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41396 Publications

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. M.; 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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Permalink: https://www.hzdr.de/publications/Publ-27662
Publ.-Id: 27662


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

Permalink: https://www.hzdr.de/publications/Publ-27661
Publ.-Id: 27661


Inelastische Streuung schneller Neutronen an 56 Fe

Beyer, R.

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

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  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Dr. A.R. Junghans

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Permalink: https://www.hzdr.de/publications/Publ-27660
Publ.-Id: 27660


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

Permalink: https://www.hzdr.de/publications/Publ-27659
Publ.-Id: 27659


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.

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Publ.-Id: 27658


Publikationen, Daten und Software am HZDR

Reschke, E.; Frust, T.; Juckeland, G.; Konrad, U.; Rücker, C.

3 Komponenten wissenschaftlichen Publizierens: ihre Vernetzung, Verwaltung und technische Untersetzung am HZDR

Keywords: RODARE; ROBIS; Open Access; Publizieren; Publikation; Datenpublikation; Softwarepublikation

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Publ.-Id: 27657


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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Permalink: https://www.hzdr.de/publications/Publ-27656
Publ.-Id: 27656


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.

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

Permalink: https://www.hzdr.de/publications/Publ-27655
Publ.-Id: 27655


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).

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Permalink: https://www.hzdr.de/publications/Publ-27654
Publ.-Id: 27654


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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Permalink: https://www.hzdr.de/publications/Publ-27653
Publ.-Id: 27653


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

Permalink: https://www.hzdr.de/publications/Publ-27652
Publ.-Id: 27652


Synthesis and Characterization of Heterometallic Iron–Uranium Complexes with a Bidentate N-Donor Ligand (2,2′-Bipyridine or 1,10-Phenanthroline)

Schöne, S.; Radoske, T.; März, J.; Stumpf, T.; Ikeda-Ohno, A.

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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Publ.-Id: 27651


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

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  • Lecture (Conference)
    XII-th International Conference "Ion Implantation and Other Applications of Ions and Electrons", ION 2018, 18.-21.06.2018, Kazimierz Dolny, Poland

Permalink: https://www.hzdr.de/publications/Publ-27650
Publ.-Id: 27650


Stability of U(VI) doped calcium silicate hydrate gel in repository-relevant brines studied by leaching experiments and spectroscopy

Wolter, J.-M.; Schmeide, K.; Weiss, S.; Bok, F.; Brendler, V.; 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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Permalink: https://www.hzdr.de/publications/Publ-27649
Publ.-Id: 27649


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

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  • Invited lecture (Conferences)
    European Materials Research Society Spring Meeting 2018, 18.-22.06.2018, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-27648
Publ.-Id: 27648


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

Permalink: https://www.hzdr.de/publications/Publ-27647
Publ.-Id: 27647


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

Permalink: https://www.hzdr.de/publications/Publ-27646
Publ.-Id: 27646


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

Permalink: https://www.hzdr.de/publications/Publ-27645
Publ.-Id: 27645


Sensitive, Selective and Biodegradable – New biosorbents for metal recovery

Braun, R.; Matys, S.; Schoenberger, N.; Jain, R.; Lederer, F.; Pollmann, K.

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

Permalink: https://www.hzdr.de/publications/Publ-27644
Publ.-Id: 27644


Heavy metal binding peptides – biosorbents with economic and ecological potential

Braun, R.; Matys, S.; Schoenberger, N.; Jain, R.; Lederer, F.; Pollmann, K.

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

Permalink: https://www.hzdr.de/publications/Publ-27643
Publ.-Id: 27643


Sensitive, selective and biodegradable – new biosorbents for metal recovery

Braun, R.; Matys, S.; Schoenberger, N.; Jain, R.; Lederer, F.; Pollmann, K.

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

Permalink: https://www.hzdr.de/publications/Publ-27642
Publ.-Id: 27642


Heavy metal biosorbents – New approaches for old problems

Braun, R.; Matys, S.; Jain, R.; Schoenberger, N.; Lederer, F.; 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

Permalink: https://www.hzdr.de/publications/Publ-27641
Publ.-Id: 27641


A simple route to synchronized nucleation of self-catalyzed GaAs nanowires on Si for sub-Poissonian length distributions

Tauchnitz, T.; Berdnikov, Y.; Dubrovskii, V. G.; Schneider, H.; Helm, M.; Dimakis, E.

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

Related publications

  • Lecture (Conference)
    Nanowire Week 2018, 11.-15.06.2018, Hamilton, Ontario, Kanada

Permalink: https://www.hzdr.de/publications/Publ-27640
Publ.-Id: 27640


Preparation of nanowire cross-sections by ultramicrotomy

Formanek, P.; Hübner, R.; Balaghi, L.; Wagner, J.; Dimakis, E.

Preparation of nanowire cross-sections by ultramicrotomy

Related publications

  • Lecture (others)
    6. Sächsisches TEM-Präparatorentreffen, 10.04.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27639
Publ.-Id: 27639


Bridging the gap between spectroscopy and thermodynamics of mineral’s surface reactions for safety assessment

Foerstendorf, H.; Jordan, N.; Mayordomo, N.; Lützenkirchen, J.; 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

Permalink: https://www.hzdr.de/publications/Publ-27638
Publ.-Id: 27638


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

Permalink: https://www.hzdr.de/publications/Publ-27637
Publ.-Id: 27637


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

Related publications

  • 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

Permalink: https://www.hzdr.de/publications/Publ-27636
Publ.-Id: 27636


Reversible pH-dependent curium(III) biosorption by the bentonite yeast isolate Rhodotorula mucilaginosa BII-R8

Lopez-Fernandez, M.; Moll, H.; Merroun, M. L.

This work describes the molecular characterization of the interaction mechanism of a bentonite yeast isolate, Rhodotorula mucilaginosa BII-R8, with curium(III) as representative of trivalent actinides and europium(III) used as inactive analogue of Cm(III). A multidisciplinary approach combining spectroscopy, microscopy and flow cytometry was applied. Time-Resolved Laser Induced Fluorescence Spectroscopy (TRLFS) analyses demonstrated that the biosorption of Cm(III) is a reversible and pH-dependent process for R. mucilaginosa BII-R8 cells. Two Cm(III)-R. mucilaginosa BII-R8 species were identified having emission maxima at 599.6 and 601.5 nm. They were assigned to Cm(III) species bound to phosphoryl and carboxyl sites from the yeast cell, respectively. Phosphate groups were involved in the sorption of this actinide, as demonstrated by the Eu(III)-phosphate accumulates at the cell membrane shown by microscopy. In addition, cell viability and metabolic potential were assessed to determine the negative effect of Eu(III) in the yeast cells.
The results obtained in this work showed that the interaction of Cm(III) with the yeast R. mucilaginosa BII-R8 cells at circumneutral and alkaline pH values will make this radionuclide more mobile to reach the biosphere. Therefore, geochemical conditions in the bentonite engineering barrier need to be carefully adjusted for the safe deep geological disposal of radioactive wastes.

Keywords: curium; europium; biosorption; yeast Rhodotorula mucilaginosa; Time-Resolved Laser Induced Fluorescence Spectroscopy (TRLFS)

Permalink: https://www.hzdr.de/publications/Publ-27635
Publ.-Id: 27635


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

Permalink: https://www.hzdr.de/publications/Publ-27634
Publ.-Id: 27634


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

Permalink: https://www.hzdr.de/publications/Publ-27633
Publ.-Id: 27633


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

Permalink: https://www.hzdr.de/publications/Publ-27632
Publ.-Id: 27632


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
  • Other report
    Vancouver: Zeiss, 2018

Permalink: https://www.hzdr.de/publications/Publ-27630
Publ.-Id: 27630


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.; 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.

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Permalink: https://www.hzdr.de/publications/Publ-27629
Publ.-Id: 27629


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

Permalink: https://www.hzdr.de/publications/Publ-27628
Publ.-Id: 27628


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

Related publications

  • Lecture (Conference)
    2nd EUFN Workshop 2018, 19.-20.06.2018, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-27627
Publ.-Id: 27627


Rayleigh–Ritz based expansion method for wakefields in dielectrically lined rectangular waveguides

Reimann, F.; Michel, P.; Lehnert, U.; van Rienen, U.

