Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The complexation of the trivalent Americium ion with salicylic acid was investigated using a Liquid Waveguide Capillary Cell (LWCC) for UV/vis spectroscopy, enabling measurements at very low metal concentrations.

Thermodynamic data for reactions of trivalent Actinides in the host rock environment are required for analysis of long-term safety of nuclear waste disposals in clay. We analyzed the complexation behaviour of Eu(III) and Am(III) with benzoic acid derivatives, which structures are similar to the natural organic matter.

Mittels UV-vis Spektroskopie wurden die Stabilitätskonstanten von Am-Citratkomplexen bei verschiedenen temperaturen zwischen 20 und 60°C bestimmt. Durch den Einsatz einer Liquid Waveguide Capillary Cell (LWCC) konnte mit sehr kleinen Am-Konzentrationen gemessen werden.

Krebserkrankungen entstehen aus Veränderungen in den Wechselwirkungen zwischen Onkogenen und Tumorsupressorganen, welche unter normalen physiologischen Bedingungen für die Regulierung des Zellwachstums und der Zellteilung verantwortlich sind. Das Verhalten der Krebszelle wird dabei durch eine Vielzahl von Faktoren aus dem genetischen und Mikormilieu des Organismus bestimmt. Als Ergebnis der genetischen Abweichungen treten bestimmte funktionale Veränderungen auf. So sind Tumorzellen durch erhöhten Stoffwechsel (Glukosemetabulismus, Aminosäuretransport, Protein-, DNA- und Lipidsynthese) sowie durch angiogene und hypoxische Prozesse charakterisiert, welche unweigerlich zu der Ausbildung von unkontrollierten Läsionen führen.

Der vorliegende Artikel gibt einen kurzen Überblick über die zur Zeit in der Klinik verwendeten mit den Radionukliden ¹⁸F und ¹¹C markierten PET Radiotracer für die onkologische Diagnostik und beschreibt kurz ihre Herstellung und das Prinzip ihrer spezifischen Anreicherung.

The new technology of laser acceleration, which promises radiotherapy accelerators of compact size and reasonable costs, results in ultra-short pulsed particle beams (in the region of 100 fs) with very high pulse dose rate (more than 1012 Gy/min). One important step before potential medical application is the radiobiological characterisation of this new radiation quality. Therefore, in vitro cell irradiations with laser accelerated electrons have been performed at the Jena Titanium:Sapphire (JETI) laser system. The obtained dose-effect-curves have been measured for two cell lines (tumor cell line FaDu, normal tissue cell line184A1) and biological endpoints (residual H2AX/53BP1 foci and clonogenic survival assay) revealing a reduced biological effectiveness of laser accelerated MeV electrons in comparison to continuous 200 kV X-ray reference irradiation.
In addition to the ultra-high pulse dose rate of the JETI electron beam this radiation quality differs also in energy spectrum and average dose rate from the 200 kV X-rays.
A negligible influence of the mean dose rate on biological effectiveness was confirmed by measuring the same cell response to 200 kV X-ray irradiation at 0.35 Gy/min (mean dose rate of the JETI electron beam) and at 1.4 Gy/min applied for reference irradiation. The influence of the energy spectrum was investigated by cell irradiation at a medical linear accelerator (LINAC). The two cell lines already studied at JETI have been irradiated with monoenergetic 6 MeV electrons according to the mean energy of the JETI electron beam. Clonogenic survival and residual DNA-DSB were determined for the LINAC electrons and compared to 200 kV X-rays, both radiations being similar in time-structure and mean dose rate. No difference in the number of residual H2AX/53BP1 foci after 24 h has been measured for both (quasi) continuous beams. In contrast increased clonogenic survival was found for the LINAC electrons compared to 200 kV X-rays as expected by the known increase of biological effectiveness with decreasing secondary electron energy. However, the decreased biological effectiveness is less pronounced for the LINAC electrons in comparision to the JETI laser electrons. Therefore, the remaining influence of the ultra-high pulse dose rate of JETI electrons is currently investigated.

This work has been supported by BMBF (no. 03ZIK445).

The novel technology of particle acceleration based on high intensity lasers is characterised by ultra-short pulse particle beams and high pulse dose rate. Before a potential medical application such beams have to be characterized in terms of their radiobiological properties. Hence, systematic in vitro cell experiments were performed with laser accelerated electrons by using the Jena titanium:sapphire (JETI) laser system. As presented last year, residual H2AX/53BP1 foci and clonogenic survival for four human cell lines were therefore analysed. The dose response curves show a reduced radiobiological effectiveness for laser accelerated MeV electrons in comparison to the continuous 200 kVp X-rays. Conceivable reasons for the measured differences in the radiobiological effectiveness between both radiation qualities could be the difference in energy spectrum and mean dose rate as discuss in a separate contribution. The influence of the high pulse dose rate of the laser accelerated electron beam was investigated by using pulsed electron beams generated by the electron accelerator ELBE (Electron Linac for beams with high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf. The variable time structure of the ELBE electron beam allows pulsed irradiation as well as quasi-continuous irradiations, whereas the pulse doses are tunable over more than six orders of magnitude. Hence, ELBE can be used to mimic both ultra-short pulses of laser accelerated electrons as well as quasi-continuous electron beam as delivered by a conventional therapeutic linac. These two pulse regimes were applied in systematic in vitro cell studies by using monoenergetic electrons of 20 MeV. For a comparison the ELBE experiments were performed similar to the JETI experiments. Therefore, the same cell lines (FaDu, 184A1, additional HDF and F153) and the two biological endpoints (residual H2AX/53BP1 foci, clonogenic survival) were investigated. Preliminary results show no difference in the biological effectiveness between pulsed and quasi-continuous ELBE electrons as well as continuous X-rays.

The work was supported by the BMBF, grant no. 03ZIK445

The influence of surface bound Fe(II) on uranium oxidation state and speciation was studied as a function of time and pH (6.1-8.5) in U(VI)-Fe(II)-montmorillonite (Ca-montmorillonite) system under CO2-free, anoxic (O2 <1 ppmv) conditions. The results show a rapid removal of U(VI) from the aqueous solution within 1 h under all pH conditions. U LIII-edge X-ray absorption near-edge structure (XANES) spectroscopy shows that 96% of the total sorbed U(VI) is reduced at pH 8.5. However, the extent of reduction significantly decreases at lower pH values, in line with specifically sorbed Fe(II) decreasing. The reduction kinetics followed by X-ray photoelectron spectroscopy (XPS) during 24 h at pH 7.5 demonstrates the presence of partially reduced surface species containing both U(VI) and U(IV). Thermodynamically predicted mixed valence solids like U3O8/β-U3O7/U4O9 do not precipitate as verified by transmission electron microscopy (TEM) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. This is also supported by the bicarbonate extractionresults. The measured redox potentials of Fe(II)/montmorillonite suspensions are controlled by the Fe(II)/ hydrous ferric oxide (HFO(s)) couple at pH 6.1 and by the Fe(II)/ γ-FeOOH(s) couple at pH 7.5. The U(VI) reduction mechanism is suggested by considering individual U(VI), U(IV) surface complexes with Fe(II) specifically sorbed on strong and weak sites of montmorillonite.

Mixing of fluids in T-junction geometries is of significant interest for nuclear safety research. The most prominent example is the thermal striping phenomena in piping T-junctions, where hot and cold streams join and turbulently mix, however not completely or not immediately at the T-junction. This results in significant temperature fluctuations near the piping wall, either at the side of the secondary pipe branch or at the opposite side of the main branch pipe. The wall temperature fluctuation can cause cyclical thermal stresses and subsequently fatigue cracking of the wall. The issue of thermal striping has been observed in light water reactors (LWRs) as several incidents of high-cycle fatigue at coolant mixing junctions have been detected - mainly in piping T-junctions - in nuclear plants, like the failure event at Civaux 1. These incidents occurred usually in piping of diameter 5-20 cm and the most susceptible parts to thermal fatigue are mixing T-junctions of the Residual Heat Removal (RHR) system in both boiling (BWR) and pressurized water reactors (PWR). This has raised thermal fatigue to be a serious safety concern and an important aspect on ageing and life management of nuclear plants with LWR. A typical value for the temperature difference between the hot/cold streams is 160°C. Critical parameters for thermal fatigue analyses are frequencies (ω), temperature differences (T), number of cycles (N), and material properties. Most damaging thermal loads appear to be due to large scale turbulent fluctuations of low frequency (3-10 Hz). From a thermal hydraulic standpoint, the accurate prediction of such large coherent eddies is a challenging task, requiring CFD and advanced turbulence modelling. Significant effort has been put in the experimental investigation of the thermal fatigue and thermal striping phenomena due to thermal mixing in pipe T-junctions. In November 2008, a T-junction thermal mixing test was carried out at the Älvkarleby Laboratory of Vattenfall Research and Development (VRD) in Sweden. Data from this test have been reserved specifically for this CFD benchmark exercise. The test section is constructed from Plexiglas, and the junction itself from one solid block into which the main and branch pipes fit. The temperatures of the water in the main and branch pipes were maintained at 15°C and 30°C, respectively, with minimal heat loss. Special care was taken to provide simple and well-defined inlet boundary conditions to remove ambiguities in defining the CFD input data. Temperature fluctuations near pipe walls were measured using thermocouples. These were placed around the inner wall perimeter of the main pipe at seven stations downstream of the junction and at one station upstream. All thermocouples were positioned 1 mm from the wall. Velocity profiles upstream and downstream of the junction were measured using a two-component LDV system. These were positioned at each inlet, and at the outlet. Data are in the form of mean values, RMS values and turbulence statistics. The numerical prediction of thermal mixing and striping in terms of temperature amplitude and frequency using the current CFD technology is a computational intensive and challenging task. By the physics of the phenomenon, the flow is turbulent and highly transient and the thermal striping at pipe walls is affected by the formation and propagation of large-scale turbulent structures in space and time. The aim is therefore a CFD turbulence model validation study and a detailed CFD experiment comparison. Turbulence model approaches to be studied in the present validation study include URANS SST as well as scale resolving turbulence models (LES).

The aim of the numerical simulations carried out in this study was to determine how and where mineral wool fibres are deposited across the grid spacers of the fuel elements of a German PWR. The spacer grid is modelled as a strainer which completely retains the insulation material carried by coolant and reaching the plane of the spacers. The accumulation of the insulation material gives rise to the formation of a compressible fibrous cake whose permeability to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity. The calculations showed that the fibers material at the uppermost spacer grid plane is not evenly distributed. Later when the inner circulation has stopped, the insulation material can also be distributed into other regions of the spacer plane. Further investigations are necessary to determine the accumulation of insulation material for a longer period of time. Also steam production in the core or re-suspension of the insulation material during back flow should be considered.

The presentation gives an overview of the history of nuclear power, radioactive waste - it's classification and composition, as well as final waste disposals in deep geological formations.

