Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Semiconductor nanocrystals in dielectric matrices are of great interest for a broad range of applications, especially in the field of photon management in solar cells and for non-volatile memories. In this work we investigate the formation of crystalline Ge nanoparticles in superlattice stacks by flash lamp annealing. In detail, amorphous ZrO2/Ge and SiN/Ge superlattices confined by two SiO2 layers on Si were produced by magnetron-sputtering and plasma-enhanced chemical vapor deposition, respectively. Raman and TEM investigations reveal that, depending on the original Ge layer thickness, crystalline Ge nanoparticles with different aspect ratios will be formed under annealing. As shown by electrical measurements, these layers feature large charge trapping capabilities. We compare these two types of layer systems with regard to the formation process of the Ge nanoparticles, the trapped charge density, the memory window and the retention. Finally, the perspectives for non-volatile memories are discussed, if these layer stacks are downscaled to current device dimensions.

Die Genauigkeit und Reproduzierbarkeit des Standardized Uptake Value (SUV) zur quantitativen Auswertung von Ganzkörper-PET/CT-Untersuchungen wird von messtechnischen und biologischen Faktoren beeinflusst, welche die Aussagekraft des SUV einschränken, insbesondere seine Eignung als Surrogat des Glukosemetabolismus in der FDG-PET. In messtechnischer Hinsicht wird der SUV unmittelbar von der Güte der Kreuzkalibrierung zwischen PET-Gerät und Dosiskalibrator wie auch von der Genauigkeit des Patientengewichts beeinflusst. Adäquate Qualitätskontrolle vorausgesetzt können diese Einflussgrößen aber beherrscht werden. Eine grundsätzliche Beschränkung bei kleinen Läsionen stellen Partialvolumeneffekte dar, welche sich gar nicht oder nur mit ungenügender Verlässlichkeit korrigieren lassen. Bei Läsionsgrößen unterhalb etwa des 3-Fachen der räumlichen Auflösung ist eine sinnvolle SUV-Bestimmung nur noch sehr bedingt möglich. Neben messtechnischen Faktoren beeinflussen 2 biologische Effekte maßgeblich die Verlässlichkeit der SUV-Bestimmung, zum einen die nicht unbeträchtliche Zeitabhängigkeit des SUV, zum anderen die Tatsache, dass der SUV sich proportional zum gegebenen Tracerangebot im arteriellen Blut ändert, wobei Letzteres selbst nach Normierung auf SUV-Einheiten eine beträchtliche Variabilität zwischen verschiedenen Untersuchungen aufweist. Diese biologischen Faktoren führen zu einer schlechten Test/Retest-Stabilität des SUV, was insbesondere nachteilig für Verlaufsuntersuchungen oder die schwellwertbasierte Unterscheidung zwischen benignen und malignen Läsionen ist. Beide Effekte können durch den Übergang vom SUV zum Tumor-zu-Blut Standard Uptake Ratio (SUR) eliminiert werden. Der SUR ist bildgestützt leicht zu bestimmen, sofern ein großes Gefäß (Aorta, Herzventrikel) in der Untersuchung miterfasst wird. Der Scanzeit-korrigierte SUR weist eine im Vergleich zum SUV deutlich verbesserte lineare Korrelation zur metabolischen Umsatzrate auf, wodurch sich die diagnostische Aussagekraft der PET erhöht, wie erste klinische Studien belegen.

Abstract
Accuracy and reproducibility of the Standardized Uptake Value (SUV) for quantitative evaluation of whole body PET/CT investigations is influenced by technical and biological factors which limit its value, notably suitability of the SUV as a surrogate of glucose metabolism in FDG PET. On the technical side the SUV is directly influenced by the quality of the cross calibration between the PET system and the dose calibrator as well as by accuracy of the assumed patient weight. Given adequate quality control these factors can be handled. A principal limitation in small lesions are partial volume effects, which cannot be corrected at all or only with insufficient reliability. For lesion sizes below approximately three times the given spatial resolution a meaningful SUV determination is only possible with substantial reservations. Beside the technical factors, 2 biological factors strongly influence the reliability of SUV determination, the notable time dependency of the SUV on the one hand and on the other hand the fact that the SUV changes in proportion to the given tracer supply in the arterial blood, where the latter exhibits substantial variability even after normalization to SUV units. These biological factors lead to poor test/retest stability of the SUV which is especially disadvantageous for follow-up investigations or threshold based discrimination between benign and malign lesions. Both effects can be eliminated by a transition from SUV to the tumor to blood Standard Uptake Ratio (SUR). Image-based determination of the SUR is easy, provided a large vessel (aorta, heart ventricle) is covered by the investigation. In comparison to SUV, the scantime corrected SUR exhibits a distinctly improved linear correlation to the metabolic uptake rate which increases the diagnostic power of PET as could be demonstrated in first clinical studies.

Flash Lamp Annealing (FLA) is a technique in which Si can be heated to temperatures close to and above its melting point within a few milliseconds [1, 2] and it has been shown to be suitable for annealing of implantation-induced damage [2, 3] and for activation of implanted dopants [4]. Recently, FLA was also proved to be effective in forming shallow Phosphorous (P) emitters in Si through diffusion from a P surface source deposited by spin coating [5].
In this work, it is demonstrated that shallow Boron (B) emitters can be formed in crystalline Silicon (Si) by spin coating and subsequent in-diffusion using FLA. A 300 μm Float Zone mono-crystalline Si wafer was spin-coated at 6000 rpm for 30 seconds by a polyboron spin-on diffusant (Filmtronics B155 SOD) before being processed with FLA. After heat treatment by FLA, the film was oxidized in HNO₃:H₂SO₄ (1:1) before being removed by HF. Secondary Ion Mass Spectrometry (SIMS), sheet resistance measurements and Transmission Electron Microscopy (TEM) analysis were performed to determine the B diffusion profile, the sheet resistance and crystal quality of the samples, respectively.
Annealing for 10 and 20 ms with an energy density of 93-105 J/cm² leads to B emitter depths of 140- 200 nm and peak B concentrations of 1-3·10²⁰cm⁻³. Sheet resistance values below 200 Ω/ indicate high dopant activation. These values are well suited for e.g. emitters in crystalline Si solar cells as the shallow emitters will only absorb photons with a wavelength below 420 nm [6] and most of the available sunlight will be absorbed in the base of the cell while the low sheet resistance gives a low series resistance. High-resolution TEM images of the surface and junction regions did not show any crystal defects demonstrating that the FLA treatment does not induce high defect concentrations in the samples. TEM did however reveal a rough surface resulting from the etching treatment to remove the SOD.
Annealing for 10 and 20 ms with energy densities below 90 J/cm² produce even shallower profiles with a maximum B extension of <100 nm while the peak concentration still remains above 1·10²⁰cm⁻³ whilst the sheet resistance increases to 300-3000 Ω/. In conclusion, spin-coating with subsequent in- diffusion by FLA is thus a versatile technique with possibility to tailor the emitter depth in Si while still keeping the peak concentration high.
References
[1] H. A. Bomke, H. L. Berkowitz, M. Harmatz, S. Kronenberg, R. Lux, Applied Physics Letters 33, 955 (1978).
[2] J. T. Lue, Applied Physics Letters 36, 73 (1980).
[3] R. Klabes, et al., Physica Status Solidi A: Applications and Materials Science 66, 261 (1981).
[4] T. Ito, et al., Japanese Journal of Applied Physics, Part 1: Regular Papers, Brief Communications & Review Papers 41, 2394 (2002).
[5] H. B. Normann, et al., Applied Physics Letters 102, 132108 (2013).
[6] M. A. Green, Solar Energy Materials & Solar Cells 92, 1305 (2008).

Ion beam sputtering (IBS) is a universal phenomenon that can be used for the production of nanopatterns in a wide range of materials and scales. Many semiconductor systems are suitable for this kind of processing, but Si is certainly the most studied one due to its technological relevance and mono-elemental nature [1]. In the last years, the key role of metal impurities for the initial formation of the pattern has been clearly established [2], changing the field in a significant way. Still, several questions remain open, such as the segregation effect of metal silicides [3], the relevance of preferential sputtering for the different metal species [4], or the threshold metal concentration needed for nanopatterning at given experimental conditions. Most of these works are restricted to low energetic beams (0.5-5 keV) produced with conventional ion guns and different set-ups to induce indirect metal codeposition [5]. However, in order to have an appropriate control of the metal species more dedicated systems, where metal could be also directly incorporated, are becoming essential. In this communication, we will present our recent experimental works on IBS nanopatterning of Si at medium energies (40 keV) with simultaneous metal incorporation [6]. In order to understand the influence of the metal on the pattern formation we study three different experimental systems produced with (a) direct metal implantation, (b) indirect metal co-deposition, i.e., with simultaneous irradiation of a metallic plate adjacent to the target, and (c) with non-metal implantation (used as a reference). In all cases, irradiation was carried out in a high-flux ion implanter using an incidence angle of 60º with respect to the target surface normal and for different ion fluences. The dynamics of the pattern is studied using atomic force microscopy (AFM) to characterize the pattern morphology, and particularly to quantify the surface roughness and pattern wavelength. Metal content was determined with Rutherford backscattering spectrometry and the formation of silicides mapped with X-ray photoelectron spectroscopy. In addition, we performed current sensing AFM as well as transmission electron microscopy analysis of the metal containing samples in order to disclose the formation of any compositional pattern and its eventual correlation with the morphological one. We will discuss the main differences arising from the different metal incorporation paths, paying special attention to effects such as geometrical shadowing, the threshold contents required to trigger the pattern in every case and the formation of metal silicides. [1] J. Muñoz-García et al., Mater. Sci. Eng. R-Rep. 86, 1 (2014) [2] C. Madi et al., Phys. Rev. Lett. 101, 246102 (2008) [3] M. Engler et al., Nanotechnology 25, 115303 (2014) [4] R. Gago et al., Nanotechnology 25, 415301 (2014) [5] K. Zhang et al., Nanotechnology 25, 085301 (2014) [6] A. Redondo-Cubero et al. Phys. Rev. B 86, 085436 (2012)

In a previous work, the authors investigated the formation of thin barrier-like oxide films on aluminium using pulse anodizing [1]. The electrochemical experiments have shown differences in the properties and behaviour of the anodic films depending on the pulse frequency. Furthermore, the results suggest a relationship to the microstructure (e.g. thickness or composition) of the oxide films. Therefore, the authors have completed the former investigation by new research using transmission electron microscopy (TEM) and ellipsometry. All results were compared with electrochemical measurements. Again, the anodic films were formed at 3V_Ag/AgCl with various pulse frequencies in an acetate buffer solution (pH5.9). The aluminium was chemical vapour deposited on silicon wafers to get a smooth and well-defined surface which is favourable for subsequent analytical analysis (TEM, ellipsometry). The TEM investigation confirms the tendency that the oxide thickness decreases with increasing pulse frequency. The film thicknesses determined by coulometry and microscopy fit very well assuming a native oxide layer of approximately 1nm. Additionally, the Al:O ratio across the film thickness clearly depends on the pulse frequency. A model concept explaining this fact will be presented. Furthermore, there are no indications to the formation of crystalline domains within the oxide layers deposited at various pulse frequencies.
[1] M. Schneider, C. Lämmel, C. Heubner, A. Michaelis: Surface and Interface Analysis 45 (2013) 1497-1502

Ceramic foams are promising alternatives for packing internals used in chemical engineering processes due to their high porosity and high specific surface area, which results in low pressure drop and high catalytic utilization of the packing. The application of solid foam packings as catalyst carriers, particularly for gasliquid systems, are not yet well understood. Due to their highly porous nature, it is very tough to understand the interplay between hydrodynamic behaviour and process performance [1]. The aim of this work is to perform three-dimensional Computational Fluid Dynamics (CFD) simulations of the evolving gas-liquid flow patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies The closures applied for trickle bed simulation studies are modified according to the hydraulic/geometric properties of the ceramic foam considering the flow domain as porous. The influence of the liquid and gas drag is taken into consideration via Relative Permeability approach [2] and added as external source term to the liquid and gas momentum equations separately. The influence of dispersion forces are further included inorder to steady the liquid spreading and liquid saturation. The geometrical parameters of the ceramic foam packing are estimated using µCT image analysis. Empirical correlations proposed in earlier experimental studies are included in 3D CFD models. Initial results of trickle bed reactor simulations were presented earlier [3]. In this work, the validation of CFD simulation with X-ray tomographic experimental studies will be presented and discussed in detail.

Reference 1 :: S. Calvo., d. Beugre.,m.Crine., a. Leonard., p. Marchot.,d.Toye.,phase distribution measurements in metallic foam packing using x-ray radiography and micro-tomography, chemical engineering and processing, 48, 1030–1039 (2009).
Reference 2 :: A.E. Saez,, R.G.Carbonell, Hydrodynamic parameters for gas-liquid cocurrent flow in packed beds,AIChE Journal, Vol. 31, No.1, 52-62 (1985).
Reference 3 :: K.Subramanian, M. Schubert, D. Lucas, U. Hampel, Closures for simulation of gas-liquid flows in solid foam structures, ISCRE23 & APCRE7, Sep 7 – 10 2014, Bangkok, Thailand.

At ASTER (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and DREAMS (DREsden Accelerator Mass Spectrometry) sophisticated ion sources are used for ³⁶Cl and ¹²⁹I. Both facilities have dedicated ³⁶Cl chemistry labs. At DREAMS it is also used for storage and pressing of AgCl in sample holders (SHs). Most ³⁶Cl-AMS labs, reduce the isobar ³⁶S from the SH by a labor-intensive AgBr-backing. Though, at ASTER and DREAMS only ultrapure Ni and Cu is used, respectively. To find out the pros and cons of the two materials, we have (a) exposed AgCl pressed in Ni and Cu to air (in the dark). After 2 h only, cauliflower-type NiCl₂ (analysed by EDX) has been formed from AgCl and Ni preventing any later AMS, whereas AgCl in Cu after 3 days looks unweathered and is still measurable. (b) compared S-decline in AgCl pressed in Ni and Cu (ASTER SHs). After ∼5 min S decreases by a factor of ∼5 for both reaching the same low S-rate after 20 min. However, S is higher at 5-20 min in Cu showing that Cu is contaminated at the surface. High S is not seen at all at DREAMS for DREAMS Cu SHs. Thus, chemical etching and controlled storage of Cu SHs might be a cheaper and better alternative for ³⁶Cl-AMS.
For ¹²⁹I AMS a sophisticated tuning strategy is minimising sputtering of any iodine containing material at DREAMS.

Using accelerator mass spectrometry, we have conducted a search for live, supernova-produced, 60Fe atoms within biogenically produced magnetite (Fe₃O₄)crystals contained in two Pacific Ocean sediment cores. We have found a time-resolved ⁶⁰Fe signal in both sediment cores, above background, centered at approximately 2.1 Myr ago and spanning approximately 800 kyr duration (full width half maximum). The onset of this signal coincides with a known marine extinction event at the Pleiocene/Pleistocene boundary, and its shape will require eventual astrophysical interpretation to understand.

