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35836 Publications

On the thermal decomposition of tert.-butyl hydroperoxide, its sensitivity to metals and its kinetics, studied by thermoanalytic methods.

Willms, T.; Kryk, H.; Oertel, J.; Hempel, C.; Hampel, U.; Knitt, F.

The decomposition of hydroperoxides like tert.-butyl hydroperoxide (TBHP) due to reactions with reactor materials (wall reactions) is an important issue in the frame of industrial processes and the analysis of such compounds. Because of the high surface-volume ratio such heterogeneous reactions are also especially important in case of thermo-analytical measurements. Therefore, the decomposition of TBHP has been studied for the first time extensively by Differential Scanning Calorimetry (DSC) using differently coated high pressure stainless steel crucibles (uncoated, gilded, silicon coated) and a medium pressure crucible. Furthermore, the interaction of such materials with TBHP has been measured for the first time by Thermal Activity Monitoring (TAM). The material of the gilded copper blowout disc turned out to be the reason for the very different DSC curves published in literature and had the highest influence compared to the crucible body material and the pressure. To protect the sample against the blowout disc, an aluminium foil has been placed below the blowout disc. This changed the shape of the DSC curve completely. It became more similar to that obtained with the medium pressure crucible. Furthermore, the reaction mechanism, kinetics and chemical aspects of the decomposition of TBHP at different conditions have been discussed and kinetics has been investigated for the first time by an overall evaluation of the DSC curves and a model free kinetics approach. Using the linear relationship between the kinetic activation parameters the published values are compared to those of the present work.

Keywords: t-butyl hydroperoxide; DSC; steel crucible; silcosteel®; gold; TAM

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Permalink: https://www.hzdr.de/publications/Publ-25788
Publ.-Id: 25788


The decomposition of tert.-butyl hydroperoxide studied by differential scanning calorimetry.

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

Due to the investigation the oxidation of isobutane to t-butyl hydroperoxide (TBHP), studied for the first time as a two-phase process in a micro reactor at high temperatures and pressures, the prevention of the decomposition of TBHP was crucial. The observed by-products t butyl per-oxide, tert.butanol, acetone, and methanol decreasing the selectivity and thus the TBHP yield are due to the thermal decomposition of TBHP, which is influenced by the wall effect to a large extend. Therefore, the decomposition of TBHP has been studied by Differential Scanning Calorimetry (DSC) at higher temperatures using for the first time different crucible types, pressure conditions, heating rates etc.. Aluminium (low pressure) crucibles, medium pressure crucibles and differently coated high pressure stainless steel crucibles (uncoated, gilded, silicon coated) have been utilized to show the influence of the crucible material as well as of the pressure on the DSC curve. It has been found that the material of the blowout disk has an important influence on the thermal decomposition behaviour. Therefore, within further DSC studies, the sample has been protected against the gilded copper blowout disk by aluminium foil in the crucible. Kinetics of the decomposition reactions has been investigated experimentally by evaluation of the DSC curves using an nth order approach and by a model free kinetics (MFK) approach.

Keywords: differential scanning calorimetry; t-butyl hydroperoxide; crucible type; material

  • Lecture (Conference)
    22. Kalorimetrietage Braunschweig, 07.-09.06.2017, Braunschweig, Deutschland
  • Contribution to proceedings
    22. Kalorimetrietage Braunschweig, 07.-09.06.2017, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25787
Publ.-Id: 25787


Oxidation of isobutane to TBHP – a chemical process with high energy saving potential.

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

Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen under two phase conditions at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction is investigated for the first time at supercritical conditions using DTBP as an initiator in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantage of micro reactors are the high surface – volume ratio for an efficient heat transfer, the related, improved – nearly inherent – safety and the resulting possibility to investigate unusual process windows, for instance within the explosive region of a reaction mixture using high oxygen concentrations. Besides two phase flow conditions, super¬critical conditions i.e. pressures above 40 bars and temperatures above 140°C are especially interesting because of the higher reaction rate and lacking mass transfer limitations. The reaction has been performed in both regimes at different conditions and the results compared. Furthermore, the influence of process parameters on the start-up time has been investigated. For all experiments, the selectivity and conversion of the reaction have been studied. Therefor, the reaction course is followed by sampling and analyzing the reaction by GC/MS and GC–TCD where analytical methods have been developed to detect a maximum of by-products and inter¬mediates.

Keywords: isobutane; oxidation; energy efficiency; t-butyl hydroperoxide; micro reactor

  • Poster
    Jahrestreffen Frankfurt I Jahrestreffen der ProcessNet-Fachgruppen Hochdruckverfahrenstechnik, Mikroverfahrenstechnik, Molekulare Modellierung, 08.-10.03.2017, Frankfurt, Deutschland
  • Contribution to proceedings
    Jahrestreffen Frankfurt I Jahrestreffen der ProcessNet-Fachgruppen Hochdruckverfahrenstechnik, Mikroverfahrenstechnik, Molekulare Modellierung, 08.-10.03.2017, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25786
Publ.-Id: 25786


Micro reactor experiments on the partial isobutane oxidation as a multiphase process - Comparison of t-butyl hydroperoxide and di-t-butyl peroxide as initiators.

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

Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decom-position of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction has been investigated for the first time as a Taylor-Flow process in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantages of micro reactors are the high surface – volume ratio for an efficient heat transfer and the improved, nearly inherent, safety. This permits to investigate yet unexplored process windows, for instance within the explosive region of a reaction mixture.
The reaction has been studied varying the molar ratio of the starting pro¬ducts, temperature, pressure, and initiator concentration using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments the selectivity of the reaction products and the conversion of the reaction have been studied. The reaction course has been followed by sampling and analyzing the reaction by GC/MS where a new analytical method has been developed. The use of TBHP as initiator increases the selectivity of the reaction for the target product TBHP. The beneficial effect on the TBHP selectivity compared to DTBP might be explained on the basis of the suitable thermochemical properties of TBHP. TBHP seems to give a better selectivity since at high temperatures as they are necessary for the initiator effect of DTBP the formation of propanone already becomes important which favours the decomposition of TBHP.

Keywords: isobutane; oxidation; t-butyl hydroperoxide; t-butyl peroxide; micro reactor

  • Poster
    Jahrestreffen Reaktionstechnik 2017, 22.-24.05.2017, Würzburg, Deutschland
  • Contribution to proceedings
    Jahrestreffen Reaktionstechnik 2017, 22.-24.05.2017, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25785
Publ.-Id: 25785


TACN Ligands – A journey through radiopharmaceutical applications

Stephan, H.; Graham, B.; Spiccia, L.

The design of tailor-made bifunctional copper radionuclide-complexing agents for nuclear medical application as well as acquisition of reliable information about the biodistribution of different materials represents an intensive and rapidly developing field of research. In this context, the tridentate macrocycle 1,4,7-triazacyclononane (TACN) is of special interest since it forms stable complexes with Cu(II) and the ligand structure can be easily modified. The introduction of further donor groups on the ligand scaffold, such as pyridine units, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. TACN ligands containing one or two pendant 2-picolyl arms prefer the formation of square-pyramidal coordination geometry with Cu(II). A hexadentate ligand with two picoline coordination groups as well as a carboxylic functionality, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (DMPTACN-COOH), enforces a six-coordinate, distorted octahedral structure. DMPTACN-based ligands rapidly chelate copper(II) radionuclides under ambient conditions and the resulting complexes show high in vivo stability. The carboxylic acid group in DMPTACN-COOH allows for the ready introduction of linker groups, such as maleimide or isothiocyanate, thereby facilitating coupling of targeting molecules and bio(nano)materials.

Examples of target-specific peptides and bio(nano)materials equipped with DMPTACN ligands for labeling with 64Cu as an ideal positron emitter are discussed. This enables tumor imaging and the biodistribution of the materials to be studied over a period of days via positron emission tomography (PET).

  • Invited lecture (Conferences)
    6th Asian Conference on Coordination Chemistry, 24.-28.07.2017, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-25784
Publ.-Id: 25784


MicroTCA.4-based LLRF for the superconducting CW Linac ELBE – Status and Outlook

Kuntzsch, M.; Steinbrück, R.; Schurig, R.; Hierholzer, M.; Killenberg, M.; Schmidt, C.; Gümüs, C.; Butkowski, L.; Hoffmann, M.; Iatrou, C.; Rahm, J.; Rutkowski, I.; Grzegrzółka, M.

The superconducting linear accelerator ELBE is operated in continuous wave operation (CW). The analogue LLRF system, used since 2001, is going to be replaced by a digital solution based on µTCA.4. The new system enables a higher flexibility, better performance and more advanced diagnostics. The contribution will show the performance of the system at ELBE, the hardware and the software structure.
Further it will summarize the last steps to bring it into full user operation and give an outlook to the envisioned beam-based feedback system that will take advantage of the capabilities of the digital LLRF system.

Keywords: ELBE LLRF Feedback MicroTCA µTCA MTCA

  • Poster
    Low Level Radio Frequency Workshop 2017, 16.-19.10.2017, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-25783
Publ.-Id: 25783


MicroTCA.4-based LLRF for CW operation at ELBE – Status and Outlook

Kuntzsch, M.; Steinbrück, R.; Hierholzer, M.; Killenberg, M.; Schmidt, C.; Butkowski, L.; Hoffmann, M.; Iatrou, C.; Rahm, J.; Rutkowski, I.; Grzegrzółka, M.

The superconducting linear accelerator ELBE is operated in continuous wave operation (CW). The analogue LLRF system, used since 2001, is going to be replaced by a digital solution based on µTCA.4. The new system enables a higher flexibility, better performance and more advanced diagnostics. The contribution will show the performance of the system at ELBE, the hardware and the software structure.
Further it will summarize the last steps to bring it into full user operation and give an outlook to the envisioned beam-based feedback system that will take advantage of the capabilities of the digital LLRF system.

Keywords: ELBE LLRF Feedbacks MicroTCA µTCA MTCA

  • Poster
    International Beam Instrumentation Conference, 20.-24.08.2017, Grand Rapids, USA
  • Open Access Logo Contribution to proceedings
    International Beam Instrumentation Conference, 20.-24.08.2017, Grand Rapids, USA
    MicroTCA.4-based LLRF for CW operation at ELBE – Status and Outlook

Permalink: https://www.hzdr.de/publications/Publ-25782
Publ.-Id: 25782


Optical Synchronization and Electron Bunch Diagnostic at ELBE

Kuntzsch, M.

The talk summarizes the activities at ELBE in the fields of optical synchronization and electron bunch diagnostic.

Keywords: Optical Synchronization Diagnostic ELBE

  • Invited lecture (Conferences)
    Graduiertenkolleg "Accelence", 06.07.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25781
Publ.-Id: 25781


Active tumor pretargeting using peptide nucleic acid bioconjugates as complementary system

Zarschler, K.

The ability of early-stage diagnosis of tumor malignancies and personalized treatment ultimately relies on the availability of highly tumor-affine compounds with purposeful pharmacological profile. In this regard, monoclonal antibodies (mAbs) are particularly valuable as these molecules bind to tumor-associated epitopes with high specificity and affinity. The conventional concept of directly radiolabeled tumor-specific mAbs for radioimmunodetection (RID) and -therapy (RIT) has certainly several drawbacks, most prominently the prolonged radiation exposure of healthy tissues and organs. Fortunately, however, several of these shortcomings can be eliminated by implementing the pretargeting strategy allowing for the rational use of long circulating, high-affinity mAbs for both non-invasive cancer RID and RIT [1].
This keynote lecture will give a general overview about the pre-targeting strategy and present the different approaches for specific radionuclide delivery to pretargeted tissues. Furthermore, the different in vivo recognition systems will be introduced, with particular emphasis on synthetic complementary oligonucleotides such as peptide nucleic acid (PNA) derivatives. Regarding the latter, their synthesis as well as characterization will be described and, finally, an active tumor pretargeting approach using PNA bioconjugates will be exemplified [2].

References
[1] M. Patra, K. Zarschler, H.-J. Pietzsch, H. Stephan and G. Gasser, Chem Soc Rev 45 (2016) 6415-6431.
[2] A. Leonidova, C. Foerster, K. Zarschler, M. Schubert, H.-J. Pietzsch, J. Steinbach, R. Bergmann, N. Metzler-Nolte, H. Stephan, and G. Gasser, Chem Sci 6 (2015) 5601-5616.

  • Invited lecture (Conferences)
    2nd Internacional Caparica Christmas Congress on Translational Chemistry 2017 - IC3TC, 04.-07.12.2017, Caparica, Portugal

Permalink: https://www.hzdr.de/publications/Publ-25780
Publ.-Id: 25780


Diagnostic Tumor Imaging Using Renally Excretable Nanoparticles: Focus on Active and Passive Targeting

Zarschler, K.; Pant, K.; Neuber, C.; Pufe, J.; Steinbach, J.; Haag, R.; Pietzsch, J.; Stephan, H.

Introduction
Depending on their size, shape and surface functionalities, nanoparticles can passively extravasate and accumulate in the tumor tissue through the enhanced permeability and retention (EPR) effect. Being an accumulative process, this effect favors nanoparticles with long blood retention time. Renally excretable, ultrasmall nanoparticles with short blood half-lives are therefore less prone to passive tumor targeting as they rapidly diffuse back to the vasculature and re-enter the systemic circulation, which results in only transient intratumoral presence without substantial retention. To prevent their rapid efflux from malignant tissues by increasing the interactions between nanoparticles and tumor cells as well as by improving cellular nanoparticle uptake, the strategy of active or ligand-mediated targeting is pursued. Here, we describe the development of renally excretable dendritic polyglycerols (dPGs) functionalized with different targeting units to differentiate between active and passive tumor targeting.

Methods
Fluorescent dye labels for optical imaging and small camelid single-domain antibodies (sdAbs) as targeting units - both equipped with maleimide functionalities - were simultaneously attached in a one-pot reaction to thiol groups of the dPGs. As the presented work focusses on the epidermal growth factor receptor (EGFR) acting as a model receptor, an EGFR-specific sdAb was attached to the dPGs to obtain an active targeting probe. In parallel, a probe with similar surface characteristics but a nonspecific sdAb (passive targeting) was synthesized. Both conjugates were purified using affinity chromatography, which selectively separates the sdAb-conjugated dPGs.

Results
In vitro binding studies on different human epithelial cancer cell lines using dye-labeled sdAb-conjugated dPGs showed a high specificity, co-localization and a receptor-mediated cellular uptake of the EGFR-specific probes. Optical imaging studies using murine xenografts revealed a substantial accumulation of the EGFR-specific probes in comparison to its nonspecific counterparts and a minimum off-target accumulation of both conjugates.

Discussion and Conclusion
The direct comparison of specific and nonspecific probes with similar surface characteristics allows the straight-forward preclinical discrimination between active and potential passive tumor targeting of renally excretable nanoparticles in small animal models. Furthermore, it provides important information on the extent to which ligand-mediated targeting contributes to total nanoparticle accumulation in malignant and normal tissues.

  • Lecture (Conference)
    EANM'17 - Annual Congress of the European Association of Nuclear Medicine, 21.-25.10.2017, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-25779
Publ.-Id: 25779


DFO* - An Improved Chelating System for 89Zr-Immuno-PET Applications

Briand, M.; Zarschler, K.; Vugts, D.; Stephan, H.; Steinbach, J.; Gasser, G.; Mindt, T.

Objectives
The potential of 89Zr-labelled antibodies as diagnostic probes for 89Zr-immuno-PET has been demonstrated by a number of clinical trials.[1] The only chelator used thus far in the clinic is the siderophore desferrioxamine (DFO). However, DFO does not satisfy the preferred ocatadentate coordination of zirconium-89, which results in vivo into unspecific uptake of the radiometal in, e.g., the bones. This can interfere with the detection of bone metastases and leads to additional radiation dose to non-targeted tissue.
We have previously reported the development of an extended, octadentate version of DFO, termed DFO*,[2] which provides complexes with [89Zr]Zr4+ of remarkably increased stability in vitro and in vivo. [2, 3] DFO* and derivatives thereof already fulfil a number of prerequisites to become a new standard chelator for zirconium-89; however, its solubility could be improved to facilitate further its application in conjugation chemistry. We here wish to report our efforts in developing novel DFO* derivatives which display an improved water solubility.

Methods
Based on the DFO* scaffold, new derivatives containing pharmacological modifiers to improve the water solubility were synthesized. In addition, different functional groups for bioconjugation chemistry were included. LogP values of the novel bifunctional chelating agents were determined by HPLC. First bioconjugations and radiolabelling experiments with 89Zr were performed according to published procedures. [1,3]

Results
All new derivatives exhibited an increased hydrophilicity and thus, enhanced water solubility in comparison to the original DFO* (as well as DFO) system. Preliminary results on their reactivity in bioconjugations, capability of 89Zr-complexation, and stability of radiometal complexes will be reported.

Conclusions
Structural modifications provided novel derivatives of DFO* with improved water solubility which could facilitate their application in bioconjugation chemistry for the 89Zr-labelling of delicate proteins under aqueous (e.g., organic solvent free) reaction conditions.

Acknowledgements
This work is supported by the Swiss National Sciences Foundation (grant N° 205321–157216).

References
[1] G.A.M.S. Van Dongen, M.C. Huisman, R. Boellaard et al. Q. J. Nucl. Med. Mol. Imaging 2015, 59, 18-38
[2] M. Patra, A. Bauman, C. Mari et al. Chem. Commun. 2014, 50, 11523-11525
[3] D. Vugts, C. Klaver, C. Sewing et al. Eur. J. Nucl. Med. Mol. Im. 2016, doi:10.1007/s00259-016-3499-x S394: Poster 22nd International Symposium on Radiopharmaceutical Sciences

  • Poster
    22nd International Symposium on Radiopharmaceutical Sciences (ISRS 2017), 14.-19.05.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25778
Publ.-Id: 25778


Kombinierte externe und interne Bestrahlung von Tumoren: präklinischer Nachweis des kurativen Potenzials

Pietzsch, H.-J.; Dietrich, A.; Andreeff, M.; Koi, L.; Schreiner, L.; Bergmann, R.; Löck, S.; Sihver, W.; Faulhaber, D.; Kotzerke, J.; Baumann, M.; Krause, M.; Steinbach, J.

Die Therapie von Tumorerkrankungen gründet sich stadienabhängig auf die drei Säulen Chirurgie, Strahlen- und Chemotherapie. Grundprinzip der Strahlentherapie ist die gezielte Einwirkung von ionisierender Strahlung auf erkranktes Gewebe, um die Zerstörung maligner Tumorzellen zu erreichen. Neben der klassischen externen Strahlentherapie unter Verwendung von Photonen hat sich die Endoradionuklidtherapie durch Entwicklung geeigneter Targetingvektoren in den letzten Jahren zu einer zunehmend angewandten Therapieform entwickelt. Insbesondere die Radioimmuntherapie hat das Potential, auch (Mikro-) Metastasen zu zerstören. Die Kombination von externer und interner Strahlentherapie ist eine vielversprechende Behandlungsstrategie, da sie unter Schonung gesunden Gewebes potenziell die Vorteile beider Modalitäten kombiniert.