Natural clays are dicussed as possible host rocks for nuclear waste repositories. Natural clays contain also organic substances, like humic acids (HA), known for their ability to bind metal ions, e.g. actinides like uranium. Due to this, HA can influence the actinide migration. In this study the effect of HA presence on the U(VI) sorption onto the natural clay, opalinus clay from Mont Terri (Switzerland), is presented.
Beside the mineralogy of the clay and the composition of the synthetic opalinus clay pore water, the speciation of U(VI) in opalinus clay pore water and the sorption results onto opalinus clay in the two background electrolytes, 0.1M NaClO4 and synthetic opalinus clay pore water, are shown. It was concluded, that the released calcium ions determine the speciation and affect as a consequence the sorption behavior of U(VI) and also HA onto opalinus clay.

For nuclear waste disposal in geological formations, possible host rocks in Germany are salt rock (Gorleben), granite rock and clay. Currently, intense examinations on natural clay are taking place in a joint project funded by the Federal Ministry of Economics and Technology. An important part of this is the investigation of sorption and migration processes resulting from the actinide interaction with natural clay and the determination of the influence of clay organic matter on these processes. In this regard, the sorption of uranium(VI) on natural clay is examined. Furthermore, the influence of organic matter, such as fulvic acids (FA) and humic acids (HA), known for their ability to bind metal ions, is investigated.
Here some characteristics of the natural clay, opalinus clay from Mont Terri (Switzerland), and the synthetic opalinus clay pore water are shown. The speciation of uranium(VI) in this pore water in the absence and presence of HA is presented. The sorption of uranium(VI) in the absence and presence of HA onto opalinus clay and onto the reference clay mineral kaolinite is compared .

Vibrational spectroscopy potentially provides structural information of molecule complexes. Actinyl ions, e.g. AnO2 n+ (An=U,Np; n=1,2) can be identified by the frequency of their antisymmetric stretching vibrational mode νas which generally correlates with the character of the molecular environment, i.e. number and type of ligand, of the actinyl ion group. [1]
The migration behavior of actinides in the geosphere is strongly influenced by sorption processes at water-mineral oxide interfaces [2]. The sorption of neptunium(V) at low concentration levels (50 μM) on model oxide surfaces (TiO2, SiO2, ZnO) was investigated in situ at different pH (4.0 – 7.6). For the first time, in situ formation of inner-sphere bidentate Np(V) surface complexes onto oxides was observed by FT-IR spectroscopy [3]. Unequivocal assignments of thermodynamic reaction constants are feasible.
To investigate the U(VI) chemotoxicity at a molecular level, the coordination between U(VI) and different protein functional groups under
physiological relevant conditions is investigated.The highly phosphorylated protein phosvitin serves as a model system for the elucidation of the molecular interaction of uranyl with native proteins in aqueous solution. [4,5] Soluble protein-U(VI) complexes in aqueous solution evidence preferential U(VI) complexation to phosphoryl groups of the protein side chains. In combination with X-ray spectroscopy molecular structures such as the postulated “Feldman complex” can be verified [6].

[1] K. Müller, H. Foerstendorf, S. Tsushima, V. Brendler, G. Bernhard (2009), Journal of Physical Chemistry A 113, 6626-6632.
[2] G. R. Choppin (2007), Journal of Radioanalytical and Nuclear Chemistry 273, 695-703
[3] K. Müller, H. Foerstendorf, V. Brendler, G. Bernhard (2009) Environmental Science & Technology, 43, 7665-7670
[4] R. Shainkin, G.E. Perlmann (1971) Journal of Biological Chemistry 246, 2278-2284.
[5] B.M. Byrne, A.D.V. Schip, J.A.M. Vandeklundert, A.C. Arnberg, M. Gruber, G. Ab (1984) Biochemistry 23, 4275-4279.
[6] B. Li, H. Foerstendorf, J. Raff, G. Bernhard (2007) Geochim. Cosmochim. Acta 71, A567.

An(III) exhibit very high radioactivity and therefore pose a great health risk for humans in case of accidental release/incorporation. Their metabolism and speciation in body fluids is not yet fully known and our studies shall help to adress this lack of knowledge. Ln(III) are used in radiological medicine e.g. as contrast agents and exhibit similar physico-chemical properties as An(III) but no radioactivity. Therefore Ln(III) are often used as analogs for An(III). In the present study the complexation of Eu(III) with different organic ligands, which are components of natural biofluids, as well as its speciation in natural human urine samples were investigated. Results show, that Eu(III) speciaition in urine samples with lower pH is dominated by citric acid complexation while in samples with higher pH inorganic complexes are formed.

The sorption behavior of uranium(VI) to the monocellular green algae Chlorella vulgaris was investigated in tap water and mineral medium. The initial and final solutions as well as the formed uranyl-algae-complexes were characterized by time-resolved laser-induced fluorescence spectroscopy.

The confocal laser scanning microscopy is often referred to as computer tomography for the cells. Its main advantage in comparison to the common fluorescence microscopy is the possibility to generate optical slices inside of a sample. The CLSM-System of the Institute of Radiochemistry (IRC) comprises some special characterizing highlights which were presented in this poster.

Characteristics and policy of radioactive waste disposal in Germany.

The binding of uranium(VI) to the green algae Chlorella vulgaris was investigated with different spectroscopic techniques.

Investigation of Biofilms from naturally uranium contaminated environments

Uranium(IV) colloids were investigated by ultrafiltration, ultracentrifugation and light scattering techniques. Results confirm that the particle size of these colloids depends on the initial silicic acid content and pH.

The paper shows the results of an experimental investigation of flow control by periodic actuation by streamwise Lorentz forces at the leading edge of a NACA0015 profile. Synchronized force and time resolved particle image velocimetry (PIV) measurements were performed in a sodium hydroxide channel for Reynolds numbers of Re = 0.5 10⁵ and 10⁵. A wavelet algorithm was used to detect vortical structures and allows to relate these large scale structures to the observed lift and drag forces. Additional information about the mechanism of momentum transfer in the flow was gained by proper orthogonal decomposition of the data. In order to minimize the energetic effort of the flow actuation, the investigation focuses on small momentum coefficients. For small angles of attack a complete reattachment of the flow can be established by the actuation, whereas for large angles of attack the interaction of vortical structures becomes more prominent. The paper discusses the effects of excitation frequency and wave form for two qualitatively different flow regimes .It shows that the proper choice of the excitation frequency is very important for large angles of attack. The optimal excitation frequency was examined as a function of the angle of attack.

Es gibt hierzu kein Abstract.

Two-photon quantum well infrared photodetectors (QWIPs) take advantage of a resonant intermediate state, thus leading to a resonantly enhanced optical nonlinearity which is six orders of magnitude stronger than in a bulk semiconductor. This approach results in an extremely sensitive quadratic detector for mid-infrared and terahertz radiation, which is useful for quadratic autocorrelation measurements of mid-infrared optical pulses from free-electron lasers (FEL), modelocked quantum cascade lasers, and nonlinear optical converters. The time resolution of this detector is limited by the intersubband dynamics associated with the intermediate state. Therefore, the two-photon QWIP provides interesting opportunities for studies of the associated intersubband population and polarization lifetimes.
We report on electron intersubband relaxation and dephasing in n-type InGaAs/AlGaAs quantum wells by femtosecond two-photon photocurrent spectroscopy. The approach enables us to determine systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes [1]. By varying the excitation energy, it is also possible to tune the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state [2]. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.
Exploiting the two-photon QWIP approach for pulse monitoring of mid-infrared sources, we have performed autocorrelation measurements at wavelengths in the mid-infrared and Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, quadratic detection at wavelengths around 5.5 μm is still possible at room temperature [3], which is crucial for applications in practical systems. A two-photon detector which works below the Reststrahlen band at 42 μm (7.1 THz) will also be reported.
[1] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).
[2] H. Schneider, T. Maier, H. C. Liu, M. Walther, Opt. Express 16, 1523 (2008).
[3] H. Schneider, H. C. Liu, S. Winnerl, O. Drachenko, M. Helm, J. Faist, App. Phys. Lett. 93, 101114 (2008).

Es wird allgemein davon ausgegangen, dass in Wissenschaft, Technologie, Medizin und täglichem Leben eine schnelle Zunahme der Anwendung von Engineered Nanoparticles (ENPs) bevorsteht. Gegenwärtig existiert noch relativ wenig Wissem über das Verhalten von ENPs in der aquatischen Umwelt. Unsere Untersuchungen hatten das Ziel, Informationen über das Verhalten von Carbon Nanotubes (CNTs) als potentiellen Trägern von Schadstoffen im Falle einer unbeabsichtigten Freisetzung von CNTs in die Umwelt zu gewinnen. Die Experimente zeigten, dass unbehandelte CNTs in wässriger Suspension wenig kolloidale Stabilität besitzen. Auch die Sorptionskapazität der unbehandelten CNTs für Uran(VI) ist gering. Die Oberflächenmodifizierung der CNTs durch Oberflächenoxidation mittels eines Gemischs aus konzentrierter HNO3 und konzentrierter H2SO4 erhöhte die kolloidale Stabilität in neutralem Wasser jedoch sehr stark. Außerdem stieg die Sorptionskapazität für Uran, welches als ein Beispiel für ein toxisches Schwermetall diente, stark an durch die Oberflächenbehandlung. Die Sorptionsdaten des Urans konnten am besten durch eine Langmuir-Adsorptionsisotherme gefittet werden. Der Anstieg der kolloidalen Stabilität und der Sorptionskapazität war zurückzuführen auf die Bildung von neuen funktionellen Gruppen auf der CNT-Oberfläche durch Oberflächenoxidation. Diese Gruppen (Carboxylgruppen) konnten durch FTIR-Spektroskopie auch detektiert werden. Ein anderer Weg, die kolloidale Stabilität der CNTs zu erhöhen war die Zugabe von kleinen Mengen an Huminsäure zu Suspensionen von unbehandelten CNTs.

The anomalous wear-out phenomena of Eu-implanted metal–oxide-semiconductor devices were investigated. It will be shown that in contrast to other rare earth elements the electroluminescence (EL) intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances this rise may amount up to two orders of magnitude. The EL behaviour will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy and Rutherford backscattering spectroscopy were applied to trace the development of Eu / Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer. The hydrogen profile within the SiO2-SiON interface region was determined by nuclear reaction analysis. Current-voltage characteristics, EL decay times and the progression of the voltage and the EL spectrum with increasing charge injection were measured to study charge and trapping phenomena in the oxide layer to reveal details of the EL excitation mechanism. A first qualitative model for the anomalous life time behaviour is proposed.

