Different polymer materials were used for the purpose: polypropylene (PP), poly-tetrafluor-ethylene (Teflon), ultra-high-molecular-weight-polyethylene (UHMWPE) and UHMWPE+Bi. Ion implantation with Si+ and C+ was performed at energies of 30 keV with doses in the range 1013 – 1017 cm⁻². The results show that a PL enhancement (PLE) effect may occur for some polymer materials if proper implantation energy and doses are employed, the effect in the case of some polymer materials implanted with Si+ and C+ being considerable. While the effect is observed for all doses of C+ implanted in UHMWPE, PLE is only observed for the lowest dose of Si+ (D=1×1015 cm⁻²) implanted in Teflon, the further dose increase resulting in PL quenching only, presumably due to processes of structural degradation The appearance of ultra-violet (UV) range PL in the case of Si+ implanted UHMWPE could be originating from the formation of Si-related new defect sites, but more data are needed to explore this effect further into the deeper UV range (λ<350 nm).

In the first part we report on progress in measuring and understanding the dynamics of mesoscopic magnetic objects. These are studied in a scanning transmission x-ray microscope (STXM) which provides information about the space- and time resolved magnetization. We study individual objects, arrays and multilayer samples. The multilayer samples are of particular interest because the coupling between the layers can be tuned from anti-ferromagnetic to ferromagnetic using ion-beam irradiation. In a second part we present results on the unusual magnetic phase transition in RhFe taking place above room temperature. Here an anti-ferromagnetic low-temperature phase changes to a ferromagnetic high-temperature phase. This phase transition can be initiated using an ultra-fast laser pulse. We have studied the evolution of the crystal lattice in this transition using a pump-probe scheme. The pump-pulse is a fs laser pulse, the probe pulse is an x-ray pulse (width ~200 fs) produced by laser slicing of the stored electron beam. The data provide quantitative information about the time evolution of the lattice constants and the domain sizes. These data can be compared to optical MOKE data which measure the time dependant magnetization.

The idea of terahertz-time-domain spectroscopy (THz-TDS) is to exploit a single cycle, spectrally broad THz radiation pulse to gain insight into the response of matter. Photoconductive devices and nonlinear crystals are utilized in both the generation as well as the coherent detection of THz radiation. The relatively high cost and the complexity of commonly used titanium-sapphire lasers hinder a more widespread use of pulsed THz systems for commercial applications. Er-doped femtosecond fiber lasers operating at 1.55 μm could offer a viable alternative. In this thesis nonlinear crystals and photoconductive emitters are discussed for excitation in the near infrared (NIR) window of between 800 nm to 1550 nm. The main focus of this thesis is a detailed study of substrate materials for an interdigitated photoconductive antenna. Photoconductive antennas with microstructured electrodes provide high electric acceleration fields at moderate voltages because of small electrode separations. The scalability of these devices allows for large active areas in the mm^2 range, which are sufficient for excitation at large optical powers. In comparison with conventional emitter structures, these antennas have more favourable characteristics regarding THz power, spectral properties, and ease of handling. Depending on the utilized substrate material, photoconductive antennas can then be operated using different excitation wavelengths. By employing substrates with short carrier trapping times these antennas can be operated as THz-detectors. Moreover the design of electrode structures for generating radially and azimuthally polarized THz waves are presented. A second topic deals with the signal analysis and signal interpretation of THz pulses transmitted through several material systems. These experiments show the potential for tomographic and spectroscopic applications. The third part deals with THz emission by frequency mixing in nonlinear organic and inorganic crystals. Hereby the focus is on polaritonic phase matching in GaAs. Furthermore, indications of THz tunability by the excitation wavelength were found by utilizing waveguide structures. However, the observed tuning range is much lower then theoretically predicted. Specific reasons for this are discussed.