The talk is focussed on fabrication, in particular non-standard or alternative fabrication routes towards ODS steels. There is a natural reference for that, namely state-of-the-art ODS steels produced by the ‘classical’ PM route, which consists of the production of a pre-alloy, gas atomization, mechanical alloying, consolidation and thermal, mechanical or thermo-mechanical treatment. The motivation to consider alternative routes is derived from problems such as the multi-step/multi-parameter character of the PM process and the resulting high production costs, limited throughput and limited reproducibility. These problems can be addressed by way of improving, simplifying, skipping or combining individual steps, by way of reconsidering alloy fabrication from the melt or by looking for hybrid routes. It is demonstrated that there is a wide and fascinating potential for alternative fabrication routes towards ODS steels. For this to be achieved, each of the steps involved in the classical PM route has to be carefully reconsidered. Moreover, the liquid metal route and hybrid routes composed of PM and LM elements have to be taken into account. Significant progress has been made on particular process steps. These include substitution of mechanical alloying, scaling up of SPS and the contactless excitation of cavitation.

Elevated shorelines and lake sediments surrounding Issyk Kul, the world’s second largest mountain lake, record fluctuating lake levels during Quaternary times. Together with bathymetric and geochemical data, these markers document alternating phases of lake closure and external drainage in the Late Pleistocene. The uppermost level of lake sediments requires a former blockage of the lake’s western outlet through the Boam gorge. Previous studies hypothesised that failures of Pleistocene ice or landslide dams in the gorge generated partial outburst floods of Issyk Kul. We test this hypothesis by exploring possible links between late Quaternary lake levels and outbursts. We dated stranded shorelines using ¹⁴C in shells, snails, and plant detritus, as well as sand lenses in delta and river sediments using Infrared Stimulated Luminescence. Our dates are consistent with lake levels expanding into Boam gorge between ~46 ka and 22 ka. Cosmogenic ¹⁰Be and ²⁶Al exposure ages of fan terraces containing erratic boulders downstream of the gorge constrain the timing of possible outburst floods to 22-24 ka, postdating a highstand of Issyk Kul. A flow competence analysis gives a peak discharge of >10⁴ m³ s^–1 for entraining and transporting these boulders. Palaeoflood modelling, however, shows that naturally dammed lakes unconnected to Issyk Kul could have produced such high discharges upon sudden emptying. Hence, although our data are consistent with hypotheses of catastrophic outburst flooding, we caution against directly these to Pleistocene lake levels of Issyk Kul. Average lake-level changes of up to 90 mm yr^–1 in the past 150 years were highly variable without any outburst event, so that attributing catastrophic lake-level drops to dam breaks is ambiguous using sedimentary archives alone. Nevertheless, the Pleistocene flood events that we reconstruct are among the largest reported for the Tien Shan mountains, and motivate further research into the palaeoflood hydrology in Central Asia.

Effects of neutron flux (or dose rate) on the characteristics of irradiation-induced nanofeatures in neutron-irradiated pressure vessel steels were occasionally reported. Such effects let one expect that the mechanical properties mediated by the operation of the nanofeatures as dislocation obstacles would also depend on flux. However, there are controversial views on the presence of flux effects on mechanical properties. The present approach is based on the investigation of pairs of samples from the same batch of material for a number of RPV steels including different levels of Cu as well as base and weld materials. The samples of each pair were irradiated at about the same temperature but different fluxes up to about the same fluence, thus automatically revealing potential flux effects. Small-angle neutron scattering and Vickers hardness testing were applied to characterize the nm-scale solute clusters and the resulting irradiation hardening. A number of analytic models of cluster evolution, namely deterministic growth and coarsening, and hardening as well as combinations thereof were applied to interpret the trends extracted from the experimental results. It is found that there are indeed trends of the cluster size and volume fraction as functions of flux but no resolvable trend for hardening. The absence of a flux effect on hardening can be rationalized in terms of size and number density of solute clusters that enter the hardening expressions. Size and number density depend on flux in opposite directions and, therefore, partly cancel out. Flux effects for the whole set of experimental data including low- and high-Cu base metals and welds can be consistently described by a combination of deterministic growth and dispersed barrier hardening using a unique value of the obstacle strength of solute clusters.

Introduction:

Compact laser-driven ion accelerators are a potential alternative to complex, large and expensive conventional accelerators. High-power short-pulse lasers, impinging on e.g. thin metal foils enable multi-MeV ion acceleration on µm length and ps time scale. The generated ion bunches (typically protons) show unique beam properties, like ultra-high pulse dose. Nevertheless, laser accelerators still require substantial development in reliable beam generation and transport. We present first experimental results on a beamline prototype based on high-field magnet technology specifically designed for capture and transport of laser-accelerated particles.

Material and methods:

Since the mid-1950s, pulsed high-field magnets serve as versatile research tools for solid state physics and material research. Recently developed pulsed magnet technology, specifically designed to meet the demands of laser acceleration [1], open up new research opportunities: We present a pulsed solenoid for effective collection and focusing of laser-accelerated ions which could function as a first component in a laser-driven gantry system [2]; furthermore, we present a dipole magnet for beam deflection and energy dispersion. The magnets were combined to form a first, pulsed high-field beamline and are powered by portable pulse. Characterization of both magnets has been carried out using a 10 MeV proton beam from a conventional Tandetron accelerator at Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The transported beam was detected by means of radiochromic film and scintillator.

Result:

The transport experiments clearly show the functionality of both magnets: The solenoid focuses the large, divergent ion beam to a millimeter-sized spot showing no aberration. The dipole deflects the protons by a 45° angle and can be used as energy selection device via energy dispersion. For the several 10 µs long proton bunches no effect of the time structure of the magnetic pulse (~ several 100 µs) was observed thus making the magnets well suited for even shorter, laser-driven ion bunches. The beam position accuracy, after passing the beamline, was measured to be of the same order as the beam position fluctuations itself, showing the precision of the installed beamline. The maximum magnetic field strength achieved was 20 T for the solenoid and 5 T for the dipole. For operation at higher proton energies, i.e. above 200 MeV, an increase by a factor of only 1.5 – 2 is requested.

Summary:

Our experimental results show that compact high-field magnets can be used to precisely guide charged particle bunches. The pulsed nature of laser-accelerated particles is matched by the magnet technology. The maximum field strengths reached are sufficient for experiments with protons of several 10 MeV kinetic energy. For clinically relevant energies above 200 MeV, however, a slight increase is required. Experimental studies at a laser-accelerator are scheduled.
References
[1] T. Burris-Mog, et al., Laser accelerated protons captured and transported by a pulse power solenoid, PRSTAB 14, 121301 (2011)
[2] U. Masood, et al., A compact solution for ion beam therapy with laser accelerated protons, Appl. Phys. B 117, 41 (2014)

Magnesium (Mg) is one of the lightest industrially used metals. However, wide applications of Mg-based components require a substantial enhancement of their mechanical characteristics. This can be achieved by introducing small particles or fibers into the metal matrix. Using first-principles calculations, we investigate the stability and mechanical properties of a nanocomposite made of magnesium reinforced with boron nitride (BN) nanostructures (BN nanotubes and BN monolayers). We show that boron vacancies at the BN/Mg interface lead to a substantial increase in BN/Mg bonding establishing an efficient route towards the development of BN/Mg composite materials with enhanced mechanical properties.

We theoretically study the atomic structure and energetics of silicon and silicon-nitrogen impurities in graphene. Using density-functional theory, we get insight into the atomic structures of the impurities, evaluate their formation energies and assess their abundance in realistic samples. We find that nitrogen, as well as oxygen and hydrogen, are trapped at silicon impurities, considerably altering the electronic properties of the system. Furthermore, we show that nitrogen doping can induce local magnetic moments resulting in spin-dependent transport properties, even though neither silicon nor nitrogen impurities are magnetic by themselves. To simulate large systems with many randomly distributed impurities, we derive tight-binding models that describe the effects of the impurities on graphene π electron structure. Then by using the linear-scaling real-space Kubo-Greenwood method, we evaluate the transport properties of large-scale systems with random distribution of impurities, and find the fingerprintlike scattering cross sections for each impurity type. The transport properties vary widely, and our results indicate that some of the impurities can even induce strong localization in realistic graphene samples.

This chapter is an introduction to the fields of Positron Emission Tomography (PET), hybrid Positron Emission Tomography and Magnetic Resonance Imaging (PET/MR), attenuation correction (AC), and MRI-based attenuation correction (MRAC). Since this work represents a cumulative dissertation, the aim of this chapter is to provide the required background to understand the intentions and the context of the three publications [Schramm et al., 2013a,b, 2014] dealing with the evaluation and improvement of MRAC. These publications are included in chapter 3 of this work.

Scattering-type scanning near-field optical microscopy (s-SNOM) is an AFM-based technique for achieving nanoscale resolution even at infrared wavelengths [1]. s-SNOM thus is of valuable impact when investigating low-dimensional conductors or semiconductors. Nevertheless, the scattered near-field signal strongly depends on the dielectric function of both tip and sample. In order to enhance this signal strength we face two options, by either tuning the tip or sample into resonance using appropriate or tunable laser light sources, and resonant tip materials.


In this work we use a CO₂-laser with a tunable center wavelength from 9.7 µm to 11.3 µm as an infrared excitation source in combination with self-prepared AFM particle-tips as probes [2]. The tip particles consist of spherical silicon carbide (SiC), silicon nitride (Si₃N₄) or silicon oxide (SiO₂) nanoparticles with a diameter of ~ 60 nm. Those materials show phonon resonances in or around the CO₂-laser wavelength range and thus enhance the signal significantly. We explored here the scenario when using both resonant tips AND samples, hence resulting in a tip-sample coupled super-resonance where both the tip and the sample contribute to the signal-enhancement. Accordingly, a significantly increased near-field image contrast and resolution is expected in this case.

References:


[1] S.C. Kehr et al., Nat. Commun. 2, 249 (2011).

[2] M.T. Wenzel et al., Optics Express 16 (16), 12302-12312 (2008).

DREAMS, the DREsden AMS-facility, is performing routine accelerator mass spectrometry for the isotopes ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca and ¹²⁹I. Sample ratios of ¹⁰Be/⁹Be as low as 8 x 10^-15 (background-corrected) have been measured and an exposure age of about 330 years of a boulder of 3000 t in Nepal could be determined [1]. We could demonstrate that a by-product of ice core drilling, so-called drilling chips, are also suitable for ¹⁰Be analysis of ice cores, instead of using valuable ice core samples. A set of several in-house ²⁶Al and ⁴¹Ca standards has been made traceable to primary standards by cross-calibration [2]. Numerous ²⁶Al and ⁴¹Ca concentrations of meteorites could be determined, but for marine sediments there is still a need for a low-level (10^-13) ²⁶Al standard. ICP-MS measurements have shown that the steel pins used to fix the CaF₂ sample material in the cathodes have high K-concentrations of (44.6 ± 2.2) μg/g. By replacing the steel pins with copper pins the ⁴¹K background during ⁴¹Ca measurements could be lowered by a factor of three.
Ref. : [1] W. Schwanghart et al., Science (2015), DOI:10.1126/ science.
aac9865. [2] G. Rugel et al., Nucl. Instr. Meth.B (2015), in review.

Fortschritte auf dem Gebiet der Molekularbiologie haben im letzten Jahrzehnt etablierte wissenschaftliche Ansichten über die Entstehung von Tumorerkrankungen wesentlich verändert. Im Gegensatz zur früheren Sichtweise, dass Tumore einzig eine Ansammlung relativ homogener Krebszellen sind, verweisen die Erkenntnisse der letzten Jahre auf deren sehr komplexe Biologie. Dabei sind Krebszellen in nicht entartete Zellverbände, bestehend aus Fibroblasten, Pericyten, Endothelzellen sowie entzündungsauslösende Immunzellen eingebettet, die maßgeblich an der Bildung des Tumormikromilieus beteiligt sind, welches insbesondere bei der Tumorgenese und Metastasierung eine entscheidende Rolle spielt. Hanahan und Weinberg entwickelten ein Konzept zur Klassifizierung sogenannter "Hallmarks of Cancer" die das komplexe Zusammenspiel auf wenige grundlegende und allgemeingültige Organisationsprinzipien zurückführen. Die Verbesserung des Verhältnisses von Tumorerkrankungen soll dazu beitragen neue und effektivere Strategien für deren Therapie zu entwickeln. Besonders die Entwicklung weg vom standardisiertenTherapieverfahren hin zu einer zielgerichteten und auf den jeweiligen Patienten zugeschnittenen "individualisierten" Behandlung gewinnt in der Pharmazie zunehmend an Bedeutung. Von großem Interesse hierbei sind, Molekülstrukturen, die basierend auf supramolekularen Bindungsmotiven mit einer hohen Spezifität und Selektivität an Zielstrukturen im entarteten Gewebe binden. Eine Substanzklasse, die dabei im Fokus des pharmazeutischen Interesses steht, sind monoklonale Antikörper (mAk). Angesichts ihrer hohen Affinität gegenüber bestimmten Epitopen tumorassoziierter Antigene sind sie unter anderem in der Lage, tumorspezifische Signalwege zu beeinflussen und so das Tumorwachstum zu hemmen.

Als erste klinisch zugelassene Radioimmuntherapeutika werden die beiden radioaktiv markierten Antikörperpräparate Zevalin ([⁹⁰Y]Y-ibritumomab tiuxetan) und Bexxar ([¹³¹I]I-tositumomab) bereits mit großem Erfolg zur ergänzenden Behandlung von Non-Hodgkin's Lymphomen angewandt. Mittels ionisierender Strahlung hervorgerufene DNA-Doppelstrangbrüche stellen dabei das eigentliche zellinaktivierende Ereignis dar. Der Vorteil einer solchen Radioimmuntherapie besteht vor allem darin, metastasierende Tumorerkrankungen zu behandeln, welche mit den klassischen Verfahren wie Chirurgie oder externer Bestrahlung nur schwer zu erfassen sind. Dennoch ist der Einsatz radioaktiv markierter monoklonaler Antikörper vor allem bei der Behandlung strahlenresistenter solider Tumore, trotz ihrer hervorragenden Bindungseigenschaften, limitiert. Ein weiterer Nachteil besteht darin, dass aufgrund ihrer hohen Blutverweildauer und nur langsamen Anreicherung im Zielgewebe, bedingt durch ihre Molekülgröße, der gesamte Organismus einer hohen Strahlenbelastung ausgesetzt wird.

Eine Alternative dazu stellt die Strategie des Pretargeting von Tumoren dar. Wie schematisch in Abbildung 1 am Konzept komplementärer Oligonukleotid-Bausteine gezeigt, besteht die Intention dieses Prinzips darin, mittels einer mehrstufigen Applikationsfolge die Injektion eines targetspezifischen Antikörper-Konjugates und einer kleinen radioaktiv markierten Verbindung zu trennen, welche zueinander ein komplementäres System bilden. Aufgrund der hohen Blutverweildauer wird das Antikörper-Konjugat zur Anreicherung im Tumorgewebe bereits einige Tage vor der eigentlichen Radionuklidanwendung appliziert. Nicht am Antigen gebundene Antikörper-Konjugate werden innerhalb der Wartezeit aus der Blutbahn eliminiert. Erst dann erfolgt in einem zweiten Schritt die Injektion der radioaktiv markierten komplementären Verbindung, welche nach kurzer Verteilungsphase am im Tumor lokalisierten Antikörper-Konjugat hybridisiert. Für eine möglichst geringe Strahlenbelastung sollte sich die radioaktiv markierte Verbindung durch eine schnelle Verteilung im Organismus, einer vorwiegend renalen Ausscheidungscharakteristik sowie einer sehr hohen Affinität und schnellen Bindungskinetik zum im Zielgewebe lokalisierten Antikörper-Konjugat auszeichnen. Besonders die schnelle renale Elimination solch kleiner Moleküle ist die Hauptursache für die deutlich geringere Strahlenbelastung des Gesamtorganismus gegenüber der konventionellen Radioimmuntherapie.

