Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Computational fluid dynamics simulations for two-phase flows are important in different fields of engineering and science. Since two-phase flows are inherently complex, also CFD modeling development requires special attention. The validation of model implementation and the derivation of physics based models for momentum, heat, and mass transfer in two-phase flow require experiments with generation of high-resolution measurement data. This, however, is a great challenge, since most standard flow measurement tools used in single phase flow situations, are not suited for multiphase flows.
In this article we report on advanced imaging and measuring methods for two-phase flow ex-periments, which have been extensively used in the recent past to conduct experiments for two-phase flows at the Helmholtz-Zentrum Dresden-Rossendorf. In particular the application of wire-mesh sensors, ultrafast X-ray tomography, gamma ray tomography and positron emis-sion tomography will be introduced and discussed.

In the past years a growing community of measurement scientists and engineers has been struggling with new and optimized measurement and imaging techniques for process engineering applications. This research and development is mainly driven by needs in industry and fundamental science to obtain quantitative parameters from industrial processes. The commonality behind these needs is the fact, that many industrial processes are governed by multiphase flows of educts and products, whose parameters must be obtained in many places of plants and facilities. Most prominent examples of such are multiphase chemical reactors, separation units and solids processing units, thermal hydraulic circuits in nuclear reactors and solar power plants, as well as multiphase streams in mineral oil production. Moreover, there is also a constant pressure from fundamental flow mechanical science to have high resolution experimental data from multiphase flows available for the validation of CFD codes.

Tomographic imaging techniques naturally provide a good basis for multiple parameter measurements, though the requirements for high resolution in space and time, robustness with respect to harsh process conditions and cost issues are difficult to meet, particularly within one instrument or technique. Hence the field of process tomography has been seen to develop continuously since almost 30 years. Mature concepts of robust and non-intrusive tomographic imaging techniques, such as electrical resistance (ERT), capacitance (ECT) or impedance (EIT) tomography, are today constantly improved regarding particular needs of industrial applications, such as real-time monitoring and parameter extraction, 3D imaging and sensor data fusion. Now, however, they become more and more complemented by new techniques, such as electromagnetic tomography (EMT), electromagnetic flow metering with distributed sensors and industrial hard field imaging techniques. Furthermore, emerging process and environmental technologies, like carbon capture and storage, ionic liquids for chemical engineering applications, geothermal energy harvesting and new routes of mineral oil and gas production, such shale gas exploitation, deep-water offshore oil production and processing of high viscosity crudes and and oil sands, demand also new ideas and sensors from industrial process tomography.

The 4th International Workshop on Industrial Process Tomography IWPT-4 held in Chengdu, China, Sept. 21st-23rd, 2011 was a platform for specialists to present and discuss their most recent advancements in the development and application of process tomography techniques. The workshop was the fourth in a successful series of workshops held in Beijing and Hangzhou (2005), Macau (2006), and Tokyo (2009). It was organized by the International Society for Industrial Process Tomography (ISIPT) together with the Institute of Mechanics of the Chinese Academy of Science and hosted by Southwest Petroleum University.

Die Energieeffizienz großtechnischer Prozesse ist ein wichtiges Ziel von Forschungs- und Entwicklungsaktivitäten in Unternehmen und Forschungsinstitutionen. Zum einen sichern Maßnahmen zur Erhöhung der Energieeffizienz unmittelbar die Wettbewerbsfähigkeit von Unternehmen, zum anderen besteht ein gesellschaftlicher Konsens über die Notwendigkeit der Erreichung klima- und energiepolitischer Zielstellungen, insbesondere zur Reduktion der produktionsbedingten Treibhausgasemissionen. Die politischen Ziele dazu sind ehrgeizig und wurden insbesondere in Deutschland durch den im Jahr 2011 beschlossenen Umbau der Energieversorgung durch schrittweise Abschaltung der deutschen Kernkraftwerke bis 2022 und eine deutliche Steigerung der Energieerzeugung aus erneuerbaren Energiequellen neu justiert. Mit dem Umbau der Energieversorgung sind eine Reihe technischer, wirtschaftlicher und gesellschaftlicher Probleme zu lösen. Dies betrifft die effiziente Gewinnung, Speicherung und Verteilung von elektrischer Energie aus erneuerbaren Energiequellen ebenso wie ein bedarfs- und angebotsoptimiertes Netz- und Lastmanagement im Energienetz. Parallel dazu sind weitere umfassende Maßnahmen zur Senkung des Primärenergieverbrauchs durch eine Steigerung der Energieeffizienz in Wirtschaft, Privathaushalten und im Transportsektor unerlässlich.
Die Helmholtz-Gemeinschaft deutscher Forschungszentren (HGF) stellt sich dieser Aufgabe durch verstärkte Investitionen in Forschungsinfrastrukturen und eine weitere Vernetzung der Forschungsaktivitäten zwischen Helmholtz-Zentren und Universitäten. Im Hinblick auf die neuen energiepolitischen Rahmenbedingungen in der Bundesrepublik Deutschland startete die Helmholtz-Gemeinschaft deutscher Forschungszentren im Jahr 2011 eine Initiative zur Förderung neuer Themen der Energieforschung. Die in diesem Beitrag vorgestellte Helmholtz-Energie-Allianz ist ein Forschungsverbund, der Kompetenzen und Forschungsaktivitäten im Bereich der chemischen Verfahrenstechnik bündelt. Die Ziele des auf drei Jahre angelegten Forschungsvorhabens bestehen in der Weiterentwicklung von Entwurfs- und Auslegungsmethoden sowie numerischen und experimentellen Techniken zur Effizienzsteigerung chemischer Mehrphasenprozesse, die in der chemischen Produktion von herausragender Bedeutung sind.

The structural and magnetic properties of 20-nm-thick FexPt100-x films that were processed by 20 ms flash-lamp annealing were investigated. A maximum in coercivity of (10.4 ± 0.5) kOe was achieved for a composition of Fe53Pt47, which shows also a high degree of L10 chemical order. A variation of the chemical composition toward either higher or lower Fe content leads to a lowering of the coercivity, which can be attributed to a reduction in L10 ordered volume fraction. Thus, in the millisecond time regime, the fastest ordering transformation occurs for slightly Fe-rich FePt films.

YSZ (yttria-stabilized zirconia) with cubic phase is a promising nuclear material. YSZ has excellent radiation resistance and chemical stability and can be applied for the inter matrix layer of fuel cells or for the covering and storage of nuclear waste. The effect of irradiation on YSZ has been intensively investigated in recent years via single beam implantation.[1,2] Most of experimental works were performed to simulate the radiation damage from alpha particles by He+ implantation [2] or to simulate the neutron radiation damage and the damage introduced from alpha recoils by implantation of heavy ions. [1] In fact, the radiation damages created by the simultaneous dual beam implantation of Zr+ and He+ ions is much more adequate to reflect the real irradiation conditions. However this case is rarely reported in the literature due to the experimental restrictions. In this work the dual beam facility in Rossendorf is used for the investigation of the radiation damage in YSZ created either by simultaneous implantation of Zr+ & He+ or by separate single beam implantation. The samples were analyzed by a variety of methods such as Rutherford backscattering spectrometry in channeling mode, high resolution x-ray diffraction, positron annihilation spectroscopy, nanointendation and transmission electron microscopy.
The results show that the excitation by the additional Zr+ implantation can activate and enhance the out diffusion of the simultaneously implanted He. The release of He.from YSZ substrate, instead to be trapped by implantation induced vacancies generated by the heavy Zr+ ions, avoids the formation and growth of He bubbles. Such bubbles make the material hard and brittle. In this way the ability of YSZ for the stable inclusion of nuclear waste in the long term is verified. Possible mechanisms are discussed.

[1] S. Moll et al., Journal of Applied Physics 105, 023512 (1999).
[2] G. Velisa et al., Journal of Nuclear Materials 402, 87 (2010).

The resistive switching (RS) of functional oxide thin films has attracted tremendous interest recently due to its promising application as building blocks in non-volatile memory devices. [1] By applying voltage pulses, the functional oxide films are switched between different resistance states and may store information, which is the basis of resistance random access memory (RRAM). However, the RS performance of the oxides still needs improvement for a future commercial application, and the physical mechanism of the RS is not fully understood yet. The point defects, especially oxygen vacancies, play an important role on determining the electrical conduction of oxide thin films. [2] This work reports a low cost and effective approach to tune the resistive switching behavior of BiFeO3 films which have been deposited by pulsed laser deposition [3] and irradiated with low energy Ar+ ions. Due to the preferential sputtering of BiFeO3 films, oxygen vacancies as well as the surface morphology can be tuned by low energy irradiation in a controllable way to enhance the RS performance. The obvious improvement of key switching parameters, i.e. the resistance stability and retention, was observed in the irradiated BiFeO3 (Figure 1). These improvements give an opportunity to design a nonvolatile memory with a multilevel RS function which is more scalable than a memory based on bistable RS reported by most of studies [3]. The changing of the conduction mechanism in the BiFeO3 from Poole-Frenkel to space-charged-limited conduction after irradiation will be discussed. The combination of the microstructure analysis and the electrical characterization of the irradiated BiFeO3 will gain an insight into the resistive switching mechanism.

Figure 1(a) I-V characteristic curves showing a significant improvement of the stability of resistive switching in BiFeO3 film after irradiation. The distinguishable neighboring resistance states in the irradiated sample allow for designing multilevel RS memory devices based on BiFeO3 films. (b) Retention test showing the nonvolatile resistance states in irradiated BiFeO3 film on an extrapolated time scale of 10 years.

[1] R. Waser et al., Nature Materials 6, (2007) 833.
[2] D. W. Reagor et al., Nature Materials 4, (2005) 593.
[3] Y. Shuai et al., Applied Physics Letters 98, (2011) 232901.
[4] Y. Shuai X. Ou et al., Journal of Applied Physics 111, (2012) 07D906.

The periodical semiconductor nanostructure arrays have the potential for nano-electronic and nano-optoelectronic application. Comparing to the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface.[1] Based on a “self-organized” erosion process, periodical nanoripple, nanohole, nanodot and nanotip arrays can be created due to the interplay of different processes.[2] As the ion beam erosion is performed on Si /Ge thin layer on insulator substrate and precisely ceased when the nanopattern moves to the interface of the buried oxide layer, an array of separate nanostructure can be fabricated on insulator. This work reports the fabrication of the horizontal silicon nanowire arrays on insulator by Xe+ beam erosion of Si-on-insulator substrate [3] (figure 1a). A periodic ripple surface pattern on Si is created by ion irradiation with Xe+ at an incidence angle of 67o to the surface normal. The transfer of the pattern to the oxide interface results in an array of disconnected parallel ordered Si nanowires.The electrical doping behaviour of the fabricated Si nanowire was investigated by scanning spreading resistance microscopy (SSRM). Meanwhile, we will also report our recent discover of single crystal Ge nanopattern formation based on “negative epitaxy” process (figure 1b). The vacancies created during the ion beam sputtering will be distributed according to the crystallographic anisotropy, which results in the orientation-dependent pattern formation on single crystal Ge surface. The mechanism of this novel process will be discussed.
[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] C. S. Madi et al. Phys. Rev. Lett. 106, 066101 (2011).
[3] Xin Ou et al. AIP Advances, 1, 042174 (2011).

The periodical semiconductor nanostructure arrays have the potential for electronic and optoelectronic application. Comparing to the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate the nanostructure patterns on semiconductor surface.[1] Based on a “self-organized” erosion process, periodical nanoripple, nanohole, nanodot and nanotip arrays can be generated due to the interplay of different processes.[2] As the ion beam erosion is performed on Si /Ge thin layer on insulator substrate and precisely ceased when the nanopattern moves to the interface of the buried oxide layer, an array of separate nanostructure can be fabricated on insulator. This work reports the fabrication of the horizontal silicon nanowire arrays on insulator by ion beam erosion of Si-on-insulator substrate [3] and the fabrication of different single crystal Ge nanopattern and nanostructure based on novel “negative epitaxy” process induced by ion beam erosion. The electrical doping behaviour of the fabricated Si nanowire and formation mechanism of the Ge nanopattern will be discussed.
[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] C. S. Madi et al. Phys. Rev. Lett. 106, 066101 (2011).
[3] Xin Ou et al. AIP Advances, 1, 042174 (2011).

Low-energy Ar+ ion irradiation has been applied to an Au/BiFeO3/Pt capacitor structure before deposition of the Au top electrode. The irradiated thin film exhibits multilevel resistive switching (RS) without detrimental resistance degradation, which makes the intermediate resistance states more distinguishable, as compared with the nonirradiated thin film. The stabilization of resistance states after irradiation is discussed based on the analysis of the conduction mechanism during the RS, which was investigated by means of temperature-dependent current–voltage measurement from room temperature to 423 K

The Cu^II complex of H₄TETP (H₄TETP = 1,4,8,11-tetraazatetradecane-1,4,8,11-tetrapropionic acid) is five-coordinate with a distorted square-pyramidal structure (τ = 0.45; i.e. the geometry is nearly half-way between square-pyramidal and trigonal-bipyramidal) and a relatively long Cu–N and a short Cu–O bond; the comparison between powder and solution electronic spectroscopy, the frozen solution EPR spectrum and ligand-field-based calculations (angular overlap model, AOM) indicate that the solution and solid state structures are very similar, i.e. the complex has a relatively low “in-plane” and a significant axial ligand field with a d_x ² _−y ² ground state. The ligand-enforced structure is therefore shown to lead to a partially quenched Jahn–Teller distortion and to a relatively low complex stability, lower than with the corresponding acetate-derived ligand H₄TETA. This is confirmed by potentiometric titration and by the biodistribution with ⁶⁴Cu-labeled ligands which show that the uptake in the liver is significantly increased with the H₄TETP-based system.

