Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

33412 Publications

Technetium retention by siderite under anoxic conditions

Schmeide, K.ORC; Rossberg, A.; Weiss, S.; Brendler, V.; Scheinost, A. C.
99Tc is a long-lived (t1/2 = 2.1 × 105 years) β-emitter formed during the fission of U and is of major concern for radioactive waste disposal. Its environmental mobility is primarily governed by the oxidation states VII and IV, with TcVII forming the highly mobile TcO4 aquo anion, whereas TcIV is rather immobile due to the low solubility of its hydrolysis products. Redox processes, which are able to convert TcVII into TcIV, are hence of paramount importance for the safety of radioactive waste repositories. FeII-bearing minerals, ubiquitous in nature and also forming as corrosion products of the carbon steel canisters foreseen as a possible first enclosure of radioactive waste, play a vital role in these redox reactions due to their high redox reactivity and high sorption capacity, as has been shown not only for Tc, but also for Se, U, Np and Pu.
Here we focus on the retention of TcVII by a typical FeII mineral in carbonate-rich environments, siderite (FeCO3), which we studied in the relevant pH range (7 – 12.6) under anoxic conditions by means of batch sorption experiments and by X-ray absorption spectroscopy. Sorption experiments showed that Tc retention by siderite is fast (within minutes) and efficient (log Rd ~5) across the investigated pH range and independent of ionic strength (0.1 – 1 M NaCl). Tc K-edge X-ray absorption near-edge structure (XANES) data confirmed that the Tc immobilization is due to the surface-mediated reduction of TcVII to TcIV. The local structure of TcIV as probed by extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed two different species: in the pH range 7.8 to 11.5, TcO2-dimers form inner-sphere sorption complexes at the surface of siderite or of an FeII,III (hydr)oxide potentially formed during the redox reaction. At pH 11.8 to 12.6, the retention proceeds through the (near-surface) incorporation of TcIV by siderite.
In conclusion, siderite contributes effectively to the retention of Tc in the near-field of nuclear waste repositories.
Keywords: Technetium, siderite, reduction, adsorption, incorporation, technetium carbonate, X-ray absorption spectroscopy
  • Lecture (Conference)
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland

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


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

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

My PhD topic focuses on the development of open, manycore-driven particle-in-cell (PIC) simulations in order to model highly non-linear processes that happen on a time scale of atto- to pico-seconds inside this new class of particle accelerators. This includes the development of the world's fastest PIC code PIConGPU which scales up to the full size of Titan (ORNL). I am further extending the PIC algorithm to model previously unreachable multi-physics processes in high-energy density plasmas such as the interaction with XFEL laser beams at the European XFEL, enabling a new quality in predictability.
Keywords: laser plasma modeling HED atomic physics PIC GPU open source LPA ion acceleration
  • Lecture (Conference)
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

  • available with HZDR-Login

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


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

Kulenkampff, J.; Barthen, R.; Gründig, M.; Karimzadeh, L.; Lippold, H.; Schymura, S.; Lippmann-Pipke, J.
A current application that needs improved understanding of coupled reactive transport processes and fluid-rock interactions is in situ leaching of ore minerals. These processes are largely controlled by the chemical and hydrological heterogeneity of the material and the respective transport process.
We apply GeoPET as method for quantitative spatiotemporal imaging of tracer concentrations, which combines molecular sensitivity (picomolar) with suitable spatial resolution (ca. 1 mm) for elucidating heterogeneous effects on the core scale. This laboratory imaging method is virtually unique for crossing the scale from molecular processes to the macrosphere with its typical heterogeneous geoscienctific characteristics. It requires labelling the relevant substance with an appropriate positron-emitting radionuclide, like 18F or 64Cu. PET then makes use of the space-resolved detection of the decay radiation for deriving the tracer concentration.
From the time series of 3D frames of the tracer concentration of conservative flow experiments we compute the distribution of both the process-dependent effective volume and the local velocity distribution of the tracer. These experimental data are the basis of exceptionally efficient finite-element reactive transport models on the millimetre scale with a COMSOL-PhreeqC-coupling.
Our study was conducted within the framework of the French-German project “EcoMetals” which aims at the development of innovative processes for copper (and associated metals) extraction by means of biotechnology. In our showcase experiment we leached copper from pebbles that had been artificially coated with [64Cu]covellite. The PET-experiment has two stages. At first we observed the depletion of the 64Cu activity concentration in the surface layer during leaching with glutamic acid. From this, we derived local covellite leaching rates. After decay of the radionuclide we conducted a conservative flow experiment with pore water labelled with 18F. This experiment identifies strongly localized preferential flow zones. From this, we compute porosity and velocity distributions, which serve as input parameters for the numerical simulation. The simulation results are validated in comparison with observed leaching rates.
  • Lecture (Conference)
    GeoBremen2017, 24.-29.09.2017, Bremen, Deutschland

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


Roughness-induced domain structure in perpendicular Co/Ni multilayers

Lee-Hone, N. R.; Thanhoffer, R.; Neu, V.; Schäfer, R.; Arora, M.; Hübner, R.; Suess, D.; Broun, D. M.; Girt, E.
We investigate the correlation between roughness, remanence and coercivity in Co/Ni films grown on Cu seed layers of varying thickness. Increasing the Cu seed layer thickness of Ta/Cu/8×[Co/Ni] thin films increases the roughness of the films. In-plane magnetization loops show that both the remanence and coercivity increase with increasing seed layer roughness. Polar Kerr microscopy and magnetic force microscopy reveal that the domain density also increases with roughness. Finite element micromagnetic simulations performed on structures with periodically modulated surfaces provide further insight. They confirm the connection between domain density and roughness, and identify the microsocpic structure of the domain walls as the source of the increased remanence in rough films. The simulations predict that the character of the domain walls changes from Bloch-like in smooth films to Néel-like for rougher films
Keywords: Domain density, Domain structure, In-plane magnetization, Micromagnetic simulations, Modulated surfaces, Polar-Kerr, Seed layer thickness, Varying thickness

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

  • available with HZDR-Login

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


High-field ESR in low-D spin systems

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

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


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

Lippold, H.
The mobility of toxic or radioactive contaminant metals in the subsurface hydrosphere can be essentially governed by their interaction with humic colloids. Predictions on migration processes need thorough consideration of kinetic aspects in the ternary system metal / humic substance / mineral surface. In reactive transport models, reversibility is commonly presumed. However, for adsorption of humic matter, strong hysteresis is observed (hardly any desorption upon dilution), and recoveries in column experiments are far from complete. Complexation of higher-valent metals with humic substances is accompanied by slow processes leading to an increase in complex inertness, i.e., a growing resistance to dissociation.
In view of these uncertainties, the aim of our studies was to elucidate the reversible / irreversible character of interactions controlling humic-bound transport. For this purpose, the principle of tracer exchange was employed to gain insight into the dynamics of equilibria within the ternary system. A radioactive probe, introduced as a reactant into pre-equilibrated systems, will represent the overall equilibrium if there is a dynamic exchange. In case of a static equilibrium, the tracer will not get involved. The chosen model system for these experiments consisted of terbium(III) (as an analogue of trivalent actinides), humic acid and kaolinite. 160Tb as a radioisotope was produced by neutron activation of 159Tb. Humic acid was radiolabelled by azo coupling with [14C]aniline.
After introducing trace amounts of [14C]humic acid into pre-equilibrated adsorption systems of kaolinite and non-labelled humic acid in the state of surface saturation, quantitative exchange was found to take place. Evidently, adsorption equilibria of humic colloids are not static, notwithstanding their size and multiple bonding, albeit an exchange time of more than 4 weeks was required. Isotope exchange of 159Tb / 160Tb on saturated humic acid was completed within a very short time frame, independently of the time of pre-equilibration 159Tb / humic acid. However, if the tracer 160Tb was introduced prior to saturation with 159Tb, the expected partial desorption of 160Tb occurred at much lower rates, decreasing with time of pre-equilibration. Inertisation phenomena are thus confined to the strongest sites of humic molecules. Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium.
  • Lecture (Conference)
    GeoBremen 2017, 24.-29.09.2017, Bremen, Deutschland

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


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

Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S. E.; Schwengner, R.; Wagner, A.
The fast neutron-induced fission cross section of 242Pu was determined in the range of 0.5 MeV to 10 MeV relative to 235U(n,f) at the neutron time-of-flight facility nELBE. The number of target nuclei was calculated by means of measuring the spontaneous fission rate of 242Pu. Neutron transport simulations with Geant 4 and MCNP 6 are used to correct the relative cross section for neutron scattering. The determined results are in good agreement with current experimental and evaluated data sets.
Keywords: neutron-induced fission cross section, neutron scattering corrections, fast neutrons, nELBE
  • Invited lecture (Conferences)
    Scientific Workshop on Nuclear Fission dynamics and the Emission of Prompt Neutrons and Gamma Rays, 19.-23.06.2017, Varna, Bulgaria
  • Open Access Logo Contribution to proceedings
    Scientific Workshop on Nuclear Fission dynamics and the Emission of Prompt Neutrons and Gamma Rays, 20.-22.06.2017, Varna, Bulgaria
    European Physical Journal: Web of Conferences, Vol. 169, 00009, Les Ulis Cedex A: EDP Sciences
    DOI: 10.1051/epjconf/201816900009

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

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


Ultrasonic Study on the Hexagonal Antiferromagnet Dy3Ru4Al12

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

Downloads:

  • available with HZDR-Login

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


Protracted river response to medieval earthquakes

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

Downloads:

  • available with HZDR-Login

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


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

Jantschik, K.; Kulenkampff, J.; Moog, H. C.
Cement-based salt concrete (concrete with crushed salt filler) is a potential building material for seals in rock salt formations. The contact seam between sealing element and the excavation damaged zone (EDZ) of the host rock is a critical path way for transport of aqueous solutions and the release of radionuclides to the biosphere. For an assessment for the long-term integrity of seals it is therefore important to know at which rate the seam closes up upon contact with saline solution and confining stress.
The investigation of the sealing capacity and the closure of the contact seam influenced by saline solutions and confining stress was investigated in laboratory tests at GRS. The available core material originates from a sealing element of a former German salt mine and was exposed to confining pressure of the host rock for about ten years. The rock salt originates from the EZD of the sealing element. The salt concrete core was coated with salt slurry and inserted in a hollow rock salt cylinder for the preparation of a combined sealing element at laboratory scale.
Afterwards the combined sample was dried and installed in an isostatic cell. The development of permeability by percolation of saturated NaCl solution and confining pressure was investigated on various combined samples at GRS. All samples showed a significant reduction of permeability with time. One sample was dismantled and prepared for investigation with PET.
Following, transport of radiotracers through the sample and along the seam was investigated with positron emission tomography (PET). PET could clearly and quantitatively display the propagation of the tracer along the seam and inside the salt concrete matrix. It is thus a laboratory-scale method that is capable of non-destructive quantitative visualization and parametrization of this particular heterogeneous tracer transport . The investigation also substantiated the issue of unfavorable conditions of the seam for the safety of the barrier.
The method of GeoPET has been developed and advanced at HZDR. A number of show case experiments could prove its capability for spatiotemporal quantification of tracer transport experiments (Kulenkampff et al., 2016) with very high sensitivity (“picomolar”) and reasonable spatial resolution (about 1 mm).
Here, a small volume of brine, labelled with the PET-tracer 22Na, was injected into the head space between the end cap and the sample. It was observed that a portion of the tracer was sucked into the contact zone between rock salt and cement immediately after injection. The spatial tracer distribution rapidly stabilized as a patchy structure (Fig. 2). Then, during the observation period of 71 days it diffused into the cement and reached a mean depth of 5 mm.
  • Lecture (Conference)
    SaltMech IX, 12.-14.09.2018, Hannover, Deutschland
  • Open Access Logo Contribution to proceedings
    Saltmech IX, 12.-14.09.2018, Hannover, Deutschland
    The Mechanical Bevior of Salt IX, Hannover: BGR, 978-3-9814108-6-0, 261-273

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


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

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

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

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


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

Orlova, A.; Green, E. L.; Law, J. M.; Gorbunov, D. I.; Chanda, G.; Krämer, S.; Horvatic, M.; Kremer, R. K.; Wosnitza, J.; Rikken, G. L. J. A.
We report a 51V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and focused on high-field phases up to 56 T. For the crystal orientations H‖c and H‖b, we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO4 compound.

