Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The diffusion of U(VI) (c0 = 1×10-6 M) in compacted Opalinus Clay from the Mont Terri underground laboratory, Switzerland, was studied in the absence and presence of humic acid (10 mg/L) at two different temperatures (25 °C, 60 °C) under anaerobic conditions. As background electrolyte a synthetic Opalinus Clay pore water (pH 7.6, I = 0.36 M) was used. The diffusion-accessible porosity, ε, was determined for each Opalinus Clay bore core sample by through-diffusion experiments with tritiated water (HTO) before the U(VI) diffusion experiments were carried out. The values for the effective diffusion and distribution coefficients De and Kd obtained for U(VI) and humic acid at 25 °C as well as at 60 °C showed that humic acid has no significant influence on the U(VI) diffusion. The diffusion profiles of humic acid in Opalinus Clay at 25 and 60 °C indicate the contributions of two different humic acid particle size fractions (< 1 kD and 10-100 kD). The small-sized humic acid fraction diffused through the whole Opalinus Clay samples at both temperatures within the three months duration of the U(VI) diffusion experiments. At 60 °C, diffusion profiles of two different U(VI) species were observed. In a separate experiment the U(VI) speciation in the source reservoir solution at 60 °C was analyzed by laser-induced fluorescence spectroscopy, photon correlation spectroscopy and scanning electron microscopy with an energy dispersive X-ray detector. The two diffusion profiles could be attributed to an unknown colloidal and a known aquatic U(VI) species (Ca2UO2(CO3)3(aq)). The diffusion results showed that the interaction of U(VI) and of the large-sized humic acid colloid fraction with the clay is stronger at 60 °C. An increase of Kd from 0.025 ± 0.003 m3/kg at 25 °C to 0.25 ± 0.05 m3/kg for U(VI)colloidal at 60 °C was determined. In addition, the value for De of U(VI) increased with increasing temperature. Using the De values at 25 and 60 °C, a preliminary activation energy for the diffusion of U(VI) through Opalinus Clay of 10 kJ/mol was calculated. The observed increased Kd and De values for U(VI)aqueous at 60 °C compensated each other to almost equal values of the apparent diffusion coefficient Da at 25 and 60 °C. Hence, the migration of U(VI) through OPA was not significantly influenced by the investigated higher temperature of 60 °C.

Presentation of current activities and results from the NanoTrack project, especially results from radiolabelling of Ag(0) and TiO2 nanoparticles

Presentation of the current research activivities concerning the radiolabelling of Ag(0) and TiO2 nanoparticles within the NanoTrack project at HZDR and first results from the QNANO research stay at the Joint Research Center in Ispra, Italy

Although transition metal cyano bimetallic compounds have been well known for decades for their interesting optical and magnetic properties, reports on actinide hexacyanoferrate compounds are scarce. For instance, a thorough structural description is still lacking. Another question is the possible covalency or charge transfer effects in these materials that are known to foster electron delocalization with a large variety of transition metal cations. In this paper, new members of the actinide(IV) hexacyanoferrates have been synthesized with Th, Np and Pu. This is the first review of thorium to plutonium hexacyanoferrate compounds since the early investigations during the Manhattan Project some 70 years ago. We have carried out an extensive structural characterization using powder X-ray Diffraction (XRD), X-ray Absorption Spectroscopy (XAS) and X-ray microscopy for the plutonium adduct. The crystallographic space group of microcrystalline Th, Np and Pu hexacyanoferrate compounds appears to be very similar to that of the early lanthanide adducts, suggesting that the tetravalent actinides are arranged in a tricapped trigonal prismatic polyhedron of coordination number 9, in which the actinide atom is bonded to six nitrogen atoms and to three water molecules. Further combined analysis of the iron K-edge and actinide LIII-edge EXAFS data and XRD data provided the basis for a threedimensional molecular model. Structural data in terms of actinide–ligand bond lengths have been compared to those reported for the parent lanthanide(III) compounds, confirming the structural similarities. In addition, two new structures with the thorium cation have been obtained and described using single-crystal XRD: (H5O2)Th(DMF)5(H2O)]2[Fe(CN)6]3 and [Th(DMF)4(H2O)3][Fe(CN)62H2O. This structural description of the Th, Np and Pu hexacyanoferrate system will be followed by a semi-quantitative electronic description of the actinide–cyano bond using NEXAFS data analysis in a coming paper.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) has been extensively used as a sensi-tive and selective technique to analyze actinide complexation with inorganic and organic ligands in trace metal concentrations. However, the application of TRLFS onto Am(III) complexation systems was up to now limited because of the much lower luminescence intensity and much shorter lifetime of Am(III) in comparison to U(VI) or Cm(III).
We investigated the complexation behavior of Am(III) complexes with lactate (Lac) and substituted benzoic acids like pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) at ambient and ele-vated temperatures with TRLFS.
Using the emission of the 5D1-7F1 transition at around 691 nm, spectral data like luminescence life-times, luminescence maxima and complex stability constants were calculated. Temperature dependent stability constants were determined to estimate thermodynamic data (reaction enthalpy, reaction en-tropy).
The Am(III) aquo ion shows at pH 4-6 a luminescence lifetime of 23 ns, corresponding to approxi-mately 9 coordinating water molecules. Complexation with BTC shows no change of the excitation and emission maximum but an increase of the luminescence intensity and lifetime. The luminescence lifetime was prolonged to 27 ns, corresponding to 8 remaining water molecules in the first coordina-tion shell. This indicates an exchange of 1 water molecule with 1 coordination site of the ligand, re-sulting in an Am-BTC 1:1 complex [1]. In contrast, complexation with lactate causes a red shift of the excitation wavelength of Am(III) (Fig. 1), resulting in a red shift of the luminescence emission maxi-mum of about 5 nm. The luminescence lifetime is prolonged up to 37 ns which corresponds to 5-6 re-maining water molecules. This indicates an exchange of about 3-4 water molecules with coordination sites of ligand molecules which implies the formation of 1:1, 1:2 and 1:3 complexes. The stability con-stants increase slightly with rising temperature which is consistent with an endothermic complexation reaction.

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

A new type of a positron annihilation lifetime spectroscopy (PALS) system has been set up at the superconducting electron accelerator ELBE [1] at Helmholtz-Zentrum Dresden-Rossendorf. In contrast to existing source-based PALS systems, the approach described here makes use of an intense photon beam from electron bremsstrahlung which converts through pair production into positrons inside the sample under study. The article focusses on the production of intense bremsstrahlung using a superconducting electron linear accelerator, the production of positrons inside the sample under study, the efficient detector setup which allows for annihilation lifetime and Doppler-broadening spectroscopy simultaneously. Selected examples of positron annihilation spectroscopy are presented.

In many engineering applications, the way natural fluid flows behave leaves some room for improvement. While geometric optimizations, such as streamlined shapes, require no additional energy input, they might not always be possible, feasible, or sufficient.

Another option is active flow control, where a suitable actuator more or less directly alters flow structures. Of the variety of such devices proposed for flow control applications, we focus on Lorentz force actuators. They consist of (permanent) magnets and electrodes, generating a body force near the wall it is attached to. The momentum added to the flow is linearly driven by an electric current.

The actuator can be applied to prevent transition from laminar to turbulent flow, a process that would otherwise lead to a rapid increase in drag. Its linear response is also advantageous when suppressing flow separation at inclined airfoils to prevent the loss of lift. The talk will cover both applications, and include numerical as well as experimental results.

Radiation transport simulations had to be done in preparation of operation of the X-ray tube ISOVOLT 320 kV/13mA in a special laboratory. At first simulation was done without shielding the roof of the laboratory, showing a dose rate maximum of more than 100 mSv/h. This dose rate results in a skyshine dose rate of at most 2 lSv/h in the surrounding of the building without shielding the roof. For similar geometries the skyshine is negligible for dose rates at the unshielded roof of less than 3 mSv/h (exclusion area).

We compare the accuracy achievable with different methods of calculating time-averaged airfoil loads if the surrounding velocity field is known, e.g., from Particle Image Velocimetry. These methods require integration over a control volume enclosing the body. For separated flow around an inclined flat plate at Re=10^4, we investigate the effect of varying the control volume. Some methods yield excellent results for both lift and drag.
Preliminary results for a corresponding experiment indicate that the calculated lift coincides well with direct force measurements, whereas agreement for the drag can be considered fair.
Implementation of the methods was validated using a circular cylinder flow at Re=200.

Mikroorganismen in ehemaligen Uran Bergwerken leben meist unter extremen Bedingungen, wie auch in der ehemaligen Mine Königstein. Dort müssen die Mikroben einem saurem pH Wert (2,7), hohen Konzentrationen an Sulfationen, Eisenionen und Uran standhalten. Nachdem die Schächte unter tage weitestgehend geflutet wurden, sind die Bedingungen noch selektierender, da Sauerstoff im Wasser fehlt und keine organische Kohlenstoffquelle vorhanden ist. Der Vergleich der Mikroorganismen in der Grube vor der Flutung und nachher zeigt, dass sich die veränderten Bedingungen auf die Biodiversität auswirken. Vor der Flutung waren in den Schächten neben Bakterien auch zahlreiche Eukaryonten vorhanden. Diese konnten bisher im Flutungswasser nicht nachgewiesen werden.

We report the first short-pulse amplification results to several hundred millijoule energies in ceramic Yb:LuAG. We have demonstrated ns-pulse output from a diode-pumped Yb:LuAG amplifier at an energy of 550 mJ and an optical-to-optical efficiency of 27%. In cavity dumped operation of a nanosecond oscillator we obtained 1mJ at up to 100 Hz repetition rate. A gain bandwidth of 5.4 nm was achieved at room temperature by measuring the small-signal single-pass gain. Furthermore, we compared our results with Yb:YAG within the same amplifier system.

A study is presented, where agglomerated magnetite nanoparticles with a crystallite size of 15 nm are transferred from water to an immiscible organicphase and tend to deagglomerate under certain conditions using different types of chemically adsorbing fatty acid. It is shown that the longer fatty acids lead to more stable dispersions and for the longest fatty acids, the functionality of the molecules defines stability with best results for ricinoleic acid. The disjoining force as a function of the brush layer thickness and adsorption density is calculated with a physical modelapplying the well-established Alexander de Gennes theory. We further investigate the colloidal stability of the transferred and stabilized magnetite nanocrystals in polymer solutions of destabilizing PMMA and stabilizing PVB. A DLVO-like theory presents the governing attractive and repulsive interactions for the case of destabilizing non-adsorbing polymers. The theory can be used to explain the influencing parameters in a mixture of sterically stabilized nanoparticles in an organic solvent based solutionofpolymercoils.Finally,by spray drying, we produce polymer–nanoparticle composite microparticles. Based on BET, laser diffraction and backscatter electron SEM measurements, we draw conclusions on the nanoparticle distribution within the composite in correlation with the stability investigations.