Polyoxometalates (POMs) are inorganic cluster compounds that have been shown to possess a number of pharmacological properties, including antidiabetic, antibacterial, antiprotozoal, antiviral and anticancer activities. Their molecular mechanism of action is largely unknown. However, several studies indicate that many of their activities may be due to the inhibition of enzymes, in particular, of those enzymes that are accessible from the extracellular space and do not require the penetration of cell membranes. In this review, we describe the recent progress in the preparation and optimization of POMs, and an evaluation of their use as inhibitors of different families of enzymes. The next important steps in this area of research will be to gain a better understanding of the interactions of POMs with enzymes on a structural level through an X-ray crystallographic study of enzyme–POM complexes and the analysis of structure–activity relationships. Furthermore, POMs with increased stability and in vivo half-lives have to be prepared. Surface modification may allow the targeting of POM drugs at their sites of action.

The search for new methods of cancer diagnosis is leading to the development of multimodal imaging agents that may be detected by techniques such as Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET). A new bimodal imaging agent has been prepared which can be used for dual mode detection of cancer by both MRI and PET imaging. The imaging agent consists of an azamacrocyclic ligand, 1,4-bis (2-pyridilmethyl)-1,4,7-triazacyclononane (DMP-TACN), linked to iron oxide nanoparticles through polyethylene glycol (PEG) chains (M_n ~ 600) that are attached to the nanoparticle surface by silanization. The azamacrocyclic ligands serve as complexing agents for radioactive copper (⁶⁴Cu) for PET imaging, while the iron oxide nanoparticles work both as a carrier and an imaging agent for MRI. The iron oxide nanoparticles have been synthesized by thermal decomposition from iron oleate. The functionalized nanoparticles have sizes ranging between 7–10 nm, as determined by TEM, whilst Nanoparticle Tracking Analysis (NTA) experiments suggest an average hydrodynamic diameter of 50 nm. ⁶⁴Cu labeling experiments revealed that the nanoparticles loaded with DMP-TACN have a labeling yield of around 10%. MRI experiments in rats showed the nanoparticles accumulate in the liver 15 min after intravenous administration. 64Cu labeling and breast tumor cell labeling studies are currently being performed using the new nanoparticles.

The tridentate macrocycle 1,4,7-triazacyclononane (TACN) forms stable complexes especially with Cu(II) whereby the metal ion lying out of the plane defined by the three nitrogen atoms. The donor atoms are oriented in such a way as to maximize orbital overlap and thereby produce complexes with very high stabilities. The introduction of further donor groups on the ligand skeleton, such as pyridine units, significantly influences the thermodynamic stability as well as the kinetic inertness of the metal complexes formed. We have developed a ligand scaffold based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) [1]. This structure allows for the introduction of linker groups, such as carboxylic acids, maleimide or isothiocyanate, thereby facilitating coupling of targeting molecules (see Figure).
TACN ligands containing one or two pendant 2-picolyl arms prefer the formation of square-pyramidal coordination geometry with copper(II). A hexadentate ligand with two picoline coordination groups as well as a carboxylic functionality (DMPTACN-COOH) enforces a six-coordinate copper(II) complex having a distorted octahedral structure. It has been found that relevant peptide conjugates of this hexadentate bis(2-pyridylmethyl)-TACN-acetic acid derivative can readily form radiocopper complexes under physiologically relevant conditions and show high in vivo stability. Such radiolabeled peptides are thus attractive candidates for radiopharmaceutical applications.
We want to present the synthesis of peptide conjugates with DMPTACN derivatives capable of gastrin releasing peptide receptor (GRPR) and epidermal growth factor receptor (EGFR) targeting. Both types of receptors are overexpressed on different cancer cells. In vitro binding characteristics of [⁶⁴Cu]Cu^II-labeled DMPTACN-peptide conjugates in GRPR and EGFR overexpressing cancer cells (PC-3, FaDu, A431) will be presented. Small animal PET studies confirmed a high extent of tumor accumulation in NMRI nu/nu mice bearing the human prostate tumor PC-3. Derived from that, it can be concluded that ^64CuII complexes of DMPTACN-peptide conjugates have considerable potential for tumor imaging, since these peptide derivatives can effectively display receptor-rich tissue in vivo.
[1] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran, M. Walther, J.-U. Künstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 9, 719-730.

No abstract needed

Since the DREAMS (Dresden Accelerator Mass Spectrometry) facility went operational in 2011, constant effort was put into enabling routine measurements of long-lived radionuclides as ¹⁰Be, ²⁶Al and ⁴¹Ca. For precise AMS-measurements of the volatile element Cl the key issue is the minimization of the long term memory effect [1]. For this purpose one of the two original HVE sources was mechanically modified, allowing the usage of bigger cathodes with individual target apertures. Additionally a more open geometry was used to improve the vacuum level. To evaluate this improvement in comparison to other up-to-date ion sources, a small interlaboratory comparison had been initiated.
The long-term memory effect in the Cs sputter ion sources of the AMS facilities VERA, ASTER and DREAMS had been investigated by running samples of natural ³⁵Cl/³⁷Cl-ratio and samples containing highly enriched ³⁵Cl (³⁵Cl/³⁷Cl > 500). Primary goals of the research are the time constants of the recovery from the contaminated sample ratio to the initial ratio of the sample and the level of the long-term memory effect in the sources.
[1] R. Finkel et al., NIMB 294 (2013) 121.

In 2011 the DREAMS (Dresden Accelerator Mass Spectrometry) facility [1] based on a HVE 6 MV Tandetron went operational. Since then constant effort was put into enabling routine measurements of long-lived radionuclides such as ¹⁰Be, ²⁶Al and ⁴¹Ca. In the case of ³⁶Cl the main focus was set on understanding and minimization of the ion source memory effect, which is the key issue for precise AMS-measurements of volatile elements like Cl and I [2,3]. For this purpose, one of the two original HVE sources was mechanically modified. The new design has a more open geometry to improve the vacuum level and a modified target loading and positioning system, which allows exchanging the individual cathode aperture with each target.
To evaluate this improvement in comparison to other up-to-date ion sources, a small interlaboratory comparison had been initiated. The long-term memory effect in the four Cs sputter ion sources of VERA [3] (Vienna Environmental Research Accelerator, NEC ion source: MC-SNICS), ASTER [4] (Accélérateur pour les Sciences de la Terre, Environnement, Risques, modified HVE SO110) and DREAMS (original HVE and modified HVE ion source) [1] had been investigated by running samples of natural ³⁵Cl/³⁷Cl-ratio and samples containing highly enriched ³⁵Cl (³⁵Cl/³⁷Cl > 500).
Primary goals of the research are the time constants of the recovery from the contaminated sample ratio to the initial ratio of the sample and the level of the long term memory effect in the sources.

[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5.
[2] R. Finkel et al., Nucl. Instr. Meth. B 294 (2013) 121.
[3] M. Arnold et al., Nucl. Instr. Meth. B 294 (2013) 24.
[4] M. Martschini et al., Nucl. Instr. Meth. B 269 (2011) 3188.

Geologische Karte mit Erläuterungen des Freistaates Sachsen 1 : 25000 (Blatt 5047 Freital)

At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at the prototype THz pump probe facility at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 microJ limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162."

The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges for in particular the life sciences will be discussed on the example of recent pilot experiments.

[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys. Lett. 99 (2011), 141117.

Zircon and monazite from the Stolpen granite and related rhyolitic dyke show magmatic as well as post-magmatic textures. The magmatic textures are overprinted by post-magmatic fluid interaction which is indicated by elevated contents of Y, P, Th, and U in altered zircon domains. This can be observed both in the granite and rhyolite; however these processes were less intensive in the rhyolite. Patchy zoning in primary monazite from the granite also suggests fluid-induced alterations. High Ca, Pb, and Si contents and depletion in Th, as well as porous, spongy textures in monazite from the rhyolite are results of fluid-induced alterations that caused also crystallization of cheralite. Zircon and monazite from the granite are accompanied by fluorite, Y-rich and Nb-rich minerals. The alteration of primary, magmatic accessory minerals and formation of secondary minerals is interpreted as related to magmatic fluids, which origin cannot be defined precisely on the base of the present data, however their composition suggests some mantle contribution. The presence of fluorine and CO2 which promoted the transport of some HFSE and LILE accounts for their enrichment in the accessory minerals. Fluids that affected the accessory minerals from the rhyolite show different features (silica- and Ca-enrichment) and most probably came from another source

Vorstellung des technischen Konzepts und der analytischen Möglichkeiten der Super-SIMS.

Sophisticated sample preparation including the determination of stable nuclides are an essential prerequisite for high-accuracy accelerator mass spectrometry (AMS) data. Improvements in the low-level regime already paid back [1], however, some pitfalls still exist or are (re-) appearing due to recent developments:

1.) As most samples prepared for ¹⁰Be-AMS need the addition of ⁹Be in the form of a liquid solution of known ⁹Be-concentration and commercial solutions contain too much ¹⁰Be, solutions from minerals originating from deep mines have been established. Special attention has recently been paid to the preparation of such a ⁹Be-carrier by the determination of the ⁹Be-value by an interlaboratory comparison. It could be shown that deviations between different labs exist, thus, it is strongly advised to have such solutions analysed at more than a single lab to prevent incorrect ¹⁰Be-results.
2.) In our approach to analyse as many radionuclides as possible in a single meteorite sample, small changes in the established chemical separation [2] have been tested. Though, the secondary formation of partially insoluble compounds of Mg and Al by the pressure digestion is strongly influenced, thus, yielding to too low ²⁷Al-results in the taken aliquot and overall incorrect ²⁶Al-results.
Ackn.: DREAMS-team and colleagues performing ⁹Be- and ²⁷Al-measurements (BAM, GFZ, HZDR, CEREGE, TUBAF, U Cologne, VKTA). Ref.: [1] NIMB 266 (2008) 4921. [2] RCA 84 (1999) 215.

We report on an experimental analysis of the charge transport through sulfur-free photochromic molecular junctions. The conductance of individual molecules contacted with gold electrodes and the current-voltage characteristics of these junctions are measured in a mechanically controlled break-junction system at room temperature and in liquid environment. We compare the transport properties of a series of molecules, labeled TSC, MN, and 4Py, with the same switching core but varying side-arms and end-groups designed for providing the mechanical and electrical contact to the gold electrodes. We perform a detailed analysis of the transport properties of TSC in its open and closed states. We find rather broad distributions of conductance values in both states. The analysis, based on the assumption that the current is carried by a single dominating molecular orbital, reveals distinct differences between both states. We discuss the appearance of diode-like behavior for the particul!
ar species 4Py that features end-groups, which preferentially couple to the metal electrode by physisorption. We show that the energetic position of the molecular orbital varies as a function of the transmission. Finally, we show for the species MN that the use of two cyano end-groups on each side considerably enhances the coupling strength compared to the typical behavior of a single cyano group.

Seltenerdbasierte MOS Emitter zeigen bei elektrischer Anregung die für Seltene Erden typischen Lumineszenzspektren. Die Anregung erfolgt über Stoßanregung heißer Elektronen, die aber gleichzeitig zu einer Degradation des Oxides führt. Die für die Elektronen erforderliche Beschleunigungsstrecke in der Größenordnung von 10-20 nm begrenzt die Dicken- und Spannungsskalierung nach unten. Mögliche Strategien zur Optimierung von Effizienz und Betriebslebensdauer beinhalten u. a. die Verwendung von Sensitizern zur Erhöhung des Anregungsquerschnittes bzw. das Einfügen einer SiON-Pufferschicht. Anwendungsmöglichkeiten liegen in der Sensorik mittels integrierter, optoelektronischer Chips.

Neptunium ist eines der wichtigsten Radionuklide in der Problematik der Endlagerung nuklearer Abfälle. Obwohl die Np-Konzentrationen im radioaktiven Abfall aus der Energiegewinnung gering sind, zählt es aufgrund seiner hohen Halbwertszeit (2x106 Jahre), seiner physiologischen Verfügbarkeit und seiner potenziell gesundheitlichen Schadwirkung zu den gefährlichsten Nukliden [1].

Die Sorption von Neptunium an der Wasser-Mineral Grenzfläche spielt eine wesentliche Rolle in der Abschätzung seines Migrationsverhaltens in der Umwelt. Frühere Untersuchungen zeigen, dass die Np(V) Sorption an Tonmineralen durch eine Vielzahl verschiedener Faktoren beeinflusst wird, z. B. pH-Wert, Np-Konzentration, Vorhandensein anderer Kationen und Ionenstärke. Bekannte Sorptionseigenschaften wurden vorrangig mittels Batch Versuchen erhalten [2-4]. Aussagen über die Struktur und Stöchiometrie der bei der Sorption entstandenen Neptuniumkomplexe konnten bisher nur über die Modellierung von Sorptions- und thermodynamischen Daten gewonnen werden und sind durch geeignete spektroskopische Methoden zu überprüfen [4].

Die Infrarotspektroskopie kann durch die Erfassung von charakteristischen Schwingungsfrequenzen von funktionellen Gruppen (z. B. NpO2+) Informationen zur Struktur von Molekülen bzw. von Molekülkomplexen liefern [5]. In wässrigem Milieu werden diese Untersuchungen mittels der „Attenuated Total Reflection“-Technik (ATR) durchgeführt. Somit kann die Sorption von Ionen an mineralischen Phasen in situ (z. B. in Durchfluss-experimenten) eingehend studiert werden. Durch das definierte Einstellen physikalisch-chemischer Parameter der wässrigen Lösung (pH-Wert, Ionenstärke, etc.) lassen sich definierte, naturnahe Reaktionsbedingungen schaffen.
Als Modellsystem für komplexe Tonminerale soll sich diese Untersuchung mit der Np Sorption an verschieden Mineraloxiden (z. B. Al2O3, SiO2, TiO2) beschäftigen. Die zu erhaltenden IR-Spektren sind von großer Bedeutung, um die Komplexierung der NpO2+ Kationen mit den Aluminol-, Silanol- oder Titanol- Oberflächengruppen zu verstehen und dienen als Basis für spätere Untersuchungen komplexerer Mineralsysteme.

