Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32337 Publications
Reactive transport modeling using heterogeneous flow field data based on positron emission tomography
Lippold, H.; Kulenkampff, J.; Karimzadeh, L.; Stuhlfauth, C.; Lippmann-Pipke, J.; Fischer, C.;
Discrepancies between experimental and RTM results are often attributed to flow field heterogeneities. Positron emission tomography (PET) provides direct and quantitative insight into flow fields in complex media, such as barrier materials or porous rocks.
Adsorption and transport of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) in a homogeneous sand-goethite system were investigated as a function of pH. Interaction of MCPA with the solid surface was geochemically modeled using the charge distribution multisite complexation (CD-MUSIC) approach. Based on this calibrated surface complexation model, retardation of MCPA in transport experiments was significantly underestimated by 1D simulations with hydrodynamic parameter values obtained from a fit to the breakthrough of HTO as a conservative tracer.
On the basis of flow field data derived from PET measurements, heterogeneous flow observed for 18F as a tracer was reproduced in 2D simulations (with flow velocities controlled by the pressure gradient field according to Darcy’s law) assuming a peripheral zone with increased porosity and permeability. Using this flow model, the predicted breakthrough of MCPA was significantly more realistic compared to 1D simulations with the same chemical parameter values. Thus, this study demonstrates quantitatively that inconsistencies between static (batch) and dynamic (column) systems can be caused by heterogeneities in fluid flow, i.e., not necessarily by non-equilibrium conditions. This in turn highlights the need to consider real flow fields in predictive transport models.
  • Lecture (Conference)
    Goldschmidt 2018, 12.-17.08.2018, Boston, United States of America

Publ.-Id: 27273 - Permalink


Magnetic field-induced proton dose enhancement: Experimental verification and Monte-Carlo simulation
Lühr, A.ORC; Burigo, L. N.; Gantz, S.; Schellhammer, S.; Hoffmann, A. L.
Introduction
Proton therapy (PT) is expected to benefit from integration with magnetic resonance (MR) imaging. However, the magnetic field distorts the dose distribution and induces a local dose enhancement at tissue-air interfaces by the electron return effect (ERE). For MR-integrated photon therapy, a dose enhancement ratio (DER) of 40% compared to no magnetic field has been reported. Here, measurements and calculations of DER for proton beams in transverse magnetic fields are reported.

Methods
Two measurement setups were used: EBT3 films were either attached to the distal face of one or sandwiched between two 10 mm PMMA slabs. Films were irradiated with a 200 MeV proton beam, both with and without transverse magnetic field (0.92 T). High-resolution Monte-Carlo simulations were used to reproduce the experimental findings and to calculate the DER for proton energies between 50−200 MeV and magnetic field strengths between 0.35−3 T within the first 0.05 mm (DERmax) and as function of distance from the air interface.

Results
A DER of (2.2±0.4)% and (0.5±0.6)% was measured at 0.156 and 0.467 mm from the interface, respectively (Fig.1). Measurements and simulations agreed within 0.15%. Simulations using a 200 MeV beam showed a DERmax of 2.6% and 8.2% for 0.35 and 1.5 T, respectively (Fig.2). At 1 T, DERmax increased from 3.2% to 7.6% between 50 and 200 MeV.
Conclusion
For proton beams, the ERE in transverse magnetic fields is measurable. The dose enhancement is well predictable, decreases with distance from the interface, and is negligible after 1 mm. Although small, the impact of the ERE cannot be ignored for dosimetry with air-filled ionization chambers and in porous media (e.g. lung treatment).
Keywords: proton therapy, magnetic resonance imaging, MRI, MR, radiotherapy, dosimetry, electron return effect
  • Abstract in refereed journal
    TBD (2018)

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  • Secondary publication expected

Publ.-Id: 27272 - Permalink


Synthesis and radiofluorination of novel fluoren-9-one based derivatives for the imaging of α7 nicotinic acetylcholine receptor with PET
Teodoro, R.; Scheunemann, M.; Wenzel, B.; Peters, D.; Deuther-Conrad, W.; Brust, P.;
By structure-activity relationship studies on the tilorone scaffold, the ‘one armed’ substituted dibenzothiophenes and the fluoren-9-ones were identified as the most potential α7 nAChR ligands. While the suitability of dibenzothiophene derivatives as PET tracers is recognized, the potential of fluoren-9-ones is insufficiently investigated. We herein report on a series of fluoren-9-one based derivatives targeting α7 nAChR with compounds 8a and 8c possessing the highest affinity and selectivity. Accordingly, with [18F]8a and [18F]8c we designed and initially evaluated the first fluoren-9-one derived α7 nAChR selective PET ligands. A future application of these radioligands is facilitated by the herein presented successful implementation of fully automated radiosynthesis.
Keywords: α7 nAChR PET Radiofluorination Fluoren-9-one Dibenzothiophenes

Publ.-Id: 27271 - Permalink


Consolidation of surface speciations by a combined spectroscopic and modeling approach
Foerstendorf, H.ORC; Jordan, N.; Heim, K.; Mayordomo, N.; Steudtner, R.; Stockmann, M.
A reliable risk assessment of a deep geological waste disposal site for spent nuclear fuel refers to thermodynamic data bases which must contain resilient data sets. This information can be obtained from Surface Complexation Modeling (SCM) of batch sorption data, which is in turn consolidated by molecular information of relevant, prevailing species at mineral surfaces derived from spectroscopic investigations.
A combined approach of optical spectroscopic techniques, such as vibrational and luminescence spectroscopy, classical batch sorption studies and SCM was applied for the study of the surface speciation of actinide- and selenium oxyanions on mineral phases. In this study, spectroscopic findings of the surface speciation of uranium(VI) and selenium(IV) and (VI) on different mineral oxide phases, serving as models for complex naturally occurring minerals in a host rock of a nuclear waste repository, are presented.
From the ternary sorption system U(VI)/phosphate/SiO2, the formation of two binary uranyl surface species and of a precipitate was found to be sufficient to satisfactorily fit the respective batch results by SCM. For the selenium(IV) and selenium(VI) binary sorption systems, a single predominant inner-sphere selenite and outer-sphere selenate surface species on alumina phases were identified by vibrational spectroscopy, respectively. With respect to the bidentate binding mode observed for both oxyanionic surface species, SCM provided excellent fitting results of the batch sorption data.
The results of this study demonstrated that the combined approach of in situ spectroscopy and batch sorption studies contributes to an improved performance of future assessments for the migration of radionuclides an fission products in the environment of a repository site.
  • Lecture (Conference)
    Goldschmidt 2018, 12.-17.08.2018, Boston, U.S.A.

Publ.-Id: 27270 - Permalink


Einfluss der Bildgebung eines in beam MR-Scanners auf die Dosisprofile eines Protonenstrahls
Karsch, L.; Gantz, S.; Pawelke, J.; Schellhammer, S.; Smeets, J.; Hoffmann, A.;
Einleitung
Eine in Echtzeit ausgeführte Magnetresonanztomografie (MRT) könnte die geometrische Präzision der Protonentherapie künftig verbessern. Zur MR-Bildgebung werden jedoch magnetische Gradientenfelder in Pulssequenzen auf- und abgebaut, die mit den Protonen wechselwirken. Aufgrund der geringen Stärke der Gradientenfelder wird theoretisch keine Änderung der Dosisverteilung des Protonenstrahls durch diese magnetischen Felder erwartet. Ziel dieser Arbeit war einerseits die Entwicklung eines Aufbaus zur gleichzeitigen Strahldetektion und MR-Bildaufnahme und andererseits die experimentelle Untersuchung der Beeinflussung des Protonenstrahls durch die gleichzeitige MR-Bildgebung.

Material & Methoden
Ein offener 0.22 T MR-Scanner (MrJ2200, Paramed) wurde an einer horizontalen Protonenstrahlführung installiert, so dass der Protonenstrahl auf das magnetische Isozentrum des MR-Scanners gerichtet ist. Um den Einfluss der MR-Bildgebung auf den Protonenstrahl zu untersuchen wurden zwei Experimente mit unterschiedlichen Aufbauten und MR-Pulssequenzen durchgeführt.
Im Absorptionsexperiment wurde im Isozentrum des MR-Scanners ein mit Flüssigszintillator (BC517H, Saint Gobain) gefülltes Phantom aus PMMA platziert. Das vom bestrahlten Szintillator emittierte Licht wurde mittels einer Kamera aufgezeichnet. Aus den Kamerabildern wurde auf die statistische Genauigkeit des Verfahrens geschlossen und diese mit der Differenz der über mehrere Aufnahmen gemittelten Dosisprofile verglichen.
Beim Transmissionsexperiment wurde auf ein bildgebendes Phantom verzichtet und die Dosisprofile ca. 1 m hinter dem Isozentrum des MR-Scanners mit einem Festkörper-Szintillator basierten 2D-Detektor (Lynx, IBA) aufgezeichnet. Die gemessenen Dosisprofile wurden durch eine gedrehte zweidimensionale Normalverteilung angenähert.

Ergebnisse
Im Absorptionsexperiment liegen die Unterschiede in den Pixelwerten der Kamerabilder zwischen laufender und ausgeschalteter MR-Bildgebung innerhalb der statistischen Schwankungen. Auch im Transmissionsexperiment zeigen die fünf Anpassungsparameter der Normalverteilung keine Änderung in den Dosisprofilen durch die Bildaufnahme des MR-Scanners.

Zusammenfassung
Gleichzeitige Detektion des Protonenstrahles während einer MR-Bildaufnahme ist mit Hilfe von Phantomen, die mit Flüssigszintillator gefüllt sind, möglich. Die einzelnen MR-Pulssequenzen zeigen keinen Einfluss auf den Protonenstrahl, so dass in der Bestrahlungsplanung einer MR-integrierten Protonentherapie nur das statische Magnetfeld des MR-Scanners berücksichtigt werden muss.
Keywords: MR, Radiation Therapy, Proton Therapy
  • Poster
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.09.2018, Nürnberg, Deutschland

Publ.-Id: 27269 - Permalink


Quantitative Measurement of Interaction between Solidification and Convection in Ammonium-Chloride Solutions
Anders, S.; Noto, D.; Eckert, S.;
An experimental investigation of double-diffusive convection with simultaneous crystallisation in ammonium-chloride solutions will be presented. Measurements were performed in a transparent Hele-Shaw with controlled thermal boundary conditions. The flow field of the liquid was measured by PIV. Using thermochromic liquid crystals, the temperature field inside the fluid was established. PTV was used to determine the size-evolution and the trajectories of the salt crystals. Alternating lighting methods and digital image filtering allow for simultaneous operation of PIV, PTV and temperature field measurement. This enables a quantitative study of the interplay of convection regimes and solidification processes like columnar and equiaxed crystallization, chimney-formation and remelting.
Keywords: Iron Snow, PTV, PIV, TLC, Multiphase Flow, Solidification, Double-diffusive Convection
  • Lecture (Conference)
    Symposium zur Simulation Metallurgischer Prozesse 2018, 30.01.-02.02.2018, Feuerkogel, Österreich

Publ.-Id: 27268 - Permalink


The mineralogy of weathering products of Bi-bearing tennantite – clues for the process and the mobilisation of heavy metals and toxic elements
Keim, M.; Staude, S.; Marquardt, K.; Bachmann, K.; Opitz, J.; Markl, G.;
Since the complex sulfosalts of the tennantite-tetrahedrite solid-solution series [(Cu,Ag)6Cu4(Fe,Zn,Cu,Hg,Cd)2(Sb,As,Bi,Te)4(S,Se)13] are widespread in many geological environments and accommodate heavy metals and toxic elements, a better understanding of the general weathering process and mobility of elements are important to evaluate environmental risks. In this study, the weathering of Bi-rich members of this mineral group were investigated in detail using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, µXRD and MLA. Observation reveal a subdivision in four temporally distinguishable weathering stages, spatially attributed to weathering environments of different chemical potentials. During the first stage, weathering occurs as tubes within the fahlore producing a phase assemblage of nm-sized roméite group minerals, tripuhyite, a crystalline Cu-oxide phase and crystalline Cu-sulfides. The textural appearance and the occurrence of these secondary sulfide indicates a low oxidation potential during this stage, typical for cementation zones. Mass balance calculations show that during this stage As, Zn and partially S are released to the weathering fluids. In contrast, Sb, Bi, Fe, S and Cu are stored in the roméite group minerals, tripuhyite, the copper oxide phase, and sulfides. During weathering stage 2, amorphous and nano-crystalline arsenates were formed replacing fahlore in most cases as weathering fronts. Their textures indicate a fluid with higher oxidation potential than in stage 1, typical for oxidation zones. The occurrence of arsenates shows that arsenic in contrast to stage 1 behaves immobile during this stage. Bismuth behaves immobile and is stored in the amorphous nano-crystalline phase. Mass balance calculations reveal that Zn, Sb, and S and partially Cu are lost, whereas Fe is added. Weathering stage 3 occurs only locally and reflects processes in micro compartments that are different for each locality and not characteristic for the general weathering process including the dissolution of former phases but also precipitation of new ones such as amorphous Cu-silicates. Stage 4 is characterized by the formation of crystalline Cu-Ba-Ca-Al-arsenates and Cu-carbonates mostly along cracks and in voids, spatially independent of the precursor fahlore. This stage reflects the increasing importance of the local geology, host rock and gangue mineralogy on weathering, typical in near surface environments of oxidation zones, where elements are highly mobile and a high fluid rock ratio is realized.
Keywords: Tennantite-tetrahedrite, weathering, bismuth, cementation zone, oxidation zone, Schwarzwald

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  • Secondary publication expected from 05.11.2019

Publ.-Id: 27267 - Permalink


Applied Mineralogy for Resource Efficiency of Platinum Metals - Towards a Geometallurgical Model
Bachmann, K.; Menzel, P.; Tolosana-Delgado, R.; Gutzmer, J.;
A geometallurgical model allows to predict parameters relevant for mineral beneficiation in a spatial domain. Therefore, we need a basic understanding of the geolocial architecture which can be provided by 3D geological models. Additionally, a tailored sample selection and characterization is crucial. This may include drill core logging data, whole rock geochemistry, modal mineralogies, micro-textures and mineral association as well as mineral chemistry data. In a next step, it is necessary to integrate the data into a spatial context and to derive process-relevant paramters. Finally, the development of domains with similar mineral beneficiation characteristics as well as geostatistical interpolation of relevant parameters onto a 3D geometry is possible.
  • Invited lecture (Conferences)
    Joint AMREP & DST-CIMERA Symposium, 14.-15.03.2018, Johannesburg, South Africa

Publ.-Id: 27266 - Permalink


Microbial diversity and activity in rock salt formations
Cherkouk, A.; Bader, M.; Bachran, M.; Swanson, J. S.; Steudtner, R.; Drobot, B.; Schmidt, M.; Musat, N.; Rossberg, A.; Ikeda-Ohno, A.; Stumpf, T.;
Rock salt formations are considered as potential host rocks for the long-term storage of highly radioactive waste in a deep geological repository. A combination of culture-dependent and culture-independent methods was used to investigate the microbial diversity in rock salt. Extremely halophilic archaea, e.g. Halobacterium species, dominate this habitat. For long-term risk assessment it is of high interest to study how these microorganisms can interact with radionuclides if released from the waste repository. Therefore, the interactions of the extremely halophilic archaeon Halobacterium noricense DSM 15987T with uranium, one of the major radionuclides of concern in the geological repository, were investigated in detail in batch experiments. A multi-spectroscopic and microscopic approach was used to decipher the interaction mechanisms on a molecular level. H. noricense DSM 15987T showed a multistage bioassociation of uranium. By using time-resolved laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy the formation of U(VI) phosphate minerals, such as meta-autunite, was observed. Furthermore, the presence of U(VI)-phosphate mineral could be visualized by scanning electron microscopy. These findings highlight the potential significance of the microbial life in deep geological hypersaline environments and offer new insights into the microbe-actinide interactions at highly saline conditions relevant to the disposal of highly radioactive waste as well as bioremediation.
  • Poster
    ISME17 - 17th International Symposium on Microbial Ecology, 12.-17.08.2018, Leipzig, Deutschland

Publ.-Id: 27265 - Permalink


Variation in PGM and BMS assemblages in the LG-6 and LG-6A chromitites of the western Bushveld Complex, South Africa
Bachmann, K.; Osbahr, I.; Tolosana-Delgado, R.; Chetty, D.; Gutzmer, J.;
This study focuses on the LG-6 and LG-6A chromitite seams at the Thaba mine located on the western limb of the Bushveld Complex. Platinum group minerals and base-metal sulfides are studied by mineral liberation analysis and electron microprobe analysis to define distinct assemblages and to evaluate the potential for beneficiation. Two distinct major mineral assemblages are defined: The first assemblage is rich in PGE-sulfides and alloys of Fe and Sn as well as chalcopyrite, pentlandite while second assemblage is rich in PGE-sulfarsenides and -arsenides and -alloys of Sb and Bi, pentlandite and Co-rich pentlandite.
  • Contribution to proceedings
    International Platinum Symposium, 30.06.-06.07.2018, Polokwane, South Africa

Publ.-Id: 27264 - Permalink


PGE Distribution and Mineralogy in the LG-6 and Middle Group Chromitite Layers, Thaba Mine, Bushveld Complex
Kaufmann, F.; Hecht, L.; Bachmann, K.; Trumbull, R.; Veksler, I.; CRONIMET Chrome Mining (Pty.) Ltd.;
Here we present information about concentrations, distribution and mineralogy of platinum group elements (PGE) in the sequence of chromitite layers from LG-6 to MG-4 at the Thaba mine in the north-western sector of the Bushveld Complex in South Africa. The information is based on assay analyses of drill core samples and studies of platinum group minerals and base-metal sulfides by mineral liberation analysis. Total concentrations of PGE gradually increase with the stratigraphic height from the LG-6 layer to MG-4. Detailed sampling of the LG-6, LG-6A, MG-1 and MG-2 layers revealed uneven vertical distribution of PGE with the highest concentrations at the footwall contacts. Pt-Pd ratios vary broadly from one layer to another and tend to increase from top to bottom within the individual layers. The assemblage of platinum group minerals in the LG-6 and LG-6A layers comprises equal proportions of (Pt,Pd)S, malanite and laurite, and minor amounts of Fe-Sn alloys sperrylite. PGE tellurides and bismuthotellurides are largely absent. In contrast, the PGE mineralogy of the MG-1 and MG-2 layers is dominated by laurite.
  • Contribution to proceedings
    International Platinum Symposium, 30.06.-06.07.2018, Polokwane, South Africa

Publ.-Id: 27263 - Permalink


Spatially-resolved characterization of Eu(III) interaction with granitic rock (Eibenstock, Germany)
Schmidt, M.ORC; Molodtsov, K.
The mobility of (radio-)contaminants in the geosphere is controlled by their interaction with the surfaces of surrounding minerals. Typically these interactions are studied either with single mineral phases, or in field studies in natural rock formations consisting of multiple mineral phases. In the former case, the involved reactions can be characterized at the molecular level with appropriate spectroscopic tools, but the complexity of the natural rock is lost, while the latter case often only allows a quantitative approach due to the inherent complexity of the natural system.
Here we present a novel approach to bridge this gap in the understanding of sorption processes. Time-resolved laser-induced fluroescence spectroscopy (TRLFS) is a well established technique to characterize the speciation of luminescent metal ions, e.g Eu(III)[1] or Cm(III).[2] We have adapted the technique to allow scanning a rock sample consisting of a variety of mineral grains, through a focused laser beam with a spatial resolution ~ 20 µm (µTRLFS). This way we are able to obtain full emission spectra and lifetimes in each spot. Through this improvement, it is possible to not only map the distribution of a fluorescent probe on the rock, but also to determine its speciation in each location, with respect to its coordination strength and hydration state.
The interaction of Eu(III) with granitic rock thick sections from the former uranium mine Eibenstock, Germany, were investigated by µTRLFS. The investigation is complemented by mineral characterization using µXRF, EMPA, and thin section microscopy. The results clearly show the differing sorption capacity and sorption strength of the minerals contained in the granite, with the highest sorption capacity found for feldspars. In addition, grain boundaries often show a reactivity distinct from both bordering mineral grains, e.g. a quartz/biotite grain boundary showing higher adsorption than both, quartz and biotite.
In summary, the results highlight the necessity to complement studies of model systems with more realistic whole system investigations. The technical improvement to a well-established spectroscopic tool also offers opportunities for other fields of (bio)geochemistry.

(1) Binnemans, K., Coord. Chem. Rev. 2015, 295, 1-45.
(2) Edelstein, N.M., Coord. Chem. Rev. 2006, 250, 948-973.
Keywords: TRLFS, europium, sorption, granite, microscopy, µTRLFS
  • Lecture (Conference)
    Goldschmidt 2018, 12.-17.08.2018, Boston, USA

Publ.-Id: 27262 - Permalink


Regge Trajectories of Radial Meson Excitations: Exploring the Dyson-Schwinger-- Bethe-Salpeter Approach
Greifenhagen, R.; Kämpfer, B.; Kaptari, L. P.;
The combined Dyson-Schwinger and Bethe-Salpeter equations in rainbow-ladder approximation are used to search for Regge trajectories of mesons in the pseudo-scalar and vector channels. We focus on the often employed Alkofer-Watson-Weigel kernel which is known to deliver good results for the ground state meson spectra; it provides linear Regge trajectories in the JP=0− channel.