Transports THz pulses to XUV beamline for pump-probe experiments

The radiation source ELBE at the Helmholtz-Zentrum Dresden-Rossendorf (former Forschungszentrum Dresden-Rossendorf (FZD)) is built around a superconducting electron linear accelerator, constructed to produce quasi cw electron beams up to 1 mA beam current at 12 - 34 MeV. The electron beam is used to generate various kinds of secondary radiation, mainly to drive the two free-electron lasers U27 and U100 in the infrared region (4-250 μm). Starting in summer 2005 user beam time is offered to external users in the frame of the EC funded “Integrating Activity on Synchrotron and Free Electron Laser Science” (FELBE project). FELBE is an acronym for the free-electron laser (FEL) at the Electron Linear accelerator with high Brilliance and Low Emittance (ELBE). Twice a year users are invited to submit proposals for experiments at ELBE. For the period January - June 2012 the deadline will be November 14th, 2011. Access is free of charge for all non- proprietary research. Proposals are evaluated by the scientific advisory committee of ELBE. Based on their recommendations the final decision and allocation of beam time will be made by an local panel headed by the Scientific Director of the HZDR.
The IR light from the two FELs is transported to several laboratories in the same building and to the adjacent building (through a 27 m long tunnel) of the High Magnetic Field Laboratory (HLD) as well, where the experimental setups are up to 70 m away from the FELs. Here, self-designed magnets for fields up to 90 T have successfully been tested and first experiments with IR beams have been carried out.

The broad spectral range spanning from THz to X-rays combined with pulse durations from the femtosecond (fs) to nanosecond (ps) regime provided by THz and X-ray FELs are in principal optimally suited to investigate the rich and complex physics occurring in photoinitiated processes in materials. Unfortunately, these experiments require often specific conditions (e.g. high pressure, cryogenic temperatures, nanoscale resolution or ultra high vacuum) that complicate the alignment and the diagnostic of temporal and spatial overlap and lead to unacceptably long preparation times. In order to overcome this problematic, scientific groups working in the field teamed up with experts from different 4th generation photon facilities to develop more suitable instrumentation and infrastructure. Concepts and first developments will be presented.

At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 kHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at FLASH the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses as well as for novel electron bunch diagnostic (see also poster WEAP13). Pulse energies are expected to exceed the 100 μJ limit at scalable repetition rates between 1 and 200 kHz. The current status of the project and planned experiments are presented.

kein Abstract verfügbar

kein Abstract verfügbar

The IR and THz FEL at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 500 microns. A single-plane-focusing undulator combined with a 5.4 m long cavity is used in the mid-IR (< 50 micron), while a two-plane-focusing undulator in combination with a 7.2 m long cavity with a 1-D waveguide for the optical mode, will be used for the far-IR. A key aspect of the accelerator performance is low longitudinal emittance, < 50 keV-psec, at 200 pC bunch charge and 50 MeV, from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the 15 - 50 MeV energy range. "First Light" is targeted for the centennial of the FHI in October 2011. Installation and commissioning progress to date is described.

An IR and THz FEL with a design wavelength range from 4 to 500 µm has been commissioned at the Fritz-Haber-Institut (FHI) in Berlin, Germany, for applications in, i.a., molecular and cluster spectroscopy as well as surface science. The linac comprises two S-band standingwave copper structures. The first one operates at near fixed field to accelerate the electrons to 20 MeV, while the second one is designed to accelerate (or decelerate) to any final energy between 15 and 50 MeV. A key aspect of the system is low longitudinal emittance, < 50 keVpsec, at more than 200 pC bunch charge with a max. micro pulse rep. rate of 1 GHz. The up to 15 µs long macro pulses come at a rate of up to 20 Hz. The electrons are steered through either one of two FELs. A single-plane-focusing, 40 mm period hybrid magnet undulator combined with a 5.4 m long cavity has been commissioned for the mid-IR (< 50 µm). In addition, a two-plane- focusing undulator in combination with a 7.2 m long cavity with a 1-d waveguide for the optical mode is planned for the far-IR. In February 2012 we observed 'first lasing' at 28 MeV
and a wavelength of 18 µm. We will present first results characterizing the system.

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated before and after exposure to remote H-plasma. Defect characterization has been made by two complementary techniques of positron annihilation: positron lifetime spectroscopy and coincidence Doppler broadening. The high-momentum parts of the of the annihilation photon momentum distribution have been calculated from first principles in order to assist in defect identification. The positron annihilation results are supplemented by Atomic Force Microscopy for characterization of the crystal surface. It was found that virgin ZnO crystal contains Zn-vacancies associated with hydrogen. H-plasma treatment causes a significant reduction in concentration of these complexes. Physical mechanism of this effect is discussed in the paper.

Hydrogen absorption in Pd causes a significant volume expansion. In free-standing bulk Pd, the hydrogen-induced volume expansion is isotropic. However, the situation becomes more complicated in thin Pd films. Contrary to bulk samples, thin films are clamped to an elastically stiff substrate, which prevents in-plane expansion. Hence, the volume expansion of a thin film is strongly anisotropic because it expands in the out-of-plane direction only. Internal stresses introduced by absorbed hydrogen may become so high that detachment of a film from the substrate is energetically favorable and buckles of various morphologies are formed. In the present work, we studied hydrogen-induced buckling in a nanocrystalline thin Pd film deposited on a sapphire substrate. Slow positron implantation spectroscopy (SPIS) was employed as a principal tool for the characterization of defects and investigation of defect interactions with hydrogen. SPIS studies were combined with X-ray diffraction and direct observations of buckling by light microscopy. It was found that buckling of thin Pd film occurs at hydrogen concentrations xH > 0.1 and is accompanied by a strong increase of dislocation density.

An important issue when restaurating organ pipes made from lead alloys is the engineering of such material by mechanical hammering to increase the density. Microscopic effects of work-hardening on the surface near layers of lead sheets were investigated by depth resolving Doppler Broadening Spectroscopy measurements using the slow positron beam SPONSOR [1] of the Helmholtz-Zentrum Dresden-Rossendorf. The influence of small differences in the chemical composition of the samples is also discussed.

Recent experimental and theoretical investigations on a variety of yttria-stabilised zirconia (YSZ) nanomaterials are reviewed. The investigations were conducted within the frame of a collaboration of three institutions: (i) Charles University in Prague (CZ), (ii) Helmholtz Centre Dresden-Rossendorf (GER) and (iii) Nat. Academy of Science in Donetsk (UA), Materials studied involved pressure-compacted nanopowders of binary and ternary (with Cr2O3 additive) YSZ and YSZ ceramics obtained by sintering the nanopowders. The nanopowders were prepared by the co-precipitation technique. Positron annihilation spectroscopy including the conventional positron lifetime (LT) and coincidence Doppler broadening (CDB) techniques was employed as the main experimental tool. Slow positron implantation spectroscopy (SPIS) was used in investigation of commercial YSZ single crystals for reference purposes. Extended state-of-art theoretical ab-initio calculations of positron response in the ZrO2 lattice were carried out for various vacancy-like defect configurations. It was suggested by these calculations that none of the oxygen-vacancy related defects are capable to trap positrons. On the other hand, zirconium vacancy was demonstrated by the calculations to be a deep positron trap, even in case that a hydrogen atom is adjointed to the vacancy. The measured positron LT data clearly indicated that positrons annihilate in nanopowders predominantly from trapped states at defects of two kinds: (a) the vacancy-like misfit defects concentrated in layers along the grain boundaries and characterised with lifetimes of ≈ 0.180 ns, and (b) the larger defects of open volume comparable to a few vacancy cluster which are situated at intersections of three (or more) grain boundaries (characteristic lifetimes of ≈ 0.380 ns. Intensity ratio of LT components corresponding to these two kinds of defects was found to be correlated with the mean particle size. This correlation reconfirms the above interpretation of LT components and, moreover, the measured ratios could be used to estimate changes of the mean particle size with chromia content or sintering temperature. It was shown in this way that chromia addition to the YSZ nanopowder leads to a smaller particle size compared to the binary YSZ. Similarly, grain growth during sintering could be monitored via this intensity ratio. A portion of ≈ 10 % of positrons was found to form positronium (Ps) in binary YSZ compacted nanopowders. The observed ortho-Ps lifetimes correspond to Ps pick-off annihilation in cavities of ≈ 3 nm size which may be expected to occur between the primary nanoparticles. On the other hand, an addition of chromia at concentration as low as 0.3 mol.% appeared to be sufficient to suppress Ps formation below detection limit. Similarly, Ps formation could not be detected in binary YSZ sintered for 1 hour at a temperature of 1000 °C or higher. The former effect indicates an enhanced concentration of Cr cations at the particle surfaces, while the latter one appears due to a decrease of cavity concentration induced by sintering. The measured CDB data supported the idea that vacancy-like trapping centres are similar to zirconium vacancies and gave further evidence of a strong segregation of Cr segregation at particle interfaces.
SPIS was further involved in a trial experiment on binary YSZ nanopowders and sintered ceramics. This experiment clearly demonstrated that SPIS may reveal a valuable information about changes of depth profiles of microstructure during sintering,, e.g. a sintering induced diffusion of defects from sample interior to its surface.

A study of irradiation-induced damage in HAVAR® foils was initiated in order to extract the highest proton dose the foils can sustain. The lattice structure of HAVAR® foils in different metallurgic conditions is presented, as well as visible internal structure, measured by Transmission Electron Microscopy (TEM). Positron Annihilation Spectroscopy (PAS) techniques were used to investigate these foils, and another foil that had been irradiated to the maximal proton dose limit, set by the manufacturer, of 1 mAh. PAS techniques included Doppler Broadening (DB) measurement in the SPONSOR beam and Lifetime (LT) measurements, both carried at Helmholtz Zentrum Dresden-Rossendorf (HZDR). Both positron spectroscopy methods show clear differences between the investigated foils, with distinguished characteristics for annealed, cold-rolled and irradiated foils. The advantages of using a slow positron beam to study thin foils and defect profiles, over a table-top LT spectrometer, are discussed and demonstrated by the HAVAR® measurements.