Electromagnetic induction (EMI) is known as a technique which is very sensitive to variation of electrical conductivity of materials. In the present study we simulate numerically the work of electromagnetic sensor which consists of two differential coils. Such a detector rejects the basic signal and monitors the perturbations of electromagnetic field caused by the heterogeneity of electrical conductivity. We investigate the capability of this method for detecting non-metallic inclusions, such as gas bubbles in liquid metal (GaInSn) and sensitivity of differential detector to variation of its configuration.

The contactless inductive flow tomography (CIFT) allows to visualize the mean flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one, or several, applied magnetic fields. The reliable measurement of these very small field changes, and the involved mathematics to solve the inverse problem, are the main challenges for this flow diagnostic method. We present preliminary results of CIFT applied to a thermally driven flow within a setup showing some similarity to Czochralski silicon crystal growth. As working fluid GaInSn was used. Due to the low velocities in the order of 1 cm/s, the dynamic range of the measurement system has to be enhanced to 5 orders of magnitude which set high demands on the stability of the installation and the current source. Large efforts were made to adapt CIFT to the experimental setup in order to compensate thermal expansion during the measurement. Typical features of the thermally driven turbulent flow could be detected in the magnetic field measurements and were verified by simultaneous temperature measurements recorded by thermocouples placed in the vicinity of the rim of the heat sink.

The flow structure of liquid steel in the mold of a continuous caster has huge impact on the quality of the produced steel. In order to influence the flow during the casting process electromagnetic brakes (EMBr) are used. Even a rough knowledge of the flow field would be highly desirable. The contactless inductive flow tomography is a technique for reconstructing the velocity field in electrically conducting melts from externally measured induced magnetic fields. For a physical model of a mold with a cross section of 140 mm × 35 mm we present preliminary measurements of the flow field in the mold in the presence of a magnetic brake. In addition, we show first reconstructions of the flow field in a mold with the cross section of 400 mm × 100 mm, demonstrating the upward scalability of CIFT.

Die vorliegende Arbeit wurde beginnend am 01.01.2011 am Institut für Radiopharmazeutische Krebsforschung des Helmholtz-Zentrums Dresden-Rossendorf (HZDR) durchgeführt. Sie ist in den Forschungsbereich „Gesundheit“ und hier speziell in das Programm „Strahlungsbasierte Theragnostik in der Onkologie“ der Helmholtz-Gemeinschaft einzuordnen. Am HZDR arbeiten Forscher aus unterschiedlichsten Bereichen zusammen, um Fortschritte im Kampf gegen Krebserkrankungen zu erzielen. Der Fokus liegt hierbei auf der Entwicklung neuer, innovativer Verfahren zur onkologischen Bildgebung, der Optimierung einer individualisierten Strahlentherapie, sowie der Erforschung neuartiger Therapiebeschleuniger auf Basis von Laser-Technologien. Die am HZDR durchgeführte Tumorforschung erfolgt dabei stets translational - die Erkenntnisse aus der Forschung sollen zum Nutzen des Patienten in die klinische Anwendung transferiert werden.

In Deutschland stellt Krebs schon seit vielen Jahren die zweithäufigste Todesursache dar. Es wird angenommen, dass maligne Tumore bis Mitte des Jahrhunderts zur häufigsten Todesursache in den Industrienationen aufsteigen werden. Vor dem Hintergrund dieser Zahlen wird deutlich, dass die Diagnose und Therapie von malignen Erkrankungen eine der größten medizinischen Herausforderungen des 21. Jahrhunderts sein wird.

Bei der Behandlung von Tumorerkrankungen ist es essentiell, diese so früh wie möglich diagnostizieren und anschließend möglichst zuverlässig und nebenwirkungsarm therapieren zu können. Neue radiopharmazeutische und nuklearmedizinische Methoden haben dabei das Potential, einen wesentlichen Beitrag zur Bewältigung dieser Problematik zu liefern. Das Prinzip der Radiopharmazie beruht dabei auf der Verwendung radioaktiver Substanzen zur Diagnose und Therapie verschiedener Erkrankungen, die mit Veränderungen des zellulären Stoffwechsels einhergehen. Bei jeder möglichen Anwendung ist es essentiell, dass sich die in den Körper eingebrachte radioaktive Substanz möglichst selektiv und schnell im gewünschten Zielgewebe oder Zielorgan anreichert. Dort kann diese dann in Abhängigkeit des eingesetzten Radionuklides entweder zur Diagnostik mittels Positronen-Emissions-Tomographie (PET) beziehungsweise Einzelphotonen-Emissions-Computertomographie (SPECT) oder zur Zerstörung des Tumorgewebes eingesetzt werden.

Krebszellen besitzen häufig bestimmte Moleküle auf ihrer Oberfläche, durch die sie sich von gesunden Zellen unterscheiden. Ein Beispiel für ein solches Molekül ist der epidermale Wachstumsfaktor-Rezeptor (EGF-Rezeptor). Der EGF-Rezeptor reguliert unter anderem das Zellwachstum und den apoptotischen Zelltod. In geringer Zahl ist er auf der Oberfläche aller menschlichen Zellen vorhanden. Bei einer Vielzahl maligner Tumore befindet sich aber eine stark erhöhte Zahl des EGF-Rezeptors auf der Zelloberfläche. Diese Überexpression korreliert mit der Bildung von Metastasen und einer häufigeren Therapieresistenz - und damit mit deutlich schlechteren
Heilungsaussichten für den Patienten. Aus diesem Grund ist der EGF-Rezeptor eine äußerst bedeutsame Zielstruktur für die Entwicklung neuer, vielversprechender pharmazeutischer und radiopharmazeutischer Wirkstoffe. [1]
Das übergeordnete Ziel der vorliegenden Arbeit war deshalb die Entwicklung eines neuen Radiotracers zur ‚Theragnostik‘ von EGFR-überexprimierenden Krebserkrankungen.

The self-catalyzed (or Ga-induced) growth of vertical GaAs nanowires on Si(111) by molecular beam epitaxy has offered the possibility to obtain nanowires with fairly good control of the structural polytypism (especially in favor of the zinc-blende phase), without the risk of contamination by foreign elements like Au. The growth is typically performed close to the congruent temperature of GaAs (580-630 °C) in combination with relatively high V/III ratios. Those conditions ensure the efficient surface diffusion of Ga adatoms from the substrate and the nanowire side-walls to the apex of the nanowires, and suppress the thermal decomposition of the {110} side-walls. Nevertheless, the specific growth conditions impose several limitations: 1) the growth temperature exceeds largely the thermal budget limit of the Si-CMOS technology, rendering the future integration of the two material technologies impossible; 2) the interruption of the axial growth cannot be abrupt because of the long shut-off transient of the As-flux, which is typically accompanied by the formation of a segment that is rich in stacking faults below the Ga droplet; 3) significant inter-diffusion at high temperatures will deteriorate the compositional/doping profile of axial heterostructures; 4) it is difficult to avoid the unintentional radial (shell) growth, which is undesirable in axial heterostructures.
Aiming to surmount the inherent limitations of the conventional self-catalyzed growth mode, we developed a new growth scheme that expanded successfully the growth window to temperatures as low as 450 °C, minimized the radial growth, and allowed for accurate and defect-free interruptions of the axial growth. Our scheme is inspired by the migration-enhanced epitaxy of GaAs thin films, where the Ga and As fluxes are supplied alternately and in doses comparable to the atom sheet-density of the growth interface. In the case of nanowires, though, we adapted the alternate supply of Ga and As to achieve targeted delivery of the Ga atoms to the apex of the nanowires, minimizing in that way the radial growth. This work did not concern the nucleation stage, thus nanowires grown in a conventional way were used as templates for all experiments.
The results of our study include quantitative descriptions of the Ga adatom migration kinetics, the incorporation efficiency of As through the Ga droplet, and the dependence of both on the growth temperature. Having constructed a complete picture of the growth kinetics, we were able to identify the optimal growth conditions and beam-shutter sequence for different growth temperatures, covering the range from 550 to 450 °C. The structural analysis of our nanowires by transmission electron microscopy showed a zinc-blende structure with a small number of twin defects (Fig. 1). However, the spacing between the twins is irregular and does not correlate with the periodic beam-shutter sequence. The success of our growth scheme is interpreted on the basis of the atomic arrangement of the non-reconstructed {110} side-facets.
Ongoing work concerns the nucleation stage at 450 °C, as well as the fine tuning of the growth scheme parameters in order to eliminate the formation of twin defects.

Electromagnetic induction (EMI) is known as a technique which is very sensitive to variation of electrical conductivity of materials. In this paper, we investigate capability of this method for detecting non-metallic inclusions, such as gas bubbles in liquid metal (GaInSn). We make both numerical simulation and experiment in order to build the sensitivity map for the interior of a rectangular column filled with liquid metal. The electromagnetic sensor consists of two differential coils. Such a detector rejects the basic signal and monitors the perturbations of electromagnetic field caused by heterogeneity of electrical conductivity. Theoretical results are used for validation of measured signals. The method is capable of detecting spherical target we used instead of real gas bubbles and produce a good agreement with numerical data.

The contactless inductive flow tomography (CIFT) allows to visualize the mean flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one, or several, applied magnetic fields. The reliable measurement of these very small field changes, and the involved mathematics to solve the inverse problem, are the main challenges for this flow inference method. We demonstrate the applicability of CIFT for various model experiments devoted to the continuous casting process, by employing a new measurement system using induction coils and AC excitation. This enables the determination of the flow structure even in the presence of a strong static magnetic brake field which is often used in continuous casting for controlling the flow in the mold. Additionally, we present preliminary results of CIFT applied to a thermally driven flow with some similarity to Czochralski silicon crystal growth. Due to the low velocities in the order of 1 cm/s, the dynamic range of the measurement system has to be enhanced by about one order of magnitude in comparison with the continuous casting application.

We present the results of the study of the correlation between the electrical and structural properties of individual GaAs nanowires measured in their as-grown geometry. The resistance and the effective charge carrier mobility were extracted for several nanowires, and subsequently, the same nano-objects were investigated using X-ray nanodiffraction. This revealed a number of perfectly stacked zincblende and twinned zincblende units separated by axial interfaces. Our results suggest a correlation between the electrical parameters and the number of intrinsic interfaces.

In many metallurgical and silicon crystal growth applications the knowledge about the flow field of the respective liquid metals is vital for proper process management. The high temperatures and the opaqueness of those melts set severe restrictions on the applicable flow measurement methods. The Contactless Inductive Flow Tomography (CIFT) is able to reconstruct the mean flow structure of liquid metals by measuring the flow induced perturbation of an applied magnetic field outside the melt. Typically, these perturbations are about 4 orders of magnitude smaller than the applied magnetic field. Therefore, special care has to be taken to ensure a very high dynamic range of the utilized magnetic field sensors and to minimize the effect of electromagnetic interferences. In this paper we give a short overview on CIFT and delineate some methods to increase its electromagnetic compatibility.

The AC electromagnetic induction is the most appropriate mechanism for monitoring of metallic objects and media with inhomogeneous distribution of electrical conductivity. In particular, the liquid metal flows with gas bubbles inside can be controlled by this method. In the present work we show a particular case when the series of 1D measurements can be applied for definition of position of a single gas bubble in y and z directions. The numerical experiment was made within a rectangular column filled with the liquid metal as it is shown in Figure (a). The basic AC (100 Hz) magnetic field was generated by a rectangular excitation coil. Typical distribution of the amplitude value of secondary magnetic field caused by a single bubble (5 mm) is shown in Fig.(c). The wall of measurement is opposite to the excitation coil. The shown normal component of magnetic field can generate an electrical signal in a measuring coil applied to the wall. In our experiment we use a system of rectangular coils stretched in horizontal and vertical directions (Fig. a,c).
A detector of such configuration averages the value of magnetic field flux within the long direction of the coil. Vice versa, a number of detectors can give the detailed information about distribution of magnetic field along the short sides of the coils. So far as the secondary magnetic field is presented by a dipolar structure (Fig. c) where the central singular point corresponds to position of the bubble, the signal collected from the series of coils has a zero point situated between two extremes (Fig. b, c). This zero point indicates position of the bubble. Thus, using a system of vertical and horizontal coils placed on the rear walls (Fig. a,c), one can estimate position of a single bubble in y and z directions according to two 1D distributions of the signal. In our numerical experiment a single bubble moves in vertical direction by a spiral trajectory (Fig. d). In Figure (e) we reconstruct the y and z coordinates of the bubble (red circles). The real positions of the bubble are marked by the small blue circles in this figure.

Local velocity measurement of liquid metals continues to be an unsolved issue. Contact or even contactless measurement techniques cannot be used due to the fact that metal melts, like liquid steel, are usually at high temperatures, aggressive and opaque. Fortunately, there is a contactless velocity measurement technique called Lorentz force velocimetry in which a static magnetic field is applied on the electrically conductive metal stream. This static magnetic field is produced by permanent magnets, and if their size is smaller in comparison with the cross-section of the flow, a localized magnetic field distribution on the liquid metal is achieved. As a result and according to the principles of magnetohydrodynamics, eddy currents are generated within the liquid giving rise to a localized flow-breaking Lorentz force. Additionally and owing to Newtons third law, a force of the same magnitude but in the streamwise direction acts on the permanent magnet system which is connected to an optical interference force measurement device, giving access to local velocity information. This paper presents the results of local Lorentz force velocimetry at the mini-Limmcast facility at Helmholtz-Zentrum Dresden - Rosendorf using a 10mm cubic magnet and having as test fluid Galinstan in eutectic composition. In addition, partial results of Lorentz LFV using a multi-degree-of-freedom force/torque sensor are presented.