In 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

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Permalink: https://www.hzdr.de/publications/Publ-27626
Publ.-Id: 27626


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.

Permalink: https://www.hzdr.de/publications/Publ-27625
Publ.-Id: 27625


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.

Permalink: https://www.hzdr.de/publications/Publ-27624
Publ.-Id: 27624


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.

Permalink: https://www.hzdr.de/publications/Publ-27623
Publ.-Id: 27623


Proton beam electron return effect: Monte Carlo simulations and experimental verification

Lühr, A.; Burigo, L. N.; Gantz, S.; Schellhammer, S.; Hoffmann, A. L.

Proton therapy (PT) is expected to benefit from integration with magnetic resonance (MR) imaging. However, the magnetic field distorts the dose distribution and enhances the dose at tissue-air interfaces by the electron return effect (ERE). The objectives were (a) to provide experimental evidence for the ERE in proton beams and (b) to systematically characterise the dependence of the dose enhancement ratio (DER) on magnetic field strength, orientation, proton energy and voxel size by computer simulations.

EBT3 films were irradiated with 200 MeV protons with and without a 0.92 T transverse field of a permanent magnet to determine the DER at effective measurement depths of 0.156 and 0.467 mm from an air interface. High-resolution Monte Carlo simulations were performed to reproduce the irradiation experiments and to calculate the DER for proton energies between 50–200 MeV and magnetic field strengths between 0.35–3 T as function of distance from the air interface. Voxel sizes of 0.05, 0.5 and 1 mm were analysed.

DERs of (2.2  ±  0.4)% and (0.5  ±  0.6)% were measured at 0.156 and 0.467 mm from the air interface, respectively. Measurements and simulations agreed within 0.15%. For a 200 MeV proton beam, the maximum DER in 0.05 mm voxels increased with magnetic field strength from 2.6% to 8.2% between 0.35 and 1.5 T, respectively. For a 1.0 T magnetic field, maximum DER increased from 3.2% to 7.6% between 50 and 200 MeV, respectively. Voxel sizes of 0.5 and 1 mm resulted in maximum DER values of 2.6% and 1.4%, respectively.

The ERE for proton beams in transverse magnetic fields is measurable. The local dose enhancement is significant, well predictable, decreases rapidly with distance from the air interface, and is negligible beyond 1 mm depth. Its impact on air-filled ionisation chambers and porous tissues (e.g. lung) needs to be considered.

Keywords: proton therapy; MRI; MR-guided radiotherapy; dosimetry; magnetic field; electron return effect

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Permalink: https://www.hzdr.de/publications/Publ-27622
Publ.-Id: 27622


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

Permalink: https://www.hzdr.de/publications/Publ-27621
Publ.-Id: 27621


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

Permalink: https://www.hzdr.de/publications/Publ-27620
Publ.-Id: 27620


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

Related publications

  • 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

Permalink: https://www.hzdr.de/publications/Publ-27619
Publ.-Id: 27619


Stability of U(VI) doped calcium silicate hydrate phases in repository-relevant brines studied by leaching experiments and spectroscopy

Wolter, J.-M.; Schmeide, K.; Weiss, S.; Bok, F.; Brendler, V.; 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

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Permalink: https://www.hzdr.de/publications/Publ-27618
Publ.-Id: 27618


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.

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.

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Permalink: https://www.hzdr.de/publications/Publ-27617
Publ.-Id: 27617


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

Permalink: https://www.hzdr.de/publications/Publ-27616
Publ.-Id: 27616


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.

Related publications

  • Contribution to proceedings
    44th European Radiation Research Congress, 21.-25.08.2018, Pecs, Hungary

Permalink: https://www.hzdr.de/publications/Publ-27615
Publ.-Id: 27615


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

Permalink: https://www.hzdr.de/publications/Publ-27614
Publ.-Id: 27614


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.

Related publications

  • Invited lecture (Conferences)
    44th European Radiation Research Congress, 21.-25.08.2018, Pecs, Hungary

Permalink: https://www.hzdr.de/publications/Publ-27613
Publ.-Id: 27613


Best Practices in Running Collaborative GPU Hackathons: Advancing Scientific Applications with a Sustained Impact

Chandrasekaran, S.; Juckeland, G.; Lin, M.; Otten, M.; Pleiter, D.; Stone, J. E.; Lucio-Vega, J.; Zingale, M.; Foertter, F.

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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Permalink: https://www.hzdr.de/publications/Publ-27612
Publ.-Id: 27612


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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Permalink: https://www.hzdr.de/publications/Publ-27611
Publ.-Id: 27611


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.

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Permalink: https://www.hzdr.de/publications/Publ-27608
Publ.-Id: 27608


Integrating a low-field open MR scanner with a static proton research beam line: proof of concept

Schellhammer, S. M.; 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

Permalink: https://www.hzdr.de/publications/Publ-27607
Publ.-Id: 27607


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

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  • Lecture (Conference)
    Nanowire Week, 11.-15.06.2018, Hamilton, Ontario, Canada

Permalink: https://www.hzdr.de/publications/Publ-27606
Publ.-Id: 27606


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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Permalink: https://www.hzdr.de/publications/Publ-27605
Publ.-Id: 27605


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

Permalink: https://www.hzdr.de/publications/Publ-27603
Publ.-Id: 27603


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

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  • 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
  • Lecture (others)
    invited talk at CTFEL User Meeting, 14.10.2019, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-27602
Publ.-Id: 27602


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; NTPDase1; fluorescent enzyme assay; fluorescein; ectonucleotidase; CD39

Permalink: https://www.hzdr.de/publications/Publ-27601
Publ.-Id: 27601


Isolated Proton Bunch Acceleration by a Petawatt Laser Pulse

Hilz, P.; Ostermayr, T. M.; Huebl, A.; Bagnoud, V.; Borm, B.; Bussmann, M.; Gallei, M.; Gebhard, J.; Haffa, D.; Hartmann, J.; Kluge, T.; Lindner, F. H.; Neumayr, P.; Schaefer, C. G.; Schramm, U.; Thirolf, P. G.; Rösch, T. F.; Wagner, F.; Zielbauer, B.; Schreiber, J.

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

Permalink: https://www.hzdr.de/publications/Publ-27599
Publ.-Id: 27599


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

Permalink: https://www.hzdr.de/publications/Publ-27598
Publ.-Id: 27598


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

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  • 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

Permalink: https://www.hzdr.de/publications/Publ-27597
Publ.-Id: 27597


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

Related publications

  • Poster
    7th International Conference on Solidification and Gravity (SG’18), 03.-06.09.2018, Miskolc – Lillafüred, Hungary

Permalink: https://www.hzdr.de/publications/Publ-27596
Publ.-Id: 27596


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

Permalink: https://www.hzdr.de/publications/Publ-27595
Publ.-Id: 27595


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

Related publications

  • Invited lecture (Conferences)
    BioGeo-Colloquium, 19.06.2018, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27594
Publ.-Id: 27594


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

Related publications

  • 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

Permalink: https://www.hzdr.de/publications/Publ-27593
Publ.-Id: 27593


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.

Related publications

  • Lecture (Conference)
    Uranium biogeochemistry - transformations, isotopes, and applications, 21.-26.10.2018, Monte Verita Ascona, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-27592
Publ.-Id: 27592


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

Permalink: https://www.hzdr.de/publications/Publ-27591
Publ.-Id: 27591


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

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Permalink: https://www.hzdr.de/publications/Publ-27590
Publ.-Id: 27590


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

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  • Lecture (Conference)
    Plutonium Futures - The Science 2018, 09.-14.09.2018, San Diego, California, USA

Permalink: https://www.hzdr.de/publications/Publ-27589
Publ.-Id: 27589


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.

Permalink: https://www.hzdr.de/publications/Publ-27588
Publ.-Id: 27588


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

Permalink: https://www.hzdr.de/publications/Publ-27587
Publ.-Id: 27587


Recent experiments on plasma immersion ion implantation (and deposition) using discharges inside metal tubes

Ueda, M.; Silva, C.; Marcondes, A. R.; Reuther, H.; de Souza, G. B.