The effect of Cr on the microstructure of neutron-irradiated Fe-Cr alloys is not yet known in detail. Available experimental results indicate that the addition of Cr to Fe or steels significantly influences the behavior of Fe-Cr alloys or ferritic/ martensitic high-Cr steels with regard to neutron irradiation. Neutron irradiation induced damage at its early stage was simulated by ion implantation. Positron Annihilation Spectroscopy, known as a very sensitive method for revealing smallest open-volume defects with lowest concentrations, was applied to identify irradiation-induced defects depending on the Cr-content in Fe-Cr alloys. Different irradiation scenarios were used to investigate the influences of irradiation step by step.

On the basis of the design and construction of the slow positron beam “SPONSOR” at the Helmholtz-Centre Dresden-Rossendorf an example is given how to build-up a simple slow positron beam for solid surface investigations within a short time and without high financial costs. The system uses a 22Na source and consists of three main parts: (1) the source chamber with a thin film tungsten moderator used in transmission, and a pre-accelerator stage, (2) the vacuum system with magnetic transport, a bent tube for energy selection and an accelerator, (3) the sample chamber with a sample holder, Ge detectors and (4) facilities for remote control and data acquisition. These parts are described in detail. The paper is preferentially addressed to beginners in the field of slow positron beam techniques and other readers being generally interested in positron annihilation spectroscopy.

Tungsten is often used as a positron moderator in mono-energetic positron beams [1] with 22Na positron sources. Therefore, mono-crystalline W foils with a thickness of about 2 µm are commonly used. The efficiency of such tungsten moderators strongly depends on the heat treatment of the tungsten foils. Currently, the annealing of such thin foils is mostly done at temperatures of about 2000 oC under vacuum conditions with a considerable difficulty. For this reason, a new method was sought to quickly anneal W foils to produce manageable, low-cost moderators with a high efficiency suitable for mono-energetic positron beams.
Flash lamp annealing (FLA) offers a chance for the optimization of the moderator properties. With FLA, the surface of a W foil can be heated above the melting point (3422ºC) in 1 to 3 ms without melting the whole volume. The heat treatment was carried out in an Ar flow. In this way, a surface cleaning and a considerably longer positron diffusion length could be reached.
Conventional poly-crystalline W foils with a thickness of 9 µm + 25% and heat treated by FLA were characterized by Auger electron spectroscopy, scanning electron microscopy and slow positron implantation spectroscopy and then tested as positron moderators. First promising results obtained with these W foils will be presented and it will be shown that this technique is applicable to tungsten meshes too.

[1] P.G. Coleman, Positron Beams and their applications, World Scientific Publishing, Singapore, 2000

The ELI Whitebook contains the description of the science, the technology basis and the implementation of the new international scientific infrastructure Extreme Light Infrastructure (ELI)

The ²H(α,γ)⁶Li cross section has been measured by in-beam gamma-spectrometry at the deep underground 400 keV LUNA accelerator in Italy's Gran Sasso laboratory. An α-beam of 280-400 keV energy was incident on a windowless deuterium gas target, and the γ-rays from the reaction were detected in a large high-purity germanium detector. Due to elastically scattered deuterons, there is a low but not negligible parasitic neutron production of the order of 10 neutrons per second. These neutrons give rise to a significant background in the germanium detector. In addition to the underground in-beam experiment, also studies using americium-beryllium and deuterium-deuterium neutron sources and Monte Carlo simulations have been performed. The analysis of signal and background is described in detail.

The free electron laser (FEL) at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 400 microns. A single-plane-focusing undulator combined with a 5.4 m long optical cavity is used for the generation of mid-infrared (MIR) radiation up to 50 microns. A two-plane-focusing undulator, in combination with a 7.2 m long cavity with a 1-D waveguide for the optical mode, is planned for the far-infrared (FIR). Beam was delivered to the MIR beam dump in October 2011 and first light at 18 microns was achieved on Valentine’s Day, 2012. We describe progress to date and plans to complete the
commissioning of the MIR beamline and the installation of the FIR beamline.

HAVAR foils are used in the medical industry as a window material for the production of 18FDG for PET scans. First comparative measurements of HAVAR foils, 25 μm thick, are presented. Three samples were measured: cold rolled (CR), annealed (AN), and proton irradiated (IR). These HAVAR foils were studied by means of Slow Positron Implantation Spectroscopy (SPIS), Positron Annihilation Lifetime spectroscopy (PAL), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). TEM and XRD results show that HAVAR has a fcc structure with a small amount of dislocations in the AN sample and a high density of dislocation nets in the CR sample. The positron diffusion lengths, extracted from the SPIS measurements, are ~8 nm and ~66 nm in the CR and AN samples, respectively, in agreement with TEM observations. The results of PAL measurements show significant differences between positron mean lifetimes in the three samples. Differences of ~50 ps and ~70 ps were measured between the mean lifetime in the AN sample and these in the CR and IR samples, respectively. GEANT4 simulations were used for the first time in PAL analysis. The simulation method and its benchmarking against previous measurements are described. Lifetime results obtained using conventional PAL analysis and GEANT4 based analysis are consistent within uncertainties for both the HAVAR and a Si reference sample.

Die Untersuchung von Metallen in Biosystemen stellt einen wichtigen Faktor im Verständnis von Mobilität und Stabilität, von z. B. Schwermetallen, in der Umwelt dar. Um diese Prozesse zu verstehen, bzw. um Aussagen zu verschiedenen Reaktionen treffen zu können, ist es notwendig die genauen Mechanismen zu bestimmen. Untersuchungen zeigten bei den hier verwendeten mikrobiellen Haldenisolaten sehr hohe Metallbindungskapazitäten. Da bisher größtenteils nur ganze Zellsysteme untersucht wurden, soll hier der Fokus auf die Einzelkomponenten von Gram-positiven Mikroorganismen gelegt werden. Dazu ist es notwendig diese zu isolieren und zu charakterisieren bevor Aussagen zu Bindungsereignissen und Wechselwirkungs-mechanismen getroffen werden können. In diesen Ausführungen sollen die gram-positiven Stämme JG-B53 und Lysinibacillus sphaericus JG-A12 in einem Batch-Verfahren kultiviert werden. Anschließend werden die Zellen geerntet und deren Zellwandbestandteile durch verschiedene Verfahren gewonnen. Zu den Extraktionsverfahren zählen die mechanisch-biochemische Gewinnung und die Lösungsmittelextraktion. Die zu isolierenden Komponenten sind vor allem Lipide und Hüllproteine, die auch als S-Layer bezeichnet werden. Die extrahierten Bestandteile werden mittels biochemischer, chemischer und strukturanalytischer Analysemethoden charakterisiert.

Physical and mechanical properties of Fe–Al alloys are strongly influenced by atomic ordering and point defects. In the present work positron lifetime (LT) measurements combined with slow positron implantation spectroscopy (SPIS) were employed for an investigation of quenched-in vacancies in Fe–Al alloys with the Al content ranging from 18 to 49 at.%. The interpretation of positron annihilation data was performed using ab-initio theoretical calculations of positron parameters. Quenched-in defects were identified as Fe-vacancies. It was found that the lifetime of positrons trapped at quenched-in defects increases with increasing Al content due to an increasing number of Al atoms surrounding the Fe vacancies. The concentration of quenched-in vacancies strongly increases with increasing Al content from 105 in Fe82Al18 (i.e. the alloy with the lowest Al content studied) up to 101 in Fe51Al49 (i.e. the alloy with the highest Al content studied in this work).

Der ständige Zuwachs an Rechenleistung und die Entwicklung größerer Speichermedien fördert eine nie dagewesene Datenflut zu Tage. In Bereichen wie Astronomie, Biologie, Medizin, Physik und Wirtschaft werden Datenmengen im Petabyte-Bereich und darüber hinaus gemessen, beobachtet und berechnet.

Ein konkretes Beispiel liefert der am Institut für Strahlenphysik entwickelte PIConGPU-Code, welcher zur Simulation von Laser-Plasma-Kollisionen eingesetzt wird.

Zur effizienten Auswertung dieser Datenmengen bedarf es neuer Methoden und Werkzeuge, die eine intuitive und flexible Analyse ermöglichen. Ein natürliches Interface und eine immersive Darstellung der Visualisierung nutzt die kognitiven Fähigkeiten des Anwenders und erlaubt ihm sein Expertenwissen optimal einzusetzen.

Deshalb wurde in dieser Arbeit in Kooperation zwischen dem Helmholtz-Zentrum Dresden-Rossendorf und der TU Dresden ein Visualisierungssystem entwickelt, welches die Vorteile der visuellen Datenanalyse mit einem intuitiven Gesteninterface verbindet. Die Microsoft Kinect dient dabei als Trackinggerät für die Gestenerkennung. Einen wichtigen Beitrag zur Steigerung der Immersion leistet neben einer großen Displayfläche das implementierte Stereo-Rendering.

An IR and THz free-electron laser for applications in, i.a., molecular and cluster spectroscopy as well as surface science has been installed at the Fritz-Haber-Institut in Berlin. Commissioning has started at the end of July 2011. On February 14th ‘first lasing’ was observed at a wavelength of about 18 µm.
The normal-conducting electron linac together with a gun-to-dump electron beam line has been designed, fabricated, and installed by Advanced Energy Systems, Inc. It comprises two S-band (2.99 GHz) standing-wave copper structures. The first one is designed to accelerate the electron bunches to a fixed energy of 20 MeV, while the second one shall accelerate or decelerate the electrons to any final energy between 15 and 50 MeV. Electron bunches of up to 300 pC charge are accelerated at a maximum rate of 1 GHz. A chicane between the two structures allows for variable bunch-compression down to 1 ps. Further, the design length of the electron macro-pulses is as long as 15 µs with a maximum repetition rate of 20 Hz.
The electrons will, eventually, be steered through either one of two oscillator FELs, So far, the first FEL has been installed. It includes a 2-m-long planar hybrid-magnet undulator made by STI Optronics, Inc. with a period of 40 mm, which is enclosed within a 5.4 m long IR cavity. At a minimum gap of 16.5 mm a maximum undulator parameter of more than 1.6 is reached. As a result, it is expected that MIR radiation in the range from 4 µm up to almost 50 µm can be produced with this system. Hole-outcoupling is used to extract a beam from the IR cavity. The cavity length will be stabilized using the feedback signal from a HeNe-laser interferometer.
The design of the FIR FEL, so far, has been outlined. It shall employ a 7.2 m long cavity containing a full-length 1-dimensional waveguide and a more than 4 m long undulator with a period of 11 cm. The design wavelength range covers the FIR from about 30 µm all the way to the THz regime up to about 500 µm. We will present the status of commissioning and design of the MIR and FIR FEL, respectively.

