Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

33407 Publications

A study of the structural and magnetic properties of ZnO implanted by Gd ions

Macková, A.; Malinsky, P.; Sofer, Z.; Šimek, P.; Sedmidubsky, D.; Mikulics, M.; Wilhelm, R. A.
The structural and magnetic properties of ZnO (0 0 0 1) single crystals implanted with 200 keV Gd ions up to a fluence of 5 × 1015 cm−2 and subsequently annealed at 800 °C in various atmospheres were studied. The chemical composition and concentration depth profiles of ion-implanted layers were characterised by Rutherford Back-Scattering spectrometry (RBS) and compared to SRIM simulations. The as-implanted Gd depth profiles were found to be broader than those simulated by SRIM, but the projected range coincided well with that simulated. After annealing at 800 °C, the depth profiles became narrower. The structural changes in the layers modified by ion implantation and subsequent annealing were characterised by RBS channelling. The annealing led to partial recrystallisation and a decrease in the number of Gd atoms situated in substitutional positions. Raman spectroscopy showed that the point defects in Zn and O vacancies had been created by implantation and that these defects are most effectively cured after annealing in oxygen atmosphere. AFM analysis was used to determine the surface-morphology changes after the implantation and annealing procedures. The as-implanted samples exhibited ferromagnetism persisting up to room temperature. The annealing procedure led to paramagnetic behaviour, probably caused by the formation of gadolinium clusters.
Keywords: ZnO; Gd implantation; Depth profiles; RBS channelling; Raman spectroscopy; AFM

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20522
Publ.-Id: 20522


A combinatorial study of the mechanical and magnetic properties of a gradually nitrided austenitic stainless steel single crystal

Menéndez, E.; Templier, C.; Abrasonis, G.; Lopez-Barbera, J. F.; Nogués, J.; Temst, K.; Sortef, J.
The mechanical and magnetic properties of a nitrided austenitic stainless steel are studied using a combinatorial approach. Plasma nitriding of a [100]-oriented 316L single crystal is carried out using a loose shadow mask to produce an in-plane lateral gradient of nitrogen concentration that extends up to 100 μm. The local mechanical and magnetic properties across the gradually nitrided area are resolved by nanoindentation and the polar magneto-optic Kerr effect, respectively. The hardness, reduced Young's modulus and remanence qualitatively depict the nitrogen profile, suggesting that the nitrogen concentration is a central effect for these observed dependencies. Conversely, the coercivity exhibits a non-monotonic behaviour due to the interplay between magnetic anisotropy and the strength of the induced ferromagnetism. Fingerprints of the expected transition from a nitrogen supersaturated solid solution to a multiphase nature of expanded austenite are evidenced along the gradually nitrided area.
Keywords: Austenitic stainless steel, plasma nitriding, magnetic and mechanical properties

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20521
Publ.-Id: 20521


The structural changes and optical properties of LiNbO3 after Er implantation using high ion fluencies

Macková, A.; Malinsky, P.; Pupíková, H.; Nekvindová, P.; Cajzl, J.; Sofer, Z.; Wilhelm, R. A.; Kolitsch, A.; Oswald, J.
The structural and compositional changes of LiNbO3 implanted with 190 keV Er+ ions into various crystallographic cuts with fluencies of 1 × 1016 and 5 × 1016 cm−2 were studied. The effect of post-implantation annealing at 1000 °C in oxygen atmosphere was also examined. Concentration depth profiles of implanted erbium, determined by Rutherford Backscattering Spectrometry (RBS), are broader than those from the SRIM simulation. The maximum erbium concentration (of up to 8 at.%) is observed at the depth of about 50 nm, for all crystal cuts. The structure of the implanted layers were characterised by RBS-channelling method. The lower relative number of disordered atoms in the crystalline matrix was observed in the lithium niobate (LN) implanted at a fluence of 1 × 1016 cm−2, where also the preferential position of the erbium in substitutional sites was observed when compared to the randomly distributed erbium in interstitial positions at a fluence of 5 × 1016 cm−2 after the annealing. Surface-morphology changes at the highest implantation fluencies were studied using Atomic Force Microscopy (AFM). Since we were interested in the relation between the structural changes and optical properties, erbium luminescence properties were measured in the region of 1440–1650 nm. The positive effect of post-implantation annealing on the luminescence properties caused by structural recovery was proved.
Keywords: Implanted lithium niobate; Erbium implantation; RBS channeling structural study; Luminesent properties

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20520
Publ.-Id: 20520


Europium(III) lactate structure determination using spectroscopic (ATR FT-IR, NMR) and theoretical (DFT) methods

Barkleit, A.; Kretzschmar, J.; Tsushima, S.; Acker, M.
Small organic molecules like lactic acid (HO-CH(CH3)-COOH), which can bind heavy metal ions, are ubiquitous in nature. They can be found in nearly all biological systems as a product of various biochemical processes and in the geosphere as well, i.e. as part of organic matter of argillaceous rocks. This renders lactate a suitable model molecule for a multi-technique structure determination. Eu(III) was chosen as non-radioactive model for trivalent actinides.
Current structural suggestions for the Eu(III) lactate are only assumptions from indirect methods [1,2]. We want to provide direct structural information. ATR FT-IR spectroscopy combined with calculations of structure and spectroscopic data using DFT reveals structural features. Lanthanide induced shifts (LIS) in NMR spectroscopy as caused by the interaction of nuclear spins with electronic unpaired spins can be used as a helpful tool for signal separation, probing the potential binding sites and structure including geometries and distances [3].
The combination of all these methods offers new insights concerning the structure of the Eu(III) lactate 1:1 complex thereby resolving contradictions in the previous works whether the hydroxyl group is protonated or not.
From ATR FT-IR measurements, bidentate coordination of exclusively the carboxylate group could be ruled out because of the characteristic degree of spectral splitting of the asymmetric and symmetric stretching vibrations νas and νs of the carboxylate group. The best accordance of the DFT calculated vibrational spectra to the measured spectrum is given for monodentate coordinating carboxylate group and additional coordination of the deprotonated hydroxyl group (Fig. 1). NMR findings strongly support the results obtained from ATR FT-IR measurements in combination with DFT calculations. The correlation between the chemical shift changes of the 13C NMR signals and the Eu-C distances calculated by DFT suites perfectly this structure model [4].
The finding that the hydroxyl group seems to be deprotonated under complex formation [4] contradicts former structure suggestions, which suppose a coordination of the trivalent metal ion with the protonated hydroxyl group [1,2]. Both experimental methods, ATR FT-IR and NMR, as well as the DFT calculations yielded an impressively homogeneous structural explanation of the investigated Eu(III) lactate 1:1 species.

[1] Tian, G.X. et al. (2010) Inorg. Chem. 49, 10598-10605.
[2] Dickins, R.S. et al. (2002) J. Am. Chem. Soc. 124, 12697-12705.
[3] Mayo, B.C. (1973) Chem. Soc. Rev. 2, 49-74.
[4] Barkleit, A. et al. (2014) Dalton Trans. DOI: 10.1039/c4dt00440j
  • Poster
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland
  • Open Access Logo Contribution to proceedings
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, Dresden, Deutschland
    Wissenschaftlich-Technische Berichte HZDR-054: Helmholtz-Zentrum Dresden-Rossendorf

Permalink: https://www.hzdr.de/publications/Publ-20519
Publ.-Id: 20519


Introduction to the Minimum Rainbow Subgraph problem

Matos Camacho, S.
Consider an p edge coloured graph G, then a Minimum Rainbow Subgraph is a subgraph H of G of minimum order, such that every colour occurs in H. This phd thesis provides a comprehensive introduction to this problem.
Keywords: graph theory, chromatic index, colouring
  • Doctoral thesis
    TU Bergakademie Freiberg, 2012
    Mentor: Prof. Dr. Ingo Schiermeyer
    59 Seiten

Permalink: https://www.hzdr.de/publications/Publ-20518
Publ.-Id: 20518


The rainbow connection number of 2-connected graphs

Ekstein, J.; Holub, P.; Kaiser, T.; Koch, M.; Matos Camacho, S.; Ryjáček, Z.; Schiermeyer, I.
The rainbow connection number of a graph G is the least number of colours in a (not necessarily proper) edge-colouring of G such that every two vertices are joined by a path which contains no colour twice. Improving a result of Caro et al., we prove that the rainbow connection number of every 2-connected graph with n vertices is at most ⌈n/2⌉. The bound is optimal.
Keywords: Rainbow connection number; Graph; Connectivity

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20517
Publ.-Id: 20517


Algorithmic approaches for the minimum rainbow subgraph problem

Koch, M.; Matos Camacho, S.; Schiermeyer, I.
We consider the Minimum Rainbow Subgraph problem (MRS): Given a graph G, whose edges are coloured with p colours. Find a subgraph F⊆G of minimum order and with p edges such that each colour occurs exactly once. This problem is APX-hard. In this paper we will show that the Greedy algorithm for the MRS problem has an approximation ratio of Δ/2 + (lnΔ+1)/2 for graphs with maximum degree Δ. If the average degree d of a minimum rainbow subgraph is known, then the approximation ratio is d/2 + (ln[d]+1)/2.
Keywords: 10.1016/j.endm.2011.10.028

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20516
Publ.-Id: 20516


Approximation algorithms for the minimum rainbow subgraph problem

Matos Camacho, S.; Schiermeyer, I.; Tusa, Z.
We consider the minimum rainbow subgraph problem (MRS): given a graph G, whose edges are coloured with p colours. Find a subgraph F⊆G of G of minimum order and with p edges such that each colour occurs exactly once. For graphs with maximum degree Δ(G) there is a greedy polynomial-time approximation algorithm for the MRS problem with an approximation ratio of Δ(G). In this paper we present a polynomial-time approximation algorithm with an approximation ratio of View the MathML source for Δ≥2.
Keywords: Edge colouring; Minimum rainbow subgraph; Approximation algorithm

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20515
Publ.-Id: 20515


Colourings of graphs with prescribed odd cycle lengths

Matos Camacho, S.; Schiermeyer, I.
In 1992 Gyárfás showed that a graph G having only k odd cycle lengths is (2k+1)-colourable, if it does not contain a K2k+2. In this paper, we will present the results for graphs containing only odd cycles of length 2m−1 and 2m+1 as done in [S. Matos Camacho, Colourings of graph with prescribed cycle lengths, diploma thesis, TU Bergakademie Freiberg, 2006. [3]]. We will show that these graphs are 4-colourable.
Keywords: Colouring; Cycles; Chromatic number

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20514
Publ.-Id: 20514


Studying the constancy of the galactic cosmic rays using cosmogenic noble gases and radionuclides on iron meteorites

Smith, T.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.; Wallner, A.; Fifield, K.; Tims, S.; Korschinek, G.
Introduction: The constancy of the galactic cosmic rays (GCR) is a long-standing question in meteorite research. The temporal variability of GCR intensities over the last billion years can be investigated studying meteorites [1]. Indeed, during their travel in space, meteoroids are exposed to GCRs; the interactions producing (among others) stable and radioactive cosmogenic nuclides. Being interested in the long-term GCR variability, we study iron meteorites because they typically have cosmic ray exposure (CRE) ages in range of a few hundred millions years (Myr) and – for some – even up to two billion years [2]. It has been demonstrated that periodic GCR flux variations can induce peaks in CRE age histograms. Therefore, setting up a consistent exposure age histogram and searching for periodic peaks permits us to study hypothetical GCR flux variations.
Experimental methods: Noble gas isotopes (He, Ne, and Ar) are analyzed by noble gas mass spectrometry at the University of Bern, using two self-made mass spectrometers [3,4]. Analyses of the cosmogenic radionuclides (10Be, 26Al, 36Cl, and 41Ca) are performed at the DREsden Accelerator Mass Spectrometry facility (DREAMS, [5]) adapted from the procedure described in [6].
Results: So far, 28 iron meteorite samples, mainly of class IIIAB, have been investigated for their noble gas and cosmogenic radionuclide contents. The first terrestrial ages have been deter-mined using the 36Cl/10Be-10Be method [1]. They range between 10 kyr and 500 kyr. Because doubts exist on the use of 26Al, 21Ne and probably 10Be as proxies for CRE age determination, due to inhomogeneous sulfur and phosphorus distribution [3,7], the CRE ages were calculated using the radioactive-stable nuclide pair 36Cl-36Ar, as described in [1]. The calculated ages range between ~5 and ~700 Myr, which is in the expected range for iron meteorites [2,8]. Additionally, the first 53Mn and 60Fe measurements have been performed at the Australian National University (ANU) and at the TUM in Munich. On the CRE ages histogram, two peaks, centered at ~50 and ~350 Myr are visible, but statistics are still poor. Additional measurements of iron meteorites are thus needed and ongoing, that will help to study possible variation in the GCR intensities over the last billion years.
References: [1] Lavielle B. et al. 1999. Earth Planetary and Science Letters 170:93–104. [2] Wieler R. et al. 2013. Space Science Reviews 176:351-363. [3] Ammon K. et al. 2008. Meteoritics and Planetary Science 43:685-699. [4] Ammon K. et al. 2011. Meteoritics and Planetary Science 46:785-792. [5] Akhmadaliev S. et al. 2013. Nuclear Instruments and Methods in Physic B 294:5-10. [6] Merchel S. and Herpers U. 1999. Radiochimica Acta 84:215-219. [7] Ott U. et al., Meteoritics and Planetary Science, in press. [8] Eugster O. et al. 2006. Meteorites and the Early Solar System II, Part IX: 829-851.
Keywords: GCR, AMS, accelerator mass spectrometry, cosmogenic nuclide, cosmic radiation
  • Lecture (Conference)
    77th Annual Meeting of the Meteoritical Society, 07.-12.09.2014, Casablanca, Marocco
  • Abstract in refereed journal
    Meteoritics & Planetary Science 49(2014), A371

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20513
Publ.-Id: 20513


Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures

Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.; Schmidt, B.; Bougeard, D.
The renewed interest in Germanium as base material for electronic applications has stimulated extensive experimental and theoretical studies. Successful integration of Ge in nanoelectronic devices requires fundamental understanding of ion-implantation-induced target modification and damage. In this contribution the temperature dependence of ion-beam mixing induced by 310 keV gallium (Ga) ion implantation in crystalline and preamorphized germanium (Ge) is reported. Isotopically enriched multilayer structures of alternating 70Ge and natGe layers are used to visualize the self-atom mixing. The distribution of the implanted Ga atoms and the ion-beam induced self-atom mixing was determined by means of secondary ion mass spectrometry. Different temperature regimes of self-atom mixing are observed. At temperatures up to 423 K the mixing is independent of the initial structure whereas at 523 K the intermixing of the preamorphized Ge structure is about twice as high as that of the crystalline material. At 623 K the intermixing of the initially amorphous Ge structure is strongly reduced and approaches the mixing of the crystalline material. The temperature dependence of ion-beam mixing is consistently described by competitive amorphization and recrystallization processes.
Keywords: ion beam mixing, isotopically enriched multilayer structures, amorphous germanium, self mixing, thermal spike
  • Lecture (Conference)
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-20512
Publ.-Id: 20512


Formation, coarsening and band gap engineering of sponge-like Si-SiO2 nanocomposites – materials design by theoretical predictions

Liedke, B.; Heinig, K. H.; Friedrich, D.; Schmidt, B.; Mücklich, A.; Hübner, R.; Keles, U.; Bulutay, C.
It has been found by energy filtered transmission electron microscopy (EFTEM) that metastable SiOx≈1 films decay during thermal treatment by spinodal decomposition into a Si nanowire network embedded in SiO2 forming a nanocomposite [1,2]. This nanoscale material is promising candidate as absorber layer for next generation solar cells as it exhibits a widened band gap due to quantum confinement and electrical interconnectivity due to percolation of the nanostructured Si. The formation of Si-SiO2 nanocomposites was predicted by a kinetic Monte Carlo simulations [1,3]. Additionally, the band gap and the band offset of the nanocomposite were predicted by large scale atomistic pseudopotential computations [4]. Experimentally, the sponge-like morphology was verified by EFTEM and atom probe tomography [2], whereas its band gap measured via light absorption is still under discussion. The predicted morphology of the sponge-like Si-SiO2 nanocomposite appears to be almost identical to the measured ones. Also the predicted scaling behavior of the coarsening of the nanostructure during thermal treatment was verified experimentally. Combining theory with experiments delivers the understanding for tailoring the properties like quantum confinement of the sponge-like Si. [1] Müller, et al. Appl. Phys. Lett. 85, 2373 (2004) [2] Friedrich, et al. Appl. Phys. Lett. 103, 133106 (2013) [3] Liedke, et al. Appl. Phys. Lett. 103, 131911 (2013) [4] Keles, et al. Appl. Phys. Lett. 103, 203103 (2013)
Keywords: sponge, Si-SiO2 nanocomposite, kinetic Monte-Carlo, modeling, EFTEM, PV, nanostructure
  • Lecture (Conference)
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-20511
Publ.-Id: 20511


Sponge-like Si-SiO2 nanocomposite absorber for next generation PV cells

Liedke, B.; Friedrich, D.; Schmidt, B.; Heinig, K. H.; Mücklich, A.; Hübner, R.; Wolf, D.; Kölling, S.
To increase the market share of Si-based thin film PV cells their efficiency has to be improved without increasing of the module costs. Sponge-like Si-SiO2 nanocomposite has a potential to be a low cost and efficient absorber for next generation PV. It consists of Si embedded in SiO2 fabricated by spinodal decomposition of sputter-deposited silicon-rich oxide SiOx≈1. Thermal treatment using rapid thermal processing and furnace annealing requires annealing times of few tens of sec. up to few tens of min. However, in a thin film technology the phase separation of SiOx at high temperatures requires a very rapid thermal processing of few tens of ms in order to avoid substrate damage. Here, the structure of the Si-SiO2 nanocomposite was investigated by energy-filtered transmission electron microscopy (EFTEM), EFTEM tomography and atom probe tomography which revealed a percolated Si morphology [1]. This is in excellent agreement with atomistic simulations using kinetic Monte-Carlo method [2]. Depending on the annealing time and temperature a feature size in the range of 2..5 nm was found, which is small enough for band gap widening due to quantum confinement [3]. We show that the favorable properties of Si-SiO2 nanocomposite, e.g. quantum size effect and percolated morphology, make it a suitable material for PV absorber. [1] Friedrich, et al. Appl. Phys. Lett. 103,133106(2013) [2] Liedke, et al. Appl. Phys. Lett. 103,131911(2013) [3] Keles, et al. Appl. Phys. Lett. 103,203103(2013)
Keywords: sponge, Si-SiO2 nanocomposite, PV, quantum confinement, absorber, thin-film solar cells
  • Poster
    EMRS 2014 Spring Meeting, 26.-30.05.2014, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-20510
Publ.-Id: 20510


Structural studies of thin Pd films loaded with hydrogen

Melikhova, O.; Cizek, J.; Vlcek, M.; Lukac, F.; Prochazka, I.; Anwand, W.; Brauer, G.
In this work variable energy positron annihilation spectroscopy was employed for investigation of defects created in Pd films electrochemically charged with hydrogen. The development of hydrogen-induced defects in nanocrystalline, polycrystalline and epitaxial Pd films were compared. It was found that absorbed hydrogen causes plastic deformation and increases defect density in all Pd films studied. Moreover, buckling was observed in nanocrystalline and polycrystalline films loaded above certain critical hydrogen concentration.
Keywords: Pd films, hydrogen loading, defects, positron annihilation

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20509
Publ.-Id: 20509


Sintering of zirconia-based nanomaterials studied by variable-energy slow-positron beam

