Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Effect of time–modulated magnetic fields on the solidification structure and extrusion properties of wrought aluminium
Räbiger, D.; Resewski, C.; Müller, S.; Willers, B.; Reimers, W.; Eckert, S.;
The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification.
Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front. It has been shown recently under laboratory conditions that an accurate tuning of the magnetic field parameters can avoid segregation effects and homogenize the mechanical properties.
This present study examines the directional solidification of commercial wrought aluminium alloys from a water-cooled copper chill. Rotating time-modulated magnetic fields were used to agitate the melt. The impact of flow on the resulting macro and micro structure are investigated. The solidified structure was reviewed in comparison to an unaffected solidified ingot and ingot prepared with chemical grain refiner. In addition results from extrusion process experiments are introduce. Our results demonstrate the potential of time–modulated magnetic fields to control the grain size, the formation of intermetallic phases and the morphology and distribution of pores.
Keywords: wrought aluminum alloy, time modulated magnetic field, bar extrusion
  • Lecture (Conference)
    The 9th International Symposium on Electromagnetic Processing of Materials, 14.-18.10.2018, Hyogo, Japan
  • Contribution to proceedings
    The 9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Hyogo, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012039
    DOI: 10.1088/1757-899X/424/1/012039

Publ.-Id: 27700 - Permalink


Trends in valence band electronic structure of mixed uranium oxides
Kvashnina, K. O.; Kowalski, P. M.; Butorin, S. M.; Leinders, G.; Pakarinen, J.; Bes, R.; Li, H.; Verwerft, M.;
Valence band electronic structure of mixed uranium oxides (UO2, U4O9, U3O7, U3O8, b-UO3) has been studied by the resonant inelastic X-ray scattering (RIXS) technique at the U M5 edge and by computational methods. We show here that the RIXS technique and recorded U 5f - O 2p charge transfer excitations can be used to proof the validity of theoretical approximations.

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  • Secondary publication expected from 08.08.2019

Publ.-Id: 27699 - Permalink


Influence of Al-alloy composition on the potential of forced convection to reduce grain size and prevent macrosegregation
Räbiger, D.; Willers, B.; Eckert, S.;
In addition to alloy composition, the grain size and a homogeneous phase distribution plays a major role to adjust the properties of cast and wrought aluminium alloys. To achieve grain refinement in solidification processes several methods are common: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring, or ultrasonic treatment.
The generation of an additional forced flow in the melt offers the possibility to control the grain size without chemical additives.
AC magnetic fields permit a contactless method to generate such forced flow in the liquid metal. Even more: It is possible to control the flow inside the bulk and tune the grain size of the solidified metal. Many studies have shown the complex interaction of magnetic field and melt flow and between melt flow and solidification structure. Therefore, a profound understanding of the mechanisms and well-justified flow structures in space and time are necessary to produce superior casting structures.
In this presentation experimental results are shown to understand the impact of alloy composition on the grain size and phase distribution for different flow conditions. To typify different solidification behaviors we compare various compositions. For this study pure aluminium, wrought aluminium alloy and an AlSi7-alloy was used. Our results demonstrate the restriction of meaningful implementation in low-alloy and the potential to control the grain size in wrought and cast alloys.
Keywords: grain refinement, forced convection, electromagnetic stirring, aluminium alloy, macrosegregation
  • Lecture (Conference)
    The 7th International Conference on Solidification and Gravity, 03.-06.09.2018, Miskolc - Lillafüred, Hungary
  • Contribution to proceedings
    The 7th International Conference on Solidification and Gravity, 03.-06.09.2018, Miskolc - Lillafüred, Hungary
    Proceedings of the 7th International Conference on Solidification and Gravity

Publ.-Id: 27698 - Permalink


Flow structure optimization and the impact on the solidification structure
Räbiger, D.; Willers, B.; Eckert, S.;
The adjustment of fine grain morphologies has been approved to be a crucial issue for improving characteristics and properties of cast and wrought aluminium alloys. Several methods are known to achieve grain refinement in solidification processes: add-on of grain refiners, rapid cooling conditions, mechanical or electromagnetic stirring, or ultrasonic treatment.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification, which in turn requires a detailed knowledge of the flow structures and a profound understanding of the complex interaction between melt flow, temperature and concentration field.
Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front [1, 2]. It has been shown recently under laboratory conditions, that an accurate tuning of the magnetic field parameters can avoid segregation effects [3] and homogenize the mechanical properties [4].
This present study examines the directional solidification of commercial cast and wrought aluminium alloys from a water-cooled copper chill. Rotating magnetic fields were used to agitate the melt. The application of different stirring strategies, e.g. time-modulated magnetic fields, reveals the impact of diverse flow conditions on the resulting macro and micro structure. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Our results demonstrate the potential of magnetic fields to control the grain size and the formation of segregation freckle. In particular, time–modulated rotating fields show their capability to homogenize both the grain size distribution and phase distribution.
  • Lecture (Conference)
    The Third Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russland

Publ.-Id: 27697 - Permalink


Competitive adsorption of ZrO2 nanoparticle and alkali cations (Li+ – Cs+) on muscovite (001)
Qiu, C.; Eng, P. J.; Hennig, C.ORC; Schmidt, M.ORC
We studied the adsorption behavior of ZrO2 nanoparticles on muscovite (001) surface in the presence of cations from the alkali series (Li+, Na+, K+, Rb+ and Cs+). The results of surface X-ray diffraction, i.e. crystal truncation rod and resonant anomalous X-ray reflectivity in combination with AFM images, shows that the sorption of ZrO2 nanoparticles is significantly affected by the binding mode of alkali ions on the muscovite (001) surface. From solutions containing alkali ions binding as outer sphere surface complexes (i.e. Li+ and Na+), higher uptake of Zr4+ is observed corresponding to the binding of larger nanoparticles, which relatively easily replaces the loosely bound alkali ions. However, Zr4+ uptake in solutions containing alkali ions binding as inner sphere surface complexes (i.e. K+, Rb+, and Cs+) is significantly lower and smaller nanoparticles are found at the interface. In addition, uptake of Zr4+ in the presence of inner sphere bound cations displays a strong linear relationship with hydration energy of the coexisting alkali ion. The linear trend can be interpreted as competitive adsorption between ZrO2 nanoparticles and inner sphere bound alkali cations, which are replaced on the surface and undergo rehydration after release to the solution. The rehydration of alkali ion gives rise to a large energy gain, which dominates the reaction energy of the competitive adsorption process. The competitive adsorption mechanism of ZrO2 nanoparticle and alkali ions is discussed comprehensively to highlight the potential relationship between the hydration effect of alkali ions and the effect of charge density of the nanoparticles.
Keywords: Surface X-ray diffraction, zirconium, muscovite, CTR, RAXR, nanoparticles, sorption

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  • Secondary publication expected from 16.10.2019

Publ.-Id: 27696 - Permalink


Leveraging extreme laser-driven magnetic fields for gamma-ray generation and pair production
Jansen, O.; Wang, T.; Stark, D. J.; D'Humieres, E.; Toncian, T.; Arefiev, A. V.;
he ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dense beams. Presented simulations show that more than 103 pairs can be produced in such a setup, and the directionality of the positrons can be controlled by the angle of incidence between the beams.
Keywords: high energy radiationlaser accelerationpair creationplasmaplasma channelrelativistic transparencyultra-high magnetic fields

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Publ.-Id: 27694 - Permalink


Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics
Santos, J. J.; Bailly-Grandvaux, M.; Ehret, M.; Arefiev, A. V.; Batani, D.; Beg, F. N.; Calisti, A.; Ferri, S.; Florido, R.; Forestier-Colleoni, P.; Fujioka, S.; Gigosos, M. A.; Giuffrida, L.; Gremillet, L.; Honrubia, J. J.; Kojima, S.; Korneev, P.; Law, K. F. F.; Marquès, J.-R.; Morace, A.; Mossé, C.; Peyrusse, O.; Rose, S.; Roth, M.; Sakata, S.; Schaumann, G.; Suzuki-Vidal, F.; Tikhonchuk, V. T.; Toncian, T.; Woolsey, N.; Zhang, Z.;
Powerful nanosecond laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance Ilasλlas2. The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 μm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes, and to laboratory astrophysics.

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Publ.-Id: 27693 - Permalink


Transient Modelling of Wire-Mesh Sensor
Dias, F. A.; Schleicher, E.; Da Silva, M. J.ORC; Hampel, U.ORC
Wire-Mesh sensor (WMS) is a device to measure transient phase fraction distributions of multiphase fluids, e.g. in a cross-section of a pipe. It has an enormous potential to be applied in many fields, i.e. chemical, energy and oil processing. However, some questions about its operational behavior are difficult to answer with experiments only. Therefore, we present in this paper a new finite element model of a capacitive WMS that is able to solve the transient current end electric field of the system. In this way, the model is coupled with an electrical circuit to amplify the currents flowing on the receiver electrodes allowing direct comparison with experimental data. In order to validate this approach, an experiment with deionized water was carried out and compared with two models: finite element model; and an electric circuit model, where the fluid impedance is considered as a capacitor with two parallel plates.
Keywords: Finite Element Method, Numerical model, Wire-Mesh Sensor
  • Lecture (Conference)
    9th World Congress on INDUSTRIAL PROCESS TOMOGRAPHY, 02.-06.09.2018, City of Bath, England

Publ.-Id: 27692 - Permalink


Validation of a closure model framework for turbulent bubbly two-phase flow in different flow situations
Krepper, E.; Rzehak, R.; Lucas, D.;
In the present paper a set of closure relations for interphase momentum exchange and for bubble-induced turbulence within the Euler-Euler framework is presented and validated against a set of tests performed at the HZDR-facility MT-Loop. The facility was equipped with wire-mesh sensors that allow cross sectional distributions of gas fraction, gas velocity, and bubble sizes to be measured at different distances from the gas injection.
The radial gas fraction profile of fully developed turbulent vertical upward bubbly flow in a pipe is the result of the ratio of the radial force components of the so-called non-drag forces and can be used for model validation. However, only the ratio, not the absolute value of the bubble forces can be tested in this way. In the present paper more detailed information from the experiment is exploited by consideration of the evolution of gas fraction distribution particularly after the gas injection region. The change of cross sectional gas volume fraction distribution is the result of the action of non-drag forces.
In addition to vertical pipe flow tests further insight is obtained from the investigation of the effect of a slight tube inclination which shifts the gas distribution. Here the disturbance of the cylindrical symmetry of a vertical pipe gives hints on the absolute value of the non-drag force components.
The results show that the presented model framework at least is able to describe the phenomena qualitatively. Possible reasons for quantitative deviations are discussed and require further investigations.
Keywords: CFD, two phase flow, Euler-Euler, closure model, validation

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  • Secondary publication expected from 18.10.2019

Publ.-Id: 27691 - Permalink


Real space bonding and stability analysis of tetravalent f-element complexes with N-, O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
N-/O-donor ligands are promising complexing ligands for actinides in high-level liquid wastes. Especially the covalency of the An–N/O bonds and a comparison to lanthanides, e.g. Ce, is of interest for these complexes. Thus, the bond character for [M(salen)2] with M = Ce, Th, Pa, U, Np, Pu was investigated. Furthermore the stability of the complexes is compared and correlated with the bonding character.
Keywords: real-space bonding analysis, stability analysis, DFT, actinides, Schiff bases
  • Poster
    16th International Congress of Quantum Chemistry, 18.-23.06.2018, Menton, Frankreich
  • Poster
    Summer School on Modern Wavefunction Methods, 30.09.-05.10.2018, Gelsenkirchen, Deutschland

Publ.-Id: 27690 - Permalink


Investigation of a wetland contaminated by uranium mine tailings in Central France
Fichtner, A.; Sachs, S.; Rossberg, A.; Scheinost, A. C.; Arnold, T.; Montavon, G.; Stumpf, T.;
The release of uranium from mine tailings may present a hazard to the environment, which is the reason for the monitoring of the relevant storage sites in many countries. Studying the behavior of released radionuclides at these sites serves to better estimate the local risk and can help to improve the understanding of the geochemistry of the involved contaminants, e.g. for the application in transport modelling.
The storage site Roffin, located in the Region of Auvergne, France, contains approximately 30 000 t of mill tailings from the adjacent processing plant of the same name, which operated from 1947 to 1956. After the shutdown of the plant, the responsible operator has remodeled the site several times over the decades, in order to meet updated environmental standards [1].
Recent gamma-ray surveys have shown elevated radiation levels alongside a creek downstream of the storage site, especially in a wetland area in some two hundred meters distance of the site. Drill cores taken in this area show uranium concentrations up to 2000 ppm in the upper 30 cm, with peak concentrations in a whitish,clayey layer with a thickness of about 5 cm at a depth of 20 cm. Besides this anomalous layer, the soil is of the histosol type, with very high contents of organic matter and mostly saturated with water. The goal of our study is to identify the involved uranium species in the solid and aqueous phases, in order to understand the influence of discharge history and geochemistry on the risk presented by this contamination.
Sequential extractions performed on the different layers of the soil following the protocol of Tessier et al. [2] indicate a majority of the uranium to be bound to soil organic matter. Yet scanning electron microscopy analysis (SEM) of the white layer shows the presence of particles containing high uranium concentrations with sizes around 10 μm. Energy dispersive X-ray spectra (EDS) of some of these particles give compositions corresponding to a specific mineral processed in the plant, which is Parsonsite [Pb2(UO2)(PO4)2]. Dating the soil with the C-14 of the soil organic matter and the depth profile of Cs-137 from nuclear fallout further suggests that the origin of the white layer is connected to the active period of the site. X-ray absorption spectroscopy performed on the soil shows a variable distribution of U(IV) and U(VI) in the different layers. Porewater obtained by centrifugation contains uranium concentrations up to 1000 ppb.
Further studies aim to quantify the distribution of uranium between the different solid phases of the soil, as well as the identification of the main species in the porewater.

[1] Himeur, N., Andres, C.: Bilan environnemental - Sites miniers du Puy-de-Dôme. AREVA Operational Report (2010).
[2] Tessier, A., Campbell, P.G.C., Bisson, M.: Sequential Extraction Procedure for the Speciation of Particulate Trace Metals. Anal. Chem. (1979) Issue 51, pp. 844-851.
Keywords: Uranium, wetland, mine tailing, speciation, characterization
  • Contribution to proceedings
    RadChem 2018-18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic
    Czech Chemical Society Symposium Series, 18th Radiochemical Conference, Mariánské Lázně, Czech Republic, 13-18 May 2018, Booklet of Abstracts, 214
  • Poster
    RadChem 2018-18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic
  • Poster
    8. RCA-Workshop, 12.-14.06.2018, Dresden, Deutschland
  • Poster
    International Conference Uranium Biogeochemistry, 21.-26.10.2018, Monte Veritá Ascona, Switzerland

Publ.-Id: 27689 - Permalink


Intensified deaeration by means of Rotating Packed Beds
Gross, K.; Bieberle, A.; de Beer, M.; Schmuhl, R.; Skiborowski, M.; Górak, A.;
Metal piping and equipment corrosion related to the presence of oxygen is a severe problem in the industry. It may lead to longer down times or a replacement of the equipment, as a consequence additional maintenance effort increases the production costs.
Commonly used equipment types for the deaeration in the chemical industry are (bulky) vacuum tower de-gasifiers or forced draft degasifiers.
However, acquiring the necessary low oxygen concentrations is challenging.
Application of Rotating Packed Beds (RPBs) allows for a high removal rate of oxygen for less than <50 ppb
Equipment size reduction by a factor of 6 to 9, due to the increased volumetric gas-liquid mass transfer rates.
Keywords: Rotating Packed Beds, Process Intensification
  • Poster
    A journey through the world of salt: past, present and future, 12.07.2018, Enschede, Niederlande

Publ.-Id: 27687 - Permalink


Elucidating the impact of elevated temperature on the complexation of Cm(III) and Eu(III) with phosphate ions by luminescence spectroscopy
Jordan, N.; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.; Huittinen, N.;
Orthophosphate ions (H2PO4−, HPO42−, and PO43−) are ubiquitous in the environment and may originate from the natural decomposition of rocks and minerals (e.g. monazite or apatite), agricultural runoff, or from phosphate fertilizer plants. Solid phosphate monazites are one of the most important ore bodies for the recovery of REE[1], while future monazite applications may involve their use as immobilization matrices for specific HLW streams.[2] Among the inorganic ligands, phosphates are strong complexants and can be expected to influence the speciation of dissolved contaminants when present in solution. However, very little data is available on the complexation of actinides and lanthanides with aqueous phosphates, even though they precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters, in the proximity of monazite-containing high-level waste repositories as well as in the processing of rare earth elements.
The existing data also suffers from an almost complete absence of independent spectroscopic validation of the stoichiometry of the proposed complexes. Furthermore, there are no studies dealing with the impact of elevated temperatures on An/Ln complexation with aqueous phosphates, despite the relevance of high temperatures both in the proximity of heat-generating HLW repositories and in REE leaching from monazites minerals.

In this study, the complexation of Cm(III) (5×10−7 M) and Eu(III) (5×10−6 M) was investigated by means of laser-induced luminescence spectroscopy as a function of the total phosphate concentration (0–0.5 M Σ(PO4)) using NaClO4 as a background electrolyte (I = 0.5–3.1 M), in the temperature range from 25 to 80 °C. Experiments were conducted in the acidic pH range (−log[H+] = 1 and 2.5) to avoid the precipitation of solid Cm/Eu rhabdophane (MePO4×nH2O). The formation of MeH2PO42+, Me(H2PO4)2+, and Me(HPO4)+ was observed, depending on the solution pH and the total phosphate concentration.
Upon increasing both the ionic strength and temperature, complexation was found to be promoted.[3] By applying the specific ion interaction theory (SIT), the obtained conditional constants at varying ionic strengths and temperatures were extrapolated to infinite dilution (log β0). The molal standard enthalpy of reaction ΔRHm° (assumed constant between 25 to 80 °C) and molal standard entropy of reaction ΔRSm° were derived by using the Van’t Hoff equation.

The new thermodynamic data derived in this fundamental study will support the optimization of technological strategies applied to access raw materials and contribute to a fundamental process understanding necessary to critically assess the environmental fate of actinides and lanthanides.
  • Contribution to proceedings
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2018), 06.-09.11.2018, Nice, France
  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2018), 06.-09.11.2018, Nice, France

Publ.-Id: 27686 - Permalink


Zero Overhead Modern C++ for Mapping to Any Programming Model
Huebl, A.ORC; Matthes, A.ORC; Worpitz, B.; Zenker, E.ORC; Widera, R.ORC; Juckeland, G.ORC; Bussmann, M.ORC
Towards exascale computing, today's HPC systems have become heterogeneous and diverse. Accounting for both host and accelerator, the TOP10 supercomputers in 11/2017 alone provided as much as 11 different computing architectures. On top of the hardware follow the accompanying programming models: from directive based, implicit and explicit descriptions up to task-based. Scientific code developers are facing a tough choice as commitment to a specific hardware and/or programming model narrows down potential target systems. With limited development resources but usually multi-decade long project lifetimes, maintaining multiple implementations of the same algorithms to widen platform support is unfeasible for most teams. Alpaka is a standard C++, compile-time meta-programming library providing a unified, explicit, parallel programming model. On typical MPI+X parallelized applications, Alpaka enables developers to describe shared-memory, in-node parallelism. Zero-overhead abstraction is achieved by compile-time specializing C++ templates to native backends (e.g. CUDA, OpenMP, TBB, ...). Alpaka stays with modern C++ as a standardized, widely supported language without introducing pre-processor or pragma-based annotations to the user directly. It naturally allows inlining, kernel fusion and code-reuse on a single-source programming paradigm. With such, abstractions and control within the final software stack are achievable without duplicating implementations leading to a maintainable code base even for large applications.
Keywords: HPC, performance portability, programming model, open source, alpaka, cuda, gpu, openpower, portability, high performance computing
  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2018, 02.-04.07.2018, Basel, Switzerland
    DOI: 10.5281/zenodo.1304272

Publ.-Id: 27685 - Permalink


Draft Genome Sequence of Bacillus safensis JG-B5T isolated from a uranium mining waste pile
Fischer, S.; Krause, T.; Jordan, N.; Lederer, F.; Jain, R.;
Bacillus safensis JG-B5T was isolated from soil of the uranium mining waste pile Haberland near Johanngeorgenstadt (Saxony, Germany). We report the draft genome sequence of the bacteria strain with 3.7 Mbp, which will provide information about high metal resistant abilities. This can be useful in the bioremediation of metal and metalloid-contaminated environments.