Actinides are elements with atomic numbers between 89 and 103. All actinides are radioactive, heavy elements. Due to their occurrence the can be separated into two groups: Naturally occurring actinides and synthetic elements. However, the line between these two groups is not a sharp one. This is due human activities in use and testing nuclear power and nuclear weapons as well as in a very smaller amount due to natural nuclear reactors in the Proterozoic era. Thorium, protactinium, uranium and in much smaller amounts plutonium are the naturally occurring elements. Neptunium and all elements with atomic numbers (AN) larger than 94 are synthetic elements. The isotopes of elements beginning with einsteinium (AN=99) have relatively short lifetimes of the radioactive decay (< 472d Es-252) and there availability is very limited, therefore no information about their behaviour in biological systems have been published up to now.
Especially uranium, neptunium, plutonium and partly also americium can exist in different oxidation states. Therefore for these elements redox reactions in biological systems are of great significance.
Actinoides can be accumulated in the human body. However, the accumulating organs are different. While protactinium is mainly accumulated in kidneys and bones, plutonium is incorporated in lung, liver and bones. All actinoides show long residence times in the human body. Therefore it is sometimes not easy to distinguish between chemical toxicity and radiotoxicity.
Most of the literature deals with monitoring of radioactivity and calculation of doses in living systems, however, this will be not the focus of this contribution.
Thorium exits in the natural environment only in the oxidation state +4. Therefore it precipitates very easily. Due to this the transfer of thorium from soil to plants is much lower compared to uranium, for instance.
The only long living isotope of protactinium is Pa-231, a member of the U-235 decay chain. Up to now the biology of this element focuses only on the radiometric determination.
The use of depleted uranium in recent years increased the research in the behaviour of this element in biological environments latterly. New results show that due to the comprising coordination chemistry of uranium a change in the coordination of uranium occurs, when uranium is transported to different biological compartments. Additionally a lot of work to study the influence of uranium to microorganism and plants has been done in the past.
The next element in the actinoides series is neptunium. All members of this naturally occurring decay series have been decayed. Only studies with artificial neptunium isotopes have been done. It is known that microorganisms are able to reduce neptunium(V). Also neptunium is able to bond to transferrin and other proteins of the blood plasma.
Due to its high radio toxicity plutonium has been mainly studied with complexing agents as transferrin. Additionally several studies with microorganisms have been performed. Due to the five possible oxidation states the redox behaviour of plutonium in biological systems is of basic interest.
The next elements in the series of actinoides exits mainly in the oxidation state +3. Therefore it can be expected that their biological behaviour is similar. Nevertheless, several examples for americium, curium will be given. Some sorption behaviour of microorganisms towards americium has been published.
For curium the interaction with microorganism has been studied. It should be lined out here that curium shows an extraordinary high fluorescence emission yield, which enables studies at extremely low concentrations of this element down to 10-11 Mol/l. As an example the speciation of curium in human urine (Cm addition to urine) was determined.
No studies for berkelium in biological systems are reported.
Californium has been used as neutron source to irradiate blood lymphocytes.
Several data are available, dealing with questions of the decontamination of inhaled or ingested actinoides into human body.
Lanthanoides (elements of the 4f series) show similar chemical behaviour as actinoides in the same oxidation state.

Les mécanismes d’interaction entre cations et minéraux peuvent inclure des processus d’adsorption, de (co-)précipitation de surface, et aller jusqu’à l’incorporation au sein du matériau, ce qui peut entraîner l'irréversibilité de certaines réactions de sorption. Le minéral choisi pour cette étude est la calcite, présente dans les argilites du Callovo-Oxfordien et également produit d’altération des ciments sur des échelles géologiques, ce qui justifie son intérêt pour l’évaluation de la sûreté d’un site de stockage de déchets radioactifs en site géologique profond. Le cation étudié est l’europium, en tant qu’analogue de certains actinides. La démarche adoptée est la combinaison de données macroscopiques de rétention avec une étude spectroscopique : SLRT pour tenter d’élucider les mécanismes de sorption, et RBS pour confirmer la précipitation de surface ou l’incorporation au sein du matériau et obtenir les profils de diffusion.
Les expériences en réacteur fermé ont été menées sous conditions atmosphériques (pCO2 = 10-3.5 atm) en milieu NaCl 0,1 mol.L-1, pour des concentrations d’europium variant de 10-6 à 10-3 mol.L-1 et des temps de contact variant de quelques heures à 1 mois. Les analyses ICP-AES des surnageants montrent une rétention très forte par la calcite quelles que soient les conditions expérimentales.
Les résultats de SLRT montrent un comportement différent de l’europium en fonction de la concentration initiale et du temps de contact. Pour chacune des concentrations, deux espèces sont mises en évidence, leurs temps de vie augmentant lorsque la concentration initiale diminue, et lorsque le temps de contact augmente, ce qui correspond à une perte progressive des molécules d’eau entourant l’europium.
Pour les concentrations les plus fortes, les espèces identifiées semblent correspondre à un (co-)précipité de surface et un complexe de surface ayant conservé deux molécules d’eau en sphère interne. Les mesures RBS effectuées pour ces concentrations, montrent une accumulation de l’europium à la surface de l’échantillon, ce qui confirme l’hypothèse du précipité de surface. Pour les concentrations plus faibles, les temps de vie observés sur l’une des espèces, beaucoup plus longs, et proches de ceux obtenus par Fernandes et al. [1] qui ont effectué des synthèses directes par coprécipitation, semblent indiquer une incorporation de l´europium au sein du matériau.

High quality ZnO crystal with the sharp band-edge excitonic emission and very weak green emission was implanted by nitrogen ions. An additional red emission band was observed in the as-implanted ZnO crystal and investigated as a function of temperature. By employing the underdamped multimode Brownian oscillator model for general electron-phonon coupling system, both the original green and nitrogen-implantation induced red emission bands were theoretically reproduced at different temperatures. Excellent agreement between theory and experiment enables us determine the energetic positions of the pure electronic levels associated with the green and red emission bands, respectively. The determined energy level of the red emission band is in good agreement with the data obtained from the deep-level transient spectroscopic measurements.

Background: The endocannabinoid system is involved in many physiological and pathological processes. Two receptors (cannabinoid receptor type 1, CB1, and type 2, CB2) are known so far. Many unwanted psychotic side effects of inhibitors of this system can be addressed to the interaction with CB1. While CB1 is one of the most abundant neuroreceptors, CB2 is expressed in the brain only at very low levels. Thus, high potent and selective compounds for CB2 are desired. N-Aryl-((hetero)aromatic)-oxadiazolyl-propionamides represent a promising class of such selective ligands for the human CB2. Here, a library of various derivatives is studied for suitable routes for labelling with [18F]. Such [18F]-labelled compounds can then be employed as CB2 selective radiotracers for molecular imaging studies employing positron emission tomography (PET).
Results: By varying the N-arylamide substructure we could explore the binding pocket of the human CB2 receptor and identified the 9-ethyl-9H-carbazole amide as the group with optimal size. Radioligand replacement experiments revealed that the modification of the (hetero)aromatic moiety in 3-position of the 1,2,4-oxadiazoles shows only moderate impact on affinity to CB2 but high impact on selectivity towards the CB2 with respect to CB1. Further, we could show by autoradiography studies, that the most promising compounds bind selectively on CB2 receptors in mouse spleen tissue. Molecular docking studies based in a novel 3D structural model of the human CB2 receptor in its activated form indicate that the compounds bind with the N-arylamide substructure in the binding pocket. [18F]-labelling at (hetero)aromatic moiety at the opposite site of the compounds via radiochemistry were carried out.
Conclusions: The synthesized selective CB2 compounds have high affinity towards CB2 and good selectivity against CB1 receptors. The introduction of labelling groups at the (hetero)aromatic moiety shows only moderate impact on CB2 affinity, indicating the introduction of potential labelling groups at this position as a promising approach to develop selective CB2 ligands suitable for molecular imaging with PET. The high affinity for human CB2 and selectivity against human CB1 of the herein presented compounds renders them as suitable candidates for molecular imaging studies.

The FELBE user facility located at the Helmhotz-Zentrum Dresden-Rossendorf operates two free-electron lasers (FELs). Here we discuss the basic parameters of the FELs and the experimental opportunities at the facility. The FELs are based on the superconducting electron linear accelerator ELBE, which provides short (picosecond) electron bunches with energies up to 35 MeV at a 13 MHz repetition rate. The two FELs of FELBE (FELBE stands for FEL@ELBE) are equipped with two undulators, one for the mid-infrared spectral range (wavelengths 4 – 22 µm) and one for the far-infrared or THz range (wavelengths 20 – 250 µm).
The key feature which distinguishes FELBE from other FEL user facilities is the possibility of “quasi cw” operation (meaning a continuous train of pulses, also called micropulses), made possible by the superconducting accelerator cavities. The FEL thus provides picosecond optical pulses at a repetition rate of 13 MHz. In this mode, the average power can reach up to 30 W (depending on the wavelength) corresponding to more than 1 µJ pulse energy. Additionally FELBE can be operated in a macrobunch mode and, via pulse-picking, a 1 kHz mode.
The two FELs can be synchronized to a number of tabletop femtosecond and picosecond lasers, enabling two-color experiments from the near-infrared to the THz frequency range. The main techniques at FELBE are pump-probe spectroscopy [1-3] and time-resolved photoluminescence [4]. Furthermore there is a lab devoted to near-field microscopy [5,6]. Spectroscopy with FELBE radiation is also possible in pulsed high magnetic fields up to 70 T (150 ms magnetic pulse duration) [7].
FELBE is operated as a user facility, i.e., scientists from other institutions are invited to submit short research proposals and apply for beamtime.