Prochazka, I.; Cizek, J.; Melikhova, O.; Anwand, W.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.
A variable-energy slow-positron beam was applied to the investigations of the tetragonal yttria-stabilised zirconia (YSZ), the YSZ co-doped with small amount of Cr2O3. The initial nanopowders exhibiting the mean particle size of ≈ 20 nm were prepared by co-precipitation technique. Prior the sintering, the nanopowders were calcined and compacted using a pressure of 500 MPa. The ordinary shape parameters of the Doppler-broadened annihilation peak and the relative positronium 3γ-fractions were determined as functions of positron energy. The results are consistent with a remarkable sintering-induced grain growth and disappearance of porosity which is driven out from the sample interior toward a thin sub-surface layer.
Keywords: yttria-stabilised zirconia, sintering, positronium, positron annihilation

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20508
Publ.-Id: 20508


Defect studies of thin ZnO films prepared by pulsed laser deposition

Vlcek, M.; Cizek, J.; Prochazka, I.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Mosnier, J. P.
Thin ZnO films were grown by pulsed laser deposition on four different substrates: sapphire (0 0 0 1), MgO (1 0 0), fused silica and nanocrystalline synthetic diamond. Defect studies by slow positron implantation spectroscopy (SPIS) revealed significantly higher concentration of defects in the studied films when compared to a bulk ZnO single crystal. The concentration of defects in the films deposited on single crystal sapphire and MgO substrates is higher than in the films deposited on amorphous fused silica substrate and nanocrystalline synthetic diamond. Furthermore, the effect of deposition temperature on film quality was investigated in ZnO films deposited on synthetic diamond substrates. Defect studies performed by SPIS revealed that the concentration of defects firstly decreases with increasing deposition temperature, but at too high deposition temperatures it increases again. The lowest concentration of defects was found in the film deposited at 450°C.
Keywords: ZnO films, pulsed laser deposition, defects, positron annihilation

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20507
Publ.-Id: 20507


Paleoarchean sulfur cycling: multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa

Montinaro, A.; Strauss, H.; Mason, P. R. D.; Roerdink, D.; Münker, C.; Schwarz-Schampera, U.; Arndt, N.; Farquhar, J.; Beukes, N.; Gutzmer, J.; Peters, M.
Mass-dependent and mass-independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the Barberton Greenstone Belt (3550–3215 Ma), South Africa, provide constraints for sulfur cycling on the early Earth. Four different samples suites were studied: komatiites and tholeiites, barite, massive and disseminated sulfide ores, and non-mineralized black shales. Previous multiple sulfur isotope centered either on specific areas and/or lithologies from the Barberton Greenstone Belt, while this study provides results for a much wider sample selection across the stratigraphic succession.
Variable but generally slightly positive δ34S values between -0.7 and +5.0‰, negative Δ33S values between -0.51 and -0.09‰, and a negative correlation between δ34S and Δ33S as well as between Δ33S and Δ36S for komatiites and tholeiites from the Komati Formation and from the Weltevreden Formation are outside the expected range of unfractionated juvenile sulfur. Instead, results indicate variable degrees of alteration through ambient seawater during serpentinisation of these rocks.
Barite from the Mapepe Formation displays positive δ34S values between 3.1 and 8.1‰ and negative Δ33S values between -0.77 and -0.34‰. Moreover, samples reveal a linear negative correlation between Δ33S and Δ36S with a slope of -0.7. The mass-independent sulfur isotope fractionation indicates an atmospheric sulfur source, whereas the positive δ34S values suggest bacterial sulfate reduction of the marine sulfate reservoir. The latter process is further discernible through a weak positive correlation between δ34S and δ18O of the barite.
Non-mineralized black shales from the presumed stratigraphic equivalent of the Mapepe Formation show positive δ34S values between 0.0 and 1.2‰ and positive Δ33S values between 0.59 and 2.48‰. These results are interpreted to result from the mixing between the two principal atmospheric sources, i.e. elemental sulfur, carrying a positive Δ33S signature and sulfate, carrying a negative Δ33S value, with its δ34S signature subsequently modified through bacterial sulfate reduction.
Positive δ34S values ranging from +0.5 to +3.4‰ and slightly negative Δ33S values between -0.17 and -0.13‰ characterize massive and disseminated sulfides from the Bien Venue Prospect. Results suggest a mixture between the unfractionated juvenile magmatic sulfur source and a contribution from recycled seawater sulfate indicative of submarine hydrothermal activity. Considering the isotope values, these three sets of samples show a common source of sulfur, characterized by negative Δ33S and positive Δ36S, represented by seawater sulfate.
Massive and disseminated sulfides from the M’hlati prospect are characterized by different values compared to massive and disseminated sulfide from the Bien Venue Prospect. They show negative δ34S values between -1.4 and -0.1‰ and positive Δ33S values between +2.66 and +3.17‰, thus, displaying a sizeable mass-independent sulfur isotopic fractionation. Again, these samples clearly exhibit the incorporation of an atmospheric MIF-S signal. The source of sulfur for these samples has positive Δ33S values, thus this is related to elemental sulfur.
In conclusion, the sulfur isotope inventories in the Paleoarchean rocks and hydrothermal precipitates from the Barberton Greenstone Belt are quite diverse and indicate the incorporation of at least two sources of sulfur. Komatiites and tholeiites, barite and massive and disseminated sulfides from Bien Venue show a common sulfur source, related to seawater sulfate, while massive and disseminated sulfides from M’hlati are related to elemental sulfur and not mineralized black shales with a mixing between these two sulfur sources.
Keywords: Archean; multiple sulfur isotopes; Barberton Greenstone Belt.

Permalink: https://www.hzdr.de/publications/Publ-20506
Publ.-Id: 20506


Untersuchung von Gammakaskaden und Stärkefunktionen in der Neutroneneinfangsreaktion 77Se(n,γ)

Robert, J.
Eine der wichtigsten nuklearen Prozesse stellt der Neutroneneinfang dar. In der kosmischen Nukleosynthese (s-Prozess) schwerer Elemente werden Kerne mit Massenzahlen größer als die von Eisen (A = 56) produziert, welche durch Kernfusion nicht produziert werden können. Dabei fängt ein Kern ein Neutron ein, wird durch die frei werdende Bindungsenergie angeregt und kann sich anschließend unter Aussenden von Photonen (Gamma-Quanten) wieder abregen. Aus der Abregung über Gammastrahlung können Rückschlüsse auf die Struktur des aktivierten Nuklids gezogen werden. Im Rahmen dieser Arbeit werden die ausgesendeten Photonen des angeregten Elements 78Se, welches durch Neutroneneinfang an 77Se am Reaktor des Instituts Laue-Langevin in Grenoble, Frankreich produziert wurde, näher untersucht. Dazu mussten zunächst Effizienzkalibrierung und Addback-Korrekturen vorgenommen werden. Im Anschluss konnten mit Hilfe des EXILL-Multidetektoraufbaus Koinzidenzbeziehungen mehrerer aufeinander folgender Photonen untersucht und in einem Niveauschema zusammengefasst werden. Mit Hilfe der Winkelverteilung konnten diversen Zuständen Spins zugeordnet werden. Des Weiteren wurden die Ergebnisse einer Simulation von Gammakaskaden (DEX) und eines Photonenstreuungsexperiments am Elektronenbeschleuniger ELBE des HZDR mit den in Grenoble aufgenommenen experimentellen Daten verglichen.
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-046 2014

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20505
Publ.-Id: 20505


Analysis and simulation of photon scattering and neutron capture gamma spectra

Schramm, G. A.
Within this thesis two twin experiments consisting of neutron capture and photon scattering on the neighbour isotopes 77Se / 78Se and 195Pt / 196Pt have been analysed to gain qualitative and quantitative information about the photon strength function and level density in the respective compound nuclei. For the analysis and simulation of both experimental types a new Monte Carlo simulation using a fast and efficient, extreme statistical treatment of radiative nuclear deexcitations, was developed. Furthermore the influence of fluctuations of transition widths on photon scattering were investigated and quantified. It could be shown that those lead to an enhancement of elastic scattering processes. The data analysis of both twin experiments reveals non-Lorentzian extra E1 photon strength below the neutron separation energy.
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-045 2014

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20504
Publ.-Id: 20504


Positron Emission Tomography for the dose monitoring of intra-fractionally moving Targets in ion beam therapy

Stützer, K.
Ion beam therapy (IBT) is a promising treatment option in radiotherapy. The characteristic physical and biological properties of light ion beams allow for the delivery of highly tumour conformal dose distributions. Related to the sparing of surrounding healthy tissue and nearby organs at risk, it is feasible to escalate the dose in the tumour volume to reach higher tumour control and survival rates. Remarkable clinical outcome was achieved with IBT for radio-resistant, deep-seated, static and well fixated tumour entities. Presumably, more patients could benefit from the advantages of IBT if it would be available for more frequent tumour sites. Those located in the thorax and upper abdominal region are commonly subjected to intra-fractional, respiration related motion. Different motion compensated dose delivery techniques have been developed for active field shaping with scanned pencil beams and are at least available under experimental conditions at the GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany.
High standards for quality assurance are required in IBT to ensure a safe and precise dose application. Both underdosage in the tumour and overdosage in the normal tissue might endanger the treatment success. Since minor unexpected anatomical changes e.g. related to patient mispositioning, tumour shrinkage or tissue swelling could already lead to remarkable deviations between planned and delivered dose distribution, a valuable dose monitoring system is desired for IBT. So far, positron emission tomography (PET) is the only in vivo, in situ and non-invasive qualitative dose monitoring method applied under clinical conditions. It makes use of the tissue autoactivation by nuclear fragmentation reactions occurring along the beam path. Among others, +-emitting nuclides are generated and decay according to their half-life under the emission of a positron. The subsequent positron-electron annihilation creates two 511 keV photons which are emitted in opposite direction and can be detected as coincidence event by a dedicated PET scanner. The induced three-dimensional (3D) +- activity distribution in the patient can be reconstructed from the measured coincidences. Conclusions about the delivered dose distribution can be drawn indirectly from a comparison between two +-activity distributions: the measured one and an expected one generated by a Monte-Carlo simulation. This workflow has been proven to be valuable for the dose monitoring in IBT when it was applied for about 440 patients, mainly suffering from deep-seated head and neck tumours that have been treated with 12C ions at GSI.
In the presence of intra-fractional target motion, the conventional 3D PET data processing will result in an inaccurate representation of the +-activity distribution in the patient. Fourdimensional, time-resolved (4D) reconstruction algorithms adapted to the special geometry of in-beam PET scanners allow to compensate for the motion related blurring artefacts. Within this thesis, a 4D maximum likelihood expectation maximization (MLEM) reconstruction algorithm has been implemented for the double-head scanner Bastei installed at GSI. The proper functionality of the algorithm and its superior performance in terms of suppressing motion related blurring artefacts compared to an already applied co-registration approach has been demonstrated by a comparative simulation study and by dedicated measurements with moving radioactive sources and irradiated targets. Dedicated phantoms mainly made up of polymethyl methacrylate (PMMA) and a motion table for regular one-dimensional (1D) motion patterns have been designed and manufactured for the experiments. Furthermore, the general applicability of the 4D MLEM algorithm for more complex motion patterns has been demonstrated by the successful reduction of motion artefacts from a measurement with rotating (two-dimensional moving) radioactive sources. For 1D cos2 and cos4 motion, it has been clearly illustrated by systematic point source measurements that the motion influence can be better compensated with the same number of motion phases if amplitudesorted instead of time-sorted phases are utilized. In any case, with an appropriate parameter selection to obtain a mean residual motion per phase of about half of the size of a PET crystal size, acceptable results have been achieved. Additionally, it has been validated that the 4D MLEM algorithm allows to reliably access the relevant parameters (particle range and lateral field position and gradients) for a dose verification in intra-fractionally moving targets even from the intrinsically low counting statistics of IBT-PET data.
To evaluate the measured +-activity distribution, it should be compared to a simulated one that is expected from the moving target irradiation. Thus, a 4D version of the simulation software is required. It has to emulate the generation of +-emitters under consideration of the intra-fractional motion, their decay at motion state dependent coordinates and to create listmode data streams from the simulated coincidences. Such a revised and extended version that has been compiled for the special geometry of the Bastei PET scanner is presented within this thesis. The therapy control system provides information about the exact progress of the motion compensated dose delivery. This information and the intra-fractional target motion needs to be taken into account for simulating realistic +-activity distributions. A dedicated preclinical phantom simulation study has been performed to demonstrate the correct functionality of the 4D simulation program and the necessity of the additional, motionrelated input parameters.
Different to the data evaluation for static targets, additional effort is required to avoid a potential misleading interpretation of the 4D measured and simulated +-activity distributions in the presence of deficient motion mitigation or data processing. It is presented that in the presence of treatment errors the results from the simulation might be in accordance to the measurement although the planned and delivered dose distribution are different. In contrast to that, deviations may occur between both distributions which are not related to anatomical changes but to deficient 4D data processing. Recommendations are given in this thesis to optimize the 4D IBT-PET workflow and to prevent the observer from a mis-interpretation of the dose monitoring data. In summary, the thesis contributes on a large scale to a potential future application of the IBT-PET monitoring for intra-fractionally moving target volumes by providing the required reconstruction and simulation algorithms. Systematic examinations with more realistic, multi-directional and irregular motion patterns are required for further improvements. For a final rating of the expectable benefit from a 4D IBT-PET dose monitoring, future investigations should include real treatment plans, breathing curves and 4D patient CT images.
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-044 2014

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20503
Publ.-Id: 20503


Mini-Proceedings of the 15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies

van der Bij, J. J.; Czyż, H.; Eidelman, S.; Fedotovich, G.; Ferber, T.; Ivanov, V.; Korobov, A.; Liu, Z.; Lukin, P. A.; Müller, S. E.; Venanzoni, G.; Zaremba, J.; (Editors)
The mini-proceedings of the 15th Meeting of the "Working Group on Rad. Corrections and MC Generators for Low Energies" held in Mainz on April 11, 2014, are presented. These meetings, started in 2006, have as aim to bring together experimentalists and theorists working in the fields of meson transition form factors, hadronic contributions to (g−2)μ and the effective fine structure constant, and development of Monte Carlo generators and Radiative Corrections for precision e+e- and tau physics.
  • Open Access Logo Contribution to proceedings
    15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies, 11.04.2014, Mainz, Germany
    Mini-Proceedings of the 15th meeting of the Working Group on Rad. Corrections and MC Generators for Low Energies

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20502
Publ.-Id: 20502


International round robin test on Master Curve reference temperature evaluation utilizing Miniature C(T) specimen

Yamamoto, M.; Onizawa, K.; Yoshimoto, K.; Ogawa, T.; Mabuchi, Y.; Valo, M.; Lambrecht, M.; Viehrig, H.-W.; Miura, N.; Soneda, N.
The Master Curve (MC) method is a promising technique for evaluating the fracture toughness of ferritic steels. It enables the determination of the reference temperature, To, of a probabilistic fracture toughness curve using small specimens. The Central Research Institute of Electric Power Industry (CRIEPI) investigated this capability of the MC method using different size of C(T) specimens, and it was found that 0.16T-C(T) specimen with the dimensions of 10mm by 10mm by 4mm, hereafter called “Mini-CT specimen”, can be used to obtain valid To values. The advantage of this Mini-CT specimen technique is that multiple specimens can be machined from one of broken halves of Charpy size specimens, which are used in a standard surveillance capsule of a reactor pressure vessel (RPV).
In order to ensure the robustness of this technique, a round-robin test was planned. The idea is to perform MC tests using Mini-CT specimens by different investigators to see if consistent To values can be obtained. All the specimens used were machined and pre-cracked by one fabricator from unique RPV material to avoid any possible effect of specimen preparation on To values. Seven institutes participated in this exercise, and obtained valid To values. No specific difficulty was found in the MC tests performed in accordance to the ASTM E1921 protocol. The scatter of the obtained To values was well within the uncertainty range defined in Appendix X4.2 of ASTM E1921, indicating the robustness of the Mini-CT specimen technique in terms of the testing procedure.
Throughout this activity, we could obtain 182 KJc (1Teq) for a single material. We investigated the statistics of this large database, and found that there is no remarkable difference not only in the To values but also in the fracture toughness distribution between the Mini-CT specimen and the standard 1T-C(T) specimen results.
Keywords: reactor pressure vessel steel, fracture toughnes, miniature specimen, Master Curve approach
  • Contribution to proceedings
    6th International Symposium on Small Specimen Test Techniques, 29.-31.01.2014, Houston, United States
    ASTM Special Technical Publication, Vol. STP 1576: ASTM, 978-080317597-6, 53-69
    DOI: 10.1520/STP157620140020

Permalink: https://www.hzdr.de/publications/Publ-20501
Publ.-Id: 20501


Wechselwirkung von Uran und Plutonium mit Ton, Tonorganika und bakteriellen Tonisolaten

Schmeide, K.; Jordan, N.; Moll, H.; Cherkouk, A.; Lippold, H.; Poetsch, M.; Kulenkampff, J.; Fritsch, K.
In the talk, the most important results obtained in the project for the system radionuclide/clay organics/clay rock are presented. The influence of salinity and temperature on complexation, sorption as well as diffusion/transport of radionuclides is discussed.
Keywords: Uranium, plutonium, terbium, fulvic acid, propionic acid, microorganisms, montmorillonite, Opalinus Clay, PET
  • Lecture (others)
    6. Workshop des Verbundprojekts "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 08.-09.04.2014, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20500
Publ.-Id: 20500


Ferromagnetism and structural defects in V-doped titanium dioxide

Yildirim, O.; Butterling, M.; Cornelius, S.; Mikhailovskiy, Y.; Novikov, A.; Semisalova, A.; Orlov, A.; Gan’Shina, E.; Perov, N.; Anwand, W.; Wagner, A.; Potzger, K.; Granovsky, A. B.; Smekhova, A.
We report recent experimental results about influence of negatively charged structural defects on room-temperature ferromagnetism in V-doped TiO2-δ thin films with different electric conductivities. Films were prepared on LaAlO3 (001) substrates by RF magnetron sputtering in reduced argon-oxygen atmosphere, while the V to Ti metal ratio was fixed at 1 at.%. The ferromagnetic order at room temperature (RT) was confirmed by SQUID magnetometry. Positron annihilation spectroscopy (PAS) was applied to check the presence of open-volume defects in the TiO2-δ matrix. The relation between ferromagnetic properties and amount of negatively charged defects in the studied films was established. The collection of structural, magnetometry, magnetotransport, magneto-optic and PAS data hints towards the defect-induced model of ferromagnetism in1 at.% V-doped TiO2-δ thin films.
Keywords: diluted magnetic semiconductors, defect-induced ferromagnetism, doped TiO2, PAS

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20499
Publ.-Id: 20499


Uranium(VI) retention in clay and crystalline rock: How and why does it differ

Schmeide, K.; Joseph, C.; Brendler, V.
The long-term disposal of high-level nuclear waste in deep geological formations is discussed worldwide as main strategy for nuclear waste management. This approach requires the use of a multiple barrier system consisting of engineered, geo-engineered, and geological barriers to prevent any release of radionuclides into the geo- and biosphere. Sorption of radionuclides on the host rock of a repository is one important process for retarding their migration. Potential host rocks for nuclear waste repositories that are investigated internationally are salt domes, clay rock, and crystalline rock.
In the present work, the retention behavior of clay and crystalline rock towards U(VI) is compared. For this, sorption of U(VI) onto Opalinus Clay from the Mont Terri rock laboratory (Switzerland) was studied in the presence of Opalinus Clay pore water (pH = 7.6; I = 0.36 M) [1]. This is compared to U(VI) sorption onto anoxic diorite from Äspö Hard Rock Laboratory (Sweden) that was studied in the presence of Äspö groundwater (pH = 7.8; I = 0.18 M) [2]. The impact of various parameters, such as solid-to-liquid ratio, initial U(VI) concentration, temperature and atmosphere, on U(VI) sorption was studied.
Distribution coefficients, Kd values, determined for the U(VI) sorption onto Opalinus Clay and diorite at 25 °C, amount to 22.2 ± 0.4 L/kg [1] and 3.8 ± 0.6 L/kg [2], respectively. Thus, U(VI) sorption onto Opalinus Clay is stronger than onto diorite, which can be attributed to its larger surface area. TRLFS and ATR FT-IR spectroscopic measurements showed that the U(VI) speciation in Opalinus Clay pore water as well as in diorite groundwater is predominated by the weakly sorbing Ca2UO2(CO3)3(aq) complex. Reduction processes of U play only a subordinate role. The U(VI) sorption increases with increasing temperature.
U(VI) diffusion experiments with intact Opalinus Clay bore cores [3] also showed that Opalinus Clay has a good retardation potential for U(VI) since the molecular diffusion process through Opalinus Clay retards the migration of Ca2UO2(CO3)3(aq).
Generally, it can be concluded that U(VI) retention by clay rock is stronger than that by crystalline rock. This supports decisions to use clay rock not only as host rock but also as backfill material. In case of crystalline rock the natural retention capacity for U is insufficient and has to be strengthened by additional geo-technical and technical barriers that preserve their enclosing capabilities over very long time scales.