Downloads:

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


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

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

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

  • available with HZDR-Login

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


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

Kloditz, R.; Radoske, T.; Schöne, S.; Patzschke, M.; Stumpf, T.
The electronical properties of f-elements, especially of the actinides, are a very puzzling topic to investigate. The frontier orbitals (5f, 6d, 7s) all lying in a similar energy regime along with open shells and relativistic effects contribute to a very complex situation, where single-reference methods like DFT and Hartree-Fock may be not suitable any more1. In recent years, the investigation of actinides in combination with organic ligands revealed a very rich chemistry with many forms of coordination and chemical bonding. Besides that, many visually appealing and intuitive tools have been developed, with which the chemical bond can be analysed. These tools for bond analysis include natural-bonding orbitals (NBO) and density-difference plots. The aim of this study is therefore to apply these bond analysis tools to a range of tetravalent actinide complexes with N-donor ligands2, like Schiff bases and amidinates (Figure 1), to elucidate their complicated electronic properties. Thermodynamic computations on the stability of the complexes will also be presented to understand the chemical properties of the actinides and predict yet unknown complexes.
Keywords: Actinides, quantum chemistry, bonding analysis
  • Poster
    GDCh Wissenschaftsforum, 10.-14.09.2017, Berlin, Deutschland

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


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

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

Downloads:

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


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

Pausch, G.ORC
The promise of particle therapy at ultimate precision can only be fulfilled once the particle range can be controlled and verified with millimeter precision. In spite of considerable efforts made by research groups and commercial enterprises throughout the world, means or devices for routinely measuring the particle range in situ and in real time during treatments are still missing. On the one hand, prompt gamma-ray imaging (proposed almost 15 years ago) has become widely accepted as the most promising strategy for online range verification. On the other hand, none of the Compton camera concepts pursued by several groups (including our group at HZDR/OncoRay) could prove to be applicable under treatment conditions. The only prototype system ever used in a clinical trial is the passively collimated knife-edge slit camera by IBA. This “camera” cannot provide 3D images, but measures one-dimensional prompt gamma-ray intensity profiles that allow quantifying possible shifts of the distal edge of high-weighted single pencil beam spots. Alternative, potentially less expensive approaches have been proposed by MGH (prompt gamma spectroscopy) and OncoRay (prompt gamma timing). Efforts to translate these ideas in applicable technologies are underway.
The talk will review the state-of-the art in prompt-gamma based range verification, with a focus on contributions of OncoRay: (1) the development and exploration of the prompt gamma-ray timing technique, and (2) the preparation and execution of first-in-man prompt gamma-ray imaging with the IBA knife-edge slit camera.
Keywords: Partikeltherapie, particle therapy; Protonentherapie, proton therapy; Bestrahlungskontrolle, treatment verification; Reichweitekontrolle, range verification; Prompte Gammastrahlung, prompt gamma rays; Gammakamera, prompt gamma imaging; Zeitmessung, prompt gamma timing; Gammaspektroskopie, gamma spectroscopy
  • Lecture (others)
    VARIAN Engineering Colloquium (eingeladener Vortrag), 15.11.2017, Bergisch Gladbach, Deutschland

Downloads:

  • available with HZDR-Login

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


Curvilinear magnonics

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

In Magnonics, spin waves (SWs) or magnons are proposed to be used to carry, transport and process information analogous to the electron currents in electronics. Engineering magnon properties to control the SW excitation and propagation is an unavoidable task. The membrane curvature can be used to extend the toolbox of operations for controlling SWs, required in communication and logic devices [6–8]. Geometries like Möbius rings, helices, grooves stripes, and nanotubes can be accounted as few sets of layouts wherein the system curvature has an impact on the SW dynamics. Such examples will be referred in this talk, being the later (magnetic nanotubes) the one of our main focus. The tunable non-reciprocal SW properties induced by the nanotubular curvature [6–8] will be highlighted. In particular, that the dispersion relation is asymmetric regarding the sign of the propagation vector. Therefore the counter propagating magnons have different wave vectors and characteristic length for the transport. Figure 1(a) sketches a Permalloy nanotube in circular magnetic state wherein the SWs are excited by an rf-field applied at the center of the tube. Quasi-monocromatic magnons of different orders (n = 0, ±1, ±2) excited at 4.7 GHz are shown in Figure 1(b, c). The radial component of the excited magnon modes is represented by the color code in Figure 1(b). Note that the wavelength and transport length of counter-propagating magnons differ. Figure1(c) shows the magnon field distribution along the nanotube perimeter. The case of non-reciprocal SW dispersion and intrinsic linewidth are presented in Figure 2 (a) and (b), respectively. Aspects like the optimization of the curvature-induced non-reciprocity as function of the system size and magnetic ground state, some means to control the magnons mode profile and the tuning of non-reciprocity via weak DC external magnetic fields, will be also discussed.
We believe that three dimensional curvilinear magnetic membranes, in particular nanotubes, can be exploited as a novel layouts for non-reciprocal conduits, for magnons transport along curved paths, and as one-dimensional magnonic crystals.
Keywords: Curvature, magnonics, nanotubes, spin-waves.
  • Invited lecture (Conferences)
    62nd Annual Conference on Magnetism and Magnetic Materials, 06.-10.11.2017, Pittsburgh, USA

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


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

Laube, M.; Gassner, C.; Neuber, C.; Bergmann, R.; Kniess, T.; Steinbach, J.; Pietzsch, J.
Objectives
Cyclooxygenase-2 (COX-2), a key player in inflammation, is an attractive target for functional characterization of solid tumors by PET because its overexpression has been associated with chemo-/radioresistance and poor prognosis in cancer. We recently developed a novel series of selective COX-2 inhibitors based on a tricyclic core structure with IC50 values in the nanomolar range1 and herein report on the 18F-labeling and evaluation of a promising candidate.
Methods
5-(4-[18F]Fluorophenyl)-4-[4-(methylsulfonyl)phenyl]-1,2-dihydropyrrolo[3,2,1-hi]indole ([18F]2) was synthesized according to our recently reported 18F-fluorination and McMurry cyclization approach2 with modifications reported herein. [18F]2 was evaluated in vitro in cell lines with different COX-1/COX-2 expression patterns. In vivo dynamic small animal PET imaging and biodistribution studies were performed in NMRI nu/nu mice bearing a COX-2-positive A2058 tumor-xenograft.
Results
18F-Fluorination under standard conditions2 was hampered by basic hydrolysis leading primarily to side product [18F]1b. Optimization experiments focused on the use of different bases with varying concentrations (K2CO3, KHCO3, KH2PO4) or no base using the ‘minimalist approach’3. As one result, the use of decreased amounts of K2CO3 (5 instead of 20 μmol) effectively suppressed hydrolysis and gave [18F]1a in high yield (Figure 1). An automated synthesis comprising mild 18F-fluorination, McMurry cyclization, and purification using a TracerLabFX-N module provided [18F]2 in 16% isolated RCY (d.c.) with a molar activity of 45-106 GBq/μmol at EOS. A LogDpH7.4 of 4.66 and a CHI IAM value of 48 indicated high lipophilicity and non-specific binding. Cell uptake was independent of COX-2 expression. Biodistribution and PET studies revealed highest uptake of [18F]2 in liver and adipose tissue but only low accumulation in A2058 tumors (tumor/muscle < 1) at 60 min post injection. Celecoxib pre-injection (20 mg/kg) did not significantly change tumor uptake although a trend towards decreased radiotracer uptake was observed by PET in a subset of mice.
Conclusions
Despite of a high COX-2 selectivity and metabolic stability, [18F]2 did not emerge as suitable radiotracer for imaging COX-2 in vitro and in vivo, likely due to its high lipophilicity and fast hepatobiliary excretion.4 Future efforts for the development of COX-2-targeted radiotracers should focus on adaption of lipophilicity and/or use of targeted delivery systems.
References
1Laube et al. J. Org. Chem. 2015, 80, 5611-5624. 2Kniess et al. Biorg. Med. Chem. 2012, 20, 3410-3421. 3Richarz et al. Org. Biomol. Chem. 2014, 12, 8094-8099. 4Gassner et al. ChemistrySelect, 2016, 1, 5812–5820.
Figure 1.: Radiosynthesis of [18F]2 by 18F-fluorination and McMurry cyclization. S156: Poster 22nd International Symposium on Radiopharmaceutical Sciences
J
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S156-S156
    DOI: 10.1002/jlcr.3508

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


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

Pilz, W.; Laufer, P.; Tajmar, M.; Böttger, R.; Bischoff, L.
High current liquid metal ion sources are well known and found their first application as field emission electric propulsion (FEEP) thrusters in space technology. The aim of this work is the adaption of such kind of sources in broad ion beam technology.
Surface patterning based on self-organized nano-structures on e.g. semiconductor materials formed by heavy mono - or polyatomic ion irradiation from liquid metal (alloy) ion sources (LMAIS) is a very promising technique. LMAIS are nearly the only type of sources delivering polyatomic ions from about half of the periodic table elements. To overcome the lack of only very small treated areas by applying a focused ion beam (FIB) equipped with such sources, the technology taken from space propulsion systems was transferred into a large single-end ion implanter. The main component is an ion beam injector based on high current LMAIS combined with suited ion optics allocating ion currents in the µA range in a nearly parallel beam of a few mm in diameter. The mass selection of the needed ion species can be performed either by an ExB mass separator (Wien filter) and/or an existing dipole magnet of the ion implanter itself.
Different types of LMAIS (needle, porous emitter, capillary) are presented and characterized. The ion beam injector design is specified as well as the implementation of this module into a 200 kV high current ion implanter (Danfysik model 1090) operate at the HZDR Ion Beam Center (IBC). Finally, the obtained results of large area surface modification of Ge using polyatomic Bi2+ ions at room temperature from a GaBi capillary LMAIS will be presented and discussed.
Keywords: Polyatomic ions, liquid metal alloy ion source, implanter, surface pattern
  • Open Access Logo Review of Scientific Instruments 88(2017), 123302-1-123302-4
    DOI: 10.1063/1.4995537

Downloads:

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


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

Pausch, G.ORC
Die Zerstörung bösartiger Tumoren mit Ionenstrahlen ist mittlerweile ein etabliertes Verfahren der Radioonkologie. Im Gegensatz zur klassischen Radiotherapie kann man gesundes Gewebe weitgehend schonen, was bei Tumoren nahe kritischer Organe überlebenswichtig sein kann. Dieser Vorteil wird klinisch nicht voll ausgeschöpft, da die Vorhersage (Planung) der Strahlreichweite im Körper mit Unsicherheiten behaftet ist. Der Vortrag erläutert Ansätze und Erfolge bei der Entwicklung klinisch einsetzbarer Verfahren zur in-vivo Reichweitemessung von Ionenstrahlen, mit denen die Präzision der Therapie erhöht werden kann. Entsprechende Forschungsvorhaben profitieren von einer engen Zusammenarbeit der öffentlichen Forschung mit Industriepartnern.
Keywords: Radioonkologie, radiooncology Partikeltherapie, particle therapy Reichweitemessung, range assessment
  • Lecture (others)
    Berliner Industriegespräch im Magnushaus Berlin, 27.09.2017, Berlin, Deutschland

Downloads:

  • available with HZDR-Login

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


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

Kniess, T.; Bechmann, N.; Steinbach, J.; Pietzsch, J.
kein Abstract verfügbar
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S578
    DOI: 10.1002/jlcr.3508

Downloads:

  • available with HZDR-Login

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


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

Kniess, T.; Fischer, S.; Ludwig, F.-A.; Steinbach, J.
kein Abstract verfügbar
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S448
    DOI: 10.1002/jlcr.3508

Downloads:

  • available with HZDR-Login

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


Hydrous 18F-Fluoroethylation - leaving off the azeotropic drying

Kniess, T.; Laube, M.; Steinbach, J.
kein Abstract verfügbar
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S152
    DOI: 10.1002/jlcr.3508

Downloads:

  • available with HZDR-Login

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


PET Imaging Evaluation of Four sigma1 Radiotracers in Nonhuman Primates

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

Downloads:

  • available with HZDR-Login

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


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

Krauter, N.; Stefani, F.
Eddy current flow meters (ECFM) are widely used for measuring the flow velocity of electrically conducting fluids. Since the flow induced perturbations of a magnetic field depend both on the geometry and the conductivity of the fluid, extensive calibration is needed to get accurate results. Transient eddy current flow metering (TECFM) has been developed to overcome this problem. It relies on tracking the position of an impressed eddy current system which is moving with the same velocity as the conductive fluid. We present an immersed version of this measurement technique and demonstrate its viability by numerical simulations and a first experimental validation.
Keywords: flow measurement, inductive methods, calibration-free
  • Measurement Science and Technology 28(2017), 105301
    DOI: 10.1088/1361-6501/aa7b1e
  • Lecture (Conference)
    3rd Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russland

Downloads:

  • available with HZDR-Login

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


Actinide Bonding Analysis in Position Space

Patzschke, M.
Actinides are a fascinating class of elements. They are difficult to work with in the laboratory, but they are also very challenging for the theoretician. The open f-shell sometimes necessitates the use of multi-reference calculations. They contribute many electrons, making the calculation more demanding. And lastly, relativistic effects become important. These problems certainly contribute to the situation in which far less is known and understood about actinide chemistry compared to e.g. the lanthanides. In this contribution, we use analysis methods that work in real space, i.e. on the electronic density. We present different tools and the application to the bonding in BTP complexes on actinides and lanthanides . BTP complexes have been investigated for numerous years now and it is still not entirely understood, why they bind actinides more strongly than lanthanides. The presented data is hopefully a step towards the solution of that problem.
Keywords: DFT, CASPT2, Lanthanides, Actinides, Covalency
  • Poster
    Magical Mystery Tour of Electron Correlation - A Symposium in Honour of Jeppe Olsen on the Occasion of his 60th Birthday, 24.-27.10.2016, Oslo, Norwegen

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


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

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

Downloads:

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


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

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

Downloads:

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


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

Wawro, A.; Kurant, Z.; Tekielak, M.; Jakubowski, M.; Pietruczik, A.; Böttger, R.; Maziewski, A.
Molecular beam epitaxy-grown layered structures Co/Mo/Co exhibit an antiparallel coupling of Co films magnetization in the Mo spacer thickness range between 0.5 nm and 1.0 nm and parallel beyond this range. Magnetic properties are substantially modified by beam irradiation of 35 keV Gaþ ions. With the increase in ion fluence, antiparallel coupling switches to the parallel one. Further increase in fluence results in gradual suppression of ferromagnetic behavior of the system. Experimental results are correlated with numerical simulations of layered structure evolution driven by irradiation.
Keywords: ion irradiation, magnetic multilayers, molecular beam epitaxy, ion implantation

Downloads:

  • available with HZDR-Login

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


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

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

References
[1] Kryk, H. , Harm, U., Hampel, U.: Reducing in-core zink borate precipitation after loss-of-coolant accidents in pressurized water reactors, Proceedings of the Annual Meeting on Nuclear Technology (AMNT), Hamburg, 2016
[2] Seeliger, A.; Alt, S.; Kästner, W., Renger, S., Kryk, H., Harm, U. : Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - thermo- and fluid- dynamic effects. Nuclear Engineering and Design, 2016, 305, 489-502
Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments
  • Contribution to proceedings
    The Energy and Materials Research Conference (EMR 2017), 05.-07.04.2017, Lissabon (Lisbon), Portugal
    Book of Abstracts
  • Lecture (Conference)
    The Energy and Materials Research Conference (EMR 2017), 05.-07.04.2017, Lisabon (Lisbon), Portugal

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


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

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


References:
[1] C. Anders et al., Phys. Rev. B 87, 245434 (2013).
[2] L. Bischoff et al., Nucl. Instr. Meth. Phys. Res. B 272, 198-201 (2012).
[3] R. Böttger et al., J. Vac. Sci Technol. B 30, 06FF12 (2012).
[4] R. Böttger et al., Phys. Stat. Sol. RRL 7, 501-505 (2013).
[5] L. Bischoff et al., Appl. Surf. Sci. 310 154-157 (2014).
Keywords: polyatomic ions, surface modification, FIB
  • Lecture (Conference)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

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


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

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

References:
[1] C. Anders, K.-H. Heinig and H. M. Urbassek, Polyatomic bismuth impacts into germanium: Molecular dynamics study, Phys. Rev. B 87 (2013) 245434.
[2] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, and W. Pilz, Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions, Nucl. Instr. and Meth. B 272 (2012) 198.
[3] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, From sponge to dot arrays on (100)Ge by increasing the energy of ion impacts, Journal of Vacuum Science and Technology B 30 (2012) 06FF12.
[4] R. Böttger, K-.H Heinig, L. Bischoff, B. Liedke, R. Hübner, and W. Pilz, Silicon nanodot formation and self-ordering under bombardment with heavy Bi3 ions, physica status solidi – Rapid Research Letters 7 (2013) 501.
[5] L. Bischoff, R. Böttger, K.-H. Heinig, S. Facsko, and W. Pilz, Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions, Applied Surface Science 310 (2014) 154.
[6] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender and S. Facsko, Faceted nanostructure arrays with extreme regularity by self-assembly of vacancies, Nanoscale 7 (2015) 18928.
Keywords: Self organization, polyatomic ion, surface pattern
  • Lecture (Conference)
    Nanopatterning2017: Nanoscale Pattern Formation at Surfaces & FOR3NANO: Formation of 3D Nanostructures by Ion Beams, 26.-30.06.2017, Helsinki, Finland

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


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

Höhne, T.
Two-phase flows occur in many industrial processes. Reliable predictions on flow characteristics are necessary for the design, process optimization and safety analysis of related apparatuses and processes. Experimental investigations are expensive and in most cases not transferable to modified geometries or different scales and flow conditions. For this reason there is a clear requirement for numerical tools. Due to the 3D nature of flows and the importance of turbulence in most cases this means a strong need for reliable 3D CFD-tools rather than 1D system codes or simplified correlations. The general aim is to provide simulation tools for the design, optimization and safety analyses of medium and large scale applications in which multiphase flows are involved. Such tools can contribute to improve the efficient use of energy and resources (e.g. in chemical engineering and oil industries) and to guarantee the safe operation (especially nuclear safety) – provided that they are predictive. Since large scale applications are considered such as chemical reactors or components of the cooling system of a nuclear power plant the Euler-Euler two- or multi fluid model is the base for the development. Presently the predictive capabilities for basic hydrodynamics are restricted due to limitations of the closure models. For this reason one focus of our multiphase flow research is the improvement of the closures first for adiabatic flow modelling but also phase transfer, chemical reactions etc. have to be considered. A second focus is to establish modelling frameworks as iMUSIG, AIAD and GENTOP to allow a proper consideration of the local physical phenomena. These activities will help to improve the CFD code capabilities in energy related industrial applications.
Keywords: multi-phase, CFD, AIAD, GENTOP, MUSIG
  • Invited lecture (Conferences)
    International Conference on Thermofluid 2017, 09.-10.11.2017, Yogyakarta, Indonesien
  • Contribution to proceedings
    International Conference on Thermofluid 2017, 09.-10.11.2017, Yogyakarta, Indonesien

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


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

Moonesi Shabestary, A.; Krepper, E.; Lucas, D.
The current job is presenting the CFD- modelling and simulation of condensation inside passive heat removal systems. Designs of future nuclear boiling water reactor concepts are equipped with emergency cooling systems which are passive systems for heat removal. The emergency cooling system consists of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. At normal operation conditions, the pipes are filled with water and no heat transfer to the secondary side of the condenser occurs. In the case of an accident the water level in the core is decreasing, steam comes in the emergency pipes and due to the subcooled water around the pipe, this steam will condense. The emergency condenser acts as a strong heat sink which is responsible for a quick depressurization of the reactor core when any accident happens. The actual project is defined to model the phenomena which are occurring inside the emergency condensers. The focus of the project is on detection of different morphologies such as annular flow, stratified flow, slug flow and plug flow and also modeling of the laminar film which is occurring during the condensation near the wall.
The condensation procedure inside the pipe can be divided to two steps. The first step is the wall condensation and the second step is the direct contact condensation (DCC). The Algebraic Interfacial Area Density (AIAD) concept is used in order to model the interface between liquid and steam. In the next steps the Generalized Two-Phase Flow (GENTOP) model will be used to model also the dispersed phases which are occurring inside the pipe. Finally, the results of the simulations will be validated by experimental data which will be available in HZDR. In this paper the results of the first part has been presented.
Keywords: Film Condensation, Heat and mass transfer, Heat transfer coefficient, CFD
  • Lecture (Conference)
    Annular Meeting on Nuclear Technology, 16.-17.05.2017, Berlin, Germany

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


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

Patzschke, M.
Understanding the chemistry of actinides is crucial for the safety guarantees required for final repositories for nuclear waste. Pathways of distribution of actinides in the environment are discussed and calculations on model compounds to understand the bonding of actinides are presented.
Keywords: DFT, Real space analysis, actinide compounds
  • Invited lecture (Conferences)
    X. MMQC Mariapfarr, 06.-10.03.2017, Mariapfarr, Österreich

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


Bond analysis of actinide complexes in real space

Patzschke, M.
Subtle effects are important in the bonding of actinides. Understanding of these effects is crucial for the prediction of the fate of actinides in the environment. In this talk we will focus on QTAIM, NCI and ELI calculations to understand the difference in bonding between actinides and lanthanides.
Keywords: DFT, CASPT2, Real space analysis, QTAIM, ELF/ELI, NCI, actinide complexes
  • Invited lecture (Conferences)
    UCT und IOCB Seminar Prag, 31.03.2017, Prag, Tschechien

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


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

Patzschke, M.
Real space analysis of the chemical bond is a valuable tool for understanding the bonding in chemical compounds. Especially in the field of actinide complexes and actinide-actinide bonds, there is still much to be learned. In this talk we will shoe how encaged uranium is forced to bond and how the bond depends on the cage size.
Keywords: Real Space Analysis, DFT, CASPT2, Actinides
  • Invited lecture (Conferences)
    Chemical Bonding in Position Space, 27.11.-01.12.2016, Dresden, Deutschland

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


Technetium Complexes with Arylselenolato and Aryltellurolato Ligands

Noschang Cabral, B.; Kirsten, L.; Hagenbach, A.; Piquini, P. C.; Patzschke, M.ORC; Schulz Lang, E.; Abram, U.
Reactions of (NBu4)[TcOCl4] or [TcCl3(PPh3)2(CH3CN)] with in situ-prepared lithium arylselenolates and -tellurolates
give (NBu4)[TcVO(ArE)4] (E = Se, Te; Ar = phenyl) and [TcIII(ArE)3(PPh3)(CH3CN)] (E = Se, Te; Ar = phenyl, 2,6-Me2phenyl,
mesityl) complexes, respectively. The products contain square-pyramidal (TcV compounds) and trigonal bipyramidal (TcIII
complexes) coordinated technetium atoms. Density Functional Theory calculations indicate that the Tc-chalcogen bonds in
the TcIII compounds have greater bond order than in the TcV compounds.
Keywords: Technetium, new compounds, crystal structure, DFT, bond analysis

Downloads:

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


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

Deinert, J.-C.ORC; Green, B. W.; Kovalev, S.; Stähler, J.ORC; Gensch, M.
In this contribution we present the concept for a novel experimental setup at the THz facility TELBE at Helmholtz-Zentrum Dresden-Rossendorf [1], which combines THz excitation with time- and angleresolved photoelectron spectroscopy (tr-ARPES). This challenging combination of two state-of-the-art techniques promises new insights into highly relevant non-equilibrium processes in matter, since THz excitation provides resonant access to a multitude of fundamental modes, e.g., lattice vibrations, molecular rotations, spin precession and the motion of free electrons. Until now, the corresponding changes to the electronic structure of a material can be probed only indirectly, e.g., by measuring the material's optical properties. The obvious method – tr-ARPES – which gives direct access to the electronic states on a femtosecond timescale (cf. Fig. 1) has not been implemented due to the previously unaccomplishable high duty cycle of the THz source (>> 10 kHz repetition rate quasi-cw) to provide sufficient statistics for tr-ARPES. This limitation is overcome at the TELBE which provides tunable and CEP-stable THz pulses at a repetition rate of 100 kHz based on superradiant emission, and timing stability of < 30 fs due to a novel pulse-to-pulse diagnostics scheme [3]. Over the next three years a tr-ARPES setup shall hence be implemented at the THz facility TELBE which aims at establishing feasibility and dynamic range despite obvious obstacles such as residual streaking of the photoelectrons by the high THz excitation fields (see, e.g., [2]). This contribution is discussing the challenges and the opportunities of tr-ARPES in THz control experiments and will outline the current design of the planned tr-ARPES endstation.
[1] B. Green et al., Sci. Rep. 6 (2016), 22256.
[2] U. Fruehling et al., Nat. Phot.. 3 (2009), 523.
[3] see poster presentation of S. Kovalev
  • Poster
    Optical Terahertz Science and Technology, 06.04.2017, London, United Kingdom

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


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

Lin, L.; Souris, K.; Kang, M.; Glick, A.; Lin, H.; Huang, S.; Stützer, K.; Janssens, G.; Sterpin, E.; Lee, J. A.; Solberg, T. D.; Mcdonough, J. E.; Simone Ii, C. B.; Ben-Josef, E.
Purpose: To determine whether individual liver tumor patients can be safely treated with pencil beam scanning proton therapy. This study reports a planning preparation workflow that can be used for beam angle selection and the evaluation of the efficacy of abdominal compression (AC) to mitigate motion.

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

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

Conclusion: A workflow for screening patients’ motion characteristics and optimizing beam angle selection was established for the pencil beam scanning proton therapy treatment of liver tumors. Abdominal compression was found to be useful at mitigation of moderate and large motion.
  • Poster
    AAPM 59th Annual Meeting & Exhibition, 30.07.-03.08.2017, Denver, Colorado, United States of America

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

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


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

Merchel, S.; Rugel, G.; Scharf, A.; Ziegenrücker, R.; DREAMS-Users; DREAMS-Friends
Since 2009, the DREAMS (DREsden Accelerator Mass Spectrometry) facility offers users to do their own sample preparation for producing AMS-targets. Two years after the 6 MV-based tandem accelerator measured the first unknown samples for long-lived radionuclides [1]. AMS reduces background and interfering signals resulting from molecular ions and isobars enormously. Thus, AMS provides much lower detection limits compared to conventional MS or decay counting. DREAMS offers excellent measurement capabilities also for external users [2].
AMS allows thousands of exciting applications, especially within environmental and geosciences. In nature, the so-called cosmogenic nuclides (CNs) are products of nuclear reactions induced by primary and secondary cosmic rays. Hence, they can be found in extraterrestrial material such as meteorites - originating from the asteroid belt, the Moon or Mars - and lunar samples in higher concentrations (e.g. ~1010 10Be atoms/g or < 0.5 mBq/g). A combination of several CNs is used to reconstruct the exposure history of this unique material while in space (irradiation age) and on Earth (terrestrial age).
Though, in terrestrial material the concentrations are typically only on the order of 104-109 atoms/g (i.e. μBq/g - nBq/g) for 10Be produced in the Earth’s atmosphere, then transported to the surface and further absorbed and incorporated at and in e.g. sediments or ice. Some of the lowest 10Be concentrations (~103 atoms/g), produced in-situ by neutron- and muon-induced nuclear reactions from e.g. oxygen and silicon in quartz, can be found in samples taken from the Earth’s surface. The concentrations of atmospheric or in-situ produced CNs record information that is used to reconstruct sudden geomorphological events such as volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earthquakes [e.g. 3] and glacier movements. These movements and data from ice cores give also hints for the reconstruction of historic climate changes and provide information for the validation of climate model predicting future changes. Slower processes such as sedimentation, river incision and erosion rates can also be investigated and indirect dating of bones as old as several Ma’s is possible. Finally, remnants of supernova-produced nuclides can also be found in deep-sea archives (sediment, crust, nodule) [e.g. 4].
Anthropogenic production e.g. by release from nuclear reprocessing, accidents and weapon tests led to increased radionuclide levels in surface water, ice and soil (36Cl, 129I,…). Hence, some nuclides can be used as tracers to follow pathways in oceanography, to date and identify sources of groundwater, to perform retrospective dosimetry and to study aspects in radioecology and pharmacology. Obviously, also nuclear installation materials are radioactive (36Cl, 41Ca,…).