Der Rossendorf Low-Amplitude-Neutron Detector (RoLAND) besteht aus 1000 × 42 × 11mm3 großen Streifen des Materials EJ-200, dessen Szintillationslicht mit hoch-verstärkenden Photomultipliern an zwei Seiten detektiert wird. Durch koinzidenten Nachweis von Signalen geringer Amplitude liegt die Nachweisschwelle für Neutronen bei weniger als 10 keV. Zur Bestimmung absoluter Wirkungsquerschnitte von (𝛾, n)- und (n, n’𝛾)-Reaktionen, wie sie in den Bereichen nukleare Astrophysik oder Transmutation benötigt werden, wurden am supraleitenden Elektronen-Linearbeschleuniger ELBE Experimente durchgeführt, bei denen sich die Detektoren im Gegensatz zu einer früheren Bestimmung der Effektivität in einem wesentlich kleineren Abstand und in einer Abschirmung aus Blei befanden. Ein Vergleich der Neutronennachweiseffektivität mit Simulationen und neueren Messungen relativ zu einer 235U-Spaltkammer zeigten deutliche Abweichungen insbesondere nahe der Schwelle. Daher wurde an der PTB Braunschweig eine weitere Kalibrierung im Energiebereich 20 − 5000 keV durchgeführt,
deren Ergebnisse vorgestellt werden.

Die für die primordiale Nukleosynthese wichtige Reaktion 𝑑(𝛾, 𝑛)𝑝 wurde am supraleitenden Elektronen-Linearbeschleuniger ELBE mit Bremsstrahlung bei einer Endpunktenergie von 5,0 MeV untersucht. Neutronen mit einer kinetischen Energie von 20 − 1400 keV wurden mit Hilfe der Flugzeit-Detektoren RoLAND (Rossendorf Low-Amplitude-Neutron Detector) nachgewiesen, deren Effektivität 2011 an der PTB Braunschweig bestimmt wurde. Wechselwirkungen der emittierten Neutronen mit dem Targetmaterial (23 Schichten aus Aluminium und deuteriertem Polyethylen) wurden simuliert. Der Photonenfluss wurde mit Hilfe der resonanten Streuung an Aluminiumkernen bei Energien von 2,2 und 3,0 MeV bestimmt. Der experimentelle Aufbau, die Datenanalyse sowie vorläufige Ergebnisse werden präsentiert.

Objectives: In 2010, a hybrid whole body PET/MR system (Philips Ingenuity TF PET/MR) was installed at our institute. PET/MR is expected to offer many new possibilities in the field of quantitative bimodal functional imaging. Quantitative PET image reconstruction requires attenuation correction (AC) which is commonly based on a measurement of photon attenuation using either a transmission scan in stand-alone PET
(TRAC) or a CT scan in PET/CT systems. In PET/MR, however, AC is performed with a software-based approach (MRAC) using dedicated tissue segmentation and tissue type identification (air, lung, soft tissue) of an MR image. Here, we present a first evaluation of the accuracy of the vendor-provided MRAC in whole body investigations.
Methods: We performed sequential PET scans of 9 patients on a stand-alone Siemens ECAT HR+ and on the Ingenuity PET/MR with a time delay of approximately 2h. In addition to the standard reconstruction using MRAC, we performed a second reconstruction of the emission data from the PET/MR using the coregistered transmission-based attenuation maps from the HR+. For the two resulting PET image volumes, we performed a voxel-by-voxel correlation analysis and a comparison of the SUVs in different ROIs.
Results: The PET correlation analysis yielded a Pearson correlation coefficient of 0.93 and 0.96 and average deviations of 4% and 3% between the two reconstructed images for all voxels in the lung and in the torso, respectively. In one patient we observed failure of correct lung detection because of severe motion artifacts of the heart in the MR image. Accordingly we found a very large average deviation of 65% in the lung.
Conclusions: The MRAC algorithm generally yields satisfactory results with respect to soft tissue and air segmentation. The average deviation between PET images reconstructed with TRAC and MRAC is usually small and quantitative accuracy is adequate. Failure of segmentation occur rarely which necessitates manual intervention to achieve adequate segmentation.

kein Abstract verfügbar

The production of the stable isotope ⁶Li in standard Big Bang nucleosynthesis has recently attracted much interest. This is so because some recent observations in metal-poor stars suggest that a cosmological ⁶Li plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of ⁷Li abundances and would point to a primordial origin of ⁶Li, contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang ⁶Li production must be revisited. The present work reports on the neutron-induced background encountered in a new study of the ²H(α,γ)⁶Li reaction. In the experiment, an α-beam from the ultra-low background underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the ²H(d,n)³He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3 MeV neutrons on well-shielded high purity germanium detectors has been studied in detail. Data have been taken at 280 and 400 keV α-beam energy and for comparison also using an americium-beryllium neutron source. The ramifications for the planned ²H(α,γ)⁶Li measurement are discussed.

The present study has been done in the framework of the Central Design Team european project (CDT), which has the goal to design the FAst Spectrum Transmutation Experimental Facility (FASTEF), able to demonstrate efficient transmutation of high level waste and associated ADS technology. On the FASTEF design will be based the MYRRHA facility at SCK•CEN in Mol (Belgium), which should start the construction phase in 2015. The heart of the system is a 100 MW lead-bismuth eutectic (LBE) cooled reactor, working both in critical and sub-critical modes. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV, 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core.
Starting from the initial need to assess the shielding of the reactor building and to characterize the irradiation of the materials in the last part of the proton beam-line, an extensive simulation study has been done to define the radiation fields around the spallation target, with special attention to the neutron component. Using a description that includes the last part of the proton beamline and the LBE spallation target, neutron yields and spectra have been computed with both Monte Carlo codes FLUKA (version 2011.2) and MCNPX (version 2.6.0), where in the second case different fragmentation/ evaporation models have been compared. As second step the neutron fluence behavior has been estimated in the whole structure around the reactor core, including fission neutrons. In this case a full MCNPX model has been used, including the vertical part of the proton beamline, the spallation target, the reactor core and the structure around, from the coolant until the external vessel, the reactor cover and the shielding walls. With the aim to compare the results, an additional simulation has been performed with the FLUKA code, using neutron source terms evaluated in the previous MCNPX calculations on suitable surfaces close to the reactor core. The results of the neutronics analysis are presented, together with the main implications on the design solutions.

The density of nicotinic acetylcholine receptor (nAChR) subtypes is reduced in brain of Alzheimer’s disease (AD) patients. Imaging of α4β2 receptors, the predominant subtype, could thus contribute to early diagnosis of AD. Existing radiotracers for α4β2 nAChRs have suffered from inadequate affinity, or very slow binding kinetics, but the novel compound [18F]Flubatine presents several advantages. Both enantiomers display high affinity in vitro and fast cerebral binding kinetics in living mice and pigs. Initial human PET imaging studies have confirmed high uptake in the thalamus, low non-specific binding, and attainment of equilibrium binding in less than two hours. Dosimetry studies in healthy human volunteers indicate that effective doses for (-)-[18F]Flubatine (< 10 mSv/300 MBq) are compatible with application in routine clinical studies.
We have described the organic synthesis of enantiomerically pure (–)-Flubatine and (+)-Flubatine. Moreover, several precursors with different protecting groups and leaving groups have been synthesized for optimised radiosynthesis. The best radiochemical results were obtained with a trimethylammonium precursor carrying a Boc-protecting group, employing a two-step radiosynthesis. Radiolabelling under phase transfer conditions afforded the protected 18F-intermediate in yields of 90%. Subsequent deprotection under mild conditions gave the final products with a radiochemical yield of 70±5%, and specific activity >350 GBq/µmol. [18F]Flubatine was stable in dilute HCl, NaOH and K2CO3 solutions, as well as under physiological conditions.

A series of 4-{4-[2-(4-(2-substitutedquinoxalin-3-yl)piperazin-1-yl)ethyl] phenyl} thiazoles were synthesized in an effort to prepare novel atypical antipsychotic agents. The compounds were designed, synthesized, and characterized by spectral data (IR, 1H NMR, and MS) and the purity was ascertained by microanalysis. The D2 and 5-HT2A affinity of the synthesized compounds was screened in vitro by radioligand displacement assays on membrane homogenates isolated from rat striatum and rat cortex, respectively. Furthermore, all the synthesized final compounds (10a–g; 11a–g; 12a–g) were screened for their in vivo pharmacological activity in Swiss albino mice. D2 antagonism studies were performed using climbing mouse assay model and 5-HT2A antagonism studies were performed using quipazine-induced head twitches in mice. It was observed that none of the new chemical entities exhibited catalepsy and 12d, 11f, and 10a were found to be the most active compounds with 5-HT2A/D2 ratio of 1.23077, 1.14286, and 1.12857, respectively, while the standard drug risperidone exhibited 5-HT2A/D2 ratio of 1.0989. Among the twenty one new chemical entities, three compounds (12d, 11f, and 10a) were found to exhibit better atypical antipsychotic activity as they were found to have higher Meltzer index than the standard drug risperidone.

Resistive plate chamber (RPC) prototypes of 2 m length were simulated and built. The experimental tests using a 31 MeV electron beam, discussed in details, showed an efficiency higher than 90% and an excellent time resolution of around σ=100 ps. Furthermore, comprehensive simulations were performed by Geant4 toolkit in order to study the possible use of these RPCs for fast neutron (200 MeV–1 GeV) detection and multi–neutron event identification. The validation of simulation parameters was carried out via a comparison to experimental data. A possible setup for invariant mass spectroscopy of multiple neutron emission is presented and the characteristics are discussed. The results show that the setup has a high detection efficiency and is capable of determining the momentum of the outgoing neutrons and reconstructing the relative energy between the fragments from nuclear reactions.

The role of natural circulation in advanced water cooled reactor design has been extended with the adoption of passive safety systems. Some designs utilize natural circulation to remove core heat during normal operation. Most passive safety systems used in evolutionary and innovative water cooled reactor designs are driven by natural circulation. The use of passive systems based on natural circulation can eliminate the costs associated with the installation, maintenance and operation of active systems that require multiple pumps with independent and redundant electric power supplies. However, considering the weak driving forces of passive systems based on natural circulation, careful design and analysis methods must be employed to ensure that the systems perform their intended functions.

Vorstellung des Helmholtz-Instituts Freiberg für Ressourcentechnologie

The state of the art of low-energy experiments for nuclear astrophysics is reviewed, with an emphasis on the nuclear physics of the Sun, and on the production of the supernova marker titanium-44. An outlook will be given on the topics to be addressed at future underground low-energy ion accelerators, an important complement to the studies at FAIR.

There are a wealth of precise observations on our nearest star, the Sun, including spectroscopical, helioseismological, and neutrino data. The Sun may therefore be an ideal testing ground for stellar models, which have to be applied to scenarios where much less is known. After the long-standing solar neutrino problem had been spectacularly resolved one decade ago, hopes were high to develop the standard solar model to a precision of a few percent. However, a new discrepancy has since cropped up, called the solar abundance problem. In the talk, it will be discussed how nuclear physics experiments may help improve our understanding of the Sun. The impact of new nuclear data on the creation of the three lightest chemical elements in the first minutes of our universe will also be shown.