Electrically driven Si-based light emitters will give a major impact on the development of integrated photonic applications. However, despite the remarkable success which was achieved in the last two decades on this field none of the different Si-based light emitters of today can compete with III-V light emitters or organic LEDs in terms of efficiency and life time. In many cases the applied voltage is also uncomfortably high.
The present work explores the physical limitations of voltage downscaling for those light emitters whose electrical excitation mechanism is based on impact excitation of hot electrons. In detail, the drop down of the electroluminescence power efficiency with decreasing SiO2 thickness of Tb-implanted devices is investigated. It will be experimentally shown that there is a dark zone with an extension of about 20 nm behind the injecting interface in which the hot electrons have not yet gained enough kinetic energy in order to excite the Tb3+ luminescence centers. In addition, the replacement of the host matrix SiO2 by SiON results in a decrease of power efficiency by two orders of magnitude which is consistent with experimental data about the hot energy distribution in these media.

Electrically driven Si-based light emitters will give a major impact on the development of integrated photonic applications. However, despite the remarkable success which was achieved in the last two decades on this field none of the different Si-based light emitters of today can compete with III-V light emitters or organic LEDs in terms of efficiency and life time. In many cases the applied voltage is also uncomfortably high.

The presentation discusses several aspects of the suitability of Si-based light emitters for applications on the example of rare earth implanted MOS structures. In the first part it will be shown that in case the electrical excitation mechanism is based on impact excitation of hot electrons there is a dark zone behind the injection interface in which luminescence centers will not be excited. With a dark zone extension in the order of 20 nm this limits the possibility to downscale the oxide layer thickness and thus the applied voltage. The second part of the presentation reports about ongoing activities to utilize Si-based light emitters for biosensors. Finally, the topic of Si-based light emitters embedded in photonic architectures is briefly addressed.

Rare earth implanted MOS light emitting devices are one of the most promising candidates for Si-based light emission and provide – depending on the implanted element – strong electroluminescence from the UV through the visible up to the IR. The talk will start with an introduction to rare earth’s and the special features of their electronic structure, and will focus than on the electroluminescence properties and the possibilities to enhance efficiency and operation life time of such devices. Finally the suitability for potential applications, especially in biosensing, will be discussed.

Current research results contradict the previously assumed high mobility of the radionuclide Se-79 from nuclear waste repositories

overview on technical aspects as well as on research highlights in 2009

The complexation of thorium, neptunium and plutonium at oxidation state +IV with three ligands of increasing complexity has been investigated. These ligands are relevant for bio inorganic systems. The first ligand is the small nitrilotriacetic acid that often play the role of protecting ligands against hydrolysis. EXAFS results for the Th to Pu series have been correlated to quantum chemical calculations and show an homogeneous behavior of the actinide at oxidation state +IV. For larger ligands, steric effects may become significant and one can ask how the ligand may accommodate the large actinide cation coordination sphere. Model pentapeptides have been synthesized and tested as complexing agents. Comparison with NTA shows that the molecular arrangements are radically different. The third ligand system is transferrin, a diferric metalloptrotein that is well known to coordinate a large variety of cations from transition metals of f-elements. Metalloproteins bear primary, secondary and tertiary structures that all play a crucial role in bonding. At a given oxidation state (+IV), but for various atomic numbers (Th, Np, Pu) EXAFS data at the cation LIII edge exhibit significant coordination discrepancies that are related to a changes in protein geometry. In that sense, the metalloprotein may be viewed as a complex system.

The high financial and environmental costs associated with remediation of land contaminated through 60 years of global nuclear activity has underpinned the development of new passive in situ bioremediation processes for sites contaminated with nuclear waste. Many of these processes rely on successfully harnessing newly discovered natural biogeochemical cycles of key radionuclides and fission products. Of particular note are strategies that involve enzymatic and indirect redox transformations of actinides such as uranium, neptunium and plutonium and fission products such as technetium. This chapter will discuss the recent advances that have been made in understanding the microbial colonization of radioactive environments and the biological basis of microbial transformations of radioactive waste in these settings. In addition, the impact of co-contaminants such as nitrate on both the microbial ecology of sediments and radionuclide speciation will also be discussed.

Natural bacterial community structures in the wetlands of uranium mill-tailings with different geographic origin (Germany and USA) and possessing various levels of uranium contamination were studied. Comparative analyses of bacterial communities via direct molecular approaches based on 16S rRNA gene sequences revealed strong predominance of Gamma-, Beta-, or Deltaproteobacteria in dependence on the geographic origin and on the anthropologic history of the studied wastes. In all studied samples novel, yet to be cultured, Betaproteobacterial populations were identified. It was possible to culture representatives of Gamma-Pseudomonas as well as some Alphaproteobacteria (mainly representatives of Sphingomonas sp.) and also different groups of Firmicutes.
Treatments of the samples from one of the studied uranium wastes with uranyl nitrate resulted in a strong shifting in the natural bacterial community and proliferation of representatives of Gamma-, Betaproteobacteria, and/or Firmicutes, depending on the aeration conditions of the experiments. The increased size of the mentioned bacterial populations was confirmed by using a combination of direct monitoring methods based on 16S rRNA and narG genes.
The fate of the added U(VI) in a form of uranyl nitrate was monitored via Time Resolved Laser-induced Fluorescence Spectroscopic (TRLFS) analysis. The latter demonstrated that almost all added uranium was complexed in uranyl phosphate compounds.
Transmission Electron Microscopic (TEM) and X-ray Absorption Spectroscopic (XAS) analyses of the interactions of particular uranium waste bacterial isolates with U(VI) under conditions, corresponding to the natural ones, revealed that the added uranium is immobilized mainly on their cell walls via sorption by organic phosphate groups and/or via precipitation in inorganic uranyl phosphate mineral phases (biomineralization). The observed biomineralization process was connected to release of orthophosphate by the stressed by the treatments bacterial cells. No reduction of U(VI) to U(IV) was observed at the studied oligotrophic conditions which are relevant to the natural ones in the studied wastes.

Bacteria and archaea are the most ubiquitous organisms in terrestrial and aquatic environments. They play a major role in deposition and weathering of a large variety of minerals enriched with or consisting mainly of different metals, such as iron, manganese, copper, gold, and even radionuclides (e.g. uranium). The structure of biologically synthesized minerals is strongly influenced by the metabolic properties of the bacterial or archaeal strains involved in their production and also by the different metal binding potential of their cell wall components.
The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from uranium mining wastes. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting the oligotrophic uranium mining waste pile soils immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Particular Gram-positive isolates, possessing highly ordered proteinaceous surface layers (S-layers), are immobilizing U(VI) by both phosphate groups from their peptidoglycan and also by the carboxylic groups of the aspartate and glutamate stretches of their S-layers.
In addition, the cell wall supported formation of metallic palladium and gold nano-clusters by some bacteria and archaea will be presented. Despite of the different mechanisms of the biological deposition of Pd by Gram-negative and Gram-positive bacteria, the nanoparticles formed by both had almost identical size and catalytic activity. The Au nanoclusters formed by bacteria and archaea had significantly different physical properties.

Interactions of the natural isolate Pseudomonas rhodesiae R5 with U(VI) and different compounds were studied by using TEM, EXAFS and wet chemistry experiments. The ability of the strain to accumulate U(VI) via bio-sorption and bio-mineralization was demonstrated. TEM analyses revealed that the U(VI) accumulates were exclusively localized on the cell wall. EXAFS analyses demonstrated that the formed U(VI) accumulates represented meta-autunite-like phases.
The strain P. rhodesiae R5 demonstrated a high capability to utilize phenol compounds as well and was used for construction of biofilms on polyethylene oxide cryogels (PEO-biogels). The latter were effectively applied for decontamination of phenol polluted waters.

Positron emission tomography (PET) is a well-established functional imaging method used in nuclear medicine. It allows for retrieving information about biochemical and physiological processes in vivo. The currently achievable spatial resolution of PET is about 5mm for brain acquisitions and about 8mm for whole-body acquisitions. However, recent improvements in image reconstruction methods point to a resolution of 2mm in the near future. Typical acquisition times range from minutes to hours due to the low signal-to-noise ratio of the measuring principle of PET, as well as due to the monitoring of the metabolism of the patient over a certain time. Therefore, patient motion increasingly limits the possible spatial resolution of PET. In addition, patient immobilizations are only of limited benefit in this context. Thus, if kept uncorrected, patient motion leads to a relevant resolution degradation and incorrect quantification of metabolic parameters.
In this talk, the results of a novel motion compensation method for clinical brain PET acquisitions developed at the research centre Dresden-Rossendorf (Forschungszentrum Dresden-Rossendorf ) in cooperation with the nuclear medicine department of the university hospital of the Technical University Dresden are presented. By using an external motion tracking system, information about the head motion of a patient is continuously acquired during routine PET acquisitions. Based on the motion information, an event-based motion compensation algorithm performs spatial transformations of all registered coincidence events, thus utilizing the raw data of a PET system - the so-called list-mode data. For routine acquisition of this raw data, methods have been developed which allow for the first time to acquire list-mode data from an ECAT Exact HR⁺ PET scanner within an acceptable time frame. Furthermore, methods for acquiring the patient motion in clinical routine and methods for an automatic analysis of the registered motion have been developed. For the clinical integration of the aforementioned motion compensation approach, the development of additional methods (e.g. graphical user interfaces) was also part of this work.
After development, optimisation and integration of the event-based motion compensation in clinical use, analysis with example data sets have been performed. Noticeable changes could be demonstrated by analysis of the qualitative and quantitative effects after the motion compensation. From a qualitative point of view, image artefacts have been eliminated, while quantitatively, the results of a tracer kinetics analysis of a FDOPA acquisition showed relevant changes in the R0k3 rates of an irreversible reference tissue two-compartment model. Thus, it could be shown that an integration of an event-based motion compensation method which is based on the utilization of the raw data of a PET scanner, as well as the use of an external motion tracking system, is not only reasonable and possible for clinical use, but also shows relevant qualitative and quantitative improvements for PET imaging.

Los océanos cubren aproximadamente un 70% de la superficie terrestre, de ahí que sean uno de los mayores sumideros de radionucleidos de origen antropogénicos (1). En el caso del mar mediterráneo, se ha estimado una deposición de 12 y 0.12 PBq de 137Cs and 239,240Pu, respectivamente, entre 1956 y 1996, debido principalmente a la realización de pruebas nucleares (2). El destino final de estos radionucleidos son los sedimentos marinos, aunque pueden permanecer en la columna de agua a concentraciones bajas, quedando biodisponibles para los organismos presentes. Algunos estudios han demostrado que estos ambientes marinos están habitados por una variedad de especies microbianas que podrían interaccionar con estos radionucleidos mediante diferentes mecanismos tales como bioadsorción, acumulación intracelular y precipitación, entre otros. Estos mecanismos ayudan tanto a la movilización como la inmovilización de estos elementos en el medio acuático, alterando, por tanto, su biodisponibilidad. El objetivo del trabajo actual era determinar la especiación química del uranio precipitado por la bacteria marina Idiomarina loihiensis MAH1 en agua de mar mediante espectroscopia de fluorescencia inducida por laser en tiempo resuelto (TRLFS) bajo condiciones medioambientales (a bajas concentraciones de U in agua de mar)

The oceans cover approximately 70% of the Earth’s surface. Hence, they are one of the biggest sinkhole for anthropogenic released radionuclides. In case of the Mediterranean sea, there has been estimated a deposition of 12 and 0.12 PBq of 137Cs and 239,240Pu, respectively, between 1956 and 1996 primarily due to the performance of nuclear tests. The marine sediments are the final destination of these radionuclides, although they can remain in the water column to low concentrations, remaining bioavailable for the present organisms. Some studies have demonstrated that these marine environments are inhabited by a variety of microbial species that might interact with these radionuclides by means of such different mechanisms like, for example, biosorption, intracellular accumulation and precipitation. These mechanisms support the mobilization or immobilization of these elements in the aquatic environment, altering, therefore, his bioavailability. The objective of the present work was to determine the chemical speciation of the uranium precipitated by the marine bacterium Idiomarina loihiensis MAH1 at environmental conditions (low concentrations of U) in sea water by using time-resolved laser-induced fluorescence spectroscopy (TRLFS).