The Contactless Inductive Flow Tomography (CIFT) allows the reconstruction of the mean three dimensional flow structure in conducting liquids [1]. Exposing the liquid to one or multiple applied magnetic fields and measuring the flow induced magnetic field around the fluid volume, it is possible to infer the velocity field by solving a linear inverse problem with appropriate regularization techniques. One challenge is the reliable detection of the tiny flow induced perturbation of the applied magnetic field. Typically, the flow induced magnetic field is about 3 to 5 orders of magnitude smaller than the applied magnetic field, so that a measurement system with a high dynamic range is required.
We start with a short overview of the first demonstration experiment of CIFT [1]. In a cylindrical vessel filled with GaInSn a propeller generates a three dimensional flow structure with a maximum velocity of 1 m/s. The flow induced magnetic field is about 3 orders of magnitude smaller than the applied magnetic field.
One promising application for CIFT is the continuous casting of steel in which the flow structure in the mould is very important for the quality of the produced steel. For a model of a continuous slab caster operated with GaInSn we developed a measurement system consisting of one excitation coil around the mould and 14 magnetic field sensors [2]. In this industrially relevant setup the flow induced magnetic field is about 4 orders of magnitude smaller than the applied magnetic field. We were able to reconstruct different flow transitions in the mould in case that Argon was injected into the submerged entry nozzle (SEN) [3], and various effects of an electromagnetic stirrer at the SEN on the flow in the mould [3]. Recent developments concerned the reconstruction of the flow in the mould in the presence of a strong static magnetic field. Additionally, we show preliminary measurements at a modified Rayleigh-Bénard setup operated with GaInSn demonstrating the applicability of CIFT for thermally driven convection systems with velocities in the order of 0.01 m/s. Typical features of the thermally driven turbulent flow could be detected in the magnetic field measurements and were verified by simultaneous temperature measurements recorded by small thermocouples.

References
1. F. Stefani et al., Physical Review E, 70 (2004), 056306
2. T. Wondrak et al., Measurement Science & Technology 21 (2010), 045402
3. T. Wondrak et al., Metallurgical and Materials Transactions B 42 (2011), 1201-1210

We study the effects of electrically conducting walls on the interaction between a permanent magnet and a liquid-metal flow in a cylindrical pipe using experiments and numerical simulation. The problem is motivated by Lorentz force velocimetry, where the drag force on the magnet due to the induced eddy currents in the flow is used for flow measurement. Compared with insulating walls, the conducting walls lead to an increased drag force on the magnet. Except for low distances, the experimental results are satisfactorily reproduced in simulations using two different approximations of the magnetic field distribution.

The late Mesoproterozoic Giles Complex of the West Musgrave province hosts one of the largest concentrations of mafic-ultramafic layered intrusions on Earth. Therefore, the area is highly prospective for hosting significant Ni-Cu and platinum-group element (PGE) mineralization, especially following the discovery of a large magmatic sulfide deposit at Nebo-Babel in 2000. More recently, a significant occurrence of massive to disseminated sulfide mineralization reaching up to 0.62 wt % Cu, 0.47 wt % Ni, and 1 ppm Pt + Pd was identified at the Manchego prospect. The magmatic sulfide mineralization at Manchego is hosted by a range of gabbronoritic rock types situated below a linear magnetic anomaly interpreted to be a magnetite layer belonging to the layered mafic-ultramafic Jameson Range intrusion, which predates the Manchego intrusion. The principal ore minerals comprise massive to disseminated pyrrhotite, chalcopyrite, pentlandite, magnetite, and ilmenite. The presence of several geochemically distinct gabbronoritic lithotypes and an abundance of xenoliths strongly indicate a dynamic magmatic plumbing system, such as a conduit-type environment. Whole-rock samples of sulfide-rich gabbronoritic lithologies have δ34S values ranging from -11.8 to -8.4%, which clearly demonstrates the addition of crustal sulfur at Manchego and therefore the availability of crustal sulfur in the West Musgrave province. In comparison to Nebo-Babel, the lithologies intersected at Manchego geochemically resemble the high Ti basaltic NB-4 dikes described by Godel et al. (2011), which are compositionally distinct from the proposed parental magma for the Nebo-Babel intrusion. Therefore, the Manchego prospect provides evidence for the prospectivity of intrusions derived from high Ti basalts in the area, such as the Alcurra Dolerite. Manchego shares many genetic similarities with the Pants Lake intrusion in northern Labrador; both are situated in a magma conduit-type system and assimilated crustal sulfur. However, neither intrusion was sufficiently dynamic to allow the emplacement of chalcophile-undepleted magma pulses, which could have led to an upgrading of metals. Based on present knowledge, this very important step in the formation of economic sulfide deposits is seemingly missing at Manchego; however, exploration is at an early stage.

The Dresden Accelerator Mass Spectrometry (DREAMS) facility is designed for the measurement of ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca and ¹²⁹I [1]. The actual goal is to extend the measurement capabilities to actinides. For this purpose, a time-of-flight system was designed and is currently under construction. The system is based on a 1.5 m long flight path and thin carbon foils with Micro Channel Plates as start and stop detectors. For an optimal tuning of the system with low currents, special beam diagnostic elements are planned. In order to characterize the existing system, first measurements of actinide samples have been performed in collaboration with the ANU and ANSTO, using an ionization chamber as detector. Measurements of Pu-isotopes in the 3+ and the 5+ charge state have been conducted.

[1] S. Akhmadaliev et al., NIMB 294 (2013) 5.

Routine measurements of ³⁶Cl at the Dresden Accelerator Mass Spectrometry (DREAMS) facility have resulted in an astrophysical application: the determination of the Maxwellian averaged cross-section (MACS) of the reaction ³⁵Cl(n,γ)³⁶Cl. As ³⁵Cl acts as a neutron poison in the nucleosynthesis processes during later burning phases of stars, the reaction is important for astrophysical calculations of elemental abundances. The neutron irradiations with a quasi Maxwell Boltzmann spectrum for the production of ³⁶Cl were performed at the Karlsruhe Institute of Technology and the Soreq Applied Research Accelerator Facility. AMS measurements were performed at VERA and DREAMS and are planned at the Australian National University in 2015. Acknowledgement: Alberto Mengoni, CERN.

Running chemical reactions in monolithic structures is being considered as highly promising for intensifying industrial reaction processes. A potential pitfall of such structures is the difficulty to achieve homogeneous and well defined gas/liquid distributions patterns with economically feasible distribution mechanisms. Experimental studies on gas/liquid distribution in monoliths are often hampered by missing measurement and visualization technique to disclose the two-phase flow inside the narrow and opaque channels.
This paper presents results of a study carried out with ultrafast single-slice X-ray tomography, a novel imaging techniques , which can overcome these limitations. We investigated two-phase flow in two different types of square-channel monolith structures, one with high cell density of 400 cpsi and one with low cell density of 39 cpsi. Our study discloses in-channel flooding and draining behavior via extraction of characteristic distribution parameters, such as averaged and channel-linked liquid holdup, two-phase flow patterns and liquid maldistribution from X-ray images using advanced image processing techniques.

Computed tomography requires the solution of an inverse problem, that is, the reconstruction of an object distribution from measurement data. In hard field tomography this problem can be more specifically referred to as the reconstruction of an object distribution from its line integrals. A first solution to the mathematical problem was given by Johann Radon in 1917 long before anyone thought about computed tomography. The transformation of an object distribution into the space of its line integrals is hence today called the Radon transformation. With the development of computed tomography technology later quite powerful algorithms basing on analytic and algebraic inversion schemes for the Radon transform were developed. This chapter shall introduce the mathematical fundamentals of the forward and inverse problem of hard field computed tomography, the discretization of the problem and further discuss some distinct features and specialties of image reconstruction, such as 3D inversion approaches and concepts for limited and local tomography.

Radionuclides such as ²³⁶U and ²³⁹Pu were introduced into the environment by atmospheric nuclear weapon tests, reactor accidents (Chernobyl, Fukushima), releases from nuclear reprocessing facilities (Sellafield, La Hague), radioactive waste disposal, and accidents with nuclear devices (Palomares, Thule) [1]. Accelerator Mass Spectrometry (AMS) is the most sensitive method to measure these actinides.
The DREsden AMS (DREAMS) facility is located at a 6 MV accelerator, which is shared with ion beam analytics and implantation users, preventing major modifications of the accelerator and magnetic analyzers. DREAMS was originally designed for ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca, and ¹²⁹I [2,3]. To modify the system for actinide AMS, a Time-of-Flight (TOF) beamline at the high-energy side has been installed and performance tests are on-going. Ion beam and detector simulations are performed to design a moveable ionization chamber. Especially, the detector window and anode dimensions have to be optimized. This ionization chamber will act as an energy detector of the system and its installation is planned as closely as possible to the stop detector of the TOF beamline for highest detection efficiency.
[1] Srncik et al., J. Environ. Radioact. 132 (2014) 108. [2] Akhmadaliev et al., Nucl. Instr. Meth. B. 294 (2013) 5. [3] Rugel et al., under review in Nucl. Instr. Meth. B.

Computed tomography with X-rays is widely used in medicine and non-destructive testing today. In process applications X-ray tomography is, however, until now more seldom used, which is obviously due to its high complexity and costs. Nonetheless, particularly in laboratory studies it has frequently proven its superior capability to measure multiphase flow parameters, such as local phase fractions in pipes, vessels or other process system components, with high resolution and accuracy. Most recently different technologies were presented, which allow faster tomographic imaging of flows with X-ray CT, which now opens the door for a wider application of this technique in process analysis, monitoring and control. The chapter gives a concise overview over basic principles and hardware of X-ray CT with particular respect to process applications and provides state-of-the-art examples of its application in multiphase flow analysis.

Die funktionelle Wiederherstellung geschädigter Zellen, Gewebe oder Organe ist das Hauptziel der regenerativen Medizin. Der Einsatz innovativer Biomaterialien, die mit dem Organismus positiv interagieren, gilt als besonders aussichtsreicher Ansatz zur Realisierung dieses Ziels. Aus diesem Grund sind die Entwicklung neuartiger Biomaterialkonzepte und die Verbesserung des Verständnisses der Wechselwirkungen zwischen Biomaterial und Organismus Kernthemen der aktuellen Biomaterialforschung.
Die vorliegende Arbeit wurde im Kontex des von der Helmholtz-Gemeinschaft geförderten Portfoliothemas "Technologie und Medizin - Multimodale Bildgebung zur Aufklärung des in-vivo-Verhaltens von polymeren Biomaterialien" angefertigt. Die Aufgabe der beteiligten Helmholtz-Zentren und Universitäten besteht in der Entwicklung und Optimierung multiskaliger und multimodaler Bildgebungsverfahren zur Untersuchung des Verhaltens polymerer Biomaterialien im Körper. Das Hauptaugenmerk soll dabei auf der Aufklärung der auftretenden Wechelwirkungen zwischen Biomaterial und Organismus sowie der Identifizierung der Abbauprodukte des jeweiligen Biomaterials liegen, mit dem Ziel, dessen in-vivo-Verhalten besser vorhersagen zu können und so die Entwicklungszeiten erheblich zu verkürzen.
Gegenstand der vorliegenden Arbeit war es, eine Gruppe vielversprechender polymerer Biomaterialien auf der Basis von Gelantine hinsichtlich ihrer Wechselwirkungen mit ausgewählten Zelltypen und dem gesamten Organismus eingehend zu charakterisieren. Die zu untersuchenden Gelantine-basierten Hydrogele wurden im Rahmen des oben genannten Helmholtz-Portfoliothemas von der Arbeitsgruppe um Dr. Axel Neffe am Helmholtz-Zentrum Geesthacht, Institut für Biomaterialforschung Teltow, synthetisiert sowie hinsichtlich ihrer Materialeigenschaften charakterisiert und ersten in-vitro-Experimenten mit murinen Fibroblasten und mesenchymalen Stammzellen eingesetzt. In der vorliegenden Arbeit sollte die Reaktion verschiedener humaner Zellsysteme, die Schlüsselrollen während der Gewebereaktion und Neovaskularisierung einnehmen, auf die Hydrogele und deren Abbauprodukte untersucht werden. Darüber hinaus sollte das In-vivo-Verhalten der Hydrogele in einem subkutanen Implantationsmodell in immunkompetenen Mäusen analysiert werden. Im Ergebnis sollte die vorliegende Dissertation einerseits dazu beitragen das Anwendungspotential der untersuchten Hydrogele zu beurteilen und andererseits das allgemeine Verständnis der Biomaterial-Gewebe-Interaktion zu erweitern.

Solar thermal power plants that use parabolic troughs for direct steam generation depict a commercially available technology for a renewable electricity production. The once-through operation mode is the most cost-effective approach for this type of power plant and, consequently, is mainly considered in the current research. This operation mode preheats and evaporates water and superheats steam within one continuous pipe. Hence, all mass qualities are passed along the pipe and various flow patterns are present. It is presumed that intermittent flow pattern influence the position of the mixture-vapor transition point at the end of evaporation and lead to undesired thermal stresses in the receiver pipe. In order to get an insight in the two-phase flow a numerical analysis is performed with ATHLET. This code provides a one-dimensional mass, momentum and energy balance for both phases water and steam, respectively. The applicability of ATHLET on intermittent flows is discussed and confirmed. In the result an intermittent flow is numerically determined at specific void fraction ranges in the design of the DISS test facility at the Plataforma Solar de Almería, Spain. The occurrence of these unsteady flow pattern diminishes at a pressure P > 60 bar. Furthermore, it is shown that the oscillating nature of the two-phase flow effects the position of the mixture-vapor transition point. For the validation of the numerical results an experiment with a wire-mesh sensor is designed. The obtained results deliver a substantial contribution to understand the two-phase flow behavior in the direct steam generation process.

The presentation gives an overview on the code DYN3D which is a three-dimensional core model for steady-state, dynamic and depletion calculations in reactor cores with quadratic or hexagonal fuel assembly geometry being developed by the Helmholtz-Zentrum Dresden-Rossendorf for more than 20 years. An overview on the basic DYN3D models and the available code couplings is given. The verification and validation status is shortly outlined.

Das Leben sämtlicher Orgnismen beruht auf einem vielschichtigen, feinabgestimmten System enzymatischer Reaktionen, die ein komplexes Regulationssystem erfordern. Da sich die meisten Erkrankungen auf Fehlfunktionen verschiedener Enzyme zurückführen lassen, ist es ein wichtiges Anliegen der Forschung, diese enzymatischen Prozesse zu verstehen und beeinflussen zu lernen.

Aufgrund des engen Zusammenspiels verschiedener Prozesse ist für das Verständnis der Rolle unterschiedlicher Enzyme an Krankheitsbildern wie Krebs die Beobachtung der in vivo stattfindenden Reaktionen nötig. Dafür stehen verschiedene Bildgebungsverfahren zur Verfügung. Besonders geeignet sind hierbei PET (Positronenemissionstomographie) und SPECT (single photon emission computed tomography). Beide Verfahren sind nichtinvasiv, beeinflussen den untersuchten Organismus minimal und können mit hoher Sensitivität funktionelle Informationen geben.

Die Suche nach geeigneten Targeting-Strategien und die Entwicklung problemspezifischer Tracer sind daher wichtige Schritte auf dem Weg zu einem besseren Verständnis der Prozesse, die verschiedenen Krankheitsbildern zugrunde liegen und damit auch auf dem Weg zur Heilung dieser Erkrankungen.