Referenzen:

[1] Kaszuba, J.P. et al. (1999) Environ. Sci. Technol. 33, 4427-4433.
[2] Li, W.J. et al. (2003) J. Colloid Interface Sci. 267, 25-31.
[3] Del Nero, M. et al. (2004) Chem. Geol. 211, 15-45.
[4] Tochiyama, O. et al. (1995) Radiochim. Acta 68, 105-111.
[5] Müller, K. et al. (2009) Environ. Sci. Technol. 43, 7665-7670.

Geplante Arbeiten:

FT-IR Durchflussexperimente zur Sorption von Np(V) an Al2O3, SiO2, TiO2 bei Variation sorptionsbestimmender Parameter (pH, Np(V)-Konzentration, Ionenstärke, Anwesenheit von anorganischen Liganden, z. B. Carbonat)

Die vorliegende Diplomarbeit entstand vom 15.04.2012 bis zum 15.10.2012 in der Abteilung Grenzflächenprozesse des Instituts für Ressourcenökologie des Helmholtz-Zentrums Dresden-Rossendorf.
Für abgebrannte Brennelemente aus Kernkraftwerken wird neben der Wiederaufarbeitung vor allem die direkte Endlagerung als Entsorgungskonzept verfolgt. Die Endlagerbehälter korrodieren während der Einlagerungszeit, sodass der uranhaltige Abfall in die Geosphäre eintreten kann und dort physikalischen und chemischen Einflüssen ausgesetzt ist. Hohe Bedeutung kommt hier der Bildung von Hydroxo- und Carbonatokomplexen des Uranyl-Ions (UO22+) zu, welche die Chemie des Urans in wässrigen Systemen (Grundwasser) dominieren.
Die einzelnen Komplexe weisen dabei je nach Zusammensetzung unterschiedliche Affinität zu natürlichen Oberflächen – wie zum Beispiel Mineraloberflächen – auf, wobei die Beschaffenheit sowohl dieser Grenzflächen als auch der Koordinationssphäre des UO22+-Ions starke Temperatur- und pH-Anhängigkeiten zeigen. In der vorliegenden Arbeit wurde vorrangig der Temperatureinfluss auf die Sorptionsprozesse des Uran(VI) an Mineraloxidoberflächen im Temperaturbereich zwischen 25 °C und 60 °C eingehend untersucht. Dies wurde mittels zweier experimenteller Ansätze bewerkstelligt: Die Infrarot-Spektroskopie liefert Informationen zu Art und Struktur der infolge Sorption gebildeten Oberflächenkomplexe, während klassische Batch-Versuche zur Betrachtung des Verteilungsgleichgewichts zwischen gelöstem und sorbiertem Uran nützlich sind. Als Modelloberflächen für natürliche Gesteine und Minerale dienten verschiedene Metalloxide wie TiO2, SiO2, α-Fe2O3, γ-Al2O3 und γ-Al(OH)3.
Die schwingungsspektroskopischen Versuche wurden im schwach sauren pH-Bereich von 5 bis 6 durchgeführt. Es konnte gezeigt werden, dass sich die Zusammensetzung der Oberflächenkomplexe in Abhängigkeit von der Temperatur stark ändert: Bei höheren Temperaturen nimmt der Anteil koordinativ gebundener Komplexe gegenüber elektrostatisch gebundenen zu. Auch zwischen den einzelnen Oxiden wurden deutliche Unterschiede festgestellt: Während z. B. bei TiO2 elektrostatisch gebundene Komplexe von U(VI) vorherrschen, sind bei α-Fe2O3 und γ-Al(OH)3 eher die koordinativ gebundenen Komplexe zu finden. Der Carbonat-Anteil in den sorbierten Komplexen nimmt mit steigender Temperatur meist ab, lediglich α-Fe2O3 zeigte hier ein abweichendes Verhalten. Auch in den Batch-Versuchen verhielten sich die untersuchten Oxide im pH-Bereich von 2,5 bis 7 recht unterschiedlich: Wurde beispielsweise bei TiO2 eine verbesserte Sorption bei höherer Temperatur gefunden, war es bei SiO2 umgekehrt, während das Verteilungsgleichgewicht zwischen Fest- und Flüssigphase bei γ-Al(OH3), γ-Al2O3 und α-Fe2O3 durch die Temperatur eher schwach beeinflusst wurde. Grundsätzlich wurde bei steigendem pH-Wert eine Verschiebung des Gleichgewichts in Richtung Festphase beobachtet, nur bei γ-Al2O3 war ein Minimum bei pH ≈ 3 zu verzeichnen.
Die im Rahmen dieser Arbeit durchgeführten Experimente konnten die Temperatur- und pH-Abhängigkeit der Sorption von U(VI)-Komplexen an verschiedenen Oxiden weiter beleuchten, aber es besteht noch ein großer Bedarf an weiteren Experimenten, insbesondere zur Untersuchung der Sorptionsvorgänge in stark saurem oder basischem Milieu.

Für die Sicherheitsanalyse eines Endlagers für radioaktive Stoffe ist es notwendig, das Verhalten von Uran im wässrigen Medium und im Boden zu kennen. Während der Wiederaufarbeitung oder eines Störfalls, einer unkontrollierten Freisetzung, kann Uran mit organischen Säuren im Boden oder im radioaktiven Abfall in Kontakt kommen. Speziationsuntersuchungen der Systeme Uran(VI)-Citronensäure und Uran(VI)-Oxalsäure in equimolarer Konzentration (c = 10 mM) und umweltrelevanter Ionenstärke (I = 0,1 M) bestätigten zum Teil bekannte Uranspezies, wurden aber auch durch noch nicht beschriebene Komplexe erweitert. Dazu wurde die Methode der ATR FT-IR Spektroskopie verwendet. Uran(VI) und Citronensäure bilden zwischen pH 2,5 und 5 den bekannten Komplex (UO2)2(cit)22-. Zwischen pH 5 und 6,5 ist der gemischte Uranyl-Citrat-Hydroxo-Komplex (UO2)2(cit)2OH3- und oberhalb von pH 6,5 der Komplex (UO2)3(cit)3(OH)58- zu finden, welche noch nicht in der Literatur beschrieben sind. Im System U(VI)-Oxalsäure wurde zwischen pH 1 bis etwa pH 5 der bekannte Komplex (UO2)(ox) bestätigt. Oberhalb von pH 5 bis pH 8 konnte eine neue Spezies festgestellt werden, der Komplex (UO2)2(ox)2OH-. Diese Urankomplexe zeigen eine erhöhte Migrationsfähigkeit aufgrund der Löslichkeit bis hin in den basischen pH Wert (pH 8). Das Sorptionsverhalten von U(VI) wurde an den Modelloxiden Hämatit und SiO2 in Anwesenheit der o. g. Liganden untersucht. Bereits eine equimolare Konzentration von U(VI) und Citronensäure (c = 20 µM) hemmt die Sorption von Uran an Hämatit durch Komplexierung im wässrigen Medium. Bei Beladung der Hämatitoberfläche mit U(VI) entstehen durch Kontakt mit Citronensäure kurzzeitig ternäre Oberflächenkomplexe, die durch stärkere Komplexierung im wässrigen Medium wieder abgebaut werden. U(VI) und Oxalsäure bilden ebenfalls kurzzeitig einen U(VI)-Oxalat-Hämatit-Oberflächenkomplex. SiO2 bildet mit U(VI) und den organischen Liganden keinen ternären Oberflächenkomplex. Eine uranbeladene SiO2-Oberfläche neigt zur Desorption und wässrigen Komplexierung des Schwermetalls durch die organischen Liganden. Die Immobilisierung von Uran durch Sorption an Hämatit oder SiO2 wird durch Anwesenheit von Citronen- oder Oxalsäure gehemmt.
Abstract
For a reliable safety assessment of final repositories of nuclear waste, knowledge the behaviour, i.e. molecular reactions of uranium in aqueous solutions and at mineral-water interfaces is of major concern. During an accidental release, uranium may interact with organic acids and geologic material in the near- and far-field of the nuclear waste repository.
In this work the speciation of U(VI)-citric acid and U(VI)-oxalic acid in equimolar concentration (c = 10 mM) and at environmentally relevant ionic strength (I = 0.1 M) was investigated by ATR FT-IR spectroscopy. The obtained data confirm previously described uranium complexes, however, new species could be identified as well. Between pH 2.5 and 5 the known species (UO2)2(cit)22- was found. For the first time, the mixed uranyl-citrate-hydroxo-species (UO2)2(cit)2OH3- (pH 5 – 6.5) and (UO2)3(cit)3(OH)58- (> pH 6.5) were detected. These species have not been described in the literature so far. In the system U(VI)-oxalic acid between pH 1 to 5 the known species (UO2)(ox) was confirmed. Above pH 5 to pH 8 there was a new species identified, (UO2)2(ox)2OH-. The mixed uranyl-organic ligand-hydroxo-species increase the U(VI) migration behavior, because of their high solubility till pH 8.
The sorption behavior of U(VI) was investigated on the model oxides hematite and silicon dioxide in presence of above mentioned organic ligands. Equimolar concentration of U(VI) and citric acid (c = 20 µM) decrease uranium sorption on hematite through complexation in aqueous solution. A U(VI) loaded mineral oxide surface in contact with citric acid forms an intermediate ternary surface complex with citric acid and U(VI). The complexation in aqueous medium is stronger than the ternary surface complex, hence, U(VI) desorption occurs. U(VI) and oxalic acid forms also an intermediate ternary surface complex with hematite. Silica forms no ternary surface complex with U(VI) and the organic acids. An uranium loaded silica surface desorbs U(VI) und forms aquatic species with the organic acids. The immobilization of uranium through sorption on hematite and silicon dioxide is inhibited in the presence of citric- and oxalic acid.

Ziel der Arbeit war die schwingungsspektroskopische Identifizierung und Charakterisierung der Hydrolyseprodukte des Uran(VI) in wässriger Lösung und von U(VI) Oberflächenkomplexen an der Fest-Flüssig Grenzfläche bei erhöhten Temperaturen. Diese Spezies des U(VI) können mithilfe der ATR FT-IR Spektroskopie in situ untersucht werden. Anhand charakteristischer Schwingungsfrequenzen bestimmter funktioneller Gruppen, z. B. UO22+, werden somit strukturelle Informationen über die jeweilige Bindungsform auf molekularer Ebene erhalten.

Zunächst sollte im Rahmen der Masterarbeit die bisher genutzte Durchflussapparatur für ATR FT-IR spektroskopische Untersuchungen für Experimente bei erhöhten Temperaturen weiterentwickelt werden. Bei der Verwendung der Differenzspektroskopie hat die Temperaturkonstanz eine entscheidende Bedeutung, da schon Unterschiede von einigen wenigen Grad Celsius zu Instabilitäten der Basislinie und damit zu schwer interpretierbaren bis hin zu nicht auswertbaren Infrarotspektren führen. Das von Herrn Meusel entwickelte Messsystem besteht zum Einen aus einem thermostatisierbaren Block zur Präparation und Lagerung der Proben vor und während der IR Messungen. Dabei stellen die exakte Einstellung der pH-Werte als auch die Volumenänderung der Proben durch Evaporation kritische Faktoren dar. Zum Anderen gehören ein thermostatisierbarer Metallring zum Erwärmen der direkten Umgebung des ATR-Kristalls, als auch eine Durchflusszelle mit integriertem Temperatursensor zum weiterentwickelten Aufbau. Des Weiteren wurden eine Isolation der Schlauch- und Verbindungsstücke realisiert und eine detaillierte Bedienvorschrift entwickelt. Während des Zeitraumes der Masterarbeit wurde dieser Aufbau soweit optimiert, dass eine ausreichende Grundlinienstabilität über mehrstündige Reaktionszeiträume für Untersuchungen bei Temperaturen von bis zu 70°C gewährleistet wird.

Somit konnten erstmalig die U(VI)-Hydrolysereaktionen bei erhöhten Temperaturen schwingungsspektroskopisch erfasst werden. Es wurden U(VI)-Lösungen im milli- und mikromolaren Konzentrationsbereich bei 25, 40 und 60°C untersucht. Die erhaltenen IR Spektren zeigen, dass sich mit steigender Temperatur das Hydrolysegleichgewicht zu niedrigeren pH-Werten verschiebt. Des Weiteren wurde in Lösungen mit erhöhter U(VI) Konzentration und bei Temperaturen über 25°C eine geringere Löslichkeit des U(VI) beobachtet.

Ein weiterer Aufgabenschwerpunkt der vorliegenden Masterarbeit bestand in Untersuchungen zur Komplexierung von U(VI) an der Mineraloxid-Wasser Grenzfläche in Abhängigkeit der Temperatur. Als Modellmineral wurde Titandioxid (TiO2) ausgewählt. TiO2 zeigt eine hohe thermodynamische Stabilität und wurde zudem in früheren spektroskopischen Untersuchungen am IRC intensiv hinsichtlich seiner U(VI) Retentionskapazitäten untersucht. Im Rahmen der Masterarbeit wurde der Einfluss der Temperatur bis 70°C in situ und in zeitaufgelösten Experimenten ermittelt. Im Vergleich zu Sorptionsprozessen bei 25°C verlaufen die Oberflächenreaktionen bis 50°C kinetisch beschleunigt, die U(VI) Speziesverteilung an der TiO2 Oberfläche ändert sich jedoch wenig. Anhand der erhaltenen Spektren konnten ein stark gebundener innersphärischer Komplex bei geringer Oberflächenbeladung (z. B. im frühen Sorptionsstadium) und ein weniger stark gebundener außersphärischer Komplex bei hoher Oberflächenbeladung (z. B. im späten Sorptionsstadium) nachgewiesen werden. Bei Temperaturen oberhalb 50°C deuten die Ergebnisse auf eine drastische Änderung der Sorptionsprozesse hin. Während der innersphärische Komplex vermutlich kinetisch gehemmt und die Bildung des außersphärischen Komplexes nicht mehr beobachtet wird, konnte eine neue polymere Spezies identifiziert werden. Möglicherweise handelt es sich hier um eine U(VI) Oberflächenausfällung deren spektralen Charakteristika denen von U(VI) Kolloiden in Lösung und Sorptionsprozessen an anderen Mineraloxidoberflächen (Al2O3) sehr ähneln. Die Ergebnisse belegen die entscheidende Rolle der Temperatur auf die Grenzflächenprozesse, die das Migrationsverhalten von (radioaktiven) Schwermetallen in der Umwelt maßgeblich beeinflussen.