Plasma immersion ion implantation (PIII) of nitrogen inside metallic tubes of different diameters and configurations were attempted recently. PIII tests in practical size metallic tubes of SS304, ranging from 1.1 to 16 cm∅ and length of 20 cm, were carried out as a continued effort in our lab, to explore PIII inside tubes. Tubes in laying down positions and configurations including metallic lid in one side or both sides open were used, as well as, plane sample support placed 10 cm far from the tube mouth and without bias, taking advantage of plasma flowing out the tube. In particular, nitrogen and argon PIIIs were tested for tube inner wall sputtering and deposition studies, running the PIII system in the last configuration of sample support detached from the tube. During the nitrogen ion implantation runs in other cases, it was found that the final temperature of the tubes and the plasma turn-on voltages were both inversely proportional to the dimensions of the tubes, except for the smallest tube tested. High voltage glow and hollow cathode discharges were produced inside the tubes, either alternately, during the pulse or independently, depending on the tube geometry and pulser used (LIITS, a current controlled source or RUP-4, a voltage controlled one). In the case of smallest diameter of 1.1 cm∅, a suspended tube of SS304 was tested using lower power pulser (RUP-4), at its near maximum capability of 1.2 kW. In this case also, very bright plasmas were formed, mainly inside the tube and resulted in high temperature there (~700 °C). Nitrogen uptake was superior for higher temperature PIII treatments (>700 °C), combining ion implantation and thermal diffusion, which allowed the formation of TiN and Ti2N on the Ti alloy samples inside tubes with diameters ≤4 cm. In this paper, detailed discussion of results of above cited PIII tests with diversified tubes and configurations are presented, together with the analysis of the corresponding treated surfaces of the samples inside, outside and on the support detached from the tube.

Keywords: Plasma immersion ion implantation; Sputtering and deposition inside metallic tubes; TiN and Ti2N in high temperature PIII; Tubes with different dimensions and configurations

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Permalink: https://www.hzdr.de/publications/Publ-27586
Publ.-Id: 27586


cupla - C++ User interface for the Platform Independent Library alpaka

Widera, R.; Ehrig, S.
Other: Bastrakov, Sergei; Other: Bocci, Andrea; Other: Huebl, Axel; Other: Knespel, Maximilian; Other: Kelling, Jeffrey; Other: Mewes, Hauke; Other: Ridder, Vincent; Other: Stephan, Jan; Other: Werner, Matthias

cupla [qχɑpˈlɑʔ] is a simple user interface for the platform independent parallel kernel acceleration library alpaka. It follows a similar concept as the NVIDIA® CUDA® API by providing a software layer to manage accelerator devices. alpaka is used as backend for cupla.

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Permalink: https://www.hzdr.de/publications/Publ-27585
Publ.-Id: 27585


Commissioning of a 4D MRI phantom for use in MR-guided radiotherapy

Schneider, S.; Dolde, K.; Engler, J.; Hoffmann, A.; Pfaffenberger, A.

Purpose:

Systems for integrated magnetic resonance guided radiation therapy (MRgRT) provide real-time and on-line MRI guidance for unequalled targeting performance of moving tumors and organs at risk. The clinical introduction of such systems requires dedicated methods for commissioning and routine machine quality assurance (QA). The aim of the study was to develop a commissioning protocol and method for automatic quantification of target motion and geometric accuracy using a 4D MRI motion phantom.

Material and Methods:

The commissioning was performed on a clinically used 3T MR scanner. The phantom was positioned on a flat tabletop overlay using an in-house constructed base plate for a quick and reproducible setup. The torso-shaped phantom body, which was filled with mineral oil as signal generating medium, includes a 3D grid structure for image distortion analysis and a cylindrical thru-hole in which a software-controlled moving rod with a hypo-intense background gel and a decentralized hyper-intense target simulates 3D organ motion patterns. To allow for sequence optimization, MR relaxometry was performed to determine the longitudinal T1 and transverse T2 relaxation times of both target and background gel in the movable cylinder. The geometric image distortion was determined as the mean and maximum 3D Euclidean distance (∆mean, ∆max) of grid points determined by non-rigid registration of a 3D spoiled gradient echo MRI scan and a CT scan. Sinusoidal 1D/2D/3D motion trajectories, varying in amplitude and frequency, as well as an exemplary 1D MR-navigator diaphragm motion pattern extracted from a volunteer scan were scanned by means of 2D cine MRI. Target positions were automatically extracted from 2D cine MRI using an in-house developed software tool.

Results:

The base plate enabled a reproducible setup with a deviation of <1 mm in all directions. Relaxometry yielded T1/T2 values for target and background gel of 208.1±2.8 / 30.5±4.7 ms and 871 .36±36 / 13.4±1.3 ms respectively. The geometric distortion in the MRI scan increased with distance from the magnetic isocenter, with ∆mean=0.58±0.30 mm and ∆max=1.31 mm. The frequencies of the reconstructed motion patterns agreed with the pre-set values within 0.5%, whereas the reconstructed amplitudes showed a maximum deviation to the pre-set amplitudes of <0.4 mm in AP/LR direction and <0.2 mm in IS direction.

Conclusion:

A method and protocol for commissioning of a 4D MRI motion phantom on a 3T MR scanner for MRgRT was developed. High-contrast and geometrically reliable 2D cine MR images of the phantom’s moving target could be obtained. The pre-set motion parameters could be extracted with sufficient spatio-temporal accuracy from 2D cine MRI in all motion directions. The measured geometric image distortion of <1.31mm within the phantom grid confirms geometric accuracy of the clinically utilized 3D spoiled gradient echo sequence.
The method developed can be used for routine QA tests of spatio-temporally resolved MRI data in MRgRT.

Keywords: MRI; dynamic phantom; image-guided radiation therapy; commissioning

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Permalink: https://www.hzdr.de/publications/Publ-27584
Publ.-Id: 27584


Microstructural degradation and creep fracture behavior of conventionally and thermomechanically treated 9% Chromium Heat Resistant steel

Vivas, J.; Capdevila, C.; Altstadt, E.; Houska, M.; Sabirov, I.; San-Martín, D.

The microstructural degradation and the creep fracture behavior of conventionally and thermomechanically treated Grade 91 steel were investigated after performing Small Punch Creep Tests. A remarkable reduction in creep ductility was observed for the samples thermomechanically treated in comparison to those conventionally treated under the tested conditions of load (200 N) and temperature (700 ºC). A change in the fracture mechanism from a ductile transgranular fracture to a brittle intergranular fracture was observed when changing from the conventionally treated to the thermomechanically treated processing condition, leading to this drop in creep ductility. The change in the fracture mechanism was associated to the localized concentration of creep deformation, close to coarse M23C6 carbides, at the vicinity of prior austenite grain boundaries (PAGB) in the thermomechanically treated samples. The preferential recovery experienced at the vicinity of PAGB produced the loss of the lath structure and the coarsening of the M23C6 precipitates. The electron microscopy images provided suggest that the creep cavities nucleate in these weak recovered areas, associated to the presence of coarse M23C6. After the coalescence of the cavities the propagation of the cracks was facilitated by the large prior austenite grain size produced during the austenitization which favors the propagation of the cracks along grain boundaries triggering the intergranular brittle fracture. This fracture mechanism limits the potential use of the proposed thermomechanical processing routes.

Keywords: Creep resistant steels; thermomechanical treatment; creep fracture behavior; microstructural degradation; small punch creep tests; ausforming

Permalink: https://www.hzdr.de/publications/Publ-27583
Publ.-Id: 27583


The use of assay data as a foundation for a geometallurgical model – the case of the Thaba Chromite Mine, South Africa

Bachmann, K.; Menzel, P.; Tolosana-Delgado, R.; Schmidt, C.; Hill, M.; Gutzmer, J.