[1] Joseph, C. et al. (2011) Chem. Geology 284, 240-250.
[2] Schmeide, K. et al. (2014) Appl. Geochem. 49, 116-125.
[3] Joseph, C. et al. (2013) Geochim. Cosmochim. Acta 109, 74-89.
Keywords: Uranium, sorption, retention, clay rock, crystalline rock
  • Invited lecture (Conferences)
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn/Bad Godesberg, Deutschland
  • Contribution to proceedings
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn/Bad Godesberg, Deutschland
    Berichte des Forschungszentrums Jülich, Jül-4376, Institut für Energie- und Klimaforschung, Nukleare Entsorgung und Reaktorsicherheit (S. Neumeier, P. Kegler, D. Bosbach, eds.), Jülich, 46 (2014).

Permalink: https://www.hzdr.de/publications/Publ-20498
Publ.-Id: 20498


Ferromagnetic Resonance Analysis on Periodic Surface Defects: The Transition from Perturbed Thin Films to Magnonic Crystals

Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokirtov, S. O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
The magnetic relaxation in 1-dimensional periodic nanostructures (quasi magnonic crystals) is investigated by ferromagnetic resonance (FMR). In thin ferromagnetic films, the magnetization dynamics are governed by intrinsic effects like Gilbert damping and spin-pumping but also by extrinsic effects like two-magnon scattering (TMS). The latter is in demand for latest research and can be induced within magnetic thin films by defects and inhomogeneities. Thereby, acting as scattering centers, defects cause a dipolar field at the film surface crucial for the magnon-magnon interaction. By ion Irradiation of the material, a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the properties of the modification such as the reduction of the effective magnetic moment and the geometry (depth d , periodicity a 0 ). The investigated films consist of 30 nm thick permalloy (Ni80Fe20) deposited by molecular beam epitaxy at room temperature on Si/SiO2 substrate. All films are protected by a Cr Cap layer of 3 – 5 nm. On top of the structure, PMMA resist of 140 nm thickness was added and patterned by EBL, to create a symmetric array of stripe defects with a periodicity ranging from 100 – 400 nm optimal for the investigation of TMS. Subsequently, the mask was employed for ion beam patterning. Parameters for the Cr ion irradiation were selected according to Monte-Carlo simulations calculating the effects of the ion irradiation on the depth-dependent composition using SRIM [2] and TRIDYN [3]. The irradiation energies were defined in the range of 5 – 10 keV in which the fluence varies from 5·1015 1/cm2 to 8·1015 1/cm2. Due to the lowering of the Curie temperature underneath room temperature when Cr content in permalloy is extending 8 at.% [4], after irradiation, magnetically dead layers are generated. For lower Cr concentrations, the saturation magnetization of permalloy is reduced and hence, the dead layers are accompanied by a concentration gradient where MS increases gradually to the value of the saturation magnetization of permalloy. By varying the ion energy and fluence, this gradient and hence, the effective defect depth can be set. This allows the investigation of the transition from a surface perturbed thin film to a full magnonic crystal. The energies and fluences used to prepare the samples presented in this work are summarized in Table I. The spin wave dynamics and TMS are studied using FMR and Brillouin light scattering (BLS). The dispersion relation of backward volume modes in an unperturbed thin film is known to be quadratically dependent on the wave vector k due to exchange interaction. If an array of surface perturbations is assumed to exist on the surface of such a thin film, an additional dipolar field contribution to the magnons dispersion must be taken into account. This term is proportional to –k (for ultrathin films: k ·d << 1) and hence, causes a degeneration. Investigating such system by FMR, spin wave excitation is carried out uniformly. Thus, to scatter into the degenerate spin wave mode, the k -vector must match a multiple reciprocal lattice vector g 0 = 2/a 0 . If this is valid, TMS can be observed and mode repulsion takes place. We measured the FMR spectra f (H ) of different defect samples showing repulsion at each crossing point of higher spin wave modes with the uniform mode. Theoretical calculations based on a model using perturbation theory [5] are accompanied and reveal a good agreement of experiment and theory. Applying the external field parallel to the axis of the stripe’s edge, the f (H ) measurement of the FMR signal reveals one single FMR mode, referred to as the Kittel mode, equal to the one of unperturbed films. Since in this orientation magnetization aligns parallel to the stripe axis, there are no dipolar fields present to generate a coupling between several magnons. By a field rotation towards the axis perpendicular to the stripes, the TMS is switched on and multiple resonance modes can be observed with a culminating mode splitting at a field direction perpendicular to the stripe axis. The f (H ) mode spectra of Sample 1 (for details see Table I) for several in-plane field angles were measured to show the gradual development of TMS-induced mode splitting and are accompanied by theoretical calculations. The angular dependent measurement of the same sample for a fixed frequency of 15 GHz can be found in Fig. 1. To study the impact of the defect depth on the resonance mode positions, the resonance spectra f (H ) perpendicular to the stripe axis were analyzed for all samples shown in Table I. Again, the available theoretical model was used to explain the observed mode structures. For a precise determination of the dispersion relation of the magnons in such systems, BLS measurements have been performed showing a good Agreement to the theoretically predicted band structure.
  • Poster
    IEEE International Magnetics Conference - Intermag 2014, 08.05.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20497
Publ.-Id: 20497


Vacancy type defect formation in irradiated α-iron investigated by positron beam Doppler broadening technique

He, C. W.; Dawi, K.; Platteau, C.; Barthe, M. F.; Desgardin, P.; Akhmadaliev, S.
Vacancy type defects formations have been investigated in virgin and irradiated a-iron samples using slow positron beam Doppler broadening technique.
Mono-vacancies and vacancy clusters are observed in 1.5 MeV 4He ions irradiated Fe samples at varying fluences from 1×1013 to 1×1017 cm-2.
In the 1.2 MeV Yttrium ions implantation at low fluence 1×1014 cm-2 vacancy clusters with higher concentration and larger size are formed.
In this sample, vacancy defects are detected deeper than predicted by SRIM calculation due to channelling.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20496
Publ.-Id: 20496


Ion Beam Induced Periodic Surface Defects: The Transi- tion from a Thin Film to a Magnonic Crystal

Langer, M.; Gallardo, R.; Banholzer, A.; Jansen, A.; Schneider, T.; Wagner, K.; Demidov, V.; Demokirtov, S. O.; Landeros, P.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
Periodic arrays of magnetic stripe defects are fabricated by Cr+ ion implantation on a 30 nm permalloy lm. Modifying the mean ion penetration depth, the defect height can be controlled, which allows an investigation of the gradual transition from a magnetic thin lm towards a magnonic crystal.
Spin wave dispersion and two-magnon scattering are studied using brillouin light scattering (BLS) as well as broadband ferromagnetic resonance (FMR). The obtained results are corroborated by theoretical calculations based on a perturbation theory.
Keywords: Magnonics, Magnonic Crystals, Magnetization Dynamics, Spin Waves, Magnons, Ferromagnetic Resonance
  • Poster
    DPG Spring Meeting 2014, 04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20495
Publ.-Id: 20495


Uranium Contents in Plants and Mushrooms Grown on a Uranium Mining Waste Tip Site in Former Eastern Germany

Baumann, N.; Arnold, T.; Haferburg, G.
There were extensive uranium mining-activities in former Eastern Germany in 1945 to 1990, with ecological consequences, like districts with U contaminated grounds. U concentrations in plants, and mushrooms, grown on a test site within a U-contaminated area in Eastern Thuringia, were analyzed. This test site is situated on the ground of a former U mine waste leaching heap. For determination of the U concentrations, the saps of the samples were squeezed out by an ultracentrifuge; after that, the U concentrations in the saps and in the remaining residues were measured by ICP-MS. The study showed that U concentrations observed in plant compartment and mushroom sap samples were always higher than in their associated solid residues. Also, it was found that the detected U concentrations in the root samples were always higher than those in their associated above ground biomass. But, the U concentrations in plants and mushrooms were always lower than in the associated surface and soil waters. This study confirmed that the amount of extracted U from plants and mushrooms is insufficient comparing to the U contaminated in soil and water. Thus these results indicated that none of the plant and mushroom species turned out to be a hyper-accumulator for U. In addition, it was found that the detected U concentrations in the sap samples, proved to be too low - in combination with the presence of fluorescence quenching substances, e.g., Fe and Mn, and/or organic quenchers - to extract a useful fluorescence signal, which could have helped to identify the uranium speciation in plants.
Keywords: uranium, TRLFS, heavy metal-contaminated soil, phytoremediation
  • Lecture (Conference)
    International Nuclear Science and Technology Conference 2014 (INST 2014), 28.-30.08.2014, Bangkok, Thailand
  • Contribution to proceedings
    International Nuclear Science and Technology Conference 2014 (INST 2014), 28.-30.08.2014, Bangkok, Thailand

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20494
Publ.-Id: 20494


Microorganisms and their impact on radionuclide speciation

Moll, H.; Cherkouk, A.
Microorganisms are ubiquitous in the environment. Hence, for the long-term safety assessment of a nuclear waste repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay) and how these microorganisms can influence the performance of a repository. The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock for nuclear waste disposal [1]. It is well known that indigenous bacteria in such underground environments can affect the speciation and the mobility of actinides [2-5].
From our point of view, the understanding of the speciation and the structure of the actinide (An)/lanthanide (Ln) complexes formed in presence of indigenous bacteria over a wide range of geochemical parameters (e.g., pH, metal concentration) becomes indispensable for predicting the safety of a planned nuclear waste repository.
Our research is focused on broaden the knowledge concerning the bacterial diversity in potential host rocks for nuclear waste storage (e.g., Mont Terri Opalinus Clay) by applying direct molecular culture-independent retrievals and cultivation experiments. After cultivation and characterization of dominant bacterial populations we investigate their influence on the geo-chemical behaviour of selected An/Ln (uranium, plutonium, and curium/europium). The indirect (e.g., actinide mobilization by microbially produced bioligands) and direct (e.g., biosorption, bioaccumulation, biotransformation) influence of microorganisms on the speciation/migration processes of An/Ln will be highlighted during the lecture by using selected examples. This helps to understand the manifold interaction processes in such biological systems on a molecular level.

Acknowledgements. The authors thank the BMWi for financial support (contract no.: 02E9985, 02E10618 and 02E10971) and the BGR for providing the clay samples.

[1] M. Thury, P. Bossart, Eng. Geol., 52 (1999) 347-359
[2] J.R. Lloyd, G.M. Gadd, Geomicrobiol. J., 28 (2011) 383-386
[3] H. Moll, et al. Geomicrobiol. J., 30 (2013) 337-346
[4] L. Lütke, et al. Dalton Trans., 42 (2013) 6979-6988
[5] M.P. Neu, et al. Radiochim. Acta, 93 (2005) 705-714
Keywords: microorganisms, radionuclide speciation, nuclear waste disposal
  • Invited lecture (Conferences)
    8th European Summer School on supramolecular, intermolecular, interaggregate interactions and separation chemistry, 07.-09.07.2014, Bonn - Bad Godesberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20493
Publ.-Id: 20493


High conversion Th-U233 fuel cycle for current generation of PWRs

Baldova, D.; Fridman, E.
The main goal of this study is to evaluate the operational feasibility of the high conversion (HC) Th-U233 PWR core through performing the 3D fully coupled neutronic and thermal-hydraulic (T-H) analysis. The proposed HC core model consists of 193 typical 17×17 PWR fuel assemblies. Each fuel assembly is subdivided into two regions designated as seed and blanket. The central seed re-gion, which has high U233 content, serves as a neutron supplier for the peripheral blanket region. The blanket region consists mostly of Th232 and acts as a U233 breeder.
  • Contribution to proceedings
    Thorium Energy Conference THEC13, 27.-31.10.2013, CERN, Geneva, Switzerland
    Proceedings of the Thorium Energy Conference THEC13
  • Poster
    Thorium Energy Conference THEC13, 27.-31.10.2013, CERN, Geneva, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-20492
Publ.-Id: 20492


64Cu-labelled dendritic polyglycerol derivatives for biodistribution studies

Pant, K.; Steinbach, J.; Stephan, H.; Bergmann, R.; Haag, R.; Gröger, D.; Nowag, S.; Graham, B.; Spiccia, L.
Objectives
Dendritic polyglycerols (dPG) and dendritic polyglycerol sulfates (dPGS) are easily synthesized macromolecules. These polymers are highly water-soluble, biocompatible, practically non-toxic and non-immunogenic. Hence, these properties make them highly interesting for application in biomedicine and offers excellent prospects for the development of new non-invasive strategies for the diagnosis and treatment of diseases. dPGS have already been developed as fully synthetic heparin analogues that show anti-inflammatory properties and accumulation in tumor tissue, which makes them promising agents for therapeutic applications. Since information about the biodistribution and the metabolism of dPGS in living systems is quite scarce, one approach is to radiolabel them so as to be able to track them with, for example, positron emission tomography (PET). 64Cu has suitable decay characteristics that allow for PET imaging and a variety of chelator systems are available for attachment to these macromolecules using appropriate anchor groups. Herein, we report the conjugation of bifunctional chelating agents based on bis(2-pyridylmethyl)triaza-cyclononane [DMPTACN] onto the dPG/dPGS scaffolds. The structure of DMPTACN allows for the introduction of various functional groups, such as carboxylic, maleimide or isothiocyanate groups, for coupling to various functional groups
(amino and mercapto surface groups) on the dPG derivatives. 64Cu-labeling experiments and stability studies of the resulting radiocopper complexes are presented and discussed.
Methods & materials
DMPTACN was synthesized by a 10-step process starting from diethylenetriamine to form a TACN ring containing tosyl protecting groups. After deprotection and subsequent introduction of two pendant 2-picolyl arms, coupling
groups, such as a carboxylic acid, maleimide or isothiocyanate, have been attached. The dPG and dPGS samples can be synthesized on a kilogram scale by utilizing ring-opening and copolymerization reactions. Surface modification with
amino and mercapto groups provides the target molecules needed for attachment of copper-binding agents. After conjugation of BFCAs to the dPG/dPGS, the compounds were purified by size exclusion chromatography. 64Cu-labeling of DMPTACN-dPG(dPGS) conjugates were performed using [64Cu]CuCl2 in 0.1 M MES/NaOH buffer at a pH of 5.5 at room temperature, resulting in a radiochemical purity of higher than 95% within a few minutes. Animal experiments were carried out in male Wistar rats.
Results & conclusion
dPG and dPGS have been synthesized with various percentages of amine and mercapto functionalities capable of coupling to BFCAs based on a DMPTACN backbone with maleimide, carboxylic and isothiocyanate groups. The
conjugates can be purified by size exclusion chromatography, and have been obtained in good yields. 64Cu-labeling experiments confirmed rapid copper(II) complex formation under mild conditions. The 64Cu-labelled conjugates exhibit high in vitro stability in human serum. These probes can thus be utilized to derive quantitative distribution data in vivo. Biodistribution and pharmacokinetic properties of 64Cu-labelled dendritic polyglycerol derivatives can be conveniently studied by PET.
Financial disclosure
This work is part of a research initiative within the Helmholtz-Portfoliothema “Technologie und Medizin - Multimodale Bildgebung zur Aufklaerung des In vivo-Verhaltens von polymeren Biomaterialien”.
  • Poster
    World Conference on Regenerative Medicine, 21.-23.10.2013, Leipzig, Deutschland
  • Abstract in refereed journal
    Regenerative Medicine 8(2013)6s, 297

Permalink: https://www.hzdr.de/publications/Publ-20491
Publ.-Id: 20491


Microstructure and mechanical properties of sub-rapidly solidified Fe-18wt%Mn-C alloy strip

Song, C.; Lu, W.; Xie, K.; Zhang, Y.; Xia, W.; Han, K.; Zhai, Q.
High-Mn steels exhibit both high tensile strength and good ductility and have attracted much attention as a promising candidate for next-generation automotive steel. However, there are still problems in conventional production, such as severe slab crack and pronounced element segregation, which restrict their widespread applications. An alternative way to produce this alloy is the near net shape method under a sub-rapid solidification process. We studied the microstructure and mechanical properties of Fe-18Mn-(0.14, 0.50)C alloy thin strip produced by injecting casting at a sub-rapid solidification rate, in which the cooling rate was about 5×103K/s. The results demonstrated that the formation of cementite particles was suppressed, but apart from the γ-phase, the ε-martensite and α'-martensite also formed in the Fe-18Mn-C thin strips. The lath width of ε-martensite is lower than that of sample produced by conventional method. The mechanical properties of Fe-18Mn-0.50C surpass the Fe-18Mn-0.60C alloy steel processed by hot rolled and heat treated. This paper discusses the relationship between the microstructure and the mechanical properties of the strips.
Keywords: Mechanical property; Microstructure; Sub-rapid solidification; TWIP steel

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20490
Publ.-Id: 20490


Examination of the interaction of a halophilic Archaea with uranium regarding the long term storage of radioactive waste in rock salt