Publ.-Id: 27684 - Permalink


Single Plane Compton Imaging A noval concept for radionuclide imaging
Deneva, B.; Roemer, K.; Enghardt, W.; Pausch, G.; Wagner, A.; Koegler, T.;
Radionuclide imaging is a well-established and important diagnostic tool. The collected data contain physiological information as opposed to other traditional anatomical imaging techniques like X-ray computed tomography. The Anger Camera remains the primary device for nuclear medical imaging since its invention in 1957 [1]. However, despite the achieved advance in the imaging quality through the years, there are still performance limitations, resulting from the limited detection efficiency, reduced spatial resolution of highly energetic gamma rays, fixed dependency of the spatial resolution and detection efficiency from the used collimator and others. In order to overcome these limitations, the concept of “Single Plane Compton Imaging” (SPCI) has been proposed [2]. This concept, based on the idea of a “Directional Gamma Radiation Detector” [3] - [4] is now being explored experimentally.
We will present first experimental results obtained with a GAGG scintillator pixel array read out by a digital silicon photomultiplier array. The detector is operated in our laboratory and exposed to gamma radiation emitted from radioactive sources. Information about the source positions is derived from the energy spectra of coincident events in adjacent scintillator pixels.
Keywords: Anger Camera, radionuclide imaging, Single Plane Compton Imaging, GAGG
  • Poster
    Student Research Expo 2018, 4.07.2018, Dresden, Deutschland

Publ.-Id: 27683 - Permalink


Wide acceptance measurement of K/K+ ratio from Ni+Ni collisions at 1.91A GeV
Piasecki, K.; Herrmann, N.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Cordier, E.; Crochet, P.; Czerwiakowa, O.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Le Fèvre, A.; Liu, J. L.; Lopez, X.; Mangiarotti, A.; Manko, V.; Marton, J.; Matulewicz, T.; Merschmeyer, M.; Münzer, R.; Pelte, D.; Petrovici, M.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Stoicea, G.; Suzuki, K.; Tymiński, Z.; Wagner, P.; Weber, I.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.;
The FOPI Collaboration at GSI SIS-18 synchrotron measured the charged kaons from central and semi-central collisions of Ni+Ni at the beam energy of 1.91A GeV. We present the distribution of K−/K+ ratio on the plane of energy vs polar angle in the nucleon-nucleon centre-of-mass frame, with and without the subtraction of the contribution of φ(1020) meson decays to the K− yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The K−/K+ ratio is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate, that no mass-shift effect is needed to explain the difference between energy slopes of charged kaon spectra within uncertainties. The K−/K+ ratios obtained in this experiment, even after correction for the contribution due to the φ(1020) meson decays, decrease with increasing kinetic energy, as generally predicted in models assuming mass modifications.

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Publ.-Id: 27681 - Permalink


Precise nuclear data of the 14N(p,γ)15O reaction for solar neutrino predictions
Wagner, L.;
The 14N(p,γ)15O reaction is the slowest stage of the carbon-nitrogen-oxygen cycle of hydrogen burning and thus determines its reaction rate. Precise knowledge of its rate is required to improve the model of hydrogen burning in our sun. The reaction rate is a necessary ingredient for a possible solution of the solar abundance problem that led to discrepancies between predictions of the solar standard model and helioseismology. The solar 13N and 15O neutrino fluxes are used as independent observables that probe the carbon and nitrogen abundances in the solar core. This could settle the disagreement, if the 14N(p,γ)15O reaction rate is known with high precision. After a review of several measurements its cross section was revised downward due to a much lower contribution by one particular transition, capture to the ground state in 15O. The evaluated total relative uncertainty is still 7.5%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range.
The present work reports experimentally determined cross sections as astrophysical S- factor data at twelve energies between 0.357 – 1.292 MeV for the strongest transition, capture to the 6.79MeV excited state in 15O with lower uncertainties than before and at ten energies between 0.479 – 1.202 MeV for the second strongest transition, capture to the ground state in 15O.
In addition, an R-matrix fit is performed to estimate the impact of the new data on the astrophysical relevant energy range. The recently suggested slight S-factor enhancement at the Gamow window could not be confirmed and differences to previous measurements at energies around 1 MeV were observed. The present extrapolated zero-energy S-factors are S679(0) = (1.19±0.10) keV b and SGS(0) = (0.25±0.05) keV b and they are within the uncertainties consistent with values recommended by the latest review.
  • Doctoral thesis
    TU Dresden, 2018
    Mentor: Prof. Dr. Kai Zuber und Privatdozent Dr. Daniel Bemmerer
    111 Seiten
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-092 2018

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Publ.-Id: 27680 - Permalink


Multiscale-modelling of gas liquid flows – GENTOP
Lucas, D.;
In multiphase flows interfaces may span over a wide range of sizes. In a multi fluid approach interfaces smaller as well as larther than the typical size of the numerical grid may occur. While the small interfaces (bubbles and drops) should be represent by smeared phase volume fractions the large structures should be resolved in a CFD simulation. Also transitions between contineous and dispersed morphologies of teh phases may occur.
The lecture discusses the issues for modelling such flows and the basic ideas of the GENTOP concept. Domonstration simulations using the GENTOP concept show the cpabablities of this approach.
Keywords: multiphase, morphology, multi-scale, bubble, drop, seggregated flow, coalescence, breakup
  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.-08.06.2018, Changsha, China

Publ.-Id: 27677 - Permalink


Two-phase flow experiments and measuring techniques @ HZDR
Lucas, D.;
TOPFLOW-experiments on vertical pipes and within the TOPFLOW pressure chamber are presented. Innovative measuring techniques as wire-mesh sensors and ultrafast X-ray tomography provide detailed information on the interfacial structure in gas-liquid flows. Details on these measuring techniques are discussed and experiments on flows under adiabatic conditions as well as flows with phase transfer are presented.
Keywords: wire-mesh sensor, ultrafast X-ray tomography, pipe flow, pressure chamber, TOPFLOW
  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.-08.06.2018, Changsha, China

Publ.-Id: 27676 - Permalink


The Institute of Fluid Dynamics at HZDR
Lucas, D.;
The Institute of Fluid Dynamics within the HZDR was introduced in frame of a lecture series at Central South University inn Changsha, China. Special focus was on the activities of the CFD-department.
Keywords: HZDR, multiphase flow, CFD
  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.06.2018, Changsha, China

Publ.-Id: 27675 - Permalink


Multiphase flow CFD activities at HZDR
Lucas, D.;
The HZDR strategy on the qualification of multiphase CFD in frame of the Euler-Euler-concept is presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. The baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them. Finally the HZDR activities are illustrated by several applications of multiphase CFD on industrial problem.
Keywords: CFD, MUSIG, AIAD, GENTOP, baseline, Euler-Euler
  • Lecture (others)
    Presentation at the Institute of Mechanics, Chinese Academy of Science, 12.06.2018, Beijing, China

Publ.-Id: 27674 - Permalink


Multi-fluid models for industrial gas-liquid flows
Lucas, D.;
The HZDR concepts for Euler-Euler-modelling of gas-liquid flow are presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. A baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them.
Keywords: CFD, multiphase, MUSIG, AIAD, GENTOP
  • Invited lecture (Conferences)
    DANSIS Seminar on Computational Techniques for Gas-Liquid Flows, 16.05.2018, Copenhagen, Denmark

Publ.-Id: 27673 - Permalink


CFD-modelling for bubbly flows in medium and large scales
Lucas, D.; Liao, Y.; Ma, T.; Krepper, E.; Ziegenhein, T.;
For gas-liquid flows in large and medium scale industrial applications the Euler-Euler approach is frequently used and for many problems it is the only feasible one. During the derivation of the basic conservation equations the information on the interface gets lost and all interfacial exchange between gas and liquid has to be reflected by appropriate closure models. They have to reflect local phenomena that usually are similar in different global flow situations as bubble columns, pipe flows and others. For this reason a unified setup for closure models should be applicable without any modification for such a spectrum of flow situations. The HZDR baseline model for bubbly flows defines such a set of closures. It was applied to more than 150 different cases indicating a good overall performance, but showing also the limits of the present model. For this reason the model has to be improved continuously.
Recently a new model for bubble-induced turbulence in the RANS framework was included into the baseline model. It was developed basing on DNS of a bubbly channel flow. Other activities aim on the lateral lift force, which is closely connected to the bubble shape. Weak points in the present setup are the near wall simulation and the consideration of swarm effects. For these issues more basic research is required to improve the understanding of the phenomena and to derive better closure models. The present model also shows clear deviations from experimental findings for cases with high liquid superficial velocities which are connected with large gradients in the liquid flow field and a high turbulence level.
The focus of the presentation is on recent and ongoing activities to improve closure models and on the requirements for further improvements.
Keywords: CFD, bubbly flow, Euler-Euler, baseline
  • Lecture (Conference)
    8th European-Japanese Two-Phase Flow Group Meeting, 22.-26.04.2018, New York, USA

Publ.-Id: 27672 - Permalink


Euler-Euler simulation and X-ray measurement of bubble chain in a shallow container filled with liquid metals
Liu, L.; Keplinger, O.; Ma, T.; Ziegenhein, T.; Shevchenko, N.; Eckert, S.; Yan, H.; Lucas, D.;
An Euler-Euler two-fluid approach was used to simulate the behavior of gas bubbles rising in a stagnant liquid metal. A single point injection with four gas flow rates resulted in the formation of bubble chains undergoing either slight or distinct oscillations of the bubble trajectories. A set of interfacial closures with a shear stress transport (SST) k-ω turbulence models was applied for simulating the transient behavior of the bubble chain. X-ray radiography measurements were conducted to establish an experimental data base for validating the numerical results. The experiments provide a visualization of the bubble chain in a flat container and allow determining the bubble size and integral void fraction. Two bubble induced turbulence (BIT) models (Rzehak and Krepper, 2013a, Sato et al., 1981) and a modified turbulent viscosity approach (Johansen et al., 2004) were applied within this study. For all gas flow rates, the Rzehak and Sato BIT model alone predicted a steady bubble chain in contrast to the oscillating bubble plume observed in the experiments. Without a BIT model the oscillating bubble chain can be predicted but the oscillation frequency is underestimated especially for high gas flow rates. In addition, calculations without a BIT model predicted over-dispersion of the averaged gas fraction through the whole fluid container for the high gas flow rates. The best results in terms of a satisfying agreement with the experimental data were achieved by adopting a modified turbulent viscosity approach proposed by Johansen together with the Rzehak and Krepper BIT model. These findings demonstrate the significance of the turbulence model.
Keywords: Liquid metal two-phase flow; Bubble chain; X-ray radiography; Bubble induced turbulence model; CFD; Euler-Euler two-fluid model

Publ.-Id: 27670 - Permalink


Ion Irradiation Induced Cobalt/Cobalt Oxide Heterostructures: From Materials to Devices.
Hilliard, D.; Yildirim, O.; Fowley, C.; Arekapudi, S. S. P. K.; Cansever, H.; Böttger, R.; Hlawacek, G.; Hellwig, O.; Lindner, J.; Fassbender, J.; Deac, A.;
The demand on high data transfer and storage capacities requires smaller devices to transmit or save data. Forming well-defined ferromagnetic and electrically conducting volumes within a non-magnetic and insulating matrix in the dimensions of several nanometers can pave a way to the production of such small devices. It has been demonstrated that the reduction of oxygen in Co₃O₄/Pd multilayers is possible via local proton irradiation resulting in ferromagnetic and conducting Co embedded in a nonmagnetic and insulating Co₃O₄ matrix [1]. However, the physical mechanism behind the ion irradiation-induced oxide reduction was not addressed clearly. There are two possible mechanisms suggested to play a role behind this oxide reduction. The first one is the chemical reduction of oxygen by reacting with implanted H+ ions, while the second possible mechanism is atomic displacements induced by ion irradiation. To address this issue, we analysed cobalt oxide thin films after irradiation with H+ and Ne+ ions at different doses. The irradiation parameters for Ne+ were chosen to give the same displacements per atom (dpa) as that of H+ which is required to reduce cobalt oxide. We also confined irradiated areas on the films in the range of microns to submicron, in order to ascertain the lateral distribution of oxygen after irradiation.
We prepared single layer films of CoO (6-12nm) and Co₃O₄ (10nm) capped with Pt protection layers. Broad-beam H+ irradiations were performed at 0.3 keV for ion doses ranging from 10¹⁵ to 10¹⁷ ions/cm² on unpatterned films. After irradiation the films were characterized structurally and magnetically and compared to un-irradiated films. Extended films showed approximately 7% of the Co bulk metal saturation magnetization (MS) after irradiation at a dose of 5 x 10¹⁶ ions/cm² (fig. 1a inset). The increase is more pronounced with Co₃O₄ than CoO (fig. 1a). A sample was also prepared with a striped irradiation mask of 40 μm pitch. These films showed a higher magnetization after irradiation at lower doses as compared to unpatterned films, 0.14 MA/m for a dose of 10¹⁶ ions/cm² (striped) as opposed to 0.025 MA/m (extended) for a dose of 10¹⁷ ions/cm².
Figure 1 (b) shows the effect of stripe width (0.5, 5, 10, 20 μm) on the resulting magnetization after H+ irradiation at the same energy with a dose of 10¹⁷ ions/cm². No clear correlation between stripe width and MS was seen in either oxide phase for stripes down to 0.5 μm. However, the CoO sample with 0.5 μm stripes and a thinner oxide thickness of 6 nm (gold line) as opposed to 12 nm exhibited larger MS after irradiation, indicating oxygen displacements occur in the first few nanometers of the oxide.
We also performed 5 keV Ne+ irradiations with the helium-ion microscope (HIM) varying the ion dose from 10¹⁴ to 10¹⁶ ions/cm². After Ne+ irradiations magnetic force microscopy (MFM) images were taken along with a topography image in the remnant state (fig. 2). Starting from the ion dose of 5x10¹⁴ ions/cm², a magnetic contrast could be observed by MFM, suggesting that oxygen atoms were successfully removed locally by reducing paramagnetic CoO to ferromagnetic Co. The formation of topographical bubbles was observed upon increasing the ion dose from 10¹⁵ ions/cm² to 10¹⁶ ions/cm². The lateral and horizontal sizes of the observed bubbles show a clear dependence on the ion dose with a narrow size distribution.
In conclusion, our results show that, oxygen removal by means of H+ irradiation is more efficient in Co₃O₄ films as opposed to CoO. Additionally, although there is little dependence of the resulting Ms on the pitch of the stripes (in the range of 0.5 - 20 μm), the use of a stripe mask has a more pronounced effect on the oxygen removal process as compared to the irradiations on extended films. Therefore, the physical mechanism behind the ion-irradiation induced oxide reduction process cannot purely be a chemical reaction between oxygen and hydrogen. As an outlook, the lateral size and spacing of the ferromagnetic regions generated by H+ irradiation is only limited by the resolution of EBL. This method and the successful formation of ferromagnetic regions upon Ne+ irradiation using the HIM can be exploited to print smaller, closer and synchronized contacts for nanocontact spin torque oscillators.
Keywords: oxygen reduction, oxygen removal, magnetization, CoO, Co3O4, ion beam, cobalt, cobalt oxide
  • Open Access LogoContribution to proceedings
    Intermag 2018, 23.-27.04.2018, Marina Bay Sands Convention Center, Singapore

Publ.-Id: 27668 - Permalink


Raw Materials for Future Energy Supply
Wellmer, F. W.; Buchholz, P.; Gutzmer, J.; Hagelüken, C.; Herzig, P.; Littke, R.; Thauer, R. K.;
This is the first book that analyses the future raw materials supply from the demand side of a society that chiefly relies on renewable energies, which is of great significance for us all. It addresses primary and secondary resources and substitution, not only from technical but also socioeconomic and ethical points of view.

The “Energiewende” (Energy Transition) will change our consumption of natural resources significantly. When in future our energy requirements will be covered mostly by wind, solar power and biomass, we will need less coal, oil and natural gas. However, the consumption of minerals, especially metallic resources, will increase to build wind generators, solar panels or energy storage facilities. Besides e.g. copper, nickel or cobalt, rare earth elements and other high-tech elements will be increasingly used. With regard to primary metals, Germany is 100 % import dependent; only secondary material is produced within Germany. Though sufficient geological primary resources exist worldwide, their availability on the market is crucial. The future supply of the market is dependent on the development of prices, the transparency of the market and the question of social and ethical standards in the raw materials industry, as well as the social license to operate, which especially applies to mining. The book offers a valuable resource for everyone interested in the future raw material supply of our way of life, which will involve more and more renewable energies.
Keywords: Primary Resources, Secondary Resources, Raw Material Markets, Exploration, Mining, Recycling, Substitution, Critical Raw Materials, Bioenergy, Minerals, Supply, Demand, Key Natural Resources, Geological Energy Resources

Publ.-Id: 27667 - Permalink


Rohstoff-Forschung in Freiberg: „Excellent with the potential to become outstanding“
Gutzmer, J.;
The presentation is an invited keynote for the 12. Sächsischer Rohstofftag organised by the Geokompetenzzentrum Freiberg. The presentation focused on the interaction of different stakeholders in the resource technology landscape in Freiberg, including research, education and public institutions such as geological survey or the mining authority. Case studies were presented to illustrate the process and success of interaction. Recommendations were given to illustrate how the stakeholders could collaborate even more effectively.
Keywords: Freiberg, Saxony, resource technology
  • Invited lecture (Conferences)
    12. Sächsischer Rohstofftag, 21.-22.06.2018, Dresden, Germany

Publ.-Id: 27666 - Permalink


Evaluation of the microlayer contribution to bubble growth in horizontal pool boiling with a mechanistic model that considers dynamic contact angle and base expansion
Ding, W.; Krepper, E.; Hampel, U.;
Recently a new mechanistic model for pool and nucleate flow boiling was developed in our group. This model is based on the balance of forces acting on a bubble and considers the evaporation of the microlayer underneath the bubble, thermal diffusion around the cap of bubble due to the super-heated liquid and condensation due to the sub-cooled liquid. Compared to other models we particularly consider the temporal evolution of the microlayer underneath the bubble during the bubble growth by consideration of the dynamic contact angle and the dynamic bubble base expansion. This enhances, in our opinion, the model accuracy and generality. In this paper we further evaluate this model with experiments and direct numerical simulation (DNS) in order to prove the importance of dynamic contact angle and bubble base expansion.
Keywords: Nucleate boiling; Microlayer; Force balance; Dynamic contact angle; Dynamic base expansion; Bubble geometry

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  • Secondary publication expected from 12.06.2019

Publ.-Id: 27665 - Permalink


Attachment of colloidal particles to a fluidic interface – Aplication to the flotation process
Lecrivain, G.; Yamamoto, R.; Taniguchi, T.; Hampel, U.;
The attachment of colloidal particles to the fluidic surface of immersed fluid droplets is central to a wide variety of industrial applications, among which stand out the stabilisation of emulsion (Jansen et al., 2011) and the recovery of minerals by gas bubbles (Albijanic et al., 2010), a process known as forth flotation. Flotation, which is here of primary interest, is a separation process which plays a major role in the mining industry. It is employed to recover a vast array of different valuable commodities such as rare earth minerals essential to the manufacture of high-tech products. The process essentially involves the attachment of hydrophobised colloidal particles to the surface of rising air bubbles. The commercially valueless hydrophilic material settles down the flotation. Experimental and numerical works dealing with the attachment of spherical and non-spherical particles to a fluidic interface are here presented (See Figure 1). Using an optical microbubble sensor the various microprocesses (Lecrivain et al, 2015) associated with the colloidal attachment of elongated fibres are first investigated. In a second stage, direct numerical simulations are used to simulate the dynamics of such particles at a fluidic interface. Unlike spherical colloidal particles, it is found that plate-like particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force.
  • Lecture (Conference)
    Jahrestreffen Merseburg / Jahrestreffen der ProcessNet-Fachgruppen Mechanische Flüssigkeitsabtrennung, Trocknung und Grenzflächenbestimmte Systeme und Prozesse, 26.-28.02.2018, Halle-Merseburg, Germany