First experiments ausing a multi-detector setup for 2-D tomographic Positron Annihilation Lifetime Spectroscopy are presented.

A new method for the fabrication of spherical gallium nanoparticles (Ga-NPs) on diamond-like carbon (DLC) layers with high precision in their desired diameter and positioning is presented. The basic principle is the pre-patterning of a DLC film by focused Ga+ ion beam irradiation and subsequent annealing. During thermal treatment the evolution of single Ga NPs with spherical shape on irradiated areas is driven by phase separation and surface segregation of Ga from the supersaturated DLC layer. Shape and size of the implanted areas as well as the ion fluence serve as a Ga reservoir for the NP evolution which is strongly correlated with the NP diameter. For the formation of segregation seeds to avoid random segregation of the NPs small spots are additionally implanted with Ga within the irradiated areas. The NP evolution is than assessed to the seed position and the material for the Ga NP growth is gathered from the surrounding reservoir. Using this technique Ga NPs were fabricated with a diameter ranging from 40 nm up to several hundred nm. Prospective applications i.e. in the field of plasmonics arise from the arrangement in chains as well as in periodical two-dimensional arrays with defined NP size and interparticle distance.

The design of sub-critical accelerator-driven systems requires high energy and high power proton accelerators, of the order of hundreds MeV and some MW for the proposed demonstration experiments. The use of high energy Mega-Watt beams presents many serious challenges for various aspects of accelerator design, radiation shielding and reliable operations, being the induced activation a central problem.
A key issue is the introduction of low-activation materials to improve the accessibility and the long-term treatment of the irradiated elements, maintaining - and sometimes improving - the shielding efficiency with a suitable material configuration. In this work a simulation study based on the FLUKA Monte Carlo transport code is presented: different solutions for the main beam dump of the 600 MeV, 4 mA MYRRHA proton beamline are investigated and discussed. For each proposed solution a complete analysis of the secondary radiation fields and of the residual activation is shown: the inventory of the produced radionuclides and the residual ambient dose equivalent at different distances from the dump are estimated, both for short-term and long-term irradiation conditions and for all the significant cooling times.

Accelerator-driven systems (ADS) are one of the options studied for the transmutation of nuclear waste in the European Community. The design of sub-critical ADS requires high energy and high power proton accelerators, of the order of hundreds MeV and some MW for the proposed demonstration experiments. The use of high energy Mega-Watt proton beams, in combination with a nuclear reactor core operating in sub-critical or critical mode, presents many challenges for various aspects of the design. Radiation shielding and minimization of the induced activation are key points.
The present study has been done in the framework of the Central Design Team european project (CDT), which has the goal to design the FAst Spectrum Transmutation Experimental Facility (FASTEF), able to demonstrate efficient transmutation of high level waste and associated ADS technology. The heart of the system is a 100 MW LBE cooled reactor, working both in critical and sub-critical modes. A beamline aims to transport a 600 MeV, 4 mA proton beam produced by a linear accelerator up to the spallation target for the neutron production, which is located inside the reactor core. Based on the FASTEF design, the MYRRHA facility, which should enter the construction phase in 2015, will be built at SCK•CEN in Mol (Belgium). MYRRHA is conceived as a multi purpose facility: as technology demonstrator for lead-bismuth cooled fast reactor, as demonstrator for efficient transmutation, and as high flux irradiation facility for material testing and medical isotope production.
An extensive simulation study has been done to assess the shielding of the reactor building and the proton accelerator, as well as to fix the activation problems that have a heavy influence on the beamline and building design. Here the shielding assessment around the proton accelerator is presented, together with the optimization of the elements of the beamline that are devoted to the partial or total beam absorption (beam dump, collimators). This study has been fully carried out by using the FLUKA code, which has the unique feature to perform the transport of the residual radiation via a full Monte Carlo method, allowing in addition modifications in the geometry and material characterization from the prompt to the residual radiation transport. It will be shown how a suitable material configuration, with the introduction of low-activation materials, is a key issue: it will improve the accessibility and the long-term treatment of the irradiated elements allowing to maintain - and sometimes to improve – the shielding efficiency.

The long-lived fission product 126Sn is of substantial interest in the context of nuclear waste disposal in deep underground repositories. However, the redox state (di- or tetravalent) under the expected anoxic conditions is still a matter of debate. We therefore investigated sorption and oxidation of Sn(II) in the presence of a typical corrosion product, magnetite (FeIIFeIII2O4), with a mean particle size of 9.4 nm. In order to simulate waste disposal conditions, the experiments were performed under strictly anoxic conditions in a glovebox at <2 ppm O2. Macroscopic parameters (pH, Eh, [Sn], [Fe]) were monitored along with redox state and local structure of Sn (X-ray absorption spectroscopy) and Fe (XPS) as a function of time, pH, and surface loading.
Magnetite rapidly sorbed Sn(II), reducing Sn concentration within 0.5 h from 10 to 0.0084 μμM. Tin was strongly sorbed by magnetite across a wide pH range from 3 to 9. Reduced sorption at pH <3 is in line with electrostatic repulsion between the positively charged surface of the magnetite nanoparticles (IEP ~6.7) and cationic Sn2+ or Sn4+ complexes. The reduced sorption at pH > 9 is in line with the transition from Sn(OH)20 to the anionic Sn(OH)3- which occurs at pH 9. Across the pH range 3-9 and reaction periods ≥1 h, EXAFS-derived sixfold oxygen coordination and XANES edge energy positions of ~29207 eV both indicate the presence of Sn(IV) at the magnetite surface. EXAFS shell fitting as well as Monte Carlo simulations showed formation of edge-sharing complexes of Sn(IV) with FeO6 octahedra (Sn-Fe distance of 3.15 Å), and formation of corner-sharing complexes with FeO4 tetrahedra (Sn-Fe distances of 3.60 Å). Even after the longest reaction periods of 1 month, we did not observe incorporation of Sn(IV) into the (compatible) magnetite structure. Also, precipitation of SnO2 was not observed in spite of an (initial) supersaturation.
In order to elucidate the reaction pathway, we also studied Fe in solution and at the surface (XPS). Starting with the PZC and increasing with [H+], the magnetite surface released Fe(II) into solution (0.11 g/L at pH 2). After addition of Sn(II), however, [Fe] in solution decreased as a function of Sn loading, in spite of the expected increase of structural Fe(II) due to the coupling to Sn(II) oxidation. This suggests a re-adsorption and possible re-precipitation of Fe(II) at the magnetite surface. Nevertheless, due to a protonation at low pH, Fe(II) again re-dissolved as a function of time. With XPS we were not able to detect an adequate increase of the Fe(II)/Fe(III) ratio at the surface, supporting an electron redistribution between bulk and surface Fe centers.
In conclusion, our study demonstrates that Sn is strongly retained by magnetite across a wide pH range, forming stable surfaces complexes and stabilising the magnetite surface against dissolution.

Biogenic mackinawite (FeS) produced by Shewanella putrefaciens CN32 is submicron in size but nanosized in one dimension (film-like morphology)
Biogenic FeS is very reactive evident by its propensity to reduced U(VI) and rapid oxidation to form lepidocrocite upon exposure to air.
U(VI) reduction is observed in the pasteurized control indicative of a non-enzymatic redox process.
XAS and nanodiffraction techniques (bulk and nanoscale analyses) confirm the formation of UO2.
UO2 particles are nanoparticulate measuring c.a. 2.5 nm in size.
The present work suggests that a remediation strategy could potentially incorporate subsurface abiotic redox interactions between biogenic Fe(II)-bearing minerals such as mackinawite & contaminant U(VI) to immobilize U as UO2 – an in-situ waste form.

More and more computationally intensive scientific applications make use of hardware accelerators like general purpose graphics processing units (GPGPUs). Compared to software development for typical multi-core processors their programming is fairly complex and needs hardware specific optimizations to utilize the full computing power. To achieve high performance, critical parts of a program have to be identified and optimized. This paper proposes an approach for performance analysis of CUDA kernel source code regions, which for the first time allows measuring the execution times within GPGPU kernels. We developed a tool, which implements the presented method and supports the application developer to easily identify hot spots within the kernel. The presented tool uses compile time code analysis to automatically instrument suitable instrumentation points for minimal program perturbation and further provides support for manual instrumentation. To the best of our knowledge this is the first approach, which allows for scalable runtime analysis within GPGPU kernels. Combined with existing performance analysis techniques this facilitates obtaining the full potential of modern parallel systems.

Viele Mikroorganismen haben spezielle Oberflächenstrukturen entwickelt, die eine hohe Affinität zu Metallen besitzen. Diese Strukturen können zur Entwicklung von Filtermaterialien genutzt werden, um Metalle aus stark verdünnten wässerigen Lösungen zu binden und zurückzugewinnen.
Derartige biosorptive Materialien gewinnen zunehmend an Bedeutung für industrielle Anwendungen. Vorteile sind die nahezu vollständige Entfernung der Metalle, die geringen Kosten und die häufig gute Verfügbarkeit, ihre Regenerationsfähigkeit sowie die Möglichkeit der Gewinnung abgetrennter Metalle [1-3]. Ihre Leistungsfähigkeit ist vergleichbar mit der von Ionenaustauscher¬materialien, und sie liefern häufig bessere Ergebnisse als Aktivkohle oder natürliche Zeolithmaterialien [3]. Die Anwendung der Biomaterialien in Säulen erfordert meist ihre Immobilisierung auf geeigneten Trägermaterialien. Herausforderungen bei der Herstellung derartiger Biokompositen sind eine hohe Materialstabilität bei gleichzeitigem Erhalt der Funktion.
In unserer Gruppe werden Hüllproteine (S-Layer) von Bakterien zur Entwicklung von derartigen Materialien verwendet. Diese Proteine bilden auf den Zelloberflächen und nach ihrer Isolation auf Trägermaterialien durch Selbstorganisation zweidimensionale Gitterstrukturen aus. Sie eignen sich zur Beschichtung von unterschiedlichsten Trägermaterialien, aber auch zur Einbettung in Keramiken. Derartig immobilisierte Proteine wurden bereits zur Uranentfernung aus Wässern eingesetzt [4]. Neben Uran werden aber auch Edelmetalle wie Palladium oder Platin oder toxische Elemente wie Arsen gut gebunden. In der Präsentation werden Ergebnisse dieser Arbeiten vorgestellt und Perspektiven zur weiteren Entwicklung von Filtermaterialien zur selektiven Aufkonzentrierung von strategisch relevanten Metallen aufgezeigt.
[1] Volesky, B., Biosorption of heavy metals. 1990, Boca Raton, Florida: CRC Press. 396.
[2] Volesky, B., Advances in biosorption of metals: Selection of biomass types. FEMS Microbiology Reviews, 1994. 14: p. 291-302.
[3] Matheickal, J.T. and Q. Yu, Biosorption of Lead(II) from aqueous solutions by Phellinus badius. Minerals Engineering, 1997. 10(9): p. 947-957.
[4] Raff, J., et al., Biosorption of uranium and copper by biocers. Chem. Mater., 2003. 15: p. 240-244.