Alkaline complexes containing eudialyte group minerals (EGM) comprise one of the most promising sources for future rare earth element (REE) supply. The accurate quantification of the chemical composition of EGM is complicated by both mineralogical and X-ray-specific challenges. These include:

1) structural and chemical variability of EGM composition (e.g., [1-3]);
2) mutual interferences of X-ray lines from major and trace elements, in particular REEs [4];
3) the diffusive volatility of light anions as F and Cl and cations such as K and Na;
4) particular instability of EGM under the electron beam.
A novel analytical approach has been developed to account for the above-mentioned analytical challenges. Additionally, loss on ignition and differential scanning calorimetry data has been applied to constrain the content and composition of volatiles in the EGM structure. The influence of the electron beam on the structure of EGM has been explored with Raman spectroscopy. All correction for the overlapping of X-ray lines is processed offline. For comparison a subset of samples was analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry. The results demonstrate that the abovementioned parameters need to be considered and carefully optimized to perform accurate quantitative analyses on the chemical composition of EGM with the electron microprobe.

Diese Bachelorarbeit befasst sich mit der Petrographie den Seltenerdelement-Thorium-Gängen von Lemhi Pass in Idaho und Montana. Im Rahmen des Projektes sollen die Seltenerdgehalte der Gänge, über die bisher nur wenig bekannt ist, untersucht und eine Wertung der Seltenerdelement-Gehalte gegeben werden.

Bei den metamorphen Karbonaten von Sheep Creek, Montana handelt es sich ursprünglich entweder um flachmarine Sedimentite oder kabonatitische Gänge. Diese wurden durch LREE-reiche (light rare earth elements), metamorph mobilisierte Wässer wenigstens partiell vererzt. Sie stehen als linsen- bis bandförmige Strukturen mit maximal 2,40 m Mächtigkeit in Wechsellagerung mit Amphiboliten an. Diese Abfolge ist wiederum in 2,7 Ga alten und somit neoarchaischen Gneisen eingeschaltet. Die bearbeiteten Proben konnten wie folgt gruppiert werden: In Allanit-Monazit-Calcit-, allanitreiche Karbonat-Silikat-, Ankerit-Magnetit-Ilmenit-, Ankerit-Calcit-Ferrosilit-, Enstatit-Calcit- und massive Ilmenit-Magnetit-Gesteine.
Als wesentliche SEE-Minerale sind in den Marmoren Monazit und Allanit vertreten. Es sind allerdings auch andere potentiell ökonomisch relevante Minerale in Form von Ilmenit, Magnetit, Titanit, Apatit und Baryt partiell angereichert. Monazit und Allanit machen insgesamt stellenweise mehr als 80 wt-% der Gesteine aus, wobei hauptsächlich leichte Elemente angereichert sind. In den Monaziten sind 11 wt-% bis 53 wt-% an leichten SEE in Form von Cer, Lanthan und Neodym eingebaut.
Bei den Allaniten fallen die Gehalte mit insgesamt 11 wt-% bis 26 wt-% Cer, Lanthan und Neodym geringer aus. Eine Verwachsung mit radioaktiven Mineralen wie z. B. Thorit ist hier praktisch bedeutungslos.
In einer Probe sind Ilmenitgehalte von ~ 66 wt-% anzutreffen, Magnetit ist dagegen mit Massenanteilen von stets weniger als 10 wt-% nur untergeordnet anzutreffen. Selbiges gilt für Titanit mit maximal ~ 2,5 wt-% und für Apatit mit generell < 5 wt-%. Baryt ist dafür stellenweise mit bis zu ~ 17 wt-% angereichert.

CFD simulations of bubbly flow on the scale of technical equipment become feasible within the Eulerian two-fluid framework of interpenetrating continua. For practical applications suitable closure relations are required which describe the interfacial exchange processes. To facilitate predictive simulations a reference set of closure relations has been defined for bubble forces and bubble-induced turbulence including numerical values for all parameters. Models for bubble coalescence and breakup are not yet included at present due to their lacking maturity. This means that the bubble size distribution must still be estimated by other means or treated as a parameter in a sensitivity study. Using measured bubbles sizes the validity of model predictions for gas fraction, mean velocities of gas and liquid, and liquid turbulent kinetic energy have been validated over a range of conditions. These include both pipe flows and bubble columns and circular and rectangular cross sections. The bubble size is limited to the range of 1 to 10 mm and the gas fraction to at most 10 to 20 %. The present report gives a brief but complete description of the model, a few validation examples, and references for further study.

It has been shown that glasses containing silver metal nanoparticles are promising photonics materials for the fabrication of all-optical components. The resulting optical properties of the nanocomposite glasses depend on the composition and structure of the glass, as well as on the type of metal ion implanted and the experimental procedures involved. The main aim of this article was to study the influence of the conditions of the ion implantation and the composition of the glass on the formation of metal nanoparticles in such glasses.

Four various types of silicate glasses were implanted with Ag+ ions with different energy (330 keV, 1.2 MeV and 1.7 MeV), with the fluence being kept constant (1 × 1016 ions cm−2). The as-implanted samples were annealed at 600 °C for 1 h. The samples were characterised in terms of: the nucleation of metal nanoparticles (linear optical absorption), the migration of silver through the glass matrix during the implantation and post-implantation annealing (Rutherford backscattering spectroscopy), and the oxidation state of silver (photoluminescence in the visible region).

The practical development of novel optoelectronic materials with appropriate optical properties is strongly connected to the structural properties of the prepared doped structures. We present GaN layers oriented along the (0 0 0 1) crystallographic direction that have been grown by low-pressure metal–organic vapour-phase epitaxy (MOVPE) on sapphire substrates implanted with 200 keV Co+, Fe+ and Ni+ ions. The structural properties of the ion-implanted layers have been characterised by RBS-channelling and Raman spectroscopy to obtain a comprehensive insight into the structural modification of implanted GaN layers and to study the subsequent influence of annealing on crystalline-matrix recovery. Photoluminescence was measured to control the desired optical properties. The post-implantation annealing induced the structural recovery of the modified GaN layer depending on the introduced disorder level, e.g. depending on the ion implantation fluence, which was followed by structural characterisation and by the study of the surface morphology by AFM.

Applying hydrostatic pressure leads to dramatic changes in the band structure of semiconductors. In particular, it enables a continuous tuning of the bandgap energy of a given sample. Here we study ultrafast carrier dynamics in gallium arsenide (GaAs) at pressures up to 3 GPa. The optical pump-probe spectroscopy traces the nonlinear response in the vicinity of the bandgap. Thus, we are able to observe the changes in the ultrafast response caused by tuning the bandgap energy across the spectrum of the femtosecond probe pulse.
Our setup employs a femtosecond Ti:sapphire laser which provides pulses with the spectrum centered around 1.55 eV and a FWHM of ~0.1 eV. The experiment is performed in a non-collinear reflection geometry (fig. 1) where the pump and probe beams are focused by an all-reflective Schwarzschild objective to a ~5μm spot on the sample. Pressure is applied in a diamond anvil cell (DAC) with CsI used as pressure transmitting medium in order to ensure a good contact between the sample and diamond anvil. The sample studied is a semi-insulating GaAs crystal with thickness of about 50μm. The pump pulse with energy of 0.03 nJ induces changes in the optical reflectivity of the sample which is probed by the delayed weaker probe pulse.
In agreement with a previous study at ambient and low pressures, pumping induces an increase in reflectivity which decays on a timescale of hundred picoseconds and is assigned to the recombination of the photogenerated charge carriers [1]. With pressure increase, this relaxation becomes slower as shown in fig. 2. Finally, for pressures above 2 GPa, the pump-probe signal changes its sign and the relaxation components vanish completely. The nonlinear response appears only around zero pump-probe delay and probably originates from the negative real part of the thirdorder susceptibility of GaAs [2]. We interpret this phenomenon as a shifting of the bandgap energy above the excitation spectrum of our experiment. This assumption is in good agreement with the known bandgap pressure coefficient of 0.11 eV/GPa in GaAs leading to a complete transparency of the sample for pump and probe pulses at pressures above 2 GPa [3].
[1] D. G. McLean, M. G. Roe, A. I. D’Souza, P. E. Wigen, Appl. Phys. Lett. 48, 992 (1986).
[2] A. A. Said, M. Sheik-Bahae, D. J. Hagan, T. H. Wei, J. Wang, J. Young, E. W. Van Stryland, J. Opt. Soc. Am. B 9, 405 (1992).
[3] A. R. Goñi, K. Strössner, K. Syassen, M. Cardona, Phys. Rev. B 36, 1581 (1987).

Applying hydrostatic pressure leads to dramatic changes in the band structure of semiconductors. In particular, it enables continuous tuning of the bandgap energy. Thus, optical pump-probe spectroscopy under high pressures allows the study of nonlinear optical response in the vicinity of the interband resonance.
Here, we study ultrafast carrier dynamics in gallium arsenide (GaAs) at pressures up to 3 GPa. Our setup employs a femtosecond Ti:sapphire laser which provides pulses with the spectrum centered around 1.55 eV with a FWHM of ~0.1 eV. The experiment is performed in a non-collinear reflection geometry (fig. 1) where the pump and probe beams are focused by an all-reflective Schwarzschild objective to a ~5µm spot on the sample. Pressure is applied in a diamond anvil cell with CsI used as pressure transmitting medium. The studied sample is a semi-insulating GaAs crystal with thickness of about 50µm. The pump pulse with energy of 0.03 nJ induces changes in the optical reflectivity of the sample which is probed by the delayed weaker probe pulse.
In agreement with a previous study at ambient pressure, pumping induces an increase in reflectivity which decays on a timescale of hundred picoseconds and is assigned to the recombination of the photogenerated charge carriers [1]. With increasing pressure this relaxation becomes slower as demonstrated in fig. 2. Finally, for pressures above 2 GPa, the pump-probe signal changes its sign and the relaxation component vanishes completely. The nonlinear response appears only around zero pump-probe delay and its origin is attributed to the negative real part of the third-order susceptibility of GaAs [2]. We interpret this phenomenon as a shifting of the bandgap energy above the excitation spectrum of our experiment. This assignment is in good consistency with the known bandgap pressure coefficient of 0.11 eV/GPa in GaAs leading to a complete transparency of the sample for pump and probe pulses at pressures above 2 GPa [3].
In the future we plan to study the response of the photoexcited electron-hole plasma in GaAs using optical pump / THz probe spectroscopy under pressure. The all-reflective optics of our experimental setup enables us to couple coherent THz radiation pulses from the free-electron laser at the HZDR into a diamond anvil cell.
[1] D. G. McLean, M. G. Roe, A. I. D’Souza, P. E. Wigen, Appl. Phys. Lett. 48, 992 (1986).
[2] A. A. Said, M. Sheik-Bahae, D. J. Hagan, T. H. Wei, J. Wang, J. Young, E. W. Van Stryland, J. Opt. Soc. Am. B 9, 405 (1992).
[3] A. R. Goñi, K. Strössner, K. Syassen, M. Cardona, Phys. Rev. B 36, 1581 (1987).

Radially polarized beams represent an important member of the family of vector beams, in particular due to the possibility of using them to create strong and tightly focused longitudinal fields, a fundamental property that has been exploited by applications ranging from microscopy to particle acceleration. Since the properties of such a focused beam are intimately related to the Gouy phase shift, proper knowledge of its behavior is crucial. Terahertz microscopic imaging is used to extract the Gouy phase shift of the transverse and longitudinal field components of a tightly focused, radially polarized beam. Since the applied terahertz time-domain approach is capable of mapping the amplitude and phase of an electromagnetic wave in space, we are able to directly trace the evolution of the geometric phase as the wave propagates through the focus. We observe a Gouy phase shift of 2π for the transverse and of π for the longitudinal component. Our experimental procedure is universal and may be applied to determine the geometric phase of other vector beams, such as optical vortices, or even arbitrarily shaped and polarized propagating waves.

Base metals such as copper, lead, nickel, cobalt, zinc etc. form the basic crucial carrier metals for a sustainable society – the Web of Metals. This paper discusses the special and crucial role these metals have in acting as enablers in any recycling efforts as they carry and release important and vital minor elements at the heart of high-tech applications and products. Through examination of the rising needs for such carriers, this paper examines the approach and technologies which need to be considered by any producer of base metals. Attention is paid to the limits and extent of this carrier role in the typical processing of materials.
Examples of specialised technology and flowsheet needs are presented with consideration given to a “whole of chain” or Systems-Integrated Metal Production (SIMP) approach as a cornerstone of a circular economy. Also outlined are the challenges facing not only producers, but legislators who need to consider the balance between providing our societal needs with baseline technology infrastructure requirements for valuable metals extraction. In summary, the message of this paper states simply that not only is the criticality of metals important but the criticality of the infrastructure (Infrastructure Criticality) that can recover metals from complex designed “mineral” mixtures. Base metals are at the heart of a Circular Economy, therefore key enablers of the Internet-of-Metallurgical-Things.

Kreislaufwirtschaft 4.0

After a spent fuel assembly is removed from the reactor core, its decay heat production is still too large for pure conductive cooling. It is placed in a Spent Fuel Pool, where the decay heat is removed from the assembly by means of natural convection, while the pool cooling system keeps the water temperature at about 40-50°C. The fuel assemblies are typically arranged in high density racks which consist of borated steel in order to prevent criticality accidents. The rack cells are closed to the sides and force the coolant flow along the axial direction. In the event of a failure of the cooling system followed by boil-off, the water level might decrease below the top of the assemblies. Then the natural circulation path in the water phase is blocked and the dominant cooling mechanisms for the uncovered section of the fuel assemblies are the forced convection due to steam production and the solid heat conduction into the remaining water, as well as towards the upper end. The latter mechanism depends on the boundary conditions at the fuel assembly head, which are determined by the temperature and velocity field in the pool and reactor building atmosphere. Additionally, if the decay heat load of the neighboring fuel assemblies differs significantly, some heat will be exchanged in the radial direction. In the nuclear community, system codes are widely used for safety studies. They deliver fast and reliable results for the flow and heat transfer inside the fuel assemblies. But since three-dimensional convective phenomena can only be taken into account in the form of simplified assumptions, they do not entirely qualify for studies related to Spent Fuel Pools. In this work, CFD is used to study the flow field above and around the exposed storage racks in order to identify large scale convective phenomena. It is expected that the large scale flow field is dictated by the temperature field in the pool, which in turn influences the cooling of the individual fuel assemblies. These interdependencies need to be quantified as a function of the storage rack arrangement and the overall distribution of the fuel assemblies with respect to their decay heat. A porous body approach is employed for the modeling of the fuel assemblies. Best Practice Guidelines are applied as far as possible, since there is no experimental data available that allows a straightforward validation of the simulation results. In this work, the Spent Fuel Pool design of Fukushima's Unit 4 serves as a test case. A loss of coolant by boil-off is postulated, leading to partially uncovered fuel assemblies. Several pool loading strategies for a constant total decay heat load will be presented and conclusions will be drawn as to which configuration is the most favorable from a thermohydraulic standpoint.

Recently we have demonstrated anisotropic excitation and relaxation of charge carriers in graphene [1]. A near-infrared pump probe experiment with varied angle between pump and probe polarization revealed anisotropic carrier populations on a 100 fs timescale as predicted by microscopic theory. An isotropic distribution is then reached by scattering via optical phonons.
Now we perform an experiment where scattering of electrons with optical phonons is strongly suppressed. To this end a photon energy of 88 meV, i.e. far below the optical phonon energy, is applied and the sample is kept at 20 K. The experiments, where the free-electron laser FELBE was used as a source, revealed an anisotropic charge carrier distribution on timescales of up to 10 ps (cf. Fig. 1). In particular we investigate the dependence of the pump-probe signals on pump fluence. We find that the anisotropy is most pronounced for low fluences and vanishes for fluences in the µJ/cm2 range. These results, complemented by microscopic theory, give clear insights in the role of Coulomb scattering on the carrier dynamics. Due to the predominantly collinear nature of Coulomb scattering, the anisotropy at low fluences is preserved on timescales larger than the ~30 fs timescale of the thermalization due to Coulomb scattering. At high fluences, however, Coulomb scattering efficiently redistributes carriers towards an isotropic distribution.