Publ.-Id: 27664 - Permalink


Attachment of colloidal particles to a fluidic interface – application to the flotation process
Lecrivain, G.; Hampel, U.; Yamamoto, R.; Taniguchi, T.;
The attachment of colloidal particles to the fluidic surface of immersed fluid droplets is central to a wide variety of industrial applications, among which stand out the stabilisation of emulsion (Jansen et al., 2011) and the recovery of minerals by gas bubbles (Albijanic et al., 2010), a process known as flotation. Flotation, which is here of primary interest, is a separation process which plays a major role in the mining industry. It is employed to recover a vast array of different valuable commodities such as rare earth minerals essential to the manufacture of high-tech products. The process essentially involves the attachment of hydrophobised colloidal particles to the surface of rising air bubbles. The commercially valueless hydrophilic material settles down the flotation. Experimental and numerical works dealing with the attachment of spherical and non-spherical particles to a fluidic interface are here presented (See Figure 1). Using an optical microbubble sensor the various microprocesses (Lecrivain et al, 2015) associated with the colloidal attachment of elongated fibres are first investigated. In a second stage direct numerical simulations are used to simulate the dynamics of such particles at a fluidic interface. Unlike spherical colloidal particles, it is found that plate-like particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force.
  • Contribution to proceedings
    C2E – Colloids and Complex fluids for Energies / Systems understanding: From preparation to process design, 04.-06.12.2017, Rueil-Malmaison, France
    Proceedings of C2E

Publ.-Id: 27663 - Permalink


Emission and Propagation of Multi-Dimensional Spin Waves in Anisotropic Spin Textures
Sluka, V.; Schneider, T.; Gallardo, R. A.; Kakay, A.; Weigand, M.; Warnatz, T.; Mattheis, R.; Roldan-Molina, A.; Landeros, P.; Tiberkevich, V.; Slavin, A.; Schütz, G.; Erbe, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.; Wintz, S.;
Spin waves offer intriguing novel perspectives for computing and signal processing, since their damping can be lower than the Ohmic losses in conventional CMOS circuits. For controlling the spatial extent and propagation of spin waves on the actual chip, magnetic domain walls show considerable potential as magnonic waveguides. However, low-loss guidance of spin waves, in particular around angled tracks, remains to be shown. Here we experimentally demonstrate that such advanced control of propagating spin waves can be obtained using natural features of magnetic order in an interlayer exchange-coupled, anisotropic ferromagnetic bilayer. Using Scanning Transmission X-Ray Microscopy, we image the generation of spin wave and their subsequent propagation across distances exceeding multiple times the wavelength, in extended planar geometries as well as along one-dimensional domain walls, which can be straight and curved. These results show routes towards the practical implementation of magnonic waveguides employing domain walls in future spin wave logic and computational circuits.
Keywords: magnon, spin-wave, propagation, emission

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Publ.-Id: 27662 - Permalink


Oxidation and luminescence quenching of europium doped BaMgAl10O17 probed by HERFD-XANES
Amidani, L.; Korthout, K.; Joos, J. J.; van der Linden, M.; Sijbom, H. F.; Meijerink, A.; Poelman, D.; Smet, P. F.; Glatzel, P.;
Eu-doped BaMgAl10O17 (BAM) is an excellent inorganic phosphor. Its luminescence efficiency is however severely degraded during prolonged vacuum-ultraviolet (VUV) excitation. Furthermore, the degradation process at the atomic level is not yet fully understood. To shed light on this process, we simultaneously employed X-rays as an equivalent but accelerated source of damage, as an excitation source of luminescence and as an element-selective probe of both dopants and host-lattice chemical species.
We investigated commercial samples of Eu doped and Mn, Eu co-doped BAM. We measured High-Energy Resolution Fluorescence Detected (HERFD)-XANES at Eu and Ba L3-edges and at Mn K-edge. The X-ray induced radio-luminescence (RL) and the HERFD-XANES spectra were simultaneously acquired while progressive damage was induced.
The evolution of the RL spectra confirms that the degradation induced by X-rays and by VUV irradiation are equivalent. The HERFD-XANES reveals that Ba and Mn are stable under the X-ray beam, while Eu2+ undergoes a rapid oxidation to Eu3+. We found that the correlation between Eu oxidation and RL intensity decay is non-linear and that a significant fraction of Eu2+ resists to irradiation, implying that an additional mechanism is responsible for the quenching of the remaining Eu2+. A kinetic Monte Carlo simulation indicates that the creation of defects acting as killer centers in the vicinity of a photo-oxidized Eu3+ can reproduce the dynamics observed on RL and Eu oxidation.
By simultaneously degrading and probing Eu-doped BAM we found [1] that the degradation process is due to oxidation of the luminescence impurities combined with the formation of killer centers that quench the luminescence of the remaining Eu2+.
Keywords: HERFD, inorganic phosphors, Eu oxidation
  • Lecture (Conference)
    XAFS 2018 - 17th International Conference on X-Ray Absorption Fine Structure, 22.-27.07.2018, Krakow, Poland
    DOI: 10.1021/acs.chemmater.7b03918

Publ.-Id: 27661 - Permalink


Inelastische Streuung schneller Neutronen an 56 Fe
Beyer, R.ORC
An der Neutronen-Flugzeit-Anlage nELBE des Helmholtz-Zentrums Dresden-Rossendorf sollen Reaktionsquerschnitte mit Relevanz für die nukleare Transmutation bestimmt werden. Die Transmutation hochradioaktiver Abfälle aus abgebrannten Brennelementen thermischer Kernreaktoren in schnellen Neutronenspektren hat das Potential die langlebige Radiotoxizität der Abfälle deutlich zu reduzieren. Zum grundlegenden Verständnis der Physik der Transmutation müssen sowohl Spalt- und Neutroneneinfang-Wahrscheinlichkeiten von Brennelementbestandteilen als auch inelastische Streuquerschnitte an Konstruktionsmaterialien im schnellen Neutronenspektrum mit möglichst kleinen Unsicherheiten bekannt sein.
Diese Arbeit beschäftigt sich mit der Messung des inelastischen Neutronen-Streuquerschnittes mit Hilfe einer neu entwickelten Doppel-Flugzeit-Methode. Mit einem kombinierten Aufbau aus Plastik- und BaF 2 -Szintillationsdetektoren werden die beim Streuprozess emittierten Neutronen und Photonen in Koinzidenz erstmalig nachgewiesen und dadurch der bei der Streuung angeregte Zustand des Zielkerns identifiziert.
An nELBE wird weltweit einzigartig der Elektronenstrahl eines supraleitenden Linearbeschleunigers, des ELBE-Beschleunigers, zur Erzeugung schneller Neutronen benutzt. Dieser wird auf einen Kreislauf flüssigen Bleis fokussiert, in dem die Elektronen Bremsstrahlung erzeugen, die wiederum Neutronen aus Bleikernen herauslöst. Durch die kurze Zeitdauer der Elektronenstrahlimpulse von ca. 5 ps kann mit einem kompakten Neutronenquellvolumen auch mit einer kurzen Flugstrecke eine gute Zeitauflösung erzielt werden. Das emittierte Neutronenspektrum hat eine einem Maxwell-Boltzmann-Spektrum ähnliche Verteilung und reicht von etwa 10 keV bis etwa 10 MeV. Bei einem verwendbaren Elektronenstrom von 15 μA beträgt die Quell-Stärke etwa 1,6 · 10 11 n/s.
Die Neutronen werden kollimiert und auf eine Probe natürlichen Eisens geschossen, die bei einer Flugstrecke von etwa 6 m positioniert war. Die Probenposition ist von einem Array von bis zu 42 BaF 2 -Szintillationsdetektoren zur Photonendetektion umgeben. In einem Abstand von 1 m sind fünf 1 m lange Plastik-Szintillationsdetektoren zum Neutronennachweis aufgebaut. Zur Bestimmung des einfallenden Neutronenflusses wurde eine 235 U-Spaltkammer verwendet, die bei einer Flugstrecke von etwa 4,3 m zwischen Neutronenquelle und Probe aufgestellt war. Die Signale aller Detektoren werden von einer speziell dafür entworfenen VME basierten Datenaufnahmeelektronik verarbeitet und die Zeit- und Ladungs-Werte bestimmt.
Aus dem Detektionszeitpunkt des Photons wird die Flugzeit und damit die Energie des einfallenden Neutrons bestimmt. Aus der Zeitdifferenz zwischen der Photonen- und Neutronendetektion ergibt sich die Flugzeit bzw. Energie des gestreuten Neutrons. Mit Hilfe von Kinematik-Rechnungen können die Ereignisse herausgefiltert werden, die der inelastischen Streuung unter Anregung eines bestimmten Kernniveaus eines bestimmten Isotops entsprechen. Aus dem Verhältnis von eingefallenem Neutronenstrom und nachgewiesenen Streuereignissen jeder Kombination aus einem Plastik- und einem BaF 2 -Szintillationsdetektor wurde entsprechend der Raumwinkelabdeckung der Detektoren der winkel- und energiedifferentielle inelastische Streuquerschnitt d 3 σ/dE n dΩ n ′ dΩ γ bestimmt.
Keywords: nELBE, inelastic scattering, Fe-56, fast neutrons, double-time-of-flight
  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Dr. A.R. Junghans

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Publ.-Id: 27660 - Permalink


Radioecological research of WG NORM within the ALLIANCE
Arnold, T.; Sachs, S.;
NORM sites are characterized by their waste type and by complex mixtures of different soil types, heavy metals, minerals, microbial diversities, present flora and fauna, as well as disequilibria in radionuclide decay chains. Due to this complexity, challenges arise not only from the lack of comprehensive scientific data, but also from existing model concepts themselves, which do not adequately describe the interplay between simultaneously occurring chemical and biological processes at a NORM site. Therefore, a promising strategy is to reduce modelling uncertainties by identifying and parameterizing the key processes that influence the radionuclide behaviour in these sites and to transfer this knowledge into mechanistic models sufficiently complex to describe the radionuclide behaviour in the environment, however, at the same time being simple enough to be practical and applicable to different NORM sites. In view of potential hazards associated with the exposure to enhanced natural radiation, proper evaluation of NORM sites related to former, current or future human activities, as well as the need for developing preventive methods at different stages of a technological process in a NORM industry are essential tasks here.
Working group (WG) NORM, currently composed of 20 organisations from 10 European countries, was established within the European Radioecology Alliance. One of the initial tasks of this WG was to develop a roadmap document, which covers a time frame of five years. This roadmap is part of a prolonged vision aiming at continuously incorporating new knowledge to progressively improve risk assessments of NORM contaminated sites and thereby helps to reduce the risk for humans and wildlife. The main objectives specified in the roadmap can be summarized as follows: (1.) improve risk assessment for existing and future NORM sites, (2.) extend transport modelling of radionuclides into the uncontaminated environments by including chemical/geochemical and biological/microbiological processes, i.e. to identify and mathematically describe processes that make significant contributions to the environmental transfer of radionuclides, and (3.) develop a mechanistic understanding of chemical and biological processes on a molecular scale and translate this knowledge into robust sub-models thus paving the way for new strategies for a sustainable rehabilitation and remediation of NORM sites.
WG NORM is a research platform for NORM interested scientists for sharing and exchanging knowledge on radionuclide behaviour in the environment. Its objectives aim at reducing the uncertainty of human and environmental risk assessment for NORM via an improved mechanistic process-based transport modelling and by integrating chemical process understanding as well as biological/microbiological processes in transport codes.
Keywords: Radioecology, NORM, ALLIANCE
  • Lecture (Conference)
    3rd European Radiological Protection Research Week (ERPW), 01.-05.10.2018, Rovinj, Croatia

Publ.-Id: 27659 - Permalink


Peculiar thermal behavior of UO2 local structure
Prieur, D.; Epifano, E.; Dardenne, K.; Rothe, J.; Hennig, C.; Scheinost, A.; Neuville, D.; Martin, P.;
Most materials expand in one, two or all three dimensions with temperature because of the anharmonicity of lattice vibration, and only few behave in the opposite way, i.e. shrink with increasing temperature1. Uranium dioxide, whose thermal properties are of significant importance for the safe use of the nuclear energy2, was considered for a long time to belong to the first group from room temperature to the melting point at 3147 ± 20 K3,4,5. This view was challenged by recent in situ synchrotron X-ray diffraction measurements, showing an unusual thermal decrease of the U-O distances up to the melting point6. This thermal shrinkage was interpreted as a consequence of the splitting of the U-O distances due to a change in the U local symmetry from Fm-3m to Pa-37. In contrast to these previous investigations and using an element-specific synchrotron-based spectroscopic method, we show here that the U sublattice remains locally of the fluorite type from 50 K to 1265 K, and that the decrease of the first U-O bond lengths with increasing temperature is associated to an increase of the disorder, which we modelled using the Einstein model. These findings are of significant importance in order to predict the thermal behaviour of nuclear fuel, as well as to understand the accumulation of fission product in the nuclear fuel.
  • Inorganic Chemistry 57(2018)23, 14890-14894
    DOI: 10.1021/acs.inorgchem.8b02657
  • Lecture (Conference)
    ATAS 2018 - 4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

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  • Secondary publication expected from 09.11.2019

Publ.-Id: 27658 - Permalink


Publikationen, Daten und Software am HZDR
Reschke, E.ORC; Frust, T.ORC; Juckeland, G.ORC; Konrad, U.ORC; Rücker, C.
3 Komponenten wissenschaftlichen Publizierens: ihre Vernetzung, Verwaltung und technische Untersetzung am HZDR
Keywords: RODARE, ROBIS, Open Access, Publizieren, Publikation, Datenpublikation, Softwarepublikation

Publ.-Id: 27657 - Permalink


Silver Accumulation in the Green Microalga Coccomyxa actinabiotis: Toxicity, in Situ Speciation, and Localization Investigated Using Synchrotron XAS, XRD, and TEM
Leonardo, T.; Farhi, E.; Pouget, S.; Motellier, S.; Boisson, A. M.; Banerjee, D.; Rebeille, F.; Den Auwer, C.; Rivasseau, C.;
Microalgae are good candidates for toxic metal remediation biotechnologies.
This study explores the cellular processes implemented by the green microalga Coccomyxa actinabiotis to take up and cope with silver over the concentration range of 10−7 to 10−2 M Ag+. Understanding these processes enables us to assess the potential of this microalga for applications for bioremediation. Silver in situ speciation and localization were investigated using X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy. Silver toxicity was evaluated by monitoring microalgal growth and photochemical parameters. Different accumulation mechanisms were brought out depending on silver concentration. At low micromolar concentration, microalgae fixed all silver initially present in solution, trapping it inside the cells into the cytosol, mainly as unreduced Ag(I) bound with molecules containing sulfur. Silver was efficiently detoxified. When concentration increased, silver spread throughout the cell and particularly entered the chloroplast, where it damaged the photosystem. Most silver was reduced to Ag(0) and aggregated to form crystalline silver nanoparticles of face-centered cubic structure with a mean size of 10 nm. An additional minor interaction of silver with molecules containing sulfur indicated the concomitant existence of the mechanism observed at low concentration or nanoparticle capping. Nanoparticles were observed in chloroplasts, in mitochondria, on the plasma membrane, on cytosolic membrane structures, and in vacuoles. Above 10−4MAg+, damages were irreversible, and photosynthesis and growth were definitely inhibited. However, high silver amounts remained confined inside microalgae, showing their potential for the bioremediation of contaminated water.
Keywords: Algae Ag Coccomyxa actinabiotis EXAFS

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Publ.-Id: 27656 - Permalink


Strain-specific metastatic phenotypes in pheochromocytoma allograft mice
Ullrich, M.; Liers, J.; Peitzsch, M.; Feldmann, A.; Bergmann, R.; Sommer, U.; Richter, S.; Bornstein, S. R.; Bachmann, M.; Eisenhofer, G.; Ziegler, C. G.; Pietzsch, J.ORC
Somatostatin receptor-targeting endoradiotherapy offers potential for treating metastatic pheochromocytomas and paragangliomas, an approach likely to benefit from combination radiosensitization therapy. To provide reliable preclinical in vivo models of metastatic disease, this study characterized the metastatic spread of luciferase-expressing mouse pheochromocytoma (MPC) cells in mouse strains with different immunologic conditions. Bioluminescence imaging showed that, in contrast to subcutaneous non-metastatic engraftment of luciferase-expressing MPC cells in NMRI nude mice, intravenous cell injection provided only suboptimal metastatic spread in both NMRI nude mice and hairless SCID (SHO) mice. Treatment of NMRI nude mice with anti Asialo GM1 serum enhanced metastatic spread due to substantial depletion of natural killer cells. However, reproducible metastatic spread was only observed in natural killer cell-defective SCID/beige mice and in hairless immunocompetent SKH1 mice bearing disseminated or liver metastases, respectively. Liquid chromatography tandem mass spectrometry of urine samples showed that subcutaneous and metastasized tumor models exhibit comparable renal monoamine excretion profiles characterized by increasing urinary dopamine, 3 methoxytyramine, norepinephrine, and normetanephrine. Metastases-related epinephrine and metanephrine were only detectable in SCID/beige mice. Positron emission tomography and immunohistochemistry revealed that all metastases maintained somatostatin receptor-specific radiotracer uptake and immunoreactivity, respectively. In conclusion, we demonstrate that intravenous injection of luciferase-expressing MPC cells into SCID/beige and SKH1 mice provides reproducible and clinically relevant spread of catecholamine-producing and somatostatin receptor-positive metastases. These standardized preclinical models allow for precise monitoring of disease progression and should facilitate further investigations on theranostic approaches against metastatic pheochromocytomas and paragangliomas.
Keywords: neuroendocrine tumors; catecholamines; bioluminescence imaging; somatostatin receptors; small animal positron emission tomography; metastasis

Publ.-Id: 27655 - Permalink


Crystallographic structure and charge distribution of AUO4 and A3UO6 uranates (A= Ca, Sr, Ba or Pb)
Prieur, D.; Popa, K.; Vigier, J.-F.; Scheinost, A.; Martin, P.;
AUO4 and A3UO6 uranates (A=Ca, Sr, Ba or Pb) have been synthesized by solid-state reaction. Their crystallographic struc-tures have been studied combining Powder X-ray Diffraction (PXRD) and Extended X-ray Absorption Fine Structure (EXAFS). To our knowledge, this is the first time the local environment of these uranates have been investigated by EXAFS. Depending on the nature of the alkali earth metal, the uranates compounds crystallize in different structures, in which the uranium local environment around the atoms have been identified. The U geometry is then compared to the oxidation states determined from X-ray Absorption Near Edge Spectroscopy (XANES).

Publ.-Id: 27654 - Permalink


Optimization of Uranium-Doped Americium Oxide Synthesis for Space Application
Vigier, J. F.; Freis, D.; Pöml, P.; Prieur, D.; Lajarge, P.; Gardeur, S.; Guiot, A.; Bouëxière, D.; Konings, R.;
mericium 241 is a potential alternative to plutonium 238 as an energy source for missions into deep space or to the dark side of planetary bodies. In order to use the 241Am isotope for radioisotope thermoelectric generator or radioisotope heating unit (RHU) production, americium materials need to be developed. This study focuses on the stabilization of a cubic americium oxide phase using uranium as the dopant. After optimization of the material preparation, (Am0.80U0.12Np0.06Pu0.02)O1.8 has been successfully synthesized to prepare a 2.96 g pellet containing 2.13 g of 241Am for fabrication of a small scale RHU prototype. Compared to the use of pure americium oxide, the use of uranium-doped americium oxide leads to a number of improvements from a material properties and safety point of view, such as good behavior under sintering conditions or under alpha self-irradiation. The mixed oxide is a good host for neptunium (i.e., the 241Am daughter element), and it has improved safety against radioactive material dispersion in the case of accidental conditions.