The Lower and Middle Group chromitites of the Bushveld Igneous Complex in South Africa are the source of a very large portion of the global chrome supply. The recovery of platinum group elements and base metals (Ni, Cu) as by-products has the potential to add value to these chrome resources. Yet, the effectiveness of chromite and platinum-group element beneficiation circuits is highly sensitive to variations in feed composition. Of particular relevance is the abundance of alteration silicates, which have a negative impact on recoveries and concentrate grade. The use of geochemical proxies, based on data acquired routinely during the exploration and mining process may provide a cost- and time-efficient alternative to more time-consuming and expensive mineralogical analyses. Such an approach is presented in this study, which focuses on the LG-6, LG-6A, MG-1 and MG-2 chromitite seams at the Thaba mine located on the western limb of the Bushveld Complex. An extensive assay data set comprising of data for Cr2O3, FeO, Al2O3, MgO, SiO2, CaO and P provided by the mine owner was evaluated and corrected for systematic bias between different sample batches. A statistical assessment was performed to discuss the variability within and between the chromitite seams and to separate the mine lease area into distinct geochemical clusters. The distribution of the samples belonging to the different geochemical clusters was then transposed onto the geology of the mine lease area. This allowed the definition of spatial domains. These spatial domains, recognized by the assessment of assay data only, are then validated by mineralogical attributes; implications for mineral beneficiation are critically assessed. According to this assessment, the chromitites of the Thaba mine area can be subdivided into three distinct domains, domains that constitute the suitable fundament for a geometallurgical model. An extensive supergene altered domain is distinguished from a domain affected by hydrothermal alteration. The latter domain occurs below the depth of modern weathering, but in obvious proximity to faults and around a prominent dunite pipe. The third domain is represented by ores least affected by post-magmatic alteration processes. This domain occupies the centre of fault blocks below the extent of modern weathering.

Keywords: Cluster analysis; Lower Group chromitites; Middle Group chromitites; chromite ore; chromite deposits; chromite beneficiation

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Permalink: https://www.hzdr.de/publications/Publ-27582
Publ.-Id: 27582


Explicit decay heat calculation in the nodal diffusion code DYN3D

Bilodid, Y.; Fridman, E.; Kotlyar, D.; Shwageraus, E.

The residual radioactive decay heat plays an important role in some accident scenarios and, therefore, needs to be accurately calculated when performing accident analyses. The current reactor simulation codes used for accident analysis account for the residual decay heat by means of simplified models. Typically, these models rely on semi-empirical correlations which are defined over a limited range of burnup and fuel types. Therefore, the applicability of such correlations is limited and any deviation from the definition range may lead to high uncertainties, which is detrimental in evaluating safety margins.
Reactor dynamic code DYN3D was originally developed for transient and accident analysis of LWRs. In DYN3D, the residual radioactive decay heat calculation is based on the German national standard DIN Norm 25463 model. The applicability of this model is limited to a low enriched uranium dioxide fuel for light water reactors.
This paper describes a new general decay heat calculation model implemented in DYN3D. The radioactive decay rate of each nuclide in each spatial node is calculated by recently implemented depletion module and the cumulative released heat is used to obtain the spatial distribution of the decay power for every time step. Such explicit approach is based on first principles and is free from approximations and, thus, can be applied to any reactor system (e.g. thermal and fast) and fuel type. The proposed method is verified against the reference Serpent 2 Monte Carlo solutions for a range of reactor types.

Keywords: DYN3D; Decay heat; Microdepletion

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Permalink: https://www.hzdr.de/publications/Publ-27581
Publ.-Id: 27581


Comparison of radionuclide association of fungi under laboratory and natural conditions

Wollenberg, A.; Großmann, S.; Günther, A.; Raff, J.; Stumpf, T.

The varied use of different radionuclides in medicine, industry and research and their disposal has repeat-edly led to the release of these radionuclides into the environment. Through leaching and migration, the anthropogenic released radionuclides can reach the groundwater, endangering the environment, animals and humans. However, the mobility and thus the migration behavior of radionuclides in the soil are influ-enced by the microorganisms living there.
Fungi play an important role in the microbial community of soil and can therefore have a major influence on radionuclide mobility, for example through sorption, accumulation or reduction processes. Therefore, the aim of this research is to investigate the influence of fungi on radionuclide migration in soil by using column and field experiments and to determine the potential of fungi for radiation protection precaution-ary methods or even remediation methods.
For the assessment of the suitability of fungi the first step is to investigate the molecular interactions with radionuclides under laboratory conditions to identify dominant interaction processes. Therefore binding experiments with different media were performed and the molecular binding form was investigated with time-resolved laser-induced fluorescence spectroscopy. In the next step, column experiments were carried out with soil and under natural conditions, in which the retention capacity of the fungi for radionuclide migration in the soil was investigated.
The experiments so far showed that the biochemistry of the fungi determines the metal interaction and not the surrounding environment. Furthermore, it was clearly demonstrated by column experiments, that fungi are able to retain radionuclides significantly.

Keywords: Fungi; Radionuclide; TRLFS; Column

  • Poster
    RCA-Workshop, 12.-14.06.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27580
Publ.-Id: 27580


C++ & Python API for Scientific I/O with openPMD

Hübl, A.; Pöschel, F.; Koller, F.; Gu, J.
Other: Fortmann-Grote, Carsten; Other: Stańczak, Dominik; Other: Amundson, James; Other: Donnelly, Ray; Other: Widera, René; Other: Zenker, Erik; Other: Bastrakov, Sergei; Other: Lehe, Rémi; Other: Amorim, Lígia Diana; Other: Bastrakova, Kseniia; Other: Pausch, Richard; Other: Ordyna, Paweł; Other: Ganyushin, Dmitry; Other: Kirkham, John; Other: Schnetter, Erik; Other: Bez, Jean Luca; Other: Gruber, Bernhard Manfred; Other: Schild, Nils

openPMD is an open metadata format for open data workflows in open science. This library provides a common high-level API for openPMD writing and reading. It provides a common interface to I/O libraries and file formats such as HDF5 and ADIOS. Where supported, openPMD-api implements both serial and MPI parallel I/O capabilities.

Keywords: openPMD; Open Science; Open Data; HDF5; ADIOS; data; MPI; HPC; research; file-format; file-handling

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Permalink: https://www.hzdr.de/publications/Publ-27579
Publ.-Id: 27579


99Tc retention on pyrite and alumina: the effect of Fe2+

Rodríguez, D.; Mayordomo, N.; Stumpf, T.; Mueller, K.

For the safety case of a nuclear waste repository, Tc is treated very conservatively, assuming no retention by the geotechnical and geological barriers. Tc(VII), pertechnetate (TcO4-), the most dominant species in oxidizing environment is considered to be inert, hardly interacting with minerals and highly mobile. In contrast, the reduced form Tc(IV) is mainly found as solid, TcO2, and its mobility is limited.
The presence of reductants in the near-field of a nuclear waste repository, e.g. Fe2+ is expected due to canister corrosion. Therefore, most of recent studies consider Tc reductive immobilization by mineral containing reductant moieties, such as magnetite (FeIIFe2IIIO4) or mackinawite (FeS) [1,2] or pre-sorbed reductants on mineral phases, like Fe2+ on corundum (a-Al2O3), diaspore (a-AlOOH), goethite (a-FeOOH), and hematite (a-Fe2O3)[3,4].
In this work, we compare the Tc immobilization by two systems: i) pyrite (FeS2) and ii) nano particular alumina in presence of Fe2+ (ternary system).
Pyrite is capable to remove almost 100% of Tc(VII) from solution within 7 days at pH = 6.5. In a further step, we study the effect of ionic strength on the Tc immobilization under different NaCl concentrations, as the retention mechanism could be affected by the change of Tc(IV) solubility, due to different degrees of salinity [4].
Alumina is capable to retain 6.5% of Tc in the absence of reducing Fe2+. However, in the ternary system Tc retention is 100% for pH > 6.5. In this case, the improvement on the Tc reduction is not only due to Fe2+ presence, but also to the surface properties of alumina, triggering heterogeneous reduction of Tc by high Fe2+ surface coverage or possible LDH formation.

This work has been developed in the frame of VESPA II project (02E11607B), supported by the German Federal Ministry of Economy and Energy (BMWi).

Keywords: Technetium; sorption; pyrite; alumina; iron

  • Lecture (Conference)
    The 10th International Symposium on Technetium and Rhenium – Science and Utilization, 03.-06.10.2018, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-27578
Publ.-Id: 27578


Amphiphilic Siderophore Marinobactin for Froth Flotation Process

Schrader, S.; Kutschke, S.; Rudolph, M.; Pollmann, K.