Liebe, M.; Cherkouk, A.; Stumpf, T.
For the long term storage of radioactive waste in a deep geological repository rock salt is one of the possible host rocks, next to clay and crystalline formations. To date only little is known about the microbial diversity in German rock salt and the interactions of halophilic microorganisms with radionuclides. Microorganisms indigenous to potential host rocks are able to influence the oxidation state and speciation and hence the mobility of radionuclides. Therefore, for the safety assessment of a radioactive waste disposal it is important to know what microorganisms are present in the potential host rocks (e.g. salt) and how these microorganisms can affect the performance of a repository.
The reference organism Halobacterium noricense DSM 15987 was used to investigate the interactions with uranium at high ionic strength. For instance this halophilic Archaea was found in an Austrian salt mine1 and in the halite of the Waste Isolation Pilot Plant (WIPP, Carlsbad, USA)2. The cells were incubated for 48 h with uranium concentrations between 5 - 60 μM in 3.0 M NaCl (pH 6.0, room temperature, shaking) for sorption studies. After 48 h the cells were still living when incubated with uranium concentrations up to 60 μM, which demonstrates that Halobacterium noricense can tolerate uranium concentrations up to this level. The formed uranium sorption species were examined with IR-spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Furthermore the time-depending and pH-depending biosorption of Halobacterium noricense with uranium will be presented.
1. Gruber, C.; Legat, A.; Pfaffenhuemer, M.; Radax, C.; Weidler, G.; Busse, H. J.; Stan-Lotter, H., Halobacterium noricense sp. nov., an archaeal isolate from a bore core of an alpine Permian salt deposit, classification of Halobacterium sp. NRC-1 as a strain of H. salinarum and emended description of H. salinarum. Extremophiles 2004, 8 (6), 431-439.
2. Swanson, J. S.; Reed, D. T.; Ams, D. A.; Norden, D.; Simmons, K. A., Status report on the microbial characterization of halite and groundwater samples from the WIPP. Los Alamos National Laboratory 2012.
  • Poster
    Microbiology and Infection 2014, 4. Gemeinsamer Kongress von DGHM und VAAM, 05.-08.10.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20489
Publ.-Id: 20489


High-Speed PIXE: Fast multi-elemental analysis with lateral resolution using a Colour X-Ray Camera

Buchriegler, J.; Munnik, F.; Hanf, D.; von Borany, J.; Nowak, S. H.; Scharf, O.; Ziegenrücker, R.; Merchel, S.; Renno, A. D.
A new PIXE-beamline equipped for fast, laterally resolved elemental analysis has recently been put into operation at HZDR. The system uses a full-field energy dispersive X-ray camera, the SLcam® [1,2]. It consists of a poly-capillary lens guiding the proton-induced Xray fluorescence radiation towards a pnCCD-chip with 264×264 pixels, each with an energy resolution of 156 eV (@Mn Kα). The CCD pixel size is 48×48 µm². In combination with a 1:1 X-ray lens, this results in a lateral resolution better than 100 µm with a field of view of 12×12 mm². A 6:1 X-ray lens with a field of view of 2×2 mm² and envisaged lateral resolution < 10 µm is also available.
The camera is mounted on a vacuum chamber containing a precision sample manipulator. The chamber is optimised for high throughput of large samples. A beam broadening system is needed to ensure a homogeneous illumination of the entire detection area. The installed optical microscope together with the image processing software allows correlative superimposition of the PIXE-maps with optical images or electron microprobe element distribution maps. The simultaneous measurement of a large pixel array enables a fast overview over a large region of the sample with first tentative results becoming visible almost immediately.
The new setup is mainly developed for the investigation of geological samples for resource technology research, which comprises the analysis of grain composition and intergrowths as well as the determination of trace element distributions, e.g. rare earth elements. However, the setup can be used for the analysis of every kind ofsample respecting dimensions, roughness and vacuum stability.
First results concerning lateral resolution and detection limits are encouraging. Due to the low background in the PIXE-spectra investigation of trace elements with concentrations below hundreds of µg/g is achievable. The main limitation s for the detection limits are pile-up and the small solid angle of the capillaries. Total count-rate is not a limitation due to the different readout compared to conventional detectors; therefore high beam currents of a few µA can be used.
[1] O. Scharf et al., Anal. Chem., Vol. 83, pp. 2532-2538 (2011).
[2] I. Ordavo et al., NIM A, Vol. 654, pp. 250-257 (2011).
Keywords: PIXE, lateral resolution, colour camera
  • Invited lecture (Conferences)
    8th International Symposium on BioPIXE, 15.-19.09.2014, Bled, Slovenia

Permalink: https://www.hzdr.de/publications/Publ-20488
Publ.-Id: 20488


Light element analysis and imaging using Particle Induced Gamma-ray Emission

Munnik, F.; Freiherr, C.; Renno, A.
Spatially resolved analytical methods are important in many fields of application. One area of research is the interdisciplinary field of geometallurgy, which combines geology with extractive metallurgy to explore and exploit ore bodies and extract valuable minerals. The characterisation of the chemical composition and structure of ores and intermediate products is important for the material- and energy-efficient utilization of primary and secondary resources of minerals and metals.
Information on “mineralogical light” elements, i.e. hydrogen to fluorine, is needed over a broad concentration range from traces to major elements. These elements can be a useful resource in itself, like lithium. Besides, they provide information about the genesis of e.g. ore deposits and rocks or have a strong influence on the mechanical behaviour of rocks.
The analysis of such elements, especially at the trace level, is a challenge for many standard microanalytical methods. Particle Induced Gamma-ray Emission has the advantage of 1) obtaining quantitative results without matrix-matched standards, 2) being non-destructive and 3) wide applicability. In addition, it can be combined with other ion beam analysis methods like Rutherford Backscattering Spectrometry and Particle Induced X-ray Emission, for which a new set-up has been developed (see the presentation of Josef Buchriegler).
The nuclear microprobe of the Helmholtz-Zentrum Dresden-Rossendorf has been upgraded with a Gamma-ray detector (HPGe) to facilitate the spatially-resolved analysis of light elements (lithium to phosphorus). This upgrade is presented in this work. Extensive calibrations have been performed. Next, the implementation of the analysis and imaging procedures are discussed. Finally, the first results of the application on mineralogical samples are shown.
Keywords: PIGE, light elements
  • Poster
    14th International Conference on Nuclear Microprobe Technology and Applications, 07.-11.07.2014, Padua, Italy

Permalink: https://www.hzdr.de/publications/Publ-20487
Publ.-Id: 20487


Energetics, structure, and composition of nanoclusters in oxide dispersion strengthened Fe-Cr alloys

Posselt, M.; Murali, D.
The main structural characteristic of Oxide Dispersion Strengthened (ODS) Fe-Cr alloys is the finely dispersed distribution of nm-size clusters that may contain O, Y, and Ti. Many details of the structure and composition of these nanoclusters are not yet fully understood. Numerous experiments demonstrated that number and size of the nanoclusters do not change significantly when ODS alloys are exposed to high dose irradiation and/or high temperatures. Furthermore, it was shown that the fine dispersion of the nanoclusters prevents recrystallization, i.e. the increase of grain size, which usually occurs at elevated temperatures. The extraordinary properties of the nanoclusters are deemed to be the cause of the superior high-temperature creep strength and the high radiation resistance of the ODS Fe-Cr alloys. Therefore, these materials are promising candidates for applications as structural materials in extreme environments, i.e. at high temperature and intense particle irradiation, such as in advanced nuclear fission and fusion reactors.
In this work a multiscale modeling approach is developed and successfully applied to interpret a large number of experimental data on the properties of nanoclusters in the ODS Fe-Cr alloys. Extensive first-principle calculations on embedded clusters containing few O, Y, Ti, and Cr atoms as well as vacancies are performed to obtain interaction parameters to be applied in Metropolis Monte Carlo simulations, within the framework of a rigid lattice model. A novel description using both pair and triple parameters is shown to be more precise than the commonly used pair parameterization. Simulated annealing provides comprehensive data on the energetics, structure and stoichiometry of nm-size clusters at T=0. The results are fully consistent with the experimental finding of negligible coarsening and a high dispersion of the clusters, with the observation that the presence of Ti reduces the cluster size, and with the reported radiation tolerance of the clusters. In alloys without vacancies clusters show a planar structure, whereas the presence of vacancies leads to three-dimensional configurations. Additionally, Metropolis Monte Carlo simulations are carried out at high temperature in order to investigate the dependence of nanocluster composition on temperature. A good agreement between the existing experimental data on the ratios (Y+Ti):O, Y:Ti, (Y+Cr):O, and Y:Cr, and the simulation results is found. In some cases it is even possible to draw the conclusion that the respective alloys contained a certain amount of vacancies, or that the clusters analyzed were frozen-in high-temperature configurations. The comparison of experimental data with those obtained by simulations demonstrates that the assumption of nanoclusters which are coherent with the bcc lattice of the Fe-Cr matrix leads to reasonable results.
Keywords: Monte Carlo simulations, Oxide Dispersion Strengthened Fe-Cr alloys, nanoclusters, Density Functional Theory calculations
  • Poster
    Computer Simulation of Radiation Effects in Solids 2014 (COSIRES 2014), 08.-13.06.2014, Alicante, Spain

Permalink: https://www.hzdr.de/publications/Publ-20485
Publ.-Id: 20485


Phase diagrams of MgO magnetic tunnel junctions including the perpendicular spin-transfer torque in different geometries

Bernert, K.; Sluka, V.; Fowley, C.; Lindner, J.; Fassbender, J.ORC; Deac, A. M.
We calculate the switching voltages for MgO-based magnetic tunnel junctions taking into account both the inplane and the fieldlike spin-torque terms. To this end, we analytically solve the Landau-Lifshitz-Gilbert equation for a generalized geometry. We assume that the in-plane spin-torque varies linearly with the applied voltage, while the fieldlike torque exhibits a quadratic voltage dependence. Specifically, we consider that the free layer has two generic, orthogonal anisotropy components, one of which is along the direction defined by the magnetization of the reference layer, which also serves as a polarizer. The resulting formalism is applied to three different, experimentally relevant geometries: tunnel junctions with both the free and the reference layers magnetized in the plane of the layers, junctions with fully perpendicular anisotropy, and perpendicular junctions with an additional in-plane easy axis, respectively. We find that for in-plane devices, the quadratic dependence of the fieldlike torque on the applied voltage can lead to back hopping, which remains possible if we insert an additional linear term for the bias dependence of the fieldlike spin-torque comparable to current experimental results. For perpendicular anisotropy junctions neither back hopping nor spin-transfer-driven steady-state precession are expected. An additional in-plane shape anisotropy component stabilizes canted states in tunnel junctions with perpendicular anisotropy for specific values of voltage and field. The results are consistent with numerical integration of the Landau-Lifshitz-Gilbert equation and in good agreement with recent experiments involving perpendicular magnetic anisotropy magnetic tunnel junctions.
Keywords: Spin-transfer torque, Spin transport effects, magnetic tunnel junctions, switching phase diagrams, voltage-induced magnetisation switching, back hopping

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20484
Publ.-Id: 20484


Geometric degree of non-conservativity

Lerbet, J.; Aldowaji, M.; Challamel, N.; Kirillov, O. N.; Nicot, F.; Darve, F.
This paper deals with nonconservative mechanical systems subjected to nonconservative positional forces leading to nonsymmetric tangential stiffness matrices. The geometric degree of nonconservativity of such systems is then defined as the minimal number of kinematic constraints necessary to convert the initial system into a conservative one. Finding this number and describing the set of corresponding kinematic constraints is reduced to a linear algebra problem. This index of nonconservativity is the half of the rank of the skew-symmetric part S of the stiffness matrix K that is always an even number. The set of constraints is extracted from the eigenspaces of the symmetric matrix S^2. Several examples including the well-known Ziegler column illustrate the results.
Keywords: Stability, nonconservative systems, constraints

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20483
Publ.-Id: 20483


Role of preparation and implantation-related defects for the magnetic properties of Zn0.9Co0.1O epitaxial films

Ney, V.; Lenz, K.; Ollefs, K.; Wilhelm, F.; Rogalev, A.; Ney, A.
A systematic variation of preparation conditions for epitaxial Zn0.9Co0.1O films grown by reactive magnetron sputtering on c-plane sapphire has been carried out to study the correlation of crystalline perfection with the corresponding magnetic properties. The crystalline perfection of the resulting films was found to vary over a wide range, nonetheless all samples were found to be paramagnetic. The further extent the study, three samples, which were paramagnetic in the as-grown state, were subsequently implanted using Cu, Li and Zn ions. Only Zn ion-implantation was found to slightly alter the magnetic properties at low temperatures, however, synchrotron-based techniques could not evidence the formation of a secondary, metallic Co phase. The origin of this weak, low-temperature magnetism is more likely to be carrier-mediated rather than defect-induced.
Keywords: ZnO, diluted magnetic semiconductors, ion implantation, induced magnetism

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20482
Publ.-Id: 20482


Quantitative imaging of the magnetic fields of a nano-modulated permalloy thin film by electron holography

Lenz, K.; Körner, M.; Röder, F.; Fritzsche, M.; Lindner, J.; Lichte, H.; Fassbender, J.ORC
Dipolar magnetic stray fields are the origin of most coupling and interaction effects among patterned ferromagnetic micro- and nanostructures. For example, they are the source of Neel coupling in trilayer films with orange-peel-type or modulated interfaces [1], they are responsible for two-magnon scattering in ultrathin films [2] or uniaxial magnetic anisotropy, and many other effects. Although intuitively clear and easy to grasp the detailed magnetic configuration of nanostructured films is not easy to detect. Micromagnetic simulations are a possible method to calculate the stray fields and magnetic configuration. However, they results relies on the exact modeling of the magnetic structure and knowledge of sample parameters.
Off-axis electron holography (EH) using a transmission electron microscope (TEM) is the method of choice to image the magnetization and stray field of a ferromagnetic sample directly. Moreover it allows a quantitative analysis compared to conventional imaging of magnetic domains. Modern aberration corrected TEMs provide enough resolution to image the stray fields even of nanostructures.
In our work we have investigated those stray fields as well as the magnetic state of a thin permalloy film deposited on a rippled Si template quantitatively.
The rippled Si template was prepared by Xe+ ion beam erosion of a Si substrate under an oblique angle of 65°. The ion beam energy determines the period of the ripples, which was selected such to yield ripples with a periodicity of about 220 nm. A 30 nm thick Permalloy (Ni81Fe19) film with a 3 nm Cr cap layer was subsequently evaporated onto this template [4]. The film follows the morphology of the template as cross-checked by atomic force microscopy before and after deposition. From this sample a cross-section lamella was cut out and subsequently thinned to below 100 nm using a focused ion beam system for the transmission electron holography imaging. The geometry for the micromagnetic simulations was taken from the conventional TEM images.
The cross-sectional electron holographic measurements yield the electric and magnetic phase images [3]. The magnetic phase image allows to determine the local orientation of the magnetization inside the permalloy film (see Fig. 1). The magnetization follows nearly perfectly the surface modulation of the film with a saturation magnetization of roughly 1000 mT. Regarding the magnetic stray field outside the film the micromagnetic simulation shows the periodic change due to rising and falling ripple slopes in good agreement with the holographic images.
The resulting dipolar stray fields are around 10-20 mT [5].
Keywords: ferromagnetism, ripples, electron holography, nanostructures
  • Lecture (Conference)
    IEEE International Magnetics Conference 2014, 08.05.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20481
Publ.-Id: 20481


Electroluminescent properties of Tb-doped carbon-enriched silicon oxide

Tiagulskyi, S. I.; Nazarov, A. N.; Gordienko, S. O.; Vasin, A. V.; Rusavsky, A. V.; Rebohle, L.; Voelskow, M.; Skorupa, W.
An electroluminescent device utilizing a heterostructure of amorphous Terbium doped carbon-rich SiOx (a - SiOx : C : Tb) on silicon has been developed. The a - SiOx : C : Tb active layer was formed by RF magnetron sputtering of a - SiO1–x : Cx : H(:Tb) film followed by high-temperature oxidation. It was shown that, depending on the polarity of the applied voltage, the electroluminescence is either green or white, which can be attributed to different mechanisms of current transport through the oxide film – space charge limited bipolar double injection current for green electroluminescence and trap assisted tunneling or Fowler-Nordheim tunneling for White electroluminescence.
Keywords: electroluminescence, a-SiO:C/Si heterostructure, Tb, RF magnetron sputtering, charge transport mechanisms
  • Open Access Logo Semiconductor Physics, Quantum Electronics & Optoelectronics 17(2014)1, 34-40

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20480
Publ.-Id: 20480


Recent advances in the study of the UO2–PuO2 phase diagram at high temperatures

Böhler, R.; Welland, M. J.; Prieur, D.; Cakir, P.; Vitova, T.; Pruessmann, T.; Pidchenko, I.; Hennig, C.; Guéneau, C.; Konings, R. J. M.; Manara, D.
Recently, novel container-less laser heating experimental data have been published on the melting behaviour of pure PuO2 and PuO2-rich compositions in the uranium dioxide–plutonium dioxide system. Such data showed that previous data obtained by more traditional furnace heating techniques were affected by extensive interaction between the sample and its containment. It is therefore paramount to check whether data so far used by nuclear engineers for the uranium-rich side of the pseudo-binary dioxide system can be confirmed or not. In the present work, new data are presented both in the UO2-rich part of the phase diagram, most interesting for the uranium–plutonium dioxide based nuclear fuel safety, and in the PuO2 side. The new results confirm earlier furnace heating data in the uranium-dioxide rich part of the phase diagram, and more recent laser-heating data in the plutonium-dioxide side of the system. As a consequence, it is also confirmed that a minimum melting point must exist in the UO2–PuO2 system, at a composition between x(PuO2) = 0.4 and x(PuO2) = 0.7 and 2900 K 6 T 6 3000 K. Taking into account that, especially at high temperature, oxygen chemistry has an effect on the reported Phase boundary uncertainties, the current results should be projected in the ternary U–Pu–O system. This aspect has been extensively studied here by X-ray diffraction and X-ray absorption spectroscopy. The current results suggest that uncertainty bands related to oxygen behaviour in the equilibria between condensed phases and gas should not significantly affect the qualitative trend of the current solid–liquid phase boundaries
Keywords: EXAFS PuO2

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20479
Publ.-Id: 20479


Natural Distribution of Heavy Metals in Wetlands - Evaluation of Sources and Processes

Franzen, C.
kein Abstract vorhanden
  • Lecture (others)
    Lecture at North-West University, 28.08.2014, Vanderbijlpark, South Africa

Permalink: https://www.hzdr.de/publications/Publ-20478
Publ.-Id: 20478


Berufsfelder in den Geowissenschaften - Als Mineralogin in der Endlagerforschung

Franzen, C.
kein Abstract vorhanden
Keywords: -
  • Lecture (others)
    Berufsfelder in den Geowissenschaften, 23.06.2014, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20477
Publ.-Id: 20477


Electrophysical and Structure-Sensitive Properties of liquid Ga-In Alloys

Plevachuk, Y.; Sklyarchuk, V.; Shevchenko, N.; Eckert, S.
The broad interest in the thermophysical properties of gallium-based melts is stimulated by their extensive use in various applications, such as sliding contacts, heat-sensitive elements of liquid-metal thermometers and thermocouples, carrier liquid for electrically conducting magnetic fluids and the working medium for physical modeling in solidification and magnetohydrodynamic studies. The electrical conductivity, thermal conductivity, viscosity, density and thermoelectric power were determined for different alloy compositions in a wide temperature range below and above the liquidus temperature. Respective scaling relations are proposed. A comparison with data available in the literature is given.
Keywords: Liquid metal; Gallium--indium; Thermophysical properties

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20476
Publ.-Id: 20476


Innovative Methoden in der Bionanotechnologie – Die Quarzkristallmikrowaage (QCM-D)

Suhr, M.
Funktionsprinzip und Modellierungsansätze der QCM-D.
Anwendungsmöglichkeiten und Grenzen der QCM-D.
Nutzung der QCM-D in der ressourcenökologischen Forschung.
Keywords: QCM-D, AFM, Biosorption, Metalle
  • Lecture (others)
    Umweltkolloquium der Fakultät Maschinenbau/ Verfahrenstechnik, Studiengang Chemieingenieurwesen, 20.05.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20475
Publ.-Id: 20475


A comparison of the structural changes and optical properties of LiNbO3, Al2O3 and ZnO after Er+ ion implantation

