Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34800 Publications

Electromagnetic Dipole Strength in 124,128,134Xe

Massarczyk, R.; Schwengner, R.; Junghans, A. R.

The electromagnetic dipole strength in several even nuclei in the chain of Xenon isotopes has been investigated at the bremsstrahlung facility of the ELBE accelerator in Dresden, Germany and at the HIγS facility in Durham, USA. The goal of these measurements is to extend the knowledge about the general behavior of the dipole strength in the energy region below the neutron separation energy under the aspect of neutron excess and nuclear deformation.

Publ.-Id: 21709

Staining on heritage building stone identified by NMR spectroscopy

Franzen, C.; Kretzschmar, J.; Franzen, C.; Weiss, S.

Brown staining on both pristine and painted sandstone surfaces is a regular problem reported from new building construction and restoration actions. During the recent restoration of the Großer Wendelstein, an impressive airy stone staircase in the castle Hartenfels in Torgau, Germany, extensive brown staining appeared in distinctive places. Due to the fact that such an incidence occurred while desalination with poultice compresses the usually extreme rare chance of sampling was possible and executed. Several chemical tests combined with Nuclear Magnetic Resonance (NMR) and Infrared (IR) spectroscopy proved humic substances as causation of the intensive staining. In the consequence restorative recommendations are drawn.

Keywords: NMR; IR-spectroscopy; staining; stone restoration; humic fulvic acid

Publ.-Id: 21708

Uptake of Selenium by delta-alumina at elevated temperatures

Franzen, C.; Bok, F.; Jordan, N.

The temperature impact on sorption processes of selenium oxyanions onto alumina was investigated.

Keywords: sorption oxyanions selenate selenite

  • Poster
    HiTAC-II Workshop; High Temperature Aqueous Chemistry, 16.04.2015, Heidelberg, Deutschland

Publ.-Id: 21706

Noise reduction of ultrasonic Doppler velocimetry in liquid metal experiments with high magnetic fields

Seilmayer, M.; Stefani, F.; Gundrum, T.

The last decades have seen a number of liquid metal experiments on the interaction of magnetic fields with the flow of electrically conducting fluids. The opaqueness of liquid metals requires non-optical methods for inferring the velocity structure of the flow. Quite often, such experiments are carried out in the presence of high electrical currents to generate the necessary magnetic fields. Depending on the specific purpose, these currents can reach several kiloamperes. The utilized switching mode power supply can then influence seriously the measurement system by electromagnetic interference. A recent experiment on the azimuthal magnetorotational instability (AMRI) has shown that a hydrodynamically stable Taylor-Couette flow becomes unstable under the influence of a high azimuthal magnetic field. Therefor an electrical current along the axis of the experiment with up to 20 kA generates the necessary field to destabilize the flow. We present experimental results on this AMRI experiment carried out at the PROMISE facility with an enhanced power supply. For this setup, we discuss the elaborate measures that were needed to obtain a reasonable signal-to-noise ratio of the ultrasonic Doppler velocimetrie (UDV) system. In dependence on various parameter variations, some typical features of the observed instability, such as the energy content, the wavelength, and the frequency are analyzed and compared with theoretical predictions.

Keywords: Taylor-Couette flow; magnetorotational instability; noise reduction; Ultrasonic Doppler velocimetry; electromagnetic interference

Publ.-Id: 21705

Validation and verification of the coupled neutron kinetic/thermalhydraulic system code DYN3D/ATHLET

Kozmenkov, Y.; Kliem, S.; Rohde, U.

One of the most intensively developing areas in the LWR multi-physics is a coupling of different best estimate 3-D neutron kinetic (BIPR, DYN3D, KIKO3D, NEM, PARCS, etc.) and thermal hydraulic (ATHLET, CATHARE, RELAP5, etc.) codes. Resulting coupled code systems have advanced capabilities of modeling both steady-state spatial distributions of the core power and their evolutions during different kinds of reactor transients. They are also highly useful in the analyses of possible reactor instabilities. Initial steady-state core power distributions can be disturbed by changes in the reactor loop mass flow rates and/or temperatures, by relocations of the low-temperature/diluted-boron water slugs within the primary system or by movements of control rods.
The coupled code used for LWR simulations in HZDR is DYN3D/ATHLET, which includes the 3-D core neutron kinetic and thermal hydraulic model of own development – DYN3D. The paper reports major capabilities of DYN3D as well as different ways of its coupling with the thermal hydraulic code ATHLET (external, internal and parallel), but mainly focuses on the validation and verification of the coupled code DYN3D/ATHLET. In the course of DYN3D/ATHLET validation/verification nearly 20 real plant transients and dynamic benchmarks have been simulated and analysed. The LWR types covered by these tasks are: VVER-440 (Bohunice-3, Greifswald-5 and Loviisa-1 units), VVER-1000 (Balakovo-1, Balakovo-4, Kalinin-3, Kozloduy-6, Saporozhye-6 and Temelin-2 units), B&W PWR (TMI-1) and BWR/4 MK-1 (Peach Bottom-2). For each reactor unit a computational model was developed according with the benchmark specifications. The simulated tasks describe different scenarios of increasing complexity, including the transients initiated by the main steam header or main steam line breaks, switching off/on of main circulation pumps, turbine trip and generator load drop. Some of the transients are characterized by a strongly asymmetric behavior of the primary system (e.g. caused by a steam line break), and the processes of coolant mixing in the lower and upper reactor plenums as well as in the downcomer are important for these cases. The coupled code DYN3D/ATHLET models the primary coolant mixing in two ways – whether by an appropriate nodalization of the mixing area or by using two specific models for mixing in the lower plenum. The first of the lower plenum mixing models is a part of the coupling interface at the core inlet plane, while the second one is the analytical coolant mixing model developed for the downcomer and the lower plenum regions of VVER-440.
The results of DYN3D/ATHLET simulations were assessed both against available measured data and calculations performed with similar multi-physics codes. The paper includes an overview of the simulated problems and the most representative results of DYN3D/ATHLET validation/verification for all coupling modes. The obtained experience of code validation provides a better understanding of reactor transients with a strong interaction between neutron kinetics and thermal hydraulics, helping to improve computation models. This experience is also useful for the present and further activities in coupling of DYN3D with other best estimate codes, like CFX, TRANSURANUS, etc.

Publ.-Id: 21704

Experimental investigation of irregular motion impact on 4D PET based particle therapy monitoring

Tian, Y.; Stützer, K.; Enghardt, W.; Priegnitz, M.; Helmbrecht, S.; Bert, C.; Fiedler, F.

Particle therapy positron emission tomography (PT-PET) is an in vivo and non-invasive imaging technique to monitor treatment delivery in particle therapy. The inevitable patient respiratory motion during irradiation causes artefacts and inaccurate activity distribution in PET images. 4D maximum likelihood expectation maximization (4D MLEM) allows for a compensation of these effects, but has up to now been restricted to regular motion for PT-PET investigations. However, intra-fractional motion during treatment might differ from that during acquisition of the 4D-planning CT (e.g. amplitude variation, baseline drift) and, therefore, might induce inaccurate 4D PET reconstruction results. This study investigates the impact of different irregular analytical motion patterns on PT-PET imaging by means of experiments with radioactive source and irradiated moving phantoms. Three sorting methods, namely phase sorting, equal amplitude sorting and event-based amplitude sorting, were applied to manage PET list-mode data. The inuence of these sorting methods on the motion compensating algorithm has analysed. The event-based amplitude sorting presented superior performance, although the 4D PT-PET reconstructions still suffered partly from the inexact deformation specifications due to the irregular motion.

Keywords: irregular target motion; 4D PET; particle therapy; dose monitoring

Publ.-Id: 21703

Open volume defects and magnetic phase transition in Fe60Al40 transition metal aluminide

Liedke, M. O.; Anwand, W.; Bali, R.; Cornelius, S.; Butterling, M.; Trinh, T. T.; Wagner, A.; Salamon, S.; Walecki, D.; Smekhova, A.; Wende, H.; Potzger, K.

Magnetic phase transition in the Fe60Al40 transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000°C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation and Mössbauer spectroscopy. The positron annihilation spectroscopy (PAS) has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis (AIDA) that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate importance of the open volume defects onto the magnetic phase transition. No evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400-600°C) has been found, whereas higher temperatures showed an increase in the vacancy concentration.

Keywords: FeAl; transition metal aluminides; open volume defects; AIDA; SPONSOR; phase transition; annealing; XRD; CEMS; MOKE; PAS

Publ.-Id: 21702

Charged defects and defect-induced processes in nitrogen films

Savchenko, E.; Khyzhniy, I.; Uyutnov, S.; Barabashov, A.; Gumenchuk, G.; Ponomaryov, A.; Bondybey, V.

Radiation effects in solid nitrogen irradiated with an electron beam were studied with emphasis on the role of charged centers in radiation-induced phenomena. The experiments were performed employing luminescence method and activation spectroscopy techniques - spectrally resolved thermally stimulated luminescence TSL and thermally stimulated exoelectron emission. Samples were probed in depth by varying electron energy, thus discriminating radiation-induced processes in the bulk and at the surface. Spectroscopic evidence of the excited N2 * (C3Πu) molecule desorption was obtained for the first time and mechanism of the phenomenon based on recombination of electron with intrinsic charged center N4 + was proposed. The key role of N3 + center dissociative recombination in generation of N radicals is suggested.

Publ.-Id: 21701

Prompt-Gamma-Imaging für die Echtzeit-Reichweiten-Verifikation in der Protonentherapie: Auf dem Weg zur klinischen Implementierung

Barczyk, S.; Golnik, C.; Priegnitz, M.; Vander Stappen, F.; Janssens, G.; Smeets, J.; Clementel, E.; Hotoiu, L.; de Xivry, J. O.; Baumann, M.; Enghardt, W.; Fiedler, F.; Krause, M.; Prieels, D.; Pausch, G.; Richter, C.

Eine besondere Herausforderung der Protonentherapie besteht in der Unsicherheit der Protonenreichweite im Patienten und den resultierenden Unsicherheiten der Dosisverteilung. Hier bietet die Methode der Reichweiten-Verifikation anhand der protoneninduzierten Prompt-Gamma-Emission einen vielversprechenden Ansatz zur Verringerung der Unsicherheiten. Hierfür wurde ein Prototyp einer Prompt-Gamma-Kamera von der Firma IBA entwickelt und für die zukünftige klinische Anwendung an der Dresdner Protonentherapieanlage installiert. In Zusammenarbeit mit IBA erfolgte die umfangreiche Charakterisierung und Vorbereitung der Kamera für die klinische Anwendung. Dies beinhaltete die Hardware- und Softwareentwicklung, Kalibrierung und Qualitätssicherung sowie die Erprobung am Phantom für unterschiedliche Bestrahlungsmodalitäten.

  • Lecture (Conference)
    21. Jahrestagung der DEGRO, 25.-28.06.2015, Hamburg, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 191(2015)1, S35-S36
    DOI: 10.1007/s00066-015-0847-x

Publ.-Id: 21700

Micro-focused Brillouin light scattering: imaging spin waves at the nanoscale

Sebastian, T.; Schultheiss, K.; Obry, B.; Hillebrands, B.; Schultheiss, H.

Spin waves constitute an important part of research in the field of magnetization dynamics. Spin waves are the elementary excitations of the spin system in a magnetically ordered material state and magnons are their quasi particles. In the following article, we will discuss the optical method of Brillouin light scattering (BLS) spectroscopy which is a now a well established tool for the characterization of spin waves. BLS is the inelastic scattering of light from spin waves and confers several benefits: the ability to map the spin wave intensity distribution with spatial resolution and high sensitivity as well as the potential to simultaneously measure the frequency and the wave vector and, therefore, the dispersion properties.

For several decades, the field of spin waves gained huge interest by the scientific community due to its relevance regarding fundamental issues of spindynamics in the field of solid states physics. The ongoing research in recent years has put emphasis on the high potential of spin waves regarding information technology. In the emerging field of \textit{magnonics}, several concepts for a spin-wave based logic have been proposed and realized. Opposed to charge-based schemes in conventional electronics and spintronics, magnons are charge-free currents of angular momentum, and, therefore, less subject to scattering processes that lead to heating and dissipation. This fact is highlighted by the possibility to utilize spin waves as information carriers in electrically insulating materials. These developments have propelled the quest for ways and mechanisms to guide and manipulate spin-wave transport. In particular, a lot of effort is put into the miniaturization of spin-wave waveguides and the excitation of spin waves in structures with sub-micrometer dimensions.

For the further development of potential spin-wave-based devices, the ability to directly observe spin-wave propagation with spatial resolution is crucial. As an optical technique BLS does not only allow to map the spin-wave intensity in general, but it, in particular, enables the realization of sub-micron space resolution. Focusing of the laser beam to a sub-micrometer spot size can be realized by implementing a microscope objective into the optical setup. Over the last decade, this micro-focus BLS technique has become an established method for the investigation of spin waves in microstructured magnetic elements and proved its value in particular regarding magnonics.

In this article, we will discuss the basic principles of the BLS process and illustrate the experimental optical setup. Particular emphasis will be put on the implementation of the high spatial resolution of the BLS microscope and the consequences this has for the experimental realization. In addition, the outline of a computer based operation principle and automated sample positioning will be given. Owing to these improvements in ease of use as well as experimental applicability, the BLS technique has maintained its relevance for investigations of today's research on spin waves in miniaturized magnetic structures. A selection of experiments in this field will be described.

Keywords: Brillouin light scattering; microscopy; spin waves; magnons; magnonics

Publ.-Id: 21698

The Tayler instability in liquid metal batteries and dynamo theory

Weber, N.; Galindo, V.; Kasprzyk, C.; Landgraf, S.; Stefani, F.; Weier, T.

The Tayler instability (TI), a kink-type current-driven instability, is discussed as a crucial ingredient of an alternative α-Ω stellar dynamo model. In the framework of the Tayler-Spruit dynamo, a finite current helicity generated by the TI may produce an α-effect, transforming an azimuthal into a poloidal magnetic field. Going from astrophysics to engineering, the TI may be relevant for Liquid Metal Batteries, too. In the context of renewable energies, such batteries have recently received considerable interest for large scale energy storage. Their main advantages (cheap raw materials, long life-time, low cost) result from their simple construction. Built as a stable density stratification of two liquid metals separated by a molten salt layer, such batteries can be easily scaled up. In that case, currents in the order of a few kA will appear and possibly trigger the TI. If the resulting fluid flow becomes too strong, it may disrupt the electrolyte layer, leading to a battery failure.
A quasi-static numerical model, using an integro-differential approach for the coupling of velocity and magnetic field, is presented and used to simulate the TI in the medium to low magnetic Prandtl number range (1e−3 to 1e−6 ). The properties of the instability (growth rate, velocities in saturation), the influence of the geometric aspect ratio and scaling laws are explored. The relevance of the TI for Liquid Metal Batteries as well as several possible ountermeasures are discussed. Further, the influence of different axial boundary conditions and the interaction of TI and electro-vortex flow is analysed.
The saturation mechanism of the TI at high magnetic Prandtl numbers is commonly explained by the β-effect. We propose a second, hydrodynamic saturation mechanism for the TI at low magnetic Prandtl numbers. This allows us to explain the moderate fluid velocities, observed by Seilmayer et al. in a liquid metal TI experiment. Finally, we analyse the occurence of kinetic and current helicity at magnetic Prandtl numbers between 1e−3 and 1e−6 and show the limit of the quasi-static approximation. We finish with a description of helicity waves of the saturated TI. It’s occurence, frequency and amplitude are characterised in the astrophysical context.

Keywords: Tayler instability; Liquid Metal Battery; stellar dynamo

  • Lecture (Conference)
    Bifurcations and Instabilities in Fluid Dynamics, 15.-17.07.2015, Paris, Frankreich

Publ.-Id: 21697

Low-dimensional compounds containing cyanido groups. XXVIII. Crystal structure, spectroscopic and magnetic properties of two copper(II) tetracyanidoplatinate complexes with 1,2-diaminopropane

Vavra, M.; Potočňák, I.; Dušek, M.; Čižmár, E.; Ozerov, M.; Zvyagin, S. A.

Violet crystals of {[Cu(pn)2]2[Pt(CN)4]}[Pt(CN)4]·2H2O (1, pn=1,2-diaminopropane) and blue crystals of [Cu(pn)Pt(CN)4]n·nH2O (2) were prepared under hydrothermal conditions and characterized using elemental analysis, IR and UV–vis spectroscopy and by X-ray crystal structure analysis. Different number of ν(C≡N) absorption bands of these two compounds reflects their different structures. An X-ray crystal structure analysis has shown that complex 1 is of ionic character and is formed from trinuclear [Cu(pn)2–Pt(CN)4–Cu(pn)2]2+ complex cation and discrete [Pt(CN)4]2– anion together with two molecules of crystal water. On the other hand, complex 2 is of polymeric character and is formed by 2D networks of [Cu(pn)Pt(CN)4]n composition and completed by n molecules of crystal water. Magnetic measurements show the presence of a weak antiferromagnetic exchange interaction in complex 1 (Θ = –0.2 K), while the magnetic susceptibility of complex 2 is well described by the model of uniform S = 1/2 spin chain with exchange interaction J/kB = –1.64 K.

Publ.-Id: 21696

Laser Fluoride Nanoceramic And Method For Production Thereof / Lasertechnische, fluoridische Nanokeramika und Methode zur Herstellung

in Russian

Siebold, M.; Schramm, U.; Garibin, E. A.; Gusev, P. E.; Krutov, M. A.; Mironov, I. A.; Osiko, V. V.; Smirnov, A. N.; Tchernova, Y. V.; Hein, J.; Nietzold, D.; Pohl, H.-J.