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  • Secondary publication expected

Publ.-Id: 27653 - Permalink


A novel fluorescence anisotropy‐based assay to investigate the GTP-binding site of human tissue transglutaminase
Hauser, C.; Kasprzyk, R.; Wodtke, R.; Kowalska, J.; Löser, R.; Jemielity, J.; Pietsch, M.;
Tissue transglutaminase (TGase 2) is a multifunctional enzyme that catalyzes the formation of covalent crosslinks between protein-bound glutamine and primary amine substrates (transamidase activity) but also functions as a GTP-binding protein (Gh protein). These two functions are associated with an “open” and a “closed” conformation, respectively, being tightly regulated by Ca2+ and GDP/GTP levels. In recent years, several assays for the transamidase activity have been published [1], leaving the GTP-binding function virtually untouched.
Here, we report a novel assay to quantify the GTP-binding activity of human TGase 2, which follows the increase in fluorescence anisotropy of an optimized fluorescein-labeled GTP probe upon binding to the protein. Validity of the assay was ensured by means of the (endogenous) ligands GTP, GTPγS and GDP showing inhibitory potencies (IC50) for displacement of the new probe comparable to reported values [2]. ATP, commonly not considered as being an inhibitor of TGase 2, was found to diminish binding of the probe to TGase 2 at unphysiologically high concentrations. The binding assay was then applied for the characterization of a small library of GDP and GTP analogs to obtain structure-activity relationships.
In addition, assays quantifying the transamidase [3] and GTP-binding activities, respectively, were subjected to a titration with calcium chloride (Ca2+) to elucidate its influence on the conformation of TGase 2. Exclusive interaction of ligands/substrates with the GTP binding site and with the active site were found in the absence of Ca2+ and at [Ca2+] > 10 mM, respectively. Both assays exhibit an activity of ~60% at [Ca2+] = 0.5 mM, with this intermediate calcium concentration being applicable to identify ligands of both the active and the GTP-binding site at the same time. This finding was confirmed in both assays by means of GTPγS and recently reported N6-acryloyllysine piperazides [4,5] shown to irreversibly interact with the active-site cysteine residue.


[1] Pietsch et al., Bioorg. Med. Chem. Lett. 2013, 23, 6528.
[2] Schaertl et al., J. Biomol. Screen. 2010, 15, 478.
[3] Hauser et al., Amino Acids 2017, 49, 567.
[4] Wityak et al., ACS Med. Chem. Lett. 2012, 3, 1024.
[5] Wodtke et al., J. Med. Chem. 2018, accepted.
  • Lecture (Conference)
    Transglutaminases in Human Disease Processes, 17.-21.06.2018, Les Diablerets, Schweiz

Publ.-Id: 27652 - Permalink


Synthesis and Characterization of Heterometallic Iron–Uranium Complexes with a Bidentate N-Donor Ligand (2,2′-Bipyridine or 1,10-Phenanthroline)
Schöne, S.ORC; Radoske, T.; März, J.; Stumpf, T.; Ikeda-Ohno, A.ORC
The coordination chemistry of the diamine ligands, 2,2’-bipyridine (bipy) and 1,10-phenanthroline (phen), with d- and f-block metals has been extensively explored during the last century to yield many technological and industrial applications. Despite this long history, the chemistry of these diamine ligands in hetero-metallic systems containing multiple metals is poorly understood even to date. This study reports, for the first time, a systematic investigation into the coordination behavior bipy/phen in the hetero-metallic iron-uranium system covering all the combination of the possible redox couples (i.e. Fe2+/Fe3+ and U4+/U6+) that are potentially relevant to the actual engineered or environmental systems. In total, eleven new compounds of pure-uranium and hetero-metallic Fe-U complexes were successfully synthesized and structurally characterized. The synthesized compounds show an intriguing structural variety in terms of the nuclearity of the metal center (mono- and dinuclear for both Fe and U) and the manner of crystal packing based on different intra- and intermolecular interactions (e.g. π•••π interactions, hydrogen bonding, etc.). The results also highlight the similarity of the fundamental coordination properties of bipy and phen towards Fe and U, regardless of the oxidation states of the metals, as well as the striking dissimilarity in their chemical behavior upon crystal packing.
Keywords: actinide, uranium, iron, diamine ligands, bipyridine, phenanthroline, hetero-metallic system, crystal structure, complex structure, characterisation, X-ray diffraction

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  • Secondary publication expected from 10.10.2019

Publ.-Id: 27651 - Permalink


Intermediate-band silicon nanowires realized by ion beam hyperdoping
Berencén, Y.; Prucnal, S.; Möller, W.; Hübner, R.; Rebohle, L.; Böttger, R.; Glaser, M.; Schönherr, T.; Yuan, Y.; Wang, M.; Georgiev, Y. M.; Erbe, A.; Lugstein, A.; Helm, M.; Zhou, S.; Skorupa, W.;
The intentional introduction of deep-level dopants into a semiconductor in excess of equilibrium concentrations causes a broadening of dopant energy levels into an intermediate band between the valence and conduction bands.[1,2] This phenomenon is referred to as hyperdoping. As intermediate-band material, bulk Si hyperdoped with chalcogens or transition metals holds promises for Si-based short-wavelength infrared photodetectors and solar cells.[3,4] Intermediate-band nanowires could potentially be used instead of bulk materials to overcome the Shockley-Queisser limit and to improve efficiency in solar cells.[5,6]
Here, we show a CMOS-compatible method based on non-equilibrium processing for the controlled doping of Si at the nanoscale with dopant concentrations several orders of magnitude above the equilibrium solid solubility. The approach relies on using ion implantation followed by flash lamp annealing for hyperdoping Si/SiO2 core/shell nanowires. We induce, by millisecond-flash lamp annealing, a bottom-up template-assisted solid-phase epitaxy recrystallization of the nanowires. This results in the formation of intermediate-band Se-hyperdoped nanowires which exhibit room-temperature sub-band gap optoelectronic photoresponse when configured as a photoconductor device.
References
[1] Sher M J, Mazur E, Appl. Phys. Lett. 2014;105:032103.
[2] Ertekin E, Winkler M, T, Recht D, Said A J, Aziz M J, Buonassisi T, Grossman J C, Phys. Rev. Lett. 2012;108:026401.
[3] Berencén Y, Prucnal S, Liu F, Skorupa I, Hübner R, Rebohle L, Zhou S, Schneider H, Helm M, Skorupa W, Sci. Rep. 2017;7:43688.
[4] Mailoa J P, Akey A J, Simmons C B, Hutchinson D, Mathews J, Sullivan J T, Recht D, Winkler M T, Williams J S, Warrender J M, Persans P D, Aziz M J, Buonassisi T, Nat. Commun. 2014;5:3011.
[5] Beard M C, Luther J M, Nozik A J, Nat. Nanotech. 2014;9:951.
[6] Tian B, Zheng X, Kempa T J, Fang Y, Yu N, Yu G, Huang J, Lieber C M, Nature 2007:449;885.
Keywords: Intermediate-band nanowires, ion beam hyperdoping, flash lamp annealing
  • Lecture (Conference)
    XII-th International Conference "Ion Implantation and Other Applications of Ions and Electrons", ION 2018, 18.-21.06.2018, Kazimierz Dolny, Poland

Publ.-Id: 27650 - Permalink


Stability of U(VI) doped calcium silicate hydrate gel in repository-relevant brines studied by leaching experiments and spectroscopy
Wolter, J.-M.; Schmeide, K.ORC; Weiss, S.; Bok, F.; Brendler, V.ORC; Stumpf, T.
The stability of calcium silicate hydrate (C-S-H) gel doped with uranium to form calcium uranium silicate hydrate (C-U-S-H) gel was investigated in 2.5 M NaCl, 2.5 M NaCl/0.02 M Na2SO4, 2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3 solutions relevant to the geological disposal of radioactive waste. The C-U-S-H gel samples were synthesized by direct U(VI) incorporation and characterized with time-resolved laser-induced luminescence spectroscopy (TRLFS), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Time-dependent pH changes as well as the Ca, Si and U release from C-U-S-H gels into the brines, determined by inductively coupled plasma mass spectrometry (ICP-MS), were monitored for three calcium-to-silicon (C/S) ratios (0.99, 1.55 and 2.02) over 32 d. Subsequently, changes of the U(VI) speciation and C-S-H mineralogy caused by leaching were investigated with TRLFS, IR spectroscopy and XRD. Results indicated that composition and pH value of the leaching solution, the presence of portlandite as well as formation and solubility of calcite as secondary phase determine the U(VI) retention by C-S-H gel under high saline and alkaline conditions. At high ionic strengths, the Ca release from C-S-H and secondary phases like calcite is increased. Under hyperalkaline conditions only small amounts of U(VI) were released during leaching. A decrease of the pH due to the additional presence of carbonate was linked with an increased U(VI) release from C-S-H gel leading to the formation of aqueous calcium uranyl carbonate in the supernatant solution.
Keywords: uranium, C-S-H, portlandite, carbonate, ionic strength, TRLFS

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  • Secondary publication expected from 14.11.2019

Publ.-Id: 27649 - Permalink


Advanced thermal processing of group-IV materials and beyond
Rebohle, L.; Skorupa, W.; Prucnal, S.; Berencén, Y.; Zhou, S.; Helm, M.;
One of the main issues in semiconductor research is doping and crystallization. To meet the high standards of today’s microelectronic industry, especially in the context of nanostructures, more and more non-equilibrium processing technologies has been entered. This applies, above all, to thermal processing which usually has to activate dopants and anneal out defects, but has to suppress diffusion and segregation at the same time. This presentation is focused on the use of millisecond flash lamp annealing (FLA) for advanced thermal processing of group-IV materials including Si, Ge and GeSn alloys. FLA is able to exceed the solid solubility limit of dopants which is discussed for the cases of P and Sn in thin Ge films as well as for Se in Si nanowires. Moreover, the specific conditions of FLA determine whether a thin amorphous film on a crystalline substrate, e.g. an amorphous Ge layer on Ge after ion implantation, recrystallizes in a poly- or monocrystalline way. Finally, perspectives of FLA for other materials will be presented.
Keywords: flash lamp annealing, ion implantation, hyperdoping of silicon, Sn doping of germanium, silicon nanowire
  • Invited lecture (Conferences)
    European Materials Research Society Spring Meeting 2018, 18.-22.06.2018, Strasbourg, France

Publ.-Id: 27648 - Permalink


Crystallization of thin amorphous silicon films on glass by magnetron sputtering and flash lamp annealing
Rebohle, L.; Neubert, M.; Schumann, T.; Skorupa, W.;
Flash lamp annealing (FLA) is an innovative annealing method already used in semiconductor industry, for flexible electronics and for thin, functional coatings on glass. Due to the short time scale of milliseconds, FLA is cost and time effective, suitable for temperature-sensible substrates and allows the exploitation of non-equilibrium crystallization processes.
In this contribution we present a new approach in which magnetron sputtering is combined with FLA. In detail, thin polycrystalline Si films have been fabricated and characterized with respect to their structural, optical and electrical properties. Special focus is set on the non-equilibrium crystallization process within the millisecond time scale. Furthermore, strategies to avoid thermal stress, to minimize defects and to obtain layers with a low electrical resistivity are discussed.
Keywords: flash lamp annealing, magnetron sputtering, amorphous silicon
  • Lecture (Conference)
    European Materials Research Society Spring Meeting 2018, 18.-22.06.2018, Strasbourg, France

Publ.-Id: 27647 - Permalink


Sputtering in combination with flash lamp annealing for thin film deposition on glass
Rebohle, L.; Neubert, M.; Schumann, T.; Skorupa, W.;
Flash lamp annealing (FLA) is an innovative annealing method already used in semiconductor industry, for flexible electronics and for thin, functional coatings on glass. Due to the short time scale of milliseconds, FLA is cost and time effective, suitable for temperature-sensible substrates and allows the exploitation of non-equilibrium processes. Recently, FLA was combined with atomic layer deposition to improve the properties and functionality of thin films by in-situ annealing.
In this contribution we present a new approach in which magnetron sputtering is combined with FLA. Whereas the first part covers technological aspects of this new approach, the second part reports on first experiments to fabricate thin films (e.g. polycrystalline silicon) on glass carriers and thin glass foils. The improvement of sputtered films by post-deposition treatment is a general issue in order to achieve the desired structural, optical and electrical properties. In detail, the functionalization process on the millisecond time scale and strategies to avoid thermal stress, to minimize defects and to obtain layers with a low electrical resistivity are discussed.
Keywords: Flash lamp annealing, magnetron sputtering, amorphes Silicon
  • Poster
    ICCG 12 – Conference on Coatings on Glass and Plastics, 11.-15.06.2018, Würzburg, Deutschland

Publ.-Id: 27646 - Permalink


The Precession Dynamo Experiment at HZDR
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.;
Cosmic magnetic fields are ubiquitous phenomena that are observed on all scales, from planets and stars to galaxies and clusters of galaxies. The origin of these fields involves the formation of electrical currents by means of complex flows of conducting fluids or plasmas.
Fluid flow induced magnetic fields via this dynamo effect have also been observed in experiments, which, however, require considerable technical efforts due to the significantly smaller scales available in the laboratory. The project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) provides a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. The most ambitious experiment within this project is a precession driven dynamo experiment that currently is under construction and will consist of a cylinder filled with liquid sodium that simultaneously rotates around two axes. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo or the ancient lunar dynamo.
In our presentation we will address corresponding numerical and experimental examinations aimed at an optimization of the precession driven flow with regard to improve the dynamo process in the planned experiment. Both approaches show that in the strongly nonlinear regime the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves that arise from nonlinear self-interactions. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm_crit ∼430, which is well within the range of the planned liquid sodium experiment.
Keywords: Dynamo Precession DRESDYN
  • Lecture (Conference)
    The Third Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russia

Publ.-Id: 27645 - Permalink


Sensitive, Selective and Biodegradable – New biosorbents for metal recovery
Braun, R.ORC; Matys, S.ORC; Schoenberger, N.; Jain, R.; Lederer, F.ORC; Pollmann, K.ORC
Low concentrated heavy metal ions are causing diverse problems for conventional metal processing. Artificial peptides with metal binding affinities are a new, innovative challenger for conventional metal recovery. They combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential for geobiotechnology.
Here, we aimed for the development of novel peptidic bio-materials for the recovery of cobalt and nickel. Combining Phage Surface Display Technology (PSD) with deep sequencing approaches, suitable sequences were identified and genetically optimized for heterologous expression and production. Methods used for characterizing the peptide metal interaction, were e.g. quartz crystal microbalance with dissipation monitoring (QCM-D) and UV/Vis spectroscopy. Our system can be adapted to many different purposes/materials and the identified motifs can provide information for a deeper understanding of bio-inorganic interactions, leading to the discovery of novel metal-interacting biomolecules.
Introduction. With biomining first applie
Keywords: phage display; biosorption; peptide; biohydrometallurgy; metallopeptide; metal binding, bioremediation
  • Lecture (Conference)
    Sustainable Minerals '19, 14.-15.06.2018, Windhoek, Namibia

Publ.-Id: 27644 - Permalink


Heavy metal binding peptides – biosorbents with economic and ecological potential
Braun, R.ORC; Matys, S.ORC; Schoenberger, N.; Jain, R.; Lederer, F.ORC; Pollmann, K.ORC
Critical heavy metal concentrations can be found in environmental and/or industrial systems. Removal of metals for detoxification (bioremediation) and recovery of metals (geobiotechnology) from natural water bodies or waste waters is challenging because of low concentrated metal ions. Artificial peptides, that are able to bind metal ions, are of great potential as they combine unique sensitivity and high specificity.
Here we present the development of peptide-based biosorptive materials for heavy metal removal, including identification, adaptation and characterization of specific peptides binding nickel and cobalt. Using Phage Surface Display (PSD) and deep sequencing we identified and produced metal binding peptides. Metal-peptide interactions were studied using e.g. quartz crystal microbalance with dissipation monitoring (QCM-D), and UV/Vis spectroscopy. With this study we provide a system that can be adapted to other materials and knowledge about the nature of metal-peptide interaction, which may lead to the discovery of novel metal-interacting biomolecules, e.g. enzymes and peptides.
Keywords: phage display; biosorption; peptide; biohydrometallurgy; metallopeptide; metal binding, bioremediation
  • Lecture (Conference)
    Biohydrometallurgy '18, 12.-13.06.2018, Windhoek, Namibia

Publ.-Id: 27643 - Permalink


Sensitive, selective and biodegradable – new biosorbents for metal recovery
Braun, R.ORC; Matys, S.ORC; Schoenberger, N.; Jain, R.; Lederer, F.ORC; Pollmann, K.ORC
Low concentrated heavy metal ions are causing diverse problems for conventional metal processing. Artificial peptides with metal binding affinities are a new, innovative challenger for conventional metal recovery. They combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential for geobiotechnology.
Here, we aimed for the development of novel peptidic bio-materials for the recovery of cobalt and nickel. Combining Phage Surface Display Technology (PSD) with deep sequencing approaches, suitable sequences were identified and genetically optimized for heterologous expression and production. Methods used for characterizing the peptide metal interaction, were e.g. quartz crystal microbalance with dissipation monitoring (QCM-D) and UV/Vis spectroscopy. Our system can be adapted to many different purposes/materials and the identified motifs can provide information for a deeper understanding of bio-inorganic interactions, leading to the discovery of novel metal-interacting biomolecules.
  • Lecture (Conference)
    69. BHT - Freiberger Universitätsforum, 06.-08.06.2018, Freiberg, Germany

Publ.-Id: 27642 - Permalink


Heavy metal biosorbents – New approaches for old problems
Braun, R.ORC; Matys, S.ORC; Jain, R.; Schoenberger, N.; Lederer, F.ORC; Pollmann, K.
Low concentrations of heavy metal ions are causing diverse problems from the environmental and economic viewpoints. Conventional metal processing is complicated, both from a technical and economic perspective with low heavy metal concentrations e.g. in mine tailing waste waters. Additionally, even in low concentrations particular heavy metal ions are highly toxic and do have a severe influence on environmental systems. Artificial peptides with special metal binding affinities are therefore a new, innovative challenger for conventional metal recovery methods. They combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential both for geobiotechnology and bioremediation.
In the present study we aimed for the development of novel bio-based materials of peptidic nature for the recovery of cobalt and nickel. Combining Phage Surface Display Technology (PSD) with deep sequencing approaches, suitable sequences were identified and subsequently genetically optimized for heterologous expression, production and purification. Different methods were used for characterizing the peptide metal interaction, e.g. quartz crystal microbalance with dissipation monitoring (QCM-D), fast protein liquid chromatography (FPLC) and UV/Vis spectroscopy. The developed system can be adapted to many different purposes and desired materials and the identified motifs can provide information for a deeper understanding of bio-inorganic interactions, potentially leading to the discovery of novel metal-interacting biomolecules, e.g. enzymes and peptides.
  • Lecture (Conference)
    3rd Green & Sustainable Chemistry Conference, 13.-16.05.2018, Berlin, Germany