A consequence of a total loss of AC power supply (station blackout) leading to unavailability of major active safety systems is that the safety criteria ensuring a secure operation of the nuclear power plant would be violated and a consequent core heat-up with possible core degradation would occur. In such an accident a special accident management measure (primary side depressurization) can be applied to reduce the primary pressure and to activate the injection from the passive emergency core cooling systems (accumulators). The analyses presented in this paper are aiming at a detailed investigation of the accident sequence and the possibilities to prevent or to mitigate a damage of the reactor core. A main objective of the investigation is to evaluate the effectiveness of the applied accident management measure. The analyses are performed using the codes ASTEC and ATHLET developed by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH).

The experimental realization of dynamo excitation as well as theoretical and numerical examinations of the induction equation have shown the relevance of boundary conditions and material properties for a self-sustaining dynamo. Generally, in non-spherical geometry typical insulating boundary conditions are described by elaborated schemes (e.g. solving of the Laplace equation in an extended domain) or by simplifying approximations (pseudo vacuum). A different approach is provided by a modified integral equation procedure, commonly known as the boundary element method (BEM). Integrating the Laplace equation on the boundaries allows to overcome the difficulties of the non-local character of insulating boundary conditions and the direct computation of the magnetic field next to an insulator becomes possible. However, within the interior of a field producing domain geometric constraints or varying material properties (e.g. electrical conductivity of the container walls or localized high-permeability material) might also play a role.

In this paper we report on the investigation of electrostatic forces between a conductive probe and semiconducting materials by means of Kelvin probe force microscopy measurements. Due to the formation of an asymmetric electric dipole at the semiconductor surface, the measured Kelvin bias is related with the difference between Fermi energy and respective band edge. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to buried doped regions in cross-sectionally prepared Si epilayer structures and to shallow doped regions in a conventional dynamic random access memory (DRAM) cell. Frequency dependent KPFM measurements were performed under ambient conditions by means of an Anfatec Level-AFM with a 2nd amplifier and p- and n-type conductive NSC15 probes from MikroMasch. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent of the operation frequency. The frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped Si are probed.

A free electron laser covering a wavelength range of nearly two spectral decades (3-300 µm or 1-100 THz) has been in operation at our research center for a few years. I will present a few examples of the research done with it, taking advantage if its high peak and average power and picosecond time structure.
I will present measurements of carrier relaxation in semiconductor quantum dots, where the relaxation time varies by three orders of magnitude (2 ps to 1.5 ns), if the energy level spacing is changed by only a factor of two (30 meV to 15 meV). This can be explained in the quantum dot polaron picture.
The high average power allows one to perform near-field microscopy experiments. We can image ferroelectric domains on BaTiO3 surfaces purely due to their optical contrast resulting from a slight anisotropy of the dielectric function. Sweeping the FEL wavelength across a phonon resonance results in a reversal of optical contrast, which demonstrates the resonant nature of the interaction. The spatial resolution is 150 nm, about 1/100 of the wavelength.
Finally I will discuss a nonlinear mixing experiment, where THz sidebands of 800 nm radiation are generated in a semiconductor quantum well system, and briefly describe first cyclotron resonance experiments using the FEL in the pulsed magnetic field.

Four different liquid metal ion sources (LMIS), working with pure Bi as well as with Bi containing alloys (Au13Bi87, Ga38Bi62, Ga35Bi60Li5) were investigated with respect to the emission behaviour as a function of current and temperature, the mass spectra and the energy distribution of the individual ion species. Additionally, for the pure Bi LMIS the sputtering rates for Bi ions and clusters on a Si, SiO2 and Ge substrates were compared with that of Ga projectile ions using a mass separating focused ion beam system.

In this paper state of the art electrical nanometrology techniques are reviewed with the focus on semiconducting materials. The basics of scanning capacitance microscopy, scanning spreading resistance microscopy, scanning microwave microscopy, and Kelvin probe force microscopy, and their applicability on various material systems are discussed. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.

Over the last years multiple research groups achieved multi-MeV to GeV electron beams. Ultrashort bunches and a very low emittance combined with a high bunch charge offer a wide range of applications nevertheless the reproducibility of those beams is one of the main problems. External injection into a plasma wake is a promising concept to separate the influence of different input parameters from each other for more control of experimental results and to improve reproducibility. At the Research Center Dresden-Rossendorf the 150TW laser system DRACO was set up next to an superconducting electron accelerator. This will give the opportunity to study wake field acceleration in more detail. In this talk the present status of the experiment, ongoing upgrades and future plans will be described.

Die Injektion von Gasblasen wird oft in metallurgischen Prozessen zur Veredlung oder Entgasung metallischer Schmelzen eingesetzt. Eine Optimierung der Prozessabläufe kann nur auf Grundlage eines umfassenden Verständnisses der Strömungs- und Transportvorgänge erfolgreich sein. Dies erfordert neben numerischen Simulationen eine realitätsnahe experimentelle Modellierung in Flüssigmetallen. Für diese Modellexperimente besteht ein großer Bedarf an geeigneter Messtechnik zur Bestimmung der Strömungsstruktur und der Blaseneigenschaften.
In den letzten Jahren hat die Ultraschallströmungsmesstechnik im Hinblick auf einen Einsatz in Flüssigmetallen eine spürbare Entwicklung erfahren und ihre Eignung für Messungen in Zweiphasenströmung unter Beweis gestellt. Im Vortrag werden das Ultraschall-Doppler und das Ultraschall-Laufzeitverfahren vorgestellt. Mit Hilfe des Ultraschall-Doppler Verfahrens können gleichzeitig Flüssigmetall- und Blasengeschwindigkeit bestimmt werden. Das Laufzeitverfahren liefert komplementäre Daten über die geometrische Struktur der Blasen und des Blasenschwarms. Dies betrifft insbesondere Blasendurchmesser, Blasenform und raumzeitliche Ausdehnung des Blasenschwarms. Spezifische Probleme der Verfahren, insbesondere bei höheren Gasgehalten, werden diskutiert und zukünftige Entwicklungsperspektiven aufgezeigt.

The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled by the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for a small-size test problem confirm the correctness of the implementation of the prototype coupling. This test problem was a mini-core consisting of nine real-size fuel assemblies. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the ANSYS CFX/DYN3D codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.

Die 14^N(p,gamma)^15O-Reaktion ist die langsamste im Bethe-Weizsäcker-Zyklus des Wasserstoffbrennens und bestimmt dessen Rate. Der Wirkungsquerschnitt dieser Reaktion wurde in der Vergangenheit über einen weiten Energiebereich gemessen. Erneute, genauere Messungen im niederenergetischen Bereich hatten gezeigt, dass der Wirkungsquerschnitt um einen Faktor zwei niedriger ist als erwartet. Im Rahmen dieser Arbeit soll überprüft werden, ob sich das auch für höhere Energien bestätigt.
Hierzu wurden Messungen am Protonenstrahl des 3 MV Tendetron-Beschleunigers, Forschungszentrum Dresden-Rossendorf, durchgeführt. Zunächst wird eine experimentelle Kalibrierung der gamma-Nachweiswahrscheinlichkeit dreier comptonunterdrückter Reinstgermanium-Detektoren im energiebereich von 0,7 bis 12 MeV durchgeführt. Das Ergebnis wird mit der bisher simulierten Effizienzkurve verglichen. Dann wird im Energiebereich von 0,5 bis 1,5 MeV der Wirkungsquerschnitt für 14^N(p,gamma)^15O*(6.7929), das heißt für den Einfang in den vierten angeregten von 15^O bei 6.792 keV, bestimmt. Der Einfang in diesen Zustand trägt mehr als die Hälfte zum extrapolierten Wirkungsquerschnitt bei Energien wie im Inneren der Sonne bei.

The UVI complex with a pentadentate Schiff base ligand (N,N’-disalicylidenediethylene-triaminate = saldien2–) was prepared as a starting material of a potentially stable UV complex without any possibility of UVO2+•••UVO2+ cation-cation interaction, and was found in three different crystal phases. Two of them had the same composition of UVIO2(saldien)•DMSO in orthorhombic and monoclinic systems (DMSO = dimethyl sulfoxide, 1a and 1c, respectively). The DMSO molecule in both 1a and 1c does not show any coordination to UVIO2(saldien), but it is just present as a solvent in the crystal structures. The other isolated crystals consisted only of UVIO2(saldien) without incorporation of solvent molecules (1b, orthorhombic). Different conformation of the coordinated saldien2– in 1c from those in 1a and 1b was observed. The conformers exchange each other in a solution through a flipping motion of the phenyl rings. The pentagonal equatorial coordination of UVIO2(saldien) remains unchanged even in strongly Lewis-basic solvents, DMSO and N,N-dimethylformamide. Cyclic voltammetry of UVIO2(saldien) in DMSO showed a quasireversible redox reaction without any successive reactions. The electron stoichiometry determined by the UV-vis-NIR spectroelectrochemical technique is close to 1, indicating that the reduction product of UVIO2(saldien) is [UVO2(saldien)]– which is stable in DMSO. The standard redox potential of [UVO2(saldien)]–/UVIO2(saldien) in DMSO is –1.584 V vs. Fc/Fc+. This UV complex shows the characteristic absorption bands due to f-f transitions in its 5f1 configuration and charge-transfer from the axial oxygen to U5+.

Ziel/Aim:

Despite the fact that all modern PET scanners support 3D data acquisition protocols, up to now only a few of them have supported full 3D image reconstruction. Normally the reconstruction task is performed in sinogram space and reduced to a 2D problem using Fourier rebinning. This implies certain approximations and can degrade image quality. 3D list-mode reconstruction potentially is able to overcome these limitations while allowing at the same time flexible integration of motion correction methods into the reconstruction. The very limited availability of corresponding open-sourced software motivated us to develop our own, platform independent, fully 3D list-mode reconstruction with the final goal of integration of our event-based motion correction into it.