In this talk, the following topics will be discussed:

(1) Why magnetic semiconductors are important;
(2) Diluted magnetic semiconductors by ion implantation: successful cases and pit-falls;
(3) Defect-induced ferromagnetism in semiconductors: ion beam irradiation provides a controllable approach.

The correlation between colossal magnetocapacitance (CMC) and colossal magnetoresistance (CMR) in CdCr2S4 system has been revealed. The CMC is induced in polycrystalline Cd0.97In0.03Cr2S4 by annealing in cadmium vapor. At the same time, an insulator-metal transition and a concomitant CMR are observed near the Curie temperature. In contrast, after the same annealing treatment, CdCr2S4 displays a typical semiconductor behavior and does not show magnetic field dependent dielectric and electric transport properties. The simultaneous occurrence or absence of CMC and CMR effects implies that the CMC in the annealed Cd0.97In0.03Cr2S4 could be explained qualitatively by a combination of CMR and Maxwell-Wagner effect.

In the uranium mine Königstein (Saxony, Germany) the uranium production was achieved by leaching the sandstone with sulphuric acid in the past. As a consequence the geochemical nature of the deposit was changed with an increase of sulphate and heavy metals, (especially uranium) in acidic, sulfate-rich waters. Since 2001 the mine has been flooded for remediation processes. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO2SO4). According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to > 4.8.
In the underground rock characterization facility tunnel "ONKALO" in Finland massive biofilms were observed attached to the fractured bedrock at a depth of 70 m. Experiments were performed in the laboratory to study the effect on the behavior of uranium in biofilms by adding uranium to the fracture water with a final uranium concentration (410-5 M) relevant for what can be expected from an injured and leaking waste canister in the far-field during a nuclear event in a HLW repository. The results obtained by analysis, microsensor measurements, TRLFS investigation, EF-TEM/EELS studies and thermodynamic calculations clearly indicate that biofilms have to be considered as microenvironments, which differ significantly from the surrounding medium. EF-TEM investigations showed that in the biofilm uranium was immobilized intracellular in bacteria by a biologically mediated uranyl phosphate formation similar to needle-shaped Autunite (Ca[UO2]2[PO4]2•2-6H2O) or meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O). In contrast, TRLFS studies of the contaminated fracture water showed aqueous uranium carbonate species, most likely (Ca2UO2[CO3]3), which was formed using the available high amount of carbonate from the water. The results are in agreement with the thermodynamic calculation of the theoretical predominance field of uranium species, formed in the uranium contaminated fracture water at the measured geochemical parameters.

Nickel-Titanium (Ni-Ti) thin film shape memory alloys (SMAs) have been widely projected as a novel material, which can be utilized in microdevices. Characterization of their physical properties and its correlation with phase transformations has been a challenging issue. In the present study, X-ray beam diffraction has been utilised to obtain the structural information at different temperatures while cooling. Simultaneously, electrical resistivity (ER) was measured in the phase transformation temperature range. The variation of ER and integral area of the individual diffraction peaks of the different phases as a function of temperature have been compared. A mismatch between the conventional interpretation of ER variation and the results of the XRD data has been clearly identified.

As part of long-term safety assessments for radioactive waste disposals, scenarios have to be considered, which lead to the mobilization of radionuclides from the waste and to their transport through the repository system. Any repository sites (such as Gorleben) the sedimentary overburden is an important barrier for radionuclide transport. For most radionuclides the transport is retarded by sorption on mineral phases. Mica and feldspars are major components of the Gorleben sediments. However, almost no sorption parameters are available (www.hzdr.de/res³t [1]) for these systems.
The WEIMAR-project (Further Development of the Smart Kd-Concept for Long-Term Safety Assessment) shall address these shortcomings. Batch sorption experiments and spectroscopic investigations will allow the assessment, the evaluation as well as the processing of sorption data for U, Np, La(III) onto muscovite and orthoclase. Generally, the amount of sorption can depend on the pH-value, ionic strength, redox potential, concentrations of the contaminant as well as of the sorbent, of complexing ligands and competing ions. All batch experiments are carried out under ambient atmosphere and with 0.01 M NaClO4 as background electrolyte.
For muscovite and orthoclase the background concentration of the sorbing elements, the tendency of wall sorption and the dissolution behavior has to be determined. For both minerals an optimal solid-to liquid ratio has to be optimized. This means that the sorption is neither too low nor too high, so the sorption has to be between 5 and 95%. All those problems will be illustrated for the case of U(VI) sorption.

This project is funded by the German Federal Ministry of Economics and Technology (BMWi) under contract number 02 E 11072B

[1] Brendler, V. et al. (2003), J. Cont. Hydrol. 61, 281-291.

Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is obviously related with the formation of An(IV) eigencolloids or the sorption on other colloids.
We report some examples of investigated colloids of An(IV) ( An= Th, U, Np): An(IV) silica colloids.
The main characteristic properties (eg. particlesize distribution, longterm monitored time stability, surfacecharge) of these colloids are presented.

Knowledge of the migration and mobility of actinides is an important issue to predict potential release of radiotoxic elements from nuclear waste repositories. Under the reducing conditions expected for the disposal zone, the tetravalent form of the actinides An (An = Th, U, Np, Pu) is predominant. Due to the low solubility at neutral pH, An(IV) are considered as immobile under these conditions. Nevertheless, high environmental mobility has been found. This fact is related with the formation of An(IV) eigencolloids or the sorption on other colloids.

Here Neptunium(IV) forms silicate-containing colloids when the limit of solubility is exceeded in presence of soluble silicate.
The formation and stability of Np(IV)-silica colloids was investigated by liquid LSC, ICP-MS, UV-Vis spectroscopy and light scattering

Samples from three medieval rock avalanches from the French (Le Claps, Mont Granier) and Austrian Alps (Dobratsch) and a man-made structure, i.e. the Stephansdom in Vienna, have been analysed for in-situ produced ³⁶Cl by accelerator mass spectrometry (AMS). All four sampling sites of independently known exposure duration turned out to be not appropriate as calibration sites for the determination of the ³⁶Cl production rate from Ca. Indeed, the determination of short exposure ages for dating rock avalanches and man-made structures by ³⁶Cl is hindered dramatically by inheritance production, especially for samples characterized by high ^natCl concentrations. Generally, there are hints that the theoretical calculation of ³⁶Cl production from epithermal and thermal neutron-capture on ³⁵Cl is highly underestimated in all existing models, thus, asking for particular precaution if working on high-Cl samples for any project. Hence, this work evidences that potential high inheritance, even for samples reasonably shielded before exhumation, has to be considered especially when dealing with recently exposed surfaces such as glacially polished rocks, alluvial terraces, fault scarps etc.

We have studied the magnetic properties and crystal structure of Sr₃CoIrO₆ and Sr₃NiIrO₆ as a function of temperature. Two characteristic temperatures, T₁ = 90 K and T₂ = 25 K for Sr₃CoIrO₆, and T₁ = 85 K and T₂ = 15 K for Sr₃NiIrO₆, were observed. Below T₁ a significant increase of magnetization and below T₂ a weak temperature dependence of magnetization in the field-cooled and practically zero magnetization values in the zero-field-cooled mode were detected for both compounds. The existence of Ir⁴⁺ in Sr₃CoIrO₆ was confirmed by an Ir-L_III x-ray absorption measurement. Magnetoelastic effects have been observed in the temperature dependence of the lattice parameters of Sr₃CoIrO₆ and Sr₃NiIrO₆. The magnetic structure of Sr₃CoIrO₆ in zero fields can be described as a commensurate modulated antiferromagnet with a propagation vector k = (0,0,1). Neutron powder diffraction with polarized neutrons gave evidence of short-range magnetic order, above and below the magnetic ordering temperature.

We present results of μSR, dHvA, and SQUID magnetization measurements on borocarbide superconductors, which show a remarkable correlation between an order-disorder transition of the vortex lattice, observed in the μSR measurements, and enhanced additional damping of dHvA oscillations in the peak-effect region. It is, therefore, concluded that an important mechanism of additional damping of dHvA oscillations in the superconducting state should be associated with enhanced scattering of quasi particles by the pair potential in disordered vortex lattices.

We study the Fe-catalyzed chemical vapor deposition of carbon nanotubes by complementary in situ grazing-incidence X-ray diffraction, in situ X-ray reflectivity, and environmental transmission electron microscopy. We find that typical oxide supported Fe catalyst films form widely varying mixtures of bcc and fcc phased Fe nanoparticles upon reduction, which we ascribe to variations in minor commonly present carbon contamination levels. Depending on the as-formed phase composition, different growth modes occur upon hydrocarbon exposure: For γ-rich Fe nanoparticle distributions, metallic Fe is the active catalyst phase, implying that carbide formation is not a prerequisite for nanotube growth. For α-rich catalyst mixtures, Fe3C formation more readily occurs and constitutes part of the nanotube growth process. We propose that this behavior can be rationalized in terms of kinetically accessible pathways, which we discuss in the context of the bulk iron−carbon phase diagram with the inclusion of phase equilibrium lines for metastable Fe3C. Our results indicate that kinetic effects dominate the complex catalyst phase evolution during realistic CNT growth recipes.

DNA origami: from shape to functionality

Demixing of binary fluids under slow temperature ramps shows repeated waves of nucleation which arise as a consequence of the competition between generation of supersaturation by the temperature ramp and relaxation of supersaturation by diffusive transport and flow. Here, we use an advection-reaction-diffusion model to study the oscillations in the weak- and strong-diffusion regime. There is a sharp transition between the two regimes, which can only be understood based on the spatial distribution of the composition, rather than in terms of the average composition. Our results shed light on the parameter drift and secondary features observed in phase separating fluids subjected to a temperature ramp, and they bear intriguing communalities with macroscopic oscillations due to synchronization of life cycles in ageing populations.

In recent years, a new generation of high repetition rate (∼10 Hz), high power (∼100 TW) laser systems has stimulated intense research on laser-driven sources for fast protons. Considering experimental instrumentation, this development requires online diagnostics for protons to be added to the established offline detection tools such as solid state track detectors or radiochromic films. In this article, we present the design and characterization of a scintillator-based online detector that gives access to the angularly resolved proton distribution along one spatial dimension and resolves 10 different proton energy ranges. Conceived as an online detector for key parameters in laser-proton acceleration, such as the maximum proton energy and the angular distribution, the detector features a spatial resolution of ∼1.3 mm and a spectral resolution better than 1.5 MeV for a maximum proton energy above 12 MeV in the current design. Regarding its areas of application, we consider the detector a useful complement to radiochromic films and Thomson parabola spectrometers, capable to give immediate feedback on the experimental performance. The detector was characterized at an electrostatic Van de Graaff tandetron accelerator and tested in a laser-proton acceleration experiment, proving its suitability as a diagnostic device for laser-accelerated protons.

Untersuchung der S-Layer-Proteine bezüglich Stabilität und Auswirkungen der Hydroxylradikale auf deren Molekülstruktur, Radikalfängereigenschaften und Verminderung der Hydroxylradikalausbeute im photokatalytischen System sowie den Gesamteinfluss auf die Hydroxylradikalbildung.
Identifizierung der Einflussgrößen und Aufklärung der Einflussgrößenordnung der S-Layer-Hüllproteine auf die Bildung von Hydroxylradikalen und deren katalytisch nutzbare Ausbeute im photokatalytischen System (Suspension mit kommerziellem ZnO). Desweiteren wurden die Auswirkungen der Hydroxylradikale auf die S-Layer-Proteine im photokatalytischen System und mit Diamantelektrode untersucht und verglichen. Es konnte die Stabilität der S-Layer-Proteine im Rahmen verschiedener bioanalytischer Untersuchungen nachgewiesen werden. So wird die Stabilität der Proteinschicht im photokatalytischen System durch Radikaleinwirkung durch intermolekulare Vernetzung erhöht. Weitere Untersuchungen zur Langzeitstabilität der Proteine gegenüber Radikalen sind geplant

The downscaling and stressor technology of Si based devices is extending the performance of the silicon channel to its limits. One solution for the performance progress which can overcome the downsizing limit in the silicon technology is the integration of different functional optoelectronic elements within one chip. For the on-chip optical interconnections a different material has to be used, e.g. a direct band gap III-V compound semiconductor material. Besides efficient light emission many of the binary semiconductors exhibit much larger carrier mobility than silicon. This feature is crucial for a further performance enhancement of advanced devices.
Recently we have demonstrated a compact, CMOS compatible and fully integrated solution for the integration of III-V semiconductor nanocrystals with silicon technology for optoelectronic applications. They are synthesized in silicon using combined ion beam implantation and millisecond flash lamp annealing (FLA) techniques [NanoLett. 11, 2814 (2011)]. FLA appears to be the most suitable technique for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during ion implantation and to form III-V nanocrystals (NCs) via the liquid phase processes. Microstructural, optical and electrical properties of III-V nanostructures (InAs, GaAs and InP) formed in silicon or on SOI wafers will be presented. The evolution of the III-V nanostructures growth during FLA and the influence of the annealing parameters on theirs crystallographic orientation, shape and size will be explored. Moreover, a self-organization of the III-V nano-objects on the SOI wafers after flashing will be presented. A unique nano-swelling effect appearing during ion implantation of the SOI wafers combined with millisecond range liquid phase epitaxy leads to the evolution of the III-V semiconductors from the quantum dots to the nano-films. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. Current-voltage measurements confirm the heterojunction diode formation between n-type III-V quantum dots and p-type Si substrate. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based self-powered photronic devices.

