Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

34133 Publications

Advances in radiotherapy special feature.

Krause, M.; Supiot, S.

there is no abstract

Permalink: https://www.hzdr.de/publications/Publ-22849
Publ.-Id: 22849


Comparison of [18F]-FMISO, [18F]-FAZA and [18F]-HX4 for PET imaging of hypoxia - a simulation study.

Wack, L. J.; Mönnich, D.; van Elmpt, W.; Zegers, C. M.; Troost, E. G.; Zips, D.; Thorwarth, D.

BACKGROUND:

To investigate the effect of hypoxia tracer properties on positron emission tomography (PET) image quality for three tracers [18F]-fluoromisonidazole (FMISO), [18F]-fluoroazomycinarabinoside (FAZA) and [18F]-flortanidazole (HX4), using mathematical simulations based on microscopic tumor tissue sections.
MATERIAL AND METHODS:

Oxygen distribution and tracer binding was mathematically simulated on immunohistochemically stained cross-sections of tumor xenografts. Tracer diffusion properties were determined based on available literature. Blood activity and clearance over a four-hour period post-injection (p.i.) were derived from clinical dynamic PET scans of patients suffering from head and neck or bronchial cancer. Simulations were performed both for average patient blood activities and for individual patients, and image contrast between normoxic and hypoxic tissue areas was determined over this four-hour period p.i.
RESULTS:

On average, HX4 showed a six-fold higher clearance than FMISO and an almost three-fold higher clearance than FAZA based on the clinical PET data. The absolute variation in clearance was significantly higher for HX4 than for FMISO (standard deviations of 5.75 *10-5 s-1 vs. 1.55 *10-5 s-1). The absolute tracer activity in these scans at four hours p.i. was highest for FMISO and lowest for HX4. Simulated contrast at four hours p.i. was highest for HX4 (2.39), while FMISO and FAZA were comparable (1.67 and 1.75, respectively). Variations in contrast of 7-11% were observed for each tracer depending on the vascularization patterns of the chosen tissue. Higher variations in clearance for HX4 resulted in an increased inter-patient variance in simulated contrast at four hours p.i.
CONCLUSIONS:

In line with recent experimental and clinical data, the results suggest that HX4 is a promising new tracer that provides high image contrast four hours p.i., though inter-patient variance can be very high. Nevertheless, the widely used tracer FMISO provides a robust and reproducible signal four hours p.i., but with a lower contrast. The simulations revealed tracer clearance to be the key factor in determining image contrast.

Permalink: https://www.hzdr.de/publications/Publ-22848
Publ.-Id: 22848


Valproic acid modulates radiation-enhanced matrix metalloproteinase activity and invasion of breast cancer cells.

Artacho-Cordón, F.; Ríos-Arrabal, S.; Olivares-Urbano, M. A.; Storch, K.; Dickreuter, E.; Muñoz-Gámez, J. A.; León, J.; Calvente, I.; Torné, P.; Salinas, M. D.; Cordes, N.; Núñez, M. I.

PURPOSE:

To evaluate matrix metalloproteinase (MMP) activity and invasion after ionizing radiation (IR) exposure and to determine whether MMP could be epigenetically modulated by histone deacetylase (HDAC) inhibition.
MATERIAL AND METHODS:

Two human breast cancer cell lines (MDA-MB-231 and MCF-7) were cultured in monolayer (2D) and in laminin-rich extracellular matrix (3D). Invasion capability, collagenolytic and gelatinolytic activity, MMP and TIMP protein and mRNA expression and clonogenic survival were analyzed after IR exposure, with and without a HDAC inhibition treatment [1.5 mM valproic acid (VA) or 1 μM trichostatin-A (TSA)].
RESULTS:

IR exposure resulted in cell line-dependent stimulation of invasion capacity. In contrast to MCF-7 cells, irradiated MDA-MB-231 showed significantly enhanced mRNA expression of mmp-1, mmp-3 and mmp-13 and of their regulators timp-1 and timp-2 relative to unirradiated controls. This translated into increased collagenolytic and gelatinolytic activity and could be reduced after valproic acid (VA) treatment. Additionally, VA also mitigated IR-enhanced mmp and timp mRNA expression as well as IR-increased invasion capability. Finally, our data confirm the radiosensitizing effect of VA.
CONCLUSION:

These results suggest that IR cell line-dependently induces upregulation of MMP mRNA expression, which appears to be mechanistically linked to a higher invasion capability that is modifiable by HDAC inhibition.

Keywords: Matrix metalloproteinases; breast cancer; epigenetic regulation; histone deacetylases; invasion; ionizing radiation; tumour microenvironment

Permalink: https://www.hzdr.de/publications/Publ-22847
Publ.-Id: 22847


ILKAP, ILK and PINCH1 control cell survival of p53-wildtype glioblastoma cells after irradiation.

Hausmann, C.; Temme, A.; Cordes, N.; Eke, I.

The prognosis is generally poor for patients suffering from glioblastoma multiforme (GBM) due to radiation and drug resistance. Prosurvival signaling originating from focal adhesion hubs essentially contributes to therapy resistance and tumor aggressiveness. As the underlying molecular mechanisms remain largely elusive, we addressed whether targeting of the focal adhesion proteins particularly interesting new cysteine-histidine-rich 1 (PINCH1), integrin-linked kinase (ILK) and ILK associated phosphatase (ILKAP) modulates GBM cell radioresistance. Intriguingly, PINCH1, ILK and ILKAP depletion sensitized p53-wildtype, but not p53-mutant, GBM cells to radiotherapy. Concomitantly, these cells showed inactivated Glycogen synthase kinase-3β (GSK3β) and reduced proliferation. For PINCH1 and ILKAP knockdown, elevated levels of radiation-induced γH2AX/53BP1-positive foci, as a marker for DNA double strand breaks, were observed. Mechanistically, we identified radiation-induced phosphorylation of DNA protein kinase (DNAPK), an important DNA repair protein, to be dependent on ILKAP. This interaction was fundamental to radiation survival of p53-wildtype GBM cells. Conclusively, our data suggest an essential role of PINCH1, ILK and ILKAP for the radioresistance of p53-wildtype GBM cells and provide evidence for DNAPK functioning as a central mediator of ILKAP signaling. Strategies for targeting focal adhesion proteins in combination with radiotherapy might be a promising approach for patients with GBM.

Keywords: DNA repair; ILK; ILKAP; PINCH1; radioresistance

Permalink: https://www.hzdr.de/publications/Publ-22846
Publ.-Id: 22846


Abschätzung des Sekundärneutronenfeldes bei der Protonentherapie mit passiv geformten Feldern

Lutz, B.; Enghardt, W.; Swanson, R.; Fiedler, F.

Die Strahlentherapie mit Protonen erlaubt, im Vergleich zur Bestrahlung mit Photonen, eine stärkere Lokalisierung der durch die primäre Strahlung verabreichten Dosis im Tumor. Die damit verbundene Schonung gesunden Gewebes ist der größte Vorteil dieser Form der Strahlentherapie.

Die verbleibende Belastung des gesunden Gewebes wird hauptsächlich durch sekundäre Neutronen verursacht. Der Fluss und das Spektrum der sekundären Neutronen hängen dabei stark von der gewählten Konfiguration der Therapieanlage ab.

Um das Sekundärneutronenfeld an der Protonentherapieanlage des Universitätsklinikum Carl Gustav Carus in Dresden abschätzen zu können, wird eine detaillierte Simulation der Strahlformung mit Hilfe der Software TOPAS entwickelt. Der Vortrag beschreibt die Implementation der Anlage und die erwarteten Neutronenspektren. Der Einfluß verschiedener Maschinenparameter auf das Neutronenfeld wird diskutiert. Abschließend wird die Vorhersage mit ersten Messungen der Ortsdosis am Therapieplatz verglichen.

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Materie und Kosmos (SMuK), 29.02.-04.03.2016, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22845
Publ.-Id: 22845


On the use of HERFD-XANES at the U L3 and M4-edges to determine the uranium valence state on [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3]

Bès, R.; Rivenet, M.; Solari, P. L.; Kvashnina, K. O.; Scheinost, A. C.; Martin, P. M.

We report and discuss here the unambiguous uranium valence state determination on the complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using High Energy Resolution Fluorescence Detection - X-ray Absorption Near Edge Structure spectroscopy (HERFD-XANES). The spectra at both uranium L3- and M4-edges confirm that all the five non-equivalent uranium atoms are solely in the hexavalent form in this compound, as previously suggested by Bond Valence Sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the pre-edge feature, due to the 2p3/2-5f quadrupole transition, has been observed in the U L3-edge HERFD-XANES spectrum, in agreement with theoretical and experimental observations of other uranium based compounds. Recently, this feature has been proposed as a possible tool to determine the uranium oxidation state in a manner similar to 3d and 4d metals. Nevertheless, this feature is also very sensitive to the uranium local environment, as revealed by our theoretical calculations, and consequently could not be used to attribute without ambiguity the uranium valence state. In contrast, U M4-edge HERFD-XANES appears to be the most straightforward and reliable way to assess uranium valence state in very complex materials such as [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] or mixture of compounds.

Keywords: XANES; XES; HERFD; uranium oxidation state

Permalink: https://www.hzdr.de/publications/Publ-22844
Publ.-Id: 22844


Pulsed-Magnet Developments at the Dresden High Magnetic Field Laboratory

Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.

  • Lecture (Conference)
    MT24 - International Conference on Magnet Technology 24, 18.-23.10.2015, Seoul, Korea

Permalink: https://www.hzdr.de/publications/Publ-22843
Publ.-Id: 22843


Magneto-Acoustic Studies of Frustrated Quantum Magnets

Pham, T.-C.

  • Invited lecture (Conferences)
    International Symposium on Frontiers in Materials Science 2015, 19.-21.11.2015, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-22842
Publ.-Id: 22842


The gas chromatographic analysis of the reaction products of the partial isobutane oxidation as a two phase process.

Willms, T.; Kryk, H.; Hampel, U.

The partial oxidation of isobutane to t-butyl hydroperoxide (TBHP) has been studied analytically for the first time as a two-phase process in a capillary micro reactor. In order to obtain detailed information on products, yields, selectivity and reaction pathways, the products have been investigated by GC/MS. An Rxi-5ms column and a PTV-injector have been used to analyze the liquid products. TBHP, di-t-butyl peroxide (DTBP), t-butanol (TBA), and propanone as main products as well as further by-products e.g. methanal, isopropanol, isobutanol and isobutanal in minor quantities have been identified by MS. The liquid products have been obtained by quenching the reaction and vaporizing the isobutane afterwards by pressure reduction using a mass flow controller allowing a constant mass flow. For all liquid reaction products calibrations, a validation of the method including limits of quantification and detection as well as calculation of uncertainties has been performed. The results have been applied successfully for the investigation of the selectivities of the main products (TBHP, DTBP, TBA, propanone) of the isobutane oxidation. In the frame of the analytical investigation of this reaction a correlation coefficient of r2 > 0.999 for TBHP and DTBP, which is necessary to perform a validation, has been obtained for the first time. The gaseous phase has been analyzed using a GASPRO Column, a DEANS switch, a mole sieve column and a TCD detector. Apart from the gaseous reactants, isobutene has been found.

Keywords: Isobutane oxidation; t-butyl hydroperoxide; di-t-butyl-peroxide; GC/MS; multiphase process

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-22840
Publ.-Id: 22840


Flüssig-Flüssig-Extraktion von Seltenen Erden mit Hilfe von Calix[4]arenen

Mansel, A.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    1. Verbundtreffen zum BMBF/PtJ-Projekt "SE-FLECX" an der Universität Leipzig, Institut für Anorganische Chemie, 26.11.2015, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22839
Publ.-Id: 22839


How Details of the Geometallurgical Optimisation Influence Overall Value

van den Boogaart, K. G.; Tolosana Delgado, R.; Müller, U.; Matos Camacho, S.

The precise formulation of a geometallurgical optimisation problem is by necessity a simplification of reality. It includes implicit choices such as data availability or mining block geometry. Additional data can be ore body data, production data or market data. Often these choices are predetermined by the software, the workflow or corporate culture and as such are not even queried. There are several aspects that might play a role in the optimization. They include not only the spatial model on which the selection of mining blocks and the potential mining sequence are based, but also the complexity of the processing model, the way in which uncertainty is treated, the scope of responsibility and the complexity of the model. In addition the timing of the optimization and the availability (or lack thereof) of information influence the outcome of any optimization.

We show that different modelling choices and different model formulations for the same mine can lead to very different processing choices, substantially different NPV’s , opposite investment decisions and so to overall different values for the entire operation. The selection of adequate simplifications and corresponding formulations for the optimisation problem is thus an important task in itself.

For this purpose we introduce a method quantifying the impact of certain simplifications prior to the optimization itself. E.g. for the effect of mining block choices the effect depends mainly on the spatial structure and the structure of the processing gain function. Both can be quantified beforehand. Likewise the effect of additional data depend on the increase of information. Again this can be quantified from a spatial model.

Based on the outcome appropriate simplifications can be selected for the geometallurgical optimization.

Keywords: geometallurgy; model choice; adaptive processing

  • Contribution to proceedings
    GeoMet 2016, The third AusIMM International Geometallurgy Conference, 15.-17.06.2016, Perth, Australia
    Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, Melbourn: The Australasian Institute of Mining and Metallurg, 303-312
  • Lecture (Conference)
    GeoMet 2016, The third AusIMM International Geometallurgy Conference, 15.-17.06.2016, Perth, Australia

Permalink: https://www.hzdr.de/publications/Publ-22838
Publ.-Id: 22838


Time-Resolved Two Million Year Old Supernova Activity Discovered in the Earth’s Microfossil Record

Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Deneva, B.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gómez-Guzmán, J.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.

Massive (>10M_⊙) stars, which terminate their evolution as core collapse supernovae (CCSN), are theoretically predicted 1 to eject >10-5M_⊙ of the radioactive isotope 60Fe (half-life t1/2=(2.61±0.04) Ma; weighted average of Ref. 2 and 3). If such an event occurs sufficiently close to our solar system, one expects that traces of the supernova (SN) debris could be deposited on Earth. Since 60Fe has no or little expected anthropogenic or cosmogenic production mechanisms, its detection in terrestrial reservoirs would be an immediate proxy for a past Earth-SN interaction within the past few million years. Herein, we report for the first time a time-resolved 60Fe signal residing, at least partially, in a biogenic reservoir. Using the experimental technique of accelerator mass spectrometry (AMS), this signal was found through the direct detection of live 60Fe atoms contained within secondary Fe-oxides, among which are magnetofossils 4; the fossilized chains of magnetite crystals produced by magnetotactic bacteria 5, 6. Magnetofossil preservation precludes post-depositional Fe mobilization events, ensuring that the 60Fe record is correctly preserved. The magnetofossils were chemically extracted from two Pacific Ocean sediment drill cores. Our results show that the 60Fe signal onset occurs around 2.7 Ma, near the lower Pleistocene boundary, terminates between 1.4 Ma and 1.8 Ma, and peaks at about 2.2 Ma.

Keywords: accelerator mass spectrometry; AMS; supernova; cosmogenic nuclide

  • Open Access Logo Proceedings of the National Academy of Sciences of the United States of America 113(2016)33, 9232-9237
    DOI: 10.1073/pnas.1601040113

Permalink: https://www.hzdr.de/publications/Publ-22837
Publ.-Id: 22837


On the Lorentz-force driven flow around an insulating sphere

Massing, J.; Baczyzmalski, D.; Weier, T.; Landgraf, S.; Cierpka, C.

The Lorentz-force driven flow around an insulating sphere in a parallel electric and magnetic field was investigated experimentally and numerically. From the results, the lift force acting on the bubble due to the pressure reduction caused by the Lorentz-force driven flow was estimated, which was discussed in the literature as the primary cause for a faster bubble detachment in a parallel magnetic field. It could be shown, that the pressure force is several orders of magnitudes smaller than the buoyancy force and therefore has no significant effect on the bubble detachment. This finding is supported by the measurement results of the 3D3C velocity field around an elevated, axially magnetized sphere in an electric field. In the final paper the 3D3C flow around the bubble will be analyzed in greater detail and hydrodynamic mechanisms to explain the faster detachment will be further discussed.

Keywords: Lorentz force; electrolysis; Astigmatism Particle Tracking Velocimetry

  • Lecture (Conference)
    18th Lisbon International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics, 04.-07.07.2016, Lissabon, Portugal
  • Open Access Logo Contribution to proceedings
    18th Lisbon International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics, 04.-07.07.2016, Lissabon, Portugal, 978-989-98777-8-8

Permalink: https://www.hzdr.de/publications/Publ-22836
Publ.-Id: 22836


Sodium-bismuth-lead low temperature liquid metal battery

Lalau, C.-C.; Ispas, A.; Weier, T.; Bund, A.

The development of a low temperature liquid metal battery based on ionic liquids namely, sodium-bis(trifluoromethylsulfonyl) imide (Na[TFSI]) in tetraethylammonium-bis(trifluoromethylsulfonyl) imide ([TEA][TFSI]) will be discussed. Such a battery should be easily accessible for fluid flow measurements which is still a challenge with the conventional high temperature systems. Cells comprising a Na negative electrode, 20 mole % Na[TFSI] in [TEA][TFSI] ionic liquid electrolyte and a Pb-Bi eutectic positive electrode were constructed and operated at 160 °C. Galvanostatic cycling experiments were conducted at low C rates (C/26) for 13 h corresponding to 50 % depth of discharge. A discharge capacity of 565 mAh/g was found. Furthermore electrochemical impedance spectroscopy was used to characterize the aging of the cells.