Ziel dieses Projektes war es, im Tiermodell zu überprüfen, ob eine interne Bestrahlung mit Hilfe des anti-EGFR-gerichteten, 90Y-markierten Antikörpers Cetuximab (C225) eine lokale Tumorkontrolle nach vorhergehender externer Bestrahlung bei verringerter Dosis ermöglicht.

Cetuximab wurde mit dem bifunktionellen Chelator p-SCN-Bn-CHX-A‘‘-DTPA funktionalisiert und nach 90Y-Markierung in einem Kopf-Hals-Plattenepithelkarzinom-Xenograftmodell (FaDu) eingesetzt. Die externe Bestrahlung erfolgte nach klinisch relevanten Protokollen mit 30 Bestrahlungsfraktionen (fx) verteilt über 6 Wochen. Nach 10 Fraktionen wurden jeweils 2,3 MBq des 90Y-markierten Cetuximab-Konjugats injiziert.
Die kombinierte Anwendung von externer und interner Bestrahlung erhöhte massiv die Wahrscheinlichtkeit einer lokalen Tumorkontrolle im Vergleich zur externen Bestrahlung allein oder in Kombination mit unmarkiertem Cetuximab.
In der Gruppe mit der niedrigsten externen Strahlendosis (1 Gy/Fraktion, Gesamtdosis = 30 Gy,) plus 90Y-Cetuximab wurden alle Tumore noch permanent kontrolliert (Beobachtungszeitraum = 120 d). Im Gegensatz dazu betrug die gesamte externe Strahlendosis, die notwendig ist um 50% der Tumore ohne zusätzliche Gabe von 90Y-Cetuximab zu heilen, 63,9 Gy (58,7, 73,9).

Unsere Ergebnisse zeigen, dass die kombinierte Anwendung von radiomarkierten Therapeutika nach fraktionierter externer Strahlentherapie ein bemerkenswertes Potenzial hat, das Behandlungsergebnis zu verbessern. Eine effiziente Aufnahme des Y-90-markierten Cetuximab-Konjugates ist die Voraussetzung für den Erfolg der kombinierten Strahlentherapie.

  • Lecture (Conference)
    Wissenschaftsforum Chemie, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25777
Publ.-Id: 25777


Recovery of iron and lead from a secondary lead smelter matte by magnetic separation

Kukurugya, F.; Rahfeld, A.; Möckel, R.; Nielsen, P.; Horckmans, L.; Spooren, J.; Broos, K.

A secondary Pb smelter matte containing ca. 50 wt.% Fe (as FeS, Fe3O4, FeO and metallic Fe), shows good potential for being used as a secondary Fe source. However, requirements for Fe ore are: Fe content >60% and absence of sulphide phases. Therefore, further pre-treatment steps are necessary to increase the Fe content in the matte. Dry low intensity, wet low intensity and wet high intensity magnetic separation experiments were performed on different particle size fractions of the matte. Mineral liberation analysis (MLA) was performed to explain different behaviour of Pb in the different size fractions during magnetic separation. Moreover, oxidizing roasting at 600°C was performed to transform FeS to Fe2O3. Results show that by combining low and high intensity magnetic separation and oxidizing roasting, material containing up to 61 wt% Fe (as oxide) can be recovered in the magnetic fraction representing circa 50% of the initial weigth of the sample.

Keywords: matte; MLA; LIMS; WLIMS; WHIMS; recycling

Permalink: https://www.hzdr.de/publications/Publ-25776
Publ.-Id: 25776


Upgrade of the Superconducting CW Linac ELBE From Klystrons zu Silid State Amplifiers

Büttig, H.

Overview on the status of ELBE and the activities to upgrade ELBE within the HSQ project.

Keywords: Solid state RF power amplifiers; Resonant ring

  • Invited lecture (Conferences)
    Graduiertenkolleg Seminar Uni Mainz und Uni Darmstadt, 06.07.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25775
Publ.-Id: 25775


Polyethyleneimine Methylphosphonate : towards the design of a new class of macromolecular actinide chelating agent in case of human exposition

Lahrouch, F.; Sofronov, O.; Creff, G.; Rossberg, A.; Hennig, C.; Den Auwer, C.; Di Giorgio, C.

The use of uranium and to a minor extent plutonium as fuel for nuclear energy production or as components in military applications is under increasing public pressure. Uranium is weakly radioactive in its natural isotopy but its chemical toxicity, combined with its large scale industrial utilization, makes it a source of concern in terms of health impact for workers and possibly the general population. Plutonium is an artificial element that exhibits both chemical and radiological toxicities.
So far, uranium (under its form uranyl, U(VI)) or plutonium (as Pu(IV)) decorporation or protecting strategies based on molecular design have been of limited efficiency to remove the actinide once incorporated after human exposure. In all cases, after human exposure, plutonium and uranium are retained in main target organs (liver, kidneys) as well as skeleton although they exhibit differences in their biodistribution. Polymers could represent an alternative strategy as their tropism for specific target organs has been reported. We recently reported a methylcarboxylated polyethyleneimine (PEIMC) as a potential uranium decorporation agent. In this report, we extend our work and report on the ability of methylphosphonated polyethyleneimine (PEI-MP) to act as a new class of uranyl and plutonium chelating agent. As a first step, thorium (Th(IV)) was used as a chemical surrogate of plutonium because of the difficulty of handling the latter in the laboratory. For both cations, U(VI) and Th(IV), the uptake curve of PEI-MP was recorded. The functionalized PEI-MP exhibits a maximum loading capacity comprised of between 0.56 and 0.80 mg of uranium (elemental) and 0.15 - .20 mg of thorium (elemental) per milligram of PEI-MP. Complexation sites of U(VI) and Th(IV) in model conditions close to physiological pH were then characterized with a combination of Fourier transformed Infra Red (FT-IR) and Extended X-Ray Absorption Fine Structure (EXAFS). Although both cations exhibit different coordination modes, similar structural parameters with phosphonate functions were obtained. For example, the coordination sites are composed of fully monodentate phosphonate functions of the polymer chains.

Keywords: Polyethyleneimine Methylphosphonate; macromolecular actinide chelating agent; FT-IR; EXAFS; uranium; thorium

Permalink: https://www.hzdr.de/publications/Publ-25774
Publ.-Id: 25774


Structural characterization of Am(III) and Pu(III)-DOTA complexes

Audras, M.; Berthon, L.; Berthon, C.; Guillaumont, D.; Dumas, T.; Illy, M. C.; Martin, N.; Zilbermann, I.; Ben-Eliyahu, Y.; Moissev, Y.; Bettelheim, A.; Camelli, S.; Hennig, C.; Moisy, P.

The complexation of DOTA ligand (1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid) with two trivalent actinides (Am3+ and Pu3+) was investigated by UV-visible spectrophotometry, Nuclear Magnetic Resonance (NMR) spectroscopy and extended X-ray absorption fine structure (EXAFS) in conjunction with computational methods. The complexation process of these two cations is similar to what has been previously observed with lanthanides(III) of similar ionic radius. The complexation takes places in different steps and ends up with the formation of a (1:1) complex [(An(III)DOTA)(H2O)]- where the cation is bonded to the nitrogen atoms of the ring, the four carboxylate arms and a water molecule is completing the coordination sphere. Nevertheless, the formation of An(III)-DOTA complexes is faster than the Ln(III)-DOTA systems of equivalent ionic radius. Furthermore, it is found that An-N distances are slightly shorter than Ln-N distances. Theoretical calculations have shown that the slightly higher affinity of DOTA toward Am over Nd is correlated with slightly enhanced Ligand-to-metal charge donation arising from oxygen and nitrogen atoms.

Keywords: DOTA; UV-visible spectrophotometry; NMR; EXAFS; DFT calculations; Americium; Plutonium; lanthanides

Permalink: https://www.hzdr.de/publications/Publ-25773
Publ.-Id: 25773


Purely Antiferromagnetic Magnetoelectric Random Access Memory

Kosub, T.

Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency1. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM)2 that offers a remarkable 50 fold reduction of the writing threshold compared to state-of-the-art ferromagnet-based counterparts2,3, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature [Figure 1], The basics of RAM operation - writing, storage and reading information - are demonstrated repeatedly. Furthermore, the all-electric writing and read out interfaces can be harnessed for in-depth studies of the magnetoelectric selection processes in these thin film elements, which turn out to be markedly deviant from the theory of the linear magnetoelectric effect.

While omitting the ferromagnet enables the large improvement in the writing threshold over conventional exchange biased MERAM2,3, it also eliminates all possibilities for conventional magnetoresistive read out, such as the AMR/GMR/TMR effects. Thus, a key aspect of the AF-MERAM functionality is its new all-electric read out of the pure Hall resistance4. This method is both ultra-sensitive to tiny net magnetization in metallic antiferromagnets and to boundary magnetism between nonmagnetic metals and magnetic insulators, suggesting its considerable applicability to the growing fields of antiferromagnetic spintronics and insulator spintronics.

Access to the pure Hall resistance is enabled by a new electric measurement scheme called Resistance Tensormetry, which determines electrical resistance not as a scalar quantity peculiar to the used measurement layout but instead as a tensor quantity including diagonal and off-diagonal (Hall) components. Since electrical resistance is one of the most crucial material properties for both science and technology, the more comprehensive view provided by resistance tensormetry is highly relevant for emergent topics and materials. Via µΩ level sensitivity and tensor resolution, previously unattainable figures are now open to experimental scrutiny.

1. Matsukura, F., Tokura, Y. & Ohno, H., Nat. Nano. 10, 209–220 (2015).
2. Kosub, T. et al., Nat. Commun. 7, 13985 (2017).
3. He, X. et al., Nat. Mater. 9, 579–585 (2010).
4. Kosub, T., Kopte, M., Radu, F., Schmidt, O. G. & Makarov, D., Phys. Rev. Lett. 115, 097201 (2015).

  • Invited lecture (Conferences)
    Spin X Seminar Mainz/Kaiserslautern, 08.06.2017, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25772
Publ.-Id: 25772


Biasing in MC transport calculations

Müller, S. E.

The method of biasing in radiation transport simulations is described.

Keywords: Radiation transport; variance reduction; biasing; simulation

  • Lecture (others)
    Mu2e software and simulations workshop, 21.06.2017, Batavia, USA

Permalink: https://www.hzdr.de/publications/Publ-25771
Publ.-Id: 25771


The use of FLUKA in the Mu2e experiment

Müller, S. E.

The use of FLUKA in the mu2e experiment

Keywords: FLUKA; mu2e

  • Lecture (others)
    Mu2e Sotware and Simulation Meeting, 07.06.2017, Batavia, USA

Permalink: https://www.hzdr.de/publications/Publ-25770
Publ.-Id: 25770


LaFeOxNy perovskite thin films: Nitrogen location and its effect on morphological, optical and structural properties

Haye, E.; Bruyère, S.; André, E.; Boulet, P.; Barrat, S.; Capon, F.; Miska, P.; Migot, S.; Carteret, C.; Coustel, R.; Gendarme, C.; Munnik, F.

This paper reports on the first study of chemical, optical, and structural properties of lanthanum ferrite oxynitride thin films deposited by reactive magnetron sputtering. Thin films were deposited in a Ar/O2/N2 mixture as reactive plasma, from two elemental La and Fe targets, at room and high temperature (25 and 800°C). Films deposited at room temperature are amorphous and have been flash annealed to crystallize the perovskite. Oxynitride properties were investigated and compared to oxide films deposited in Ar/O2 gas mixture. All oxide and oxynitride films present an orthorhombic structure. However, nitrogen doping limited to 1-1.5% leads to lattice expansion (4%), bandgap narrowing, a lower electrical resistivity in range [25-350°C] , and modification of Infrared and Raman spectra. Electron Energy Loss Spectroscopy measurements clearly show the presence of two nitrogen sites with an “active” intra-granular nitrogen associated to an enhancement of the physical properties.

Keywords: Oxynitride perovskite; Thin film; LaFeO3; Nitrogen doping

Permalink: https://www.hzdr.de/publications/Publ-25769
Publ.-Id: 25769


Preliminary combination of the KLOE08, KLOE10 KLOE12 ISR measurements

Keshavarzi, A.; Müller, S. E.; Teubner, T.; Venanzoni, G.

Preliminary combination of the KLOE08, KLOE10 KLOE12 ISR measurements

Keywords: KLOE; g-2; hadronic contribution

  • Invited lecture (Conferences)
    First Workshop of the muon g-2 Theory Initiative, 04.06.2017, St. Charles, USA

Permalink: https://www.hzdr.de/publications/Publ-25768
Publ.-Id: 25768


Irradiation study of UV Silicon Photomultipliers for the Mu2e calorimeter

Baccaro, S.; Cemmi, A.; Cordelli, M.; Diociaiuti, E.; Donghia, R.; Ferrari, A.; Giovannella, S.; Loreti, S.; Miscetti, S.; Müller, S.; Pillon, M.; Sarra, I.

The Mu2e calorimeter is composed of 1400 un-doped CsI crystals, coupled to large area UV extended Silicon Photomultipliers (SiPMs), arranged in two annular disks. This calorimeter has to provide precise information on energy, timing and position resolutions. It should also be fast enough to handle the high rate background and it must operate and survive in the high radiation environment. Simulation studies estimated that, in the highest irradiated regions, each photo-sensor will absorb a dose of 20 krad and will be exposed to a neutron fluency of 5.5E11 n(1MeV)/cm2 in three years of running, with a safety factor of 3 included. At the end of 2015, we have concluded an irradiation campaign at the Frascati Neutron Generator (FNG, Frascati, Italy) measuring the response of two different 16 array models from Hamamatsu, which differ for the protection windows and a SiPM from FBK. In 2016, we have carried out two additional irradiation campaigns with neutrons and photons at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR, Dresden, Germany) and at the Calliope gamma irradiation facility at ENEA-Casaccia, respectively. A negligible increment of the leakage current and no gain change have been observed with the dose irradiation. On the other hand, at the end of the neutron irradiation, the gain does not show large changes whilst the leakage current increases by around a factor of 2000. In these conditions, the too high leakage current makes problematic to bias the SiPMs, thus requiring to cool them down to a running temperature of ~0 C.

Keywords: Calorimeters; Photon detectors for UV; EMCCDs; EBCCDs; CCDs; G-APDs; Si-PMTs; APDs; PIN diodes; visible and IR photons (solid-state)

  • Lecture (Conference)
    14th Topical Seminar on Innovative Particle and Radiation Detectors, 03.-06.10.2016, Siena, Italy
  • Open Access Logo Contribution to proceedings
    14th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD16), 03.-06.10.2016, Siena, Italy
    Irradiation study of UV Silicon Photomultipliers for the Mu2e calorimeter: Journal of Instrumentation 12 (2017), IOP Pub.
    DOI: 10.1088/1748-0221/12/02/C02022

Permalink: https://www.hzdr.de/publications/Publ-25767
Publ.-Id: 25767


Measurement techniques for liquid metals

Ratajczak, M.; Hernández, D.; Richter, T.; Otte, D.; Buchenau, D.; Krauter, N.; Wondrak, T.

The measurement of flow properties of liquid metals, such as flow rate, flow structure and gas distribution, is a challenging task due to the opaqueness, the high temperatures (e. g. 1500 ◦ C for liquid steel or liquid silicon) and the corrosiveness of those fluids. In this paper a short review about the recent developments of measurement techniques in the framework of the Helmholtz Alliance Liquid Metal Technologies (LIMTECH) is presented which focuses on the development of contactless inductive measurement techniques exploiting the high electrical conductivity of those melts. These measurement techniques include the contactless inductive flow tomography (CIFT), which is able to reconstruct the mean three-dimensional velocity structure in liquid melts, local Lorentz force velocimetry (local LFV), which enables the local assessment of flows close to the wall, and inductive methods for bubble detection, which are based on mutual inductance tomography (MIT). Additionally, a short overview of contactless inductive flow rate measurement techniques is given. Furthermore, an ultrasound technique called ultrasound transit-time technique (UTTT) will be presented which enables the measurement of position and size of bubbles in large vessels.

Permalink: https://www.hzdr.de/publications/Publ-25766
Publ.-Id: 25766


Energy Transfer Kinetics in Photosynthesis as an Inspiration for Improving Organic Solar Cells

Nganou, C.; Lackner, G.; Teschome, B.; Deen, M. J.; Adir, N.; Pouhe, D.; Lupascu, D. C.; Mkandawire, M.

Clues to designing highly efficient organic solar cells may lie in understanding the architecture of light-harvesting systems and exciton energy transfer (EET) processes in very efficient photosynthetic organisms. Here, we compare the kinetics of excitation energy tunnelling from the intact phycobilisome (PBS) light-harvesting antenna system to the reaction center in photosystem II in intact cells of the cyanobacterium Acaryochloris marina with the charge transfer after conversion of photons into photocurrent in vertically aligned carbon nanotube (va-CNT) organic solar cells with poly(3-hexyl)thiophene (P3HT) as the pigment. We find that the kinetics in electron hole creation following excitation at 600 nm in both PBS and va-CNT solar cells to be 450 and 500 fs, respectively. The EET process has a 3 and 14 ps pathway in the PBS, while in va-CNT solar cell devices, the charge trapping in the CNT takes 11 and 258 ps. We show that the main hindrance to efficiency of va-CNT organic solar cells is the slow migration of the charges after exciton formation.

Keywords: Acaryochloris marina; carbon nanotubes; chromophore; exciton; photosynthesis; photovoltaic; polarons; solar energy conversion

Permalink: https://www.hzdr.de/publications/Publ-25765
Publ.-Id: 25765


First application of the Oslo method in inverse kinematics - Nuclear level densities and gamma-ray strength functions of 87Kr

Ingeberg, V. W.; Siem, S.; Wiedeking, M.; Sieja, K.; Zeiser, F.; Bleuel, D. L.; Brits, C. P.; Bucher, D. T.; Dinoko, T. S.; Easton, J. L.; Görgen, A.; Jones, P.; Kheswa, B. V.; Khumalo, N. A.; Larsen, A. C.; Lawrie, E. A.; Lawrie, J. J.; Majola, S. N. T.; Malatji, K. L.; Makhathini, L.; Maqabuka, B.; Negi, D.; Noncolela, S. P.; Papka, P.; Sahin, E.; Schwengner, R.; Tveten, G. M.; Zikhali, B. R.

A novel technique for extracting the gamma-ray strength function (SF) and nuclear level density (NLD) from inverse kinematics experiments is presented, which allows for measurements of these properties, across a vast range of previously inaccessible nuclei. Proton-gamma coincidence events from the d(86Kr, p)87Kr reaction were measured at iThemba LABS and the SF and NLD in 87 Kr obtained with the Oslo Method.The SF and NLD are important parameters in Hauser-Feshbach calculations to constrain (n,gamma) cross sections of nuclei for which these cannot be measured directly. The extracted SF and NLD are used as input in Hauser-Feshbach calculations to constrain the 86Kr(n,gamma)87Kr cross section which is important for the 87Rb production in the s-process. The nature of the low-energy region of the SF is explored through comparison to shell model calculations with the LNPS-SDG interaction.

