Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

European activities on crosscutting thermal-hydraulic phenomena for innovative nuclear systems

Cheng, X.; Batta, A.; Bandini, G.; Roelofs, F.; van Tichelen, K.; Gerschenfeld, A.; Prasser, M.; Papukchiev, A.; Hampel, U.; Ma, W. M.

Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. In Europe, a consortium is established consisting of 24 institutions of universities, research centers and nuclear industries with the main objectives to identify and to perform research activities on important crosscutting thermal-hydraulic issues encountered in various innovative nuclear systems. For this purpose the large-scale integrated research project THINS (Thermal-Hydraulics of Innovative Nuclear Systems) is launched in the 7th Framework Programme FP7 of European Union. The main topics considered in the THINS project are (a) advanced reactor core thermal-hydraulics, (b) single phase mixed convection, (c) single phase turbulence, (d) multiphase flow, and (e) numerical code coupling and qualification. The main objectives of the project are:
Generation of a data base for the development and validation of new models and codes describing the selected crosscutting thermal-hydraulic phenomena.
Development of new physical models and modeling approaches for more accurate description of the crosscutting thermal-hydraulic phenomena.
Improvement of the numerical engineering tools for the design analysis of the innovative nuclear systems.
This paper describes the technical tasks and methodologies applied to achieve the objectives. Main results achieved so far are summarized.

Publ.-Id: 22269

Hyperspectral remote sensing for mineral mapping of structural related mineralizations around Mount Isa, Queensland, Australia

Jakob, S.; Salati, S.; Gloaguen, R.

Alone or combined with other remote sensing data, hyperspectral mineral mapping can be used to investigate mineralizations and deposits via alteration minerals. Their kind, abundance and spatial distribution can deliver important statements about the occurrence and formation of mineralizations and their relation to structural features. The high spectral and spatial resolution of HyMap data exceeds multispectral data distinctly and makes the recognition of even smaller geological structures possible. The spectral unmixing of single endmembers can be used for the accurate mapping of specific materials or minerals.The support of hyperspectral imaging by spectral data gathered in the field and the analysis of the composition of rock samples can help to determine endmembers and to identify absorption features.
This study demonstrates the possibilities and limitations of remote sensing, especially hyperspectral data, for mineral mapping purposes, using the example of the Mount Isa Inlier. This geological area is situated in Northern Queensland, Australia, and is known for its considerable ore deposits and consequent mining of predominantly copper, zinc, lead, silver and gold. Beside hyperspectral HyMap data, multispectral Landsat 8 and SRTM digital elevation data were analyzed. A three-week field study in 2014 supported the investigations.
After preprocessing and vegetation masking the data were analyzed using Spectral Feature Fitting (SFF) and Mixture Tuned Matched Filtering (MTMF) for alteration mineral mapping. The outcomes were combined with results from decorrelation stretch, band ratioing, topographic indices and automated lineament analysis. Additional information was provided by field spectrometer measurements and the XRF and XRD analysis of rock samples.
Throughout the study, mineral mapping using remote sensing data, especially hyperspectral data, turned out to deliver high qualitative results when it is supported by additional information. In situ investigation of the observed mineralizations for validation is important and can deliver such data, for instance by the investigation of rock samples or spectral measurements. Since mineralizations and alterations are often related to structures, their analysis and consideration can provide crucial hints.
The most significant result throughout the study was the determination of a new site of gossanous, silicified ridges south of the Mount Isa mining complex. Their occurrence was validated through fieldwork observations including rock sampling and spectral measurements. The gathered information additionally supported the accurate mapping of those ridges using HyMap data, which confirmed the connection between the north-south trending ridges and the Mount Isa mine deposits. The observed ridges coincide compositionally and spectrally with the outcrops of mineralized parts of the Urquhart Shale, which form the mined Pb-Zn-Ag deposits and are probably related to structures. In samples of the new site, amounts of Pb, Zn, Ag and other metals could be detected. Contrary to the mineralized outcrops of the Urquhart Shale deposits, those ridges occur outside of the common host rock and are not mentioned as mineralizations in any available map or publication.

  • Poster
    EGU General Assembly 2015, 14.04.2015, Wien, Österreich

Publ.-Id: 22268

Formation of Ge-0 and GeOx nanoclusters in Ge+-implanted SiO2/Sithin-film heterostructures under rapid thermal annealing

Zatsepin, A. F.; Zatsepin, D. A.; Zhidkov, I. S.; Kurmaev, E. Z.; Fitting, H. J.; Schmidt, B.; Mikhailovich, A. P.; Lawniczak-Jablonska, K.

The results of X-ray photoelectron spectra (XPS valence band and core levels) measurements for Ge+ implanted SiO2/Si heterostructures are presented. These heterostructures have a 30 nm thick Ge+ ion implanted amorphous SiO2 layer on p-type Si. The chemical-state transformation of the host-matrix composition after Ge+ ion implantation and rapid thermal annealing (RTA) are discussed. The XPS-analysis performed allows to conclude the formation of Ge-o and GeOx clusters within the samples under study. It was established, that the annealing time strongly affects the degree of oxidation states of Ge-atoms


Publ.-Id: 22267

Modelling of the electromagnetic braking effect in the continuous casting process of steel

Timmel, K.; Willers, B.; Kratzsch, C.; Schwarze, R.; Eckert, S.; Gerbeth, G.

It is known from industry and from scientific studies that the steel quality is significantly governed by the melt flow in the mold. Therefore, big efforts are made to adjust and to control the flow in the mold in a proper way by plant design or by the contactless, adjustable and flexible use of electromagnetic fields. These electromagnetic fields are already in industrial use for decades, but direct flow measurements about the actual effect are still rather scarce.
Three experimental facilities operating with low melting liquid metals were built at HZDR to investigate the continuous casting process of steel and to provide data for the validation of numerical simulations. The effect of the electromagnetic brake was one of the topics investigated in these low melting liquid metal experiments [1]. This paper will present new results from the LIMMCAST liquid metal experiments. Compared to previous results, the new experiments are operated in a continuous mode, providing a possibility to study the flow behavior in the stationary regime. Additional measurements focus on the behavior of the free liquid metal surface in the mold and the effect of the bulk flow on it. The paper also presents numerical results using Scale Adaptive Simulations (SAS).

Keywords: Continuous casting of steel; electro-magnetic flow control; liquid metal models; numerical simulation; scale adaptive simulations

  • Lecture (Conference)
    8th International Conference on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, Frankreich
  • Contribution to proceedings
    8th International Conference on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, Frankreich, 978-2-9553861-0-1, 373-376

Publ.-Id: 22266

Simulating Multi-Scale Physics in Solid Target Laser-Ion Acceleration

Huebl, A.; Kluge, T.; Hilz, P.; Bussmann, M.

Laser-ion acceleration from solid targets with ultra-intense laser pulses on the fs time scale is a central research topic for next generation particle accelerators. Accompanying processes are highly non-linear and require precise knowledge about the influence of both ab-initio electro-magnetic and atomic evolution of the plasma.

Consequently, modeling the acceleration process with simulations does not only require kinetic models with very high resolution (from the order of the inverse plasma frequency to the ns acceleration process) but also self-consistent models for non-equilibrium plasma and ionization processes.

We present large scale, 3D3V simulations with the fully-relativistic particle-in-cell code PIConGPU on the ORNL Titan cluster of mass-limited droplet targets related to recent experiments levitating these in Paul-traps.
In comparison with large 2D surveys the dependence of plasma instabilities and resulting ion energies under the variation of target material and laser properties is shown.

Keywords: laser particle acceleration; ion acceleration; mass limited targets; HPC; GPU; simulation; PIConGPU

  • Lecture (Conference)
    42nd EPS Conference on Plasma Physics 2015, 22.-26.06.2015, Lisbon, Portugal

Publ.-Id: 22265

Photocapacitive light sensor based on metal-YMnO3-insulator-semiconductor structures

Bogusz, A.; Choudhary, O. S.; Skorupa, I.; Bürger, D.; Lawerenz, A.; Lei, Y.; Zeng, H.; Abendroth, B.; Stäcker, H.; Schmidt, O. G.; Schmidt, H.

Technology of light sensors, due to the wide range of applications, is a dynamically developing branch of both, science and industry. This work presents a novel concept of photodetectors based on a metal-ferroelectric-insulator-semiconductor, a structure which has not been explored yet in the field of photodetectors. Functionality of the presented light sensor exploits the effect of ferroelectric polarization, charge trapping and photocapacitive phenomena. This is accomplished by an interplay between polarization alignment, subsequent charge distribution and charge trapping processes under given illumination condition and gate voltage. Change of capacitance serves as a read out parameter indicating the wavelength and intensity of illuminating light. The operational principle of the proposed photocapacitive light sensor is demonstrated in terms of capacitance-voltage and capacitance-time characteristics of an Al/YMnO3/SiNx/p-Si structure exposed to green, red, and near infrared light. Obtained results are discussed in the terms of optical properties of YMnO3 and SiNx layers contributing to the performance of photodetectors. Presented novel concept of light sensing might serve as the basis for the development of more advanced photodetectors.

Keywords: light; sensor; photodetector; YMnO₃; photocapacitance

Publ.-Id: 22264

Annual Report 2014 - Institute of Ion Beam Physics and Materials Research

Fassbender, J.; Heera, V.; Helm, M.; Zahn, P.

This past year 2014 was the year when we finally completely arrived as a “full member” in the Helmholtz Association. This is related to the successfully passed research evaluation in the framework of the Program Oriented Funding (POF), which will give us a stable and predictable funding for the next five years (2015 – 2019). This is particularly true for our large-scale user facilities, like the Ion Beam Center (IBC) and the electron accelerator ELBE with the free-electron laser. Most of our activities are assigned to the program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”.

Our research and facilities were well appreciated by the evaluation committee, who made the following judgement about the Ion Beam Center:
“The Ion Beam Centre (IBC) of HZDR is an internationally leading ion-beam facility (with ion energies ranging from several eV to several tens of MeV). At both the national and international level it is one of the key players and is unique in its kind. The synergy between forefront research and user service has been leading to a very good publication output for both in-house research and user research. …
The very broad range of beam energies, the versatility of techniques and applications – both for ion beam modification of materials and for ion-beam analysis – makes the IBC unique in its kind. …
The strength of IBC is that its activities are based on a combination of forefront research and user service, which mutually interact in synergy and strengthen one another. In turn, this synergy has been leading to a very good publication output for both in-house research and user research.”
In order to make our Annual Report a bit more compact, we have decided to include only four full journal papers this year. This was also triggered by the fact that our publication activities have turned out be become more diverse, in more diverse journals than in the past, and often through longer papers, which would be too long to reprint them here. However, apart from the constantly quantitatively high publication output, we succeeded to publish in excellent journals such as Nature Physics, Nano Letters and Physical Review Letters, in fields as diverse as ion beam physics, magnetism and terahertz spectroscopy.
Two of our scientists, Dr. Artur Erbe and Dr. Alexej Pashkin obtained their Habilitation in 2014, both at University of Konstanz. For the first time, we are hosting an Emmy Noether Young Investigator Group funded by the Deutsche Forschungsgemeinschaft (DFG); the group works on the hot topic of magnonics and is headed by Dr. Helmut Schultheiß.
Finally we would like to cordially thank all partners, friends, and organizations who supported our progress in 2014. Special thanks are due to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Minister of Education and Research of the Federal Government of Germany. Numerous partners from universities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank again all IIM staff for their efforts and excellent contributions in 2014.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-060 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 22263

Destination and transport of engineered nanoparticles along the process wastewater – sludge – plant

Fricke, T.; Schymura, S.; Hildebrand, H.; Franke, K.

The presence of engineered nanomaterials in various consumer products leads to a significant load of nanoparticles (NP) also in urban and industrial wastewater. Consequently, wastewater treatment plants (WWTP) play a key role in managing these NP-loaded wastewaters considering that the purified WWTP effluent must be harmless when entering the recipient and the (aquatic) environment. Up to now, there is little information or practical guidelines available to safeguard these ambitious provisions. As another product of wastewater treatment (WWT), sewage sludge is considered to act as a sink for NPs during WWT process. Quite often, sewage sludge is used as an organic fertilizer in the agriculture and horticulture. Under these purposes, it cannot be excluded that a significant amount of engineered NPs might find their way into the treated soil and finally into plants and the way back in the human food chain.
Within the project “nanoSuppe” (sludge uptake particle plant environment) guidelines for WWTP and for the usage of sewage sludge as fertilizer will be created based on laboratory studies to support WWTP companies and authorities in terms of this difficile problem. To reach this goal a strong consortium from WWTPs, related companies and a research centre is formed. The project is focused on the usage of engineered NPs like TiO2, CeO2 multiwalled carbon nanotubes (MWCNT) and quantum dots. These NPs are representatives for nanomaterials that are used in many consumer products like sunscreens, paints and also in the industry.
The process of characterization of NP from the lab into the scale of a field is one of the important focuses. It includes the radio labelling of NP as a strong detection tool, the characterization of these NP in liquid phase and sewage sludge and the uptake of NP into plants. The use of radiolabeled NPs guarantee a highly sensitive identification, localisation and quantification of NPs even at the low environmentally concentrations. It is independent of the used matrices (sewage, sludge, soil, plant) and background levels of natural NPs, colloids or substances of the same elemental composition.
Within this presentation, latest results on translocation of NPs from different matrices like tap water, sewage and sewage sludge into the plant will be shown and discussed. Furthermore the chemical and physical interactions of these matrices might have a huge impact on the destination of the NP in the different media. So the uptake of NP into the plants is limited to their availability in the media. Different approaches with four plant species such as lamb’s lettuce, sunflowers, ryegrass and red radish are under investigation. These test plants cover a wide spectrum of agricultural and horticultural interest. Lamb’s lettuce and red radish end up directly in the human food chain. Besides that ryegrass functioned as animal food for cows, goats and other animals which can end up in the food chain as well.

  • Poster
    ICCE 2015, 15th EuCheMS International Conference on Chemistry and the Environment, 20.-24.09.2015, Leipzig, Deutschland

Publ.-Id: 22262

Measuring at relevant concentrations - Radiolabelling as a versatile tool for sensitive nanoparticle detection in complex systems

Hildebrand, H.; Schymura, S.; Holzwarth, U.; Bellido, E.; Ojea-Jimènez, I.; Dalmiglio, M.; Cotogno, G.; Gibson, N.; Franke, K.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories, a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as geological formations, ground water or organisms is nearly impossible or at least extremely laborious in terms of sample preparation using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research under laboratory conditions. Radiolabelling allows to localize, to trace and to detect nanoparticles in complex media without intensive sample pre-treatment for the measurements.

We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, CeO2, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag0 [1], [124/125/131I]CNTs, [139Ce]CeO2, [48V]TiO2 [2], [7Be]MWCNT, [7Be]SiO2 [3], [44/45Ti]TiO2 [4], etc.. The radiolabelled nanoparticles were intensively tested concerning radiolabel stability and nanoparticle properties (size, zeta potential) were compared with the original (non-labelled) material. It could be shown, that radiolabels are suitable for application in scientific studies under the individual experimental conditions and nanoparticle properties remained largely unalterd by the radiolabelling procedure.

The developed radiolabelling methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. This means that nanoparticles can be localized also in e.g. intact geological samples or during transport studies using appropriate detector arrangement.

Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations.

[1] H. Hildebrand and K. Franke: A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media, J Nanopart Res (2012) 14:1142.
[2] K. Abbas, I. Cydzik, R. Del Torchio, M. Farina, E. Forti, N. Gibson, U. Holzwarth, F. Simonelli, W. Kreyling: Radiolabelling of TiO2 nanoparticles for radiotracer studies, J Nanopart Res (2010) 12:2435–2443.
[3] U. Holzwarth, E. Bellido, M. Dalmiglio, J. Kozempel, G. Cotogno, N. Gibson: 7Be-recoil radiolabelling of industrially manufactured silica nanoparticles, J Nanopart Res (2014) 16:2574.
[4] H. Hildebrand, S. Schymura, U. Holzwarth, N. Gibson, M. Dalmiglio, K. Franke: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection in complex matrices, J Nanopart Res (2015) 17:278.

  • Lecture (Conference)
    ICCE 2015, 15th EuCheMS International Conference on Chemistry and the Environment, 20.-24.09.2015, Leipzig, Deutschland

Publ.-Id: 22261

Building a New Assessment Tool for Potential Rare Earth Underground Mining Projects

Barakos, G.; Mischo, H.

Once an ore body has been probed and outlined and initial resource indications deserve further attention, the evaluation stage has to begin to determine the potential exploitation. This analysis is a sophisticated process, let alone when it comes to underground mining projects and especially on rare earth deposits that are governed by notable boundary conditions. However, the significant numbers of the parameters to be considered and their complexity, as well as the solvency of the outcomes, often result in questioning the suitability of common evaluation methods. This has created a necessity for a new evaluation procedure that focuses on potential rare earth underground mining projects. This paper describes the construction development of an assessment tool that considers not only the mining method selection process but identifies social, economic and environmental impact factors and Rare Earth Element industry-specific criteria as well. Based on the philosophy of previous linguistic and numerical approaches, this combined tool is based on a step-by-step numerical analytical hierarchical process with weighted criteria. The purpose of building this tool is to adjust to the specifications of rare earth underground mining projects and to contribute into having accurate and secure con-clusions for if and when investment decisions should be made and minimize the potential risks regarding the viability of any mining project.

Keywords: rare earths; underground mining method selection; viability; assessment tool

  • Open Access Logo Contribution to proceedings
    7th Sustainable Development In Minerals Industry Conference (SDIMI 2015), 12.-15.07.2015, Vancouver, Canada
    Proceedings of SDIMI 2015, Vancouver: University of British Columbia

Publ.-Id: 22260

Setting the REE industry-specific criteria and their significant role in the viability of rare earth underground mining projects

Barakos, G.; Mischo, H.

To evaluate the feasibility of a future underground mining operation is a complex problem in itself, with several different parameters to be accounted for and evaluated to secure investment decisions over the viability of any potential underground mining project. This procedure gets even more complicated when it comes to exploiting rare earth deposits. Various concerns are expressed regarding the environmental impacts that an underground mining operation may cause due to the radioactivity of the rare earth elements during mining and in waste treatment. Furthermore, the fragile market and the diversified supply and demand of the different rare earth elements can significantly affect the viability of such a venture, among other factors. This paper deals with the definition and classification of the specific criteria that govern the REE mining industry. Moreover, a thorough investigation is made of how these criteria can determine not only the selection of the underground mining method to be applied, but also of the impact that they may have to the overall feasibility of any given potential project.

Keywords: rare earth elements; underground mining; sustainability; environmental impacts; balance problem

  • Open Access Logo Contribution to proceedings
    26th Annual Meeting & Conference of the Society of Mining Professors, 21.-26.06.2015, Freiberg, Deutschland
    Proceedings of the 26th Annual Meeting & Conference of the Society of Mining Professors, Backnang, Stuttgart: WIRmachenDRUCK, 978-3-86012-505-2

Publ.-Id: 22259

Broken vertex symmetry and finite zero-point entropy in the artificial square ice ground state

Gliga, S.; Kákay, A.; Heyderman, L. J.; Hertel, R.; Heinonen, O. G.