Publ.-Id: 27261 - Permalink


Impact of Dipolar Interaction on Superfluid Spin Transport
Schneider, T.; Barsukov, I.; Smith, A.; Upadhyaya, P.; Liu, Y.; Fan, Y.; Wang, K.; Macdonald, A.; Tserkovnyak, Y.; Krivorotov, I. N.;
Ferromagnetic easy-plane system are theoretically excepted to support a long-range coherent transport flow, normally referred as spin superfluid. However, the influence of local dipole-dipole interaction on these states are not fully investigated. Here, the present a detailed micromagnetic study of the superfluid flow in a easy-plane ferromagnetic in the presence of local dipole-dipole interactions.
  • Lecture (others)
    Spintronics group seminar, 15.03.2018, Irvine, CA, USA
  • Lecture (others)
    Group seminar Prof. Tserkovnyak, 19.03.2018, Los Angeles, USA

Publ.-Id: 27260 - Permalink


Charakterisierung der MR-Relaxations- und Bewegungseigenschaften eines 4D MRT Phantoms im Rahmen der Kommissionierung an einem 3T MR Scanner
Schneider, S.; Dolde, K.; Engler, J.; Hoffmann, A. L.; Pfaffenberger, A.;
Einleitung
Für die klinische Etablierung von Magnetresonanztomographen (MRT) in der bildgestützten Strahlentherapie, allen voran der hybriden MR-Linacs, bedarf es der Analyse und regelmäßiger Qualitätssicherung der Bewegungscharakterisierung auf Basis der MRT Bilder. Ziel dieser Studie war die Kommissionierung eines programmierbaren 4D MRT-Bewegungsphantoms bezüglich seiner bildgebenden MR-Relaxations- und Bewegungseigenschaften an einem 3T MRT und die Entwicklung einer Methode zur automatisierten Qualitätssicherung von MRT-Sequenzen zur Bewegungsanalyse.
Material & Methoden
Das MRI-LINAC Dynamic Phantom (Model 008M, CIRS) wurde mit Mineralöl (Marcol Blend, Philips) gefüllt und mit einer Hilfskonstruktion auf einer flachen Tischauflage (Medibord Ltd) positioniert. Messungen wurden an einem 3.0T MRT (Ingenuity TF PET/MR, Philips) durchgeführt. Mittels MR-Relaxometrie wurden die Relaxationszeiten des Gel-gefüllten beweglichen Zylinders und des Targets bestimmt. Die T1-Relaxationszeit wurde durch eine Inversion-Recovery Spin-Echo (IR-SE) Methode , die T2-Relaxationszeit durch eine Multi-Echo Gradient-and-Spin-Echo (GraSE) berechnet. Sinusförmige 1D, 2D und 3D Target-Trajektorien mit patiententypischen Organauslenkungen (5-40mm) und Frequenzen (0.1-0.2Hz) sowie eine 1D Patientennavigator Atemkurve wurden im Phantom generiert und mittels 2D-cine MR Sequenzen (Zeitauflösung von <0.5s) aufgenommen. Mit einer selbst entwickelten MATLAB-basierten Tracking-Software wurden die 2D-cine Bilder automatisiert analysiert.
Ergebnisse
Die Relaxationsparameter für Zylinder (T1=871±36ms / T2=13.4±1.3ms) und Target (T1=208±2.8ms / T2=30.5±0.7ms) wurden bestimmt. Die extrahierten Amplituden der Sinustrajektorien zeigen Abweichungen zu den eingestellten Werten von <0.4mm in AP/LR und <0.2mm in IS Richtung, während die Frequenzen mit Abweichungen von <0.001Hz bestimmt wurden. Die Navigatorkurve konnte mit einer mittleren Amplitudenabweichung von 0.3mm bestimmt werden, bei einer maximalen Abweichung von <1.0mm.
Zusammenfassung
Das 4D-Phantom wurde an einem klinischen 3T MRT bezüglich seiner Relaxationseigenschaften und der Möglichkeit einer 3D Bewegungsanalyse kommissioniert. Der entwickelte Aufbau und die Methodik erlauben regelmäßige Qualitätskontrollen der Bewegungscharakterisierung auf MR-Basis.
Keywords: MRT, Bewegungs-Phantom, Kommissionierung
  • Poster
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik und 21. Jahrestagung der Deutschen Sektion der ISMRM, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27259 - Permalink


Interaction of fluid flow with heat and mass transfer in Liquid Metal Batteries
Personnettaz, P.; Landgraf, S.; Nimtz, M.; Weber, N.; Weier, T.;
Liquid metal batteries (LMBs) are suggested as a possible solution of the energy storage problem. An LMB consists of three stably stratified layers, two liquid metals are separated by a molten salt electrolyte.
Operation was so far demonstrated for small prototypes only. In order to upscale cells to a viable commercial scale a deep knowledge of the physics involved is required.
The relatively simple chemistry and geometry, the presence of multiple and multi-physics phenomena and the completely fluid nature of the active materials have made the LMB an intriguing candidate for continuum mechanics studies.
The cell is in fact subject to a coexistent transport of mass, heat, charge and momentum together with chemical and electrochemical reactions.
The fluid flow that naturally occur can be beneficial if it is able to improve the mass transport, delaying the formation of solid intermetallic phases.
In our work the attention is focused on heat and mass transfer. The continuum balances are defined in general terms, taking into account the electrochemical nature of the system. The corresponding scalar fields (e.g. temperature and solute concentration) are then computed with pure diffusive models. In a second step the interaction with the induced fluid flow is taken into account. Thermal convection in Li||Bi LMBs is studied with an improved version of the multiphase VOF solver multiphaseInterFOAM. Advection-diffusion mass transfer is investigated in the positive electrode with single-phase CFD solvers.
The first results of thermo-solutal convection are presented, the modeling limits and the future development are discussed.
Keywords: LMB, Heat Transfer, Mass Transfer
  • Lecture (Conference)
    12th European Fluid Mechanics Conference, 09.-13.09.2018, Wien, Österreich

Publ.-Id: 27258 - Permalink


Machbarkeitsstudie zur Integration eines offenen MR-Scanners in die horizontale Strahlführung einer Protonentherapie-Anlage
Schellhammer, S. M.ORC; Karsch, L.; Smeets, J.; Pawelke, J.; Hoffmann, A. L.
Einleitung
Aufgrund der steilen Dosisgradienten kann die Treffgenauigkeit in der Protonentherapie (PT) durch Bewegungen und anatomische Veränderungen stark kompromittiert werden. Eine gleichzeitige Bildgebung mittels Echtzeit-Magnetresonanztomographie (MRT) könnte die Treffgenauigkeit erhöhen. Bis heute existieren jedoch keine kombinierten Systeme aus MRT und PT. Ziele dieser Studie waren deshalb die erste Integration eines MR-Scanners in eine PT-Strahlführung, die Überprüfung der Machbarkeit einer gleichzeitigen MR-Bildgebung und Bestrahlung, und die Kontrolle der MR-Bildqualität mit und ohne Strahleinfluss.

Material & Methoden
Ein offener MR-Scanner für muskuloskelettale Bildgebung mit einem vertikalen Magnetfeld von 0.22 T (MRJ2200, Paramed) wurde an einer strahldüsenlosen horizontalen Strahlführung (IBA Proton Therapy) installiert, und durch einen kompakten Faraday-Käfig von Hochfrequenz-Interferenzen abgeschirmt. Um den Protonenstrahl trotz der Strahlablenkung im Magnetfeld des Scanners zentral auf dessen Field-of-View zu richten, wurde das Magnetfeld mit einer Hall-Sonde (HHP-VU, Arepoc) vermessen. Auf dieser Grundlage wurde die mittlere Strahlablenkung für Energien zwischen 70−230 MeV mittels Monte-Carlo-Simulationen (Geant4) berechnet und der Scanner daraufhin um 2 cm versetzt zum Strahlaustritt platziert. Der Strahl wurde kollimiert (Ø=10 mm) und durch ein Strahlrohr in den Faraday-Käfig geführt. Die Strahllage im Field-of-View wurde mittels radiochromischer Filme (EBT3, Ashland) verifiziert. Zur Überprüfung der MR-Bildgebung wurden anatomische MR-Bilder eines Probanden bei deaktivierter Strahlführung sowie MR-Bilder eines Gewebephantoms mit und ohne Strahleinfluss (215 MeV, 5 nA) aufgenommen.

Ergebnisse
Die MR-Aufnahmen (Abb. 1) des Probanden zeigten die für den verwendeten Scanner übliche Bildqualität. Relevante anatomische Strukturen waren klar unterscheidbar. Am Gewebephantom wurde keine Bildverzerrung durch die Strahlführungsmagneten und den Protonenstrahl beobachtet, jedoch eine gleichförmige Bildverschiebung (< 1 mm) in Frequenzkodierrichtung, die vermutlich entweder auf statistische Schwankungen in der scannereigenen Frequenzkalibrierung oder auf das Randfeld der Strahlführungsmagnete zurückzuführen ist.

Zusammenfassung
Die Integration eines offenen MR-Scanners in den experimentellen Strahlengang einer Protonentherapie-Anlage war erfolgreich. Eine gleichzeitige MR-Bildgebung und Bestrahlung ohne Bildverzerrung ist möglich. Eine geringe und potentiell korrigierbare MR-Bildverschiebung wurde festgestellt.
  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27257 - Permalink


THEREDA, the thermodynamic reference database for a nuclear waste disposal in Germany
Bok, F.; Moog, H. C.; Altmaier, M.; Voigt, W.; Thoenen, T.;
The disposal of nuclear waste including the assessment of long-term safety is still an open question in Germany. In addition to the still pending decision about the repository host rock (salt, granite, or clay) the basic necessity of a consistent and obligatory thermodynamic reference database persists. Specific challenges are comprehensive datasets covering high temperatures and salinities. In response to deficiencies of other databases THEREDA, a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany and Switzerland, was started in 2006.
The core of THEREDA consists of a relational databank whose structure has been designed in a way that promotes the internal consistency of thermodynamic data. Data considered cover the needs of Gibbs Energy Minimizers and Law-of-Mass-Action programs alike. Pitzer coefficients to describe solute activity coefficients in high-saline solutions are considered. Both thermodynamic data and interaction coefficients can be described by temperature functions.
Ready-to-use parameter files are created from the databank in a variety of formats. Supported target codes are ChemApp, PHREEQC, EQ3/6, and Geochemist’s Work-bench. Data can alos be downloaded in a generic JSON-type format to promote conversion for other geochemical codes Prior to their release all parameter files are submitted to internal test calculations – one essential element of the quality assurance scheme. The results are documented and provided to the users and accessible via internet through http://www.thereda.de/.
Data are currently available to describe the solubility of the following radionuclides or fission elements: U(IV/VI), Th(IV), Np(IV/V), Pu(IV) Am(III), Nd(III), Cm(III), Tc(IV/ VII), Sr, Cs and the matrix elements (oceanic salt system, cement phases).
Future develpoments are thermodynamic data sets for Selenium and Oxygen in high saline solutions as well as the inclusion of low saline sorption data.
Keywords: THEREDA, Database, Thermodynamic Modelling, Radionuclides
  • Poster
    Goldschmidt2018, 12.-17.08.2018, Boston, USA

Publ.-Id: 27256 - Permalink


Thermodynamic modelling of Selenium in environmental conditions: traps, pitfalls and perspectives
Bok, F.; Jordan, N.; Brendler, V.;
Any safety assessment of nuclear waste disposal concepts requires comprehensive and consistent thermodynamic data for the respective reactive transport modelling. This includes sorption, ion exchange or surface precipitation as major retardation processes, as well as a correct description of the aqueous chemistry including redox processes.
Selenium (with the isotope Se-79 being an important fission product) can occur in oxidation states varying between +VI and –II, the latter also including several polynuclear species. Most often negatively charged species are formed rendering them extraordinarily mobile in groundwater systems. Namely for Se solubility in highly saline solutions and for Se sorption onto minerals several competing thermodynamic datasets are published to predict the behavior of selenium under environmental conditions. However, there are still critical data gaps. For example, recent findings like the selenite dimerization have to be parameterized and included into thermodynamic data collections. In addition, for the selenide chemistry, solubility data are missing as well as ion-ion interaction parameters for the calculation in brines.
Another aspect of the reactive transport of selenium is the retardation of mainly selenate and selenite via sorption onto mineral phases. For these processes, recent spectroscopic investigations in combination with batch experiments have enabled deeper insights into the sorption chemistry of selenium. Here, the various data received must be processed into consistent data sets.
Several approaches to close critical selenium data gaps will be presented. These are essential steps towards a consistent and quality approved thermodynamic data set that can be included into databases needed for the geochemical and reactive transport calculations, namely THEREDA (http://www.thereda.de) and RES³T (http://www.hzdr.de/res3t).
Keywords: Radionuclides, Selenium, Thermodynamic Modelling, Databases
  • Lecture (Conference)
    256th ACS National Meeting & Exposition, 19.-23.08.2018, Boston, USA

Publ.-Id: 27255 - Permalink


Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings
Li, Z.; Klopf, J. M.; Wang, L.; Yang, K.; Lukaszew, R. A.;
Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD) and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.

Publ.-Id: 27254 - Permalink


U(VI) sorption by Ca-bentonite at pH 8-13: Spectroscopic investigation of retention mechanisms
Philipp, T.; Schmeide, K.; Rossberg, A.; Stumpf, T.;
Bentonite is considered as buffer and backfill material in deep geological repositories for radioactive waste. Therefore, profound understanding of radionuclide retention processes at the bentonite surface under environmentally relevant conditions is essential for a long-term safety assessment. Such conditions can involve high pH, as hyperalkaline cement pore waters evolve from corroding concrete within a repository. Since the U(VI) sorption behavior at alkaline conditions is still poorly understood, batch experiments were combined with spectroscopic investigations in order to gain insight into the underlying retention processes on the molecular level.
pH-dependent batch sorption experiments (pH 8-13) in a diluted Gipshut solution (2.5 M NaCl, 0.02 M CaCl2, 0.02 M Na2SO4, 0.0051 M KCl) at different carbonate concentrations (absence, 0.5 and 100 mM) showed a decreased U(VI) retention in the presence of carbonate up until a certain pH (pH 9.5 or pH 11, depending on [CO32-]) due to the formation of weakly sorbing (calcium) uranyl carbonate complexes in aqueous solution, confirmed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This is in accordance with previous studies [1]. However, also in the presence of carbonate, U(VI) retention is increased in even stronger alkaline solutions, which is attributed to the preferred formation of hydrolyzed U(VI) species at these conditions.
In order to clarify the mechanisms responsible for the very strong U(VI) retention in the pH range 10-12 (absence and 0.5 mM CO32-), uranyl complexes on the bentonite surface were examined directly, using site-selective TRLFS and EXAFS (ESRF, Grenoble). Selective excitation of different sorption species by varying laser energy allowed the identification of both, surface complexation and, to a smaller degree, surface precipitation. EXAFS spectra did not show any indication of precipitates, verifying that adsorption is the dominant retention process and precipitates form only as small fractions, below the EXAFS detection limit. According to atomic distances and coordination numbers for U-Oeq, U(VI) surface complexes shift from a 5-fold to a 4-fold coordination in the equatorial plane with increasing pH.
  • Lecture (Conference)
    Goldschmidt2018, 12.-17.08.2018, Boston, USA

Publ.-Id: 27253 - Permalink


Data for "Complexation of trivalent lanthanides (Eu) and actinides (Cm) with aqueous phosphates at elevated temperatures"
Jordan, N.ORC; Starke, S.; Huittinen, N.ORC

At the Institute of Resource Ecology, the complexation of Eu(III) and Cm(III) with aqueous phosphate was studied using laser-induced luminescence spectroscopy at low pH ([H+] = 0.1 M), different ionic strengths (0.6 to 3.1 M) and different temperatures (25 to 80 °C). The data set contains the species distribution, slope analysis and the extrapolation to zero ionic strength using R.

Keywords: Curium; Europium; phosphate complexation; linear regression
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-05-22
    DOI: 10.14278/rodare.5
    License: CC-BY-4.0

Downloads:

Publ.-Id: 27252 - Permalink


CMOS‐compatible controlled hyperdoping of silicon nanowires
Berencén, Y.; Prucnal, S.; Möller, W.; Hübner, R.; Rebohle, L.; Böttger, R.; Glaser, M.; Schönherr, T.; Yuan, Y.; Wang, M.; Georgiev, Y. M.; Erbe, A.; Lugstein, A.; Helm, M.; Zhou, S.; Skorupa, W.;
Hyperdoping consists of the intentional introduction of deep‐level dopants into a semiconductor in excess of equilibrium concentrations. This causes a broadening of dopant energy levels into an intermediate band between the valence and the conduction bands. Recently, bulk Si hyperdoped with chalcogens or transition metals is demonstrated to be an appropriate intermediate‐band material for Si‐based short‐wavelength infrared photodetectors. Intermediate‐band nanowires can potentially be used instead of bulk materials to overcome the Shockley–Queisser limit and to improve efficiency in solar cells, but fundamental scientific questions in hyperdoping Si nanowires require experimental verification. The development of a method for obtaining controlled hyperdoping levels at the nanoscale concomitant with the electrical activation of dopants is, therefore, vital to understanding these issues. Here, this paper shows a complementary metal‐oxide‐semiconductor (CMOS)‐compatible technique based on nonequilibrium processing for the controlled doping of Si at the nanoscale with dopant concentrations several orders of magnitude greater than the equilibrium solid solubility. Through the nanoscale spatially controlled implantation of dopants, and a bottom‐up template‐assisted solid phase recrystallization of the nanowires with the use of millisecond‐flash lamp annealing, Se‐hyperdoped Si/SiO2 core/shell nanowires are formed that have a room‐temperature sub‐bandgap optoelectronic photoresponse when configured as a photoconductor device.
Keywords: Flash lamp annealing, hyperdoping, intermediate band, ion implantation, nanowires

Publ.-Id: 27251 - Permalink


Interaction of U(VI) with α-isosaccharinic acid under acidic conditions: characterization of the formed complexes
Brinkmann, H.; Patzschke, M.; Roßberg, A.; Moll, H.; Stumpf, T.;
Cellulose is a very common organic polymer and also present in considerable amounts in low and intermediate level wastes (LILW). Since it is considered to stabilize LILW with cementitious materials and to use cement-based materials as construction and backfilling material, the alkaline degradation of cellulosic material has to be taken into account. This process will lead to the formation of water-soluble carboxylates and hydroxycarboxylates, with isosaccharinic acid (isa) being the main degradation product. It was shown that the α-form of the polyhydroxy-carboxylic acid is a stronger complexant compared to the β-form and that the interaction with radionuclides affects the solubility and the sorption behavior adversely [1]. Only a limited number of studies focused on the interaction of isa with UO22+. Hence, there are gaps in thermodynamic databases for this system. The basis for reliable thermodynamic data is a detailed structural knowledge about the formed species in the system of interest.

This issue prompted us to characterize the formed complexes in the UO22+-isa system on a molecular level. Our approach to elucidate the mechanisms in aqueous solution combines different spectroscopic techniques (UV-vis, ATR-FTIR, EXAFS, and luminescence) with DFT-calculations. The mutual influence of UO22+ and isa on their speciation as well as the three detected complexes will be discussed. The outcomes are on the one hand the basis for thermodynamic investigations as well as for studies under neutral and alkaline conditions. They provide on the other hand also important information concerning the behavior of α-isa as ligand, including dominant binding motifs.

[1] Van Loon, L. R., et al., Radiochimica Acta, 1999, Vol. 86, https://doi.org/10.1524/ract.1999.86.34.183.

This project has received funding from the Euratom research and training programme 2014-2018 under Grant Agreement no. 61880.
Keywords: uranium, isosaccharinic acid, spectroscopy, speciation
  • Lecture (Conference)
    18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic

Publ.-Id: 27250 - Permalink


Binding of Antimony to Natural Organic Matter in a Finish Mine-Water Influenced Peatland
Besold, J.; Eberle, A.; Kujala, K.; Kumar, N.; Scheinost, A. C.; Pacheco, L.; Fendorf, S.; Planer-Friedrich, B.;
Antimony (Sb) is a toxic element typically of low natural abundance but human activities have led to highly elevated concentrations in many soils and sediments. Recently, natural organic matter (NOM) has been discussed as effective sink for arsenic [1] and first spectroscopic studies [2,3] indicated that sulfhydryl moieties of NOM also play an important role in controlling Sb mobility in wetland sediments. However, Sb speciation in NOM-rich wetlands has not yet been studied comprehensively and direct spectroscopic evidence for this sequestration mechanism is still lacking. In order to investigate the role of NOM for Sb sequestration, we used bulk Sb K-edge X-ray absorption fine structure spectroscopy (EXAFS) from a peatland in northern Finland which receives high Sb loads from an adjacent gold mine. Sampled peat cores were kept under argon atmosphere at cool and dark conditions until freeze-drying to prevent Sb speciation changes. The peat contained up to 52 % carbon and 265 mg/kg Sb (dry weight basis). Sulfur and iron contents ranged between 4 to 8 and 2 to 10 g/kg, respectively. Aqueous Sb concentrations decreased with lateral distance from the inflow from 190 µg/L in surface waters to 8 µg/L in 80 cm depth. Based on linear combination fitting of EXAFS spectra, we found Sb to be mainly coordinated to NOM moieties in all peat samples. At 10-20 cm depth, Sb was sorbed up to 47% to iron (hydr)oxides and with increasing depth, up to 50% of trivalent Sb was complexed tri-fold to sulfhydryl moieties of NOM. At these deep peat layers, Sb was up to 100% complexed to NOM. Our results show that sorption of Sb to particulate NOM can act as an important sequestration mechanism under sulfate reducing conditions and therefore strongly influences Sb mobility in the environment.

[1] Langner et al. (2012) Nat. Geosci. 5, 66-73. [2] Benett et al. (2017) Environ. Chem. 2017, 14, 345–349. [3] Arsic et al. (2018) Environ. Sci. Technol. 52, 1118-1127.
Keywords: antimony arsenic peat organic matter EXAFS XANES
  • Lecture (Conference)
    Goldschmidt Conference 2018, 12.-17.08.2018, Boston, U.S.A.

Publ.-Id: 27249 - Permalink


Core-Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction - Kern-Schale-Strukturierung rein metallischer Aerogele für eine hocheffiziente Nutzung von Platin für die Sauerstoffreduktion
Cai, B.; Hübner, R.; Sasaki, K.; Zhang, Y.; Su, D.; Ziegler, C.; Vukmirovic, M. B.; Rellinghaus, B.; Adzic, R. R.; Eychmüller, A.;
The development of core-shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of PdxAu-Pt core-shell aerogels composed of an ultrathin Pt shell and a composition-tunable PdxAu alloy core. The universality of this strategy ensures the extension of core compositions to Pd transition-metal alloys. The core-shell aerogels exhibited largely improved Pt utilization efficiencies for the oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mgPt-1 and 2.53 mA cm-2, which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core-shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core-shell electrocatalysts.
Die Entwicklung von rein metallischen Aerogelen mit Kern-Schale-Strukturen ist nach wie vor eine grundlegende Herausforderung. Hier stellen wir die Synthese von PdxAu-Pt-Kern-Schale-Aerogelen vor, welche aus einer ultradünnen Pt-Schale und einem Kern aus einer PdxAu-Legierung mit einstellbarer Zusammensetzung bestehen. Die universelle Synthesestrategie ermöglicht eine Erweiterung der Kern-Zusammensetzung hin zu Pd-Übergangsmetall-Legierungen. Die Kern-Schale-Aerogele zeigen eine stark verbesserte Nutzungseffizienz von Pt in der Sauerstoffreduktion und ihre Aktivitäten folgen einem vulkanförmigen Verlauf bezüglich der Gitterparameter des Kern-Substrats. Mit einer maximalen massenbezogenen bzw. spezifischen Aktivität von 5.25 A mgPt-1 und 2.53 mA cm-2, welche 18.7- bzw. 4.1-mal höher sind als die für Pt/C, zeigt sich die Überlegenheit dieser metallischen Kern-Schale-Aerogele. Die vorgeschlagene kernbasierte Aktivitätsabhängigkeit liefert eine neue mögliche Strategie für den Entwurf zukünftiger Kern-Schale-Elektrokatalysatoren.
Keywords: aerogels, electrocatalysis, core-shell structures, oxygen reduction reaction, sol-gel processes - Aerogele, Elektrokatalyse, Kern-Schale-Strukturen, Nanostrukturen, Sol-Gel-Prozess

Publ.-Id: 27248 - Permalink


The analysis of nothing and nearly nothing – concepts for reference materials for the Super-SIMS
Renno, A. D.ORC
The Super-SIMS idea goes back to the year 1979 [1]. Since then several attempts have been made to install such instruments [2-5], although with varied success.
Most of the published data were either analysis of semiconductor materials or isotope ratios of natural materials. Having a strong focus on natural, metal, and mineral resources the Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This new Super-SIMS will be embedded into a system of consecutive micro-analytical methods devoted to the characterization of minerals and ores. Therefore, our focus will lie on the analysis of ultra-trace elements in these natural matrices.
Despite the high precision, the accuracy of SIMS analysis can be problematic. The sensitivity factor as well as the instrumental mass fractionation vary with the chemical composition. This so-called matrix effect demands that the sample and the reference material (RM) should have exactly the same chemical composition and structure, this is difficult to achieve. Even trace elements and in the case of the Super-SIMS ultra-trace elements may affect the sensitivity factor. The compromise is the usage of matrix matched RMs.
The combination of good lateral and depth resolution of the SIMS instrument with the resulting small sample volumes / masses (sub ng-range) and the aspired detection limits in the pg/g range yield to the fact that the probability to meet one atom of the analyte in the sample volume will be < 1.
This contribution will stimulate the discussion about the concepts of detection limit, homogeneity and heterogeneity in RMs and present considerations about the design of future RMs for ultra-trace element analysis with the Super-SIMS.