Publ.-Id: 27641 - Permalink


A simple route to synchronized nucleation of self-catalyzed GaAs nanowires on Si for sub-Poissonian length distributions
Tauchnitz, T.ORC; Berdnikov, Y.; Dubrovskii, V. G.ORC; Schneider, H.; Helm, M.; Dimakis, E.ORC
The achievement of sub-Poissonian length distributions (LDs) in VLS-grown III-V nanowire (NW) ensembles, as theoretically predicted by Glas and Dubrovskii, requires synchronized nucleation of all NWs on their substrate. This is especially challenging for self-catalyzed GaAs NWs on a natively-oxidized Si(111) substrate because their nucleation involves a sequence of different physical mechanisms: the formation of Ga droplets at random positions on the substrate, their interaction with SiOx and the formation of nano-sized holes, and finally the droplet-assisted nucleation of GaAs inside these holes.
Here, we demonstrate that it is possible to achieve highly-synchronized nucleation of MBE-grown GaAs NWs and, thus, very narrow LDs if a simple in situ procedure is employed prior to the growth in order to decouple the formation of SiOx holes from the subsequent nucleation of NWs. This procedure consists of three steps (substrate annealing – Ga deposition – substrate annealing) and produces SiOx holes (free of Ga droplets) of controlled size and number density.
Our study compares the LD of GaAs NWs grown on Si substrates with different size or number density of SiOx holes. The results were fitted with a continuum-growth theoretical model that accounts for nucleation fluctuations, kinetic fluctuations and nucleation antibunching in individual NWs. We have found that the formation of large-enough holes before the initiation of the NW growth can shorten the characteristic nucleation time of the NWs by one order of magnitude and narrow the LD by a factor of 2. The LD was further improved by decreasing the number density of SiOx holes/GaAs NWs, which is attributed to the suppression of beam-shadowing effects. In the best case, we obtained GaAs NWs that exhibit a remarkably short characteristic nucleation time of 10 ms and a sub-Poissonian LD. All in all, our results (unpublished) not only prove the validity of theoretical considerations about the sub-Poissonian LD for self-catalyzed NWs, but also demonstrate a simple route to low-cost fabrication (without substrate patterning) of GaAs NW-based devices with controllable number density and length uniformity.
Keywords: surface modification, SiOx holes, synchronized nucleation
  • Lecture (Conference)
    Nanowire Week 2018, 11.-15.06.2018, Hamilton, Ontario, Kanada

Publ.-Id: 27640 - Permalink


Preparation of nanowire cross-sections by ultramicrotomy
Formanek, P.; Hübner, R.; Balaghi, L.; Wagner, J.; Dimakis, E.;
Preparation of nanowire cross-sections by ultramicrotomy
  • Lecture (others)
    6. Sächsisches TEM-Präparatorentreffen, 10.04.2018, Dresden, Deutschland

Publ.-Id: 27639 - Permalink


Bridging the gap between spectroscopy and thermodynamics of mineral’s surface reactions for safety assessment
Foerstendorf, H.ORC; Jordan, N.ORC; Mayordomo, N.; Lützenkirchen, J.ORC; Stockmann, M.
A combined approach of optical spectroscopic techniques, such as vibrational and luminescence spectroscopy, classical batch sorption studies and Surface Complexation Modeling (SCM) was applied for the study of the surface speciation of U(VI) and Se(VI/IV) at aqueous-mineral interfaces. In the present study, different single oxides are considered as models for complex natu-rally occurring minerals in a host rock of a nuclear waste repository.
For the ternary sorption system, U(VI)/phosphate/SiO2, the formation of two binary uranyl surface species was derived from spectroscopic findings irrespective of the presence or absence of phosphate. Additionally, the formation of a phosphate phase precipitate was observed with increasing exposure time. Based on these results, we were able to satisfactorily fit the respective batch results by SCM.[1] For the sorption of selenium(IV) or selenium(VI) on alumina phases, a single predominant inner-sphere selenite and outer-sphere selenate surface species were identi-fied by vibrational spectroscopy. With respect to the bidentate binding mode observed for both oxyanionic surface species, SCM provided excellent fitting results of the batch sorption data.[2,3] Moreover, the final model proposed in our study was used to predict data obtained from a literature survey of recently published batch data related to the Se(VI)/γ-Al2O3 binary system. It could be shown that our model is quite capable of predicting literature data collected in the same background electrolyte.[2]
The results of this study demonstrated that the combined approach of in situ spectroscopy and batch sorption studies contributes to an improved performance of future assessments for the mi-gration of radionuclides and fission products in the environment of a repository site.

Ref.:
[1] Comarmond, M. J. et al. (2016) Environ. Sci. Technol. 50, 11610-11618.
[2] Jordan, N. et al. (2018) Environ.-Sci. Nano, in press, DOI: 10.1039/C8EN00293B.
[3] Mayordomo, N. et al. (2018) Environ. Sci. Technol. 52, 581-588.
  • Poster
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2018), 06.-09.11.2018, Nice, France

Publ.-Id: 27638 - Permalink


Thermodynamic Reference Database - Recent and present activities in THEREDA
Moog, H. C.; Bok, F.; Marquardt, C.; Thoenen, T.; Voigt, W.; Yalçintaş, E.;
Five institutions joined efforts to create a common thermodynamic reference database (THEREDA), dedicated to the calculation of radionuclide solubility in high-saline solutions in underground nuclear disposal sites. The principal output of the project are ready-to-use parameter files for thermodynamic equilibrium codes, among them ChemApp.
The presentation will give an account on the development of the project in the past ten years. Results from recent and upcoming releases will be given. Some emphasis will be given to lessons learnt in recent activities, where redox equilibria were involved.
The presentation will conclude on the long-term perspective of THEREDA and an outlook to the envisaged support of another Gibb energy minimizer.
Keywords: THEREDA, Thermodynamic reference database, ChemApp, Gibb energy minimizer
  • Lecture (Conference)
    GTT Users' Meeting 2018, 27.-29.06.2018, Herzogenrath-Kohlscheid, Deutschland

Publ.-Id: 27637 - Permalink


Comparison of the response of NiO, ZnO and TiO2 micro- and nano-structures on azimuthally rotating Swift Heavy Ion irradiation
Bolse, W.; Ferhati, R.; Amirthapandian, S.; Fritzsche, M.; Bischoff, L.;
In a previous paper [1] we have reported on the shaping of rectangular NiO-platelets (thickness: 100 nm , side-lengths: 100 – 5000 nm) on oxidized Si-substrate (250 nm SiO2) by swift heavy ion (SHI) irradiation under grazing (5o – 10o) and azimuthally rotating incidence. At low fluences ion hammering resulting in lateral shrinkage and vertical growth dominated the reshaping process. At higher fluences (the earlier the smaller the initial lateral size of the platelet) curving of edges and corners and finally saturation of deformation occurs due to the influence of surface tension. The deformation of the NiO is accompanied by huge sputtering and creeping of the exposed SiO2-layer. Especially the latter affects the NiO deformation in the interfacial region.
In the present report we will compare those results with similar experiments on thin ZnO- and TiO2-platelets on oxidized Si. As in case of NiO also here pre-structuring of the thin oxide-films was done with the focused ion beam (FIB) technique. The development of the platelets under swift heavy ion irradiation was monitored using our “High Resolution In-Situ Scanning Electron Microscope” installed in the beam line of the UNILAC ion accelerator at the GSI Helmholtz Centre for Heavy Ion Research [2]. This instrument allows us to in-situ monitor the morphological and compositional modification of individual objects in the micro- to nanometer-range under swift heavy ion bombardment, from the very first ion impact up to fluences of some 1015 cm-2. The irradiation can be carried out at any incidence angle between 0o and 90o and under stepwise or continuous azimuthal rotation of the sample.
In contrast to NiO the deformation rate of ZnO and TiO2 is smaller by more than a factor of 5. While in case of ZnO similar objects are formed compared to our previous study on NiO, the TiO2 also shrinks laterally, but remains as an almost flat layer on the underlying pyramidal basis formed by sputtering of SiO2. The results will be discussed regarding the mechanical, thermal and electrical properties of the materials.
Acknowledgement
We thankfully acknowledge the help of D. Severin, M. Bender and C. Trautmann from GSI during the experiments and "Deutsches Bundesministerium für Bildung und Forschung" for project funding.
References
1. R. Ferhati,S. Amirthapandian, M. Fritzsche, L. Bischoff, W. Bolse, REI 19, Nucl. Instr. Meth. B, (2018) in press. 2. S. Amirthapandian, F. Schuchart, and W. Bolse, Rev. Sci. Instrum. 81, (2010) 33702.
Keywords: ZnO- and TiO2-platelets, FIB , UNILAC
  • Lecture (Conference)
    SHIM-ICACS 2018 - 10th International Symposium on Swift Heavy Ions in Matter & 28th International conference on Atomic Collisions in Solids, 01.-06.07.2018, Caen, France

Publ.-Id: 27636 - Permalink


DFT studies on the nature of Y-Ti-O nanoclusters in bcc Fe
Vallinayagam, M.; Posselt, M.; Faßbender, J.;
Nanostructured Ferritic Alloys (NFA) are promising candidates for structural materials of future fusion and fission reactors. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer-size yttria-based oxide particles. In this research project the nature of the yttria-based oxide nanoclusters in a bcc Fe matrix is investigated by Density Functional Theory (DFT). The main goal of the studies is the better understanding of structure, energetics and composition of the clusters.
In the first part of the work three types of structures are considered: (i) clusters consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe, (ii) clusters with Y, Ti, and O on bcc sites, and (iii) clusters with of Y, Ti, on bcc sites and O on octahedral interstitial sites of the bcc lattice. Simulation cells containing the three different structures but the same composition of atoms (Fe, Y, Ti, O) are considered, and relaxation calculations are performed using the DFT code VASP. It is found that in the three cases the energetics, i.e. the total binding energy of the clusters, is very similar. This contradicts the statement of Barnard et al. [1] that type (i) structures are most favorable. Further alternative cluster models with a core similar to the NaCl structure and an oxygen atom in the center are constructed and investigated in the second part of the work. For the compositions considered some of these clusters are more stable than those investigated before. Finally, the binding energy of O, Y, Ti atoms, and of the vacancy to selected cluster structures was studied. Oxygen and the vacancy are strongly attracted by the nanoclusters, while the interaction with metal atoms is weaker.
[1] L. Barnard et al. Acta Mater. 60, 935 (2012)
Keywords: Y-Ti-O nanoclusters in Fe, Density Functional Theory
  • Poster
    The 14th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2018), 18.-22.06.2018, Shanghai, China
  • Lecture (Conference)
    NuMat2018: The Nuclear Materials Conference, 14.-18.10.2018, Seattle, USA

Publ.-Id: 27634 - Permalink


Diffusion of oxygen in bcc Fe under the influence of other foreign atoms
Wang, X.; Posselt, M.; Faßbender, J.;
Density Functional Theory (DFT) and Atomistic Kinetic Monte Carlo (AKMC) simulations are applied to investigate the diffusion of oxygen in bcc Fe under the influence of substitutional foreign atoms, such as Al, Si, P, S, Ti, Cr, Mn, Ni, Y, Mo, and W. These atoms are assumed to be immobile since their diffusion coefficient is much smaller than that of oxygen.
In the first part of the work jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites are investigated by DFT. It is found that the first-neighbor jump is most relevant with the tetrahedral site as the saddle point. The second-neighbor jump consists of two consecutive first-neighbor jumps whereas the barrier of the third-neighbor jump is too high to be significant for the diffusion process. In the second part DFT is applied to determine the modified migration barriers, i.e. for the oxygen jump between the first and the second neighbor of the substitutional foreign atom, etc. Si, P, Ni, Mo and W influence the migration barriers of oxygen and their interaction energy with O is mainly repulsive. While Al, Cr and Mn have also a significant influence on the barriers they show strong attractive interactions. The strongest modification of the barriers is found for S, Ti, and Y where deep attractive states exist. At large distance from the solutes the O migration barriers converge to the value for pure Fe. The most relevant migration paths are first-neighbor jumps between (modified) octahedral sites with (modified) tetrahedral sites as saddle points. Finally, the diffusion coefficient of oxygen is determined by AKMC simulations on a rigid lattice, considering a dilute iron alloy and using the migration barriers calculated by DFT. Si, P, Ni, Mo, and W have almost no influence on the diffusivity of O, i.e. it is nearly identical to that in pure bcc Fe. The presence of Al, Cr, Mn, S, Ti, and Y causes a reduction of the mobility of oxygen. The strongest decrease of the diffusion coefficient is obtained for the foreign atoms S, Ti, and Y.
Keywords: Diffusion of oxygen in iron, Density Functional Theory, Atomistic Monte Carlo simulations
  • Poster
    The 14th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2018), 18.-22.06.2018, Shanghai, China

Publ.-Id: 27633 - Permalink


Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study
Al Motasem, A. T.; Posselt, M.; Bergström, J.;
Molecular dynamics simulations are applied to investigate the wear/friction behavior of a ferrite/austenite iron bi-crystal, as a model system for duplex stainless steels. The plasticity of the ferrite phase is dominated by dislocations while both dislocations and stacking faults are the primary cause of plastic deformation of the austenite phase. Interestingly, the responses of tribological parameters vary depending on the scratch direction. For instance, the scratch hardness is increased by about 46% whereas the friction coefficient is reduced by about 22% when scratch starts from austenite to ferrite. At the interface, a local softening/hardening occurs because of dislocation-interface interaction. The present results demonstrate that martensitic phase transformation is responsible for experimentally observed high amount of ferrite of the pile-up.
Keywords: Atomistic simulation Ferrite Austenite Wear

Publ.-Id: 27632 - Permalink


Predictive Geometallurgy - State of The Art
Birtel, S.; Kern, M.; Büttner, P.; Bachmann, K.; Frenzel, M.; Gutzmer, J.;
SEM-based automated image analysis is well established as a key tool in geometallurgical assessments, as it provides quantitative data on mineralogy and microstructure. It is also widely used in the mining industry to improve recoveries and to monitor process efficiency of processing plants. More recently, automated mineralogy has been also used to assess the presence and distribution of possible by-product or even penalty constituents. The approach at the Helmholtz Institute Freiberg of Resource Technology goes beyond these current applications: data from SEM-based automated analyses such as MLA in combination with complementary analytical methods (such as XRD and EPMA) is statistically assessed in order to predict the behavior of material during beneficiation. The purpose of this approach is to confidently reduce technical risk of raw materials projects whilst also reducing the need for empirical test work.
This study will exemplify this approach with four very different case studies, including (1) on the recovery of Sn from a historic flotation tailings storage facility; (2) on by-product recovery from a chromite ore deposit, (3) on simulating sensor-based presorting; and (4) by-product recovery from a polymetallic base metal ore. All studies were performed by interdisciplinary teams including resource characterization, minerals processing and statistical modelling.
1) A predictive geometallurgical model of a tailings storage facility in the Erzgebirge (Germany) was created based the assessment and weighting of grade, modal mineralogy, liberation, grain size and flotation behavior of tailings intersected by a series of drill cores. All data was geo-referenced and combined to construct a 3D model illustrating the amount of cassiterite–bound tin that can realistically be recovered from the tailing. Results of this study illustrate the importance of combining different tangible parameters to assess the recoverable value that remains in industrial residues – such as flotation tailings.
2) A predictive geometallurgical model was created for an ore body comprising several stratiform chromitite seams in the Bushveld Complex (South Africa). The focus of this study was the assessment of the potential for PGE recovery as a by-product. Samples were collected from a series of drill core intersections of the different chromitite seams. More than 100 individual samples were studied in detail. Results were clustered, focusing on parameters relevant for beneficiation of PGE, such as PGE mineralogy, mineral association, grain sizes etc. These predictions were validated by selected metallurgical tests. Compositional clusters were then related back to well-known geological features.
This integration of data served to define geometallurgical domains.
3) Assessing the success of sensor-based presorting currently requires time-consuming and expensive empirical test work. Yet, the prospects of success can be simulated with automated mineralogy data.
This is illustrated using the example of a mineralogically and texturally complex skarn ore from the Hämmerlein Sn-In-Zn deposit, Germany. Cassiterite is the most important ore mineral and Sn is the major value constituent in the polymetallic skarn ore. The presence and abundance of cassiterite itself (< 4 Vol. %) is not a suitable target for sensor-based sorting. Yet, it appears intimately associated with a cogenetic chlorite-fluorite-sulfide assemblage. Parameters from MLA datasets, such as modal mineralogy and mineral density distribution were used to simulate the prospects of sensor-based sorting using different sensors. The results illustrate that the abundance of rock-forming chlorite and/or the density anomalies may well be used as proxies for the abundance of cassiterite.
4) The mineralogical deportment of Indium in mineralogically complex base metal sulphide ores from a mine in the Iberian pyrite belt was defined in order to constrain the potential to realize credits from this valuable by-product. Different to the previous case study, Indium does deport mostly into major ore-forming sulphides – and rarely forms its own ore minerals. The study is based on a combination of data from assays and MLA, data for geological and processing samples. In addition, an extensive set of mineral chemical data was acquired by EPMA to constrain the In deportment. Statistical regularities in the deportment of In are then used to predict In deportment from assay data alone. This predictive assessment includes statistical uncertainties, achievable recoveries and payable concentrate compositions. This, in turn, may be used in future mine planning.
Key innovations introduced by these three case studies are of general applicability to other metals and ore types. They clearly illustrate the value of conducting predictive geometallurgical assessments already during the latter stages of exploration in a process that will benefit from regular follow-up during the phase of active exploitation.
Keywords: SEM-based automated Image Analysis, mineral liberation, deportment, statistics, deposit, mining operation, geometallurgiacl model
  • Invited lecture (Conferences)
    Application and Technological Developments for Ore Characterization within Geometallurgy, 22.06.2018, Vancouver, Canada

Publ.-Id: 27630 - Permalink


Lithium Niobate Crystal with Embedded Au Nanoparticles: A New Saturable Absorber for Efficient Mode‐Locking of Ultrafast Laser Pulses at 1 µm
Pang, C.; Li, R.; Li, Z.; Dong, N.; Cheng, C.; Nie, W.; Böttger, R.; Zhou, S.ORC; Wang, J.; Chen, F.
Plasmonic Au nanoparticles embedded in LiNbO3 crystals as efficient saturable absorbers to realize 74.1 ps mode‐locked laser pulse generation at 1 µm are reported. The system is fabricated by Au ion implantation and subsequent annealing, a well‐developed chip technology. The strong optical absorption band peaking at 640 nm is observed due to the localized surface plasmon resonance. Z‐scan investigation shows that the LiNbO3 crystals with embedded Au nanoparticles possess ultrafast saturable absorption properties at near‐infrared 1 µm wavelength. With this feature the Au nanoparticles embedded LiNbO3 wafer is applied as saturable absorber into a laser‐written Nd:YVO4 waveguide platform. Stable laser pulses at 1064 nm based on an efficient passive Q‐switched mode‐locking process, reaching a fundamental repetition rate of 6.4 GHz and a pulse duration of 74.1 ps, are obtained. Since LiNbO3 has broadband applications in various optical systems, this work opens the way to develop intriguing devices in LiNbO3‐based photonic circuits by using embedded metallic nanoparticles.