Keywords: Nuclear structure; nuclear reactions; (d; p) recation; inverse kinematics; gamma-ray strength function; level density; shell model; Hauser-Feshbach model; s-process

Permalink: https://www.hzdr.de/publications/Publ-25764
Publ.-Id: 25764


Single bubble rise in GaInSn in a horizontal magnetic field

Richter, T.; Keplinger, O.; Shevchenko, N.; Wondrak, T.; Eckert, K.; Eckert, S.; Odenbach, S.

The rise of single gas bubbles of moderate size in a liquid metal was studied in a flat container filled with the eutectic alloy GaInSn. The bubble motion is affected by a homogeneous horizontal magnetic field which is perpendicular to the width side of the fluid container. Measurements of the bubble trajectory, bubble velocity and deformation were performed by means of a combination of ultrasound transit time technique and X-ray radiography. In the hydrodynamic case without a magnetic field, the bubbles show the typical zig-zag movement whose attenuation can be observed for sufficiently high magnetic fields of B > 270 mT. The bubble trajectory becomes straight at a field strength of about 500 mT. A damping of the zig-zag path does not result in case of small magnetic fields applied. In this parameter range, even an increase of the amplitude of the lateral path oscillation is observed. Furthermore, this study revealed a discontinuity in the bubble path, which is called as ”initial path instability” on the basis of its occurrence in the early stage of the bubble rise shortly after the bubble injection. This instability is characterized by an extreme inclination of the ellipsoidal bubble which often leads to a bubble “somersault”. This instability is suppressed by a suffciently high enough magnetic field. The reason for this instability and the magnetic field effect thereon are qualitatively discussed.

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Permalink: https://www.hzdr.de/publications/Publ-25763
Publ.-Id: 25763


A Review of Surfactant Role in Soil Clogging Processes at Wastewater Exfiltration Locations in Sewers

Nikpay, M.; Krebs, P.; Ellis, B.

Wastewater contains significant sources of pollutants and contaminants. often the failure of a pipe, inadequate sealing or corrupt pipe-connections cause the loss of raw sewage, which percolates into the nearby soil. As a consequence, a colmation layer in conjunction with soil clogging is developing, which regulates the exfiltration rate. Recently, literature has emerged that offers findings about the effects of wastewater surfactants on the change of physical properties of the soil. A survey of published literature in this field provides information highlighting the influential mechanisms of surfactants in soil clogging through physical, chemical and biological processes. Therefore, to provide a comprehensive approach, this review describes the adsorption mechanisms of surfactants on organic and inorganic particles, at gas-bubbles and at biomass.
We also provided our own input to the description of the adsorption of surfactants at fluid/fluid and fluid/solid interfaces in porous media associated with the clogging process.

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Permalink: https://www.hzdr.de/publications/Publ-25762
Publ.-Id: 25762


Liquid metal based magnetic cooling: velocity measurements

Lei, Z.; Raebiger, D.; Eckert, S.; Eckert, K.

Heat transfer enhancement in a segment of the active magnetic regenerator (AMR), consisting of a magnetocaloric material (Gadolinium) and a heat transfer fluid in between, which is periodically magnetized and demagnetized, is investigated in this work. After giving a brief account on how magnetohydrodynamic (MHD) convection can be used to enhance the heat transfer from flat plate gadolinium toward the heat transfer fluid we apply two different techniques for MHD flow generation. In the first approach, an electric current I was injected into an electrically conducting, aqueous heat transfer fluid (NaOH). A heat transfer enhancement of about 40% (I=3mA) was found by means of a Mach-Zehnder interferometer. In the second approach, a liquid metal (GaInSn) was used which is potentially an interesting candidate for a heat transfer fluid in an AMR operating with high cycling frequency. Velocity measurements by means of ultrasound doppler velocimetry with a quasi uniform static magnetic field (220mT) in the gadolinium channel are presented.

  • Open Access Logo Magnetohydrodynamics 53(2017)2, 403-410

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Permalink: https://www.hzdr.de/publications/Publ-25761
Publ.-Id: 25761


Ultrasonic measurements of the bulk flow field in foams

Nauber, R.; Büttner, L.; Eckert, K.; Fröhlich, J.; Czarske, J.; Heitkam, S.

The flow field of moving foams is relevant for basic research and for the optimization of industrial processes such as froth flotation. However, no adequate measurement technique exists for the local velocity distribution inside the foam bulk. We have investigated the ultrasound Doppler velocimetry (UDV), providing the first two-dimensional, non-invasive velocity measurement technique with an adequate spatial (10 mm) and temporal resolution (2.5 Hz) that is applicable to medium scale foam flows. The measurement object is dry aqueous foam flowing upward in a rectangular channel. An array of ultrasound transducers is mounted within the channel, sending pulses along the main flow axis and receiving echoes from the foam bulk. This results in a temporally and spatially resolved, planar velocity field up to a measurement depth of 200 mm, which is approximately one order of magnitude larger than those of optical techniques. A comparison with optical reference measurements of the surface velocity of the foam allows to validate the UDV results. At 2.5 Hz frame rate an uncertainty below 15 percent and an axial spatial resolution better than 10 mm is found. Therefore, UDV is a suitable tool for monitoring of industrial processes as well as the scientific investigation of three-dimensional foam flows on medium scales.

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Permalink: https://www.hzdr.de/publications/Publ-25760
Publ.-Id: 25760


Demonstration of a beam loaded nanocoulomb-class laser wakefield accelerator

Couperus, J. P.; Pausch, R.; Köhler, A.; Zarini, O.; Krämer, J. M.; Garten, M.; Huebl, A.; Gebhardt, R.; Helbig, U.; Bock, S.; Zeil, K.; Debus, A.; Bussmann, M.; Schramm, U.; Irman, A.

Laser-plasma wakefield accelerators have seen tremendous progress, now capable of producing quasi-monoenergetic electron beams in the GeV energy range with few-femtoseconds bunch duration. Scaling these accelerators to the nanocoulomb range would yield hundreds of kiloamperes peak-current and stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and γ-ray sources, compact FELs and laboratory-size beam-driven plasma accelerators. However, accelerators generating such currents operate in the beam loading regime where the accelerating field is strongly modified by the self-fields of the injected bunch, potentially deteriorating key beam parameters.
Here we demonstrate that, if appropriately controlled, the beam loading effect can be employed to improve the accelerator's performance. Self-truncated ionization injection enabled loading of unprecedented charges of about 0.5 nC within a mono-energetic peak. As the energy balance is reached, we show that the accelerator operates at the theoretically predicted optimal loading condition and the final energy spread is minimized.

Keywords: LWFA; beam loading

Permalink: https://www.hzdr.de/publications/Publ-25759
Publ.-Id: 25759


Multidisciplinary characterization of U(VI) sequestration by Acidovorax facilis for bioremediation purposes

Krawczyk-Bärsch, E.; Gerber, U.; Müller, K.; Moll, H.; Rossberg, A.; Steudtner, R.; Merroun, M.

The contamination of the environment by U may affect plant life and consequently may have an impact on animal and human health. The present work describesU(VI) sequestration by Acidovorax facilis using a multidisciplinary approach combining wet chemistry, transmission electron microscopy, and spectroscopy methods (e.g.cryo-time resolved laser-induced fluorescence spectroscopy, extended X-ray absorption fine structure spectroscopy, and in-situ attenuated total reflection Fourier transform infrared spectroscopy). This bacterial strain is widely distributed in nature including U-contaminated sites. In kinetic batch experiments cells of A. facilis were contacted for 5 minutes to 48 hours with 0.1 mM U(VI). The results show that the local coordination of U species associated with the cells depends upon time contact. U is bound mainly to phosphate groups of lipopolysaccharide (LPS) at the outer membrane within the first hour. And, that both, phosphoryl and carboxyl functionality groups of LPS and peptidoglycan of A. facilis cells may effectuate the removal of high U amounts from solution at 24-48 hours of incubation. It is clearly demonstrated that A. facilis may play an important role in predicting the transport behaviour of U in the environment and that the results will contribute to the improvement of bioremediation methods of U-contaminated sites.

Keywords: Uranium; Acidovorax facilis; spectroscopy; bioremediation

Permalink: https://www.hzdr.de/publications/Publ-25758
Publ.-Id: 25758


Development and validation of a gene signature for patients with head and neck carcinomas treated by postoperative radio(chemo)therapy

Schmidt, S.; Linge, A.; Zwanenburg, A.; Leger, S.; Lohaus, F.; Krenn, C.; Appold, S.; Gudziol, V.; Nowak, A.; von Neubeck, C.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Bunea, H.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S. E.; Mönnich, D.; Zips, D.; Baretton, G. B.; Buchholz, F.; Baumann, M.; Krause, M.; Löck, S.

The aim of this study was to identify and independently validate a novel gene signature predicting loco-regional tumor control (LRC) for treatment individualization of patients with locally advanced head and neck squamous cell carcinomas (HNSCC) who are treated with postoperative radio(chemo)therapy (PORT-C). Gene expression analyses were performed using nanoString technology on a multicenter training cohort of 195 patients and an independent validation cohort of 142 patients. The analyzed gene set was composed hypothesis-driven and included genes with previously reported association to radio(chemo)sensitivity or resistance to radio(chemo)therapy. Gene selection and model building were performed within a specifically developed statistical framework comparing several machine-learning algorithms. This procedure identified a 7-gene signature for HPV16 DNA negative tumors consisting of the genes: SERPINE1, INHBA, P4HA2, ACTN1, HILPDA, CD24 and TCF3. The 7-gene signature was used to fit a multivariable Cox model to the training data (concordance index, ci=0.84), which was successfully validated (ci=0.71). Thus, the signature showed improved performance compared to a clinical model (ci=0.66) and to a previously published model including hypoxia-associated genes and cancer stem cell markers (ci=0.65). Furthermore, the signature was used to stratify patients into groups with low and high risk of recurrence. Significant differences in LRC between these groups were found in training and validation (p<0.001). A prospective validation is planned in an ongoing prospective clinical trial of the DKTK-ROG before potential application in clinical trials for patient stratification.

Keywords: Radiochemotherapy; HNSCC; Biomarker; Loco-regional control; Gene signature; HPV status

Permalink: https://www.hzdr.de/publications/Publ-25757
Publ.-Id: 25757


Laser spectroscopy measurement of the 2s-hyperfinesplitting in lithium-like bismuth

Sánchez, R.; Lochmann, M.; Jöhren, R.; Andelkovic, Z.; Anielski, D.; Botermann, B.; Bussmann, M.; Dax, A.; Frömmgen, N.; Geppert, C.; Hammen, M.; Hannen, V.; Kuehl, T.; Litvinov, Y.; Coto, R. L.; Stoehlker, T.; Thompson, R.; Vollbrecht, J.; Wen, W.; Weinheimer, C.; Will, E.; Winters, D.; Noertershaeuser, W.

We have recently reported on the first direct measurement of the 2s hyperfine transition in lithium-like bismuth (209Bi80+) at the GSI Helmholtz Centrefor Heavy Ion Research (GmbH) in Darmstadt, Germany. Combined with a newmeasurement of the 1s hyperfine splitting in hydrogen-like (209Bi82+) the so-called specific difference Δ’E = -61.37(36) meV could be determined and was found to bein good agreement with its prediction from strong-field bound-state QED. Here wereport on additional investigations performed to estimate systematic uncertainties of these results and on details of the experimental setup. We show that the dominating uncertainty arises from insufficient knowledge of the ion beam velocity which is determined by the electron-cooler (voltage). Two routes to obtain a cooler-voltage calibration are discussed and it is shown that agreement can be reached either of the experimental Δ’E with the theoretical result, or between the two measurements of the hyperfine splitting in hydrogen-like bismuth, but not both at the same time.

Keywords: qed; spectroscopy; bismuth; hyperfine; lithium-like; storage ring; laser

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Permalink: https://www.hzdr.de/publications/Publ-25756
Publ.-Id: 25756


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe

Vallinayagam, M.; Posselt, M.; Faßbender, J.

Nanostructured Ferritic Alloys (NFA) are considered as promising candidates for the structural materials of future fusion and fission reactors [1]. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer size yttria-based oxide particles. In this research project (started in November 2016) the nature of nanometer-size yttria-based oxide clusters in a bcc Fe matrix are investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the nanoclusters.
The investigations shall clarify the conditions for the formation of nonstoichiometric clusters that are coherent with the bcc lattice and for the formation of oxide phases (in particular Y2O3 and Y2Ti2O7). Three models are considered: (i) clusters consisting of Y, Ti atoms on bcc lattice sites and O on octahedral site [2-4], termed as On-Lattice (OL) model, (ii) cluster consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe [5] termed as Structure Matching (SM) model, and (iii) substituting O also on Fe site, termed as OFe model. In all cases vacancies are introduced into the simulation cell in order to provide additional volume for O atoms. We studied clusters of different sizes in the framework of the three models. Our results show that all three models lead to almost the same energy for considered cluster configurations. This revises the statement of Barnard et al. [5] who claimed that clusters with SM configuration are generally favored energetically.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403,
113 (2010)
[3] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[4] M. Posselt, D. Murali, B. K. Panigrahi, Model. Simul. Mater. Sc. 22, 085003 (2014)
[5] L. Barnard, G. R. Odette, I. Szlufarska, D. Morgan. Acta Mater. 60 (2012) 935 (2012)

Keywords: DFT; Y-Ti-O nanoclusters in bcc-Fe; structure and energetics

  • Lecture (Conference)
    4th International Workshop on ODS materials, 26.-28.06.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25755
Publ.-Id: 25755


Influence of foreign atoms on the diffusion of oxygen in bcc Fe

Wang, X.; Posselt, M.; Faßbender, J.

Iron-based ferritic alloys are widely used in industrial applications. They contain varying concentrations of foreign atoms or solutes, most of which are purposely included in order to improve the mechanical properties, the corrosion and radiation resistance as well as the high-temperature stability. The diffusion of the solutes plays a crucial role in determining all these properties during fabrication and processing, and also influences the behavior of the materials in the various applications. In many cases the diffusion proceeds via bcc lattice sites by means of intrinsic point defects, i.e. vacancies and self-interstitial atoms, and in some cases via interstitial sites. Solute diffusion determines the micro- and nanostructure obtained after heat treatments, and the detailed knowledge of the atomistic diffusion mechanisms is necessary to obtain the desired properties. Moreover, micro- and nanostructure evolution under irradiation is controlled by atomic diffusion.
In this research project (started in September 2016) the diffusion of foreign atoms in bcc Fe shall be investigated by first-principle methods and kinetic Monte Carlo simulations. The focus of the present work is on the diffusion of oxygen under the influence of other foreign atoms such as Al, Cr, Ti, and Y. Oxygen plays an important role in the formation and evolution of a high dispersion of nanometer-size particles containing Y, Ti, and O in ODS steels which are considered as promising candidates for structural materials of future fusion and fission reactors [1]. The presence of foreign atoms and intrinsic point defects modifies the original migration path of oxygen [2-4]. Using DFT calculations the binding energy between oxygen and a foreign atom for different neighbor distances and the modified migration barriers, i.e. for the O jump between the first and the second neighbor of a foreign atom, etc are calculated.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] S.L. Shang, H.Z. Fang, J. Wang, C.P. Guo, Y. Wang, P.D. Jablonski, Y. Du, Z.K. Liu, Corrosion
Sci. 83, 94 (2014)
[3] P. Liu, W. Xing, X. Cheng, D. Li, Y. Li, X.-Q. Chen, Phys. Rev. B 90, 024103 (2014)
[4] C. Barouh, T. Schuler, C.-C. Fu, T. Jourdan, Phys. Rev. B 92, 104102 (2015)

Keywords: DFT; diffusion of oxygen in bcc-Fe

  • Lecture (Conference)
    4th International Workshop on ODS materials, 26.-28.06.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25754
Publ.-Id: 25754


Simulations of a precession driven flow in a cylindrical cavity

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.; Herault, J.

The project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) provides a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics [1]. The most ambitious experiment will be a dynamo experiment which consists of a large precessing cylindrical cavity filled with liquid sodium. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo [2] or the ancient lunar dynamo [3].

Our presentation addresses corresponding hydrodynamic simulations that provide characteristic properties of the precession-driven flow such as amplitudes or helicity and their implications for the dynamo effect. Our results show that the primary response of the fluid to the precession is an azimuthally rotating inertial wave, called Kelvin mode [4]. Increasing the precession ratio the fundamental Kelvin mode becomes unstable which goes along with the emergence of two free inertial waves due to a parametric resonance caused by the periodic perturbation of the primary flow [5]. The free inertial waves only exist within a narrow range of rather small precession ratios because increasing non-linear interactions give rise to the formation of an azimuthal circulation flow which alters the resonance condition (detuning effect) [6].

For large precession ratios, instead, we find a clear signature of Kelvin modes with the frequency of the forcing and higher azimuthal and/or axial wave numbers. In the turntable frame these Kelvin modes correspond to standing inertial waves that are caused by non-linear self-interaction of the fundamental forced mode. The contributions of these modes provide a breaking of the parity with respect to the equatorial plane which has proven to be beneficial for dynamo action [7].

Further considerations on the dynamo-ability of the precession driven flow require larger Reynolds numbers which are numerically no longer accessible. Therefore, they have to be based solely on data from the downscaled water experiment that currently is running at HZDR in preparation for the large liquid sodium facility (see contribution of T. Vogt). Comparisons of our simulations with experimental data from Ultrasonic Doppler Velocimetry (UDV) measurements at similar Reynolds number show a surprisingly good consistency thus providing a basis for the development of flow models at larger Reynolds numbers for future kinematic dynamo models.

[1] Stefani, F. et al., Magnetohydrodynamics, 48 (1), 103--114, 2012.
[2] Malkus, W. V. R., Science, 160, 259--264, 1968.
[3] Noir, J., and D. C{\'e}bron, J. Fluids Mech., 737, 412--439, 2013.
[4] Thomson W, Phil. Mag. J. Sci. 10 (61), 155--168, 1880.
[5] Kerswell, R. R., J. Fluids Mech., 382, 283--306, 1999.
[6] Herault, J. et al., Phys. Rev. Fluids, in preparation, 2017.
[7] Tilgner, A., Phys. Fluids, 17 (3), 034, 104, 2005.

Keywords: Dynamo; DRESDYN; precession

  • Lecture (Conference)
    Natural Dynamos, 26.-30.06.2017, Valtice, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-25753
Publ.-Id: 25753


Structural elucidation of U(VI)-isosaccharinic acid complexes under acidic conditions: spectroscopic and theoretical investigations

Brinkmann, H.; Moll, H.; Patzschke, M.; Rossberg, A.; Stumpf, T.