We study degeneracy and entropy in the ground state of artificial square ice. In theoretical models, individual nanomagnets are typically treated as single spins with only two degrees of freedom, leading to a twofold degenerate ground state with intensive entropy and thus no zero-point entropy. Here, we show that the internal degrees of freedom of the nanostructures can result, through edge bending of the magnetization and breaking of local magnetic symmetry at the vertices, in a transition to a highly degenerate ground state with finite zero-point entropy, similar to that of the pyrochlore spin ices. We find that these additional degrees of freedom have observable consequences in the resonant spectrum of the lattice, and predict the occurrence of edge “melting” above a critical temperature at which the magnetic symmetry is restored.

Keywords: zero-point entropy; artificial spin-ice

Publ.-Id: 22258

Compton camera and prompt gamma ray timing: two methods for in vivo range assessment in proton therapy

Hueso-González, F.; Fiedler, F.; Golnik, C.; Kormoll, T.; Pausch, G.; Petzoldt, J.; Römer, K. E.; Enghardt, W.

Proton beams are promising means for treating tumours. Such charged particles stop at a defined depth, where the ionization density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimises the damage to normal tissue compared to photon therapy. Nevertheless, inherent range uncertainties cast doubts on the irradiation of tumours close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of protons over photons. In this context, several research groups are developing experimental tools for range verification based on the detection of prompt gammas, a nuclear by-product of the proton irradiation. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf, detector components have been characterised in realistic radiation environments as a step towards a clinical Compton camera. Corresponding experimental methods and results obtained during the ENTERVISION training network are reviewed. On the other hand, a novel method based on timing spectroscopy has been proposed as an alternative to collimated imaging systems. The first tests of the timing method at a clinical proton accelerator are summarised, its applicability in a clinical environment for challenging the current safety margins is assessed, and the factors limiting its precision are discussed.

Keywords: proton therapy; range verification; in vivo dosimetry; Compton imaging; block detector; scintillation; prompt gamma ray timing

Publ.-Id: 22257

Simulation studies for the in-vivo dose verification of particle therapy

Rohling, H.

An increasing number of cancer patients is treated with proton beams or other light ion beams which allow to deliver dose precisely to the tumor. However, the depth dose distribution of these particles, which enables this precision, is sensitive to deviations from the treatment plan, as e.g. anatomical changes. Thus, to assure the quality of the treatment, a non-invasive in-vivo dose verification is highly desired. This monitoring of particle therapy relies on the detection of secondary radiation which is produced by interactions between the beam particles and the nuclei of the patient’s tissue.
Up to now, the only clinically applied method for in-vivo dosimetry is Positron Emission Tomography which makes use of the beta+-activity produced during the irradiation (PT-PET). Since from a PT-PET measurement the applied dose cannot be directly deduced, the simulated distribution of beta+-emitting nuclei is used as a basis for the analysis of the measured PT-PET data. Therefore, the reliable modeling of the production rates and the spatial distribution of the beta+-emitters is required. PT-PET applied during instead of after the treatment is referred to as in-beam PET. A challenge concerning in-beam PET is the design of the PET camera, because a standard full-ring scanner is not feasible. For instance, a double-head PET camera is applicable, but low count rates and the limited solid angle coverage can compromise the image quality. For this reason, a detector system which provides a time resolution allowing the incorporation of time-of-flight information (TOF) into the iterative reconstruction algorithm is desired to improve the quality of the reconstructed images.
Secondly, Prompt Gamma Imaging (PGI), a technique based on the detection of prompt gamma-rays, is currently pursued. Concerning the emissions of prompt gamma-rays during particle irradiation, experimental data is not sufficiently available, making simulations necessary. Compton cameras are based on the detection of incoherently scattered photons and are investigated with respect to PGI. Monte Carlo simulations serve for the optimization of the camera design and the evaluation of criteria for the selection of measured events.
Thus, for in-beam PET and PGI dedicated detection systems and, moreover, profound knowledge about the corresponding radiation fields are required. Using various simulation codes, this thesis contributes to the modelling of the beta+-emitters and photons produced during particle irradiation, as well as to the evaluation and optimization of hardware for both techniques.
Concerning the modeling of the production of the relevant beta+-emitters, the abilities of the Monte Carlo simulation code PHITS and of the deterministic, one-dimensional code HIBRAC were assessed. The Monte Carlo tool GEANT4 was applied for an additional comparison. For irradiations with protons, helium, lithium, and carbon, the depth-dependent yields of the simulated beta+-emitters were compared to experimental data. In general, PHITS underestimated the yields of the considered beta+-emitters in contrast to GEANT4 which provided acceptable values. HIBRAC was substantially extended to enable the modeling of the depth-dependent yields of specific nuclides. For proton beams and carbon ion beams HIBRAC can compete with GEANT4 for this application. Since HIBRAC is fast, compact, and easy to modify, it could be a basis for the simulations of the beta+-emitters in clinical application. PHITS was also applied to the modeling of prompt gamma-rays during proton irradiation following an experimental setup. From this study, it can be concluded that PHITS could be an alternative to GEANT4 in this context.
Another aim was the optimization of Compton camera prototypes. GEANT4 simulations were carried out with the focus on detection probabilities and the rate of valid events. Based on the results, the feasibility of a Compton camera setup consisting of a CZT detector and an LSO or BGO detector was confirmed. Several recommendations concerning the design and arrangement of the Compton camera prototype were derived. Furthermore, several promising event selection strategies were evaluated. The GEANT4 simulations were validated by comparing simulated to measured energy depositions in the detector layers. This comparison also led to the reconsideration of the efficiency of the prototype. A further study evaluated if electron-positron pairs resulting from pair productions could be detected with the existing prototype in addition to Compton events. Regarding the efficiency and the achievable angular resolution, the successful application of the considered prototype as pair production camera to the monitoring of particle therapy is questionable.
Finally, the application of a PET camera consisting of Resistive Plate Chambers (RPCs) providing a good time resolution to in-beam PET was discussed. A scintillator-based PET camera based on a commercially available scanner was used as reference. This evaluation included simulations of the detector response, the image reconstructions using various procedures, and the analysis of image quality. Realistic activity distributions based on real treatment plans for carbon ion therapy were used. The low efficiency of the RPC-based PET camera led to images of poor quality. Neither visually nor with the semi-automatic tool YaPET a reliable detectability of range deviations was possible. The incorporation of TOF into the iterative reconstruction algorithm was especially advantageous for the considered RPC-based PET camera in terms of convergence and artifacts.
The application of the real-time capable back projection method Direct TOF for the RPCbased PET camera resulted in an image quality comparable to the one achieved with the iterative algorihms. In total, this study does not indicate the further investigation of RPC-based PET cameras with similar efficiency for in-beam PET application.
To sum up, simulation studies were performed aimed at the progress of in-vivo dosimetry. Regarding the modeling of the beta+-emitter production and prompt gamma-ray emissions, different simulation codes were evaluated. HIBRAC could be a basis for clinical PT-PET simulations, however, a detailed validation of the underlying cross section models is required. Several recommendations for the optimization of a Compton Camera prototype resulted from systematic variations of the setup. Nevertheless, the definite evaluation of the feasibility of a Compton camera for PGI can only be performed by further experiments. For PT-PET, the efficiency of the detector system is the crucial factor. Due to the obtained results for the considered RPC-based PET camera, the focus should be kept to scintillator-based PET cameras for this purpose.

Keywords: Monte-Carlo Simulation; Partikeltherapie; in-vivo Reichweitenkontrolle; GEANT4; PHITS; Prompt Gamma Imaging; Compton-Kamera; Positronen-Emissions-Tomographie; Paarbildungskamera; Monte Carlo simulation; particle therapy; in-vivo range verification; GEANT4; PHITS; Prompt Gamma Imaging; Compton camera; positron emission tomography

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-062 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 22256

Surface modification with focused polyatomic ion beams

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

In the last decades Focused Ion Beams (FIB) have evolved from a sophisticated idea to a distinguished standard technique for sample preparation for SEM and TEM, prototyping in research and development and analytics in fields like microelectronics or nanotechnology. Most of FIB systems work with Ga beams, but liquid metal ion sources (LMIS) provide a much broader spectrum of other ion species using different source materials and an ion optical column equipped with an ExB mass separator [1]. From the source tip, beside single and double charged monatomic ions also dimers, trimers and heavier projectiles are extracted, which play an increasing role due to their special properties, like shallow penetration depth, enhanced sputtering efficiency and the huge energy deposition due to the simultaneous impact of several atoms in the same point of the sample surface.
Beside others heavy elements or alloys, those containing Au but in particular Bi are very suitable for the emission of polyatomic ions. Such projectiles with masses up to about 1000 amu have an energy spread in the range of EFWHM = 30 … 150 eV, which restrict the final FIB resolution (spot size) due to chromatic aberration to 10 … 100 nm. This is a result of the complex appearance of polyatomic species in the area around the emission point.
One of the main application fields at present is SIMS, which increasingly works with polyatomic Bi beams for defined surface erosion of inorganic as well as organic specimens. Another exciting field of application is the surface modification in terms of surface patterning by heavy dimer and trimer ions (e.g. Aunm+, Binm+). Due to the enormous, surface-near energy density deposition of cluster ions a self-organization process of hexagonally ordered dot arrays on Ge and Si based on transient melt pool formation can be triggered (Fig. 1) [2].
The authors would like to thank S. Facsko and B. Schmidt from HZDR for fruitful contributions to this work.

[1] L. Bischoff, Nucl. Instr. Meth. B 2008, 266, 1846.
[2] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, B. Schmidt, J. Vac. Sci. Technol. B 2012, 30, 06FF12.

Keywords: Surface modification; ion; cluster; FIB; sputtering

  • Lecture (Conference)
    Workshop Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Germany

Publ.-Id: 22255

Polyatomic Focused Ion Beams – Origin and Applications

Bischoff, L.

In the last four decades Focused Ion Beams (FIB) have evolved from a sophisticated idea to a distinguished standard technique for sample preparation for SEM and TEM, prototyping in research and development and analytics in fields like microelectronics or nanotechnology. Most of the FIB systems works with Ga beams, but liquid metal ion sources (LMIS) provide a much broader spectrum of other ion species using different source materials and an ion optical column equipped with an ExB mass separator [1]. From the source tip beside single and double charged monatomic ions also dimers, trimers and heavier projectiles are extracted, which play an increasing role due to their special properties, like slight penetration depth, enhanced sputtering efficiency and the huge energy deposition due to the simultaneous impact of several atoms in the same point of the surface.
Beside others heavy elements or alloys, those containing Au but in particular Bi are very appropriate for the emission of polyatomic ions. Such projectiles with masses up to about 1000 amu have an energy spread in the range of ΔEFWHM = 30 … 150 eV, which restrict the final FIB resolution (spot size) due to chromatic aberration to 10 to 100 nm. This is a result of the complex appearance of polyatomic species in the area around the emission point.
One of the main application fields at present is SIMS, which increasingly works with polyatomic Bi beams for defined surface erosion on inorganic as well as organic specimen [2]. A second exciting field of application is the surface modification in terms of surface patterning by heavy dimer and trimer ions (e.g. Aunm+, Binm+). Due to the enormous energy transfer by the cluster ions to the surface a self-organization process of hexagonal ordered dot arrays on Ge and Si could be found surprisingly for pure elemental targets at normal incidence, described by the formation of tiny melt pools [3] shown in the figure.

[1] L. Bischoff, Nucl. Instr. Meth. B 266 (2008) 1846.
[2] F. Kollmer, Appl. Surf. Sci. 231-232 (2004) 153.
[3] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, JVST B 30 (2012) 06FF12.

Keywords: FIB; Cluster ions; LMIS; self-assembly

  • Lecture (Conference)
    10. Dreiländer-FIB-Workshop, 29.-30.06.2015, Halle, Germany

Publ.-Id: 22254

Uptake of Selenium Oxyanions by δ-alumina at elevated Temperatures

Franzen, C.; Jordan, N.

One major process controlling the mobility and bioavailability of selenium, a long-lived fission product in nuclear waste, is the adsorption onto mineral surfaces of both the engineered and geological barrier. In this context, it is important to understand to what extent this sorption is influenced particularly by characteristic parameters as expected in deep underground repositories for high level and long-lived radioactive waste. These parameters include inter alia elevated temperatures originating from heat generating waste and natural ground heat. For the investigation of the sorption processes, δ−Al2O3 was chosen because it is omnipresent in the environment and it represents a model oxide for more complex aluminosilicates.
In the present study, a combination of macroscopic sorption experiments, electrophoretic mobility and in-situ ATR FT-IR spectroscopy measurements was used to study the interaction of selenate and selenite with aged δ-Al2O3 at different temperatures between 25°C and 60°C. From in-situ ATR FT-IR spectra, a change in the symmetry of the aqueous tetrahedral selenate anion can be derived evidencing the formation of a surface complex on δ-Al2O3. From batch experiments, we observe a decreasing sorption of both selenate and selenite upon increasing temperature.
The isoelectric point (pHIEP) of δ-Al2O3 was located at pH 9.6 at 25°C. At higher temperatures, the pHIEP was shifted towards lower pH with a value of 8.6 at 60 °C. In addition, the absolute values of the zeta potential were lowered at higher temperatures. Both findings were in good agreement with the batch experiments.
The observed decrease in selenate and selenite sorption at higher temperatures could be assigned to a change in the surface properties of δ−Al2O3.
This effect may significantly increase the mobility of these Se−species and must be taken into account in future safety assessments of nuclear waste repositories.

Keywords: selenate; selenite; sorption

  • Poster
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 22253

Spin-transfer effects in MgO-based tunnel junctions with an out-of-plane free layer and in-plane polarizer

Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Deac, A. M.

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane (IP) magnetized polarizer (also acting as read-out layer) and out-of-plane (OOP) magnetized free layer allow for the full parallel (P)-to-antiparallel (AP) resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based MTJs under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices, including the spin-torque angular dependence.
Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based MTJs with an IP polarizer and an OOP free layer. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation for a nano-pillar MTJ with circular cross-section, under a constant perpendicular applied current and field. To sustain steady-state precession, the energy supplied by the in-plane spin-torque term and energy dissipated through damping must compensate over a full precession period.
In an MgO-MTJ, the magnitude of the STT is determined by the voltage across the barrier [6]. As the magnetization of the free layer precesses around the put-of-plane direction, the angle between the magnetic moments of the two layers changes and through the magnetoresistance effect the voltage changes if the experiment is conducted at constant applied current [7,8]. This cosine-like angular dependence of the MTJ resistance effectively introduces a spin-torque angle dependence asymmetry. In addition, for a given angle, the resistance exhibits a specific bias dependence, with the resistance of the AP state decreasing approximately linearly with increasing bias, while remaining mostly constant in the P configuration. In this work, we demonstrate that the spin-torque angular asymmetry exhibited in such systems is sufficient to sustain STT-driven dynamics.
Fig. 1 shows dynamic and static phase diagrams of the STNO obtained when neglecting (Fig. 1(a) and 1(c)) and taking into account (Fig. 1(b) and 1(d)) the bias dependence of the AP state resistance. In both cases, stable dynamics occur only for positive currents (colored area), defined as electrons flowing from the free to the reference layer. In MTJs exhibiting no bias dependence of the resistance (dRAP/dV = 0 Ω/V), the onset current for steady-state dynamics (solid lines) scales linearly with the applied current. High output powers can be obtained for relatively low values of applied currents and fields for realistic MTJ parameters, which is beneficial from the point of view of applications. Introducing an experimentally realistic value of dRAP/dV affects mostly the steady-state dynamics, while most of the trends observed for static states are maintained (Fig. 1(b) and 1(d)). Indeed, in this case current-driven precession is only excited for fields lower than the effective anisotropy of the free layer (but still only for positive currents). Moreover, while the symmetry versus field sign is conserved, the onset current no longer increases linearly with the field, but rather exhibits a parabolic-like dependence.

Keywords: spin-torque nano-oscillators (STNOs); magnetic tunnel junctions (MTJs)

  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS 2015), 12.-17.07.2015, Cracow, Poland

Publ.-Id: 22252

Tomographic investigations on centrifugal pumps conveying gas-liquid two phase flow

Schäfer, T.; Neumann, M.; Bieberle, A.; Hampel, U.

This contribution presents an investigation study of two-phase flow distribution in an industrial centrifugal pump and its effect to the hydrodynamic behaviour. Therefore, high-resolution gamma-ray computed tomography has been applied especially in the impeller region of an industrial centrifugal pump. To observe gas-liquid phase distributions within a sharply mapped impeller wheel, which rotates with up to 1900 rpm, time-averaged rotation-synchronized computed tomography as well as radiography has been applied. The accumulation of the gas phase was studied for varying injected gas volume fractions and flow regimes. Furthermore, various internally accumulated gas holdup patterns could be identified and, eventually, associated with characteristic pump performance behaviours. Moreover, the measuring method allowed gas holdup analysis in each chamber of the impeller wheel along selected streamlines. As a result, specific phase holdup profiles could be evaluated.

Keywords: gamma-ray computed tomography; centrifugal pump; two-phase flow; gas entrainment

  • Lecture (Conference)
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland
  • Contribution to proceedings
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland
    Proceedings of the 7th International Symposium on Process Tomography

Publ.-Id: 22251

Ion microprobe PIXE and PIGE analysis of standards’ trace elements for electron microprobe calibration.

Le Bras, L.; Munnik, F.; Renno, A. D.

The purpose of this study is, with the recorded data, to be able to calibrate microanalytical methods, in particular electron microprobe with high precision chemical data standards. Analysis on selected standards by ion microprobe Particle-Induced-X-ray-Emission (PIXE) and Particle-Induced-Gamma-ray-Emission (PIGE) are used to detect and quantify the trace and light elements present in these samples. The presence of those elements makes a specific calibration of the machines necessary.
Electron- and X-ray measurements need good standards for a good quantification of the elements of interest. Actually, certified reference materials for microanalytical methods are very rare. In addition they are mainly glass samples. Utilisation of chosen minerals fixed in a matrix instead of glasses for calibration makes possible the application of the matrix-matched principle and the detection and quantification of trace elements in natural minerals for a resource technology application.
The widespread utilisation of Smithsonian Microbeam Standards makes this study relevant. That is why a 10 sample selection has been made in this collection. The samples’ theoretical compositions in major and trace elements are very important for the achievement of the analysis. In addition to the given element concentrations [1], a bibliographic study has also been performed for each standard in order to find possible trace elements which could be detected.
The standards received from the Smithsonian Institute are composed of crushed particles (500 µm diameter). The sample preparation is also essential. It consists in the fixation of three particles with epoxy resin into a 3 mm diameter messing cylinder.
The analyses are performed with an incident proton beam of 3.5 MeV in order to acquire simultaneously X- and Gamma-ray spectra. The data analysis is performed with GeoPIXE in order to add qualitative and quantitative data about trace elements to the given composition of the major elements. Preliminary results on apatite (NMNH 104021) are in agreement with the literature and show the presence of vanadium, arsenic, strontium, yttrium and light Rare Earth Elements such as lanthanum, cerium and neodymium. These trace elements are important for mineral resources analysis. Elemental mapping is also achieved in order to check the homogeneity of the samples’ particles.