Nanoscalic bio-inorganic hybrid materials are very attractive for various technical applications. Especially the use of self-assembling highly ordered proteins as part of such hybrid materials is an attractive approach and offer new possibilities to add novel properties to surfaces. In our group we use the proteinaceous paracrystalline bacterial surface layers (S-layers) that envelop bacterial cells as nanostructures for the assembly of novel materials. These proteins are mostly composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. These features are used for the nano-patterning of various technical surfaces. The regular distributed pores of these paracrystalline arrays are binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1, 2]. In addition, the proteins can be modified with organic groups, thus adding additional functions to the nanocoatings.
We will present new results on the fabrication of S-layer based functional composite materials. The S-layer coatings are used as template for the bio-inspired mineralization and formation or deposition of various inorganic nanoparticles such as Pd, Pt, Au, ZnO and TiO2. The thus fabricated hybrid materials exhibit interesting chemical, physical and mechanical properties that can be used for different applications. Current projects concentrate on the development of photocatalytic materials based on S-layer supported metal oxide coatings. In another project we used TiO2 deposited on S-lLayer proteins for the high efficient removal of arsenic from waters.
Multifunctionality can be introduced to the materials either by genetic or by chemical engineering. In such an approach, we used S-layers for the assembly of sensory layers. These S-layers are functionalized by aptamers (oligonucleotides) that work as receptor and two different fluorophores working as donor/acceptor for detection via FRET. The binding of the analyte to the aptamer should influence the fluorescence, ideally causing the interruption of the FRET.
[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68

Metallgewinnung mit Bakterien

Bergbau mit Bakterien

Überblick über Biomining

In many two-phase flows a mixture of both stratified and dispersed flow regimes is encountered. Depending on the interfacial scale resolving and averaging methods are established for the numerical simulation of these special flow regimes. However, multiphase flows that cover a wide range of scales should be investigated considering coexistent segregated and dispersed flow. The simulation of such flows is a challenging task which led to the recent field of research known as multi-scale CMFD-simulations. Especially the transitions between different flow regimes play an essential role for a better understanding of many flow applications. No general technique for the simulation of such a flow situation has evolved yet. This contribution introduces a new CMFD-strategy of a generalized two-phase flow (GENTOP) dealing with such complex flow situations.
Currently, the GENTOP-concept is presented using a three-field two-fluid simulation based on the Eulerian methodology. The flow is described by a continuous liquid phase, a polydispersed gas phase, consisting of different bubble size groups, and a continuous gas phase. By using the framework of the recently developed inhomogeneous Multiple Size Group (MUSIG)-model, transfers between different bubble sizes due to coalescence and breakup processes are described. The GENTOP-concept extends this framework by adding a continuous gas phase summarizing all gas structures characterized by an interfacial scale large enough to be resolved. Thus, two gaseous fields are assumed, each field having its own set of mass-, momentum- and energy balance. An additional interface stabilizing force is introduced enabling the resolution of the gas-liquid interface. By modelling an additional mass transfer between the continuous and the polydispersed gas phase, transitions between different gas morphologies can be considered. The modelling of interfacial transfer requires a detection of interfacial structure in order to accurately involve the resolved gas-liquid interface. Based on the Algebraic Interfacial Area Density (AIAD)-model a generalized formulation for interfacial area density and drag has been found considering free surfaces within a multi-field simulation. This new concept can provide a more general insight into non-homogeneous multiphase flows by capturing continuous as well as polydispersed gas structures simultaneously.
Many multiphase flows relevant for industrial and scientific issues can be described by the GENTOP-concept. One of them is the impingement of a liquid jet on a water pool with an associated bubble entrainment playing a key role for nuclear safety issues during a loss-of-coolant accident. This flow phenomenon shows the mass transfer from a continuous into a polydispersed gas phase forming a bubble plume of different bubble sizes. Various multiphase flows with high gas fractions show inverse transfers from a dispersed into a continuous gaseous morphology such as the transition from bubbly to slug flow in a vertical pipe. This paper presents the principles of the new concept and illustrates them within such representative flow situations using the CFD-code CFX 13.0. First computational results are compared to experiments carried out at HZDR and theoretical data reported in literature. Both characteristic polydispersed and continuous gas structures are captured and show qualitative agreement. Further developments will concentrate on new generalized closure models for coalescence and breakup processes between continuous and dispersed gas phases.

We study the ratio of bulk to shear viscosity in gluodynamics within a phenomenological quasiparticle model. We show that at large temperatures this ratio exhibits a quadratic dependence on the conformality measure as known from weak coupling perturbative QCD. In the region of the deconfinement transition, however, this dependence becomes linear as known from specific strongly coupled theories. The onset of the strong coupling behavior is located near the maximum of the scaled interaction measure. This qualitative behavior of the viscosity ratio is rather insensitive to details of the equation of state.

Das Institut für Fluiddynamik beschäftigt sich unter anderem mit der Untersuchung mehrphasiger verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate und -reaktoren.
Ein solches neuartiges Konzept stellt der geneigte und rotierende Festbettreaktor dar. Im Gegensatz zur herkömmlichen zeitlich-periodischen Betriebsweise vertikaler Rieselbettreaktoren erfolgt die Prozessintensivierung hier durch die Aufprägung einer örtlichen Periodizität unter stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich durch die Wahl von Reaktorneigung und Reaktordrehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der Diplomarbeit wurde der Einfluss von Reaktorneigung und -drehzahl auf die Stoffübertragung bei ausgewählten Gas- und Flüssigkeitsdurchsätzen am Beispiel des flüssigkeitsseitigen Stoffdurchgangskoeffizienten untersucht und im Vergleich zum etablierten Rieselbettreaktor bewertet.

Conclusion of the calibration campaign at the IR-FEL (FELBE) with detailed results on the calibration of a prism-based spectrometer using an MCT array detector in the wavelength range from 2-12 µm. An outlook onto the next stage of development, i.e. extension into the NIR, VIS and UV, is given.

Presentation in the Oncoray Journal Club. Explained to a mainly medicine- and biology-oriented audience the benefits of a recent Nature paper: "Ptychographic X-ray computed tomography at the
nanoscale." (September 2010)

Topics addressed in presentation:

• What is this all about and what can one do with it? (+ link to biology and medicine as modern x-ray imaging)
• How does it work?
• What are the technical requirements and limitations?
• Briefly addressed towards the end: Current directions in research (challenges) and who works on it (people)

This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation.

Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide.

In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser.

The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).

Travelling-Wave Thomsonstreuung (TWTS) ist eine neuartige Thomsonstreuungsgeometrie mit großer Strahlungsausbeute pro Puls, bei der ultrakurze Laserpulse mit verkippten Pulsfronten als optische Undulatoren oder lichtgetriebene Freie-Elektronen-Laser für relativistische Elektronenpulse genutzt werden. Auf diese Weise können Röntgenstrahlungspulse mit hohem Kontrast und schmaler Bandbreite erzeugt werden.
Zur Untersuchung der Propagation von TWTS-Pulsen wird in dieser Arbeit ein wellenoptischer, analytischer Formalismus entwickelt, welcher die zeitliche Entwicklung des elektrischen Feldes eines hochintensiven und ultrakurzen Laserpulses mit Dispersionseigenschaften nach Beugung an VLS-Gittern beschreibt. Damit können die durch Dispersion verursachten Veränderungen am Laserpuls bei der Beugung in beliebiger Ordnung numerisch analysiert werden. Das habe ich genutzt, um für zwei Beispiele die TWTS-Pulse zu charakterisieren. Für eines der Beispiele wird anhand der Ergebnisse eine vereinfachte Darstellung des Pulses abgeleitet und die Dynamik eines relativistischen Elektrons bei der Wechselwirkung mit dem Puls und gestreuter Strahlung beschrieben. Daraus werden Schlüsse für die Anwendbarkeit des Schemas als Freie-Elektronen-Laser gezogen.

This paper presents an experimental study of the influence of the growth rate on the microstructure of multi-crystalline silicon (mc-Si). Crystals with a diameter of 105 mm were grown from an inductively heated, well-mixed melt by the conventional vertical Bridgman technique. Axial and vertical samples were prepared from the crystals to analyze the grain structure as well as the distribution of dislocations and precipitates. The results show that the growth rate influences the microstructure of the crystals mainly at the beginning of the solidification process. Growth with a low growth rate, for instance, favors the formation of radially elongated grains near the bottom of the crystal and suppresses the heterogeneous nucleation of SiC precipitates at the inner crucible wall. The effect of the grain shape is restricted to the bottom region of the crystals, whereas the precipitates are identified to be the origin of dislocations or dislocation clusters propagating throughout the crystal during growth. As a consequence, the dislocation density in a slowly grown crystal is found to be significantly lower than in a fast grown crystal.

Cobalt–nickel oxide films of known stoichiometry (x = Ni / (Co + Ni) = 0.30–0.63) were deposited on glass slides by using a spin-coating method and were UV irradiated for 2 h. The structure and morphology of thin films evidenced nanocrystalline spinel structures. Thin films with x = 0.63–0.5 have a mixed phase structure and good sensing properties for ethanol. Thin films with x = 0.30–0.40 have a single spinel phase, are ferrimagnetic and highly conductive at 300 K and have magnetoresistance ratios of 5–8%. Four-probe measurements indicate an insulator–metal transition at temperatures slightly below ferromagnetic Curie temperature. Metallic Ni and Co particles improve thin film functional properties.

We study finite-size effects in the process of e+ e− pair production via the non-linear Breit-Wheeler process in ultra short laser pulses. Based on the Nikishov-Ritus method we use laser dressed electron and positron wave functions to derive the differential and total pair production cross section, focusing on the effects of a finite pulse duration. Hence, we go beyond the infinite laser pulse approximation and provide a more exact description of experiments with modern femtosecond laser systems.