(EN) FIELD: chemistry. SUBSTANCE: fluoride nanoceramic is obtained by thermomechanical treatment of the starting crystalline material made from CaF2-YbF3, at plastic deformation temperature to obtain a workpiece in form of a polycrystalline microstructured substance, which is characterised by crystal grain size of 3-100 mcm and a nanostructure inside the grains, by annealing on air at temperature of not less than 0.5 of the melting point with compaction of the obtained workpiece in a vacuum at pressure of 1-3 tf/cm2 until the end of the deformation process, followed by annealing in an active medium of carbon tetrafluoride at pressure of 800-1200 mmHg. The starting crystalline material used can be a fine powder which has been subjected to heat treatment in carbon tetrafluoride, or a moulded workpiece of crystalline material made from the powder and heat treated in carbon tetrafluoride. EFFECT: invention enables to obtain a fluoride nanoceramic with high degree of purity and high uniformity of the structure of said optical material. 4 cl, 3 ex

(RU) Изобретение относится к технологии получения оптических поликристаллических материалов, а именно фторидной керамики, имеющей наноразмерную структуру и усовершенствованные оптические, лазерные и генерационные характеристики. Фторидную нанокерамику получают термомеханической обработкой исходного кристаллического материала, выполненного из CaF2-YbF3, при температуре пластической деформации до получения заготовки в виде поликристаллического микроструктурированного вещества, характеризующегося размером зерен кристаллов 3-100 мкм и наноструктурой внутри зерен, путем отжига на воздухе при температуре не менее 0,5 от температуры плавления с уплотнением полученной заготовки в вакууме при давлении 1-3 тс/см2 до окончания процесса деформации, после чего отжигают в активной среде тетрафторида углерода при давлении 800-1200 мм рт.ст. В качестве исходного кристаллического материала могут быть использованы мелкодисперсный порошок, прошедший термообработку в тетрафториде углерода, или отформованная заготовку кристаллического материала, полученная из порошка и термообработанная в тетрафториде углерода. Изобретение позволяет получать фторидную нанокерамику высокой степени чистоты с повышенной однородностью структуры данного оптического материала. 2 н. и 2 з.п. ф-лы, 3 пр., 1 табл.

  • Patent
    RU2484187 - Erteilung 08.12.2013

Publ.-Id: 21695

Structural investigation of (U0.7Pu0.3)O2-x mixed oxides

Vigier, J.-F.; Martin, P. M.; Martel, L.; Prieur, D.; Scheinost, A. C.; Somers, J.

Uranium-plutonium mixed oxide containing 30% of PuO2 is a candidate fuel for several fast neutron and accelerator driven reactor systems. In this work, a detailed structural investigation on sol-gel synthesized stoichiometric U0.7Pu0.3O2.00 and substoichiometric U0.7Pu0.3O2-x, using X-ray diffraction (XRD), oxygen 17 magic angle spinning nuclear magnetic resonance (17O MAS-NMR) and X-ray absorption spectroscopy is described. As observed by XRD, the stoichiometric U0.7Pu0.3O2.00 is monophasic with a lattice parameter in good agreement with Vegard’s law, while the substoichiometric U0.7Pu0.3O2-x material is biphasic. 17O MAS-NMR confirmed a random distribution of metal atoms and hence an ideal solid solution behaviour for U0.7Pu0.3O2.00. X-ray absorption near-edge structure (XANES) spectroscopy showed the prevalence of plutonium (III) in U0.7Pu0.3O2-x. Extended X-ray absorption fine-structure (EXAFS) spectroscopy indicated a similar local structure around U and Pu, in agreement with the long-range order determined by XRD.

Keywords: MOX; 17O MAS-NMR; XAS; XRD; uranium; plutonium

Publ.-Id: 21694

Partikeltherapie-PET – Optimierung der Datenverarbeitung für die klinische Anwendung

Helmbrecht, S.

Die Strahlentherapie ist einer der drei Partner im interdisziplinären Feld der Onkologie. In Europa, Asien und den USA besteht zunehmend die Möglichkeit einer Therapie mit Strahlen aus geladenen Ionen anstelle von Photonen. Eine Anlage in Dresden befindet sich in der Kommissionierungsphase.
Die Ionenstrahltherapie bietet den Vorteil einer sehr konformalen Behandlung des Tumorvolumens durch die endliche Reichweite der Strahlen und ein ausgeprägtes Dosismaximum kurz vor dem Ende des Strahlpfades. Da eine Therapie in der Regel über bis zu 30 Sitzungen an verschiedenen Tagen durchgeführt wird und der Strahlweg stark von dem durchdrungenen Gewebe beeinflusst wird, sind Verfahren für eine in vivo Verifikation der Strahlapplikation wünschenswert. Eine dieser Methoden ist die Partikeltherapie–Positronen-Emissions-Tomografie (PT-PET). Sie beruht auf der Messung der vom Therapiestrahl erzeugten β+-Aktivitätsverteilung. Da eine direkte Berechnung der Dosis aus der Aktivität in lebendem Gewebe nicht möglich ist, wird die gemessene Aktivitätsverteilung mit einer berechneten Vorhersage verglichen und anschließend entschieden, ob die nächste Therapiesitzung wie geplant erfolgen kann oder Anpassungen notwendig sind. Die vorliegende Arbeit beschäftigt sich mit drei Themen aus dem Bereich der Datenverarbeitung für die PT-PET.
Im ersten Teil wird ein Algorithmus zur Bestimmung von Reichweitendifferenzen aus zwei β+- Aktivitätsverteilungen adaptiert und evaluiert. Dies geschieht zunächst anhand einer Simulationsstudie mit realen Patientendaten. Ein Ansatz für eine automatisierte Analyse der Daten lieferte keine zufriedenstellenden Ergebnisse. Daher wird ein Software-Prototyp für eine semiautomatische, assistierte Datenanalyse entwickelt. Die Evaluierung erfolgt durch Experimente mit Phantomen am 12C-Strahl.
Die erzeugte Aktivitätsverteilung wird von physiologischen Prozessen im Organismus beeinflusst.
Dies führt zu einer Entfernung von Emittern vom Ort ihrer Erzeugung und damit zu einer Verringerung der diagnostischen Wertigkeit der erfassten Verteilung. Zur Quantifizierung dieses als Washout bezeichneten Effektes existiert ein am Tierexperiment gewonnenes Modell. Dieses Modell wird im zweiten Teil der Arbeit auf reale Patientendaten angewendet. Es konnte gezeigt werden, dass das Modell grundsätzlich anwendbar ist und für die betrachtete Tumorlokalisation Schädelbasis ein Washout mit einer Halbwertszeit von (155,7±4,6) s existiert.
Die Berechnung der Vorhersage der β+-Aktivitätsverteilung kann durch übliche Monte-Carlo-Verfahren erfolgen. Dabei werden die Wechselwirkungsquerschnitte zahlreicher Reaktionskanäle benötigt. Als alternatives Verfahren wurde die Verwendung gemessener Ausbeuten (Yields) radioaktiver Nuklide in verschiedenen Referenzmaterialien vorgeschlagen. Auf Basis einer vorhandenen Datenbank dieser Yields und einer existierenden Condensed-History-Monte-Carlo-Simulation wird ein Programm zur Berechnung von Aktivitätsverteilungen auf Yieldbasis entwickelt. Mit der Methode kann die β+-Aktivitätsverteilung in Phantomen und Patienten zufriedenstellend vorhergesagt werden.
Die entwickelten Verfahren sollen einen Einsatz der PT-PET im klinischen Umfeld erleichtern und damit einen breiten Einsatz ermöglichen, um das volle Potential der Ionenstrahltherapie nutzbar zu machen.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-058 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 21693

Field-dependent de Haas-van Alphen frequencies in the non-centrosymmetric compound CrGe

Klotz, J.; Goetze, K.; Bruin, J.; Geibel, C.; Rosner, H.; Weber, K.; Schmidt, M.; Wosnitza, J.

  • Poster
    DPG Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21692

Improving material properties and performance of nuclear targets for transmutation-relevant experiments

Vascon, A.; Wiehl, N.; Runke, J.; Drebert, J.; Reich, T.; Trautmann, N.; Cremer, B.; Kögler, T.; Beyer, R.; Junghans, A. R.; Eberhardt, K.; Düllmann, C. E.

To improve the properties and performance of thin layers produced by molecular plating as targets for nuclear experiments investigations with lanthanide elements (i.e., natural Nd and 147Sm-enriched Sm) were carried out. Plating parameters like roughness of the deposition substrate, plating solvent, electrolyte concentration, and applied current density were varied. The influence of each parameter on the properties of the layers was studied by characterizing the deposits. The characterizations showed that nuclear targets perform differently depending on their layer properties. The results obtained from the investigations were applied for the quantitative preparation of homogeneous large-area (i.e., 42 cm2) 242Pu targets to be used for transmutation-relevant experiments.

Keywords: Molecular plating Improved layer properties α-Particle spectroscopy 242Pu Transmutation

Publ.-Id: 21691

Magnetfelder für die Forschung

Wosnitza, J.

Magnetfelder wirken auf bewegliche Ladungsträger und die magnetischen Freiheitsgrade eines Materials. Sie können somit das Verhalten von Materialien ebenso vielfältig beeinflussen wie z. B. Temperatur und Druck. Hohe Magnetfelder erlauben deshalb in der Physik und vielen anderen Forschungsdisziplinen grundlegende Untersuchungen der elektronischen und magnetischen Eigenschaften der Materie. So sind mehr als 15 Nobelpreise in Physik, Chemie und Medizin eng mit der Forschung in Magnetfeldern verknüpft. Nicht nur deshalb wächst die wissenschaftliche Nachfrage nach Forschungsanlagen, in denen Experimente in hohen Magnetfeldern möglich sind.

  • Book chapter
    in: Physik für Wissenschaftler und Ingenieure 7. deutsche Auflage, Berlin Heidelberg: Springer-Verlag, 2015, 978-3-642-54165-0, 904
    DOI: 10.1007/978-3-642-54166-7

Publ.-Id: 21690

Selenium uptake by cementitious materials: Effect of the redox state

Tits, J.; Rojo, H.; Scheinost, A. C.; Lothenbach, B.; Wieland, E.

Safety assessment studies for low- and intermediate level nuclear waste (L/ILW) repositories predict selenium-75 to be an important dose-determining radionuclide due to its long half-live and its presence in the anionic form resulting in weak retention by common near- and far field minerals. However, such predictions ignore the potential uptake by positively charged anion exchangers present in the cementitious near-field of a L/ILW repository, such as ettringite and hydrocalumite (AFm phases), a group of Ca, Al–layered double hydroxides.
The objective of this work is to investigate the immobilisation of Se under the alkaline and reducing conditions existing in a cement-based repository (-230mV < Eh < -750 mV, 10.0 < pH < 13.5). Under these conditions, Se(IV) and Se(-II) are the dominating redox states and the aqueous Se speciation is dominated by anionic species SeO32-, HSe2- and a series of polyselenides, mainly Se22-, Se32- and Se42-.

Keywords: Selenium; Nuclear waste; Redox; cement

  • Lecture (Conference)
    Migration 2015, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 21689

Influence of Growth Temperature on Structural, Optical, Electrical Properties and the Material Composition of RF Sputtered Zn1-xMgxO:Al Thin Films

Schurig, P.; Kramm, B.; Zhou, S.; Polity, A.; Meyer, B.

Zn1-xMgxO:Al (0.32 ≤ x ≤ 0.43) films were prepared by RF sputter deposition on c-sapphire and soda lime glass substrates with increasing growth temperatures from 298 up to 673 K. A ceramic ZnMgO:Al target was used as deposition material. The influence of the growth temperature on the structural, optical and electrical properties as well as the surface morphology and thin film composition was investigated. The grown films were all poly crystalline with a preferred out of plane orientation associated with the (002) XRD-reflection of ZnO but with a rising (111) MgO peak for higher temperatures. An increase in growth temperature results in a phase evolution from hexagonal to a mixed wurzite/rocksalt phase, a shift of the band gap to higher values as well as a rise in Mg concentration. A direct influence on surface

  • Lecture (Conference)
    2015 MRS Spring Meeting, 06.-10.04.2015, San Francisco, USA

Publ.-Id: 21688

Iron and phosphorus speciation in Fe-conditioned membrane bioreactor activated sludge

Wu, H.; Ikeda-Ohno, A.; Wang, Y.; Waite, T. D.

Iron dosing of membrane bioreactors (MBRs) is widely used as a means of meeting effluent phosphorus targets but there is limited understanding of the nature of iron and phosphorus-containing solids that are formed within the bioreactor (an important issue in view of the increasing interest in recovering phosphorus from wastewaters). In this study, bench scale MBRs were dosed with either ferrous or ferric salts and the Fe and P-containing mineral distributions in the Fe-conditioned sludges determined using X-ray absorption spectroscopy (XAS). Regardless of whether iron was dosed to the anoxic or aerobic chambers and regardless of whether ferrous (Fe(II)) or ferric (Fe(III)) iron was dosed, iron present in the minerals in the conditioned sludges was consistently in the +III oxidation state. Significant proportions of an Fe(III) mineral exhibiting very similar EXAFS spectra to strengite were present in all cases with the remaining fraction dominated by lepidocrocite in the Fe(II)-dosed case and ferrihydrite in the Fe(III)-dosed case. Approximately half the phosphorus in the activated sludge samples was present as a distinct Fe-PO4 mineral (such as strengite or an amorphous ferric hydroxyl phosphate analog) and half as phosphorus adsorbed to an iron oxyhydroxide mineral phase indicating that both co-precipitation and adsorption of phosphorus with iron contribute to removal of phosphorus from the MBR supernatant.

Keywords: Iron; Phosphor; Sulfur; Waste water treatment; Membrane Bioreactors; XAS; Speciation

Publ.-Id: 21687

Positron studies of interaction between yttrium atoms and vacancies in bcc iron with relevance for ODS nanoparticles formation

He, C. W.; Barthe, M. F.; Desgardin, P.; Akhmadaliev, S.; Behar, M.; Jomard, F.

The very high calculated binding energy of vacancy (V)-Y-sub (1.45 eV) in Fe makes it be one possible earliest formation stage of (Y, Ti, O) nanoclusters in ODS alloy. Our direct slow positrons annihilation observations are used to valid the interaction between V and Y. The pure bcc iron samples have been implanted by 1.2 MeV Y ions at three fluences from 1 x 10(14) to 3 x 10(15) cm(-2). Vacancy clusters are observed for all these three fluences. Their size and concentration decrease with Y concentration measured by using SIMS. Two hypotheses are proposed to explain the results, including the formation of complexes V-m-Y-n, and/or of precipitates Y-m-X-n (X = Y, O, etc.). In addition, vacancy clusters are detected deeper than predicted by SRIM calculation due to, at least for a part, channelling which is confirmed by Marlowe calculation and SIMS measurements.

Keywords: Nanostructured ferritic alloys; Dispersion; Metals; FE

Publ.-Id: 21686

New RP-CVD grown ultra-high performance selectively B-doped pure-Ge 20 nm QWs on (100)Si as basis material for post-Si CMOS technology

Mironov, O. A.; Hassan, A. H. A.; Uhlarz, M.; Kiatgamolchai, S.; Dobbie, A.; Morris, R. J. H.; Halpin, J. E.; Rhead, S. D.; Allred, P.; Myronov, M.; Gabani, S.; Berkutov, I. B.; Leadley, D. R.

Magnetotransport studies at low and room temperature are presented for two-dimensional hole gases (2DHG) formed in fully strained germanium (sGe) quantum wells (QW). Two designs of modulation doped heterostructure grown by reduced pressure chemical vapour deposition (RP-CVD) were used and included a normal structure (doping above the Ge channel and inverted structure (doping beneath the Ge channel). The mobility (μH) for the normal structure was measured to be 1.34×106 cm2/Vs with a sheet density (ps) of 2.9×1011 cm-2 at 1.5 K, and μH = 3970 cm2/Vs and ps ~1×1011 cm-2 for room temperature, determined from simulation using the Maximum Entropy- Mobility Spectrum Analysis (ME-MSA) method.
For the inverted structure a μH of 4.96×105 cm2/Vs and ps of 5.25×1011 cm-2 was measured at 90 mK. From the temperature dependent amplitude of Shubnikov de Haas oscillations, the normal structure was found to have a very low effective mass (m*) value of 0.063 m0 and a ratio of transport to quantum lifetime (α) of ~78. This extremely high α is indicative of the carrier transport being dominated by small angle scattering from remote impurities i.e. a sample having an extremely low background impurity level and very smooth hetero-interfaces. The inverted structure had an m* of 0.069 m0 and α ~29, which also indicates exceedingly high quality material.

Keywords: pure strained Ge channel; ultra-high mobility; SdH oscillation; impurity scattering

Publ.-Id: 21685

Bi2Se3Q-switched Nd:YAG ceramic waveguide laser

Tan, Y.; Zhang, H.; Zhao, C.; Akhmadaliev, S.; Zhou, S.; Chen, F.

Using a topological insulator (TI) Bi2Se3 as a saturable absorber, highly stable Q-switched laser pulses were realized in an Nd:YAG ceramic waveguide fabricated by carbon ion irradiation. The laser operation was at a wavelength of 1064 nm, with a repetition rate ranging from 2.7 to 4.7 MHz. The minimum pulsed duration was 46 ns. The maximum output power was up to 168.6 mW corresponding to the pulse energy of 31.3 nJ. This work opens up a practical way for implementation of TI modulated pulsed laser devices in dielectric waveguide platforms.

Keywords: Integrated optics; Lasers; Q-switched; Waveguides; Ion irradiation

Publ.-Id: 21684

Visualization of Heterogeneous Diffusion Processes with PET aligned with 3D FE simulation results

Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Schikora, J.; Gerasch, R.; Lippmann-Pipke, J.