Keywords: Liquid metal batteries; Ionic liquids; Sodium; Electrochemical impedance spectroscopy; Storage

Permalink: https://www.hzdr.de/publications/Publ-22835
Publ.-Id: 22835


Strange meson production in Al+Al collisions at 1.9 A GeV

Gasik, P.; Piasecki, K.; Herrmann, N.; Leifels, Y.; Matulewicz, T.; Andronic, A.; Averbeck, R.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Caplar, R.; Crochet, P.; Czerwiakowa, O.; Deppner, I.; Dupieux, P.; Dzelalija, M.; Fabbietti, L.; Fodor, Z.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kis, M.; Koczon, P.; Kotte, R.; Lebedev, A.; Le Fevre, A.; Liu, J. L.; Lopez, X.; Manko, V.; Marton, J.; Münzer, R.; Petrovici, M.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Weber, I.; Widmann, E.; Wisniewski, K.; Xiao, Z. G.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.

The production of K+, K- and φ(1020) mesons are studied in Al+Al collisions at beam energy of 1.9A GeV which is close or below the production threshold in NN reactions. Inverse slopes, anisotropy parameters, and total emission yields of K± mesons are obtained. A comparison of the ratio of kinetic energy distributions of K- and K+ mesons to transport model calculations (IQMD and HSD) suggests that the inclusion of in-medium modifications of kaon properties is necessary to reproduce the ratio. The inverse slope and total yield of φ mesons are deduced. The contribution to K- production from φ meson decays is found to be 17 ± 3%. The results are in line with previous K± and φ data obtained for different colliding systems at similar incident beam energies.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-22834
Publ.-Id: 22834


Abschirmungs- und Aktivierungsberechnungen für den MYRRHA-Forschungsreaktor in Mol

Ferrari, A.; Konheiser, J.; Mueller, S. E.

No abstract provided

  • Lecture (Conference)
    15. AAA Workshop, 07.12.2015, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-22833
Publ.-Id: 22833


AER Working Group D on VVER Safety Analysis – Report of the 2015 Meeting

Kliem, S.

The AER Working Group D on VVER reactor safety analysis held its 24th meeting in Madrid, Spain, during the period 18-19 May, 2015. The meeting was hosted by UPM Madrid and was held in conjunction with the ninth workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 19 participants attended the meeting of the working group D, 17 from AER member organizations and 2 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting. The meeting started with a general information exchange about the recent activities in the participating organizations.
The given presentations and the discussions can be attributed to the following topics:
• Safety analyses methods and results
• Code development and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
• Thermal hydraulic analyses of fuel assemblies
• Future activities
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairman.

  • Contribution to proceedings
    25th Symposium of AER on VVER Reactor Physics and Reactor Safety, 13.-16.10.2015, Balatongyörök, Hungary
    Proceedings of the 25th Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA EK, 9789637351259, 247-253
  • Lecture (Conference)
    25th Symposium of AER on VVER Reactor Physics and Reactor Safety, 13.-16.10.2015, Balatongyörök, Hungary

Permalink: https://www.hzdr.de/publications/Publ-22832
Publ.-Id: 22832


Band-gap narrowing in Mn-doped GaAs probed by room-temperature photoluminescence

Prucnal, S.; Gao, K.; Skorupa, I.; Rebohle, L.; Vines, L.; Schmidt, H.; Khalid, M.; Wang, Y.; Weschke, E.; Skorupa, W.; Grenzer, J.; Hübner, R.; Helm, M.; Zhou, S.

The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here, we present room-temperature photoluminescence and ellipsometry measurements of Ga100%−xMnxAs alloy. The upshift of the valence band is proven by the redshift of the room temperature near band-gap emission from the Ga100%−xMnxAs alloy with increasingMn content. It is shown that even a doping by 0.02% of Mn affects the valence-band edge, and it merges with the impurity band for a Mn concentration as low as 0.6%. Both x-ray diffraction pattern and high-resolution cross-sectional transmission electron microscopy images confirmed full recrystallization of the implanted layer and GaMnAs alloy formation.

Keywords: diluted magnetic semiconductors; (Ga; Mn)As; ion implantation; flash lamp annealing

Permalink: https://www.hzdr.de/publications/Publ-22831
Publ.-Id: 22831


YMnO3- based MIS structure with a selective, capacitive photo-detecting properties

Bogusz, A.; Choudhary, O. S.; Skorupa, I.; Bürger, D.; Lawerenz, A.; Schmidt, O. G.; Schmidt, H.

This work investigates the YMnO3/Si3N4 /p-Si structures in terms of novel, capacitance-based photo-detecting properties. Photocapacitance-voltage (C-V) characteristics of the YMnO3/Si3N4 /p-Si structures have been determined at room temperature for a wide spectral range (300-980 nm). C-V characteristics indicate a charge trapping process which is used as the basis for novel approach to photodetectors. Our model discusses the immobilization of otherwise mobile charges in Si3N4 when the negative polarization charge of the multiferroic YMnO3 is at the YMnO3/Si3N4 interface. The observed capacitance minima are well-defined by the direction of bias ramp. Voltages corresponding to these minima were further used as a reference point for a read out of capacitance in retention and optical selectivity tests. Results indicate that investigated structures exhibit a good photo-sensitivity of red light and the retention properties are non-volatile for one capacitance branch.

  • Lecture (Conference)
    DPG Spring Meeting 2015, 15.-20.03.2015, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-22830
Publ.-Id: 22830


Resistive switching of polycrystalline, multiferroic YMnO3 thin films

Bogusz, A.; Prucnal, S.; Blaschke, D.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.

Resistive switching (RS) phenomena have been widely investigated in the field of materials science, physics, and electrical engineering in the past decade. Recently, multiferroics have been considered as promising candidates for memristive switches. Specific properties of multiferroics might bring additional and/or new functionalities into the memristive switches. This work investigates the RS properties of multiferroic YMnO3 thin films reported as a unipolar resistive switches. YMnO3 was grown at 400°C on Pt/Ti/SiO2/Si substrates by pulsed laser deposition (PLD) and crystallized by flash lamp annealing (FLA). Film thickness and the concentration of point defects were controlled during the PLD process. Transport and Rs properties of Au/YMnO3/Pt/Ti/SiO2 structures were determined by two-point probe measurements in a top-bottom configuration. Results imply that the filamentary, unipolar RS in YMnO3 originates from the electro-redox reactions induced by the Joule heating.

  • Lecture (Conference)
    DPG Spring Meeting, 15.-20.03.2015, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-22829
Publ.-Id: 22829


Interaction of europium and curium with alpha-amylase

Barkleit, A.; Heller, A.; Ikeda-Ohno, A.; Bernhard, G.

The complexation of Eu(III) and Cm(III) with the protein α-amylase (Amy), a major enzyme in saliva and pancreatic juice, was investigated over wide ranges of pH and concentration at both ambient and physiological temperatures. Macroscopic sorption experiments demonstrated a strong and fast binding of Eu(III) to Amy between pH 5 and 8. The protein provides three independent, non-cooperative binding sites for Eu(III). The overall association constant of these three binding sites on the protein was calculated to be log K = 6.4 ± 0.1 at ambient temperature. With potentiometric titration the averaged deprotonation constant of the carboxyl groups (the aspartic and glutamic acid residues) of Amy was determined to be pKa = 5.23 ± 0.14 at 25 °C and 5.11 ± 0.24 at 37 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) revealed two different species for both Eu(III) and Cm(III) with Amy. In the case of the Eu(III) species, the stability constants were determined to be log β11 = 4.7 ± 0.2 and log β13 = 12.0 ± 0.4 for Eu:Amy = 1:1 and 1:3 complexes, respectively, while the values for the respective Cm(III) species were log β11 = 4.8 ± 0.1 and log β13 = 12.1 ± 0.1. Furthermore, the obtained stability constants were extrapolated to infinite dilution to make our data compatible with the existing thermodynamic database.

Permalink: https://www.hzdr.de/publications/Publ-22828
Publ.-Id: 22828


First tests of the prompt gamma ray timing method at a clinical proton accelerator

Hueso-González, F.; Golnik, C.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Janssens, G.; Kormoll, T.; Petzoldt, J.; Prieels, D.; Priegnitz, M.; Römer, K. E.; Smeets, J.; Sobiella, M.; Vander Stappen, F.; Wagner, A.; Weinberger, D.; Pausch, G.

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potentialities of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine.
Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment, the prompt gamma ray timing method has been recently proposed and tested at a research accelerator. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile.
In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies.
From the resulting distributions, particle range differences of around 5 millimetres in heterogeneous phantoms were observed by simple qualitative inspection. In conclusion, our preliminary analysis points out that the prompt gamma ray timing method for range verification is feasible in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.

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

  • Open Access Logo Contribution to proceedings
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-22827
Publ.-Id: 22827


Correct temporal averaging in gamma-ray tomography

Wagner, M.; Bieberle, A.; Bieberle, M.; Hampel, U.

The dynamic bias error is a well-known effect in transmission radiometry. It appears when scanned processes offering a high dense variability such as phase distribution in turbulent multi-phase flows. If phases vary strongly during the data acquisition, the projection data is inherent time-averaged. Because of the non-linear relation between attenuation and measured stochastic intensity, the calculation of the classic time-averaged attenuation from the time-averaged projection data by the attenuation law produces a non-negligible phase fraction deviation. In general, this leads to an underestimation of the real attenuation which equals an overestimation of the gas phase in tomography images of two-phase flows for instance.
There are several approaches for the correction of this so called dynamic bias error. Recently, a method for correct averaging in transmission radiometry was developed. The method does not take any a priori knowledge about the flow into account but considers the Poisson distributed emission process of the radiation source. By deconvolving the Poisson distribution from the measured intensity distribution, the distribution of the attenuation is obtained. This demands the solution of an ill-conditioned equation system.
In this contribution the application of the correct averaging method (CAM) on time-averaged gamma-ray tomography is demonstrated using a mock-up of a centrifugal pump. A highly turbulent two-phase flow scenario is simulated based on both a virtual tomography data set as well as real measured data. By applying CAM, an elimination of the systematic dynamic bias error could be achieved even for very small numbers of gamma photons.

Keywords: gamma-ray tomography; dynamic bias error; correct averaging

  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
    Proceedings of the 7th International Symposium on Process Tomography
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22826
Publ.-Id: 22826


Synthesis, dynamic NMR characterization and XRD studies of novel N,N’-substituted piperazines for bioorthogonal labeling

Mamat, C.; Pretze, M.; Gott, M.; Köckerling, M.

Novel, functionalized piperazine derivatives were successfully synthesized and fully characterized by 1H/13C/19F NMR, MS, elemental analysis and lipophilicity. All piperazine compounds occur as conformers resulting from the partial amide double bond. Furthermore, a second conformational shape was observed for all nitro derivatives due to the limited change of the piperazine chair conformation. Therefore, two coalescence points were determined and their resulting activation energy barriers were calculated using 1H NMR. To support this result, single crystals of 1-(4-nitrobenzoyl)piperazine (3a, monoclinic, space group C2/c, a = 24.587(2), b = 7.0726(6), c = 14.171(1) Å, β = 119.257(8)°, V = 2149.9(4) Å3, Z = 4, Dobs = 1.454 g/cm3) and the alkyne derivative 4-(but-3-yn-1-yl)-1-(4-fluorobenzoyl)piperazine (4b, monoclinic, space group P21/n, a = 10.5982(2), b = 8.4705(1), c = 14.8929(3) Å, β = 97.430(1)°, V = 1325.74(4) Å3, Z = 4, Dobs = 1.304 g/cm3) were obtained from a saturated ethyl acetate solution. The rotational conformation of these compounds was also verified by XRD. As proof of concept for future labeling purposes, both nitropiperazines were reacted with [18F]F–. To test the applicability of these compounds as possible 18F-building blocks, two biomolecules were modified and chosen for conjugation either using the Huisgen-click reaction or the traceless Staudinger ligation.

Keywords: building blocks; coalescence; dynamic NMR; labeling; Staudinger ligation

Permalink: https://www.hzdr.de/publications/Publ-22825
Publ.-Id: 22825


P1404 - Strukturierungsverfahren

Facsko, S.; Ou, X.

Die Erfindung betrifft ein Strukturierungsverfahren zum Herstellen eines nanostrukturierten Bauelements mit periodisch angeordneten Strukturelementen, aufweisend die Schritte: Bereitstellen eines Substrats mit einer Schicht aus einem einkristallinen Schichtmaterial aus mindestens zwei chemischen Elementen; Heizen des Substrats mit der Schicht; und Bestrahlen einer Oberfläche der Schicht mit einem Ionenstrahl unter Erzeugung von Leerstellen in der Schicht.

  • Patent
    DE102014107458 - Offenlegung 03.12.2015, Nachanmeldung: 3x CN

Permalink: https://www.hzdr.de/publications/Publ-22824
Publ.-Id: 22824


The Radiochemical and radiopharmaceutical applications of radium

Gott, M.; Steinbach, J.; Mamat, C.

This review focuses on the chemistry and application of radium isotopes to environmental monitoring, analytical, and medicinal uses. In recent years, radium has been used primarily as a tracer to study the migration of radioactive substances in environmental systems. Tracing the naturally occurring radium isotopes in mineral and water sources allows for the determination of source location, residence time, and concentrations. An understanding of the concentration of radionuclides in our food and water sources is essential to everyone’s health as alpha particle decay is highly damaging in vivo. Due to this high radiobiological effectiveness, there is increased interest in using alpha-emitting radionuclides to prepare new, therapeutic radiopharmaceutical drugs. Selected studies from the recent literature are provided as examples of these modern applications of radium isotopes.

Keywords: Alpha emitters; Radium; Radiochronology; Radiotracers; Radiotherapy

Permalink: https://www.hzdr.de/publications/Publ-22823
Publ.-Id: 22823


Design und Synthese von neuartigen Fluor-18-Radiotracern für PET-Imaging von Eph-Rezeptoren

Mamat, C.

kein Abtract verfügbar

  • Lecture (others)
    GDCh-Kolloquium TU Dresden, 22.10.2015, Dresden, Deutschland
  • Lecture (others)
    GDCh-Kolloquium Universität Rostock, 10.12.2015, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22822
Publ.-Id: 22822


Laser-Driven Proton Acceleration: Experimental Observation of Spatially Modulated Proton Beams & Diagnostics of the Plasma Formation Dynamics

Metzkes, J.; Kluge, T.; Zeil, K.; Bussmann, M.; Kraft, S. D.; Rehwald, M.; Cowan, T. E.; Schramm, U.

Large effort is currently put into translating laser-driven particle sources from the status of experimental machines to accelerators ready for applications. The program at HZDR thereby focuses on laser-ion accelerators for medical applications [1]. Besides qualifying laser-accelerators for stable and reliable acceleration, the main challenge is the achievement of sufficient (~ 200 MeV for protons) particle energies. Fs-PW laser systems, going into operation in different laboratories worldwide now, might provide the necessary laser powers [2]. Hence, careful testing of the laser power scaling of the established acceleration mechanisms (e.g. TNSA) is needed, considering not only the achievable particle energies but properties as the spatial/angular distribution of particles (beam profile) as well.
In that context, we report on the experimental observation of spatially modulated proton beams emitted from micrometer thick targets which were irradiated with ultrashort (30 fs) laser pulses of a peak intensity of 5•1020W/cm2. The net-like proton beam modulations were recorded using radiochromic film and the investigation of different target systems for a laser energy range of 0.9 to 2.9 J revealed a clear dependence on laser energy and target thickness for the onset and strength of the modulations. Numerical simulations performed suggest filamentary instabilities, such as the parametric two plasmon decay and a Weibel-like instability, which occur in the laser-produced target front side plasma, as the source of the observed proton beam modulations [3].
The study is supported by pump-probe experiments of the plasma dynamics at the target front and rear surface. The method allows to connect the typical third-order autocorrelation traces [4] of the temporal pulse intensity contrast with the on-targets plasma conditions at pulse peak arrival. In that way, numerical simulations, necessary to investigate phenomena as plasma instabilities, can be matched to the real target plasma conditions more precisely.
We propose that the presented results on laser energy dependent plasma instabilities may have implications for the scaling of present acceleration mechanisms, such as target normal sheath acceleration, to higher proton energies and hence higher laser powers.

  • Lecture (Conference)
    Laser Plasma Acceleration Workshop, 10.-15.05.2015, Fort Royal, Guadeloupe

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-22821
Publ.-Id: 22821


Towards Laser-Driven Ion Sources For Radiotherapy

Metzkes, J.

The talk gives an overview over the multi-disciplinary research program in Dresden, which aims at the development of laser-driven ion sources for radiotherapy, including the translation of the technology into clinical application. The progress of the program will be discussed by presenting experimental results from the last years and discussing the laser facility at the Helmholtz-Zentrum Dresden – Rossendorf.

  • Invited lecture (Conferences)
    V International Symposium Topical Problems of Biophotonics – 2015 Novel Laser Applications in Biomedicine, 20.-24.07.2015, Nizhny Novgorod, Kazan, Elabuga, Russland

Permalink: https://www.hzdr.de/publications/Publ-22820
Publ.-Id: 22820


Cyclam Derivatives with a Bis(phosphinate) or a Phosphinato−Phosphonate Pendant Arm: Ligands for Fast and Efficient Copper(II) Complexation for Nuclear Medical Applications

David, T.; Kubićek, V.; Gutten, O.; Lubal, P.; Kotek, J.; Pietzsch, H.-J.; Rulíśek, L.; Hermann, P.