[1] Purser et al. Surface and Interface Analysis 1(1), 1979, 12.; [2] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470.; [3] Ender et al. NIMB 123 (1997) 575.; [4] Maden, PhD thesis, ETH Zurich 2003.; [5] Fahey et al. Analytical Chemistry 88(14), 2016, 7145
Keywords: Reference Materials, SIMS, Super-SIMS
  • Poster
    Geoanalysis 2018, 08.-13.07.2018, Sydney, Australia

Publ.-Id: 27247 - Permalink


A Super-SIMS for resource technology
Renno, A. D.ORC; Akhmadaliev, S.; Belokonov, G.; Böttger, R.; von Borany, J.; Gutzmer, J.; Kaever, P.; Meyer, M.; Noga, P.; Rugel, G.; Tiessen, C. J.; Voigtländer, J.; Wagner, N.; Wiedenbeck, M.; Winter, A.; Wu, H.; Ziegenrücker, R.
The integration of an ion source with very high spatial resolution with a tandem accelerator is a long-standing concept for improving analytical selectivity and sensitivity by orders of magnitude [1-3]. Translating this design concept to reality has its challenges [e.g. 4-6]. Supporting a strong focus on natural, metallic and mineral resources the, Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This so-called Super-SIMS will be at the core of a comprehensive pallet of micro-analytical methods devoted to the characterization of minerals and ores. Secondary ion beam from a CAMECA IMS 7f-auto are injected into the pre-existing 6MV Dresden Accelerator Mass Spectrometry facility [7,8], which quantitatively eliminates isobaric molecular species from the ion beam. Our SIMS component can function as either a stand-alone device or can be used to inject the negatively charged secondary ions at energies of up to 40 keV (to match the acceptance conditions) into the accelerator. A dedicated ion optical unit has been constructed and installed to match the SIMS ion beam to the maximum acceptance of the accelerator.
We will present measurements of the performance parameters of the instrument as well as first results of halogen (F, Cl, Br, and I) determinations in galena, sphalerite and pyrrhotite.
[1] Purser et al. Surface and Interface Analysis 1(1), 1979, 12. [2] J. M. Anthony, D. J. Donahue, A. J. T. Jull, MRS Proceedings 69 (1986) 311-316. [3] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470. [4] Ender et al. NIMB 123 (1997) 575. [5] Maden, PhD thesis, ETH Zurich 2003. [6] Fahey et al. Analytical Chemistry 88(14), 2016, 7145. [7] Akhmadaliev et al., NIMB 294 (2013) 5. [8] Rugel et al. NIMB 370 (2016) 94.
Keywords: Super-SIMS, SIMS
  • Lecture (Conference)
    Geoanalysis 2018, 08.-13.07.2018, Sydney, Australia

Publ.-Id: 27246 - Permalink


Box-profile implants as geochemical reference materials for EMP and SIMS
Wu, H.; Belokonov, G.; Böttger, R.; Couffignal, F.; Munnik, F.; Renno, A. D.ORC; Wiedenbeck, M.; Ziegenrücker, R.
EMP (Electron Microprobe) and SIMS (Secondary Ion Mass Spectrometry) are widely used analytical techniques for geochemical and mineralogical applications. Nevertheless, metrologically rigorous quantification remains a major challenge for these methods. SIMS in particular is a matrix sensitive method; the use of matrix-matched reference materials (RMs) is essential in order to avoid significant analytical bias. A major problem is that the list of available reference materials for SIMS is vanishingly short compared to the needs of the analyst. A current evaluation of the GeoReM database [1] shows a strong focus on using the well-known NIST SRM 610-617 glasses for trace element analysis along with several zircons for isotope analysis, with few other matrices being readily available.
One approach for the production of matrix specific RMs is the use of ion implantation that introduces a known amount of a selected isotope into a material. This strategy is widely-used for SIMS applications in materials science, but rarely used for geochemical applications. Bumett et al. (2015) [2] demonstrated the appropriateness of this method. We choose the more elaborate way of implanting a so-called box profile to generate a homogeneous concentration of the selected isotope in three dimensions.
For proof of concept we used the mineralogically and chemically “simple” SiO2 system which addresses many interesting scientific challenges, such as the Ti-in-quartz geothermometer [3]. We implanted either 47Ti or 48Ti into synthetic, ultra-high purity silica glass. Several box profiles with concentrations between 10 and 1000 µg/g Ti and a maximum depth of homogeneous Ti distribution between 200 and 3000 nm were produced at the Ion Beam Center in Dresden-Rossendorf. Multiple implantation steps using differing ion energies and ion doses were simulated with the SRIM (Stopping and Range of Ions in Matter) software [4], optimizing for the target concentrations, implantation-depths and technical limits of the implanter. A thorough TEM assessment showed that the Ti is dispersed throughout the glass structure. We characterized several implanted test-samples by means of SIMS, EMP and other analytical techniques. The homogeneity of the Ti-concentration is within ± 5% uncertainty in all 3 dimensions.
[1] http://georem.mpch-mainz.gwdg.de, [2] D. S. Bumett, et al., Geostandards and Geoanalytical Research 39(3), 2015, 265-276., [3] J. B. Thomas, et al., Contrib. Mineral. Petr. 160(5), 2010, 743–759., [4] J. F. Ziegler, Nucl. Instrum. Meth. B 219-220, 2004, 1027-1036.
Keywords: Reference Materials, SIMS, EMP, Super-SIMS, implantation
  • Poster
    Geoanalysis 2018, 08.-13.07.2018, Sydney, Australia

Publ.-Id: 27245 - Permalink


Detecting and quantifying the relativistic Kelvin-Helmholtz instability in interstellar jets via radiation observable on Earth
Pausch, R.; Bussmann, M.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Debus, A.;
We present a microscopic model of the radiation emitted during the relativistic Kelvin-Helmholtz instability (KHI) and validate our findings with particle-in-cell simulations at unprecedented spatial resolution and size that including complete far-field radiation spectra.

The KHI is expected in shear flow regions of astrophysical plasma jets, which are significant sites for particle acceleration and radiation. We demonstrate that the emitted polarized radiation can be used to identify and characterize the microscopic plasma dynamics of a KHI light-years away. We have simulated the radiation of the KHI using the particle-in-cell code PIConGPU. With this code's synthetic radiation diagnostic, based on Liénard-Wiechert potentials, quantitative predictions of the far field radiation for hundreds of observation directions and a frequency range covering 3 orders of magnitude were performed on the TITAN cluster at Oak Ridge National Laboratory. The simulation showed that the time-dependent changes in the radiation polarization and power correlate directly with the stages of the KHI. This allows identifying the linear growth phase of the KHI and quantifying its characteristic growth rate as predicted by our microscopic model.
Keywords: Kelvin Helmholtz instability, Particle-in-cell, PIConGPU, radiation
  • Lecture (Conference)
    DPG-Frühjahrstagung Würzburg, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 27244 - Permalink


In-situ synthetic radiation diagnostics for laser wakefield acceleration
Pausch, R.; Debus, A.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Bussmann, M.;
We present recent results of LWFA simulations including in-situ radiation diagnostics performed with the particle-in-cell code PIConGPU. Our results demonstrate the power provided by synthetic radiation diagnostics to determine the laser-plasma dynamics with regard to applications in experiments.

PIConGPU is currently one of the fastest 3D3V particle-in-cell codes and provides an in-situ radiation diagnostic based on Liénard-Wiechert potentials. This synthetic diagnostic is capable of quantitatively predicting the spectrally and directionally resolved far-field radiation of billions of macro-particles by an in-situ implementation in the PIC cycle. Among other things, the code enables resolving the spatial origin and temporal evolution of the radiation, determine the polarization, quantifying both coherent and incoherent radiation simultaneously and covering a frequency range from infrared to x-rays.

The talk briefly introduces the technical background of computing the radiation in-situ on GPUs. Its main focus, however, is the characteristic radiation of LWFA that allows identifying the various stages of the laser-plasma dynamics. Possible applications of these radiation signatures in laboratory experiments will be discussed.
Keywords: Laser Wakefield Accelerator, Particle-in-cell, radiation
  • Lecture (Conference)
    DPG-Frühjahrstagung Würzburg, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 27243 - Permalink


The prognostic value of FMISO-PET-based synchronous tumor and lymph node hypoxia outperforms that of tumor hypoxia only in patients with advanced stage HNSSC – secondary analysis of Dresden FMISO trail
Bandurska-Luque, A.; Löck, S.; Haase, R.; Richter, C.; Zöphel, K.; Perrin, R.; Seidlitz, A.; Zschaeck, S.; Appold, S.; Krause, M.; Steinbach, J.; Kotzerke, J.; Zips, D.; Baumann, M.; Troost, E.;
Purpose: Primary tumor (Tu) hypoxia based on hypoxia-PET is a known prognostic parameter for locally-advanced head-and-neck squamous cell carcinoma (HNSCC) patients. This secondary analysis of the prospective clinical trial [1] on repeat [18F]fluoromisonidazole (FMISO) PET/CT before and during radiochemotherapy (RCT) compared the prognostic value of synchronous Tu and lymph node metastases (LN) hypoxia with that of hypoxia only determined in Tu.

Methods: Forty-five LN-positive patients with 103 LNs were included in this analysis. FMISO-PETs were performed at baseline, week 1, 2 and 5 of RCT. Based on a qualitative scale, Tu and LN were independently categorized as hypoxic or normoxic, being FMISO uptake higher than or equal to background, respectively. Two prognostic parameters were defined: Tu-hypoxia (patients with a hypoxic Tu, independent of the LN oxygenation status) and synchronous Tu-and-LN-hypoxia. In fifteen patients with a large LN (n = 21) a quantitative analysis of FMISO PET was performed to validate hypoxia scale and to correlate with regional control (RC). Log-rank, uni- and multivariate Cox test were used to assess the parameters’ prognostic impact on locoregional control (LRC), RC and time to progression (TTP).

Results: Synchronous Tu-and-LN-hypoxia was a strong adverse prognostic factor for LRC and TTP at all time-points (p ≤ 0.005) whereas Tu-hypoxia only was significantly associated with poor LRC in week 2 and 5 (p ≤ 0.004) and with short TTP in week 1, 2 and 5 (p ≤ 0.043). The quantitative FMISO parameters correlated with RC. There was a significant correlation between the qualitative and quantitative FMISO parameters (R > 0.6–0.8).

Conclusions: FMISO-based synchronous hypoxia in the primary tumor and lymph node metastases holds strong prognostic information in HNSCC patients outperforming that based on primary tumor hypoxia only. Confirmation in ongoing prospective trials is intended before introducing in personalized radiation oncology.
  • Lecture (Conference)
    33. Deutscher Krebskongress 2018, 21.-24.02.2018, Berlin, Deutschland

Publ.-Id: 27241 - Permalink


Dose-dependent changes after proton and photon irradiation in zebrafish model
Brunner, S.; Tőkés, T.; Szabó, E. R.; Szabó, I. Z.; Polanek, R.; Beyreuther, E.; Pawelke, J.; Hideghéty, K.;
Purpose/Objective: The laser-driven ionizing (LDI) beams have unique property of ultra-high dose rate, ultra-short pulses and carry the potential toward special clinical application. Our aim was to establish an in vivo zebrafish model for radiobiological research on later LDI radiation.
Material/methods: 24 hours post-fertilization (hpf) zebrafish (Danio rerio) embryos were irradiated at the University Proton Therapy Dresden with escalated doses (5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve, at the plateau and at the middle of Spread Out Bragg Peak, and with reference 6 MV photon beams from a clinical linac (n=96 in each group). The experiment was 3 times repeated under the same conditions. On the 3th (96 hpf) and 4th (120 hpf) days after irradiation morphological malformations were documented (photo) and determined quantitatively. Two independent observers measured the length of the embryos, the degree of the yolk sac edema and the diameter of the eyes. Additionally, we have detected the DNA double-strand breaks immunohistochemically (gamma-H2AX foci) after 30 min of the irradiation at the two positions of the proton (mSOBP and plateau) and photon beams, at 5 Gy dose level.
Results: Dose-dependent organ developmental deteriorations could be detected morphologically at >10 Gy dose levels. The length of the embryo and the size of the eyes reduced, while the yolk sac edema increased significantly in dose dependent degree after 10 Gy, 15 Gy, 20 Gy and 30 Gy irradiation, at both developmental stages. At 5 Gy dose irradiation we have found significant elevation in the number of DNA double-strand breaks, as compared to the unirradiated control groups. Furthermore, data showed that after proton irradiation the degree of the DNA damage was higher, as compared to the photon irradiation.
Conclusion: We could establish a reliable quantitative morphological analysis of dose-dependent organ malformations using an in vivo vertebrate system. The zebrafish embryo model proved to be appropriate for complex evaluation of the irradiation-caused damages, molecular changes and for comparison of the biological effects of different radiation qualities. We could define the optimal parameters for future radiobiological experiments with the LDI beams.
Supported by: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund. The project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no 654148 Laserlab-Europe and by the German BMBF, grant no. 03Z1N511.
  • Open Access LogoAbstract in refereed journal
    Radiotherapy and Oncology 127(2018)1, S588
    DOI: 10.1016/S0167-8140(18)31356-2
  • Poster
    37. ESTRO Meeting, 20.-24.04.2018, Barcelona, Spain

Publ.-Id: 27240 - Permalink


Development of zebrafish embryo model for radiobiology research at ELI-ALPS on laser driven hadron beams
Szabó, E. R.; Tőkés, T.; Polanek, R.; Szabó, Z.; Brunner, S.; Czifrus, S.; Fenyvesi, A.; Biró, B.; Beyreuther, E.; Pawelke, J.; Hideghéty, K.;
Purpose/objective: High power lasers provide the basis of particle acceleration, but at the actual status of the development, low energy, limited size beams with special properties (ultrahigh dose rate, pulsed mode) are available under technical conditions for radiobiology experiments. Our main aim was to introduce, optimize and validate a vertebrate system for in vivo experiments to study the biological effects of novel hadron beams.
Material/methods: Series of zebrafish embryos in different ages (from 1 hour post-fertilization (hpf) to 72 hpf), in different holders varying the number/well were prepared. For irradiation we used fission neutron (0, 1.25, 1.875, 2, 2.5 Gy), cyclotron-based neutron (0, 2, 4, 6.8, 8.12, 10.28 Gy) and proton (0, 5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve (PDDC): at the plateau and at the middle of Spread Out Bragg Peak (mSOBP), furthermore, with reference linear accelerator photon (0, 5, 10, 15, 20 Gy) beam (n=96 in each group), repeated several times (≥3). Thereafter, survival, any type of organ developmental disturbance (pericardial edema, spine curvature, shortening of the body length and micro-opthalmia) were detected each days up to 7 post irradiation days (pid). Histological evaluation (size of the eye, brain necrosis, intestinal changes, liver vacuolization, hyper eosinophilic necrotic muscle-fibers) and molecular changes were evaluated with RT-PCR method at certain time points post irradiation.
Results: A higher vulnerability and radiation sensitivity could be observed at earlier stages of the embryogenesis (1-12 hpf). The LD50 was determined with the well reproducible survival curves, resulting in RBE between 10 and 4.8 for the 1MeV and 14MeV neutrons and the Relative Biological Effectivity (RBE) around 1.1-1.4 for proton sources at the two positions respectively. The morphological distortions shown close correlation to the dose delivered and their evaluation on the 4th pid exhibited a good agreement to the survival derived RBE. The gravity of the histopathological changes on the basis of semi-quantitative analysis corresponded well to the macro morphological abnormalities (eye layer disorganization, degree of brain necrosis, increased numbers of the goblet cells in the gastrointestinal tract, and muscle fibrosis).
Conclusion: Numerous features of the zebrafish embryo model makes it amenable for large scale of radiobiological investigations. On the basis of our experimental series the optimal embryonal age (hpf), radiation setup and observation time points for assessment of the different biological endpoints could be established. The defined parameters proved to be suitable for reliable RBE determination.

Acknowledgement: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund, and by the German BMBF, grant nos. 03ZIK445 and 03Z1N511. The project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no 654148 Laserlab-Europe.
  • Poster
    37. ESTRO Meeting, 20.-24.04.2018, Barcelona, Spain
  • Open Access LogoAbstract in refereed journal
    Radiotherapy and Oncology 127(2018)Suppl1, S586
    DOI: 10.1016/S0167-8140(18)31353-7

Publ.-Id: 27239 - Permalink


Hazard statements: looking for alternatives to toxicity evaluation using LCA
Rodriguez-Garcia, G.; Braun, J.; Peters, J.; Weil, M.;
Life Cycle Assessment is a methodology for the evaluation of potential hazards to the environment and to human health. It can be used for decision support when selecting materials for a product. It is a detailed method that can become very labor intensive. As alternatives, we introduce here two methodologies for ranking products and materials according to their safety: Both methods are built on two pieces of European legislation. Hazard Traffic Lights is a qualitative visual way to quickly identify potential hazards. Total Hazard Points is a quantitative method for weighting the different hazards related to a product. It is based on the method developed for the German Environmental Agency (UBA), but its scope includes all materials and hazards, rather than a selection of them. As a case study, we evaluated the 9 batteries described in the UBA study and compared our results with those presented there. In our opinion, batteries are in general terms more hazardous in the UBA study. This is due to more thorough identification of hazards –including some potentially more significant – and the inclusion of all the potential hazards of a material. Since not all the materials present in the battery were quantified, both sets of results should be considered an underestimation of the possible hazard.

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Publ.-Id: 27237 - Permalink


AMS of 93 Zr: Passive absorber versus gas-filled magnet
Hain, K.ORC; Deneva, B.; Faestermann, T.; Fimiani, L.; Gómez-Guzmán, J. M.; Koll, D.; Korschinek, G.; Ludwig, P.; Sergeyeva, V.; Thiollay, N.
Two different isobar separation techniques were tested for the detection of the long-lived fission product 93Zr (T1/2T1/2 = 1.64 ·· 106 a) using Accelerator Mass Spectrometry (AMS), i.e. a passive absorber and a gas-filled magnet, respectively. Both techniques were used in combination with a Time-of-Flight path for the identification of the stable neighboring isotopes 92Zr and 94Zr. The passive absorber was represented by a stack of silicon nitride foils for high flexibility regarding the thickness for optimal isobar separation. Ion beams with a large variety of energies, between 80 and 180 MeV, were provided for this experiment by the tandem accelerator at the Maier-Leibnitz Laboratory in Garching, Germany. With these beams, the stopping powers of 93Zr and 93Nb as a function of energy were determined experimentally and compared to the results obtained with the simulation program SRIM. Considerable discrepancies regarding the energy dependence of the two stopping power curves relative to each other were found. The lowest detection limit for 93Zr achieved with the passive absorber setup was 93Zr/Zr = 1 ·· 10−10. In comparison, by optimizing the gas-filled magnet set-up, 93Nb was suppressed by around six orders of magnitude and a detection limit of 93Zr/Zr = 5 ·· 10−11 was obtained. To our knowledge, these results represent the lowest detection limit achieved for 93Zr until now.
Keywords: 93Zr; AMS; Gas-filled magnet; Passive absorber

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Publ.-Id: 27236 - Permalink


Bubbly Flow in Stirred Tanks: Euler-Euler / RANS Modeling
Shi, P.ORC; Rzehak, R.
Aerated stirred tanks are frequently used equipment in industries ranging from chemical engineering and biotechnology to minerals processing. In principle, CFD simulation of such equipment on industrial scales is feasible within the Euler-Euler framework of interpenetrating continua. Practical application, however, requires suitable closure models to account for phenomena on the scale of individual bubbles, which are not resolved in this approach. The present work applies a set of closure relations that was previously used with good success to describe bubbly flows in pipes and bubble columns. It turns out that model extensions are needed concerning turbulence and the drag force. To validate the model a comprehensive set of experimental data including gas fraction as well as liquid velocity and turbulence has been assembled from different literature sources. The finally proposed extended model compares reasonably well with this dataset.
Keywords: aerated stirred tanks, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, closure relations, Reynolds-stress turbulence model, CFD simulation, model validation

Publ.-Id: 27235 - Permalink


Integrating a low-field open MR scanner with a static proton therapy research beamline: proof of concept
Schellhammer, S. M.ORC; Karsch, L.; Smeets, J.; Pawelke, J.; Hoffmann, A. L.
Purpose
On-line image guidance using magnetic resonance (MR) imaging is expected to improve targeting precision in proton therapy (PT). However, to date no hybrid MR-PT system exists. This is partly due to unknown mutual electromagnetic interactions between the MR scanner and the PT beamline, which may compromise the quality of the proton beam or the MR image. The aim of our study was to integrate an MR scanner with a static PT research beamline and to test the feasibility of simultaneous irradiation and imaging.

Materials & methods
An open MR scanner (MrJ2200, Paramed) featuring a 0.22 T vertical permanent magnetic (B0) field was RF-shielded by a compact Faraday cage and placed at the beam exit of a horizontal static PT research beamline (IBA Proton Therapy). To account for Lorentz force-induced beam deflection in B0, the scanner had to be laterally displaced by 2 cm from the beam’s central axis, such that a proper co-alignment of the beam and the scanner’s field-of-view (FOV) could be confirmed by radiochromic film (Gafchromic EBT3, Ashland) measurements. The beam was collimated to Ø10 mm before entering the Faraday cage through a cylindrical beam guide (Fig. 1).

MR test: With the beamline magnets off, the knee, wrist and hip of a volunteer were scanned with STIR gradient echo (GE), T1-weighted GE, and T1-weighted spin echo (SE) imaging, respectively. T1-weighted SE images of a mixed-meat sausage were acquired using a knee coil without beam, with beamline magnets on and while being irradiated at 215 MeV and 5 nA for 5 minutes.

Beam test: With Faraday cage removed, beam profiles were acquired with and without MR scanner for 72, 125 and 219 MeV beams using a pixelated scintillation detector (Lynx, IBA Dosimetry) positioned 110 cm downstream of the MR scanner's isocentre. These measurements were repeated with the MR scanner in place during acquisition of three different SE and GE images (max. gradient strength up to 5.7 mT/m).

Results
MR test: MR imaging in the nearby presence of a PT beamline was feasible and showed sufficient quality for anatomical imaging of human musculoskeletal structures. MR images of the meat sausage acquired with operating beamline showed a uniform translation of <2 mm in frequency encoding direction, but no geometrical distortions.