The alkaline degradation of cellulosic material present in low and intermediate level waste leads to the formation of water soluble organic compounds. α-Isosaccharinic acid (ISA) as main degradation product can act as complexing agent for radionuclides. This may affect the mobility as well as the sorption behavior adversely. Studies regarding to the interaction of ISA with U(VI) are scarce. Hence, the aim of this study is to describe the U(VI)-ISA complexes formed under acidic conditions on a molecular level. Since U(VI) can coordinate to different binding sites of the polyhydroxy carboxylic acid, the number of possible complexes is large. To elucidate the number and structure of those U(VI)-ISA species, different spectroscopic methods were applied to obtain information from the metal and from the ligand.
UV-vis measurements lead to the conclusion that three complexes are formed and that both, the carboxylic as well as hydroxylic groups, are involved. Attenuated total reflection-Fourier-transformation-infrared spectroscopy (ATR-FTIR) and extended X-ray absorption fine structure-spectroscopy (EXAFS) offer structural information of the formed complexes. DFT-calculations provide data of optimized structures (e.g. figure below: [UO2(ISA)2(H2O)2]), which were used to underpin experimental results in order to identify the formed U(VI)-ISA species.
These results are the basis for further investigations under neutral and alkaline conditions. Moreover, this study helps to elucidate the U(VI) speciation in long term tissue degradation experiments in the presence of microorganisms.

Keywords: Uranium; Isosaccharinic acid; UV-vis; IR; DFT; EXAFS

  • Lecture (Conference)
    Goldschmidt 2017, 13.-18.08.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-25752
Publ.-Id: 25752


Σ0-production in proton nucleus collisions near threshold

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

We have studied the production of Σ0 baryons in the nuclear reaction p (3.5 GeV) + Nb. The measurement has been performed with the HADES detector at GSI, Darmstadt. Σ0->Λγ decays were identified via the decay Λ->pπ- coincident to e+e- pairs from external and internal (Dalitz decay) gamma conversion. The differential cross section integrated over the detector acceptance, i.e. within the rapidity interval 0.5 < y < 1.1, has been extracted to be 2.3 +- 0.2 (stat) +- 0.6 (sys) +- 0.2 (norm) mb and the total cross section is obtained by using different extrapolation methods to 5.8 +- 0.5 (stat) +- 1.4 (sys) +- 0.6 (norm) +- 1.7 (extrapol) mb. The Λ/Σ0 ratio is estimated for the full phase space to be 2.6 +- 0.2 (stat) +- 0.8 (sys) +- 0.7 (extrapol). The obtained rapidity and momentum distributions are compared to predictions from transport model calculations. The Σ0 cross section is discussed in the context of statistical particle production in nuclear reactions.

Permalink: https://www.hzdr.de/publications/Publ-25751
Publ.-Id: 25751


A Facility For Pion Induced Nuclear Reaction Studies With HADES

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, C.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer6, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt, C. J.; Schmidt-Sommerfeld, K.; Schuldes, H.; Schwab, E.; Scordo, A.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.

The combination of a production target for secondary beams, an optimized ion optical beam line setting, in-beam detectors for minimum ionizing particles with high rate capability, and an efficient large acceptance spectrometer around the reaction target constitutes an experimental opportunity to study in detail hadronic interactions utilizing pion beams impinging on nucleons and nuclei. For the 0.4 - 2.0 GeV/c pion momentum regime such a facility is located at the heavy ion synchrotron accelerator SIS18 in Darmstadt (Germany). The layout of the apparatus, performance of its components and encouraging results from a first commissioning run are presented.

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Permalink: https://www.hzdr.de/publications/Publ-25750
Publ.-Id: 25750


Solvent extraction: fundamental equilibrium studies of neodymium and DEHPA

Scharf, C.; Ditze, A.

This article presents equilibrium studies into the NdCl3–HCl (or NaOH)–H2O–DEHPA (di-(2-ethylhexyl) phosphoric acid)–kerosene system. The system plays a role in solvent extraction of rare earth elements from aqueous chloride solutions. Thereby neodymium is transferred into the organic phase consisting of DEHPA solved in kerosene. Measurements were taken at DEHPA concentrations between 1 and 40 vol.% and at concentrations of neodymium which prevent a gelatinous organic phase. Results are presented in tables. Three charts of process variables were evaluated which, under the assumption of ideal behaviour, should lead to slopes of 3 in double logarithmic scale in all three cases. Since the actual slopes of measured variables were 2.4, 2.5 and 3.8, ideal behaviour is only a first approximation, and non-ideal aspects need to be further studied. The plot of percentage extraction versus pH shows that neodymium is completely extracted at pH values above 1.

Keywords: solvent extraction; equilibrium system; neodymium; DEHPA; law of mass action

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Permalink: https://www.hzdr.de/publications/Publ-25749
Publ.-Id: 25749


Experimental study on the influence of horizontal channel vibration on the mass transfer rate of bubbles in milli-channels

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

Millimeter-sized reactors have gained a great research interest from the industry and academia because of their advantages such as large interfacial area, high mass transfer rates, low pressure drop, and ease of scale-up over the conventional reactor technology. Optimization of the multiphase flow processes is one of main requirements of modern industry to achieve the higher efficiency and environment-friendly processes. A new design and technique for measurement of mass transfer rate of single bubbles in vibrating milli-channels is being developed with the claimed goal of process intensification [1].
In this study, the absorption rate of a single Taylor bubble of carbon dioxide in water is investigated using high resolution X-ray radiography technique in an oscillating vertical channel. The liquid-side mass transfer coefficient is calculated by measuring the changes in the size of the bubble at constant pressure. The channel is a glass pipe with 6 mm inside diameter and circular cross section. The glass channel is vibrated using a calibrated vibrator in horizontal direction. The amplitude and frequency of vibration is controlled by a wave generator accurately. The method which is used to measure the variation of the bubble size is X-ray radiography. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles. The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is filtered-deionized water and the gas phase is carbon dixide.
The results for the short term dissolution of single carbon dioxide bubbles confirmed that the channel vibration causes to increase of mass transfer rate for single Taylor bubbles. The dissolution rate of bubbles increases as the frequency of vibration rises and there is a maximum value at the channel resonance frequency where large surface oscillation of bubbles exists. Furthermore, it was shown that the liquid-side mass transfer coefficient of dissolving bubbles grow up as the vibration amplitude of channel enlarges.

Keywords: vibration; mass transfer rate; milli-channels

  • Contribution to proceedings
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels,, Belgium
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-25747
Publ.-Id: 25747


Experimental analysis of Taylor bubble behavior and mass transfer during lateral oscillation of a vertical milli-channel

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

In this paper, we report on an experimental study on the influence of low-frequency horizontal vibration of a vertical millimeter-size channel with Taylor bubbles. We investigated the motion, shape and dissolution rate of individual elongated Taylor bubbles of air and CO2, which were freely rising in stationary water. Bubble size and dissolution rate were determined from microfocus X-ray radiographs. From the shrinking rate we calculated the liquid-side mass transfer coefficient. The rise velocity of bubbles and surface wave motion were analyzed using a videometric technique. The comparison of the results for the stationary and the oscillating channel showed that mechanical vibration of the channel is able to enhance the mass transfer coefficient from gas to the liquid phase by 80% to 186%, depending on the frequency and amplitude of vibration. It was found that channel oscillation causes the increase of free rise velocity of bubbles which is mainly attributed to the development of propelling interfacial waves and increase of liquid film flow rate. Furthermore, analyzing the surface wave motion of bubbles revealed that the enlargement of contact area between the phases and the increased mixing enhances the mass transfer additionally up to 30% compared to non-agitated bubbles of similar Peclet number.

Keywords: Vibration; Milli-channels; Mass transfer; Taylor bubble; Carbon dioxide

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Permalink: https://www.hzdr.de/publications/Publ-25746
Publ.-Id: 25746


Technetium retention by siderite under anoxic conditions

Schmeide, K.; Rossberg, A.; Weiss, S.; Brendler, V.; Scheinost, A. C.

99Tc is a long-lived (t1/2 = 2.1 × 105 years) β-emitter formed during the fission of U and is of major concern for radioactive waste disposal. Its environmental mobility is primarily governed by the oxidation states VII and IV, with TcVII forming the highly mobile TcO4 aquo anion, whereas TcIV is rather immobile due to the low solubility of its hydrolysis products. Redox processes, which are able to convert TcVII into TcIV, are hence of paramount importance for the safety of radioactive waste repositories. FeII-bearing minerals, ubiquitous in nature and also forming as corrosion products of the carbon steel canisters foreseen as a possible first enclosure of radioactive waste, play a vital role in these redox reactions due to their high redox reactivity and high sorption capacity, as has been shown not only for Tc, but also for Se, U, Np and Pu.
Here we focus on the retention of TcVII by a typical FeII mineral in carbonate-rich environments, siderite (FeCO3), which we studied in the relevant pH range (7 – 12.6) under anoxic conditions by means of batch sorption experiments and by X-ray absorption spectroscopy. Sorption experiments showed that Tc retention by siderite is fast (within minutes) and efficient (log Rd ~5) across the investigated pH range and independent of ionic strength (0.1 – 1 M NaCl). Tc K-edge X-ray absorption near-edge structure (XANES) data confirmed that the Tc immobilization is due to the surface-mediated reduction of TcVII to TcIV. The local structure of TcIV as probed by extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed two different species: in the pH range 7.8 to 11.5, TcO2-dimers form inner-sphere sorption complexes at the surface of siderite or of an FeII,III (hydr)oxide potentially formed during the redox reaction. At pH 11.8 to 12.6, the retention proceeds through the (near-surface) incorporation of TcIV by siderite.
In conclusion, siderite contributes effectively to the retention of Tc in the near-field of nuclear waste repositories.

Keywords: Technetium; siderite; reduction; adsorption; incorporation; technetium carbonate; X-ray absorption spectroscopy

  • Lecture (Conference)
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25745
Publ.-Id: 25745


FoMICS Prize for PhD Students: Presentation "Modeling ultrafast processes in laser-driven plasmas on modern compute hardware"

Huebl, A.

Conventional particle accelerators are approaching fundamental material limits which drive up machine sizes and costs. But both fundamental research and mid-energy range applications such as tumor therapy with ion beams are demanding further progress. Plasma-based accelerators driven by high-power lasers promise a fresh approach to overcome today's limits in accelerator physics. Providing a substantiation increase in accelerating gradients, this new generation of particle accelerators potentially fits on the size of a table if controlled correctly.

My PhD topic focuses on the development of open, manycore-driven particle-in-cell (PIC) simulations in order to model highly non-linear processes that happen on a time scale of atto- to pico-seconds inside this new class of particle accelerators. This includes the development of the world's fastest PIC code PIConGPU which scales up to the full size of Titan (ORNL). I am further extending the PIC algorithm to model previously unreachable multi-physics processes in high-energy density plasmas such as the interaction with XFEL laser beams at the European XFEL, enabling a new quality in predictability.

Keywords: laser plasma modeling HED atomic physics PIC GPU open source LPA ion acceleration

  • Lecture (Conference)
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-25744
Publ.-Id: 25744


Combining dynamic modelling codes with medium energy ion scattering measurements to characterise plasma doping

England, J.; Möller, W.; van den Berg, J. A.; Rossall, A.; Min, W. J.; Kim, J.

Plasma doping ion implantation (PLAD) is becoming increasingly important in the manufacture of advanced semiconductor device structures but a fundamental understanding of PLAD is complicated. A model of PLAD into planar substrates has been constructed using the one dimensional computer code TRIDYN to predict collision cascades and hence substrate compositional changes during implantation. Medium Energy Ion Scattering (MEIS) measurements of dopant profiles in PLAD processed samples were used to calibrate the input ion and neutral fluxes to the model. Rules could then be proposed for how post implant profiles should be modified by a cleaning step. This learning was applied to a three dimensional TRI3DYN based model for PLAD implants into FinFET like structures. Comparison of the model to dopant profile measurements made by time of flight (TOF)-MEIS revealed the angular distributions of neutral species and doping mechanisms acting in three dimensional structures.

Keywords: FinFET; Ion beam modelling; Ion-Implantation; PLAD; Plasma Doping; TRI3DYN; TRIDYN

Permalink: https://www.hzdr.de/publications/Publ-25743
Publ.-Id: 25743


Spatiotemporal quantitative imaging of leaching processes with positron emission tomography (PET), improving process understanding and modelling performance

Kulenkampff, J.; Barthen, R.; Gründig, M.; Karimzadeh, L.; Lippold, H.; Schymura, S.; Lippmann-Pipke, J.

A current application that needs improved understanding of coupled reactive transport processes and fluid-rock interactions is in situ leaching of ore minerals. These processes are largely controlled by the chemical and hydrological heterogeneity of the material and the respective transport process.
We apply GeoPET as method for quantitative spatiotemporal imaging of tracer concentrations, which combines molecular sensitivity (picomolar) with suitable spatial resolution (ca. 1 mm) for elucidating heterogeneous effects on the core scale. This laboratory imaging method is virtually unique for crossing the scale from molecular processes to the macrosphere with its typical heterogeneous geoscienctific characteristics. It requires labelling the relevant substance with an appropriate positron-emitting radionuclide, like 18F or 64Cu. PET then makes use of the space-resolved detection of the decay radiation for deriving the tracer concentration.
From the time series of 3D frames of the tracer concentration of conservative flow experiments we compute the distribution of both the process-dependent effective volume and the local velocity distribution of the tracer. These experimental data are the basis of exceptionally efficient finite-element reactive transport models on the millimetre scale with a COMSOL-PhreeqC-coupling.
Our study was conducted within the framework of the French-German project “EcoMetals” which aims at the development of innovative processes for copper (and associated metals) extraction by means of biotechnology. In our showcase experiment we leached copper from pebbles that had been artificially coated with [64Cu]covellite. The PET-experiment has two stages. At first we observed the depletion of the 64Cu activity concentration in the surface layer during leaching with glutamic acid. From this, we derived local covellite leaching rates. After decay of the radionuclide we conducted a conservative flow experiment with pore water labelled with 18F. This experiment identifies strongly localized preferential flow zones. From this, we compute porosity and velocity distributions, which serve as input parameters for the numerical simulation. The simulation results are validated in comparison with observed leaching rates.

  • Lecture (Conference)
    GeoBremen2017, 24.-29.09.2017, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25742
Publ.-Id: 25742


Roughness-induced domain structure in perpendicular Co/Ni multilayers

Lee-Hone, N. R.; Thanhoffer, R.; Neu, V.; Schäfer, R.; Arora, M.; Hübner, R.; Suess, D.; Broun, D. M.; Girt, E.

We investigate the correlation between roughness, remanence and coercivity in Co/Ni films grown on Cu seed layers of varying thickness. Increasing the Cu seed layer thickness of Ta/Cu/8×[Co/Ni] thin films increases the roughness of the films. In-plane magnetization loops show that both the remanence and coercivity increase with increasing seed layer roughness. Polar Kerr microscopy and magnetic force microscopy reveal that the domain density also increases with roughness. Finite element micromagnetic simulations performed on structures with periodically modulated surfaces provide further insight. They confirm the connection between domain density and roughness, and identify the microsocpic structure of the domain walls as the source of the increased remanence in rough films. The simulations predict that the character of the domain walls changes from Bloch-like in smooth films to Néel-like for rougher films

Keywords: Domain density; Domain structure; In-plane magnetization; Micromagnetic simulations; Modulated surfaces; Polar-Kerr; Seed layer thickness; Varying thickness

Permalink: https://www.hzdr.de/publications/Publ-25741
Publ.-Id: 25741


Impact of Self-Trapped Excitons on Blue Photoluminescence in TiO2 Nanorods on Chemically Etched Si Pyramids

Saini, C. P.; Barman, A.; Banerjee, D.; Grynko, O.; Prucnal, S.; Gupta, M.; Phase, D. M.; Sinha, A. K.; Kanjilal, D.; Skorupa, W.; Kanjilal, A.

Temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV At+ ions. The origin of observed PL has been examined by X-ray absorption near-edge spectroscopy (XANES) at Ti-K,L and O-K edges, revealing the reduction of ligand field splitting owing to the formation of oxygen vacancies (OVs) by destroying TiO6 octahedral symmetry. Detailed PL and XANES analyses suggest that the fluence (ions/cm(2)) dependent increase in OVs not only boosts the conduction electrons but also increases the density of holes in localized self-trapped exciton (STE) states near the valence band. Based on these observations, we propose a model in which doped conduction electrons are recombining radiatively with the holes in STE states for blue light emission.

Keywords: titanium oxide; ion implantation; photoluminescence; X-ray absorption near-edge spectroscopy; oxygen vacancy; localized self-trapped exciton

Permalink: https://www.hzdr.de/publications/Publ-25740
Publ.-Id: 25740


High-field ESR in low-D spin systems

Zvyagin, S.

  • Invited lecture (Conferences)
    L. A. Prozorova Workshop on Spin Dynamics, 17.-18.05.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-25739
Publ.-Id: 25739


Radiotracer exchange studies for gaining direct insight into the equilibrium characteristics of elementary processes determining humic-bound metal transport

Lippold, H.

The mobility of toxic or radioactive contaminant metals in the subsurface hydrosphere can be essentially governed by their interaction with humic colloids. Predictions on migration processes need thorough consideration of kinetic aspects in the ternary system metal / humic substance / mineral surface. In reactive transport models, reversibility is commonly presumed. However, for adsorption of humic matter, strong hysteresis is observed (hardly any desorption upon dilution), and recoveries in column experiments are far from complete. Complexation of higher-valent metals with humic substances is accompanied by slow processes leading to an increase in complex inertness, i.e., a growing resistance to dissociation.
In view of these uncertainties, the aim of our studies was to elucidate the reversible / irreversible character of interactions controlling humic-bound transport. For this purpose, the principle of tracer exchange was employed to gain insight into the dynamics of equilibria within the ternary system. A radioactive probe, introduced as a reactant into pre-equilibrated systems, will represent the overall equilibrium if there is a dynamic exchange. In case of a static equilibrium, the tracer will not get involved. The chosen model system for these experiments consisted of terbium(III) (as an analogue of trivalent actinides), humic acid and kaolinite. 160Tb as a radioisotope was produced by neutron activation of 159Tb. Humic acid was radiolabelled by azo coupling with [14C]aniline.
After introducing trace amounts of [14C]humic acid into pre-equilibrated adsorption systems of kaolinite and non-labelled humic acid in the state of surface saturation, quantitative exchange was found to take place. Evidently, adsorption equilibria of humic colloids are not static, notwithstanding their size and multiple bonding, albeit an exchange time of more than 4 weeks was required. Isotope exchange of 159Tb / 160Tb on saturated humic acid was completed within a very short time frame, independently of the time of pre-equilibration 159Tb / humic acid. However, if the tracer 160Tb was introduced prior to saturation with 159Tb, the expected partial desorption of 160Tb occurred at much lower rates, decreasing with time of pre-equilibration. Inertisation phenomena are thus confined to the strongest sites of humic molecules. Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium.

  • Lecture (Conference)
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25738
Publ.-Id: 25738


The determination of the fast neutron-induced fission cross section of Pu(242) at nELBE

Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S. E.; Schwengner, R.; Wagner, A.