Positron-Emission-Tomography (PET) provides directly the spatial distribution of tracer concentrations with ultimate sensitivity and thus is particularly suited for visualizing the propagation of chemical species in opaque media (Kulenkampff et al. 2013). The method of sequential PET-imaging of the tracer distribution for quantifying diffusion parameters of heterogeneous opaque materials overcomes fundamental problems of common analytical methods, which either are destructive or without spatial resolution. However, these parameters are crucial for the safety analysis of geologic waste repositories in clay (Van Loon et al. 2004), for instance.
We apply longer-living nuclides than in common clinical PET-applications, like 58Co (T1/2=70.86 d) and 22Na (T1/2=2.603 a), and we have to consider the higher density of our specimens, which causes significant attenuation and scattering of photon radiation. These attenuation and scattering effects of the material, as well as the effects of parasitic gamma-radiation of the non-standard PET-nuclides have been quantified with Monte-Carlo-Simulations and are corrected (Zakhnini et al. 2013).
For instance, Opalinus clay rock cores were charged with solutions labelled with the PET-nuclide, and then the tracer distribution was sequentially imaged with PET (Kulenkampff et al. 2015). We aligned the 4D data set with FE simulation results (Comsol Multiphyiscs) and obtained the anisotropic diffusion coefficients. The residuals from the optimized model are attributed to structural inhomogeneities and heterogeneous composition.

Keywords: Diffusion; positron-emission-tomography; tracer

  • Lecture (Conference)
    7th International Symposium on Prcess Tomography, 01.-03.09.2015, Dresden, Deutschland

Publ.-Id: 21683

The Rossendorf Beamline at ESRF – dedicated to investigate radionuclides with X-ray absorption spectroscopy

Hennig, C.

Overwiew about research activities at the Rossendorf Beamline/Grenoble.

Keywords: EXAFS; XRD; Actinides

  • Lecture (others)
    Laboratoire d'Electrochimie et de Physicochimie des Matériaux et des Interfaces, CNRS, Grenoble, 13.02.2015, Grenoble, France

Publ.-Id: 21682

Uranium and uranyl luminescence in agate/chalcedony

Götze, J.; Gaft, M.; Möckel, R.

A systematic investigation of agates from occurrences around the world revealed that macrocrystalline quartz and chalcedony of these samples have unusual high U content. The content of U in agates may reach more than 70 ppm and is in contrast to crystalline quartz from magmatic and metamorphic rocks as well as pegmatite quartz which have U concentrations in the sub-ppm level. Spatially resolved trace-element analyses by LA-ICP-MS illustrate that the distribution of U within the agate samples is heterogeneous and is related to the structural banding. The results indicate that U is incorporated as uranyl ion which is bound to the silica surface and originates from the parallel accumulation of Si and U by alteration processes of surrounding host rocks during agate formation.
The uranyl ion is the cause for the greenish photoluminescence (PL) in agate, which can only be excited by short wavelengths (< 300 nm). The green PL is due to the electron transition from an excited level 1φ1u(1δ1u) back to the 1π3g level and is shown by a typical emission line at ca. 500 nm accompanied by several equidistant lines. These are due to the harmonic vibration of oxygen atoms along the uranyl axis. Luminescence can be detected in samples with U content down to the 1 ppm level.

Keywords: Luminescence; green PL; uranium; uranyl; agate; chalcedony; quartz

Publ.-Id: 21681

Analysis of mineral grades for geometallurgy: combined element to mineral conversion and quantitative X-ray diffraction

Parian, M.; Lamberg, P.; Möckel, R.; Rosenkranz, J.

Knowledge of the grades of valuable elements and their variation is rarely sufficient for geometallurgy. Minerals define not only the value of the deposit, but also the method of extraction and concentration. A number of methods for obtaining mineral grades were evaluated with a focus on geometallurgical applicability, precision and trueness. For geometallurgical program, the number of samples to be analyzed is huge, therefore a method for obtaining mineral grades needs to be cost-efficient, relatively fast, and reliable. Scanning electron microscopy based automated mineralogy is generally regarded as the most reliable method for analyzing mineral grades. However, the method is time demanding and expensive. Quantitative X-ray diffraction has a relatively high detection limit, 0.5%, while the method is not suitable for some base and precious metal ores, but still provides significant details on gangue mineral grades. The usage of the element to mineral conversion has been limited to simple mineralogy because the number of minerals is limited by the number of elements analyzed. This study investigates a new method for the estimation of mineral grades applicable for geometallurgy by combining both quantitative X-ray diffraction with Rietveld refinement and the element to mineral conversion method. The proposed method not only delivers the required turnover for geometallurgy, but also overcomes the shortcomings if XRD or EMC is used alone.

Publ.-Id: 21680

On the Feasibility of using Ex-core Neutron Instrumentation for Reactor State Diagnosis during Accidents

Brachem, C.; Konheiser, J.; Hampel, U.

In the case of a severe reactor accident, knowledge of the coolant level and the state of the core, including the progress of a possible core melt, would be of crucial interest. In such a scenario, the in-core instrumentation will most likely not be available. In this work, we explore the possibility of using the ex-core neutron detectors to gain information about the state of the reactor pressure vessel (RPV) inventory for a light water reactor. These detectors, which are typically implemented as ionization chambers, are located inside the biological shield and might still be operational during a severe accident. Stationary Monte Carlo calculations using the radiation transport code MCNP were performed to simulate the transport of neutrons outside the RPV and the reactions of the ionization chambers. These detector signals are computed for different model reactor states which might occur during a severe accident with core meltdown. The reactor model is based on data from a typical German Pressurized Water Reactor.
The results indicate that a change in coolant level should be detectable. Due to the core’s neutron self-shielding, deformations in the inner core region, such as the formation of a cavity, do not yield different signal rates in the ex-core neutron chambers. Changes not confined to the centre of the core, such as the relocation of corium into the lower head, re detectable by their change in the ionization chambers’ reaction rates.

Keywords: reactor accident; ex-core neutron detectors; MCNP; Pressurized Water Reactor

  • Lecture (Conference)
    23rd International Conference on Nuclear Engineering (ICONE), 17.-21.05.2015, Chiba, Japan
  • Contribution to proceedings
    23rd International Conference on Nuclear Engineering (ICONE), 17.-21.05.2015, Chiba, Japan

Publ.-Id: 21679

SRF Gun – A Candidate for Future CW Linear Accelerators

Arnold, A.

The success future continuous wave (CW) linear accelerators (LINAC) depend strongly on the development of appropriate sources. Thus, high brightness electron injectors for CW operation with megahertz pulse repetition rates and high bunch charges up to 1 nC are a hot topic of contemporary accelerator research and development. Present state-of-the-art CW photo electron sources are limited to a medium acceleration field; DC guns because of high-voltage discharge and normal conducting RF (NCRF) guns because of the dissipated power that scales with the square of the surface magnetic field (P~H²). Thus, in both cases the beam quality as well as the maximum extractable bunch charge is limited.
To get rid of these limitations the SRF gun concept is merging the well-established NCRF gun technology with the superconductivity. The resulting saving on dissipated power allows comparable high acceleration fields in continuous wave operation and thus high brightness and high average current at the same time. The talk will concentrate on the most advance electron source of this kind, the ELBE 3.5 cell SRF gun of Helmholtz-Zentrum Dresden-Rossendorf. Beside a historical classification and an overview on different design concepts, recent results as well as future challenges are discussed.

  • Lecture (others)
    Beschleunigerseminar am Institut für Kernphysik, 28.01.2015, Mainz, Deutschland

Publ.-Id: 21678

Study of the uncertainties due to position change of the PWR aeroball measurement system (AMS)

Konheiser, J.; Seidl, M.; Brachem, C.; Mueller, S.

The Aeroball measurement system (AMS) is an important in-core instrumentation in German pressurized water reactors. Therefore it is essential to know the possible uncertainties of this system. One is the lack of knowledge of the positions of balls in the guide tubes. The position changes can be up to 7 mm. Since the neutron flux distribution is not constant across the guide tubes, different reaction rates can result from the displacements. Both fuel assembly and full core calculations were carried out with the Monte Carlo code MCNP5. Differences in the reaction rates of up to 2% could be determined. In the most cases, differences are only up to 0.5%. The results were hardly influenced by burnup and boron concentration in the water moderator. For fuel assemblies containing gadolinium as a burnable poison a more pronounced reduction could be observed in the direction towards the gadolinium fuel rods. Overall it was found that the AMS measurement values are very robust with regard to possible variations of ball positions.

Keywords: PWR; Aeroball measurement system (AMS); uncertainty; Monte Carlo caculation

Publ.-Id: 21677

U(VI) retention by montmorillonite at high salinities: Surface complexation modeling

Fritsch, K.; Schmeide, K.

Argillaceous rock is one option for hosting radioactive waste repositories in deep geological formations in Germany. Furthermore, clays are considered as backfill material in a variety of nuclear repository types. While South German clay deposits have ionic strengths below 0.5 mol kg-1, the ionic strengths found in North German clay deposits can be as high as 4.5 mol kg-1. Radionuclide retention by clays at such high ionic strengths is rarely investigated and therefore dealt with in the present work.
Montmorillonite serves as model clay in uranium sorption experiments. NaCl is used as background electrolyte. The sorption data generated in the experiments are then processed with surface complexation models to generate thermodynamic formation constants.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength; surface complexation modelling

  • Contribution to proceedings
    International Workshop ABC-Salt (IV) - Actinide Brine Chemistry in a Salt-Based Repository, 14.-15.04.2015, Heidelberg, Deutschland
  • Lecture (Conference)
    International Workshop ABC-Salt (IV) - Actinide Brine Chemistry in a Salt-Based Repository., 14.-15.04.2015, Heidelberg, Germany

Publ.-Id: 21675

Felsenkeller shallow-underground accelerator laboratory for nuclear astrophysics

Bemmerer, D.; Akhmadaliev, S.; Cowan, T. E.; Gohl, S.; Grieger, M.; Ilgner, C.; Junghans, A. R.; Müller, S. E.; Reinhardt, T. P.; Rimarzig, B.; Reinicke, S.; Röder, M.; Schmidt, K.; Schwengner, R.; Stöckel, K.; Szücs, T.; Takács, M. P.; Wagner, A.; Wagner, L.; Zuber, K.

Underground, low-background accelerator-based experiments are an important tool to study nu- clear reactions directly at energies relevant for astrophysical processes. This technique has been developed and proven at the 0.4 MV LUNA accelerator in the Gran Sasso laboratory in Italy, shielded from cosmic rays by 1400 m of rock. However, the nuclear reactions of helium and car- bon burning and the neutron source reactions for the astrophysical s-process require higher beam energies. The same is true for the study of solar fusion reactions. Therefore, the NuPECC long range plan for nuclear physics in Europe strongly recommends the installation of one or more higher-energy underground accelerators.
Detailed background studies have shown that the Felsenkeller shallow-underground laboratory in Dresden, with a rock overburden of 45 m, has very low background in γ -ray detectors typical for nuclear astrophysics experiments when an additional active shield is used to veto the remaining muon flux.
A used 5 MV pelletron tandem with 250 μ A upcharge current and external sputter ion source is currently being refurbished for installation in Felsenkeller. Work on an additional radio-frequency ion source on the high voltage terminal is underway. The project is fully funded, and the installa- tion of the accelerator in the Felsenkeller laboratory is expected for the near future.

Keywords: Felsenkeller; Nuclear Astrophysics; Low-background techniques; Solar fusion

  • Open Access Logo Contribution to proceedings
    Nuclei in the Cosmos XIII, 07.-11.07.2014, Debrecen, Ungarn
    Proceedings of Science 044


Publ.-Id: 21674

Development and application of computational fluid dynamics approaches within the European project THINS for the simulation of next generation nuclear power systems

Papukchiev, A.; Roelofs, F.; Shams, A.; Lecrivain, G.; Ambrosini, W.

Today computational fluid dynamics (CFD) is widely used in industrial companies, research institutes and technical safety organizations to supplement the design and analysis of diverse technical components and large systems. Such numerical programs are applied to better understand complex fluid flow and heat transfer phenomena. In the last decades there is an increasing interest in the nuclear community to utilize such advanced programs for the evaluation of different nuclear reactor safety issues, where traditional analysis tools show deficiencies. Within the FP7 European project THINS (Thermal Hydraulics of Innovative Nuclear Systems), CFD and coupled 1D-3D thermal–hydraulic simulations are being carried out. These are dedicated to the analysis of the thermal–hydraulics of gas, liquid metal and supercritical water cooled reactors. Such concepts utilize innovative fluids, which have different properties from the ones used in the current nuclear reactors. In order to improve the thermal–hydraulic predictions of their behavior, CFD development, application and validation activities are performed within THINS. This overview paper highlights some of the CFD related work within the European project.

Publ.-Id: 21673

Experimental study on the radial distribution of the main transition velocities in bubble columns

Nedeltchev, S.; Hampel, U.; Schubert, M.

The effect of the radial position on the main transition velocities in bubble columns has not been reported in the literature hitherto. In this work, the information entropies IE were extracted in a new way from local gas holdup fluctuations measured by a wire-mesh sensor at different radial positions in both small (0.15 m in ID) and large (0.4 m in ID) bubble columns. On the basis of well-defined local minima in the IE profiles, the transition velocities Utrans at the different radial positions were identified successfully. It was found that in the small column the first transition velocity Utrans,1 (corresponding to the end of the gas maldistribution regime) was somewhat lower in the center of the column as compared to the wall. In the large column, the Utrans,1 value in the center was somewhat higher than the one at the wall. The second transition velocity Utrans,2 (corresponding to the onset of the churn-turbulent regime) in the small column was slightly higher at the core of the column. In the large column, the Utrans,2 value was changing constantly from UG=0.089 m/s to 0.101 m/s and vice versa. The IE results showed that only at the fifth radial position in the small column and at the third and fourth radial positions in the large column there was a division of the transition regime into first and second transition sub-regimes.

Keywords: Bubble columns; transition velocities; information entropies; number of crossings; local gas holdup fluctuations; wire-mesh sensor

  • Open Access Logo Contribution to proceedings
    Eight International Conference On Computational and Experimental Methods in Multiphase and Complex Flow ("Multiphase Flow 2015"), 20.-22.04.2015, Valencia, Spanien
    WIT Transactions On Engineering Sciences (volume 89), Southampton (UK): WIT Press, 1743-3533, 127-138
    DOI: 10.2495/MPF150111

Publ.-Id: 21672

First test of the prompt gamma ray timing method with heterogeneous targets at a clinical proton therapy facility

Hueso Gonzalez, F.; Enghardt, W.; Fiedler, F.; Golnik, C.; Janssens, G.; Petzoldt, J.; Prieels, D.; Priegnitz, M.; Römer, K.; Smeets, J.; Vander Stappen, F.; Wagner, A.; Pausch, G.

Ion beam therapy promises enhanced tumour coverage compared to conventional radiotherapy, but particle range uncertainties significantly blunt the achievable precision. Experimental tools for range verification in real-time are not yet available in clinical routine. The prompt gamma ray timing method has been recently proposed as an alternative to collimated imaging systems. The detection times of prompt gamma rays encode essential information about the depth-dose profile thanks to the measurable transit time of ions through matter. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden - Rossendorf and IBA, the first test at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen, Germany) with several detectors and phantoms is performed. The robustness of the method against background and stability of the beam bunch time profile is explored, and the bunch time spread is characterized for different proton energies. For a beam spot with hundred million protons and a single detector, range differences of five millimetres in defined heterogeneous targets are identified by numerical comparison of the spectrum shape. For higher statistics, range shifts down to two millimetres are detectable. A proton bunch monitor, higher detector throughput and quantitative range retrieval are the upcoming steps towards a clinically applicable prototype. In conclusion, the experimental results highlight the prospects of this straightforward verification method at a clinical pencil beam and settle this novel approach as a promising alternative in the field of in vivo dosimetry.

Keywords: proton therapy; prompt gamma ray timing; range verification; in vivo dosimetry


Publ.-Id: 21671

Modélisation d’un Ecoulement Turbulent à Bulles dans un Mélangeur Statique type Kenic

Zidouni, F.; Krepper, E.; Rzehak, R.; Lucas, D.; Mataoui, A.

Des simulations numériques de l’écoulement à bulles dans un mélangeur Kenic ont été effectuées par ANSYS-CFX.14 en utilisant le modèle eulérien à deux fluides mono-dispersés. Une prédiction fiable de la structure de l'écoulement et le comportement des bulles à l'intérieur des éléments du mélangeur est l'objectif de ce travail. Le modèle résout les équations de Reynolds Navier- Stocks en régime stationnaire à trois dimensions pour la phase liquide et gazeuse. Le modèle de la turbulence SST a été considéré pour traiter l'aspect turbulent de l'écoulement. Un nouveau terme source dans les équations de la turbulence permet de considérer l'influence des bulles sur le champ turbulent de l'écoulement. Ce nouveau terme a été développé et validé précédemment pour deux cas simples d’écoulement en conduite et d’une colonne à bulles. Les résultats de la simulation sont comparés aux mesures expérimentales obtenues par la technique de tomographie à rayons X. Les paramètres les plus sensibles du modèle ont été identifiés dans cette étude. La distribution de l’air présente une agglomération importante des bulles au niveau du dernier segment du mélangeur indépendamment de la taille des bulles. Cependant on ne dispose pas de mesures de la fraction volumique d’air au niveau de cette position. Une recommandation pour investiguer expérimentalement cette région et d'autres perspectives on été dégagées dans cette étude.

Keywords: helical static mixer; dispersion; gas-liquid multiphase flow; Euler-Euler two fluid model; CFD simulation

  • Contribution to proceedings
    5ème Congrès Algérien de Mécanique, 25.-29.10.2015, El-Qued, Algerie
  • Lecture (Conference)
    5ème Congrès Algérien de Mécanique, 25.-29.10.2015, El-Qued, Algerie

Publ.-Id: 21670

Prediction method of countercurrent flow limitation in a pressurizer surge line and its evaluation for a 1/10-scale model

Murase, M.; Utanohara, Y.; Kusunoki, T.; Lucas, D.; Tomiyama, A.