Acknowledgements: Special thanks to Andreas Bartzsch, from the sample’s preparation laboratory of the Helmholtz Institute Freiberg, Germany, for his expertise.

[1] E. Jarosewich, J. A. Nelen, J. A. Norberg, Geostandards Newsletter 4 1980, p. 43-47

Keywords: Mineral standards; PIXE; PIGE; calibration; electron microprobe

  • Lecture (Conference)
    Workshop für Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Germany

Publ.-Id: 22249

A comprehensive study on iodine uptake by selected LDH phases via coprecipitation, anionic exchange and reconstruction

Iglesias, L.; Walther, C.; Medina, F.; Holzer, A.; Neumann, A.; Lozano-Rodriguez, M. J.; Alvarez, M. G.; Torapava, N.

We explored the use of selected layered double hydroxides (LDHs) of different compositions and obtained by means of different routes (i.e., coprecipitation, anionic exchange and reconstruction) as iodine/iodate adsorbents. The influence of speciation (iodide vs. iodate) on iodine uptake was rather strong, resulting in much lower iodide incorporation. The Fourier transform of iodine K X-ray absorption edge data (EXAFS) of all iodate-LDHs showed a single I–O scattering path of 1.8 A ° . Thermal stability and leaching experiments showed that the incorporated iodate and iodide were rather loosely bound in the interlayer space and were easily released under heating to 180 C and leaching with Milli-Q water and brine solution.

Keywords: Iodine; Layered double hydroxide; Immobilization; Nuclear waste; Aqueous systems

Publ.-Id: 22248

Coffinite, USiO4, Is Abundant in Nature: So Why Is It So Difficult To Synthesize?

Mesbah, A.; Szenknect, S.; Clavier, N.; Lozano-Rodriguez, J.; Poinssot, C.; Den Auwer, C.; Ewing, R. C.; Dacheux, N.

Coffinite, USIO4, is the second most abundant U4+ mineral on Earth, and its formation by the alteration of the UO2 in spent nuclear fuel in a geologic repository may control the release of radionuclides to the environment. Despite its abundance in nature, the synthesis and characterization of coffinite have eluded researchers for decades. On the basis of the recent synthesis of USiO4, we can now define the experimental conditions under which coffinite is most efficiently formed. Optimal formation conditions are defined for four parameters: pH, T, heating time and U/Si molar ratio. The adjustment pf pH between 10 and 12 leads probably to the formation of a uranium (IV) hydroxo-silicate complex that acts as a precursor of uranium (IV) silicate colloids and then of coffinite. Moreover, in this pH range, the largest yield of coffinite formation (as compared with those of the two competing byproduct phases, nanometer-scale UO2 and amorphous SiO2) is obtained for 250 C, 7 days and 100% excess silica.

Keywords: coffinite; PXRD; EXAFS; XANES; Raman spectra

  • Inorganic Chemistry 54(2015)14, 6687-6696
    Online First (2015) DOI: 10.1021/ic502808n

Publ.-Id: 22247

High Conversion Th–U233 fuel for current generation of PWRs: Part III – Fuel availability and utilization considerations

Baldova, D.; Fridman, E.; Shwageraus, E.

In the previous studies, reported in Parts I and II of the paper, the high conversion (HC) Th-U233 fuel design for current generation of PWRs was proposed and investigated in details on single fuel assembly and 3D full core levels. One of the important limitations of the previous studies was the reliance on the availability of pure U233 as a fissile driver. In reality, however, U233 will always be accompanied by other U isotopes. Part III of the paper deals with a number of fuel cycle aspects associated with the use of HC Th-U fuel in PWRs including: (1) more realistic estimation of neutronic properties and conversion performance of HC Th-U fuel by accounting for the evolution of U isotopic composition with a number of recycle stages; (2) reassessment of the HC Th-U PWR core performance through 3D full core coupled neutronic and T-H analysis; (3) demonstration of a feasible way of generating U233; and finally (4) evaluation of potential savings in available resources that can be achieved by using HC Th-U fuel cycle as compared to the current fuel cycle practices.

Keywords: High conversion; PWR; Th-U233 fuel; seed-blanket; DYN3D

Publ.-Id: 22246

Liquid Metal Alloy Ion Sources - an Alternative for Focused Ion Beam Technology

Bischoff, L.; Mazarov, P.; Bruchhaus, L.; Gierak, J.

Today Focused Ion Beam (FIB) processing is nearly exclusively based on gallium Liquid Metal Ion Sources (LMIS). But, many applications in the µm- or nm range could benefit from ion species other than gallium: local ion implantation, ion beam mixing, ion beam synthesis or Focused Ion Beam Lithography (IBL). Therefore Liquid Metal Alloy Ion Sources (LMAIS) represent a promising alternative to expand remarkable the application fields for FIB. Especially the IBL process shows potential advantages over e.g. electron beam (EBL) or other lithography techniques: direct, resistless, and three-dimensional patterning, enabling a simultaneous in-situ process control by cross sectioning and inspection. Taking additionally into account that the used ion species influence significantly the physical and chemical nature of the resulting nanostructures -in particular the electrical, optical, magnetic and mechanic properties- leading to a large potential application area which can be tuned by choosing a well suited LMAIS. Nearly half of the elements of the Periodic Table are recently available in FIB technology as a result of continuous research in this area during the last forty years. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources feasible for nano patterning issues as an alternative technology more in research than in industry. The authors will review existing LMAIS, working with pure elements (LMIS) other than Ga or binary or ternary alloys, their physical properties as well as the fabrication technology and prospective domains for modern FIB applications. Other emerging ion sources will be also presented and their performances discussed.

Keywords: Liquid Metal Alloy Ion Sources; Focused Ion Beam; Mass Separation

  • Applied Physics Reviews 3(2016), 021101-1-021101-30
    Online First (2016) DOI: 10.1063/1.4947095

Publ.-Id: 22245

Relationship Between Kolmogorov Entropy and Characteristic Mixing Length in Narrow Bubble Columns Operated in the Transition Flow Regime

Nedeltchev, S.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.

The mixing performance of bubble column reactors depends strongly on the prevailing flow regime. Kawase and Tokunaga (Can. J. Chem. Eng. 69, 1228-1231, 1991) introduced the characteristic mixing length L as an important mixing parameter. In the homogeneous regime the liquid mixing is at the scale of the bubble diameter, whereas in the heterogeneous regime it is at the scale of the column diameter. Our research is aimed at determining the scale of liquid mixing in the transition flow regime by using some advanced methods.
The Kolmogorov entropies (KE) were extracted from gas holdup time series measured (at 2000 Hz) by a new type of wire mesh sensor. It was found that in a relatively narrow bubble column (0.15 m in ID, clear liquid height = 2 m) operated with an air-water system in the transition flow regime the KE values could be correlated to L. The KE in the transition flow regime decreases monotonously and can be correlated to the superficial gas velocity (KE=1.5Ug^-0.38). The same exponent (-0.38) for UG was reported by Kawase and Tokunaga (1991) in their correlation for prediction of L. Therefore, the KE and L values (in a narrow bubble column) are correlated as follows: KE=222.222L.
A new parameter called maximum number of visits per region Nv-max was also introduced and in the same way was related to L in the transition flow regime.

Keywords: Narrow bubble column; Transition flow regime; Kolmogorov entropy; Mixing length; New statistical parameter

  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-26.03.2014, Fulda, Deutschland

Publ.-Id: 22244

18F-FDG PET/MRI for therapy response assessment in sarcoma: Comparison of PET and MR imaging results

Schuler, M. K.; Platzek, I.; Beuthien-Baumann, B.; Fenchel, M.; Ehninger, G. E.; van den Hoff, J.

Background: 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) has proven to be of substantial benefit in imaging of sarcoma patients. We therefore investigated the feasibility and benefit of combined PET/magnetic resonance imaging (MRI). Methods: Twelve patients with sarcoma who underwent FDG PET/MRI for staging and response assessment after chemotherapy were included. Results: Based on contrast-enhanced MRI and application of Choi criteria, therapy response was classified as stable disease in 6/12 patients (50%) and as partial remission in 6/12 patients (50%). Conclusion: In sarcoma patients, response assessment using Choi criteria based on contrast-enhanced MRI in comparison to FDG PET imaging only demonstrates slight correlation.

Keywords: Cancer imaging; Choi criteria; FDG PET/MRI; Sarcoma

Publ.-Id: 22243

2-[18F]Fluoroethyl tosylate - a versatile tool for building 18F-based radiotracers for positron emission tomography

Knieß, T.; Laube, M.; Brust, P.; Steinbach, J.

Positron emission tomography (PET) is a modern in vivo imaging technique and an important diagnostic modality for clinical and pre-clinical research. The incorporation of a radionuclide like fluorine-18 into a target molecule to form PET radiopharmaceuticals is a repeated challenge for radiochemists. 18F-Fluoroethylation is a well acknowledged method for 18F-radiolabeling and 2-[ 18F]fluoroethyltosylate ([ 18 F]FEts) is a preferred reagent because of its high reactivity to phenolic, thiophenolic, carboxylic and amide functions. The review will highlight the role of [ 18F]FEts in PET-chemistry, and summarize its applicability in radiotracer design. The radiolabeling conditions and pros and cons of direct and indirect radiolabeling as well the aspects of reactivity of [ 18F]FEts compared with other [ 18F]fluoroalkylating reagents will be discussed comprehensively.

Publ.-Id: 22242

New Methods for Flow Regime Identification in Bubble Columns and Fluidized Beds

Nedeltchev, S.

New methods for flow regime identification were developed and applied to photon count time series measured in a bubble column (0.162 m in ID) and fluidized bed (0.438 m in ID). The signals in the bubble column (operated with an air-therminol system) were measured by means of Computed Tomography (CT), whereas the data in the fluidized bed (operated with an air-polyethylene system) were recorded by means of Nuclear Gauge Densitometry (NGD). The hidden information in the time series was extracted by means of two new parameters: entropy (bit/s) and information entropy (bit). Both of them were calculated on the basis of multiple reconstructions of the time series. In the case of the bubble column, the well-pronounced local minima were used for identification of three transition velocities (0.04, 0.08 and 0.13 m/s). They distinguished the boundaries of the bubbly flow, transition and churn-turbulent flow regimes. In the case of the fluidized bed, the minimum fluidization velocity (0.086 m/s) and minimum bubbling velocity (0.12 m/s) were also identified on the basis of the well-pronounced local minima in the profiles of the new parameters. They distinguished the boundaries of both the transition and bubbling fluidization regimes.

Keywords: Flow regime identification; Bubble column; Fluidized bed; Transition velocities; Entropy; Information entropy

Publ.-Id: 22241

Terahertz emission based on large-area photoconductive emitters illuminated via beam interference

Krauß, N.; Haas, M.; Niemeyer, L.; Winnerl, S.; Helm, M.; Dekorsy, T.

The use of beam interference in combination with large-area photoconductive emitters for the generation of pulsed terahertz radiation is presented. An interference pattern with a periode twice that of the terahertz emitter is generated with a transmission phase grating, placed directly in front of the photoconductive emitter. This way, efficient terahertz generation is achieved with a single metallization layer and a single lithography step in the fabrication technology of the THz emitter.

Keywords: THz photoconductive emitter; large-area THz emitter

Publ.-Id: 22240

Characterization of microbiological community in natural REE-containing matrixes

Kutschke, S.; Raff, J.; Pollmann, K.

Biochemistry of REE is very poorly understood. As microbes drive biogeochemistry in many ecosystems it can be expected with various yet unknown organisms that play a role in REE biogeochemistry. Thus these environments are a promising source for the recovery of microbes that are suitable candidates for their application in REE extraction and recycling.
The microbial community is a close metabolic network, where some of the organisms actively contribute to the carbon, nitrogen, sulfur, and phosphorus cycle and other microorganisms interact with minerals, metals, and pollutants. On the one hand such a microbial community is well adapted to environment and on other hand it is influenced by the geochemical parameters. Investigation of microbial community of REE containing matrixes has to be accompanied by (geo)-chemical analyses. Geochemical and structural soil parameters like organic compounds, ion exchange or waterholding capacity and porosity influence the microbial population. Moreover daily or seasonal changes of physical matrix properties force the microbial community to adapt. Reflection of environmental circumstances is one challenge describing natural microbial community (Xu 2006). The most sensitive describing tools are culture independent genomic methods. These genomic methods describe and characterize the majority of microorganisms including even the uncultivated microorganisms. Generated metagenomic data will be matched with already existing genomic databases. Up to now genetic methods like PCR fingerprinting techniques and fluorescence in situ hybridization used to identify and quantify microorganisms interacted with REE containing ore. Nevertheless genomic information of energetic metabolism, phosphate, sulfur and iron metabolism, quorum sensing, and genes involved in metal resistance and amino acid biosynthesis pathways were identified (Jerez 2008). As already mentioned the data base for comparative genomic is small. To extent this fundament it is necessary to extract single strains, to cultivate them and to analyze their genomes.
Jerez, C. A. (2008). "The use of genomics, proteomics and other OMICS technologies for the global understanding of biomining microorganisms." Hydrometallurgy 94(1–4): 162-169.
Xu, J. (2006). "Microbial ecology in the age of genomics and metagenomics: Concepts, tools, and recent advances." Molecular Ecology 15(7): 1713-1731.

  • Poster
    World Congress and Expo on Applied Microbiology 2015, 18.-20.08.2015, Frankfurt, Deutschland

Publ.-Id: 22239

Efficient Auger scattering in Landau-quantized graphene

Wendler, F. H. F.; Mittendorff, M.; Winnerl, S.; Helm, M.; Knorr, A.; Malic, E.

We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene.

Keywords: Graphene; ultrafast spectroscopy; Landau quantization; Auger scattering

  • Lecture (Conference)
    Photonics West Conference, 07.-12.02.2015, San Francisco, USA
  • Contribution to proceedings
    Photonics West Conference, 07.-12.02.2015, San Francisco, USA
    Proceedings of SPIE, 936105
    DOI: 10.1117/12.2075458

Publ.-Id: 22238

Theoretical Prediction of Mass Transfer Coefficients in Two-Phase and Slurry Bubble Columns

Nedeltchev, S.

Two-phase and slurry bubble columns are characterized with high volumetric mass transfer coefficients kLa at low energy input. The design, modelling, optimization and scale-up of these reactors require precise knowledge of the mass transfer parameters. The mass transfer coefficients determine the efficiency and dimensions of (slurry) bubble columns. Nedeltchev et al. (2007) developed a correlation for prediction of mass transfer coefficients in gas-liquid bubble columns operated in the homogeneous flow regime. It was based on experimental gas holdups. On the other hand, Nedeltchev and Schumpe (2008) developed a correlation for prediction of gas holdups in gas-liquid bubble columns operated in the homogeneous regime. In this work, the theoretically calculated gas holdups were substituted in the mass transfer model (in the correlation for the interfacial area) of Nedeltchev et al. (2007) and the mass transfer coefficients were recalculated by means of a purely theoretical approach. The same gases and liquids (18 pure organic liquids, 14 adjusted liquid mixtures and tap water) were used and 263 kLa values (only in the homogeneous regime) were successfully predicted at ambient and high pressures (up to 1 MPa).
The same approach was tested in a slurry bubble column. Nedeltchev et al. (2014) predicted successfully the experimental mass transfer coefficients in a slurry bubble column based on bubble sizes which depended on the experimental gas holdups. On the other hand, Nedeltchev (2014) established a new approach for predicting the gas holdups in a slurry bubble column. When these theoretical gas holdups were substituted in the mass transfer model (in the correlations for prediction of bubble size and interfacial area), a purely theoretical kLa values in a slurry bubble column were obtained. The predictions were good not only in the homogeneous regime but also in the heterogeneous regime. The theoretical approach was applicable up to relatively high (18 %) solids concentrations. Six different liquid-solid systems were used and 66 kLa values were successfully predicted. In both mass transfer models, correction factors (a function of Eӧtvӧs numbers) were introduced due to the non-spherical (ellipsoidal) shape of the bubbles.

Keywords: Mass transfer coefficients; Penetration theory; New contact time; Gas-liquid bubble columns; Slurry bubble columns

  • Lecture (Conference)
    12th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York, USA

Publ.-Id: 22237

Hydrothermal Alteration of Trachyte Satellite Intrusions in the Cripple Creek District

Rahfeld, A.; Kelly, N.; Monecke, T.

The Cripple Creek deposit located in southwestern Colorado represents one of the largest epithermal gold deposits hosted by alkaline volcanic rocks. A petrographic study of the mostly barren satellite intrusions surrounding the deposit was undertaken to investigate and identify regional alteration patterns. Transmitted light, optical cathodoluminescence, and scanning electron microscopy, integrated with whole-rock geochemical data, revealed a complex history of fluid-rock interaction.
Early albitization of trachyte is preserved within weakly potassic-altered rocks. In more intensely altered rocks, potassium feldspar pervasively replaced the sanidine-dominated groundmass. Late alteration of the trachyte involved the formation of white mica and later kaolinite. The mineralogical changes imply a change in the physiochemical conditions of alteration from early sodic to later potassic alteration, followed by alteration caused at progressively decreasing temperatures and increasing acidity.
Tephrite intrusions within the trachyte satellite bodies have not been influenced by these styles of alteration. The tephrite has been altered to Fe-hydroxide minerals and biotite, most likely caused by influx of Fe-rich fluids. Within the mineralized trachyte of the main diatreme, Au-Te mineralization is at least locally associated with this style of Fe-rich alteration.

Keywords: Alkaline rocks; epithermal deposits; Cripple Creek; hydrothermal Alteration

  • Poster
    13th SGA Biennial Meeting (SGA2015), 24.-27.08.2015, Nancy, Frankreich
  • Contribution to proceedings
    13th SGA Biennial Meeting (SGA2015), 24.-27.08.2015, Nancy, Frankreich
    Mineral resources in a sustainable world. 13th SGA Biennial Meeting (SGA2015)

Publ.-Id: 22236

Geochemical and Mineralogical Analysis of Kupferschiefer

Rahfeld, A.; Möckel, R.; Gutzmer, J.