The fast neutron-induced fission cross section of 242Pu was determined in the range of 0.5 MeV to 10 MeV relative to 235U(n,f) at the neutron time-of-flight facility nELBE. The number of target nuclei was calculated by means of measuring the spontaneous fission rate of 242Pu. Neutron transport simulations with Geant 4 and MCNP 6 are used to correct the relative cross section for neutron scattering. The determined results are in good agreement with current experimental and evaluated data sets.

Keywords: neutron-induced fission cross section; neutron scattering corrections; fast neutrons; nELBE

  • Invited lecture (Conferences)
    Scientific Workshop on Nuclear Fission dynamics and the Emission of Prompt Neutrons and Gamma Rays, 19.-23.06.2017, Varna, Bulgaria
  • Open Access Logo Contribution to proceedings
    Scientific Workshop on Nuclear Fission dynamics and the Emission of Prompt Neutrons and Gamma Rays, 20.-22.06.2017, Varna, Bulgaria
    European Physical Journal: Web of Conferences, Vol. 169, 00009, Les Ulis Cedex A: EDP Sciences
    DOI: 10.1051/epjconf/201816900009

Permalink: https://www.hzdr.de/publications/Publ-25737
Publ.-Id: 25737


Enhancement of superconductivity in FeSe thin crystals induced by biaxial compressive strain

Wang, X. F.; Zhang, Z. T.; Wang, W. K.; Zhou, Y. H.; Kan, X. C.; Chen, X. L.; Gu, C. C.; Zhang, L.; Pi, L.; Yang, Z. R.; Zhang, Y. H.

We report on the enhancement of superconductivity in FeSe thin crystals induced by in-plane biaxial compressive strain, with an underlying scotch tape as an in-situ strain generator. It is found that, due to the compressive strain, the superconducting transition temperature Tc ≈ 9 K of FeSe is increased by 30%–40% and the upper critical field Hc2(0) ≈ 14.8 T is increased by ∼ 20%. In parallel, the T*, which characterizes an onset of enhanced spin fluctuations, is raised up from 69 K to 87 K. On the other hand, the structural transition temperature Ts ≈ 94 K, below which an orthorhombic structure and an electronic nematic phase settle in, is suppressed down by ∼ 5 K. These findings reveal clear evolutions of the orders/fluctuations under strain effect in FeSe, the structurally simplest iron-based superconductor where the lattice/spin/charge degrees of freedom are closely coupled to one another. Moreover, the presented research provides a simple and clean way to manipulate the superconductivity in the layered iron compounds and may promote applications in related materials. © 2017 Elsevier B.V.

Keywords: Biaxial compressive strains; FeSe; Superconductivity

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Permalink: https://www.hzdr.de/publications/Publ-25736
Publ.-Id: 25736


Ultrasonic Study on the Hexagonal Antiferromagnet Dy3Ru4Al12

Ishii, I.; Takezawa, K.; Goto, H.; Kamikawa, S.; Andreev, A. V.; Gorbunov, D. I.; Henriques, M. S.; Suzuki, T.

In the distorted kagome lattice antiferromagnet Dy3Ru4Al12 with TN = 7 K, a crystal electric field (CEF) effect is expected at high temperatures. To investigate the CEF effect and the phase transition at TN, we performed ultrasonic measurements on a single-crystalline sample. At high temperatures, both the longitudinal elastic modulus C11 and the transverse modulus C44 increase monotonically with decreasing temperature. Below 60 K a characteristic elastic softening is observed in C44 in contrast to C11 with monotonic hardening down to TN. We analyzed C44 using the Curie-Weiss-type equation and obtained a negative parameter: Θ which is proportional to a quadrupole-quadrupole coupling constant under the hexagonal CEF. With further decreasing temperature, both moduli exhibit abrupt elastic hardening at TN due to a magnetostriction.

Permalink: https://www.hzdr.de/publications/Publ-25735
Publ.-Id: 25735


Protracted river response to medieval earthquakes

Stolle, A.; Schwanghart, W.; Andermann, C.; Bernhardt, A.; Wittmann, H.; Merchel, S.; Rugel, G.; Fort, M.; Adhikari, B. R.; Korup, O.

Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from seismic disturbances, depending on how recovery is defined. We examine several proxies of river recovery around Pokhara, Nepal’s second largest city. We use a freshly exhumed cohort of floodplain trees in growth position as a geomorphic marker of rapid sedimentation that formed a fan covering 150 km2 in a Lesser Himalayan basin with tens of meters of debris. Radiocarbon dates of these buried trees are consistent with those of nearby valley fills linked to major medieval earthquakes, and allow estimating average rates of sedimentation and re-incision.
We combine high-resolution digital elevation data, geodetic field surveys, aerial photos, and dated re-exhumed tree trunks to reconstruct dated geomorphic marker surfaces. The volumes of sediment lost from beneath these surfaces require net sediment yields of up to 4200 t km –2 yr –1, averaged over some 650 years since the last inferred earthquake. These rates exceed rates of catchment-wide Denudation inferred from concentrations of cosmogenic 10Be in river sands. The lithological composition of active channel-bed load differs from that of local bedrock, confirming that rivers still mostly evacuate medieval valley fills, locally incising at rates of 160 to 220 mm yr –1. Pronounced knickpoints and epigenetic gorges at tributary junctions further document a protracted fluvial response; only the distal portions of the earthquake-derived sediment wedge have been incised to near their base. Our results challenge the notion that mountain rivers recover from earthquakes within years to decades. The valley fills around Pokhara show that even highly erosive Himalayan rivers need at least centuries to millennia to adjust. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in mountain regions.

Keywords: Fluvial recovery; sediment yield; medieval earthquakes; Nepal

  • Open Access Logo Earth Surface Processes and Landforms 44(2019), 331-341
    Online First (2018) DOI: 10.1002/esp.4517

Permalink: https://www.hzdr.de/publications/Publ-25734
Publ.-Id: 25734


Experimental characterization of the contact seam between salt cement and rock salt

Jantschik, K.; Kulenkampff, J.; Moog, H. C.

Cement-based salt concrete (concrete with crushed salt filler) is a potential building material for seals in rock salt formations. The contact seam between sealing element and the excavation damaged zone (EDZ) of the host rock is a critical path way for transport of aqueous solutions and the release of radionuclides to the biosphere. For an assessment for the long-term integrity of seals it is therefore important to know at which rate the seam closes up upon contact with saline solution and confining stress.
The investigation of the sealing capacity and the closure of the contact seam influenced by saline solutions and confining stress was investigated in laboratory tests at GRS. The available core material originates from a sealing element of a former German salt mine and was exposed to confining pressure of the host rock for about ten years. The rock salt originates from the EZD of the sealing element. The salt concrete core was coated with salt slurry and inserted in a hollow rock salt cylinder for the preparation of a combined sealing element at laboratory scale.
Afterwards the combined sample was dried and installed in an isostatic cell. The development of permeability by percolation of saturated NaCl solution and confining pressure was investigated on various combined samples at GRS. All samples showed a significant reduction of permeability with time. One sample was dismantled and prepared for investigation with PET.
Following, transport of radiotracers through the sample and along the seam was investigated with positron emission tomography (PET). PET could clearly and quantitatively display the propagation of the tracer along the seam and inside the salt concrete matrix. It is thus a laboratory-scale method that is capable of non-destructive quantitative visualization and parametrization of this particular heterogeneous tracer transport . The investigation also substantiated the issue of unfavorable conditions of the seam for the safety of the barrier.
The method of GeoPET has been developed and advanced at HZDR. A number of show case experiments could prove its capability for spatiotemporal quantification of tracer transport experiments (Kulenkampff et al., 2016) with very high sensitivity (“picomolar”) and reasonable spatial resolution (about 1 mm).
Here, a small volume of brine, labelled with the PET-tracer 22Na, was injected into the head space between the end cap and the sample. It was observed that a portion of the tracer was sucked into the contact zone between rock salt and cement immediately after injection. The spatial tracer distribution rapidly stabilized as a patchy structure (Fig. 2). Then, during the observation period of 71 days it diffused into the cement and reached a mean depth of 5 mm.

  • Lecture (Conference)
    SaltMech IX, 12.-14.09.2018, Hannover, Deutschland
  • Open Access Logo Contribution to proceedings
    Saltmech IX, 12.-14.09.2018, Hannover, Deutschland
    The Mechanical Bevior of Salt IX, Hannover: BGR, 978-3-9814108-6-0, 261-273

Permalink: https://www.hzdr.de/publications/Publ-25733
Publ.-Id: 25733


Manifestation of the Jahn-Teller effect in elastic moduli of strontium fluorite crystals doped with chromium ions

Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Shakurov, G. S.; Ulanov, V. A.; Surikov, V. T.

Attenuation and phase velocity of ultrasound have been measured in strontium fluoride single crystal doped with chromium in the temperature range of 4 – 185 K at 56 -162 MHz. Anomalies have been found for all the normal modes corresponding to the non-vanishing elastic moduli of a cubic crystal. Interpretation of the observed anomalies has been done in the frame work of relaxation in the system of Jahn-Teller (JT) complexes CrF8 subject to full T2g X (eg+t2g)JT problem. Relaxation time has been calculated from the experimental data on ultrasonic attenuation and adiabatic and isothermal contributions of the impurity subsystem to the total elastic moduli have been obtained.

Permalink: https://www.hzdr.de/publications/Publ-25732
Publ.-Id: 25732


Anisotropic physical properties of single-crystal U2Rh2Sn in high magnetic fields

Prokes, K.; Gorbunov, D. I.; Reehuis, M.; Klemke, B.; Gukasov, A.; Uhlirova, K.; Fabreges, X.; Skourski, Y.; Yokaichiya, F.; Hartwig, S.; Andreev, A. V.

We report on the crystal and magnetic structures,magnetic, transport, and thermal properties of U2Rh2Sn single crystals studied in part in high magnetic fields up to 58 T. The material adopts a U3Si2-related tetragonal crystal structure and orders antiferromagnetically below TN = 25 K. The antiferromagnetic structure is characterized by a propagation vector k = (0 0 1/2). The magnetism in U2Rh2Sn is found to be associated mainly with 5f states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non-negligible magnetic moments also on Rh sites. U moments of 0.50(2) μB are directed along the tetragonal axis while Rh moments of 0.06(4) μB form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above ∼15 K the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the c axis. While for the a axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field-polarized state. A magnetic phase diagram for the field applied along the c axis is presented.

Permalink: https://www.hzdr.de/publications/Publ-25731
Publ.-Id: 25731


Euler-Euler Multiphase CFD-Simulation with Full Reynolds Stress Model and Anisotropic Bubble-induced Turbulence

Parekh, J.; Rzehak, R.

In the present work, Euler-Euler modelling of bubbly flows is combined with a full Reynolds stress model for the turbulence in the liquid carrier phase. Reynolds stress models have only rarely been explored in this context, although effects requiring this level of description are frequently encountered in industrial applications towards which the Euler-Euler approach is geared. In particular, source terms describing the additional bubble-induced contribution to the liquid phase turbulence with proper account for its anisotropy have not been established yet. A formulation based on the direction of bubble motion relative to the liquid is given here. Two well-known variants of Reynolds stress models due to Launder, Reece and Rodi and Speziale, Sarkar and Gatski are compared. Closure relations for the bubble forces are applied that have been shown previously to work well over a range of conditions. The model is validated by comparison with a set of pipe flow data that contains variations of liquid and gas flow rates as well as different pipe diameters. An important criterion for the selection of the data was to provide measurements of individual components of the Reynolds stress tensor.

Keywords: dispersed gas liquid multiphase flow; Euler-Euler two-fluid model; Reynolds stress turbulence model; bubble-induced turbulence; CFD simulation; model validation

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Permalink: https://www.hzdr.de/publications/Publ-25730
Publ.-Id: 25730


Nuclear Magnetic Resonance Signature of the Spin-Nematic Phase in LiCuVO4 at High Magnetic Fields

Orlova, A.; Green, E. L.; Law, J. M.; Gorbunov, D. I.; Chanda, G.; Krämer, S.; Horvatic, M.; Kremer, R. K.; Wosnitza, J.; Rikken, G. L. J. A.

We report a 51V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and focused on high-field phases up to 56 T. For the crystal orientations H‖c and H‖b, we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO4 compound.

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Permalink: https://www.hzdr.de/publications/Publ-25729
Publ.-Id: 25729


Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compound Mn1.5FeV0.5Al

Stinshoff, R.; Nayak, A. K.; Fecher, G. H.; Balke, B.; Ouardi, S.; Skourski, Y.; Nakamura, T.; Felser, C.

The Slater-Pauling rule states that L21 Heusler compounds with 24 valence electrons never exhibit a total spin magnetic moment. In the case of strongly localized magnetic moments at one of the atoms (here Mn) they will exhibit a fully compensated half-metallic ferrimagnetic state instead, in particular, when symmetry does not allow for antiferromagnetic order. With the aid of magnetic and anomalous Hall effect measurements, it is experimentally demonstrated that Mn1.5V0.5FeAl follows such a scenario. The ferrimagnetic state is tuned by the composition. A small residual magnetization, which arises due to a slight mismatch of the magnetic moments in the different sublattices, results in a pronounced change of the temperature dependence of the ferrimagnet. A compensation point is confirmed by observation of magnetic reversal and sign change of the anomalous Hall effect. Theoretical models are presented that correlate the electronic structure and the compensation mechanisms of the different half-metallic ferrimagnetic states in the Mn-V-Fe-Al Heusler system.

Permalink: https://www.hzdr.de/publications/Publ-25728
Publ.-Id: 25728


Sediment-bound trace metals in Golfe-Juan Bay, northwestern Mediterranean: Distribution, availability and toxicity

Tiquio, M. G. J.; Hurel, C.; Marmier, N.; Taneez, M.; Andral, B.; Jordan, N.; Francour, P.

The concentration, potential mobility, cation exchange capacity and toxicity of eight sediment-bound metals in Golfe-Juan Bay, France were examined. Results revealed significant spatial gradient of metal contamination along Golfe-Juan coast. The distribution and concentration of the metals appear to be influenced by the geochemical properties of the sediment, proximity to anthropogenic sources and general water circulation in the bay. The portion of trace metals found in the exchangeable, carbonate, oxidizable and reducible fractions of the sediment constitute 31%-58% ofthe total sediment-bound trace metal content, suggesting significant potential for remobilization of metals into the water column. Pb and Ni content ofthe sediment exceed the limits ofthe French marine sediment quality. Whole sediment extracts showed acute toxicity to marine rotifers. This study concludes that monitoring and management ofsediment-bound trace metals in Golfe-Juan Bay are important so as not to underestimate their availability and risk to the marine ecosystems.

Keywords: trace metals; sediment; mussels; remobilization

Permalink: https://www.hzdr.de/publications/Publ-25727
Publ.-Id: 25727


Analysis of the covalent bond character of tetravalent actinide complexes with N- and O-donor ligands

Kloditz, R.; Radoske, T.; Schöne, S.; Patzschke, M.; Stumpf, T.

The electronical properties of f-elements, especially of the actinides, are a very puzzling topic to investigate. The frontier orbitals (5f, 6d, 7s) all lying in a similar energy regime along with open shells and relativistic effects contribute to a very complex situation, where single-reference methods like DFT and Hartree-Fock may be not suitable any more1. In recent years, the investigation of actinides in combination with organic ligands revealed a very rich chemistry with many forms of coordination and chemical bonding. Besides that, many visually appealing and intuitive tools have been developed, with which the chemical bond can be analysed. These tools for bond analysis include natural-bonding orbitals (NBO) and density-difference plots. The aim of this study is therefore to apply these bond analysis tools to a range of tetravalent actinide complexes with N-donor ligands2, like Schiff bases and amidinates (Figure 1), to elucidate their complicated electronic properties. Thermodynamic computations on the stability of the complexes will also be presented to understand the chemical properties of the actinides and predict yet unknown complexes.

Keywords: Actinides; quantum chemistry; bonding analysis

  • Poster
    GDCh Wissenschaftsforum, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25726
Publ.-Id: 25726


Effect of Ag doping on electronic structure of cluster compounds AgxMo9Se11 (x=3.4; 3.9)

Butorin, S. M.; Kvashnina, K. O.; Klintenberg, M.; Kavcic, M.; Zitnik, M.; Bucar, K.; Gougeon, P.; Gall, P.; Candolfi, C.; Lenoir, B.

The electronic structure of AgxMo9Se11 as potential material for thermoelectric applications was studied using high-energy-resolution fkuorescence-detection x-ray absorption spectroscopy (HERFD-XAS) and resonant inelastic x-ray scattering (RIXS) technique. The experiments were supported by first-principle calculations using density functional theory (DFT). The analysis of obtained spectra indicate the presence of subvalent (less than 1+) Ag in the AgxMo9Se11. The advanced HERFDXAS measurements allowed us to resolve the contribution of the electronic states at the Fermi level of AgxMo9Se11 and monitor its dependence on the x value. Comparison of the experimental data with the results of the DFT calculations suggests an importance of the Ag2-type sites with the shortest Ag-Se distance for affecting the properties of AgxMo9Se11

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Permalink: https://www.hzdr.de/publications/Publ-25724
Publ.-Id: 25724


Range verification by prompt gamma-ray imaging and timing: Activities at OncoRay

Pausch, G.

The promise of particle therapy at ultimate precision can only be fulfilled once the particle range can be controlled and verified with millimeter precision. In spite of considerable efforts made by research groups and commercial enterprises throughout the world, means or devices for routinely measuring the particle range in situ and in real time during treatments are still missing. On the one hand, prompt gamma-ray imaging (proposed almost 15 years ago) has become widely accepted as the most promising strategy for online range verification. On the other hand, none of the Compton camera concepts pursued by several groups (including our group at HZDR/OncoRay) could prove to be applicable under treatment conditions. The only prototype system ever used in a clinical trial is the passively collimated knife-edge slit camera by IBA. This “camera” cannot provide 3D images, but measures one-dimensional prompt gamma-ray intensity profiles that allow quantifying possible shifts of the distal edge of high-weighted single pencil beam spots. Alternative, potentially less expensive approaches have been proposed by MGH (prompt gamma spectroscopy) and OncoRay (prompt gamma timing). Efforts to translate these ideas in applicable technologies are underway.
The talk will review the state-of-the art in prompt-gamma based range verification, with a focus on contributions of OncoRay: (1) the development and exploration of the prompt gamma-ray timing technique, and (2) the preparation and execution of first-in-man prompt gamma-ray imaging with the IBA knife-edge slit camera.

Keywords: Partikeltherapie, particle therapy; Protonentherapie, proton therapy; Bestrahlungskontrolle, treatment verification; Reichweitekontrolle, range verification; Prompte Gammastrahlung, prompt gamma rays; Gammakamera, prompt gamma imaging; Zeitmessung, prompt gamma timing; Gammaspektroskopie, gamma spectroscopy

  • Lecture (others)
    VARIAN Engineering Colloquium (eingeladener Vortrag), 15.11.2017, Bergisch Gladbach, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25723
Publ.-Id: 25723


Curvilinear magnonics

Otalora, J. A.; Lindner, J.; Schultheiss, H.; Hertel, R.; Thomas, A.; Nielsch, K.; Kákay, A.