The method for predicting countercurrent flow limitation (CCFL) and its uncertainty in an actual pressurizer surge line of a pressurized water reactor (PWR) using 1/10-scale air–water experimental data, one-dimensional (1D) computations, and three-dimensional (3D) numerical simulations was proposed. As one step of the prediction method, 3D numerical simulations were carried out for countercurrent air–water flows in a 1/10-scale model of the pressurizer surge line to evaluate capability of the 3D simulation method and decide uncertainty of CCFL characteristics evaluated for the 1/10-scale model. The model consisted of a vertical pipe, a vertical elbow, and a slightly inclined pipe with elbows. In the actual 1/10-scale experiment, air supplied into the lower tank flowed upward to the upper tank and water supplied into the upper tank gravitationally flowed downward to the lower tank through the pressurizer surge line. In the 3D simulation, however, water was supplied from the wall surface of the vertical pipe to avoid effects of flooding at the upper end (the 3D simulation largely underestimated falling water flow rates at the upper end). Then, the flow pattern in the slightly inclined pipe was successfully reproduced, and the simulated CCFL values for the inclination angle of θ = 0.6 deg (slope of 1/100) agreed well with the experimental CCFL data. The uncertainty among air–water experiments, 1D computations, and 3D simulations for the 1/10-scale model was dC = +- 0.015 for the CCFL constant of C = 0.50. The effects of θ (θ = 0; 1.0 deg) on CCFL characteristics were simulated and discussed.

Keywords: CCFL; CFD; PWR; surge line

  • Journal of Nuclear Engineering and Radiation Science 2(2016)3, 031021
    DOI: 10.1115/1.4033629

Publ.-Id: 21669

Interaction of anaerobic Mont Terri Opalinus Clay bacteria with plutonium(VI)

Moll, H.; Cherkouk, A.; Bernhard, G.

The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock tested for nuclear waste disposal [1]. Bacteria indigenous to such subterranean environments can affect the speciation and hence the mobility of actinides [2]. Thus various investigations [3-7] documented the manifold impact of bacteria on the speciation of plutonium.
Recently, we studied the interaction between Pu and Sporomusa sp. MT-2.99 cells at pH 6.1 with and without adding an electron donor (10 mM Na-pyruvate). This bacterium was isolated from Mont Terri Opalinus clay core samples. At pH 6.1, a moderate to strong impact of Sporomusa sp. cells on the Pu speciation was observed. In contrast to the electron donor free experiments, a clear enrichment of Pu(III) in the biomass (bioreduction) was observed in the presence of 10 mM Na-pyruvate. However, more information is necessary to understand the Pu interaction mechanism in the electron donor free experiments, i.e. the influence of biomass on the reduction of Pu(VI) in the biomass suspensions. In the present study, our focus lies on an improved understanding of the pH-dependent Pu redox chemistry in 0.1 M NaClO4 with and without Sporomusa sp. MT-2.99 cells. The pH range was extended to 3, 4, and 7.
The time-dependent Pu concentrations measured in the supernatants were successfully fitted with bi-exponential decay functions and the time-dependent Pu oxidation state distributions by using mono-exponential decay or growth functions. Redox potential measurements indicated that the cells generated reducing conditions. This ability is pH-dependent. A clear pH influence on both the amount of accumulated Pu and on the interaction process with the biomass could be proven.

The authors thank the BMWi for financial support (contract no.: 02E10618 and 02E10971), Velina Bachvarova and Sonja Selenska-Pobell for isolation and Monika Dudek for cultivation of the strain, as well as the BGR for providing the clay samples.

[1] M. Thury, P. Bossart, Eng. Geol. 52,347-359 (1999).
[2] J.R. Lloyd, G.M. Gadd, Geomicrobiol. J. 28, 383-386 (2011).
[3] P. Panak, H. Nitsche, Radiochim. Acta 89, 499-504 (2001).
[4] M.P. Neu, et al., Radiochim. Acta 93, 705-714 (2005).
[5] H. Moll, et al., Radiochim. Acta 94, 815-824 (2006).
[6] J.C. Renshaw, et al., Biogeochemisty 94, 191-196 (2009).
[7] T. Ohnuki, et al., J. Nucl. Sci. Technol. 46, 55-59 (2009).

Keywords: plutonium; bacteria; Sporomusa sp; Mont Terri Opalinus Clay; biosorption; bioreduction

  • Contribution to proceedings
    MIGRATION 2015, 13.-18.09.2015, Santa Fe, NM, USA
  • Poster
    MIGRATION 2015, 13.-18.09.2015, Santa Fe, NM, USA

Publ.-Id: 21668

Visualisation of high-tech metals in rare earth element ores using High-Speed PIXE

Ziegenrücker, R.; Buchriegler, J.; Dreßler, S.; Hanf, D.; Munnik, F.; Nowak, S.; Renno, A. D.; Scharf, O.; von Borany, J.

Contrary to popular opinion we have to accept that not every significant enrichment of rare-earth-elements (REE) in the earth’s crust is economically and ecologically exploitable. Deposits of heavy rare earth elements are of particular interest. A further critical point is the knowledge in which phases the elements of interest, ecotoxical as well as deleterious elements are concentrated. This information must be complemented by the determination of grain size and possible intergrowths of mineral phases. These are typical geometallurgical analytical tasks routinely performed by methods of automated mineralogy, like MLA or QEMSCAN. The newly established High-Speed PIXE (Particle Induced X-ray Emission) set-up at HZDR combines the capabilities of electron beam based devices with fast determination of trace elements. On the basis of qualitative studies of the distribution of REE in REE-mineralizations as well as in different REE-minerals like bastnaesite, monazite and xenotim we will prove the importance of this innovative concept for geometallurgical research.

Keywords: SLcam; HSPIXE; High-Speed PIXE; PIXE; Proton; X-Ray

  • Poster
    ANAKON 2015, 23.-26.03.2015, Graz, Österreich

Publ.-Id: 21667

Non-Thermal Induction of Conforamtional Rearrangment in Proteins by Far-Infrared Excitation

Lörincz, I. Z.; Schay, G.; Rauscher, A. A.; Kellermayer, M. S. Z.; Gensch, M.; Malnasi-Csizmadia, A.

How does a protein respond to infrared excitation? Our aim was to induce a specific non-thermal conformational change of a protein by infrared laser excitation. The fluorescence intensity of an intrinsically fluorescent protein, LSS-mOrange was monitored upon irradiation with a free electron laser at two of its IR absorption peaks (11.36/9.56 microns) and at a wavelength (9.06 microns) where the protein has no absorption. The irradiation at the absorption peaks caused a reversible fluorescence intensity increase on the sec-min timescale.

Publ.-Id: 21666

Bruchmechanische Prüfung von “Alten“ Konstruktionsstählen

Viehrig, H.-W.; Houska, M.; Stroetmann, R.; Sieber, L.; Vetter, B.; Schubert, V.

In the framework of a research project concerning the brittle fracture resistance of “old” civil steel structures, mechanical and fracture mechanics parameters are determined on specimens from such structural steels. The specimens were sampled from steel structures erected between the years 1904 and 1930. The main focus was on fracture toughness testing according to the Master Curve (MC) approach according to the test standard ASTM E1921. Except one steel all fracture toughness values followed the Master Curve description and gave valid T0 values. The dataset was characterised as inhomogeneous and the MC based evaluation approaches of the SINTAP procedure characterising the brittle fraction of a dataset had to be applied.

Keywords: brittle fracture; impact energy; fracture toughness; Master Curve

  • Contribution to proceedings
    47. Tagung DVM Arbeitskreis Bruchvorgänge und Bauteilsicherheit: Bruchmechanische Werkstoff- und Bauteilbewertung: Beanspruchungsanalyse, Prüfmethoden und Anwendungen, 10.-11.02.2015, Freiberg, Deutschland
    Proceedings der 47. Tagung DVM Arbeitskreis Bruchvorgänge und Bauteilsicherheit: Bruchmechanische Werkstoff- und Bauteilbewertung: Beanspruchungsanalyse, Prüfmethoden und Anwendungen, Berlin: DVM

Publ.-Id: 21665

Master Curve testing of reactor pressure vessel multilayer welding seams

Viehrig, H.-W.; Houska, M.; Altstadt, E.

Reactor pressure vessel (RPV) multilayer welding seams welded by submerged arc welding show an inhomogeneous welding bead structure. It raises concern whether evaluation of non-uniform material is not amenable to the statistical analysis methods on which the Master Curve approach is based. Particularly with regard to weld metal it can be expected that the cleavage fracture toughness is strongly influenced by the orientation of the Charpy size SE(B) specimen. The T L oriented SE(B) specimen (axis axial and crack propagation in circumferential direction) comprises of various welding beads along the crack front whereas in a L S specimen (axis axial and crack propagation through the thickness) the crack tip is located in one welding bead with an approximately uniform structure.
The paper summarises fracture toughness results measured on welding seams of decommissioned and non-commissioned RPVs of WWER type nuclear reactors and the non-commissioned Biblis-C RPV. Specimens of T L and T S orientation were tested. The results show, that in general the cleavage fracture toughness values, KJc-1T, follow the Master Curve description. However, the number of KJc-1T data outside the 2% and 98% tolerance bounds are more than predicted by the underlying model, which indicates non-uniform material.
There is a large variation in the evaluated through thickness T0 values of the investigated multilayer beltline welding seams. Within the sampling range of the surveillance specimens, T0 values vary with a span of 30 to about 60 K depending on the applied welding technology. The fracture toughness strongly depends on the intrinsic weld bead structure. Hence, the position of the fatigue crack tip of the pre-cracked SE(B) specimen at the multilayer welding seam is crucial and defines the cleavage fracture toughness. Modified Master Curve based evaluation procedures like the MC based approach of the SINTAP procedure were applied to get fracture toughness values which are representative for the most brittle fraction the test series.
Despite of the pronounced non-homogeneity of the micro-structure along the crack front of T L specimens, crack initiation sites are randomly distributed along the crack front. This means that one of the basic assumptions in ASTM E1921, i.e. the uniform distribution of initiation sites, is fulfilled also for the T L specimens from the multilayer weld metal.

Keywords: reactor pressure vessel; welding seam; fracture toughness; Master Curve

  • Contribution to proceedings
    ASME 2015 Pressure Vessels & Piping Conference, PVP2015, 19.-23.07.2015, Boston, USA
    Proceedings of the ASME 2015 Pressure Vessels & Piping Conference Vol. 1B, New York: ASME

Publ.-Id: 21664

Geometallurgy of iron ores

Gutzmer, J.

Geometallurgy is an emerging field of research that has the aim to quantify compositional variability of ores contained in a deposit. Relevant parameter spaces to be considered include geochemistry, mineralogy, metal deportment and microfabric. These quantitative parameters need to be integrated with macroscopic geological and technical characteristics to define so-called geometallurgical domains, i.e., portions of an ore body that will exhibit similar beneficiation characteristics. This knowledge may then be used to optimize mining schedules and beneficiation routes, to optimize resource and energy efficiency, to maximize product quality and to minimize environmental impact. The value of developing a geometallurgical model is obvious for ore bodies that are either complex and/or of low grade. Important examples include PGE and Au deposits as well polymetallic base metal deposits. In accordance there are a number of case studies for such ore deposit types readily available in literature.

Iron ore deposits are, at least at first sight, not at all complex. In the last four decades very few deposit types have dominated the global supply of iron ore. High-grade iron ore deposits hosted by Precambrian iron formations clearly dominate, as these are often able to produce a direct shipping lump ore (DSO with > 60 wt%) Fe by simple crushing, screening and desliming. In fact, these deposits form the world’s largest virtually monomineralic ore bodies, not uncommonly reaching billions of tons of ore in size. Other deposit types that contribute significantly to the worlds iron ore supply are metamorphosed iron formation deposits (often referred to as taconites), Kiruna-type magnetite-apatite deposits and Robe River-type deposits. Magnetite deposits hosted by mafic/ultramafic intrusive complexes are increasingly gaining economic significance. Common to these deposit types are high concentrations of iron (≥ 50 wt.% Fe, but note that taconite only contains about 35 wt. % Fe) and uniform ore mineralogy, with only hematite, magnetite, and goethite of any significance.

The question thus arises what value geometallurgy may add to the utilization of iron ore deposits. In fact, a number of tangible benefits are being realized by taking this approach. Ore bodies that do not produce DSO require grinding followed by magnetic separation and/or flotation. Pellets need to be produced from the concentrate in order to have a saleable product. To assure that stringent quality requirements by the customer steel mills are being met consistently requires detailed knowledge of ore and gangue mineralogy – and its spatial variability across the ore body. Variations in gangue mineralogy, in particular, will determine concentrations of deleterious elements (Si, Ti, Al, P, S and alkali elments), whereas ore mineralogy will determine the suitability of beneficiation unit operations. Even if mineral assemblages remain uniform, relative proportions and microfabric relations (e.g., mineral grain sizes, intergrowth) will determine comminution and liberation characteristics, thus determining comminution energy requirements.

Keywords: geometallurgy; iron ores

  • Contribution to proceedings
    The Arctic Conference Days 2014, 02.-06.06.2014, Tromso, Norway
    Abstracts and Proceedings of the Geological Survey of Norway, Trondheim: Norsk Geologisk Forening, 72-73

Publ.-Id: 21663

Complexation of f-elements with humic carriers – how dynamic is the equilibrium?

Lippold, H.; Lippmann-Pipke, J.

In the far-field of a repository, complexation with dissolved humic matter can be crucial in controlling the mobility of actinides in case of their release [1, 2]. For transport modeling, all interactions in the system metal / humic substance / solid surface are presumed to be dynamic equilibrium processes where association and dissociation run permanently. For metal-humic complexes, however, there are indications of a growing resistance to dissociation over time [3-7]. It is thus questionable whether full reversibility is actually given for this interaction. So far, the existence of a dynamic equilibrium has never been proven. In this study, the isotope exchange principle was employed to gain direct insight into the inner dynamics of the complexation equilibrium, including kinetic stabilization phenomena.

Purified humic acids were contacted with terbium(III) as an analogue of trivalent actinides. The systems contained the radioisotope 160Tb at a very small amount, whereas concentrations of non-radioactive 159Tb were varied at a high level, covering a binding isotherm up to the state of saturation. Owing to the high metal loads, flocculation of humic colloids generates a solid-liquid system where adsorbed amounts of 160Tb can be determined by radiometric analysis of the supernatant. 159Tb and 160Tb were introduced simultaneously or consecutively (159Tb followed by 160Tb or vice versa). Contact times with both isotopes were varied within a range of 3 months.

In a first series of experiments, 160Tb was contacted with humic acid that had been pre-equilibrated with 159Tb at a range of concentrations.
Adsorbed amounts of 160Tb were found to be equal to those obtained if both isotopes were introduced at the same time, i.e., the radioisotope represented the solid-liquid distribution of total Tb throughout the binding isotherm, including the plateau region where all available binding sites are occupied. Obviously, there is a permanent exchange of free and humic-bound Tb – evidence of a dynamic equilibrium. The rate of exchange was very high, regardless of how long 159Tb and humic acid had been in contact prior to the addition of 160Tb. There were no indications of stabilization processes.

Completely different results were obtained if the small amount of 160Tb (strictly, [160Tb]Tb) was added first, followed by saturation with non-radioactive 159Tb. For representing the solid-liquid distribution of total Tb in a dynamic equilibrium, the radioisotope was expected to be partly desorbed since the bound fraction of total Tb is lower in the plateau region of the binding isotherm. Desorption occurred in fact, but at much lower rates than those observed for the equilibration process in the reverse procedure. Moreover, the rates proved to be dependent on the time of pre-equilibration with 160Tb (increasing hindrance of desorption). The existence of kinetic stabilization processes was thus substantiated. Evidently, they are confined to the most reactive sites, occupied by the radiolabeled fraction of Tb.

Fitting the time-dependent course of isotope exchange according to first-order kinetics was only successful if at least two components with different rate constants were assumed, suggesting that the very small fraction of sites occupied by [160Tb]Tb (~ 1/10^6) is still only partly affected by the slow exchange kinetics (~ 1/3 slow component).
Nonetheless, this is of relevance since just such extremely low metal loads are to be considered. Extrapolating the fits indicates that it takes up to 2 years until equilibrium is attained. This is, however, a short period compared to the time scale to be covered in predictive transport models. Very low flow velocities must be taken into account.
Therefore, metal exchange between humic carriers and mineral surfaces cannot be neglected, notwithstanding the observed stabilization process since complexation is not restricted in its reversibility.

[1] K. H. Lieser et al., Radiochim. Acta 49, 83 (1990).
[2] G. R. Choppin, Radiochim. Acta 58/59, 113 (1992).
[3] L. Rao et al., Radiochim. Acta 66/67, 141 (1994).
[4] R. Artinger et al., J. Contam. Hydrol. 35, 261 (1998).
[5] S. J. King et al., Phys. Chem. Chem. Phys. 3, 2080 (2001).
[6] H. Geckeis et al., Environ. Sci. Technol. 36, 2946 (2002).
[7] H. Lippold et al., Appl. Geochem. 27, 250 (2012).

  • Poster
    MIGRATION 2015 - 15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 21661

Countercurrent flow limitation in slightly inclined pipes with elbows

Murase, M.; Kinosgita, I.; Kusunoki, T.; Lucas, D.; Tomiyama, A.

One-dimensional (1D) sensitivity computations were carried out for air-water countercurrent flows in a 1/15-scale model of the hot leg and a 1/10-scale model of the pressurizer surge line in a pressurized water reactor to generalize the prediction method for countercurrent flow limitation (CCFL) characteristics in slightly inclined pipes with elbows. In the 1D model, the wall friction coefficient fwG of single-phase gas flows was used. The interfacial drag coefficient of fi = 0.03, an appropriate adjustment factor of NwL = 6 for the wall friction coefficient fwL of single-phase liquid flows (NwG = 1 for fwG of single-phase gas flows) and an appropriate adjustment factor of Nde = 6 for the pressure loss coefficient ζe of elbows in single-phase flows were determined to give good agreement between the computed and measured CCFL characteristics. The adjusted factors were used to compute and then discuss effects of the inclination angle and diameter on CCFL characteristics.

Keywords: CCFL; inclined pipe; PWR

  • Journal of Nuclear Engineering and Radiation Science 1(2015)4, 041009
    DOI: 10.1115/1.4031032

Publ.-Id: 21660

Recycling of rare earths from fluorescent lamps: Value analysis of closing-the-loop under demand and supply uncertainties

Machacek, E.; Richter, J. L.; Habib, K.; Klossek, P.