Kupferschiefer, i.e. very fine-grained and disseminated polymetallic Cu-Ag ores of the extensive stratabound deposits of the Central European Copperbelt is well known for its mineralogical complexity and the challenges surrounding its characterization. It is marked by a combination of high metal sulfide contents (up to 25 wt%) and organic matter (up to 30 wt%) within a matrix predominantly composed of fine-grained clay and carbonate minerals. Conventional analytical procedures often yield unreliable results of this very complex raw material. Regardless, recent research into the hydrometallurgical and microbiological beneficiation of Kupferschiefer has raised the demand for supplying reliable quantitative data of the mineralogy and the geochemistry for both the raw material and process samples. A research project was thus initiative to establish a robust analytical procedure to quantify both mineralogical as well as geochemical attributes of Kupferschiefer-type ores. A combination of analytical techniques is employed for this purpose, including quantitative X-ray diffraction (QXRD), image analysis based on scanning electron microscopy/mineral liberation analysis (MLA), XRF, ICP-AES, and INAA. Method development was based on selected Kupferschiefer samples obtained from Sangerhausen (Germany) and Polkowice-Sieroszowice (Poland) deposits.

QXRD by Rietveld refinement is particularly well-suited to determine the modal mineralogy of fine-grained samples. Five types of layer silicates were identified in Kupferschiefer samples. These are being characterized in detail in order to build crystal structure files needed to enable a full quantification of the minerals present. The necessary characterization of this set of layer silicates has been inhibited by the presence of organic matter, requiring chemical pre-treatment of the raw material that is specifically developed for this purpose.
SEM-based mineral liberation analysis (MLA) on grain mounts of crushed aliquots of the powder samples used for QXRD is used to verify mineral identification and to determine the amounts, liberation, and types of sulphide minerals contained in the samples. This technique is not suited to determine the abundance of the silicate minerals due to their fine-grained and intimately intergrown texture. Further obstacles, such as misidentification of disordered carbonate minerals by XRD or copper sulfides by MLA, are encountered often and can only be recognized and minimized by verifying results using multiple analytical methods. Independent observations from microscopy or bulk geochemistry by fusion XRF are useful in ensuring a high data quality and to test for consistency.
Whole rock trace element data are acquired using INAA, XRF, and ICP-OES. While INAA can guarantee a full analysis without requiring a problematic digestion treatment, the procedure itself is not available for routine measurements. XRF analysis of pressed pellets has been inhibited by the variable content of organic material and matrix effects caused by high sulfide concentrations. ICP-AES/MS analysis is considered to be the most appropriate technique in this case. Different combinations of hydrogen peroxide, nitric acid, and perchloric acid digestion techniques are tested to identify an optimal procedure for the acid digestion of the diverse sulfide compounds as well as the organic matter contained in Kupferschiefer.

Keywords: Kupferschiefer; Analysis; XRD; MLA; XRF; TXRF; ICP-OES; INAA

  • Poster
    The 9th International Conference on the Analysis of Geological and Environmental Materials - Geoanalysis 2015, 10.-13.08.2015, Leoben, Östereich

Publ.-Id: 22235

Multiscale structural characterizations of mixed U(IV)-An(III) oxalates (An(III) = Pu or Am) combining XAS and XRD measurements

Arab-Chapelet, B.; Martin, P.; Costenoble, S.; Delahaye, T.; Scheinost, A. C.; Grandjean, S.; Abraham, F.

Mixed actinides(III,IV) oxalates of general formula M2.2UIV1.8AnIII0.2(C2O4)5·nH2O (An = Pu or Am and M = H3O+ and N2H5+) have been quantitatively precipitated by oxalic precipitation in nitric medium (yield> 99%). Thorough multiscale structural characterizations by XRD and XAS measurements evidenced the existence of oxalate solid solutions. The XANES analysis confirmed that the oxidation states of the metallic cations, tetravalent for uranium and trivalent for plutonium and americium are kept during the precipitation step. The local environments around U+IV, Pu+III and Am+III determined by EXAFS measurements are similar and show that cations are surrounded by five oxalate ligands. The mean metal-oxygen distances by XAS measurements are in agreement with those calculated from XRD lattice parameters. Finally, these An(III)-An(IV) oxalate solid solutions can be used to synthetize mixed actinide oxides characterized by a high homogeneity at molecular scale.

Keywords: Plutonium; Americium; XAFS; XRD; nuclear fuel; transmutation

Publ.-Id: 22234

Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP

Shekhar, C.; Nayak, A. K.; Sun, Y.; Schmidt, M.; Nicklas, M.; Leermakers, I.; Zeitler, U.; Skourski, Y.; Wosnitza, J.; Liu, Z.; Chen, Y.; Schnelle, W.; Borrmann, H.; Grin, Y.; Felser, C.; Yan, B.

Recent experiments have revealed spectacular transport properties in semimetals, such as the large, non-saturating magnetoresistance exhibited by WTe2. Topological semimetals with massless relativistic electrons have also been predicted as three-dimensional analogues of graphene. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states, distinct from those of topological insulators. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temperature) in a magnetic field of up to 9 T, without any signs of saturation, and an ultrahigh carrier mobility of 5x106 cm2 V-1 s-1 that is accompanied by strong Shubnikov–de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topological and conventional electronic phases, with intriguing physical properties resulting from their interplay.

Publ.-Id: 22233

Controllable Broadband Absorption in the Mixed Phase of Metamagnets

Pregelj, M.; Zaharko, O.; Zorko, A.; Gomilsek, M.; Sendetskyi, O.; Günther, A.; Ozerov, M.; Zvyagin, S. A.; Luetkens, H.; Baines, C.; Tsurkan, V.; Loidl, A.

Materials with broad absorption bands are highly desirable for electromagnetic filtering and processing applications, especially if the absorption can be externally controlled. Here, a new class of broadband-absorption materials is introduced. Namely, layered metamagnets exhibit an electromagnetic excitation continuum in the magnetic-field-induced mixed ferro-and anti-ferromagnetic phase. Employing a series of complementary experimental techniques involving neutron scattering, muon spin relaxation, specific heat, ac and dc magnetization measurements, and electron magnetic resonance, a detailed magnetic phase diagram of Cu3Bi(SeO3)2O2Br is determined and it is found that the excitations in the mixed phase extend over at least ten decades of frequency. The results, which reveal a new dynamical aspect of the mixed phase in metamagnets, open up a novel approach to controllable microwave filtering.

Publ.-Id: 22232

Depth Resolved Structural and Compositional Characterization of Ion-Implanted Polystyrene that Enables Direct Covalent Immobilization of Biomolecules

Bilek, M. M. M.; Kondyurin, A.; Dekker, S. A.; Steel, B. C.; Wilhelm, R. A.; Heller, R.; Mckenzie, D. R.; Weiss, A. S.; James, M.; Möller, W.

A polystyrene film spun onto polished silicon substrates was implanted with argon ions using plasma immersion ion implantation (PIII) in order to activate its surface for single step immobilization of biological molecules. The film was subsequently investigated by X-ray and neutron reflectometry, ultraviolet (UV)-visible (VIS) and Fourier transform infrared (FTIR) ellipsometry, FTIR and Raman spectroscopy, as well as nuclear reaction analysis to determine the structural and compositional transformations associated with the surface activation. The ion irradiation resulted in a significant densification of the carbon structure, which was accompanied by hydrogen loss. The density and hydrogen profiles in the modified surface layers were found to agree with the expected depths of ion implantation as calculated by the Stopping and Range of Ions in Matter (SRIM) software. The data demonstrate that the reduction in film thickness is due to ion-induced densification rather than the removal of material by etching. Characterization by FTIR, atomic force microscopy (AFM), ellipsometry and X-ray reflectometry shows that polystyrene films modified in this way immobilize dense layers of protein (tropoelastin) directly from solution. A substantial fraction of the immobilized protein layer remains after rigorous washing with sodium dodecyl sulfate solution, indicating that its immobilization is by covalent bonding.

Keywords: Plasma immersion ion implantation; polystyrene; protein immobilization; nuclear reaction analysis; X-ray reflectometry; neutron reflectometry; spectroscopic ellipsometry; Raman and FTIR spectroscopy

Publ.-Id: 22230

An investigation of the interactions of Eu3+ and Am3+ with uranyl minerals: implications for the storage of spent nuclear fuel

Biswas, S.; Steudtner, R.; Schmidt, M.; Mckenna, C.; Vintró, L. L.; Twamley, B.; Baker, R. J.

The reaction of a number of uranyl minerals of the (oxy)hydroxide, phosphate and carbonate types with Eu(III), as a surrogate for Am(III), have been investigated. A photoluminescence study shows that Eu(III) can interact with the uranyl minerals Ca[(UO2)6(O)4(OH)6]·8H2O (becquerelite) and A[UO2(CO3)3]·xH2O (A/x = K3Na/1, grimselite; CaNa2/6, andersonite; and Ca2/11, liebigite). For the minerals [(UO2)8(O)2(OH)12]·12H2O (schoepite), K2[(UO2)6(O)4(OH)6]·7H2O (compreignacite), A[(UO2)2(PO4)2]·8H2O (A = Ca, meta-autunite; Cu, meta-torbernite) and Cu[(UO2)2(SiO3OH)2]·6H2O (cuprosklodowskite) no Eu(III) emission was observed, indicating no incorporation into, or sorption onto the structure. In the examples with Eu3+ incorporation, sensitized emission is seen and the lifetimes, hydration numbers and quantum yields have been determined. Time Resolved Laser Induced Fluorescence Spectroscopy (TRLFS) at 10 K have also been measured and the resolution enhancements at these temperatures allow further information to be derived on the sites of Eu(III) incorporation. Infrared and Raman spectra are recorded, and SEM analysis show significant morphology changes and the substitution of particularly Ca2+ by Eu3+ ions. Therefore, Eu3+ can substitute Ca2+ in the interlayers of becquerelite and liebigite and in the structure of andersonite, whilst in grimselite only sodium is exchanged. These results have guided an investigation into the reactions with 241Am on a tracer scale and results from gamma-spectrometry show that becquerelite, andersonite, grimselite, liebigite and compreignacite can include americium in the structure. Shifts in the U=O and C-O Raman active bands are similar to that observed in the Eu(III) analogues and Am(III) photoluminescence measurements are also reported on these phases; the Am3+ ion quenches the emission from the uranyl ion. An unusual structure of a 3D uranyl framework is also reported.

Keywords: uranium; europium; emission spectroscopy

Publ.-Id: 22229

Polymer and cluster chemistry of tetravalent cerium in aqueous solutions - Comparison with tetravalent actinides

Ikeda-Ohno, A.; Weiss, S.; Hennig, C.

Cerium (Ce) is known to be the only lanthanide (Ln) which can be stabilized in the tetravalent state (i.e., Ce(IV)) in aqueous solutions. Owing to this chemical specificity, the aqueous chemistry of Ce(IV) shows unique characters as compared to that for the other Ln. For instance, due to its high charge density, the aqueous chemistry of Ce(IV) is predominantly characterised by strong hydrolysis. This strong hydrolysis results in the formation of a variety of hydroxide species even under acidic conditions.1 Moreover, the hydrolysis of Ce(IV) is often a primary step of many wet syntheses to yield nano-sized CeO2 particles which have many technological applications. Despite these chemical uniqueness and importance in applications, the aqueous chemistry of Ce(IV) is poorly understood even to date. Based on this background, this study aims to comprehensively understand the chemical behaviour of Ce(IV) in aqueous solutions by combining several spectroscopic (XAS, HEXS, DLS) and microscopic (TEM) techniques.

Keywords: f-elements; lanthanides; actinides; tetravalent; hydrolysis; aqueous solution; X-ray spectroscopy; TEM

  • Lecture (Conference)
    The 9th International Conference on f-Elements (ICfE 9), 08.09.2015, Oxford, United Kingdom

Publ.-Id: 22228

Bimodal grain size distribution of nanostructured ferritic ODS Fe-Cr alloys

Hilger, I.; Bergner, F.; Weißgärber, T.

Oxide dispersion strengthened Fe-Cr alloys produced by mechanical alloying and spark plasma sintering were found to form different heterogeneous hardness distribution and microstructures depending on the milling parameters. Microstructure investigations by means of electron diffraction techniques and atom probe tomography revealed the presence of large particle-free zones in one material, which is, together with the inhomogeneous deformation at short milling times, considered the main reason for the formation of a heterogeneous microstructure. The inhomogeneous temperature distribution in the sample volume during the sintering process is also expected to contribute to the formation of a heterogeneous grain size distribution in the final material.

Keywords: Spark plasma sintering; bimodal grain size; EBSD; Atom probe tomography; Nanoindentation; microstructure

Publ.-Id: 22227

Response of GaN to energetic ion irradiation: conditions for ion track formation

Karlušić, M.; Kozubek, R.; Lebius, H.; Ban-D’Etat, B.; Wilhelm, R. A.; Buljan, M.; Siketić, Z.; Scholz, F.; Meisch, T.; Jakšić, M.; Bernstorff, S.; Schleberger, M.; Šantić, B.

We investigated the response of wurzite GaN thin films to energetic ion irradiation. Both swift heavy ions (92 MeV Xe23+, 23 MeV I6+) and highly charged ions (100 keV Xe40+) were used. After irradiation, the samples were investigated using atomic force microscopy, grazing incidence small angle x-ray scattering, Rutherford backscattering spectroscopy in channelling orientation and time of flight elastic recoil detection analysis. Only grazing incidence swift heavy ion irradiation induced changes on the surface of the GaN, when the appearance of nanoholes is accompanied by a notable loss of nitrogen. The results are discussed in the framework of the thermal spike model.

Keywords: GaN; swift heavy ion; highly charged ion; ion track; thermal spike

Publ.-Id: 22226

Formation of shallow boron emitters in crystalline silicon using flash lamp annealing: Role of excess silicon interstitials

Riise, H. N.; Schumann, T.; Azarov, A.; Hübner, R.; Skorupa, W.; Svensson, B. G.; Monakhov, E.

Shallow, Boron (B)-doped p+ emitters have been realized using spin-on deposition and Flash Lamp Annealing (FLA) to diffuse B into monocrystalline float zone Silicon (Si). The emitters extend between 50 and 140 nm in depth below the surface, have peak concentrations between 9x1019 cm-3 and 3x1020 cm-3, and exhibit sheet resistances between 70 and 3000 Ohm/Square. An exceptionally large increase in B diffusion occurs for FLA energy densities exceeding approximately 93 J/cm2 irrespective of 10 or 20 ms pulse duration. The effect is attributed to enhanced diffusion of B caused by Si interstitial injection following a thermally activated reaction between the spin-on diffusant film and the silicon wafer.

Publ.-Id: 22225

Indium als Beiprodukt – Bedeutung von Geometallurgie und Rohstoffcharakterisierung

Frenzel, M.; Krause, J.; Bachmann, K.; Gutzmer, J.

Anhand des Beispiels von Indium wird gezeigt wie geometallurgische Denkweisen und Methoden auf typische Beiprodukte angewendet werden können. Besonders für Elemente wie Gallium, Germanium, Selen und Tellur fehlen bisher leider ähnliche Arbeiten völlig. Es wäre daher wünschenswert, dass solche an ausgewählten Lagerstätten durchgeführt werden. Auch für typische Strafelemente wie Cadmium oder Arsen könnte dies sinnvoll sein. Allerdings würde der Fokus bei letzteren eher auf der Vermeidung ihrer Anreicherung in den Konzentraten liegen. Die hier vorgestellte Arbeit könnte für solche Studien als Muster dienen.

  • ACAMONTA - Zeitschrift des Vereins der Freunde und Förderer der TU Bergakademie Freiberg 22(2015), 25-28

Publ.-Id: 22224

Petrographic characterization of REE-Nb-Zr mineralization at the Dubbo trachyte, NSW Australia

Müller, C.; Mentoren: Schulz, B.; Atanasova, P.; Gutzmer, J.

This thesis was the first study which intensively investigated the mineralisation and described the mineral transition between the supergene alterated and the main Toongi trachyte. Compared to other works on this trachyte the identified ore minerals differ. The works of Ramsden [1990, 1992] as well as the actually published mineral lists of Alkane resources Ltd. primarily deal with minerals of the supergene alterated zone. Within all three mineral lists there are major differences (cf. Table 5).
Due to the fact that this thesis, as well as the works of Ramsden, only used EDS measurements, a final evaluation is not possible.
The observed ore minerals often occur as small grains and as impregnation-like patches within the alterated matrix. Within the supergene alterated trachyte LREE are primary hosted by REEphosphates (monazite (Ce)) and zircon minerals, REE-fluorites (bastnaesite (Ce)) are not so important. HREE are primarily hosted by a Nb-Ta mineral. Major Nb hosting minerals are columbite and a Nb-Ta mineral. Zr is hosted by various Zr silicates, especially zircon. Within the main trachyte, LREE are hosted by REE-fluorites (bastnaesite (Ce)) and Zr-silicates (especially poikiloblastic zircon), REE-phosphates are not so important. HREE are primarily hosted by HREEY-(As) minerals. Major Zr hosting minerals are zircon and poikiloblastic zircon. Nb is primarily hosted by a Nb-Na mineral (natroniobite/lueshite) and less by a Nb-REE mineral. Most of the valuable minerals have a hydrothermal origin or they are products of alterated ores, respectively.
Only poikiloblastic zircon and Nb-Na-mineral have a magmatic origin.
Further investigations should confirm the mineral names by using more accurate measurements like X-Ray microanalysis. To determine the composition and temperature of the hydrothermal fluids the fluid inclusions should be investigated. Further investigations of samples out of the depths between 12 and 25 m (between sample DUB 5 and 6) could show the process of supergene mineral transformation more detailed.

Keywords: rare earth elements; metal deportment; trachyte

  • Master thesis
    TU Bergakademie Freiberg, 2015
    Mentor: Bernhard Schulz, Petya Atanasova, Jens Gutzmer
    116 Seiten

Publ.-Id: 22223

Distinguishing magmatic and metamorphic processes in the Norra Kärr alkaline complex, Southern Sweden

Atanasova, P.; Marks, M.; Krause, J.; Markl, G.; Gutzmer, J.

The Norra Kärr rare metal deposit in Southern Sweden represents one of the largest resources of rare earth elements (REE) in Europe. The mineralization is hosted by deformed agpaitic nepheline syenites covering an area 350 by 1100 m in size. REE-bearing minerals include eudialyte-group minerals (EGM) and minor mosandrite and britholite-group minerals. Zr is hosted by catapleiite and EGM.
The intrusion was emplaced between 1.55-1.40 Ga within the Transscandinavian Igneous Belt in an anorogenic (post Svecofennian) environment and deformed and metamorphosed during the Sveconorwegian (Grenvillian) orogeny between 1.25-0.85 Ga (e.g. Andersson et al., 2007). Microtextures and compositional variations in clinopyroxene and EGM are used to distinguish magmatic and metamorphic processes during the evolution of this rare metal mineralization.
Clinopyroxenes are invariably sodic and are characterized by early magmatic Zr-rich cores, euhedrally overgrown by presumably late magmatic aegirine, anhedrally overgrown by metamorphic Al-rich aegirine (jadeite). Similarly, EGM show complex distribution patterns of major and minor elements suggesting multiphase influence of fractional crystallization, recrystallization, fluid-induced re-mobilization and late alteration.