The downscaling and stressor technology of Si based devices is extending the performance of the silicon channel to its limits. The further downsizing of CMOS devices below 16 nm will need to solve some of the practical limits caused by one of the integration issues, such as chip performance, cost of development and production, power dissipation, reliability, etc. One solution for the performance progress which can overcome the downsizing limit in silicon technology is the integration of different functional optoelectronic elements within one chip.
We propose to realize a compact, CMOS compatible and fully integrated solution for the integration of III-V compound semiconductors with silicon technology for optoelectronic applications. The III-V nanostructured semiconductors are synthesized in silicon using the combined ion beam implantation and millisecond flash lamp annealing (FLA) techniques [1]. The FLA appears to be the most suitable one for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during the ion implantation and to form III-V nanocrystals (NCs). In this paper we will present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs and InP) formed in silicon. Conventional selective etching was used to form the n-III-V/p-Si heterojunction. The current-voltage measurement confirms the heterojunction diode formation between n-type III-V quantum dots and p-type Si. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based photronic devices.
[1] S. Prucnal, S. Facsko, Ch. Baumgart, et al. NanoLett. 11, 2814 (2011).

One of the solutions enabling performance progress, which can overcome the downsizing limit in silicon technology, is the integration of different functional optoelectronic devices within a single chip. Silicon with its indirect band gap has poor optical properties, which is its main drawback. Therefore, a different material has to be used for the on-chip optical interconnections, e.g. a direct band gap III-V compound semiconductor material. In the paper we present the synthesis of single crystalline InP nanodots (NDs) on silicon using combined ion implantation and millisecond flash lamp annealing techniques. The optical and microstructural investigations reveal the growth of high quality (100) oriented InP nanocrystals. The photocurrent and current-voltage measurements confirm the formation of n-p heterojunction between the InP NDs and silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based self-powered electronic devices.

We present first results on the laser cooling of relativistic ion beams at the Experimental Storage Ring, ESR, at GSI using a cw laser with a broad frequency scanning range.

Laser-driven radiation sources can potentially help us to cure cancer or understand the dynamics of matter on the atomistic scale. With GPUs we today can simulate these sources at a frames-per-second rate. This in turn enables us to make them affordable to more users than ever before.

In our talk we show that optical SASE FELs are in reach with next generation short-pulse Petawatt Lasers and low-energy electron accelerators.
We discuss the fundamental problems of optical undulators compared to standard magnetic undulators and present ideas on how to solve these problems.
We furthermore provide insight into the generation of high-energy electron beams with lasers and how this can help to reach X-ray FEL operation on a much smaller scale than with conventional accelerator techniques.
Finally, we try to highlight problems of modelling classical SASE FELs using computer simulations, that migh also occur when modelling FELs in the quantum regime.

This Minireview summarizes the recent efforts to solve forward and inverse problems as they occur in different branches of fundamental and applied magnetohydrodynamics. As for the forward problem, the main focus is on the numerical treatment of induction processes, including self-excitation of magnetic fields in non-spherical domains and/or under the influence of non-homogeneous material parameters. As an important application of the developed numerical schemes, the functioning of the von-K\'{a}rm\'{a}n-sodium (VKS) dynamo experiment is shown to depend crucially on the presence of soft-iron impellers.
As for the inverse problem, the main focus is on the mathematical background and some first practical applications of the Contactless Inductive Flow Tomography (CIFT), in which flow induced magnetic field perturbations are utilized for the reconstruction of the velocity field. The promises of CIFT for flow field monitoring in the continuous casting of steel are substantiated by results obtained at a test rig with a low melting liquid metal. While CIFT is presently restricted to flows with low magnetic Reynolds numbers, some selected problems of non-linear inverse dynamo theory, with possible application to geo- and astrophysics, are also discussed.

Titanium aluminide (TiAl) alloys are attractive lightweight materials for medium-temperature (500°-750°C) structural applications including components such as jet engine and industrial gas turbine blades, turbocharger rotors and automotive engine valves. However, envisaged service temperatures for future advanced applications will have to be in the range of 750° to 1000°C, over which these alloys suffer from both oxidation and oxygen embrittlement. Therefore, development of surface-engineering techniques for preventing high-temperature environmental damage is critical in exploiting the advantages of TiAl alloys to their fullest extent.

Two efficient approaches to protecting candidate TiAl alloys from high-temperature (>750°C) environmental degradation have been developed at HZDR. The first technique involves a single step, namely treating TiAl alloy components directly by plasma immersion ion implantation (PIII) of fluorine using a mixture of difluoromethane and argon (CH2F2 + 25% Ar) as the precursor gas. The oxidation performance of the fluorine-implanted alloys has been evaluated by thermal gravimetric analysis (TGA) over the temperature range of 750° to 1050°C under conditions of both isothermal and thermal cyclic oxidation in air, and for times as long as 6000 h. This type of surface modification has been shown to produce a stable, adherent and highly protective alumina scale. The second technique involves the fabrication of a durable protective coating in a two-step process, namely formation of a thin aluminum-rich TiAl layer (Ti-60Al) by chemical vapor deposition (CVD) employing a mixture of inorganic precursors, followed by PIII of fluorine. Subsequent long-term oxidation exposures to air at 900°C of a GE 4822 alloy (Ti-48Al-2Cr-2Nb; alloy composition qualified for aerospace applications) have shown that the coating so developed is able to successfully prevent oxidation damage to the base material while maintaining up to 90% of its initial mechanical properties (strength and ductility).

Titanium is a widely used structural material for applications below approximately 500 degrees C but right now it cannot be used at higher temperatures. Titanium forms a fast growing rutile layer under these conditions. Furthermore enhanced oxygen uptake into the metal subsurface zone leads to embrittlement which deteriorates the mechanical properties. To overcome this problem a combined Al- plus F-treatment was developed. The combination of Al-enrichment in the surface zone so that intermetallic TixAly-layers are produced which form a protective alumina layer during high temperature exposure plus stabilization of the Al2O3-scale by the fluorine effect led to significantly improved resistance against increased oxidation and embrittlement in high temperature exposure tests of several Ti-alloys. In this paper, the experimental procedures and achieved improvements are described. The results will be discussed for the use of Ti-alloys at elevated temperatures.

Die Stufenweise Oxidationsprofilierung (SWOP) wurde zur Ladungsträgertiefenprofilierung an Bor-implantierten Silizium eingesetzt. Das Meßverfahren basiert auf einer alternierenden elektrischen Messung des Schichtwiderstandes mit van-der-Pauw (VDP)-Strukturen zwischen jeweils einem Si-Schichtabtrag durch elektrochemische anodische Oxidation. Es konnte gezeigt werden, dass die SWOP-Profile sehr gut mit SIMS-Referenzprofilen übereinstimmen und eine Tiefenauflösung von 1 nm sowie eine Nachweisgrenze 1•1016cm-3 erreicht wird.

Control over surface and bulk atomistic processes in carbon-transition metal films

Plasma nitriding of austenitic stainless steel (ASS) at moderate temperature (~400°C) produces a modified near surface layer, often called S phase, which shows significantly improved tribological properties, conserved or improved (electro)chemical properties and induced ferromagnetism. Here, the study of the nature of the S phase in nitrided ASS 304L is presented. A combination of global probes (X-ray diffraction (XRD), nuclear reaction analysis, glow discharge optical emission spectroscopy) and local probes (field ion microscopy, extended x-ray absorption fine structure spectroscopy) is employed to reveal the phase structure, morphology, atomic ordering and chemical environment. While XRD shows only the presence of the presence of the S phase, the local analysis techniques
consistently demonstrate the heterogeneous nature of the nitrided layer. It consists of nanometric CrN precipitates embedded in a Fe4N-like matrix. The size of the CrN precipitates is found to be larger at the surface than at the nitrided layer-steel interface. Moreover, X-ray spectroscopic investigations disclose three different intermetallic distances and different chemical environments for Fe, Cr and Ni, accompanied with a large static disorder. These findings suggest that the presence of the interstitial nitrogen can destabilize the homogeneous matrix element distribution in ASS 304L even at the rather low temperature of 400°C. Based on the heterogeneous nature of the S phase revealed in plasma nitrided ASS 304L, an alternative insight into its remarkable combination of properties is presented.

The stability of the steady laminar flow driven by the meridional electromagnetic force due to an electric current from a hemispherical electrode to a hemispherical cavity surface is studied using a multi-domain pseudospectral method. The analysis is performed for a broad ratio of electrode and cavity radii. The most unstable azimuthal wave number is found as m=4, which differs from literature results for the flow in a cone with a point-electrode where the most unstable wave number was found as m=0. In the presence of an external uniform magnetic field the fluid rotates in azimuthal direction. Already for a rather low strength of the external magnetic field, the meridional flow in the main toroidal eddy changes its direction from counter-clockwise to clockwise

Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400°C) leads to the formation of a modified layer which shows increased hardness and induced magnetism without compromising the corrosion resistance. In this study, a three-dimensional atomic characterization of plasma nitrided ASS 304L and 316L has been achieved with atom probe tomography (APT). While only a single phase, usually called the S phase or expanded austenite, can be detected by the X-ray diffraction, the APT reveals the formation of nanometric CrN precipitates. The precipitates have irregular oblate-spheroid-like shape. Small CrN clusters of only few nanometers in diameter have been observed close to the nitrided layer-steel interface as well as close to the surface. The regions which have been under nitrogen supersaturated conditions during the entire process, i.e. the regions close to the surface, exhibit also larger precipitates with a diameter more than 10 nm. In addition, preferential precipitation of CrN precipitates at grain boundaries and dislocations has been observed. These observations suggest that incorporation of large amounts of N provides strong driving force for CrN formation even at 400°C, a rather low temperature.

Ion assistance during film growth provides unique opportunities (i) toinfluence the film microstructure due to energy transfer and (ii) impose the directionality due to momentum transfer effects. Ion induced displacements occur in a thin surface layer of the growing film where they increase the atomic mobility. Therefore the ion assistance can be used to control the phase separation occurring during co-deposition of materials with low miscibility, and hence the resulting nanocomposite morphology. As the structure at the nanoscale determines the properties at the macroscale, the control over the microstructure is a key issue in nanomaterials science. In this contribution, a comparison of the growth-structure relationship of carbon-transition metal (Ni, Cu) nanocomposite films grown by ion beam assisted deposition (IBAD) and pulsed filtered cathodic vacuum arc (PFCVA) is reported. The formation of elongated nickel nanoparticles is strongly promoted by temperature and ion beam assistance. Moreover, the metal nanocolumns no longer align with the advancing surface, as in the case without ion assistance, but with the incoming ions. Although the energy in PFCVA is carried by film forming ions themselves while for IBAD it is delivered by a separate ion beam, both deposition techniques show a window of deposition conditions where the ion assistance leads to the formation of regular nanopatterns. As the dominating factors (ion induced ballistic effects) are of physical origin, this approach might be applicable to other materials systems with limited solubility.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379, and by DEEWR, Australia, in the framework of Endeavour Research Fellowship (Contract No. 837_2008), is gratefully acknowledged.

Ion assistance during film growth provides unique opportunities to influence the microstructure due to energy transfer and imposed directionality. During nanocomposite film growth at low temperatures, phase separation occurs at the growing film surface. Ion-assistance is a key parameter to control the surface processes during multiphase film growth, and hence the resulting nanocomposite morphology. A systematic study of ion irradiation as a pure energy and momentum transfer agent in the context of surface diffusion assisted phase separations is, however, lacking. Here the influence of low energy (50-130 eV) assisting Ar+ ion irradiation on the morphology of C-Ni thin films will be reported. Ion-beam assisted deposition (IBAD) promotes the columnar growth of carbon encapsulated metallic nano-columns at low deposition temperatures for Ar+ ion energy ranges of 50-100 eV. Moreover, the momentum transfer results in a tilting of the columns relative to the film surface. The potential to grow complex matrix encapsulated metallic structures such as chevrons is demonstrated. Furthermore, a window of deposition conditions will be reported where the ion assistance leads to the formation of regular 3D nanopatterns with well-defined periodicity. The influence of such anisotropic film morphology on the optical properties is highlighted.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379, is gratefully acknowledged.

Magnetic fields are applied to electrically conducting fluids, in order to influence electrochemical processes by leveraging the magnetohydrodynamic effect. Various phenomena, e.g. on electrodeposited metal layers, were observed, which can be attributed to forced convections. To provide information about acting forces, the laser Doppler velocity profile sensor was applied to measure the transition layer of a Lorentz force influenced backward-facing step and the velocity boundary layer during copper-deposition. With this sensor, the electrolyte convection is revealed within < 500 μm of an electrode with a spatial resolution down to 15 μm. The interaction of buoyant, Lorentz and magnetic field gradient force is studied by measuring the velocities down to 10 μm in front of the cathode. It is shown that complex electrolyte convection is induced inside the concentration boundary layer, which varies not only in time but also in its structure, depending on the present forces and their temporal influence. At inhomogeneous magnetic field configurations, the magnetic field gradient force dominates the velocity boundary layer at steady state and transports electrolyte toward regions of high magnetic gradients, where maximum deposit thicknesses are found. In this way, the measurements confirm the predicted influence of the magnetic field gradient force on the structuring of copper-deposits.

We observe electrolysis with gas evolution, a phenomenon occurring in a number of industrial scale electrochemical processes. Here, water electrolysis takes place in a small undivided electrolysis cell consisting of vertical electrodes embedded in a larger glass vessel which contains a dilute NaOH solution. Fluid flow velocities are measured by Particle Image Velocimetry with fluorescent tracers, while size distribution and velocities of the bubbles are determined from bubble shadow images obtained with a high speed camera. Coalescence phenomena are observed in the flow and explain the relatively wide distribution of bubble sizes.
Depending on the gap width and the current density, bubbles ascending near the electrodes form two discernible bubble curtains (low average void fraction, wide gaps) or a flow profile more akin to a channel flow (high average void fraction, small gaps). If the flow consists of separate bubble curtains, instabilities develop not unlike to that of a single phase wall jet.
Finally, the influence of different wall parallel Lorentz force configurations on the velocity distribution in the cell is investigated. These Lorentz forces are generated by permanent magnets mounted behind the electrodes. Depending on gap width, current density, and magnet configuration, liquid phase velocities can be increased by several times compared to the baseline case.