Methodik/Methods:

As the basis for our reconstruction we have taken the Ordinary Poisson List-mode Ordered Subsets Expectation Maximization algorithm (OP-LMOSEM) with on-the-fly system matrix simulation using a ray-tracing technique. The source code (C++) supports multi-threading and allows distributed computing, both of which decreases reconstruction time considerably. It also includes all
necessary corrections (attenuation, normalization, randoms etc.). We use the Single Scatter Simulation algorithm to compensate for Compton scatter and have evaluated the new reconstruction by comparison with the standard OSEM-reconstruction available with our Siemens EXACT HR+ scanner. Phantom measurements were performed in list-mode using the software previously developed in our lab. The evaluation procedure has been divided into three parts: i) quantitative accuracy (ROI's mean value comparison); ii) spatial resolution (FWHM comparison); iii) Signal to Noise Ratio, SNR (ratio of standard deviation to mean value in homogeneous ROIs).

Ergebnisse/Results:

Relative to the standard reconstruction we obtain the following results: quantitatively, images show reasonable concordance with the reference, abstract-dialog | Abstract Management System
the differences are below 8%. The reconstructed spatial resolution is on average 10% better (up to 20% in smaller structures). The mean SNR shows 6% improvement (especially at the axial edges of the field of view). Currently, reconstruction time for a typical 5 minute FDG brain scan is 13 minutes using 64 cores running at 2.3 GHz.

Schlussfolgerungen/Conclusions:

3D list-mode reconstructions are approaching clinical usefulness and prospectively offer the optimal framework for incorporating event-based motion correction methods into the reconstruction. Our implementation has proven to provide results, which already are better then those of the standard reconstruction on our system, although there is still room for much improvement. In the next step we plan to incorporate motion correction into the algorithm.

Aim:

Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique for quantitative blood flow measurements. While the principal validity of the technique has been shown, e.g. for human brain investigations, its practical applicability and accuracy depends very sensitively on the specific experimental setting. The purpose of this work was the evaluation of ASL for perfusion measurements in the rat brain by a comparison with microsphere derived regional perfusion information using dedicated small animal PET and SPECT systems.

Methods:

MRI measurements were performed first, immediately followed by the microsphere measurements. Before measurements, catheters were implanted through the right carotid artery into the left ventricle of the heart for administration of radio-labeled microspheres (20). The in-vivo distribution of radio-labeled microspheres was evaluated by PET (microPET P4, Siemens) using Cu-64 and Ga-68 microspheres. For SPECT (NanoSPECT, Bioscan) measurements Tc-99m microspheres were used. MRI perfusion measurements were performed in a 7T small animal system (BioSpec 70/30, BRUKER) with the vendor provided ASL protocol using a FAIR (flow-sensitive alternating inversion recovery) sequence with an adiabatic hyperbolic secant inversion pulse (length-bandwidth product: 80). The global and selective T1 images were used for calculation of perfusion values.

Results:

For normal rat brain (without catheter) we measured perfusion values using FAIR-ASL ranging from 1.2 to 1.4 ml/min/g in the caudate putamen. The implantation of the catheter created differences in the perfusion between the right and left hemisphere of the brain (due to the partial blocking of the right carotid artery), which are apparent from the left/right differences in the microsphere distribution. These differences are visible in the ASL-derived perfusion as well, ranging from 25 - 60%. ASL-derived perfusion exhibits substantial inter- and intra-individual variability, the cause of which is currently under investigation.

Conclusions:
Quantitative perfusion measurements in the rat brain using ASL seem possible but are very susceptible to minor deviations from the optimal setup (e.g. concerning shimming of the magnetic field and motion artifacts). Overall regional contrast is on average concordant with regional distribution of microspheres. In order to be useful for routine application in small animal imaging, ASL data acquisition and data evaluation needs to be further optimized. A final calibration via a quantitative comparison with radio-labeled microspheres seems mandatory.

We discuss intensity effects in collisions between beams of optical photons from a high-power laser and relativistic electrons. Our main focus are the modifications of the emission spectra due to realistic finite-beam geometries. By carefully analyzing the classical limit we precisely quantify the distinction between strong-field QED Compton scattering and classical Thomson scattering. A purely classical, but fully covariant, calculation of the bremsstrahlung emitted by an electron in a plane wave laser field yields radiation into harmonics, as expected. This result is generalized to pulses of finite duration and explains the appearance of line broadening and harmonic substructure as an interference phenomenon. The ensuing numerical treatment confirms that strong focussing of the laser leads to a broad continuum while higher harmonics become visible only at moderate focussing, hence lower intensity. We present a scaling law for the backscattered photon spectral density which facilitates averaging over electron beam phase space. Finally, we propose a set of realistic parameters such that the observation of intensity induced spectral red-shift, higher harmonics, and their substructure, becomes feasible.

Ziel/Aim:

Vor dem Hintergrund einer kontinuierlichen Verbesserung der apparativ erreichbaren räumlichen Auflösung in der PET stellen Patientenbewegungen einen maßgeblichen Faktor dar, der die praktisch realisierbare räumliche Auflösung beschränkt. Bei PET-Aufnahmen vom Thorax und Abdomen kommt es insbesondere durch die unvermeidbare Atembewegung des Patienten zur zyklischen Verschiebung der inneren Organe sowie anderer Zielstrukturen. Hieraus resultiert eine unter Umständen beträchtliche Bewegungsunschärfe in den tomographischen Bilddaten. Dies erschwert die visuelle Beurteilung und führt zu Fehlern bei der Bestimmung quantitativer Parameter wie der maximalen Traceranreicherung und dem Volumen der Strukturen. Besonders betroffen hiervon sind kleine Strukturen wie etwa die Nierenkelche. So war es Ziel dieser Arbeit, die Quantifizierung und die Erkennbarkeit von kleinen Strukturen im Abdomen zu verbessern.

Methodik/Methods:

Bei 40 Patienten wurde eine Ganzkörperuntersuchung mit F18-FDG am PET-Scanner ECAT Exact HR+ durchgeführt. Gleichzeitig erfassten Infrarot-Tracking-Kameras die Atembewegung der Patienten. Anschließend wurde eine Atemtriggerung anhand der Atembewegungsamplitude durchgeführt. Die Bewegung der Nieren wurde durch die Differenz der Nierenpositionen in der end-exspiratorischen und der end-inspiratorischen Atemphase bestimmt. Die Korrektur der Nierenbewegung erfolgte mit Hilfe einer rigiden Transformation, die alle Atemphasen auf eine gemeinsame Atemphase abbildet.

Ergebnisse/Results:

Von 40 F18-FDG Patienten konnte bei 26 die Bewegung der linken und bei 24 die Bewegung der rechten Niere ermittelt werden. Bei den übrigen Patienten war die F18-FDG-Anreicherung in den Nieren zu gering, um die Bewegung zu bestimmen. Die mittlere kraniokaudale Bewegung der linken Niere betrug 8,6 mm und die der rechten Niere 8,2 mm. Es wurde ein Vergleich des maximalen SUV und des Volumens einer lokalen Traceranreicherung in der Niere zwischen dem bewegungskorrigierten und dem unkorrigierten PET-Bild durchgeführt. Bei den Patienten zeigte sich eine maximale Reduktion des Volumens um 40% und eine maximale Zunahme des SUV um 20%.

Schlussfolgerungen/Conclusions:

Die Atembewegung beeinflusst maßgeblich die Darstellung und Quantifizierung im Abdomenbereich. Für eine verlässliche Quantifizierung ist eine Korrektur der Bewegung im Abdomen notwendig.

Ziel/Aim:

Patientenbewegungen sind in der PET unvermeidbar. So können hierdurch die Bilddaten z. B. verfälscht oder bei dynamischen Hirnuntersuchungen die Bestimmung von Zeit-Aktivitäts-Kurven (TAC) bzw. die Quantifizierung pharmakokinetischer Parameter beeinflusst werden. Die in diesem Zusammenhang in den letzten Jahren entwickelten Methoden zur Registrierung und Korrektur der Patientenbewegung stellen nützliche Werkzeuge zur Minimierung dieser Effekte zur Verfügung. In der vorliegenden Arbeit war es Ziel, den Einfluss einer bereits routinemäßig an unserer Einrichtung angewandten event-basierten Bewegungskorrektur, die auf der räumlichen Transformation jeder Line-of-Response (LOR) basiert, innerhalb eines größeren Patientenkollektivs zu untersuchen. Hierdurch sollten Aussagen darüber getroffen werden, in welchem Maße die Korrekturmethode in der Lage ist, den Einfluss der Bewegung auf die Auswertung von dynamischen Hirnuntersuchungen zu reduzieren.

Methodik/Methods:

Bei 645 [¹⁸F]DOPA-Untersuchungen mit Fragestellung Morbus Parkinson wurde eine Bewegungskorrektur durchgeführt. Hierbei wurde bei 20% eine maximale Bewegung größer 7 mm festgestellt. Für diese Untersuchungen wurden die Einstromraten (R₀k₃) mittels eines irreversiblen Zweikompartment-Modells mit Referenzgewebe (Patlak-Auswertung) sowohl vor als auch nach Bewegungskorrektur bestimmt. Hierfür wurden 8 ROIs innerhalb des Striatum sowie eine ROI im Referenzgewebe positioniert und für jede ROI im Striatum die Zeit-Aktivitäts-Kurve (TAC) sowie die Einstromrate berechnet. Des Weiteren wurden für jeden Datensatz parametrische Bilder erzeugt und mit den unkorrigierten Daten verglichen.

Ergebnisse/Results:

Die maximale Bewegung in den insgesamt 645 Untersuchungen verteilt sich wie folgt: (i) 31%: 0,5 – 3 mm, (ii) 31%: 3 – 5 mm, (iii) 18%: 5 – 7 mm, (iv) 20%: > 7 mm. Bei der quantitativen Auswertung zeigten sich Unterschiede im Verlauf der TAC von bis zu 30-40%. Die R₀k₃ Werte zeigten zum Teil Änderungen von mehreren hundert Prozent. Im Vergleich der parametrischen Bilder konnte dies verifiziert werden.

Schlussfolgerungen/Conclusions:

Die Quantifizierung tracerkinetischer Parameter wird von Patientenbewegungen, deren Ausmaß vergleichbar mit der Größe der Zielstrukturen ist, empfindlich beeinflusst und verliert u.U. ihre Gültigkeit. Eine event-basierte Bewegungskorrektur ist in der Lage, diese Fehlerquelle zu minimieren.