References: [1] G. Rugel et al., Nucl. Instr. Meth. Phys. Res. B. 2016, 370,94. [2] www.hzdr.de/ibc for beam time application. [3] W. Schwanghart et al., Science 2016, 351,147. [4] A. Wallner et al., Nature 2016, 532, 69.
Keywords: AMS, radionuclide
  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 ─ Jubiläumskongress "GDCh - 150 Jahre", Jahrestagung der Fachgruppe Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

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


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

Merchel, S.; Gurlit, S.; Rugel, G.; Scharf, A.; DREAMS-Users; DREAMS-Friends
Since 2009, the DREAMS (DREsden Accelerator Mass Spectrometry) facility offers users to do their own sample preparation for producing AMS-targets. Several projects are aiming at analysing 10Be, 26Al, and 36Cl (as BeO, Al2O3, AgCl). In cooperation with other AMS-facilities, also actinides (coprecipitation as Fe2O3) and 60Fe (as Fe2O3) are investigated.
Hence, essential steps are hydroxide or AgCl precipitation. For the determination of in-situ or atmospheric 26Al in marine and terrestrial sediments, we had sometimes unaccountable low chemical yields, which might be explained by redissolving Al(OH)3 in the last washings. Thus, we investigated these potential losses by ICP-MS as a function of alteration (waiting) times. Indeed, up to 31% of the precipitated Al was redissolved by immediate triple washings. After 2 h of waiting, this could be reduced to 11%. Further waiting (over-night) resulted in losses of 6% of Al (equally for Be) only.
We also tested the behaviour of Fe(III), U(VI) (also as analogue for ~Pu(VI) and Np(VI)), and Er(III) (as analogue for Am(III), Cm(III), Pu(III)) when Fe(OH)3 is washed. Even including the supernatant, total losses of 3-times washing of over-night altered hydroxides are as low as 2.6-3.5%. Thus, repeated washing cycles are very advisable to reduce ions such as NH4+ and Cl- before drying and ignition.
For a single project, we explored the possibility to measure 36Cl and natCl by (isotope dilution) AMS in “dirty” permafrost ice wedge samples as heavy as 1.6 kg. The chemical yield of AgCl was only 20-35% and is a function of total natCl. Thus, we tested preconcentration steps like ion exchange (DOWEX 1x8, 5 ml), which look promising.
Very often DREAMS projects focus at analysing quartz for in-situ-produced 10Be and 26Al. Dissolving quartz only will minimise other troublesome elements such as Al, Be, and Ti from coexisting mineral phases. Obviously, low stable Al leads to higher 26Al/27Al, i.e. better 26Al-statistics. However, low Ti is also helpful for fewer problems in Be-chemistry, i.e. better 10Be-statistics. For correct calculation of exposure ages and erosion rates, “pure quartz”, i.e. similar target elements as the calibration site used for production rates and no natural 9Be, is needed, too. One of the earliest quartz cleaning methods is routinely used at DREAMS: H2SiF6/HCl on a shaker table at room temperature. It produces up to 1.8% residue of the original “quartz” mass with a mean maximum value of 0.6% (values from >100 samples from six different projects). SEM-EDX identified the most prominent minerals to be zircon Zr[SiO4], white sillimanite Al2[O|SiO4], transparent to blue kyanite Al2[O|SiO4], black chromite Fe2+Cr2O4, and orange rutile TiO2. For comparison, we treated 3.5 g of these residues by microwave (MW) digestion resulting in further dissolving 31% of the original residue. SEM-EDX analyses of the MW-residue showed mainly pristine kyanite and heavily-attacked sillimanite only. ICP-MS of the MW-solution validated the dissolution of Al, Ti, Cr, Fe, and Zr. For a typical 50 g-“quartz sample” the MW-method would add more than 3 mg of Ti, over 7 mg of Al and, and, worst of all, about 25 μg of Be to the sample.
Ackn.: Thanks to B. Bookhagen, A. Gärtner, T. Opel, P. Steier, F. Quinto & S. Weiss.
Keywords: AMS, sample preparation, exposure dating, erosion rate
  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 ─ Jubiläumskongress "GDCh - 150 Jahre", Jahrestagung der Fachgruppe Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

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


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

Groos, A. R.; Struck, J.; Wüthrich, L.; Veit, H.; Gnägi, C.; Merchel, S.; Scharf, A.; Rugel, G.; Zech, R. Keywords: LGM, AMS, 10Be Surface Exposure Dating
  • Poster
    Annual CH-QUAT Meeting Faculty of Science, University of Neuchâtel Topic: "Quaternary topics in the Jura Mountains and the Seeland region", 01.04.2017, Neuchâtel, Schweiz

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


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

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

Downloads:

  • available with HZDR-Login

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


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

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

Downloads:

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


Microbial transformation of bentonite

Matschiavelli, N.; Steglich, J.; Kluge, S.; Cherkouk, A.
For the storage of highly radioactive waste in a deep geological repository a multi-barrier concept is favoured, which combines a technical barrier (canister including the highly radioactive waste), a geotechnical barrier (e.g. Bentonite) and the geological barrier (host rock). Due to their properties, namely a high swelling capacity and a low hydraulic conductivity, Bentonites fulfil in this system a sealing and buffering function. For the potential repository of nuclear waste the microbial mediated transformation of Bentonite could influence its properties as a barrier material. To elucidate the microbial potential within selected Bentonites, microcosms were set up, which contain 20g Bentonite and 40ml anaerobic synthetic Opalinus-clay-pore water solution under an N2/CO2-gas-atmosphere. Substrates like acetate and lactate were supplemented to stimulate potential microbial activity. Microcosms were incubated in the dark, without shaking at 30°C. Within an indefinite time scale samples were taken at different time-points of incubation and were analysed regarding geochemical parameters like pH, O2-concentration, redox potential, iron-concentration and sulphate-concentration as well as biological parameters like the consumption and formation of metabolites. First results show that bentonites represent a source for microbial life, demonstrated by the consumption of lactate and the formation of acetate and pyruvate. Furthermore, microbial iron-reduction was determined. The results reveal the importance of the selection of the best suitable Bentonite in order to avoid transformation of the mineral structure by indigenous microbes.
  • Poster
    16th International Clay Conference - Clays, from the oceans to space - Granada 17-21 July 2017, 17.-21.07.2017, Granada, Spain

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


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

Bader, M.; Swanson, J.; Foerstendorf, H.; Müller, K.; Steudtner, R.; Drobot, B.; Schmidt, M.; Cherkouk, A.
Rock salt is a potential host rock for the final storage of radioactive waste in a deep geological formation. Indigenous microorganisms and their interactions with radionuclides must be considered for the safety performance of the repository, considering the worst case scenario, the release and subsequent migration of radionuclides. Therefore, the extremely halophilic microorganism Halobacterium noricense DSM 15987T, which occurs naturally in the potential host formation rock salt, was used to study its interactions with uranium.
A time-dependent sorption experiment showed that bioassociation of uranium onto cells of H. noricense DSM 15987T is not only a sorption process; i.e. fast sorption within the first hours until reaching a stable equilibrium state. The obtained kinetic data showed a multistage process with fast sorption during the first two hours of exposure time. Over the next hours, an increasing amount of uranium was detectable in the supernatant, implying that the uranium already sorbed was again released from the cells. Subsequently, the amount of bioassociated uranium increased very slowly until a maximum sorption of 80% was reached after 48 h. To investigate this multistage bioassociation process on archaeal cells in detail several spectroscopic as well as microscopic methods were applied. With in situ attenuated total reflection fourier-transform infrared spectroscopy the initial sorption process of uranium to cells of H. noricense DSM 15987T within the first two hours was proven. Results showed that the radionuclide binds to carboxylic as well as to phosphate groups simultaneously within the first two hours of incubation time. Additionally, cryo time-resolved laser-induced fluorescence spectroscopic investigations were performed, which showed the involvement of polynuclear carboxylate species and the presence of a meta-autunite like mineral. By using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, uranium could be localized on the cell surface of the halophilic archaeon within the first sorption phase and later in the biomineral-like agglomerates. Hence, our study showed that uranium can be immobilized by halophilic archaea via biomineralization and bioassociation, which might influence the further migration of the actinide.
  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 Interdisziplinäre Symposien Jahrestagung Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

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


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

Huebl, A.ORC; Widera, R.ORC; Pausch, R.; Garten, M.ORC; Burau, H.; Kluge, T.; Vorberger, J.; Debus, A.ORC; Cowan, T. E.ORC; Schramm, U.ORC; Chung, H.-K.; Bussmann, M.ORC
PIConGPU is reportedly the fastest electro-magnetic particle-in-cell code in the world in terms of sustained Flop/s. Its computational power does not only enable 3D3V simulations with unprecedented detail and fast time-to-solution but also allows improving predictive capabilities of simulations by estimating stochastic and systematic errors via repeated simulations. Synthetic in-situ diagnostics drive the exploration of high-detail simulations whose signatures, e.g. emitted radiation spectra, would be inaccessible in post-processing due to sheer data size. Upcoming experiments at the European XFEL require us to take PIConGPU even one step further: modeling XFEL-matter interaction on top of laser-driven particle acceleration processes requires the introduction of non-trivial X-ray photon scattering, photon generation and advanced non-LTE atomic models. Coupled with an open-science centered strategy, from open performance portable source code over open standardized data formats to documented workflows for PByte scale simulation we strive towards a new quality of predictive, reproducible simulations within our community.
Keywords: PIC GPU XFEL Modeling HPC laser-plasma LPA pump-probe HED IO OpenSource OpenData OpenScience
  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz

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


Open Science with openPMD

Huebl, A.ORC; Lehe, R.; Vay, J.-L.ORC; Grote, D. P.; Sbalzarini, I. F.ORC; Kuschel, S.; Bussmann, M.ORC
Nobody needs yet an other data format for HPC. But why have so-called self-describing data formats never provided out-of-the-box cross application portability? Why are most open-access datasets not self-describing for both the domain scientist and after-use? And why do communities need to implement their data readers in various post-processing, visualization and analysis frameworks over and over again?

We present the open meta data format openPMD for data format agnostic markup of particle-mesh data. Based on a minimal kernel of meta information and enriched with domain-specific extensions, we develop an open ecosystem of interoperable simulations and data processing frameworks from the domains of laser-plasma interaction, X-ray photon sciences, astrophysics up to systems biology. This poster presents our efforts to enable & establish workflows suitable to frictionless transposition between those domains, using highly scalable I/O methods (e.g. ADIOS BP or HDF5), a truly self-describing data markup and peer reviewed participation.
Keywords: I/O OpenScience OpenData HPC OpenAccess HDF5 ADIOS metadata
  • Poster
    Platform for Advanced Scientific Computing (PASC) Conference 2017, 26.-28.06.2017, Lugano, Schweiz
    DOI: 10.5281/zenodo.822396

Downloads:

  • available with HZDR-Login

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


Data Management in Small Animal Imaging: Conceptual and Technical Considerations

Maus, J.ORC; Hofheinz, F.
Small animal imaging in general and multimodal tomographic imaging in particular generate a substantial amount of heterogeneous data that can be challenging to handle. Besides computed tomographic images, there are also the primarily acquired raw data such as listmode data in positron emission tomography (PET), projection data in X-ray computed tomography (CT), or even k-space data in magnetic resonance imaging (MRI). Additionally, further image data might be created by postprocessing (e.g., filtering) or by using alternative image reconstruction methods. All these data have to be stored; thus, the required disk space can easily exceed several terabyte (TB) over time. Therefore, good data storage planning and management strategies are required. In this context, data management obviously does not just mean storing the data. Rather, the data have to be easily accessible for all involved researchers, they also have to remain accessible years after the measurement, and the data have to be backed up in a save and secured place.
Keywords: PET, Small Animal Imaging
  • Book chapter
    Fabian Kiessling, Bernd J. Pichler, Peter Hauff: Small Animal Imaging: Basics and Practical Guide, Heidelberg: Springer International Publishing, 2017, 978-3-319-42200-8, 581-590
    DOI: 10.1007/978-3-319-42202-2_22

Downloads:

  • available with HZDR-Login

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


Range verification in proton therapy and related activities at OncoRay

Pausch, G.ORC
Range verification with millimeter accuracy is considered to be a key for improving the precision and for reducing side effects of radiotherapy with ion beams. The detection and analysis of prompt gamma rays with respect to their emission points, emission time, and emission energy can provide appropriate means for range verification in situ and in real time. The research group “In-vivo Dosimetry” at Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology - OncoRay, has focused considerable efforts on developing and testing prompt-gamma based techniques of range verification in under treatment conditions in proton therapy. The talk reviews complementary approaches and presents recent results of corresponding research activities.
Keywords: Particle therapy; proton therapy; treatment verification; range verification; prompt gamma rays; prompt gamma imaging; prompt gamma timing; gamma spectroscopy
  • Invited lecture (Conferences)
    Annual Meeting of the Gilbert H. Fletcher Society, 21.-22.06.2017, Dresden, Germany

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25684
Publ.-Id: 25684


Towards probing THz-driven transient electronic states with time-resolved ARPES

Deinert, J.-C.ORC; Green, B. W.; Kovalev, S.; Gensch, M.
In this contribution, we present the concept for a novel experimental setup at the THz facility TELBE at Helmholtz-Zentrum Dresden-Rossendorf [1], which combines THz excitation with intrinsically surface-sensitive time- and angle-resolved photoelectron spectroscopy (tr-ARPES). THz excitation provides resonant access to a multitude of fundamental modes, e.g., lattice vibrations, molecular rotations, spin precession and the motion of free electrons. Thereby it can be a handle to control highly relevant transient material properties, from metal-insulator-transitions [2] to superconductivity [3] and catalytic activity [4]. The obvious way of probing these THz-driven dynamics is tr-ARPES which enables direct access to the surface electronic states on a femtosecond timescale, thereby complementing current purely optical techniques. However, the implementation of THz pump – tr-ARPES probe experiments (cf. Fig. 1) has been impeded, because of the unmet requirement for high duty cycle THz sources (>> 10 kHz repetition rate quasi-cw) to provide sufficient statistics for tr-ARPES.
This limitation is overcome at TELBE which offers tunable and CEP-stable THz pulses at a repetition rate of 100 kHz based on superradiant emission, and timing stability of < 30 fs due to a novel pulse-to-pulse diagnostics scheme [5]. Over the next three years, a tr-ARPES setup shall hence be implemented at the THz facility TELBE which aims at establishing feasibility and dynamic range despite obvious obstacles such as residual streaking of the photoelectrons by the high THz excitation fields.
This contribution discusses the challenges and the opportunities of tr-ARPES in first THz control experiments and will outline the current design of the planned tr-ARPES endstation.