New routes to affect the characteristics of materials with ferromagnetic order are to bend the thin film membranes. Bending the membrane can lead to internal strains and to a break of the local inversion symmetry [1], resulting for example in an unambiguous distinction between the outer and inner surfaces in case of curved geometries like nanotubes. The internal energies are also affected, especially when the curvature radius reaches intrinsic length scales. As shown in [2], in strongly curved systems the off-diagonal elements of the exchange interaction are not negligible, leading to chiral ordering. The dipolar fields are also influenced by the break of the inversion symmetry. Due to the modified energies the magnetic ordering and the magnetization dynamics differs from those known for thin-films [3-5]. Therefore the curvature can be accounted as an extra degree of freedom for controlling the characteristics of ferromagnetic materials.

In Magnonics, spin waves (SWs) or magnons are proposed to be used to carry, transport and process information analogous to the electron currents in electronics. Engineering magnon properties to control the SW excitation and propagation is an unavoidable task. The membrane curvature can be used to extend the toolbox of operations for controlling SWs, required in communication and logic devices [6–8]. Geometries like Möbius rings, helices, grooves stripes, and nanotubes can be accounted as few sets of layouts wherein the system curvature has an impact on the SW dynamics. Such examples will be referred in this talk, being the later (magnetic nanotubes) the one of our main focus. The tunable non-reciprocal SW properties induced by the nanotubular curvature [6–8] will be highlighted. In particular, that the dispersion relation is asymmetric regarding the sign of the propagation vector. Therefore the counter propagating magnons have different wave vectors and characteristic length for the transport. Figure 1(a) sketches a Permalloy nanotube in circular magnetic state wherein the SWs are excited by an rf-field applied at the center of the tube. Quasi-monocromatic magnons of different orders (n = 0, ±1, ±2) excited at 4.7 GHz are shown in Figure 1(b, c). The radial component of the excited magnon modes is represented by the color code in Figure 1(b). Note that the wavelength and transport length of counter-propagating magnons differ. Figure1(c) shows the magnon field distribution along the nanotube perimeter. The case of non-reciprocal SW dispersion and intrinsic linewidth are presented in Figure 2 (a) and (b), respectively. Aspects like the optimization of the curvature-induced non-reciprocity as function of the system size and magnetic ground state, some means to control the magnons mode profile and the tuning of non-reciprocity via weak DC external magnetic fields, will be also discussed.
We believe that three dimensional curvilinear magnetic membranes, in particular nanotubes, can be exploited as a novel layouts for non-reciprocal conduits, for magnons transport along curved paths, and as one-dimensional magnonic crystals.

Keywords: Curvature; magnonics; nanotubes; spin-waves

  • Invited lecture (Conferences)
    62nd Annual Conference on Magnetism and Magnetic Materials, 06.-10.11.2017, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-25722
Publ.-Id: 25722


Synthesis and radiopharmacological evaluation of a novel 18F-labeled cyclooxygenase-2 inhibitor based on dihydropyrrolo[3,2,1-hi]indole core structure

Laube, M.; Gassner, C.; Neuber, C.; Bergmann, R.; Kniess, T.; Steinbach, J.; Pietzsch, J.

Objectives
Cyclooxygenase-2 (COX-2), a key player in inflammation, is an attractive target for functional characterization of solid tumors by PET because its overexpression has been associated with chemo-/radioresistance and poor prognosis in cancer. We recently developed a novel series of selective COX-2 inhibitors based on a tricyclic core structure with IC50 values in the nanomolar range1 and herein report on the 18F-labeling and evaluation of a promising candidate.
Methods
5-(4-[18F]Fluorophenyl)-4-[4-(methylsulfonyl)phenyl]-1,2-dihydropyrrolo[3,2,1-hi]indole ([18F]2) was synthesized according to our recently reported 18F-fluorination and McMurry cyclization approach2 with modifications reported herein. [18F]2 was evaluated in vitro in cell lines with different COX-1/COX-2 expression patterns. In vivo dynamic small animal PET imaging and biodistribution studies were performed in NMRI nu/nu mice bearing a COX-2-positive A2058 tumor-xenograft.
Results
18F-Fluorination under standard conditions2 was hampered by basic hydrolysis leading primarily to side product [18F]1b. Optimization experiments focused on the use of different bases with varying concentrations (K2CO3, KHCO3, KH2PO4) or no base using the ‘minimalist approach’3. As one result, the use of decreased amounts of K2CO3 (5 instead of 20 μmol) effectively suppressed hydrolysis and gave [18F]1a in high yield (Figure 1). An automated synthesis comprising mild 18F-fluorination, McMurry cyclization, and purification using a TracerLabFX-N module provided [18F]2 in 16% isolated RCY (d.c.) with a molar activity of 45-106 GBq/μmol at EOS. A LogDpH7.4 of 4.66 and a CHI IAM value of 48 indicated high lipophilicity and non-specific binding. Cell uptake was independent of COX-2 expression. Biodistribution and PET studies revealed highest uptake of [18F]2 in liver and adipose tissue but only low accumulation in A2058 tumors (tumor/muscle < 1) at 60 min post injection. Celecoxib pre-injection (20 mg/kg) did not significantly change tumor uptake although a trend towards decreased radiotracer uptake was observed by PET in a subset of mice.
Conclusions
Despite of a high COX-2 selectivity and metabolic stability, [18F]2 did not emerge as suitable radiotracer for imaging COX-2 in vitro and in vivo, likely due to its high lipophilicity and fast hepatobiliary excretion.4 Future efforts for the development of COX-2-targeted radiotracers should focus on adaption of lipophilicity and/or use of targeted delivery systems.
References
1Laube et al. J. Org. Chem. 2015, 80, 5611-5624. 2Kniess et al. Biorg. Med. Chem. 2012, 20, 3410-3421. 3Richarz et al. Org. Biomol. Chem. 2014, 12, 8094-8099. 4Gassner et al. ChemistrySelect, 2016, 1, 5812–5820.
Figure 1.: Radiosynthesis of [18F]2 by 18F-fluorination and McMurry cyclization. S156: Poster 22nd International Symposium on Radiopharmaceutical Sciences
J

  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S156-S156
    DOI: 10.1002/jlcr.3508

Permalink: https://www.hzdr.de/publications/Publ-25721
Publ.-Id: 25721


Polyatomic Ions from Liquid Metal Ion Source driven High Current Ion Implanter

Pilz, W.; Laufer, P.; Tajmar, M.; Böttger, R.; Bischoff, L.

High current liquid metal ion sources are well known and found their first application as field emission electric propulsion (FEEP) thrusters in space technology. The aim of this work is the adaption of such kind of sources in broad ion beam technology.
Surface patterning based on self-organized nano-structures on e.g. semiconductor materials formed by heavy mono - or polyatomic ion irradiation from liquid metal (alloy) ion sources (LMAIS) is a very promising technique. LMAIS are nearly the only type of sources delivering polyatomic ions from about half of the periodic table elements. To overcome the lack of only very small treated areas by applying a focused ion beam (FIB) equipped with such sources, the technology taken from space propulsion systems was transferred into a large single-end ion implanter. The main component is an ion beam injector based on high current LMAIS combined with suited ion optics allocating ion currents in the µA range in a nearly parallel beam of a few mm in diameter. The mass selection of the needed ion species can be performed either by an ExB mass separator (Wien filter) and/or an existing dipole magnet of the ion implanter itself.
Different types of LMAIS (needle, porous emitter, capillary) are presented and characterized. The ion beam injector design is specified as well as the implementation of this module into a 200 kV high current ion implanter (Danfysik model 1090) operate at the HZDR Ion Beam Center (IBC). Finally, the obtained results of large area surface modification of Ge using polyatomic Bi2+ ions at room temperature from a GaBi capillary LMAIS will be presented and discussed.

Keywords: Polyatomic ions; liquid metal alloy ion source; implanter; surface pattern

  • Open Access Logo Review of Scientific Instruments 88(2017), 123302-1-123302-4
    DOI: 10.1063/1.4995537

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Permalink: https://www.hzdr.de/publications/Publ-25720
Publ.-Id: 25720


Reichweitekontrolle in der Partikeltherapie – eine Herausforderung für öffentliche und industrielle Forschung

Pausch, G.

Die Zerstörung bösartiger Tumoren mit Ionenstrahlen ist mittlerweile ein etabliertes Verfahren der Radioonkologie. Im Gegensatz zur klassischen Radiotherapie kann man gesundes Gewebe weitgehend schonen, was bei Tumoren nahe kritischer Organe überlebenswichtig sein kann. Dieser Vorteil wird klinisch nicht voll ausgeschöpft, da die Vorhersage (Planung) der Strahlreichweite im Körper mit Unsicherheiten behaftet ist. Der Vortrag erläutert Ansätze und Erfolge bei der Entwicklung klinisch einsetzbarer Verfahren zur in-vivo Reichweitemessung von Ionenstrahlen, mit denen die Präzision der Therapie erhöht werden kann. Entsprechende Forschungsvorhaben profitieren von einer engen Zusammenarbeit der öffentlichen Forschung mit Industriepartnern.

Keywords: Radioonkologie; radiooncology; Partikeltherapie; particle therapy; Reichweitemessung; range assessment

  • Lecture (others)
    Berliner Industriegespräch im Magnushaus Berlin, 27.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25719
Publ.-Id: 25719


Celecoxib based fluorine-18 radiolabelled probes for cyclooxygenase-2 monitoring - COX-2 affinity, radiosynthesis and in vitro studies.

Kniess, T.; Bechmann, N.; Steinbach, J.; Pietzsch, J.

kein Abstract verfügbar

  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S578
    DOI: 10.1002/jlcr.3508

Permalink: https://www.hzdr.de/publications/Publ-25718
Publ.-Id: 25718


Radio-U(H)PLC - the optimal flow cell for the gamma-detector ?

Kniess, T.; Fischer, S.; Ludwig, F.-A.; Steinbach, J.

kein Abstract verfügbar

  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S448
    DOI: 10.1002/jlcr.3508

Permalink: https://www.hzdr.de/publications/Publ-25717
Publ.-Id: 25717


Hydrous 18F-Fluoroethylation - leaving off the azeotropic drying

Kniess, T.; Laube, M.; Steinbach, J.

kein Abstract verfügbar

  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S152
    DOI: 10.1002/jlcr.3508

Permalink: https://www.hzdr.de/publications/Publ-25716
Publ.-Id: 25716


PET Imaging Evaluation of Four sigma1 Radiotracers in Nonhuman Primates

Baum, E.; Cai, Z.; Bois, F.; Holden, D.; Lin, S.-F.; Lara-Jaime, T.; Kapinos, M.; Chen, Y.; Deuther-Conrad, W.; Fischer, S.; Dukic-Stefanovic, S.; Bunse, P.; Wünsch, B.; Brust, P.; Jia, H.; Huang, Y.

The s1 receptors (S1Rs) are implicated in a variety of diseases including Alzheimer disease and cancer. Previous PET S1R radiotracers are characterized by slow kinetics or off-target binding that impedes their use in humans. Here, we report the first PET imaging evaluation in rhesus monkeys of 4 18F-labeled spirocyclic piperidine-based PET radiotracers (18F-1 to 18F-4). Methods: Baseline scans for the 4 radiotracers were obtained on an adult male rhesus monkey. Blocking scans were obtained with the S1R-selective agonist SA4503 to assess binding specificity of 18F-2 and 18F-4. Arterial input functions were measured, and binding parameters were determined with kinetic modeling analysis. Results: In the rhesus brain, all 4 radiotracers showed high and fast uptake. Tissue activity washout was rapid for 18F-2 and 18F-4, and much slower for 18F-1 and 18F-3, in line with their respective in vitro S1R-binding affinities. Both the 1-tissue-compartment and multilinear analysis-1 kinetic models provided good fits of time-activity curves and reliable estimates of distribution volume. Regional distribution volume values were highest in the cingulate cortex and lowest in the thalamus for all radiotracers. 18F-4 showed greater differential uptake across brain regions and 3-fold-higher binding potential than 18F-2. SA4503 at the dose of 0.5 mg/kg blocked approximately 85% (18F-2) and 95% (18F-4) of radiotracer binding. Conclusion: Tracers 18F-2 and 18F-4 displayed high brain uptake and fast tissue kinetics, with 18F-4 having higher specific binding signals than 18F-2 in the same monkey. Taken together, these data indicate that both 18F-2 and 18F-4 possess the requisite kinetic and imaging properties as viable PET tracers for imaging S1R in the human brain.

Keywords: 18F; PET; Radioligand; Rhesus monkey; Sigma-1 receptor

Permalink: https://www.hzdr.de/publications/Publ-25715
Publ.-Id: 25715


Immersed transient eddy current flow metering: a calibration-free velocity measurement technique for liquid metals

Krauter, N.; Stefani, F.

Eddy current flow meters (ECFM) are widely used for measuring the flow velocity of electrically conducting fluids. Since the flow induced perturbations of a magnetic field depend both on the geometry and the conductivity of the fluid, extensive calibration is needed to get accurate results. Transient eddy current flow metering (TECFM) has been developed to overcome this problem. It relies on tracking the position of an impressed eddy current system which is moving with the same velocity as the conductive fluid. We present an immersed version of this measurement technique and demonstrate its viability by numerical simulations and a first experimental validation.

Keywords: flow measurement; inductive methods; calibration-free

  • Measurement Science and Technology 28(2017), 105301
    Online First (2017) DOI: 10.1088/1361-6501/aa7b1e
  • Lecture (Conference)
    3rd Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russland

Permalink: https://www.hzdr.de/publications/Publ-25714
Publ.-Id: 25714


Actinide Bonding Analysis in Position Space

Patzschke, M.

Actinides are a fascinating class of elements. They are difficult to work with in the laboratory, but they are also very challenging for the theoretician. The open f-shell sometimes necessitates the use of multi-reference calculations. They contribute many electrons, making the calculation more demanding. And lastly, relativistic effects become important. These problems certainly contribute to the situation in which far less is known and understood about actinide chemistry compared to e.g. the lanthanides. In this contribution, we use analysis methods that work in real space, i.e. on the electronic density. We present different tools and the application to the bonding in BTP complexes on actinides and lanthanides . BTP complexes have been investigated for numerous years now and it is still not entirely understood, why they bind actinides more strongly than lanthanides. The presented data is hopefully a step towards the solution of that problem.

Keywords: DFT; CASPT2; Lanthanides; Actinides; Covalency

  • Poster
    Magical Mystery Tour of Electron Correlation - A Symposium in Honour of Jeppe Olsen on the Occasion of his 60th Birthday, 24.-27.10.2016, Oslo, Norwegen

Permalink: https://www.hzdr.de/publications/Publ-25713
Publ.-Id: 25713


From cubic palladium to concave core-shell platinum palladium nanoparticles: Evolution of the structure and their electrochemical properties

Tymen, S.; Scheinost, A. C.; Lozano Rodriguez, M. J.; Friebe, C.; Schubert, U. S.

Pt-Pd nanoparticles, from pure Pd nanocubes to Pd-Pt core-shell nanoparticles, are synthesized following different methods and intensively investigated, in view of a potential application in fuel cells, as catalysts for the oxygen reduction reaction (ORR). The galvanic replacement is an attractive method to prepare bimetallic particles with high catalytic activity and a high control of the size, shape and chemical composition of the particles, varying with the experimental conditions during the synthesis. The influence of the time with the transformation from pure Pd nanocubes to concave core-shell Pt-Pd nanoparticles synthesized by galvanic replacement (with a Pd core and a mix of Pt and Pd in the surface) is examined: after different times of preparation, the morphology of the particles was monitored by Transmission Electronic Microscopy (TEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDS) for the chemical composition. Via X-Ray diffraction spectroscopy (XRD), the crystallographic structure and the variation of size, lattice parameters, d-spacing, and composition were determined. The Extended X-ray Fine Structure (EXAFS) measurements show the formation of a Pt-Pd alloy at the surface of the particles for all samples. Finally, the electrochemical determination of the catalytic activity and stability tests revealed two different particle types as candidates to replace pure Pt as catalyst in the Proton Exchange Membrane Fuel Cells (PEMFC) due to their enhanced stability, higher catalytic activity, and lower Pt content.

Keywords: Platinum; palladium; nanoparticles; oxygen reduction reaction; EXAFS

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Permalink: https://www.hzdr.de/publications/Publ-25711
Publ.-Id: 25711


Speciation of the trivalent f-elements Eu(III) and Cm(III) in digestive media

Wilke, C.; Barkleit, A.; Stumpf, T.; Ikeda-Ohno, A.

In case radioactive materials are released into the environment, their incorporation into our digestive system would be a significant concern. Trivalent f-elements, i.e., trivalent actinides (An(III)) and lanthanides (Ln(III)), could potentially represent a serious health risk due to their chemo- and radiotoxicity, nevertheless the biochemical behavior of these elements are mostly unknown even to date. This study, therefore, focuses on the chemical speciation of trivalent f-elements in the human gastrointestinal tract. To simulate the digestive system artificial digestive juices (saliva, gastric juice, pancreatic juice and bile fluid) were prepared. The chemical speciation of Ln(III) (as Eu(III)) and An(III) (as Cm(III)) was determined experimentally by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the results were compared with thermodynamic modelling. The results indicate a dominant inorganic species with phosphate/carbonate in the mouth, while the aquo ion is predominantly formed with a minor contribution of the enzyme pepsin in the stomach. In the intestinal tract the most significant species are with the protein mucin. We demonstrated the first experimental results on the chemical speciation of trivalent f-elements in the digestive media by TRLFS. The results highlight a significant gap in chemical speciation between experiments and thermodynamic modelling due to the limited availability of thermodynamic stability constants particularly for organic species. Chemical speciation strongly influences the in vivo behavior of metal ions. Therefore, the results of this speciation study will help to enhance the assessment of health risks and to improve decorporation strategies after ingestion of these (radio-) toxic heavy metal ions.

Keywords: trivalent f-elements; actinides and lanthanides; time-resolved laser-induced fluorescence spectroscopy (TRLFS); metal ion speciation; simulated digestive system; Unified Bioaccessibility Method (UBM)

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Permalink: https://www.hzdr.de/publications/Publ-25710
Publ.-Id: 25710


Modifications of the magnetization ordering in Co/Mo/Co layers by Ga+ ion irradiation

Wawro, A.; Kurant, Z.; Tekielak, M.; Jakubowski, M.; Pietruczik, A.; Böttger, R.; Maziewski, A.

Molecular beam epitaxy-grown layered structures Co/Mo/Co exhibit an antiparallel coupling of Co films magnetization in the Mo spacer thickness range between 0.5 nm and 1.0 nm and parallel beyond this range. Magnetic properties are substantially modified by beam irradiation of 35 keV Gaþ ions. With the increase in ion fluence, antiparallel coupling switches to the parallel one. Further increase in fluence results in gradual suppression of ferromagnetic behavior of the system. Experimental results are correlated with numerical simulations of layered structure evolution driven by irradiation.