The allosteric regulation of biomolecules such as enzymes or receptors is based on structural changes that are initiated at a ligand-binding site and become transmitted to a "distant" active site where enzymatic efficiency or interaction with effectors is altered. Understanding the molecular mechanisms of this long range coupling between distinct protein domains is crucial for many pharmacoligically relevant systems where the conformation of a target molecule has to be specifically affected by a designed ligand. We have developed a generalized multidimensional spectoscopic approach to investigate long range conformational coupling in proteins. It employs the integration of fluorescence emission and infrared absorption data recorded simultaneously from the same protein sample that undergoes conformational transitions in response to an external perturbation. Using attenuated total relfectance (ATR) Fourier-transform infrared (FTIR) difference spectroscopy, additional channels for excitation and detection of fluorescence where established by light guides positioned above the sample on the ATR crystal. Long range coupling in the signal transfer through rhodopsin has recently been identified by Fluorescence-IR-cross-correlation [1]. Using 2D-cross-correlation techniques, the kinetic asynchronicity of the emission from natural or artificial site-specific fluorophores relative to the secondary structure-sensitive IR-absorption bands can be determined. Thereby, IR absorptions can be identified in a model-free and unbiased way that can be assigned to secondary-strutural elements that become specifically stabilized by ligand interactions. Here, we demonstrate in a cytoskeletal protein the correlation of the loss of ligand-dependent static quenching of intrinsic tryptophan emission during thermal unfolding with the loss of structure monitored by FTIR spectroscopy. The high signal to noise ratio in 2D-correlation and the "synchronicity tagging" of the IR bands through their correlation with an independent monitor of ligand dissociation allows detecting ligand protein interactions with an accuracy that is not achieved by FTIR-spectroscopy alone. In addition, topological information can be obtained from the emission wavelength of the tryptophans that become gradually unquenched during temperature-induced ligand dissociation. Fluorescence-IR-cross-correlation spectroscopy thus extends the IR-based conformational analysis by the inclusion of site-specific information on local physical parameters (polarity, electrostatics, etc.) specifically affecting the emission of fluorophores. We show how this approach provides structural information on flavonoid binding to actin, a cytoskeletal and nuclear protein that has recently been shown to respond to the binding of these natural compounds by flavonoid-specific conformational changes [2].

Acknowledgement
We acknowledge financial support by the Deutsche Forschungsgemeinschaft to KF (grant 248/4)

References
[1] N. Lehmann, U. Alexiev, K. Fahmy, J. Mol. Biol. 336 (2007) 1129–1141.
[2] M. Boehl, S. Tietze, A. Sokoll, S. Madathil, F. Pfennig, J. Apostolakis, K. Fahmy, H.-O. Gutzeit,
Biophys. J. 93 (2007) 2767-2780.

The strain Lysinibacillus sphaericus JG-A12, isolated from the uranium mining site at Haberland, Saxony (Germany) selectively and reversibly accumulates radionuclides and toxic metals. Metal binding occurs to its surface layer (S-layer) surrounding the cells. Here, we have studied by Fourier-transform infrared (FTIR) spectroscopy the protein structure and stability as a function of AuIII binding and the subsequent reductively induced formation of Au-nanoclusters. Similar to previously studied complexes with PdII, Au-treated S-layers become resistant to acid denaturation evidenced by little response of their amide I absorption frequency. However, the strong effect of PdII exerted on the side chain carboxylate IR absorption intensity is not observed with gold. Particularly after reduction, the carboxyl absorption responds little to acidification and a fraction appears to be protonated already at neutral pH. We ascribe this to a hydrophobic environment of the carboxyl groups after formation of Au-nanoclusters. EXAFS spectra agree with the metallic Au-Au distance but the reduced coordination number indicates that the Au-nanoclusters do not exceed ~2 nm. Thus, the S-layer of L. sphaericus JG-A12 provides a biotemplate for efficient Au-nanocluster formation in an acid-resistant matrix and independently of cysteins.

The Arava Desert is a hostile oligotrophic, extremely dry and hyper saline environment in Israel. Such environments are usually inhabited by microorganisms called extremophiles. In this study, an extreme halophilic Archaeon was cultivated from sand samples of the Arava Desert. The interactions of this archaeal isolate with radionuclides will be studied in the next future. Such studies are important because saline environments are perspective sites for deposition of radioactive wastes.

Biofilme sind Lebensgemeinschaften von verschieden Mikroorganismen, die allgegenwärtig sind. Über Poren und Kanäle in den Biofilmen werden Wasser, Nährstoffe, Signalstoffe, aber auch toxische Schwermetalle aus der umgebenden Lösung zu den einzelnen Mikroorganismen gebracht und Stoffwechselprodukte abgeführt. Am Beispiel von Uran als toxisches Schwermetall konnte eine Schutzfunktion und Überlebensstrategie der Biofilme nachgewiesen werden, durch die gelöstes Uran in wässrigen Lösungen zu unlöslichem Uran reduziert und in der Zwischenzellsubstanz der Biofilme „gespeichert“ wird.

Protein secondary structure and stability of S-layers from B. sphaericus JG-A12 in Au-complexes with Au(III) and in Au(0) nanoparticles, produced by reduction of Au(III), was studied by FTIR spectroscopy.
The data show a different role of side chain carboxylates in complex formation as compared to an analogous study on complexation of Pd(II) or Pt(II).

Editorial - Materials have become an ever more important factor in most advanced technologies. It was no coincidence when the former State Secretary Christoph Matschie stated, at the opening of WING (Materials Innovations for Industry and Society initiated by the German Ministry for Education and Research), that nearly any new product is based on the improvement of an engineered material. This comes along with a constant quest for new materials, improved performance and decreased development costs. This quest is particularly strong for high-wage countries in the global market situation. Thus there is a steadily growing importance of systematic materials development supported by computer simulation methods in tailoring new materials for more and more specific demands for a wide range of applications from everyday household goods to opto-electronics and even further to medicine. In this context the tailoring of materials interfaces, respectively that of corresponding condensed matter systems, often used as model systems for the first ones, plays a particularly important role. The reason for this is that a material’s functional properties are to a large extent determined by its inner and outer interfaces. Prominent examples are corrosion-resistant surfaces of household goods, or likewise inert surfaces of prostheses engineered for medical applications. During materials processing the inner and outer interfaces of such functional materials evolve driven by the complex interplay of all the physical and chemical mechanisms contributing to interface energetics, interface kinetics and interface dynamics. Essentially, this opens a multiscale problem ranging from the quantum mechanical to the continuum scale.

The separated flow around inclined airfoils can be controlled by unsteady actuation near the leading edge (LE), increasing the maximum lift coefficient without the need for heavy and complex high lift devices such as flaps. Zero net mass flow devices (ZNMF) are often used for this purpose. While certainly favorable for industrial application, actuation via ZNMF faces some problems. In particular, to independently control both amplitude and frequency of the excitation is considered a ``great challenge'' This is even more severe when the wave form of the actuation is non-sinusoidal, i.e., contains more than one frequency component. Lorentz forces do not suffer from such limitations; driven by an electric current, arbitrary wave forms can be generated easily. The main purpose here is to identify possibly different mechanisms triggered by different wave forms. In particular, we investigate electromagnetic excitation using a) a sinusoidal wave and b) rectangular waves at duty cycles of DC=1/4 and DC=1/8.

Neptunium (93Np) is one of the most important elements to be considered for the geological disposal of high-level radioactive wastes, because of a considerable content in the wastes, and the high radioactivity, half-lives and radiotoxicity of its nuclides. From a chemist’s point of view, it is also a very interesting element because of its diversity of oxidation states from III to VII [1]. Whether Np may be retained in the waste repository for millions of years, or whether it will migrate to the biosphere, depends heavily on its chemical forms (speciation). We assume that oxidation state will have a strong influence on the speciation. Therefore detailed knowledge about the interrelation between oxidation state and the structure of chemical species is critical for the development of safe nuclear waste repositories. This motivated us to perform X-ray absorption fine structure (XAFS) studies to determine the complex structure of Np species in aqueous solutions at different oxidation states. The experiments were performed at the Rossendorf Beamline (BM20), the only beamline at the ESRF, where such studies with aqueous Np samples can be performed.

Protactinium occupies a key position in the actinide series between thorium and uranium. In aqueous acidic solution, it is stable at oxidation state (V), occurring either as an oxocation or as a naked ion, depending on the media. Very few structural information on the hydration sphere of Pa(V) in acidic medium is available, in particular in hydrofluoric acid. Combined EXAFS and theoretical calculations have been used in this work to characterize the protactinium coordination sphere at various HF concentrations. The correlation of the XAFS data with quantum chemical calculations provides complementary structural and electronic models from ab initio techniques. At HF concentrations from 0.5 to 0.05 M, both theoretical calculations and EXAFS data suggest that the protactinium coordination sphere is mainly composed of fluoride ions. At the lowest HF concentration, the occurrence of a monooxo bond is observed with EXAFS, in agreement with the literature. A comparison of these data with related neptunium(V) and plutonium(V) diooxocations in perchloric acid is also presented.

The complexation of uranium(VI) to variant functional groups of the highly phosphorylated protein phosvitin in aqueous solution was investigated by Attenuated Total Reflection Fourier-transform Infrared (ATR FT-IR) spectroscopy. For the verification of the affinity of the actinyl ions to carboxyl and phosphate groups of the amino acid side chains, samples with different phosphate to uranium(VI) (P/U) ratios were investigated under denaturing conditions and as well as aqueous complexes. From a comparative study with other heavy metal ions, i.e. Ba2+ and Pb2+, a strong coordination of U(VI) to carboxyl and phosphoryl groups can be derived. Furthermore, the spectra indicate a preferential binding to phosphate groups at deficient U(VI) concentrations. These findings are confirmed by spectra of aqueous U(VI)-phosvitin complexes reflecting an explicit coordination of the uranyl ions to phosphate groups at a high P/U ratio. Our study provides a deeper insight into the molecular interactions between actinyl ions and basic biomolecules such as proteins, polysaccharides, nucleic acids.

Purpose: To examine relationships between tumour hypoxia, perfusion and metabolic microenvironment at themicroregional level in three different human squamous cell carcinomas (hSCC). Materials and methods: Nude mice bearing FaDu, UT-SCC-15, and UT-SCC-5 hSCC were injected with pimonidazole hypoxia and Hoechst perfusion markers. Bioluminescence imaging was used to determine spatial distribution of glucose and lactate content in serial tumour sections. Metabolite levels were grouped in 10 concentration ranges. Images were co-registered and at each concentration range the proportion of area stained for pimonidazole and Hoechst was determinedin 11–13 tumours per tumour line.
Results: The spatial distribution of metabolites in pimonidazole hypoxic and Hoechst perfused areas is characterised by pronounced heterogeneity. In all three tumour lines glucose concentration decreased with increasing pimonidazole hypoxic fraction and increased with increasing perfused area at the microregional level. A weak albeit significant positive correlation between lactate concentration and pimonidazole hypoxic fraction was found only in UT-SCC-5. Lactate concentration consistently decreased with increasing perfused area in all three tumour lines. Conclusions: Both glucose consumption and supply may contribute to the microregional glucose levels. Microregional lactate accumulation in tumours may be governed by clearance potential. The extent of microregional hypoxia cannot be predicted from the lactate concentration indicating that both parameters need to be measured independently.