We employed density functional theory (DFT) calculations, and ultraviolet–visible (UV-Vis), extended X-ray absorption fine-structure (EXAFS) and attenuated total reflection Fourier-transform infrared (IR) spectroscopy analyzed with iterative transformation factor analysis (ITFA) to determine the structures and the pH-speciation of aqueous acetate (ac) and succinate (suc) U(VI) complexes. In the acetate system, all spectroscopies confirm the thermodynamically predicted pH-speciation by Ahrland (1951), with the hydrated uranyl ion and a 1:1, a 1:2 and a 1:3 U(VI)-ac complex. In the succinate system, we identified a new 1:3 U(VI)-suc complex, in addition to the previously known 1:1 and 1:2 U(VI)-suc complexes and determined the pH-speciation for all complexes. The IR spectra show absorption bands of the antisymmetric stretching mode of the uranyl mojety (υ3(UO2)) at 949, 939, 924 cm−1 and at 950, 938, 925 cm−1 for the 1:1, 1:2 and 1:3 U(VI)-ac and U(VI)-suc complexes, respectively. IR absorption bands at 1535 and 1534 cm−1 and at 1465 and 1462 cm−1 are assigned to the antisymmetric υ3,as(COO) and symmetric υ3,s(COO) stretching mode of bidentately coordinated carboxylic groups in the U(VI)-ac and U(VI)-suc complexes. The assignment of the three IR bands (υ3(UO2), υ3,as(COO) υ3,s(COO)) and the stoichiometry of the complexes is supported by DFT calculations. The UV-Vis spectra of the equivalent U(VI)-ac and U(VI)-suc complexes are similar suggesting common structural features. Consistent with IR spectroscopy and DFT calculations, EXAFS showed a bidentate coordination of the carboxylic groups to the equatorial plane of the uranyl moiety for all uranyl ligand complexes except for the newly detected 1:3 U(VI)-suc complex, where two carboxylic groups coordinate bidentately and one carboxylic group coordinates monodentately. All 1:1 and 1:2 complexes have a U-Owater distance of ~2.36 Å, which is shorter than the U-Owater distance of ~2.40 Å of the hydrated uranyl ion. For all complexes the U-Ocarboxyl distance of the bidentately coordinated carboxylic group is ~2.47 Å, while the monodentately coordinated carboxylic group of the 1:3 U(VI)-suc complex has a U-Ocarboxyl distance of ~2.36 Å, i.e. similar to the short U-Owater distance in the 1:1 and 1:2 complexes.

The e+ e− pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit-Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold √s = 2m a similar enhancement of the pair production rate as for circular polarization. The strong subthreshold enhancement is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

Boltzmann transport theory for electrical and thermal transport in Bi2Te3 will be discussed

the calculation of the intrinsic anomalous Hall conductivity as a pure Fermi surface property is demonstrated

thermoelectric properties of Bi2Te3/Sb2Te3 superlattices are discussed

thermoelectric properties of Si strained along (111) and Si/Ge(111) superlattices are discussed

presentation of the planned activities, pre-requisites and know-how of the newly established Helmholtz Virtual Institute Memeriox

ZnO belongs to the class of wide band gap semiconductors (Eg>3eV), with Eg=3.37eV, and exhibits very interesting optical and electrical properties. Used as a transparent conductive oxide (TCO) electrode in optoelectronic devices [1], ZnO has been developed as a low costs material, an alternative to commonly used and indium tin oxide (ITO). Due to the required transparency, at least in the solar spectral range and a low resistivity, ZnO has to be doped degenerately. While doping with Al leads to the required high carrier concentration [1], alloying with Mg increases the band gap up to 4.5 eV [2]. However, the increase of the conductivity by the increase of the carrier concentration (i.e. reaching the level of N=10^21cm^-3) can lead to a significant increase of the absorption of the light. Therefore, many researches focus on the increase of the electron mobility μ, in accordance with formula ρ=(eNμ)^-1.
The electron mobility is determined by the typical scattering processes in semiconductors, among other the extrinsic scattering on dopants and defects in the film. Since Al doped ZnO and ZnMgO layers, used for transparent electrodes are polycrystalline films, this process can be connected directly with dopants but also with local structure defects as Zn or/and O vacancies, stacking faults and grain boundaries are. These together with the small crystallographic domain size, in the range of 100nm, preferred growing orientation in c axis (perpendicular to the substrate), together with the Al and Mg dopants ionic radius smaller than for Zn [3] (respective crystal radii in tetrahedral coordination are: Al3+ 0.53Å, Mg2+ 0.71Å and Zn2+ 0.74Å), can cause the decrease of the local ordering of the samples.
In this paper we present XAS measurements on the Al doped ZnO and ZnMgO. The XANES spectra were fitted with the simulation program FEFF9 [4]. First results on the Al K edge, see Figure 1, show that the Al substitutes preferably the Zn lattice site in the material. For both dopants, Al and Mg, the spectra show a similar behaviour. The only clearly visible difference, the decrease of the intensity of the first peak for Al and Mg doped ZnO, in comparison to Al doped ZnO, can be attributed to the higher doping level (a similar effect is observed for double Al substitution of ZnO). The comparison of the experimental data with the simulation shows that the measured samples (3 at. % Al doped ZnO and 3 at. % Al doped ZnMgO (6 at.% Mg)) are in the low doping regime, where only single ion doping can be considered. The effect of the expansion of the c axis and the compression of a axis for the growth on glass substrate is also observed.

Acknowledgments: This work was supported by the German Ministry for Economy (AiF Köln).

Reference
[1] K. Ellmer, A. Klein, B. Rechs (Eds.), "Transparent Conductive Zinc Oxide: Basics and Applications in Thin Film Solar Cells", Springer, Berlin (2008)
[2] S. Choopun, R. D. Vispute, W. Yang, R. P. Sharma, T. Venkatesan, H. Shen, “Realization of band gap above 5.0 eV in metastable cubic-phase MgxZn1-xO alloy films” Appl. Phys. Lett. 80 (2002) 1529
[3] R.D. Shannon, “Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides”, Acta Cryst. A32 (1976) 751
[4] J.J. Rehr, J.J. Kas, M.P. Prange, A.P. Sorini, Y. Takimoto, F. Vila, “Ab initio theory and calculations of X-ray spectra”, Comptes Rendus Physique 10 (2009) 548-559

This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits.
Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Regarding photovoltaic applications, we dealt with two aspects: (i) the ion beam doping and thermal processing of so-called dirty silicon demonstrating a distinct improvement of the minority carrier diffusion length compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation
Whereas all these examples base on solid phase processing the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (NanoLett. 11, 2814 (2011)). Moreover a new approach of measuring temperatures in the subsecond time range will be mentioned as well as the interesting field of large area-low cost electronics.

The persistent competition for the cost-effective production of solar cells and displays requires low cost and high throughput production of transparent conductive oxides (TCOs). Nb-doped titania (TiO2:Nb) is a promising novel TCO material for these applications. The results of investigations of TiO2:Nb thin film deposited on large area substrates by sputtering with high deposition rates are reported. As a deposition method we used the direct current sputtering of a 780 mm length substoichiometric oxide tubular target arranged in a rotatable magnetron system in a pilot scale inline sputtering plant. The films were grown on unheated substrates and then thermally annealed at temperatures of 450°C. The influence of the magnetron magnetic field strength and oxygen partial pressure in the sputtering gas on the properties and structure of TiO2:Nb was investigated. A 100 nm thin film deposited on Borofloat® substrate shows after annealing a resistivity of 9.4 x 10-4Ωcm, 82% transmittance in the visible range and a refractive index of ~2.5 (λ=550 nm). The film properties were compared with those of the films grown using a planar oxidic target.

Combining first principles density functional theory and semi-classical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi2Te3/Sb2Te3 superlattices and their bulk constituents. It was found that already for the bulk materials Bi2Te3 and Sb2Te3, the Lorenz function is not a pellucid function on charge carrier concentration and temperature. For electron-doped Bi2Te3/Sb2Te3 superlattices large oscillatory deviations for the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods.

Experimental evidence links the receptor tyrosine kinases EphA2 and EphB4 to melanoma progression and metastasis. Another factor contributing to melanoma invasion-metastasis cascade is hypoxia. However, data on the influence of tumor hypoxia on regulation of Eph receptors and their ephrin ligands are scarce. This study aimed at clarifying whether hypoxia influences expression and synthesis of EphA2 and EphB4 and, furthermore, ephrinA1 and ephrinB2, respectively, in four human melanoma cell lines (A375, A2058, MeWo, and MelJuso). In order to investigate Eph/ephrin expression under hypoxic conditions we used cell monolayer cultures as extrinsic hypoxia models and A2058 spheroids as intrinsic hypoxia model. Hypoxic conditions were approved by measurement of VEGF expression and cellular uptake of [18F]fluoromisonidazol ([18F]FMISO). In all models, both VEGF expression and ([18F]FMISO) uptake increased under hypoxic conditions. In normoxia, EphA2, EphB4, ephrinA1, and ephrinB2 expression was detectable in all cell lines showing a substantially varying extent. Protein synthesis of EphA2 was detected in all cell lines and, moreover, of EphB4 in A375 and A2058 cells. However, no effect of experimental hypoxia on Eph/ephrin expression and protein synthesis could be observed. The findings contribute to debating the hypothesis that hypoxia is an important regulator of Eph/ephrin expression in tumors.

The thermoelectric transport properties of Bi2Te3/Sb2Te3 superlattices are analyzed on the basis of first-principles calculations and semi-classical Boltzmann theory. The anisotropy of the thermoelectric transport under electron and hole-doping was studied in detail for different superlattice periods at changing temperature and charge carrier concentrations. A clear preference for thermoelectric transport under hole-doping, as well as for the in-plane transport direction was found for all superlattice periods. At hole-doping the electrical transport anisotropies remain bulk-like for all investigated systems, while under electron-doping quantum confinement leads to strong suppression of the cross-plane thermoelectric transport at several superlattice periods. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity and the resulting figure of merit are given.

In relativistically strong laser fields with intensities well above 10^19 W/cm^2, multi-photon emission processes are important in collisions of relativistic electron beams with the laser pulse. We present results on the coherent two-photon process (double Compton scattering) in the presence of strong and short laser pulses, taking into account the finite temporal pulse length exactly for the first time.