References
[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl, Nano Lett., 14, 1504-1507, (2014)

Anisotropic carrier distribution in optically excited graphene: The role of Coulomb scattering

After the accident at the Fukushima Daiichi nuclear power plant, the safety of Spent Fuel Pools moved into the focus of nuclear safety research. For the thermo-hydraulic analysis, system- or severe accident codes are used predomenantly, although simplified assumptions have to be made for the flow paths around the storage racks and inside the reactor building. The present work uses CFD in order to investigate the large scale convective phenomena involved and to examine their influence on the cooling of the individual fuel assemblies. All relevant thermophysical phenomena are discussed together with the corresponding modeling. The Spent Fuel Pool of Fukushima’s Unit 4 with the loading at the time of the accident serves as a test case. The paper gives a first qualitative impression on the emerging flow paths for the scenario of partially as well as fully uncovered fuel assemblies. Finally an outlook is given, how CFD can help to study the safety of Spent Fuel Pools as a standalone tool or by delivering input to one-dimensional codes.

Calculations of non-equilibrium charge carrier distributions excited by polarized light indicate anisotropic occupations in momentum space. For most materials experimental insight in this anisotropy is obscured due to complex valence band structures [1]. Recently we have experimentally verified anisotropic carrier distributions and investigated their relaxation in graphene [2]. A near-infrared pump probe experiment with varying angle between pump and probe polarizations revealed anisotropic carrier populations on a 100 fs timescale as predicted by microscopic theory. An isotropic distribution is then reached by scattering via optical phonons. In graphene the Coulomb scattering, in first approximation, is restricted to collinear scattering along a line of the cone-like band structure and therefore preserves the angular orientation of the distribution.
By shifting the photon energies into the THz range (88 meV) and cooling the sample down to 20K we were now able to observe anisotropic charge carrier distributions with a lifetime as long as several picoseconds. Under these conditions scattering via optical phonons, with energies of about 200meV, is strongly suppressed. Note that the observed distribution has a very unusual character: It is completely thermalized for each k-direction pointing radially away from the Dirac point, but at the same time it is strongly anisotropic. The anisotropy is most pronounced for low pump fluences. Increasing the pump fluence from several nJ/cm² to µJ/cm² results in a transition from anisotropic to isotropic distributions. We suggest that this is associated with optical phonon scattering that is enabled at high electron temperatures. The experimental results are compared with microscopic theory that takes into account combined effects of Coulomb and carrier-phonon scattering.

References
[1] J. Rioux, J.E. Sipe, Physica E 45, 1-15 (2012)
[2] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl, Nano Lett. 14, 1504-1507 (2014)

Electronic band structure of CdSe/ZnS quantum dots under high pressures is studied using fluorescence spectroscopy. We observe a strong blue shift of about 40 meV/GPa for the emission line at 655 nm. At moderate pressures (below 3GPa) this shift is linear and it is dominated by increase of the fundamental band gap of CdSe under pressure [1,2]. In contrast to bulk CdSe where the fluorescence is quenched above 3GPa as a result of the phase transition into the rock-salt structure [3,4], the CdSe/ZnS quantum dots remain structurally stable up to 6.5GPa. This structural robustness together with the high fluorescence yield and the large pressure-induced line shift, exceeding that of bulk ruby crystals by a factor of 40, make CdSe quantum dots a promising candidate for precise pressure calibration at moderate pressures.
[1] W. Shan et al., Appl. Phys. Lett. 84, 67 (2004).
[2] B. S. Kim et al., J. Appl. Phys. 89, 8127 (2001).
[3] S. H. Tolbert and A. P. Alivisatos, J. Chem. Phys. 102, 4642 (1995).
[4] S. H. Tolbert and A. P. Alivisatos, Science 265, 373 (1994).

We demonstrate that in graphene a nonequelibrium charge carrier distribution retains its anisotropic nature on a 10 ps timescale if the photon energy is below the optical phonon energy. Recently evidence for an anisotropic carrier distribution has been found in near-infrared pump-probe experiments with varied angle between the orientation of pump and probe polarization [1]. This anisotropy vanishes after 150 fs due to electron optical-phonon scattering. Extending this study to the mid-infrared range (E_Photon = 74 meV), i.e. to energies below the optical phonon energy, allows to strongly suppress this scattering mechanism. In accord with microscopic theory, traces of an anisotropic distribution on a 10 ps timescale are found. Note that carrier-carrier scattering, acting on a 10 fs timescale, is mainly colinear and therefor preserves the anisotropic distribution on rather long timsecales.
[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl Nano Lett. 2014, 14, 1504-1507

The thermo-hydraulic analysis of Spent Fuel Pool accident scenarios is predominantly carried out using one-dimensional codes. This implies that simplified assumptions have to be made for the flow paths around the storage racks and inside the reactor building. Here, CFD is employed to investigate the convective phenomena involved and to examine their relevance for the cooling of the individual fuel assemblies, which themselves are modeled as porous bodies. The paper includes a discussion of relevant thermohydraulic aspects and the modeling on the fuel assembly scale as well as the reactor building scale. First preliminary large scale simulations are presented, using the design of Fukushima’s Unit 4 with the corresponding Spent Fuel Pool loading as a test case. A loss of coolant due to the outage of the cooling system and subsequent boil-off is assumed, leading to partially or fully uncovered fuel assemblies. The emerging flow paths are described qualitatively. This ongoing work gives an outlook how CFD can help to study the safety of Spent Fuel Pools as a standalone tool or by delivering input to one-dimensional codes.

Ion beam mechanisms present in plasma doping have been investigated by comparing SIMS measurements of Ge implants into deposited layers of As on Si wafers to planar dynamic ion beam models of the implants and SIMS analyses. Industrial devices are overcoming the limitations of lateral scaling by using the vertical direction. The same modelling approach would be valuable for interpreting 1.5D SIMS analyses of plasma doping of 3D-NAND test structures but 3D dynamic codes do not yet have all the capabilities to allow this. The required features are being developed within a static 3D code, TRI3DSTP, which has been used to qualitatively explain the good uniformity of a P plasma doping process and indicate where more quantitative explanations will be possible once the full dynamic capabilities are available.

Die Erfindung betrifft eine schaltbare Widerstandsstruktur (3) mit einem ersten elektrisch leitfähigen Kontakt (T1), einem zweiten elektrisch leitfähigen Kontakt (T2), einer ersten piezoelektrischen oder ferroelektrischen Schicht (11a) und einer zweiten piezoelektrischen oder ferroelektrischen Schicht (11b), wobei die beiden piezoelektrischen oder ferroelektrischen Schichten miteinander in körperlichem Kontakt stehen und zwischen den beiden Kontakten angeordnet sind, wobei mindestens einer der Kontakte mit der betreffenden piezoelektrischen oder ferroelektrischen Schicht einen Schottky-Kontakt bildet und wobei die zweite piezoelektrische oder ferroelektrische Schicht (11b) mit mindestens einem zusätzlichen Metall und/oder einem zusätzlichen Halbmetall als Dotand dotiert ist.

In this work an experimental study using a 1:3 scale acrylic glass model of the round bloom caster from voestalpine Stahl Donawitz GmbH is presented. The model experiment uses the eutectic alloy GaInSn at room temperature. An electromagnetic stirrer was installed at the mould producing a rotating magnetic field (RMF). The flow field inside the mould was measured using the ultrasound Doppler velocimetry (UDV). Up to 10 ultrasonic transducers were employed simultaneously in order to obtain a two-dimensional reconstruction of the flow structure. The experiment provides an extensive and valuable data base for validation of numerical methods. The application of electromagnetic fields for flow and solidification control in continuous casting will be a crucial point of our future work

At first the role of σ₁ receptors in various neurological, psychiatric and neurodegenerative disorders is discussed. In the second part, the principle of positron emission tomography (PET) is described and the known fluorinated PET tracers for labeling of σ₁ receptors are presented. The third part focuses on fluoroalkyl substituted spirocyclic PET tracers, which represent the most promising class of fluorinated PET tracers reported so far. The homologous fluoroalkyl derivatives 12-15 show high σ2 subtype (408 – 1331-fold). The enantiomers of the fluoroethyl derivative fluspidine 13 were prepared and pharmacologically characterized. Whereas the (S)-configured enantiomer (S)-13 (Ki = 2.3 nM) is 4-fold less active than the (R)-enantiomer (R)-13 (Ki = 0.57 nM), (S)-13 is metabolically more stable. The interactions of (S)-13 and (R)-13 with the σ₁ receptor were analyzed on molecular level using the 3D homology model. In an automated radiosynthesis ¹⁸F](S)-13 and [¹⁸F](R)-13 were prepared by nucleophilic substitution of the tosylates (S)-17 and (R)-17 with K[¹⁸F]F in high radiochemical yield, high radiochemical purity and short reaction time. Application of both enantiomers [¹⁸F](S)-13 and [¹⁸F](R)-13 to mice and piglets led to fast uptake into the brain, but [¹⁸F](R)-13 did not show washout from the brain indicating a quasi-irreversible binding. Both radiotracers [¹⁸F](S)-13 and [¹⁸F](R)-13 were able to label regions in the mouse and piglet brain with high σ₁ receptor density. The specific binding of the enantiomeric tracers [¹⁸F](S)-13 and [¹⁸F-13 could be replaced by the selective σ₁ ligand SA4503.

Interplanetary Dust Particles (IDPs) are small grains, a few hundred micrometers in size and mainly originated in the Asteroid Belt. During their flight to the Earth they are irradiated by GCR and SCR and ⁴¹Ca (T_1/2 = 1.03 × 10⁵) and ⁵³Mn (T_1/2 = 3.68 × 10⁶ yr) are formed.
Since there are no significant terrestrial sources for those radionuclides they can be used as a key tracer to determine the accretion rate of IDPs onto the Earth. For this project, 550 kg of snow have been collected at the Antarctic German station Kohnen to be processed to extract ⁴¹Ca and ⁵³Mn. Also the filter used will be processed to check the existence of IDPs surviving evaporation during their entry in the atmosphere. The AMS measurements will be made at the MLL in Garching, a facility with sensitivity down to 10⁻¹⁶ for ⁴¹Ca and 10^-14 for ⁵³Mn.

It is possible for a nearby supernova (SN) explosion to deposit a fraction of its ejecta on Earth. Due to the lack of significant anthropogenic and cosmogenic background, ⁶⁰Fe (T_1/2 = 2.6 Ma) is perfectly suited to serve as a radioactive tracer of recent SN events. The ratio of ⁶⁰Fe/Fe was measured in over 100 samples extracted from two sediment cores from the Eastern Equatorial Pacific. The AMS samples were produced using a carefully tuned chemical leaching technique that specifically targets fine-grained iron-oxides, such as magnetofossils.
Magnetofossils are the remains of magnetosome chains, built up by magnetotactic bacteria, which are abundantly present in our sediment, as shown by magnetic analysis and electron microscopy.
The AMS samples were measured at the GAMS setup at the Maier-Leibnitz-Laboratory in Garching, where the use of a gas-filled magnet for isobaric suppression provides a sensitivity of ⁶⁰Fe/Fe ≈ 5 x 10^-17.
Our results reveal a ⁶⁰Fe signature over a time-range of about 1.7-2.7 Ma, which is attributed to the deposition of SN debris.

Up to 80 % of the total energy budget of wastewater treatment plants is consumed by the activated sludge process. Current optimizations are mostly based on limited instrumentation for single points of measurement which cannot express the complex hydrodynamic and biochemical processes. Therefore, the ultrafast electron beam X-ray tomography system ROFEX of HZDR is used as a new measurement technique to capture the temporal evolution of the multiphase flow in the opaque active sludge. A detailed study has been carried out in a vertical column of 3.5 m height at HZDR to obtain an improved understanding of the hydrodynamics of aerated sludge and an evaluation of different aerators. The target parameters are bubble size distribution, equivalent Sauter mean diameter of the bubbles, bubble rise velocity and local gas hold-up under the variation of sparger type (rubber, monolithic material), gas flow rate, rheology of the fluid (deionized water, salty water, sludge) and height in the liquid column. Therefore, in-house developed advanced image analysis algorithms were applied to the reconstructed tomographic images, which are also presented in the paper. The experiments showed that with ROFEX reliable measurement data of opaque multiphase flows is produced and is expected to be used in further investigations for the validation of computational fluid dynamics (CFD) models. The different sparger types showed comparable hydrodynamic performance.

Calculating Debye-Scherrer diffraction patterns from polycrystalline materials under dynamic compression has been done in the Voigt (iso-strain) limit or in the Reuss (iso-stress) limit for small deviatoric stresses. These methods are appropriate for materials with low yield strength, where only small deviations from the hydrostat can be supported by the crystal structure or materials with low elastic anisotropy where the Voigt limit is valid. Here we present a method to calculate Debye-Scherrer diffraction patterns from polycrystalline samples under an arbitrary stress field. This method can calculate the strain tensor for each crystallite and can account for arbitrary sample texture and probe x-ray sources.

Particle therapy is a strongly growing field in cancer therapy. Almost 60 treatment centres are currently operating worldwide and the total number will reach more than 90 by 2017~\cite{PTCOG}. The majority of the centres uses protons to treat patients.

With the increasing importance of particle therapy, the development of application-specific monitoring systems has received a significant boost. On the one side, there are the radio-protection questions like the secondary dose to patients or to radio-sensitive equipment. On the other side, there are the methods that intend to verify the correct application of the treatment dose, during or short after the treatment, like prompt-gamma-imaging or -timing, or PET. For both groups of measurements, a good understanding of the secondary radiation field is crucial.

The greatest challenge in determining the secondary radiation field comes from neutrons. The spectra of the neutrons, generated by protons of therapeutic energies, extend far beyond the specification of most commercially available dosimeters. Additionally, the generated neutron fields are spatially nonuniform and in case of passive field formation strongly dependent on the operational setting. Combined with the very limited spatial and spectral resolution of the available neutron detectors, many details of the field cannot be experimentally resolved. Therefore, a dependable measurement of the neutron field requires a detailed simulation of the neutron generation in the treatment system.

The OncoRay treatment centre at the University Hospital Carl Gustav Carus operates an IBA universal nozzle that is capable of providing both scattered and scanned proton beams. This nozzle has been modelled in detail by means of the TOPAS software~\cite{TOPAS}. TOPAS provides a text-file based interface to Geant4~\cite{Geant4} Simulation Toolkit with focus on proton therapy applications.

The talk gives an overview of the specific implementation of the IBA nozzle. It presents the predicted secondary neutron fields and discusses how these depend on the operational parameters of the nozzle. Finally the results are compared to experimental measurements.