Mackova, A.; Malinsky, P.; Pupikova, H.; Nekvindova, P.; Cajzl, J.; Svecova, B.; Oswald, J.; Wilhelm, R. A.; Kolitsch, A.
This paper reports on the structural as well as compositional changes of LiNbO3, Al2O3 and ZnO crystals, implanted with Er+ ions at 190 keV a with fluence of 1.0 × 1016 cm−2 into the <0001> crystallographic cuts. Post-implantation annealing at 1000 °C in oxygen atmosphere was also done. The chemical compositions and erbium concentration-depth profiles of implanted layers were studied by Rutherford Backscattering Spectrometry (RBS) and compared to SRIM simulations. The same value of the maximum erbium concentration (up to 2 at.%) was observed at a depth of about 40 nm for all crystals. The structural properties of the prepared layers were characterised by RBS/channelling. The relative numbers of disordered atoms in the prepared implanted layers were compared with each other and discussed for various crystals. It has been found that erbium is located in LiNbO3 and in Al2O3 preferably in interstitial positions, unlike ZnO, where the largest amount of erbium (about 83%) is placed in substitutional positions after the implantation. The erbium position in the host matrix was substantially influenced by the annealing procedure. In ZnO, after the annealing, the erbium amount in substitutional positions significantly decreased; in LiNbO3 and Al2O3 the increase of erbium in substitutional positions was observed simultaneously with the improvement of the quality of the reconstructed host matrix. Since we are interested in the relationship between structural changes and optical properties, the erbium luminescence properties were measured in the region of wavelength 1440–1650 nm for all crystals. After ion implantation LiNbO3 samples had zero luminescence intensity, while ZnO and Al2O3 samples had one significant luminescence band at 1537 and 1530 nm, respectively. The annealing improved the luminescent properties significantly in all investigated crystalline materials.
Keywords: Er ion implantation; Crystals; Depth profiles; RBS; RBS/channelling; Photoluminescence

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20474
Publ.-Id: 20474


Verification of the spectral history correction method with fully coupled Monte Carlo code BGCORE

Bilodid, Y.; Fridman, E.; Kotlyar, D.; Margulis, M.; Shwageraus, E.
Recently, a new method for accounting for burnup history effects on few-group cross sections was developed and implemented in the reactor dynamic code DYN3D. The method relies on the tracking of the local Pu-239 density which serves as an indicator of burnup spectral history. The validity of the method was demonstrated in PWR and VVER applications. However, the spectrum variation in BWR core is more pronounced due to the stronger coolant density change. Therefore, the purpose of the current work is to further investigate the applicability of the method to BWR analysis. The proposed methodology was verified against recently developed BGCore system, which couples Monte Carlo neutron transport with depletion and thermal hydraulic solvers and thus capable of providing a reference solution for 3D simulations. The results clearly show that neglecting the spectral history effects leads to a very large deviation (e.g. 2000 pcm in reactivity) from the reference solution. However, a very good agreement between DYN3D and BGCore is observed (on the order of 200 pcm in reactivity), when the Pu-correction method is applied.
Keywords: history effects, spectral history, DYN3D, BGCore, Monte-Carlo
  • Contribution to proceedings
    PHYSOR 2014, 28.09.-03.10.2014, Kyoto, Japan
    Proceedings of the PHYSOR 2014
  • Lecture (Conference)
    PHYSOR 2014, 02.10.2014, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-20473
Publ.-Id: 20473


Investigation of spark plasma sintered oxide-dispersion strengthened steels by means of small-angle neutron scattering

Hilger, I.; Bergner, F.; Ulbricht, A.; Wagner, A.; Weißgärber, T.; Kieback, B.; Heintze, C.; Dewhurst, C. D.
Spark plasma sintering (SPS) is an advanced consolidation technique, which particularly allows coarsening of the microstructure to be limited. The basis for the characteristics of the strengthening nanofeatures is already set in the milling process preceding SPS. The present study is focused on the dependence of the size distribution and nature of the nanofeatures in an ODS Fe-14Cr-1W-0.4Ti alloy as a function of the applied milling parameters and amount of added yttria while keeping the SPS parameters constant. Statistically reliable averages of the particle characteristics representative of a macroscopic sample volume have been obtained by means of small-angle neutron scattering (SANS). The measured magnetic-to-nuclear scattering ratios have been critically compared to values calculated on the basis of structures and compositions reported in the literature. Milling parameters suitable to completely transform the added yttria into Ti-containg nm-sized oxide particles have been identified. Two size ranges of particles have been analyzed separately: 0.5 to 3 nm and 3 to 15 nm (radius). The former size range is dominant in all ODS samples, the magnetic-to-nuclear scattering ratio indicates these particles to be predominantly Y2Ti2O7.
Keywords: ODS, oxide dispersion strengthened steel, nuclear materials, Fe-14Cr, small-angle neutron scattering, SANS, spark plasma sintering, SPS, nano particles

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20472
Publ.-Id: 20472


Test of Compton camera components for prompt gamma imaging at the ELBE bremsstrahlung beam

Hueso-González, F.; Golnik, C.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Heidel, K.; Kormoll, T.; Rohling, H.; Schöne, S.; Schwengner, R.; Wagner, A.; Pausch, G.
In the context of ion beam therapy, particle range verification is a major challenge for the quality assurance of the treatment. One approach is the measurement of the prompt gamma rays resulting from the tissue irradiation. A Compton camera based on several position sensitive gamma ray detectors, together with an imaging algorithm, is expected to reconstruct the prompt gamma ray emission density map, which is correlated with the dose distribution. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a Compton camera setup is being developed consisting of two scatter planes: two CdZnTe (CZT) cross strip detectors, and an absorber consisting of one Lu2SiO5 (LSO) block detector. The data acquisition is based on VME electronics and handled by software developed on the ROOT framework.

The setup has been tested at the linear electron accelerator ELBE at HZDR, which is used in this experiment to produce bunched bremsstrahlung photons with up to 12.5 MeV energy and a repetition rate of 13 MHz. Their spectrum has similarities with the shape expected from prompt gamma rays in the clinical environment, and the flux is also bunched with the accelerator frequency.

The charge sharing effect of the CZT detector is studied qualitatively for different energy ranges. The LSO detector pixel discrimination resolution is analyzed and it shows a trend to improve for high energy depositions.

The time correlation between the pulsed prompt photons and the measured detector signals, to be used for background suppression, exhibits a time resolution of 3 ns FWHM for the CZT detector and of 2 ns for the LSO detector. A time walk correction and pixel-wise calibration is applied for the LSO detector, whose resolution improves up to 630 ps. In conclusion, the detector setup is suitable for time-resolved background suppression in pulsed clinical particle accelerators. Ongoing tasks are the quantitative comparison with simulations and the test of imaging algorithms. Experiments at proton accelerators have also been performed and are currently under analysis.
Keywords: Compton imaging Instrumentation for hadron therapy

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20471
Publ.-Id: 20471


S-layer proteins as an immobilization matrix for aptamers on different sensor surfaces

Weinert, U.; Vogel, M.; Reinemann, C.; Strehlitz, B.; Pollmann, K.; Raff, J.
In this work, S-layer proteins were used as an immobilization matrix to link aptamers on different solid supports. In nature, S layers operate amongst others as an immobilization matrix for exoenzymes. Consequently, they provide a biocompatible environment with different kinds of chemical groups perfect for the sequential coupling of any kind of biofunctional molecules. In addition, their nanostructure ensures a regular arrangement of these biomolecules. In biosensors, different biological recognition molecules are used. In this study, aptamers were chosen as bio-receptors. Aptamers are oligonucleotide ligands that are especially selected for high-affinity binding to target molecules. Because of their small size and stability, they exhibit a high potential as biological sensing molecules. By coupling aptamers to different surfaces or combining them with other biofunctional molecules, target binding can be detected for example optically or gravimetrically. In this work, a thrombin-binding aptamer and an ofloxacin-binding aptamer were immobilized by different chemical crosslinkers to surfaces modified with S-layer proteins. To verify the functionality of immobilized aptamers, the aptamer-target-binding was proven by Laser Induced Fluorescence Spectroscopy (LIFS), a Resonant Mirror Sensor (IAsys) and a Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D), respectively. Due to their properties of building up a physiological environment on their surface, their high content of modifiable functional groups on their surface and their ability to crystallize in a nanometer thick monolayer on surfaces, S-layer proteins are suitable as biotemplates for various recognition biomolecules like enzymes, antibodies and aptamers. Hence, this paper presents with S-layer proteins an interesting alternative to existing immobilization matrices for recognition biomolecules.
Keywords: S-layer, aptamer, QCM-D, Resonant mirror sensor, LIFS

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20470
Publ.-Id: 20470


The nature of chemical bonding in actinide and lanthanide ferrocyanides determined by X-ray absorption spectroscopy and density functional theory

Dumas, T.; Guillaumont, D.; Fillaux, C.; Scheinost, A.; Moisy, P.; Petit, S.; Shuh, D. K.; Tyliszczak, T.; Den Auwer, C.
The electronic properties of actinide cations are of fundamental interest to describe intramolecular interactions and chemical bonding in the context of nuclear waste reprocessing or direct storage. The 5f and 6d orbitals are the first partially or totally vacant states in these elements, and the nature of the actinide ligand bonds is related to their ability to overlap with ligand orbitals. Because of its chemical and orbital selectivities, X-ray absorption spectroscopy (XAS) is an effective probe of actinide species frontier orbitals and for understanding actinide cation reactivity toward chelating ligands. The soft X-ray probes of the light elements provide better resolution than actinide L3-edges to obtain electronic information from the ligand. Thus coupling simulations to experimental soft X-ray spectral measurements and complementary quantum chemical calculations yields quantitative information on chemical bonding. In this study, soft X-ray XAS at the K-edges of C and N, and the L2,3-edges of Fe was used to investigate the electronic structures of the well-known ferrocyanide complexes K4FeII(CN)6, thorium hexacyanoferrate ThIVFeII(CN)6, and neodymium hexacyanoferrate KNdIIIFeII(CN)6. The soft X-ray spectra were simulated based on quantum chemical calculations. Our results highlight the orbital overlapping effects and atomic effective charges in the FeII(CN)6 building block. In addition to providing a detailed description of the electronic structure of the ferrocyanide complex (K4FeII(CN)6), the results strongly contribute to confirming the actinide 5f and 6d orbital oddity in comparison to lanthanide 4f and 5d.
Keywords: XANES DFT

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20469
Publ.-Id: 20469


Spectral History Modeling in the Reactor Dynamics Code DYN3D

Bilodid, Y.
A new method of treating spectral history effects in reactor core calculations was developed and verified in this dissertation. The nature of history effects is a dependence of fuel properties not only on the burnup, but also on the local spectral conditions during burnup. The basic idea of the proposed method is the use of the plutonium-239 concentration as the spectral history indicator. The method was implemented in the reactor dynamics code DYN3D and provides a correction for nodal cross sections according to the local spectral history.
A verification of the new method was performed by single-assembly calculations in comparison with results of the lattice code HELIOS. The application of plutonium-based history correction significantly improves the cross section estimation accuracy both for UOX and MOX fuel, with quadratic and hexagonal geometry.
The new method was applied to evaluate the influence of history effects on full-core calculation results. Analysis of a PWR equilibrium fuel cycle has shown a significant effect on the axial power distribution during a whole cycle, which causes axial temperature and burnup redistributions. The observed neutron flux redistribution improves neutron economy, so the fuel cycle is longer than in calculations without history corrections. Analyses of hypothetical control rod ejection accidents have shown a minor influence of history effects on the transient course and safety relevant parameters.
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-051 2014

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20468
Publ.-Id: 20468


Time-resolved laser-fluorescence spectroscopy (TRLFS) – A spectroscopic tool to investigate f-element interactions in solids and solutions on the molecular level

Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Baumann, N.; Stumpf, T.
Time-resolved laser-fluorescence spectroscopy (TRLFS) is a spectroscopic technique with outstanding sensitivity, based on the spontaneous emission of light. Spontaneous emission of light or luminescence describes the process of radiative decay where an excited substance emits electromagnetic radiation upon relaxation. Some f-elements, such as the actinides U4+, and Cm3+, and the lanthanide Eu3+, relax through intense luminescence emission from an excited f-state to the ground f-level. These f-f transitions are sensitive to changes in the ligand field, thus, making TRLFS an extremely useful tool to account for the complex speciation of these elements. Depending on the f-element, the recorded emission spectra can provide information on e.g. the complexation mechanism of the ion on a solid surface or the symmetry of the adsorption/incorporation site of the metal. Information about the hydration state of the f-element cation can be gained from the fluorescence lifetime, i.e. the residence time in the excited state. In aquatic environments f-element spectroscopy is characterized by relatively short fluorescence lifetimes due to the transfer of electronic energy from an excited f-level to the vibrational levels of water molecules in the first coordination sphere of the metal. When some of these quenching entities are lost upon inner sphere surface complexation a longer lifetime is acquired, thus, providing information on the sorption mechanism. If incorporation occurs, the complete hydration sphere is replaced by the ligands of the crystal lattice and the lifetimes become very long.

In the present work we have used site-selective TRLFS to investigate the structural incorporation of Eu3+, as an analogue for Pu3+, Am3+ and Cm3+ found in spent nuclear fuel, in rare earth phosphate ceramics. These crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes due to their stability over geological time scales [1] and their tolerance to high radiation doses [2]. The REPO4 crystallize in two distinct structures, depending on the ionic radius of the cation: the larger lanthanides (La3+ to Gd3+) crystallize in the nine-fold coordinated monazite structure, the smaller ones as Lu3+ form eight-fold coordinated xenotime structures. Here, we present results on the influence of the ionic radius of the host cation and the crystalline structure of the REPO4 on Eu3+ substitution in the ceramic.
  • Poster
    8th European Summer School on supramolecular, intermolecular, interaggregate interactions and separation chemistry, 07.-09.07.2014, Bonn - Bad Godesberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20467
Publ.-Id: 20467


P1226 - Funktionalisierte Festkörperoberflächen aus Zwei- und Mehrstoffsystemen mit Komposit-Nanostrukturen aus Metallen, Halbleitern und Isolatoren

Schmidt, H.; Bürger, D.; Skorupa, I.
Die Erfindung betrifft funktionalisierte Festkörperoberflächen mit Kompositen aus Zwei- und Mehrstoffsystemen aus Metallen, Halbleitern und Isolatoren, welche eine definierte chemische Komposition auf der Nanometer und Mikrometer-Längenskala aufweisen für neuartige Komposit-Nano- und Mikrostrukturen.
  • Patent
    DE102012221409 - Offenlegung 22.05.2014

Permalink: https://www.hzdr.de/publications/Publ-20466
Publ.-Id: 20466


Magnetization states and magnetization processes in nanostructures: From a single layer to multilayers

Maziewski, A.; Fassbender, J.ORC; Kisielewski, J.; Kisielewski, M.; Kurant, Z.; Mazalski, P.; Stobiecki, F.; Stupakiewicz, A.; Sveklo, I.; Tekielak, M.; Wawro, A.; Zablotskii, V.
The results of combined (experimental, analytical, and micromagnetic simulations) studies on the evolution of magnetization states and processes in ultrathin films and multilayered systems are presented. We show ways to manipulate magnetization distributions in ultrathin magnetic single or multilayers by tuning: the thickness of the magnetic layer, the thickness of either the non-magnetic cap or spacer layer, the magnetic anisotropy, and the geometrical constrictions of the system. In ultrathin magnetic films, both the magnetization distribution and the critical thickness of the magnetization reorientation phase transition (RPT) between perpendicular and in-plane states can be also controlled by post-growth treatments, e.g., by either ion or light irradiation. By changing the geometrical parameters of the nanostructure, as well as by an applied external magnetic field, one can tune magnetic domain sizes in a giant range (of a few orders of magnitude) and induce the RPT. Transitions between two- and three-dimensional magnetization distributions are discussed. The authors present possibilities of the engineering of magnetic properties (e.g. magnetic anisotropy and coercivity field) of nanostructures during deposition processes and post growth treatments, e.g. by ion irradiation and laser annealing. Magnetization distributions in single ultrathin layer and multilayers have been studied both experimentally (using Co films sandwiched between Au, Pt or Mo layers) and theoretically. These huge distribution changes, driven by nanostructure geometry or magnetic field, are shown.
Keywords: light and ions irradiation effects; magnetic anisotropy; magnetic domains; magnetic ordering; magnetic ultrathin films and multilayers

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20465
Publ.-Id: 20465


Study of growth kinetics and depth resolved composition of a-SiN x:H thin films by resonant soft X-ray reflectivity at the Si L 2,3-edge

Bommali, R. K.; Modi, M. H.; Zhou, S.; Ghosh, S.; Srivastava, P.
Angle dependent resonant soft X-ray reflectivity (R-SoXR) measurements in the energy range (82.67-206.7 eV) were performed on PECVD grown amorphous hydrogenated silicon nitride (a-SiNx:H) thin films of different compositions near the Si-L2,3 edge (∼100 eV). The compositional difference is reflected in the optical density (δ) of the two films. It is demonstrated that R-SoXR can non-destructively distinguish between the compositional variations through the depth of a given thin film, whereby it becomes possible to differentiate between the growth kinetics of the films prepared under different conditions. The compositions determined from R-SoXR, are in qualitative agreement with those determined from Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA).
Keywords: Optical constant; Reflectivity; Silicon nitride; Soft X-Ray; Thin film

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20464
Publ.-Id: 20464


Detecting Ferromagnetic Resonance of Single Nanostructures with the Microresonator

Banholzer, A.; Narkowicz, R.; Lenz, K.; Grebing, J.; Fassbender, J.ORC; Lindner, J.
Nowadays the magnetic characterization of nanosized objects is of major interest, as they are used in the field of nanosized magnetic recording [1] and spintronic devices. With conventional resonance methods, e.g. in an X-band cavity, the minimum number of spins, which can be detected, is about 1012 for permalloy [2]. Therefore, only large arrays of small nanoobjects can be detected. Here, the specific characteristics of small nanoobjects disappear in the averaged signal [3]. Hence, for the analysis of single nanoobjects a much higher sensitivity is required.
We developed a microresonator to measure the ferromagnetic resonance (FMR) of single nanosized objects [4], [5]. We optimized the device for different sample sizes. We show that it is possible to measure FMR on a single Cobalt nanodot with a diameter of 139 nm and 25 nm thickness. Taking the signal-to-noise ratio into account, we extrapolate the detection limit to 105 spins. Not only the uniform excitation mode, but also signals of standing spinwaves like e.g. edgemodes can be observed. Their state can be visualized and interpreted with micromagnetic simulations (OOMMF) [6]. We show results of a variety of nanosized samples and their interpretation.