Rare earth element (REE) recycling remains low at 1%, despite significant uncertainties related to future supply and demand and EU 2020 energy efficiency objectives. We use a global production network framework of REE flows from mine to REE phosphors in energy-efficient lamps to illustrate the potential of closed-loop recycling for secondary supply under different scenarios of primary supply and forecasted demand for LEDs, CFLs and LFLs. We find that different End-of-Life Recycling Rate scenarios for REE secondary supply range between meeting forecasted REE demand and filling primary supply gaps, and competing with primary supply. Our argument centres on diversifying REE sourcing with recycling and the choice between primary and secondary supply. We stress that secondary REE phosphor supply requires further policy support for lamp collection and a discussion of the value of REE phosphor recycling which underlies its economic feasibility.

Keywords: Energy-efficient lamps; Value chain; Recycling; Rare earth elements

Publ.-Id: 21659

Near-wall velocity measurements in the two-phase flow at a gas-evolving electrode

Baczyzmalski, D.; Weier, T.; Kähler, C. J.; Cierpka, C.

Renewable energy technologies are indispensable in order to limit the CO2 emissions while the worldwide energy demand is steadily growing. Efficient energy storage systems will be required for renewable energy sources which are not available continuously, e.g. wind and solar energy. Chemical energy storage in the form of hydrogen offers a very high energy density in contrast to other systems such as thermal or mechanical energy storage and is therefore one of the most promising candidates for a long-term energy storage. An important technique to convert electric energy from a wind turbine or solar panel into chemical energy is the electrolysis of water, where hydrogen and oxygen gas is generated. However, low efficiencies of about 60 % for typical water electrolyzers are a significant drawback of this technique (Pletcher and Li (2011)). These low efficiencies are partly the result of hydrogen and oxygen gas bubbles, which evolve at the electrodes of the electrolyzer and reduce its free area available for the chemical reaction and increase the ohmic resistance of the electrolyte. Therefore, the efficiency of water electrolysis can be improved by an accelerated removal of the hydrogen gas bubbles from the electrode surface (Fern ́ andez et al (2014), Koza et al (2011)). One method that has been found to be effective in this regard is the use of forced convection.
Forced convection can be generated by simple stirring or more elegantly by body forces. A method that has been a subject of recent studies is the application of magnetic fields (Koza et al (2011), Monzon and Coey (2014), Weier and Landgraf (2013)). The superposition of a magnetic field with the electric field, which is is already present during the electrolysis of water, gives rise to body forces acting directly in the electrolyte, i.e. the so-called Lorentz force. The Lorentz force has its largest value at the wall and decreases exponentially with the distance from the electrode. The advantage of this force distribution is the large shear generated directly in the vicinity of the wall. Due to the viscosity of the fluid also the bulk flow is strongly influenced. At present, there have been only few experimental studies on the effect of Lorentz forces on bubble growth and on the fluid dynamics of the two-phase flow at gas-evolving electrodes (Weier and Landgraf (2013)).
Especially the characterization of the near-wall region is essential to understand the influence of the strong shear on the bubble detachment and the interaction of the bubble driven and Lorentz force driven flow.
In order to investigate both the near-wall and the bulk flow, experiments with advanced measuring and evaluation techniques have been carried out in an undivided electrolysis cell with and without the application of magnetic fields. Bubble trajectories and the velocity field of the surrounding electrolyte were measured simultaneously for this purpose. Fluorescent tracer particles and a laser light illumination were used to measure fluid velocities in the electrolyte. A background illumination with a different wavelength was used to measure the size and trajectory of bubbles by means of shadowgraphy. Bubble shadow and tracer particle images were captured simultaneously by two sCMOS cameras with two different wavelength filters to separate both signals. Fluid velocities were evaluated using particle image velocimetry (PIV) as well as particle tracking velocimetry (PTV). It turned out that the PIV results obtained near the electrode, where high velocity gradients occur, were substantially biased as the result of the high void fraction and the associated light absorption in this region.
However, the knowledge of the near-wall fluid velocities and its gradients is essential as they influence the detachment of bubbles from the electrode. In contrast to correlation based evaluation methods as PIV, particle tracking techniques do not depend on the particle image intensity itself but on the ability to detect particles and track them correctly. For this reason, different image filters were applied to enhance the particle images for a more reliable particle detection. More importantly, a sophisticated tracking algorithm proposed by Ohmi and Li (2000) and adapted by Cierpka et al (2013) was used, which takes the similar movement of neighboring particles into account and thus helps to avoid spurious vectors resulting from particle images which were undetectable in one of two consecutive frames. This approach allows for more precise measurements closer to the electrode as exemplified in Fig.1a). This way, the influence of Lorentz forces on the near-wall velocity distribution was investigated. It will be shown in the final paper that Lorentz forces lead to a significant acceleration close the electrode, especially for higher electric current densities (see Fig.1b)). In addition to the velocity fields, the bubble trajectories were of interest. Therefore, multiple image filters were applied on the bubble shadow images to obtain discernible bubble images. A simple PTV algorithm was used to determine the size and trajectory of bubbles. It will be shown that most of the large rising bubbles have path oscillations and can have a significant impact on the near-wall fluid velocities and mass transfer to the electrode.
The full article will give detailed information on how to extract proper data for the presented experiment with the help of the aforementioned tracking algorithm and will discuss the limits of this approach. The velocity fields obtained with PTV will be compared to those determined with PIV for different current densities with and without the application of Lorentz forces. Moreover, the size and trajectrories of bubbles with path oscillations and their impact on the velocity field and velocity fluctuations will be shown for some exemplary cases.

Keywords: Particle Image Velocimetry; PIV; Particle Tracking Velocimetry; PTV; water electrolysis; Lorentz force

  • Lecture (Conference)
    11th International Symposium on Particle Image Velocimetry (PIV 2015), 14.-16.09.2015, Santa Barbara, California, USA
  • Contribution to proceedings
    11th International Symposium on Particle Image Velocimetry (PIV 2015), 14.-16.09.2015, Santa Barbara, California, USA

Publ.-Id: 21658

A new set of Pitzer parameters for dissolved oxygen and its implication on the U(IV)/U(VI) system.

Bok, F.; Richter, A.; Brendler, V.; Altmaier, M.

Uranium as a major component in nuclear waste can form various mineral phases in mainly two oxidation states: +IV and +VI. For the modelling of different chemical aspects of a nuclear waste repository in salt rock, a thermodynamic database including Pitzer parameters for all relevant aqueous species is necessary. The latest THEREDA (Thermodynamic Reference Database) data release (no. 9) enables the modelling of uranium species in high saline solutions. The amount of dissolved oxygen is an important parameter for the description of redox-sensitive systems like U(IV)/ U(VI) in aqueous solution, namely when geochemical speciation codes and associated thermodynamic databases directly use oxygen as reaction partner for redox reactions. The O2 solubility’s in aqueous solutions according to the reaction O2(g) ↔ O2(aq) follows Henry’s law (Henry’s law constant KH expressed in mol/kg·101.35 kPa). The respective constant as well as a new set of Pitzer parameters for the solubility in solutions of the oceanic salt system (Na, K, Mg, Ca / Cl, SO4, HCO3/CO3 - H2O(l)) was deduced from data sets collected by IUPAC.

Keywords: THEREDA; database; Pitzer; uranium; oxygen; solubility

  • Lecture (Conference)
    Workshop on Actinide-Brine-Chemistry (ABC-Salt 4), 14.-15.04.2015, Heidelberg, Deutschland

Publ.-Id: 21657

Optical imaging of COX-2: Studies on an autofluorescent 2,3-diaryl-substituted indole-based cyclooxygenase-2 inhibitor.

Tondera, C.; Ullm, S.; Laube, M.; Meister, S.; Neuber, C.; Mosch, B.; Kniess, T.; Pietzsch, J.

This study aimed at in vivo visualization of cyclooxygenase-2 (COX-2) by optical imaging using a representative compound of a class of autofluorescent 2,3-diaryl-substituted indole-based selective COX-2 inhibitors (2,3-diaryl-indole coxibs). COX-2 was successfully visualized in mice models with phorbol myristate ester (TPA)-induced inflammation or bearing xenografted human melanoma cells by 2-[4-(aminosulfonyl)phenyl]-3-(4-methoxyphenyl)-1H-indole (C1). COX-2 protein expression in both TPA-induced inflammatory sites and human melanoma xenografts was confirmed by immunoblotting. Control experiments using surrogate markers, sham injections, and non-COX-2 expressing melanoma cells further confirmed specificity of tissue association of C1. The merging of therapeutic and diagnostic properties of 2,3-diaryl-indole coxibs may widen the range of applications of COX-2-targeted treatment, e.g., for in situ-guided surgery and ex vivo diagnostics.

Keywords: Fluorescence; Luminescence; Melanoma-associated inflammation; Phorbol myristate ester-induced COX-2 expression; Rodent melanoma xenograft model

Publ.-Id: 21656

Measurement of prompt gamma profiles in inhomogeneous targets with a knife-edge slit camera during proton irradiation

Priegnitz, M.; Helmrecht, S.; Janssens, G.; Perali, I.; Smeets, J.; Vander Stappen, F.; Sterpin, E.; Fiedler, F.

Proton and ion beam therapies become increasingly relevant in radiation therapy. To fully exploit the potential of this irradiation technique and to achieve maximum target volume conformality, the verification of particle ranges is highly desirable. Many research activities focus on the measurement of the spatial distributions of prompt gamma rays emitted during irradiation. A passively collimating knife-edge slit camera is a promising option to perform such measurements. In former publications, the feasibility of accurate detection of proton range shifts in homogeneous targets could be shown with such a camera. We present slit camera measurements of prompt gamma depth profiles in inhomogeneous targets. From real treatment plans and their underlying CTs, representative beam paths are selected and assembled as one-dimensional inhomogeneous targets built from tissue equivalent materials. These phantoms have been irradiated with monoenergetic proton pencil beams. The accuracy of range deviation estimation as well as the detectability of range shifts is investigated in different scenarios. In most cases, range deviations can be detected within less than 2 mm. In close vicinity to low-density regions, range detection is challenging. In particular, a minimum beam penetration depth of 7 mm beyond a cavity is required for reliable detection of a cavity filling with the present setup. Dedicated data post-processing methods may be capable of overcoming this limitation.

Keywords: proton therapy; prompt gamma imaging; range verification; sensitivity; slit camera

Publ.-Id: 21655

Tracing outburst floods with 10Be and 26Al: Terraces and megaclasts in Boam Gorge, Issyk Kul, Kyrgyzstan

Rosenwinkel, S.; Landgraf, A.; Korup, O.; Schwanghart, W.; Vollkmer, F.; Dzhumabaeva, A.; Merchel, S.; Rugel, G.

In mountainous areas, some naturally dammed lakes that have formed behind large landslides or glacier-derived debris can remain intact and trap large water bodies over hundreds to several thousands of years. Sudden failure of such natural dams, however, may trigger catastrophic outburst flooding with often substantial geomorphic consequences for downstream river reaches. In this context we investigate Pleistocene to Holocene lake-level fluctuations along the western outlet of the world’s second-largest mountain lake Issyk Kul in the northern Kyrgyz Tien Shan. Specifically, we explore whether the alternating phases of lake closure and external drainage, which was manifested by sedimentary deposits, bathymetric, and geochemical data, were associated with catastrophic outbursts or whether lake-level changes were solely driven by the longer-term effects of climate and basin hydrology. We compute exposure ages from cosmogenic 10Be and 26Al of three large (~4 m) boulders to constrain the timing of potential outburst floods at the outlet of the Boam Gorge where it leaves the mountain belt and debouches onto the Chu Basin, downstream of former spillways from Issyk Kul. We used boulder dimensions to constrain hydraulic palaeo-flood models based on flow competence analysis of different flood scenarios. Our results are consistent with the hypothesis of one or more catastrophic lake outbursts, and compatible with palaeo-lake levels reconstructed from lacustrine sediment stacks upstream. We further report 10Be ages from six depth profiles on terraces at the outlet of the Boam Gorge and the Chon Kemin valley in order to put into context the potential geomorphic work of such outburst floods with the longer-term incision history of the gorge.

Keywords: AMS; geomorphologie; cosmogenic nuclide; TCN

  • Poster
    Meeting of Working Group Geomorphology (AK Geomorphologie) as part of the Deutscher Kongress für Geographie (DKG), 03.-04.10.2015, Berlin, Deutschland

Publ.-Id: 21654

Absolute value determination of vacancy concentration in silicon crystals using low-temperature ultrasonic measurements

Yamada-Kaneta, H.; Okabe, K.; Akatsu, M.; Baba, S.; Mitsumoto, K.; Nemoto, Y.; Goto, T.; Saito, H.; Kashima, K.; Saito, Y.

For the samples taken from the void region of the CZ silicon crystal grown with the same solidification condition and different thermal histories after the solidification, we measure the magnitude S of the elastic softening which is proportional to the concentration of the single vacancies [V], For these samples, we also measure the size distribution of the void density by using the infrared lightscattering tomography, to evaluate the concentration [Vc] of the vacancies consumed for the void formation. From these two experiments, we find a sum rale [Vc] + a S= C, where C depends only on the solidification condition and is independent of the thermal history after the solidification. This enables us to find the conservation rale of the vacancies [Vc] + [V] = C. The value of the proportionality constant a in the relation [V] = a S is determined. Demonstration of determining the absolute values of [V] from the measured S is given. An estimate is made for the value of the quadrupole-strain coupling constant.

Keywords: Coupling constants; Different thermal history; Elastic softening; Light-scattering tomography; Low temperatures; Single vacancies; Solidification condition; Vacancy concentration

Publ.-Id: 21653

Production and Diagnostics of Dense Matter

Brambrink, E.; Amadou, N.; Benuzzi-Mounaix, A.; Geissel, M.; Harmand, M.; Pelka, A.; Vinci, T.; Koenig, M.

High energy lasers are a unique tool to create high pressure states above 10 Mbar at ns time scales, which allow to study material properties under these extreme conditions. These conditions are, for example, comparable with planetary cores, where material properties play an important role for the properties and evolution of a planet. The rapid compression allows also to study dynamic effects of phase transitions as compression times are comparable to relaxation times. We will present recent results of laser compression of iron reaching conditions of so called “super-Earth” cores. A description of the compression schemes as well as present and future diagnostics is presented. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Keywords: Warm dense matter; high energy density physics; ramp compression

Publ.-Id: 21652

Evaluation of the cone-shaped pickup performance for low charge sub-10 fs arrival-time measurements at free electron laser facilities

Angelovski, A.; Kuntzsch, M.; Czwalinna, M. K.; Penirschke, A.; Hansli, M.; Sydlo, C.; Arsov, V.; Hunziker, S.; Schlarb, H.; Gensch, M.; Schlott, V.; Weiland, T.; Jakoby, R.

An evaluation of the cone-shaped pickup performance as a part of the high bandwidth bunch arrival-time monitors (BAMs) for a low charge sub-10 fs arrival-time measurements is presented. Three sets of pickups are installed at the free electron laser FLASH at Deutsches Elektronen-Synchrotron, the quasi-cw SRF accelerator ELBE at the Helmholtz-Zentrum Dresden-Rossendorf and the SwissFEL injector test facility at Paul Scherrer Institute. Measurements and simulations are in good agreement and the pickups fulfill the design specifications. Utilizing the high bandwidth BAM with the cone-shaped pickups, an improvement of the signal slope by a factor of 10 is demonstrated at ELBE compared to the BAM with a low bandwidth.

Keywords: BAM ELBE FLASH Arrival-Time Diagnostic

Publ.-Id: 21651

Synthetic Scattering Images from Laser-Plasma Interaction - Heating and Ionization

Huang, L. G.; Bussmann, M.; Chung, H. K.; Zacharias, M.; Cowan, T. E.; Kluge, T.

We present the dynamics of bulk electron heating and ionization in ultra-short relativistic laser plasmas interactions. In order to connect the plasma dynamics seen in simulations with experiments we also discuss the role of in-situ synthetic Scattering Images that mimic experimental diagnostics.

Keywords: Heating; Ionization; Laser-Plasma interaction; Synthetic Scattering

  • Poster
    European XFEL Users' Meeting 2015, DESY Photon Science Users' Meeting 2015, 28.-30.01.2015, Hamburg, Germany

Publ.-Id: 21650

Photophysical Property of Catena-Bis(thiocyanato)aurate(I) Complexes in Ionic Liquids

Aoyagi, N.; Shinha, Y.; Ikeda-Ohno, A.; Haga, Y.; Shimojo, K.; Brooks, N. R.; Izuoka, A.; Naganawa, H.; Kimura, T.; Binnemans, K.

The photochemistry of a gold(I) thiocyanate complex has been investigated to determine the coordination structure in both the solid and liquid states. The coordination geometries of the supramolecular [Au(SCN)2]n complex and the concomitant exciplex have mainly been analyzed by crystallographic analysis and X-ray absorption spectroscopy. The Au-S bond distance and Au···Au separation of the compound in the S0 ground state and in the T1 phosphorescent excited state (λex = 340 nm) were compared. Upon irradiation with UV light, the excimeric interactions were enhanced, resulting in a contraction of the AuI···AuI aurophilic distance by 0.0113(4) Å. A broad luminescence spectrum was observed for the one-dimensional chain suprastructure. The time-resolved luminescence spectra indicated the entity of several oligomeric species in the crude liquid without neutral solvent molecules. In addition, EXAFS spectroscopy exhibited a slight change in the nearest Au-S distance due to the photo-switched transformation. The deformation of the (Au---Au)* exciplexes was not apparently promoted in the liquid state with the asymmetrical imidazoium cations having a non-local charge distribution in the present observation.

Keywords: Gold; Au(I); thiocyanate; aurophilic interaction; ionic liquids; exciplex; XAS; TRLFS; polymers

Publ.-Id: 21649

Coordination chemistry for separation of nuclear-related metals

Ikeda, A.