The consumption of metallic raw materials increased in the last years. The coverage of demand is getting more difficult, because both primary and secondary raw materials become more and more complex. To find a solution, some new ways have to be gone, like the combination of biotechnology with classic processing methods.
The idea of this work is the biotechnological production of siderophores for the application in the classic froth flotation process. Siderophores are small organic molecules with a high affinity for binding Fe(III) and to form strong complexes also with other metals. They are produced by microorganisms (aerobic bacteria and fungi) and some plants to equalize the low bioavailability of iron in their environment. Especially the group of amphiphilic siderophores are very interesting. The hydrophilic part, carrying hydroxamate groups, is responsible for the binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully in this processing method. It can be suggested siderophores carrying the same functional groups, also work well as collectors. The fatty acid tail, that is representing the hydrophobic part, gets in contact with the bubble and spares additional chemicals and further working steps for making the target mineral particles hydrophobic.
This work includes on the one hand the biotechnological production of the marine siderophore marinobactin for the first time using a bioreactor and optimized conditions to make the production more efficient. On the other hand, the produced siderophore is tested in different froth flotation micro scale experiments like “Bubble-pick-up-test” and micro flotation in the Halimond Tube. These results show for the first time that amphiphilic siderophores are working in the froth flotation process and supply first concepts about the required concentration of siderophores in this processing process. In addition, the results also include interaction studies of different metals.
The application of amphiphilic siderophores as biochemicals in the froth flotation process can change the classic processing method in a more sustainable process – the bioflotation process. This will reduce the usage of other chemical agents. Moreover the specific metal binding of siderophores changes flotation in a more purposeful and efficient process.

Keywords: Bioflotation; Flotation; Siderophore; Marinobactin

  • Lecture (Conference)
    Applied Biotechnology in Mining, 25.-27.04.2018, Dnipro, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-27577
Publ.-Id: 27577


Re-irradiation of recurrent gliomas: pooled analysis and validation of an established prognostic score-report of the Radiation Oncology Group (ROG) of the German Cancer Consortium (DKTK)

Combs, S.; Niyazi, M.; Adeberg, S.; Bougatf, N.; Kaul, D.; Fleischmann, D.; Gruen, A.; Fokas, E.; Rodel, C.; Eckert, F.; Paulsen, F.; Oehlke, O.; Grosu, A.; Seidlitz, A.; Lattermann, A.; Krause, M.; Baumann, M.; Guberina, M.; Stuschke, M.; Budach, V.; Belka, C.; Debus, J.; Kessel, K.

The heterogeneity of high-grade glioma recurrences remains an ongoing challenge for the interdisciplinary neurooncology team. Response to re-irradiation (re-RT) is heterogeneous, and survival data depend on prognostic factors such as tumor volume, primary histology, age, the possibility of reresection, or time between primary diagnosis and initial RT and re-RT. in the present pooled analysis, we gathered data from radiooncology centers of the DKTK Consortium and used it to validate the established prognostic score by Combs et al. and its modification by Kessel et al. Data consisted of a large independent, multicenter cohort of 565 high-grade glioma patients treated with re-RT from 1997 to 2016 and a median dose of 36 Gy. Primary RT was between 1986 and 2015 with a median dose of 60 Gy. Median age was 54 years; median follow-up was 7.1 months. Median OS after re-RT was 7.5, 9.5, and 13.8 months for WHO IV, III, and I/II gliomas, respectively. All six prognostic factors were tested for their significance on OS. Aside from the time from primary RT to re-RT (P = 0.074) and the reresection status (P = 0.101), all factors (primary histology, age, KPS, and tumor volume) were significant. Both the original and new score showed a highly significant influence on survival with P < 0.001. Both prognostic scores successfully predict survival after re-RT and can easily be applied in the routine clinical workflow. Now, further prognostic features need to be found to even improve treatment decisions regarding neurooncological interventions for recurrent glioma patients.

Keywords: Outcome; prognostic score; recurrent glioma; re-irradiation

Permalink: https://www.hzdr.de/publications/Publ-27576
Publ.-Id: 27576


A Timing RPC with low resistive ceramic electrodes

Sultanov, R.; Akindinov, A.; Beyer, R.; Dreyer, J.; Fan, X.; Greifenhagen, R.; Kämpfer, B.; Kotte, R.; Laso Garcia, A.; Malkevich, D.; Naumann, L.; Plotnikov, V.; Prokudin, M.; Shirinkin, S.; Stach, D.

For precise start time determination a Beam Fragmentation T0 Counter (BFTC) is under development for the Time-of-Flight Wall of the Compressed Baryonic Matter Spectrometer (CBM) at FAIR/Darmstadt. This detector will be located around the beam pipe, covering the front area of the Projectile Spectator Detector. The fluxes at this region are expected to exceed 10^5cm^{-2}s^{-1}.
Ceramic RPCs could be use because of their high rate capabilities and radiation hardness of material. Efficiency >/=97%, time resolution /=10^5cm^{-2}s^{-1} were confirmed during many tests with high beam fluxes of relativistic electrons. We confirm the stability of these characteristics with low resistive Si3N4/SiC floating electrodes for a prototype of eight small RPCs, where each of them contains six gas gaps. The active RPC size amounts 20x20 mm^2 produced on basis of Al3O2 and Si3N4/SiC ceramics. Recent test results obtained with relativistic electrons at the linear accelerator ELBE of the Helmholtz-Zentrum Dresden-Rossendorf with new PADI-10 Front-end electronic will be presented.

Keywords: RPC; ceramic composite electrodes; high rate capability; signal cross-talk

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Permalink: https://www.hzdr.de/publications/Publ-27575
Publ.-Id: 27575


Platinum transport in chloride-bearing fluids and melts: Insights from in situ X-ray absorption spectroscopy and thermodynamic modeling

Tagirov, B. R.; Filimonova, O.; Trigub, A. L.; Akinfiev, N. N.; Nickolsky, M. S.; Kvashnina, K. O.; Chareev, D. A.; Zotov, A. V.

Hydrothermal chloride-rich fluids are identified at the late stages of the formation of platinum group element (PGE) deposits in giant layered intrusions, and are considered as the PGEs transport media in Cu(-Mo,Au) porphyry systems. In order to quantify the hydrothermal mobility of Pt we performed an investigation of the speciation of Pt in hydrothermal chloride-bearing fluids and dry melt by means of X-ray absorption spectroscopy (XAS). The experiments consisted in recording the Pt L-3-edge X-ray absorption near edge structure/extended X-ray absorption fine structure (XANES/EXAFS) spectra of Pt-bearing fluids obtained by dissolution of Pt metal in KCl/HCl and CsCl/HCl fluids in the temperature range from 450 to 575 degrees C at pressures from 0.5 to 5 kbar. A spectrum of Pt dissolved in dry CsCl/NaCl/KCl + K2S2O8 melt was recorded at 650 degrees C. The capillary method, when the experimental solution together with Pt((cr) )is sealed inside a silica glass capillary, was used. As was determined from the XANES spectra, in all the experimental systems Pt existed in the +2 oxidation state. Analysis of EXAFS spectra showed that Pt is coordinated by four Cl atoms with Rpt-cl = 2.31 +/- 0.01 angstrom independently of the T-P-compositional parameters. No evidence of the formation of complex with alkali metal cations in the second coordination sphere of Pt was found by the analysis of the EXAFS spectra of concentrated CsCl brines and melt. Our results imply that PtCl42- is the main Pt-Cl complex which predominates in hydrothermal fluids at t > 400 degrees C and fluid density d > 0.3 g.cm(-3). Experimental data obtained for dry melt of alkali metal chlorides suggest that Pt-Cl complexes can dominate Pt speciation in chloride-bearing aluminosilicate melts where Cl exhibits a salt-like atomic arrangement and ionic bonding. The literature data on the Pt solubility constant, Pt-(cr) + 2HCl((aq))degrees + 2Cl(-) = PtCl42- + H-2(aq), are compiled and fitted to the simple density model equation log K-s degrees (PtCl42- ) = 0.973 - 8202. T(K)(-1) - 5.505 . log d (w) + 2223 . log d(w) .T(K)(-1), where d(w) is the pure water density in g.cm(-3). The equation, combined with the extended Debye-Hiickel equation for activity coefficients, can be used to calculate the solubility of Pt up to 1000 degrees C/5 kbar. It accurately predicts the solubility of Pt in concentrated chloride brine (up to 50 wt% NaCl) at parameters of magmatic-hydrothermal transition (800 degrees C/1.4 kbar). At fluid/vapor density below 0.3 g.cm(-3) a neutral complex PtCl2 degrees((aq)) is suggested as the dominant Pt species. Our data demonstrate that Pt is highly mobile in high-temperature oxidized chloride-rich hydrothermal fluids. For example, at 800 degrees C/2 kbar the concentration of Pt can reach a few wt% in the 1 wt% HCl/50 wt% NaCl fluid which is in equilibrium with magnetite-hematite buffer. Once a Cl-reach fluid exsolves from alumuinosilicate melt, Pt follows Cl and enriches the fluid phase where it exists mostly in the form of PtCl42-. Decrease of temperature, acidity, and fluid chlorinity results in precipitation of Pt from the fluid phase.