Cyclam derivatives bearing one geminal bis-(phosphinic acid), −CH2PO2HCH2PO2H2 (H2L1), or phosphinic−phosphonic acid, −CH2PO2HCH2PO3H2 (H3L2), pendant arm were synthesized and studied as potential copper(II) chelators for nuclear medical applications. The ligands showed good selectivity for copper(II) over zinc(II) and nickel(II) ions (log KCuL = 25.8 and 27.7 for H2L1 and H3L2, respectively). Kinetic study revealed an unusual threestep complex formation mechanism. The initial equilibrium step leads to out-of-cage complexes with Cu2+ bound by the phosphorus-containing pendant arm. These species quickly rearrange to an in-cage complex with cyclam conformation II, which isomerizes to another in-cage complex with cyclam conformation I. The first in-cage complex is quantitatively formed in seconds (pH ≈5, 25 °C, Cu:L = 1:1, cM ≈ 1 mM). At pH >12, I isomers undergo nitrogen atom inversion, leading to III isomers; the structure of the III-[Cu(HL2)] complex in the solid state was confirmed by X-ray diffraction analysis. In an alkaline solution, interconversion of the I and III isomers is mutual, leading to the same equilibrium isomeric mixture; such behavior has been observed here for the first time for copper(II) complexes of cyclam derivatives. Quantum-chemical calculations showed small energetic differences between the isomeric complexes of H3L2 compared with analogous data for isomeric complexes of cyclam derivatives with one or two methylphosphonic acid pendant arm(s). Acid-assisted dissociation proved the kinetic inertness of the complexes. Preliminary radiolabeling of H2L1 and H3L2 with 64Cu was fast and efficient, even at room temperature, giving specific activities of around 70 GBq of 64Cu per 1 μmol of the ligand (pH 6.2, 10 min, ca. 90 equiv of the ligand). These specific activities were much higher than those of H3nota and H4dota complexes prepared under identical conditions. The rare combination of simple ligand synthesis, very fast copper(II) complex formation, high thermodynamic stability, kinetic inertness, efficient radiolabeling, and expected low bone tissue affinity makes such ligands suitably predisposed to serve as chelators of copper radioisotopes in nuclear medicine.

Permalink: https://www.hzdr.de/publications/Publ-22819
Publ.-Id: 22819


Gamma-ray computed tomography for multiphase flow analysis

Bieberle, A.

Übersichtsvortrag zu aktuellen Ergebnissen der Gamma-CT des HZDR mit Fokussierung auf Verfahrenstechnik

Keywords: Gamma-ray-CT; chemical engineering

  • Lecture (others)
    Strategiegespräch mit Linde (Pullach), 03.12.2015, Höllriegelskreuth, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22818
Publ.-Id: 22818


Gamma-ray computed tomography for non-destructive testing and multiphase flow analysis

Bieberle, A.

Vortrag zu aktuellen Ergebnissen des Gamma-ray-CT-Messsystems für industrielle Anwendungen.

Keywords: Gamma-ray CT; two phase flow; multi phase flow

  • Lecture (Conference)
    Innovation Days 2015, 08.-09.12.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22817
Publ.-Id: 22817


Developments for the application of the Wire-Mesh Sensor in industries

Kipping, R.; Brito, R.; Schleicher, E.; Hampel, U.

Wire-Mesh Sensors (WMS) are applied in many research applications to determine the distribution of the phase fraction and to visualize the flow behavior within a pipe. However their application in industries is restricted due to the procedure of data acquisition. Here a new design of Wire-Mesh Sensor for monitoring void fraction and flow pattern behavior is presented. As result of online data evaluation cross-sectional void fraction information is provided in almost real-time. Additionally, the present flow pattern is determined by statistical analysis of recorded data of a time period of 10 s. This is the first time a Wire-Mesh Sensor was used for this purpose. With the help of fuzzy methodology a distinction of the four main flow patterns of vertical upward gas-liquid flow is possible. Furthermore transition regions can be identified. The algorithm is based on the evaluation of statistical void fraction distribution as result of Wire-Mesh Sensor data. Validation experiments of the new adopted algorithms are carried out in a 50 mm-ID two-phase air-water flow-loop at Tulsa University Horizontal Well and Artificial Lift Projects (TUHWALP).

Keywords: Wire-Mesh Sensor; gas-liquid flow; flow pattern identification

Permalink: https://www.hzdr.de/publications/Publ-22816
Publ.-Id: 22816


Research with HIBEF, the Helmholtz International Beamline for Extreme Fields at the European XFEL

Schramm, U.

  • Invited lecture (Conferences)
    Applications of Laser-driven Particle Acceleration (ALPA 2015), 19.-21.11.2015, Venedig, Italien
  • Lecture (others)
    MLL Kolloquium Garching, 28.01.2016, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22815
Publ.-Id: 22815


Surfen auf der Plasmawelle - Teilchenbeschleunigung mit Laserlicht

Schramm, U.

Mit modernen Hochleistungslasern können fuer die Dauer weniger Schwingungszyklen des Lichts elektrische Feldstärken erzielt werden, die Elektronen in nur einer Halbwelle auf relativistische Energien beschleunigen. In dem Vortrag soll anschaulich vorgestellt werden, wie diese transversalen Felder in sogenannten "relativistischen" Laserplasmen gleichgerichtet werden können, um eine effiziente Beschleunigung von Elektronen und Ionen auf nur wenigen Millimetern zu ermöglichen und für welche Anwendungsbereiche diese junge Technologie Vorteile bietet. Der Schwerpunkt wird dabei auf die Ionenstrahltherapie von Krebserkrankungen gelegt und mit etablierten Ansätzen verglichen.

Keywords: Laser Ionenbeschleunigung; Krebstherapie

  • Invited lecture (Conferences)
    Physikalisches Kolloquium Uni Halle, 03.12.2015, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22814
Publ.-Id: 22814


Influence of background electrolyte on Th(IV) sorption behavior

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

Studying and understanding the behavior of radionuclides at the water-mineral interface on a molecular level is of high importance for making reliable statements for the safety assessment of nuclear waste disposals. Clay minerals are relevant for nuclear waste disposal sites, due to their retardation properties. Muscovite, a phyllosilicate material, is structurally similar to clay minerals but forms large single crystals with high quality surfaces, necessary for surface X ray diffraction.
In a series of experiments we demonstrate that the background electrolyte has a significant influence on the sorption behavior of actinides, specifically thorium(IV). We study the sorption of Th(IV) (cTH = 10-4 mol/L), the softest of the tetravalent actinides, at the muscovite basal plane with several background electrolytes (NaClO4, KClO4, LiClO4). Previous investigations, with sodium chloride (10 1 mol/L) as background electrolyte, act as reference for these experiments. We find that the sorption behavior of thorium is substantially affected by both, changes in the electrolyte cation (Li+, K+) and anion (Cl-, ClO4-).
Briefly, compared to NaCl as background electrolyte, we observed increased sorption with LiClO4 in the system. On the other hand NaClO4 almost completely supressed sorption at high ionic strength, while a lower ionic strength of NaClO4, as well as KClO4, decreases sorption.

Keywords: Muscovite; Thorium; Background electrolyte; Sorption

  • Poster
    Goldschmidt (2015), 16.-21.08.2015, Praha, Česká republika
  • Poster
    MIGRATION 2015, 13.-18.09.2015, Santa Fe, USA
  • Lecture (Conference)
    GDCh-Wissenschaftsforum, 30.08.-02.09.2015, Dresden, Deutschland
  • Poster
    Doktorandenseminar des Kompetenzverbundes für Kerntechnik Ost (KOMPOST), 08.12.2015, Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22813
Publ.-Id: 22813


First-principles calculation of defect free energies: General aspects illustrated in the case of bcc-Fe

Posselt, M.; Murali, D.

Modeling of nanostructure evolution in solids requires comprehensive data on the properties of intrinsic point defects, foreign atoms and defect clusters. Since most processes occur at elevated temperatures not only the energetics of these species in the ground state but also their temperature-dependent free energies must be known. These data can be used to obtain improved, temperature-dependent input parameters for atomistic or object kinetic Monte Carlo simulations and rate theory.
The first-principles calculation of contributions of phonon and electron excitations to free formation, binding, and migration energies is illustrated in the case of bcc-Fe. First of all, the ground state properties of the defects are determined under constant volume (CV) as well as zero pressure (ZP) conditions, and relations between the results of both kinds of calculations are discussed. Second, vibrational and electronic contributions to defect free energies are calculated using the equilibrium atomic positions determined in the ground state for the CV and the ZP case. Additionally, the quasi-harmonic approach is applied to ZP-based data in order to obtain results closest to the experimental conditions at elevated temperatures. However, in most cases considered this leads only to minor modifications. In contrast to ground state energetics the CV- and ZP-based defect free energies do not become equal with increasing supercell size. A simple transformation is found between the CV- and ZP-based frequencies and between the corresponding free energies. Finally, self-diffusion via the vacancy mechanism is investigated. The ratio of the respective CV- and ZP-based results for the vacancy diffusivity is nearly equal to the reciprocal of that for the equilibrium concentration. This behavior leads to almost identical CV- and ZP-based values for the self-diffusion coefficient. Obviously, this agreement is accidental and cannot be generalized to other cases.The consideration of the temperature dependence of the magnetization yields self-diffusion data in very good agreement with experiments

Keywords: defect free energy; first-principles calculation; bcc-Fe

  • Invited lecture (Conferences)
    MRS 2015 Fall Meeting, Symposium YY: Advanced Atomistic Algorithms in Materials Science, 29.11.-04.12.2015, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-22812
Publ.-Id: 22812


Unwilling U–U bonding in U2@C80: cage-driven metal–metal bonds in di-uranium fullerenes

Foroutan-Nejad, C.; Vıcha, J.; Marek, R.; Patzschke, M.; Straka, M.

Endohedral actinide fullerenes are rare and a little is known about their molecular properties. Here we characterize the U2@C80 system, which was recently detected experimentally by means of mass spectrometry (Akiyama et al., JACS, 2001, 123, 181). Theoretical calculations predict a stable endohedral system, 7U2@C80, derived from the C80:7 IPR fullerene cage, with six unpaired electrons. Bonding analysis reveals a double ferromagnetic (one-electron-two-center) U–U bond at an rU–U distance of 3.9 Å. This bonding is realized mainly via U(5f) orbitals. The U–U interaction inside the cage is estimated to be about −18 kcal mol−1. U–U bonding is further studied along the U2@Cn (n = 60, 70, 80, 84, 90) series and the U–U bonds are also identified in U2@C70 and U2@C84 systems at rU–U ∼ 4 Å. It is found that the character of U–U bonding depends on the U–U distance, which is dictated by the cage type. A concept of unwilling metal–metal bonding is suggested: uranium atoms are strongly bound to the cage and carry a positive charge. Pushing the U(5f) electron density into the U–U bonding region reduces electrostatic repulsion between enclosed atoms, thus forcing U–U bonds.

Keywords: computational chemistry; AIM; DFT; Actinide chemistry

Permalink: https://www.hzdr.de/publications/Publ-22811
Publ.-Id: 22811


Partikelentstehung und –transport im Kern von Druckwasserreaktoren - Phase 2; Physikochemische Mechanismen (Abschlussbericht zum BMWi-Vorhaben 150 1467)

Kryk, H.; Hoffmann, W.

Im Rahmen der deutschen Reaktorsicherheitsforschung wurden die generischen experimentellen Untersuchungen zur Aufklärung physikochemischer Mechanismen der Korrosionsproduktbildung und -ablagerung unter den wasserchemischen Bedingungen des Sumpfumwälzbetriebes in der Spätphase von Kühlmittelverluststörfällen in Druckwasserreaktoren weitergeführt. Das Vorhaben baute auf den Ergebnissen des Projektes 150 1430 auf und wurde in Kooperation mit der Hochschule Zittau/Görlitz (Vorhaben 150 1468) realisiert. Inhalt waren Laboruntersuchungen zu Entwicklung und Test von Maßnahmen zur Verhinderung der Bildung von Zinkborat-Ablagerungen an heißen Oberflächen.
Der Kontakt des borsäurehaltigen Kühlmittels mit feuerverzinkten Containment-Einbauten bewirkt eine Korrosion der Verzinkung, wodurch Zink im Kühlmittel gelöst wird. Aufgrund des im Vorhaben 150 1430 gefundenen Löslichkeitsverhaltens der entstehenden Zinkborate ist die Bildung und Ablagerung fester Korrosionsprodukte nicht auszuschließen, wenn zinkhaltiges Kühlmittel in heiße Regionen innerhalb des Kühlkreislaufes gelangt. Experimente in einer Labor-Korrosionsversuchsanlage zeigten, dass eine Zugabe von Alkalisierungsmitteln zu einer Reduzierung der Abscheideprozesse führt. Sowohl die Korrosionsrate von Zink als auch die Abscheiderate von Zinkborat verringern sich mit steigendem pH-Wert. Eine wesentliche Verringerung der Abscheiderate ist jedoch erst ab einem pH-Wert von ca. 7,5 feststellbar, wofür erhebliche Mengen Alkalisierungsmittel erforderlich sind. Eine vollständige Verhinderung der Korrosionsproduktbildung und –abscheidung war im untersuchten pH-Wert-Bereich nicht möglich. Des Weiteren hat die Differenz zwischen Sumpf- und Kerntemperatur Einfluss auf die Bildungsrate von Zinkborat. Signifikante Zinkborat-Mengen werden allerdings schon bei geringen Temperaturdifferenzen von ca. 10 K gebildet.
Untersuchungen zur Kinetik der Bildung von gelöstem Zink durch Korrosion von verzinkten Einbauten im Sicherheitsbehälter waren nicht Projektgegenstand, weshalb eine direkte quantitative Übertragbarkeit der Ergebnisse auf postulierte KMV in DWR-Anlagen derzeit noch nicht gegeben ist.

Keywords: Druckwasserreaktor; Kühlmittelverluststörfall; Korrosion; Zink; Zinkborat; Experiment

  • Other report
    Karlsruhe: FIZ Karlsruhe, 2015
    57 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22810
Publ.-Id: 22810


Liquid metal batteries for large-scale stationary storage

Weier, T.; Galindo, V.; Landgraf, S.; Seilmayer, M.; Stefani, F.; Weber, N.

Liquid metal batteries (LMBs) are high temperature systems consisting of liquid metal electrodes and a molten salt ionic conductor. The densities are chosen in such a way that a stable density stratification of the inmiscible layers results. LMBs were considered mainly as part of energy conversion systems in the 1960s and have only recently received renewed interest for economic large-scale storage. Typically, LMBs allow for high current densities due to the fast kinetics at liquid/liquid interfaces and the rapid mass transport in fluids.

Our work concentrates on the fluid dynamic aspects of this cell type with a special focus on the effects and properties of the Tayler instability (TI) and on electro-vortex flows. Both phenomena are driven by electromagnetic forces and should be considered for large cells. Due to the completely liquid interior of LMBs, fluid flow is an important aspect of their operation. It can be beneficial, when enhancing mass transfer in the cathode, or it might have harmful consequences, if the integrity of the electrolyte layer is disrupted. The latter case can result from the action of the current-driven TI or electrically driven vortex flows. We therefore studied the characteristics of the TI as well as some exemplary cases of electro-vortex flows using an integro-differential approach implemented in the open source library OpenFOAM. The TI occurs if a critical value of a dimensionless parameter Ha, the Hartmann number describing the ratio of electromagnetic to viscous forces, is exceeded. The critical Ha is lowest for an infinitely high vessel and corresponds to a total current of approx. 1 kA in the case of Na. Decreasing the aspect ratio increases the critical Ha and thereby the critical current since the wavelength selection for the TI becomes more and more restricted.

As mentioned above, current densities in LMBs are typically very high. A current density of 10 kA/m2 is a characteristic value for a Na|NaI-NaCl-NaF|Bi-system and results in an approximately 10 mm thick sodium layer transferred per hour from the anodic to the cathodic compartment. Depending on the design capacity and cell area, aspect ratios of the anodic compartment up to one seem imaginable. While flat enough cells will not suffer from TI induced short circuits, for taller ones stabilization measures can be applied to prevent negative consequences.

Using thin feeding lines to contact relatively large current collectors will most certainly result in inhomogeneous current density distributions in the fluid. They will generate electro-vortex flows that may again compromise the integrity of the electrolyte layer. A careful distribution of the charging current by several wires should solve the problem. Properly designed electro-vortex flows might even be used to gently stir the cathode thereby increasing mass transfer and improving cell performance.

Keywords: liquid metal batteries; Tayler instability; electro-vortex flows

  • Lecture (Conference)
    3rd Dresden Conference "Energy in Future", 10.-11.11.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22809
Publ.-Id: 22809


Towards a life-time-limited 8-octave-infrared photoconductive germanium detector

Pavlov, S. G.; Deßmann, N.; Pohl, A.; Abrosimov, N. V.; Mittendorff, M.; Winnerl, S.; Zhukavin, R. K.; Tsyplenkov, V. V.; Shengurov, D. V.; Shastin, V. N.; Hübers, H.-W.

Ultrafast, ultra-broad-band photoconductive detector based on heavily doped and highly compensated germanium has been demonstrated. Such a material demonstrates optical sensitivity in the more than 8 octaves, in the infrared, from about 2 mm to about 8 μm. The spectral sensitivity peaks up between 2 THz and 2.5 THz and is slowly reduced towards lower and higher frequencies. The life times of free electrons/holes measured by a pump-probe technique approach a few tenths of picoseconds and remain almost independent on the optical input intensity and on the temperature of a detector in the operation range. During operation, a detector is cooled down to liquid helium temperature but has been approved to detect, with a reduced sensitivity, up to liquid nitrogen temperature. The response time is shorter than 200 ps that is significantly faster than previously reported times.

Keywords: fast detection; germanium; photoconductive THz detector

  • Open Access Logo Journal of Physics: Conference Series 647(2015), 012070
    DOI: 10.1088/1742-6596/647/1/012070
  • Poster
    19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 19), 29.06.-02.07.2015, Salamanca, Spain

Permalink: https://www.hzdr.de/publications/Publ-22808
Publ.-Id: 22808


Direct numerical simulation of a particle attachment to an immersed bubble

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

The selective attachment of hydrophobic particles by gas bubbles immersed in water is at the heart of the flotation process. The valuable hydrophobic particles, such as for instance fine-grained particles of ore mineral, adhere to the fluidic interface of rising bubbles while the valueless hydrophilic material settles down the bottom of the flotation cell to eventually be discharged. The attachment process, i.e. the capture of a single hydrophobic particle by a bubble, can be divided into a sequence of three microprocesses: the particle approach, the collision process and the sliding down the bubble surface. The absence of explicit boundary between two consecutive events along with the multiphase nature of the system renders the development of predictive computer model difficult. A numerical model is here suggested for the direct numerical simulation of the particle attachment on a stationary bubble. The two fluid-particle boundaries and the fluidic boundary are replaced with diffuse interfaces. The attachment of a single particle on a stationary bubble is presently tested. Particle trajectories and velocities in the near bubble region are captured and compare qualitatively well with available experimental data.