In order to understand the separation mechanism of metals in chemical processes, the chemical species formed in the processes should be characterised particularly on a molecular level. Structural characterisation is of particular importance to understand the interaction between the metal of interest and separating reagents (i.e. ligands), which would be also beneficial to further improve the efficiency of separation processes and/or to develop new separation ligands. This talk will cover the application of X-ray-based characterisation techniques (single-crystal X-ray diffraction (SC-XRD) and X-ray absorption spectroscopy (XAS)) to the separation chemistry of nuclear-related elements, such as actinides (An) or strontium (Sr).

Keywords: actinides; lanthanides; f-elements; nuclear-related elements; X-ray technique; synchrotron; XAS; XRD; coordination chemistry; separation

  • Invited lecture (Conferences)
    LEPMI-CNRS internal seminar, 13.02.2015, Grenoble, France

Publ.-Id: 21648

Floating Zone Growth of Oxides and Metallic Alloys

Hermann, R.; Priede, J.; Gerbeth, G.

Single crystals of congruently and incongruently melting oxides have been grown by the optical floating zone (OFZ) and traveling solvent floating zone techniques. Both relatively low-cost methods work especially well for oxides melting above the maximum operating temperature of conventional crucibles or that were previously impossible to grow due to crucible oxidation or reaction of the melt with the crucible material. For incongruently melting oxides, solvents with experimentally determined composition allow for creation of practical steady state conditions. This extends the range of materials that now can be crystallized in oxidizing, reducing, and neutral atmospheres and elevated pressure. Distribution of dopants is relatively uniform.

The important problems of zone stabilization and its dependence on the conditions applied are discussed from the experimental point of view. Basic characterization of the grown crystals and most characteristic defects is presented. An extensive list of oxide crystals grown by the OFZ method is included.

Floating zone crystal growth with radio frequency (RF) heating is an important technique for the preparation of single bulk crystals. The absence of any crucible is advantageous for the growth of single crystals of reactive materials with high melting points. The melt convection driven by the induction heating and the heat radiation from the surface leads usually to a solid–liquid interface being concave toward the solid phase outer rim. These concave parts inhibit the growth of single crystals over the whole cross-section. The concave solid–liquid interface can be prevented by a two-phase inductor that melts the material but also stirs it in a certain way. The basic design of this two-phase inductor is given, and its application for the growth of industrially relevant single crystals of RuAl and TiAl intermetallic compounds as well as interesting compounds for research such as antiferromagnetic Heusler MnSi compounds or biocompatible TiNb alloys is described.

Keywords: Crystal growth; Image furnace; Optical floating zone; Oxides; Travelling solvent floating zone; Intermetallic compounds; RF-floating zone; Single crystals

  • Book chapter
    P. Rudolph: Handbook of Crystal Growth: Bulk Crystal Growth, Vol. 2A, Amsterdam: Elsevier, 2014, 9780444633033, 281-329
    DOI: 10.1016/B978-0-444-63303-3.00008-0

Publ.-Id: 21647

Carbide formation and optical properties in carbon:transition metal nanocomposite films

Heras, I.; Guillén, E.; Abrasonis, G.; Krause, M.; Pardo, A.; Endrino, J. L.

The physical vapour deposition of transition metals with carbon leads to the formation of metal nano-clusters or nanocrystalline metallic carbides embedded in a carbon matrix. Interstitial carbides are very stable at high temperature, have high melting points and possess a high reflectivity. In contrast, carbon: transition metal nanocomposites can show optical selective properties such as good absorptance in the visible with high reflectance in the infrared. These properties make them very attractive for applications were high temperature resistant materials with selective optical properties are required.
In this study, Carbon: transition metal nanocomposites were grown using a physical vapour deposition system incorporating two pulsed filtered cathodic arc sources, one provided with a graphite cathode and the other with a metal cathode (Zr, V and Mo). The metal content in the composite was controlled by adjusting the ICarbon/IMetal pulse ration between the two sources, and determined by Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). Comprehensive structure characterization was carried out using a combination of X-ray diffraction (XRD), Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). Optical characterization has been done using both with ellipsometry and spectrophotometer measurements in order to obtain the optical constants and the reflectance spectra of the samples.
Together with experimental characterization, the computer program CODE is used to simulate the reflectance spectra of different carbon: transition metal films. Bruggeman effective medium theory was used to average the dielectric functions of the two components which compose the film. According to our simulations, the resulting reflectance of the nanocomposite films is strongly affected by the same metal content, independently if it results in metallic nano-clusters or nanocrystalline metallic carbides. Simulated spectra were compared with the measured reflectance of the deposited films obtaining good agreement between simulations and experimental results.

  • Lecture (Conference)
    International Conference on Nanotechnology, Nanomaterials & Thin Films for Energy Applications (Nanoenergy), 19.-21.02.2014, London, Großbritannien

Publ.-Id: 21646

Comprehensive environmental testing of optical properties in thin films

Heras, I.; Guillén, E.; Krause, M.; Wenisch, R.; Escobar-Galindo, R.; Endrino, J. L.

Environmental characterization of optical and structural properties of thin films continues to be a challenging task. To understand the failure mechanism in high temperature thin film applications, it is crucial to understand how material properties change with temperature. An accurate knowledge of the variation of the dielectric function of thin films and its relation to compositional and microstructural changes could help to prevent failures. This article presents an environmental in-situ characterization methodology that combines the study of the optical constants in an environmental chamber by spectroscopic ellipsometry, with compositional depth profile analysis using ion beam analysis techniques and a structure analysis by Raman spectroscopy. The main novelty of this methodology is that all analytical techniques are carried out sequentially in a multi-chamber cluster tool without sample exposure to undefined atmospheres. Carbon-titanium metal thin film had been studied following the described characterization methodology.

Keywords: Thin films; optical constants; cluster tool; high temperature applications; thermal degradation; real time spectroscopic ellipsometry; ion beam analysis; Raman spectroscopy

  • Open Access Logo Contribution to proceedings
    3rd International Conference on Through-life Engineering Services, 04.-05.11.2014, Cranfield, United Kingdom
    Procedia CIRP 22 ( 2014 ), 271-276
  • Lecture (Conference)
    3rd International Conference on Through-life Engineering Services, 04.11.2014, Cranfield, United Kingdom

Publ.-Id: 21645

Magnetic characterization of curved thin [Co/Pd]-multilayers and Py films

Steinbach, G.; Göhler, F.; Wolf, D.; Sluka, V.; Lindner, J.; Gemming, S.; Albrecht, M.; Erbe, A.

In the last decades thin film technology has led to a vast increase in the variety of fabricated magnetic nano- and microstructures with desired shape, size and properties. Usually flat substrates are used to grow structures. Recently, a study on magnetic thin films with perpendicular anisotropy on curved substrates, for instance on silica spheres [1], has shown that the film curvature enormously influences the magnetic properties. In contrast to structures on flat substrates those so-called magnetic caps exhibit a spatial change of the magnetic easy axis and a film thickness variation across the cap. These features extend the possibilities in tailoring the magnetic specifications such as the magnetic anisotropy [2,3] and coercivity [1,4] or magnetization reversal process [1,2,5]. This complex structure geometry, however, leads to difficulties in characterizing the magnetic properties of the caps using standard techniques: In the case of micrometer-sized structures magnetic imaging methods suffer, for example, from beam deflection or the huge structure height due to the surface curvature.
We will present our results on 4.5µm and 0.33µm sized magnetic caps consisting of [Co(0.28nm)/Pd(0.9nm)]x8-multilayers with perpendicular magnetic anisotropy. First, we concentrate on the interior materials’ properties by studying the magnetic switching process of the cap in external fields and the spin dynamics. Second, the stray field is investigated, which determines the cap’s interaction with the environment.
The magnetization reversal in micron-sized caps has been studied by both, superconducting quantum interference device and magnetic force microscopy, for two distinct directions of an externally applied magnetic field: normal and parallel to the substrate surface. We observe clear deviations from curves measured for the flat film: The caps also show a hysteretic behavior with a very small coercivity of 150Oe in the field parallel to the substrate surface. In the normal field there is no abrupt switching as known from the flat film, but a continuous, two-step like reversal. The origin of the switching features is investigated with in-field and remanent MFM. We will present the magnetic reversal as a multi-step process across the different regions of the cap. In the parallel field two different nucleation processes during the magnetization switching have been observed: a ring nucleation, which is also mentioned in [2], and isolated domain nucleation.
The dynamic properties of the [Co/Pd]-caps have been investigated with ferromagnetic resonance. Due to the small particle size the use of conventional FMR setups does not allow single particle detection. Therefore we prepared micron sized resonators using electron beam lithography [6]. The angular dependence of the FMR modes is investigated. The results are compared with FMR measurements on geometrically similar permalloy caps with in-plane magnetic anisotropy.
The curvature-induced spatial modulation of the magnetic anisotropy further leads to a complicated stray field around the cap. So far, micromagnetic simulations [2] have been carried out to calculate the spin distribution giving rise to the stray field. Here we experimentally visualize the magnetic stray field of 0.33 µm particles by off-axis electron holography (figure 2, left). This technique provides access to the projected in-plane component of the magnetic induction by reconstructing the phase shift of the electron wave when passing through the magnetic stray field of the sample [7]. The projected stray field can be obtained by the gradual rotation of the cap. In contrast to standard measurements on flat samples, for magnetic caps the interpretation of the electron holograms is not straightforward since the stray field is not constant along the electron path. Therefore, we compare the experimentally obtained results with the outcome of micromagnetic simulations performed with the finite element based simulation software SpinFlow 3D (figure 2, right). The qualitative agreement proves the reliability of the simulation.

  • Poster
    IEEE International Magnetics Conference, INTERMAG Europe 2014, 05.05.2014, Dresden, Deutschland

Publ.-Id: 21644

Crystallization of quasiantiferromagnetic colloids

Steinbach, G.; Gemming, S.; Erbe, A.

The microscopic interactions between atomic magnetic moments determine the macroscopic magnetic properties of matter. For strongly correlated magnetic systems the local spin configuration plays a key role. High relaxation times, however, make direct investigations of dynamic processes such as crystallization very difficult. Here, we present an artificial spin system of magnetic colloids, which are often discussed as potential mesoscopic model systems for condensed matter. The very low relaxation rates of interacting colloids enable the visualization of phase transitions or crystallization processes by video microscopy. The used colloids have a predened net magnetic moment, as analogue to the atomic spin. These micromagnets show a quasiantiferromagnetic interaction. They form two-dimensional hexagonal clusters with a spin configuration similar to the 120° antiferromagnetic Neel state in the cluster center and strong deviations along the edges. The cluster size emerged as critical parameter for the occurrence of spin defects. Dur-ing the cluster growth the total magnetization of the system increased in discrete steps. Further we obtained a linear increase of the inverse spin pair correlation for particles in the center. The influence of an external constant or uctuating magnetic field is investigated as control tool for cluster growth and defect formation.

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21643

Cluster-Tool zur In situ Modifizierung und Analyse von Werkstoffen unter extremen Bedingungen am 6 MV Ionenbeschleuniger des HZDR

Wenisch, R.; Schumann, E.; Lungwitz, F.; Hanf, D.; Heller, R.; Gemming, S.; Krause, M.

Moderne Werkstoffe sind bei vielen Anwendungen extremenUmgebungsbedingungen ausgesetzt. Dazu zählen hohe und tiefe Temperaturen bzw. große Temperaturschwankungen, die teilweise in Verbindung mit korrosiven oder reaktiven Atmosphären oder hohen mechanischen Belastungen auftreten. Sie stellen hohe Anforderungen an die Beständigkeit und Stabilität der verwendeten Werkstoffe. Als Beispiele seien solarselektive Absorber, Komponenten des Antriebsstranges von Verbrennungsmotoren und Rotoren von Turboladern und Turbinen genannt. Die Gewährleistung der Werkstofffunktionalität über die gesamte Lebensdauer erfordert neue Konzepte der Analyse und Prüfung. Dazu wurde am 6MV Ionenbeschleuniger des HZDR mit Fördermitteln des Impuls- und Vernetzungsfonds des Präsidenten der HGF sowie des KFSI ein Cluster-Tool zur in situ Modifizierung und Analyse von Werkstoffen bei Temperaturen von bis zu 1000°C, unter korrosiven Atmosphären und mechanischem Verschleiß aufgebaut.
Kernbestandteil des Cluster-Tools ist eine zentrale Hochvakuum (HV)-Probenaufnahme- und Transferkammer. Diese ist mit weiteren HV-Kammern verbunden, in denen die sequentielle Probensynthese und -modifizierung, die Element- und Strukturanalytik und die optische Charakterisierung erfolgt, ohne das Vakuum zu brechen und die Werkstoffe undefinierten Umgebungsbedingungen auszusetzen. In allen Kammern besteht die Möglichkeit, in situ Heizexperimente bei Temperaturen von bis zu 1000°C durchzuführen. Die mit dem 6MV Tandem-Ionenbeschleuniger verbundene Kammer zur Ionenstrahlanalytik ermöglicht die Untersuchung der Elementzusammensetzung durch Rutherford Rückstreuung und Nuklearer Reaktionsanalyse. Die Schichtzusammensetzung kann bis in eine Tiefe von ca. 1μm auf bis zu 10 nm genau bestimmt werden. Bei Hochtemperaturuntersuchungen reduziert sich die Tiefenauflösung auf etwa 25 nm. Zur strukturellen Charakterisierung der Proben dient ein fasergekoppeltes Ramanspektrometer an der Analysenkammer des Cluster-Tools, dessen Probenkopf über eine Kamera auch die visuelle Beurteilung der Proben ermöglicht. Die Untersuchung der optischen Eigenschaften und deren Abhängigkeit von Temperatur und Atmosphäre erfolgt durch spektroskopische Ellipsometrie in einer Umweltkammer, in der korrosive Umgebungen simuliert werden können. Für 2015 ist die Installation eines in situ Tribometers in Vorbereitung, mit dem das Reib- und Verschleißverhalten von Werkstoffen unter definierten Atmosphären untersucht werden kann.
Zusammengefasst entsteht mit dem Cluster-Tool am 6 MV Ionenbeschleuniger des HZDR ein Messplatz zur umfassenden in situ Modifizierung und Analyse von Werkstoffen, mit Hilfe dessen komplexe Probenbehandlungsprotokolle unter extremen Umgebungsbedingungen bearbeitet werden können.

  • Poster
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014, 21.-23.09.2014, Bonn, Deutschland

Publ.-Id: 21642

Optical nanoscopy of transient states in condensed matter

Kuschewski, F.; Kehr, S. C.; Green, B.; Bauer, C.; Gensch, M.; Eng, L. M.

Recently, the fundamental and nanoscale understanding of complex phenomena in both, materials research and the life sciences, has witnessed considerable progress. However, elucidating the underlying complex mechanisms, often governed by disentangled degrees of freedom such as lattice, spin, orbit, charge for solids or conformation, electric potentials and ligands for proteins, has remained an experimental challenge. . Techniques that allow for distinguishing between different contributions to these processes by their spectral and/or temporal responses and/or by their characteristic lenght scales are hence urgently required.
In this paper we demonstrate the application of scattering-type scanning near-field optical microscopy (s-SNOM) as a novel nano-probe for tracking transient states of matter. We introduce a sideband-demodulation technique that allows for probing exclusively the stimuli-induced change of near-field optical properties. We exemplify this development by probing the transient decay of an electron-hole plasma generated in SiGe thin films through near-infrared laser pulses. This method can universally be applied to optically track ultrafast/-slow transient processes over the whole spectral range from UV to THz frequencies.

Keywords: THz; near-field microscopy; phase transitions; accelerator-based THz sources

Publ.-Id: 21641

Nanostructuring CaF2 surfaces with slow highly charged ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Ritter, R.; Wachter, G.; Facsko, S.; Lemell, C.; Burgdörfer, J.; Aumayr, F.

In recent years the potential of slow highly charged ions (HCI) as tools for nanostructuring purposes has received considerable attention and a wide range of material classes, from insulating ionic crystals, polymers and ultrathin films, to semiconducting and conducting substrates have been investigated regarding their response to individual HCI impact. For the majority of investigated materials, however, consistent theoretical modeling to supplement with experimental evidence and to satisfactorily explain the complete physical process from ion approach and impact to the formation of an individual nanostructure is still lacking. CaF2, from both an experimental and theoretical point of view, might be considered the most thoroughly investigated material. Combining results from numerous studies has allowed for the generation of a "phase diagram" for nanostructuring of CaF2 in dependence of ion beam parameters. This paves the way for a first unified picture, as implications from this phase diagram should be applicable to similar materials as well.

Publ.-Id: 21640

Terahertz field control of in-plane orbital order in La0.5Sr1.5MnO4

Miller, T. A.; Chhaajlany, R. W.; Tagliacozzo, L.; Green, B.; Kovalev, S.; Prabhakaran, D.; Lewenstein, M.; Gensch, M.; Wall, S.

In-plane anisotropic ground states are ubiquitous in correlated solids such as pnictides1, cuprates2 and manganites3. They arise naturally from doping Mott insulators4 and compete with phases such as superconductivity5. However, strong coupling between lattice, charge, orbital and spin degrees of freedom results in simultaneous ordering of multiple parameters, masking the mechanism that drives the anisotropy6. We demonstrate that orbital domains in a manganite can be oriented by the polarization of an external pulsed THz light field. The THz control field non-resonantly couples to electrons, indicating that Coulomb interactions are the primary driving factor for the orbital order. Field control is explained by a simple Hubbard model that shows the force on the domain originates from the Coulomb interaction. Our results demonstrate the key role played by charge localization in driving orbital order in manganites and show how THz can be utilized in new ways to understand and manipulate anisotropic phases in a broad range of correlated materials.

Keywords: THz; Domains; correlated solids; ultra-fast

Publ.-Id: 21639

AIDA - Apparatus for In-situ Defect Analysis: Investigations on Fe60Al40

Trinh, T.; Wagner, A.; Liedke, M. O.; Anwand, W.; Butterling, M.; Potzger, K.