Twin boundaries in NiMnGa can be moved by applying either magnetic fields or mechanical stresses, which favour one of the two variants next to the twin boundary. We have used polarized light microscopy to study the two different ways of twin boundary motion in bulk NiMnGa. By placing magnetic indicator films on top of the sample surface we were able to detect the magnetic domain structure of the sample. Without the indicator films, the different variants can be seen by using polarized light illumination.
We found qualitative differences in the resulting magnetic state after a twin boundary has been moved by magnetic field or mechanical stress. By applying a magnetic field along the easy axis of one variant this variant is magnetically saturated and upon reducing the magnetic field the domain state consists of wide anti-parallel domains with 180° domain walls. Moving the twin boundary by applying mechanical stress results in a different domain state. Here the magnetization rotates by about 90° as the twin boundary passes through the area and we found the domain state to consist mainly of smaller patchy domains. The domain state with wide anti-parallel domains can be reached by demagnetizing the sample in an ac magnetic field. This suggests that the magnetic state after stress induced twin boundary motion is not in its global energy minima but rather trapped in a higher energy state

We studied the motion of twin boundaries in NiMnGa shape memory alloy bulk samples using time-resolved optical polarisation microscopy. The sample was excited by pulsed magnetic fields with variable rise-time. The restoring force to reset the sample, necessary for stroboscopic imaging, was set by applying mechanical stress along the long axis of the bulk sample perpendicular to the magnetic field. Upon decreasing the rise-time from 10 to 1 ms we found an increase of the twin boundary motion. This dependency of the actuation range on the pulsed field rise-time can be used in actuation devices to improve the magnetic field-induced strain by changing the field rise-time without having to change the repetition rate of the magnetic field.

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations.

Production of the Sigma(+) hyperon through the pp -> K(+)n Sigma(+) reaction has been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and 2.020 GeV. At low energies, correlated K+pi(+) pairs can only originate from Sigma(+) production so their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the K+-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive K+ momentum distributions, also provide conservative upper limits on Sigma(+) production rates. The measurements show a Sigma(+) production cross section that varies roughly like phase space, and, in particular, none of the three experimental approaches used supports the anomalously high, near-threshold pp -> K(+)n Sigma(+) total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].

The effect of Cr on the microstructures of neutron-irradiated Fe-Cr alloys is not yet known in all details including types, sizes, concentrations and compositions of irradiation-induced features on the nanoscale. Such details are needed in order to develop and validate models devoted to the long-term evolution of microstructures. Among other techniques, small-angle neutron scattering (SANS) can contribute to this task. Results obtained for a set of Fe-Cr alloys of Cr levels of 2.5, 5, 9 and 12.5 at%, irradiated at 300°C up to neutron exposures of 0.6 and 1.5 dpa are reported. We have found that the incoherent magnetic scattering of the unirradiated alloys exhibits a systematic variation with the Cr content and that there is an irradiation-induced increase of the coherent magnetic scattering for each of the irradiated conditions. The effect of Cr on size and type of irradiation-induced scatterers is discussed.

Small-angle neutron scattering (SANS) was applied to characterize the microstructure of weld material taken from the reactor pressure vessel (RPV) of the decommissioned VVER440(230)-type nuclear power plant (NPP) Greifswald, units 1, 2 and 4. The welding seam of highest neutron exposure of unit 1 was subject to a large-scale annealing treatment in 1988 after about 11.5 effective years of operation. The same type of annealing was applied to unit 2 in 1990 after about 11 effective years of operation. After final decommissioning of NPP Greifswald in 1990, RPV material was left in the reirradiated condition (unit 1), in the as-annealed condition (unit 2) and in the as-irradiated condition (unit 4). Trepans of material from the highly irradiated RPV welds of these units have recently become available for examination. The results of the SANS investigation are reported and compared with published results obtained for asirradiated, post-irradiation annealed and reirradiated surveillance material of the same type. We have found general agreement indicating in particular the formation of irradiation-induced Cu-enriched clusters and efficient recovery as a result of the largescale annealing treatments. The only essential difference was observed for the ratio of magnetic and nuclear scattering indicating differences of the cluster composition for the RPV wall and surveillance material.