  • Open Access Logo Contribution to proceedings
    Goldschmidt 2015, 17.-21.08.2015, Prag, Tschechische Republik
    Goldschmidt2015 Abstracts: Cambridge Publications, 138-138
  • Poster
    Goldschmidt 2015, 20.08.2015, Prag, Tschechische Republik

Publ.-Id: 22222

Mass of GaAsN in Pulsed Magnetic Fields up to 60 T with Free-Electron Laser IR Radiation

Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Helm, M.

We use the unique combination of the widely tunable (4 μm – 250 μm) Free-Electron laser (FEL) FELBE and pulsed magnetic fields up to 60T of the High Magnetic Field Laboratory HLD to perform spectroscopic investigations on the dilute nitride system GaAsN. We carry out systematic cyclotron resonance (CR) spectroscopy and analyze the dependence of the electron effective mass on the nitrogen content. The red triangles in Figure 1 illustrate our findings for the illumination wavelength 46 μm at 100 K. We observe a slight increase of the effective mass with nitrogen content, which is in very good agreement with the Band Anti-Crossing (BAC) model [1], the empirical Tight Binding (TB) calculations [2] and the Two band BAC model [3], which are represented in Figure 1 by dashed, dotted and dash-dotted black lines, respectively. We compare our results with magneto-photoluminescence (PL) investigations performed by Alberi et al. [4] and Masia et al. [5], which are presented with blue circles and stars respectively. Magneto-PL investigations reveal a very fast increase of the effective mass with nitrogen content, well above the mentioned models [1-3], but consistent with the modified k·p calculations by Lindsay and O’Reilly [6]. Our magneto-PL study (not shown) exhibits a very similar behavior as shown by Alberi et al. and Masia et al., which allows us to exclude the different samples as a source for the deviation.
It is well known that nitrogen tends to form pairs and clusters during the growth, which is only considered in the modified k·p calculations [4]. Magneto-PL is a method which is very sensitive to localization of the neighboring atoms and thus to clusters. For this reason the magneto-PL results are consistent with [4], but cannot be described by [1-3], which do not take clusters into account. On the other hand, CR spectroscopy is only sensitive to delocalized states and this is why our results are in such good agreement with [1-3].

[1] J. Wu et al. Phys. Rev. B 64, 085320 (2000).
[2] N. Shtinkov et al. Phys. Rev. B 67, 081202(R) (2003).
[3] Tomic et al. Phys. Rev. B 69, 245305 (2004).
[4] Alberi et al. Phys. Rev. Lett. 110, 156405 (2013).
[5] Masia et al. Phys. Rev. B 73, 073201, (2006).
[6] A. Lindsay and E. P. O’Reilly Phys. Rev. Lett. 93, 196402 (2004).

Keywords: GaAsN; effective mass; cyclotron resonance spectroscopy; THz spectroscopy in pulsed magnetic fields

  • Lecture (Conference)
    RHMF 2015; International Conference on Research in High Magnetic Fields 2015, 01.-04.07.2015, Grenoble, France

Publ.-Id: 22221

Constraining big bang lithium production with recent solar neutrino data

Takács, M. P.; Bemmerer, D.; Szücs, T.; Zuber, K.

The 3He(α, γ)7Be reaction affects not only the production of 7Li in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He(α,γ)7Be provide precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However, there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavour oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He(α,γ)7Be astrophysical S-factor at the solar Gamow peak, Sν (23+6 keV) 34 −5 = 0.548±0.054 keVb. This new data point is then included in a re-evaluation of the 3He(α,γ)7Be S-factor at Big Bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The re-evaluated S-factor curve is then used to re-determine the 3He(α,γ)7Be thermonuclear reaction rate at Big Bang energies. The predicted primordial lithium abundance is 7Li/H = 5.0 ×10−10, far higher than the Spite plateau.

Keywords: solar neutrinos; S34; Big Bang; Standard Solar Model

Publ.-Id: 22220

Cyclotron Resonance Spectroscopy of GaAsN in Pulsed Magnetic Fields up to 60 T with Free-Electron Laser IR Radiation

Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Pettinari, G.; Helm, M.

The unique combination of the high magnetic field laboratory Dresden (HLD) and the free-electron laser facility FELBE allow us to perform cyclotron resonance spectroscopy experiments with tunable, intense, coherent infrared radiation of high brilliance in the range of 4 - 250 µm in pulsed magnetic fields up to 60 T. The material system of interest is the dilute nitride GaAsN, a promising candidate for electro-optical applications, because of its band gap tunability. The incorporation of a few percent of nitrogen into GaAs enables the gradual decrease of the band gap, which is proportional to the nitrogen content. The description of the band structure and in particular of the effective mass are still challenging despite the number of experimental works (e.g. [1, 2]) that have been performed on this system. In order to contribute to a clarification of this problem, we apply different investigation methods on one sample series of GaAsN with different nitrogen contents (0%; 0.1%; 0.2%).
Probably the most direct and reliable method for the investigation of the effective mass is cyclotron resonance spectroscopy, which has never been applied to bulk GaAsN layers before, according to our best knowledge. Figure 1 illustrates our CR spectroscopy investigation of three samples with different nitrogen contents illuminated with the FEL at wavelengths of 30 µm and 70 µm. These wavelengths have been chosen intentionally to investigate the effective mass behavior below and above the Reststrahlenband of GaAs. We discuss the significance of these CR studies, which were conducted using a range of temperatures, illumination wavelengths and n-type doping of the GaAsN layers. Using a simple Drude-like absorption model we deduce the electron CR mass, the electron mobility, the density of free carriers and the electron relaxation time.

[1] F. Masia et al., Phys. Rev. B 73, 07320 (2006).
[2] K. Alberi et al., Phys. Rev. Lett. 110, 156405 (2013).

Keywords: GaAsN; effective mass; cyclotron resonance spectroscopy; THz spectroscopy in pulsed magnetic fields

  • Lecture (Conference)
    EDiSON'19 19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures, 29.06.-02.07.2015, Salamanca, España

Publ.-Id: 22219

THz free-electron laser investigation of GaAsN in pulsed magnetic fields up to 60 T

Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Helm, M.

We use the unique combination of the free-electron laser FELBE and the High Magnetic Field Laboratory Dresden to perform cyclotron resonance (CR) spectroscopy on the dilute nitride alloy GaAsN. FELBE is a tunable (4 – 250 µm) laser source of high brilliance, which can be used in pulsed magnetic fields up to 60 T. Our CR studies enable us to measure fundamental electronic properties of GaAsN, a very interesting candidate for optoelectronic applications because of the tunability of its band gap energy in the range of 1.4 eV – 0.9 eV by the incorporation of a small concentration of N-atoms (~ 1%). Figure 1 illustrates a typical CR spectrum and our values of the CR electron mass at 100 K and 6.5 THz. We observe a slight increase of the electron CR mass with nitrogen content. This dependence is in very good agreement with that described by the band anticrossing (BAC) model [1] and the empirical tight binding (TB) calculations [2], which are represented in Figure 1 by dashed and dotted black lines, respectively. The comparison with magneto-photoluminescence (PL) investigations performed by Alberi et al. [3] and Masia et al. [4] reveal instead a steep increase of the electron effective mass with nitrogen content, which is consistent with a modified k·p calculation by Lindsay and O’Reilly [5]. This model assumes that nitrogen can form pairs and clusters, not considered in [1,2]. Since PL is very sensitive to carrier localization effects, the results in [3,4] can be well described by [5]. In contrast, CR spectroscopy is only sensitive to delocalized states, which explains the good agreement of the present results with [1,2].

[1] J. Wu et al. Phys. Rev. B 64, 085320 (2000).
[2] N. Shtinkov et al. Phys. Rev. B 67, 081202(R) (2003).
[3] Alberi et al. Phys. Rev. Lett. 110, 156405 (2013).
[4] Masia et al. Phys. Rev. B 73, 073201, (2006).
[5] A. Lindsay and E. P. O’Reilly Phys. Rev. Lett. 93, 196402 (2004).

Keywords: GaAsN; effective mass; cyclotron resonance spectroscopy; THz spectroscopy in pulsed magnetic fields

  • Poster
    German THz Conference 2015, 08.-10.06.2015, Dresden, Deutschland

Publ.-Id: 22218

Triadic resonances in nonlinear simulations of a fluid flow in a precessing cylinder

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

We present results from three-dimensional non-linear hydrodynamic simulations of a precession driven flow in cylindrical geometry. The simulations are motivated by a dynamo experiment currently under development at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which the possibility of generating a magnetohydrodynamic dynamo will be investigated in a cylinder filled with liquid sodium and simultaneously rotating around two axes.
In this study, we focus on the emergence of non-axisymmetric time-dependent flow structures in terms of inertial waves which – in cylindrical geometry – form so-called Kelvin modes. For a precession ratio Γ = Ωp /Ωc = 0.014 considered by us, the amplitude of the forced Kelvin mode reaches up to one fourth of the rotation velocity of the cylindrical container confirming that precession provides a rather efficient flow driving mechanism even at moderate values for Γ.
More relevant for dynamo action might be free Kelvin modes with higher azimuthal wave number. These free Kelvin modes are triggered by non-linear interactions and may constitute a triadic resonance with the fundamental forced mode when the height of the container matches their axial wave lengths. Our simulations reveal triadic resonances at aspect ratios close to those predicted by the linear theory except around the primary resonance of the forced mode. In that regime we still identify various free Kelvin modes, however, all of them exhibit a retrograde drift around the symmetry axis of the cylinder and none of them can be assigned to a triadic resonance.
The amplitudes of the free Kelvin modes always remain below the forced mode but may reach up to 6% of the of the container’s angular velocity. The properties of the free Kelvin modes, namely their amplitude and their frequency, will be used in future simulations of the magnetic induction equation to investigate their ability to provide for dynamo action.

Keywords: Precession; DRESDYN; Dynamo

Publ.-Id: 22217

Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias

Nayak, A. K.; Nicklas, M.; Chadov, S.; Khuntia, P.; Shekhar, C.; Kalache, A.; Baenitz, M.; Skourski, Y.; Guduru, V. K.; Puri, A.; Zeitler, U.; Coey, J. M. D.; Felser, C.

Rational material design can accelerate the discovery of materials with improved functionalities. This approach can be implemented in Heusler compounds with tunable magnetic sublattices to demonstrate unprecedented magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn–Pt–Ga, a giant exchange bias (EB) of more than 3 T and a large coercivity are established.
The large exchange anisotropy originates from the Exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. Our design approach is also demonstrated on a second material with a magnetic transition above room temperature, Mn–Fe–Ga, exemplifying the universality of the concept and the feasibility of room-temperature applications. These findings may lead to the development of magneto-electronic devices and rareearth-free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.

Publ.-Id: 22216

Preferential adsorption of Cu in a multi-metal mixture onto biogenic elemental selenium nanoparticles

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

Preferential adsorption of Cu contained in wastewaters is desirable as the Cu can then be reprocessed and reused more easily. In this study, biogenic elemental selenium nanoparticles (BioSeNPs) were assessed for their ability to preferentially adsorb Cu from an equimolar mixture containing Cu, Cd and Zn. Both metal to BioSeNPs ratio and initial metal solution pH have been shown to affect the preferential adsorption capacity of BioSeNPs towards Cu. BioSeNPs adsorbed 2.3 times more Cu from an equimolar mixture of Cu, Zn and Cd at an initial metal solution pH of 5.2 and metal to BioSeNPs ratio of 0.21 mg mg−1, while adsorbing more than 78% of added Cu. Infrared spectroscopy revealed that the Cu, Cd and Zn were interacting with hydroxyl and carboxyl surface functional groups of the BioSeNPs. The modeling of BioSeNPs' acid-base titration revealed the presence of high concentrations of carboxylic groups (C = 60.26 mol Kg−1) with a pKa of 3.9 providing, further evidence of their interaction with Cu. The adsorption of Cu resulted in a lower colloidal stability of the BioSeNPs as indicated by less negative ζ-potential values. BioSeNPs showed good preferential adsorption capacity towards Cu when compared to oxidized carbon nanotubes. This study provides proof-of-concept for preferential adsorption of Cu onto BioSeNPs which are present in the effluent of a bioreactor treating selenium oxyanions containing wastewater.

Keywords: preferential adsorption; biogenic; selenium nanoparticles; heavy metals; FT-IR

Publ.-Id: 22215

Ga, Ge, In and other trace elements in sphalerite from different geological deposit types, with reference to mineralisation events at Freiberg.

Frenzel, M.

Sphalerite (ZnS) is an important source of a number of high-tech metals. However, while a large amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last decades, our understanding of the geological controls on their enrichment or depletion remains limited. No comprehensive meta-analysis of this data has ever been conducted. This talk presents the results of such a meta-analysis, based on an extensive collection of data from the scientific literature. Nine elements (Ag, Cd, Co, Cu, Fe, Ga, Ge, In and Mn) were considered. For five of these elements (Fe, Ga, Ge, In, Mn) significant differences were found between different geological types of deposits. The regularity of these differences suggests the operation of a single underlying control parameter – possibly formation temperature – with obvious implications for the identification of future sources of these elements.

  • Lecture (others)
    BHMZ Seminar, 06.05.2015, Freiberg, Deutschland

Publ.-Id: 22214

The role of geoscientists in securing the future supply of high technology minerals and metals

Gutzmer, J.; Birtel, S.; Frenzel, M.

The availability of minerals and metals required for high technology applications has in recent years been widely recognized as being of strategic importance for future development - especially for highly industrialized economies. Because the absolute tonnage of such high technology minerals and metals in industrial products is typically small, inventories in the technosphere will remain limited and widely disseminated. This will significantly hamper recycling efforts. As a direct consequence, primary resources will need to be utilized to secure supply into the foreseeable future. Tapping primary resources appears as a reasonable approach, as these are readily available for most high technology metals. Geoscientists will have to make an important contribution – not only towards exploration and discovery, but also to the implementation of technological concepts for comprehensive resource utilization, i.e., mining operations that are not only economic, but also resource-efficient and environmentally benign.

Keywords: High technology metals; criticality; exploration; mineral systems analysis; geometallurgy

  • Lecture (Conference)
    12th Biennial SGA Conference, 12.-15.08.2013, Uppsala, Sverige

Publ.-Id: 22213

A general method for the assessment of the geological and technological limitations to high-tech metal supply

Frenzel, M.; Tolosana-Delgado, R.; Gutzmer, J.

The demand for some of the rarer elements in the Earth's crust for high-tech applications is increasing rapidly. Many of these elements are produced exclusively as by-products resulting in potentially significant supply limitations. However, despite their increasing importance, reliable assessments of these limitations are not readily available. Gallium, germanium, indium, tellurium and rhenium are good examples of such elements.
In this work, a general methodology is presented for the estimation of the supply potential of by-product elements as a function of their distribution in the relevant raw materials, the state of technology and market prices. Geochemical data from the scientific literature is used to generate numerical models of the distribution of the elements over separable production volumes, while data on the partitioning behaviour of the elements during the production of the main products is used to assess the fraction which is profitably extractable as a function of cut-off grade in a waste or intermediate process stream. The exact value of this cut-off grade may be taken to reflect both the current state of extraction technology as well as market prices for the element in question. A combination of the distribution and process behaviour models in Monte Carlo-type numerical simulations yields a median estimate and confidence interval for the supply potential as a function of the cut-off grade.
The results can be presented in the form of availability curves. This allows not only for the assessment of the current situation but also enables simple adaptation to changed technological and market conditions. Furthermore it makes it possible to assess the chief supply limitations, i.e. whether they are geological or technological, as well as the magnitude of inefficiencies in the markets of these metals. A simple example is used to illustrate the application of the method.

  • Lecture (Conference)
    The 17th annual conference of the International Association for Mathematical Geosciences, 05.-12.09.2015, Freiberg, Deutschland

Publ.-Id: 22212

Mineralogical deportment of indium in the Neves-Corvo deposit - Implications for recovery and extraction

Frenzel, M.; Bachmann, K.; Krause, J.; Carvalho, J. R. S.; Relvals, J. M. R. S.; Pacheco, N.; Gutzmer, J.

Neves-Corvo is a world-class volcanic-hosted massive sulphide (VHMS) deposit located in the Iberian Pyrite Belt (IPB). It is both one of the largest and richest deposits in the IPB. Besides its size, other notable features include its high tin content and the unusual ore types within which most of this tin was originally hosted. High indium concentrations (30 - 50 ppm in whole ore) also make it an attractive source of this rare metal. However, the mine does not currently profit from this potential.

It was the aim of this study to generate the data required for a detailed quantitative evaluation of different valorisation options for indium at Neves-Corvo. In addition to data on the spatial distribution of the element, this also requires a detailed understanding of its mineralogical deportment. While previous studies had reported elevated indium concentrations in a number of different minerals (e.g. stannite, sphalerite, cassiterite, tetrahedrite-tennantite, chalcopyrite) as well as the occurrence of two discrete indium minerals (roquesite, CuInS2, and sakuraiite, (Cu, Zn, Fe)3(In,Sn)S4), modal mineralogy and consequently the deportment of indium in the studied samples were never quantified.

In the present work, a combination of whole ore geochemistry, automated scanning electron microscope (SEM)-based image analysis and electron probe microanalysis (EPMA) was used to study the mineralogical deportment of indium in a representative set of more than 70 ore and process samples. It was found that, depending on ore type, sphalerite and/or chalcopyrite are the most important host minerals while stannite, roquesite and sakuraiite are not important due to their generally low abundance. Indium concentrations in sphalerite are highly variable, but are usually 2 - 3 times higher than in coexisting chalcopyrite. The exact concentrations depend on the total concentration of indium in the ore in relation to the abundance of these two minerals. This apparent equilibrium partitioning behaviour is thought to be mostly a consequence of the extensive syntectonic recrystallisation of the ore minerals.

The clear dominance of sphalerite and chalcopyrite as indium carriers has obvious consequences for valorisation options at the mine. First, the indium contained in the ores should be recoverable from the ores with the zinc and copper concentrates. Second, the production of separate concentrates enriched to the minimum concentrations required by smelters will only be possible by the separate processing of indium-rich ores.

To the best knowledge of the authors, this is the first detailed deportment study for indium ever conducted. The results have obvious implications not only for indium valorisation at Neves-Corvo, but also in other massive sulphide deposits affected by extensive tectonically induced recrystallisation. They should therefore be of interest to the wider geometallurgical and economic geology communities.

This is a contribution to the ZHINC project (PTDC/CTE-GIX/114208/2009). Thanks are due to the authors' host institutions for the provision of the funding and infrastructure necessary to conduct this work.

  • Poster
    SEG 2015 - World-Class Ore Deposits: Discovery to Recovery, 27.-30.09.2015, Hobart, Australia

Publ.-Id: 22211

Concentration of Ga, Ge, In and Fe in sphalerite as a function of deposit type – A meta-analysis

Frenzel, M.; Hirsch, T.; Gutzmer, J.