Temperature dependence of the nitrogen diffusion coefficient in the expanded austenite γN of single crystalline austenitic stainless steel (ASS) during ion beam nitriding is investigated. Single crystalline [orientations (001), (110) and (111)] AISI 316L ASS samples have been ion beam nitrided in the temperature range of 370-430 °C for 60 min with an ion acceleration voltage of 1 keV and a current density of 0.5 mA cm−2. The N depth distribution profiles have been determined by means of nuclear reaction analysis (NRA), while the N diffusion coefficients D have been extracted by fitting the NRA profiles with the “trapping-detrapping” model. The results show that the nitrogen diffusivity strongly depends on the single crystal orientation in the sequence D001>D011>D111. These differences are not related to the activation energy which is similar for all three orientations, but to the diffusion coefficient exponential pre-factor D0 whose value varies by 3 orders of magnitude depending on the orientation. The results are discussed on the basis of ion irradiation effects such as defects and vibrational lattice excitations.

Reactor pressure vessel (RPV) steels consist of polycrystalline alpha-Fe with different alloying elements, e.g. nickel, and different impurities, e.g. copper. During the operation of a nuclear fission reactor at a temperature of about 300 °C this material is continuously irradiated by neutrons and both vacancies and self-interstitials are formed. The presence of point defects enhances the diffusion of impurities and leads to precipitation if their solid solubility is small. The precipitates may not only contain the impurity species but also point defects since vacancies and/or self-interstitials take part in the process of clustering. Furthermore, pure vacancy and self-interstitial clusters may be formed. Copper-rich precipitates (CRP) are assumed to be the main cause of hardening and embrittlement of Cu-bearing RPV steels since these defects act as obstacles to dislocation motion within the grains of polycrystalline alpha-Fe. There is clear evidence that these nanoclusters remain small and have the bcc structure of the surrounding matrix. CRP and nanovoids have been observed by different experimental methods such as small angle neutron scattering, tomographic atom probe, positron annihilation spectroscopy, and high-resolution transmission electron microscopy. On the other hand, multiscale modeling contributes to a better understanding of the various physical processes that occur during the formation of clusters and precipitates. Rate theory is a useful and efficient tool to simulate defect evolution on realistic time and length scales. However, the values of many parameters used in rate theory, such as diffusion coefficients of mobile species and free binding energies of clusters, are not very well known from experimental investigations. Atomic-level computer simulations can provide these data.

In the present work a combination of Metropolis Monte Carlo simulations on a rigid bcc lattice and molecular dynamics simulations [1,2] is applied in order to determine the most stable configuration of numerous CunVm clusters. In all calculations the most recent Fe-Cu interatomic potential by Pasianot and Malerba [3] is used. Present investigations do not only yield formation energies of the most stable clusters but also the corresponding binding energies. The results are compared with literature data [1,2] obtained by the potentials of Ackland-Bacon [4] and Ludwig-Farkas [5]. The configuration of some clusters containing both copper and vacancies are visualized and their morphology is compared with the interpretation of recent experimental investigations.

References
[1] A. Takahashi, N. Soneda, S. Ishino, and G. Yagawa, Phys. Rev. B 67, 024104 (2003).
[2] D. Kulikov, L. Malerba, and M. Hou, Philos. Mag. 86, 141 (2006).
[3] R. C. Pasianot and L. Malerba, J. Nucl. Mater. 360, 118 (2007).
[4] G. J. Ackland, D. J. Bacon, A .F. Calder, and T. Harry, Philos. Mag. A 75, 713 (1997).
[5] M. Ludwig, D. Farkas, D. Pedraza, and S. Schmauder, Modelling Simul. Mater. Sci. Eng.
6, 19 (1998).

Quenched-in vacancies in Fe3Al-based intermetallics were studied in this work. A stoichiometric Fe3Al alloy was compared with non-stoichiometric specimens either with a deficiency or with an excess in Al content. Vacancies in specimens quenched from the disordered A2 phase were investigated by three independent techniques of positron annihilation spectroscopy: positron lifetime (LT) studies, slow positron implantation spectroscopy (SPIS) with a continuous slow positron beam, and coincidence Doppler broadening (CDB). It was found that the combination of LT and SPIS enables to determine reliably even very high concentrations of vacancies. Infor-mation about the local chemical environment of quenched-in vacancies was obtained from CDB measurements.

Polishing of titanium and enhancing the wear resistance of the titanium alloys with a low-energy high-current electron beam

In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. Recently, experiments have shown that a gaseous target can produce proton beams with characteristics comparable to those obtained with solid targets. In underdense laser proton acceleration, volume effects dominate the acceleration, while in target normal sheath acceleration, the electric field value is directly related to the electron surface density. Using Particle-In-Cell simulations, we have studied in detail the effect of an underdense density gradient on proton acceleration with high intensity lasers. Underdense laser ion acceleration strongly depends on the length, the shape and the amplitude of the density gradient and on the laser pulse shape. The accelerated proton beam characteristics in the shock-like regime are very promising.

In this paper, we report on experiments performed on the 200 TW Trident laser (80 J, 600 fs, ~7 µm spot size, S-polarization and ~1.5x10²⁰ W/cm²) at an intrinsic (to the system’s regenerative amplifier) ASE contrast of 10-8, using various geometries of conical Cu targets, as well as Cu flat foils for comparison. The work presented in this paper follows on some earlier work on proton acceleration on Trident (20 J, ~14 µm spot size, P-polarization, ~1019 W/cm² and also at the intrinsic contrast of 10-8), using Flat Top Cone (FTC) targets [1] and which demonstrated an enhancement in both proton energies and conversion efficiencies. In the current experiment, an electron spectrometer was added, which shows linear correlation of electron temperatures and proton energies, as well as a Cu Kα imaging diagnostic, to determine the characteristics of laser absorption in the FTC, which demonstrates that the laser is absorbed in the preplasma filling the cone, preventing the previously observed enhancement in proton energies.

Nevada Terawatt Facility (NTF) currently operates a high-intensity laser system—Leopard. NTF already operates a powerful z-pinch device, called Zebra, for plasma and High Energy Density physics research. The unique research opportunities arise from the combination of NTF’s terawatt Zebra z-pinch with 50-terawatt-class Leopard laser. This combination also provides opportunities to address fundamental physics of inertial fusion and high energy density physics with intense laser beam. We report on the status, design and architecture of the Leopard laser project. A first experiments carried out with Leopard will be also briefly mentioned.

Obtaining keV ion temperatures at solid density, i.e. “warm dense matter”, in the laboratory would be of great interest to measure opacity and equations of state of matter under extremes conditions. Here we report a new means to effectively confine the energetic electrons and localize the energy deposition to a small, more uniformly heated, volume at the tip of nanofabricated micro-cone targets. This is achieved with very high contrast laser irradiation, which interacts with the cone wall to generate strong (~10 MG) localized resistive magnetic fields within the target bulk. Temperatures of up to ~200 eV are observed, with an input laser energy of 10 J. This new means has been investigated both experimentally and with Particle-In-Cell simulations.

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The structural and electronic properties of neutral and anionic molybdenum sulfide clusters with the composi-tion Mo3Sn (n=0-12) were studied by density-functional calculations. The theoretical results are confirmed by a comparison with photoelectron spectra of the correspond-ing W3Sn- anions providing experimental values for the vertical detachment energies and the HOMO-LUMO gaps. For sulfur contents up to n=9 the clusters are com-posed of a central Mo3 unit, which is decorated by bridg-ing, terminal and three-fold coordinated S atoms. For n>9, a cleavage of the Mo3 center is observed. The formation of disulfide like ions is found for Mo3S9 and larger spe-cies. In accordance with investigations of MoSn, Mo2Sn and Mo4Sn clusters, the heat of formation and the vertical detachment energy reaches a maximum in the sulfur-rich region beyond the composition Mo : S = 1 : 2.

The present study aims at the computer-aided design of suitably functionalizedoxide surfaces for the integration of nanotubes into multi-purpose nano-electronic devices. The adsorption of cytidine monophosphate on the rutile(110) surface is investigated by density-functional-based tight-binding calculations. The most favorable amchoring of the nucleotide is bidentate via oxygen sites of the phosphate part. Adsorption occurs preferentially at two neighboring five-fold coordinated Ti atoms along the [001] direction, thus opening a pathway to an ordered adsorption of nanotubes along [001]. The electronic densities of states show that the aromatic part of the cytidine part remains unchanged upon adsoption on rutile. This implies that no significant changes occur in the nanotube binding capacity by pi-stacking of the aromatic part, hence, nucleotide-functionalized oxide surfaces are ideal substrates for the ordered, stable and electronically and chemically inert immobilization of nanotubes.

In situ application of an electric field to a SrTiO3 single crystal plate during nanoindentation led to a reversible change of the mechanical properties at room temperature. When a field of 8 kV/cm was applied, Meyer hardness and Young's modulus decreased by 0.6 GPa and 11 GPa, respectively. An explanation for this behaviour is given by the diffusion of oxygen vacancies resulting in a distortion of the perovskite-type of structure in the near-surface layer tested by nanoindentation. Simulations using density functional theory support the dependence of elasticity on the presence of vacancies. Thus, we can show the remarkable influence of electric fields on oxide materials which should be considered and used in designing future applications.

Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in nonequilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth. According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation. We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].
[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

Nobel metal nanoparticles exhibit distinct optical properties due to their localized surface plasmon resonance. They are used nowadays in various applications, like solar cells, nonlinear optical devices or sensors. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favored [1]. Ion beam sputtered surfaces featuring self-organized ripple patterns are excellent templates for the alignment of these metal nanoparticles. Depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanostructures align parallel to the ripples, eventually coalescing and forming nanowires [2]. Because of alignment the nanoparticles exhibit a strongly anisotropic plasmonic resonance [3]. We will present how Ag nanoparticles grow and align on ion beam rippled Si surfaces and how the optical properties depend on their shape, size, and alignment.

[1]S.A. Maier and H.A. Atwater, Jour. Appl. Phys. 98, 011101 (2005).
[2]T.W.H. Oates, A. Keller, S. Noda, et al., Appl. Phys. Lett. 93 (2008).
[3]T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).

Oberflächen und Grenzflächen spielen eine große Rolle in allen technologischen Bereichen. Kaum eine Anwendung kommt ohne Materialien aus, die aus Mehrfachschichten aufgebaut sind oder funktionale Oberflächen aufweisen. Die Herstellung und Erforschung dieser funktionalen Oberflächen bzw. Schichten mit Strukturen im Submikrometerbereich wurde deshalb in den letz-ten Jahren verstärkt vorangetrieben, da eine steigenden Nachfrage in der mikro- und optoe-lektronischen Industrie nach derartigen Strukturen zu erwarten ist. Zwei komplementäre Ansätze existieren zur Erzeugung von Nanostrukturen: Der Top-down- und der Bottom-up-Ansatz.
Der Top-down-Ansatz umfasst konventionelle Techniken wie optische oder Elektronen¬stahllithographie kombiniert mit Übertragung der geschriebenen Strukturen, während der Bot-tom-up-Ansatz Selbstorganisationsphänomene an Oberflächen oder beim Wachstum dünner Schichten ausnutzt. Die Ionenerosion von Festkörperoberflächen mit niederenergetischen Ionen ist eine vielversprechende Bottom-up-Methode zur Herstellung großflächiger Felder von Na-nostrukturen [1]. Diese Methode und Anwendungen, die darauf basieren, werden im Folgenden vorgestellt.