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 monitored with surveillance program results or predicted by trend curves. Embrittlement forecast with trend curves and surveillance specimens may not reflect the reality. Accordingly, the most realistic evaluation of the toughness response of RPV material to irradiation is done directly on RPV wall samples from decommissioned nuclear power plants (NPP). Such a unique opportunity is now offered with material from the decommissioned Greifswald NPP. The four Greifswald NPP units representing the first generation of WWER-440/V-230 reactors were shut down in 1990 after 11–17 years of operation. Material from RPVs in three different conditions is available: Unit 1 is irradiated, annealed and reirradiated. Unit 2 is irradiated and annealed. Unit 4 is in the as-irradiated condition. Small-angle neutron scattering (SANS) was applied in order to characterize the microstructure of weld material taken from the core-belt regions of Units 1, 2 and 4. Furthermore, material from Unit 4 exposed to post-irradiation annealing corresponding to the large-scale annealings of Units 1 and 2 was also investigated. The results of the SANS experiments are reported and compared with mechanical properties as well as results obtained for surveillance material of the same type.

Oxide dispersion strengthening of ferritic/martensitic chromium steels is a promising route for the extension of the range of operation temperatures for nuclear applications. The investigation of dedicated model alloys is an important means in order to separate individual effects contributing to the mechanical behaviour under irradiation and to improve mechanistic understanding. A powder metallurgy route based on spark plasma sintering was applied to fabricate oxide dispersion strengthened (ODS) Fe9Cr model materials. These materials along with Eurofer97 and ODS-Eurofer were investigated by means of small-angle neutron scattering (SANS) and TEM. For Fe9Cr–0.6 wt.%Y2O3, TEM results indicate a peak radius of the size distribution of Y2O3 particles of 4.2 nm with radii ranging up to 15 nm, and a volume fraction of 0.7%, whereas SANS indicates a peak radius of 3.8 nm and a volume fraction of 0.6%. It was found that the non-ODS Fe9Cr and Eurofer97 are suitable reference materials for ODS-Fe9Cr and ODS-Eurofer, respectively, and that the ODS-Fe9Cr variants are suitable model materials for the separated investigation of irradiation-Y2O3 particle interaction effects.

In order to explore the effects of Cr and dispersion strengthening on microstructure and properties, two sets of Fe-Cr-based alloys were investigated. The binary Fe-Cr alloys were obtained by means of furnace melting of industrial pure Fe and Cr [Matijasevic, JNM 377 (2008) 147]. Cr levels are in the range from 2.4 to 11.6 wt%. The ODS-Fe-9wt%Cr alloys were produced by spark plasma sintering starting from industrial elemental powders of Fe and Cr and two different qualities of Y2O3 powder [Franke, Diploma Thesis, TUB Freiberg, 2009]. Milling time (5, 10 and 20 hours) and ODS fraction (0, 0.3 and 0.6%) were varied. For part of the ODS-Fe-Cr alloys an additional HIP treatment was performed in order to reduce porosity. Several techniques including small-angle neutron scattering (SANS) were applied in order to characterize the microstructure of the alloys. Sound velocity measurements, nanoindentation, tensile testing and impact testing were applied in order to characterize the mechanical behaviour. The effects of Cr and ODS on microstructure and properties are reported. Using SANS a significant increase of the scattering cross sections was found in comparison with the respective non-ODS variant. The reconstructed size distribution indicates the presence of ODS particles in the size range from 2 to 20 nm. Significant effects of both Cr content and disperion strengthening on the polycrystalline elastic properties and nanohardness were also observed.