Permalink: https://www.hzdr.de/publications/Publ-22805
Publ.-Id: 22805


Batch sorption and spectroscopic speciation studies of neptunium uptake by montmorillonite and corundum

Elo, O.; Müller, K.; Ikeda-Ohno, A.; Bok, F.; Scheinost, A.; Hölttä, P.; Huittinen, N.

Detailed information on neptunium(V) speciation on montmorillonite and corundum surfaces was obtained by batch sorption and desorption studies combined with surface complexation modelling using the Diffuse Double-Layer (DDL) model and in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and X-ray Absorption (XAS) spectroscopies. The pH-dependent batch sorption studies and the spectroscopic investigations were conducted under carbonate-free conditions in 10 mM NaClO4 or 10 mM NaCl. Solid concentrations of 0.5 g/l and 5 g/l were used depending on the experiment. The reversibility of the neptunium(V) uptake reaction by the two minerals was investigated in desorption experiments using the replenishment technique. Neptunium(V) sorption was found to be highly reversible, however, the degree of reversibility was dependent on the solution pH. The reversibility of the sorption reaction was confirmed in the ATR FT-IR spectroscopic studies at pH 10, where all of the identified inner-sphere complexed neptunium(V), characterized by a vibrational band at 790 cm-1, was desorbed from both mineral surfaces upon flushing the mineral films with a blank electrolyte solution. In XAS investigations of neptunium(V) uptake by corundum, the obtained structural parameters confirm the formation of an inner-sphere sorbed complex adsorbed on the surface in a bidentate fashion. As the inner-sphere complexes found in the IR-studies are characterized by identical sorption bands on both corundum and montmorillonite, we tentatively assign the neptunium(V) inner-sphere complex on montmorillonite to the same bidentate complex found on corundum in the XAS investigations. Finally, surface complexation modelling using obtained batch sorption and spectroscopic results were performed to explain the neptunium(V) speciation on montmorillonite over the entire investigated pH range. The modelling results show that cation exchange in the interlayer space as well as both outer-sphere and inner-sphere complexation are required to fully explain the neptunium(V) speciation on the montmorillonite surface

Permalink: https://www.hzdr.de/publications/Publ-22804
Publ.-Id: 22804


Interaction of highly charged ions with carbon nano membranes

Gruber, E.; Wilhelm, R. A.; Smejkal, V.; Heller, R.; Facsko, S.; Aumayr, F.

Charge state and energy loss measurements of slow highly charged ions (HCIs) after transmission through nanometer and sub-nanometer thin membranes are presented. Direct transmission measurements through carbon nano membranes (CNMs) show an unexpected bimodal exit charge state distribution, accompanied by charge exchange dependent energy loss. The energy loss of ions in CNMs with large charge loss shows a quadratic dependency on the incident charge state, indicating charge state dependent stopping force values. Another access to the exit charge state distribution is given by irradiating stacks of CNMs and investigating each layer of the stack with high resolution imaging techniques like transmission electron microscopy (TEM) and helium ion microscopy (HIM) independently. The observation of pores created in all of the layers confirms the assumption derived from the transmission measurements that the two separated charge state distributions reflect two different impact parameter regimes, i.e. close collision with large charge exchange and distant collisions with weak ion-target interaction.

Permalink: https://www.hzdr.de/publications/Publ-22803
Publ.-Id: 22803


Incorporation of Cm3+ and Eu3+ in LnPO4 ceramics – a site-selective TRLFS study

Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Stumpf, T.

The chemical durability and structural flexibility of lanthanide phosphates make these ceramics attractive as host phases for the conditioning of long-lived radionuclides produced during the nuclear fuel cycle. In the present work we have studied the structural incorporation of Cm3+ and Eu3+ in various LnPO4 monazite and xenotime phases with site-selective time-resolved laser fluorescence spectroscopy (TRLFS). The europium results indicate a full structural incorporation in the LnPO4 ceramics crystallizing in the nine-fold coordinated monazite structure (LaPO4-GdPO4) independent of the host cation radius. A local disordering can, however, be seen in mixed monazite solid solutions when going from the pure endmembers (LaPO4 and GdPO4) toward the La0.5Gd0.5PO4 composition. The smaller lanthanides crystallizing in the eight-fold coordinated xenotime structure (TbPO4-LuPO4) show only a partial uptake of Eu3+ within the host cation sites. The remainder of the dopant appears to be present as an ill-defined, partially hydrated europium species on or within the xenotime solid. Actinide (Cm3+)-doped LnPO4 samples have been synthesized similarly to the Eu3+ solids. The results of the Cm-TRLFS measurements will be compared to the Eu3+-data and presented at the symposium.

  • Lecture (Conference)
    Scientific Basis for Nuclear Waste Management XXXIX, 02.-06.11.2015, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-22802
Publ.-Id: 22802


Curium(III) and europium(III) incorporation in lanthanide phosphate ceramics for conditioning of radioactive wastes

Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Schmidt, M.; Neumeier, S.; Stumpf, T.

The high-level radioactive waste (HLW) from spent nuclear fuel reprocessing facilities is currently immobilized in borosilicate glass. The vitrification process is well established and the flexible glass matrix is able to incorporate a very large range of elements present in the waste solution [1]. With the development of partitioning strategies, enabling the extraction of long-lived fission products and minor actinides (MA) from the PUREX raffinate, specific waste streams will be created that may require durable host matrices for their safe disposal. Especially for MA immobilization, some ceramic materials have been envisioned as host materials due to their thermal stability, high radiation tolerance, and chemical durability [2].
Lanthanide phosphate ceramics (LnPO4) are able to incorporate radionuclides in well-defined atomic positions within the crystal lattice [3] up to high (27 %) loadings [2]. The existence of very old natural analogues containing high concentrations of uranium and thorium shows that the crystalline phosphate structure is very tolerant towards self-irradiation damages as well as chemical weathering [4]. The dehydrated, high-temperature LnPO4 phases are known to crystallize in two distinct structures, depending on the ionic radius of the lanthanide cation: the larger lanthanides from La3+ to Gd3+ crystallize in the nine-fold coordinated monazite structure with a low symmetry, while the smaller lanthanides Tb3+ to Lu3+ form tetragonal, eight-fold coordinated xenotime structures.
In the present study we have used site-selective time-resolved laser fluorescence spectroscopy (TRLFS) to investigate the influence of the host cation radius as well as the crystal structure of the ceramic (monazite vs. xenotime) on the incorporation of the trivalent metal ions Eu3+ and Cm3+. We have synthesized pure monazites and xenotimes doped with 500 ppm Eu3+ or 50 ppm Cm3+ by precipitation of LnPO4 from a 0.3-0.5 M lanthanide nitrate solution with phosphoric acid followed by sintering of the precipitate at 1450°C to obtain the crystalline ceramic. The laser spectroscopy was performed either with a pulsed Nd:YAG-pumped tunable optical parametric oscillator or dye laser setup at cryogenic temperatures (~ 10 K). Excitation and emission spectra as well as luminescence lifetimes were collected for all measured samples.
Results on Eu3+-doped monazites show very narrow excitation spectra (Figure 1, left) for all investigated phases (LaPO4, SmPO4, GdPO4), indicating a complete incorporation of the dopant within the monazite crystal structure independent of the host cation radius. The emission spectra show a maximum splitting of the 7F1 and 7F2 bands (Figure 1, right), confirming the incorporation of Eu3+ on the low symmetry cation sites in the monazites.
The xenotime structure is not able to fully incorporate the europium ion within the crystal lattice. The excitation spectrum of Eu3+-doped LuPO4 in Figure 2 shows two regions of europium intensity that, upon excitation, decay with very different lifetimes. The broad signal in the wavelength region 575-580 nm corresponds to an ill-defined, partially hydrated europium species with a lifetime of approximately 580 µs (1.2 H2O). The species at 583.00 nm has a lifetime of 2700 µs indicating a full loss of the europium hydration sphere upon incorporation. The emission spectrum at this excitation wavelength shows a 2 and 4-fold splitting of the 7F1 and 7F2 bands, respectively, which is expected for an ion within the tetragonal cation site in the xenotime structure.
Our Eu3+ results demonstrate the importance of spectroscopic methods to probe the local environment of a guest cation within a solid matrix. According to our results, monazites can be considered as suitable host matrices for the immobilization of trivalent dopants. The xenotime structure on the other hand is not an ideal host for the larger lanthanide or actinide dopants due to the structure mismatch that does not allow for a complete guest ion substitution within the ceramic structure. Actinide (Cm3+)-doped LnPO4 samples have been synthesized similarly to the Eu3+ solids. The samples will be measured with TRLFS in the near future and results will be analyzed and compared to the existing Eu3+-data in order to confirm the incorporation behavior of trivalent dopants in the investigated solids. The results obtained for both dopants will be presented at the conference.

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

Permalink: https://www.hzdr.de/publications/Publ-22801
Publ.-Id: 22801


Mass transfer measurement in a square milli-channel and comparison with results from a circular channel

Haghnegahdar, M.; Boden, S.; Hampel, U.

In this work, we report on an experimental investigation of mass transfer from stagnant Taylor bubbles in a small square channel via measurement of the dissolution rate of an individual elongated bubble of carbon dioxide into water. As a measurement technique we used high resolution X-ray radiography and tomography. The changes in the size of the bubble at constant pressure obtained from the high-resolution X-ray images were used to calculate the liquid side mass transfer coefficient. The bubbles were continuously monitored by hydrodynamic fixation of the bubble in a down flow of the liquid. The results are compared with the available recently published data for circular channels.
The results show that the bubble dissolution curves in square channels are relatively even while the dissolution curves for bubbles in circular channels show some noticeable change in the slope. Furthermore, it is shown that the calculated liquid side mass transfer coefficient based on the measured data show good agreement with the data predicted by the penetration theory when the contact time between two phases is defined as the ratio of bubble length to the relative velocity. In addition, the comparison of the results with the data for circular channels showed that despite the fact that the rise velocity of bubbles in square channel is about three times faster than in circular channel, the liquid side mass transfer coefficients are approximately the same.

Keywords: mass transfer; Taylor bubble; carbon dioxide; square channels; X-ray imaging

Permalink: https://www.hzdr.de/publications/Publ-22800
Publ.-Id: 22800


High-energy resolution XAS/XES reveals insight into unique selectivity of La-based nanoparticles for CO2

Hirsch, O.; Kvashnina, K. O.; Luo, L.; Suess, M.; Glatzel, P.; Koziej, D.

The lanthanum-based materials, due to their layered structure and f-electron configuration, are relevant for electrochemical application. Particularly, La2O2CO3 shows a prominent chemoresistive response to CO2. However, surprisingly less is known about its atomic and electronic structure and electrochemically significant sites and therefore, its structure–functions relationships have yet to be established. Here we determine the position of the different constituents within the unit cell of monoclinic La2O2CO3 and use this information to interpret in situ high-energy resolution fluores cence-detected (HERFD) X-ray adsorption near-edge structure (XAS) and valence-to-core X-ray emission spectroscopy (vtc XES). Compared with La(OH)3 or previously known hexagonal La2O2CO3 structures, La in the monoclinic unit cell has a much lower number of neighboring oxygen atoms, which is manifested in the whiteline broadening in XAS spectra. Such a superior sensitivity to subtle changes is given by HERFD method, which is essential for in situ studying of the interaction with CO2. Here, we study La2O2CO3-based sensors in real operando conditions at 250 °C in the presence of oxygen and water vapors. We identify that the distribution of unoccupied La d states and occupied O p- and La d states changes during CO2 chemoresistive sensing of La2O2CO3. The correlation between these spectroscopic findings with electrical resistance measurements leads to a more comprehensive understanding of the selective adsorption at La site and may enable the design of new materials for CO2 electrochemical applications.

Keywords: lanthanum oxycarbonate; HERFD XAS; valence-to-core XES; structure; CO2 sensing

  • Proceedings of the National Academy of Sciences of the United States of America 112(2015)52, 15803-15808
    DOI: 10.1073/pnas.1516192113

Permalink: https://www.hzdr.de/publications/Publ-22799
Publ.-Id: 22799


Neptunium characterization in uranium dioxide fuel: Combining a XAFS and a thermodynamic approach

Chollet, M.; Martin, P.; Degueldre, C.; Poonoosamy, J.; Belin, R. C.; Hennig, C.

The effect of Np incorporation in a UO2 matrix on redox state of U and Np cations has been investigated by X-ray absorption spectroscopy (XAS) on three samples: (U0.9Np0.1)O2, (U0.9Np0.1)O2+x and pure NpO2 as a reference for Np(IV) oxidation state. XANES and EXAFS analysis show that only Uranium is oxidized in higher (V) and (VI) oxidation states in the hyperstoichiometric (U0.9Np0.1)O2+x sample in comparison to the stoichiometric (U0.9Np0.1)O2 where U appears at the (IV) oxidation state. Neptunium cation always remains at the (IV) oxidation state whatever the oxygen stoichiometry. Thermodynamic calculations performed to complete the experimental study, lead to the same conclusion. Separate UO2-NpO2 phases and homogeneous solid solution were considered. The latter case shows that the energy of mixing is insignificant in this system. These combined experimental and theoretical approaches demonstrate that any excess of oxygen in the system is carried by Uranium.

Keywords: neptunium oxide; uranium oxide; solid solution; stoichiometry; oxidation state

Permalink: https://www.hzdr.de/publications/Publ-22798
Publ.-Id: 22798


Magnetic structure of the antiferromagnetic half-Heusler compound NdBiPt

Müller, R. A.; Desilets-Benoit, A.; Gauthier, N.; Lapointe, L.; Bianchi, A. D.; Maris, T.; Zahn, R.; Beyer, R.; Green, E.; Wosnitza, J.; Yamani, Z.; Kenzelmann, M.

We present results of single-crystal neutron-diffraction experiments on the rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits an AFM phase transition at TN = 2.18 K with an ordered moment of 1.78(9) μB per Nd atom. The magnetic moments are aligned along the [001] direction, arranged in a type-I AFM structure with ferromagnetic planes, alternating antiferromagnetically along a propagation vector τ of (100). The RBiPt (R = Ce–Lu) family of materials has been proposed as candidates for a new family of antiferromagnetic topological insulators (AFTIs) with a magnetic space group that corresponds to a type-II AFM structure where ferromagnetic sheets are stacked along the space diagonal. The resolved structure makes it unlikely that NdBiPt qualifies as an AFTI.

Permalink: https://www.hzdr.de/publications/Publ-22797
Publ.-Id: 22797


Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI

Park, J.; Jin, K. H.; Jo, Y. J.; Choi, E. S.; Kang, W.; Kampert, E.; Rhyee, J.-S.; Jhi, S.-H.; Kim, J. S.

We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for the outer Fermi surface shows an abrupt phase shift. In comparison with band structure calculations, we find that these unusual behaviors originate from the Fermi surface shape change due to pressure-induced band inversion. These results clearly demonstrate that the topological quantum Phase transition is intimately tied to the shape of bulk Fermi surfaces enclosing the time-reversal invariant momenta with band inversion.

Permalink: https://www.hzdr.de/publications/Publ-22796
Publ.-Id: 22796


Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films

Molatta, S.; Haindl, S.; Trommler, S.; Schulze, M.; Wurmehl, S.; Hühne, S.

Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications.

Permalink: https://www.hzdr.de/publications/Publ-22795
Publ.-Id: 22795


Severe accident management research at HZDR

Tusheva, P.; Schäfer, F.; Altstadt, E.; Kliem, S.

Presentation at the 1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology.

Keywords: severe accidents; accident management measures

  • Invited lecture (Conferences)
    1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology, 09.-12.03.2015, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-22794
Publ.-Id: 22794


EDUKEM project - first spectroscopic insights into the U(IV)/U(VI) speciation in concentrated NaCl solution

Lehmann, S.; Steudtner, R.; Brendler, V.

This work is embedded into the EDUKEM project, a collaboration with GRS Braunschweig and KIT-INE. Its major purpose is the provision of quality assured thermodynamic data for both tetra- and hexavalent uranium. This shall enable a better assessment of speciation and solubility limits in diluted to highly saline solutions as expected near nuclear waste repositories.
Respective experiments are based on parallel developments in electrochemical and spectroscopic tools being complementary to each other. In such a way difficult to access, systems and conditions should be explored to obtain an integral overview about aqueous uranium chemistry. This especially holds for reducing conditions. This will not only promote the characterization of complex system, e.g., encountered in nuclear waste management, but also allow a fingerprinting of unknown substances and mixtures.
We started to investigate the spectroscopic characteristics of 0.01M U(IV) and U(VI) in different background media (ClO4-, Cl-, SO42-, PO43-, CO32-) using UV/vis and fluorometry. The U(VI) was reduced by potentiostatic electrolysis using Ag/AgCl reference electrode. The reduction was monitored by UV/vis spectroscopy. The residual content of U(VI) was less than 1 %. We observed no formation of precipitations under the experimental conditions with exception of the PO43- system. There, we changed the uranium/ligand ratio from 1:100 to 1:5000 to suppress uranium phosphate precipitation. In general, the UV/vis spectra show variations in intensities and peak shifts to higher wavelengths in dependence of complexation strength in following order ClO4– < Cl– < SO42– < PO43– < CO32–.
In contrast to U(VI), which is often quenched by ions in the solution such as chloride, we obtained a luminescence spectrum of U4+ in 0.1 M HCl excited by λexc = 245 nm at a temperature of 1°C. The obtained luminescence spectrum is similar to the luminescence spectra of the free U4+ ion in acidic published by Kirishima et al. [1]. Under the experimental conditions, hydrolysis species as well as a complex formation between U(IV) and chloride should occur. The UV/vis spectra show spectral modifications which could be induced by the hydrolysis species. However, the luminescence spectra do not show spectral modifications.
In case of U(VI), first TRLFS results show the capabilities of fluorescence spectroscopy even in high chloride concentrated solutions to study U(VI) speciation. Despite the high concentration of 3 M chloride, a luminescence spectrum could be recorded in presence of carbonate in the alkaline pH region. Comparing the position of these bands with literature, we suggest a U(VI) complexation by carbonate [2].
The preliminary results of this study and of Bader et al. [3] shown that chloride quench mechanism for U(IV) and U(VI) luminescence is not fully understood yet in literature. Therefore, further studies will be performed on the spectroscopic behavior and chemistry of U(IV) as well as for U(VI) in highly concentrated chloride solutions.