[1] B. Green et al., Sci. Rep. 6, 22256 (2016).
[2]T. Kampfrath et al., Nature Photonics 7, 680-690 (2013)
[3]D. Nicoletti and A. Cavalleri, Adv. Opt. Photon. 8, 401 (2016).
[4]L. A. Pellouchoud and E. J. Reed, Phys. Rev. A 91, 052706 (2015).
[5]S. Kovalev et al., Struct. Dyn. (2017) (under review).
  • Poster
    Ultrafast Surface Dynamics 10, 11.-16.06.2017, Inzell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25683
Publ.-Id: 25683


Hyperdoping silicon with tellurium by ion implantation and ultra-short annealing for optoelectronics

Wang, M.; Liu, F.; Yuan, Y.; Prucnal, S.; Berencén, Y.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.
Hyperdoping silicon with chalcogen atoms is a topic of increasing interest due to the strong sub-band gap absorption exhibited by the resulting materials, which can be exploited to develop infrared photodectectors and intermediate band solar cells [1-3]. In our work, tellurium-hyperdoped silicon layers have been fabricated by ion implantation followed by flash lamp annealing (FLA) or pulsed-laser melting (PLM). The Rutherford backscattering spectrometry / Channeling (RBS/C) results reveal the high-quality recrystallization of tellurium implanted silicon by both FLA and PLM. From the transport measurements, an insulator-to-metal transition is observed with increasing tellurium concentration. Moreover, the ellipsometry measurements show that the band gap narrows with increasing doping concentration. And the Fourier transform infrared (FTIR) spectroscopy show that tellurium hyperdoped Si has strong infrared absorption. All these results give us a signal that hyperdoped silicon with tellurium could enable silicon-based optoelectronics in the infrared band.

[1] Kim, T. G., et al., Appl. Phys. Lett. 88, 241902 (2006)
[2] Tabbal, M., et al., Appl. Phys. A 98, 589–594 (2010)
[3] Umezu, I., et al., J. Appl. Phys. 113, 213501 (2013)
Keywords: Hyperdoping silicon, infrared absorption, ion implantation
  • Lecture (Conference)
    DPG-Frühjahrstagung (DPG Spring Meeting), 19.-24.03.2017, Dresden, Germany, Germany

Permalink: https://www.hzdr.de/publications/Publ-25682
Publ.-Id: 25682


Bentonite - geotechnical barrier and source for microbial life

Matschiavelli, N.; Steglich, J.; Kluge, S.; Cherkouk, A.
The safe storage of high-level radioactive waste is a challenging task for our society. For a deep geological deposition of the waste, a multi-barrier concept is favoured, which combines a technical barrier (canister), a geotechnical barrier (e.g. Bentonite) and the geological barrier (host rock). Due to their properties, namely a high swelling capacity and a low hydraulic conductivity, Bentonites fulfil in this system a sealing and buffering function. Depending on the mineral composition, Bentonites contain many suitable electron-donors and -acceptors, enabling potential microbial life. For the potential repository of nuclear waste, the microbial mediated transformation of Bentonite could influence its properties as a barrier material. To elucidate the microbial potential within selected Bentonites, microcosms were set up containing 20g of Bentonite and 40ml anaerobic synthetic Opalinus-clay-pore water solution under an N2/CO2-gas-atmosphere. Substrates like acetate, lactate and H2 were supplemented to stimulate microbial activity. Microcosms were incubated in the dark, without shaking at 30°C and 60°C. Within a year, samples were taken at six different time-points and were analysed regarding geochemical parameters like pH, O2-concentration, redox potential, iron-concentration and sulphate-concentration as well as biological parameters like the consumption and formation of metabolites. Our results show that indigenous microbes from Bentonite are active and could therefore facilitate diverse transformations within the respective Bentonite.
Keywords: Bentonite, anaerobic metabolism, storage of high-level radioactive waste
  • Lecture (Conference)
    Goldschmidt 2017, 13.-17.08.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-25681
Publ.-Id: 25681


Bentonite – geotechnical barrier and source for microbial life

Matschiavelli, N.; Kluge, S.; Cherkouk, A.
Due to their properties, namely a high swelling capacity and a low hydraulic conductivity, bentonites fulfil as geotechnical barrier a sealing and buffering function in a high-level waste repository. Depending on the mineral composition, bentonites contain many suitable electron-donors and –acceptors, enabling potential microbial life. For the potential repository of highly radioactive waste, the microbial mediated transformation of bentonite could influence its properties as a barrier material. Microcosms were set up containing bentonite and anaerobic synthetic Opalinus-clay pore water solution under an N2/CO2 gas atmosphere to elucidate the microbial potential within selected bentonites. Substrates like acetate, lactate and hydrogen were supplemented as electron donors to stimulate potential microbial activity. First results show that bentonites represent a source for microbial life, demonstrated by the consumption of lactate and the formation of pyruvate and hydrogen sulphide.
Keywords: bentonite, sulfate reduction, redox potential
  • Lecture (Conference)
    PETRUS-ANNETTE PhD Conference, 23.-30.06.2017, Lissabon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-25680
Publ.-Id: 25680


Microbial processes in bentonite transformation

Steglich, J.; Matschiavelli, N.; Kluge, S.; Cherkouk, A.
A safe and long-term storage of highly radioactive waste in deep geological layers should be achieved by a multi-barrier concept consisting of geological (host rock), geotechnical (e.g. bentonite) and technical barriers (canister including the highly radioactive waste). Suitable materials for a geotechnical barrier are the so-called bentonites. These clay minerals have due to their mineralogical composition a high swelling capacity and a low solvent permeability and can therefore fulfil in this system a sealing and buffering function.
Like in all natural materials, different microorganisms inhabit bentonites. These microorganisms can influence the conditions in a potential nuclear repository by microbial transformation of bentonite. To elucidate the microbial potential within a selected bentonite, microcosms were set up, which contain 20 g bentonite and 40 ml anaerobic synthetic Opalinus-clay-pore water solution under N2/CO2-gas-atmosphere. Substrates like acetate and lactate were added for the stimulation of the potential microbial activity and anthraquinone-2,6-disulfonate was added as an electron shuttle. Microcosms were incubated in the dark, without shaking at 30°C for 98 days. The samples were taken at different time points of incubation and were analysed regarding geochemical parameters like pH, O2-concentration, redox potential, iron concentration and sulphate concentration as well as biological parameters like the consumption and formation of metabolites.
The results confirm the presence of microbial life in the selected bentonite for example by consumption of lactate and the formation of acetate and pyruvate. Moreover, a fast microbial reduction of iron was detected. The results show the importance of the selection of suitable bentonites for a safe storage of highly radioactive waste in order to avoid the transformation of bentonite by microorganisms, which could cause the loss of its barrier function.
  • Poster
    GDCh-Wissenschaftsforum Chemie 2017 Interdisziplinäre Symposien Jahrestagung Nuklearchemie, 10.-14.09.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25679
Publ.-Id: 25679


Properties and application perspectives of S-layer protein self-assembly

Raff, J.
Nature develops different strategies to allow microorganisms to successfully interact with their environment, which encompasses diverse aspects such as nutrition, protection and communication. One strategy realized in case of bacteria and archaea is the formation of multilayered cell envelopes. The oldest known cell component of such multifunctional cell structures is the so-called surface layer (S-layer). S-layers are composed of proteins being able to self-assemble in highly regular layers forming oblique, square or hexagonal lattices on the surface of cells. These layers protect especially bacteria living in extreme habitats against diverse harmful environmental influences. In case of uranium mining waste pile isolates belonging to the genera Lysinibacillus and Bacillus it was proven that these S-layers act as scavenger for reactive oxygen species and as selective binding matrix for toxic elements and heavy metals. Based on these interesting natural functions and by combining S-layers with layer-by-layer techniques the development of various materials being interesting for an industrial application is possible. Thus, new metals selective filter materials, diverse nano-particular catalysts and sensor materials were successfully produced and tested for their applicability.
Keywords: S-layer, self-assembly, functional coating
  • Invited lecture (Conferences)
    18. Wörlitzer Workshop "Selbstorganisierende Schichtstrukturen, 19.-20.06.2017, Wörlitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25678
Publ.-Id: 25678


Quantum criticality in the coupled two-leg spin ladder Ba2CuTeO6

Glamazda, A.; Choi, Y. S.; Do, S.-H.; Lee, S.; Lemmens, P.; Ponomaryov, A. N.; Zvyagin, S. A.; Wosnitza, J.; Sari, D. P.; Watanabe, I.
We report on zero-field muon spin rotation, electron-spin resonance, and polarized Raman scattering measurements of the coupled quantum spin ladder Ba2CuTeO6. Zero-field muon spin rotation and electron spin resonance probes disclose a successive crossover from a paramagnetic through a spin-liquid-like into a magnetically ordered state with decreasing temperature. More significantly, the two-magnon Raman response obeys a T -linear scaling relation in its peak energy, linewidth, and intensity. This critical scaling behavior presents an experimental signature of proximity to a quantum-critical point from an ordered side in Ba2CuTeO6.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25676
Publ.-Id: 25676


Bose-Einstein condensation of triplons in the S = 1 tetramer antiferromagnet K2Ni2(MoO4)3: A compound close to a quantum critical point

Koteswararao, B.; Khuntia, P.; Kumar, R.; Mahajan, A. V.; Yogi, A.; Baenitz, M.; Skourski, Y.; Chou, F. C.
The structure of K2Ni2(MoO4)3 consists of S = 1 tetramers formed by Ni2+ ions. The magnetic susceptibility χ(T ) and specific heat CP (T ) data on a single crystal show a broad maximum due to the low dimensionality of the system with short-range spin correlations. A sharp peak is seen in χ(T ) and CP (T ) at about 1.13 K, well below the broad maximum. This is an indication of magnetic long-range order, i.e., the absence of spin gap in the ground state. Interestingly, the application of a small magnetic field (H >0.1 T) induces magnetic behavior akin to the Bose-Einstein condensation (BEC) of triplon excitations observed in some spin-gap materials. Our results demonstrate that the temperature-field (T -H) phase boundary follows a power law (T − TN) ∝ H1/α with the exponent 1/α close to 2/3 , as predicted for the BEC scenario. The observation of BEC of triplon excitations in small H infers that K2Ni2(MoO4)3 is located in the proximity of a quantum critical point, which separates the magnetically ordered and spin-gap regions of the phase diagram.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25675
Publ.-Id: 25675


Forced-ferromagnetic state in a Tm2Fe17H5 single crystal

Tereshina, E. A.; Kuz´Min, M. D.; Skourski, Y.; Doerr, M.; Iwasieczko, W.; Wosnitza, J.; Tereshina, I. S.
We report the attainment of the ferromagnetic state in an interstitially modified heavy rareearth-iron intermetallic compound in an external magnetic field. The starting composition is E2Fe17, which is the RE–Fe binary richest in iron. We concentrate on the Tm–Fe compound, which is the most sensitive to magnetic field. The maximum possible amount of hydrogen (5 at.H/f.u.) is inserted into a Tm2Fe17 single crystal. We demonstrate that in a magnetic field of 57 T Tm2Fe17H5 reaches the ferromagnetic state with an enviably high polarization of 2.25 T.
Keywords: single crystal, hydride, forced-ferromagnetic state, rare-earth-iron intermetallic, compound

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25674
Publ.-Id: 25674


Narrow band tunable spintronic THz emission from ferrimagnetic nanofilms

Awari, N.; Kovalev, S.; Fowley, C.; Rode, K.; Lau, Y.-C.; Betto, D.; Thiyagarajah, N.; Green, B.; Yildrim, O.; Lindner, J.; Fassbender, J.ORC; Coey, M.; Deac, A.; Gensch, M.
we report on narrow band THz emission from ferrimagnetic Mn3-xGa nanofilms based. The emission originates from coherently excited spin precession. The central frequency of the emitted radiation is determined by the anisotropy field, while the bandwidth relates to Gilbert damping. It is shown how THz emission spectroscopy can be used for the material characterization of ultra-thin magnetic films. We furthermore discuss the potential of these types of films as efficient on-chip spintronic THz emitters.
Keywords: THz Emitter, Spintronics, Ferrimagnetic
  • Lecture (Conference)
    INTERMAG 2017, 24.-28.04.2017, Dublin, Ireland

Permalink: https://www.hzdr.de/publications/Publ-25673
Publ.-Id: 25673


OpenACC for Programmers - Concepts and Strategies

Chandrasekaran, S.ORC; Juckeland, G.ORC
Klappentext noch nicht vorhanden
  • Book (Editorship)
    New York, USA: Addison-Wesley Professional, 2017
    320 Seiten
    ISBN: 978-0134694283