Downloads:

  • Secondary publication expected from 30.05.2019

Publ.-Id: 27629 - Permalink


Radiobiological effects and proton RBE determined by wildtype zebrafish embryos
Szabo, E. R.; Brand, M.; Hans, S.; Hideghety, K.; Karsch, L.; Leßmann, E.; Pawelke, J.; Schürer, M.; Beyreuther, E.;
During the last decade, the increasing application of proton radiotherapy and the rising number of long-term survivors gave rise to a vital discussion on potential effects on normal tissue. So far, deviations from clinically applied generic RBE (relative biological effectiveness) of 1.1 were just obtained by in vitro studies, whereas indications from in vivo trials and clinical studies are rare. In the present work, wildtype zebrafish embryos (Danio rerio) were applied to characterize effects of plateau and mid-SOBP proton radiation relative to that induced by clinical MV photon beam reference.
Based on embryonic survival data, RBE values of 1.13 ± 0.08 and of 1.20 ± 0.04 were determined four days after irradiations with 20 Gy plateau and SOBP protons relative to 6 MV photon beams. These RBE values were confirmed by relating the rates of embryos with morphological abnormalities for the respective radiation qualities and doses. Besides survival, the rate of spine bending, as one type of developmental abnormality, and of pericardial edema, as an example for acute radiation effects, were assessed. The results revealed that independent on radiation quality both rates increased with time approaching almost 100 % at the 4th day post irradiation with doses higher than 15 Gy.
To sum up, the applicability of the zebrafish embryo as a robust and simple alternative model for in vivo characterization of radiobiological effects in normal tissue was validated and the obtained RBE values are comparable to previous finding in animal trials.
Keywords: zebrafish embryos, proton irradiation, relative biological effectivity

Publ.-Id: 27628 - Permalink


Comparison of FIB Resolution for Different Ion Species in Imaging and Writing Mode
Bischoff, L.; Pilz, W.; Hlawacek, G.; Mazarov, P.; Bauerdick, S.; Gierak, J.;
Focused Ion Beam (FIB) processing, which is nearly exclusively based on gallium Liquid Metal Ion Sources (LMIS) [1] expands more and more to other ion species also by implementation of other types of ion sources. Many applications in nano-technology could benefit from ion species other than gallium, like local doping by ion implantation, ion beam mixing, ion beam synthesis [2], or direct milling using various ions [3]. The application of Gas Field Ion Sources (GFIS) opens the sub-nm range for ion microscopy in the case of He [4].
A key parameter of FIB applications is the spatial resolution in terms of full width at half maximum (FWHM) of the beam profile, which can be described by e.g. two Gaussian functions or a Holtsmark distribution. Three main parts contribute to the obtainable resolution: a source term containing the virtual source size and the magnification, the spherical aberration, describing geometrical effects and the chromatic aberration depending on the energy spread of the ion source [5]. All contents are influenced by the ion source itself as well as the performance of the ion optics. For an optimum image resolution another shape of the beam profile with a sharp tip should be chosen by a suited alignment than for surface patterning by ion milling where more parallel slopes of the distribution a preferred. For a minimum feature size the beam interaction with the surface as well as the combination of ion species and target material must be put into consideration.
In this contribution the beam resolution will be basic discussed for a broad spectrum of ions beginning for light species, Helium Ion Microscope (Fig. 1) and Be from an AuSiBe LMAIS in a mass separated FIB (Fig. 2) up to very heavy ones, like Au, Bi and polyatomic clusters from them. The obtainable FIB resolution in the image and the patterning mode will be compared and discussed.

[1] J. Gierak; Focused ion beam technology and ultimate applications, Sem. Sci. Technol. 24 (2009), 1.
[2] L. Bischoff, P. Mazarov, L. Bruchhaus and J. Gierak; Liquid metal alloy ion sources – An alternative for focused ion beam technology, Appl. Phys. Rev. 3 (2016), 021101.
[3] S. Bauerdick et al.; Multispecies focused ion beam lithography system and its applications, J. Vac. Sci. Technol. B 31 (2013), 06F404-1.
[4] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema; Helium ion microscopy, J. Vac. Sci. Technol. B 32 (2014), 020801-1.
[5] R.G. Forbes in Charged Particle Optics, ed. J. Orloff, CRC Press (2009).
Keywords: Focused ion beam, Liquid Metal Alloy Ion Source, Helium microscope
  • Lecture (Conference)
    2nd EUFN Workshop 2018, 19.-20.06.2018, Grenoble, France

Publ.-Id: 27627 - Permalink


Rayleigh–Ritz based expansion method for wakefields in dielectrically lined rectangular waveguides
Reimann, F.; Michel, P.; Lehnert, U.; van Rienen, U.;
n this work, a semi-analytical method for determining wakefields in dielectrically lined rectangular waveguides is presented. This approach is based on a Rayleigh–Ritz method to analytically identify the eigenmodes of the structure, which is currently studied for the application as a so-called ‘wakefield dechirper’. The electric field is subsequently determined through an eigenmode expansion, and the wakefield is calculated from the electric field. By virtue of using an analytic ansatz throughout the wakefield determination, an expression for the Green's function wakefield is found.

The semi-analytical method is then benchmarked against simulations using purely numerical approaches. Compared to numerical approaches, the advantages of the presented method are the independence from any need of discretisation, the computational efficiency of the method's presented Python-based implementation and finally the opportunity to calculate a true Green's function wakefield. From this Green's function, the wake potentials of different bunch shapes can be obtained via convolution.
Keywords: Wakefields Wakefield dechirping Eigenmode expansion Green's function

Publ.-Id: 27626 - Permalink


Magnetic-field-induced quadrupolar ordering and the crystal electric field effect in the distorted kagome lattice antiferromagnet Dy3Ru4Al12
Ishii, I.; Mizuno, T.; Takezawa, K.; Kumano, S.; Kawamoto, Y.; Suzuki, T.; Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.;
To investigate the 4f -electronic states under a crystal electric field (CEF) and the phase transition inDy3Ru4Al12
with the antiferromagnetic transition temperature TN = 7 K, we performed ultrasonic measurements on a single-crystalline sample at zero magnetic field and under fields. The transverse elastic modulus C44 shows a characteristic elastic softening. The CEF analyses indicate that the softening is caused by an interlevel quadrupole interaction between the ground and excited Kramers doublets. Under fields, we found a magnetic-field-induced phase transition along both the [100] and [001] directions in addition to the antiferromagnetic ordering. A plausible origin of the field-induced transition is quadrupolar ordering, which is estimated from our CEF calculation. These results and the negative sign of a quadrupole-quadrupole coupling constant suggest that the effect of geometrical frustration alignment due to the kagome lattice also appears on the electric quadrupoles of the Dy ions with the antiferroquadrupolar-type interaction.

Publ.-Id: 27625 - Permalink


OC-0594: Postoperative [11C]MET-PET predicts radiochemotherapy outcome in glioblastoma: a prospective trial
Krause, M.; Seidlitz, A.; Löck, S.; Jentsch, C.; Platzek, I.; Zöphel, K.; Petr, J.; van den Hoff, J.; Steinbach, J.; Krex, D.; Schackert, G.; Falk, M.; Baumann, M.; Beuthien-Baumann, B.;
Despite combined modality treatment involving surgery and adjuvant radiotherapy, a relevant percentage of chordoma and chondrosarcoma patients develop a local recurrence. In a previous study, we identified optic apparatus and/or brainstem compression, histology and GTV volume as prognostic factors for the risk of local failure. The present study aims to analyze patterns of recurrence and correlate local control with a detailed dosimetric analysis.

Publ.-Id: 27624 - Permalink


EP-2137: Development of a modular MRI processing workflow for volumetric analysis of healthy brain tissue
Gommlich, A.; Petr, J.; Raschke, F.; van den Hoff, J.; Krause, M.; Troost, E.;
An inherent problem of magnetic resonance imaging (MRI)-based analyses of morphological tissue changes is the absence of a ground truth. A particular issue in cerebral imaging is the lack of consensus regarding the order and manner, in which registration and segmentation algorithms are employed to evaluate volumes and longitudinal changes of different tissue types, e.g., grey and white matter (GM and WM).
Considering shortcomings of a procedure widely applied for global segmentation of the entire brain we developed a modular MRI processing workflow particularly suitable for volumetric analysis of the contralateral hemisphere in brain tumor patients.

Publ.-Id: 27623 - Permalink


Plasmonic response of III-V semiconductor core/shell nanowires studied by pump-probe terahertz spectroscopy
Fotev, I.; Balaghi, L.; Shan, S.; Hübner, R.; Schmidt, J.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, A.;
We utilize ultrafast optical pump – terahertz probe spectroscopy in order to investigate charge carrier response of GaAs nanowires with InxGa1-xAs and InxAl1-xAs shells. The estimated electron mobilities reach 4000 cm2V−1s−1 and the carrier lifetimes range from 100 to 300 ps depending on the type of the shell.
Keywords: nanowires; terahertz; mobility
  • Poster
    6th EOS Topical Meeting on Terahertz Science & Technology, 06.-09.05.2018, Berlin, Germany

Publ.-Id: 27621 - Permalink


Electron mobility and lifetime in GaAs/In𝑥Ga1−𝑥As core/shell nanowires studied by optical pump – THz probe spectroscopy
Fotev, I.; Balaghi, L.; Hübner, R.; Schmidt, J.; Hähnel, M.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, A.;
We utilize ultrafast optical pump – terahertz probe spectroscopy in order to investigate charge carrier response of GaAs/In𝑥Ga1−𝑥As core/shell nanowires (NWs) produced by molecular beam epitaxy. The NWs were ≈2 𝜇m long. The GaAs core diameter was 25nm and the InGaAs shell thickness was 80 nm. We studied the shells with different compositions, from 𝑥 = 0.20 to 𝑥 = 0.44.
From the pump-probe measurements we extracted terahertz photoconductivity of NWs and used the localized surface plasmon model to fit the results. The charge carrier lifetimes were estimated to be around 80–100 ps while the extracted electron mobilities reach 3700 cm2V−1s−1 at room temperature. Even without a surface passivation shell, these values are higher than those in previously studied GaAs/AlGaAs core/shell nanowires, but still lower than the ones for bulk InGaAs. Possible reasons (sources of electron scattering) which affect the mobility will be discussed.
Keywords: nanowires; terahertz; mobility
  • Lecture (Conference)
    DPG Spring Meeting 2018, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 27620 - Permalink


Nonlinear Plasmonic Response of Doped GaAs Nanowires Observed in sSNIM
Lang, D.; Balaghi, L.; Dimakis, E.; Hübner, R.; Kehr, S. C.; Eng, L. M.; Pashkin, A.; Winnerl, S.; Schneider, H.; Helm, M.;
We present nanoscopic infrared-optical investigations on highly n-type doped GaAs-based nanowires, revealing interesting nonlinear phenomena such as a pronounced redshift of the plasma resonance by the strong THz fields of a free-electron laser.
Keywords: nanowires, nonlinear plasmonics, free-electron laser, terahertz, s-SNOM, nanoscopy
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO), 14.05.2018, San José, USA
    Conference on Lasers and Electro-Optics, JM2A.3
    DOI: 10.1364/CLEO_AT.2018.JM2A.3
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO), 14.-18.05.2018, San José, USA

Publ.-Id: 27619 - Permalink


Stability of U(VI) doped calcium silicate hydrate phases in repository-relevant brines studied by leaching experiments and spectroscopy
Wolter, J.-M.; Schmeide, K.ORC; Weiss, S.; Bok, F.; Brendler, V.ORC; Stumpf, T.

The stability of U(VI) doped calcium silicate hydrate (CSH) phases was evaluated in claystone formation waters that possess high ionic strengths and carbonate contents. Such phases were synthesized by direct U(VI) incorporation and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The time-dependent release of Ca, Si and U from U(VI) doped CSH phases into brines that contained 2.5 M NaCl, 2.5 M NaCl/0.02 M Na2SO4, 2.5 M NaCl/0.02 M NaHCO3 or 0.02 M NaHCO3 was monitored for three calcium-to-silicon (C/S) ratios over 32 days. Subsequently, changes of the U(VI) speciation and CSH phase mineralogy caused by leaching were investigated with TRLFS, IR spectroscopy and XRD. Results indicated that composition and pH of the leaching solution as well as presence and solubility of secondary phases such as portlandite and calcite determine the U(VI) retention by CSH phases under high saline and alkaline conditions. At high ionic strengths, the Ca release from CSH and secondary phases like calcite is increased. Under hyperalkaline conditions only small amounts of U(VI) were release during leaching. A decrease of the pH due to the additional presence of carbonate was linked with an increased U(VI) release from CSH phases caused by the occurrence of a calcium uranyl carbonate in the supernatant solution.

Keywords: uranium, CSH, portlandite, carbonate, ionic strength, TRLFS
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-12-31
    DOI: 10.14278/rodare.37

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Publ.-Id: 27618 - Permalink


Enhancing the Magnetic Moment of Ferrimagnetic NiCo2O4 via Ion Irradiation driven Oxygen Vacancies
Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Meyer, D. C.; Chin, Y. Y.; Lin, H. J.; Chen, C. T.; Gemming, S.; Helm, M.; Chu, Y. H.; Zhou, S.ORC
Ion irradiation has emerged as a powerful tool for the efficient control of uniaxial lattice expansion to fine tune and modulate the otherwise inaccessible complex correlated phases in oxide thin-films. We report the fine tuning of the magnetic moment, ferromagneticparamagnetic and metal-insulator transition temperatures in the NiCo2O4 inverse-spinel oxide by creating oxygen deficiencies, employing high energy He-ion irradiation. Tailoring of oxygen vacancies and consequently a uniaxial lattice expansion in the out-of-plane direction drives the system towards the increase of the magnetic moment by two-times in magnitude.
The magnetic moment increases with the He-ion irradiation fluence up to 2.5×1016/cm2 . Our results are corroborated well by spin-polarized electronic structure calculations with density functional theory and X-ray absorption spectroscopic data which show peak-height change and energy shift of Co-L2,3 and Ni-L2,3 edges driven by the oxygen vacancies. These results demonstrate a new pathway of tailoring oxygen vacancies via He-ion irradiation, useful for designing new functionalities in other complex oxide thin-films.

Publ.-Id: 27617 - Permalink


Vergleich der Wirkung von Alpha- und Protonenstrahlung an Normal- und Tumorzellen
Maucksch, U.; Runge, R.; Wetzig, K.; Naumann, A.; Freudenberg, R.; Lühr, A.; Beyreuther, E.; von Neubeck, C.; Kotzerke, J.;
Ziel:
Für Alpha-Strahler ist bekannt, dass diese aufgrund eines hohen linearer Energietransfers (LET) bei gleicher Dosis eine höhere relative biologische Wirksamkeit (RBE) im Vergleich zu Gammastrahlern zeigen. Als Ursache werden die hohe lokale Dosisdeposition sowie die erhöhte Wahrscheinlichkeit für DNA-Doppelstrangbrüche (DSB) angenommen. Für Protonenstrahlung ist eine RBE von 1,1 zu erwarten. Untersucht wurde die Wirksamkeit von 150 MeV Protonenbestrahlung im Vergleich zum Alpha-Emitter Ra-223 auf das verwendete Zellsystem.
Methodik:
Die Wirkung der Protonenbestrahlung und des Alpha-Emitters Ra-223 wurde durch Bestrahlung der Schilddrüsennormalgewebszelllinie FRTL-5 sowie der Tumorzelllinie FaDu überprüft. Die Protonenbestrahlung im Dosisbereich von 0,5 bis 10 Gy erfolgte mit 3 Gy/min am Protonenstrahl der Universitätsprotonentherapie Dresden. Um Dosispunkte zwischen 0,125 und 2 Gy des Alpha-Strahlers Ra-223 zu applizieren, wurden die Zellen mit verschiedene Aktivitätskonzentrationen über 24 h inkubiert. Das klonogene Zellüberleben und die Anzahl der residualen DNA-DSB (H2AX-Assay) wurden 24 h nach Bestrahlung untersucht.
Ergebnisse:
Aus den Dosiswirkungskurven des Koloniebildungsassays wurde die Dosis für 37 % Überleben (D37) für die Normalzelllinie FRTL-5 nach Protonenbestrahlung mit 2,96 Gy und für Ra-223 mit 0,35 Gy bestimmt. Die Tumorzelllinie FaDu zeigte nach Protonenbestrahlung eine D37 von 2,32 Gy und nach Inkubation von Ra-223 eine D37 von 0,31 Gy. Für beide Zelllinien war die Anzahl an residualen DNA-DSB (H2AX-Assay) nach Protonenbestrahlung signifikant geringer als bei Bestrahlung mit Ra-223.
Schlussfolgerung:
Der erhöhte LET des Alpha-Strahlers Ra-223 (max. 250 keV/µm) führt zu einem geringenen Zellüberleben und zu einer höheren Anzahl der residualen DNA-DSB im Vergleich zur Protonenbestrahlung (LET ca. 2 keV/µm).
  • Lecture (Conference)
    56. Jahrestagung der Deutschen gesellschaft für Nuklearmedizin, 18.-21.04.2018, Bremen, Deutschland

Publ.-Id: 27616 - Permalink


Radiobiological characterization of laser driven particle beams – Dresden activities
Beyreuther, E.;
The long-term aim of developing laser based particle acceleration towards clinical application requires not only substantial technological progress, but also new technical solutions for dose delivery and quality assurance as well as comprehensive research on the radiobiological consequences of ultra-short radiation pulses with high pulse dose.
During the last years the laser driven technology was developed at such a rate that cell samples and small animals can be irradiated. Within the joint research project “onCOOPtics” extensive in vitro studies with several human tumor and normal tissue cells were performed revealing comparable radiobiological effects of laser driven and conventional electron and proton beams1,2. Using the same cell lines, these results were substantiated comparing the radiobiological response to ultra-short pulsed electron bunches (pulse dose rates of ≤1012 Gy/min) and continuous electron delivery at the radiation source ELBE3.
In a second translational step, in vivo experiments were established. Although the experiments were motivated by future proton trials, first attempts were performed with electrons at the laser system JETI4, since the delivery of prescribed homogeneous doses to a 3D target volume is easier for electrons than for protons. A full scale animal experiment was realized for the HNSCC FaDu grown on nude mice ear. The radiation induced tumor growth delay was determined and compared to those obtained after similar treatment at a conventional clinical LINAC. Again, no significant difference in the radiation response to both radiation qualities was revealed, whereas the successful performance of such a comprehensive experiment campaign underlines the stability and reproducibility of all implemented methods and setup components.
During this experiment campaign several limitations of the model were identified which were in the following redressed by co-injection of LN229 glioblastoma tumour cells with Matrigel5. Results of this optimization process and the status of the experiments with laser driven protons at the laser system DRACO will be presented.
The work was supported by the German Government, Federal Ministry of Education and Research, grant nos. 03ZIK445 and 03Z1N511.
1Laschinsky L et al. (2012) J. Radiat. Res. 53(3): 395-403.
2Zeil K et al. (2012) Appl. Phys. B 110(4): 437-444.
3Beyreuther E et al. (2015) Int. J. Radiat. Biol. 91(8): 643-652.
4Oppelt M et al. (2015) Radiat. Environ. Biophys. 54(2): 155-166.
5Beyreuther E et al. (2017) PloS One 12.5 (2017): e0177428.
  • Contribution to proceedings
    44th European Radiation Research Congress, 21.-25.08.2018, Pecs, Hungary

Publ.-Id: 27615 - Permalink


Simple vertebrate model development for radiobiology research at ELI-ALPS on laser driven hadron beams
Szabo, E. R.; Tőkés, T.; Polanek, R.; Brunner, S.; Czifrus, S.; Fenyvesi, A.; Biró, B.; Beyreuther, E.; Pawelke, J.; Hideghéty, K.;
Purpose/objective: High power lasers provide the basis of particle acceleration, but at the actual status of the development, low energy, limited size beams with special properties (ultrahigh dose rate, pulsed mode) are available under highly technical conditions for radiobiology experiments.
Our main aim was to introduce and validate a vertebrate system for in vivo experiments to investigate the biological effects of novel hadron beams. The endpoints at diverse dose levels were observed during a certain time frame in order to establish the most relevant factors for relative biological effectiveness (RBE) definition.
Material/methods: Series of zebrafish embryos in 24 hour post fertilization ages in different holders like tubes and 96 well plates varying the number (n) of embryos/well were prepared. For irradiation we used fission neutron (0, 1.25, 1.875, 2, 2.5 Gy), cyclotron-based neutron (0, 2, 4, 6.8, 8.12, 10.28 Gy) and proton (0, 5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve (at the plateau and at the middle of Spread Out Bragg Peak), furthermore, with reference linear accelerator photon (0, 5, 10, 15, 20 Gy) beams (n=96 in each group), repeated several times (≥3). Thereafter, survival, any type of organ developmental disturbance (pericardial edema, spine curvature, shortening of the body length and micro-opthalmia) were detected each days up to 7 days post irradiation (dpi). Histological evaluation (size of the eye, brain necrosis, intestinal changes, liver vacuolization, hyper eosinophilic necrotic muscle-fibers) and molecular changes were evaluated with RT-PCR method at certain time points post irradiation.
Results: The RBE was highly sensitive in this system to time, dose and endpoints. The most robust result could be revealed by survival analysis with RBE of definition on the base of LD50- s at the 5th to 7th dpi: RBE between 10 and 4.8 for the fission and = 3.5 MeV cyclotron based neutrons and around 1.1-1.4 for protons, respectively. The morphological distortions and its severity exhibited a good agreement to the survival derived RBE with a narrow time and dose frame for the different type (i.e. pericardial edema: 3 dpi 20 Gy, spine curvature 4 dpi 15 and 20 Gy). The gravity of the histopathological changes on the basis of semi-quantitative analysis corresponded well to the macro morphological abnormalities (eye layer disorganization, degree of brain necrosis, increased numbers of the goblet cells in the gastrointestinal tract, and muscle fibrosis).
Conclusion: Numerous features of the zebrafish embryo model makes it amenable for large scale of radiobiological investigations. On the basis of our experimental series the optimal radiation setup, radiation dose and observation time points for assessment of the different biological endpoints could be established. This vertebrate model proved to be highly reproducible, reliable, and seems to be well applicable for RBE determination.