Literature:
1. A. Kirishima et al., “Luminescence properties of tetravalent uranium in aqueous solution” Radiochim. Acta, 92, 705-710 (2004).
2. Z. Wang et al., “Cryogenic laser induced fluorescence characterization of U(VI) in Hanford vadose zone pore waters“, Environ. Sci. Technol., 38, 5591-5597 (2004).
3. M. Bader et al., “Biosorption of uranium on the cells of the halophilic archaea Halobacterium noricense DSM 15987 under highly saline conditions”, Abstract – ABC-Salt IV Workshop 2015 – Heidelberg, Germany.

Keywords: Uranium; high salinity; fluorescence; UV/vis; speciation

  • Poster
    ABC-Salt IV Workshop 2015, 14.-15.04.2015, Heidelberg, Deutschland
  • Poster
    The ThUL School in Actinide Chemistry, 28.09.-02.10.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22793
Publ.-Id: 22793


Effect of anisotropic microstructure of a 12Cr ODS steel on the fracture behaviour in the small punch test

Altstadt, E.; Serrano, M.; Houska, M.; Garcia-Junceda, A.

Oxide dispersed strengthened steels can exhibit a strongly anisotropic microstructure with elongated pancake-like grains in the rolling plane. This gives rise to intergranular fracture and subsequent delamination along large-area grain boundaries. We investigated an oxide dispersed strengthened alloy with 12 mass percent Cr, manufactured by mechanical alloying, hot extrusion and cold rolling by means small punch tests and subsequent fractographic analysis. The fracture behaviour was analysed in dependence of the specimen orientation. The results from small punch tests were contrasted with those from impact tests with sub-sized samples. In both tests, the ductile to brittle transition temperatures as well as the upper shelf energies depend significantly on the orientation of the specimens. However, the delamination affects the fracture of impact and small punch test samples in different ways. Thus, it depends on the load situation whether delamination has a beneficial or a detrimental effect on the fracture behaviour.

Keywords: ODS-steel; small punch test; anisotropy; delamination

Permalink: https://www.hzdr.de/publications/Publ-22792
Publ.-Id: 22792


Disclosing the hydrodynamics of 3D foam networks for application in advanced catalytic multiphase reactors

Zalucky, J.

In the course of the 10th PhD seminar, the so-far achieved results of the PhD are presented in a short presentation. Starting with the economical and scientific background, the topic of multiphase hydrodynamics in solid foam trickle bed reactors is presented. The results cover the highlights of the regime transition measurements as well as studies carried out using ultrafast X-ray computed tomography.

Keywords: SiSiC solid foam packed trickle-bed reactors; co-current downflow hydrodynamics; ultrafast X-ray computed tomography

  • Lecture (Conference)
    10th HZDR PhD seminar, 02.-04.11.2015, Altenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22791
Publ.-Id: 22791


Disclosing the hydrodynamics of 3D cellular networks for application in multiphase reactors

Zalucky, J.; Wagner, M.; Bieberle, M.; Schubert, M.; Hampel, U.

On behalf of the closing symposium of the Helmholtz Energy Alliance 'Energy Efficient Chemical Multiphase Processes' the scientific highlights of working packages 3.1 and 5.3 are presented. In the first part, the results concering the regime transition measurements for SiSiC solid foam packed trickle-bed reactors are presented. In the second part, the investigations concering the liquid and gas distribution studied by using ultrafast X-ray computed tomography are discussed. In the third part, the hydrodynamics in bubble columns packed with periodic open-cellular structures (POCS) are presented.

Keywords: SiSiC solid foam packed trickle-bed reactor; regime transition; phase distribution; bubble column; periodic open-cellular structures; ultrafast X-ray computed tomography

  • Lecture (Conference)
    Abschlusssymposium der Helmholtz-Energie-Allianz Energieeffiziente Chemische Mehrphasenprozesse, 30.11.-01.12.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22790
Publ.-Id: 22790


Qualitative and quantitative analysis of liquid flow distribution in SiSiC foams using X-ray tomography

Zalucky, J.; Claußnitzer, T.; Schubert, M.; Hampel, U.

In the recent years, solid foams have attracted engineer’s interest as novel functional internals for different chemical process applications. Beside their potential usage as static mixers, distillation packings and heat transfer equipment, solid foams have been envisaged as single and multiphase catalytic support as well. The present contribution focusses on the investigation of the liquid flow distribution inside SiSiC solid foams operated in co-current downward flow. Time-averaged and dynamic flow behaviour has been studied over wide ranges of gas and liquid su-perficial velocities using the non-invasive ultrafast X-ray tomography system.

Keywords: SiSiC solid foam hydrodynamics; co-current downflow; ultrafast X-ray computed tomography; liquid saturation; pulse flow parameters

  • Poster
    European Symposium on Chemical Reaction Engineering, 27.-30.10.2015, Fürstenfeldbruck, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22789
Publ.-Id: 22789


Hydrodynamics and transport processes in structured reactor devices: Project status report april 2015

Zalucky, J.; Schubert, M.; Hampel, U.

On the occasion of half-annual project status report, work package progress is presented. The first part covers the regime transition measurement and modelling for the co-current downflow in SiSiC solid foam packed trickle-bed reactor. The second part summarizes the results found by investigating the time-dependent liquid gas distribution using ultrafast X-ray computed tomography in the same reactor system.

Keywords: regime transition measurement; regime transition modelling; SiSiC solid foam hydrodynamcs; ultrafast X-ray computed tomography

  • Lecture (others)
    Helmholtz-Energie-Allianz EECMP: Half-annular project meeting, 13.-14.04.2015, Fürth, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22788
Publ.-Id: 22788


Co-current downward flow regime transition in solid SiSiC foams: Flow regime prediction and measurement

Zalucky, J.; Möller, F.; Schubert, M.; Hampel, U.

In recent years, solid foams have gained rising interest as multiphase reactor internals for highly exo- or endothermic processes due to relatively low pressure drop, high specific surface areas and elevated radial transport properties. Beside the geometric bed properties, the over-all reactor performance is significantly affected by the prevailing flow regime. In the present contribution, the flow regime transition of co-current downward flows in open-cell SiSiC solid foams has been investigated by optical and acoustical observations as well as fast pressure transducer. Measurements were performed with a water-air system in different bed geometries of varied pore densities and packing diameters of 20, 30, and 45 ppi and DN50 and DN100, respectively. Additionally, aqueous systems with reduced surface tension and increased viscosity have been tested. In order to predict the regime transition from trickle to pulse flow in multiphase systems, the two predictive models of Grosser et al. (1988) and Attou & Ferschneider (2000) have been adapted from trickle bed reactors to structured solid foam fixed bed reactors and validated by the experimental transition data. Determining the onset of flow instabilities at different liquid and gas velocities based on different force balances, both models allow the prediction of regime transition by means of known single phase pressure drop, static liquid holdup and characteristic geometric parameters of the solid foam.

Keywords: Stability based regime transition predictive modelling; SiSiC solid foam

  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmung, 19.-20.03.2015, Lüneburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22787
Publ.-Id: 22787


INTRA r³+ Vernetzung der r³ Projekte und Transfer der Ergebnisse

Dürkoop, A.

In diesem Vortrag werden die Ergebnisse der Begleitforschung zu r³ vorgestellt. Dabei werden Methoden zur Bewertung von innovativen Technologien und Verfahren präsentiert, erfolgte Vernetzung der r³ Projekte erläutert und der Transfer der r³ Ergebnisse in die Anwendung gezeigt.

Keywords: Ressourceneffizienz; Strategische Metalle und Mineralien

  • Invited lecture (Conferences)
    Berliner Recycling- und Rohstoffkonferenz 2016, 07.-08.03.2016, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22786
Publ.-Id: 22786


INTRA r³+ Integration und Transfer der r³ Fördermaßnahme - Ergebnisse der Begleitforschung

Dürkoop, A.; Brandstetter, P.; Erdmann, M.; Gräbe, G.; Höck, M.; Kleeberg, K.; Moller, B.; Ostertag, K.; Schneider, K.; Tercero, L.; Wilken, H.; Pfaff, M.; Büttner, P.

Die r³ Fördermaßnahme wurde in einem Zeitraum von gut vier Jahren zwischen Ende 2011 bis Anfang 2016 durch das Bundesministerium für Bildung und Forschung mit 30 Mio. € gefördert. In 28 r³ Verbundprojekten forschten bundesweit mehr als 100 Unternehmen, Forschungseinrichtungen und Behörden daran, wie nicht-energetische mineralische Rohstoffe zukünftig effizienter genutzt werden können (Abb. 1). Der Fokus lag auf den wirtschaftsstrategisch wichtigen Metallen wie Indium, Germanium, Gallium und seltene Erden, aber auch Industrieminerale wie beispielsweise Flussspat, die zukünftig effizienter gewonnen, recycelt und in Produkten verwendet werden sollen (BMBF 2010). Strategische Metalle und Mineralien werden vor allem für die Herstellung von Hightech-Produkten (Abb. 2) und Energiesparlampen, aber auch für Dauermagnete benötigt. Zwar werden diese Ressourcen nicht in großen Mengen verwendet, sind aber wirtschaftsstrategisch von großer Bedeutung. Da die Rohstoffe zunehmend schlechter verfügbar sind, steigen die Produktionskosten für solche Hightech-Produkte. Die Versorgungslage für diese strategischen Rohstoffe ist in Deutschland unsicher, was zu Versorgungsengpässen im Rohstoffimportland Deutschland führen könnte. Die Ergebnisse der r³ Verbundprojekte zeigen, dass die Versorgungslage für einige dieser Rohstoffe für Deutschland verbessert werden könnte.
Die Bewertung der Ergebnisse aus r³ erfolgte im Rahmen des Projekts INTRA r³+ (Abb. 3) unter der Leitung des Helmholtz-Instituts Freiberg für Ressourcentechnologie (HIF). Zur Bewertung der Nachhaltigkeit der r³ Ergebnisse wurden zum einen ökonomisch-ökologisch-soziale Aspekte analysiert und zum anderen gesamtwirtschaftliche Betrachtungen durchgeführt. Zudem wurde die Vernetzung der r³ Verbundprojekte untereinander aber auch mit externen Initiativen und Projekten mit diversen Maßnahmen angeregt. Darüber hinaus wurde mit Öffentlichkeitsarbeit-Maßnahmen durchgeführt und der Technologietransfer in die Wirtschaft vorbereitet. Partner von INTRA r3+ sind neben dem HIF die Technische Universität Bergakademie Freiberg (TUBAF), der Lehrstuhl für Ganzheitlich Bilanzierung an der Universität Stuttgart (LBP), das Fraunhofer Institut für System- und Innovationsforschung (ISI), das Fraunhofer-Institut für Chemische Technologie (ICT) und die Deutsche Rohstoffagentur (BGR/DERA).

Keywords: Ressourceneffizienz; strategische Metalle; Versorgungssicherheit; Nachhaltigkeitsbewertung

  • Open Access Logo Contribution to proceedings
    Berliner Recycling- und Rohstoffkonferenz, 07.-08.03.2016, Berlin, Deutschland
    Recycling und Rohstoffe Band 9, Neuruppin: TK Verlag, 978-3-944310-27-5, 253-272
  • Book chapter
    Karl J. Thomé-Kozmiensky; Daniel Goldmann: Recycling und Rohstoffe Band 9, Neuruppin: TK Verlag, 2016, 978-3-944310-27-5

Permalink: https://www.hzdr.de/publications/Publ-22785
Publ.-Id: 22785


Experimental investigation of cocurrent water/air down flow in SiSiC solid foam packed reactors

Claußnitzer, T.

Trickle bed reactors (TBR) are widely used in the chemical industry, especially for oxidation, hydrogenation and hydrodesulfurization processes. Since overall performance of TBR is essentially affected by the hydrodynamic properties of the package, lot of work has been done to improve characteristics of the reactor interior. Decreasing the particle size of conventional packings like spheres and cylinders increases the specific surface area but also the pressure drop.
Compared to commonly used packings, solid foams are promised to provide less pressure drop but higher surface area at once. To investigate to hydrodynamics in these packings, solid foams of three different pore densities (20 ppi, 30 ppi, 45 ppi) have been studied in an air/water cocurrently downflow system using ultrafast X-ray tomography to determine their hydrodynamic properties as well as their suitability as reactor packing.
Experiments were carried out at a broad range of gas and liquid superficial velocities of 0.2 ms-1 to 1.0 ms-1 and 0.01 ms-1 to 0.04 ms-1, respectively, covering different flow regimes, namely trickle flow, pulsing flow as well as the transition region.
With spatially-resolved measurements the liquid distribution behavior of solid foams has been investigated. It was shown, that the initial liquid distribution primarily depends on liquid distributor and the pore density of the applied foam, but is not as good as expected.
Following, temporally-resolved measurements at fixed measurement height were carried out. There, for each measurement setup the liquid saturation has been determined and a correlation has been proposed to describe the liquid saturation as a function of pore size as well as gas and liquid flow rate.
In the pulsing regime, investigations were accomplished regarding pulse properties like frequency and velocity. A strong influence of the pore density of the applied foams was found.

Keywords: trickle bed reactor; SiSiC solid foams; ultrafast X-ray tomography; hydrodynamics; co-current downflow

  • Diploma thesis
    TU Dresden, 2015
    Mentor: Zalucky, J., Hampel, U.
    160 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22784
Publ.-Id: 22784


Zum Verständnis der Flotierbarkeit - Untersuchungen zu spezifischen Oberflächenenergieverteilungen und hydrophoben Wechselwirkungen

Rudolph, M.

Spätestens seit dem Patent der Gebrüder Bessel aus Dresden von 1877 nutzt man die Anhaftung hydrophober Partikel an Gasblasen in der Flotation, einer Heterokoagulationstrennung, technologisch aus, um Partikelgemische auf Basis ihrer chemisch veränderlichen Benetzungseigenschaften voneinander zu trennen. Ein wesentlicher Mikroprozess ist hierbei der Anlagerungsvorgang, bestimmt durch das Wechselwirkungspotential zwischen einem Partikel und einer Gasblase. Die klassische DLVO Wechselwirkungstheorie beinhaltet für diese Partner nur repulsive Terme, d.h. abstoßende Doppelschichtwechselwirkung und abstoßende van der Waals Wechselwirkung durch eine negative Hamaker-Konstante. Über die Physik der zwingend notwendigen, weil prozessbestimmenden, weit reichenden, anziehenden Wechselwirkungskomponente ist man sich in der Literatur noch nicht einig. Viele Wissenschaftler sehen feinste Gasdomänen auf hydrophoben Oberflächen, oft als Nanobubbles oder Micropancakes bezeichnet, als Vermittler von weit reichenden kapillaren Anziehungskräften. Andere sehen eine weit reichende Wasserstrukturstörung an hydrophoben Oberflächen als Ursache für eine somit entropisch begründete Anziehung.
Am Helmholtz-Institut Freiberg für Ressourcentechnologie werden in Grundlagenuntersuchungen zur Flotation atomare Gesamtwechselwirkungen zwischen unterschiedlich benetzenden Oberflächen (z.B. Mineralen) und hydrophoben Modellpartikeln in Lösung mit Hilfe der Partikelsonden Rasterkraftmikroskopie analysiert. Zudem wird mit der Methode der inversen Gas Chromatographie die Änderung der spezifischen Oberflächenenergieverteilung als fundamentaler Benetzungsparameter untersucht und mit der Flotierbarkeit in der Mikroflotation in Verbindung gebracht. Der Vortrag fasst den aktuellen Stand der grundlegenden Untersuchungen zusammen. Im Zusammenhang mit den rasterkraftmikroskopischen Untersuchungen werden hydrophobe Wechselwirkungen diskutiert. Auf Basis der Analyse von Oberflächenenergieverteilungen im Zusammenhang mit der Mikroflotation wird ein neues Flotierbarkeitskriterium, die freie Wechselwirkungsenthalpie zwischen einem Partikel und einer Gasblase im Wasser eingeführt und kritisch diskutiert.

Keywords: Flotation; iGC; AFM; Hydrophobicity; Minerals; Collectors

  • Lecture (Conference)
    Aufbereitung und Recycling Jahrestagung 2015, 11.-12.11.2015, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22783
Publ.-Id: 22783


The energy of interactions between bubbles and particles – specific surface free energy distributions and microflotation

Rudolph, M.; Chelgani, S.; Meier, K.; Hartmann, R.