The migration behavior of actinide contaminants is influenced by humic substances (fulvic acids and humic acids (HA)) due to their complexing and redox properties and their ability to form colloids. The redox activity of humic substances is attributed to the reversible hydroquinone/quinone redox couple with semiquinone-type free radicals as significant electron donor/acceptor intermediate species and furthermore, to the oxidation of phenolic OH groups to phenoxy radicals. Also nitrogen and sulfur containing functional groups of HA are discussed as redox-active groups. While sulfur functional groups of HA have not been studied as reducing agents toward actinides like U, Np or Pu so far, organic compounds containing sulfur in the reduced form as thiol groups (R-SH) were found to reduce Np(VI).
In the present work, the influence of sulfur functional groups of HA on their capability to reduce Np(V) in aqueous solution has been studied. For this, HA model substances type M1-S with different sulfur contents (1.9, 3.9, 6.9 wt.%) were applied. Reduced sulfur species, such as thiols, dialkylsulfides and/or disulfides, were determined as the dominating sulfur functionalities in the HA. Their Np(V) reduction behavior was studied in comparison to a sulfur-free HA type M1.
At pH 5.0, the Np(V) reduction strongly increases with increasing content of reduced sulfur functional groups of the HA. That means that the sulfur functionalities contribute to the reduction capability of HA at pH 5.0. In contrast to this, at pH 7.0 and 9.0, the sulfur functionalities of HA have only a slight influence on the Np(V) reduction (not shown). This implies that the contribution of the sulfur functionalities to the reduction capability of HA toward Np(V) depends on pH value.

The KERENA(TM) boiling water reactor (BWR) is a proven further developed design, based on Gundremmingen NPP and the whole accumulated German BWR operating experience. Especially for the passive safety systems, which are described in the paper more in detail, not only an experimental testing and validation is needed, but also thermal-hydraulic system codes have to be qualified, to be able to consider the mostly gravity driven 3D-flow phenomena correctly. Since in some countries the code ATHLET is well established, it is useful to prove its capabilities or to enhance the capabilities, if necessary. Therefore the FZD in co-operation with E.ON and AREVA is performing a model development and calculations for code validation with help of test results from INKA test facility (INtegral test facility in KArlstein, Germany). The paper gives an introduction into condensation phenomena and describes the condensation models applicable for a special heat removal system driven by natural circulation, it presents a detailed description of the ATHLET-model for the emergency condenser and first results from an estimation of the heat removal power.

The prototype of a "tunk key" 10kW@1.3GHz solid state power amplifier, designed and built by Bruker BioSpin Wissembourg/France has been tested at the superconducting linac ELBE in the Research Center Dresden-Rossendorf. The talk gives an overview on the design, its RF-parameters and the first 8-week period of test and operation at the superconducting CW-linac ELBE.

Tuning ferromagnetic resonance frequencies in soft ferromagnetic films relies on the possibility to tailor the uniaxial anisotropy of the film material. A systematic change of anisotropy field, being the solely changing material property, was achieved by preparing Ni81Fe19/Co60Fe20B20 multilayers. We show that in patterned films deviations from the regular Landau domain pattern occur, which compensate magnetic anisotropy effects and thereby lead to a precessional frequency independent of anisotropy. The results manifest the significance of even small changes in the magnetic domain structure over magnetic anisotropy adjustments for the optimization of the magneto-dynamic response in mesoscopic thin film elements.

Experimental techniques as neutron diffraction with isotopic substitution, extended X-ray absorption fine structure spectroscopy and quasielastic neutron scattering, in combination with molecular dynamics simulations, are usually applied to the study of non-crystalline solids, but they are also very useful for the study of complex systems, where the short range order provides an insight of its structure and dynamics. Here they are used in the study of the coordination of the Sm3+ in the interlayer of hydrated synthetic montmorillonite and hectorite. The neutron diffraction results indicate that not all O atoms in the first coordination shell of the Sm3+ belong to water molecules, supporting the formation of the Sm3+ innersphere complex. On the other hand, the other techniques suggest that the adsorbed Sm3+ cations form outersphere complexes with the clay surface. The hypothesis making compatible all results is that there are different Sm species adsorbed in the clay interlayer: a part of Sm is in the Sm3+ cationic form, forming outer-sphere adsorption complexes, another part is hydrolyzed and present in the interlayer space as Sm(OH)2+, Sm(OH)+ 2 or Sm(OH)03 species. The latter are more hydrophobic than Sm3+ cations and can be dehydrated and are able to stick to the clay surface.