Acknowledgement: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund., The project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no 654148 Laserlab-Europe and by the German BMBF, grant no. 03Z1N511.
  • Contribution to proceedings
    44th European Radiation Research Congress, 21.-25.08.2018, Pecs, Hungary

Publ.-Id: 27614 - Permalink


Radiation quality influence on normal tissue cell response
Beyreuther, E.;
Objective: From the various factors that are known to influence the radiobiological response to therapeutic beams, the radiation type and beam energy or LET (linear energy transfer), and the beam pulsing and dose rate are object of comprehensive investigations. Alterations of these parameters might result in altered damage pattern and consequently in a different radiobiological effectiveness, for example for the FLASH, single pulse, irradiation regime [1] and the use of multiple, ultra-short laser driven particle pulses [2] where therapeutic relevant doses are administered within the fraction of a second, i.e. at high dose rate. To characterize the influence of radiation quality, i.e. beam energy, dose rate and pulsing, systematic in vitro studies performed at different accelerators will be summarized in the talk.
Methods and results: Two normal human cell lines were applied to study the response to photons in the range of 10 kV to 34 MV, to conventional and laser driven electrons, and to continuous and pulsed proton beams. By measurements of chromosomal aberrations and DNA double-strand breaks (DSB) the inverse correlation of photon energy and biological damage was revealed, whereas for the proton studies no clear influence of pulsing was found. Furthermore, no influence on clonogenic survival was observed comparing laser driven electrons of ultra-high dose rate (109 Gy/s, multiple electron pulses) and conventional, linac electrons (continuous dose rate 3 Gy/min). By contrast, a trend towards less effectiveness of pulsed laser driven electrons was revealed by measurements of residual DNA DSB. To investigate this finding in more detail, radiobiological experiments were performed at the superconducting research electron linac ELBE, which is able to provide electron beams with very variable pulse sequences and to mimic both laser driven and clinical linac electron beams. Thereby, the DSB studies were complemented by DSB repair kinetics.
Conclusion:
Comprehensive in vitro studies of the effects of various radiation qualities revealed the influence of beam energy and LET, but show no clear result with respect to pulse structure and dose rate.
References:
[1] Favaudon et al. Sci Transl Med. 2014;6(245):245ra93.
[2] Karsch et al. Acta Oncol. 2017;56(11):1359-1366.
  • Invited lecture (Conferences)
    44th European Radiation Research Congress, 21.-25.08.2018, Pecs, Hungary

Publ.-Id: 27613 - Permalink


Best Practices in Running Collaborative GPU Hackathons: Advancing Scientific Applications with a Sustained Impact
Chandrasekaran, S.ORC; Juckeland, G.ORC; Lin, M.ORC; Otten, M.ORC; Pleiter, D.ORC; Stone, J. E.; Lucio-Vega, J.; Zingale, M.ORC; Foertter, F.ORC
The OLCF GPU Hackathons are a one-week code-development/learning event to better enable attendees to utilize GPUs. It only took three years to grow from a ``Let's give this a try''-event to a repeatedly copied format with several spin-offs that inspired HPC centers around the world.
Sticking to a few fundamental principles---work on your own code, learn from your mentors just what you need and when you need it, stay flexible in achieving your goal---the week-long hackathon format created at Oak Ridge Leadership Computing Facility (OLCF) has been just the spark needed by many groups of scientists to light the fire of a wider GPU adoption in leading-edge as well as university-scale HPC environments. Most interestingly, the format enabled both ends of the experience spectrum---graduate students vs. postdoc fellows---the same kind of progress and chance of success.
Keywords: B.1.4.b Languages and compilers D.1 Programming Techniques M.12.0.b Case Studies in Scientific Applications

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Publ.-Id: 27612 - Permalink


Local probe of irradiation induced structural changes and orbital magnetism in Fe60Al40 thin films via order-disorder phase transition
La Torre, E.; Smekhova, A.; Schmitz-Antoniak, C.; Ollefs, K.; Eggert, B.; Cöster, B.; Walecki, D.; Wilhelm, F.; Rogalev, A.; Lindner, J.; Bali, R.; Banerjee, R.; Sanyal, B.; Wende, H.;
Hard X-ray absorption and magnetic circular dichroism spectroscopy have been applied to study the consequential changes of the local environment around Fe atoms and their orbital polarizations in Fe60Al40 thin films of 40 nm thickness along the order-disorder (B2→A2) phase transition initiated by 20keV Ne+ ion-irradiation with fluences of (0.75 - 6) × 1014 ions cm-2. The analysis of the extended X-ray absorption fine structure spectra measured at the Fe K-edge at room temperature revealed an increased number of Fe-Fe nearest-neighbors from 3.47(7) to 5.0(1) and ~ 1% of volume expansion through the transition. The visualization of the Fe and Al nearest neighbors rearrangement in the first coordination shell of Fe absorbers via the transition was carried out by wavelet transformations. The obtained changes in Fe coordination are evidently reflected in the XMCD spectra which show an increased orbital magnetic moment of Fe atoms and a pronounced magnetic multi-electronic excitations peak at ~60 eV above the edge. The amplitudes of both peaks demonstrated similar dependencies on the irradiation fluence. The results of self-consistent DFT calculations on relaxed Fe60Al40 model structures for the ordered (B2) and the disordered (A2) phases are consistent with the experimental findings and point to the formation of Fe-rich regions in the films studied.
Keywords: Chemical disorder, ion-irradiation, magnetism, EXAFS, wavelet transform, XMCD, DFT

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Publ.-Id: 27611 - Permalink


Large-scale self-organized gold nanostructures with bidirectional plasmon resonances for SERS
Schreiber, B.; Gkogkou, D.; Dedelaite, L.; Kerbusch, J.; Hübner, R.; Sheremet, E.; Zahn, D. R. T.; Ramanavicius, A.; Facsko, S.; Rodriguez, R. D.;
Efficient substrates for surface-enhanced Raman spectroscopy (SERS) are under constant development, since time-consuming and costly fabrication routines are often an issue for high-throughput spectroscopy applications. In this research, we use a two-step fabrication method to produce self- organized parallel-oriented plasmonic gold nanostructures. The fabrication routine is ready for wafer-scale production involving only low-energy ion beam irradiation and metal deposition. The optical spectroscopy features of the resulting structures show a successful bidirectional plasmonic response. The localized surface plasmon resonances (LSPRs) of each direction are independent from each other and can be tuned by the fabrication parameters. This ability to tune the LSPR characteristics allows the development of optimized plasmonic nanostructures to match different laser excitations and optical transitions for any arbitrary analyte. Moreover, in this study, we probe the polarization and wavelength dependence of such bidirectional plasmonic nanostructures by a complementary spectroscopic ellipsometry and Raman spectroscopy analysis. We observe a significant signal amplification by the SERS substrates and determine enhancement factors of over a thousand times. We also perform finite element method-based calculations of the electromagnetic enhancement for the SERS signal provided by the plasmonic nanostructures. The calculations are based on realistic models constructed using the same particle sizes and shapes experimentally determined by scanning electron microscopy. The spatial distribution of electric field enhancement shows some dispersion in the LSPR, which is a direct consequence of the semi-random distribution of hotspots. The signal enhancement is highly efficient, making our SERS substrates attractive candidates for high-throughput chemical sensing applications in which directionality, chemical stability, and large-scale fabrication are essential requirements.

Publ.-Id: 27608 - Permalink


Integrating a low-field open MR scanner with a static proton research beam line: proof of concept
Schellhammer, S. M.ORC; Hoffmann, A. L.; Gantz, S.; Smeets, J.; van der Kraaij, E.; Quets, S.; Pieck, S.; Karsch, L.; Pawelke, J.
On-line image guidance using magnetic resonance (MR) imaging is expected to improve the targeting accuracy of proton therapy. However, to date no combined system exists. In this study, for the first time a low-field open MR scanner was integrated with a static proton research beam line to test the feasibility of simultaneous irradiation and imaging. The field-of-view of the MR scanner was aligned with the beam by taking into account the Lorentz force induced beam deflection. Various imaging sequences for extremities were performed on a healthy volunteer and on a patient with a soft-tissue sarcoma of the upper arm, both with the proton beam line switched off. T 1 -weighted spin echo images of a tissue-mimicking phantom were acquired without beam, with energised beam line magnets and during proton irradiation. Beam profiles were acquired for the MR scanner’s static magnetic field alone and in combination with the dynamic gradient fields during the acquisition of different imaging sequences. It was shown that MR imaging is feasible in the electromagnetically contaminated environment of a proton therapy facility. The anatomical MR images showed sufficient quality for target volume identification and positioning. The tissue-mimicking phantom showed no visible beam-induced image degradation. The beam profiles depicted no influence due to the dynamic gradient fields of the imaging sequences. This study proves that simultaneous irradiation and in-beam MR imaging is technically feasible with a low-field MR scanner integrated with a static proton research beam line.
Keywords: proton therapy, magnetic resonance imaging, MR guidance, beam quality, image quality

Publ.-Id: 27607 - Permalink


Strain engineering in lattice-mismatched core/shell nanowires: extending the properties of GaAs
Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Wolf, D.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.;
Strain engineering in core/shell nanowires (NWs) can be an alternative route to tailor the properties of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InxGa1-xAs or GaAs/InxAl1-xAs core/shell NWs can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic properties.
Self-catalyzed core/shell NWs were grown on SiOx/Si(111) by MBE (Fig. 1a). The growth conditions were optimized in order to minimize the bending of the NWs, a phenomenon that originates from the large misfit between the core and the shell. Synchrotron X-ray diffraction and Raman scattering measurements showed that for a given core diameter, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness (Fig. 1b), we obtain a heavily tensile-strained core and a strain-free shell. The tensile strain of the core exhibits a quasi-hydrostatic character and causes the reduction of the GaAs band gap energy in accordance with our theoretical predictions (deformation potential theory and first principle calculations), reaching the remarkable value of 40% (0.87 eV at 300 K) for 7% of strain (x = 0.54). Signatures of valence-band splitting were also identified in polarization-resolved photoluminescence measurements, as a result of the strain anisotropy in GaAs. Presuming a reduced effective mass of electrons in the tensile-strained core of GaAs/InxAl1-xAs NWs (core diameter = 22 nm, x = 0.39–0.49), the corresponding electron mobility was measured by optical-pump THz-probe spectroscopy to be in the range of 4000 cm2/V·s at 300 K. These values are the highest reported, even in comparison to GaAs/AlxGa1-xAs NWs with double the core thickness.
In conclusion, our results (unpublished) demonstrate the possibility to resemble to a large extent the fundamental properties of InxGa1-xAs alloys using strained GaAs NWs grown epitaxially on Si (Fig. 1c). This could open a new dimension in the design of nano-photonics and nano-electronics, surmounting issues with phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the device performance.
Keywords: optoelectronics, band gap reduction, InxGa1-xAs
  • Lecture (Conference)
    Nanowire Week, 11.-15.06.2018, Hamilton, Ontario, Canada

Publ.-Id: 27606 - Permalink


Implanting Germanium into Graphene
Tripathi, M.; Markevich, A.; Böttger, R.; Facsko, S.; Besley, E.; Kotakoski, J.; Susi, T.;
Incorporating heteroatoms into the graphene lattice may be used to tailor its electronic, mechanical and chemical properties, although directly observed substitutions have thus far been limited to incidental Si impurities and P, N and B dopants introduced using low-energy ion implantation. We present here the heaviest impurity to date, namely 74Ge+ ions implanted into monolayer graphene. Although sample contamination remains an issue, atomic resolution scanning transmission electron microscopy imaging and quantitative image simulations show that Ge can either directly substitute single atoms, bonding to three carbon neighbors in a buckled out-of-plane configuration, or occupy an in-plane position in a divacancy. First-principles molecular dynamics provides further atomistic insight into the implantation process, revealing a strong chemical effect that enables implantation below the graphene displacement threshold energy. Our results demonstrate that heavy atoms can be implanted into the graphene lattice, pointing a way toward advanced applications such as single-atom catalysis with graphene as the template.
Keywords: heteroatom doping; ion implantation; molecular dynamics; scanning transmission electron microscopy

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Publ.-Id: 27605 - Permalink


Wechselwirkungs- und Transportuntersuchungen dreiwertiger Radiometalle in Ton unter Berücksichtigung des Einflusses von Fulvinsäure und erhöhten Salinitäten
Poetsch, M.;
The storage of radioactive waste demands for evidence of security over a long period. Mainly because of its high sorption capacity as well as favourable geomechanical properties, clay is being explored as one of the potential host rocks for a final repository. This work contributes to the understanding of interactions between trivalent lanthanides (as analogues for trivalent actinides), fulvic acid and Opalinus clay regarding high ionic strength. High salinity and natural organic matter are both known to facilitate migration of toxic or radioactive metals in geochemical systems, but little is known on their combined effect.
The complex system was split into three binary systems with the following interactions: lanthanides (Tb, Eu) and Opalinus clay, lanthanides and fulvic acid, Opalinus clay and fulvic acid.
The binary systems were investigated at pH of 5 and 7 with variable amounts of NaCl, MgCl2 or CaCl2 within a range of 0 - 4 mol L-1. The sorption of the lanthanides and fulvic acid onto the Opalinus clay was investigated in batch experiments, employing 160Tb, 152Eu and 14C as radiotracers. For the investigation of the complexation behaviour of Tb(III) and Eu(III) with fulvic acid, time-resolved laser-induced fluorescence spectroscopy was used.
A combined Kd approach (Linear Additive Model) was tested for suitability in predicting solid-liquid distribution of metals in the presence of organic matter based on the interactions in the constituent subsystems. The metal-ion interactions with fulvic acid were modelled by using the NICA-Donnan approach. To reproduce the migration behaviour of lanthanides in clay, a diffusion-based process was modelled.
This study has shown that there is no synergism in the mobilising effects of fulvic acid and electrolytes at in-situ pH. On the contrary, a mitigating effect of ionic strength was evidenced, based on the fact that metal binding is suppressed while adsorption of humic matter is hardly influenced.
  • Doctoral thesis
    Universität Leipzig, 2018
    Mentor: Lippold, Holger
    106 Seiten

Publ.-Id: 27603 - Permalink


THz spectroscopy of solids with a free-electron laser
Helm, M.;
I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss nonlinear experiments on excitons in semiconductor quantum wells and pump-probe studies of the relaxation dynamics in graphene. If time permits, I will also introduce the new superradiant THz radiation source TELBE.
Keywords: free electron laser, terahertz, graphene
  • Lecture (others)
    Kolloquium am Max-Born-Institut Berlin, 13.06.2018, Berlin, Germany
  • Lecture (others)
    Vortrag am Paul-Drude-Institut, 23.07.2018, Berlin, Germany

Publ.-Id: 27602 - Permalink


Development of a selective and highly sensitive fluorescence assay for nucleoside triphosphate diphosphohydrolase1 (NTPDase1, CD39)
Lee, S.-Y.; Luo, X.; Namasivayam, V.; Geiss, J.; Mirza, S.; Pelletier, J.; Stephan, H.; Sevigny, J.; Müller, C. E.;
Ecto-nucleoside triphosphate diphosphohydrolase1 (NTPDase1, CD39) is a major ectonucleotidase that hydrolyzes proinflammatory ATP to AMP, which is subsequently converted by ecto-5’-nucleotidase (CD73) to immunosuppressive adenosine. Activation of CD39 has potential for treating inflammatory diseases, while inhibition was suggested as a novel strategy for the immunotherapy of cancer. In the present study, we developed a selective and highly sensitive capillary electrophoresis (CE) assay using a novel fluorescent CD39 substrate, a fluorescein-labelled ATP (PSB-170621A) that is converted to its AMP derivative. To accelerate the assays, a two-directional (forward and reverse) CE system was implemented using 96-well plates, which is suitable for screening of compound libraries (Z’-factor: approx. 0.7). The detection limits for the forward and reverse operation were 11.7 and 2.00 pM, respectively, indicating a large enhancement in sensitivity as compared to previous methods (e.g. malachite-green assay: 1,000,000-fold, CE-UV assay: 500,000-fold, fluorescence polarization immunoassay: 12,500-fold). Enzyme kinetic studies at human CD39 revealed a Km value of 19.6 µM, and a kcat value of 119 x 10-3 s-1 for PSB-170621A, which shows similar substrate properties as ATP (11.4 µM and 165 x 10-3 s-1). The compound displayed similar substrate properties at rat and mouse CD39. Subsequent docking studies into a homology model of human CD39 revealed a hydrophobic pocket that accommodates the fluorescein tag. PSB-170621A was found to be preferably hydrolyzed by CD39 as compared to other ectonucleotidases. The new assay was validated by performing inhibition assays with several standard CD39 inhibitors yielding results that were consonant with data using the natural substrates.
Keywords: capillary electrophoresis / CD39 / ectonucleotidase / fluorescein / fluorescent enzyme assay / NTPDase1

Publ.-Id: 27601 - Permalink


Isolated Proton Bunch Acceleration by a Petawatt Laser Pulse
Hilz, P.ORC; Ostermayr, T. M.ORC; Huebl, A.ORC; Bagnoud, V.; Borm, B.; Bussmann, M.ORC; Gallei, M.; Gebhard, J.; Haffa, D.; Hartmann, J.; Kluge, T.ORC; Lindner, F. H.; Neumayr, P.; Schaefer, C. G.; Schramm, U.ORC; Thirolf, P. G.; Rösch, T. F.; Wagner, F.; Zielbauer, B.; Schreiber, J.ORC
Often, the interpretation of experiments concerning the manipulation of the energy distribution of laser-accelerated ion bunches is complicated by the multitude of competing dynamic processes simultaneously contributing to recorded ion signals. Here we demonstrate experimentally the acceleration of a clean proton bunch. This was achieved with a microscopic and three-dimensionally confined near critical density plasma, which evolves from a 1μm diameter plastic sphere, which is levitated and positioned with micrometer precision in the focus of a Petawatt laser pulse. The emitted proton bunch is reproducibly observed with central energies between 20 and 40 MeV and narrow energy spread (down to 25%) showing almost no low-energetic background. Together with three-dimensional particle-in-cell simulations we track the complete acceleration process, evidencing the transition from organized acceleration to Coulomb repulsion. This reveals limitations of current high power lasers and viable paths to optimize laser-driven ion sources.
Keywords: laser-plasma interaction, laser-ion acceleration, accelerator research, paul trap, experiment, HPC, simulation, PIConGPU
  • Open Access LogoNature Communications 9(2018)1, 423
    DOI: 10.1038/s41467-017-02663-1
  • Lecture (Conference)
    18th Advanced Accelerator Concepts Workshop (AAC 2018), 12.-17.08.2018, Breckenridge (CO), United States of America

Publ.-Id: 27599 - Permalink


Normal tissue reaction following proton irradiation of the mouse brain
Suckert, T.; Müller, J.; Beyreuther, E.; Gotz, M.; Tillner, F.; Schürer, M.; Dietrich, A.; Bütof, R.; Lühr, A.; von Neubeck, C.; Krause, M.;
Objective: Radiotherapy leads to inactivation of tumor cells following radiation-induced DNA damage. Compared to conventional photon-based radiotherapy, proton therapy offers the potential of normal tissue sparring due to its favorable depth-dose distribution. However, acute or long-term side effects could still occur due to clinical safety margins and uncertainties about the relative biological effectiveness (RBE). While a variable RBE has been demonstrated in in vitro studies, especially at the end of the proton range, in clinical practice, a constant RBE value of 1.1 is applied. To elucidate the RBE issue based on in vivo experiments, proton irradiation of mouse brains was realized in Dresden.
Methods: Experiments were performed at the experimental beam line [1] of the University Proton Therapy Dresden. For beam characterization and dosimetry, a 2D scintillation detector, ionization chambers and radiochromic films [2] were used. A multi-modality mouse bed suitable for imaging, transportation and irradiation was developed in-house. Like clinical applications, the workflow includes computed tomography scans for treatment planning and X-ray images for refined positioning. By combining these images with proton radiographies [3] of the setup, it was possible to accurately locate the animals relative to the beam. To confirm positioning, DNA damage was visualized by immunofluorescent staining of gH2AX in the irradiated mouse brain.
Results and conclusion: Proton mouse brain irradiation was successfully performed. Distribution of DNA DSB via gH2AX revealed that the proton beam stopped in the beam facing brain hemisphere. The setup enables the comparison to corresponding photon experiments with SAIGRT [4] and clinically relevant long-term experiments, such as measuring cognitive functions and anomalies in imaging, to directly relate potential photon and proton side effects in brain radiotherapy.