In fundamental flotation studies typically the contact angle is used to describe wettability and correlated with floatability. However, a more fundamental parameter is the specific surface free energy, related to the contact angle via Young’s equation. Inverse gas chromatography (iGC) is a suitable method to determine specific surface free energy components and their distributions on particulate surfaces. In this study the pure minerals quartzite (SiO2), fluoro-apatite (Ca5[F,(PO4)3]) and magnetite (Fe3O4) are examined for microflotation floatability and surface energy considering different methods of sample treatment and the effect of the collectors sodium oleate and dodecyl ammonium acetate. The parameter of specific net free energy of interaction between bubbles and particles immersed in water ΔGpwb derived from the complex surface energy analysis is introduced and used to evaluate the hydrophobicity of the mineral surface correlated with microflotation floatability. Results lead to the provocative hypothesis that only small fractions of the surface and their change by flotation reagent adsorption will inherently define floatability of minerals.

Keywords: Flotation; iGC; Apatite; Quartz; Surface Free Energy; Heterogeneity; Interfaces; Collectors

  • Lecture (Conference)
    Flotation '15, 16.-19.11.2015, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-22782
Publ.-Id: 22782


Laser Ion Acceleration of Spherical Mass Limited Solid Density Targets

Huebl, A.; Kluge, T.; Widera, R.; Hilz, P.; Schreiber, J.; Schramm, U.; Bussmann, M.

We present simulation results regarding the acceleration of ions from mass limited solid density targets with short-pulse high power lasers. Taking advantage of large scale 3D3V PIC simulations (8000 GPUs each, INCITE award 2015) allows to give a detailed insight into the dynamics and unique features of truly isolated targets that were used in recent experiments.
We discuss the pre-plasma evolution, its dependence on laser contrast and its crucial influence on the dominant acceleration mechnanism and on the directionality of the laser-accelerated ion beams. Extensive 2D3V parameter scans are presented for comparison with commonly used flat, wire or mounted target designs.

Keywords: Laser Ion Acceleration; Mass Limited Target; Simulation; PIC; HPC; GPU; PIConGPU

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP), 29.02.-04.03.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22781
Publ.-Id: 22781


Charge Exchange and Energy Loss of Slow Highly Charged Ions in Graphene

Wilhelm, R. A.; Gruber, E.; Kozubek, R.; Smejkal, V.; Schleberger, M.; Facsko, S.; Aumayr, F.

Slow highly charged ion (HCI) interaction with surfaces 100 was studied extensively in recent years and revealed many 7+ interesting aspects of the underlying processes [1]. Nanostructure formation by single HCI impact was successfully 10 linked to defect mediated desorption or even surface melting due to HCI induced local electronic excitations. The neutralization dynamics of a slow (v ≪ v0 = αc, α: fine structure constant, c: speed of light) HCI in front of a solid surface is well described by the classical-over-barrier model. However, not much is known about the neutralization below the surface, i.e. in the material. Below surface neutralization becomes important for normal incidence, because here the interaction time above the surface is not sufficient for neutralization and relaxation of the HCI. We present results on charge exchange and energy loss measurements of slow highly charged Xe ions with charge states of 10 < Q < 35 transmitted through freestanding single Xe16+ layer graphene as the thinnest and lightest solid target material there is. We find that the charge exchange is not bimodal as in case of transmission through 1 nm thick carbon 1 nanomembranes [2], but only very large charge exchange is observed. We attribute this to (1) the availability of solely smallimpactparameters (p<1.5Å ̊) in graphene as well as (2) very high mobilities of charge carriers and subsequently transfer of (at least) 20-30 electrons within less than 10 fs. Especially the second fact is surprising, because here the charge transfer is hardly conceivable as a sequential, but rather as a collective electron transfer process. For incident charge states Q > 25 we observe a saturation of charge exchange, i.e. the exit charge state distribution has a mean value Qmean ≈ Qin − 20 (see fig. 1). The contributions of above surface charge transfer and charge transfer during collision as well as energy loss and its dependence on the charge state and charge exchange will be discussed.

  • Invited lecture (Conferences)
    International Workshop on Inelastic Ion-Surface Collisions (IISC), 18.-23.10.2015, San Sebastian, Spanien

Permalink: https://www.hzdr.de/publications/Publ-22780
Publ.-Id: 22780


Co2Mn0.6Fe0.4Si: A Heusler compound opening new perspectives in magnon spintronics

Sebastian, T.; Hillebrands, B.

This chapter addresses magnon propagation in the Heusler compound Co2Mn0.6Fe0.4Si and the corresponding perspectives for the emerging field of magnon spintronics. The concept of magnon spintronics requires the utilization of advanced materials providing, in particular, a low magnetic Gilbert damping and compatibility with industrial standards concerning the fabrication ofmicro-and nanostructures. We present how this challenge can be addressed by the use of low-damping Co2Mn0.6Fe0.4Si films on the basis of recent studies using micro-focus Brillouin light scattering spectroscopy. The low damping in this Heusler compound not only allows for the realization of increased propagation distances. The pronounced occurrence of nonlinear phenomena might even lead the way towards novel concepts and functionalities in magnonic devices.

  • Book chapter
    Claudia Felser, Atsufumi Hirohata: Häusler Alloys - Properties, Growth, Applications, Switzerland: Springer, 2015
    DOI: 10.1007/978-3-319-21449-8_13

Permalink: https://www.hzdr.de/publications/Publ-22779
Publ.-Id: 22779


Slow highly charged ion transmission through carbon nanomembranes and graphene

Wilhelm, R. A.; Gruber, E.; Heller, R.; Facsko, S.; Aumayr, F.

Slow highly charged ions (HCI) showed in many studies their efficiency in formation of surface nanostructures especially on insulating surfaces [1]. Here we report on transmission of HCI through carbon foils with a thickness of only 1nm and below (graphene). At these thicknesses the neutralization of the slow HCI is not completed in the solid and thus effects of pre-charge-equilibrium stopping of slow ions can be addressed experimentally.
We find that transmitted highly charged Xe ions with charge states between Q=10 and Q=30 show a bimodal charge state distribution, i.e. one part of the ions is transmitted in low exit charge states combined with a large charge exchange enhanced kinetic stopping. The other part of the ions, however, shows only a very small charge exchange with almost no kinetic energy loss [2]. Both charge exchange regimes are attributed to different impact parameter regimes, i.e. close collision lead to extremely large charge exchanges and distant collisions are connected with weak ion-target interactions. Thus, our measurements reveal that sub-surface neutralization of HCI proceeds in a step-like fashion, i.e. either the ion approaches a target atom closely and correspondingly neutralizes almost completely (∆Q > 20 for Q = 30) or it passes through the material almost unchanged (∆Q < 5) until it hits a target atom at some larger depth. A bimodal charge state distribution could therefore not be observed for larger target thicknesses [3], except for the inverse case of a swift heavy ion charging up during transmission through a silicon single crystal under random vs. channeling direction [4]. Gas phase experiments on the other hand cannot lead to slow HCI neutralization in one single scattering event using light target atoms (e.g. carbon), because here only atomically bound electrons can contribute to the neutralization process (6 electrons in case of carbon) rather than de-localized electrons in a solid target.

  • Poster
    International Summer School on Vacuum, Electron and Ion Technologies, 21.-25.09.2015, Sozopol, Bulgarien

Permalink: https://www.hzdr.de/publications/Publ-22778
Publ.-Id: 22778


Electron emission from solid surfaces due to slow highly charged ion impact

Wilhelm, R. A.; Heller, R.; Meissl, W.; Aumayr, F.; Facsko, S.

Slow highly charged ions (HCI) and their interaction with surfaces reveal many interesting phenomena, e.g. nanostructure formation, non-equilibrium ion stopping and charge exchange as well as extremely large electron emission yields [1,2].
The emission of electrons is tightly connected to the neu- tralization process of the HCI above and below the sur- face. When the ion approaches the surface it starts to capture electrons near the Fermi edge into high Rydberg states in the ion and subsequently emits Auger electrons upon de-excitation. The process is well described by the classical-over-barrier model [3]. However, for normal incidence the time for neutralization of the ion above the surface is not sufficient. Hence, the neutralization pro- ceeds below the surface with accompanied sub-surface electron emission.
We present here recent experimental data on the second- ary electron emission yield from highly charged Xe im- pinging on Au, KBr, LiF and CaF2 surfaces (see fig. 1). The data shows that so called potential emission, i.e. secondary electron emission by neutralization (potential energy conversion) becomes significant for low ion ve- locities (v < 105 m/s) [4].
The large amount of HCI induced electrons emitted from the surface opens the possibility of correlative studies of nanostructuring by HCI and subsequent electron spec- tromicroscopy.
Our planned Low Energy Ion Nano-Engineering Facility (LEINEF) at the Ion Beam Center of the Helmholtz- Zentrum Dresden-Rossendorf will comprise several HCI sources, a medium and low energy ion scattering set-up, a focused ion beam set-up, Auger and x-ray photoelec- tron spectroscopy as well as a low energy electron mi- croscope (LEEM). The latter one may be equipped with an ion gun or a HCI source to perform correlative nanostructuring and electron spectromicroscopy with electrons from the LEEM source as well as ion induced secondary electrons.

  • Poster
    Low Energy Electrons: Dynamics and Correlation near Surfaces and Nanostructures (LEE2015), 07.-11.09.2015, Hernstein, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22777
Publ.-Id: 22777


Interaction of Slow Highly Charged Ions with Ultrathin Membranes - Potential Sputtering, Energy Loss and Charge Exchange

Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Facsko, S.; Aumayr, F.

Slow highly charged ions (HCI) are known as an efficient tool for sur- face nano structuring of various insulating and semi-conducting sur- faces. We show here that slow HCI can also be used to perforate a free-standing carbon nano membrane (CNM) with a thickness of only 1 nm. Round pores with sizes of up to 15 nm in diameter and corre- sponding sputter yields of up to a few thousand atoms are observed. Recent energy loss and charge exchange measurements on ions trans- mitted through a 1 nm thick CNM and free-standing Graphene reveal a strong dependence of the ion energy loss on charge exchange. Sur- prisingly, two distinct exit charge state distributions are observed, i.e. one part of the ions is almost neutralized and the other part remains in very high charge states after transmission. The ions potential and kinetic energy dependence on pore formation is discussed in terms of charge exchange and energy loss.

  • Lecture (Conference)
    Frühjahrestagung der Deutschen Physikalischen Gesellschaft, Sektion Kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22776
Publ.-Id: 22776


Highly charged ion induced nanostructures by strong electronic excitations

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

The formation of nanostructures on surfaces without bulk damage by slow highly charged ion (HCI) irradiation was studied intensively in recent years. Especially single HCI impact on ionic crystals revealed interesting new phenomena. On alkali halides, e.g. KBr or KCl, defect mediated desorption with corresponding yields of a few thousand desorbed atoms per ion was observed [1]. Associated structures are pits with a diameter of up to 20nm and a depth of only 1 or 2 monolayers. The HCI’s potential energy was identified as the driving force for the desorption process. On alkaline earth halides (CaF2), however, hillocks were observed and this process was linked to a solid-liquid phase transition after surpassing a certain potential energy threshold. Even before nanomelting occurs damage could be revealed by wet-chemical etching of the surface [2]. Since HCI interaction with surfaces involves electron capture from and electron emission to the surface, we compare here HCI induced structures to structures observed after low energy electron bombardment [3]. Electrons and HCIs produce strong electronic excitations at the surface and subsequent de-excitation by electron-phonon interaction leads to the structure formation. Thus, potential sputtering and HCI induced phase transitions result from electronic excitations (and subsequent de-excitation) in contrast to single charged ions in the nuclear sputtering regime. To study the neutralization process of HCI in more detail we present recent data on the transmission of HCI through ultra-thin materials.

  • Lecture (Conference)
    International Workshop on Nanoscale Pattern Formation at Surfaces, 12.-16.07.2015, Kraków, Polen

Permalink: https://www.hzdr.de/publications/Publ-22775
Publ.-Id: 22775


Threshold and Efficiency for Perforation of 1nm Thick Carbon Nanomembranes with Slow Highly Charged Ions

Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Facsko, S.; Aumayr, F.

Ion collision with surfaces leads to nano-structure formation usually by cumulative ef-fects. Large ion fluencies are needed to lead to observable topographic surface features. For special classes of ions, i.e. swift heavy ions or slow highly charged ions (HCI) already single ion impacts may give rise to structural changes with a lateral extent of a few nm. Desired sur-face-only modification, however, can solely be achieved by HCI due to the very localized re-lease of their potential energy.
Different kinds of surface structures have been observed on insulating [1] and semi-conducting surfaces [2]. All these studies have in common that a certain ion charge state or potential ener-gy threshold has to be exceeded in order to form nano-hillocks, nano-pits, nano-craters, or even sub-surface damage only visible after chemical etching [3]. For high ion charge states the effi-ciency for nano-structure formation is consid-ered to be 100%, i.e. every ion produces a struc-ture upon impact. However, an accurate fluence measurement necessary to determine the struc-turing yield for HCI irradiation is challenging, because of very low ion currents (fA-range). Also it is an open question how well defined the potential energy threshold is.
Here we show that transmission of HCI through 1nm thick carbon nanomembranes (CNM) and subsequent determination of their charge state distribution and energy loss [4] allows us to measure the ion-induced nano-structure for-mation yield much more accurately. Since these insulating membranes are a surface-only mate-rial and HCI energy deposition is limited typi-cally to the surface of a solid we consider this as a model system for insulating surfaces.
Figure 1 shows the efficiency for pore for-mation by single HCI impact as function of the incident charge state. It is obvious that a thresh-old exists at about Q = 28, where the yield in-creases from 0 to about 70%. For even higher charge states the efficiency increases to about 100% for Q = 40. Thus, only for sufficiently highly charged ions the structure formation yield may be considered to be 100%.

  • Poster
    International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC), 22.-28.07.2015, Toledo, Spanien
  • Open Access Logo Journal of Physics: Conference Series 635(2015)3, 032011
    DOI: 10.1088/1742-6596/635/3/032011

Permalink: https://www.hzdr.de/publications/Publ-22774
Publ.-Id: 22774


Influence of irradiation on release of endothelial microparticles (EMP) in vitro

Neuber, C.; Pufe, J.; Pietzsch, J.

Survivors of Hodgkin's disease as well as of breast and lung cancer are at risk of radiation-associated cardiovascular disease. Recent studies demonstrated a correlation between cardiovascular risk factors and circulating endothelial microparticles (EMP) and thereby suggest increased EMP levels in circulation to be an early biomarker of endothelial dysfunction and cardiovascular risk. This prompted us to analyze the amount of EMP released by human aortic endothelial cells (HAEC) after exposure to different doses of X-ray (0.4, 2, 4, 6, and 20 Gy) using antibodies against the endothelial cell markers CD31, CD144, and CD146 by flow cytometry. In this pilot experiment only CD146 proved appropriate for quantification of HAEC-derived EMP. Exposure of HAEC to different doses of X-ray did not significantly influence formation of CD146-positive EMP. However, low doses (0.4 Gy) tended to decrease EMP formation, whereas higher doses (2 or 4 Gy) slightly increased release of CD146-positive EMP. By contrast, inflammatory activation of HAEC by TPA significantly increased EMP release about 15-fold (P <  0.01). In conclusion, under the present experimental conditions EMP did not prove a suitable biomarker for radiation-induced endothelial dysfunction in vitro.

  • Clinical Hemorheology and Microcirculation 61(2015)2, 291-299
    DOI: 10.3233/CH-151987

Permalink: https://www.hzdr.de/publications/Publ-22773
Publ.-Id: 22773


Higher Cd adsorption on biogenic elemental selenium nanoparticles

Jain, R.; Dominic, D.; Jordan, N.; Rene, E. R.; Weiss, S.; van Hullebusch, E. D.; Hübner, R.; Lens, P. N. L.

Cadmium (Cd) is a carcinogenic metal contaminating the environment and ending up in wastewaters. There is therefore a need for improved methods to remove Cd by adsorption. Biogenic elemental selenium nanoparticles have been shown to adsorb Zn, Cu and Hg, but these nanoparticles have not been tested for Cd removal. Here we studied the time-dependency and adsorption isotherm of Cd onto biogenic elemental selenium nanoparticles using batch adsorption experiments. We measured ζ-potential values to assess the stability of nanoparticles loaded with Cd. Results show that the maximum Cd adsorption capacity amounts to 176.8 mg of Cd adsorbed per g of biogenic elemental selenium nanoparticles. The ζ-potential of Cd-loaded nanoparticles became less negative from −32.7 to −11.7 mV when exposing nanoparticles to an initial Cd concentration of 92.7 mg L−1. This is the first study that demonstrates the high Cd uptake capacity of biogenic elemental selenium nanoparticles, of 176.8 mg g−1, when compared to that of traditional adsorbents such as carboxyl-functionalized activated carbon, of 13.5 mg g−1. An additional benefit is the easy solid–liquid separation by gravity settling due to coagulation of Cd-loaded biogenic elemental selenium nanoparticles.

Keywords: Cd; BioSeNPs; adsorption kinetics; adsorption isotherms; ζ-potential

Downloads:

  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-22772
Publ.-Id: 22772


Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

Kiselev, Y. T.; Hartmann, M.; Polyanskiy, A.; Paryev, E. Y.; Barsov, S.; Büscher, M.; Dymov, S.; Gebel, R.; Hejny, V.; Kacharava, A.; Keshelashvili, I.; Lorentz, B.; Maeda, Y.; Merzliakov, S.; Mikirtytchiants, S.; Ohm, H.; Serdyuk, V.; Sibirtsev, A.; Sinitsyna, V. Y.; Stein, H. J.; Ströher, H.; Trusov, S.; Valdau, Y.; Wilkin, C.; Wüstner, P.; Ye, Q. J.

The production of non-φ K+K pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K momentum dependence of the differential cross section has been measured for laboratory polar angles θK± < 12° over the 0.2–0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K-nucleus potential of about −60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K momenta.

Permalink: https://www.hzdr.de/publications/Publ-22771
Publ.-Id: 22771


Temperature relaxation in laser excited aluminium

Vorberger, J.