REFERENCES
[1]C. T. Rettner, et. al., IEEE Trans. Magn., 38, 4 (2002).
[2] Poole, Electron Spin Resonance, New York: Wiley, (1983).
[3] J. M. Shaw, et.al., J. Appl. Phys. 108, 093922 (2010).
[4] A. Banholzer, et al., Nanotechnology 22, 295713 (2011).
[5] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).
[6] http://math.nist.gov/oommf/
Keywords: ferromagnetic resonance, nanodot
  • Poster
    IEEE International Conference on Microwave Magnetics (ICMM), 29.06.-02.07.2014, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-20463
Publ.-Id: 20463


Influence of ionic strength on U(VI) sorption on montmorillonite at high salinities

Fritsch, K.; Schmeide, K.
Clay and clay minerals are potentially suitable as host rock for nuclear waste disposals due to their high sorption capacities and low permeability. In Germany, there are two types of clay that in principle are eligible to be used for the construction of deep geological disposals: South German Opalinus clay with low ionic strength pore waters and north German clay deposits with high ionic strength pore waters, e. g. with sodium chloride concentrations of up to 4 mol/l in the depths relevant for nuclear waste disposal. [1] The present work focuses on U(VI) sorption onto the clay mineral montmorillonite under high ionic strength conditions, with the Konrad mine serving as reference site for experimental conditions. The experiments are conducted in sodium and calcium chloride as well as in a mixed electrolyte that resembles the groundwater at the Konrad site.
The classic ionic strength effect, where sorption decreases with increasing ionic strength, can only be observed in the acidic pH range where cation exchange is the predominant sorption mechanism for U(VI). However, natural groundwaters at the Konrad site have pH values from 5.75 to 6.85, where the ionic strength has an already diminished influence on sorption. The sorption maxima for U(VI) in the different salt systems lie slightly below the neutral point and well within the pH range of groundwaters of the reference site. For high ionic strengths like those in north German groundwaters, U(VI) retention becomes partly irreversible. [2] Furthermore, in the calcium chloride system, U(VI) retention increases strongly with ionic strength in the alkaline pH range. Both these effects are attributed to secondary phase formation, which is promoted by increasing ionic strength.

[1] Brewitz, W. et al. (1982) Eignungsprüfung der Schachtanlage Konrad für die Endlagerung radioaktiver Abfälle. GSF-T 136.
[2] Zehlike, L. (2013) Durchführung von Sorptions- und Desorptionsversuchen von Uran(VI) an Montmorillonit, Bachelor thesis, TU Dresden.
Keywords: uranium sorption, argillaceous rock,clay, uranium, montmorillonite, high ionic strength
  • Poster
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn-Bad Godesberg, Deutschland
  • Open Access Logo Contribution to proceedings
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn-Bad Godesberg, Deutschland
    Berichte des Forschungszentrums Jülich, Jül-4376, Institut für Energie- und Klimaforschung, Nukleare Entsorgung und Reaktorsicherheit (S. Neumeier, P. Kegler, D. Bosbach, eds.), 24

Permalink: https://www.hzdr.de/publications/Publ-20462
Publ.-Id: 20462


Montmorillonite as barrier material for uranium(VI) at high ionic strengths

Fritsch, K.; Schmeide, K.
Clay and clay minerals are potential host rocks for nuclear waste disposal due to their high sorption capacities and low permeability. Thus far, research of radionuclide retention by clays has been focused on low ionic strength systems. The present work addresses North German clay deposits whose groundwaters show ionic strengths up to 4 mol/l in depths relevant for nuclear waste disposal.[1] The experimental set-up is modelled on conditions found in the Konrad mine, which serves as reference site. Montmorillonite is used as model clay for uranium sorption and diffusion experiments in sodium and calcium chloride as well as in a mixed electrolyte that resembles the groundwater at the Konrad site.
Ionic strengths effects, where sorption decreases with increasing ionic strength, can generally only be observed in the acidic pH range because they depend on cation exchange. Natural groundwaters at the Konrad site have pH values > 5.5, where cation exchange has ceased to be the predominant sorption mechanism for U(VI), which in turn diminishes ionic strength influence. The sorption maxima in different salt systems lie slightly below the neutral point and within the pH range of groundwaters of the reference site. When approaching the ionic strength of North German groundwaters, sorption becomes partly irreversible.[2] Furthermore, uranium retention greatly increases with ionic strength in the alkaline pH range in the calcium chloride system. Both effects are attributed to secondary phase formation, which is promoted by increasing ionic strength. Additionally, spectroscopic results and surface complexation modelling of the system will be presented.
[1] Brewitz, W. et al. (1982) Eignungsprüfung der Schachtanlage Konrad für die Endlagerung radioaktiver Abfälle. GSF-T 136.
[2] Zehlike, L. (2013) Durchführung von Sorptions- und Desorptionsversuchen von Uran(VI) an Montmorillonit, Bachelor thesis, TU Dresden.
Keywords: uranium sorption, argillaceous rock,clay, uranium, montmorillonite, high ionic strength
  • Contribution to proceedings
    7th Mid-European Clay Conference, 16.-19.09.2014, Radebeul, Deutschland
    Proceedings of the 7th Mid-European Clay Conference
  • Lecture (Conference)
    7th Mid-European Clay Conference, 16.-19.09.2014, Radebeul, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20461
Publ.-Id: 20461


Gamma-ray CT for multi-phase flow investigation

Bieberle, A.; Schäfer, T.; Hampel, H.
Recently, gamma-ray computed tomography (GCT) has been established at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) for the investigation of two- or multiphase flows in technical apparatuses. The GCT systems at HZDR are operated with collimated 137Cs isotopic sources emitting gamma photons with an energy of 662 keV. This gamma radiation is able to penetrate dense housings and delivers sufficient phase contrast between, e.g., liquid and gas. The radiation detector arcs consist of in-house developed gamma-ray detector modules based on scintillation detector technology. Special effort has been spent on their thermal design. With a thermal stabilisation of better than 1 K for each detector element, a high repeat measuring accuracy could be achieved for varying environmental temperatures within a temperature range of 20 K. A current project is engaged in gas phase distribution determination within industrial centrifugal pumps at various operating states. Because the application of those pumps is limited to single liquid phase flow, gas entrainment reduces its delivery performance as well as the process efficiency. For detailed studies, a thermo hydraulic test facility was assembled at HZDR replicating authentic operating conditions for industrial centrifugal pumps. Defined gas volume fractions can be injectect in form of two different flow regimes, disperse and tubular. Thus, effects onto delivery perfomance and corresponding gas fraction distribution and gas holdup within the impeller region could be determined.
Keywords: gamma-ray computed tomography, process efficiency, centrifugal pump, gas entrainment, multi-phase flow
  • Contribution to proceedings
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea
  • Lecture (Conference)
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea

Permalink: https://www.hzdr.de/publications/Publ-20460
Publ.-Id: 20460


Hydrogen accumulation in nanostructured as compared to coarse-grained tungsten

Gonzalez-Arrabal, R.; Panizo-Laiz, M.; Gordillo, N.; Tejado, E.; Munnik, F.; Rivera, A.; Perlado, J. M.
We report on the influence of sample microstructure and of irradiation conditions on the H behaviour in Tungsten (W). For this purpose, commercial coarse grained (CGW) and nanostructured W (NW) samples were implanted with (i) H at room temperature (RT), (ii) sequentially with C and H at RT, and (iii) simultaneously (co-implanted) with C and H at RT. To study the possible effect of implantation temperature on H behaviour, a CGW sample and a NW sample were sequentially implanted with C at RT and with H at 673 K. The H and C implantation fluence was 5×1020 cm−2 and the implantation energies were 160 keV for H and 650 keV for C which are above the displacement damage threshold. Scanning electron microscopy images show that nanostructured samples consist of columns with an average diameter of about 100 nm. These nanocolumns are stable under the studied implantations conditions. Moreover, blistering is absent in all studied samples. X-ray diffraction data illustrate that all samples are mono-phase (α-W phase) and that none of the implantations led to the appearance of secondary phases. Resonant nuclear reaction analysis data show that the H retention in NW samples is larger than in CGW and that synergistic effect has a significant influence on the H retention in CGW samples but not in NW samples.
Keywords: Nanostructured materials, radiation response, hydrogen behaviour, nuclear fusion

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20459
Publ.-Id: 20459


Advanced Materials in Extreme Environments

Bertolus, M.; Chichester, H.-M.; Edmondson, P.; Gao, F.; Posselt, M.; Stanek, C.; Trocellier, P.; Zhang, X.; (Editors) Keywords: advanced materials, extreme environments
  • Contribution to proceedings
    MRS 2013 Fall Meeting, 01.-06.12.2013, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-20458
Publ.-Id: 20458


Nonlinear photoresponse of field effect transistors terahertz detectors at high irradiation intensities

But, D. B.; Drexler, C.; Sakhno, M. V.; Dyakonova, N.; Drachenko, O.; Sizov, F. F.; Gutin, A.; Ganichev, S. D.; Knap, W.
Terahertz power dependence of the photoresponse of field effect transistors, operating at frequencies from 0.1 to 3 THz for incident radiation power density up to 100 kW/cm(2) was studied for Si metal-oxide-semiconductor field-effect transistors and InGaAs high electron mobility transistors. The photoresponse increased linearly with increasing radiation intensity up to the kW/cm(2) range. Nonlinearity followed by saturation of the photoresponse was observed for all investigated field effect transistors for intensities above several kW/cm(2). The observed photoresponse nonlinearity is explained by nonlinearity and saturation of the transistor channel current. A theoretical model of terahertz field effect transistor photoresponse at high intensity was developed. The model explains quantitative experimental data both in linear and nonlinear regions. Our results show that dynamic range of field effect transistors is very high and can extend over more than six orders of magnitudes of power densities (from similar to 0.5 mW/cm(2) to similar to 5 kW/cm(2)).
Keywords: Tunneling ionization, Radiation, Fluid

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20457
Publ.-Id: 20457


Liquid metal batteries

Weier, T.; Barry, L.; Galindo, V.; Gerbeth, G.; Seilmayer, M.; Starace, M.; Stefani, F.; Weber, N.
Liquid metal batteries are discussed with a focus on the role of fluid dynamics in large-scale cells.
Keywords: Liquid metal batteries, magnetohydrodynamics, Tayler instability
  • Invited lecture (Conferences)
    IKM-Seminar, 04.06.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20456
Publ.-Id: 20456


Platinum-group element distribution in base-metal sulfides of the UG2, Bushveld Complex, South Africa – a reconnaissance study

Osbahr, I.; Oberthür, T.; Klemd, R.; Josties, A.
The UG2 chromitite of the Bushveld Complex in South Africa contains the world’s largest resources of platinum-group elements (PGE). However, only limited work has been conducted on the distribution of PGE and platinum-group minerals (PGM) within the UG2. In the present study, earlier work on the PGE distribution within the Merensky Reef (Osbahr et al. 2013) is followed up and extended to the UG2. Two drill cores of the UG2 chromitite from the eastern and western Bushveld Complex were studied by whole rock analysis, ore microscopy and SEM/MLA. The PGE, Au and Ag contents of pentlandite, pyrrhotite and chalcopyrite were determined using LA-ICP-MS analysis. Whole-rock analyses of the two profiles reveal highest Pd and Pt concentrations at the top and at the base of the UG2 main seam. Sulfides mostly occur as aggregates of pentlandite, chalcopyrite and rare pyrrhotite and pyrite or as individual grains associated mostly with chromite grains.
In-situ LA-ICP-MS analyses reveal that pentlandite carries distinctly elevated PGE contents. In contrast, pyrrhotite and chalcopyrite contain very low PGE concentrations. Pentlandite shows average maximum values of 350-1000 ppm Pd, 200 ppm Rh, 130-175 ppm Ru, 20 ppm Os and 150 ppm Ir and therefore, is the principal host of Pd and Rh in the studied ores of the UG2.
Mass balance calculations were conducted for samples representing the UG2 main seam of the drill core DT46, eastern Bushveld. Accordingly, pentlandite constantly hosts elevated contents of the whole rock Pd (up to 55 %) and Rh (up to 46 %), and erratic contents of Os (up to 50 %), Ir (2 to 17 %) and Ru (1 - 39 %). PGM investigations support these mass balance results, most of the PGM are Pt-dominant PGM like braggite/cooperite and Pt-Fe alloys or laurite, (carrying elevated concentrations of Os and Ir). Palladium and Rh-bearing PGM are rare.
PGE concentrations and their distribution in BMS in the UG2 largely resemble that of the Merensky Reef, as most of the Pd and Rh are incorporated in pentlandite whereas pyrrhotite, chalcopyrite and pyrite are almost devoid of PGE. Consequently, similar mineralization processes are responsible for the PGE enrichment in the UG2 and in the Merensky Reef.
Keywords: platinum-group elements (PGE), UG2, Bushveld Complex, South Africa, LA-ICP-MS, MLA

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20455
Publ.-Id: 20455


Repeated large-magnitude earthquakes in a tectonically active, low-strain continental interior: The northern Tien Shan, Kyrgyzstan

Landgraf, A.; Dzhumabaeva, A.; Abdrakhmatov, K. E.; Strecker, M.; Macaulay, E. A.; Arrowsmith, J. R.; Sudhaus, H.; Preusser, F.; Rugel, G.; Merchel, S.
The northern Tien Shan of Kyrgyzstan and Kazakhstan has been affected by a series of major earthquakes in the late 19th and early 20th centuries. To assess the significance of such a major pulse of strain release in a continental interior, it is important to analyze and quantify strain release over multiple time scales. We have undertaken paleoseismological investigations at two geomorphically distinct sites (Panfilovkoe and Rot Front) near the Kyrgyz capital Bishkek. Although located near the historic epicenters, both sites were not affected by these earthquakes. Trenching was accompanied by dating stratigraphy and offset surfaces using luminescence, radiocarbon, and 10Be terrestrial cosmogenic nuclide methods. At Rot Front, trenching of a small scarp did not reveal evidence for surface rupture during the last five thousand years. The scarp rather resembles an extensive debris-flow lobe. At Panfilovkoe, we estimate a late Pleistocene minimum slip rate of 0.2 +- 0.1 mm/a, averaged over at least two, probably three earthquake cycles. Dip-slip motion along segmented, moderately steep faults resulted in hanging-wall collapse scarps during different events. The most recent earth quake occurred around 1.8 +- 0.2 kyr ago (1 sigma), with dip-slip off sets between 1.2 and 1.4 m. We calculate a probabilistic paleomagnitude to be between 6.7 and 7.1, which is in agreement with regional data from the Kyrgyz range. The morphotectonic signals in the northern Tien Shan are a prime example of deformation in a tectonically active intracontinental mountain belt and as such can help understand the longer-term co-evolution of topography and seismogenic processes in similar structural settings worldwide.
Keywords: earthquake, paleoseismic record, Tien Shan, Kyrgyzstan, TCN, accelerator mass spectrometry, cosmogenic nuclide

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20454
Publ.-Id: 20454


Actinide(IV) colloids at near-neutral pH due to reaction with dissolved silicic acid

Zänker, H.; Weiss, S.; Hennig, C.; Husar, R.
A new type of actinide(IV) colloids - silica-containing U(IV), Th(IV) and Np(IV) colloids formed in near-neutral solutions of background chemicals of geogenic nature (carbonate, silicic acid, Na+) - was studied. Whereas the radiocolloids hitherto addressed in the BELBaR project are formed by the adsorption of radionuclides onto pre-existing particles, the colloids here under discussion result from a reaction of dissolved actinide(IV), An(IV), with dissolved silicic acid. An-O-Si bonds, which increasingly replace the An-O-An bonds of the amorphous actinide(IV) oxyhydroxide with increasing silica concentration, make up the internal structure of these colloids. The particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) and a particle size of < 20 nm was observed. The question if such An(IV) colloids may contribute to the mobility of the actinides in the near-field or the far-field of a nuclear waste repository is discussed.
Keywords: Tetravalent actinides, silicic acid, silica, colloids, nanoparticle, nuclear waste repositories, BELBaR
  • Lecture (Conference)
    2nd Annual Workshop CP BELBaR (Bentonite erosion effects on the long term performance of the engineered barrier and radionuclide transport), 16.-18.06.2014, Meiringen, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-20453
Publ.-Id: 20453


P1227 - Verfahren zur kostengünstigeren Herstellung von Silizium Solarzellen, und mit diesem Verfahren hergestellte Solarzellen

Prucnal, S.; Voelskow, M.; Skorupa, W.
Die Erfindung beschreibt ein einfaches und vor allem kostengünstiges und damit umweltverträgliches Verfahren zur Herstellung von Solarzellen auf der Basis von Silizium, basierend auf einem einzigen, kurzen Millisekunden-Ausheilschritt unter Verwendung der effektiven Plasma-Immersions-Ion-Implantations-Technologie (PIII). Dadurch wird der Energie- und Zeitaufwand und damit die Kosten zur Herstellung einer Silizium-Solarzelle drastisch reduziert werden.
  • Patent
    DE102012221811 - Offenlegung 28.05.2014

Permalink: https://www.hzdr.de/publications/Publ-20452
Publ.-Id: 20452


The influence of naturally occurring microorganisms on the sorption of uranium

Richter, C.
The influence of naturally occurring microorganisms on the sorption of uranium, the Institute of Resource Ecology and the WEIMAR-project were presented.
  • Lecture (others)
    LLNL intern seminar, 23.-24.06.2014, Livermore, USA

Permalink: https://www.hzdr.de/publications/Publ-20451
Publ.-Id: 20451


The Influence of Mineral-Originated Microorganisms on the Sorption of Uranium

Richter, C.; Großmann, K.; Brendler, V.
Experiments on commercially available quartz, orthoclase and muscovite showed the presence of microorganisms in these minerals. So the question arose, if and how these microbes affect the sorption of uranium onto them.

Experimental work
To promote the bacterial growth 0.2 g of the minerals were incubated with 10 ml of two different culture media (NB and R2A). Directly after adding the culture media and after three weeks shaking in an incubator at 30°C, the optical density at 600 nm (OD600) was measured.
To estimate the influence of the microorganisms on the uranium sorption, batch experiments were performed under conditions inhibiting growth, e.g. darkness, autoclaving; use of laminar flow boxes; or addition of sodium azide. The amount of uranium sorbed at pH 7 was determined by ICP-MS.