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25672
Publ.-Id: 25672


Analyzing Offloading Inefficiencies in Scalable Heterogeneous Applications

Dietrich, R.ORC; Tschüter, R.; Juckeland, G.ORC; Knüpfer, A.
With the rise of accelerators in high performance computing, programming models for the development of heterogeneous applications have evolved and are continuously being improved to increase program performance and programmer productivity. The concept of computation offloading to massively parallel compute devices has established itself as a new layer of parallelism in scientific applications, next to message passing and multi-threading. To optimize the execution of a respective parallel heterogeneous program for a specific platform, performance analysis is crucial. This work abstracts from specific offloading APIs such as available with CUDA, OpenCL, OpenACC, and OpenMP and summarizes common inefficiencies for offloading. Based on the definition of inefficiency patterns, the offloading concept can be included in generic analysis techniques such as critical-path and root-cause analysis. We implemented the detection and evaluation of inefficiency patterns as a post-mortem trace analysis, which finally highlights program activities with a high potential to reduce the total program runtime.
Keywords: performance analysis computation offloading heterogeneous applications critical path
  • Contribution to proceedings
    2nd International Workshop on Performance Portable Programming Models for Accelerators (P^3MA), colocated with the ISC High Performance Conference in Frankfurt, Germany, 22.06.2017, Frankfurt/Main, Deutschland
    High Performance Computing. ISC High Performance 2017. Lecture Notes in Computer Science, vol 10524, Cham: Springer, 978-3-319-67630-2, 457-476
    DOI: 10.1007/978-3-319-67630-2_34

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25671
Publ.-Id: 25671


Narrow band tunable spintronic THz emission from ferrimagnetic nanofilms

Awari, N.ORC; Kovalev, S.; Fowley, C.; Rode, K.; Lau, Y.-C.; Betto, D.; Thiyagarajah, N.; Green, B.; Yildrim, O.; Lindner, J.; Fassbender, J.ORC; Coey, M.; Deac, A.; Gensch, M.
we report on narrow band THz emission from ferrimagnetic Mn3-xGa nanofilms based. The emission originates from coherently excited spin precession. The central frequency of the emitted radiation is determined by the anisotropy field, while the bandwidth relates to Gilbert damping. It is shown how THz emission can be used for the characterization dynamical properties of ultra-thin magnetic films. We furthermore discuss the potential of these types of films as efficient on-chip spintronic THz emitter.
Keywords: THz emission, Ferrimagnetic, Spin precession
  • Poster
    IRMMW 2016 - 41st International Conference on Infrared, Millimeter and Terahertz Waves, 26.-30.09.2016, Copenhagen, Denmark

Permalink: https://www.hzdr.de/publications/Publ-25670
Publ.-Id: 25670


Advanced Data Processing for Full-Field PIXE Imaging

Buchriegler, J.ORC; Klingner, N.ORC; Hanf, D.; Munnik, F.; Nowak, S. H.ORC; Scharf, O.; Ziegenrücker, R.; Renno, A. D.; von Borany, J.
The combination of a pnCCD-based detector with a poly-capillary X-ray optics was installed and examined at HZDR [1]. The set-up is intended for PIXE imaging with protons (2-4 MeV) to survey large, polished geological samples with respect to their trace elemental composition. The X-ray optics is used to guide the emitted photons towards the pnCCD-chip divided into nearly 70000 pixels with dimensions of 48 × 48 µm². By applying a dedicated sub-pixel algorithm to recalculate the footprint of the photon’s electron cloud in the chip [2], this limitation can be bypassed and the resolution is then mainly determined by the capillary’s diameter of 20 µm.
Nevertheless, all images gathered with this kind of set-up from are superimposed by patterns of the X-ray optics. The optics’ capillaries are grouped in hexagonal bundles during the fabrication process and these bundles are grouped together again. This process results in a reduced efficiency in the regions where the bundles are joined making the hexagonal pattern visible. This influence can be removed by the technique of multi-frame super-resolution combining several short measurements with slightly shifted positions. The optics pattern is averaged out and in addition the shifting allows further increase of the lateral resolution. The total measurement time can be kept similar by dividing the single measurement time by the number of “shots” without reducing the sampling size.
This approach of multi-frame super-resolution in combination with a sub-pixel correction algorithm will be illustrated and shown on experimental data. Additionally, a flat-field correction attempt is shown to remove general imaging inhomogeneity. Descriptive image-sets will be presented to demonstrate the potential of such techniques for full-field PIXE imaging [3].
[1] D. Hanf, J. Buchriegler, A. D. Renno, S. Merchel, F. Munnik, R. Ziegenrücker, O. Scharf, S. H. Nowak, J. von Borany, NIM B 377, pp. 17-24 (2016).
[2] S. H. Nowak, A. Bjeoumikhov, J. von Borany, J. Buchriegler, F. Munnik, M. Petric, A. D. Renno, M. Radtke, U. Reinholz, O. Scharf, L. Strüder, R. Wedell, R. Ziegenrücker, X-ray Spectrometry 44 (3), pp. 135-140 (2015).
[3] J. Buchriegler, N. Klingner, D. Hanf, F. Munnik, S. H. Nowak, O. Scharf, R. Ziegenrücker, A. D. Renno, J. von Borany, submitted to Journal of Analytical Atomic Spectrometry (2017)

This work has been supported by BMBF (INTRA r3 033R070) and by Marie Curie Actions - Initial Training Network (ITN) as an Integrating Activity Supporting Postgraduate Research with Internships in Industry and Training Excellence (SPRITE) under EC contract no. 317169.
  • Poster
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-25669
Publ.-Id: 25669


Backscattering Spectrometry with Ultimate Lateral Resolution: keV Nanoprobes vs. MeV Microprobes

Klingner, N.ORC; Heller, R.; Hlawacek, G.; Munnik, F.; Facsko, S.
Rutherford Backscattering Spectrometry with a MeV nuclear microprobe is a versatile tool for compositional and structural analysis in material science, micro-electronics and geology. The continuous shrinking of object dimensions lead to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques.
Microprobe setups have been optimized for small beam spots below 1 µm, large solid angles and good energy resolution [1]. However, their performance is limited by the ion source’s brightness and the corresponding beam spot size, sample damage, as well as by the interaction volume of the incident ions.
Recently, we implemented Time-of-Flight Backscattering Spectrometry into a Helium Ion Microscope [2, 3]. The enormous brightness of its Gas Field Ionization Source and the sharp primary ion energy of 30 keV enable an ion beam focus below 1 nm. Due to this very small probe size the achievable lateral resolution for bulk samples is limited by sample damage and the size of the collision cascade.
Different binary collision codes were utilized to simulate the ion-solid interaction for various beam and sample parameters. The origin of backscattered particles, surface sputtering and the intermixing behavior has been studied.
In this contribution we will discuss which primary ion energy, ion species and setup can reach ultimate lateral resolution in Backscattering Spectrometry. Besides simulation results and considerations about advantages and disadvantages we will show practical examples of both - classical MeV nuclear microprobes and focused ion beam keV nanoprobes.

[1] N.Klingner, J.Vogt, D.Spemann, NIMB 306, 44 (2013).
[2] N.Klingner, R.Heller, G.Hlawacek, J.vonBorany, J.Notte, J.Huang, S.Facsko, Ultramicroscopy 162, 91 (2016).
[3] R.Heller, N.Klingner, G.Hlawacek. Helium Ion Microscopy, Chapter 12, Springer International Publishing 2016, ISBN 978-3-319-41988-6
  • Poster
    23rd International Conference on Ion Beam Analysis IBA-2017, 08.-13.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-25668
Publ.-Id: 25668


SIMS using gas field ion sources to approach ultimate spatial resolution

Klingner, N.ORC; Heller, R.; Hlawacek, G.; Facsko, S.
Continuously shrinking object dimensions lead to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques. Secondary Ion Mass Spectrometry (SIMS), as one of the most powerful technique for surface analysis, performed on nanometer scale may comply with this challenge. The mass of sputtered ions directly serves elemental and molecular information and even allows measuring isotope concentrations.

During last decades, primary ion species used in SIMS have optimized in terms of best ionization probabilities and small molecule fragmentation. Thereby, highest mass-resolution has been one of the biggest design goals in the development of new SIMS spectrometers. In contrast to former developments, our approach aims for ultimate spatial resolution.

Typically the lateral resolution is limited by the probe size of the primary ion beam. Minimal probe sizes below 1 nm can be achieved using Gas Field Ionization Sources (GFIS) in a Helium Ion Microscope (HIM). Recently, SIMS has been achieved by implementing Time-of-Flight (TOF) spectrometry to the HIM [1, 2] as well by adding of a sophisticated magnetic sector field analyzer [3]. In this way SIMS could be performed with unprecedented spot sizes.

We will discuss constrains, limits, benefits and drawbacks of the approach. The technical realization will be shown as well as first results and derived conclusions for the practical use of this promising technique.
  • Lecture (Conference)
    22nd International Workshop on Inelastic Ion-Surface Collisions IISC22, 17.-22.09.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25667
Publ.-Id: 25667


Individualized risk assessment in neuroblastoma: Prediction of outcome based on metabolic activity in I-123-MIBG-SPECT

Rogasch, J.; Schatka, I.; Hundsdoerfer, P.; Furth, C.; Wedel, F.; Steffen, I.; Hofheinz, F.; Brenner, W.; Eggert, A.; Amthauer, H.
Objectives: Risk-adapted treatment in children with neuroblastoma (NB) follows clinical and genetic factors. This study evaluated the metabolic tumor volume (MTV) and its asphericity (ASP) in pre-therapeutic I-123-MIBG-SPECT (IMS) for individualized image-based prediction of outcome.

Methods: Retrospective analysis of 22 consecutive children with newly diagnosed NB (f:10; m:12; median age, 1.7 [0.3-6.8] years) undergoing pretherapeutic IMS. MTV and asphericity as the relative deviation of the MTV surface from an isovolumetric sphere were defined for each primary tumor using semi-automatic, background-adapted thresholds. Cox regression, ROC analysis (cut-off determination) and Kaplan-Meier analyses with log-rank test were performed regarding event-free survival (EFS) and overall survival (OS). Analyzed parameters included ASP, MTV, laboratory parameters (such as urinary homovanillic acid-to-creatinine ratio [HVA/C] or serum lactate dehydrogenase [LDH]), age, tumor stage and genetic factors. The predictive accuracy of the optimal multifactorial models was determined by Harrell’s C and the χ2.



Results: Median follow-up was 37 [6-102] months (disease progression / relapse, n=8; death, n=4). Only ASP (p=0.034; hazard ratio [HR], 1.03 for one-unit increase) and MTV (p=0.031; HR, 1.012) were significant predictors of EFS in univariate Cox, only ASP was predictive in multivariate analysis (p=0.024; HR, 1.041). Mean EFS for high (>31.6%) vs. low ASP was 20 vs. 82 months (p=0.022), EFS for high (>46.7 ml) vs. low MTV was 18 vs. 83 months (p=0.008). A combined risk model of high ASP and high HVA/C predicted EFS with the highest accuracy. In Kaplan-Meier analysis, shorter OS was predicted by high ASP (p=0.003), MTV (p<0.001; cut-off, >82.5 ml), HVA/C (>215 µmol/g; p=0.021), LDH (p<0.001) and MYCN amplification (p=0.001). A combination of high MTV and high HVA/C predicted OS with the highest accuracy.

Conclusion: In this explorative study, pre-therapeutic markers of tumor metabolic activity in neuroblastoma (ASP, MTV, urinary HVA-to-creatinine ratio) allowed to separate children with high and low risk for progression / relapse or shorter OS under current therapy regimens. Research Support: No external funding. Figure:Kaplan-Meier curves with log-rank test are displayed for patients with 0, 1 or 2 risk factors according to the predictive model regarding EFS (ASP, HVA/C) or OS (MTV, HVA/C), respectively. Log-rank test was performed for the overall model.
  • Contribution to proceedings
    SNMMI 2017 Annual Meeting, 11.06.2017, Denver, USA
    Journal of Nuclear Medicine 58(2017)

Permalink: https://www.hzdr.de/publications/Publ-25666
Publ.-Id: 25666


Relativistic Electron Streaming Instabilities Modulate Proton Beams Accelerated in Laser-Plasma Interactions

Göde, S.; Rödel, C.; Zeil, K.; Mishra, R.; Gauthier, M.; Brack, F.-E.; Kluge, T.; Macdonald, M. J.; Metzkes, J.; Obst, L.ORC; Rehwald, M.; Ruyer, C.; Schlenvoigt, H.-P.; Schumaker, W.; Sommer, P.; Cowan, T. E.; Schramm, U.; Glenzer, S.; Fiuza, F.
We report experimental evidence that multi-MeV protons accelerated in relativistic laser-plasma interactions are modulated by strong filamentary electromagnetic fields. Modulations are observed when a preplasma is developed on the rear side of a μm-scale solid-density hydrogen target. Under such conditions, electromagnetic fields are amplified by the relativistic electron Weibel instability and are maximized at the critical density region of the target. The analysis of the spatial profile of the protons indicates the generation of B>10  MG and E>0.1  MV/μm fields with a μm-scale wavelength. These results are in good agreement with three-dimensional particle-in-cell simulations and analytical estimates, which further confirm that this process is dominant for different target materials provided that a preplasma is formed on the rear side with scale length ≳0.13λ0√a0. These findings impose important constraints on the preplasma levels required for high-quality proton acceleration for multipurpose applications.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25665
Publ.-Id: 25665


Efficient laser-driven proton acceleration from cylindrical and planar cryogenic hydrogen jets

Obst, L.ORC; Göde, S.; Rehwald, M.; Brack, F.-E.; Branco, J.; Bock, S.; Bussmann, M.; Cowan, T.; Curry, C.; Fiuza, F.; Gauthier, M.; Gebhardt, R.; Helbig, U.; Huebl, A.; Hübner, U.; Irman, A.; Kazak, L.; Kim, J.; Kluge, T.; Kraft, S.; Loeser, M.; Metzkes, J.; Mishra, R.; Roedel, C.; Schlenvoigt, H.-P.; Siebold, M.; Tiggesbäumker, J.; Wolter, S.; Ziegler, T.; Schramm, U.; Glenzer, S.; Zeil, K.
We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (diameter 5 μm) and planar (20 μm × 2 μm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions.
Keywords: Laser-produced plasmas, Plasma-based accelerators
  • Open Access Logo Scientific Reports 7(2017), 10248
    DOI: 10.1038/s41598-017-10589-3
  • Lecture (Conference)
    European Physical Society Conference on Plasma Physics, 26.-30.6.2017, Belfast, United Kingdom
  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 25.-29.9.2017, La Biodola, Isola d'Elba, Italien
  • Lecture (Conference)
    DPG Beschleunigerphysik Tagung, 19.03.2018, Würzburg, Deutschland

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25664
Publ.-Id: 25664


Potential proton and photon dose degradation in advanced head and neck cancer patients by intra-therapy changes

Stützer, K.; Jakobi, A.; Bandurska-Luque, A.; Barczyk, S.; Arnsmeyer, C.; Löck, S.; Richter, C.
Purpose: Evaluation of dose degradation by anatomic changes for head-and-neck cancer (HNC) intensity-modulated proton therapy (IMPT) relative to intensity-modulated photon therapy (IMRT) and identification of potential indicators for IMPT treatment plan adaptation.