Der Vorstand der ProcessNet-Fachsektion Reaktionstechnik hatte sich im Februar 2009 entschlossen, für das Fachgebiet der Chemischen Reaktionstechnik eine Roadmap zu erstellen. Im September 2009 wurde ein etwa 10-köpfiges Vorbereitungskomitee installiert, das sich der Aufgabe annahm. Es erfolgte im Mitteilungsblatt der Fachsektion (Info-Brief Nr. 4, September 2009) ein Gliederungsvorschlag und ein Aufruf an alle Mitglieder, zu den einzelnen Gliederungspunkten beizutragen. Auf dieser Basis entstand die hier vorliegende Roadmap.
Zweck der Roadmap ist es, die aktuellen Arbeitsgebiete der Chemischen Reaktionstechnik zu benennen, den Forschungsbedarf zu konkretisieren und über Fallstudien zu illustrieren. Sie ist dabei ein lebendes Dokument, das einer regelmäßigen Aktualisierung bedarf.
Die Roadmap der ProcessNet-Fachsektion Reaktionstechnik soll nicht der Abschottung zu anderen Disziplinen wie der Katalyse oder der Prozessintensivierung dienen, sondern vielmehr als Wegweiser für Kooperationen. In diesem Zusammenhang sei auf andere existierende Roadmaps und Positionspapiere hingewiesen wie die "Roadmap der deutschen Katalyseforschung" der Deutschen Gesellschaft für Katalyse, die jüngst in ihrer dritten überarbeiteten Auflage erschienen ist, das Positionspaper "Prozessintensivierung - eine Standortbestimmung" der ProcessNet-Fachsektion Prozessintensivierung sowie das Positionspapier "Energieversorgung der Zukunft", das von den führenden nationalen Chemieorganisationen gemeinsam erarbeitet wurde. Auf europäischer Ebene sei insbesondere auf die "European Roadmap for Process Intensification" des EUROPIC1a und die "Roadmap for 21st Century Chemical Engineering" der IChemE1 hingewiesen und auf internationaler Ebene auf die "Vision 2020 - Reaction Engineering Roadmap" der AIChE2. Wir wünschen allen Lesern eine anregende Lektüre, freuen uns über Anregungen und Kommentare und hoffen, dass die Roadmap viele neue Impulse für die Forschung auf dem Gebiet der Reaktionstechnik liefert.

Ion irradiation and implantation allows for a focussed materials modification in the range of a few nm only [1-3]. The modification of physical properties is especially effective, if interface effects in multilayer systems or ordering phenomena in binary alloys are considered. An addi¬tional degree of freedom can be exploited by a periodic patterning of the physical properties circumventing a topographic patterning in the conventional sense. Hybrid magnetic materials are created. Their integral magnetic properties are mainly governed by the shape and arrangement of the individual areas and cannot be considered as a simple superposition of the magnetic properties of modified and unmodified areas. The interactions between both areas and hence the length scales on which the magnetic properties are modified play a key role for their overall behaviour. For a review see Refs. 4 and 5. One of the major challenges is to exploit the scaling limits of this kind of structures and the appearance of an effective medium type material. These questions are addressed by high-resolution Lorentz microscopy imaging.

This work was supported by DFG grant no. FA 314/3-1 and DAAD.

Referenzen
[1] J. Fassbender et al., New J. Phys. 11, 125002 (2009).
[2] E. Menendez et al., Small 5, 229 (2009).
[3] J. McCord et al., Adv. Mater. 20, 2090 (2008).
[4] J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[5] J. Fassbender et al., J. Phys. D: Appl. Phys. 37, R179 (2004).

Ion-erosion-induced ripples are perfect template systems to systematically investigate the influence of a periodic surface modulation on magnetic properties like magnetic anisotropy in the case of single magnetic films or interlayer exchange coupling in the case of multilayer systems. One of the key advantages of these ripples is that their periodicity can easily be varied in the range between 20 and 60 nm. This matches exactly the range where magnetic properties can be affected by a surface modulation. Two different examples will be discussed: i.) ripple-induced magnetic anisotropies in soft magnetic Permalloy films [1,2] and ii.) the appearance of roughness induced magnetic coupling, e.g. Neel coupling, in multilayer systems [3]. In both cases a significant influence of the surface and interface modulation on the magnetic properties is observed, which drastically depends on the ripple periodicity itself.