The statistical analysis of a comprehensive collection of analytical data compiled from the scientific literature shows that significant differences exist in the mean concentrations of Ga, Ge, In and Fe in sphalerite samples from different types of Pb-Zn deposits. A systematic trend is present in these mean concentrations: going from Mississippi Valley-type via vein-type to high-temperature hydrothermal replacement deposits, mean Ga and Ge concentrations decrease, while Fe and In concentrations increase. The same trend is observed going from Mississippi Valley-type via sediment-hosted massive sulphide to volcanic-hosted massive sulphide deposits. The two trends are virtually indistinguishable and seem to reflect a general increase in the magmatic contribution to the ore-forming process. While the exact geological controls remain unclear, this trend constitutes an important observation with immediate implications for the exploration for new resources of Ga, Ge and In.

Keywords: Sphalerite; mineral chemistry; trace elements; high-tech metals

  • Poster
    13th Biennial SGA Conference, 24.-27.08.2015, Nancy, France

Publ.-Id: 22210

On the current and future availability of gallium

Frenzel, M.; Ketris, M. P.; Seifert, T.; Gutzmer, J.

By-product availability curves were constructed for the production of gallium (Ga) from bauxite, sulphidic zinc ores and coal. They were used to assess both the current nature of its supply regime, as well as its potential future development. Not only was the current situation found to be firmly in the elastic supply regime for all three raw materials, indicating that significant future increases in primary Ga production are possible without increases in the production of the corresponding main products, but it was also found that estimated current supply potential from bauxite and sulphidic zinc ores alone is at least five times larger than actual primary production. Coal offers a significant additional supply potential (currently at least ~ 1.5 times primary Ga production). An extrapolation of growth trends in the primary production of Al, Zn and Ga into the future indicates that the minimum supply potential of Ga will not be exhausted before 2050. Once this point is reached, additional increases in Ga production relative to the production of Al and Zn will be possible via decreases in the relevant cut-off grades for its extraction. No significant shortages are therefore expected in the foreseeable future. Our results clearly refute the widely-held notion that the supply of certain by-product metals is currently limited by the production of the corresponding main products. Rather, the chief limitation appears to be installed production capacity.

Keywords: High-tech metals; by-products; long-term supply; reserves; resources

Publ.-Id: 22209

Gallium, germanium, indium, and other trace and minor elements in sphalerite as a function of deposit type - A meta-analysis

Frenzel, M.; Hirsch, T.; Gutzmer, J.

While a significant amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last six decades, no meta-analysis of this data has ever been conducted. In this study, the results of such an analysis are presented. While the study focusses on Ga, Ge and In, data for six other elements (Ag, Cd, Co, Cu, Fe and Mn) was also included.
The results show that there are systematic, statistically significant differences in the mean concentrations of Fe, Ga, Ge, In and Mn in sphalerite from different deposit types, while Cd and Cu concentrations show no such differences, and Ag and Co concentrations are only significantly different for vein-type deposits. A principal component analysis demonstrates that the differences between deposit types are approximately one-dimensional, being expressible in terms of a single number. This number correlates strongly with the homogenisation temperature of fluid inclusions (R2 = 0.82, p < 2∙10-16). It may be expressed as follows:

PC 1*=ln((C_Ga^0.22⋅C_Ge^0.22)/(C_Fe^0.37⋅C_Mn^0.20⋅C_In^0.11 ))

with Ga, Ge, In and Mn concentrations in ppm, and Fe concentration in wt.%. The relationship is sufficiently strong to be used as a geothermometer (GGIMFis). The empirical relationship between PC 1* and the homogenisation temperature, T, is:

T(°C)=(54.4±7.3)⋅PC 1*+(208±10)

Our results indicate a strong control of sphalerite chemistry by fluid temperature, particularly for the concentrations of Ga (R2 ~ 0.40), Ge (R2 ~ 0.65), Fe (R2 ~ 0.30) and Mn (R2 ~ 0.60), and to a lesser degree In (R2 ~ 0.10). The concentrations of Ag, Cd, Co and Cu appear to be independent of temperature.
As a consequence of the strong temperature control on PC 1*, metamorphic overprinting of Pb-Zn deposits, even by lower greenschist facies events, may lead to significant changes in sphalerite composition, namely a relative decrease in Ga and Ge concentrations, and increase in Fe, Mn and, to a lesser degree, In concentrations. The closure temperature of sphalerite in regional metamorphic events appears to be around 310 ± 50°C, such that higher-grade events will not be reflected in its composition.
Factors other than temperature, such as differences in fluid salinity or source-rock composition, do not appear to be responsible for differences between deposit types, but rather appear to cause differences between individual deposits. Particularly, the Cu activity in ore-forming systems appears to have a strong influence on In concentrations in sphalerite.
The observed trends in sphalerite compositions provide a useful tool for future studies of different types of Pb-Zn deposits, as well as for mineral exploration. They should be particularly relevant for the identification of new resources of Ga, Ge and In.

Keywords: High-tech metals; By-products; Fluid salinity; Sphalerite geothermometer; Fluid inclusions; Homogenisation temperature; GGIMFis thermometer

Publ.-Id: 22208

Assessing the supply potential of high-tech metals - A general method

Frenzel, M.; Tolosana-Delgado, R.; Gutzmer, J.

The demand for some of the rarer elements in the Earth's crust, mostly from high-tech applications, is increasing rapidly. Many of these elements are produced exclusively as by-products resulting in potentially significant supply limitations. In this article, a general method for the assessment of the supply potential of such elements is developed from a conceptual model of the supply-chain. Namely, statistical and deterministic models are introduced to quantify both the variability in by-product concentrations in the relevant raw materials, as well as the effects of this variability on achievable recoveries. The assessment of uncertainties is implemented via Monte-Carlo-type simulations. Presentation of the results in availability curves ensures adaptability to future changes in market conditions, while extensive documentation of the assessment method, available as electronic supplementary material with this article, ensures reproducibility.
A simple example is used to illustrate the complete estimation process. It shows that in addition to ensuring future adaptability of the results, availability curves are also useful for the assessment of the current supply regime of a given by-product. An elastic and inelastic regime might be distinguished – in the elastic regime, significant demand-driven increases in by-product supply are possible without increases in the production of the main product, while in the inelastic regime this is not the case. The method presented in this article is the first to enable such an assessment to be made in a reliable and transparent manner.

Keywords: Electronic metals; Availability; By-products; Germanium; Reserves; Resources

Publ.-Id: 22207

Lattice location of deep level impurities in hyperdoped Si by ion implantation and short-time annealing

Liu, F.; Prucnal, S.; Gao, K.; Heller, R.; Skorupa, W.; Helm, M.; Zhou, S.

Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell. However, deep level impurities have relatively low solid solubility limit in Si. We prepared deep level impurities doped silicon to above the Mott insulator concentration by ion implantation followed by sub-second annealing. The degree of crystalline lattice recovery in implanted layers and the lattice location of impurities in Si were analyzed by Rutherford backscattering spectrometry/Channeling. Our results show that S and Se atoms are occupying substitutional lattice sites in Si [1], while Ti impurities have no ordered lattice occupation [2].

[1] S. Zhou, F. Liu, S. Prucnal, K. Gao, M. Khalid, W. Skorupa and M. Helm, Scientific Report 5, 8329 (2015).
[2] F. Liu, et al., in preparation (2015).

Keywords: Ion implantation; deep level impurities

  • Poster
    Jaszowiec 2015, 20.-25.06.2015, Wisła, Poland

Publ.-Id: 22206

Lattice location of deep level impurities in hyperdoped Si by ion implantation and short-time annealing

Liu, F.; Prucnal, S.; Gao, K.; Heller, R.; Skorupa, W.; Helm, M.; Zhou, S.

Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell. However, deep level impurities have relatively low solid solubility limit in Si. We prepared deep level impurities doped silicon to above the Mott insulator concentration by ion implantation followed by sub-second annealing. The degree of crystalline lattice recovery in implanted layers and the lattice location of impurities in Si were analyzed by Rutherford backscattering spectrometry/Channeling. Our results show that S and Se atoms are occupying substitutional lattice sites in Si [1], while Ti impurities have no ordered lattice occupation [2].

[1] S. Zhou, F. Liu, S. Prucnal, K. Gao, M. Khalid, W. Skorupa and M. Helm, Scientific Report 5, 8329 (2015).
[2] F. Liu, et al., in preparation (2015).

Keywords: Ion implantation; deep level impurities

  • Poster
    IBA 2015 - 22nd International Conference on Ion Beam Analysis, 14.-19.06.2015, Opatija, Croatia

Publ.-Id: 22205

Use of a Cyclone 18/9 for Radiolabelling of Nanoparticles

Franke, K.; Hildebrand, H.; Schymura, S.

Nanosafety research requires versatile tools for detection of nanoparticles in living and non-living media within a wide range of concentration. This is a great challenge due to the very low environmentally relevant concentration of (engineered) nanoparticles expected and the presence of background concentrations of the respective elements. Radiolabelling of nanoparticles offers an excellent alternative to enable nanoparticle detection in these complex media down to trace amounts. Even online in situ tracing and visualisation techniques are accessible.

In this work we present different techniques for the radiolabelling of nanoparticles (Ag0, TiO2, CeO2, MWCNT) including activation of NP, radiosynthesis of NP, radiolabelling of NP, self-diffusion of radioisotopes into NP and recoil labelling. A cyclotron Cyclone 18/9 was used for the radiolabelling of the nanoparticles via proton activation (Ti-48(p,n)V-48, Ce-140(p,2n)Pr-139  Ce-139), Be-7 - recoil labelling (Li 7(p,n)Be-7) and the radioisotope production. Different targets were developed and different labelling strategies were tested. As a result, labelling yields and labelling stabilities were determined and the influence of the labelling procedure on the particle properties was evaluated.

These radiolabelled nanoparticles are successfully used in comprehensive environmental studies. Our recent studies with application of the radiolabelled nanoparticles focus on nanoparticle uptake in plants, distribution and mobility of nanoparticles in sewage sludge, and fate of nanoparticles in wastewater treatment processes.

  • Lecture (Conference)
    International Conference on Nuclear Analytical Methods in the Life Science (NAMLS11), 23.-28.08.2015, Delft, The Netherlands

Publ.-Id: 22204

High temperature stable transparent conductive oxides for solar thermal applications

Lungwitz, F.; Schumann, E.; Guillen, E.; Escobar, R.; Krause, M.; Gemming, S.

In solar thermal energy conversion systems, receivers containing the heat transfer fluid are coated by a solar selective coating which must exhibit high absorption in the solar region and low thermal emittance. Additionally, the coating materials have to be structurally, optically, and mechanically stable at high temperatures. Nowadays, temperatures of up to 450 °C and up to 550°C are reached using parabolic trough arrays and solar tower absorbers, respectively, whereas temperatures up to 800 °C could be reached if the receiver materials were stable enough. Solar selective coatings can be formed by a transparent conductive oxide (TCOs) film deposited on a black body absorber to have both, high absorption in the ultraviolet, visible and near infrared spectral range (300 nm – 2500 nm) as well as high reflectivity in the infrared (> 2500 nm). The former is to absorb as much sunlight as possible, the latter for preventing thermal radiation losses from the system to the environment. In this work Ta:TiO2 and Ta:SnO2 TCOs thin films are reactively magnetron sputtered from tantalum doped metallic targets. The oxygen flow during deposition is precisely controlled by a plasma emission unit which is crucial to obtain optimal electrical and therefore also optical properties by maintaining high sputtering rates. While the as-deposited films are amorphous and non-conductive, they are crystallized and therefore electrically activated upon a subsequent thermal treatment at 425 °C for 1 hour. The correlation between structural, optical, and electrical properties is shown by Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction (XRD), Raman Spectroscopy, Spectroscopic Ellipsometry (SE) (both at room- and high- temperatures), UV-VIS spectrometry, and Hall Effect measurements. Preliminary tests show that optical constants of Ta:TiO2 films are maintained after annealing at 700ºC.

Keywords: TCO; transparent conductive oxide; solar thermal; magnetron sputtering; TiO2; Cluster Tool; solar selectivity; high temperature

  • Lecture (Conference)
    ICMAT 2015 & IUMRS - ICA 2015, 28.06.-03.07.2015, Singapore, Singapore

Publ.-Id: 22203

Optical and electrical characterization of TiO2- based transparent conductive oxides

Lungwitz, F.; Schumann, E.; Wenisch, R.; Neubert, M.; Guillen, E.; Escobar, R.; Krause, M.; Gemming, S.

Transparent conductive oxides (TCOs) are already widely used in the optoelectronic industry e.g. as electrodes for liquid crystal displays (LCDs), organic light emitting diodes (OLEDs), or thin film solar cells. Less attention has been devoted to their optical properties and thermal stability until now.
In this work, Tantalum doped TiO2 and SnO2 TCO films are investigated with respect to their structural, optical, and electrical properties at temperatures from RT to 700°C. The films are prepared at room temperature by direct current reactive magnetron sputtering from metallic as well as ceramic targets and subsequently isothermally annealed at temperatures of 425°C. For compositional and structural analysis x-ray diffraction (XRD), Raman spectroscopy, and Rutherford backscattering spectroscopy (RBS) are used. The optical properties are determined by spectroscopic ellipsometry, spectral photometry, and subsequent modelling. Hall effect measurements are used to determine the electrical properties of the TCO films.
The as-deposited layers are amorphous and isolating. By thermal annealing they are activated and become conductive.

Keywords: TCO; transparent conductive oxide; solar-thermal; thin film; high temperature; magnetron sputtering; energy materials; Cluster Tool

  • Poster
    Frühjahrstagung der DPG, 19.03.2015, Berlin, Deutschland

Publ.-Id: 22202

Contactless magnetic excitation of acoustic cavitation in liquid metals

Grants, I.; Gerbeth, G.; Bojarevics, A.

A steady axial magnetic field is applied to a liquid metal zone heated by induction currents. The resulting alternating Lorentz force causes pressure oscillations that being strong enough lead to cavitation in the molten metal. Amplitude of the pressure oscillations is proportional to the product of the induced currents and the steady axial magnetic field induction. We follow an approach where the acoustic pressure is maximized by the induction currents. The onset of cavitation is identified by the occurrence of sub-harmonics of the drive frequency in sound recorded at the surface of the experimental cell. It is demonstrated that cavitation in a liquid metal may be excited by a superimposed axial magnetic field of a moderate 0.5 T induction.


Publ.-Id: 22199

Macro segregation formation mechanism of the primary silicon phase in directionally solidified Al-Si hypereutectic alloys under the impact of electric currents

Zhang, Y.; Miao, X.; Shen, Z.; Han, Q.; Song, C.; Zhai, Q.

Understanding the macro segregation formed by applying electric currents is of high commercial importance. This paper investigates how electric currents control the solute distribution in the directionally solidified Al-20.5wt%Si hypereutectic alloy. Experimental results show that a severe macro segregation of the primary silicon phase occurs at the initial solidification stage of the samples. This is accompanied by two interface transitions in the mushy zone: quasi planar → upwards V-shaped → quasi planar. The corresponding numerical simulations present a vortex ring flow pattern as a consequence of the electric current distortion in the mushy zone. The peculiar macro segregation phenomenon can be fully explained by considering the effect of the forced flow on the solute distribution. At the initial growth of the samples, the forced flow generates a rigorous solute exchange between the mushy zone and the bulk melt and encourages the primary silicon to continuously precipitate and segregate. As the solute content in the bulk melt gradually approaches the eutectic point, the precipitation of primary silicon is profoundly reduced. Eventually, a significant segregation of the primary silicon phase is observed in the initial directional growth. The present study not only presents a new approach to control the solute distribution by applying an electric current through a generated forced flow, it also facilitates the understanding of the underlying grain refinement mechanism and the growth of crystals in the solute that are controlled by the electric currents.

Keywords: Al-Si alloys; directional solidification; external electric field; macro segregation; melt convection

Publ.-Id: 22197

Quantitative cross-sectional measurement of solid concentration distribution in slurries using wire-mesh sensor

Dos Santos, E. N.; Schleicher, E.; Reinecke, S.; Hampel, U.; Da Silva, M. J.

Wire'mesh sensors have so far been widely applied in gas'liquid flows where resistance or capacitance distributions are measured and converted into gas or liquid holdup distributions. In this work we report on the qualification of the wire'mesh imaging technique for the measurement of cross'sectional solid concentrations in solid–liquid mixtures. As the dielectric constants of solid particles are different from those of gas, water or oil in the flow, measuring this property can be used as an indication of solids distribution. Experiments were performed in a stirred tank of 100 mm diameter equipped with a capacitance wire'mesh sensor. The wire'mesh sensor was operated 4000 frames per second acquisition speed and has a spatial resolution of 6.25 mm. As solids we used silica sand particles (diameter ~ 105 μm) which were stirred with water in a volume concentration range of 1% to 35% to form slurries. By varying the stirring speed, different solid concentration distributions were produced and investigated. In order to convert the measured relative permittivity distribution into a solid concentration distribution, an empirical approach was employed.

Keywords: wire-mesh sensor, slurry flow; solid fraction measurement, flow visualization

Publ.-Id: 22196

Regenerative amplification in Yb3+-doped fused silica

Röser, F.; Loeser, M.; Siebold, M.; Albach, D.; Grimm, S.; Langner, A.; Schötz, G.; Schramm, U.

We report to our knowledge the first short pulse generation experiment
in bulk volume Yb-doped fused silica utilizing a Q-switched cavity.

  • Contribution to proceedings
    CLEO/Europe-EQEC Conference 2015, 21.-25.06.2015, München, Deutschland
  • Poster
    CLEO/Europe-EQEC Conference 2015, 21.-25.06.2015, München, Deutschland

Publ.-Id: 22195

Code intercomparison and benchmark for muon fluence and absorbed dose induced by an 18-GeV electron beam after massive iron shielding

Fasso, A.; Ferrari, A.; Ferrari, A.; Mokhov, N. V.; Mueller, S. E.; Nelson, W. R.; Roesler, S.; Sanami, T.; Striganov, S. I.; Versaci, R.

In 1974, Nelson, Kase, and Svenson published an experimental investigation on muon shielding using the SLAC high energy LINAC. They measured muon fluence and absorbed dose induced by a 18 GeV electron beam hitting a copper/water beam dump and attenuated in a thick steel shielding. In their paper, they compared the results with the theoretical mode ls available at the time. In order to compare their experimental results with present model calculations, we use the modern transport Monte Carlo codes MARS15, FLUKA2011 and GEANT4 to model the experimental setup and run simulations. The results will then be compared between the codes, and with the SLAC data.