We performed in-situ annealing investigations of 250 nm Fe60Al40 thin films. The magnetic properties of disorderd Fe60Al40 thin films change from the ferromagnetic to paramagnetic state du to annealing. No conclusive discussion of that phase transtion as a function of the open volume defects exists in the literature. First results on the Fe60Al40 annealing driven magnetic phase transition between the ferromagnetic A1 phase and the paramagnetic B2 phase as a function of the open volume defects will be shown. The magnetization of the film after each annealing step indicates its progress reflecting chemical ordering of the alloy and dinishing of ferromagnetism [1]. Fig. 1 shows the temperature dependence of the positron annihilation spectorscopy (PAS) S-parameter indicating the open volume defects evolution during annealing. The defects are very stable with respect to annealing and do not directly relate to the change of magnetic properties. Our results indicate that Fe60Al40 could be a promising candidate for Hydrogen storage due to a large amount of stable defects. Through hybridisation the electronic structure can be modified, combined with a local lattice distortion. Hydrogen can therefore be viewed as a tool to modify the electronic structure, allowing tuning of the magnetic properties as a consequence.
For the in-situ annealing we have utilized a unique high vacuum system combining material evaporation and ion beam modification with positron annihilation spectroscopy. The system has been developed and installed in the Helmholtz-Zentrum Dresden-Rossendorf. The system is capable to perform Doppler broadening spectroscopy as well as resistometry and provides a monoenergetic positron beam pre-accelerated in the range of 80 eV to 35 keV thus enabling sample depth profiling.

Keywords: Positron anihilation; In-situ; Apparatus; Defects; Spectroscopy

  • Poster
    14th International Symposium Metal Hydride Systems, 20.-25.07.2014, Manchester, United Kingdom

Publ.-Id: 21638

Apparatus for In-situ Defect Analysis (AIDA)

Liedke, M. O.; Anwand, W.; Butterling, M.; Potzger, K.; Heidarian, A.; Bali, R.; Wagner, A.

A unique high vacuum system combining material evaporation and ion beam modication with positron annihilation spectroscopy (PAS) has been developed and installed in the Helmholtz-Zentrum Dresden-Rossendorf. The in-situ system is capable to perform Doppler broadening spectroscopy as well as resistometry (4 point probe). It is an end station of the Slow-Positron System of Rossendorf (SPONSOR) that provides a mono-energetic positron beam pre-accelerated in the range of 80 eV to 35 keV thus enabling sample depth proling. The main focus of studies is the in-situ modication (during growth, ion irradiation, cooling/annealing) and the analysis of open volume defects and the chemical environment in thin lms of, e.g., memristive oxides or metal alloys. First results on the FeAl ion irradiation/annealing driven magnetic phase transition between the paramagnetic and ferromagnetic state as a function of the open volume defects will be shown. The project is nanced by the Impuls- und Vernetzungsfonds of the Helmholtz Association (code VH-VI-442).

Keywords: MBE; ion irradiation; evaporation; annealing; FeAl; transition metals; sheet resistance

  • Lecture (Conference)
    DPG-Frühjahrstagung (DPG Spring Meeting) 2014, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21637

Apparatus for In-situ Defect Analysis (AIDA)

Liedke, M. O.; Anwand, W.; Potzger, K.; Wagner, A.

A unique high vacuum system combining material evaporation and ion beam modication with positron annihilation spectroscopy (PAS) has been developed and installed in the Helmholtz-Zentrum Dresden-Rossendorf. The in-situ system is capable to perform Doppler broadening spectroscopy as well as resistometry (4 point probe). It is an end station of the Slow-Positron System of Rossendorf (SPONSOR) that provides a mono-energetic positron beam pre-accelerated in the range of 80 eV to 35 keV thus enabling sample depth proling. The main focus of studies is the in-situ modication (during growth, ion irradiation, cooling/annealing) and the analysis of open volume defects and the chemical environment in thin lms of, e.g., memristive oxides or metal alloys. First results on the FeAl ion irradiation/annealing driven magnetic phase transition between the paramagnetic and ferromagnetic state as a function of the open volume defects will be shown. The project is nanced by the Impuls- und Vernetzungsfonds of the Helmholtz Association (code VH-VI-442).

Keywords: MBE; ion irradiation; evaporation; annealing; FeAl; transition metals

  • Lecture (Conference)
    Treffen Deutscher Positronengruppen Kiel 2014, 25.-27.02.2014, Kiel, Deutschland

Publ.-Id: 21636

Capacitance wire mesh imaging of bubbly flows for offshore treatment applications

Assima, G. P.; Larachi, F.; Schleicher, E.; Schubert, M.

The impact of ship motion bubbly flow was emulated using as well simulator to expose flow structure changes emerging in bubble columns relevant to offshore floating applications. Roll, roll+pitch, yaw, heave and sway were implemented at various frequencies and changes in bubbly flow resulting from the imposed motions were monitored for the first time by means of a dual capacitance wire mesh sensor to measure local gas holdup and velocity. Visualizations of the two-phase flow revealed that roll, roll+pitch, and high-frequency sway were the most impactful in terms of bubble zigzag and swirl, and bubble-clustering and segregation due to vessel dynamic inclinations. As a consequence of the se motions, lateral migration of bubbles and their clustering enhanced liquid recirculation and local streamwise gas velocity. Compared to static vertical bubble column, bubbly flow pattern was barely altered by yaw and low-frequency sway except the heave displacements which tended to slow down the bubble rise.

Keywords: bubble column; wire mesh capacitance sensor; gas holdup; gas interstitial velocity; swell simulator; marine applications

Publ.-Id: 21635

Highly charged ion induced nanostructures at surfaces by strong electronic excitations

Wilhelm, R. A.; El-Said, A. S.; Krok, F.; Heller, R.; Gruber, E.; Aumayr, F.; Facsko, S.

Nanostructure formation by single impacts of slow highly charged ions can be associated with high density of electronic excitations at the impact points of the ions. Experimental results show that depending on the target material these electronic excitations may lead to very large desorption yields in the order of a few 1000 atoms per ion or the formation of nanohillocks at the impact site. Even in ultra-thin insulating membranes the formation of nanometer sized pores are observed after ion impact. In this paper we show recent results on nanostructure formation by highly charged ions and compare these to structures and single defects observed after intense electron and light ion irradiation on ionic crystals and Graphene. Additional data on energy loss, charge exchange and secondary electron emission of highly charged ions clearly show that the ion's charge state dominate the defect formation at the surface.

Keywords: slow highly charged ion; HCI; ion charge state; nanostructure; electronic excitation; color centers

Publ.-Id: 21633

Development of a Laser wakefield acceleration source as a secondary radiation driver

Couperus, J. P.; Jochmann, A.; Köhler, A.; Messmer, M.; Zarini, O.; Debus, A.; Hübl, A.; Widera, R.; Bussmann, M.; Sauerbrey, R.; Cowan, T.; Schramm, U.; Irman, A.

In laser wakefield electron acceleration a high intensity ultrashort laser pulse drives plasma density waves, inducing a high accelerating field gradient (~GV/m) which can accelerate electrons to high energies within a very short distance.
For the development of secondary radiation sources, the maximization of the bunch charge is important. For this reason we investigate the beam-loading effect at the self-injected highly nonlinear regime. Beam-loading deteriorates the accelerating field structure and limits the maximum bunch charge.
Supported by intensive Particle-in-Cell code simulations run on a GPU-cluster (using the PIConGPU code), we aim on developing a stable high peak current (hundreds of kA) electron source.

Keywords: laser wakefield electron acceleration LWFA plasma PIConGPU

  • Poster
    Advanced School on Laser Applications at Accelerator, 29.09.-03.10.2014, Salamanca, Spain

Publ.-Id: 21632

Effects of the Background Electrolyte on Th(IV) Sorption to Muscovite Mica

Schmidt, M.; Hellebrandt, S.; Knope, K. E.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Soderholm, L.; Fenter, P.

The adsorption of tetravalent thorium on the muscovite mica (001) basal plane was studied by resonant anomalous X-ray reflectivity (RAXR), crystal truncation rods (CTR) and alpha spectrometry in the presence of perchlorate background electrolytes LiClO4, NaClO4, and KClO4 ([Th(IV)] = 0.1mM, I = 0.1 M or 0.01 M, pH = 3.3 ± 0.3). RAXR data show strong influence of the background electrolyte on the sorption behavior of the actinide. No significant Th adsorption was observed in 0.1 M NaClO4, i.e., the Th coverage θ(Th), the number of Th per unit cell area of the muscovite surface (AUC = 46.72 Ų), was ≤0.01 Th/AUC, whereas limited uptake (θ(Th) ~ 0.04 Th/AUC) was detected at a lower ionic strength (I = 0.01 M). These results are in stark contrast to the behavior of Th in 0.1 M NaCl which showed a coverage of 0.4 Th/AUC (Schmidt et al., 2012a). Th uptake was also influenced by the electrolyte cation. Weak adsorption was observed in 0.1M KClO4 (θ(Th) ~ 0.07 Th/AUC) similar to the results in NaClO4 at lower ionic strength. In contrast, strong adsorption was found in 0.1 M LiClO4 , with θ(Th) = 4.9 Th/AUC, a ~10-fold increase compared with that previously reported in NaCl. These differences are confirmed independently by alpha spectrometry, which shows no measurable coverage of Th in 0.1 M NaClO4 background in contrast to a large coverage of 1.6 Th/AUC in 0.1 M LiClO4. Alpha spectrometry cannot be obtained in situ, but sample preparation requires several washing steps that may affect Th(IV) sorption, RAXR, however, is considered to reflect the in situ sorption structure. The CTR/RAXR analyses show the sorption structure consisting of two types of broadly distributed Th species centered at 4.1 Å and 29 Å distance from the interface. Neither the very large distribution height of the second species nor the high coverage can be explained with (hydrated) ionic adsorption, suggesting that the enhanced uptake is presumably due to the formation and sorption of Th nanoparticles.

Keywords: thorium; sorption; RAXR; CTR; nanoparticles; surface diffraction


Publ.-Id: 21631

Investigation of the beam loading effect in laser wakefield acceleration

Couperus, J. P.; Jochmann, A.; Köhler, A.; Messmer, M.; Zarini, O.; Debus, A.; Hübl, A.; Widera, R.; Bussmann, M.; Sauerbrey, R.; Cowan, T.; Schramm, U.; Irman, A.

In laser wakefield electron acceleration a high intensity ultrashort laser pulse drives plasma density waves, inducing a high accelerating field gradient (~GV/m) which can accelerate electrons to high energies within a very short distance.
For the development of secondary radiation sources, the maximization of the bunch charge is important. For this reason we investigate the beam-loading effect at the self-injected highly nonlinear regime. Beam-loading deteriorates the accelerating field structure and limits the maximum bunch charge.

Keywords: laser plasma electron acceleration LWFA wakefield gas-jet PIConGPU

  • Poster
    International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland

Publ.-Id: 21630

Boron dilution transient simulation analyses in a PWR with neutronics/thermal-hydraulics coupled codes in the NURISP project

Jimenez, G.; Herrero, J.; Gommlich, A.; Kliem, S.; Cuervo, D.; Jimenez, J.

The detailed 3D calculation of a boron slug transient with neutronics/thermal hydraulics coupled systems has been a highly demanding and difficult exercise because of the trouble coupling with boron transport models. Within subproject 3 of the FP7 European Project NURISP, two neutron kinetics codes, COBAYA3 and DYN3D, coupled with the thermal hydraulics code FLICA4 in the NURESIM platform were employed to simulate boron dilution transients.
Three transients were defined in the project, involving increasing volumes of diluted water entering the core inlet, to test the adequacy of the coupling between the codes. This paper contains the results obtained with COBAYA3/FLICA4 and DYN3D/FLICA4 couplings for the PWR boron dilution benchmark defined. Additionally, results from the coupled codes DYN3D/FLOCAL are applied for further verification in some cases.
A thorough sensitivity study of the solutions accuracy to the time step and the axial mesh size was performed, and optimal options applicable to all three boron slugs were obtained. The results verify the applicability of the implemented couplings to this type of problems accurately, where peak powers reached can be very high during short periods after which the reactor stabilizes at a few per cent of the nominal power.

Publ.-Id: 21629

Energy-Angle Characteristic of an ICS source

Jochmann, A.

A tunable source of intense ultra-short hard X ray pulses represents a novel tool for the structural analysis of complex systems with unprecedented temporal and spatial resolution. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) we demonstrated the principle of such a light source (PHOENIX – Photon Electron collider for Narrow bandwidth Intense X-Rays) by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating femtosecond laser pulses from the 150 TW Draco Ti:Sapphire laser system. The generated narrowband X rays are highly collimated and can be reliably adjusted by tuning the electron energy. A complete spectral characterization of this source is performed with high angular and energy resolution. These intensive studies provide predictive capability for the future high brightness hard X ray source PHOENIX and potential gamma-ray sources suited to an application.

Keywords: Laser Compton Scattering X-ray pulsed source femtosecond intense backscattering inverse

  • Lecture (Conference)
    LA3NET 3rd Topical Workshop on Novel Acceleration Techniques, 28.04.2014, Dresden, Deutschland

Publ.-Id: 21628

Effect of a superimposed DC magnetic field on an AC induction semi-levitated molten copper droplet

Bojarevics, A.; Beinerts, T.; Grants, I.; Kaldre, I.; Sivars, A.; Gerbeth, G.; Gelfgats, J.

While a piece of pure Copper on a ceramic substrate was inductively melted by 9 to 18 kHz AC magnetic field with axial magnetic DC field superimposed, the liquid metal stably semi-levitated in the expected “conical” free surface shape. The diameter of the liquid metal at the basis was 30 mm, the volume – more than 20 cm3. Replacing the ceramic substrate with a Glassy Carbon, which was not wetted by the molten Copper, caused instability of the semi-levitated Copper droplet. In the absence of the DC field severe chaotic instabilities of the liquid metal shape occurred, causing splashes and uncontrolled contact with crucible walls. When axial DC magnetic field with induction 0.35 T was superimposed the liquid metal droplet exhibited harmonic azimuthal wave deformation of the free surface. Higher frequencies lead to smaller characteristic wavelength. Transverse DC magnetic field direction suppressed the travelling wave deformations of the droplet shape. Stabilizing effect of the DC magnetic field during induction melting has been shown for axial, transverse and 45 degree direction magnetic field. These results experimentally demonstrate the possibilities to improve the stability of levitated metal volumes by superimposed DC magnetic field.

  • Lecture (Conference)
    9th PAMIR conference on Fundamental and Applied MHD, 16.-20.06.2014, Riga, Lettland
  • Contribution to proceedings
    9th PAMIR conference on Fundamental and Applied MHD,, 16.-20.06.2014, Riga, Lettland
    Proceedings of the 9th PAMIR conference on Fundamental and Applied MHD, Vol 2, 125-129

Publ.-Id: 21627

Experimental modelling using liquid metals

Gerbeth, G.; Eckert, S.

An overview on liquid metal modelling experiments is presented for the steel casting process. Particular attention is given to the recent developments on measuring techniques for liquid metal flows, including the perspectives for measurements in real steel melts.

  • Invited lecture (Conferences)
    VDEh Steel Academy Workshop „Computational Fluid Dynamics in Metallurgy“, 01.-03.12.2014, Mönchengladbach, Deutschland

Publ.-Id: 21626

Recent results on flow measurements and magnetic control

Gerbeth, G.; Eckert, S.

A brief summary is given on measurements in metal melts developed at HZDR. Melt velocities can be measured by local electromagnetic probes, ultrasonic Doppler velocimetry and by the Contactless Inductive Flow Tomography (CIFT). The latter is fully contactless and offers a possibility for an online monitoring of the melt flow. We report on first test measurements with CIFT at Czochralski facilities for Si growth. Regarding the details of solidification and the occurrence of inclusions, we present results on X-ray visualizations of alloy solidification. They allowed to demonstrate for metal alloys the formation of freckles driven by the mesoscopic melt convection ahead of the solidification front. For the magnetic melt control we present results of model experiments on the reduction of buoyant temperature oscillations using a rotating magnetic field. Related studies were performed for cylindrical melt volumes and a Cz-like configuration. The melt flow in the float-zone process can be efficiently influenced by a so-called magnetic two-phase stirrer. Its principle and related growth results for intermetallic compounds will be presented.

  • Lecture (others)
    DGKK-Tagung, 12.-13.03.2014, Halle, Deutschland

Publ.-Id: 21625

Towards laser wakefield acceleration with external injection at HZDR

Irman, A.

Progress towards laser wakefield acceleration with external injection is presented.

  • Invited lecture (Conferences)
    Novel acceleration techniques ANAC2/EUCARD2 JRA meeting, 30.04.2014, HZDR, Germany

Publ.-Id: 21624

High Resolution Energy-angle Correlation Measurement of Hard X rays from Laser Thomson Backscattering

Irman, A.; Bussmann, M. H.; Couperus, J. P.; Debus, A. D.; Jochmann, A.; Pausch, R. G.; Schlenvoigt, H. P.; Schramm, U.; Steiniger, K.; Cowan, T. E.; Kuntzsch, M.; Lehnert, U.; Sauerbrey, R.; Seipt, D.; Wagner, A.; Ledingham, K.; Stöhlker, T.; Thorn, D. B.; Trotsenko, S.

A tunable source of intense ultra-short hard X ray pulses represents a novel tool for the structural analysis of complex systems with unprecedented temporal and spatial resolution. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) we demonstrated the principle of such a light source (PHOENIX – Photon Electron collider for Narrow bandwidth Intense X-Rays) by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating femtosecond laser pulses from the 150 TW Draco Ti:Sapphire laser system. The generated narrowband X rays are highly collimated and can be reliably adjusted by tuning the electron energy. A complete spectral characterization of this source is performed with high angular and energy resolution. These intensive studies provide predictive capability for the future high brightness hard X ray source PHOENIX and potential gamma-ray sources suited to an application.