[1] Helmbrecht et al. J Instrum 2016
[2] Beyreuther et al. IJPT 2018 (accepted)
[3] Müller et al. Acta Oncologica 2017
[4] Tillner et al. Phys Med Biol 2016
Keywords: normal tissue double-strand breaks proton therapy gH2AX small animal
  • Lecture (Conference)
    European Radiation Research Congress, 21.-25.08.2018, Budapest, Ungarn

Publ.-Id: 27598 - Permalink


Combining in-situ synchrotron X-ray techniques to study the dendritic growth in Ga–In alloys
Shevchenko, N.; Grenzer, J.; Keplinger, O.; Rack, A.; Hoppe, D.; Eckert, S.;
The dendrite growth kinetics and morphology have been of great interest in the solidification science and casting industry. A detailed analysis of the particular solidification phenomena (coarsening, fragmentation etc.) requires X-ray techniques with a better spatial and temporal resolution. High resolution experimental data are also very important for the verification of the existing microstructural models. In this work, in-situ synchrotron X-ray radiography and diffraction methods have been combined to study the evolution of dendritic microstructures during the solidification of Ga - In alloys. The directional solidification experiments were performed at the ID19 and BM20 beamlines (ESRF, France) at a high spatial resolution of < 1 µm. The study is especially focused on the sidearm evolution, retraction and detachment, dendrite morphology and orientation. The sidearm evolution is quantified by an image analysis in a manner appropriated for comparison to simulations. Furthermore, we report on the reconstruction of crystallographic orientation of growing dendrites by using the CaRIne crystallography software. Our measurements show that the Indium dendrites grow along the <110> orientation, typically observed in body-centered metals. Our future work will include the systematic study of the evolution of dendritic morphologies at finite cooling rates and under the impact of melt flow.
Keywords: synchrotron X-ray imaging, Ga-In alloy, directional solidification, X-ray diffraction, dendrite evolution
  • Poster
    Materials Science and Engineering Congress (MSE2018); Symposia: "Tomographic and Radiographic Imaging with Synchrotron X-rays and Neutrons: Exploiting Contrast and Time", 26.-28.09.2018, Darmstadt, Germany

Publ.-Id: 27597 - Permalink


High resolution synchrotron imaging of dendritic coarsening in Ga – In alloys
Shevchenko, N.; Grenzer, J.; Keplinger, O.; Neumann-Heyme, H.; Rack, A.; Eckert, K.; Eckert, S.;
The dendrite coarsening kinetics and dendrite morphology have been of great interest in the solidification science and casting industry. A detailed analysis of particular solidification phenomena (coalescence, fragmentation etc.) requires X-ray techniques with a high spatial and temporal resolution. High resolution experimental data are also very important for the verification of the existing microstructural models. The synchrotron radiography experiments with solidifying Ga - In alloys were performed at BM20 and ID19 (ESRF, Grenoble) at a spatial resolution of < 1 µm. The temporal dynamics of morphological transitions such as retraction, coalescence and pinch-off of the sidearms were studied in-situ. Recently, we showed that the combination of numerical modelling [1] and experiments [2,3] performed at the ESFR synchrotron X-ray source in Grenoble has allowed to improve the understanding of the pinch-off process of dendritic sidearms and to obtain material information that is relevant for quantitative modelling.
In this work, a Ga–In alloy was solidified in vertical direction starting from the top of the solidification cell at a controlled cooling rate of 0.002 K/s and at a vertical temperature gradient of ~2 K/mm. In general, all fragmentation events are located in the deceleration zone that is formed during the initial phase of solidification. Behind an advancing growth front, under slow growth conditions that are almost close to steady state conditions, the coarsening in the mushy zone does not involve a significant detachment of sidearms.
A detailed and advanced image analysis in combination with the high temporal and spatial resolution data of the experiment, allowed us to identify an additional migration process that is influenced by the existing temperature gradient. This Temperature Gradient Zone Melting (TGZM) process is characterized by a sidearm migration rate of 0.01 µm/s. Interestingly, the results of our analysis suggest that this process does not play a significant role for the sidearm detachment process itself.
References
1. H. Neumann-Heyme, et al. PHYS. REV. E, 92 (2015) 060401
2. Shevchenko et al., IOP Conf. Series: Mat. Sci. and Eng. 228 (2017), 012005
3. Neumann-Heyme, Shevchenko et al., Acta Mater. 146 (2018) 176
Keywords: solidification, dendrite morphology, coarsening, synchrotron radiography, temperature gradient, Ga-In alloy
  • Poster
    7th International Conference on Solidification and Gravity (SG’18), 03.-06.09.2018, Miskolc – Lillafüred, Hungary

Publ.-Id: 27596 - Permalink


Investigations of forced flow effects on dendritic solidification
Shevchenko, N.; Keplinger, O.; Eckert, S.;
Many studies have demonstrated that the application of electromagnetic stirring enhances the area of equiaxed grains and reduces the mean grain size (see e.g. [1-2]). It is widely accepted that flow-induced grain refinement and the CET (columnar to equiaxed transition) in metallic alloys is triggered by the appearance of additional dendrite fragments originating from the columnar front. The mechanism for grain multiplication by melt convection is supposed to be complex and is not fully understood until now. The idea to apply electromagnetic stirring to control the defects arising from the action of natural convection is not straightforward too.
The X-ray radiography was used for an in-situ study of the effect of electromagnetic stirring during the directional bottom-up solidification of a Ga-25wt%In alloy in a Hele-Shaw cell [3]. The experimental setup was extended by a magnetic wheel, which allowed for controlled excitation of a melt flow in the liquid phase. The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. The induced redistribution of solute induces different effects on dendrite morphology, such as the uneven growth of primary trunks or lateral branches, remelting of single dendrites and also of lager dendrite ensembles, changes the inclination angle of the dendrites and leads to an increasing arm spacing. The uneven growth of primary dendrites at the beginning of the solidification experiment leads to the formation of Ga-rich zones near the solidification front which develop into distinct segregation freckles.
Another interesting effect can be observed during solidification experiment: the switching off the magnetic wheel leads to "repairing" of a segregation channel due to growth of equiaxed or fine dendrites in areas of Ga-rich pools. It has been demonstrated that the appearance of small equiaxed grains in the undercooled melt in the segregation pools is triggered by quick redistribution of solute after stopping the magnetic pump. A more detailed study of the "repairing" mechanisms of channels is the subject of ongoing work.

References
1. B. Willers et al, Materials Science and Engineering A 402 (2005) 55-65
2. T. Campanella et al, Metallurgical and Materials Transactions A 35 (2004) 3201-3210
3. N. Shevchenko et al, Journal of Crystal Growth 417 (2015) 1-8
Keywords: X-ray radiography, solidification, convection, Ga-In alloy, electromagnetic stirring
  • Lecture (Conference)
    7th International Conference on Solidification and Gravity (SG’18), 03.-06.09.2018, Miskolc – Lillafüred, Hungary

Publ.-Id: 27595 - Permalink


Radio-ecological research – recent results and their application
Raff, J.;
Radionuclides occur in the environment naturally and by anthropogenic activities. Beside other processes, their interaction with the biosphere determines their fate in nature. Therefore, a detailed understanding of how organisms interact with radionuclides and how they influence the migration behavior of radionuclides in the environment is crucial for a reliable risk assessment. This presentation gives an overview of how selected microbes interact with radionuclides and their analogs. In addition, some examples will be given of how the results of radio-ecological research can be successfully transferred into the industry.
Keywords: Radio-ecology, microbes, radionuclides
  • Invited lecture (Conferences)
    BioGeo-Colloquium, 19.06.2018, Jena, Deutschland

Publ.-Id: 27594 - Permalink


Age estimates of groundwater in western Dead Sea catchment based on bomb peak environmental tracer data
Wilske, C.; Suckow, A.; Roediger, T.; Geyer, S.; Weise, S.; Merchel, S.; Rugel, G.; Pavetich, S.; Merkel, B.; Siebert, C.;
The aquifer system of the western side of the Dead Sea is investigated on groundwater recharge, groundwater flow velocities and potential mixtures. The two main limestone aquifers are of Cretaceous age, exposed in the recharge area and show karst characteristics with high transmissivities and flow velocities. Discharge is into springs in the Lower Jordan Valley and Dead Sea region. We use a multi-environmental tracer approach, combining anthropogenic bomb-derived ³⁶Cl/Cl, Tritium and the anthropogenic gases SF₆, CFC-12 and CFC-11, CFC-113 to cover the recharge period from the 1950s to recent and to estimate components in the aquifer system that were recharged less than about 70 years ago. By application of lumped parameter models, we derived residence times in the unsaturated zone, tested several age distributions and verified young groundwater components from the last 10 to 30 years. The data can only be explained assuming also an admixture of an old groundwater component, older than about 70 years, which cannot be further quantified with our tracer data.
Keywords: AMS, groundwater
  • Lecture (Conference)
    8th German-Arab Scientific Forum for Environmental Studies, 08.-09.10.2018, Amman, Jordan
  • Lecture (Conference)
    Australian Geoscience Council Convention - Big Issues & Ideas in Geoscience, 14.-18.10.2018, Adelaide, Australia

Publ.-Id: 27593 - Permalink


Interactions of halophilic microorganisms with uranium
Cherkouk, A.; Bader, M.; Swanson, J. S.; Steudtner, R.; Drobot, B.; Müller, K.; Foerstendorf, H.; Schmidt, M.; Rossberg, A.; Ikeda-Ohno, A.; Stumpf, T.;
Rock salt formations are considered as potential host rocks for the long-term storage of highly radioactive waste in a deep geological repository. Next to bacteria and fungi, extremely halophilic archaea, e.g. Halobacterium species, are predominantly present in this habitat. For long-term risk assessment it is of high interest to study how these microorganisms can interact with radionuclides if released from the waste repository. Therefore, the interactions of the extremely halophilic archaeon Halobacterium noricense DSM 15987T and the moderately halophilic bacterium Brachybacterium sp. G1 with uranium, one of the major radionuclides of concern in the geological repository of radioactive wastes, were investigated in detail in batch experiments. Furthermore, a multi-spectroscopic and -microscopic approach was used to reveal these interaction mechanisms on a molecular level. The two microorganisms exhibited different association characteristics with uranium. Brachybacterium sp. G1 cells sorbed uranium within a short time, whereas a multistage bioassociation process occurred with the archaeon. In situ attenuated total reflection Fourier-transform infrared spectroscopy, time-resolved laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy were applied to elucidate the U(VI) bioassociation behavior. By using these spectroscopic tools the formation of U(VI) phosphate mineral, such as meta-autunite, by the Halobacterium species was demonstrated. These findings highlight the microbial life in deep geological hypersaline environments and offer new insights into the microbe-actinide interactions at highly saline conditions relevant to the disposal of nuclear waste.
  • Lecture (Conference)
    Uranium biogeochemistry - transformations, isotopes, and applications, 21.-26.10.2018, Monte Verita Ascona, Switzerland

Publ.-Id: 27592 - Permalink


Joint simulation of compositional and categorical data via direct sampling technique – Application to improve mineral resource confidence
Talebi, H.; Mueller, U.; Tolosana-Delgado, R.;
Ore deposits usually consist of ore materials with different discrete (e.g. rock and alteration types) and continuous (e.g. geochemical and mineral composition) features. Financial feasibility studies are highly dependent on the modelling of these features and their associated joint uncertainties. Few geostatistical techniques have been developed for the joint modelling of high-dimensional mixed data (continuous and categorical) or constrained data, such as compositional data. The compositional nature of the mineral and geochemical data induces several challenges for multivariate geostatistical techniques, because such data carry relative information and are known for spurious statistical and spatial correlation effects. This paper investigates the application of the direct sampling algorithm for joint modelling of compositional and categorical data. In some mining projects the amount of available data may be enormous in some parts of the deposit and if the density of measurements is sufficient, multivariate geospatial patterns can be derived from the that data and be simulated (without model inference) at other undersampled areas of the deposit with similar characteristics. In this context, the direct sampling multiple-point simulation method can be implemented for this reconstruction process. The compositional nature of the data is addressed via implementing an isometric log-ratio transformation. The approach is illustrated through two case studies, one synthetic and one real. The accuracy of the results is checked against a set of validation data, revealing the potential of the proposed methodology for joint modelling of compositional and categorical information. The direct sampling technique can be considered as a smart move to assess the future risk and uncertainty of a resource by making use of all the information hidden within the early data.
Keywords: Multiple-point statistics, Isometric log-ratio transformation, Uncertainty modelling, Multivariate resource modelling, Sustainable mining

Publ.-Id: 27591 - Permalink


Preclinical imaging for establishment and comparison of orthotopic Non-Small Cell Lung Carcinoma: In search for models reflecting clinical scenarios
Aktar, R.; Dietrich, A.; Tillner, F.; Kotb, S.; Löck, S.; Willers, H.; Baumann, M.; Krause, M.; Bütof, R.;
Objectives:
Clinically relevant animal models of non-small cell lung carcinoma (NSCLC) are required for the validation of novel treatments. We compared two different orthotopic transplantation techniques as well as imaging modalities to identify suitable mouse models mimicking clinical scenarios.
Methods:
We used three genomically diverse NSCLC cell lines (NCI-H1703 adenosquamous cell carcinoma, NCI-H23 adenocarcinoma and A549 adenocarcinoma) for implanting tumour cells either as spheroids or cell suspension into lung parenchyma. Bioluminescence imaging (BLI) and contrast-enhanced cone beam computed tomography (CBCT) were performed twice weekly to monitor tumour growth. Tumour histological data and microenvironmental parameters were determined.
Results:
Tumour development after spheroid-based transplantation differs probably due to the integrity of spheroids, as H1703 developed single localized nodules, whereas H23 showed diffuse metastatic spread starting early after transplantation. A549 transplantation as cell suspension with the help of a stereotactic system was associated with initial single localized tumour growth and eventual metastatic spread. Imaging techniques were successfully applied to monitor longitudinal tumour growth: BLI revealed highly sensitive qualitative data, whereas CBCT was associated with less sensitive quantitative data. Histology revealed significant model dependent heterogeneity in proliferation, hypoxia, perfusion and necrosis.
Conclusions:
Our developed orthotopic NSCLC tumours have similarity with biological growth behavior similar to that seen in the clinic and could therefore be used as attractive models to study tumour biology and evaluate new therapeutic strategies. The use of human cancer cell lines facilitates testing of different genomic tumor profiles that may affect treatment outcomes.
Advances in knowledge:
The combination of different imaging modalities and orthotopic transplantation techniques pave the way towards representative preclinical NSCLC models for experimental testing of novel therapeutic options in future studies.
Keywords: Non-small cell lung cancer, orthotopic model, transplantation technique, preclinical imaging, microenvironment

Publ.-Id: 27590 - Permalink


Probing plutonium dioxide nanoparticles with synchrotron methods
Gerber, E.; Romanchuk, A.; Pidchenko, I.; Hennig, C.; Trigub, A.; Weiss, S.; Scheinost, A.; Kalmykov, S.; Kvashnina, K.;
INTRODUCTION

Plutonium is a chemical element of significant environmental and toxicological concern. At nuclear legacy sites, previous research has demonstrated that plutonium can migrate in colloidal form in the subsurface environment across several kilometers [1-2]. Recent spectroscopic and microscopic investigations showed that so called “colloidal Pu(IV) polymers” are in fact aggregates of PuO2 nanoparticles with diameters ~ 2 nm [3-4]. The exact stoichiometry and structure of such nanoparticles remain, however, still questionable, especially with respect to surface hydration and hydroxylation, as well as the purity of the tetravalent oxidation state considering the existence of four different oxidation states (with relatively small energy barriers III, IV, V, and VI) under environmental conditions.

RESULTS

This contribution will show first results of plutonium oxide nanoparticle studies at the large-scale facility – The European Synchrotron (ESRF) by X-ray spectroscopy and X-ray diffraction methods. Pu oxide nanoparticles were prepared by rapid chemical precipitation using precursors in the different oxidation states (Pu(III), Pu(IV), Pu(V) and Pu(VI)). These precursors were obtained by chemical reduction or oxidation of Pu stock solution. The obtained nanoparticles were characterized at the Rossendorf Beamline (ROBL) at the ESRF, dedicated to actinide science. The recently upgraded ROBL beamline provides unique opportunities to study actinide materials by several experimental techniques: high energy resolution fluorescence detection (HERFD) [5], X-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS) [6], extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) simultaneously.
We will show how the detailed information about local and electronic structure and plutonium oxidation state in different nanoparticles can be obtained using the variety of methods.
Keywords: XAFS, nanoparticles, actinides, HERFD
  • Lecture (Conference)
    Plutonium Futures - The Science 2018, 09.-14.09.2018, San Diego, California, USA

Publ.-Id: 27589 - Permalink


Ultrafast transient absorption spectroscopy of UO22+ and [UO2Cl]+
Haubitz, T.; Tsushima, S.; Steudtner, R.; Drobot, B.; Geipel, G.; Stumpf, T.; Kumke, M. U.;
For the only water coordinated "free" uranyl(VI) aquo ion in perchlorate solution, we identified and assigned several different excited states and showed that the 3∆ state is the luminescent triplet state. With additional data from other spectroscopic methods (TRLFS, UV/Vis, and TAS), we generated a detailed Jabłoński diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the 3Φ state to the 3∆ state transition to be 0.35 ps-1. In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.

Publ.-Id: 27588 - Permalink


Experimental platform for the investigation of magnetized-reverse-shock dynamics in the context of POLAR
Albertazzi, B.; Falize, E.; Pelka, A.; Brack, F.; Kroll, F.; Yurchak, R.; Brambrink, E.; Mabey, P.; Ozaki, N.; Pikuz, S.; van Box Som, L.; Bonnet-Bidaud, J. M.; Cross, J. E.; Filippov, E.; Gregori, G.; Kodama, R.; Mouchet, M.; Morita, T.; Sakawa, Y.; Drake, R. P.; Kuranz, C. C.; Manuel, M. J.-E.; Li, C.; Tzeferacos, P.; Lamb, D.; Schramm, U.; Koenig, M.;
The influence of a strong external magnetic field on the collimation of a high Mach number, plasma flow and its collision with a solid obstacle is investigated experimentally and numerically. The laser irradiation (I ∼ 2 × 1014 W cm−2) of a multilayer target generates a shock wave that produces a rear side plasma expanding flow. Immersed in a homogeneous 10 T external magnetic field, this plasma flow propagates in vacuum and impacts an obstacle located a few mm from the main target. A reverse shock is then formed with typical velocities of the order of 15–20 ± 5 km/s. The experimental results are compared with 2D radiative MHD simulations using the FLASH code. This platform allows investigating the dynamics of reverse shock, mimicking the processes occurring in a cataclysmic variable of polar type.
Keywords: accretion processes; high-power laser; hydrodynamics; laboratory astrophysics; polar; radiative shocks

Publ.-Id: 27587 - Permalink


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