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Permalink: https://www.hzdr.de/publications/Publ-27574
Publ.-Id: 27574


Towards the bottom of the periodic table

Kvashnina, K. O.

Actinide and lanthanide chemistry is currently experiencing a renaissance, due to the prospects of obtaining novel materials relevant for applications in chemical synthesis, electronics, materials science, nanotechnology, biology and medicine. Most of the fascinating properties of the lanthanide and actinide materials are related to the partially filled 4f/5f valence shell and in contrast to the rest of the periodic table, are poorly understood. This contribution will provide a brief overview of applications of advanced X-ray techniques that have recently become available for studying the electronic structure of actinide and lanthanide materials at The European Synchrotron (ESRF).

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  • Invited lecture (Conferences)
    Les Midis Minatec, 08.06.2018, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-27573
Publ.-Id: 27573


Towards the surface hydroxyl species in CeO2 nanoparticles

Plakhova, T. V.; Romanchuk, A. Y.; Butorin, S. M.; Konyukhova, A. D.; Egorov, A. V.; Shiryaev, A. A.; Baranchikov, A. E.; Dorovatovskii, P. V.; Huthwelker, T.; Gerber, E.; Bauters, S.; Sozarukova, M. M.; Scheinost, A.; Ivanov, V.; Kalmykov, S. N.; Kvashnina, K.

Understanding the complex chemistry of functional nanomaterials is of fundamental importance. Controlled synthesis and characterization at the atomic level is essential to gain deeper insight into the unique chemical reactivity exhibited by many nanomaterials. Cerium oxide nanoparticles have many industrial and commercial applications, resulting from very strong catalytic, pro- and anti-oxidant activity. However, the identity of the active species and the chemical mechanisms imparted by nanoceria remain elusive, impeding the further development of new applications. Here, we explore the behavior of cerium oxide nanoparticles of different sizes at different temperatures and trace the electronic structure changes by state-of-the-art soft and hard X-ray experiments combined with computational methods. We confirm the absence of the Ce(III) oxidation state at the surface of CeO2 nanoparticles, even for particles as small as 2 nm. Synchrotron X-ray absorption experiments at Ce L3 and M5 edges, combined with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS) and theoretical calculations demonstrate that in addition to the nanoceria charge stability, the formation of hydroxyl groups at the surface profoundly affects the chemical performance of these nanomaterials.

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Permalink: https://www.hzdr.de/publications/Publ-27572
Publ.-Id: 27572


Atomic scale reversible opto-structural switching of few atom luminescent silver clusters confined in LTA zeolites

Aghakhani, S.; Grandjean, D.; Baekelant, W.; Coutiño-Gonzalez, E.; Fron, E.; Kvashnina, K.; Roeffaers, M. B. J.; Hofkens, J.; Lievens, B. F.; Sels, P.

Luminescent silver clusters (AgCLs) stabilized inside partially Ag exchanged Na LTA zeolites show a remarkable reversible on–off switching of their green-yellowish luminescence that is easily tuned by a hydration and dehydration cycle, making them very promising materials for sensing applications. We have used a unique combination of photoluminescence (PL), UV-visible-NIR Diffuse Reflectance (DRS), X-ray absorption fine structure (XAFS), Fourier Transform-Infrared (FTIR) and electron spin resonance (ESR) spectroscopies to unravel the atomic-scale structural changes responsible for the reversible optical behavior of the confined AgCLs in LTA zeolites. Water coordinated, diamagnetic, tetrahedral AgCLs [Ag4(H2O)4]2+ with Ag atoms positioned along the axis of the sodalite six-membered rings are at the origin of the broad and intense green-yellowish luminescence in the hydrated sample. Upon dehydration, the luminescent [Ag4(H2O)4]2+ clusters are transformed into non-luminescent (dark), diamagnetic, octahedral AgCLs [Ag6(OF)14]2+ with Ag atoms interacting strongly with zeolite framework oxygen (OF) of the sodalite four-membered rings. This highly responsive on–off switching reveals that besides quantum confinement and molecular-size, coordinated water and framework oxygen ligands strongly affect the organization of AgCLs valence electrons and play a crucial role in the opto-structural properties of AgCLs.

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Permalink: https://www.hzdr.de/publications/Publ-27571
Publ.-Id: 27571


Flow Structures in a Weakly Turbulent Rayleigh-Bénard Convection affected by a Horizontal Magnetic Field

Vogt, T.; Yanagisawa, T.; Ishimi, W.; Tasaka, Y.; Eckert, S.

MHD Rayleigh-Bénard convection was studied experimentally using the eutectic metal alloy GaInSn inside a box having a square horizontal cross section and an aspect ratio of 5. Flow measurements were performed by means of ultrasound Doppler velocimetry that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two dimensional rolls arranged parallel to the magnetic field [1], [2]. If the Rayleigh number (Ra) is increased over a certain threshold Ra/Q, whereby Q is the Chandrasekhar number, the flow undergoes a transition to turbulence. Besides the primary convection rolls the measurements reveal regular flow oscillations arising from 2D and 3D deformations of the rolls, Ekman-pumping induced flow as well as smaller side vortices that develop around the convection rolls [3]. Our findings demonstrate the importance to take 3D flow effects into account in order to explain the observed flow structures, which are often considered as quasi 2D. The comparison between the experiments and accompanying direct numerical simulations shows a very good agreement.

  • Lecture (Conference)
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands
  • Open Access Logo Contribution to proceedings
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-27570
Publ.-Id: 27570


Large-scale circulations of turbulent Rayleigh-Bénard convection in a finite liquid metal layer

Akashi, M.; Tasaka, Y.; Yanagisawa, T.; Vogt, T.; Murai, Y.; Eckert, S.

Large-scale circulations of Rayleigh-Bénard convection in a finite liquid metal layer were examined experimentally by means of ultrasonic Doppler velocimetry. The fluid layer with aspect ratio of five and L = 40 mm in height was filled with eutectic alloy of GaInSn (Prandtl number, Pr = 0.03), and multiple ultrasonic transducers for the velocimetry were mounted in the side wall of the vessel to capture 3D structures of the convection.

  • Lecture (Conference)
    International Conference on Rayleigh Bénard Turbulence, 14.-18.05.2018, Enschede, Netherlands
  • Open Access Logo Contribution to proceedings
    International Conference on Rayleigh Bénard Turbulence, 14.-18.05.2018, Enschede, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-27569
Publ.-Id: 27569


LSC Oscillations in a Liquid Metal

Vogt, T.; Horn, S.; Grannan, A.; Aurnou, J.

We present experimental results of liquid metal Rayleigh Bénard convection in a Gamma = D/H = 2 cylindrical tank. The tank is filled with liquid gallium that has a Prandtl-number Pr = 0.03. Ultrasound Doppler velocimetry is used in this study to measure the instantaneous velocity distribution along four different measuring lines. This technique is a useful tool to measure the velocities in opaque fluids, such as liquid metals non-invasively. Furthermore, a total number of 29 thermocouples is used to monitor the temperature in the experiment. Thus, the experimental set-up allows for a simultaneous analysis of the velocity and temperature field. We observed a strong oscillatory behaviour of the LSC in both, the velocity and temperature signal whose characteristic behaviour remains unchanged over the investigated range of 7x10^4 < Ra < 6x10^6. We analysed the three dimensional structure of the oscillation and compare the results to direct numerical simulation, which are in excellent agreement to the experimental observation.

  • Lecture (Conference)
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands
  • Open Access Logo Contribution to proceedings
    INTERNATIONAL CONFERENCE ON RAYLEIGH BÉNARD TURBULENCE, 14.-18.05.2018, Enschede, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-27568
Publ.-Id: 27568


Controlling the lability of uranyl(VI) through intramolecular π-π Stacking

Mashita, T.; Tsushima, S.; Takao, K.