Energy- and temperature relaxation processes after laser excitation of the electrons in solids and warm dense matter take place in virtually every high-energy density experiment and play an important role in a great number of industrial processes. In inertial fusion, they are essential for a successfull burn phase of the hydrogen pellet. Here, we report on new theoretical and experimental results concerning the energy transfer between electrons and phonons in solid aluminium on a femto to pico-second timescale. The results suggest that the two-temperature model is insufficient to describe the relaxation. We instead introduce a non-thermal lattice model. Within this model, electron-phonon couplings as derived from density functional theory and Bragg-peak decay rates as measured via electron diffraction are consistent with each other.

Keywords: warm dense matter; inertial fusion; energy relaxation; temperature relaxation; energy transfer rate; electron-phonon coupling; two-temperature model

  • Invited lecture (Conferences)
    Seminar der Arbeitsgruppen Quantentheorie und Vielteilchensysteme, Statistische Physik, Molekulare Quantendynamik, Theoretische Clusterphysik und Nanophotonik, 01.12.2015, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22770
Publ.-Id: 22770


Determination of long-lived cosmogenic radionuclides by accelerator mass spectrometry

Merchel, S.; Khojasteh Mohammadi, N. B.; Pavetich, S.; Rugel, G.; Scharf, A.; DREAMS-Users; DREAMS-Friends

Applications: Long-lived radionuclides with half-lives of 0.1-16 Ma have nowadays thousands of exciting applications, especially within environmental and geosciences. In nature, the so-called cosmogenic nuclides (CNs) are products of nuclear reactions induced by primary and secondary cosmic rays. Hence, they can be found in extraterrestrial material such as meteorites - originating from the asteroid belt, the Moon or Mars - and lunar samples in higher concentrations (e.g. ~1010 10 Be atoms/g or < 0.5 mBq/g). A combination of several CNs is used to reconstruct the exposure history of this unique material while in space (irradiation age) and on Earth (terrestrial age).
Though, in terrestrial material the concentrations are typically only on the order of 104 - 109 atoms/g (i.e. μBq/g - nBq/g) for 10Be produced in the Earth’s atmosphere, then transported to the surface and further absorbed and incorporated at and in, e.g. sediments or ice. Some of the lowest 10Be concentrations (~103 atoms/g), produced in-situ by neutron- and muon-induced nuclear reactions from e.g. O and Si in quartz, can be found in samples taken from the Earth’s surface. The concentrations of atmospheric or in-situ produced CNs record information to reconstruct sudden geomorphological events such as volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earthquakes and glacier movements. Additionally, glacier movements and data from ice cores give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes. Slower processes such as sedimentation, river incision and erosion rates can also be investigated and last but not least, indirect dating of bones as old as several Ma’s is possible.
Anthropogenic production by release from nuclear reprocessing, accidents and weapon tests led to increased levels of CNs in surface water and soil (129I,…), ice (36Cl,…) and material from nuclear installations themselves (41Ca,…). Some of the CNs can, thus, be used as tracers to follow pathways in oceanography, to date and identify sources of groundwater, to perform retrospective dosimetry and to study aspects in radioecology and pharmacology.
Method: The analytical method of choice for CN determination is accelerator mass spectrometry (AMS). After simple radiochemical separation, AMS reduces enormously background and interfering signals resulting from molecular ions and isobars. Thus, AMS provides much lower detection limits compared to conventional MS or decay counting. The DREAMS (DREsden AMS) system at HZDR offers excellent measurement capabilities (Akhmadaliev et al., NIMB 294 (2013) 5) also for external users (see www.hzdr.de/ibc).

Keywords: Accelerator mass spectrometry; cosmogenic nuclides; AMS

  • Invited lecture (Conferences)
    International Conference on Radioanalytical and Nuclear Chemistry (RANC-2016), 10.-15.04.2016, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-22768
Publ.-Id: 22768


Understanding Cu mobilisation from copper shale leaching: [64Cu]CuS: Ligand identification, kinetic rates and modelling

Barthen, R.; Gründig, M.; Karimzadeh, L.; Schössler, C.; Mansel, A.; Grenzer, J.; Schymura, S.; Kulenkampff, J.; Franke, K.; Lippold, H.; Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Poster
    General Meeting 4, Ecometals, 01.-02.12.2015, Pau, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-22767
Publ.-Id: 22767


Sorption of environmentally relevant radionuclides (U(VI), Np(V)) and lanthanides (Nd(III)) on feldspar and mica

Richter, C.

Presentation of the sorption of environmentally relevant radionuclides (UO22+, NpO2+) and lanthanides (Nd3+) on feldspar and mica

  • Lecture (Conference)
    Kompetenzzentrum Ost für Kerntechnik (KOMPOST) 10.Doktorandenseminar, 08.12.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22766
Publ.-Id: 22766


Sorption of environmentally relevant radionuclides (UO22+, NpO2+) and lanthanides (Nd3+) on feldspar and mica

Richter, C.

Presentation of the results of the study about Sorption of environmentally relevant radionuclides (UO22+, NpO2+) and lanthanides (Nd3+) on feldspar and mica.

  • Lecture (others)
    Abteilungsseminar der Abteilung Hydrogeochemie und Hydrogeologie, Institut für Geowissenschaften, Universität Heidelberg, 03.12.2015, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22765
Publ.-Id: 22765


Positron spectroscopy of point defects in the skyrmion-lattice compound MnSi

Reiner, M.; Bauer, A.; Leitner, M.; Gigl, T.; Anwand, W.; Butterling, M.; Wagner, A.; Kudejova, P.; Pfleiderer, C.; Hugenschmidt, C.

Outstanding crystalline perfection is a key requirement for the formation of new forms of electronic order in a vast number of widely different materials. Whereas excellent sample quality represents a standard claim in the literature, there are, quite generally, no reliable microscopic probes to establish the nature and concentration of lattice defects such as voids, dislocations and different species of point defects on the level relevant to the length and energy scales inherent to these new forms of order. Here we report an experimental study of the archetypical skyrmion-lattice compound MnSi, where we relate the characteristic types of point defects and their concentration to the magnetic properties by combining different types of positron spectroscopy with ab-initio calculations and bulk measurements. We find that Mn antisite disorder broadens the magnetic phase transitions and lowers their critical temperatures, whereas the skyrmion lattice phase forms for all samples studied underlining the robustness of this topologically non-trivial state. Taken together, this demonstrates the unprecedented sensitivity of positron spectroscopy in studies of new forms of electronic order.

Keywords: positron annihilation spectroscopy; point defects; MnSi; magnetism; skyrmion lattice

Permalink: https://www.hzdr.de/publications/Publ-22764
Publ.-Id: 22764


Shaping and compositional modification of zinc oxide nanowires under energetic manganese ion irradiation

Möller, W.; Johannes, A.; Ronning, C.

The development of the surface contour and the local elemental composition of ZnO nanowires of 150 to 200 nm diameter under 170 keV Mn irradiation is addressed both experimentally and by means of three-dimensional dynamic Monte Carlo computer simulation using the binary collision approximation. A random rotation of the incident beam around the nanowire axis mimics the experimental irradiation under sample rotation. The simulation results demonstrate a complex interplay of sputter erosion, implant incorporation and resputtering, as well as atomic mixing, which is discussed in detail. The sputter-induced thinning of the wire is in good quantitative agreement with experimental results obtained from pre- and post-irradiation scanning electron microscopy. The experiments also confirm the predicted sharpening of the top and neck formation at the bottom interface. Due to the latter, the wire detaches from the substrate at high ion fluence. Good agreement with experimental results from nano-X-ray fluorescence is also obtained for the continuously increasing Mn/Zn ratio as function of ion fluence. The simulation yields manifold additional information which has not been accessible to the experiments, such as fractional sputtering data and three-dimensional elemental composition profiles at increasing ion fluence. From these, preferential sputtering of O vs. Zn is deduced. A significant contamination of the wires with substrate material arises from ion mixing at the wire/substrate interface rather than from redeposition of sputtered substrate atoms. Surprising hollow profiles are observed. Their formation is attributed to a special mechanism of collisional transport which is characteristic for the irradiation of nanowires at a suitable combination of wire diameter and ion energy.

Keywords: nanowire; ion irradiation; high-fluence doping; sputtering; zinc oxide; computer simulation

Permalink: https://www.hzdr.de/publications/Publ-22763
Publ.-Id: 22763


Interaction of technetium with neptunium in acidic media

Chotkowski, M.; Weiss, S.; Scheinost, A. C.

Spent nuclear fuel
Chemical properties of Tc and Np
Spectroelectrochemistry of Tc
Electrochemistry of Tc and Np in acidic media
Liquid-liquid extraction of Tc in the presence of Np
EXAFS analyses

Keywords: Spent nuclear fuel; Chemical properties of Tc and Np; Spectroelectrochemistry of Tc; Electrochemistry of Tc and Np in acidic media; Liquid-liquid extraction of Tc in the presence of Np; EXAFS analyses

  • Lecture (Conference)
    3rd Academic Symposium on Nuclear Fuel Cycle, 02.-05.12.2015, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-22762
Publ.-Id: 22762


Inductive detection of gas bubbles in a liquid metal flow

Gundrum, T.; Büttner, P.; Dekdouk, B.; Peyton, A.; Wondrak, T.; Galindo, V.; Eckert, S.

The detection of bubbles in liquid metals flow is important for many technical applications. The opaqueness and the high temperature of liquid metals set high demands on the measurement system. The electrical conductivity of the liquid metal is relatively high, which can be exploited with contactless methods based on electromagnetic induction. We will present a measurement system which consists of one transmitting coil and a planar gradiometric coil on opposite sides of the pipe. With this sensor we were able to detect bubbles in a Sodium flow inside a stainless steel pipe.

Keywords: inductive contactless measurement; two phase flow; liquid metal; bubble detection; void fraction

  • Poster
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Süd Korea
  • Contribution to proceedings
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Süd Korea
    2015 IEEE SENSORS Proceedings: IEEE, 10.978-1-4799-8202-8, 1001-1002

Permalink: https://www.hzdr.de/publications/Publ-22761
Publ.-Id: 22761


The reactor Dynamics code DYN3D – models, Validation and applications

Rohde, U.; Kliem, S.; Grundmann, U.; Baier, S.; Bilodid, Y.; Duerigen, S.; Fridman, E.; Gommlich, A.; Holt, L.; Grahn, A.; Kozmenkov, Y.; Mittag, S.

The article provides an overview on the reactor dynamics code DYN3D. The code comprises various 3D neutron kinetics solvers, a thermal-hydraulics reactor core model and a thermo-mechanical fuel rod model. The implemented models and methods and the capabilities and features of the code are described. Latest developments of models and methods are delineated. An overview on the status of verification and validation is given. Code applications for selected safety analyses are described. Furthermore, multi-physics code couplings to thermal-hydraulic system codes, CFD and sub-channel codes as well as to the fuel performance code TRANSURANUS are outlined. Developments for innovative reactor concepts, in particular Molten Salt Reactor, High Temperature Gas-cooled Reactor and Sodium Fast Reactor are delineated. The management of code maintenance is briefly described.

Keywords: Reactor dynamics; neutron kinetics; thermal-hydraulics model; fuel rod model; code coupling; verification and validation; transient analysis; innovative reactors; code maintenance

Permalink: https://www.hzdr.de/publications/Publ-22760
Publ.-Id: 22760


68Ga-DATATOC: synthesis, radiolabeling, and first in vivo studies

Waldron, B.; Seemann, J.; Bergmann, R.; Nagel, J.; Rösch, F.; Sinnes, J. P.

Objectives: 68Ga-DOTATOC is currently used as the industry standard for diagnostic imaging of NETs and its metastases. Radiolabeling can be performed manually and automated at 95°C. In order to approach the application of 68Ga following a kit-type procedure, a DATA-based chelator (6-amino-1,4-diazepine-triacetate) was used in the study as it has shown to radiolabel under very mild conditions. Conjugation with TOC to afford a DOTATOC analog may enable radiolabeling of the peptide at room temperature.
Methods: DATATOC was synthesized in a seven-step synthesis. Radiolabeling with 68Ga was performed manually at room temperature, and stability was assessed in human serum. An automated setup was also examined, using the Modular-Lab eazy (Eckert & Ziegler, Berlin, Germany). First in vivo studies using MPC-mCherry tumor–bearing mice were performed and compared with DOTATATE.
Research: Radiolabeling was performed at room temperature using N2 solution, NaOAc buffer, and 14 nmol DATATOC. An RCY of 96.3% ± 1.2% was obtained within 3 min. Stability was tested in human serum over a period of 2 h (Δ, 1.3%). Automated labeling with a 23 nmol precursor achieved quantitative complexation of 68Ga. In vivo PET/CT studies with 68Ga-DATATOC indicate a high specific uptake in the tumor region after 10 min (SUV of 3.73 ± 1.49). In a blocking study with OC, the SUV in the tumor was reduced to 0.45 ± 0.15. In addition, 68Ga-DATATOC showed high stability in mouse plasma with 93.7% of the tracer remaining intact after 120 min. Compared with 68Ga-DOTATATE a faster renal excretion of the tracer was observed.
Conclusion: DATATOC can be labeled with 68Ga in a manual or automated setup rapidly at room temperature, offering significant advantages over similar DOTA-based derivatives. Furthermore, first in vivo studies confirm excellent targeting and excretion characteristics for the novel tracer. With the perspective toward a kit-type formulation, the superior characteristics of this new compound pave the way for a new generation of 68Ga radiopharmaceuticals.

  • Abstract in refereed journal
    Journal of Nuclear Medicine 56(2015)2, 27
    DOI: 10.2967/jnm565abs
  • Lecture (Conference)
    3rd Theranostics World Congress (3TWC) on Gallium-68 and PRRT, 12.-14.03.2015, Baltimore, USA

Permalink: https://www.hzdr.de/publications/Publ-22759
Publ.-Id: 22759


[Ga-68]Ga-DATATOC imaging, biodistribution and kinetics in a pheochromocytoma model

Bergmann, R.; Ullrich, M.; Ziegler, C.; Waldron, B.; Seemann, J.; Nagel, J.; Roesch, F.; Eisenhofer, G.; Steinbach, J.; Pietzsch, J.

Objectives The novel DATA (6-Amino-1,4-diazepine-triacetate) based octreotide derivative TOC allows radiolabeling at room temperature in contrast to DOTATOC that needs 95°C for effective labeling. The main goal of this study was to evaluate the potential of [68Ga]Ga-DATATOC for SSTR2 imaging in a syngeneic mouse pheochromocytoma (Pheo) model.

Methods Radiolabeling of the DATATOC with 68Ga was performed manually at room temperature. The in vivo studies (PET, metabolic stability, biodistribution and elimination) were carried out in Pheo (MPC-mCherry) bearing mice and Wistar rats. For comparison the pheo were also imaged with [68Ga]Ga-DOTATOC and [68Ga]Ga-DOTATATE. Blocking studies in vivo were performed with octreotide (OC).

Results The radiotracer showed high in vivo stability. A faster renal elimination of the radiotracer was observed in comparison to DOTATOC and DOTATATE. [68Ga]Ga-DATATOC showed fast, highly specific uptake in the pheo and the pancreas (SUV at 1 h p.i., tumor 3.7 ± 1.5, pancreas 0.57 ± 0.17), whereas blocking with OC (3.3 mg/kg body weight) reduced the uptake in the tumor to 0.45 ± 0.15 and Patlak analysis showed that both parameters - the influx rate and the distribution volume - were significantly decreased by OC.

Conclusions [68Ga]Ga-DATATOC can be radiolabeled with 68Ga rapidly at room temperature with high radiochemical yields. The preclinical in vivo studies confirm the high stability, excellent specific targeting and fast elimination. This pharmacological profile and the perspective towards a kit-type formulation provide a great potential for diagnostic somatostatin receptor imaging.

Research Support This work was supported by The Deutsche Forschungsgemeinschaft (Grants ZI-1362/2-1 [to C.G.Z. and G.E.] and BE-2607/1-1 [to R.B. and J.P.]).

  • Abstract in refereed journal
    Journal of Nuclear Medicine 56(2015), 1129
  • Poster
    SNMMI 2015 Annual Meeting, 06.-10.06.2015, Baltimore, USA

Permalink: https://www.hzdr.de/publications/Publ-22758
Publ.-Id: 22758


Data processing performance analysis for ultrafast electron beam X-ray CT using parallel processing hardware architectures

Bieberle, A.; Frust, T.; Wagner, M.; Bieberle, M.; Hampel, U.

The ultrafast electron beam X-ray computed tomography measuring system (Fischer et al., 2008) of the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) is primarily operated for fundamental multiphase flow investigations, e.g. in various technical devices, and for validation of enhanced flow simulation models, e.g. developed for computational fluid dynamic codes (CFD). The ultrafast computed tomography (CT) scanner delivers cross-sectional material distributions by contactless measurement with a spatial resolution of approximately 1 mm and a temporal resolution of maximal 8 kHz. Currently, two central time-consuming processes have been identified limiting the efficient usage of that worldwide unique CT technique: a) the data transfer from the detector system to central data storages (e.g. computer or data base) and b) the data processing. Thus, data processing and data reconstruction has been adapted for the use at multi-core central processing units (CPUs) and many-core graphics processing units (GPUs). For optimal performance an advanced performance PC (AP-PC) with two parallel operated high performance graphics processing units (Tesla K20c, NVIDIA®), a six-core Intel® processor (Xeon E5-1650 v3,), a high internal data bus speed and a large memory block (DDR4, 2133 MHz, 128 GByte) was assembled. Finally, the modified combined multi-core CPU and many-core GPU optimized algorithms generate a performance improvement of app. 137 for the entire data processing sequence compared to the established single core CPU based data processing tool.