Methods: For 31 advanced HNC datasets, IMPT and IMRT plans were recalculated on a computed tomography scan (CT) taken after about four weeks of therapy. Dose parameter changes were determined for the organs at risk (OARs) spinal cord, brain stem, parotid glands, brachial plexus and mandible, for the clinical target volume (CTV) and the healthy tissue outside planning target volume (PTV). Correlation of dose degradation with target volume changes and quality of rigid CT matching was investigated.

Results: Recalculated IMPT dose distributions showed stronger degradation than the IMRT doses. OAR analysis revealed significant changes in parotid median dose (IMPT) and near maximum dose (D1ml) of spinal cord (IMPT, IMRT) and mandible (IMPT). OAR dose parameters remained lower in IMPT cases. CTV coverage (V95%) and overdose (V107%) deteriorated for IMPT plans to (93.4±5.4)% and (10.6±12.5)%, while those for IMRT plans remained acceptable. Recalculated plans showed similarly decreased PTV conformity, but considerable hotspots, also outside the PTV, emerged in IMPT cases. Lower CT matching quality was significantly correlated with loss of PTV conformity (IMPT, IMRT), CTV homogeneity and coverage (IMPT). Target shrinkage correlated with increased dose in brachial plexus (IMRT, IMPT), hotspot generation outside the PTV (IMPT) and lower PTV conformity (IMRT).

Conclusions: The study underlines the necessity of precise positioning and monitoring of anatomy changes, especially in IMPT which might require adaptation more often. Since OAR doses remained typically below constraints, IMPT plan adaptation might be indicated by target dose degradations.
Keywords: IMPT; IMRT; Interfractional changes; Head-and-neck cancer; Setup error; Dose degradation

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25663
Publ.-Id: 25663


Optimization of liquid metal flow pattern generated by rotating magnetic field and the effect on solidification structure of wrought aluminium alloys

Räbiger, D.; Willers, B.; Eckert, S.; Rosefort, M.; Dang, T.; Koch, H.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification. Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front. It has been shown that an accurate tuning of the magnetic field parameters can avoid segregation effects. The present study examines the directional solidification of wrought aluminium alloys from a water-cooled copper chill. Rotating magnetic fields were used to agitate the melt.
  • Lecture (Conference)
    XVIII International UIE-Congress on Electrotechnologies for Material Processing, 06.-09.06.2017, Hannover, Deutschland
  • Contribution to proceedings
    XVIII International UIE-Congress on Electrotechnologies for Material Processing, 06.-09.06.2017, Hannover, Deutschland
    XVIII International UIE-Congress Electrotechnologies for Material Processing: Vulkan-Verlag GmbH, 978-3-8027-3095-5, 255-260

Permalink: https://www.hzdr.de/publications/Publ-25662
Publ.-Id: 25662


Impact of forced flow on the solidification structure of wrought aluminium alloys by means of AC magnetic

Räbiger, D.; Willers, B.; Eckert, S.; Rosefort, M.; Dang, T.; Koch, H.
AC magnetic fields provide a contactless method to control the flow inside a liquid metal and the grain size of the solidified ingot. Many studies have shown that beneficial effects like a distinct grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic growth (CET) can be obtained. However, electromagnetically-driven melt convection may also produce segregation freckles on the macroscale. The achievement of superior casting structures needs a well-aimed control of melt convection during solidification. Previous investigations considered the use of time-modulated AC magnetic fields to control the heat and mass transfer at the solidification front. It has been shown recently under laboratory conditions, that an accurate tuning of the magnetic field parameters can avoid segregation effects and homogenize the mechanical properties. The present study examines the directional solidification of commercial wrought aluminium alloys from a water-cooled copper chill. Rotating magnetic fields were used to agitate the melt.
Our results demonstrate the potential of magnetic fields to control the grain size, the formation of segregation freckle and the morphology and distribution of pores, especially for use time modulated rotating fields.
Keywords: wrought aluminium alloys, grain size control, time modulated magnetic field
  • Lecture (Conference)
    6th Decennial International Conference on Solidification Processing, 25.-28.07.2017, Beaumont Estate, Old Windsor, UK
  • Contribution to proceedings
    6th Decennial International Conference on Solidification Processing, 25.-28.07.2017, Beaumont Estate, Old Windsor, UK
    SP17 - Solidification Processing 2017: Brunel University London, 978 1 908549 29 7, 638-641

Permalink: https://www.hzdr.de/publications/Publ-25661
Publ.-Id: 25661


Bulk production and evaluation of high specific activity 186gRe for cancer therapy using enriched 186WO3 targets in a proton beam

Mastren, T.; Radchenko, V.; Bach, H.; Balkin, E.; Birnbaum, E.; Brugh, M.; Engle, J.; Gott, M.; Guthrie, J.; Hennkens, H.; John, K.; Ketring, A.; Kuchuk, M.; Maassen, J.; Naranjo, C.; Nortier, M.; Phelps, T.; Jurisson, S.; Wilbur, S.; Fassbender, M.
Introduction

Rhenium-186g (t1/2 = 3.72 d) is a β− emitting isotope suitable for theranostic applications. Current production methods rely on reactor production by way of the reaction 185Re(n,γ)186gRe, which results in low specific activities limiting its use for cancer therapy. Production via charged particle activation of enriched 186W results in a 186gRe product with a higher specific activity, allowing it to be used more broadly for targeted radiotherapy applications. This targets the unmet clinical need for more efficient radiotherapeutics.

Methods

A target consisting of highly enriched, pressed 186WO3 was irradiated with protons at the Los Alamos National Laboratory Isotope Production Facility (LANL-IPF) to evaluate 186gRe product yield and quality. LANL-IPF was operated in a dedicated nominal 40 MeV mode. Alkaline dissolution followed by anion exchange chromatography was used to isolate 186gRe from the target material. Phantom and radiolabeling studies were conducted with the produced 186gRe activity.

Results

A 186gRe batch yield of 1.38 ± 0.09 MBq/μAh or 384.9 ± 27.3 MBq/C was obtained after 16.5 h in a 205 μA average/230μA maximum current proton beam. The chemical recovery yield was 93% and radiolabeling was achieved with efficiencies ranging from 60–80%. True specific activity of 186gRe at EOB was determined via ICP-AES and amounted to 0.788 ± 0.089 GBq/μg (0.146 ± 0.017 GBq/nmol), which is approximately seven times higher than the product obtained from neutron capture in a reactor. Phantom studies show similar imaging quality to the gold standard 99mTc.

Conclusions

We report a preliminary study of the large-scale production and novel anion exchange based chemical recovery of high specific activity 186gRe from enriched 186WO3 targets in a high-intensity proton beam with exceptional chemical recovery and radiochemical purity.
Keywords: Theranostic; 186gRe; 186WO3 target; High specific activity; Radiolabeling; SPECT phantom images

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25659
Publ.-Id: 25659


Application of Photothermal Expansion for Optical Absorption Mapping at the Nanoscale

Madeira, T. I.; Rodriguez, R. D.; Ravikumar, Y.; Shah, H.; Bortchagovsky, E.; Zahn, D. R. T.
In this work we demonstrate that photothermal expansion can be used to obtain images of nanostructured semiconductor materials such as GaSe flakes on graphite and carbon nanotubes on SiO2 in ambient conditions with high sensitivity and spatial resolution. The principle behind is the detection of the mechanical force exerted on an atomic force microscopy (AFM) tip by the thermal expansion of the materials excited with pulses of optical radiation, taking advantage of the different absorption properties between substrate and sample. Characterization of semiconductor nanostructures, with a bandgap in the optical range enables the use of cw lasers chopped and synchronized with the resonance frequency of custom-made fully metallic cantilever AFM Au tips. The spatial resolution achieved by the synchronization procedure described is indeed in the nanometer range below 60 nm, and by taking advantage of the difference between optical absorption and thermal coefficients material contrast can be achieved.
Keywords: photothermal expansion, AFM, TERS, semiconductor nanostructures
  • Invited lecture (Conferences)
    Seminar at the Academy of Sciences in Prague - Department of Thin Films and Nanostructures, 27.05.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-25658
Publ.-Id: 25658


Breaking the Electrical Barrier between Copper and Carbon Nanotubes

Milowska, K. Z.; Ghorbani-Asl, M.ORC; Burda, M.; Wolanicka, L.; Catic, N.; Bristowe, P. D.; Kozioł, K. K. K.
Improving the interface between copper and carbon nanotubes (CNTs) offers a straightforward strategy for the effective manufacturing and utilisation of Cu-CNT composite material that could be used in various industries including microelectronics, aerospace and transportation. Motivated by a combination of structural and electrical measurements on Cu-M-CNT bimetal systems (M = Ni, Cr) we show, using first principles calculations, that the conductance of this composite can exceed that of a pure Cu-CNT system and that the current density can even reach 10 11 A/cm2 . The results show that the proper choice of alloying element (M) and type of contact facilitate the fabrication of ultra-conductive Cu-M-CNT systems by creating a favourable interface geometry, increasing the interface electronic density of states and reducing the contact resistance. In particular, a small concentration of Ni between the Cu matrix and the CNT using either an "end contact" and or a "dot contact" can significantly improve the electrical performance of the composite. Furthermore the predicted conductance of Ni-doped Cu-CNT "carpets" exceeds that of an undoped system by ∼200%. Cr is shown to improve CNT integration and composite conductance over a wide temperature range while Al, at low voltages, can enhance the conductance beyond that of Cr.
Keywords: carbon nanotubes, copper, composite, electrical properties

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25657
Publ.-Id: 25657


Froth flotation of scheelite - a review

Kupka, N.; Rudolph, M.
Froth flotation of scheelite has regained new focus since the 2010s and research regarding floatability and reagents has made great progress over the years. The main objective was and remains the selective flotation of scheelite from other calcium-bearing minerals, in particular calcite, fluorite and apatite. Due to similar properties, most attempts have limited success or only specific application (linked to a type of ore or a location). This article aims at reviewing all general physical-chemical information on froth flotation of scheelite, including electrokinetic properties, influence of pH and already existing reagents as well as ones still under examination. It appears that chelating or mixed collectors and modified versions of sodium silicate and quebracho hold great promise for scheelite flotation, while the use of said depressants and/or promoters seems inevitable.
Keywords: scheelite; froth flotation; calcium-bearing minerals

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25656
Publ.-Id: 25656


Holographic Entanglement Entropy in the QCD Phase Diagram with a Critical Point

Knaute, J.; Kämpfer, B.
We calculate the holographic entanglement entropy for the holographic QCD phase diagram in [Knaute, Yaresko, Kämpfer (2017), arXiv:1702.06731] and explore the resulting qualitative behavior over the temperature-chemical potential plane. In agreement with the thermodynamic result, the phase diagram exhibits the same critical point as the starting point of a first-order phase transition curve. We compare the phase diagram of the entanglement entropy to that of the thermodynamic entropy density and find a striking agreement in the vicinity of the critical point. Thus, the holographic entanglement entropy qualifies to characterize different phase structures. The scaling behavior near the critical point is analyzed through the calculation of critical exponents.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25655
Publ.-Id: 25655


A Bayesian Approach for Measurements of Stray Neutrons at Proton Therapy Facilities: Quantifying Neutron Dose Uncertainty

Dommert, M.; Reginatto, M.; Zboril, M.; Fiedler, F.; Helmbrecht, S.; Enghardt, W.; Lutz, B.
The analysis of Bonner sphere measurements is typically done using unfolding codes. However, it is very difficult to implement reliable uncertainty propagation in standard unfolding procedures. An alternative approach, which does provide reliable estimates of the uncertainties of neutron spectra leading to rigorous estimates of uncertainties of the dose, is to analyze the data using Bayesian parameter estimation. In this work, we extend previous approaches and apply this method to secondary neutrons from radiation therapy proton beams. This requires introducing a parameterized model which can describe the main features of the neutron spectra. We choose the parameterization based on information that is available from measurements and detailed Monte Carlo simulations. To demonstrate the validity of this approach, we consider the results of an experiment carried out at the experimental hall at the OncoRay proton therapy facility in Dresden.
Keywords: Neutron measurement, proton therapy

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25654
Publ.-Id: 25654


Efficient Parallel Monte-Carlo Simulations for Large-Scale Studies of Surface Growth Processes