A reaction of UO22+ with cyclohexyldiphenylphosphine oxide (OPCyPh2) in ethanol resulted in a perchlorate salt of the 4-fold homoleptic complex, UO2(OPCyPh2)44]2+.

Permalink: https://www.hzdr.de/publications/Publ-27567
Publ.-Id: 27567


Dynamic Imaging Based Structure Tracking with Ultrafast X-Ray Tomography

Windisch, D.; Bieberle, M.; Bieberle, A.; Hampel, U.

A common problem in experimental multiphase flow studies is the tracking of structures in the flow domain. Such may be for example particles, bubbles and waves. Ultrafast electron beam X-ray computed tomography (UFXRCT) is a fast cross-sectional imaging technique, which is applicable to opaque multiphase flows. However, as it is a 2D imaging technique, we can only obtain statistical information about properties of moving structures in the given axial planes so far. To progress towards tracking of structures we now devised a novel approach for dynamic imaging-based structure tracking. For that the tomography scanner follows the structure of interest by controlled positioning basing on real-time image data analysis. This approach is described in the following.

Keywords: ultrafast X-ray CT; structure tracking; real-time control

  • Open Access Logo Contribution to proceedings
    9th World Congress on Industrial Process Tomography (WCIPT9), 02.-06.09.2018, Bath, United Kingdom
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography (WCIPT9), 03.09.2018, Bath, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-27566
Publ.-Id: 27566


Cerebrovascular Reactivity during Prolonged Breath-Hold in Experienced Freedivers

Keil, V.; Eichhorn, L.; Mutsaerts, H.; Träber, F.; Block, W.; Mädler, B.; van de Ven, K.; Siero, J.; Macintosh, B.; Petr, J.; Fimmers, R.; Schild, H.; Hattingen, E.

BACKGROUND AND PURPOSE:

Experienced freedivers can endure prolonged breath-holds of up to eleven minutes despite severe hypoxemia and are therefore ideal subjects to study apnea-induced cerebrovascular reactivity (CVR). This multi-parametric study investigates CBF, the spatial coefficient of variation (ASL-sCoV), as a correlate of arterial transit time, and brain metabolism dynamics during prolonged apnea.

MATERIALS AND METHODS:
Fifteen male freedivers (median age: 36.0, CI 32.0–50.0, years; median previous prolonged breath-holds >2.5 mins.: 384, CI 24.0–4,536) underwent repetitive 3T pseudo-continuous arterial spin labeling and 31P-/1H-MR spectroscopy scans before, during and after a five-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. CVR was temporally and regionally compared to blood gases and previous experience.

RESULTS:
ASL-sCoV decreased during the early breath-hold phase (-30.0%, P=.002), whereas CBF remained almost stable during this phase and increased in the late phase
(+51.8%; P<.0001). CVR differed between the anterior and the posterior circulation during all phases (e.g. late breath-hold: MCA 57.3±14.2 vs. PCA 42.7±10.8 mL/100 g/min.;
P=.001). There was an association between breath-hold experience and lower CBF (1,000 previous breath-holds reduced WM CBF by 0.6 mL/100 g/min.; CI 0.15 –1.1 mL/100 g/min., P=.01). While breath-hold caused peripheral lactate rise (+18.5 %) and hypoxemia (SpO2 -24.0%), cerebral lactate and ATP remained within physiological ranges, despite early signs of oxidative stress (-6.4% phosphocreatine/(ATP+ADP); P=.02).

CONCLUSIONS:

The CVR responses to prolonged apnea are complex, but guarantee the maintenance of a physiological brain metabolism in trained individuals for at least five minutes.

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Permalink: https://www.hzdr.de/publications/Publ-27565
Publ.-Id: 27565


Architecture and mineral potential of the Paleoproterozoic Karrat Group, West Greenland - Results of the 2017 Season

Rosa, D.; Bernstein, S.; Dewolfe, M. Y.; Dziggel, A.; Grocott, J.; Guarnieri, P.; Kolb, J.; Partin, C. A.; Sørensen, E.-V.; Zimmermann, R.

The main goal of the 2017 field season was to revise the geological maps of the southern area of Karrat Group exposures. This revision will encompass the 1:100 000 sheets of Maarmorilik 71V.2 Syd, Nuugaatsiaq 71V.2 Nord, Pannertooq 72V.2 Syd, and Svartenhuk 71V.1 Nord, originally compiled between 1980 and 1991. This third field season followed up on fieldwork carried out in 2015 and 2016 and, as the other two field seasons, was jointly financed by the Geological Survey of Denmark and Greenland (GEUS) and the Ministry of Mineral Resources of Greenland (MMR).
Within this framework, and since the focus of the first two seasons had been on the Paleo- proterozoic Karrat Group, the 2017 fieldwork targeted Archean rocks, namely in Panner- tooq (head of Ukkusissat Fjord), Upernivik Ø, Kigarsima/Tornit and the area south of Maarmorilik. This work led to the identification, in what was originally mapped as Archean orthogneiss, of significant paragneiss and quartzite sequences, of uncertain age. These supracrustal sequences often appear infolded with Archean orthogneiss, so some of them could possibly be unrelated to the stratigraphy of the Karrat Group. Similar infolding ob- served in the Qeqertarssuaq Formation, mapped in Kangilleq Fjord, suggests that this for- mation could possibly also be unrelated to the Karrat Group, as traditionally defined. Cor- roborating this interpretation is the fact that higher-P metamorphic assemblages, evi- denced by garnet amphibolite and kyanite micaschist, were documented in the Qeqertars- suaq Formation, but not in overlying formations. This contrasting metamorphic evolution can be interpreted as evidence for an early thermal event, prior to Qaarsukassak Formation deposition. Alternatively, the disparate metamorphic conditions could be accounted for by juxtaposition of different tectonic units during the Rinkian orogeny. T o further constrain the depositional ages of the paragneiss and quartzite (including those of the Qeqertarssuaq Formation), follow up detrital zircon geochronology is warranted. However, regardless of what the subsequent analytical work reveals, these findings appear to already imply signifi- cant revisions to the existing maps.
Within the Paleoproterozoic volcano-sedimentary succession, fieldwork allowed for the identification of the presence of the Qaarsukassak Formation (informal) in Kussinersuaq (Umiammakku Isbræ), Rinks Isbræ, Qingaarssuaq (Kangerlussuaq Fjord), Kigarsima/T ornit (Kangerluarsuk Fjord) and Kangerluarsuup Sermia. This formation hosts the stratabound mineralisation in the Rio Tinto Zinc (RTZ) Discovery area (Kangerluarsuk Fjord), where it was first defined. While no primary Zn mineralisation was observed at the defined localities, with only faint zinc zap responses obtained at Kussinersuaq, and other localities not tested for mineralisation, these findings significantly stretch the areal extent of the stratabound Zn- hosting Qaarsukassak Formation, and are therefore of economic significance. Detailed follow up photogeological mapping and interpretation of hyperspectral scenes of this min- eralisation host should consequently be carried out. Further work within the Paleoprotero- zoic Karrat Group, included the study of the mafic volcanic rocks of the Kangilleq Fm (in- formal), was aimed at recognising horizons with distinct geochemical signatures (alkaline vs. subalkaline), as identified in samples collected in previous seasons, in order to elucidate petrogenesis of the volcanic rocks.
The structural setting and metamorphism of the Prøven Igneous Complex (PIC) is key to understanding the geological evolution of the region and its lower contacts and some internal structures were studied. This work demonstrated that the PIC comprises one or more tabular intrusions. In the west, near Upernavik, the complex was emplaced close to the basement-cover contact. Farther to the east and south, it seems to have been emplaced at a higher stratigraphic position within the Paleoproterozoic sedimentary sequence. Subse- quently, the complex was displaced to the NW (north side of the PIC) and SE (south side of the PIC). Wherever it was studied, both North and South, this contact is a shear zone. The PIC contains abundant enclaves of meta-sedimentary rocks, particularly near the lower contact. The enclaves are most likely to be from a Paleoproterozoic sequence - the Karrat Group - although this assumption is unproven. In the instances where possible cross- cutting intrusive relations are found with meta-sedimentary rocks at the base of the PIC, the cross-cutting igneous rocks are late syn-tectonic biotite granite and leucogranites, rather than elements of the PIC proper. Earlier workers assumed that these late syn-tectonic granites and the PIC were part of the same magmatic event and were both late syn- tectonic. Our new field evidence from the northern contact of the PIC, consistent with re- cently published geochronology (Sanborn-Barrie et al. 2017), shows that the PIC was af- fected by intense fabric formation and folding and that its contacts with its host rocks, where we have seen them, are always concordant as a consequence of intense defor- mation. We conclude that the published interpretation that the PIC was emplaced relatively late during Rinkian orogenic evolution should be rejected (Grocott & Pulvertaft, 1990 and references therein).