Keywords: computed tomography; many-core graphics processing units; multi-core central processing units; massive parallel data processing

Permalink: https://www.hzdr.de/publications/Publ-22757
Publ.-Id: 22757


Off-target FDG-PET parameters have prognostic value in head and neck squamous cell carcinomas undergoing primary radiochemotherapy and can be used to generate radiobiological hypotheses

Zschaeck, S.; Loeck, S.; Leger, S.; Richter, C.; Zoephel, K.; Kotzerke, J.; Steinbach, J.; Zips, D.; Krause, M.; Baumann, M.

kein Abstract verfügbar

  • Abstract in refereed journal
    European Journal of Cancer 51(2015), S570
    DOI: 10.1016/S0959-8049(15)30053-8
  • Poster
    European Cancer Congress 2015, 25.-29.09.2015, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22756
Publ.-Id: 22756


Stand der Technik experimenteller Untersuchungen dichter Blasenströmungen

Kipping, R.; Kryk, H.; Hampel, U.

In der chemischen und biochemischen Industrie werden oftmals Blasensäulenreaktoren für Mehrphasenprozesse eingesetzt. Sie zeichnen sich durch ihren einfachen Aufbau, sowie gute Stoff-und Wärmeübertragungseigenschaften aus. In der Literatur sind umfangreiche Studien zur Auslegung und Dimensionierung solcher Reaktoren zu finden. Zur weiteren Prozessoptimierung ist zunehmend die Aufklärung der lokalen Mechanismen innerhalb des Reaktors, insbesondere die Interaktion von Hydrodynamik, Stofftransport und chemischer Reaktion, erforderlich. Die ortsaufgelöste Untersuchung von Hydrodynamik und Stofftransport in Blasenströmungen erfolgt bisher vornehmlich mit Hilfe optischer Verfahren, wie z.B. der Particle Image Velocimetry (PIV), Laser Doppler Anemometrie (LDA) und laserinduzierter Fluoreszenz (LIF). Während diese Messtechniken für die Untersuchung von Blasenströmungen geringen Gasgehaltes gut geeignet sind, stoßen sie bei hohen Gasgehalten an ihre Grenzen. Ziel dieses Beitrages ist es, eine Übersicht über den aktuellen Stand der Technik in Hinblick auf experimentelle Studien zur Hydrodynamik und gekoppelter Vorgänge, wie Stofftransport und Reaktion in Blasensäulenreaktoren zu geben. Dabei sollen die Notwendigkeit künftiger Studien in diesem Bereich und damit einhergehend die Anforderungen an die Messtechnik aufgezeigt werden.

Keywords: Blasensäulen; Hydrodynamik; Stofftransport; Mehrphasenströmung

  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22755
Publ.-Id: 22755


Bestimmung der zerebrovaskulären Reserve mit BOLD-MRT unter Atemanhalten bei Patienten mit Stenosen der hirnversorgenden Gefäße

Krukowski, P.; Petr, J.; Puetz, V.; Abramyuk, A.; Linn, J.; Gerber, J.

Die Autoregulation der zerebralen Perfusion ist wichtiger Mechanismus der Homöostase. Hyperkapnie führt im gesunden Gefäßbett zur Dilatation präkapillärer Gefäße und zur Aktivierung der zerebralen Perfusionsreserve (CVR). BOLD (Blood Oxygen Level Dependent)-MRT unter Atemanhalten stellt die Veränderungen dar. Bei Patienten mit Stenosen hirnversorgender Arterien akquirierten wir prospektiv ein BOLD-MRT unter Atemanhalten, evaluierten die Machbarkeit und korrelierten die Zielstenose mit den BOLD-Veränderungen.

  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Neuroradiologie e.V., 15.-17.10.2015, Gürzenich, Köln, D

Permalink: https://www.hzdr.de/publications/Publ-22754
Publ.-Id: 22754


Algorithms for flow pattern identification based on Wire-Mesh Sensor data

Kipping, R.; Brito, R.; Schleicher, E.; Hampel, U.

Within the development of an industrial type of Wire-Mesh Sensor (WMS) algorithms for flow pattern identification were developed. Based on the statistical evaluation of gas holdup distribution, the distinction of the main flow patterns in gas-liquid flow is carried out. Experimental validation of the algorithm was carried using experimental flow loop from The University of Tulsa Horizontal Well and Artificial Lift Project (TUHWALP).

Keywords: Wire-Mesh Sensor; two-phase flow; flow pattern recognition; vertical pipe flow; horizontal pipe flow

  • Lecture (Conference)
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22753
Publ.-Id: 22753


Simulation of turbulent bubbly flow in pipes of different diameter

Kriebitzsch, S.; Rzehak, R.

Many technical processes in industries such as chemical or electricity but also numerous natural phenomena involve multiphase flow. Due to the complex physics and the broad range of relevant length scales involved, it is a formidable task to achieve a better understanding of such flows. A detailed insight into the local flow field can be obtained from multiphase computational fluid dynamics, which therefore is a potentially valuable tool for the optimisation of existing and the design of new technical equipment. Such simulations are feasible within the Eulerian two-fluid framework of interpenetrating continua. Within this framework the interfacial transfer processes need to be modelled by suitable closure relations, many of which have been proposed in the literature. Predictions with multiphase CFD are only possible if a fixed set of closures is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems. As a safe starting point a baseline model applicable for adiabatic bubbly flows has recently been defined by Rzehak and Krepper (2013).
In this work we compare simulation results obtained using the baseline model with three different sets of experimental data for dispersed gas-liquid pipe flow given by Liu (1998), Shawkat et al. (2008), and Hosokawa and Tomiyama (2009). Air and water under similar flow conditions have been used in the different experiments, so that the main difference between the experiments is the variation of the pipe diameter from 25 mm to 200 mm. Overall all three experimental data sets are reasonably well reproduced by the simulation results, in particular in the bulk of the flow. The need for improved modelling of multiphase turbulence as well as wall effects manifests itself through larger differences with the experimental data in the near-wall region of the pipes.

Keywords: Euler-Euler; bubbly flow; CFD; two-fluid model

  • Lecture (Conference)
    Jahrestreffen der ProcessNet Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen, 19.-20.03.2015, Lüneburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22752
Publ.-Id: 22752


Synthesis and evaluation of 18F-labeled indole-based analogs as highly selective sigma-2 receptor probes

Wang, L.; Ye, J.; Deuther-Conrad, W.; He, Y.; Zhang, J.; Steinbach, J.; Brust, P.; Jia, H.

Objectives: The sigma-2 (σ2) receptors are overexpressed in a wide variety of human and rodent tumor cells and play a pivotal role in cancer biology. Moreover, they showed an approximately 10-fold higher expression in proliferating tumor cells compared to that in quiescent tumor cells. And thus, they proved to be a unique receptor-based biomarker of cell proliferation in solid tumors. Herein we report the synthesis and evaluate of a series of indole-based analogs with 5,6-dimethoxyisoindoline or 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline moiety as highly selective σ2 receptor ligands.

Results and discussion: The newly synthesized indole-based analogs showed low nanomolar affinity for σ2 receptors (Ki2) = 1.79-5.23 nM ) and excellent subtype selectivity (Ki1)/Ki2) = 56-708 folds). The carbon chain length of the linker between the indole group and 5,6-dimethoxyisoindoline or 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline moiety displayed significant influence on the subtype selectivity. The compounds with a butyl linker exhibited highest subtype selectivity. We synthesized 2-(4-(4-(2-[18F]fluoroethoxy)-1H-indol-1-yl)butyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline and 1-(4-(5,6-dimethoxyisoindolin-2-yl)butyl)-4-(2-[18F]fluoroethoxy)-1H-indole. The log D values of the above radioligands are 2.17 ± 0.13 and 2.14 ± 0.02, respectively. The in vivo biological evaluations are in progress.

Conclusions: These findings suggest that 18F-labeled indole-based ligands warrant further evaluation as potential PET radiotracers for σ2 receptor imaging.

Acknowledgements: Supported by NSFC (21471019).

References:
[1] van Waarde A, et al. Curr Pharm Des, 2010, 16, 3519-3537.
[2] Megalizzi V, et al. Med Res Rev, 2012, 32, 410-427.
[3] Mach RH, et al. J Med Chem, 2013, 56, 7137-7160.

Keywords: F-18; sigma-2 receptors; indole-based analogs

  • Invited lecture (Conferences)
    RANC-2016 - International Conference on Radioanalytical and Nuclear Chemistry, 10.-15.04.2016, Budapest, Ungarn
  • Contribution to proceedings
    RANC-2016 - International Conference on Radioanalytical and Nuclear Chemistry, 10.-15.04.2016, Budapest, Ungarn
    Book of Abstracts, Budabest: Akadémiai Kiadó, 35

Permalink: https://www.hzdr.de/publications/Publ-22751
Publ.-Id: 22751


Exploring ice core drilling chips from a cold Alpine glacier for cosmogenic radionuclide (10Be) analysis

Zipf, L.; Merchel, S.; Bohleber, P.; Rugel, G.; Scharf, A.

Ice cores offer unique multi-proxy paleoclimate records, but provide only very limited sample material, which has to be carefully distributed for various proxy analyses. Beryllium-10, for example, is analysed in polar ice cores to investigate past changes of the geomagnetic field, solar activity, and the aerosol cycle, as well as to more accurately date the material. This paper explores the suitability of a drilling by-product, the so-called drilling chips, for 10Be-analysis. An ice core recently drilled at a cold Alpine glacier is used to directly compare 10Be-data from ice core samples with corresponding drilling chips. Both sample types have been spiked with 9Be-carrier and identically treated to chemically isolate beryllium. The resulting BeO has been investigated by accelerator mass spectrometry (AMS) for 10Be/9Be-ratios to calculate 10Be-concentrations in the ice. As a promising first result, four out of five sample-combinations (ice core and drilling chips) agree within 2-sigma uncertainty range. However, further studies are needed in order to fully demonstrate the potential of drilling chips for 10Be-analysis in alpine and shallow polar ice cores.

Keywords: 10Be; cosmogenic nuclide; accelerator mass spectrometry; ice core analysis

Permalink: https://www.hzdr.de/publications/Publ-22750
Publ.-Id: 22750


Felsenkeller shallow-underground accelerator laboratory for nuclear astrophysics (CGS conf.proc.)

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

Favored by the low background in underground laboratories, low-background accelerator-based experiments are an important tool to study nuclear reactions involving stable charged particles. This technique has been used for many years with great success at the 0.4 MV LUNA accelerator in the Gran Sasso laboratory in Italy, proteced from cosmic rays by 1400 m of rock. However, the nuclear reactions of helium and carbon burning and the neutron source reactions for the astrophysical s-process require higher beam energies than those available at LUNA. Also the study of solar fusion reactions necessitates new data at higher energies. As a result, in the present NuPECC long range plan for nuclear physics in Europe, the installation of one or more higher-energy underground accelerators is strongly recommended.
An intercomparison exercise has been carried out using the same HPGe detector in a typical nuclear astrophysics setup at several sites, including the Dresden Felsenkeller underground laboratory. It was found that its rock overburden of 45m rock, together with an active veto against the remaining muon flux, reduces the background to a level that is similar to the deep underground scenario.
Based on this finding, a used 5 MV pelletron tandem with 250 μA upcharge current and external sputter ion source has been obtained and transported to Dresden. Work on an additional radio-frequency ion source on the high voltage terminal is underway. The project is now fully funded. The installation of the accelerator in the Felsenkeller is expected for the near future. The status of the project and the planned access possibilities for external users will be reported.

Keywords: Nuclear Astrophysics; Underground laboratory; Hydrogen burning; Solar fusion; Helium burning; Carbon burning

  • Open Access Logo Contribution to proceedings
    Fifteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, 25.-29.08.2014, Dresden, Germany
    EPJ Web of Conferences: EDP Sciences, 03010
    DOI: 10.1051/epjconf/20159303010

Permalink: https://www.hzdr.de/publications/Publ-22749
Publ.-Id: 22749


Origin and geochemistry of agates in Permian volcanic rocks of the Sub-Erzgebirge basin, Saxony (Germany)

Götze, J.; Möckel, R.; Vennemann, T.; Müller, A.

Mineralogical and geochemical investigations of agates from Permian volcanic rocks of the Sub-Erzgebirge basin (Saxony, Germany) were made to constrain the genesis and characteristics of these spectacular forms of silica. Samples from the main agate occurrences of Chemnitz, Hohenstein-Ernstthal, St. Egidien and Zwickau were selected for detailed analyses.
The results of the study show that agate formation can be related to volcanic activity (Rochlitz ignimbrite) and the subsequent alteration of the volcanic rocks. Most agates originate from the infill of silica into cavities of lithophysae (high-temperature crystallization domains), which formed during cooling of welded ignimbrite. Agate formation temperatures of probably >150°C were calculated from fluid inclusion and oxygen isotope studies, which indicate that the mobilization and accumulation of silica started already during a late phase of or soon after the volcanic activity.
The trace-element composition of chalcedony and macro-crystalline quartz in agates is dif-ferent from that of quartz from magmatic or metamorphic rocks and pegmatites. Elements of the volcanic rock matrix (Al, Ca, Fe, Na, K) were released during the alteration processes and accumulated in the SiO2 matrix of the agates. Extraordinary high contents of Ge (>90 ppm), B (46 ppm) and U (>18 ppm) were also detected, which can exceed the Clark concentration and sometimes the element concentration in the surrounding host rocks. In addition, chondrite-normalized REE distribution patterns of the agates show strong negative Eu-anomalies, enriched HREE as well as tetrad effects. These patterns are different from the REE patterns of the volcanic host rocks and point to fractionation processes during agate formation. The specific geochemical features indicate interactions of the host rocks with heated meteoric water and volatile fluids, and transport of SiO2 and other elements both in aqueous solution and via stable fluorine (and chlorine) compounds such as SiF4, BF3, GeF4, and UO2F2.
The results of cathodoluminescence (CL) microscopy and spectroscopy revealed a microstructure of the agates that is similar for all occurrences. Characteristic features are irregular internal textures and sector zoning in quartz as well as luminescence colours and spectra, respectively, which are caused by a typical high defect density (oxygen vacancies, silanol groups). According to these results, the formation of agates can be explained by crystallization via an amorphous silica precursor under non-equilibrium conditions.

Keywords: Agate; Quartz; Permian volcanics; Saxony; Trace elements; Oxygen isotopes; Cathodoluminescence

Permalink: https://www.hzdr.de/publications/Publ-22748
Publ.-Id: 22748


Emergence of comparable covalency in isostructural cerium(IV)- and uranium(IV)-carbon multiple bonds

Gregson, M.; Lu, E.; Tuna, F.; Mcinnes, E. J. L.; Hennig, C.; Scheinost, A. C.; Mcmaster, J.; Lewis, W.; Blake, A. J.; Kerridge, A.; Liddle, S. T.

The chemical bonding of actinide and transition metal cations is known to exhibit variable levels of covalency, whereas that of the lanthanides is characterised as overwhelmingly ionic like alkali and alkaline earth metals. Here, we report a structural, spectroscopic, magnetic, and computational study of the iso-structural carbene complexes [M(BIPMTMS)(ODipp)2] [M = Ce (1), U (2), Th (3); BIPMTMS = C(PPh2NSiMe3)2; Dipp = C6H3-2,6-Pri 2]. In order to avoid the deficiencies of orbitalbased theoretical treatments we probed the bonding of 1-3 with a RASSCF density-based approach that explicitly treats the orbital energy near-degeneracy and overlap contributions to covalency. For these complexes unexpected similar levels of covalency are found for cerium(IV) and uranium(IV), whereas thorium(IV) is found to be more ionic. This trend is found in all computational methods employed and is reproduced in experimental covalency-driven exchange reactions of 1-3 with MCl4 salts (M = Ce, U, Th).

Keywords: cerium; bonding; covalency; XANES

Permalink: https://www.hzdr.de/publications/Publ-22747
Publ.-Id: 22747


Spatial distribution of FMISO in head and neck squamous cell carcinomas during radio-chemotherapy and its correlation to pattern of failure

Zschaeck, S.; Haase, R.; Abolmaali, N.; Perrin, R.; Stützer, K.; Appold, S.; Steinbach, J.; Kotzerke, J.; Zips, D.; Richter, C.; Gudziol, V.; Krause, M.; Zöphel, K.; Baumann, M.

Background. Tumour hypoxia can be measured by FMISO-PET and negatively impacts local tumour control in patients with head and neck squamous cell carcinoma (HNSCC) undergoing radiotherapy. The aim of this post hoc analysis of a prospective clinical trial was to investigate the spatial variability of FMISO hypoxic subvolumes during radio-chemotherapy and the co-localisation of these volumes with later recurrences as a basis for individualised dose prescription trials with dose escalation defined by FMISO-PET. Methods. Sequential FMISO scans of 12 (of 25) patients presenting residual hypoxia taken before (FMISOpre) and during (FMISOw1–FMISOw5) radio-chemotherapy were analysed regarding the stability of the FMISO subvolumes and, in case of local failure, their correlation to local relapse. Results. Consecutive FMISO-PET positive volumes could be classified as moderately stable with Dice conformity indices of 62% and 58% up to the second week of treatment. Substantial volumetric variation during treatment was observed, with more than 20% geographic miss in all patients and more than 40% in half of the patients. The localisation of the maximum standardised uptake value (SUVmax) differed with a mean distance of 7.0 mm and 13.5 mm between the pre-therapeutic and first or second FMISO-PET during treatment. A stable hypoxic consensual volume (i.e. overlap of pre-therapeutic FMISO and intra-treatment FMISO subvolumes up to week two, generated by different contouring methods) was determined for six patients with imaging information of local recurrence. Three of these six local recurrences were located within this consensual volume. Conclusions. Our data suggest that selective dose painting to hypoxic tumour subvolumes requires adaptation during treatment and sufficient margins. An alternative strategy is to escalate the dose to the gross tumour volume, accepting lesser escalation of dose outside hypoxic areas if indicated by constraints for organs at risk.

Permalink: https://www.hzdr.de/publications/Publ-22746
Publ.-Id: 22746


Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203] [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275] [276] [277] [278] [279] [280] [281] [282] [283] [284]