Kelling, J.
Lattice Monte Carlo methods are used to investigate far from and out-of-equilibrium systems, including surface growth, spin systems and solid mixtures. Such studies require observations of large systems over long times scales, to allow structures to grow over orders of magnitude, which necessitates massively parallel simulations. This talk presents work done to address the problem of parallel processing introducing correlations in Monte Carlo updates. Studies of the effect of correlations on scaling and dynamical properties of surface growth systems and related lattice gases is investigated further by comparing results obtained by correlation-free and intrinsically correlated but highly efficient simulations using a stochastic cellular automaton. The primary subject of study is the Kardar-Parisi-Zhang surface growth in (2+1) dimensions. Key physical insights about this universality class, like precise universal exponent values and exponent relations, obtained from large-scale simulations are presented.
Keywords: Lattice Monte Carlo, GPU, Surface Growth, Kardar-Parisi-Zhang
  • Lecture (others)
    Seminar Topical Problems, 14.06.2017, Chemnitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-25653
Publ.-Id: 25653


Magnesium photocathodes in the SRF photo-injector at HZDR

Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Vennekate, H.; Xiang, R.
Magnesium photocathodes in the SRF photo-injector at HZDR
Keywords: Magnesium photocathode, SRF photoinjector
  • Poster
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-25652
Publ.-Id: 25652


Improvements of the photoemission efficiency of magnesium photocathodes

Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.; Lu, P.; Vennekate, H.; Patra, P.
To improve the quality of photocathodes is one of the critical issues in enhancing the stability and reliability of photo-injector systems. Presently the primary choice is to use metallic photocathodes for the ELBE SRF Gun II to reduce the risk of contamination of the superconducting cavity. Magnesium has a low work function (3.6 eV) and shows high quantum efficiency (QE) up to 0.3 % after laser cleaning. The SRF Gun II with an Mg photocathode has successfully provided electron beam for ELBE users. However, the present cleaning process with a high intensi-ty laser (activation) is time consuming and generates unwanted surface roughness. This paper presents the investigation of alternative surface cleaning procedures, such as thermal treatment. The QE and topography of Mg samples after treatment are reported.
Keywords: magnesium photocathodes, quantum efficiency, SRF photoinjector
  • Open Access Logo Contribution to proceedings
    The 8th International Particle Accelerator Conference (IPAC’17), 14.-19.05.2017, Copenhagen, Danmark
    Proceedings of IPAC'17
  • Poster
    The 8th International Particle Accelerator Conference (IPAC’17), 14.-19.05.2017, Copenhagen, Denmark

Permalink: https://www.hzdr.de/publications/Publ-25651
Publ.-Id: 25651


Tailoring Optical Properties of Atomically-Thin WS2 via Ion Irradiation

Tan, L. N.; Tan, Y.; Ghorbani-Asl, M.ORC; Boettger, R.; Kretschmer, S.; Zhou, S. Q.; Huang, Z. Y.; Krasheninnikov, A. V.ORC; Chen, F.
Two-dimensional transition metal dichalcogenides (TMDCs) exhibit excellent optoelectronic properties. However, the large band gaps in many semiconducting TMDCs make optical absorption in the near-infrared (NIR) wavelength regime impossible, which prevents applications of these materials in optical communications. In this work, we demonstrate that Ar+ ion irradiation is a powerful post-synthesis technique to tailor the optical properties of the semiconducting tungsten disulfide (WS2) by creating S vacancies and thus controlling material stoichiometry. First-principles calculations reveal that the S-vacancies give rise to deep states in the band gap, which determine the NIR optical absorption of the WS2 monolayer. As the density of the S-vacancies increases, the enhanced NIR linear and saturable absorption of WS2 is observed, which is explained by the results of first-principles calculations. We further demonstrate that by using the irradiated WS2 as a saturable absorber in a waveguide system, the passively Q-switched laser operations can be optimized, opening thus new avenues for tailoring the optical response of TMDCs by defect-engineering through ion irradiation.
Keywords: Ion irradiation, WS2, optical properties

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25650
Publ.-Id: 25650


Laser-Ablation-Based Ion Source Characterization and Manipulation for Laser-Driven Ion Acceleration

Sommer, P.; Metzkes, J.; Brack, F.-E.; Cowan, T. E.; Kraft, S. D.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.
For laser-driven ion acceleration from thin foils (~10 µm- 100 nm) in the target normal sheath acceleration (TNSA) regime, the hydro-carbon contaminant layer at the target surface generally serves as the ion source and hence determines the accelerated ion species, i.e. mainly protons, carbon and oxygen ions. The specific characteristics of the source layer - thickness and relevant lateral extent - as well as its manipulation have both been investigated since the first experiments on laser-driven ion acceleration using a variety of techniques from direct source imaging to knife-edge or mesh imaging.
In this publication, we present an experimental study in which laser ablation in two fluence regimes (low: F~0.6 J/cm², high: F~4 J/cm²) was applied to characterize and manipulate the hydro-carbon source layer. The high-fluence ablation in combination with a timed laser pulse for particle acceleration allowed for an estimation of the relevant source layer thickness for proton acceleration. Moreover, from these data and independently from the low-fluence regime, the lateral extent of the ion source layer became accessible.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25649
Publ.-Id: 25649


Enhancements in full-field PIXE imaging - large area elemental mapping with increased lateral resolution devoid of optics artefacts

Buchriegler, J.ORC; Klingner, N.ORC; Hanf, D.; Munnik, F.; Nowak, S. H.ORC; Scharf, O.; Ziegenrücker, R.; Renno, A. D.; von Borany, J.
The combination of a pnCCD-based pixel detector with a poly-capillary X-ray optics was installed and examined at the Helmholtz-Zentrum Dresden-Rossendorf. The set-up is intended for Particle Induced X-ray Emission imaging to survey the trace elemental composition of flat/polished geological samples. In the standard configuration a straight X-ray optics (20 µm capillary diameter) is used to guide the emitted photons from the sample towards the detector with nearly 70000 pixels. Their dimensions of 48×48 µm2 are the main limitation of the lateral resolution. This limitation can be bypassed by applying a dedicated sub-pixel algorithm to recalculate the footprint of the photon’s electron cloud in the detector. The lateral resolution is then mainly determined by the capillary’s diameter. Nevertheless, images are still superimposed by the X-ray optics pattern. The optics’ capillaries are grouped in hexagonal bundles resulting in a reduced transmission of X-rays in the boundary regions. This influence can be largely suppressed by combining a series of short measurements at slightly shifted positions using a precision stage and correcting the image-data for this shifting. The use of a sub-pixel grid for the image reconstruction allows a further increase of the spatial resolution. This approach of multi-frame super-resolution in combination with the sub-pixel correction algorithm is presented and illustrated with experimental data. Additionally, a flat-field correction is shown to remove the remaining imaging inhomogeneity caused by non-uniform X-ray transmission. The described techniques can be used for all X-ray spectrometry methods using an X-ray camera to obtain high quality elemental images.
Keywords: Color X-ray camera, full-field imaging, image stacking, multi-frame super-resolution, flat-field correction

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25648
Publ.-Id: 25648


Road to micron resolution with a color X-ray camera – polycapillary optics characterization

Nowak, S. H.ORC; Petric, M.; Buchriegler, J.ORC; Bjeoumikhov, A.; Bjeoumikhov, Z.; von Borany, J.; Munnik, F.; Radtke, M.; Renno, A. D.; Reinholz, U.; Scharf, O.; Tilgner, J.; Wedell, R.
In a color X-ray camera spatial resolution is achieved by means of a polycapillary optic conducting X-ray photons from small regions on a sample to distinct energy dispersive pixels on a CCD matrix. At present, the resolution limit of color X-ray camera systems can go down to several microns and is mainly restricted by pixel dimensions. The recent development of an efficient subpixel resolution algorithm allows a release from pixel size, limiting the resolution only to the quality of the optics. In this work polycapillary properties that influence the spatial resolution are systematized and assessed both theoretically and experimentally. It is demonstrated that with the current technological level reaching one micron resolution is challenging, but possible.
Keywords: color X-ray camera, polycapillary optics, lateral resolution

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25647
Publ.-Id: 25647


Asymmetric spin-wave dispersion in ferromagnetic nanotubes induced by surface curvature

Otálora, J. A.; Yan, M.; Schultheiss, H.; Hertel, R.; Kákay, A.
We present a detailed analytical derivation of the spin wave (SW) dispersion relation in magnetic nanotubes with magnetization along the azimuthal direction. The obtained formula can be used to calculate the dispersion relation for any longitudinal and azimuthal mode. The obtained dispersion is asymmetric for all azimuthal modes traveling along the axial direction. As reported in our recent publication [Phys. Rev. Lett. 117, 227203 (2016)], the asymmetry is a curvature-induced effect originating from the dipole-dipole interaction. Here, we discuss the asymmetry of the dispersion for azimuthal modes by analyzing the SW asymmetry deltaf (kz) = fn(kz) − fn(−kz), where fn(kz) is the eigenfrequency of a magnon with a longitudinal and azimuthal wave vectors, kz and n, respectively; and the dependence of the maximum asymmetry with the nanotube radius R. The analytical results are in perfect agreement with micromagnetic simulations. Furthermore, we show that the dispersion relation simplifies to the thin-film dispersion relation with in-plane magnetization when analyzing the three limiting cases: (i) kz = 0, (ii) kz>>1/R, and (iii) kz<<1/R. In the first case, for the zeroth-order modes the thin-film Kittel formula is obtained. For modeswith higher order the dispersion relation for the Backward-Volume geometry is recovered. In the second case, for the zeroth-order mode the exchange dominated dispersion relation for SW in Damon-Esbach configuration is obtained. For the case kz<<1/R, we find that the dispersion relation can be reduced to a formula similar to the Kalinikos-Slavin [J. Phys. C: Sol. State Phys. 19, 7013 (1986)] type.
Keywords: Spin waves, curvature, mangnonics

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-25646
Publ.-Id: 25646


TELBE: High-field high-repetition-rate photonics facility for coherent terahertz control of Matter

Wang, Z.; Deinert, J.-C.; Green, B.; Awari, N.; Chen, M.; Kovalev, S.; Gensch, M.
The TELBE user facility at Helmholtz-Zentrum Dresden-Rossendorf is based on the new class of accelerator-driven terahertz (THz) radiation sources. Superradiant THz radiation is generated from relativistic electron bunches in a compact MeV level superconducting radiofrequency electron accelerator. Compared to the laser-based table-top THz sources with moderate repetition rates of a few kHz, the superradiant THz facility TELBE provides high repetition rates (quasi-cw) up to several 100 kHz, peak electric fields of 1 GV/m, and flexibility of tuning the THz pulse form. Time resolved experiments can be performed with time resolution down to 30 fs using the novel pulse-resolved diagnostics. We will present the results from first benchmarking THz control experiments, and discuss the possibility of various pump-probe experiments for friendly users, especially at low temperatures and in magnetic fields.
  • Poster
    International Conference on Quantum Criticality and Novel Phases (QCNP 2017), 26.02.-01.03.2017, Berlin, Germany

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25645
Publ.-Id: 25645


Nanometer probing of ultrahigh intensity ultrashort pulse laser interaction with solid density plasmas, by Small Angle X-Ray Scattering using XFELs

Kluge, T.; Rödel, M.; Metzkes, J.; Pelka, A.; Laso Garcia, A.; Prencipe, I.; Hartley, N.; Nakatsutsumi, M.; Gutt, C.; Galtier, E.; Nam, I.; Lee, H. J.; Zacharias, M.; Garten, M.; Bussmann, M.; Zeil, K.; Rödel, C.; Mcbride, E.; Schramm, U.; Cowan, T. E.
Nanometer probing of ultrahigh intensity ultrashort pulse laser interaction with solid density plasmas, by Small Angle X-Ray Scattering using XFELs
  • Lecture (Conference)
    2017 European XFEL Users' Meeting and Satellite Meetings, Satellite Meeting: Status of the HED science instrument & Meeting of the HIBEF user consortium, 24.01.2017, Hamburg, Deutschland
  • Invited lecture (Conferences)
    International Conference on Extreme Light, 06.-09.11.2017, Szeged, Ungarn
  • Lecture (others)
    Plasmaphysik Seminar GSI, 17.01.2017, Darstadt, Deutschland

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25644
Publ.-Id: 25644


SAXS on ultrashort laser pulse experiments

Kluge, T.; Pelka, A.; Metzkes, J.; Rödel, M.; Laso Garcia, A.; Prencipe, I.; Gutt, C.; Schramm, U.; Cowan, T. E.
Nanometer probing of ultrahigh intensity short pulse laser interaction with solid density plasmas, by Small Angle X-Ray Scattering using XFELs
  • Lecture (Conference)
    High Intensity Laser Matter Science at The HED Instrument at The European XFEL, 05.-06.04.2017, Hamburg, Deutschland

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25643
Publ.-Id: 25643


Start-to-end simulations for photon interaction in ultra-high intensity short pulse laser experiments with solids

Kluge, T.; Burau, H.; Garten, M.; Grund, A.; Huebl, A.; Matthes, A.; Jung, F.; Widera, R.; Zacharias, M.; Fortmann-Grote, C.; Bussmann, M.
EUCALL annual meeting poster
  • Poster
    EUCALL annual meeting 2017, 07.-09.06.2017, Grenoble, Frankreich

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25642
Publ.-Id: 25642


The need for detailed scattering simulations for Small Angle X-Ray Scattering on laser driven solids

Thomas Kluge; Burau, H.; Garten, M.; Grund, A.; Huebl, A.; Matthes, A.; Jung, F.; Widera, R.; Zacharias, M.; Fortmann-Grote, C.; Bussmann, M.
SIMEX progress report June 2017
  • Lecture (Conference)
    EUCALL annual meeting 2017, 07.-09.06.2017, Grenoble, Frankreich

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-25641
Publ.-Id: 25641


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