  • Open Access Logo Contribution to proceedings
    Shielding Aspects of Accelerators, Target and Irradiation Facilities – SATIF 12, 28.-30.04.2014, Batavia (Illinois), USA
    Workshop Proceedings, Online: OECD Nuclear Energy Agency, 240-247


Publ.-Id: 22194

Fermi surface of SrCo2P2: A strongly enhanced Pauli paramagnet

Götze, K.; Klotz, J.; Bergmann, C.; Geibel, C.; Kraft, I.; Lorenz, V.; Rosner, H.; Sheikin, I.; Mccollam, A.; Bruin, J.; Wosnitza, J.

es hat kein Abstract vorgelegen

  • Poster
    RHMF 2015, 11th International Conference on Research in High Magnetic Fields, 02.-04.07.2015, Grenoble, France

Publ.-Id: 22193

NMR of the Shastry-Sutherland lattice SrCu2(BO3)2

Stern, R.; Kohlrautz, J.; Haase, J.; Kühne, H.; Green, E.; Zhang, Z.; Wosnitza, J.

SrCu2(BO3)2 is a prominent realization of the Shastry-Sutherland lattice model [1]. In this quasi-two-dimensional compound, Cu2+ ions form orthogonal spin-singlet dimers with strong geometrical frustration of the next-nearest and nearest neighbor exchange interactions. SrCu2(BO3)2 has been studied extensively using a variety of techniques, such as nuclear magnetic resonance (NMR) spectroscopy, or recent magnetization measurements up to 118 T. These experiments reveal a complex sequence of magnetization plateaus with differing commensurate magnetic superstructure, stemming from a stripe type order of triplet states [2-4]. Due to its highly sensitive local probe character, NMR can provide deep insight into the spin-coupling mechanisms and excitations at highest magnetic fields. We present 11B NMR spectra measured in pulsed magnetic fields up to 56 T, and compare those with prior results obtained in highest static magnetic fields. Herewith, we prove the feasibility and efficacy of this new technique, yielding the capability for extended studies at highest magnetic fields up to the 100 T regime that determine the spin structure in the 1/3 magnetization plateau and beyond.

  • Poster
    RHMF 2015 - 11th International Conference on Research in High Magnetic Fields, 02.-04.07.2015, Grenoble, France

Publ.-Id: 22192

Solid-state NMR in pulsed magnetic fields

Kühne, H.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    EMFL 2015 User Meeting, 01.07.2015, Grenoble, France

Publ.-Id: 22191

III-V:Mn Ferromagnetic semiconductors prepared by ion implantation

Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.

Ferromagnetic semiconductors (FSs) have been under intensive investigation during the last decade. Until now, the prototype ferromagnetic semiconductor GaMnAs has revealed a variety of unique features induced by the combination of its magnetic and semiconducting properties. As a non-equilibrium process, ion implantation can overcome the difficulty that the Mn concentration in ferromagnetic III-V (FS) is far beyond the solid solubility of Mn in III-V compounds. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing within nanoseconds regime allows the epitaxial growth from a liquid phase. The approach combining ion implantation and pulsed laser melting allows us to prepare ferromagnetic semiconductors covering the full spectrum of III-V compound semiconductors.
We have successfully synthesized ferromagnetic Mn doped III-V from InAs and GaAs to InP and GaP with different bandgaps. The results of magnetization, magnetic anisotropy, resistivity, anomalous Hall effect, magnetoresistance and x-ray magnetic circular dichroism obtained from the synthesized samples confirm the intrinsic origin and the carrier-mediated nature of the ferromagnetism. Moreover, in different III-V hosts we observe distinct differences regarding the magnetic anisotropy and conduction mechanism which are related with the intrinsic parameters such as the lattice mismatch, energy gap and the acceptor level of Mn. These results could allow a panorama-like understanding of III-V:Mn based ferromagnetic semiconductors.

  • Poster
    Jaszowiec 2015, 20.06.2015, Wisla, Poland

Publ.-Id: 22190

Hydrodynamic and mass transfer properties of a bubble column with vertically inserted tube bundles

Šimić, N.; Breiler, K.; Schubert, M.

The objective of this study is to examine the influence of different vertical tube bundle designs on the bubble dynamics and on the mass transfer rates in a bubble column. The studies in the open literature examining the performance of bubble columns with vertically inserted tube bundles have focused primarily on the coverage of the cross-sectional area of the bubble column by the tube bundle (CSA). The most frequently used coverages are the 5% and the 25% (± 3%) which mimic the heat exchangers utilized in the processes of methanol and Fischer-Tropsch syntheses. Other than that, the designs of tube bundles seem to be arbitrarily chosen and feature a number of different configurations of layouts, tube diameters and tube lengths. From the current state of research, it is thus rather difficult to draw conclusions on the optimal design of a heat exchanger suitable for use in bubble columns (Youssef et al., 2013). Intuitively, it can be concluded that the most important design features of tube bundles affecting the flow are the distance between the tubes and the unit cell area enclosed by the tubes in their respective arrangements. Accordingly, the study aims on a systematic analysis on the effect of these geometric parameters.

Keywords: bubble column; internals; heat exchanger; tube bundle; hydrodynamics; gas holdup; bubble size distribution; mass transfer; X-ray tomography

  • Poster
    12th International Conference on Gas-Liquid & Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York City, USA

Publ.-Id: 22189

Macroscopic and spectroscopic characterization of uranium(VI) sorption onto orthoclase and muscovite and the influence of competing Ca2+

Richter, C.; Müller, K.; Drobot, B.; Steudtner, R.; Großmann, K.; Stockmann, M.; Brendler, V.

The uranium(VI) sorption onto orthoclase and muscovite, representing feldspars and micas as important components of the earth crust, was investigated in the presence and absence of Ca2+ under aerobic conditions. Batch experiments were accompanied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) as well as in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. The results indicate that the U(VI) sorption is reduced by Ca2+ at pH ≥ 8 up to 30% due to the formation of the neutral aqueous Ca2UO2(CO3)3 complex. TRLFS measurements on the supernatant confirmed the predominance of this Ca2UO2(CO3)3 complex in accordance with thermodynamic calculations. Furthermore, TRLFS measurements on the mineral suspension as a function of pH (4 – 9) and Ca2+ revealed the existence of several species. Parallel factor analysis (PARAFAC) indicated the formation of three surface species totally. In the absence of Ca2+, the ≡XO UO2+ and ≡XO UO2CO3– surface complexes were formed, whereas the presence of Ca2+ leads to the formation of ≡XO UO2+ and ≡XO UO2OH as the formation of the aqueous Ca2UO2(CO3)3 complex reduces the free UO22+ concentration in the solution. Additional, ATR FT-IR confirmed an outer-sphere surface species in the absence of Ca2+. These experimental results were used for the assessment of surface complexation parameters to improve the basis for a mechanistic modeling of the sorption processes of U(VI) onto orthoclase and muscovite including the influence of Ca2+. Namely, log K≡XO-UO2+ = 1.69 and log K≡XO-UO2CO3− = 8.96 were determined for sorption onto orthoclase, whereas log K≡XO-UO2+ = 0.41 and log K≡XO-UO2CO3− = 8.71 best describe sorption onto muscovite.

Keywords: Sorption; uranium; orthoclase; muscovite; calcium; TRLFS; ATR FT-IR; PARAFAC; SCM

Publ.-Id: 22187

Ultra-fast X-ray tomographic measurement of activated sludge aerated by membrane and monolithic spargers

Sommer, A.-E.; Wagner, M.; Reinecke, S. F.; Bieberle, M.; Barthel, F.; Hampel, U.

The removal of nitrogen and organic components by micro-organisms is an essential step in the biodegradable wastewater treatment plants. These biological reactions take place in large aerated cross flow reactors. In fact, up to 80 % of the total energy budget of wastewater treatment plants is consumed by the aeration process. Engineering and design of the plants are mostly based on empirical knowledge and limited instrumentation for single points of measurement. Thus, the complex hydrodynamic and biochemical processes in the large-scale vessels are not well understood, and there is a high potential for optimization of these processes. Recently, numerical tools, such as CFD, have been used for the design and prediction of improved operation of the reactors. However, the models used in the software show a significant deviation from experimental data and need improvement due to the complexity of the multiphase flows of aerated sludges (bubbles, microbial flakes, water). A detailed study has been carried out in a vertical column of 3.5 m in height at HZDR to obtain an improved understanding of the hydrodynamics of aerated sludges. To capture the temporal evolution of the rising bubbles in the opaque liquors the ultra-fast electron beam X-ray tomography system of HZDR was used. The target parameters are bubble size distribution, equivalent sauter diameter of the bubbles, bubble rise velocity and local gas hold-up under the variation of sparger type (rubber, monolithic material), gas flow rate, rheology of the fluid (deionized water, salty water, sludge) and height in the liquid column. Therefore enhanced image analysis algorithms, developed at HZDR, were applied to the reconstructed tomographic images, which are also presented in the paper. In the future, the experimental data set will be used as reference data for the improvement of numerical models of CFD software.

Keywords: ultra-fast X-Ray tomography; activated sludge; aeration

  • Lecture (Conference)
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland
  • Contribution to proceedings
    7th International Symposium on Process Tomography (ISPT7), 01.-03.09.2015, Dresden, Deutschland
    Proceedings of the 7th International Symposium on Process Tomography

Publ.-Id: 22186

Macro-Mixing characterisation of a stirred model fermenter of non-NEWTONIAN liquid by flow following sensor particles and ERT

Reinecke, S.; Deutschmann, A.; Jobst, K.; Hampel, U.

Investigation of the fluid circulation and the macro-mixing process in a stirred model fermenter of non-NEWTONIAN liquid was conducted by the comparative use of flow following sensor particles and ERT. Average fluid circulation times were estimated from (i) the measured vertical position of the sensor particle, (ii) the fluctuating ERT signals of single ERT planes and (iii) the measured mixing times of ERT-NaCl tracer experiments. The estimated average circulation times of all the three methods are comparable for the two investigated impeller positions. Furthermore, axial residence profiles of the sensor particles were extracted, which reveal the impact of the impeller configuration to the axial mixing homogeneity. Moreover, the results confirm the conclusions about the effect of the lifted impeller position derived by Reinecke et al. (2012) in a 1000 L pilot fermenter. The excellent detectability of the particles and the consistent results confirm the feasibility of the combined method for further investigation of the complex flows in biogas fermenters.

Keywords: macro mixing; circulation time; hydrodynamics; stirred tank; biogas fermenter; flow follower; sensor particle; ERT


Publ.-Id: 22185

Instrumentierte Strömungsfolger mit erweiterter Positionsdetektion und Auftriebseinheit

S. Reinecke; Hampel, U.

Zur Untersuchung der ablaufenden Prozesse in großen Behältern, wie z. B. Biogasfermentern, Bioreaktoren und Belebtschlammbecken, wurde am HZDR das Konzept instrumentierter, strömungsfolgender Sensorpartikel entwickelt [1]. Die Sensorpartikel werden als auftriebsneutrale Strömungsfolger eingesetzt und erfassen dabei kontinuierlich Prozessparameter. Diese Daten werden nach der Rückgewinnung der Sensorpartikel aus dem Prozess einem computergestützten Analysesystem zur Verfügung gestellt. Die erweiterten Sensorpartikel bestehen aus robusten Kapseln, welche mit einer integrierten Messelektronik und einer mechanischen Auftriebseinheit ausgestattet sind (siehe Abb. 1). Das Systemkonzept berücksichtigt derzeit miniaturisierte Sensoren für die Umgebungstemperatur, die Eintauchtiefe als Funktion des hydrostatischen Drucks, die Beschleunigung, die Drehrate und das Magnetfeld. Das Konzept ist zudem offen für die Einbindung ergänzender miniaturisierter Messfühler, wie z.B. für pH-Wert und Gelöst-Sauerstoff. Die Auftriebseinheit erlaubt eine automatisierte Tarierung der Sensorpartikel im ruhenden Prozessmedium, wodurch ein aufwändiges manuelles Justieren der Partikelmasse entfällt. Zudem ist mit der Auftriebseinheit eine erleichterte Rückgewinnung der Sensorpartikel von der Flüssigkeitsoberfläche nach Beendigung der Messung möglich.
Im Beitrag werden das erweiterte Konzept zur Positionsdetektion der Strömungsfolger und erste Testergebnisse vorgestellt. Es werden zum einen die Signale der Beschleunigung, der Drehrate und der magnetischen Flussdichte zur Rekonstruktion von Positionsveränderungen genutzt. Weiterhin ist die Detektion von externen Positionsmarkern, wie z. B. dem Signal einer Tauschspule, möglich. Beide Varianten wurden in praxisrelevanten Szenarien getestet. Zudem wird sowohl die Dimensionierung und der Aufbau der integrierten Auftriebseinheit als auch der Test unter realen Strömungsbedingungen vorgestellt.

  • Open Access Logo Contribution to proceedings
    12. Dresdner Sensor-Symposium, 07.-09.12.2015, Dresden, Deutschland, 978-3-9813484-9-1
    DOI: 10.5162/12dss2015/P8.2
  • Poster
    12. Dresdner Sensor-Symposium, 07.-09.12.2015, Dresden, Deutschland

Publ.-Id: 22184

Instrumentierte Strömungsfolger zur Prozessdiagnose in gerührten Fermentern

Reinecke, S.

Die Erzeugung von Energie aus Biogas ist ein wichtiger Baustein unseres zukünftigen Energiekonzepts. Das Biogas dafür wird in Biogasfermentern gewonnen. In den letzten Jahren ist die Anzahl solcher Anlagen allein in Deutschland auf etwa 8.000 gestiegen. Allerdings zeigt sich, dass die bisherige Ausnutzung des Potenzials, das das Biogas bietet, bisher sehr gering ist. Biogasanlagen verwenden nahezu keine Instrumentierung, um die Anlagentechnik geeignet steuern und damit effizient betreiben zu können. Dadurch ist auch das Wissen über die Mischvorgänge in Biogasfermentern und die entscheidenden Einflüsse auf die Prozessführung völlig unzureichend. Es wurde untersucht, wie man durch strömungsfolgende Sensoren, die in Biogasfermentern eingebracht werden und dann die relevanten Prozessparameter räumlich verteilt messen, Kenntnis über die ablaufenden Mischprozesse erlangt. Damit lassen sich einerseits direkte Schlussfolgerungen für den Betrieb von Biogasfermentern ableiten, andererseits aber auch theoretische Prozessmodelle entwickeln, validieren und anpassen, um Biogasanlagen zukünftig viel effizienter betreiben zu können.

  • Invited lecture (Conferences)
    3. Fachkolloquium am Institut für Energie und Prozesstechnik der FH-Münster, 10.03.2015, Steinfurt, Deutschland

Publ.-Id: 22183

High Curie temperature and perpendicular magnetic anisotropy in homoepitaxial InMnAs films

Yuan, Y.; Wang, Y.; Gao, K.; Khalid, M.; Wu, C.; Zhang, W.; Munnik, F.; Weschke, E.; Baehtz, C.; Skorupa, W.; Helm, M.; Zhou, S.

We have prepared the dilute magnetic semiconductor (DMS) InMnAs with different Mn concentrations by ion implantation and pulsed laser melting. The Curie temperature of the In1−xMnxAs epilayer depends on the Mn concentration x, reaching 82K for x = 0.105. The substitution of Mn ions at the indium sites induces a compressive strain perpendicular to the InMnAs layer and a tensile strain along the in-plane direction. This gives rise to a large perpendicular magnetic anisotropy, which is often needed for the demonstration of the electrical control of magnetization and for spin-transfer-torque induced magnetization reversal

Keywords: dilute magnetic semiconductors; InMnAs; ion implantation; pulsed laser melting; perpendicular magnetic anisotropy

  • Journal of Physics D: Applied Physics 48(2015), 235002
    DOI: 10.1088/0022-3727/48/23/235002
  • Lecture (Conference)
    IEEE intermag 2015, 11.05.2015, Beijing, China

Publ.-Id: 22182

Magnetic phase transitions and large magnetic entropy change with a wide temperature span in HoZn

Li, L.; Yuan, Y.; Zhang, Y.; Poettgen, R.; Zhou, S.

CsCl-type HoZn undergoes two successive magnetic phase transitions: (i) paramagnetic to ferromagnetic (FM) at T-C similar to 72 K and (ii) a spin reorientation (SR) at T-SR similar to 26 K. Magnetization and modified Arrott plots indicate that HoZn undergoes a second-order magnetic phase transition around T-C. The obtained critical exponents have some small deviations from the mean-field theory, indicating a short range or a local magnetic interaction which is properly related to the coexistence of FM and SR transitions at low temperature. Two successive magnetic transitions in HoZn induce one broad pronounced peak together with a shoulder in the temperature dependence of the magnetic entropy change -Delta S-M(T) curves, resulting in a wide temperature range with a large relative cooling power (RCP). For a field change of 0-7 T, the maximum value of -Delta S-M is 15.2 J/kg K around T-C with a large RCP value of 1124 J/kg. The large reversible magnetocaloric effect (MCE) and RC indicate that HoZn is a good candidate for active magnetic refrigeration.

Keywords: HoZn compound; Magnetocaloric effect; Critical exponent; Large refrigeration capacity; Active magnetic refrigeration materials

Publ.-Id: 22181

Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya

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

Geomorphic footprints of past large Himalayan earthquakes are elusive, though urgently needed for gauging and predicting recovery times of seismically perturbed mountain landscapes. We present evidence of catastrophic valley infill following at least three medieval earthquakes in the Nepal Himalayas. Radiocarbon ages from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments near Pokhara, Nepal’s second largest city, match the timing of nearby M~8 earthquakes in ~1100, 1255, and 1344 AD. The upstream dip of these valley fills and X-ray fluorescence spectrometry of their provenance rule out any local source. Instead, geomorphic and sedimentary evidence is consistent with catastrophic debris flows that had invaded and plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 km away.

Keywords: accelerator mass spectrometry; earthquake

Publ.-Id: 22180

P1402 - Kontrolle einer therapeutischen Bestrahlung durch eine Bestrahlungseinrichtung mit einem mikrogepulsten Teilchenstrahl

Enghardt, W.; Fiedler, F.; Helmbrecht, S.

Die Erfindung betrifft Verfahren und Einrichtungen zur Kontrolle einer therapeutischen Bestrahlung durch eine Bestrahlungseinrichtung mit einem mikrogepulsten Teilchenstrahl mittels eines Positronen-Emissions-Tomografen. Diese zeichnen sich insbesondere dadurch aus, dass eine therapeutische Bestrahlung durch eine Bestrahlungseinrichtung mit einem mikrogepulsten Teilchenstrahl mittels eines Positronen-Emissions-Tomografen während der Bestrahlung kontrollierbar ist. Dazu werden wahre Koinzidenzen mittels – des durch die erlaubte Zeitdifferenz des Auftreffens zweier Photonen in verschiedenen Detektoren des Tomografen bestimmten Koinzidenzzeitfensters und – der Differenz zwischen prompten Fenster und verzögerten Fenster ohne wahre Koinzidenzen ermittelt. Dabei sind sowohl das Koinzidenzzeitfenster als auch die Zeitdifferenz zwischen prompten und verzögerten Fenster ein ganzzahliges Vielfaches der durch die Frequenz der beschleunigenden Wechselspannung des Hochfrequenzbeschleunigers gegebenen Zeitdauer einer Mikropulsperiode des Teilchenstrahls. Die Mikropulsperiode ist durch den Mikropuls und die Pause zwischen Mikropulsen definiert. Diese Zeitdauer ist durch die Frequenz der die Teilchen des Teilchenstrahls beschleunigenden Wechselspannung gegeben und damit zu wählen.