Results
All three minerals show an increase in OD600 during incubation. This increase varies for the three minerals and two nutrients, pointing to different microbial communities.
The batch experiments indicate that the various treatments clearly affect the microbial influence on uranium sorption. In the case of orthoclase, the biggest change is induced by the sodium azide treatment. For quartz, the use of laminar flow boxes has the largest consequences. But in both cases the changes have the same direction: destroying the microbes also stops them actively suppressing uranium sorption. In case of muscovite, the combination of autoclaving, laminar flow box and darkness affects sorption the most – but in the opposite direction. Here, the microbes obviously enhance sorption (dead or alive).
This findings show that on the three investigated minerals different microorganisms are present, and that their effect is difficult to predict. Thus, a separate investigation of microbial effects is recommended for each mineral. In addition, any autoclaving may directly change the mineral surface, e.g. by creating new or altering existing sorption sites.
  • Poster
    Goldschmidt 2014, 09.-13.06.2014, Sacramento, USA

Permalink: https://www.hzdr.de/publications/Publ-20450
Publ.-Id: 20450


Euler-Euler Scale-Adaptive Simulation of a square cross-sectional bubble column

Ma, T.; Lucas, D.; Fröhlich, J.; Ziegenhein, T.
In this paper we present detailed Euler-Euler Scale-Adaptive Simulation (SAS) of dispersed bubbly flow in a square cross-sectioned bubble column. The main objective of this study is to investigate potential of this approach for the prediction of the bubbly flows with anisotropic liquid velocity fluctuations, in terms of mean quantities. The set of physical models describing the momentum exchange between the phases was chosen according to previous experiences of the authors. Experimental data, Euler-Euler Large Eddy Simulation (LES) are used for comparison. It was found that the presented modelling combination provides very good agreement with experimental data for the mean flow and liquid velocity fluctuations. The energy spectrum made from the resolved velocity from Euler-Euler SAS and LES is presented and discussed.
  • Contribution to proceedings
    10th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements, 17.-19.09.2014, Marbella, Spain
  • Lecture (Conference)
    10th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements, 17.-19.09.2014, Marbella, Spain
  • Chemical Engineering Science 131(2015), 101-108
    DOI: 10.1016/j.ces.2015.03.047

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20449
Publ.-Id: 20449


Euler-Euler Large Eddy Simulations for dispersed bubbly flows

Ma, T.; Ziegenhein, T.; Lucas, D.; Krepper, E.; Fröhlich, J.
A bubble column provides a good experimental system for the study of turbulent phenomena in bubbly flows. It has a wide range of length and time scales on which turbulent mixing takes place. The largest turbulence scales are comparable in size to the characteristic length of the mean flow and depend on reactor geometry and boundary conditions. The small scales depend more on the bubble dynamics and hence are proportional to the bubble diameter. In bubbly flows, the small scales are responsible for the dissipation of the turbulent kinetic energy as in single-phase flow, but the bubbles can also generate back-scatter, i.e. energy transfer from smaller to larger scales. The combination of the both effects and yields an overall enhancement or attenuation of the turbulence intensity.
In the present paper the effect of turbulence modelling is investigated. In the CFD simulations of bubble columns RANS models are used for turbulence modeling traditionally, but the turbulence is modeled only isotropic and without resolved turbulence length scales. Large Eddy Simulation (LES) offers the opportunity to resolve the large-scale anisotropic turbulence directly and to model the small scales with a Subgrid-Scale (SGS) model. The filtering is mostly based directly on the grid width.
In the present work, Euler – Euler modelling of bubbly flow is performed using two types of turbulence modelling, (unsteady) RANS and LES. The simulations are carried out for two rectangular bubble columns with different inlet designs, the ones of (Pfleger et al. 1999) and (Akbar et al. 2012) and compared with the respective experimental data and previous own results of URANS simulations. During all the calculations the bubble coalescence and breakup are neglected. For the Akbar experiment with a low gas superficial velocity, the bubble size distribution is assumed to be monodispersed. The bubbles induced turbulence is dominant in this case. For such a case, LES may not represent the best option for turbulence prediction, since the largest fluctuations are close to the bubble surface and cannot be resolved, but instead are modeled with a very simple SGS model. However, good results are obtained in the same experiment with a much higher gas superficial velocity, since large-scale turbulence is present and mostly resolved. For the other configuration, LES shows a more plausible amplitude and period in liquid velocity fluctuation in the measure point than the results of URANS. The SGS turbulent kinetic energy will also be considered using two methods of estimation for zero-equation SGS models to improve the prediction.
  • Contribution to proceedings
    CFD4NRS-5 - Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, 09.-11.09.2014, Zürich, Schweiz
  • Lecture (Conference)
    CFD4NRS-5 - Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, 09.-11.09.2014, Zürich, Schweiz
  • International Journal of Heat and Fluid Flow 56(2015), 51-59
    DOI: 10.1016/j.ijheatfluidflow.2015.06.009

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20448
Publ.-Id: 20448


Large Eddy Simulation for a rectangular bubble column

Ma, T.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.; Krepper, E.
In vielen verfahrenstechnischen Apparaten wird mit Mehrphasenströmungen gearbeitet, bei denen eine kontinuierliche Flüssigkeitsphase und eine disperse gasförmige Phase vorliegen. Die Turbulenz in der Flüssigkeitsphase ist ein wichtiges Phänomen in Mehrphasenströmungen. Sie hat einen starken Einfluss auf die lokale Verteilung der dispersen Phasen.
Eine Blasensäule stellt eine gute Experimentiereinrichtung für die Untersuchung von turbulenten Phänomen in Mehrphasenströmungen dar. In den CFD Simulationen für Blasensäulen werden traditionell RANS Modelle zur Turbulenzmodellierung verwendet, allerdings wird die Turbulenz nur isotrop modelliert.
LES bietet die Möglichkeit die großskaligen anisotropen Turbulenzen direkt aufzulösen und die kleinskaligen mit einem Subgrid-Scale (SGS) Model zu modellieren. Die Filterung basiert meistens direkt auf der Gitterweite. In dieser Arbeit wird die Euler-Euler Large Eddy Simulation (LES) für eine rechteckige Blasensäule durchgeführt und mit experimentellen Daten von (Akbar 2012) verglichen. Der Euler-Euler Ansatz verlangt eine Gitterweite größer als die Blasengröße, sodass die Gitterweite in den LES Rechnungen für Blasenströmungen in der Meso-Skala bzw. im Blasengrößen Bereich liegt. Für Blasenströmungen mit geringen Leerrohrgeschwindigkeiten ist die Blasen induzierte Turbulenz dominant. Für solche Fälle stellt die LES nicht die optimale Option zur Turbulenzvorhersage dar. Die Ursache besteht darin, dass die größte Fluktuation in der Nähe der Blasenoberfläche liegt und zum Großteil nicht aufgelöst, sondern mit einem sehr einfachen SGS Modell modelliert wird. Hingegen werden für die Blasenströmung mit höheren Leerrohrgeschwindigkeiten gute Ergebnisse erzielt, da großskalige Turbulenzen vorhanden und aufgelöst werden. In der Auswertung wird die SGS turbulente kinetische Energie mit zwei Methoden zur Abschätzung ebenfalls berücksichtigt.


[Akbar 2012] Akbar MHM, Hayashi K, Hosokawa S, Tomiyama A. Bubble tracking Simulation of Bubble-induced Pseudo Turbulence. 6th Japanese-European Two-Phase Flow Group Meeting, 2012
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics, Mischvorgänge und Rheologie, 24.-25.02.2014, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20447
Publ.-Id: 20447


Novel wire-mesh sensor for visualization of threephase flows

E., S.; M., S.; R., M.; S., R.; E., S.; U., H.
For the investigation of three-phase flows, for instance as commonly found in oil and gas production, there are only few suitable measuring techniques. For this reason, in this paper a new multichannel complex impedance measuring system using wire-mesh sensors is presented. The system measures amplitude and phase componets of impedance (at single frequency) and is thus able to determine simultaneously the conductive and the capacitive parts of a fluid (complex permittivity). In the future this system can be employed for the investigation of dynamic processes in multiphase flow. The performance in measuring the complex permittivity is evaluated. First promising results for the three-phase flow are presented
Keywords: Complex impedance measurement, multiphase flow, wire-mesh sensor
  • Contribution to proceedings
    15th Brazilian Congress of Thermal Sciences and Engineering, November 10-13, 2014, Belém, PA, Brazil, 10.-13.11.2014, Belém, Brazil
    Proceedings of ENCIT 2014: ABCM
  • Lecture (Conference)
    15th Brazilian Congress of Thermal Sciences and Engineering, November 10-13, 2014, Belém, PA, Brazil, 10.-13.11.2014, Belém, Brazil, 10.-13.11.2014, Belém, Brasilien

Permalink: https://www.hzdr.de/publications/Publ-20446
Publ.-Id: 20446


Transient simulation for large scale flow in bubble columns

Ziegenhein, T.; Rzehak, R.; Lucas, D.
The transient simulation of large scale bubbly flow in bubble columns using the unsteady Reynolds averaged Navier Stockes (URANS) equations is investigated in the present paper. An extensive set of bubble forces is used with different models for the bubble induced turbulence. Criteria are given to assess the independence of the simulation time and the time step length. Using these criteria it is shown that a simulation time, time step length and mesh independent solution can be obtained for complex bubbly flows using URANS equations under certain requirements. With the obtained setup the contribution of the resolved turbulence to the total turbulence and the influence of the bubble induced turbulence modeling on the resolved turbulence is investigated. Further, it is pointed out that the virtual mass force is not negligible. The simulations are compared to data from the literature at two different superficial velocities, which cover monodisperse and polydisperse bubbly flows.
Keywords: bubble columns, bubble induced turbulence, transient multiphase flow, Euler-Euler modeling, CFD simulation, model validation

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20445
Publ.-Id: 20445


Turbulence modeling of polydispersed bubbly flow for large scale applications

Ziegenhein, T.; Rzehak, R.; Lucas, D.
Aeration of reactors is a wide used concept in biotechnology and chemical engineering to intensify processes. Beside enlarging the interface between liquid and gas phase, enhancement of mixing plays an important role. Turbulence affects these processes strongly. It is a main parameter for mixing and an important parameter for coalescence and break up processes.
Two main turbulence scales can be identified in bubbly flows. The small scale depends on the bubble itself and has a length scale in the magnitude of the bubble diameter. The large scale depends on the reactor geometry and has a length scale in the magnitude of the reactor. To characterize aerated Systems both scales are vital, but the modeling is difficult because of the multiscale problem.
A concept to describe both scales based on Euler-Euler unsteady RANS simulation with a two equation turbulence model is shown. The small scales are modeled with a new bubble induced turbulence model [Rzehak 2013][Ziegenhein 2013] and the large scales are directly computed. The contribution of the modeled and the directly computed turbulence to the total turbulence is shown and discussed on the bases of experimental data.
The aim of this approach is to model a complete reactor. The results can be used to formulate dispersion models for the specific reactor geometry, to support compartment modeling or to simulate different operating modes directly with CFD.

[Rzehak 2013] R. Rzehak and E. Krepper CFD modeling of bubble-induced turbulence, International Journal of Multiphase Flow 2013, 55, 138–155.
[Ziegenhein 2013] T. Ziegenhein, D. Lucas, R. Rzehak, E. Krepper Closure relations for CFD simulation of bubble columns, In proceeding of: International Conference on Multiphase Flow, Jeju, Korea, Volume: 8th
Keywords: Bubble column, two-fluid model, bubble forces, bubble induced turbulence, turbulence, multiscale modeling
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics, Mischvorgänge und Rheologie, 24.-26.02.2014, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20444
Publ.-Id: 20444


The electroluminescence of Er-implanted MOS structures with different silicon oxide and silicon nitride environments

Rebohle, L.; Wutzler, R.; Braun, M.; Helm, M.; Skorupa, W.; Berencén, Y.; Garrido, B.; Hiller, D.
Er-based, electrically driven light emitters, which can easily be integrated into Si-based circuitries, are of great interest for a broad range of applications, especially in the field of telecommunication and sensing. This work investigates the electrical and electroluminescence (EL) properties of Er-implanted MOS structures with different designs of the dielectric stack. The dielectric stack is essentially composed of a 30 nm thick SiO2 layer and a 40 nm thick host matrix for the Er ions made of Si-rich SiO2, silicon nitride or Si-rich silicon nitride. All structures implanted with Er show intense EL around 1550 nm which is excited by impact excitation of hot electrons. We compare the different host matrices regarding the EL efficiency, the EL excitation cross section, the EL decay time, the fraction of excited Er ions, the EL quenching cross section and the operation lifetime. This comparison reveals fundamental properties of the EL mechanism and addresses the current problems of this type of Si-based light emitter to achieve the performance level of compound semiconductors with a direct bandgap.
Keywords: Electroluminescence, rare earth, MOS structure, decay time
  • Lecture (Conference)
    E-MRS Spring Meeting 2014, 26.-30.05.2014, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-20443
Publ.-Id: 20443


Nanocrystallisation of III-V compound semiconductors in Si by ion beam implantation and thermal annealing

Wutzler, R.; Rebohle, L.; Prucnal, S.; Bregolin, F.; Helm, M.; Skorupa, W.
III-V integration into Si is a milestone in the future development of micro- and optoelectronics. Based on SiO2 capped silicon and silicon-on-insulator (SOI) substrates, we fabricated various III-V compound semiconductor nanocrystals (NCs) in Si by high fluence ion beam implantation and short-time annealing. Due to implantation, the surrounding Si material is amorphized. Recrystallization and III-V NC growth by liquid phase epitaxy are achieved through millisecond flash lamp annealing (FLA). By using lithographically patterned cover layers during implantation we were able to obtain single-crystalline GaAs, GaP, InAs, and InP NCs at defined positions.

For the investigation of the microstructure, transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM) and Rutherford Backscattering (RBS) spectroscopy have been performed. Raman measurements confirmed the formation of III-V NCs within the recrystallized Si matrix; TEM images show distinct, single-crystalline NCs of various shapes. Depending on the processing conditions, shape and size range from large dome-like structures over spherical precipitates to nano-pyramids. AFM and RBS were used to control and monitor the fabrication process.
Keywords: Ion Implantation, Flash Lamp Annealing, III-V integration, SOI, heterojunction
  • Lecture (Conference)
    E-MRS 2014 Spring Meeting, 26.-30.05.2014, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-20442
Publ.-Id: 20442


Instabilities of rotational flows in azimuthal magnetic fields of arbitrary radial dependence

Kirillov, O.; Stefani, F.; Fukumoto, Y.
Using the Wentzel–Kramers–Brillouin (WKB) approximation we perform a linear stability analysis for a rotational flow of a viscous and electrically conducting fluid in an external azimuthal magnetic field that has an arbitrary radial profile Bφ(R). In the inductionless approximation, we find the growth rate of the three-dimensional perturbation in a closed form and demonstrate in particular that it can be positive when the velocity profile is Keplerian and the magnetic field profile is slightly shallower than 1/R.
Keywords: Asymptotic methods, stability, magnetohydrodynamics, magnetorotational instability, azimuthal field

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20441
Publ.-Id: 20441


Retention of selenium by cementitious materials under reducing radioactive waste repository conditions

Rojo, H.; Tits, J.; Scheinost, A. C.; Wieland, E.
Cementitious materials play a crucial role as barrier for radionuclide transport in low and intermediate level radioactive waste repositories, where 79Se is an important redox-sensitive and dose-determining radionuclide. In current sorption databases for the cementitious near-field, only sorption data for Se(IV/VI) have been considered. Robust sorption data on reduced Se species in general, and a sufficiently detailed mechanistic understanding of their retention in cementitious environment are, however, lacking.
The aim of this work is to investigate the immobilisation of Se under the reducing conditions existing in a cement-based, deep-underground repository (-230mV < Eh < -750 mV). Under these conditions, Se(IV) and Se(-II) are the dominant redox states. We obtained Se(-II) by electrochemical reduction of Se(IV) in solution. Completion of the reduction process was determined by UV-vis spectroscopy. Se(IV) and Se(-II) sorption kinetic studies were carried out on various synthetic cement components, such as calcium silicate hydrates (C-S-H) and hydrated calcium aluminates (AFm), the principal host phases for radionuclides in hydrated cement. In addition, Se(IV) and Se(-II) sorption experiments were performed with TiO2 as reference solid, stable under alkaline conditions, at pH = 10.0 and 13.3, in the absence and presence of 10-3 M Ca. XANES studies allowed the determination of the redox state of sorbed selenium.
The sorption tests revealed that the uptake of Se(IV) by C-S-H phases is much stronger than expected. Rd values measured on C-S-H phases are approximately two orders of magnitude higher than Rd values measured on TiO2. This high affinity of the C-S-H phases for Se(IV) anions is partially explained by the high specific surface area of these solids. Furthermore, Rd values for Se(IV) on various AFm phases are correlated with their interlayer spacing. The sorption of Se(-II) on the different cementitious materials was found to be weaker than the sorption of Se(IV).
Keywords: XANES, selenium, cement, radioactive waste disposal
  • Poster
    Goldschmidt 2014, 08.-13.06.2014, Sacramento, USA

Permalink: https://www.hzdr.de/publications/Publ-20440
Publ.-Id: 20440


Synthesis of calix[4]arene-based polycarboxylate ligands and their chemical immobilization onto controlled-pore glass

Haupt, S.; Handke, M.; Kuhnert, R.; Poetsch, M.; Kersting, B.
Three new calix[4]arene-based carboxylate ligands with an appended allyl function have been synthesized, chemically immobilized onto a controlled-pore glass (CPG), and the extracting ability of selected materials towards Sr2+ in solid-liquid extraction was examined.
The calixarenes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopy, and where appropriate by X-ray crystallography. Four functionalized CPGs were prepared by radical thiol addition of the corresponding 5-allylcalix[4]arenes to γ-mercaptopropyl-modified CPG. Analysis by 13C and 29Si cross polarization/magic angle spinning (CP/MAS) NMR spectroscopy clearly showed the covalent fixation of the calix[4]arenes to CPG. The calix[4]arene phases were found to be stable up to 200° C by simultaneous thermal analysis (STA). The extraction performance of the modified CPGs towards Sr2+ were found to be superior over the unmodified CPGs as demonstrated by radiotracing using the short-lived radio nuclide 85Sr.
Keywords: calix[4]arene, controlled-pore glass, CP/MAS NMR, solid-liquid extraction, strontium

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20437
Publ.-Id: 20437


Low-temperature transport properties of Si and Ge films with Ga-rich nanoprecipitates

Heera, V.; Fiedler, J.; Skrotzki, R.; Naumann, M.; Herrmannsdörfer, T.; Skorupa, W.
Ga-rich (~ 10 at.%) Si and Ge films were fabricated by high-fluence Ga+ ion implantation through a SiO2 capping layer. The structure and the electrical transport properties of these films have been studied after flash-lamp [1-3] and rapid thermal annealing [4, 5]. Amorphous, Ga-rich nanoprecipitates are embedded in a heavily p-type doped semiconductor matrix [3, 4].
These nanoprecipitates become superconducting below critical temperatures up to 7 K. They can interact due to the proximity effect in the degenerately doped semiconductor matrix and form a random network of Josephson junctions. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. In particular, Ga-rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance [6, 7] .
The possibility to prepare and modify Ga-rich Si and Ge films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices.