Keywords: Laser Compton Scattering X-ray pulsed source femtosecond intense backscattering inverse

  • Poster
    IPAC’14 - 5th International Particle Accelerator Conference, 18.06.2014, Dresden, Deutschland

Publ.-Id: 21623

Fluid dynamics research at HZDR Dresden

Gerbeth, G.

An overview on fluid dynamics research activities is given, including multiphase and magnetohydrodynamic flows and the related computational fluid dynamics.

  • Invited lecture (Conferences)
    Shandong Universität, 11.05.2014, Jinan, China

Publ.-Id: 21622

Laser-plasma based electron acceleration

Irman, A.

The concept of laser-driven plasma-based electron acceleration is reviewed. This lecture will be started by description of plasmas and its characteristics then follows with electron injection and acceleration. In the end, recent progress in the field will be highlighted.

Keywords: laser wakefield acceleration

  • Invited lecture (Conferences)
    LA3NET Advanced School on Laser Applications at Accelerators, 28.09.-03.10.2014, Salamanca, Spain

Publ.-Id: 21621

Research on crystal growth problems at Institute of Fluid Dynamics of HZDR

Gerbeth, G.

Research activities at HZDR on the measurement and magnetic field control of melt flows in crystal growth processes are summarized. Examples are given for the tailored control by magnetic fields of Czochralski, Vertical-Gradient-Freeze as well as Float-Zone growth processes.

  • Invited lecture (Conferences)
    SICC Science & Technology, Ltd., 12.05.2014, Jinan, China

Publ.-Id: 21620

Tornado-like flows driven by magnetic body forces

Gerbeth, G.; Grants, I.; Vogt, T.; Eckert, S.

Alternating magnetic fields produce well-defined flow-independent body forces in electrically conducting media. This property is used to construct a laboratory analogue of the Fiedler chamber with a room-temperature liquid metal as working fluid. A continuously applied rotating magnetic field (RMF) provides the source of the angular momentum. A pulse of a much stronger travelling magnetic field drives a converging flow at the metal surface, which focuses this angular momentum towards the axis of the container. The resulting vortex is studied experimentally and numerically. In a certain range of the ratio of both driving actions the axial velocity changes its direction in the vortex core, resembling the subsidence in an eye of a tropical cyclone or a large tornado. During the initial deterministic spin-up stage (T. Vogt et al., JFM 736, 2013, pp. 641) the vortex is well described by axisymmetric direct numerical simulation. Being strong enough the flow develops a funnel-shaped surface depression that enables visual observation of the vortex structure. As the RMF strength is increased the eyewall diameter grows until it breaks down to multiple vortices. A number of further observed similarities to tornado-like vortices will be discussed.

  • Invited lecture (Conferences)
    APS-DFD 2014 meeting, 23.-25.11.2014, San Francisco, USA
  • Open Access Logo Abstract in refereed journal
    Bulletin of the American Physical Society 59(2014), 20

Publ.-Id: 21619

Correlation of electron and laser beam parameters to the spectral shape and bandwidth of laser-Thomson backscattering x-ray beams

Irman, A.; Jochmann, A.; Debus, A.; Couperus, J. P.; Trotsenko, S.; Kuntzsch, M.; Lehnert, U.; Wagner, A.; Schlenvoigt, H.-P.; Bussmann, M.; Sthöhlker, T.; Seipt, D.; Thorn, D. B.; Ledingham, K. D.; Cowan, T.; Sauerbrey, R.; Schramm, U.

Development of advanced x-ray sources based on laser-Thomson scattering mechanism is becoming important pushed by a strong demand for ultrashort hard x-ray pulses, which can serve as a novel tool for structural analysis of complex systems with unprecendented temporal and spatial resolution. The spectral shape and bandwidth of this x-ray beam is the result from the interplay between interacting electron and laser beam parameters. We present high resolution angle and energy resolved measurements on the x-ray photon distribution generated by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating laser pulses from the 150 TW DRACO Ti:Sapphire laser system. The measured data and an ab-initio comparison with the 3D radiation code CLARA enable us to reveal parameter influences and correlation of both interacting beams. We conclude that in the low laser intensity interaction regime the electron angular distribution and the laser bandwidth, as in the case of ultrashort laser pulses, give a strong influence to the x-ray spectral shape and bandwidth. We also show the x-ray spectral broadening as the laser intensity increases indicating nonlinear interaction on the scattering process. Controlling these parameters is necessary for designing future Thomson x-ray sources with a specific bandwidth suited to an application.

Keywords: laser-Thomson backscattering x-ray; ELBE electron beam; ultrashort x-ray; high power laser

  • Invited lecture (Conferences)
    16th Advanced Accelerator Concepts Workshop (AAC 2014), 13.-18.07.2014, San Jose, United States

Publ.-Id: 21618

LIMTECH A5: Liquid metal two-phase flows

Strumpf, E.; Eckert, S.; Richter, T.; Gerbeth, G.

Measurements for rising single bubbles were performed in a cuboid benchmark experiment filled with the liquid metal GaInSn. Data was acquired by two different ultrasound techniques simultaneously, which are Ultrasound Doppler Velocimetry (UDV) and Ultrasound Transit Time Technique (UTTT). The focus was on the influence of a horizontal magnetic field on the bubble behavior.

Keywords: liquid metal; two-phase; single bubble; horizontal magnetic field; UDV; UTTT

  • Poster
    LIMTECH annual meeting 2014, 10.-11.11.2014, Ilmenau, Deutschland

Publ.-Id: 21617

Highlights of Resonance Measurements Obtained With HADES

Epple, E.; Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Deveaux, C.; Dybczak, A.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gill, K.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kardan, K.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krebs, E.; Kuc3, H.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petousis, V.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Rehnisch, L.; Reshetin, A.; Rost, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Wendisch, C.; Wirth, J.; Wüstenfeld, J.; Zanevsky, Y.; Zumbruch, P.

This contribution aims to give a basic overview over the latest results regarding the production of resonances in dierent collision systems. The results were extracted with help of the HADES experiment which is a multipurpose detector located at the GSI Helmholtzzentrum, Darmstadt. The main points discussed here are: the properties of the strange resonances Λ(1405) and Σ(1385), the role of Δ’s as a source of pions in the final state, production dynamics reflected in form of differential cross sections, and the role of the Φ meson as a source for K- particles.

Publ.-Id: 21616

Approaches to the Simulation of Compositional Data: A Nickel-Laterite comparative case study

Mueller, U.; Tolosana-Delgado, R.; van den Boogaart, K. G.

An accurate prediction of benefit for some types of ore may require not just the ore grade, but a whole compositional characterization of the estimates, that is, its full mineral composition, including waste composition and nuisance elements. An example is Nickel laterite ores, where Ni/Co content must be complemented by estimates of many other elements, as these might have a notable impact on ore processing.
Estimates are often obtained with (co)kriging or co-simulation. However, geostatistics applied to compositional data may yield spurious and inconsistent results because of the constant sum constraint. The log-ratio approach avoids such problems. Like anamorphosis, it proposes a three-step procedure: (1) data are mapped to a set of log ratios of components, for example the additive log-ratio transformation (alr); (2) transformed scores are modelled with an appropriate fully multivariate geostatistical toolbox (e.g. direct/cross-variograms and cokriging or co-simulation); and (3) results are back-transformed to the original units. Some practical aspects may make the application of this technique difficult: the assumption of Gaussianity and the high dimensionality of the compositions combined with the need for using multivariate methods. This contribution compares several ways of treating compositional data (combining anamorphosisnormal score transformation, logratio transformations, and minimum maximummax autocorrelation decomposition) with respect to their ability to generate sensible simulations. The various approaches considered are illustrated with a Nickel laterite data set for which 10 variables are available. Both theoretical considerations and illustration results suggest that the best combination is (log)ratio-anamorphosisnormal score transform-MAF, in this order. The factors so obtained are closer to Gaussian, approximately spatially decorrelated and can be simulated independently. Simulations can later be recombined to alr-simulations, which in turn may be converted back to point compositions. The resulting simulated compositions are compared with a full Gaussian co-simulation of the raw data. The logratio methodsy show a reasonable to good reproduction of mean values and distribution of the data set and by construction honour the total sum constraint, in contrast to the simulations based on the raw data for which the total sums fluctuate strongly.

  • Contribution to proceedings
    SMP 2014, Ore body Modelling and Strategic Mine Planning Symposium 2014, 24.-26.11.2014, Perth, Australia
    Orebody Modelling and Strategic Mine Planning, SMP 2014, Integrated mineral investment and supply chain optimisation, Cartlon Victoria, Australia: Australasian Institute of Mining and Metallurgy, 987-1-925100-19-8, 61-72

Publ.-Id: 21615

A comprehensive study of the magnetic, structural, and transport properties of the III-V ferromagnetic semiconductor InMnP

Khalid, M.; Gao, K.; Weschke, E.; Hübner, R.; Baehtz, C.; Gordan, O.; Salvan, G.; Zahn, D. R. T.; Skorupa, W.; Helm, M.; Zhou, S.

The manganese induced magnetic, electrical, and structural modification in InMnP epilayers, prepared by Mn ion implantation and pulsed laser annealing, are investigated in the following work. All samples exhibit clear hysteresis loops and strong spin polarization at the Fermi level. The degree of magnetization, the Curie temperature, and the spin polarization depend on the Mn concentration. The bright-field transmission electron micrographs show that InP samples become almost amorphous after Mn implantation but recrystallize after pulsed laser annealing. We did not observe an insulator-metal transition in InMnP up to a Mn concentration of 5 at. %. Instead all InMnP samples show insulating characteristics up to the lowest measured temperature. Magnetoresistance results obtained at low temperatures support the hopping conduction mechanism in InMnP. We find that the Mn impurity band remains detached from the valence band in InMnP up to 5 at. % Mn doping. Our findings indicate that the local environment of Mn ions in InP is similar to GaMnAs, GaMnP, and InMnAs; however, the electrical properties of these Mn implanted III-V compounds are different. This is one of the consequences of the different Mn binding energy in these compounds.

Keywords: III-V magnetic semiconductors

Publ.-Id: 21614

The Tayler instability at low magnetic Prandtl numbers

Stefani, F.; Barry, L.; Gundrum, T.; Kirillov, O.; Seilmayer, M.; Weber, N.; Gellert, M.; Rüdiger, G.

The Tayler instability is a kink type instability which appears when an axial current in a cylinder crosses a certain critical value. It has been discussed as a main ingredient of the Tayler-Spruit stellar dynamo model, but may also play a role as a size-limiting factor in large-scale liquid metal batteries. We discuss several theoretical aspects and the first experimental evidence of the Tayler instability in liquid metals.

  • Lecture (Conference)
    European GdR Dynamo Meeting, 01.-04.09.2014, Cambridge, England

Publ.-Id: 21613

The present status of the DRESDYN project

Stefani, F.

The DRESDYN project at Helmholtz-Zentrum Dresden-Rossendorf is intended as a platform for large-scale liquid sodium experiments on dynamo action and magnetically triggered flow instabilities. We report on the progress of the building construction, and on the design status of the precession driven dynamo experiment. Special focus is laid on new theoretical and experimental results on the magnetorotational and Tayler instability, and on the consequences for the planned liquid sodium experiment for the combined study of those instabilities. Some very recent results of a small-scale spherical Couette experiment with an applied axial magnetic field are also discussed.

  • Invited lecture (Conferences)
    Grands séminaires ISTerre, 13.11.2014, Grenoble, France

Publ.-Id: 21612

The present status of the DRESDYN project

Stefani, F.

The DRESDYN project is new platform for a variety of liquid sodium experiments, comprising a large-scale precession driven dynamo experiment and a combined set-up for investigating different versions of the magnetorotational instability and the Tayler instability. We sketch the history of previous liquid metal experiments on cosmic magnetic field, and outline the status of preparations for the various facilities planned in the framework of DRESDYN.

  • Invited lecture (Conferences)
    MHD-Days 2014, 02.-03.12.2014, Potsdam, Germany

Publ.-Id: 21611

The new IR FEL Facility at the Fritz-Haber-Institut in Berlin

Schöllkopf, W.; Gewinner, S.; Erlebach, W.; Junkes, H.; Liedke, A.; Meijer, G.; Paarmann, A.; von Helden, G.; Bluem, H.; Dowell, D.; Lange, R.; Rathke, J.; Todd, A. M. M.; Young, L. M.; Lehnert, U.; Michel, P.; Seidel, W.; Wünsch, R.; Gottschalk, S. C.

A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 PI mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 µs. Pulsed radiation with up to 50 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 µm. Regular user operation started in Nov. 2013 with 6 user stations. These include, for instance, spectroscopy of bio-molecules (peptides and small proteins), which are conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase.

  • Poster
    36th International Free Electron Laser Conference 2014, 25.-29.08.2014, Basel, Schweiz
  • Open Access Logo Contribution to proceedings
    36th International Free Electron Laser Conference 2014, 25.-29.08.2014, Basel, Schweiz
    Proceedings of 36th International Free-Electron Laser Conference, CERN: JACoW

Publ.-Id: 21610

The new ELBE Center for High Power Radiation Sources at HZDR: Status and Opportunities

Seidel, W.

The ELBE user facility located at the Helmhotz-Zentrum Dresden-Rossendorf operates a superconducting electron linear accelerator , which provides short (picosecond) electron bunches with energies up to 35 MeV at a 13 MHz repetition rate. Here we discuss the basic parameters of the ELBE Center and the experimental opportunities at the facility.

  • Invited lecture (Conferences)
    Turkish-German Workshop on Particle Accelerators and Light Sources, 09.-10.07.2014, Istanbul, Turkey

Publ.-Id: 21609

Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection in complex matrices

Hildebrand, H.; Schymura, S.; Holzwarth, U.; Gibson, N.; Dalmiglio, M.; Franke, K.

Detection and quantification of engineered nanoparticles (NPs) in complex environmental or biological media is a major challenge since NP concentrations are generally expected to be low compared to elemental background levels. This study presents three different options for radiolabeling of commercial titania NP (TiO2-NP, AEROXIDE® P25, Evonik Industries, mean diameter 21 nm) for particle detection, localization and tracing under various experimental conditions. The radiolabeling procedures ensure stability and consistency of important particle properties such as size and morphology. For the first time, detection (and quantification) limits for TiO2-NPs in concentrations as low as 0.5 ng/L can be realized.

Publ.-Id: 21608

Theranostic mercury: 197(m)Hg with high specific activity for imaging and therapy

Walther, M.; Preusche, S.; Bartel, S.; Wunderlich, G.; Freudenberg, R.; Steinbach, J.; Pietzsch, H.-J.

The no carrier added (NCA) radionuclide 197(m)Hg is accessible through proton induced nuclear reactions on gold.The decay properties of both simultaneous produced nuclea risomers 197mHg and 197Hg like convenient half life, low energy gamma radiations for imaging, Auger and conversion electrons for therapy are combined with unique chemical and physical properties of mercury and its compounds. Gold as a monoisotopic element has a natural abundance of 100% 197Au superseding expensive enrichment for the target material. Additionally, the high thermal conductivity of gold enables high beam current irradiations. For separation of target material a liquid–liquid extraction method was applied.

Keywords: 197Hg; Theranostics; Dosimetry; 177Lu; Auger and conversion electrons

Publ.-Id: 21607

Wissens- und Innovationsgemeinschaften (KIC) am Beispiel des KIC Rohstoffe - nachhaltige Erkundung, Gewinnung, Verarbeitung, Verwertung und Substitution

Dirlich, S.; Klossek, A.

Der Vortrag erläutert anhand von drei Leitfragen (Ziele von KIC, Synergien zur nationalen Forschung und aktuelle Entwicklungen) Wissens- und Innovationsgemeinschaften im Allgemeinen und geht im Besondere auf das geplante KIC Rohstoffe ein. Mit dem KIC Rohstoffe sollen die Ziele "vom Labor in den Markt", "vom Studenten zum Unternehmer" und "von der Idee zum Produkt" auf den Rohstoffsektor übertragen werden. Dabei wird die gesamte Kette von der Erkundung bis zum Recycling berücksichtigt. Für deutsche Wissenschaftler gibt es zahlreiche Synergiemöglichkeiten angesichts eines europäischen Netzwerks aus fast 120 Partnern aus den Bereichen Forschung, Bildung und Industrie. Das KIC beschäftigt sich insbesondere mit der Rohstoffverfügbarkeit in Europa, der Substitution kritischer Rohstoffe und der Nachhaltigkeit in der gesamten Kette der Rohstoffindustrie.

Keywords: raw materials; resources supply; innovation; knowledge; KIC

  • Invited lecture (Conferences)
    11. Fona-Forum, 29.09.2014, Berlin, Deutschland

Publ.-Id: 21606

Attachment of solid elongated particles on the surface of a stationary gas bubble

Lecrivain, G.; Petrucci, G.; Rudolph, M.; Hampel, U.; Yamamoto, R.

Froth flotation is a separation process which plays a major role in the mining industry. It is essentially employed to recover a vast array of different valuable commodities such as rare earth minerals essential to the manufacture of high-tech products. Owing to its simplicity, the process is also widely used for the de-inking of recycled paper fibres and for the removal of pollutants from waste water. The flotation process essentially relies on the attachment of solid particles on the surface of gas bubbles immersed in water. The present study seeks to investigate the effect of the particle shape on the attachment mechanism. Using an in-house optical micro-bubble sensor the approach, the sliding and the adhesion of micron milled glass fibres on the surface of a stationary air bubble immersed in stagnant water is thoroughly investigated. The translational and rotational velocities were measured for fibres of various aspect ratios. The results are compared with a theoretical model and with experimental data obtained with spherical glass beads. It is found that the fibre orientation during the sliding motion largely depends on the collision area. Upon collision near the upstream pole of the gas bubble the major axis of the fibre aligns with the local bubble surface (tangential fibre alignment). If collision occurs at least 30° further downstream only head of the fibre is in contact with the gas–liquid interface (radial fibre alignment).

Keywords: Froth flotation; Three-phase system; Solid elongated particles; Particle attachment; Gas-liquid interface

Publ.-Id: 21605

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