References:

[1] M.O. Liedke et al., Phys. Rev. B 75, 220407 (2007).
[2] J. Fassbender et al. New J. Phys. 11, 125002 (2009).
[3] M. Körner et al., Phys. Rev. B 80, 214401 (2009).

The potential of ion irradiation and ion implantation for the formation of new nanoscale magnetic materials will be reviewed.

There are only few and locally restricted measurement data existing about the flow in a continuous casting mould and the influence of a magnetic field on the steel flow therein. This is related to the extremely harsh environmental conditions and the opaqueness of the media in the real steel casting process, so that there is nearly no measurement technique applicable. To overcome this lack of knowledge, there were build two experimental facilities at the FZD, working with low melting point alloys. The Ultrasonic Doppler Velocimetry (UDV) can be used for flow monitoring in the mould at these models. The resulting experimental data will be very valuable for the validation of numerical simulations.
Mainly, the two experimental facilities will be presented in the paper. Additionally, first results will be shown, which were obtained at the small scale experiment. It is shown, that the flow structures, like the emerging jet flow from the submerged entry nozzle and the recirculation zones, can be adequately resolved with the UDV-technique. Further the influence of a DC-magnetic field in the function as a electro-magnetic brake was studied. One result was, that a DC-magnetic field may give rise to non-steady, non-isotropic large-scale flow perturbations.

From the technically point of view the realisation of dynamo action in the laboratory is a demanding task because it requires magnetic Reynolds numbers of the order of 10...100. In order to reach such values in experiments, materials with high relative magnetic permeabilities have been utilized (Lowes & Wilkinson, von Karman Sodium dynamo).

The modification of the induction process by material properties is examined by means of simulations of the kinematic induction equation in hetrogenous domains where disk like assemblies with high conductivity and/or high permeability are introduced in a cylindrical volume filled with liquid sodium.

Both material properties not only lead to a decrease of the effective magnetic Reynolds number but also result in a quite distinct geometric structure of the final eigenmode. Furthermore, high permeability material even if localized in a small volume like the soft iron impellers in the VKS dynamo, essentially determines the field generation process and is reponsible for the selection of the dominating azimuthal dynamo mode.

Humic acids (HA) are soluble in the pH range of natural water, possess the ability for complex and colloid formation and show redox properties that can impact the redox state of metal ions. Therefore, HA can influence the speciation of metal ions, e.g., actinides, and thus, their migration in the environment. Knowledge of the impact of HA on the actinide migration is required for the long-term risk assessment for potential nuclear waste repositories in deep geological environments. The complex nature of HA complicates the description of their interaction with metal ions. Thus, there are a lot of difficulties in the thermodynamic description of the geochemical interaction processes of HA. A more basic understanding of the interaction processes of HA can be obtained by model investigations with model ligands representing building blocks of HA as well as with specific HA model substances. These should be characterized by similar operational and chemical properties, a more defined functionality, and a higher homogeneity compared to natural HA. Furthermore, they should offer the possibility for specific variations of functional and structural properties and for the stable isotopic labeling (e.g., 13C, 14C, 15N) of the HA structure. Model substances which achieve these requirements can be applied to study the interaction behavior of HA with metal ions in detail and to study the fate of HA in sorption and migration experiments. This work focuses on selected types of HA model substances, their synthesis and characterization in comparison to natural HA. Their use in geochemical studies will be shortly discussed.