Beam test: The scintillation detector showed a horizontal beam deflection of 22, 16 and 11 cm for 72, 125 and 219 MeV, respectively, and a vertical beam deflection <0.6 mm. Horizontal deflection was taken into account to install an in-cage beam stopper, while vertical deflection could be neglected. The beam profiles showed no influence of the gradient fields applied during image acquisition.

Conclusions
For the first time, the integration of an MR scanner and a static PT research beamline has been realized. By taking into account the scanner’s B0 field induced beam deflection, simultaneous proton beam irradiation and MR imaging of an object placed in the scanner’s FOV was feasible with acceptable beam and image quality. The beamline-induced MR image shift is subject of an ongoing performance evaluation study.
  • Lecture (Conference)
    MR in RT symposium, 30.06.-03.07.2018, Utrecht, Nederland

Publ.-Id: 27234 - Permalink


Commissioning of a 4D dynamic MRI motion phantom on a 3T MR scanner: motion validation study
Schneider, S.; Dolde, K.; Engler, J.; Hoffmann, A.; Pfaffenberger, A.;
Purpose:
Systems for integrated magnetic resonance guided radiation therapy (MRgRT) provide real-time and on-line MRI guidance for unequalled targeting performance of moving tumours and organs at risk. The clinical introduction of such systems requires dedicated methods for commissioning, routine machine quality assurance (QA) and verification of gated and adaptive treatment plans. The aim of the study was to develop a commissioning protocol and method for automatic quantification of target motion and geometrical fidelity using a 4D dynamic MRI motion phantom.

Materials & Methods:
The CIRS MRI-LINAC Dynamic Phantom (Model 008M) was positioned on a flat tabletop overlay (Medibord Ltd) in a 3.0T MR scanner (Ingenuity TF PET/MR, Philips) using an in-house constructed base plate for a quick and reproducible setup. The torso-shaped phantom body, which was filled with mineral oil (Marcol Blend, Philips), includes a 3D grid structure for image distortion analysis and a cylindrical thru-hole in which a software-controlled moving rod with a hypo-intense background gel and a decentralized hyper-intense target simulates 3D organ motion patterns. The geometric image distortion was determined as the mean and maximum Euclidean distance (∆mean, ∆max) between grid points in 3D spoiled gradient echo (THRIVE) MRI- and CT scans (Siemens Somatom Definition AS) after registration by means of the central fiducial. Sinusoidal 1D/2D/3D and a volunteer navigator scan-based 1D target motion pattern were evaluated using 2D cine MRI balanced turbo field echo sequences at a temporal resolution of 1.5-2 Hz. The motion tracking was performed with different pre-set frequencies (0.1-0.2 Hz) and amplitudes (up to 40/10/10 mm in IS/AP/LR direction). The target’s centre-of-mass motion pattern was reconstructed by an in-house developed automated image tracking algorithm implemented in MATLAB.

Results:
The base plate enabled a reproducible setup with a deviation of <1 mm in all directions. The geometric distortion increased with distance from the phantom’s centre predominantly in anterior direction, with ∆mean=0.56+/-0.28 mm and ∆max=1.5 mm in the THRIVE sequence relative to the CT scan. The frequencies of the reconstructed motion patterns from 2D cine MRI agree to the pre-set values within 2%; the reconstructed amplitudes showed a maximum deviation to the pre-set amplitudes of <0.8 mm in AP/LR direction and <0.4 mm in IS direction.

Conclusions:
A method and protocol for commissioning a 4D MRI dynamic motion phantom on a 3.0T MR scanner for MRgRT was developed. High-contrast and geometrically reliable 2D cine MR images of the phantom’s moving target could be obtained. The pre-set motion parameters could be extracted with sufficient spatio-temporal accuracy from 2D cine MRI in all motion directions. The method developed can be used for routine QA tests of spatio-temporally resolved MRI data in MRgRT.
Keywords: Phantom, Motion, MRI
  • Lecture (Conference)
    6th MR in RT Symposium 2018, 30.06.-03.07.2018, Utrecht, Niederlande

Publ.-Id: 27233 - Permalink


„Radiobiology of Proton Therapy“: results of an international expert workshop
Lühr, A.; von Neubeck, C.; Pawelke, J.; Seidlitz, A.; Peitzsch, C.; Bentzen, S.; Bortfeld, T.; Debus, J.; Deutsch, E.; Langendijk, J.; Löffler, J.; Mohan, R.; Scholz, M.; Sørensen, B.; Weber, D.; Baumann, M.; Krause, M.;
The physical properties of proton beams offer the potential to reduce toxicity in tumor-adjacent normal tissues. Towards this end, the number of proton radiotherapy facilities has steeply increased over the last 10-15 years to currently around 70 operational centers worldwide. However, taking full advantage of the opportunities offered by proton radiation for clinical radiotherapy requires a better understanding of the radiobiological effects of protons alone or combined with drugs or immunotherapy on normal tissues and tumors. This report summarizes the main results of the international expert workshop “Radiobiology of Proton Therapy” that was held in November 2016 in Dresden.
It addresses the major topics (1) relative biological effectiveness (RBE) in proton beam therapy, (2) interaction of proton radiobiology with radiation physics in current treatment planning, (3) biological effects in proton therapy combined with systemic treatments, and (4) testing biological effects of protons in clinical trials.
Finally, important research avenues for improvement of proton radiotherapy based on radiobiological knowledge are identified. The clinical distribution of radiobiological effectiveness of protons alone or in combination with systemic chemo- or immunotherapies as well as patient stratification based on biomarker expressions are key to reach the full potential of proton beam therapy. Dedicated preclinical experiments, innovative clinical trial designs, and large high-quality data repositories will be most important to achieve this goal.
Keywords: proton therapy, relative biological effectiveness, RBE, LET, radiobiology, clinical trials

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Publ.-Id: 27232 - Permalink


Integrating a low-field open MR scanner with a static proton therapy research beamline: Characterisation of in-beam imaging performance
Gantz, S.; Schellhammer, S. M.; Grossinger, P.; Karsch, L.; Smeets, J.; Serra, A.; Pawelke, J.; Hoffmann, A. L.;
Purpose
For the successful integration of MRI and proton therapy (PT), the mutual electromagnetic interaction between both systems needs to be investigated. So far, no combined system existed to investigate the MR imaging performance in the presence of a proton beam. Here, the aim is to characterize the imaging performance of a first in-beam MRI scanner during simultaneous proton irradiation and imaging.

Materials & methods
A 0.22 T open MRI scanner (MrJ2200, Paramed) has been installed at the horizontal static research beamline of our PT facility. The imaging performance characterization included both magnetic field homogeneity (MFH) measurements and ACR phantom tests for image quality. The MFH was mapped over a 22 cm diameter spherical volume by a magnetic field camera (MFC3045/48, Metrolab) being placed in the centre of the scanner’s field-of-view (FOV). To assess the effect of magnetic fringe fields of the nearby beamline magnets, the MFH was measured without and with magnets energized for beam energies between 70220 MeV. Phantom imaging tests were performed with the ACR small phantom being centrally positioned in the scanner FOV inside a knee coil (Fig. 1). Images were acquired by performing T1- and T2-weighted spin echo (SE) sequences with parameter settings according to the ACR phantom test protocol. Additionally, T1 and T2*- weighted gradient echo (GES and GEL, respectively) scans were performed. The phantom was irradiated by a 125 MeV pencil beam (Ø=10 mm) at dose rates of 1 and 80 Gy/min. Images were acquired for six different scenarios, starting from a reference scan with beamline magnets and beam off, followed by sequentially switching on first the beamline magnets and then the beam during both radiofrequency calibration and image acquisition or during image acquisition alone. A validated software tool (MATLAB) was used to extract the ACR imaging parameters and to estimate geometric transformations from image pairs acquired for the different scenarios.

Results
The peak-to-peak MFH was 88 ppm, which is within the scanner’s operating specifications. The MFH measurements with and without energized beamline magnets showed no significant differences (<3 ppm), but the mean baseline resonance frequency was increased by 70110 Hz depending on beam energy. The SE and GEL image quality was sufficient for analysis. GES images showed a low SNR (<15) and suffered from banding artefacts, which prevented automated evaluation of ACR parameters. For all six scenarios, differences in ACR parameters were within measurement uncertainties. A sequence-dependent uniform image translation of 0.53.0 mm in frequency encoding direction was observed due to operating the beamline. These image translations were in accordance with the baseline resonance frequency shift and showed to be inversely proportional to the gradient strengths of the sequences used (0.75.7 mT/m).

Conclusion
The imaging performance of a first low-field in-beam MRI scanner integrated with a static PT research beamline meets vendor and ACR image quality specifications. No degradation of the imaging performance was observed during simultaneous operation of the MRI and PT systems. Beamline induced off-resonance image translations need to be compensated for in the different imaging sequences.
  • Lecture (Conference)
    MR in RT Symposium, 30.06.2018, Utrecht, Niederlande

Publ.-Id: 27231 - Permalink


Marangoni convection at electrogenerated hydrogen bubbles
Yang, X.ORC; Baczyzmalski, D.; Cierpk, C.; Mutschke, G.; Eckert, K.ORC
Electrolytic gas evolution is a fundamental phenomenon occurring in a large number of industrial applications. In these processes gas bubbles are formed at the electrode from a supersaturated solution. Since dissolved gases can change the surface tension, a gas concentration gradient may cause the surface tension to vary locally at the gas bubble. Surface tension gradients may also form due to temperature gradients generated by ohmic heating of the electrolyte. In both cases, the resulting shear stress can impose a convection in the electrolyte and the gas bubble (Marangoni effect). This phenomenon may influence the entire electrolytic gas evolution process, e.g., by an enhanced mass transfer. In this study, the first evidence of the Marangoni convection near growing hydrogen bubbles, generated by water electrolysis, is provided. Microscopic high speed imaging was applied to study the evolution of single hydrogen bubbles at a microelectrode.
The convection near the interface of the growing bubble was measured by using a time-resolved Particle Tracking Velocimetry (PTV) technique. The results indicate a clear correlation between the magnitude of the Marangoni convection and the electric current.

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Publ.-Id: 27230 - Permalink


Noncovalently Assembled Electroconductive Hydrogel
Xu, Y.; Yang, X.ORC; Thomas, A. K.; Patsis, P. A.; Kurth, T.; Kräter, M.; Eckert, K.ORC; Bornhäuser, M.; Zhang, Y.
Crosslinking biomolecules with electroconductive nanostructures through noncovalent interaction can result in modular networks with defined biological functions and physical properties such as electric conductivity and viscoelasticity. Moreover, the resulting matrices can exhibit interesting features caused by the dynamic assembly process, such as self-healing and molecular ordering. In this paper, we present a physical hydrogel system formed by mixing peptide-polyethylene glycol and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). This combinatorial approach, which uses different modular building blocks, could lead to high tunability on aspects of rheology and electrical impedance. The proposed physical hydrogel system is characterized by both a self-healing ability and injectability. Interestingly, the formation of hydrogels at relatively low concentrations led to a network of closer molecular packing of PEDOT nanoparticles, reflected by the enhanced conductivity. The biopolymer system can be used to develop 3D cell cultures with incorporated electric stimuli, as evidenced by its contribution to the survival and proliferation of encapsulated mesenchymal stromal cells and their differentiation upon electrical stimulation.
Keywords: self-assembling, PEDOT:PSS, peptide, electroconductive hydrogel, 3D cell

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Publ.-Id: 27229 - Permalink


Results of the stationary measurements at COSMEA-I facility - CT part
Bieberle, A.ORC; Boden, S.; Beyer, M.; Hampel, U.

At the COSMEA-I facility cross-sectional distributions of the condensated steam is measured at five different positions along a slightly inclined condensator-tube using adapted conventional CT imaging technique based on X-ray. This data set contains the reconstructed raw data of the CT imaging scans.

Keywords: Passive heat transfer; Conventional CT imaging; Reconstructed raw data of the CT imaging scan
Related publications
Flow morphology and heat transfer analysis during … (Id 29452) is supplemented by this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-03-20
    DOI: 10.14278/rodare.3

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Publ.-Id: 27228 - Permalink


Molekulare Bildgebung in der Onkologie mittels Positronen-Emissions-Tomographie
Derlin, T.; Grünwald, V.; Steinbach, J.; Wester, H.-J.; Ross, T. L.;
Hintergrund: Mit der Positronenemissionstomographie (PET) steht ein Verfahren in der klinischen Bildgebung zur Verfügung, dass bei Durchführung als Hybridverfahren mit Computertomographie (CT) oder Magnetresonanztomographie (MRT) die simultane Erfassung anatomischer und molekularer Informationen ermöglicht. Die PET besitzt eine hohe Sensitivität zur Detektion von Tumormanifestationen. Unterschiedliche Radiopharmaka dienen der Charakterisierung verschiedener Stoffwechselprozesse oder der Analyse der Expression von Rezeptoren, Enzymen und weiteren molekularen Zielstrukturen.
Methode: Selektive Literaturrecherche in PubMed unter Bezug auf nationale und internationale Leitlinien sowie systematische Übersichtsarbeiten und Metaanalysen.
Ergebnisse: Etablierte PET Radiopharmaka wie 2-[18F]Fluor-2-desoxyglukose ([18F]FDG) erlauben die Darstellung physiologischer Prozesse auf molekularer Ebene und können entscheidende Informationen für die klinische Versorgung liefern. Für die PET stehen in zunehmendem Umfang neben gut erforschten und evaluierten auch neuere Radiopharmaka zur nicht-invasiven Phänotypisierung von Tumorerkrankungen zur Verfügung, beispielsweise zur Analyse der Expression des prostataspezifischen Membranantigens (PSMA) oder von Chemokinrezeptoren (z.B. CXCR4) auf Tumorzellen.
Schlussfolgerung: Die PET stellt einen wichtigen Bestandteil diagnostischer Algorithmen in der Onkologie dar, kann die Präzision der Diagnostik verbessern und helfen, die Therapie zu individualisieren. Eine zunehmende Anzahl an PET Radiopharmaka erweitert die verfügbaren Bildgebungsoptionen. Viele Radiopharmaka erlauben neben der nicht-invasiven Analyse der Expression therapeutisch relevanter
Zielstrukturen auch eine nachfolgende zielgerichtete Radionuklidtherapie.

Publ.-Id: 27227 - Permalink


Experimental Signals for Broxen Axial Symmetry in Excited Heavy Nuclei From The Valley of Stability
Grosse, E.; Junghans, A. R.;
An increasing number of experimental data indicates the breaking of axial symmetry in many heavy nuclei already in the valley of stability:
Multiple Coulomb excitation analysed in a rotation invariant way, gamma transition rates and energies in odd nuclei, mass predictions, the splitting of Giant Resonances (GR), the collective enhancement of nuclear level densities and Maxwellian averaged neutron capture cross sections. For the interpretation of these experimental observations, the axial symmetry breaking shows up in nearly all heavy nuclei as predicted by Hartree–Fock–Bogoliubov (HFB) calculations; this indicates a nuclear Jahn–Teller effect.
We show that nearly no parameters remain free to be adjusted by separate fitting to level density or giant resonance data, if advance information on nuclear deformations, radii etc. are taken from such calculations with the force parameters already fixed. The data analysis and interpretation have to include the quantum mechanical requirement of zero point oscillations and the distinction between static vs. dynamic symmetry breaking has to be regarded.
  • Open Access LogoContribution to proceedings
    XXIV Nuclear Physics Workshop “Marie and Pierre Curie”, Kazimierz Dolny, Poland, September 20–24, 2017., 20.-24.09.2017, Kazimierz Dolny, Polen
    Acta Physica Polonica B, Vol. 11, No. 1-37
    DOI: 10.5506/APhysPolBSupp.11.37

Publ.-Id: 27226 - Permalink


Diffusion of oxygen in bcc Fe under the influence of other foreign atoms
Wang, X.; Posselt, M.; Faßbender, J.;
First-principle calculations and kinetic Monte Carlo simulations are applied to investigate the diffusion of oxygen in bcc Fe under the influence of other foreign atoms, such as Al, Si, P, S, Ti,, Cr, Mn, Ni, Y, and Mo. In the first part of this work jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites were investigated by DFT. It is found that a second-neighbor jump consists of two consecutive first-neighbor jumps and that the barrier of the third-neighbor jump is too high to be relevant. In the second part DFT was applied to determine the modified migration barriers, i.e. for the oxygen jump between the first and the second neighbor of a foreign atom, etc. It is found that Si, P, Ni and Mo influence the migration barriers of oxygen only slightly. Al and Cr cause moderate changes, while S, Ti, and Y lead to strong modifications. With the exception of Y the migration paths are first-neighbor jumps between (modified) octahedral sites with (modified) tetrahedral sites as saddle points. Y changes some migration paths considerably. Using the migration barriers calculated by DFT the diffusion coefficient of oxygen was determined by kinetic Monte Carlo simulations considering a dilute iron alloy. In general the foreign atoms cause a reduction of the mobility of oxygen compared to that in pure bcc Fe. The strongest decrease is obtained for the foreign atoms S, Ti, and Y.
Keywords: Diffusion, oxygen, bcc Fe, Density Functional Theory, Kinetic Monte Carlo simulations
  • Poster
    DPG-Frühjahrstagung und EPS-CMD27, 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 27225 - Permalink


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe
Vallinayagam, M.; Posselt, M.; Faßbender, J.;
In this research project the nature of yttria-based oxide nanoclusters in a bcc Fe matrix is 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 clusters.
In the first part of the work three types of structures are considered: (i) clusters consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe, (ii) clusters with Y, Ti, and O on substitutional sites, and (iii) clusters with of Y, Ti, on substitutional sites and O on octahedral interstitial sites of the bcc lattice. Simulation cells containing different structures but the same composition of atoms (Fe, Y, Ti, O) are compared. It is found that the energetics of three different structure types, i.e. their total binding energy, is very similar. This modifies the statement of Barnard et al. [1] who only considered the first type of structure and concluded that this is the most favorable. Further, more stable cluster structures are constructed using another model with the nanocluster core similar to the metal monoxide structure. Also the binding energy of monomers like O, Y, Ti, and the vacancy to the cluster are studied. O and the vacancy are strongly attracted by the nanoclusters, while the interaction with metal atoms is weaker.
[1] L. Barnard et al. Acta Mater. 60 935 (2012)
Keywords: Density Functional Theory, Y-Ti-O nanoclusters, bcc Fe
  • Poster
    DPG-Frühjahrstagung und EPS-CMD27, 11.-16.03.2018, Berlin, Deustchland

Publ.-Id: 27224 - Permalink


The role of radiative de-excitation in the neutralization process of highly charged ions interacting with a single layer of graphene
Schwestka, J.; Wilhelm, R. A.ORC; Gruber, E.; Heller, R.; Kozubek, R.; Schleberger, M.; Facsko, S.; Aumayr, F.
X-ray emission of slow (<1 a.u.) highly charged Argon and Xenon ions is measured for transmission through a freestanding single layer of graphene. To discriminate against X-ray emission originating from the graphene's support grid a coincidence technique is used. X-ray emission of 75 keV Ar17+ and Ar18+ ions with either one or two K-shell vacancies is recorded. Using a windowless Bruker XFlash detector allows us to measure additionally Ar KLL and KLM Auger electrons and determine the branching ratio of radiative vs. non-radiative decay of Ar K-shell holes. Furthermore, X-ray spectra for 100 keV Xe22+-Xe35+ ions are compared, showing a broad M-line peak for all cases, where M-shell vacancies are present. All these peaks are accompanied by emission lines at still higher energies indicating the presence of a hollow atom during X-ray decay. We report a linear shift of the main M-line peak to higher energies for increasing incident charge state, i.e. increasing number of M-shell holes.
Keywords: Slow highly charged ions; Graphene; X-ray emission

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  • Secondary publication expected

Publ.-Id: 27223 - Permalink


Structural incorporation of the minor actinide Cm(III) in La1-xGdxPO4 rhabdophane and monazite solid solutions
Huittinen, N.; Scheinost, A. C.; Ji, Y.; Kowalski, P. M.; Arinicheva, Y.; Wilden, A.; Neumeier, S.;
Monazites (LnPO4) are envisioned as potential immobilization matrices for high-level radioactive wastes produced e.g. during the nuclear fuel cycle [1–2]. Hydrated rhabdophane (LnPO4×0.67H2O) is a precursor phase during monazite synthesis and a potential solubility-limiting solid phase under nuclear waste storage conditions [3–4]. Thus, for a reliable long-term safety assessment of nuclear waste repositories for conditioned radioactive waste, a fundamental understanding of the radionuclide incorporation process in both the pristine monazite ceramics and their alteration products is required.

In the present study we have combined time-resolved laser fluorescence spectroscopy (TRLFS), X-ray Absorption Fine Structure (XAFS) spectroscopy and ab initio atomistic simulations to investigate the structural incorporation of the minor actinide curium in synthetic La1-xGdxPO4 monazite and rhabdophane solid solutions. The solid phase was synthesized by addition of phosphoric acid to a solution containing La3+ and Gd3+ in desired relative concentrations and a small amount of the actinide (248Cm), until a white precipitate of La1-xGdxPO4 rhabdophane doped with approximately 50 ppm Cm3+ was obtained. An aliquot of the obtained solid phase was thereafter sintered at 1450°C to acquire the crystalline monazite ceramic. Structural refinement of collected XRD data for both rhabdophane and monazite solids show a linear dependency of lattice parameters as a function of Gd3+ substitution according to Vegard’s law.
Our combined spectroscopic results show that Cm3+ is incorporated in the monazite end-members (LaPO4 and GdPO4) on one specific, highly ordered lattice site. In the intermediate solid solution compositions, an increasing disorder around the Cm3+ dopant can be seen as a result of a broader distribution of possible Cm∙∙∙O bond-lengths in comparison to the end-member compositions with very well-defined nearest neighbour distances. Despite this local structural disordering, homogenous solid solutions were obtained for all synthesized monazite compositions without the formation of dopant clusters that could potentially hamper the performance of the monazite ceramics for the immobilization of minor actinide containing wastes.
The hydrated rhabdophane lattice comprises two different site types that could accommodate the actinide dopant: a 9-coordinated “hydrated” site amounting to two thirds (2/3) of the total number of lanthanide sites in the solid structure, where one coordinating oxygen atom originates from a water molecule, and an 8-fold coordinated “non-hydrated” site (1/3 of available Ln sites) where all oxygen atoms are provided by phosphate groups [4]. Based on our laser spectroscopic investigation, curium incorporation on both site types can be confirmed, however, the site occupancy is not in concordance with the hydrated rhabdophane structure. In contrast, a preferential incorporation of curium on non-hydrated lattice sites can be seen, especially for the La-rich rhabdophane compositions, implying that structural substitution reactions cannot be predicted based on the structure of the host matrix only.
Keywords: Cm(III), spectroscopy, incorporation, rhadbophane, monazite
  • Lecture (Conference)
    International Symposium on Solubility Phenomena and Related Equilibrium Processes (ISSP), 15.-20.07.2018, Tours, France

Publ.-Id: 27222 - Permalink


Unusual Coulomb effects in graphene
Winnerl, S.;
In many semiconductors Coulomb scattering plays an essential role in the thermalization process of a non-equilibrium carrier distribution. Here we discuss three surprising and fascinating manifestations of Coulomb scattering in graphene. All phenomena are explored both experimentally and by manybody theory. The first observation concerns a double-bended saturation behavior of bleaching induced by near-infrared radiation. The second phenomenon is the optically induced anisotropy in k-space for excitation with linearly polarized radiation and its relaxation to a Fermi-Dirac distribution. The third set of experiments tackles the dynamics of graphene in a magnetic field perpendicular to the graphene layer. Here evidence for strong Auger scattering is found. We discuss the possibility to apply Landau quantized graphene as a gain medium in a tunable laser and as a tunable nonlinear optical material.
Keywords: Graphene, ultrafast dynamics, Coulomb interaction
  • Lecture (others)
    Theory seminar, Charles University in Prague, 12.04.2018, Prague, Czech Repzblic

Publ.-Id: 27221 - Permalink


Intrinsic magnetic properties of hydrided and non-hydrided Nd5Fe17 single crystals
Karpenkov, D. Y.; Skokov, K. P.; Lyakhova, M. B.; Radulov, I. A.; Faske, T.; Skourski, Y.; Gutfleisch, O.;
We report on the spontaneous magnetization Ms, the exchange stiffness constant A and the magneto-crystalline anisotropy constants K1, K2, K3 and K4 of Nd5Fe17 and Nd5Fe17H16 single crystals. Field dependencies of magnetization M(H) were measured along a, b' and c principal crystallographic directions within the temperature range of 10-600 K and magnetic fields up to 40 T. Large anisotropies of spontaneous magnetization and high-field susceptibility were revealed for both compounds. The exchange stiffness parameter A was determined using Bloch's T3/2 law. In order to provide high accuracy detection of K1(T), K2(T), K3(T) and K4(T), we used two different approaches: the modified Sucksmith-Thompson technique and the Néel's phase method.