The electrical current through an incompressible, viscous and resistive liquid conductor produces an azimuthal magnetic field that becomes unstable when the corresponding Hartmann number exceeds a critical value in the order of 20. This Tayler instability, which is not only discussed as a key ingredient of a non-linear stellar dynamo model (Tayler-Spruit dynamo), but also as a limiting factor for the maximum size of large liquid metal batteries, was recently observed experimentally in a column of a liquid metal.
On the basis of an integro-differential equation approach, we have developed a fully three-dimensional numerical code, and have utilized it for the simulation of the Tayler instability at typical viscosities and resistivities of liquid metals. The resulting growth rates are in good agreement with the experimental data. We illustrate the capabilities of the code for the detailed simulation of liquid metal battery problems in realistic geometries.

The two obsidian sources from the island of Melos (Greece), Agia Nychia and Demenegakion, are chemically characterized by three complementary analytical techniques. Ion beam analysis (IBA) comprising of particle induced X-ray emission (PIXE) and particle induced gamma-ray emission (PIGE), neutron activation analysis (NAA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are applied to the same set of geological obsidian samples.
The combination of methods allows a more complete characterisation of obsidian sources and reveals a highly specific chemical composition, the so-called chemical fingerprint. This multi-methodical approach checks also the self-consistency of the analytical results and shows the most reliable and characteristic key elements Co and Sc, but also Fe, Ca and Ti of Melos obsidian deposits. NAA contributes the largest number of reliable elements to the most unambiguous chemical fingerprint comprising in total of 41 elements. Therefore, NAA is the most suitable analytical method for a clear identification of Melos obsidian deposits.
Moreover, the accuracy of methods is demonstrated by the excellent correspondences (calculated correlation coefficient R2=1.00 for IBA and NAA, R2=0.99 for LA-ICP-MS) between determined analytical results obained by IBA, NAA and LA-ICP-MS and certified values of the reference glass BAM-S005B.

An ultrasound measurement system for dual-plane, two-component flow velocity measure-ments especially in opaque liquids is presented.
Present-day techniques for measuring local flow structures in opaque liquids disclose consid-erable drawbacks concerning a line-wise measurement of single ultrasound probes. For study-ing time-varying flow patterns, conventional ultrasound techniques are either limited by a time-consuming mechanical traversing or by the sequential operation of single probes.
The measurement system presented within this paper employs 4 transducer arrays with a total of 100 single elements which allows for a flow-mapping without mechanical traversing. A high frame rate of several 10 Hz has been achieved due to an efficient parallelization scheme using time division multiplex realized by a microcontroller-controlled electronic switching matrix.
The functionality and capability of the measurement system is demonstrated at a liquid metal flow at room temperature inside a cube driven by a rotating magnetic field (RMF). For the first time, the primary and the secondary flow have been studied in detail and simultaneously using a configuration with two crossed measurement planes. The experimental data confirm predictions made by numeric simulation. After a sudden switching on of the RMF inertial oscillations of the secondary flow were observed by means of a time-resolved measurement with a frame rate of 3.4 Hz.
The experiments demonstrate that the presented measurement system is able to investigate complex and transient flow structures in opaque liquids. Due to its ability to study the tem-poral evolution of local flow structures, the measurement system could provide a considerable progress for fluid dynamics research, in particular for applications in the food industry or liq-uid metal technologies.

In magnetohydrodynamics, model experiments are commonly conducted to investigate the interaction between magnetic fields and electrically conductive fluids. The available flow instrumentation for opaque fluids usually lacks the ability to capture and visualize a velocity field in one shot. We present a multidimensional ultrasound array Doppler velocimeter that employs multiple line arrays of transducers and allows to resolve small scale structures in complex flows. The system archives a lateral resolution up to 3mm, an axial resolution of approx. 1:4mm and frame rates up to 30Hz in metal melts at room temperature. A flexible sensor arrangement allows for various measurement configurations, e.g. four planes can be measured simultaneously with one velocity component, two planes with two components or two lines with three components. We present an experiment in a square shaped container driven by a rotating magnetic field and results of a model experiment for continuous steel casting. The measurement system has proven to be a powerful tool for research in magnetohydrodynamics.

We discuss pump-probe experiments on multilayer graphene over a wide range of photon energies (10-250 meV), hereby unveiling the relevant electronic relaxation mechanisms. A slowing down is observed for smaller photon energies and lower temperature, in accord with microscopic calculations. Remarkably we observe a sign change of the probe signal, when the photon energy becomes smaller than twice the Fermi energy. This crossover from induced bleaching to induced absorption is related to the interplay between inter- and intraband absorption. Applying an additional magnetic field we have recently measured the relaxation dynamics between Landau levels, showing a strong dependence on the circular polarization of the light.

The KERENA™ reactor is a generation III+ BWR concept, which was originally proposed by AREVA and is currently being developed jointly by AREVA and German utility E.ON (AREVA, 2010). It aims to achieve a cost competitive plant with enhanced safety features and an optimal BWR balance of active and passive safety systems. The containment cooling condensers (CCC) belong to such kind of passive features, which require neither electric power nor switching operations to begin functioning. The CCC unity is connected to a shielding/storage pool, which is located above it, via an inlet to the lower end and a discharge line at the upper end. In case of overpressure or overtemperature, steam in the containment will condense at the outside wall of the condensers. Heat released by steam will be transferred to the cooling water inside the tubes. As it is heated, the cooling water will remove heat from the containment to the water of the shielding/storage pool through a natural circulation.

The performance of the complete CCC system has been investigated experimentally on the full-scale INKA test facility of AREVA in Karlstein (Leyer and Wich, 2012). During the experiment, strong flow instability or water hammer caused by the formation and subsequent destruction of steam bubbles inside the discharge line was observed. In other words, the formation of steam will have a significant influence on the safety operation and heat removal capacity of the system, which requires further investigation. In this case, the mechanism of phase change from water to steam is different from that of the traditional boiling as a result of wall heating. Due to the elevation difference between the CCC and the upper end of the discharge line, which is about 12 m, the drop of hydrostatic pressure along the discharge line exceeds 1bar. The formation of steam is a result of depressurization instead of wall-heating, which is called flashing boiling in contrast to the traditional boiling.

Water evaporation (flashing) inside a vertical pipe under pressure release transients is investigated by CFD simulations based on the Eulerian two-fluid model. Important assumptions made in the current work are: a) constant bubble diameter; b) no nucleation and c) mass transfer caused only by thermal heat transfer between phases. The predicted evolution of steam volume fraction and water temperature is compared with the measured one, respectively. The results show that the applied model setup in principle can reproduce the flashing process. Whether the evaporation of superheated water can start depends on the initial guess of steam volume fraction and especially the presumed bubble size. A large initial steam volume fraction and a small bubble size will favor the inception of evaporation. Once the flashing is successfully triggered, the maximum evaporated steam is determined by the pressure drop ultimately. Furthermore, the increase of steam volume fraction per unit evaporated mass reduces drastically at high pressure levels due to a large steam to water density ratio. As a result, a relatively small value has to be presumed for bubble size under high pressure conditions in order to launch the evaporation. In addition, the predicted maximum steam volume fraction at a pressure of 65bar is much lower than the measured one. In this case besides the interphase thermal heat transfer consideration of nucleation and bubble growth due to mechanical non-equilibrium across the interface might be helpful.

At the SRF based prototype cw accelerator ELBE a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1-200 KHz regime and with pC bunch charge and repetition rates of 13 MHz, is currently being constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class lasers and the generation of broad and narrow bandwidth coherent THz pulses. Discussed here are ideas for novel online diagnostics of the electron bunch properties (e.g. arrival time and bunch form) based on the time and frequency domain analysis of the emitted coherent THz radiation, but also based on direct measurements by e.g. electro-optic sampling. The suitability of ELBE as a testbed for diagnostic of future cw X-ray photon sources (e.g. energy recovery linacs) will be discussed.

It has been shown recently that relativistic electron bunches can be utilized for the generation of super-radiant coherent THz radiation by one single pass through an undulator, bending magnet, or CDR/CTR screens. However, the high THz fields have all been achieved at large accelerators that allow for high electron beam energies. A crucially important research topic for the next years at the HZDR is therefore to investigate whether an equally fine control over highly charged electron bunch form can be routinely achieved in a low electron beam energy accelerator like ELBE. If successful this development would allow the generation of high field THz fields by linear accelerators at considerably reduced cost. Given stable operation can be provided, TELBE, could also become a world-wide unique research facility for high field THz science. The current status and an outlook on future developments are presented.

A method for electron beam/THz to femtosecond (fs) - laser synchronization drift correction at the quasi-cw linear electron accelerator ELBE is presented, which is utilizing THz radiation generated by a CDR/CTR screen and an undulator respectively. Measurements of these pulses will allow for compensation of slow drifts in the arrival time on millisecond timescales between the THz and the fs-laser pulses. The method requires two electro-optic detection setups which allow for the sampling of a single THz pulse, at two different working points. Given a consistent pulse shape these two data points can provide information on the sign of the arrival time drift relative to the laser. This information can be used both for providing feedback on fs laser arrival time in a potential THz time domain experiment as well as the electron bunch arrival time in the accelerator.

The fundamental interactions between electrons, spins and the lattice of a solid have always been subject of large scientific interest. Here, we investigate the coupling between phonons and the ordered spin system of ferrimagnetic oxides on ultrashort time scales, an elusive and actively debated issue of modern ultrafast magnetism.
For this purpose, we use intense electromagnetic pulses at terahertz (THz) frequencies, from both table-top and accelerator-based sources, to resonantly excite a specific phonon mode. The impact of this vibrational excitation on the spin system is monitored by detecting the transient Faraday rotation of a subsequently arriving optical probe pulse. As such, we obtain access to the magnetization dynamics with a time resolution of down to 10fs.
These mode-selective pumping experiments show a response of the spin system on a timescale of few picoseconds and thus indicate an (ultra)fast spin-lattice interaction. The possible underlying coupling mechanisms will be discussed.

Today Computational Fluid Dynamic (CFD) codes are widely used for industrial applications in the case of single phase flows as in automotive or aircraft industries, but multiphase flow modeling had gain an increasing importance in the last years. Safety analyses on nuclear power plants require reliable prediction on steam-water flows in case of different accident scenarios. This is particularly true for passive safety systems as the GEKO component of the KERENA reactor. Here flashing may occur in the riser. In such a case high gas volume fractions and the churn-turbulent flow regime may occur. So far, the codes for the prediction of churn-regime have not shown a very promising behavior in the past. In this paper, a two-fluid multi-field hydrodynamic model has been developed based in the Euler-Euler framework. The main emphasis of this work has been on the modeling and applicability of various interfacial forces between dispersed gaseous phases and the continuous liquid, as well as bubble-bubble interactions, and the evolution of different bubble sizes in an adiabatic vertical pipe inside the churn-turbulent flow regime. All the expected mechanistic models that intervene in this flow pattern have been taken into account including drag force, wall force, lift force, turbulent dispersion, and bubble induced turbulence. Bubble breakup and coalescence has been defined (Liao et al., 2011), and in order to design a polydispersed model related to reality, the inhomogeneous MUSIG approach (Krepper et al., 2008) has been used to defined an adequate number of bubble size fractions, each with their own velocity field. Based on these models, a series of simulations were made on the framework of ANSYS CFX 14.0, and all of the calculations were further validated with experimental data extracted from the TOPFLOW facility at the Helmholtz-Zentrum Dresden-Rossendorf. Different water and gas flow rates were used inside the churn-turbulent flow regime, as well as for the transition from bubbly to churn flow. The calculated cross-section averaged bubble size distributions, gas velocities, and time averaged radial profile for the gas fraction have shown a promising agreement with the experimental data. Nevertheless there are also clear deviations which indicate shortcomings of the present modelling. In order to further improve the modeling of this flow regime, a discussion based on the results will be used to shown a series of limitations of the actual modeling and possible solutions to be implemented in future works.

Best Paper Award

We report on time-resolved photoluminescence of excitons and electron-hole plasma in GaAs quantum wells under intraband excitation by a free-electron laser in resonance with intersubband and intraexcitonic transitions, respectively, to study relaxation and intraexcitonic scattering.

Spin wave phenomena are an intensely studied field of magnetism, ranging from fundamental magnonics to possible spin wave applications in logic or oscillator devices. In particular, the propagation of nanoscopic spin waves has come into focus. Typically, micro-striplines or point-contacts are used to excite such spin waves in ferromagnetic media. A real-space observation of nanoscopic spin wave propagation, however, has not been reported yet. On this background we present the direct imaging of spin wave propagation as well as a novel concept for their coherent generation based on the dynamics of interlayer coupled magnetic vortex pairs.

In SRF guns, multi-bunch effects of higher order modes (HOM​​) and their influence on beam quality are of particular interest. For this reason a method is presented that considers the accelerated motion of non-relativistic electrons to calculate their coupling impedances. The results are compared with first beam-based measurements and used to discuss a new method for HOM suppression.

RUTA-70 model for simulations with the internally coupled codes DYN3D/ATHLET and DYN3D/RELAP5 was developed. A 3-D power distribution in the core is calculated by DYN3D with thermal-hydraulic feedback from the system codes. A steady-state corresponding to the full reactor power and an accident scenario initiated by failure of all primary coolant pumps were simulated with the DYN3D/ATHLET and DYN3D/RELAP5 coupled code systems to verify these codes.

The compared coupled codes give close predictions for the initial and final states of the simulated accident but not for the transition between them. The observed deviations are explained by differences in the subcooled boiling models of the employed versions of ATHLET and RELAP5. Nevertheless, both simulations confirm a high level of the reactor inherent safety. The allowed safety margins were not reached.

We consider Pareto surface based multi-criteria optimization for step and shoot IMRT planning. By analyzing two navigation algorithms, we show both theoretically and in practice that the number of plans needed to form convex combinations of plans during navigation can be kept small (much less than the theoretical maximum number needed in general, which is equal to the number of objectives for on-surface Pareto navigation). Therefore a workable approach for directly deliverable navigation in this setting is to segment the underlying Pareto surface plans and then enforce the mild restriction that only a small number of these plans are active at any time during plan navigation, thus limiting the total number of segments used in the final plan.