Zur Untersuchung der Magnetfeldwirkung auf die Stahlströmung im kontinuierlichen Stranggussverfahren wurden Experimente an einem verkleinerten Flüssigmetallmodell durchgeführt. Als Modellfluid wurde dabei eine bei Raumtemperatur flüssige Legierung, bestehend aus Gallium, Indium und Zinn, gewählt. Die Kokillenströmung wurde am Modell mittels der Ultraschall-Doppler-Methode ausgemessen. Die Anordnung von 10 Sensoren ermöglichte die zweidimensionale Aufzeichnung der horizontalen Geschwindigkeiten in der Kokille.
Basierend auf dem Konzept der Elektromagnetischen Bremse wurde ein DC-Magnetfeld im Bereich der stärksten Strömungen an die Kokille angelegt. Die Messungen mittels Ultraschall zeigen deutlich die aus dem Tauchrohr austretende Strahlströmung als auch das zeitliche Verhalten der Strömung im untersuchten Gebiet. Bei Anwesenheit des DC-Magnetfeldes verändert sich sowohl Lage als auch die Form des Flüssigmetalljets. Des Weiteren sind Gebiete mit verstärkter Rezirkulation direkt ober- und unterhalb des Jets zu beobachten. Ein weiteres, wichtiges Ergebnis dieser Messungen ist, dass das Magnetfeld unerwünschte Oszillationen in der Strömung anregen kann.
Die Kombination eines Flüssigmetallmodels, eines DC-Magnetfeldes und der Ultraschall-Doppler-Methode ist ein wichtiges Element bei der Untersuchung des Stranggussprozesses. Damit können wertvolle und bisher nur rudimentär vorhandene experimentelle Daten über den Einfluss elektromagnetische Felder auf die Strömung in der Kokille gewonnen werden, die auch für die Validierung numerischer Modell von Bedeutung sind.

The redox behavior of Pu in aqueous solution is of particular interest for the disposal of nuclear waste in deep geological formations. Iron minerals are widespread in the environment and can be formed inside a repository by corrosion of steel canisters or construction materials. Their interaction with actinides and impact on redox chemistry needs to be understood for reliable performance assessment calculations.
The sorption and redox behavior of aqueous Pu(III) and Pu(V) in presence of synthetic nanocrystalline iron mineral suspensions and in homogeneous redox buffer solutions is investigated using a combination of classical wet chemistry methods and advanced spectroscopy (XANES, EXAFS). The impact of the redox conditions (pH + EH) in solution / suspension on the oxidation state distribution of Pu is studied by comparing the results to thermodynamic model calculations.

The aim of this work is to follow the chemistry of uranium, plutonium and americium, and in particular their oxidation states, in MOX samples sintered under different oxygen potentials. To address this issue, X-ray Absorption Spectroscopy (XAS) is the ideally suited as it allows the quantitative determination of oxidation states for each cation using X-ray Absorption Near Edge Structure (XANES) and to outline potential discrepancies in actinide local environments using Extended X-ray Absorption Fine Structure (EXAFS) [3].
MOX samples with the following composition (U0.750Pu0.246Am0.004)O2-x, were manufactured at the LEFCA facility at CEA Cadarache (France). The process used is based on a direct co-milling of the oxides and leads to a homogeneous plutonium distribution [4]. Pellets were sintered at 1700°C under controlled atmosphere (moist Ar/5% H2) to obtain the following O/M ratios: 1.94, 1.97 and 2.00. These values were confirmed by thermogravimetric analysis.
XAS spectra at uranium, plutonium and americium LII,III edges were collected at the ROssendorf Beamline (ROBL) of the European Synchrotron Radiation Facility (Grenoble, France). XRD and thermogravimetric measurements were performed at the LEFCA facility.

Die ultraschnelle Röntgen-Computertomographie ist ein bildgebendes Verfahren, das am FZD für die Untersuchung von Strömungsprozessen qualifiziert wurde und auf dem Gebiet der Prozessdiagnostik zunehmend an Bedeutung gewinnt. In dem Vortrag werden das Messsystem sowie Ergebnisse von Strömungsexperimenten präsentiert sowie Ansätze für einer Weiterentwicklung des Messverfahrens aufgezeigt.

Eine Einführung in neuartige Strahlungsquellen am FZD für Schüler des Schott-Gymnasiums Jena

We present an overview of the simulation work done at the Laser Particle Acceleration Group at the Institute of Radiation Physics. We show that with highly-parallel computing codes it is possible to perform realistic simulations of laser ion acceleration, laser-electron acceleration and Thomson scattering.

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.

es hat kein Abstract vorgelegen.

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.

es hat kein Abstract vorgelegen

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.