Publ.-Id: 27220 - Permalink


Electrically pumped graphene-based Landau-level laser
Brem, S.; Wendler, F.; Winnerl, S.; Malic, E.;
Graphene exhibits a nonequidistant Landau quantization with tunable Landau-level (LL) transitions in the technologically desired terahertz spectral range. Here, we present a strategy for an electrically driven terahertz laser based on Landau-quantized graphene as the gain medium. Performing microscopic modeling of the coupled electron, phonon, and photon dynamics in such a laser, we reveal that an inter-LL population inversion can be achieved resulting in the emission of coherent terahertz radiation. The presented paper provides a concrete recipe for the experimental realization of tunable graphene-based terahertz laser systems.
Keywords: graphene, Landau quantization, laser, Landau-level laser

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Publ.-Id: 27219 - Permalink


ThMn12-type phases for magnets with low rare-earth content: Crystal-field analysis of the full magnetization process
Tereshina, I. S.; Kostyuchenko, N. V.; Tereshina-Chitrova, E. A.; Skourski, Y.; Doerr, M.; Pelevin, I. A.; Zvezdin, A. K.; Paukov, M.; Havela, L.; Drulis, H.;
Rare-earth (R)-iron alloys are a backbone of permanent magnets. Recent increase in price of rare earths has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. For this reason strong magnets with the ThMn12 type of structure came into focus. Functional properties of R(Fe,T)12 (T-element stabilizes the structure) compounds or their interstitially modified derivatives, R(Fe,T)12-X (X is an atom of hydrogen or nitrogen) are determined by the crystal-electric-field (CEF) and exchange interaction (EI) parameters. We have calculated the parameters using high-field magnetization data. We choose the ferrimagnetic Tm-containing compounds, which are most sensitive to magnetic field and demonstrate that TmFe11Ti-H reaches the ferromagnetic state in the magnetic field of 52 T. Knowledge of exact CEF and EI parameters and their variation in the compounds modified by the interstitial atoms is a cornerstone of the quest for hard magnetic materials with low rare-earth content.

Publ.-Id: 27218 - Permalink


Field-effect transistors as electrically controllable nonlinear rectifiers for the characterization of terahertz pulses
Lisauskas, A.; Ikamas, K.; Massabeau, S.; Bauer, M.; Cibiraité, D.; Matukas, J.; Mangeney, J.; Mittendorff, M.; Winnerl, S.; Krozer, V.; Roskos, H. G.;
We propose to exploit rectification in field-effect transistors as an electrically controllable higher-order nonlinear phenomenon for the convenient monitoring of the temporal characteristics of THz pulses, for example, by autocorrelation measurements. This option arises because of the existence of a gate-bias-controlled super-linear response at sub-threshold operation conditions when the devices are subjected to THz radiation. We present measurements for different antenna-coupled transistor-based THz detectors (TeraFETs) employing (i) AlGaN/GaN high-electron-mobility and (ii) silicon CMOS field-effect transistors and show that the super-linear behavior in the sub-threshold bias regime is a universal phenomenon to be expected if the amplitude of the high-frequency voltage oscillations exceeds the thermal voltage. The effect is also employed as a tool for the direct determination of the speed of the intrinsic TeraFET response which allows us to avoid limitations set by the read-out circuitry. In particular, we show that the build-up time of the intrinsic rectification signal of a patch-antenna-coupled CMOS detector changes from 20 ps in the deep sub-threshold voltage regime to below12 ps in the vicinity of the threshold voltage.
Keywords: Terahertz detection, field-effect transistor, nonlinear response, autocorrelation

Publ.-Id: 27217 - Permalink


Infrared/Terahertz Spectra of the Photogalvanic Effect in (Bi,Sb)Te based Three Dimensional Topological Insulators
Plank, H.; Pernul, J.; Gebert, S.; Danilov, S. N.; König-Otto, J.; Winnerl, S.; Lanius, M.; Kampmeier, J.; Mussler, G.; Aguilera, I.; Grützmacher, D.; Ganichev, S. D.;
We report on the systematic study of infrared/terahertz spectra of photocurrents in (Bi,Sb)Te based three dimensional topological insulators. We demonstrate that in a wide range of frequencies, ranging from fractions up to tens of terahertz, the photocurrent is caused by the linear photogalvanic effect (LPGE) excited in the surface states. The photocurrent spectra reveal that at low frequencies the LPGE emerges due to free carrier Drude-like absorption. The spectra allow to determine the room temperature carrier mobilities in the surface states despite the presence of thermally activated residual impurities in the material bulk. In a number of samples we observed an enhancement of the linear photogalvanic effect at frequencies between 30 and 60 THz, which is attributed to the excitation of electrons from helical surface to bulk conduction band states. Under this condition and applying oblique incidence we also observed the circular photogalvanic effect driven by the radiation helicity.
Keywords: Topological insulators, terahertz spectroscopy, photocurrents, photogalvanic effect

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Publ.-Id: 27216 - Permalink


Shielding and source calculations for the new cyclotron and possible activation in the soil
Konheiser, J.; Ferrari, A.; Naumann, B.; Müller, S.;
This presentation summarizes the results of the Monte Carlo simulation of the shielding calculations and estimates of the soil activation for the new cyclotron of the HZDR (Helmholtz-Zentrum Dresden-Rossendorf). The dose values were determined on base of the resulting neutron flux at the 18F production and were carried out with the Monte Carlo code MCNP6. The calculation of the soil activations was performed with FLUKA. The neutron source term was provided by manufacturer. A source check with MCNP6 and FLUKA codes, significant discrepancies were found to the manufacturer supplied data for the neutron source term. For this reason, experiments were carried out on a cyclotron in operation. The comparison confirmed the results of the MCNP/FLUKA calculations.
The estimated dose rate in the public area is about 0.035 μSv/h (28 MeV protons) and thus significantly below the reference value of 0.5 μSv/h(3). After 5 years of continuous beam operation and a subsequent decay time of 30 days, the activity concentration of the soil is about 0.34 Bq/g.
Keywords: shielding calculation, neutron source calculation, cyclotron, MCNP6, FLUKA
  • Lecture (others)
    88. Sitzung des Arbeitskreises Dosimetrie, 20.-21.03.2018, TU Dresden, Deutschland

Publ.-Id: 27215 - Permalink


Transglutaminase 2 as potential target for functional tumour imaging – development of assay methods and inhibitors for this enzyme
Wodtke, R.;
Transglutaminase 2 (TGase 2) is a unique multifunctional enzyme whose best-characterised function is the crosslinking of proteins, which has implications not only in physiological but also in a variety of pathological conditions including fibrotic and neoplastic processes. In this context, it becomes more and more apparent that TGase 2 is a key player for the progression of several kinds of cancer and elevated levels of TGase 2 expression are directly correlated with poor prognostic indicators for survival, e.g. metastatic phenotype and drug resistance of the cancer cells. Consequently, this enzyme is considered as a promising target for the diagnosis and therapy of these diseases. According to the motivation to develop radiotracers for TGase 2 imaging by positron emission tomography (PET), which will provide insight into the importance of the crosslinking function as well as the targeting of that enzyme in vivo, the PhD project was focused on two different goals.
Within the first part, a reliable fluorimetric assay method was established as prerequisite for the identification and characterisation of TGase 2-reactive molecules. The assay is based on the measurement of an increase in fluorescence due to the release of a coumarine derivative upon TGase 2-catalysed hydrolysis or aminolysis of the fluorogenic acyl donor. However, the fluorogenic acyl donors known from the literature are characterised by a low solubility in water, which limits their applicability (1). Therefore, a series of water-soluble small peptidic acyl donors were synthesised and kinetically characterised towards TGase 2. Finally, Z-Glu(HMC)-Gly-OH turned out to have the most favourable substrate properties (2). Additionally, this compound is also a suitable substrate for other TGases, which facilitates selectivity studies.
The second part was focused on irreversible inhibitors for TGase 2 as appropriate starting point for the development of radiotracers. Based on the Nε-acryloyllysine piperazides chemotype of TGase 2 inhibitors, a library of >50 inhibitors were synthesised and their inhibitory capacity towards TGase 2 and other TGases were determined on the basis of their inactivation constants kinact/KI. Structural modifications were focused on the introduction of fluorine but also other chemical groups were considered. Kinetic investigations have uncovered important structure-activity relationships, which in combination with in silico molecular docking shed light on the binding mode for this class of inhibitors. Evaluation of selected compounds at other TGases highlighted a favourable selectivity profile towards TGase 2. Regarding an initial pharmacokinetic profiling, the potential membrane permeability of the inhibitors were determined using the PAMPA method. Considering the determined inhibitory potencies in combination with these pharmacokinetic in vitro data will provide valuable hints for the development of radiotracers for TGase 2 imaging.

(1) Gillet, S. M.; Pelletier, J. N.; Keillor, J. W. Anal. Biochem. 2005, 347, 221.
(2) Wodtke et al. ChemBioChem 2016, 17, 1263.
  • Invited lecture (Conferences)
    Frontiers in Medicinal Chemistry, Verleihung Promotionspreis der GDCh-Fachgruppe Medizinische Chemie, 11.-14.03.2018, Jena, Deutschland

Publ.-Id: 27213 - Permalink


Anwendung von Anstaupackungen bei der CO2-Absorption in wässrigen Aminlösungen
Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.;
Kolonneneinbauten stellen einen wichtigen Bestandteil fluider Trennprozesse dar und haben einen erheblichen Einfluss auf die Prozessleistung. Anzustrebende Eigenschaften von Einbauten sind eine hohe Trenneffizienz bei gleichzeitig geringem Druckverlust sowie eine hohe Kapazität. In den vergangenen Jahrzehnten konnten erhebliche Fortschritte zur Verbesserung von Einbauten erzielt werden. In diesem Bereich zeigt die Entwicklung von Anstaupackungen (AP) ein wesentliches Potenzial zur Prozessintensivierung auf. Diese bestehen aus zwei alternierenden Lagen strukturierter Packungen mit unterschiedlicher spezifischer Oberfläche. Die untere Anstaulage weist eine geringere Lastgrenze als die darüber angeordnete Abscheidelage auf. AP werden üblicherweise zwischen den Flutpunkten der beiden Lagen betrieben, weshalb ein heterogenes Strömungsmuster entsteht. Dabei bildet sich oberhalb der gefluteten Anstaulage eine Sprudelschicht, die durch eine intensive Vermischung der Phasen geprägt ist und eine hohe Trennleistung erzielt.
Im Rahmen eines DFG-geförderten Forschungsprojekts gilt es nun, die Auswirkungen der einzelnen Strömungsregime von AP auf Fluiddynamik und Stofftransport separat zu untersuchen. Für diesen Zweck werden erstmalig Experimente an einer Absorptions-/ Desorptionsanlage durch bildgebende Messungen der Strömung in AP ergänzt. An der Universität Paderborn werden für verschiedene Design- und Betriebsparameter Technikumsversuche zur CO2-Absorption in einer wässrigen Monethanolamin-Lösung durchgeführt. Die Anlage ermöglicht die Aufnahme von Temperaturprofilen der Gasphase sowie von Konzentrationsprofilen beider Phasen. In Kooperation mit der Technischen Universität Dresden wird mittels ultraschneller Röntgentomographie ein detaillierter Einblick in die Phasenverteilung der verschiedenen Strömungszustände ermöglicht. Die bei beiden Untersuchungen anfallenden Messdaten sollen zur Erarbeitung von Korrelationen für Stoffübergang, Phasengrenzfläche, Holdup und Druckverlust genutzt werden, welche in einem rate-based-Model Verwendung finden. In dieser Arbeit werden neben einer Vorstellung des Vorhabens erste experimentelle Daten zur Absorption mit AP präsentiert.
  • Poster
    Jahrestreffen der ProcessNet Fachgruppen Mechanische Flüssigkeitsabtrennung, Kristallisation, Phytoextrakte, Adsorption, Extraktion, Fluidverfahrenstechnik und Membrantechnik, 08.-10.03.2017, Köln, Deutschland

Publ.-Id: 27212 - Permalink


Experimentelle Untersuchungen zum Einfluss von Betriebs- und Designparameter auf das Absorptionsverhalten von Anstaupackungen
Flechsig, S.; Utchenko, Y.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.;
Aufgrund des hohen Energiebedarfs thermischer Trennverfahren besteht ein hoher Forschungsbedarf für die Entwicklung effizienter und ressourcenschonender Prozesse. Bei Trennkolonnen weisen Einbauten ein erhebliches Entwicklungspotential auf, welche die Fluiddynamik und den Stofftransport entscheidend beeinflussen.
Die Anstaupackung stellt eine Entwicklung im Bereich der Packungskolonnen dar, die eine Intensivierung des Stofftransports und eine Kapazitätserweiterung ermöglicht. Die Anstaupackung besteht aus einer Kombination von zwei Lagen typischer strukturierter Packungen mit unterschiedlicher spezifischer Oberfläche, welche alternierend angeordnet werden. Die untere Anstaulage weist dabei eine geringere Lastgrenze als die darüber angeordnete Abscheidelage auf. Anstaupackungen werden üblicherweise zwischen den Flutpunkten der beiden Lagen betrieben, wodurch ein axial heterogenes Strömungsmuster entsteht. Dabei bildet sich oberhalb der gezielt gefluteten Anstaulage eine Sprudelschicht, die durch eine intensive Vermischung und ein hohes Maß an Turbulenz der beteiligten Phasen geprägt ist und zu deutlich höheren Trennleistungen führen kann. Oberhalb der Sprudelschicht in der Abscheidelage dominiert die für Packungen typische Rieselfilmströmung in der die aus der Sprudelschicht mitgerissenen Tropfen abgeschieden werden [1].
Da bislang das Trennverhalten von Anstaupackung fast ausschließlich theoretisch analysiert wurde [2], werden im Rahmen eines von der DFG geförderten Kooperationsprojekts die Auswirkungen der einzelnen Strömungsregime auf Fluiddynamik und Stofftransport komplementär sowohl experimentell als auch theoretisch untersucht. Für diesen Zweck werden erstmalig Experimente an einer Absorptions-/ Desorptionsanlage durch bildgebende Messungen der Strömung in Anstaupackungen ergänzt. An der Universität Paderborn werden für verschiedene Design- und Betriebsparameter Technikumsversuche zur CO2-Absorption in einer wässrigen Monoethanolamin-Lösung durchgeführt. Die Anlage ermöglicht die Aufnahme von Temperaturprofilen der Gasphase sowie von Konzentrationsprofilen beider Phasen. Am Helmholtz-Zentrum Dresden-Rossendorf wird mittels ultraschneller Röntgentomographie ein detaillierter Einblick in die Phasenverteilung der verschiedenen Strömungszustände ermöglicht. Die Messdaten beider Projektpartner werden zur Erarbeitung von Korrelationen für Stoffübergang, Phasengrenzfläche, Holdup und Druckverlust genutzt, welche in einem rate-based-Model Verwendung finden.
Im Rahmen dieser Arbeit wird der Einfluss wichtiger Betriebs- und Designparameter auf das Absorptionsverhalten in Anstaupackungen experimentell untersucht, um einerseits effizienzsteigernde Betriebsbedingungen zu identifizieren und anderseits eine Basis für die experimentelle Validierung von neuen Simulationsmodellen zu schaffen. Zusätzlich wird eine empirische Korrelationsgleichung zur Bestimmung des integralen Stoffdurchgangskoeffizienten entwickelt, die den Einfluss der Temperatur des Lösungsmittels, der Gas- und Flüssigkeitsbelastung, der CO2-Konzentration im Rohgas sowie der MEA-Konzentration in der Lösung berücksichtigt. Die vorgeschlagene Korrelation ermöglicht damit eine überschlägige Auslegung von Absorptionskolonnen mit Anstaupackungen.

[1] U. Brinkmann, B. Kaibel, M. Jödecke, J. Mackowiak, E.Y. Kenig: Beschreibung der Fluiddynamik von Anstaupackungen, Chemie Ingenieur Technik 84: 36-45 (2012).
[2] Ö. Yildirim, E.Y. Kenig: Rate-based modelling and simulation of distillation columns with sandwich packings, Chemical Engineering and Processing: Process Intensification 98, 147-154 (2015).
  • Lecture (Conference)
    Jahrestreffen der Fachgemeinschaft Prozess-, Apparate- und Anlagentechnik, 20.-21.11.2017, Würzburg, Deutschland

Publ.-Id: 27211 - Permalink


Rate-based-Modellierung von CO2-Absorptionskolonnen mit Anstaupackungen
Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.;
Eines der am häufigsten eingesetzten Trennverfahren zur Abscheidung von Kohlenstoffdioxid (CO2) aus Kraftwerksabgasen ist die Reaktivabsorption mit wässrigen Aminlösungen. Neben der Entwicklung effektiverer Lösungsmittel weisen die Kolonneneinbauten hinsichtlich Druckverlust, Kapazität und Trennleistung ein wesentliches Potenzial für die Prozessintensivierung und damit die Reduzierung des hohen Ressourcenbedarfs auf.
Eine Verbesserung der Trennleistung kann durch den Einsatz von Anstaupackungen erzielt werden. Diese bestehen aus zwei abwechselnden Lagen von Standardpackungen mit unterschiedlichen spezifischen Oberflächen. Die untere Packungslage (die sogenannte Anstaulage) hat eine geringere Belastungsgrenze im Vergleich zur darüberliegenden Abscheidelage. Anstaupackungen werden typischerweise bei Betriebsbedingungen zwischen den Flutpunkten beider Lagen betrieben. Durch das gezielte Fluten der Anstaulage bildet sich eine in die Abscheidelage hineinreichende Sprudelschicht, in der eine hohe Trennleistung mit intensiver Phasenvermischung erzielt wird. Im oberen Bereich der Abscheidelage können filmähnliche Strömungsmuster, Rinnsale und aus der Sprudelschicht mitgerissene Tropfen beobachtet werden [1]. Obwohl der für Trennverfahren vorteilhafte intensive Phasenkontakts bei dem integrierten Packungstyps bereits nachgewiesen wurde, fehlend validierte Auslegungsgrundlagen für eine breitere Anwendung [2].
Eine genaue Vorhersage der Leistungscharakteristik ist für die Auslegung von Anstaupackungen unerlässlich. In einem von der DFG geförderten Kooperationsprojekt zwischen Universität Paderborn und TU Dresden werden die Auswirkungen der einzelnen Strömungsregime auf die Fluiddynamik und den Stoffaustausch komplementär mit experimentellen und theoretischen Methoden untersucht. Um die Auswirkungen jedes einzelnen Strömungsregimes zu bestimmen, werden Experimente an einer Absorptions-/ Desorptionsanlage durch bildgebende Messungen in Anstaupackungen ergänzt. An der Universität Paderborn wird die CO2-Absorption in einer Pilotanlage für verschiedene Design- und Betriebsparameter untersucht. Die Anlage ermöglicht die Messung von Temperaturprofilen der Gasphase sowie von Konzentrationsprofilen beider Phasen. Mithilfe der ultraschnellen Röntgentomographie wird am Helmholtz-Zentrum Dresden-Rosendorf die Phasenverteilung innerhalb der Anstaupackung untersucht. Die Messdaten aus beiden experimentellen Methoden werden verwendet, um Korrelationen für Stofftransportkoeffizienten, Phasengrenzfläche, Holdup und Druckverlust zu entwickeln, die in einem rate-based-Modell für CO2-Absorptionsverfahren mit wässrigen Aminlösungen eingesetzt werden.
Der rate-based-Ansatz kann die Besonderheiten diverser Kolonneneinbauten durch einbautenspezifische Korrelationen berücksichtigen. Da die verschiedenen Fluiddynamikregime in Anstaupackungen unterschiedliche Auswirkungen auf den Stofftransport aufweisen, werden Absorptionskolonnen mit Anstaupackungen als eine Folge von abwechselnden Segmenten dargestellt und jedes Segment wird durch einen der Fluiddynamik entsprechenden Satz von Korrelationen beschrieben. Im Rahmen dieser Arbeit erfolgt eine Validierung des Modells mit experimentellen Daten zur CO2-Absorption.