  • Other report
    København, Danmark: Danmarks of Grønlands geologiske undersøgelse, 2018
    102 Seiten

Permalink: https://www.hzdr.de/publications/Publ-27564
Publ.-Id: 27564


Analysis of flow patterns in high gravity equipment using gamma-ray computed tomography

Groß, K.; Bieberle, A.; Gladyszewski, K.; Schubert, M.; Hampel, U.; Skiborowski, M.; Górak, A.

The capacity of today’s gas-liquid contacting equipment such as tray or packed columns is limited by the gravitational-driven liquid flow. Intensified equipment applying centrifugal force offers great potential for enhancing the mass transfer and for reducing equipment size. Yet, detailed knowledge about the liquid flow inside rotating packings is scarce due to limited accessibility with conventional measurement systems. In this study, a gamma-ray computed tomography is employed to quantify the liquid hold-up and its distribution in the moving packing.

Keywords: Flow behavior; gas-liquid flow pattern; local liquid hold-up; non-invasive flow imaging; rotating packed bed

Permalink: https://www.hzdr.de/publications/Publ-27563
Publ.-Id: 27563


Evaluation of liquid hold-up in a rotating packed bed for high gravity fluid separation using process-synchronized gamma-ray computed tomography

Groß, K.; Bieberle, A.; Gladyszewski, K.; Schubert, M.; Skiborowski, M.; Hampel, U.; Górak, A.; (Editors)

A Rotating Packed Bed (RPB) is a compact and flexible fluid separation equipment, which utilizes a centrifugal forces to achieve enhanced mass and energy transfer between a liquid and a vapour phase, brought in contact within a porous rotating packing. In order to perform a reliable design and scale-up of RPBs, detailed knowledge about the hydrodynamics and flow mechanisms within the equipment is strongly required. However, due to the non-transparent solid casing, such insight cannot be generated by common analytics. In the present study, liquid hold-up and gas-liquid phase distribution are determined in a porous metal foam packing of 450 mm diameter installed in a pilot-scale RPB using a high-energetic gamma-ray computed tomography (CT). The CT system consists of an isotopic source Cs 137 and an in-house developed radiation detector comprising 320 scintillation detector elements operated in photon counting mode in order to detect each single gamma photon. In particular, the liquid hold-up distribution and the lateral spreading behaviour is visualized and analysed relative to the motion of the rotating packing applying conventional CT scanning and a time-averaged angular-resolved CT scanning procedure, respectively.

Keywords: Fluid Separation; High Gravity Equipment; Rotating Packed Beds; Gamma-Ray Computed Tomography; Process-Synchronized Imaging

  • Contribution to proceedings
    World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK
  • Lecture (Conference)
    World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK

Permalink: https://www.hzdr.de/publications/Publ-27562
Publ.-Id: 27562


Compact high energy x-ray spectrometer based on forward Compton scattering for high intensity laser plasma experiments

Singh, S.; Versaci, R.; Laso Garcia, A.; Morejon, L.; Ferrari, A.; Molodtsova, M.; Schwengner, R.; Kumar, D.; Cowan, T.

This article describes the design and presents recent results from testing and calibration of a forward Compton scattering gamma-ray spectrometer. The calibration was performed using a bremsstrahlung source on the photon scattering facility at the ELBE accelerator at Helmholtz-Zentrum Dresden-Rossendorf, which provides gamma-ray photons with energies up to 18 MeV. The calibration was conducted at different bremsstrahlung end point energies - 10.5, 13, 15 and 18 MeV. Experimental spectra show systematic increase in the maximum energy, photon temperature and flux. The spectrometer is effective for an energy range of 4 to 20 MeV with 20 to 30% energy resolution. The article also describes the design and shielding considerations which helped to achieve a dynamic range greater than 30 with this spectrometer. The comparison between experimental results and Monte Carlo simulations are also presented.

Keywords: bremsstrahlung; photon scattering; gamma rays; Compton spectrometer

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Permalink: https://www.hzdr.de/publications/Publ-27561
Publ.-Id: 27561


Modification of the perpendicular anisotropy in synthetic antiferromagnets by global and local ion beam irradiation

Lenz, M.; Koch, L.; Samad, F.; Arekapudi, P.; Fallarino, L.; Hellwig, O.

We investigate sputter deposited synthetic antiferromagnets consisting of Co/Pt multilayers with perpendicular anisotropy. Repeated multilayer-blocks are antiferromagnetically coupled to each other via Ru interlayers. This complex sample structure allows an exact tuning of the energy contributions perpendicular anisotropy, interlayer exchange and demagnetization: Varying repeats within the Co/Pt multilayers (X) or a different number of multilayer-blocks (N) lead to various magnetic phases and 3-dimensional textures [1].
By ion beam irradiation we can change the balance of these energy contributions due to an intermixing at the interfaces. With this we can realize various magnetic phases within one and the same sample and by local irradiation we can even achieve a lateral coexistence of different magnetic phases.
We will present our investigations of globally and locally irradiated synthetic antiferromagnet’s field reversal behaviour, using vibrating sample magnetometry and high resolution magnetic force microscopy.
[1] O. Hellwig et al., J. Magn. Magn. Mater. 319, 13 (2007)

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  • Poster
    Joint European Magnetic Symposia (JEMS), 03.-07.09.2018, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27560
Publ.-Id: 27560


Parametric resonances in periodically perturbed dynamo models

Giesecke, A.; Stefani, F.

I present results on kinematic dynsamo models driven by an axisymmetric large scale flow impacted by periodic perturbations due to azimuthally propagating vortices. I found a strong impact on growth rates and frequencies with regimes of parametric resonances whenn the frequency of the perturbation is twice the frequency of the unperturbed case. These models behave similar to rotating mechanical systems subject to periodic distortions that are described by the Matthieu equation. A possible application are dynamo experiments like VKS dynamo in Cadarache or convection driven planetary dynamos that are influenced by tidal forces.

Keywords: dynamo; DRESDYN

  • Lecture (Conference)
    Planetary-Stellar Connection: The Sun's Lesson, 07.-09.05.2018, Freiburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27559
Publ.-Id: 27559


Advanced correction algorithms for ultrafast X-ray computed tomography

Bieberle, M.; Wagner, M.; Gücker, F.; Neumann, M.; Hampel, U.

Ultrafast electron beam X-ray computed tomography is a unique imaging technique for the investigation of multiphase flows. It provides high-resolution cross-sectional images at rates of up to 4,000 fps from two tomography planes, which also allows axial velocities to be determined. As is typical for such complex measurement systems, there are several physical effects leading to deviations from the ideal imaging system. On the one hand, these are deviations associated to X-ray computed tomography (CT) in general, such as photon scattering and beam hardening. On the other hand, there are several effects originating from the electron beam deflection, which are in particular related to electron beam X-ray CT. For example, some uncertainties about the final size and position of the X-ray focal spot path on the target are remaining. This paper addresses effects and corresponding practical correction algorithms for both categories. Scattering and beam hardening as interlinked phenomena are treated by correction based on fast ray-tracing in-plane simulations. The topic of focal spot path uncertainties has been analysed in detail with respect to different parameters. The problem is tackled with two approaches. The first approach searches the correct angular positions of the X-ray focal spot on the target by maximizing the grey value variance in the resulting reconstructed images. The second approach evaluates the resulting distance map between the two imaging planes by combining simulated distributions with measured values.

Keywords: correction algorithms; image reconstruction; ultrafast; X-ray CT

  • Contribution to proceedings
    9th World Congress on Industrial Process Tomography (WCIPT9), 02.-06.09.2018, Bath, United Kingdom
    Proceedings of the 9th World Congress on Industrial Process Tomography
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography (WCIPT9), 02.-06.09.2018, Bath, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-27558
Publ.-Id: 27558


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