Base metals such as copper, lead, nickel, cobalt, zinc etc. form the basic crucial carrier metals for a sustainable society – the Web of Metals. This paper discusses the special and crucial role these metals have in acting as enablers in any recycling efforts as they carry and release important and vital minor elements at the heart of high-tech applications and products. Through examination of the rising needs for such carriers, this paper examines the approach and technologies which need to be considered by any producer of base metals. Attention is paid to the limits and extent of this carrier role in the typical processing of materials. Examples of specialised technology and flowsheet needs are presented with consideration given to a “whole of chain” or Systems-Integrated Metal Production (SIMP) approach as a cornerstone of a circular economy. Also outlined are the challenges facing not only producers, but legislators who need to consider the balance between providing our societal needs with baseline technology infrastructure requirements for valuable metals extraction. In summary, the message of this paper states simply that not only is the criticality of metals important but the criticality of the infrastructure (Infrastructure Criticality) that can recover metals from complex designed “mineral” mixtures. Base metals are at the heart of a Circular Economy, therefore key enablers of the Internet-of-Metallurgical-Things.

Vanadium dioxide (VO2) is a prime example of a transition metal oxide with a sharp insulator-metal transition (IMT) at 340 K accompanied by a change of the lattice symmetry. A possibility to induce the metallic state in VO2 by electric field has attracted a lot of attention due to its potential applications in optics and high-speed electronics. However, numerous efforts to control the electronic state by applied electric bias have demonstrated that the switching mechanism is governed by resistive heating, dramatically limiting the operation speed. Recent developments in generation of high-field broadband THz transients offer an attractive way to apply extremely high electric fields on ultrashort timescales.
Here, we demonstrate an IMT in VO2 thin films driven by high-field multi-THz transients on a sub-100 fs timescale. Our broadband and phase-stable THz transients with extremely high peak electric fields of up to 17 MV/cm are generated via difference frequency mixing in a GaSe crystal. A typical excitation transient and the induced relative transmission change T/T traced by 8-fs-short near-infrared pulses are shown in Fig. 1(a). An ultrafast decrease of the transmission indicates the THz-driven switching into the metallic state, succeeded by a relatively slow relaxation on longer timescales. Besides that, the lattice dy-namics related to the coherent wave packet motion of the vanadium dimers manifests itself as an oscillation at a frequency of 5.9 THz [Fig. 1(a)]. Our experiments show that the observed non-thermal switching into a metastable metallic state is governed solely by the amplitude of the applied THz field. In contrast to resonant near-infrared excitation below the threshold fluence, no signatures of excitonic self-trapping are observed down to the lowest fluences of the THz excitation.
Our results can be understood as the generation of spatially separated charge pairs and a cooperative transition into a delocalized metallic state by THz field-induced tunneling. The total density of the delo-calized carriers proportional to the increase in optical conductivity Δσ1 at THz frequencies depicted in Fig. 1(b) shows a highly nonlinear dependence on the peak excitation field expected for a many-body tunneling process. We find good agreement with theoretical equation describing pair production in a Mott insulator and determine an electronic correlation length of 2.1 Å.

Timing jitter and power instabilities are crucial parameters which greatly reduce the applicability of accelerator driven light sources for time-resolved experiments. In this contribution we present a technique that allows achieving few 10 fs time-resolution in experiments operating at cw repetition rates of up to 100 kHz by employing high repetition rate data acquisition. The method employs a fs-level arrival time monitor based on electro-optic sampling of residual pulses from a coherent diffraction radiator and a fast THz detector allowing for pulse to pulse detection of arrival time and pump intensity. The monitor can operate at high repetition rates cw (presently up to a few 100 kHz) and low electron bunch charges (sub pC). The prototype device has been tested at the quasi CW SRF accelerator (ELBE) by performing an ultra-fast THz driven magnetization dynamics experiment. Our method has high potential to provide few fs level timing on next generation large scale X-ray photon sources based on high repetition rate electron accelerators such as LCLSII. A demonstrator aiming at operation up to 4.7 MHz is under development for the European X-FEL.

Mini 0,16T-C(T)-Proben wurden aus halben ISO-V-Proben von zwei RDB-Stählen und einem RDB-Schweißgut hergestellt und nach ASTM E1921 geprüft. Die mit diesen Proben ermittelten und auf eine Dicke von 1T (25,4 mm) umgerechneten Bruchzähigkeiten, KJc(1T), folgen dem Verlauf der Master Kurven. Mit 1T-, 0,5T-, 0,25T und 0,16T-C(T)-Proben aus RDB-Stahl 22 NiMoCr 3-7 wurden vergleichbare Referenztemperaturen T0 bestimmt. Die geringe Messkapazität, KJc(limit), der 0,16T-C(T)-Proben begrenzt das Messfenster auf einen Temperaturbereich von T0 minus 15 K bis 50 K. Die Seitkerbung der 0,16T-C(T)-Proben bewirkt eine gleichmäßigere Spannung und Verteilung der Rissinitiierungsorte über die Nettoprobendicke (Ermüdungsrissfront).

Miniature 0.16T-C(T) specimens were machined from halves of already tested ISO-V specimens of two RPV steels and one RPV multilayer weld metal. The specimens were tested according to ASTM E1921. The progression of the 1T (25.4 mm) size adjusted fracture toughness, KJc(1T) values follow the Master Curve. The T0 values determined with 1T , 0.5T-, 0.25T- and 0.16T-C(T) specimens of 22 NiMoCr 3-7 RPV steel are comparable. The small measuring capacity of the 0.16T-C(T) specimen limits the test temperature window to T0 minus 15 K to 50 K. Side grooving results in a more uniform stress and distribution of cleavage initiation sites along the net thickness (fatigue crack front).

FeCr alloys and oxide dispersion strengthened (ODS) FeCr steels are candidates for structural materials for Generation IV and fusion reactors, owing their advantageous physical and chemical properties for such applications as, e.g., resistance against oxidation, creep and radiation.
For an optimal steel composition, depending on the application, it is important to understand how alloying components and oxide additives affect the materials behaviour to irradiation. For this purpose, Fe-Cr alloys have been employed as model materials in irradiation experiments and subsequent characterization of irradiation damage. Ion implantation was demonstrated an efficient tool for simulation of radiation damage similar to that in fission/fusion power plant materials, but without any induced activation.
FeCrNiSiP samples with two Cr contents of 5 wt.% and 9 wt.% were implanted with 5 MeV Fe ions at different temperatures with a damage of 0.1 displacements per atom (dpa) and 0.5 dpa, respectively. The influence of the alloying elements on the evaluation of the damage after ion implantation was investigated for the complete FeCrNiSiP alloy and separately for each FeCr added with the single alloying elements.
Furthermore model Fe14wt.%Cr alloys and two ODS Fe14Cr steels with 0.3wt.%Y2O3 and with and without Ti and W additions were implanted at low temperature with 1 MeV Fe ions up to a high damage of 15 dpa.
A slow positron beam has been used in order to investigate the depth dependence of the ion implantation induced vacancy-type defect in the materials by single Doppler broadening (DB) measurements with positron energies from 30eV to 35keV, corresponding to a depth from 1 nm down to 3 µm. Furthermore, coincidence DB measurements at selected positron energies were applied for a more precise examination of a possible defect decoration of the open volume by alloying elements.
Slow positron beam techniques turned out to be an effective tool for the characterization of open-volume defects after ion implantation. It could be shown that a Ni addition to FeCr led to an increase of the open-volume defects after ion implantation, whereas Si or P reduced them. A minimal damage could be detected for the complete alloy FeCrNiSiP.
A lower Cr content of 5wt.% is advantageous against 9wt.% for a defect annealing during implantation at temperatures below 450 °C. At 450 °C all defects annealed out already during implantation.
The influence of Y2O3 nanoparticles on the stabilization of defects in FeCr steels could be demonstrated by DB and cDB measurements and will be discussed in detail.

Multiphase flows are omnipresent in many industrial sectors and engineering disciplines, such as petroleum and chemical engineering, nuclear engineering and thermal hydraulics, and fluid me-chanics and multiphase CFD.
Multiphase flows of gases, liquids, and/or solids are often highly dynamic and fully opaque, housed in pressurized and large vessels and thus, are hardly accessible with today’s commercial diagnostic tools and standard instrumentation. In turn, improvements in process efficiency, sustainability and safety depend on detailed insights – often at CFD-grade – at different scales.
The seminar will give an overview about recent developments in advanced multiphase flow sensors and imaging techniques for in-detail flow analyses, with a focus on measurement with high resolu-tion in space and/or time. Recently pioneered imaging techniques are the wire-mesh sensor, ultrafast X-ray tomography and high-resolution gamma-ray tomography.
In particular, the underlying principles of the techniques will be shown together with a variety of application examples, such as sand erosion in pipe flow, gas entrainment in centrifugal pumps and dispersive gas-liquid mixing in static mixers.

The effects of floating vessel motions and reactor rotation on the hydrodynamic behaviour of multiphase flows in porous media were studied. For elucidating such effects, laboratory-scale packed bed systems with co-current gas-liquid flow were subjected to different types of motion by using a hexapod ship motion simulator and a hollow shaft rotary actuator. The hydrodynamic characteristics in terms of bed overall pressure drop, liquid saturation, gas-liquid segregation, and flow regime transition was experimentally studied. A capacitance wire mesh sensor (WMS) and a compact gamma-ray tomography system (CompaCT) were positioned firmly on, respectively, the floating packed bed and the inclined rotating packed bed to visualize the two-phase flow patterns in terms of local liquid saturation distribution. The response of pressure drop, liquid saturation, and flow regime transition to the bed motions was monitored and compared to those corresponding to the static upright and 15°-inclined configurations. The results indicated that the known characteristics of the conventional trickle bed reactor cannot be transferred one to one on those of the moving reactor configurations.

In general, the critical current density, J_c, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (H_c2 and H_irr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe₂As₂ thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U₀ is going to zero at the extrapolated zero-kelvin H_irr value. The anisotropy of the critical current density J_c is both influenced by the H_c2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample.

This presentation discusses the status and the future developments of CFD-methods for multiphase flows.

The lesson 7 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of two phase flow. For low gas fractions the Euler/Euler approach with continuous liquid and dispersed gas can be applied. A populatioon balance model approach is described. Model validations and model applications are presented.

The lesson 5 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

Three user dedicated facilities of PAS are built at the Institute of Radiation Physics of HZDR. The first equipment, a mono-energetic slow positron beam with 22Na as positron source, is mainly used for depth dependent Doppler broadening spectroscopy of defects in solids. The other two facilities are driven in connection with a superconducting electron linear accelerator ELBE (Electron Linac for beams with high Brilliance and low Emittance), where the positrons are created by bremsstrahlung and pair production: the Gamma-induced positron annihilation spectroscopy (GiPS) and the pulsed mono-energetic positron beam (MePS).
After an explanation of the fundamentals of PAS, the talk will present an introduction in the set-up and functionality of these three facilities. On the basis of concrete examples the usefulness of the facilities for the investigation of open-volume defects of small size and low concentration in solids will be demonstrated.
At the end of the presentation, a short outline of the procedure for application of PAS beam time will be given.

This talk presents the main results obtained during the European project NURESAFE on CFD-modelling of a two-phase Pressurized Thermal Shock szenario. The focus is on simulations on steam-water TOPFLOW-PTS experiments.

In vielen Trennkolonnen werden Siebböden eingesetzt, bei der der Stoffaustausch zwischen Dampf- und Flüssigphase in der Sprudelschicht erfolgt. Eine ungleich-mäßige Überströmung des Bodens, z. B. aufgrund von Wölbungen oder Neigungen des Bodens sowie durch ungleichmäßige Überströmung der Wehre, kann dabei die Trennwirkung deutlich verschlechtern. Nach Bell und Solari [AIChE J., 20, 4, 688-695, 1974] kann anstatt aufwendiger Stoffanalysen anhand des Strömungsfelds der Flüssigphase auf die Trennleistung geschlossen werden.
In diesem Beitrag wird eine neue Messmethode zur Ermittlung dieses Strömungsfeldes vorgestellt. Diese basiert auf der hochaufgelösten Analyse der Wehr-zu-Wehr-Überströmung des Bodens mit einem Flüssigkeitstracer anhand eines Leitfähigkeitsgittersensors.
Aus den Tracer-Versuchen lassen sich charakteristische Strömungsparameter, wie die lokale Flüssigkeitsverweilzeit und die Wehr-zu-Wehr-Strömungsgeschwindigkeit extrahieren.
Im Rahmen der Studie wurden unterschiedliche hydraulische Belastungen und Wehranordnungen untersucht und die Überströmung visualisiert und charakterisiert.

Chemical reactors with a fixed-bed of catalyst particles are widely applied for continuous multi-phase processes in the petrochemical, chemical, and biochemical industry. However, the performance of these reactors often suffers from some drawbacks, such as high energy consumption due to high pressure drop as well as mass and heat transfer limitations. One solution is to replace particle catalysts such as tablets, spheres and cylinders with structured catalysts based on open-cell solid foams. This new structure provides large specific surface area of up to 2000 m2/m3 at high open bed porosities between 75 - 97%. As result, the pressure drop of the gas-liquid two-phase flow is comparatively low (Mohammed et al. 2013).
For the design of tubular reactors with foam packings knowledge about gas-liquid mass transfer is important. The goal of this study was to examine the volumetric gas-liquid mass transfer in dependence on operating conditions and foam pore density expressed in the unit pores per inch. The results will be compared to data from the literature for both foam packings and particle packings. The experiments were based on physical desorption and the volumetric mass transfer rates are calculated according the two-film theory by Whitman (1932). The entrance effects were eliminated by performing hydrodynamically identical tests with two different test section lengths, and using the shorter test section results for ‘subtraction’ of entrance effects from the longer test section.
The results show that the volumetric gas-liquid mass transfer coefficient rises with increasing liquid superficial velocity for all foam pore densities studied, while minor effects of the gas velocity were observed. A new correlation to predict the volumetric mass transfer coefficient is derived from the experiments. The gas-liquid mass transfer in foam packings was higher than in trickle beds and beds of rasching rings.

The performance of multiphase tubular reactors with co-current downward gas-liquid two-phase flow through catalyst packings is strongly affected by the quality of the gas-liquid distribution in the packing. Non-uniform liquid phase distributions in radial and axial direction cause partial catalyst surface wetting, lead to lower catalyst utilization in reduce the effective liquid-solid mass transfer to the catalyst surface [1].
In the recent years, solid foam catalyst packings were studied as promising replacements of randomly arranged catalyst particles [2]. In principle, the open-cell structure of the solid foams allows the liquid radial flow from one cell. However, the ability of solid foams to counterbalance liquid maldistribution and the liquid spreading behavior was not yet studies. The aim of this work is to investigate the cross-sectional liquid saturation distribution in a tubular column packed with solid foams and its effects on the liquid-solid mass transfer coefficient.
The axial evolution of the gas-liquid distribution patterns in solid foam packings of different pore densities has been experimentally studied using wire-mesh sensors installed at different axial heights. Both time-averaged cross-sectional liquid saturation patterns and liquid maldistribution factors were determined for different pre-wetting modes and distributor designs. In addition, effective liquid-solid mass transfer coefficients were determined based on a modified electrochemical limiting diffusion current method and correlated with the maldistribution.
The results indicate that a uniform initial distribution above the foam packing is the most important factor for a good wetting of the solid foam surface. Accordingly, a proper selection of an appropriate liquid distributor is essential for a successful application of catalytic active solid foams. To improve the homogeneity of the cross-sectional liquid saturation, the application of the Kan-Liquid pre-wetting procedure outperforms the Levec pre-wetting procedure most probably due to the transition from rivulet to film flow texture.
The electrochemical experiments revealed that low maldistribution favor the liquid-solid mass transfer. Furthermore, the results indicated decreasing effective liquid–solid mass transfer coefficients from upper to lower part of the tubular reactor, which can be related to the worsening liquid distribution.
The extended results on the liquid distribution and liquid-solid mass transfer will be shown at with the whole paper.