A detailed analysis of the plutonium burning in a representative PWR fuel pin is performed for comparison of the ThMOX and UMOX fuel performance. Special effort is made in the analysis of the changes in the spatial distribution of isotope concentrations during the burnup in a representative LWR fuel pin. This unique analysis of the changes in the spatial particle densities gives a new insight into the system behaviour. The different ways of plutonium breeding and reduction for the major isotopes of the two considered fuels are analyzed and discussed. Finally, the advantages and limitations of the use of Thorium based MOX fuel for the burning of plutonium are discussed. The calculations are performed with the licensing grade code module HELIOS 1.9.

This work represents the detailed comparison of the analytical solutions for the space and time Telegrapher’s equations with the experimental results, obtained for the YALINA-Booster subcritical facility in 2008. The derivation of analytical solution for the Telegrapher’s equation with a special temporal shape of the external source is described. The Green’s function method was applied. Qualitative results of the obtained solutions and the experimental results are analyzed. The special configuration of the YALINA-Booster facility is discussed.

Ge isotope heterostructures were irradiated with 2.5 MeV protons at temperatures between 550°C and 640°C. The applied proton flux was varied up to 3.8 μA per cm². Secondary ion mass spectroscopy (SIMS) was utilized to record concentration profiles of the Ge-isotopes after the irradiation treatment. The SIMS profiles show a homogenous broadening of the multilayer structure. Continuum theoretical simulations were performed which are based on diffusion models that consider the formation of Frenkel-defects and their annihilation. Best fits to the experimental profiles are obtained when the boundary conditions for vacancies and self-interstitials are assumed differently. Ge self-interstitials are reflected at the surface, whereas the concentration of Ge vacancies approaches the thermal equilibrium value. To check these boundary conditions, experiments on the diffusion of n-type dopants under irradiation were performed.

In den letzten Jahren hat die Mikroskopie enorme Fortschritte gemacht. Moderne Mikroskope können Moleküle dreidimensional abbilden, kleinste Strukturen bis hin zu einzelnen Atomen erkennen und vor allem auch unterschiedliche Arten von Atomen sicher voneinander unterscheiden. Die "Raster-Kelvin-Mikroskopie" ist eine besondere Technik der Rasterkraft-Mikroskopie, wobei die ihr zugrunde liegende Methode auf Lord Kelvin zurück geht. Sie kam 1991 auf den Markt. Mit dem Raster-Kelvin-Mikroskop wurde eine wissenschaftliche Erklärung mitgeliefert, wie die Aufnahmen zu interpretieren seien. Daran rüttelt nun die Physikerin Christine Baumgart, die in der "Nanospintronik-Gruppe" am Forschungszentrum Dresden-Rossendorf (FZD) promoviert.

Heavily p-type doped Ge layers were fabricated by 100 keV Ga implantation and subsequent flash lamp annealing for 3 ms in the temperature range between 700°C and 900°C. For comparison some samples were annealed in a rapid thermal processor for 60 s. Ga fluences of 2x10¹⁵cm^-2, 6x10¹⁵cm^-2 and 2x10¹⁶cm^-2 were chosen in order to achieve Ga peak concentrations ranging from values slightly below the equilibrium solid solubility limit of 4.9x10²⁰ cm^-3 up to 3.5x10²¹ cm^-3 which corresponds to a maximum Ga content of about 8 at-%. The structure of the doped layer and the Ga distribution were investigated by Rutherford backscattering spectrometry in combination with ion channelling, cross-sectional electron microscopy and secondary ion mass spectrometry. Temperature dependent Hall effect measurements were carried out in order to determine the electrical properties of the Ga doped layers. It is shown that by flash lamp annealing Ga diffusion into the bulk can be completely avoided and the Ga loss by outdiffusion from the surface is reduced. The lowest sheet resistances of 36 Ohm/sq. was achieved for the medium Ga concentration annealed at 900°C. The best Ga activation values are 73%, 60% and 24% for the three Ga fluences under investigation. The Ga activation is correlated with the layer regrowth. Incomplete epitaxial regrowth as observed in some samples leads to lower activation.

scaling (optimizing) of conventional techniques
novel techniques: dielectric wall accelerators
new concepts: laser plasma acceleration and
local beam guiding systems

Wenn die Intensität von Laserlicht, das mit Materie wechselwirkt, 1018 W/cm² übersteigt, wird die Bewegung der Elektronen im Laserfeld relativistisch. Dies führt zu einer Vielzahl neuer optischer Effekte, die unter dem Namen „Relativistische Optik“ zusammengefasst werden. Der vielleicht wichtigste und zurzeit am meisten diskutierte neue Effekt, der in diesem Zusammenhang auftritt, ist die effiziente Laserbeschleunigung von Elektronen und Ionen. Mit Hochintensitätslasern kann man heute monochromatische Elektronenstrahlen mit Energien bis zu 1 GeV erzeugen. Kürzlich wurden auch monoenergetische Ionenstrahlen im MeV-Bereich durch Hochintensitätslaser erzeugt. In dem Vortrag werden die Mechanismen der Laser Teilchenbeschleunigung im Zusammenhang mit nun möglich erscheinenden Anwendungen dieser Teilchenstrahlen in der Medizin diskutiert.

This work represents the detailed comparison of the analytical solutions for the space and time dependent diffusion and Telegrapher’s equations to the experimental results, obtained for the YALINA-Booster subcritical facility during the experimental campaign in 2008. The derivation of analytical solution for the Telegrapher’s equation with a special temporal shape of the external source (switch on followed by a switch off after a finite time period) is described. The Green’s function method was applied. Qualitative results of the obtained solutions and the experimental results are analyzed.
The special configuration of the YALINA-Booster facility is discussed.

The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites for domain walls in magnetic nanowires without geometric constrictions. Implantation of chromium ions into Ni80Fe20 nanowires is used to cause a local reduction of the saturation magnetization Ms and thus a decrease of the exchange energy associated with the domain wall. Field-driven pinning and depinning of a domain wall at the here so-called magnetic soft spots is directly observed using magnetic transmission soft X-ray microscopy. The pinning rate and the depinning field considerably depend on the wire width and the chromium fluence.

In der vorliegenden Arbeit wurde die Auswirkung von Uran speziell auf Chlorophyll a und Chlorophyll b untersucht. Die Messungen erfolgten mittels HPLC-Analytik, mit photometrischen Messungen und Dünnschichtchromatographie. Es wurden die Absorptionsmaxima sowie die Retentionszeiten der Pigmente bestimmt. Den Untersuchungen lag die Frage zugrunde, ob ein Austausch des zentralen Magnesiums aus dem Chlorophyll-Molekül durch Uran möglich ist. Für die Messungen standen Proben von Löwenzahn und Arabidopsis zur Verfügung. Neben den hydroponisch herangezogenen Arabidopsis-Kulturen (mit und ohne Uranylnitrat in der Nährlösung) wurden auch Pflanzen einer unsanierten Uranerzhalde in Johanngeorgenstadt untersucht.
Die Messung von bioverfügbarem Uran in den Bodenproben aus Johanngeorgenstadt und die Akkumulation von 5 μg Uran pro g Frischgewicht in den Pflanzenblättern stellt die Voraussetzung eines Austausches von Magnesium gegen Uran im Chlorophyll-Molekül dar. Anhand der Chromatogramme und der Absorptionsspektren ließen sich jedoch keine Anzeichen für eine Modifikation des Chlorophylls identifizieren.

We present a method to determine the saturation magnetization of samples for which the magnetic volume is unknown and thus cannot be calculated from the magnetic moment. This can happen, e.g., in multilayers, where the spacer material is likely to cause intermixing or whenever ion irradiation is used to modify the magnetic properties of samples on purpose. In both cases the active magnetic volume is altered from its nominal value in unknown manner. Therefore magnetometry like supraconducting quantum interference devices (SQUID) or vibrating sample magnetometry (VSM) fail, because they detect the magnetic moment but do not provide information on the respective magnetic volume. In this article we have used thin films of Permalloy (Py) and Py/Ta multilayers. Some of the Py/Ta samples were irradiated with Ne ions in order to modify the interfacial mixing. The saturation magnetization is determined by ferromagnetic resonance (FMR).

A mode-locking mechanism by active gain modulation is studied numerically and experimentally. The parameter window for the emission of stable pulse trains was found. Pulses as short as 3ps (~0.5pJ) were characterized by second-order autocorrelation.

We present experimental and numerical results obtained at LULI (Laboratoire pour l’Utilisation des Lasers intenses) on propagation and energy deposition of laser-generated fast electrons into conical targets. The experimental measurements were performed by means of several diagnostics in order to assess the predicted benefit of conical targets over standard planar ones. Various configurations have been tried, regarding the laser parameters with the aim of optimizing the laser-to-target coupling. Our best results have been obtained when the laser was frequency-doubled at 0.53 μm, corresponding to interaction conditions without laser pedestal due to the ASE (Amplified Spontaneous Emission). Our data pinpoint the detrimental influence of the pre-plasma generated by the laser pedestal at 1.057 μm, whose confinement is enhanced in conical geometry as evidenced by shadowgraphic measurements which is also confirmed by 2D Cu-Ka transverse images obtained from Cu cones. The consequence is the filling of the cone, preventing the laser beam from efficiently reaching the cone tip. These experimental results are compared to 2D PIC simulations modeling of the laser-cone interaction.

Deutschlands bis dahin größte Photovoltaikanlage (PVA) wurde von 2007 bis 2008 in der Nähe von Leipzig errichtet und schrittweise in Betrieb genommen. Sie befindet sich auf einer militärischen Konversionsfläche. Die PVA ist auf einer Fläche von ca. 120 Hektar mit insgesamt 589000 rahmenlosen CdTe-Modulen von First Solar (Leistung zwischen 65 und 75 W) ausgerüstet, die gesamte Modulfläche liegt bei etwa 40 Hektar. Jeweils 45 Module sind auf einen Tisch montiert und elektrisch zu 5 Strings verschaltet. Die 12440 Tische bestehen aus Aluminium-Profilen mit eingerammten Pfosten.
Betriebsergebnisse der PVA Waldpolenz wurden für die Jahre 2008 und 2009 ausgewertet. Der saisonale Verlauf der Erträge folgt den jeweiligen Einstrahlungen. Die Jahreserträge entsprechen den Erträgen von ertragstarken benachbarten PVA mit kristallinen Modulen. Auffallend sind die hohen PR-Werte der PVA (Jahr 2008: 90 %).