  • Patent
    DE102014202828 - Erteilung 02.07.2015, Nachanmeldung: WO, JP

Publ.-Id: 22178

Grid studies for the simulation of resolved structures in an Eulerian two-fluid framework

Gauss, F.; Lucas, D.; Krepper, E.

The influence of the grid size on the rise velocity of a single bubble simulated with an Eulerian two-fluid method is investigated. This study is part of the development of an elaborated Eulerian two-fluid framework, which is able to predict complex flow phenomena as arising in nuclear reactor safety research issues. Such flow phenomena cover a wide range of interfacial length scales. An important aspect of the simulation method is the distinction into small flow structures, which are modeled, and large structures, which are resolved. To investigate the requirements on the numerical grid for the simulation of such resolved structures the velocity of rising gas bubbles is a good example since theoretical values are available. It is well known that the rise velocity of resolved bubbles is clearly underestimated in a one-fluid approach if they span over only few numerical cells. In the present paper it is shown that in the case of the two-fluid model the bubble rise velocity depends only slightly on the grid size. This is explained with the use of models for the gas–liquid interfacial forces. Good approximations of the rise velocity and the bubble shape are obtained with only few grid points per bubble diameter. This result justifies the resolved treatment of flow structures, which cover only few grid cells. Thus, a limit for the distinction into resolved and modeled structures in the two-fluid context may be established.

Keywords: multiphase flow; grid study; single rising bubble; Eulerian two-fluid method; Volume of Fluid method; terminal rise velocity

Publ.-Id: 22177

Biomimetic Magnetic Silk Scaffolds

Samal, S. K.; Dash, M.; Shelyakova, T.; Declercq, H. A.; Uhlarz, M.; Banobre-Lopez, M.; Dubruel, P.; Cornelissen, M.; Herrmannsdörfer, T.; Rivas, J.; Padeletti, G.; de Smedt, S.; Braeckmans, K.; Kaplan, D. L.; Dediu, V. A.

Magnetic silk fibroin protein (SFP) scaffolds integrating magnetic materials and featuring magnetic gradients were prepared for potential utility in magnetic-field assisted tissue engineering. Magnetic nanoparticles (MNPs) were introduced into SFP scaffolds via dip-coating methods, resulting in magnetic SFP scaffolds with different strengths of magnetization. Magnetic SFP scaffolds showed excellent hyperthermia properties achieving temperature increases up to 8 °C in about 100 s. The scaffolds were not toxic to osteogenic cells and improved cell adhesion and proliferation. These findings suggest that tailored magnetized silk-based biomaterials can be engineered with interesting features for biomaterials and tissue-engineering applications.

Publ.-Id: 22176

Capture Gamma-Ray Spectroscopy and Related Topics, Proceedings of the Fifteenth International Symposium

Schwengner, R.; Zuber, K.; (Editors)

The Fifteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15) was organized by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Technische Universität (TU) Dresden and held at TU Dresden from August 25 to August 29, 2014.
CGS15 was the fifteenth symposium in a series that started in 1969.
This conference continued the general themes of earlier meetings with special emphasis on gamma-ray spectroscopy used in neutron capture and also in a wider context in nuclear structure, nuclear reactions, nuclear astrophysics, statistical properties of nuclei, nuclear probes for fundamental physics, nuclear data, novel techniques and applications.
These proceedings include a collection of articles from all these topics.

Keywords: Gamma-ray spectroscopy

  • Open Access Logo Book (Editorship)
    France: EDP Sciences, 2015
    ISBN: 978-2-7598-1794-8


Publ.-Id: 22175

Design of a 18F-labeled purinergic P2Y1 receptor (P2Y1R) ligand for brain imaging

Moldovan, R.-P.; Dukic-Stefanovic, S.; Wenzel, B.; Teodoro, R.; Deuther-Conrad, W.; Brust, P.

Objectives: Purine nucleotides such as ATP and ADP are important extracellular signaling molecules in almost all tissues. Via P2Y1R activation they mediate brain functions by trophic effects like differentiation and proliferation but also via fast synaptic transmission. The understanding of its role in brain disorders is limited because of lack of suitable brain-penetrating P2Y1R-selective drugs. Chao and co workers recently reported the first non-nucleotidic, diarylurea ligands with high affinity and selectivity for the P2Y1R[1]. We selected this scaffold for the development a 18F labeled P2Y1R ligand for brain imaging.

Methods: Based on the lead compounds 1-3 (Ki = 6-8 nM),[1] we designed derivative 5, suitable for aliphatic radiofluorination using the corresponding tosyl precursor 4. The radiolabeling was systematically optimized (eg. phase transfer catalyst, solvent, temperature, amount of precursor and heating method) and [18F]5 successfully provided for subsequent evaluation. The lead structure was further modified by fluorinating pyridine at the 2-position, replacing the urea subunit C with 2 aminothiazole, and substituting ring D with various fluoroaromatic and non-aromatic rings.

Results: Reference compound 5 has been synthesized from the tosylate 4 in 62% yield. Under optimized conditions, [18F]5 has been obtained in high radiochemical yield (30%) and purity (≥99%) at a specific activity of ~182 GBq/µmol. A series of 30 new fluorinated derivatives has been synthesized.

Conclusions: The first 18F-labeled P2Y1R ligand, [18F]5 has been successfully synthesized. To evaluate the newly designed compounds, an in vitro binding assay using stably transfected P2Y1R-1321N1 cells and [18F]5 is currently developed.

Literature: [1] Chao et al. J. Med. Chem. 2013, 56, 1704−1714

  • Lecture (Conference)
    23. Jahrestagung der AG Radiochemie / Radiopharmazie, 10.-12.09.2015, Erlangen, Deutschland

Publ.-Id: 22174

Network-like arrangement of mixed-valence uranium oxide nanoparticles after glutathione-induced reduction of uranium(VI)

Kretzschmar, J.; Haubitz, T.; Hübner, R.; Weiss, S.; Husar, R.; Brendler, V.; Stumpf, T.

Glutathione (GSH), a ubiquitous intracellular reducing tripeptide, is able to reduce hexavalent uranium, U(VI), to its tetravalent form, U(IV), in aqueous media in vitro, inducing the formation of nanocrystalline mixed-valence uranium oxide particles. After initial reduction to U(V) and subsequent dismutation, yielded U(IV) rapidly hydrolyses at near-neutral conditions forming 2–5 nm sized nanoparticles. The latter further aggregate to 20–40 nm chain-like building blocks that finally arrange as network-like structures.

Keywords: glutathione; uranium; redox reaction; uraninite; nanocrystal; TEM; environmental science

Publ.-Id: 22173

Advanced tomographic imaging for multi-phase flow investigations in industrial apparatuses

Bieberle, M.; Barthel, F.; Rabha, S.; Schubert, M.; Bieberle, A.; Hampel, U.

Investigations on two- and multiphase flow phenomena inside technical apparatuses or feedings are of highest interest for designers and operators since the knowledge helps to understand the fundamental physics behind processes, e.g. in chemical and process engineering. It expedites the development of safer and more efficiently operated industrial facilities. Furthermore, measured data are used to validate new models developed for multiphase flow simulation, e.g. CFD. For non-intrusive two-phase flow investigations, two radiation-based computed tomography (CT) scanners are operated at the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) at the department of Fluid Dynamics: a high-resolution gamma-ray computed tomography scanner (HireCT) and an ultrafast electron beam X-ray CT scanner (ROFEX). They are able to recover non-superimposed cross-sectional material distributions of the scanned plane or volume section within the flow as time averaged images or time resolved image sequences. The capabilities of both CT systems are demonstrated exemplarily at experiments on an industrial scale bubble column, a fluidized bed and a static mixer.

Keywords: computed tomography; multi-phase flow; CFD

  • Contribution to proceedings
    Fachtagung “Lasermethoden in der Strömungsmesstechnik”, 08.-10.09.2015, Dresden, Deutschland
    Lasermethoden in der Strömungsmesstechnik, Karlsruhe: Deutsche Gesellschaft für Laser-Anemometrie, 978-3-9816764-1-9, 8-1-8-8
  • Lecture (Conference)
    Fachtagung “Lasermethoden in der Strömungsmesstechnik”, 08.-10.09.2015, Dresden, Deutschland

Publ.-Id: 22172

Commissioning and first RF results of the second 3.5 cell SRF gun for ELBE

Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Eremeev, G. V.; Kneisel, P.; Stirbet, M.; Turlington, L.

As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation at Helmholtz-Zentrum Dresden-Rossendorf, it turned out that the specified performance to realize an electron energy of 9.4 MeV has not been achieved. Instead, the resonator of the gun was limited by field emission to about one third of this value and the measured beam parameters remained significantly below its expectations.

However, to demonstrate the full potential of this electron source for the ELBE linear accelerator, a second and slightly modified SRF gun was developed and built in collaboration with Thomas Jefferson National Accelerator Facility.

We will report on commissioning and first RF results of this new SRF gun. This includes in particular the characterization of the most important RF properties as well as their comparison with previous vertical test results. Additionally, investigations are presented that try to explain a particle contamination that happened recently during the first cathode transfer.

Keywords: SRF gun; superconducting radio frequency electron injector; ELBE linear accelerator

  • Lecture (Conference)
    The 56th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 07.-12.06.2015, Stony Brook, NY 11794, USA

Publ.-Id: 22171

Radiation Effects in Solid Nitrogen and Nitrogen-Containing Matrices: Fingerprints of N4+ Species

Savchenko, E. V.; Khyzhniy, I. V.; Uyutnov, S. A.; Barabashov, A. P.; Gumenchuk, G. B.; Beyer, M. K.; Ponomaryov, A. N.; Bondybey, V. E.

The radiation effects and relaxation processes in solid N2 and N2-doped Ne matrices, preirradiated by an electron beam, have been studied in the temperature range of 5–40 and 5–15 K, respectively. The study was performed using luminescence methods: cathodoluminescence CL and developed by our group nonstationary luminescence NsL, as well as optical and current activation spectroscopy methods: spectrally resolved thermally stimulated luminescence TSL and exoelectron emission TSEE. An appreciable accumulation of N radicals, N+, N2 + ions, and trapped electrons is found in nitrogen-containing Ne matrices. Neutralization reactions were shown to dominate relaxation scenario in the low-temperature range, while at higher temperatures diffusion-controlled reactions of neutral species contribute. It was conceived that in α-phase of solid N2, the dimerization reaction (N2 + + N2 → N4 +) proceeds: “hole self-trapping”. Tetranitrogen cation N4 + manifests itself by the dissociative recombination reaction with electron: N4 + + e → N2*(a’1Σu ) + N2 → N2 + N2 + hν. In line with this assumption, we observed a growth of the a’1Σu → X1Σg + transition intensity with an exposure time in CL spectra and the emergence of this emission in the course of electron detrapping on sample heating in the TSL and NsL experiments.

Publ.-Id: 22170

Dependence of the inverse magnetocaloric effect on the field-change rate in Mn3GaC and its relationship to the kinetics of the phase transition

Scheibel, F.; Gottschall, T.; Skokov, K.; Gutfleisch, O.; Ghorbani-Zavareh, M.; Skourski, Y.; Wosnitza, J.; Cakir, Ö.; Farle, M.; Acet, M.

We study the dependence of the magnetocaloric effect on the magnetic field-change-rate the first order magnetostructural transition in Mn3GaC by measuring the adiabatic temperature change ΔT at three different time scales: 11 mTs-1, 700 mTs-1, and ~1000 Ts-1. We find that the Maximum adiabatic temperature-change of about 5 K is reached in the 11 mTs-1 and 700 mTs-1 rates, whereas for the ~1000 Ts-1 the transition lags the change in the magnetic field so that the maximum adiabatic temperature-change is not attained.

Publ.-Id: 22169

Optical conductivity evidence of clean-limit superconductivity in LiFeAs

Lobo, R. P. S. M.; Chanda, G.; Pronin, A. V.; Wosnitza, J.; Kasahara, S.; Shibauchi, T.; Matsuda, Y.

We measured the optical conductivity of superconducting LiFeAs. In the superconducting state, the formation of the condensate leads to a spectral-weight loss and yields a penetration depth of 225 nm. No sharp signature of the superconducting gap is observed. This suggests that the system is likely in the clean limit. A Drude-Lorentz parametrization of the data in the normal state reveals a quasiparticle scattering rate supportive of spin fluctuations and proximity to a quantum critical point.

Publ.-Id: 22168

Doping effects of Sb in FeTe1-xSbx single crystals

Wang, X. F.; Zhang, Z. T.; Chen, X. L.; Kan, X. C.; Li, L.; Sun, Y. P.; Zhang, L.; Xi, C. Y.; Pi, L.; Yang, Z. R.; Zhang, Y. H.

We investigated the doping effects of Sb on the magnetic, transport and structural properties in FeTe1-xSbx single crystals. Resistivity, magnetic susceptibility and heat capacity experiments consistently reveal that the magnetic/structural transition temperature TN ~ 70 K in undoped Fe1.05Te is gradually suppressed by Sb doping, but no superconductivity is observed for x up to 10%. It is found that the electronic heat capacity coefficient gamma increases with Sb content, implying the increase of the density of states at Fermi level. Referring to previous calculation reports, this means that the Sb substituent plays a role of hole carrier doping, which is consistent with our measurements on Hall coefficient. Structural Analysis shows that Sb doping induces an expansion of the lattice along the a axis and a shrinkage along the c axis. Our work suggests that the antiferromagnetism in Fe1+yTe may be different in nature with other parent compounds of FeAs-based systems.

Publ.-Id: 22167

Experimental and numerical investigation of flow structure and heat transfer during high pressure condensation in a declined pipe at COSMEA facility

Geißler, T.; Szijarto, R.; Beyer, M.; Hampel, U.; Prasser, H.-M.; Walther, M.; Leyer, S.

Reliability and safety are perpetual topics in the development of nuclear installations. Generation III reactor concepts contain additional passive safety systems for improved accident control and mitigation. Main aspect of these passive systems is to operate with a minimum of external energy and signals. One example is the emergency condenser of the KERENA reactor concept, which removes heat from the core passively, e.g. after a station blackout. The governing natural circulation flow with condensation is only coarsely understood and current simulation methods need to be improved. During the condensation process a complex interaction between flow structure and heat transfer takes places and this determines the total efficiency of the passive safety system and hence the reliability in managing an incident.
The experimental facility COSMEA (condensation test rig for flow morphology and heat transfer studies) at HZDR is designated to provide experimental results to support the further development of CFD calculation methods. The test rig consists of a 3 m long emergency condenser pipe (ID 43 mm) which is 0.76° inclined and cooled by forced water flow. The experiments are conducted in a pressure range between 5 bar and 65 bar with steam mass flow rates up to 1 kg/s. Measurements of pressure, temperature, flow rate and condensation rate deliver integral understanding of the process. To investigate the details of the resulting stratified flow structures, x-ray tomography is applied. Parallel temperature measurements inside the heat transferring wall provide information about the azimuthal distribution of the heat flux.
A phase injection system was developed to operate the experiment in a stepwise condensation mode, which allows the measuring of condensation rates, flow morphologies and heat transfer distribution for different steam fraction values. The combination between cross sectional images from x-ray tomography and the azimuthally resolved heat transfer clarify the coupling between flow structure and heat transfer during condensation.
The experimental results are supported by a system code calculation. The COSMEA facility was modeled with the RELAP5 code. The original condensation model of the code was modified such that the heat transfer coefficient depends on the local mass fraction of the flow field. The experimental and calculation results agreed well for the steady state condensation process in the condensation rate, secondary side temperature and the heat flux data.

Keywords: two-phase flow; passive safety system; TOPFLOW; heat transfer; condensation; COSMEA; x-ray tomography

  • Contribution to proceedings
    NURETH-16, 16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA
    Proceedings of NURETH-16
  • Lecture (Conference)
    NURETH-16, 16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA

Publ.-Id: 22166

First evidence of low energy enhancement in Ge isotopes

Renström, T.; Nyhus, H.-T.; Utsunomiya, H.; Larsen, A. C.; Siem, S.; Guttormsen, M.; Filipescu, D. M.; Gheorghe, I.; Goriely, S.; Bernstein, L. A.; Bleuel, D. L.; Glodariu, T.; Görgen, A.; Hagen, T. W.; Lui, Y.-W.; Negi, D.; Ruud, I. E.; Sahin, E.; Schwengner, R.; Shima, T.; Takahisa, K.; Tesileanu, O.; Tornyi, T. G.; Tveten, G. M.; Wiedeking, M.

The γ-strength functions and level densities of 73,74 Ge have been extracted from particle-γ coincidence data using the Oslo method. In addition the γ-strength function of 74 Ge above the neutron separation threshold, Sn = 10.196 MeV has been extracted from photoneutron measurements. When combined, these two experiments give a γ-strength function covering the energy range of ~ 1-13 MeV for 74 Ge. This thorough investigation of 74Ge is a part of an international campaign to study the previously reported low energy enhancement in this mass region in the γ-strength function from ~ 3 MeV towards lower γ energies. The obtained data show that both 73,74 Ge display an increase in strength at low γ energies.

Keywords: gamma-ray strength

Publ.-Id: 22165

Analysis of pion production data measured by HADES in proton-proton collisions at 1.25 GeV

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Göbel, K.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Vasiliev, T.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.

Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25 GeV is investigated. The multi-differential data were measured by the HADES collaboration. Exclusive channels with one pion in the final state (nπ+ and pπ0) were put to extended studies based on various observables in the framework of a one-pion exchange model and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The results of the PWA confirm the dominant contribution of the Δ(1232), yet with a sizable impact of the N(1440) and non-resonant partial waves. The obtained resonance production cross sections provide a useful normalization for the further analysis of the Δ+ -> pe+e- Dalitz decay.

Publ.-Id: 22164

Low-Energy Magnetic Radiation

Frauendorf, S.; Beard, M.; Mumpower, M.; Schwengner, R.; Wimmer, K.

A pronounced spike at low energy in the strength function for magnetic radiation (LEMAR) is found by means of Shell Model calculations, which explains the experimentally observed enhancement of the dipole strength. LEMAR originates from statistical low-energy M1-transitions between many excited complex states.
Re-coupling of the proton and neutron high-j orbitals generates the strong magnetic radiation. LEMAR is predicted for nuclides with A ~ 132 participating in the r-process of element synthesis. It increases the reaction rates by a factor of 2.5. The spectral function of LEMAR follows Planck's Law. A power law for the size distribution of the B(M1) values is found.

Keywords: Magnetic dipole radiation; shell model

Publ.-Id: 22163

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