[1] U. Brinkmann, B. Kaibel, M. Jödecke, J. Mackowiak, E.Y. Kenig: Beschreibung der Fluiddynamik von Anstaupackungen, Chemie Ingenieur Technik 84: 36-45 (2012).
[2] Ö. Yildirim, E.Y. Kenig: Rate-based modelling and simulation of distillation columns with sandwich packings, Chemical Engineering and Processing: Process Intensification 98, 147-154 (2015).
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrentechnik, 27.-28.02.2018, München, Deutschland

Publ.-Id: 27210 - Permalink


New Phenomena in Gamma-Ray Strength Functions
Schwengner, R.;
The excitation and deexcitation of atomic nuclei by electromagnetic radiation are fundamental processes in reactions of this many-body quantum system. At high excitation energy and high level density, statistical models are applied to describe reaction rates, which use $\gamma$-ray strength functions (γSF) to describe the average transition probabilities in a certain range of excitation energy. The experimental determination and the theoretical understanding of the properties of γSF are important for the accurate description of photonuclear reactions and radiative-capture reactions, which play a central role in the synthesis of the elements in various stellar environments.
We report photon-scattering experiments using bremsstrahlung at the γELBE facility (HZDR) and quasi-monoenergetic, polarized γ beams at the HIγS facility (TUNL, Duke Univ., Durham, USA). Systematic studies of the dipole strength revealed new phenomena that are not described by the analytical approximations currently used in reaction codes. The (γ,γ') experiments at high energy show considerable contributions to the γSF from the quasicontinuum of states. Combined with (γ,n) cross sections, the (γ,γ') data provide experimental input γSF for statistical reaction codes.
Keywords: Photonuclear reactions, Nuclear resonance fluorescence, Bremsstrahlung, Monoenergetic gamma rays, Shell Model.
  • Invited lecture (Conferences)
    Frühjahrstagung 2018, 26.02.-02.03.2018, Bochum, Deutschland

Publ.-Id: 27208 - Permalink


Damage accumulation and structural modification in c-plane and a-plane GaN implanted with 400 keV Kr and Gd ions
Mackova, A.; Malinsky, P.; Jágerova, A.; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Mikulics, M.; Böttger, R.; Akhmadaliev, S.;
GaN is the most actively studied wide-bandgap material, applicable e.g. in short-wavelength optoelectronic devices, high-electron-mobility transistors, and semiconductor lasers. The crystallographic orientation of an implanted crystal can significantly influence the optical properties of the implanted layer, reflecting the rearrangement of the crystal matrix after annealing. The annealing procedure, influencing dynamic recovery, point defect diffusion and large defect stabilisation, depending on the GaN crystal orientation and the used ion implantation parameters, is still an important issue to be studied. We have studied the structural and compositional changes of the GaN-epitaxial-layers of c-plane and a-plane orientations grown by MOVPE and implanted with Gd and Kr ions using the ion energy of 400 keV and ion fluences of 5 × 1014 cm-2, 1 × 1015 cm-2 and 5 × 1015 cm-2 with subsequent annealing at 800 °C in ammonia. Dopant depth profiling was accomplished by Rutherford backscattering spectrometry (RBS). Induced structure disorder and its recovery during subsequent annealing were characterised by RBS channelling and Raman spectroscopy. Ion-implanted c-plane and a-plane GaN exhibit significant differences in damage accumulation simultaneously with post-implantation annealing, inducing a different structural reorganization of the GaN structure in the buried layer depending on the introduced disorder level, i.e. depending on the ion-implantation fluence and ion mass.
Keywords: GaN damage accumulation, RBS channelling studies of implanted GaN, Structure modification in c-plane and a-plane GaN

Publ.-Id: 27207 - Permalink


Damage accumulation and structural modification in a- and c-plane GaN implanted with 400-keV and 5-MeV Au+ ions
Mackova, A.; Malinsky, P.; Jágerova, A.; Sofer, Z.; Sedmidubský, D.; Klímová, K.; Böttger, R.; Akhmadaliev, S.;
c-plane (0001) and a-plane (11-20) gallium nitride (GaN) epitaxial layers were grown by Metal organic Vapour Phase epitaxy (MOVPE) on sapphire and subsequently implanted with 400-keV and 5-MeV Au+ ions using fluences 5 × 1014 to 5 × 1015 cm-2. The shallow Au depth profiling was accomplished by Rutherford backscattering spectrometry. The structural changes during implantation and subsequent annealing were characterised by Rutherford backscattering spectrometry channelling and Raman spectroscopy. The interplay between nuclear and electronic stopping, influencing defect accumulation, was monitored and discussed depending on GaN orientation. Post-implantation annealing induced a structural reorganisation of the GaN structure depending on the ion-implantation fluence, ion energy, and on the crystallographic orientation.
Keywords: damage accumulation in GaN, RBS channelling in ion-modified GaN, structure modification in c-plane and a-plane GaN

Publ.-Id: 27206 - Permalink


Adsorption of selenium(VI) onto nano transition alumina
Jordan, N.ORC; Franzen, C.; Lützenkirchen, J.; Foerstendorf, H.; Hering, D.; Weiss, S.; Heim, K.; Brendler, V.
The adsorption of selenium(VI) onto nano transition alumina (γ/δ-Al2O3) was investigated at both macroscopic and molecular levels. The uptake of selenium(VI) was found to decrease upon increasing pH (5-10) and ionic strength (0.01-0.1 mol∙L−1). At the molecular level, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy established the predominant formation of a bidentate outer-sphere surface complex throughout the investigated pH range. The acid-base surface properties of transition alumina (surface charge) together with the Se(VI) adsorption edges were successfully described using a 1-pK with charge distribution surface complexation model and one outer-sphere surface species, namely {(≡AlOH2+0.5)2SeO42−}, according to the IR studies. These new spectroscopic results can be implemented in reactive transport models to enable a more consistent and trustworthy prognostic modeling of the environmental fate of selenium(VI).
Keywords: Selenium(VI); transition alumina; sorption; in situ ATR FT-IR spectroscopy; surface complexation modeling

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Publ.-Id: 27204 - Permalink


Parallelisierung des Wellenfrontrekonstruktionsalgorithmus auf Multicore-Prozessoren
Schenke, J.;
Kurzfassung
Ziel dieser Arbeit war die Beschleunigung des von Elena-Ruxandra Cojocaru und Sébastien Bérujon in Python implementierten Wellenfrontrekonstruktionsalgorithmus. Dieser berechnet aus zwei Bildern einer Probe pixelweise die Fronten der elektromagnetischen Welle eines Röntgenlasers. Die Bilder werden hierbei von zwei hochempfindlichen Röntgen-CCD-Sensoren aufgenommen, welche in einem festen Abstand zueinander und zur Probe positioniert sind. Treffen Strahlen des Röntgenlasers auf diese, so lässt sich aus den so aufgenommenen Streubildern die Wellenfront rekonstruieren, was Rückschlüsse auf die Struktur der Probe zulässt. Auf Basis von Performance-Analysen der Python-Implementierung wurden Optimierungen und Parallelisierungsmöglichkeiten für die kritischen Programmabschnitte ermittelt, implementiert und evaluiert. Die schnellste vorgestellte Lösung basiert auf der Verteilung der Bildpaare auf mehrere Rechenkerngruppen und der Parallelisierung der Berechnung der Bildpaare auf diesen, was eine Skalierung über mehrere Knoten erlaubt. Kombiniert mit der Nutzung optimierter Bibliotheken und dem Übersetzen des Python-Codes wurde eine Beschleunigung von bis zu vier gegenüber der Referenzimplementierung mit gleicher Kernanzahl erreicht. Wurden 120 Kerne verwendet, so war eine Beschleunigung auf das bis zu 133-fache gegenüber der Referenz auf einem Kern möglich. Die Referenzdaten hierfür wurden an der Beamline BM05 der European Synchrotron Radiation Facility aufgenommen.

Abstract
The goal of this thesis was the acceleration of the wavefront reconstruction algorithm which was developed in Python by Elena-Ruxandra Cojocaru and Sébastien Bérujon. This algorithms calculates the electromagnetic wavefront of an X-ray laser from two images of a target pixelwise. The images were captured by two highly sensitive X-ray CCD sensors, which were positioned in a fixed distance to each other and the target. When the refracted X-ray beam hits these detectors a distortion image is generated from which the wavefront can be reconstructed. The result can be used to draw conclusions about the structure of the target. On the basis of performance measurements of the Python implementation optimization and parallelization possibilities for critical sections were determined, implemented and evaluated. The fastest proposed solution is based on the distribution of the image pairs onto CPU core groups and the parallelization of the calculation of the image pairs on these which allows scaling the problem over multiple nodes. This combined with the use of optimized libraries and the compilation of the Python code resulted in a speedup of up to four towards the reference implementation without the use of more cores. When using 120 cores a speedup of up to 133 towards the reference implementation running on a single core could be achieved. The here used datasets were recorded at Beamline BM05 of the European Synchrotron Radiation Facility.
Keywords: Wellenfrontrekonstruktionsalgorithmus, Python, HPC, High Performance Computing, Parallel, Multi-Core
  • Bachelor thesis
    TU Dresden, 2018
    Mentor: Dr. Michael Bussmann, Dr. Elena-Ruxandra Cojocaru, Matthias Werner
    58 Seiten

Publ.-Id: 27203 - Permalink


Bentonite - a natural habitat for sulfate-reducers
Matschiavelli, N.; Kluge, S.; Cherkouk, A.;
Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite plays a crucial role by using it as a barrier und buffer material in between the steel-canister, containg the HLW, and the surrounding host rock. In order to analyze the potential influence of natural occuring microorganisms within the bentonite on the bentonite barrier, we set up microcosm-experiments. Therefor, two different Bavarian bentonites (a natural and an industrial one) were supplied with an anaerobic, synthetic Opalinus-clay pore water solution under an N2/CO2-atmosphere and were incubated for one year at 30 °C and 60 °C. To some set ups organics (acetate or lactate) or H2 were supplemented. During the incubation time samples were taken and analyzed for several bio-geochemical parameters and the evolution of microbial diversity.
Our results clearly demonstrate, that natural accuring microbes affect geochemical parameters. Set ups containing the industrial bentonite supplemented with lactate show the most striking effects. The microbial diversity changed completely within 6 month. The respective batches were dominated (up to 81 %) by Desulfosporosinus spp. – spore-forming, strictly anaerobic, sulfate-reducing organisms, able to survive under very harsh conditions. Concomitantly, an increase of ferrous iron and a simoultaneous decrease of ferric iron was observed. Furthermore, the lactate and sulfate concentration decreased, whereas pyruvate and acetate were formed. Similar observations were also made in setups containg H2. Desulfosporosinus spp. also dominated the microbial population in the respective batches. Desulfosporosinus spp. are known to metabolize a brought range of substrates including H2 and organic acids, thereby reducing sulfate or iron to form H2S, acetate or ferric iron – metabolites that could effect different properties of the barrier system of an HLW.
Keywords: Bentonite, High-Level-Waste repository, sulfate-reduction
  • Lecture (Conference)
    Goldschmidt2018 Boston, 12.-17.08.2018, Boston, USA

Publ.-Id: 27202 - Permalink


Complexation of trivalent lanthanides (Eu) and actinides (Cm) with aqueous phosphates at elevated temperatures
Jordan, N.ORC; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.ORC; Huittinen, N.ORC
In this study, the complexation of Eu(III) and Cm(III) with aqueous phosphates was investigated using laser-induced luminescence spectroscopy. Experiments at 25 °C and different ionic strengths (0.6 to 3.1 mol∙L−1 NaClO4) established the formation of EuH2PO42+ and CmH2PO42+. From the conditional stability constants, the respective values at infinite dilution as well as the ε(Me(H2PO4)2+;ClO4−) (Me = Eu or Cm) ion interaction coefficients (using the specific ion interaction theory - SIT) were derived. Further experiments (at constant ionic strength of 1.1 mol∙L−1) showed, that upon increasing the temperature (25-80 °C), the formation of both EuH2PO42+ and CmH2PO42+ was favored. Using the van’t Hoff equation, the enthalpy ∆_R H_m^0 and entropy ∆_R S_m^0 of these reactions were derived, corroborating an endothermic and entropy driven complexation process. This work contributes to a better understanding of the coordination chemistry of both trivalent actinides and lanthanides with phosphate ions.
Keywords: complexation; europium; curium; aqueous phosphate; temperature; luminescence spectroscopy

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Publ.-Id: 27200 - Permalink


Effect of U(VI) aqueous speciation on the binding of uranium by the cell surface of Rhodotorula mucilaginosa, a natural yeast isolate from bentonites
Lopez-Fernandez, M.; Romero-Gonzalez, M.; Günther, A.; Solari, P. L.; Merroun, M. L.;
This study presents the effect of aqueous uranium speciation (U-hydroxides and U-hydroxo-carbonates) on the interaction of this radionuclide with the cells of the yeast Rhodotorula mucigilanosa BII-R8. This strain was isolated from Spanish bentonites considered as reference materials for the engineered barrier components of the future deep geological repository of radioactive waste. X-ray absorption and infrared spectroscopy showed that the aqueous uranium speciation has no effect on the uranium binding process by this yeast strain. The cells bind mobile uranium species (U-hydroxides and U-hydroxo-carbonates) from solution via a time-dependent process initiated by the adsorption of uranium species to carboxyl groups. This leads to the subsequent involvement of organic phosphate groups forming uranium complexes with a local coordination similar to that of the uranyl mineral phase meta-autunite. Scanning transmission electron microscopy with high angle annular dark field analysis showed uranium accumulations at the cell surface associated with phosphorus containing ligands. Moreover, the effect of uranium mobile species on the cell viability and metabolic activity was examined by means of flow cytometry techniques, revealing that the cell metabolism is more affected by higher concentrations of uranium than the cell viability.The results obtained in this work provide new insights on the interaction of uranium with bentonite natural yeast from genus Rhodotorula under deep geological repository relevant conditions.
Keywords: Uranium biosorption, cell surface, speciation

Publ.-Id: 27199 - Permalink


Laser-Rewriteable Ferromagnetism at Thin Film Surfaces
Ehrler, J.; He, M.; Shugaev, M. V.; Polushkin, N. I.; Wintz, S.; Liersch, V.; Cornelius, S.; Hübner, R.; Potzger, K.; Lindner, J.; Fassbender, J.; Ünal, A. A.; Valencia, S.; Kronast, F.; Zhigilei, L. V.; Bali, R.;
Manipulation of magnetism using laser light is considered a key to the advancement of data storage technologies. Until now, most approaches seek to optically switch the direction of magnetization rather than to reversibly manipulate the ferromagnetism itself. Here we use ~100 fs laser pulses to reversibly switch ferromagnetic ordering on and off by exploiting a chemical order-disorder phase transition in Fe60Al40, from the B2 to the A2 structure and vice versa. A single laser pulse above a threshold fluence causes non-ferromagnetic B2 Fe60Al40 to disorder and form the ferromagnetic A2 structure. Subsequent pulsing below the threshold reverses the surface to B2 Fe60Al40, erasing the laser induced ferromagnetism. Simulations reveal that the order-disorder transition is regulated by the extent of surface supercooling; above threshold the film melts-through and the consequent stability of the supercooled liquid phase suppresses vacancy diffusion, freezing the material into the disordered state. Pulsing below threshold forms a limited supercooled surface phase that solidifies at sufficiently high temperatures, enabling diffusion assisted reordering. This demonstrates that ultrafast lasers can achieve subtle atomic rearrangements in bimetallic alloys in a reversible and non-volatile fashion.
Keywords: magneto-optical devices; data storage; phase transitions; fs laser modifications; supercooling; order-disorder
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Laser schaltet Magnet an und aus (Id 27530) cites this publication

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Publ.-Id: 27198 - Permalink


Application of Gas Field Ion Source to Patterning Nanoscale Magnetic Structures
Bali, R.; Schmeink, A.; Hlawacek, G.; Lindner, J.; Faßbender, J.;
Magnetic nanostructures are necessary components in a variety of sensors and devices, and in prototypes of spin-transport and spin-wave devices. In the past, broad beam ion-irradiation has been used to modify the magnetic properties via a variety of mechanisms, such as alloying, intermixing and structural disordering. In this contribution, we describe the application of the highly focused noble gas ion beam of a gas field ion source (GFIS), to the nanoscale modification of magnetic properties in alloy thin films. Materials in which the saturation magnetization (Ms) can be drastically enhanced via small changes to the atomic arrangement are ideal for the GFIS approach.
In B2 alloys such as Fe60Al40, Fe50Rh50 and Fe60V40, light noble gas ion-irradiation leads to the formation of anti-site defects, which increases the Fe – Fe nearest neighbor interactions and generates an associated increase of the Ms. The disorder induced by the GFIS beam is highly localized, with the extent of the magnetized region determined by lateral scattering of ions. These B2 alloys can be used as non-ferromagnetic templates, on to which the highly focused ion-beam acts as a magnetic writing stylus. Here we examine the conditions necessary and experimentally achievable limits for producing magnetic nanostructures using GFIS.
  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Deutschland

Publ.-Id: 27197 - Permalink


Strong neutron pairing in core+4n nuclei
Revel, A.; Marqués, F. M.; Sorlin, O.; Aumann, T.; Caesar, C.; Holl, M.; Panin, V.; Vandebrouck, M.; Wamers, F.; Alvarez-Pol, H.; Atar, L.; Avdeichikov, V.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boillos, J. M.; Boretzky, K.; Borge, M. J. G.; Caamano, M.; Casarejos, E.; Catford, W. N.; Cederkäll, J.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Cravo, E.; Crespo, R.; Datta Pramanik, U.; Diaz Fernandez, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L. M.; Freer, M.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Golubev, P.; Göbel, K.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Hufnagel, A.; Ignatov, A.; Johansson, H. T.; Jonson, B.; Kahlbow, J.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knyazev, A.; Kröll, T.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lindberg, S.; Machado, J.; Marganiec, J.; Movsesyan, A.; Nacher, E.; Naja, M.; Nikolskii, E.; Nilsson, T.; Nociforo, C.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Reifarth, R.; Ribeiro, G.; Rigollet, C.; Röder, M.; Rossi, D.; Savran, D.; Scheit, H.; Simon, H.; Syndikus, I.; Taylor, J. T.; Tengblad, O.; Thies, R.; Togano, Y.; Velho, P.; Volkov, V.; Wagner, A.; Weick, H.; Wheldon, C.; Wilson, G.; Winfield, J. S.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.;
The emission of neutron pairs from the neutron-rich N =12 isotones 18-C and 20-O has been studied by high-energy nucleon knockout from 19-N and 21-O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay 19N(-1p)18C* -> 16-C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a 14-C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay 21-O(-1n)20-O* -> 18-O+n+n, attributed to its formation through the knockout of a deeply-bound neutron that breaks the 16-O core and reduces the number of pairs.
Keywords: R3B radioactive beams nuclear structure neutron-rich Coulomb dissociation

Publ.-Id: 27196 - Permalink


Large scale arrays of Co/Pd and Fe60Al40 nanomagnets with tunable magnetic properties for recording and magnonic applications
Krupinski, M.; Mitin, D.; Sobieszczyk, P.; Bali, R.; Zarzycki, A.; Potzger, K.; Albrecht, M.; Marszalek, M.;
The fabrication and characterization of nanopatterned magnetic thin films is an important topic for magnetic recording media, sensors, information processing, and magnonic crystals. This broad spectrum of applications results from the possibility of controlling the magnetic properties of such systems in wide range by introducing artificial defects to ferromagnetic material and arranged them in ordered or disordered arrays.
This presentation will focus on the magnetic properties and switching behaviour of magnetic Co(0,3 nm)/Pd(0,9 nm) and Fe60Al40 (40 nm) films composed of arrays of dots, antidots and triangles. Such arrays of nanostructures were created by colloidal lithography complemented by RF-plasma etching and ion irradiation with 20 keV Ne+ ions, which resulted in nanomagnets with sizes down to 30 nm [1].
Using SQUID magnetometry, changes in coercive field, saturation magnetization, loop squareness, and magnetic anisotropy constant have been determined in a temperature range of 5 K – 350 K and compared with non-patterned films. The domain shapes and sizes together with the switching behaviour were studied by scanning magnetoresistive microscopy utilizing commercial reading-writing head from HDD. We have shown that the coercivity reach a maximum values for the arrays with a separation length between nanomagnets close to the domain wall width, which is caused by strong domain wall pinning. The impact of the patterning on the magnetic anisotropy is also clearly seen. The observed influence of surface morphology on magnetic properties and magnetization switching characteristics was confirmed by the micromagnetic modelling using mumax3 software. The results demonstrated that the proposed approach can be effectively used to produce large scale magnetic arrays with properties widely tuneable by temperature and patterning period.

This work was supported by Polish National Science Centre grant No 2017/01/X/ST8/01409.
  • Lecture (Conference)
    XIV International Conference on Nanostructured Materials (Nano 2018), 24.-29.06.2018, Hong Kong, Hong Kong

Publ.-Id: 27195 - Permalink


Imaging Structure and Magnetisation in New Ways Using 4D STEM
Maclaren, I.; Nord, M.; Conner, S.; Mcgrouther, D.; Allen, C. S.; Danaie, M.; Kirkland, A. I.; Bali, R.; Hlawacek, G.; Lindner, J.; Faßbender, J.;
The Materials and Condensed Matter group at the University of Glasgow has long been experimenting with direct electron detectors, together with the Particle Physics Experimental group. A Medipix2 detector was integrated onto our Philips CM20FEG electron microscope in a bottom mount position in 2010 and used in initial studies [1,2]. More recently, a Medipix3 detector was installed onto our JEOL ARM200F in a fixed mount at the 35mm camera port, and together with a Merlin readout system (Quantum Detectors Ltd., Harwell, UK) it was possible to run 4D STEM imaging at >1000 frames per second, under the control of Gatan Digital Micrograph. A similar system has been installed in a bottom mount on the JEOL Grand ARM at ePSIC. Most recently, a retractable mount for the Medipix3 detector has been produced at Glasgow, and is now installed on our JEOL ARM200F in the 35mm port.

One area of use of pixelated detection is for the improved differential phase contrast (DPC) mapping of magnetization in materials. Traditional DPC-STEM uses split detectors to determine the deflection of the bright field disc but suffers from additional diffraction contrast redistributing contrast within the disc thus creating image speckle on the length-scale of the grains. This can be overcome using a pixelated detector, and processing the discs using edge detection and cross correlation to give a pure disc deflection without the diffraction contrast [3]. This has been used in studying the magnetic structures arising from the patterning of B2 Fe60Al40 – this structure is ordered and paramagnetic after deposition and annealing, but after exposure to a (suitably low dose) Ne+ beam it is disordered to a BCC structure, which is strongly ferromagnetic and has a larger the parameter. We recorded diffraction patterns (Fig 1a) at a camera length to show both the central bright field disc and the inner rings of crystal diffraction spots. Fig 1b shows the plotted magnetization in one of these stripes. Fig 1c shows the lattice parameters determined from the diffraction ring radii in the directions parallel to and perpendicular to the long stripe axis. It is clear that parallel to the length, the parameter is constrained by the surrounding film, whereas there is a larger expansion perpendicular to the interface, across the width of the patterned magnetic stripe. This suggests that strain can be used to bias the magnetization in films.

Another novel use for pixelated detectors is to use high angle scattering into higher order Laue zones to reveal ordering along the beam direction, B [4]. Datasets containing such high angle information have now been recorded at atomic resolution, such as Fig 2 from a perovskite oxide heterostructure. Fig 2a shows HAADF contrast for this dataset, and both La-containing layers are much brighter than the SrTiO3 layer, as expected. Fig 2b shows the integrated intensity in the inner Laue zone ring, which only appears for the LaFeO3 layer. This arises from the doubling of the unit cell along B, and the intensity roughly corresponds to the magnitude of atomic shuffles parallel to B, showing that these only reach a maximum at the layer midpoint. Careful inspection also shows that the signal is strongest on the La columns, demonstrating that they are the primary source of the period doubling. This allows detailed investigation of the local “crystal structure”, which differs from the bulk LaFeO3 structure. The plots in Fig 2c show these trends for lines drawn from left to right, together with the outer Laue zone radius, which reveals subtle changes in lattice parameter along the beam direction across this heterostructure.

This demonstrates two exciting areas for application of such fast pixelated detectors for 4D STEM imaging, and shows that it enables new kinds of investigations, not possible with traditional detectors.