Carrier lifetimes in the continuum of the quantum well of a Hg (x) Cd1 - x Te/Cd (y) Hg1 - y Te hetero-structure were studied by terahertz pump-probe spectroscopy. It is found that the relaxation duration of the transmission signal is similar to 65 ps and is independent of the pump power. Such rapid relaxation in these structures is most likely determined by the interaction of holes with acoustic phonons due to a high density of states in the valence band and a larger effective mass compared with electrons. By the obtained data, the times of the interband nonradiative recombination of holes are determined. In this publication, we report the results of numerical calculation of the energy spectrum of the model structure, in which the possibility of obtaining population inversion at specified concentrations of nonequilibrium carriers is analyzed.

Accident conditions involving significant core degradation are termed severe accidents /IAEA:

NS-G-2.15/. Despite the low probability of occurrence of such events, the investigation of severe accident scenarios is an important part of the nuclear safety research. Considering a hypothetical core melt down scenario in a VVER-1000 light water reactor, the early in-vessel phase focusing on the thermal-hydraulic phenomena, and the late in-vessel phase focusing on the melt relocation into the reactor pressure vessel (RPV) lower head, are investigated.

The objective of this work is the assessment of severe accident management procedures for VVER-1000 reactors, i.e. the estimation of the maximum period of time available for taking appropriate measures and particular decisions by the plant personnel. During high pressure severe accident sequences it is of prime importance to depressurize the primary circuit in order to allow for effective injection from the emergency core cooling systems and to avoid reactor pressure vessel failure at high pressure that could cause direct containment heating and subsequent challenge to the containment structure. Therefore different accident management measures were investigated for the in-vessel phase of a hypothetical station blackout accident using the severe accident code ASTEC, the mechanistic code ATHLET and the multi-purpose code system ANSYS.

The analyses performed on the PHEBUS ISP-46 experiment, as well as simulations of small break loss of coolant accident and station blackout scenarios were used to contribute to the validation and improvement of the integral severe accident code ASTEC. Investigations on the applicability and the effectiveness of accident management procedures in the preventive domain, as well as detailed analyses on the thermal-hydraulic phenomena during the early in-vessel phase of a station blackout accident have been performed with the mechanistic code ATHLET. The results of the simulations show, that the effectiveness of the procedures strongly depends on the ability of the passive safety systems to inject as much water as possible into the reactor coolant system.

The results on the early in-vessel phase have shown potentially delayed RPV failure by depressurization of the primary side, as slowing the core damage gives more time and different possibilities for operator interventions to recover systems and to mitigate or terminate the accident. The ANSYS model for the description of the molten pool behaviour in the RPV lower plenum has been extended by a model considering a stratified molten pool configuration. Two different pool configurations were analysed: homogeneous and segregated. The possible failure modes of the RPV and the time to failure were investigated to assess the possible loadings on the containment. The main treated issues are: the temperature field within the corium pool and the RPV and the structure-mechanical behaviour of the vessel wall.

The results of the ASTEC calculations of the melt pool configuration were applied as initial conditions for the ANSYS simulations, allowing a more detailed and more accurate modelling of the thermal and mechanical behaviour of the core melt and the RPV wall.

Moreover, for the late in-vessel phase, retention of the corium in the RPV was investigated presuming external cooling of the vessel wall as mitigative severe accident management measure. The study was based on the finite element computer code ANSYS. The highest thermomechanical loads are observed in the transition zone between the elliptical and the vertical vessel wall for homogeneous pool and in the vertical part of the vessel wall, which is in contact with the molten metal in case of sub-oxidized pool. Assuming external flooding will retain the corium within the RPV. Without flooding, the vessel wall will fail, as the necessary temperature for a balanced heat release from the external surface via radiation is near to or above the melting point of the steel.

We present experimental results on the electromagnetic excitation of neutron-rich nickel isotopes, making use of the R3B-LAND setup at GSI. Exotic beams were produced at approximately 500 MeV/u and their reactions were studied in inverse kinematics. Integral cross sections for 58Ni are discussed and compared to previous data, providing a validation of our experimental method. The E1 excitation-energy distribution of the unstable 68Ni is presented as well, showing an excess in cross section in the 1n decay channel when compared only with a typical Giant Dipole Resonance.

This article gives an overview about the recent research activities with respect to the mould flow in the continuous casting of steel in presence of DC magnetic fields. The magnetic fields appear to be an attractive tool for controlling the melt flow in a contactless way. Various kinds of magnetic systems are already in operation in industrial steel casting, but the actual impact on the melt flow has not been sufficiently verified by experimental studies. The rapid development of innovative diagnostic techniques in low-melting liquid metals over the last two decades enables new possibilities for systematic flow measurements in liquid metal model experiments. A new research program was initiated at HZDR comprising three experimental facilities providing a LIquid Metal Model for continuous CASTing of steel (LIMMCAST). The facilities operate in a temperature range from room temperature up to 400°C using the low-melting alloys GaInSn and SnBi, respectively. The experimental program is focused on quantitative flow measurements in the mould, the submerged entry nozzle and the tundish. Local potential probes, the Ultrasonic Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) are employed to measure the melt flow. The behaviour of two-phase flows in case of argon injection is investigated by means of the Mutual Inductance Tomography (MIT) and the X-ray radioscopy. The experimental results provide a substantial data basis for the validation of related numerical simulations. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. First results of the LIMMCAST program reveal important findings such as the peculiar, unexpected phenomenon that the application of a DC magnetic field may excitate non-steady, non-isotropic large-scale flow oscillations in the mould. Another important result of our study is the feature that the electrical boundary conditions, namely the wall conductivity ratio, have a serious influence on the mould flow while it is exposed to an external magnetic field.

We plan to use very small emittance electron beams created from our novel, single tip cathodes to make a channeling-radiation X-ray source for X-ray imaging, especially phase contrast imaging. We calculate that we can preserve the electron emittance from the source to the crystal , and focus to a 40 nm spot on the crystal face for 40 MeV electrons.

A hybrid positron source which is based on the generation of channeling radiation by relativistic electrons channeled along different crystallographic planes and axes of a tungsten single crystal and subsequent conversion of radiation into e+e- -pairs in an amorphous tungsten target is described. The photon spectra of channeling radiation are calculated using the Doyle-Turner approximation for the continuum potentials and classical equations of motion for channeled particles to obtain their trajectories, velocities and accelerations. The spectral-angular distributions of channeling radiation are found applying classical electrodynamics. Finally, the conversion of radiation into e+e- -pairs and the energy distributions of positrons are simulated using the GEANT4 package.

The effect of chromium on iron hardening via segregation on dislocation loops was studied by atomic scale computer modeling. A combination of Monte Carlo and molecular dynamics techniques together with the recently determined Fe–Cr interatomic potentials fitted to ab initio data was used to investigate Cr segregation on ½<111> interstitial dislocation loops and its impact on the interaction with moving dislocations. The Monte Carlo results reveal that Cr atoms segregate to the loop tensile strain region and dissolve well above the temperature corresponding to the solubility limit. The molecular dynamics results demonstrated that local micro-chemical changes near the loop reduce its mobility and increase the strength. The stress to move a dislocation through the array of Cr "decorated" loops increases due to modification of the dislocation–loop interaction mechanism. A possible explanation for a number of experimental observations being dependent on the radiation dose and for Cr concentration effects on the yield stress is given on the basis of the modeling results.

[¹⁸F]NS14490, a new potential radiotracer for neuroimaging of α₇ nicotinic acetylcholine receptors (α₇ nAChRs), was synthesized and evaluated in vitro and in vivo. Radioligand binding studies using [³H]methyllycaconitine and NS14490 as competitor showed a good target affinity (K_iα7= 2.5 nM) and a high selectivity towards other nAChR. Radiosynthesis of [¹⁸F]NS14490 was performed by two different labelling procedures: a two-step synthesis using a prosthetic group, which led to 7% labelling yield, and the convenient direct nucleophilic substitution of the corresponding tosylate precursor, which resulted in 70% labelling yield. After optimisation of the isolation, purification and formulation process, biodistribution studies were performed in CD-1 mice. The brain uptake of [¹⁸F]NS14490 was comparably low (0.16% ID g^-1 wet weight at 5 min p.i.). The radiotracer showed a high metabolic stability in plasma and brain. Also, the target specificity was proven by pre-administration of a highly affine α₇ ligand providing a rationale basis for further in vivo evaluation.

Here we present different strategies for the radiolaneling of nanoparticles such as Ag(0), TiO2 and carbon nanotubes. In particular we show the diffusion of radionuclides into Ag(0) and TiO2 nanoparticles, the direct activation of nanoparticles by proton irradiation using a cyclotron, the implantation of Be-7 into nanoparticles by the recoil of the nuclear reaction Li-7(p,n)Be-7 and the radioiodination of carbon nanotubes.
All the methods were characterized with repsect to yield, radiolabel stability and possible change of nanoparticle properties.

The implications of a carbon nanotube (CNT) release into the environment are majorly influenced by the colloidal stability of the CNTs in surface or ground waters. A main factor for this stability is the degree of oxidation of the CNTs. Pristine CNTs show very low dispersion stability in water and quickly aggregate and sediment. However, oxidation processes are expected to happen in the environment or are deliberately performed on the CNTs, for better dispersability in technical applications prior to the possible release.
For this study samples of different types of CNTs, multi wall as well as single wall CNTs, were oxidized by a microwave assisted acid treatment with concentrated nitric and sulphuric acid, which allowed a fast reproducible modification of the CNTs. The modification was verified by IR and Raman spectroscopy, thermogravimetric analysis and measurements of the iso-electric point.
The colloidal stability of the so modified CNTs was investigated using dynamic light scattering methods to follow the aggregation and sedimentation of the CNTs as well as establishing the zeta potential of the modified CNTs in waters of different ionic strength.
The colloidal stability of the CNTs in distilled and low ionic strength water exceeds months. This has implications for their transport behaviour upon release into the environment. A transport of CNTs in surface and ground waters can be expected under certain conditions.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories a careful risk assessment of their release into the environment becomes mandatory. However the monitoring of nanoparticles in such complex natural systems as geological formations or ground water is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research. We present here different radiolabelling strategies for carbon nanoparticles, in particular carbon nanotubes (CNTs) whose intriguing physical properties predestine them for widespread application, so that future release into the environment is to be expected.
We have developed three different approaches for the radiolabelling of CNTs. The first is the iodination of carbon nanotubes using radioactive iodine, e.g. I-125 or I-131. Using the Iodogen method known from protein labelling strategies it is possible to radiolabel single- and multi-wall CNTs by binding radioactive iodine on the CNT side wall.
The other strategies involve proton irradiation using a cyclotron and cause the incorporation of radioactive beryllium in between the layers of multi-wall CNTs. The first option is to directly activate carbon by high-energy proton irradiation (> 34 MeV), which causes a (p,3d) nuclear reaction creating Be-7, which intercalates between the graphitic layers of the CNT. The second option is to mix the CNTs with a lithium containing compound like LiH and irradiate at a much lower proton energy to create Be-7 via the (p,n) reaction on Li. The recoil of the Be-7 from the nuclear reaction causes the incorporation of the radiotracer into the structure of multi-wall CNTs.
The methods were tested for labeling yield, achievable activity concentration, pH-dependent stability of the labeling and the influence on NP-properties. Data thus obtained enables the selection of a radiolabeling method appropriate for different experimental conditions.

Exotic Ni isotopes have been measured at the R3B-LAND setup at GSI in Darmstadt, using Coulomb excitation in inverse kinematics at beam energies around 500 MeV/u. As the experimental setup allows kinematically complete measurements, the excitation energy was reconstructed using the invariant mass method. The GDR and additional low-lying strength have been observed in 68Ni, the latter exhausting 4.1(1.9)% of the E1 energy-weighted sum rule. Also, the branching ratio for the non-statistical decay of the excited 68Ni nuclei was measured and amounts to 24(4)%.

The directional solidification of Ga-25wt%In alloys within a Hele-Shaw cell under the influence of thermo-solutal convection was observed by means of X-ray radioscopy. The unstable density stratification at the solidification front causes the formation of rising plumes containing solute-rich liquids. The development of the chimneys and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field. Variations of the vertical temperature gradient along the solidification cell lead to the observation of different mechanisms for chimney formation. Perturbations of the dendritic structure are the origin of development of segregation freckles in case of low temperature gradients. The long-term stability of these segregation channels is strongly influenced by the transient nature of the melt convection. The situation at higher temperature gradients is characterized by two dominating convection rolls in the liquid phase which are driven by a lateral temperature gradient and the convex shape of the solidification front. The penetration of this flow pattern into the mushy zone results in continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a stable chimney.

Interpolated maps of compositional variables (in wt\% or ppm) should guarantee that results give a consistent composition: i.e., at any location, all variables must be positive and sum up to 100\%, and should preserve certain geochemical links. (Co)kriging after a normal score transformation is a common choice, though it does not ensure honoring any positivity, constant sum or geochemical constraints. Moreover, it requires a huge effort of consistent modeling of (cross-)variograms. A more suitable way is the application of log-ratio techniques. A D-component system can be univocally expressed with (D-1) log-ratios (e.g., the additive logratio transformation with common denominator TiO2). Any one-to-one logratio transformation can be applied to sampled data; variograms can be estimated for logratio scores; and cokriging can be applied. Back-transformed interpolated scores map the original system components. Consistently modeled cross-variograms provide the same interpolated compositions whatever logratio transformation is used. However, compositional variograms are best modeled through variation-variograms, the set of direct variograms of all possible logratios of two components. They carry the same information, and can be modeled in the same way, as a full set of direct and cross-variograms of any logratio transformation, but they have several advantages for computation and interpretation. First, being positive functions, logarithmic goodness-of-fit criteria can be used, which give more importance to shorter distances (influencing the interpolation itself) than to the sill, prone to larger fluctuations. Second, they can be estimated with a minimum of complete observations; zeros, missing values, values below detection limit and other irregular data have thus much less influence. Third, using ratios of components, systematic differences might be filtered out. This is important in large geochemical surveys, where all samples may have not been treated in the same labs with the same analytical techniques. Fourth and last, the fitted LMC can be rank-deficient. This allows to obtain all component maps just cokriging a few individual factors and combining them together (compositional factorial cokriging). These procedures are illustrated with the horizon C Kola data set, with 25 components and 605 samples covering most of the Kola peninsula (Finland, Norway, Russia).