[1] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, et al., Phys. Rev. Lett.,2009, 102, 217003.
[2] R. Skrotzki, T. Herrmannsdörfer, V. Heera, J. Fiedler, et. al., Low Temp. Phys., 2011, 37, 1098.
[3] V. Heera, J. Fiedler, M. Naumann, R. Skrotzki, et al., Supercond. Sci. Technol., 2014, 27, 055025.
[4] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2011, 83, 214504.
[5] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2012, 85, 134530.
[6] V. Heera, J. Fiedler, M. Voelskow, A. Mücklich, et al., Appl. Phys. Lett., 2012, 100, 262602
[7] V. Heera, J. Fiedler, R. Hübner, B. Schmidt, et al., New. J. Phys., 2013, 15, 083022
Keywords: Low-temperature transport, Si and Ge films, Ga implantation, Ga nanopreciptates, superconductor-insulator transition
  • Lecture (Conference)
    Workshop "Ionenstrahlen und Nanostrukturen" Paderborn 2014, 20.-22.07.2014, Paderborn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20436
Publ.-Id: 20436


The relevance of melt convection to grain refinement in Al-Si alloys solidified under the impact of electric currents

Räbiger, D.; Zhang, Y.; Galindo, V.; Franke, S.; Willers, B.; Eckert, S.
The present paper considers the directional solidification of Al-7wt%Si alloys under the influence of strong electric currents for the configuration of two parallel electrodes immersed from the free surface into the solidifying alloy. Solidification experiments were performed under the influence of both direct currents (DC) and rectangular electric current pulses (ECP). The interaction between the applied current and its own induced magnetic field causes a Lorentz force which produces an electro-vortex flow covering the entire melt area. Numerical simulations of the magnetohydrodynamic (MHD) problem were conducted to calculate the Lorentz force, the Joule heating and the induced melt flow. The numerical predictions were confirmed by isothermal flow measurements in eutectic Ga-20wt%In-12wt%Sn. The application of the electric current during solidification leads to the formation of refined equiaxed grain structures. There are no remarkable differences with respect to the influence of DC or ECP treatment on the mean grain size and the area of equiaxed zone in the solidified samples provided the effective values of the current strength are identical. The results demonstrate that the grain refining effect observed in our experiments can be ascribed solely to the forced melt flow driven by the Lorentz force.
Keywords: Al-Si alloys, solidification, melt convection, grain refinement

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20435
Publ.-Id: 20435


P1316 - Anordnung zur Kontaktierung eines CZT-Kristalls für das Detektormodul einer Compton-Kamera

Heidel, K.; Sobiella, M.; Dersch, U.; Berthel, M.; Golnik, C.
Offenbart wird die Kontaktierung eines quaderförmigen CZT-Kristalls zur Detektierung von Gammastrahlung in einer Compton-Kamera, wobei der CZT-Kristall eine der einfallenden Strahlung zugewandte, vollflächige Vorderseitenelektrode und auf der der Vorderseite gegenüberliegenden Rückseite mehrere, voneinander beabstandete rechteckige und als Elektroden ausgeführte Pixelflächen aufweist, wobei die zu den Pixelflächen komplementären Anschlussflächen eines oder mehrerer Flachbandkabel mit diesen Pixelflächen elektrisch leitfähig mittels eines leitfähigen Klebstoffs verbunden sind.
  • Patent
    DE102013210082 - Erteilung 15.05.2014

Permalink: https://www.hzdr.de/publications/Publ-20434
Publ.-Id: 20434


Compact Optical Free Electron Laser with Traveling-Wave Thomson Scattering

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Schramm, U.; Widera, R.
We present a fully analytical description of the field and the electrons in an optical free electron laser in the Travelling-Wave Thomson Scattering (TWTS) configuration. This scheme allows for long interaction lengths of an ultra-short, high-intensity pulsed laser with an electron bunch. The latter can be either provided by laser-accelerated electrons or by a conventional accelerator. TWTS provides for high peak brightness, high brilliance pulses from the EUV to the gamma spectrum with high flexibility in the wavelength and bandwidth of the emitted radiation.
Keywords: X-ray, optical FEL, traveling-wave, Thomson scattering
  • Lecture (Conference)
    DPG Frühjahrstagung Dresden 2014, 30.03.-05.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20432
Publ.-Id: 20432


Scaling of Optical Free-Electron Lasers in Traveling-Wave Geometries

Steiniger, K.; Debus, A.; Bussmann, M.; Sauerbrey, R.
Optical free electron lasers in the X-ray range using high power lasers are difficult to realize in the standard head-on Thomson-scattering geometry. Problems arise from the nonlinear Thomson intensity threshold and the Rayleigh-length limiting the interaction distance which prevent the SASE process to occur.

These limits can be circumvented in a Travelling-wave Thomson-scattering (TWTS) geometry, in which ultrashort and narrow-band light pulses in the X-Ray region of the spectrum are created by scattering high intensity laser pulses from relativistic electron bunches. TWTS uses lasers with a pulse front tilt in a sidescattering geometry to scale the interaction length into the centimeter to meter range with undulator periods in the region of one hundred to a few hundred micrometer.

Starting from a fully 3D, wave-optical representation of the TWTS pulse, including its dispersion properties, we present a self-consistent 1.5D FEL-theory which accounts for the coupling of the obliquely incident laser pulse to the electron dynamics. Furthermore, we give scaling laws on the interaction geometry and FEL-amplification with respect to incidence angle and electron beam parameters. Using these findings we discuss possible experimental scenarios and its requirements on laser pulses and electron beams.
Keywords: Optical FEL, Traveling-wave, thomson-scattering, X-ray
  • Lecture (Conference)
    DPG Frühjarstagung Berlin 2014, 17.-21.03.2014, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-20431
Publ.-Id: 20431


Two Years Experience with the upgraded ELBE RF-System driven by 20 kW Solid State Amplifier Blocks

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.
Since January 2012 the Superconducting CW Linac ELBE is equipped and in permanent operation with four 20 kW Solid State Amplifier Blocks. The poster gives an overview on the design of the new RF system and the experience gained within the first two years of operation.
Keywords: Solid State Power Amplifiers, Superconducting RF, ELBE-RF System
  • Poster
    IPAC 2014 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland
  • Open Access Logo Contribution to proceedings
    IPAC 2014 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland
    Proceedings of IPAC'14, CERN: JaCoW, MOPME067

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20430
Publ.-Id: 20430


Status and Operating Experience of the ELBE RF System based on 10kW SSPAs

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntsch, M.; Lehnert, U.; Michel, P.; Staats, G.; Teichert, J.; Schurig, R.
In January 2012 the 10 kW klystrons of the CW LINAC ELBE were replaced by pairs of 10kW solid state power amplifiers (SSPA).
The talk gives an overview on the SSPA based ELBE RF system. The experience gained during the first two years of operation is reviewed.
Keywords: SSPA, Solid State Power Amplifier, Superconducting Radio Frequency , Superconducting LINAC, RF-System for Particle Accelerators, 1.3GHz Power Aplifier
  • Lecture (Conference)
    Continuous Wave and High Power RF Workshop 2014 (CWRF2014), 13.-16.05.2014, Trieste, Italy

Permalink: https://www.hzdr.de/publications/Publ-20429
Publ.-Id: 20429


Process-Based Forward Numerical Modelling SIMSAFADIM-CLASTIC: The Vilomara Composite Sequence case

Clavera-Gispert, R.; Gratacós, O.; López-Blanco, M.; Tolosana-Delgado, R.
SIMSAFADIM-CLASTIC is a 3D process-based forward numerical model that simulates the stratigraphic infill and evolution of a marine sedimentary basin (Bitzer and Salas, 2001, 2002; Gratacós et al., 2009a, 2009b; Carmona et al., 2010; Clavera et al., 2013). The program is designed to model processes of transport and sedimentation for clastic terrigenous and clastic carbonate sediments. The program, also include the interaction between carbonate producing organisms and clastic sediments in suspension. Considering that, the objective of the program is to model and to represent the spatial and temporal interplay of the generated sedimentary bodies, obtaining realistic depositional architectures in order to reproduce the 3D sediment distribution and the complex heterogeneity present in the sedimentary record.

The model for siliciclastic transport and sedimentation is based on a potential fluid flow. This fluid flow model can establish the general trend of the flow system to determine the sediment transport in the basin over a geological time scale at basin scale (hundred meters to kilometres) with an acceptable computational time. Regarding to the sediment transport, the fluid flow model can determine the movement of solid particles in suspension due to fluid movement processes that include advection, diffusion, and dispersion. The carbonate production model is based in the generalized equation of Lotka-Volterra ecological modelling. The program takes into account the influence of environmental factors to model the carbonate producing organisms associations (water depth, nutrients, clastic sediment concentration is suspension, fluid flow velocity and bottom slope), and the interaction among them (predation, prey, mutualism, competition...). Other processes are modelled to generate (or reduce) accommodation space in the marine basin, including sea level variations, compaction, and isostasy.

In order to show the application and possibilities of the code, the Vilomara Composite Sequence (VCS) of Sant Llorenç del Munt (SLM) fan delta complex (NE Iberian Peninsula) is modelled.
  • Contribution to proceedings
    GeoMod, 31.08.-05.09.2014, Potsdam, Deutschland
    Proceedings of GeoMod2014 - Modelling in Geosciences: Programme and Extended Abstracts, 80-83
    DOI: 10.2312/GFZ.geomod.2014.001

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20428
Publ.-Id: 20428


Analysis of self‑assembly of S‑layer protein slp‑B53 from Lysinibacillus sphaericus

Liu, J.; Falke, S.; Drobot, B.; Oberthuer, D.; Kikhney, A.; Guenther, T.; Fahmy, K.; Svergun, D.; Betzel, C.; Raff, J.
The formation of stable and functional surface layers (S-layers) via self-assembly of surface-layer proteins on the cell surface is a dynamic and complex process. S-layers facilitate a number of important biological functions, e.g., providing protection and mediating selective exchange of molecules and thereby functioning as molecular sieves. Furthermore, S-layers selectively bind several metal ions including uranium, palladium, gold, and europium, some of them with high affinity. Most current research on surface layers focuses on investigating crystalline arrays of protein subunits in Archaea and bacteria. In this work, several complementary analytical techniques and methods have been applied to examine structure–function relationships and dynamics for assembly of S-layer protein slp-B53 from Lysinibacillus sphaericus: (1) The secondary structure of the S-layer protein was analyzed by circular dichroism spectroscopy; (2) Small-angle X-ray scattering was applied to gain insights into the three-dimensional structure in solution; (3) The interaction with bivalent cations was followed by differential scanning calorimetry; (4) The dynamics and time-dependent assembly of S-layers were followed by applying dynamic light scattering; (5) The two-dimensional structure of the paracrystalline S-layer lattice was examined by atomic force microscopy. The data obtained provide essential structural insights into the mechanism of S-layer self-assembly, particularly with respect to binding of bivalent cations, i.e., Mg2+ and Ca2+. Furthermore, the results obtained highlight potential applications of S-layers in the fields of micromaterials and nanobiotechnology by providing engineered or individual symmetric thin protein layers, e.g., for protective, antimicrobial, or otherwise functionalized surfaces.
Keywords: Surface-layer protein, Self-assembly, Bivalent cations, AFM, DSC, SAXS

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-20427
Publ.-Id: 20427


P1303 - Bauteil mit metallhaltiger, selbstorganisierter Schicht, Verfahren zu dessen Herstellung sowie Verwendung

Raff, J.; Günther, T.; Wengrzik, S.
Die Erfindung beschreibt ein Bauteil, welches eine nicht-leitende Oberfläche aufweist und mit einer selbstorganisierten Schicht sowie einer metallischen Deckschicht versehen ist. Die Erfindung beschreibt ferner ein kostengünstiges und industriell serientaugliches Verfahren zur Herstellung eines solchen Bauteils sowie die Verwendung eines solchen Bauteils als Ersatz von metallischen Bauteilen in Fahrzeugen, Haushaltsgeräten, Sanitärausstattungen sowie als gedruckte elektronische Schaltung.
In dem erfindungsgemäßen Verfahren wird die nicht-leitende Oberfläche eines Substrates mit einem Katalysator belegt, anschließend mit einer Poren enthaltenden, selbstorganisierten Schicht belegt und schließlich in einem chemischen Metallisierungsbad mit Metallen beschichtet, wobei das Metallisierungsbad die poröse selbstorganisierte Schicht durchdringt und dadurch auf der nicht-leitende Oberfläche besser mechanisch verankert wird als nach dem Stand der Technik.
Das erfindungsgemäße Bauteil wird bevorzugt hergestellt mit dem erfindungsgemäßen Verfahren und enthält:
a. eine nicht-leitende Oberfläche,
b. auf der Katalysatorpartikel aufgebracht sind
c. wobei auf und um die Katalysatorpartikel eine Poren enthaltende, selbstorganisierte Schicht aufgebracht ist,
d. wobei die selbstorganisierte Schicht mit Metallen beschichtet ist, wobei die aufgebrachte Metallschicht die Poren der selbstorganisierten Schicht durchdringt.
  • Patent
    DE102013208395 - Erteilung 12.05.2014, Nachanmeldung: WO

Permalink: https://www.hzdr.de/publications/Publ-20426
Publ.-Id: 20426


Nuclear deformation and neutron excess as competing effects for the pygmy dipole strength

Massarczyk, R.; Schwengner, R.; Dönau, F.; Frauendorf, S.
The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A = 124, 128, 132, and 134 in nuclear resonance fluorescence experiments using the ELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.
Keywords: nuclear structure, pygmy strength, photo-absorption, photo-nuclear experiments
  • Lecture (Conference)
    11th INTERNATIONAL SPRING SEMINAR ON NUCLEAR PHYSICS, 12.-16.05.2014, Ischia, Italien
  • Lecture (others)
    Seminar on Nuclear Deformation / telphone presentation, 20.05.2014, Los Alamos, USA

Permalink: https://www.hzdr.de/publications/Publ-20424
Publ.-Id: 20424


Resource potential of REE as by-product of an existing mining operation – A geometallurgical assessment

Birtel, S.; Kern, M.; Höfig, T. W.; Krause, J.; Gutzmer, J.
A systematic geometallurgical study of the rare earth mineralogy and beneficiation potential as by-product was performed, based on a currently operating flow sheet of an existing large-scale industrial mining and beneficiation operation. For this purpose, a representative suite of samples was collected from a single mining block prior to blasting. The material derived from this mining block was then tracked through beneficiation by comminution and a sequence of flotation steps. Samples were collected at all crucial steps of the beneficiation plant. Whole rock geochemical analyses and quantitative mineralogical and microstructural analyses (by MLA), complemented by mineral chemistry data for relevant REE minerals, were obtained for a suite of more than 60 samples. These data were then used to assess the deportment of REE and to track the route of REE-minerals within the beneficiation process.
Apatite was found to be the most important primary host mineral for REE. Postdepositional alteration evidently led to the breakdown of apatite, resulting in the formation of microcrystalline xenotime and monazite of secondary origin. The latter are the two most abundant rare earth minerals identified in the mining block studied. Additionally identified rare earth minerals occur only in minor or trace amounts. Other minerals were found to contribute only limited amounts to the total REE content of the ore.
Process samples from the flotation circuit illustrate that the material from the cleaner circuit tailing, being usually considered as waste, is strongly enriched in monazite and xenotime, i.e., the two most common REE minerals. The REE minerals are well liberated, thus leading to the conclusion that it may be feasible to produce REE minerals as a future by-product by only slight modification of the current flow sheet.
Keywords: geometallurgy, REE, process optimization
  • Contribution to proceedings
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft, 21.-24.09.2014, Jena, Deutschland
    Minerals at Focal Point, 126
  • Poster
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft, 21.-24.09.2014, Jena, Deutschland

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20423
Publ.-Id: 20423


Towards a novel THz-based monitor for sub picosecond electron bunches working at MHz repetition rates and low bunch charges

Gensch, M.; Green, B.; Kovalev, S.; Kuntzsch, M.; Golz, T.; Stojanovic, N.; Fisher, A.
The control and measurement of electron bunch properties at the femtosecond (fs) level has become an important field in modern accelerator physics, in particular since these became crucial parameters for the operation of 4th Generation X-ray Light-sources. In order to operate modern-day photon factories such as LCLS and the future European X-FEL reliably, a number of novel approaches have been developed that allow the noninvasive measurement of electron bunch form and arrival time. Some of those are based on the electro-optic detection of the coulomb field of the electron bunches in the electron beamline; some detect the super-radiant THz pulses from the electron bunch. However, none of these concepts allows for pulse-to-pulse detection on a quasi-CW accelerator operating at the MHz repetition rates planned for the next generation of X-ray free electron lasers. In this contribution we present first results from a new monitor concept, based on the single-shot electro-optic detection of super-radiant THz pulses, that has the potential to operate at MHz repetition rates.
  • Poster
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA

Permalink: https://www.hzdr.de/publications/Publ-20422
Publ.-Id: 20422


Ионный синтез нанокристаллов InSb в захороненном слое SiO2 структуры кремний-на-изоляторе
Ion-beam synthesis of InSb nanocrystals in the buried SiO2 layer of a silicon-on-insulator structure

in Russian
Tyschenko, I. E.; Voelskow, M.; Tscherkov, A. G.; Popov, V. P.
Исследован ионный синтез нанокристаллов InSb в слое захороненного SiO2 структуры кремний-на-изоляторе. Изучены профили распределения атомов индия и сурьмы после отжига при температуре Ta = 500−1100◦C. Установлено, что перераспределение имплантированных атомов имеет немонотонный характер в зависимости от температуры отжига. Формирование нанокристаллов InSb происходит при Ta ≥ 800◦C вблизи границы Si/SiO2 и на глубине средних пробегов Rp. Анализ профилей имплантированных атомов и структуры и распределения по глубине формирующихся нанокристаллов позволил сделать предположение о двухстадийном характере образования фазы InSb: на первой стадии происходит формирование преципитатов сурьмы, которые играют роль зародышей для дальнейшего стока на них атомов In и Sb.

The ion-beam synthesis of InSb nanocrystals in the buried SiO2 layer of a silicon-on-insulator structure is investigated. The distributions of In and Sb atoms after annealing at a temperature of T a = 500–1100°C are studied. It is established that the redistribution of implanted atoms is unsteadily dependent on the annealing temperature. The formation of InSb nanocrystals occurs at Ta ≥ 800°C near the Si/SiO2 interface and at a depth corresponding to the mean paths R p . Analysis of the profiles of implanted atoms and of the structure and depth distribution of nanocrystals formed allows an inference regarding the two-stage character of formation of the InSb phase. In the initial stage, antimony precipitates are formed; further the precipitates serve as nuclei for indium and antimony to flow to them.
Keywords: Ion beam Synthesis, InSb, SOI, RBS
  • Fizika i Tekhnika Poluprovodnikov 48(2014)9, 1228-1233
  • Semiconductors 48(2014)9, 1196-1201

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20421
Publ.-Id: 20421


Enhanced wear resistance of high-speed steel by pulsed electron-beam melting

Ivanov, Y.; Matz, W.; Rotshtein, V.; Guenzel, V.; Shevchenko, N.
  • Contribution to proceedings
    3rd International Conference on Surface Engineering, 09.-11.03.1993, Bremen, Germany
    Contributions of surface engineering to modern manufacturing and remanufacturing, Chengdu, China: Southwest Jiaotong University Press, 7810576615, 397-402

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20420
Publ.-Id: 20420


Ion beam synthesis by tungsten implantation into 6H-silicon carbide at elevated temperatures

Weishart, H.; Matz, W.; Skorupa, W.
  • Contribution to proceedings
    1995 MRS Fall Meeting & Exhibit, 27.11.-1.12.1995, Massachusetts, USA
    MRS Symposium Proceedings Series: III-Nitride, SiC, and Diamond Materials for Electronic Devices: Cambridge University Press, 9781558993266, 195-200

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-20419
Publ.-Id: 20419


Electron bunch form monitoring at quasi-cw SRF accelerators: Status at the ELBE accelerator

Gensch, M.; Green, B.; Hauser, J.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Golz, T.; Stojanovic, N.; Mueller, A. S.; Schwarz, M.; Fisher, A. S.; Neumann, N.; Plettemeier, D.; Bauer, C.
In the past few years the quasi-cw SRF electron accelerator ELBE has been upgraded so that it now allows to compress electron bunches to the sub-picosecond regime at repetition rates of up to 13 MHz and bunch charges up to 100 pC. The actual optimization and control of the electron bunch form represents one of the largest challenges of the coming years at ELBE. In particular with respect to the midterm goal to utilize the ultra-short electron bunches for Laser-Thomson scattering experiments or high field THz experiments. Since 2012, the ELBE accelerator, together with its recently established super-radiant THz facility TELBE serves as a unique test facility for the development of novel diagnostic for quasi-cw electron beams. In this contribution different diagnostic approaches for the online determination of the electron bunch form are presented. The results of the different techniques, ranging from adapted classical laser-based and interferometer-based concepts to novel on-chip THz spectrometers are compared. The merits of the different concepts: e.g. pulse to pulse diagnostics at few 100 kHz repetition rates or a sensitivity for charges down to the few 100 femto coulomb regime are discussed based on the results of recent commissioning campaigns by a multi-institutional collaboration. A careful analysis of simultaneous measurements with the different techniques allows an educated guess for the presently shortest electron bunch duration achieved at ELBE of 1.2 ps (FWHM). It is also shown that interferometric concepts at this moderately short bunch durations systematically underestimate the bunch length due to diffraction effects at low THz frequencies.
  • Poster
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA

Permalink: https://www.hzdr.de/publications/Publ-20418
Publ.-Id: 20418


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]