References:

[1] A MacRaighne et al., Journal of Instrumentation 6, (2011) C01047.
[2] R Beacham et al., Journal of Instrumentation 6 (2011) C12052.
[3] M Krajnak et al., Ultramicroscopy 165 (2016) 42
[4] M Nord et al., Microscopy and Microanalysis, 22 [S3] (2016) p. 476.
[5] This work was funded by the EPSRC (Fast Pixel Detectors: a paradigm shift in STEM imaging, EP/M009963/1). We thank Diamond Light Source for access and support in use of the electron Physical Science Imaging Centre (EM16952) that contributed to the results presented here.
  • Invited lecture (Conferences)
    Microscopy & Microanalysis 2018 Meeting, 05.-09.08.2018, Baltimore MD, USA

Publ.-Id: 27194 - Permalink


Nanoscale magnetic and structural characterization of Ne+ irradiated FeAl thin films using pixelated STEM
Nord, M.; Bali, R.; Hlawacek, G.; Lindner, J.; Fassbender, J.; Maclaren, I.; Mcgrouther, D.;
Recent advances in 2-dimensional pixelated direct electron detectors have enabled the development of high acquisition rate imaging of the diffraction pattern in the scanning transmission electron microscope (STEM), resulting in the acquisition of a 4D STEM dataset of a full diffraction pattern for every scan position. One use for this is STEM differential phase contrast (DPC) imaging [1], which allows for quantitative measurements of the in-plane magnetic induction when operating the microscope with the objective lens turned off. This imaging mode is essentially convergent beam low angle diffraction, allowing for structural information to also be extracted from the diffraction patterns (Fig. 1b). This novel technique enables both strain and magnetic information to be extracted from a single dataset.

In this work we have simultaneously characterized both magnetic and physical (crystal) structure of patterned ferromagnetic stripes in Fe60Al40. As-deposited Fe60Al40 has an ordered B2 structure and is paramagnetic, but irradiation with Ne+ ions causes transformation to a disordered A2 ferromagnetic BCC structure with a larger lattice parameter [2]. This allows for arbitrarily shaped ferromagnetic regions to be written using a focused ion beam (FIB) with a Ne+ source. By using a JEOL ARM200cF probe aberration corrected STEM equipped with a MERLIN 1R (Medipix3) fast pixelated detector [Quantum Detectors Ltd], we are able to acquire datasets at 1 nm spatial resolution in aberration-corrected field-free Lorentz (objective-off) mode from patterned stripe structures with lateral dimensions from 0.02 – 4 µm and lengths of 10 µm (Fig. 1a). These possess unexpected domain structures in which large fraction of the magnetization deviates away from the long-axis, against shape anisotropy. To uncover the origin of the induced magnetic anisotropy we determined the strain profile in the nanowires from the diffraction patterns, which was also found to be very anisotropic, with the lattice parameter along the long axis clamped to something close to that of the surrounding film (orange trace in Fig. 1c) whereas the lattice parameter along the short axis is significantly larger (blue trace in Fig. 1c), as expected from the irradiation. Our data shows that the resulting shape-dependent anisotropic strain fields exert a strong influence on observed magnetic domain structure.

[1] Matus Krajnak, et al., Ultramicroscopy, 165 (2016) 42–50, doi:10.1016/j.ultramic.2016.03.006

[2] Rantej Bali, et al., Nano Letters, 14 (2014) 435-441, doi:10.1021/nl404521c

The authors are indebted to the EPSRC for the funding of this work via the project “Fast Pixel Detectors: a paradigm shift in STEM imaging” (Grant reference EP/M009963/1).
  • Lecture (Conference)
    19th International Microscopy Congress (IMC19), 09.-14.09.2018, Sydney, Australia

Publ.-Id: 27193 - Permalink


Beryllium-7 at DREsden Accelerator Mass Spectrometry
Rugel, G.; Merchel, S.; Scharf, A.; Querfeld, R.; Steinhauser, G.; Tiessen, C.;
Half-lives of routine accelerator mass spectrometry (AMS) nuclides typically range from thousands to millions of years. We measured short-lived 7Be (T1/2 = 53.2 d) at the DREsden AMS-facility (DREAMS) [1] as low as 90 mBq, which can be challenging for rapid γ-counting. Simultaneous determination of 7Be and 10 Be (T1/2= 1.387 Ma) via AMS is advantageous for improved understanding of production, transport, and deposition of atmospherically produced 7,9,10Be [2].
Data was normalized to a 7 Be sample produced via 7Li(p,n)7Be, measured by γ-counting and chemically processed to BeO after adding low-level 9Be carrier (7Be/9Be ≈ 10-12). The isobar 7Li is completely eliminated by chemistry and the degrader foil technique (at detector 7Be4+, 10.2 MeV, no 7Li4+ possible). The blank ratio of 5 × 10-16 7Be/9Be (0.8 mBq) and simple and fast chemistry allows for the measurement of rainwater samples, collected in Germany, as small as 10 mL corresponding to a few times 10-14 7Be/9Be [3,4].
Thanks to D. Bemmerer (HZDR) and G. György (ATOMKI, Hungary) for help with the 7Be normalization material.
[1] G. Rugel et al., NIMB 370 (2016) 94.
[2] A.M. Smith et al., NIMB 294 (2013) 59.
[3] R. Querfeld et al., JRNC 314 (2017) 521.
[4] C. Tiessen et al. JRNC (to be submitted).
Keywords: Be-7, AMS
  • Lecture (Conference)
    MAT Science Week (Ionenstrahlworkshop), 24.-25.04.2018, Darmstadt, Deuschland

Publ.-Id: 27192 - Permalink


Doping beyond the solid solubility limit: from bulk to nanostructured semiconductors
Berencen, Y.;
Hyperdoping has recently emerged as a potential powerful technique to explore new functionalities of semiconductor materials with unique electrical and optical properties [1-3]. Hyperdoping facilitates to introduce dopants into a semiconductor material at concentrations far above those obtained at equilibrium conditions, viz. doping far beyond the solubility limit. Hyperdoped Si with chalcogens or transition metals like Au or Ti has been postulated to be a promising material for many applications, especially for Si-based infrared photodetectors and intermediate band solar cells ([3] and references therein).

Most of the relevant published papers [1-3] have been limited to the study of hyperdoped bulk Si with chalcogens. Particularly, S and Se have primarily been used for this kind of purpose since they can introduce a variety of deep donor states in the upper half of the band gap of Si, which give rise to the formation of an impurity band that allows a strong sub-band gap optical absorption at wavelengths larger than 1 µm [2]. To create such an impurity band in a semiconductor like Si, whose equilibrium solubility limit for the aforementioned dopants is around 1016 cm-3 [1], high dopant concentrations exceeding the so-called Mott limit are required [1]. Therefore, non-equilibrium thermal processing to obtain hyperdoped semiconductor materials is sound.

Chalcogens are commonly introduced by pulsed-laser irradiation of the material under study, which is simultaneously immersed in an atmosphere containing chalcogen atoms [2]. Another singular approach is to use ion implantation followed by either nanosecond (ns)-range pulsed-laser melting (PLM) [1] or millisecond (ms)-range flash lamp annealing (FLA) [3]. Both PLM and FLA are advantageous if compared with conventional annealing techniques. For instance, these techniques offer high crystal quality after recrystallization, high dopant solubility and low heating of the substrate [3]. Moreover, depending on the energy density and the timescale of annealing after implantation (typically, from few ns to dozens of ms), liquid-phase or solid-phase epitaxy can be induced on the implanted material surface, which accounts for the epitaxial recrystallization atop the crystalline substrate [3]. In particular, solid-phase epitaxy via ms-range FLA was reported to be superior to liquid-phase epitaxy through ns-range PLM in terms of less dopant redistribution and high electrical activation of dopants [3].

In the last years, semiconductor nanowires (NWs) have gained increasing importance as building blocks for nanodevices like field-effect transistors, light emitting devices, photovoltaic cells and integrated photodetectors ([4] and references therein). Indeed, their reduced sizes and the physical confinement along two directions allow the tuning of electro-optical properties such as conductivity, optical absorption and photoluminescence, among others. Recently, traditional dopants such as B and P have been introduced into Si NWs by ion implantation followed by conventional annealing [5]. Recrystallization and reactivation of dopants were successfully achieved at low doses. However, both phenomena were not successful at high doses since it resulted in the formation of polycrystals and a low ratio of dopant activation. To date, there are only theoretical examinations of the properties of Si NWs hyperdoped with chalcogens [4]. These results have shown that donor defects give rise to a strong hyperfine interaction in the hyperdoped Si NWs, which can be exploited to develop a Si-based nuclear spin quantum computer [4].

Therefore, the new approach to combine Si NWs and hyperdoping with chalcogens proposed here can provide important contributions to the state-of-the-art and will help to answer important fundamental and practical scientific issues.

Reference
[1] Ertekin E., Winkler M. T., Recht D., Said A. J., Aziz M. J., Buonassisi T., Grossman J. C. (2012): Insulator-to-Metal Transition in Selenium-Hyperdoped Silicon: Observation and Origin. Published in: Physical Review Letters 108, 026401.
[2] Sher M. J., Mazur E. (2014): Intermediate band conduction in femtosecond-laser hyperdoped silicon. Published in: Applied Physics Letters 105, 032103.
[3] Zhou S., Liu F., Prucnal S., Gao K., Khalid M., Baehtz C., Posselt M., Skorupa W., Helm M. (2015): Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy. Published in: Scientific Reports 5, 8329.
[4] Petretto G., Massé A., Fanciulli M., Debernardi A. (2015): Analysis of hyperfine structure in chalcogen-doped silicon and germanium nanowires. Published in: Physical Review B 91, 125430.
[5] Fukata N., Takiguchi R., Ishida S., Yokono S., Hishita S., Murakami K., (2012): Recrystallization and reactivation of dopant atoms in ion-implanted silicon nanowires. Published in: ACS NANO 6, 3278.
Keywords: Chalcogens, silicon, hyperdoping, ion implantation, flash lamp annealing, insulator to metal transition, sub-band gap photoresponse, infrared plasmonics, nanowires
  • Lecture (others)
    Leibniz institute seminar, 22.02.2018, Leibniz Institute of Polymer Research Dresden, Germany

Publ.-Id: 27187 - Permalink


A high-efficiency gas target setup for underground experiments, and redetermination of the branching ratio of the 189.5 keV 22Ne(p,γ)23Na resonance
Ferraro, F.; Takács, M. P.; Piatti, D.; Mossa, V.; Aliotta, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Depalo, R.; D'Erasmo, G.; Di Leva, A.; Elekes, Z.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marcucci, L. E.; Marigo, P.; Menegazzo, R.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Szücs, T.; Trezzi, D.; Zavatarelli, S.;
The experimental study of nuclear reactions of astrophysical interest is greatly facilitated by a low-background, high-luminosity setup. The Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator offers ultra-low cosmic-ray induced background due to its location deep underground in the Gran Sasso National Laboratory (INFN-LNGS), Italy, and high intensity, 250-500 μA, proton and α ion beams. In order to fully exploit these features, a high-purity, recirculating gas target system for isotopically enriched gases is coupled to a high-efficiency, six-fold optically segmented bismuth germanate (BGO) γ-ray detector. The beam intensity is measured with a beam calorimeter with constant temperature gradient. Pressure and temperature measurements have been carried out at several positions along the beam path, and the resultant gas density profile has been determined. Calibrated γ-intensity standards and the well-known Ep = 278 keV 14N(p,γ)15O resonance were used to determine the γ-ray detection efficiency and to validate the simulation of the target and detector setup. As an example, the recently measured resonance at Ep = 189.5 keV in the 22Ne(p,γ)23Na reaction has been investigated with high statistics, and the γ-decay branching ratios of the resonance have been determined.

Publ.-Id: 27186 - Permalink


Experimental investigation of fluid dynamics in sandwich packings with ultrafast X-ray tomography
Sohr, J.; Schubert, M.; Flechsig, S.; Kenig, E. Y.; Hampel, U.;
Sandwich packings consist of two layers of corrugated sheet structured packings with higher (holdup layer) and lower (de-entrainment layer) specific surface area alternatingly placed in the column. They are preferentially operated between the flooding points of both layers, which results in zones of bubbly flow, froth regime and liquid film flow in each sandwich element. Compared to conventional packed columns, sandwich packings can reach higher capacity and also higher separation efficiency as a result of intensive phase interactions. In the scope of a collaborative project, sandwich packings are experimentally and theoretically investigated. To provide detailed information on the heterogeneous flow patterns to derive reliable process models, ultrafast X-ray tomography is applied as a non-invasive measurement technique with high temporal and spatial resolution. In addition to local liquid holdup in the different layers of the packing, cross-sectional liquid distribution and axial transitions between the flow regimes are estimated. Furthermore, a method for the detection of the gas-liquid interfacial area is proposed.
  • Open Access LogoChemical Engineering Transactions 69(2018), 727
    DOI: 10.3303/CET1869122
  • Lecture (Conference)
    11th International Conference on Distillation & Absorption, 16.-19.09.2018, Florence, Italy

Publ.-Id: 27185 - Permalink


Rate-based modelling of CO2 absorption with sandwich packings
Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.;
The efficiency of fluid separation processes can be enhanced by the application of sandwich packings (SPs). They consist of two alternating layers of industrially available standard packings with different specific surface areas, one with lower (the so-called holdup layer, HL) and another with higher (the so-called de-entrainment layer, DL) capacity. SPs are typically used at operating conditions between the flooding points of HL and DL. Above the HL, a froth sub-layer is formed, which reveals high separation efficiency due to intensified phase contact. In a collaborative project, the effects of the individual flow regimes on fluid dynamics and mass transfer are being investigated, both experimentally and theoretically. In order to identify the impact of the individual flow regimes, experiments in an absorption/desorption plant are supplemented by flow imaging measurements. This paper focuses on a rate-based model, in which the heterogeneous flow patterns in SPs are considered via appropriate correlations. In order to validate this model, we measured CO2 absorption characteristics under the influence of different operating and design parameters and compared them with the simulation results.
  • Open Access LogoChemical Engineering Transactions 69(2018), 169
    DOI: 10.3303/CET1869029
  • Poster
    11th International Conference on Distillation & Absorption, 16.-19.09.2018, Florence, Italy

Publ.-Id: 27184 - Permalink


Peptides as Biosorbents - Promising tools for resource recovery
Braun, R.; Bachmann, S.; Schönberger, N.; Matys, S.; Lederer, F.; Pollmann, K.;
Despite many innovations, meeting both economic and ecological requirements remains challenging for conventional resource recovery technology. The development of highly selective peptides puts a new competitor on the market. We present an approach to identify peptides for resource recovery using Phage Surface Display. Here, we describe the development of peptides for binding of rare earth element terbium containing solids and for removal and enrichment of the heavy metal ions of cobalt and nickel out of waste waters and leaching solutions.
Keywords: phage display; biosorption; peptide; biohydrometallurgy

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Publ.-Id: 27183 - Permalink


Fluiddynamische Untersuchung von Anstaupackungen mittels ultraschneller Röntgentomographie
Sohr, J.; Schubert, M.; Flechsig, S.; Kenig, E. Y.; Hampel, U.;
In Anstaupackungen bilden sich durch die Kombination von Packungslagen unterschiedlicher geometrischer Oberfläche abhängig von den Betriebsbedingungen Filmströmung und Sprudelschicht gleichzeitig aus. Durch die axial stark heterogene Strömungsmorphologie lassen integrale Holdup-Messungen keine Rückschlüsse auf lokale Flüssigkeitsinhalte in einzelnen Packungslagen zu.
Die ultraschnelle Röntgentomographie bietet dank einer Bildrate von bis zu 8000 Schnittbildern pro Sekunde die Möglichkeit, bei den hochdynamischen Zweiphasenströmungen relevante fluiddynamische Parameter in einzelnen Abschnitten der Anstaupackung nichtinvasiv zu bestimmen [1]. Neben der Ermittlung von Phasenanteilen und deren radialer sowie axialer Verteilung werden auch Methoden zur Ermittlung der Gas-Flüssigkeits-Grenzfläche angewandt. Ein weiterer entscheidender Parameter für die hydrodynamische Modellierung von Anstaupackungen ist die Höhe der Sprudelschicht [2]. Deren Bestimmung erfolgt zum einen mithilfe der ultraschnellen Röntgentomographie sowie ergänzend durch eine verteilte Druckverlustmessung mit einer axialen Auflösung von 10 mm. Im Rahmen dieses Beitrags werden sowohl die Messmethoden als auch Messergebnisse der experimentellen Untersuchungen vorgestellt.
Wir danken der DFG für die finanzielle Unterstützung des Kooperationsprojekts "Experimentelle und theoretische Untersuchung der Fluiddynamik und des Stofftrennverhaltens von Anstaupackungen" (KE 837/26-1, HA 3088/10-1).
[1] A. Janzen, M. Schubert, F. Barthel, U. Hampel, E.Y. Kenig, Chemical Engineering and Processing: Process Intensification 66, 20-26 (2013).
[2] U. Brinkmann, B. Kaibel, M. Jödecke, J. Maćkowiak, E.Y. Kenig, Chemie Ingenieur Technik 84: 36-45 (2012).
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrentechnik, 27.-28.02.2018, München, Deutschland

Publ.-Id: 27182 - Permalink


Cluster Formation in the Superconducting Complex Intermetallic Compound Be21Pt5
Amon, A.; Ormeci, A.; Bobnar, M.; Akselrud, L. G.; Avdeev, M.; Gumeniuk, R.; Burkhardt, U.; Prots, Y.; Hennig, C.; Leithe-Jasper, A.; Grin, Y.;
Materials with the crystal structure of γ-brass type (Cu5Zn8 type) are typical representatives of intermetallic compounds. From the electronic point of view, they are often interpreted using the valence electron concentration approach of Hume−Rothery, developed previously for transition metals. The γ-brass-type phases of the main-group elements are rather rare. The intermetallic compound Be21Pt5, a new member of this family, was synthesized, and its crystal structure, chemical bonding, and physical properties were characterized. Be21Pt5 crystallizes in the cubic space group F4̅3m with lattice parameter a = 15.90417(3) Å and 416 atoms per unit cell. From the crystallographic point of view, the binary substance represents a special family of intermetallic compounds called complex metallic alloys (CMA). The crystal structure was solved by a combination of synchrotron and neutron powder diffraction data. Besides the large difference in the scattering power of the components, the structure solution was hampered by the systematic presence of very weak reflections mimicking wrong symmetry. The structural motif of Be21Pt5 is described as a 2 × 2 × 2 superstructure of the γ-brass structure (Cu5Zn8 type) or 6 × 6 × 6 superstructure of the simple bcc structural pattern with distinct distribution of defects. The main building elements of the crystal structure are four types of nested polyhedral units (clusters) with the compositions Be22Pt4 and Be20Pt6. Each cluster contains four shells (4 + 4 + 6 + 12 atoms). Clusters with different compositions reveal various occupation of the shells by platinum and beryllium. Polyhedral nested units with the same composition differ by the distance of the shell atoms to the cluster center. Analysis of chemical bonding was made applying the electron localizability approach, a quantum chemical technique operating in real space that is proven to be especially efficient for intermetallic compounds. Evaluations of the calculated electron density and electron localizability indicator (ELI-D) revealed multicenter bonding, being in accordance with the low valence electron count per atom in Be21Pt5. A new type of atomic interactions in intermetallic compounds, cluster bonds involving 8 or even 14 atoms, is found in the clusters with shorter distances between the shell atoms and the cluster centers. In the remaining clusters, four- and five-center bonds characterize the atomic interactions. Multicluster interactions within the polyhedral nested units and threecenter polar intercluster bonds result in a three-dimensional framework resembling the structural pattern of NaCl. Be21Pt5 is a diamagnetic metal and one of rather rare CMA compounds revealing superconductivity (Tc = 2.06 K).

Publ.-Id: 27181 - Permalink


Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study
Phuyala, D.; Safdari, M.; Pazoki, M.; Liu, P.; Philippe, B.; Kvashnina, K. O.; Karis, O.; Butorin, S. M.; Rensmo, H.; Edvinsson, T.; Kloob, L.; Gardner, J. M.;
Layered two-dimensional (2D) hybrid organic-inorganic perovskites (HOP) are promising materials for light harvesting applications due to their chemical stability, wide flexibility in composition, and recent increases in photovoltaic power conversion efficiencies. Three 2D lead iodide perovskites were studied through various X-ray spectroscopic techniques to derive detailed electronic structures and band energetics profiles at a titania interface. Core-level and valence band photoelectron spectra of HOP were analyzed to resolve the electronic structure changes due to the reduced-dimensionality of inorganic layers. The results show orbital narrowing when comparing the HOP, the layered precursor PbI2, and the conventional 3D (CH3NH3)PbI3 such that different localizations of band edge states and narrow band states are unambiguously due to the decrease in dimensionality of the layered HOPs. Support from density functional theory (DFT) calculations provide further details on the interaction and bandgap variations of the electronic structure. We observed an interlayer distance dependent dispersion in the near band edge electronic states. The results show how tuning the interlayer distance between the inorganic layers affects the electronic properties and provides important design principles for control of the interlayer charge transport properties, such as the change in effective charge masses as a function of the organic cation length. The results of these findings can aid in establishing design principles for new, layered

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Publ.-Id: 27180 - Permalink


Evidence for a dynamical ground state in the frustrated pyrohafnate Tb2Hf2O7
Anand, V. K.; Opherden, L.; Xu, J.; Adroja, D. T.; Hillier, A. D.; Biswas, P. K.; Herrmannsdörfer, T.; Uhlarz, M.; Hornung, J.; Wosnitza, J.;
We report the physical properties of Tb2Hf2O7 based on ac magnetic susceptibility χac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M(H), and heat capacity C(T ) measurements combined with muon spin relaxation (μSR) and neutron powder diffraction measurements. No evidence for long-range magnetic order is found down to 0.1 K. However, χac(T ) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz) indicating slow spin dynamics. The slow spin dynamics is further evidenced from the μSR data (characterized by a stretched exponential behavior) which show persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering) but no magnetic Bragg peaks. The analysis of the diffuse scattering data reveals a dominant antiferromagnetic interaction in agreement with the negative Weiss temperature. The absence of long-range magnetic order and the presence of slow spin dynamics and persistent spin fluctuations together reflect a dynamical ground state in Tb2Hf2O7.

Publ.-Id: 27179 - Permalink


Increasing stripe-type fluctuations in AFe2As2 (A = K, Rb, Cs) superconductors probed by 75As NMR spectroscopy
Zhang, Z. T.; Dmytriieva, D.; Molatta, S.; Wosnitza, J.; Khim, S.; Gass, S.; Wolter, A. U. B.; Wurmehl, S.; Grafe, H.-J.; Kühne, H.;
We report 75As nuclear magnetic resonance measurements on single crystals of RbFe2As2 and CsFe2As2. Taking previously reported results for KFe2As2 into account, we find that the anisotropic electronic correlations evolve towards a magnetic instability in the AFe2As2 series (with A = K, Rb, Cs). Upon isovalent substitution with larger alkali-metal ions, a drastic enhancement of the anisotropic nuclear spin-lattice relaxation rate and decreasing Knight shift reveal the formation of pronounced spin fluctuations with stripe-type modulation. Furthermore, a decreasing power-law exponent of the nuclear spin-lattice relaxation rate (1/T1)HIIab, probing the in-plane spin fluctuations, evidences an emergent deviation from Fermi-liquid behavior. All these findings clearly indicate that the expansion of the lattice in the AFe2As2 series tunes the electronic correlations towards a quantum critical point at the transition to a yet unobserved ordered phase.