A 2m x 0.5m large prototype of an MRPC-based (Multi-gap Resistive Plate Chamber) neutron Time-Of-Flight-wall for detecting relativistic neutrons in an energy range from 200MeV to 1 GeV was successfully designed and realized. It consists of steel plates which convert neutrons via hadronic interactions into charged particles, followed by a 2x2 gap MRPC-structure to detect the charged particles. Tests were carried out using 30MeV electrons with an energy close to the minimum of ionization in order to study the properties of the prototype achieving an efficiency larger than 90% and a time resolution better than 100 ps. For units with an active area of 40 cm x 20 cm and otherwise the same design, quasi-monochromatic neutrons with a peak energy of 175MeV were utilized to study their response to relativistic neutrons. Detailed montecarlo simulations were performed both for the small and for the large modules to simulate their properties to both neutrons and electrons and to study the performance of the final neutron detector assembly with an area of 2m x 2m for single-neutron and multi-neutron events.

Sewage sludge ashes (SSAs) are valuable raw materials (high P-content of up to 11 wt%; ca. 600,000 tons per year in the EU). For the conversion of sewage sludge into SSA fluidized bed incinerators are used. The aim of the present study is to test whether that finding is also relevant for a considerably different SSA, which was produced at a differently operated fluidized bed incineration facility in another municipality.

Ziel der experimentellen Promotionsarbeit war es, neue Verfahren zur Herstellung von magnetischen Halbleitern für den spinpolarisierten Ladungsträgertransport zu evaluieren. Dazu wurde in der vorliegenden Promotionsarbeit auch ein theoretisches Modell entwickelt, um die Erfolgsaussichten bei der Herstellung verdünnter magnetischer Halbleiter abschätzen zu können.
Zum Einbringen von magnetischen Fremdatomen in Halbleitermaterialien wurde die Ionenimplantation in einem ca. 100 - 200 nm dicken oberflächennahen Bereich, hier z. B. Mangan in Germanium (Ge) und Mangan in Galliumarsenid (GaAs), angewendet. Die durch die Ionenimplantation entstandenen Gitterschäden wurden anschließend mittels laserinduzierter Flüssigphasenepitaxie ausgeheilt. Die Herstellung von magnetischen Halbleitern mittels Implantation und Laserausheilung stellt einen alternativen Ansatz zum konventionellen Wachstum von magnetischen Halbleitern mittles Niedrigtemperatur-Molekularstrahlepitaxie (engl.: Low temperature molecular beam epitaxy, LT-MBE) dar und beruht auf einem anderen thermodynamischen Konzept. Beide Verfahren laufen jedoch unter thermodynamischen Nichtgleichgewichtsbedingungen ab, was eine Voraussetzung für den substitutionellen Einbau von Fremdatomkonzentrationen oberhalb der natürlichen Löslichkeit ist. Dies ist eine notwendige Voraussetzung für die Herstellung von GaAs:Mn oder Ge:Mn mit hohen Mn-Konzentrationen. Die Kopplung zwischen den magnetischen und elektrischen Eigenschaften in magnetischen Halbleitern stellt eine wichtige Voraussetzung z. B. für deren Einsatz in nichtflüchtigen Speicherbauelementen dar, da der magnetische Zustand direkt mit elektrischen Transportmessungen ausgelesen werden kann. Für das in dieser Arbeit hergestellte Materialsystem Ge:Mn konnte die Kopplung von magnetischen und elektrischen Eigenschaften nachgewiesen werden. Der Grund für diese Kopplung ist allerdings nicht der ladungsträgerinduzierte Ferromagnetismus in kristallinem Ge:Mn, sondern der Ferromagnetismus eines perkolierenden manganreichen amorphen Nanonetzes in Ge:Mn. Dabei weist die hergestellte Ge:Mn-Hybridstruktur ähnliche Magnetotransporteigenschaften wie das klassische verdünnte GaAs:Mn auf.
Der Erfolg bei der Herstellung eines amorphen Ge:Mn-Nanonetzes beruht zum großen Teil auf der Verwendung einer relativ langen Laserpulsdauer von 300 ns, welche auf dem Gebiet der Flüssigphasenepitaxie bisher eine untergeordnete Rolle spielte. Durch diese lange Laserpulsdauer kann ein Temperaturgradient in die Probe eingeprägt werden, welcher zu einer konstitutionellen Unterkühlung des Ge:Mn und darauffolgend zu einem instabilen, zellulären Wachstum führt, wobei in den Zellwänden des Ge:Mn-Nanonetzes Mangan angereichert wird.
Nach der Einleitung in Kapitel 1 werden im Kapitel 2 der vorliegenden Arbeit verschiedene Formen des Magnetismus in Festkörpern dargestellt und der Einfluss des Magnetismus auf die Magnetotransport-Eigenschaften von magnetischen Halbleitern diskutiert.
Die Herstellung von ferromagnetischen Halbleitern mittels Ionenimplantation und gepulster Laserausheilung wird im Kapitel 3 detailliert erläutert. Zudem wird ein theoretisches Modell hergeleitet, mit dem eine Abschätzung des zeitabhängigen Temperaturprofils während der Laserausheilung möglich wird.
Der physikalische Zugang, welcher die Formierung des Ge:Mn-Nanonetzes beschreibt, wird anhand von typischen Rekristallisationsphänomenen von Legierungen qualitativ dargestellt.
Im Kapitel 4 werden die zur Untersuchung des Ge:Mn-Nanonetzes verwendeten Charakterisierungsverfahren vorgestellt. Es werden physikalische Ursachen für Messfehler diskutiert, welche bei der Unversuchung von Ge:Mn mittels SQUID- und TEM-Messungen besonders in den Vordergrund treten.
Im Kapitel 5 wird ein im Rahmen dieser Arbeit entwickelter Algorithmus vorgestellt, welcher in eine Monte-Carlo-Simulation implementiert wurde, um Diffusions- und Clustervorgänge von magnetischen Fremdatomen in einem primitiven kubischen Gitter während der Abkühlphase nach einem typischen Laserpuls zu simulieren.
Da sich in den letzten 16 Jahren GaAs:Mn als der Prototyp des verdünnten ferromagnetischen Halbleiters entwickelt hat, werden Teile der im Rahmen dieser Arbeit an GaAs:Mn gewonnenen Erkenntnisse in Kapitel 6 dargestellt. Wie im Kapitel 7 gezeigt wird, weist der Magnetotransport von Ge:Mn ähnliche Eigenschaften wie der Magnetotransport in GaAs:Mn auf. Insbesondere korreliert die Hysterese im anomalen Halleffekt von Ge:Mn mit der Hysterese der Magnetisierung. Die physikalische Ursache für die Hysterese im anomalen Halleffekt in Ge:Mn wird auf die bevorzugte Streuung von spinpolarisierten Ladungsträgern in dem perkolierenden, amorphen, manganreichen Ge:Mn-Nanonetz der Ge:Mn-Hybridstruktur zurückgeführt. Die Morphologie der Ge:Mn-Hybridstruktur wurde mittels TEM ausführlich untersucht.
Im Kapitel 8 werden die gewonnenen Ergebnisse zusammengefasst und es wird ein Ausblick gegeben, welche Anwendungsmöglichkeiten die in dieser Arbeit erlangten Erkenntnisse auch in anderen Forschungsbereichen finden können.
In den Anhängen A.1 - A.8 befinden sich detaillierte Informationen über die Materialparameter von Si, Ge und GaAs, weitere Details über den entwickelten Monte-Carlo Algorithmus, eine Probenübersicht, TEM-Bilder sowie ergänzende Magnetowiderstands- und SQUID-Daten zur weiteren Charakterisierung der hergestellten Ge:Mn-Hybridstruktur.

The aim of this work is the evaluation of the producibility of ferromagnetic semiconductors with spinpolarized charge carrier transport. To reach this aim, in this experimental work also theoretical concepts were developed to estimate the chances of success for the producibility of ferromagnetic semiconductors.
For doping semiconductors with magnetic dopants, ion implantation of manganese in germanium and manganese in GaAs has been used. The damaged surface layer was annealed with laser induced liquidphase-epitaxy. This type of growth is quite different from the conventionally used low temperature molecular beam epitaxy and is based on a different thermodynamical concept. Both growth techniques can be used far from thermodynamical equilibrium conditions and therefore allow dopant concentrations above the natural solubility limit under thermodynamical equilibrium conditions. This is a necessary condition for the fabrication of charge carrier mediated ferromagnetism in GaAs:Mn, Ge:Mn or in transition metal doped silicon. The following coupling between magnetic and electric properties in such systems is a necessary condition for an application in nonvolatile memories, because the magnetic state can be directly read out over the electric response due to the anomalous Hall effect. For our fabricated material system Ge:Mn, a coupling between the electric and magnetic properties, similar to GaAs:Mn, could be reached. The reason for this coupling is not attributed to charge carrier mediated ferromagnetism in crystalline Ge:Mn. The reason is the growth of a percolating Mn-rich amorphous Ge:Mn-nanonet embedded in crystalline Ge:Mn. The successful growth of this Mn-rich nanonet relies on the fact that a laser with a 300 ns long pulse was used that is longer than the typical pulsed excimer or solid state lasers used for liquid-phase-epitaxy. Therefore, a special temperature gradient can be imprinted in the annealed wafer that lead to a constitutional undercooling with an instable, cellular growth and an accumulation of Mn in the nanonet.
The Phd-thesis is structured in the following way: After a short introduction, the different kinds of magnetism are illustrated in the chapter 2. Thereby, also its influence on the Hall effect and further magnetotransport properties are discussed.
Details about sample preparation with ion implantation followed by pulsed laser annealing are explained in chapter 3. Moreover, a model is developed to perform a rough estimation of the temperature profile during PLA. The physical mechanisms, which lead to the formation of the Ge:Mn-nanonet are qualitatively explained by discussing some textbook knowledge for liquid-phase-epitaxy of alloys. In chapter 4 the applied characterization methods of the Ge:Mn-nanonet are presented. Especially, sources of error are presented that have, based on the experience with Ge:Mn, a large influence on the measurement results.
In chapter 5 an algorithm is presented that was implemented in a Monte-Carlo simulation to model diffusion and clustering processes of magnetic dopants in a simple cubic lattice during the cooling process of pulsed laser annealing.
Because of the large experience in the last 16 years with the material system GaAs:Mn as the prototype diluted ferromagnetic semiconductor, in chapter 6 the obtained measurement results from GaAs:Mn are presented. In chapter 7 for the material system Ge:Mn, a similar correlation between the hysteresis in the anomalous Hall effect to its magnetism could be shown. The reason for the hysteretic anomalous Hall effect will be explained on the basis of a preferential scattering of spinpolarized charge carriers in a percolating, Mn-rich, amorphous Ge:Mn-nanonet. The morphology of the nanonet is investigated by TEM.
In chapter 8 the obtained findings are summarized and possible consequences for further research on ferromagnetic semiconductors are discussed. Moreover, suggestions for the use of the developed process in alternative research topics are made.
In the appendix A.1 - A.8 detailed information about the material parameters of Si, Ge, and GaAs, further details about the developed Monte-Carlo algoritm, a sample overview, further TEM pictures, magnetotransport measurements and SQUID-magnetization data for a detailed characterization of the fabricated Ge:Mn-hybridstructure can be found.

An iterative scheme is presented to solve analytically the relativistic fluid dynamics equations. The scheme is applied to the longitudinal expansion, the transversal symmetric and the transversal asymmetric (triaxial) expansion as well. Within this scheme it is possible to describe the dynamics of a strongly coupled (i.e. conformal) medium for parameters referring to heavy-ion collisions at LHC.

X-ray absorption spectroscopy is a versatile tool to investigate oxidation state and molecular structure or uranium in aqueous and solid phases and at their common interface. However, the structural analysis is often hampered by limited resolution and range. I will show recent advances to overcome these limitations, including improved XAFS data analysis approaches like Monte-Carlo and Landweber methods; coupling to XAFS-independent methods like DFT and surface complexation modeling as well as to other x-ray methods like HEXS which have a longer detection range.
I will demonstrate the usefulness of these methods by showing recent results on uranyl sorption to mineral surfaces, with a focus on polynuclear and carbonate complexes; Fe(II)-driven interfacial redox processes of uranyl, also in comparison to other actinoides; colloid formation processes of U(IV) and its tetravalent actinoide neighbors.

The magnetic characterization of nanoscale magnetic structures is one of the main prerequisites for the development of magnetoelectric memories and sensors. Here we present magnetoresistance effects of nanostructured metallic films and particles, which can exhibit anisotropic magnetoresistance or giant magnetoresistance effects. The structures are built from a variety of materials and they are measured at low tem- peratures in magnetic fields up to 1.5 T. We correlate the microscopic structure of the materials with the observed magnetic properties. Thus, a deeper understanding of switching and storage of the magnetic state in such nanostructures can be gained.

We demonstrate a broadband THz detector based on graphene flakes, which are produced by scotch-tape method on SiO2/Si, combined with a logarithmic periodic antenna. The antenna is coupled to the graphene flake with an interdigitated comb-like structure in the center. The detectors were characterized at roomtemperature using the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The responsivity is above 1nA/W for wavelengths from 30µm to 220µm. The rise time of the measured signals is below 100ps and their length is in the range of 200ps, while the pulse duration of the FEL pulses is around 20ps. The effect of the antenna coupling could be confirmed via polarization dependent measurements. Due to the spectral bandwidth combined with high temporal resolution and simple handling these detectors can be very useful for timing purposes of short laser pulses.