Keywords: ion irradiation; magnetic multilayers; molecular beam epitaxy; ion implantation

Permalink: https://www.hzdr.de/publications/Publ-25709
Publ.-Id: 25709


Interactions of coolants with hot-dip galvanized materials after loss-of-coolant accidents in pressurized water reactors

Harm, U.; Kryk, H.; Hampel, U.

During the sump recirculation phase after loss-of-coolant accidents (LOCA) in pressurized water reactors, coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps as part of the emergency core cooling system. The long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) may cause corrosion of the corresponding materials.
Generic investigations regarding the influence of such corrosion processes on the coolant chemistry and possible resulting effects in the reactor core are subject of joint research projects of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden (TUD) and Zittau-Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD are focused on elucidation of physico-chemical corrosion and precipitation processes [1].
Results of generic experiments in a lab-scale corrosion test facility suggest that there is a multi-stage corrosion process. The first stage comprises dissolution of the zinc layer in the coolant forming zinc ions and in turn affecting the coolant chemistry. During the second stage, the base material (steel) corrodes forming insoluble corrosion particles. The main influences on corrosion were identified as impact of the coolant leak jet onto the corroding surface, the coolant chemistry and the zinc surface / coolant volume ratio.
Furthermore, retrograde solubility of zinc corrosion products in boric acid containing coolants with increasing temperature was observed. Thus, formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up during its recirculation into hot downstream components (e.g. hot-spots in core). Corrosion experiments, which included formation of corrosion products at heated zircaloy cladding tubes, proved that zinc, dissolved in the coolant at low sump temperatures, turns into solid deposits of zinc borates when contacting heated zircaloy surfaces. Due to alternating heating and cooling of the coolant during sump recirculation operation, a cycle of zinc corrosion and zinc borate precipitation may be initiated.
Based on the experimental results, water chemical measures were tested to reduce corrosion and zinc borate precipitation effects [1]. Additionally, joint research projects have been established by the TUD and the HSZG dealing with local effects of corrosion, corrosion product precipitation and the interplay thereof at LOCA-specific conditions [1-2].
The investigations have been supported by the German Federal Ministry for Economic Affairs and Energy under contract nos. 1501363, 1501430, 1501467 and 1501496.

References
[1] Kryk, H. , Harm, U., Hampel, U.: Reducing in-core zink borate precipitation after loss-of-coolant accidents in pressurized water reactors, Proceedings of the Annual Meeting on Nuclear Technology (AMNT), Hamburg, 2016
[2] Seeliger, A.; Alt, S.; Kästner, W., Renger, S., Kryk, H., Harm, U. : Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - thermo- and fluid- dynamic effects. Nuclear Engineering and Design, 2016, 305, 489-502

Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments

  • Contribution to proceedings
    The Energy and Materials Research Conference (EMR 2017), 05.-07.04.2017, Lissabon (Lisbon), Portugal
    Book of Abstracts
  • Lecture (Conference)
    The Energy and Materials Research Conference (EMR 2017), 05.-07.04.2017, Lisabon (Lisbon), Portugal

Permalink: https://www.hzdr.de/publications/Publ-25708
Publ.-Id: 25708


Self-Organized Surface Patterning of Pure and Compound Semiconductors by Polyatomic Ion Irradiation

Bischoff, L.; Böttger, R.; Pilz, W.; Facsko, S.; Heinig, K.-H.

Irradiation of solids by heavy polyatomic ions (e.g. Aunm+ or Binm+) can cause localized melting at the ion impact point due to the enhanced energy density in the collision cascade of a polyatomic heavy ion impact [1,2]. Former studies demonstrated the formation of high aspect ratio, hexagonal dot patterns on Ge, Si or GaAs after high fluence, normal incidence irradiation using a mass separated FIB system choosing a suited combination of energy density deposition (i.e. poly- or monatomic ions) and substrate temperature, which facilitated transient melting of the ion collision cascade volume [2-5].
This study underscores the universality of this ion impact-melting-induced, self-organized pattern formation mechanism probing the compound semiconductor GaSb under polyatomic Aunm+ ion irradiation with various irradiation conditions in particular, ion species, fluence, energy/atom, temperature and angle of incidence.
Calculations of the needed melting energies per atom (Emelt) for different materials show, that among others GaSb is a preferring candidate for a successful surface patterning by mon- and polyatomic heavy ions whereas i.e. the surface of SiC remains stable under the given conditions. Furthermore the surface modification behavior under Aunm+ and Binm+ heavy ion impact should be compared.
HRSEM, AFM and EDX analysis of irradiated surfaces reveal that for compound semiconductors, additional superstructures are evolving on top of the regular semiconductor dot patterns, indicating superposition of a second dominant driving force for pattern self-organization.

References:
[1] C. Anders et al., Phys. Rev. B 87, 245434 (2013).
[2] L. Bischoff et al., Nucl. Instr. Meth. Phys. Res. B 272, 198-201 (2012).
[3] R. Böttger et al., J. Vac. Sci Technol. B 30, 06FF12 (2012).
[4] R. Böttger et al., Phys. Stat. Sol. RRL 7, 501-505 (2013).
[5] L. Bischoff et al., Appl. Surf. Sci. 310 154-157 (2014).

Keywords: polyatomic ions; surface modification; FIB

  • Lecture (Conference)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-25707
Publ.-Id: 25707


Self-Organized Surface Structures on Compound Semiconductors by Polyatomic Ion Irradiation

Bischoff, L.; Böttger, R.; Pilz, W.; Facsko, S.; Heinig, K.-H.

Irradiation of solids by heavy polyatomic ions of gold or bismuth can cause localized melting at the ion impact point due to the enhanced energy density in the collision cascade of a polyatomic ion impact [1]. Former studies demonstrated the formation of high aspect ratio, hexagonal dot patterns on Ge, Si and GaAs after high fluence, normal incidence irradiation choosing a suited combination of energy density deposition (i.e. poly- or monatomic ions) and substrate temperature, which facilitated transient melting of the ion collision cascade volume [2-5].
This study underscores the universality of this ion impact-melting-induced, self-organized pattern formation mechanism probing the compound semiconductor GaSb under polyatomic Au ion irradiation with various irradiation conditions. Surprisingly, GaSb irradiated with 30 keV dimer gold ions at 200°C and normal incidence shows faceted crystalline nanostructures, see Fig. 1 [6].
Calculations of the needed melting energies per atom (Emelt) for different materials show, that among others GaSb is a preferring candidate for a successful surface patterning by mon- and polyatomic heavy ions whereas for instance the surface of SiC remains stable under the comparable conditions. Furthermore the surface modification behavior under polyatomic Gold and Bismuth heavy ion impact should be compared.
HR-SEM, AFM and EDX analysis of irradiated surfaces reveal that for compound semiconductors, additional superstructures are evolving on top of the regular semiconductor dot patterns, indicating superposition of a second dominant driving force for pattern self-organization.

References:
[1] C. Anders, K.-H. Heinig and H. M. Urbassek, Polyatomic bismuth impacts into germanium: Molecular dynamics study, Phys. Rev. B 87 (2013) 245434.
[2] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, and W. Pilz, Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions, Nucl. Instr. and Meth. B 272 (2012) 198.
[3] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, From sponge to dot arrays on (100)Ge by increasing the energy of ion impacts, Journal of Vacuum Science and Technology B 30 (2012) 06FF12.
[4] R. Böttger, K-.H Heinig, L. Bischoff, B. Liedke, R. Hübner, and W. Pilz, Silicon nanodot formation and self-ordering under bombardment with heavy Bi3 ions, physica status solidi – Rapid Research Letters 7 (2013) 501.
[5] L. Bischoff, R. Böttger, K.-H. Heinig, S. Facsko, and W. Pilz, Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions, Applied Surface Science 310 (2014) 154.
[6] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender and S. Facsko, Faceted nanostructure arrays with extreme regularity by self-assembly of vacancies, Nanoscale 7 (2015) 18928.

Keywords: Self organization; polyatomic ion; surface pattern

  • Lecture (Conference)
    Nanopatterning2017: Nanoscale Pattern Formation at Surfaces & FOR3NANO: Formation of 3D Nanostructures by Ion Beams, 26.-30.06.2017, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-25706
Publ.-Id: 25706


Multiphase Flows in Energy related Industrial Applications – Theory, Experiments and CFD Validation

Höhne, T.

Two-phase flows occur in many industrial processes. Reliable predictions on flow characteristics are necessary for the design, process optimization and safety analysis of related apparatuses and processes. Experimental investigations are expensive and in most cases not transferable to modified geometries or different scales and flow conditions. For this reason there is a clear requirement for numerical tools. Due to the 3D nature of flows and the importance of turbulence in most cases this means a strong need for reliable 3D CFD-tools rather than 1D system codes or simplified correlations. The general aim is to provide simulation tools for the design, optimization and safety analyses of medium and large scale applications in which multiphase flows are involved. Such tools can contribute to improve the efficient use of energy and resources (e.g. in chemical engineering and oil industries) and to guarantee the safe operation (especially nuclear safety) – provided that they are predictive. Since large scale applications are considered such as chemical reactors or components of the cooling system of a nuclear power plant the Euler-Euler two- or multi fluid model is the base for the development. Presently the predictive capabilities for basic hydrodynamics are restricted due to limitations of the closure models. For this reason one focus of our multiphase flow research is the improvement of the closures first for adiabatic flow modelling but also phase transfer, chemical reactions etc. have to be considered. A second focus is to establish modelling frameworks as iMUSIG, AIAD and GENTOP to allow a proper consideration of the local physical phenomena. These activities will help to improve the CFD code capabilities in energy related industrial applications.

Keywords: multi-phase; CFD; AIAD; GENTOP; MUSIG

  • Invited lecture (Conferences)
    International Conference on Thermofluid 2017, 09.-10.11.2017, Yogyakarta, Indonesien
  • Contribution to proceedings
    International Conference on Thermofluid 2017, 09.-10.11.2017, Yogyakarta, Indonesien

Permalink: https://www.hzdr.de/publications/Publ-25705
Publ.-Id: 25705


Three dimensional CFD simulation of heat and mass transfer in passive heat removal systems

Moonesi Shabestary, A.; Krepper, E.; Lucas, D.

The current job is presenting the CFD- modelling and simulation of condensation inside passive heat removal systems. Designs of future nuclear boiling water reactor concepts are equipped with emergency cooling systems which are passive systems for heat removal. The emergency cooling system consists of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. At normal operation conditions, the pipes are filled with water and no heat transfer to the secondary side of the condenser occurs. In the case of an accident the water level in the core is decreasing, steam comes in the emergency pipes and due to the subcooled water around the pipe, this steam will condense. The emergency condenser acts as a strong heat sink which is responsible for a quick depressurization of the reactor core when any accident happens. The actual project is defined to model the phenomena which are occurring inside the emergency condensers. The focus of the project is on detection of different morphologies such as annular flow, stratified flow, slug flow and plug flow and also modeling of the laminar film which is occurring during the condensation near the wall.
The condensation procedure inside the pipe can be divided to two steps. The first step is the wall condensation and the second step is the direct contact condensation (DCC). The Algebraic Interfacial Area Density (AIAD) concept is used in order to model the interface between liquid and steam. In the next steps the Generalized Two-Phase Flow (GENTOP) model will be used to model also the dispersed phases which are occurring inside the pipe. Finally, the results of the simulations will be validated by experimental data which will be available in HZDR. In this paper the results of the first part has been presented.

Keywords: Film Condensation; Heat and mass transfer; Heat transfer coefficient; CFD

  • Lecture (Conference)
    Annular Meeting on Nuclear Technology, 16.-17.05.2017, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-25704
Publ.-Id: 25704


Where do the Actinides go? And why we should care…

Patzschke, M.

Understanding the chemistry of actinides is crucial for the safety guarantees required for final repositories for nuclear waste. Pathways of distribution of actinides in the environment are discussed and calculations on model compounds to understand the bonding of actinides are presented.

Keywords: DFT; Real space analysis; actinide compounds

  • Invited lecture (Conferences)
    X. MMQC Mariapfarr, 06.-10.03.2017, Mariapfarr, Österreich

Permalink: https://www.hzdr.de/publications/Publ-25703
Publ.-Id: 25703


Bond analysis of actinide complexes in real space

Patzschke, M.

Subtle effects are important in the bonding of actinides. Understanding of these effects is crucial for the prediction of the fate of actinides in the environment. In this talk we will focus on QTAIM, NCI and ELI calculations to understand the difference in bonding between actinides and lanthanides.

Keywords: DFT; CASPT2; Real space analysis; QTAIM; ELF/ELI; NCI; actinide complexes

  • Invited lecture (Conferences)
    UCT und IOCB Seminar Prag, 31.03.2017, Prag, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-25702
Publ.-Id: 25702


Real Space Analysis of Ac-Ac bonds, the case of encaged U_2

Patzschke, M.

Real space analysis of the chemical bond is a valuable tool for understanding the bonding in chemical compounds. Especially in the field of actinide complexes and actinide-actinide bonds, there is still much to be learned. In this talk we will shoe how encaged uranium is forced to bond and how the bond depends on the cage size.

Keywords: Real Space Analysis; DFT; CASPT2; Actinides

  • Invited lecture (Conferences)
    Chemical Bonding in Position Space, 27.11.-01.12.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25701
Publ.-Id: 25701


Technetium Complexes with Arylselenolato and Aryltellurolato Ligands

Noschang Cabral, B.; Kirsten, L.; Hagenbach, A.; Piquini, P. C.; Patzschke, M.; Schulz Lang, E.; Abram, U.

Reactions of (NBu4)[TcOCl4] or [TcCl3(PPh3)2(CH3CN)] with in situ-prepared lithium arylselenolates and -tellurolates
give (NBu4)[TcVO(ArE)4] (E = Se, Te; Ar = phenyl) and [TcIII(ArE)3(PPh3)(CH3CN)] (E = Se, Te; Ar = phenyl, 2,6-Me2phenyl,
mesityl) complexes, respectively. The products contain square-pyramidal (TcV compounds) and trigonal bipyramidal (TcIII
complexes) coordinated technetium atoms. Density Functional Theory calculations indicate that the Tc-chalcogen bonds in
the TcIII compounds have greater bond order than in the TcV compounds.

Keywords: Technetium; new compounds; crystal structure; DFT; bond analysis

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Permalink: https://www.hzdr.de/publications/Publ-25700
Publ.-Id: 25700


Towards direct access to THz-driven transient electronic states with time-resolved ARPES

Deinert, J.-C.; Green, B. W.; Kovalev, S.; Stähler, J.; Gensch, M.

In this contribution we present the concept for a novel experimental setup at the THz facility TELBE at Helmholtz-Zentrum Dresden-Rossendorf [1], which combines THz excitation with time- and angleresolved photoelectron spectroscopy (tr-ARPES). This challenging combination of two state-of-the-art techniques promises new insights into highly relevant non-equilibrium processes in matter, since THz excitation provides resonant access to a multitude of fundamental modes, e.g., lattice vibrations, molecular rotations, spin precession and the motion of free electrons. Until now, the corresponding changes to the electronic structure of a material can be probed only indirectly, e.g., by measuring the material's optical properties. The obvious method – tr-ARPES – which gives direct access to the electronic states on a femtosecond timescale (cf. Fig. 1) has not been implemented due to the previously unaccomplishable high duty cycle of the THz source (>> 10 kHz repetition rate quasi-cw) to provide sufficient statistics for tr-ARPES. This limitation is overcome at the TELBE which provides tunable and CEP-stable THz pulses at a repetition rate of 100 kHz based on superradiant emission, and timing stability of < 30 fs due to a novel pulse-to-pulse diagnostics scheme [3]. Over the next three years a tr-ARPES setup shall hence be implemented at the THz facility TELBE which aims at establishing feasibility and dynamic range despite obvious obstacles such as residual streaking of the photoelectrons by the high THz excitation fields (see, e.g., [2]). This contribution is discussing the challenges and the opportunities of tr-ARPES in THz control experiments and will outline the current design of the planned tr-ARPES endstation.
[1] B. Green et al., Sci. Rep. 6 (2016), 22256.
[2] U. Fruehling et al., Nat. Phot.. 3 (2009), 523.
[3] see poster presentation of S. Kovalev

  • Poster
    Optical Terahertz Science and Technology, 06.04.2017, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-25699
Publ.-Id: 25699


Evaluation of Motion Mitigation using Abdominal Compression in the Clinical Implementation of Pencil Beam Scanning Proton Therapy of Liver Tumors

Lin, L.; Souris, K.; Kang, M.; Glick, A.; Lin, H.; Huang, S.; Stützer, K.; Janssens, G.; Sterpin, E.; Lee, J. A.; Solberg, T. D.; Mcdonough, J. E.; Simone Ii, C. B.; Ben-Josef, E.

Purpose: To determine whether individual liver tumor patients can be safely treated with pencil beam scanning proton therapy. This study reports a planning preparation workflow that can be used for beam angle selection and the evaluation of the efficacy of abdominal compression (AC) to mitigate motion.

Methods: Four-dimensional computed tomography scans (4DCT) with and without AC were available from 10 liver tumor patients with fluoroscopy-proven motion reduction by AC. For each scan, the motion amplitudes and the motion-induced variation of water equivalent thickness (ΔWET) in each voxel of the target volume were evaluated during treatment plan preparation. Optimal proton beam angles were selected after volume analysis of the respective beam-specific planning target volume (BSPTV). M₈₀ and ΔWET₈₀ derived from the 80ᵗʰ percentiles of motion amplitude (M) and ΔWET were compared with and without AC. Proton plans were created on the average CT. 4D dynamic dose calculation was performed post plan by synchronizing proton beam delivery timing patterns to the 4DCT phases to assess interplay and fractionation effects, and to determine motion criteria for subsequent patient treatment.

Results: AC resulted in reductions in mean Liver-GTV dose, M, ΔWET, and BSPTV volumes and improved dose degradation (ΔD₉₅ and ΔD₁) within the CTV. For small motion (M₈₀ < 7 mm and ΔWET₈₀ < 5 mm), motion mitigation was not needed. For moderate motion (M₈₀ 7-10 mm or ΔWET₈₀ 5-7 mm), AC produced a modest improvement. For large motion (M₈₀ > 10 mm or ΔWET₈₀ > 7 mm), AC and/or some other form of mitigation strategies were required.

Conclusion: A workflow for screening patients’ motion characteristics and optimizing beam angle selection was established for the pencil beam scanning proton therapy treatment of liver tumors. Abdominal compression was found to be useful at mitigation of moderate and large motion.

  • Poster
    AAPM 59th Annual Meeting & Exhibition, 30.07.-03.08.2017, Denver, Colorado, United States of America

Permalink: https://www.hzdr.de/publications/Publ-25698
Publ.-Id: 25698


Local aspects of hydrogen-induced metallization of the ZnO(10-10) surface

Deinert, J.-C.; Hofmann, O. T.; Meyer, M.; Rinke, P.; Stähler, J.