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Publ.-Id: 27178 - Permalink


Defect induced magnetism in SiC
Zhou, S.ORC
Defect induced magnetism, which can be controllably generated by ion or neutron irradiation, is attracting intensive research interest. It not only challenges the traditional opinions about magnetism, but also has some potential applications in spin-electronics. SiC is a new candidate for the investigation of defect-induced ferromagnetism after graphitic materials and oxides due to its high material purity and crystalline quality [1, 2]. In this contribution, we present a comprehensive investigation on the structural and magnetic properties of ion implanted and neutron irradiated SiC samples. In combination with X-ray absorption spectroscopy, high-resolution transmission electron microscopy and first-principles calculations, we try to understand the mechanism in a microscopic picture.
For neon or xenon ion implanted SiC, we identify a multi-magnetic-phase nature [3]. The magnetization of SiC can be decomposed into paramagnetic, superparamagnetic and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. By combining X-ray magnetic circular dichroism and first-principles calculations, we clarify that p-electrons of the nearest-neighbor carbon atoms around divacancies are mainly responsible for the long-range ferromagnetic coupling [4]. Thus, we provide a correlation between the collective magnetic phenomena and the specific electrons/orbitals. Moreover, a negative magnetoresistance has been observed in ferromagnetic an conducting SiC, indicating the interplay between magnetism and free carriers [5].
With the aim to verify if a sample containing defects through its bulk volume can persist ferromagnetic coupling, we applied neutron irradiation to introduce defects into SiC [6]. Besides a weak ferromagnetic contribution, we observe a strong paramagnetism, scaling up with the neutron fluence. The ferromagnetic contribution only occurs in a narrow fluence window or after annealing. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: Defects favor spin polarization at the expense of magnetic interaction. Moreover, the interaction between the nuclear spin and the paramagnetic defect can effectively tune the spin-lattice relaxation time (T1) as well as the nuclear spin coherent time (T2) [7].

[1] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).
[2] Y. Wang, et al., Phys. Rev. B 90, 214435 (2014).
[3] Y. Wang, et al., Phys. Rev. B 89, 014417 (2014).
[4] Y. Wang, et al., Scientific Reports, 5, 8999 (2015).
[5] Y. Liu, et al., Phys. Rev. B 95, 195309 (2017).
[6] Y. Wang, et al., Phys. Rev. B 92, 174409 (2015).
[7] Z. Zhang, et al., Phys. Rev. B 95, 085203 (2017).
  • Invited lecture (Conferences)
    International Workshop: Functionality of Oxide Interfaces, 26.02.-02.03.2018, Benedictine Abbey of Frauenwörth, Germany

Publ.-Id: 27177 - Permalink


Interplay between localization and magnetism in (III,Mn)V dilute ferromagnetic semiconductors
Zhou, S.; Yuan, Y.; Sawicki, M.; Rushforth, A. W.; Zhao, J.; Dietl, T.; Helm, M.;
Although the interplay between hole-mediated ferromagnetism and hole localization has long been recognized as the central issue in dilute ferromagnetic semiconductors (DFSs), its understanding remains in a nascent stage and contradicting approaches are under consideration [1, 2]. Some of the difficulties lie in the sample preparation: the dual role of Mn in III-V compounds providing local spins and holes, the poor control over donor defects (Mn interstitials and As antisites) etc. In this contribution, we examine the influence of localization on the hole-mediated ferromagnetism in (III,Mn)V DFSs by utilizing the well-developed ion-beam technology for microelectronics which can overcome the aforementioned difficulties [3].
First, we have used ion implantation of Mn combined with pulsed laser melting to prepare Ga1−xMnxAs and In1−xMnxAs with Mn concentration from 0.3% to 1.8% covering both sides of the insulator-metal transition [4-8]. The system evolves with x from a paramagnetic phase (probed down to 1.8 K), to a superparamagnetic material, to reach, via a mixed phase consisting of percolating ferromagnetic clusters and superparamagnetic grains, a global ferromagnetism without any superparamagnetism. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1−xMnxAs compared to Ga1−xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Second, we use inert Helium ions to precisely compensate holes by donor defects, thereafter to shift the Fermi energy in DFSs while keeping the Mn concentration constant [9-12]. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a monotonous decrease of Curie temperature TC down to zero and a spin-reorientation transition with hole compensation while the conduction is changed from metallic to insulating. The previously questioned existence of TC below 10 K is also confirmed in heavily compensated samples. Our comprehensive results support strongly the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions even on the insulator side of the metal-insulator transition.

[1] M. Sawicki et al., Nat. Phys. 6, 22 (2010).
[2] M. Kobayashi et al., Phys. Rev. B 89, 205204 (2014).
[3] S. Zhou, J. Phys. D: Appl. Phys. 48, 263001 (2015).
[4] S. Zhou et al., Appl. Phys. Express 5, 093007 (2012).
[5] Y. Yuan…, S. Zhou, J. Phys. D: Appl. Phys. 48, 235002 (2015).
[6] S. Prucnal…, S. Zhou, Phys. Rev. B 92, 224407 (2015).
[7] Y. Yuan…, S. Zhou, Phys. Rev. Mater. 1, 054401 (2017).
[8] Y. Yuan…, S. Zhou, J. Phys.: Condens. Matter 30, 095801 (2018).
[9] L. Li…, S. Zhou, J. Phys. D: Appl. Phys. 44 099501 (2011).
[10] S. Zhou et al., Phys. Rev. B 95, 075205 (2016).
[11] M. Lonsky…, S. Zhou, J. Müller, Phys. Rev. B 97, 054413 (2018).
[12] Y. Yuan..., S. Zhou, J. Phys. D: Appl. Phys., in press (2018).
  • Poster
    34th International conference on the physics of semiconductors, 29.07.-03.08.2018, Montpellier, France

Publ.-Id: 27176 - Permalink


Hydrogen-assisted Post-growth Doping of Tellurium into Molybdenum Disulfide Monolayers with Tunable Compositions
Yin, G.; Zhu, D.; Lv, D.; Zhang, Z.; Hashemi, A.; Krasheninnikov, A. V.ORC; Komsa, H.-P.; Jin, C.
Herein we report the successful doping of tellurium (Te) into molybdenum disulfide (MoS2) monolayers to form MoS2xTe2(1−x) alloy with variable compositions via a hydrogen-assisted post-growth chemical vapor deposition process. It is confirmed that H2 plays an indispensable role in the Te substitution into as-grown MoS2 monolayers. Atomic-resolution transmission electron microscopy allows us to determine the lattice sites and the concentration of introduced Te atoms. At a relatively low concentration, tellurium is only substituted in the sulfur sublattice to form monolayer MoS2(1−x)Te2x alloy, while with increasing Te concentration (up to ∼27.6% achieved in this study), local regions with enriched tellurium, large structural distortions, and obvious sulfur deficiency are observed. Statistical analysis of the Te distribution indicates the random substitution. Density functional theory calculations are used to investigate the stability of the alloy structures and their electronic properties. Comparison with experimental results indicate that the samples are unstrained and the Te atoms are predominantly substituted in the top S sublattice. Importantly, such ultimately thin Janus structure of MoS2(1−x)Te2x exhibits properties that are distinct from their constituents. We believe our results will inspire further exploration of the versatile properties of asymmetric 2D TMD alloys.
Keywords: 2D materials, post-growth, tellurium, TMDC, MoS2

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Publ.-Id: 27175 - Permalink


Big Bang Cosmology in the Lab: The 2H(p,γ)3He reaction studied at LUNA
Stöckel, K. For The Luna Collaboration;
Recent high-precision measurements of the primordial 2H abundance have opened the path to use Big Bang nucleosynthesis to constrain the primordial baryon to photon ratio with similar precision as the cosmic microwave background. This would provide an independent cross-check on current Big Bang models. However, the interpretation of the abundance is limited by the lack of precise nuclear data, in particular on the main 2H destruction channel, the 2H(p,γ)3He reaction. A new experiment to study the 2H(p,γ)3He cross section directly in the Big Bang energy window is underway at the LUNA 400 kV accelerator, deep underground in the Gran Sasso laboratory, Italy. The progress of experiment and analysis will be summarized. – Supported by DFG (BE 4100/4-1).
  • Lecture (Conference)
    DPG-Frühjahrstagung Bochum 2018, 26.02.-02.03.2018, Bochum, Deutschland

Publ.-Id: 27174 - Permalink


Monothioarsenate transformation kinetics determines arsenic sequestration by sulfhydryl groups of peat
Besold, J.; Biswas, A.; Suess, E.; Scheinost, A. C.; Rossberg, A.; Mikutta, C.; Kretzschmar, R.; Gustafsson, J. P.; Planer-Friedrich, B.;
In peatlands, arsenite was reported to be effectively sequestered by sulfhydryl groups of organic matter. To which extent porewater arsenite can react with reduced sulfur to form thioarsenates and how this affects arsenic sequestration in peatlands, is unknown. Here, we show that in the arsenic-rich peatland Gola di Lago, Switzerland, up to 93% of all arsenic species in surface and porewaters were thioarsenates. The dominant species, monothioarsenate, likely formed from arsenite and surface-associated zero-valent sulfur (S(0)). Laboratory incubations with sulfide-reacted peat showed for both, monothioarsenate and arsenite, increasing total arsenic sorption with decreasing pH from 8.5 to 4.5. However, X-ray absorption spectroscopy revealed no binding of monothioarsenate via sulfhydryl groups. The sorption observed at pH 4.5 was acid-catalyzed dissociation of monothioarsenate, forming arsenite. The lower the pH and the more sulfhydryl sites, the more arsenite sorbed which in turn shifted equilibrium towards further dissociation of monothioarsenate. At pH 8.5, monothioarsenate was stable over 41 days. In conclusion, arsenic is effectively sequestered in anoxic, acidic environments where arsenite is the only arsenic species. Where fluctuating redox conditions enable sulfide oxidation to S(0), monothioarsenate forms and at neutral to alkaline pH, slow transformation kinetics make this species highly mobile.
Keywords: arsenic speciation wetland ground water xafs

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Publ.-Id: 27173 - Permalink


Analysis of the Electric-Double-Layer formation by in-situ Rutherford Backscattering Spectrometry
Baghban Khojasteh Mohammadi, N.; Heller, R.; Bergmann, U.; Apelt, S.;
A setup for in-situ Rutherford Backscattering Spectrometry (RBS) has been installed at the 2 MV Van-de-Graaff accelerator at the Ion Beam Center (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Online analysis of solid-liquid interfaces as well as electro-chemistry experiments are conducted by this technique. A Si3N4 window separates the liquid from the vacuum in the RBS chamber. A He+ beam (E = 1.7 MeV) is utilized for the RBS measurements. RBS as well as Particle Induced X-Ray Emission Spectroscopy (PIXE) spectra are recorded simultaneously to increase the sensitivity for trace elements. The technique was employed for direct measurements of the Electric-Double-Layer (EDL) formation on Si3N4. Investigations of the EDL formation at solid-liquid interfaces are of great significance due to the various valuable applications such as super-capacitors that can be utilized to provide a backup power supply or applied in various other fields [1-3]. In our preliminary experiments, the specific adsorption of Barium ions from a 1mM BaCl2 solution with various pH values was observed in a direct and quantitative manner. Sensitivity of the technique reaches the ppm range and areal densities can be measured down to 0.1 atomic monolayer.
[1]Kötz et al., (2002). The 12th International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Dec, USA.
[2]Faggioli et al., (1999). J. Power Sources, 84(2): 261.
[3]Simon et al., (2008). Nature materials, 7(11): 845.
Keywords: in-situ RBS, Electric-Double-Layer
  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.04.2018, Darmstadt, Germany

Publ.-Id: 27172 - Permalink


An experimental approach to reactive transport in geomaterials: GeoPET
Kulenkampff, J.; Franke, K.; Gründig, M.; Hildebrand, H.; Karimzadeh, L.; Schymura, S.; Fischer, C.;
Detailed understanding of reactive transport in geomaterials of chemical species, including radionuclides, is required for the utilization of the subsoil, e.g. for designing ore production by in-situ leaching, or for radioactive waste disposal. To complement the well-established conventional approach, i.e. computer model simulations based upon bulk material parameters and geochemical data bases, we apply process tomography with positron emission tomography (GeoPET) for direct observation and parameterization of the reactive transport processes. This enables to consider heterogeneity as pervasive feature of processes in complex media. One example is localized flow meandering along fractures, where preferential flow may jeopardize leaching efficiency. On the other hand, fissure networks through otherwise tight material could provide fast transport pathways through geological barriers.
Our workflow consist of 1) production of appropriate PET-nuclides and labelling, 2) transport experiment on samples of drill core size with the labelled species, 3) recording of PET-data (list-mode-files) during the course of tracer propagation, 4) computation of PET-frames with appropriate frame rate and correction for material effects, 5) parameterization of the spatiotemporal data set with the target parameters effective volume distribution and velocity distribution.
The choice of PET-nuclides is broader than in common biomedical PET applications, because longevity and toxicity of the tracers are inconsiderable, but spatial resolution and efficient corrections for attenuation and scatter require attention. The development of the GeoPET method during the past decade is described in Kulenkampff et al. (2016).
As illustration, we present an example from ore leaching, where the leaching solution is flown through an artificial fracture. During leaching we experimentally determined the macroscopic flow field with GeoPET. With these hydrodynamic data we are able to establish a realistic and light-weight reactive transport model which can directly serve for efficient design of leaching.
The procedure is one good example for the benefit of radiotracers for unravelling complex processes by non-destructive molecular imaging. We strongly suggest utilizing this distinguished tool, in particular for .parameterization and upscaling of heterogeneous reactive transport models.

Kulenkampff, J., Gründig, M., Zakhnini, A., Lippmann-Pipke, J. 2016. Geoscientific process monitoring with positron emission tomography (GeoPET), Solid Earth, 7, 1217-1231, 10.5194/se-7-1217-2016.
  • Lecture (Conference)
    RadChem 2018, 13.-18.05.2018, Mariánské Lázně, Czech Republic

Publ.-Id: 27171 - Permalink


Comparison of different treatment planning approaches for intensity-modulated proton therapy with simultaneous integrated boost for pancreatic cancer
Stefanowicz, S.; Stützer, K.; Zschaeck, S.; Jakobi, A.; Troost, E. G. C.ORC
Background
Neoadjuvant radio(chemo)therapy of non-metastasized, borderline resectable or unresectable locally advanced pancreatic cancer is complex and prone to cause side-effects, e.g., in gastrointestinal organs. Intensity-modulated proton therapy (IMPT) enables a high conformity to the targets while simultaneously sparing the normal tissue such that dose-escalation strategies come within reach. In this in silico study, we compared four IMPT planning strategies including robust multi-field optimization (rMFO) and a simultaneous integrated boost (SIB) for dose-escalation in pancreatic cancer patients.

Methods
For six pancreatic cancer patients referred for adjuvant or primary radiochemotherapy four rMFO-IMPT-SIB treatment strategies of two or three (non-)coplanar beam arrangements were calculated. Dose values for both targets, the elective clinical target volume (CTV) and the SIB, and the organs at risk as well as target conformity and homogeneity indexes, derived from the dose volume histograms, were statistically compared.

Results
All treatment plans of each strategy fulfilled the prescribed doses to the targets (D95%≥95%, D2%≤107%). No significant differences for the conformity index were found (p>0.05), however, treatment plans with a three non-coplanar beam approach were most homogenous to both targets (p<0.045). Dose constraints for large and small bowel as well as for the liver and the spinal cord were met with all beam arrangements. Irrespective of the planning strategies, the dose constraint for the duodenum and stomach were not met. Using the three-beam arrangements, the dose to the left kidney could be significant decreased when compared to a two-beam strategy (p<0.045).

Conclusion
Based on our findings we recommend a three-beam configuration with at least one non-coplanar beam for rMFO-IMPT-SIB in advanced pancreatic cancer patients achieving a homogeneous dose distribution in the target while simultaneously minimizing the dose to the organs at risk.
Keywords: pancreatic cancer; intensity modulated proton therapy; simultaneous integrated boost; dose escalation

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Publ.-Id: 27170 - Permalink


High-Yield Optical Undulators Scalable to Optical Free-Electron Laser Operation by Traveling-Wave Thomson-Scattering
Steiniger, K.ORC
All across physics research, incoherent and coherent light sources are extensively utilized.
Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources.
But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays.

This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources.
The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems.

TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources.
Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized.

Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods.

This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems.
The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range.
These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis.
It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser.

Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed.
The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups.
An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, too.
Keywords: Traveling-Wave, Thomson scattering, X-ray, free-electron laser, pulse-front tilt
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-089 2018

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Publ.-Id: 27169 - Permalink


Thick Permalloy films for the imaging of spin texture dynamics in perpendicularly magnetized systems
Finizio, S.; Wintz, S.; Bracher, D.; Kirk, E.; Semisalova, A. S.; Förster, J.; Zeissler, K.; Weßels, T.; Weigand, M.; Lenz, K.; Kleibert, A.; Raabe, J.;
Performance combined with simplicity: we demonstrate that thick Permalloy films exhibiting a weak growth-induced perpendicular magnetic anisotropy can be employed as an ideal test system for the study of magnetodynamical processes in perpendicularly magnetized systems exhibiting magnetic textures ranging from isolated magnetic bubbles to more complex n"pi" states.
Keywords: Skyrmion, STXM, PMA

Publ.-Id: 27168 - Permalink


Magnetic small-angle neutron scattering
Mühlbauer, S.; Honecker, D.; Perigo, E. A.; Bergner, F.ORC; Disch, S.; Heinemann, A.; Erokhin, S.; Berkov, D.; Leighton, C.; Eskildsen, M. R.; Michels, A.
Small-angle neutron scattering (SANS) is one of the most important techniques for microstructure determination, being utilized in a wide range of scientific disciplines, such as materials science, physics, chemistry, and biology. The reason for its great significance is that conventional SANS is probably the only method capable of probing structural inhomogeneities in the bulk of materials on a mesoscopic real-space length scale, from roughly 1 − 300 nm. Moreover, the exploitation of the spin degree of freedom of the neutron provides SANS with a unique sensitivity to study magnetism and magnetic materials at the nanoscale. As such, magnetic SANS ideally complements more real-space and surface-sensitive magnetic imaging techniques, e.g., Lorentz transmission electron microscopy, electron holography, magnetic force microscopy, Kerr microscopy, or spin-polarized scanning tunneling microscopy. In this review article we summarize the recent applications of the SANS method to study magnetism and magnetic materials. This includes a wide range of materials classes, from nanomagnetic systems such as soft magnetic Fe-based nanocomposites, hard magnetic Nd−Fe−B-based permanent magnets, magnetic steels, ferrofluids, nanoparticles, and magnetic oxides, to more fundamental open issues in contemporary condensed matter physics such as skyrmion crystals, noncollinar magnetic structures in noncentrosymmetric compounds, magnetic/electronic phase separation, and vortex lattices in type-II superconductors. Special attention is paid not only to the vast variety of magnetic materials and problems where SANS has provided direct insight, but also to the enormous progress made regarding the micromagnetic simulation of magnetic neutron scattering.

Publ.-Id: 27167 - Permalink


Detecting Beryllium-10 from exotic decays by Accelerator Mass Spectrometry (AMS)
Forstner, O.; Merchel, S.ORC; Lachner, J.; Rugel, G.; Is541 Kollaboration
The one-neutron halo-nucleus 11Be decays via beta-minus to the stable nucleus 11B (t1/2=13.76 s). In rare cases a subsequent emission of a proton leads to the unstable nucleus 10Be. Theoretical calculations predict a branching ratio of this rare decay channel of below 10-7. With the capability of AMS in measuring ultra-low isotopic ratios (10Be/9Be < 10-15) the branching ratio of beta-delayed proton decay to 10Be could be measured for the first time.
A beam of 11Be ions was produced at the radioactive ion beam facility ISOLDE at CERN. After mass separation the ions were implanted in Cu targets. These targets containing the produced 10Be were spiked with low-level 9Be and in the form of BeO chemically prepared as AMS targets at HZDR. The resulting 10Be/9Be ratios were determined via AMS at the VERA laboratory of the University of Vienna. With the known quantity of added 9Be the amount of implanted 10Be was calculated. Due to the low expected branching ratio and the resulting low number of implanted 10Be atoms a high efficiency paired with a low background of the 9Be carrier material was necessary.
To further widen the spectrum of radionuclides measureable by AMS and lowering the detection limits for similar nuclear physics research, we are planning to implement an optical filtering method for selective suppression of isobars by laser photodetachment (LISEL) at the 6 MV tandem accelerator at HZDR.
Keywords: AMS
  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.03.2018, Darmstadt, Deutschland

Publ.-Id: 27166 - Permalink


Plasmonic nanoparticles embedded in single crystals synthesized by gold ion implantation for enhanced optical nonlinearity and efficient Q-switched lasing
Nie, W. J.; Zhang, Y. X.; Yu, H. H.; Li, R.; He, R. Y.; Dong, N. N.; Wang, J.; Hübner, R.; Böttger, R.; Zhou, S. Q.; Amekura, H.; Chen, F.;
We report on the synthesis of embedded gold (Au) nanoparticles (NPs) in Nd:YAG single crystals using ion implantation and subsequent thermal annealing. Both linear and nonlinear absorption of the Nd:YAG crystals have been enhanced significantly due to the embedded Au NPs, which is induced by the surface plasmon resonance (SPR) effect in the visible light wavelength band. Particularly, through a typical Z-scan system excited by a femtosecond laser at 515 nm within the SPR band, the nonlinear absorption coefficients of crystals with Au NPs have been observed to be nearly 5 orders of magnitude larger than that without Au NPs. This giant enhancement of nonlinear absorption properties is correlated with the saturable absorption (SA) effect, which is the basis of passive Q-switching or mode-locking for pulsed laser generation. In addition, the linear and nonlinear absorption enhancement could be tailored by varying the fluence of implanted Au+ ions, corresponding to the NP size and concentration modulation. Finally, the Nd:YAG wafer with embedded Au NPs has been applied as a saturable absorber in a Pr:LuLiF4 crystal laser cavity, and efficient pulsed laser generation at 639 nm has been realized, which presents superior performance to the MoS2 saturable absorber based system. This work opens an avenue to enhance and modulate the nonlinearities of dielectrics by embedding plasmonic Au NPs for efficient pulsed laser operation.

Publ.-Id: 27165 - Permalink


OpenFOAM – a contributer‘s point of view
Schlegel, F.; Liao, Y.; Oertel, R.; Meller, R.;
Der Vortrag behinhaltet einen Überblick über die Arbeiten im Bereich Mehrphasen-Simulation der Abteilung FWDC mit Hilfe der C++-Bibliothek OpenFOAM.
  • Lecture (Conference)
    German CFD Meeting, 06.03.2018, München, Deutschland

Publ.-Id: 27164 - Permalink


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