The ultra-fast electron beam X-ray computed tomography was developed during last years at HZDR and turned out to be a suitable measuring technique to get detailed information on the structure of gas-liquid interfaces. Air-water as well as steam-water experiments were done at a vertical pipe with an inner diameter of 54 mm and a test section length of about 4 m. They include co-current upward and downward flows under a wide variety of flow conditions and also some measurements for counter-current flows. In the latter case the bubble rise velocity was larger than the downward liquid velocity leading to an upward flow of bubbles and downward flow of water. Beside the tomographic reconstruction further data processing is required to obtain reliable quantitative data. A new algorithm for binarisation of the reconstructed data was developed.
The measurements were done with high frequency (between 1000 and 5000 frames per second depending on the flow conditions). In the result the instantaneous gas-liquid distributions in two horizontal planes with a distance of about 10 mm are obtained. Basing on that quantitative data like gas volume fraction distributions, average radial gas velocity profiles (basing on a cross-correlation between the two planes), bubbles size distributions and radial gas volume fraction profiles in dependence on the bubble size are obtained.
Since (in contrast to previously presented wire-mesh sensor measurements) the flow is not influenced by the measurement a bubble registered in the upstream plane can be assigned to the corresponding bubble in the downstream plane. This allows the determination of the velocity vector for each bubble. Special attention is paid to the dependency of lateral bubble velocities in dependence on the bubble sizes and the local flow conditions. Different effects are observed in upward and downward flows and will be discussed in detail.

While Computational Fluid Dynamics (CFD) is already an accepted industrial tool for single phase flows it is not yet mature for two-phase flows. For this reason the qualification of CFD for reactor safety relevant applications which involve multiphase flows is a present topic of research. At the CFD division of Helmholtz-Zentrum Dresden – Rossendorf (HZDR) hereby beside an application-oriented model development and validation also more generic investigations are done. Thus, the baseline model strategy aims on the consolidation of the CFD-modelling for multiphase to enable reliable predictions for well-defined flow pattern in future. In addition the recently developed GENTOP-concept broadens the range of applicability of CFD. Different flow morphologies including transitions between them can be considered in frame of this concept.

Time-resolved optical spectroscopy is a powerful tool for studying ultrafast dynamics of quasiparticles and phonons in strongly correlated electronic systems. In particular, this technique has been efficiently utilized for investigation of charge-density-wave (CDW) compounds.1-3 In all these studies the system has been tuned across the boundary of the CDW phase by temperature variation. However, application of external (or chemical) pressure can also lead to a suppression of a CDW state caused by an impairment of the Fermi surface nesting.4
Here, we combine femtosecond time-resolved optical spectroscopy and a diamond anvil cell technology to study the electron and lattice dynamics in tri-telluride compound CeTe3. The optical pump-probe measurements (400 nm pump and 800 nm probe wavelength, respectively) are performed on single crystals mounted inside the pressure cell. CsI has been used as a pressure transmitting medium in order to ensure a contact between the sample and the diamond anvil.
Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure. In addition, we observe an anomalous softening of a CDW amplitude mode. Our observations clearly indicate a transition into the metallic state of CeTe3 induced by the external pressure of about 4 GPa.

References
[1] J. Demsar et al., Phys. Rev. Lett. 83, 800 (1999).
[2] J. Demsar et al., Phys. Rev. B 66, 041101 (2002).
[3] R.V. Yusupov et al., Phys. Rev. Lett. 101, 246402 (2008).
[4] A. Sacchetti et al., Phys. Rev. Lett. 98, 026401 (2007).

Femtosecond pump-probe spectroscopy is an efficient tool for studying ultrafast dynamics in strongly correlated electronic systems, in particular, compounds with a charge-density-wave (CDW) order. Application of external pressure often leads to a suppression of a CDW state due to an impairment of the Fermi surface nesting.
We combine time-resolved optical spectroscopy and diamond anvil cell technology to study electron and lattice dynamics in tri-telluride compound CeTe3. Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure. These observations clearly indicate a transition into the metallic state of CeTe3 induced by the external pressure.

We discuss the lambda phi(4) model in 2- and 3-dimensional non-commutative spaces. The mapping onto a Hermitian matrix model enables its non-perturbative investigation by Monte Carlo simulations. The numerical results reveal a phase where stripe patterns dominate. In d = 3 we show that in this phase the dispersion relation is deformed in the IR regime, in agreement with the property of UV/IR mixing. This "striped phase" also occurs in d = 2. For both dimensions we provide evidence that it persists in the simultaneous limit to the continuum and to infinite volume ("Double Scaling Limit"). This implies the spontaneous breaking of translation symmetry.

The gas holdup fluctuations in a bubble column (0.15 m in ID) have been recorded by means of a conductivity wire-mesh sensor in order to extract information about the main transition velocities. These parameters are very important for bubble column design, operation and scale-up. For this purpose, the classical definition of the Shannon entropy was modified and used to identify both the onset (at Ug=0.034 m/s) of the transition flow regime and the beginning (at Ug=0.089 m/s) of the churn-turbulent flow regime. The results were compared with the Kolmogorov entropy (KE) results. A slight discrepancy was found, namely the transition velocities identified by means of the KE were shifted to somewhat higher (0.045 and 0.101 m/s) superficial gas velocities Ug.

Considering the increasing deployment of renewable energies, large-scale stationary energy storage will be a key-technology for the future. One potentially ideal grid-scale energy storage system is the liquid metal battery (LMB), consisting of a totally liquid interior. The long life time and abundant raw materials of LMBs offer a very cheap way of building batteries.

Building LMBs cheap means to make them large. Strong currents in the order of kA will drive a fluid flow, which may increase the battery's performance, or lead to a short circuit in the worst case.

A numerial model for describing the MHD fluid flow is presented and used to describe the Tayler instability, electro-vortex flow and interface instabilities in LMBs.

The dynamic bias error is a well-known effect in transmission radiometry. It appears when an object distribution, e.g. a multiphase flow, changes its constitution during the scanning process and reconstructed data, e.g. a cross-sectional image, is assumed to represent a time-average of the object distribution. In gamma-ray tomography long sampling intervals are necessary in order to obtain sufficient photon count statistics. Therefore, the measured photon count projection data is inherently time-averaged. The attenuation law gives a non-linear relation between attenuation and photon counts. Therefore, the calculation of the time-averaged attenuation from the time-averaged projection data may lead to non-negligible and systematic errors, commonly an underestimation of the real attenuation, which e.g. means an overestimation of the gas holdup in tomography images of two-phase flows.
In this work the application of a recently presented dynamic bias error correction method on time-averaged gamma-ray tomography is demonstrated. As an exemplary object we scanned a mock-up of a centrifugal pump. The suitability of this method was investigated for a generic highly turbulent two-phase flow scenario with both a virtual tomography data set as well as real measured data.

Packed bubble columns are common multiphase flow reactor types in chemical engineering. Regarding process efficiency, high mass transfer rates are desirable. Especially, periodic open cell structures (POCS) are supposed to increase the interfacial density and hence the mass transfer in multiphase reactions. At the Helmholz-Zentrum Dresden – Rossendorf an ultrafast X-ray imaging technique is used to analyze a wide range of multiphase flow scenarios. A rotating electron beam induces X-ray generation on two targets which enables to produce up to 8000 cross-sectional images per second from two measurement planes with a spatial resolution of about 1 mm. We applied this tomography system in an experimental setup including POCS. In the threedimensional tomography data sets, bubbles were identified and characterized. For different gas flow rates, we determined the axial velocities of the gas-phase, bubble size distributions, bubble aspect ratios and timeaveraged gas hold-ups. We compared these results with measurements in an unpacked-bubble column. The results show that the POCS have a significant influence on the hydrodynamics, especially regarding the interfacial area density.

To ensure the optimal outcome of proton therapy, in-vivo range verification is highly desired. Prompt gamma-ray imaging (PGI) is a possible approach for in-vivo range monitoring. For PGI dedicated detection systems, e.g. Compton cameras, are currently under investigation. The presented paper deals with substantial requirements regarding hardware and software that a Compton camera used in clinical routine has to meet. By means of GEANT4 simulations, we investigate the load on the detectors and the percentage of background expected in a realistic irradiation and we simulate gamma-ray detections, i.e. input data for the reconstruction. By reconstructing events from simulated sources of well-defined geometry, we show that large-area detectors are favourable. We determine the minimum number of valid events allowing for a statistically significant range assessment. Finally, an end-to-end test for a realistic patient scenario is presented: starting with a treatment plan, the gamma-ray emissions are calculated, the detector response is modelled, and the image reconstruction is performed. We conclude that, with respect to the achievable precision, the expected complexity, and high costs of an adequate detection system, in-vivo dosimetry with Compton cameras will hardly be realised.

Within this study we conducted experimental investigations focusing on the formation of macrosegregation in Al-7wt-%Si alloys exposed to electric current pulses (ECP) during solidification. The distribution of eutectic phase was measured on various sections of the solidified samples. The results do not show the formation of reproducible segregation pattern. This finding can be attributed to the specific pattern and the turbulent character of the flow generated by the ECP treatment, the equiaxed growth of free-moving crystals and a non-symmetric distribution of the electromagnetic force due to an uneven wetting of the electrodes. An increasing input of energy by ECP intensifies the melt flow and increases the variations of phase distribution over a longitudinal section.

New ultrafast X-ray tomography data has been obtained in a bubble column (0.1 m in ID) operated with an air-deionized water system at ambient conditions. Raw reconstructed images were treated by both the information entropy (IE) and the reconstruction entropy (RE) algorithms in order to identify the main transition velocities in a bubble column. The IE values exhibited two well-pronounced minima at Ug=0.025 m/s and Ug=0.085 m/s identifying the boundaries of the homogeneous, transition and heterogeneous regimes. The reconstruction entropy extracted from the central region of the column’s cross-section exhibited only one characteristic peak at Ug=0.03 m/s, which was attributed to the transition from the homogeneous to the heterogeneous regime. This result implies that the transition regime is non-existent in the core of the column.

The gas holdup is one of the most important parameters in the bubble column operation. Its successful prediction is important for the estimation of both the interfacial areas and the volumetric liquid-phase mass transfer coefficients. In the past several years, new imaging techniques for gas holdup measurements, such as the conductivity wire-mesh sensor as well as tomographic modalities have been used successfully for gas holdup measurements. Nedeltchev et al. (2014) have also shown that this data can be used for flow regime identification.

In this work, the gas holdup values were recorded in a small (0.15 m in ID) and a large (0.4 m in ID) bubble column equipped with perforated plate spargers (open area=1 %). A new model has been established, which predicts successfully the gas holdups in an air-deionized water system. It is based on both the theoretical and empirical evaluations of the gas-liquid interfacial areas. The correlation of Akita and Yoshida (1974) was assumed to be identical with the theoretical definition of the interfacial area. The Sauter-mean bubble diameters ds were estimated from the correlation of Wilkinson et al. (1994).

The theoretical gas holdups were corrected since the classical definition of the interfacial area is strictly valid for rigid spherical bubbles. All of our experimental conditions correspond to bubble diameters larger than 4.4×10-3 m, which means that the formed bubbles have an oblate ellipsoidal shape (Fan and Tsuchiya, 1990). It has been found that the common correction factor fc depends on both the bubble diameter (Eötvös number Eo) and the column diameter Dc (Bond number Bd). The effect of the column diameter (and Bond number) on the gas holdup should be carefully checked. As the superficial gas velocity Ug increased, the correction factors fc in the small column increased from 0.13 up to 0.25, whereas in the large column they increased from 1.33 to 2.55.

The approach is very useful since it predicts the gas holdups in the range 0.02 ≤ Ug ≤ 0.15 m/s irrespective of the prevailing flow regime. In the large column, the gas holdups were predicted with an average relative error (ARE) of 3.5 %, whereas in the small column ARE was 2.5 % (twelve gas holdup values in each column).

The identification of the boundaries of the main transition velocities in a bubble column is a very important research topic since it is related to the bubble column design and scale-up. The degrees of mixing, heat and mass transfer depend on the prevailing flow regime. In the literature hitherto, very different results (even for air-water system) about the main transition velocities Utrans have been reported. A good explanation for that is the fact that different signals (differential or absolute pressure fluctuations, bubble frequency, radioactive particle trajectories, photon counts, etc.) have been recorded and further analyzed by different methods (statistical analysis, fractal analysis, chaos analysis, etc.). The main objective of this work was to perform a comparison among the transition velocities (at different radial positions) identified by different entropies (information entropy, Kolmogorov entropy, Shannon entropy, etc.). The latter were extracted from gas holdup fluctuations recorded by a conductivity wire-mesh sensor. Recently, Nedeltchev et al. (2014) have shown that this data can be used for flow regime identification.

The data were recorded in a small (0.15 m in ID) bubble column equipped with a perforated plate gas distributor (14 holes, hole diameter: ø 4×10-3 m, open area=1 %). The local gas holdup fluctuations were measured at five different dimensionless radial positions (r/R): 0.88, 0.63, 0.39, 0.14 and 0.00. It was found that there were differences between the transition velocities identified by the information entropy (IE) and the Kolmogorov entropy (KE). The KE profile at r/R=0.88 was capable of identifying (based on a well-pronounced local minima) two Utrans values at 0.045 and 0.101 m/s. The IE profiles at the same radial position distinguished almost the same Utrans values: 0.045 and 0.112 m/s. The two transition velocities discriminate the boundaries of the three main flow regimes. Nedeltchev et al. (2014) visualized the flow patterns and documented the existence of strong gas maldistribution.

The KE profiles at r/R=0.63 revealed the existence of three Utrans values: 0.034, 0.067 and 0.124 m/s. In comparison with the wall region, at this radial position the transition regime was split into two sub-regimes. They were observed by Olmos et al. (2003). The IE profile at r/R=0.63 was difficult for interpretation due to the observed multiple local minima. However, taking into account the KE results the following three Utrans values were identified: 0.034, 0.067 and 0.112 m/s. So, only the last Utrans value was somewhat lower. Our results show that the transition is only a deviation (a sharp decrease) of a single point in the entropy profiles.

Such a detailed comparison between the IE and KE values was also performed at the other three radial positions. The IE values were derived from different initial information and compared with the Shannon entropies. Such a comparison has not been performed in the literature hitherto. We have found an effect of the radial position on the Utrans values.