This study combines surface-sensitive photoemission experiments with density functional theory to give a microscopic description of H-adsorption-induced modifications of the ZnO(10-10) surface electronic structure. We find a complex adsorption behavior caused by a strong coverage dependence of the H adsorption energies: Initially, O-H bond formation is energetically favorable and H acting as an electron donor leads to the formation of a charge accumulation layer and to surface metallization. The increase of the number of O-H bonds leads to a reversal in adsorption energies such that Zn-H bonds become favored at sites close to existing O-H bonds, which results in a gradual extenuation of the metallization. The corresponding surface potential changes are localized within a few nanometers both laterally and normal to the surface. This localized character is experimentally corroborated by using subsurface bound excitons at the ZnO(10-10) surface as a local probe. The pronounced and comparably localized effect of small amounts of hydrogen at this surface strongly suggests metallic character of ZnO surfaces under technologically relevant conditions and may, thus, be of high importance for energy level alignment at ZnO-based junctions in general.

Permalink: https://www.hzdr.de/publications/Publ-25697
Publ.-Id: 25697


Nanoscale Potential Fluctuations in Zirconium Oxide and the Flash Memory Based on Such Fluctuations

Gritsenko, V. A.; Perevalov, T. V.; Kruchinin, V. N.; Aliev, V. S.; Gerasimova, A. K.; Erenburg, S. B.; Trubina, S. V.; Kvashnina, K. O.; Prosvirin, I. P.

X-ray photoelectron spectroscopy, EXAFS, XANES, spectral ellipsometry and quantum-chemistry calculations were used to examine the atomic and electronic structure of non-stoichiometric amorphous ZrOx slightly enriched with zirconium. The experimental data show that the ZrOx material consists of stoichiometric ZrO2, metallic Zr and zirconium suboxides ZrOy. The structure of ZrOx is analyzed using the Random Bonding and Random Mixture models. A model of nanoscale spatial potential fluctuations in ZrOx is substantiated. In this model, the potential fluctuations for electrons and holes arise due to the local fluctuations of bandgap energy in the range from 0 to 5.4 eV. A ZrOx-based flash memory element with giant retention time is proposed

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Permalink: https://www.hzdr.de/publications/Publ-25696
Publ.-Id: 25696


The first six to eight years of DREAMS (DREsden Accelerator Mass Spectrometry): On our way to cloud nine?

Merchel, S.; Rugel, G.; Scharf, A.; Ziegenrücker, R.; DREAMS-Users; DREAMS-Friends

Since 2009, the DREAMS (DREsden Accelerator Mass Spectrometry) facility offers users to do their own sample preparation for producing AMS-targets. Two years after the 6 MV-based tandem accelerator measured the first unknown samples for long-lived radionuclides [1]. AMS reduces background and interfering signals resulting from molecular ions and isobars enormously. Thus, AMS provides much lower detection limits compared to conventional MS or decay counting. DREAMS offers excellent measurement capabilities also for external users [2].
AMS allows 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 10Be 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. oxygen and silicon in quartz, can be found in samples taken from the Earth’s surface. The concentrations of atmospheric or in-situ produced CNs record information that is used to reconstruct sudden geomorphological events such as volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earthquakes [e.g. 3] and glacier movements. These movements and data from ice cores give also hints for the reconstruction of historic climate changes and provide 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 indirect dating of bones as old as several Ma’s is possible. Finally, remnants of supernova-produced nuclides can also be found in deep-sea archives (sediment, crust, nodule) [e.g. 4].
Anthropogenic production e.g. by release from nuclear reprocessing, accidents and weapon tests led to increased radionuclide levels in surface water, ice and soil (36Cl, 129I,…). Hence, some nuclides can 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. Obviously, also nuclear installation materials are radioactive (36Cl, 41Ca,…).

References: [1] G. Rugel et al., Nucl. Instr. Meth. Phys. Res. B. 2016, 370,94. [2] www.hzdr.de/ibc for beam time application. [3] W. Schwanghart et al., Science 2016, 351,147. [4] A. Wallner et al., Nature 2016, 532, 69.

Keywords: AMS; radionuclide

  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 ─ Jubiläumskongress "GDCh - 150 Jahre", Jahrestagung der Fachgruppe Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25694
Publ.-Id: 25694


Attempts to understand potential deficiencies in chemical procedures for accelerator mass spectrometry (AMS)

Merchel, S.; Gurlit, S.; Rugel, G.; Scharf, A.; DREAMS-Users; DREAMS-Friends

Since 2009, the DREAMS (DREsden Accelerator Mass Spectrometry) facility offers users to do their own sample preparation for producing AMS-targets. Several projects are aiming at analysing 10Be, 26Al, and 36Cl (as BeO, Al2O3, AgCl). In cooperation with other AMS-facilities, also actinides (coprecipitation as Fe2O3) and 60Fe (as Fe2O3) are investigated.
Hence, essential steps are hydroxide or AgCl precipitation. For the determination of in-situ or atmospheric 26Al in marine and terrestrial sediments, we had sometimes unaccountable low chemical yields, which might be explained by redissolving Al(OH)3 in the last washings. Thus, we investigated these potential losses by ICP-MS as a function of alteration (waiting) times. Indeed, up to 31% of the precipitated Al was redissolved by immediate triple washings. After 2 h of waiting, this could be reduced to 11%. Further waiting (over-night) resulted in losses of 6% of Al (equally for Be) only.
We also tested the behaviour of Fe(III), U(VI) (also as analogue for ~Pu(VI) and Np(VI)), and Er(III) (as analogue for Am(III), Cm(III), Pu(III)) when Fe(OH)3 is washed. Even including the supernatant, total losses of 3-times washing of over-night altered hydroxides are as low as 2.6-3.5%. Thus, repeated washing cycles are very advisable to reduce ions such as NH4 + and Cl- before drying and ignition.
For a single project, we explored the possibility to measure 36Cl and natCl by (isotope dilution) AMS in “dirty” permafrost ice wedge samples as heavy as 1.6 kg. The chemical yield of AgCl was only 20-35% and is a function of total natCl. Thus, we tested preconcentration steps like ion exchange (DOWEX 1x8, 5 ml), which look promising.
Very often DREAMS projects focus at analysing quartz for in-situ-produced 10Be and 26Al. Dissolving quartz only will minimise other troublesome elements such as Al, Be, and Ti from coexisting mineral phases. Obviously, low stable Al leads to higher 26Al/27Al, i.e. better 26Al-statistics. However, low Ti is also helpful for fewer problems in Be-chemistry, i.e. better 10Be-statistics. For correct calculation of exposure ages and erosion rates, “pure quartz”, i.e. similar target elements as the calibration site used for production rates and no natural 9Be, is needed, too. One of the earliest quartz cleaning methods is routinely used at DREAMS: H2SiF6/HCl on a shaker table at room temperature. It produces up to 1.8% residue of the original “quartz” mass with a mean maximum value of 0.6% (values from >100 samples from six different projects). SEM-EDX identified the most prominent minerals to be zircon Zr[SiO4], white sillimanite Al2[O|SiO4], transparent to blue kyanite Al2[O|SiO4], black chromite Fe2+Cr2O4, and orange rutile TiO2. For comparison, we treated 3.5 g of these residues by microwave (MW) digestion resulting in further dissolving 31% of the original residue. SEM-EDX analyses of the MW-residue showed mainly pristine kyanite and heavily-attacked sillimanite only. ICP-MS of the MW-solution validated the dissolution of Al, Ti, Cr, Fe, and Zr. For a typical 50 g-“quartz sample” the MW-method would add more than 3 mg of Ti, over 7 mg of Al and, and, worst of all, about 25 μg of Be to the sample.
Ackn.: Thanks to B. Bookhagen, A. Gärtner, T. Opel, P. Steier, F. Quinto & S. Weiss.

Keywords: AMS; sample preparation; exposure dating; erosion rate

  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 ─ Jubiläumskongress "GDCh - 150 Jahre", Jahrestagung der Fachgruppe Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25693
Publ.-Id: 25693


Using cosmogenic 10Be surface exposure dating to constrain the timing of deglaciation on the northern Swiss Plateau

Groos, A. R.; Struck, J.; Wüthrich, L.; Veit, H.; Gnägi, C.; Merchel, S.; Scharf, A.; Rugel, G.; Zech, R.

Keywords: LGM; AMS; 10Be Surface Exposure Dating

  • Poster
    Annual CH-QUAT Meeting Faculty of Science, University of Neuchâtel Topic: "Quaternary topics in the Jura Mountains and the Seeland region", 01.04.2017, Neuchâtel, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-25692
Publ.-Id: 25692


Structural Distortions and Charge Density Waves in Iodine Chains Encapsulated inside Carbon Nanotubes

Komsa, H.-P.; Senga, R.; Suenaga, K.; Krasheninnikov, A. V.

Atomic chains are perfect systems for getting fundamental insights into the electron dynamics and coupling between the electronic and ionic degrees of freedom in one-dimensional metals. Depending on the band filling, they can exhibit Peierls instabilities (or charge density waves), where equally spaced chain of atoms with partially filled band is inherently unstable, exhibiting spontaneous distortion of the lattice that further leads to metal−insulator transition in the system. Here, using high-resolution scanning transmission electron microscopy, we directly image the atomic structures of a chain of iodine atoms confined inside carbon nanotubes. In addition to long equidistant chains, the ones consisting of iodine dimers and trimers were also observed, as well as transitions between them. First-principles calculations reproduce the experimentally observed bond lengths and lattice constants, showing that the ionic movement is largely unconstrained in the longitudinal direction, while naturally confined by the nanotube in the lateral directions. Moreover, the trimerized chain bears the hallmarks of a charge density wave. The transition is driven by changes in the charge transfer between the chain and the nanotube and is enabled by the charge compensation and additional screening provided by the nanotube.

Keywords: carbon nanotubes; Peierls instabilities; charge density waves; TEM; DFT

Permalink: https://www.hzdr.de/publications/Publ-25691
Publ.-Id: 25691


Revisiting hollandites: channels filling by main-group elements together with transition metals in Bi2-yVyV8O16

Lebedev, O. I.; Hébert, S.; Roddatis, V.; Martin, C.; Turner, S.; Krasheninnikov, A. V.; Grin, Y.; Maignan, A.

Starting from the nominal BixV8O16 formula, state-of-the-art transmission electron microscopy investigation has been made to propose the new chemical formula Bi2-yVyV8O16 for this hollandite structure. This results from the filling of the channels by main-group elements together with vanadium (V5+) species, with variable content of Bi and V inside the channels. The influence of the Bi content and of this local disorder on the magnetic and transport properties has been investigated in polycrystalline samples of BixV8O16 with nominal composition x = 1.6 and x = 1.8. The rather x-independent electrical resistivity (≈ 5 m·cm) and Seebeck coefficient at high T (-35 μV·K-1 at 900 K) is discussed in terms of an unchanged V oxidation state resulting from the filling-up of the wide channels with Bi and V. It is proposed that this local disorder hinders the charge/orbital setting below 60 K on the V ions of the V8O16 framework. Hollandites exhibit complex electronic and magnetic properties with potential applications in the field of batteries, photocatalysis or nuclear waste storage, and these results show that a careful and detailed investigation of the nature and content of the cations inside the channels is crucial to better understand the doping and disorder impact on their properties.

Keywords: hollandites; defects; TEM; DFT calculations

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Permalink: https://www.hzdr.de/publications/Publ-25690
Publ.-Id: 25690


Microbial transformation of bentonite

Matschiavelli, N.; Steglich, J.; Kluge, S.; Cherkouk, A.

For the storage of highly radioactive waste in a deep geological repository a multi-barrier concept is favoured, which combines a technical barrier (canister including the highly radioactive waste), a geotechnical barrier (e.g. Bentonite) and the geological barrier (host rock). Due to their properties, namely a high swelling capacity and a low hydraulic conductivity, Bentonites fulfil in this system a sealing and buffering function. For the potential repository of nuclear waste the microbial mediated transformation of Bentonite could influence its properties as a barrier material. To elucidate the microbial potential within selected Bentonites, microcosms were set up, which contain 20g Bentonite and 40ml anaerobic synthetic Opalinus-clay-pore water solution under an N2/CO2-gas-atmosphere. Substrates like acetate and lactate were supplemented to stimulate potential microbial activity. Microcosms were incubated in the dark, without shaking at 30°C. Within an indefinite time scale samples were taken at different time-points of incubation and were analysed regarding geochemical parameters like pH, O2-concentration, redox potential, iron-concentration and sulphate-concentration as well as biological parameters like the consumption and formation of metabolites. First results show that bentonites represent a source for microbial life, demonstrated by the consumption of lactate and the formation of acetate and pyruvate. Furthermore, microbial iron-reduction was determined. The results reveal the importance of the selection of the best suitable Bentonite in order to avoid transformation of the mineral structure by indigenous microbes.

  • Poster
    16th International Clay Conference - Clays, from the oceans to space - Granada 17-21 July 2017, 17.-21.07.2017, Granada, Spain

Permalink: https://www.hzdr.de/publications/Publ-25689
Publ.-Id: 25689


Interactions of an extremely halophilic archaeon relevant in nuclear waste repositories in rock salt with uranium

Bader, M.; Swanson, J.; Foerstendorf, H.; Müller, K.; Steudtner, R.; Drobot, B.; Schmidt, M.; Cherkouk, A.

Rock salt is a potential host rock for the final storage of radioactive waste in a deep geological formation. Indigenous microorganisms and their interactions with radionuclides must be considered for the safety performance of the repository, considering the worst case scenario, the release and subsequent migration of radionuclides. Therefore, the extremely halophilic microorganism Halobacterium noricense DSM 15987T, which occurs naturally in the potential host formation rock salt, was used to study its interactions with uranium.
A time-dependent sorption experiment showed that bioassociation of uranium onto cells of H. noricense DSM 15987T is not only a sorption process; i.e. fast sorption within the first hours until reaching a stable equilibrium state. The obtained kinetic data showed a multistage process with fast sorption during the first two hours of exposure time. Over the next hours, an increasing amount of uranium was detectable in the supernatant, implying that the uranium already sorbed was again released from the cells. Subsequently, the amount of bioassociated uranium increased very slowly until a maximum sorption of 80% was reached after 48 h. To investigate this multistage bioassociation process on archaeal cells in detail several spectroscopic as well as microscopic methods were applied. With in situ attenuated total reflection fourier-transform infrared spectroscopy the initial sorption process of uranium to cells of H. noricense DSM 15987T within the first two hours was proven. Results showed that the radionuclide binds to carboxylic as well as to phosphate groups simultaneously within the first two hours of incubation time. Additionally, cryo time-resolved laser-induced fluorescence spectroscopic investigations were performed, which showed the involvement of polynuclear carboxylate species and the presence of a meta-autunite like mineral. By using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, uranium could be localized on the cell surface of the halophilic archaeon within the first sorption phase and later in the biomineral-like agglomerates. Hence, our study showed that uranium can be immobilized by halophilic archaea via biomineralization and bioassociation, which might influence the further migration of the actinide.

  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 Interdisziplinäre Symposien Jahrestagung Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25688
Publ.-Id: 25688


Beyond Electrodynamics with PIConGPU: Performance Portable, Open Multi-Physics HPC Simulations for Laser-Plasma Experiments at the European XFEL

Huebl, A.; Widera, R.; Pausch, R.; Garten, M.; Burau, H.; Kluge, T.; Vorberger, J.; Debus, A.; Cowan, T. E.; Schramm, U.; Chung, H.-K.; Bussmann, M.

PIConGPU is reportedly the fastest electro-magnetic particle-in-cell code in the world in terms of sustained Flop/s. Its computational power does not only enable 3D3V simulations with unprecedented detail and fast time-to-solution but also allows improving predictive capabilities of simulations by estimating stochastic and systematic errors via repeated simulations. Synthetic in-situ diagnostics drive the exploration of high-detail simulations whose signatures, e.g. emitted radiation spectra, would be inaccessible in post-processing due to sheer data size. Upcoming experiments at the European XFEL require us to take PIConGPU even one step further: modeling XFEL-matter interaction on top of laser-driven particle acceleration processes requires the introduction of non-trivial X-ray photon scattering, photon generation and advanced non-LTE atomic models. Coupled with an open-science centered strategy, from open performance portable source code over open standardized data formats to documented workflows for PByte scale simulation we strive towards a new quality of predictive, reproducible simulations within our community.

Keywords: PIC GPU XFEL Modeling HPC laser-plasma LPA pump-probe HED IO OpenSource OpenData OpenScience

  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-25687
Publ.-Id: 25687


Open Science with openPMD

Huebl, A.; Lehe, R.; Vay, J.-L.; Grote, D. P.; Sbalzarini, I. F.; Kuschel, S.; Bussmann, M.

Nobody needs yet an other data format for HPC. But why have so-called self-describing data formats never provided out-of-the-box cross application portability? Why are most open-access datasets not self-describing for both the domain scientist and after-use? And why do communities need to implement their data readers in various post-processing, visualization and analysis frameworks over and over again?

We present the open meta data format openPMD for data format agnostic markup of particle-mesh data. Based on a minimal kernel of meta information and enriched with domain-specific extensions, we develop an open ecosystem of interoperable simulations and data processing frameworks from the domains of laser-plasma interaction, X-ray photon sciences, astrophysics up to systems biology. This poster presents our efforts to enable & establish workflows suitable to frictionless transposition between those domains, using highly scalable I/O methods (e.g. ADIOS BP or HDF5), a truly self-describing data markup and peer reviewed participation.

Keywords: I/O OpenScience OpenData HPC OpenAccess HDF5 ADIOS metadata

  • Poster
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz
    DOI: 10.5281/zenodo.822396

Permalink: https://www.hzdr.de/publications/Publ-25686
Publ.-Id: 25686


Data Management in Small Animal Imaging: Conceptual and Technical Considerations

Maus, J.; Hofheinz, F.

Small animal imaging in general and multimodal tomographic imaging in particular generate a substantial amount of heterogeneous data that can be challenging to handle. Besides computed tomographic images, there are also the primarily acquired raw data such as listmode data in positron emission tomography (PET), projection data in X-ray computed tomography (CT), or even k-space data in magnetic resonance imaging (MRI). Additionally, further image data might be created by postprocessing (e.g., filtering) or by using alternative image reconstruction methods. All these data have to be stored; thus, the required disk space can easily exceed several terabyte (TB) over time. Therefore, good data storage planning and management strategies are required. In this context, data management obviously does not just mean storing the data. Rather, the data have to be easily accessible for all involved researchers, they also have to remain accessible years after the measurement, and the data have to be backed up in a save and secured place.

Keywords: PET; Small Animal Imaging

  • Book chapter
    Fabian Kiessling, Bernd J. Pichler, Peter Hauff: Small Animal Imaging: Basics and Practical Guide, Heidelberg: Springer International Publishing, 2017, 978-3-319-42200-8, 581-590
    DOI: 10.1007/978-3-319-42202-2_22

Permalink: https://www.hzdr.de/publications/Publ-25685
Publ.-Id: 25685


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