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31745 Publications
Hyperdoping Si with deep level impurities by ion implantation and short-time annealing
Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; 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 [1, 2]. 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 [3]. In the present work, we use ion implantation combined with short-time annealing to realize hyperdoping of Ti and chalcogens in Si. The structural, electrical and optical properties were determined by X-raydiffraction and Rutherford backscattering spectroscopy/channeling, electrical transport measurement and Raman spectroscopy. Analysis shows that the implanted Si layer can be recrystallized by both flashlamp and pulsed laser annealing. Ti ions mainly occupy the interstitial sites, while S and Se ions substitute the Si in the lattice. The consequent changes in electrical properties are also observed.

[1] J. Olea, G. González-Díaz, D. Pastor, I. Mártil, A. Martí, E. Antolín, and A. Luque, J. Appl. Phys. 109, 063718 (2011).
[2] Brion P. Bob, Atsushi Kohno, Supakit Charnvanichborikarn, Jeffrey M. Warrender, Ikurou Umezu, Malek Tabbal, James S. Williams, and Michael J. Aziz J. Appl. Phys. 107, 123506 (2010)
[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).
Keywords: Ion implantation, deep level impurities
  • Poster
    Deutsche Physikalische Gesellschaft, 30.03.-04.04.2014, Dresden, Germany

Publ.-Id: 21001 - Permalink

Ferromagnetic GaMnP prepared by ion implantation and pulsed laser annealing
Y, Yuan.;
We present the magnetic, transport and structural properties of GaMnP with different Mn concentrations prepared by ion implantation and pulsed laser annealing. The Curie temperature increases with Mn concentration and the samples show in-plane magnetic anisotropy due to the in-plane compressive strain in the GaMnP layer. Anomalous Hall effect and negative magnetoresistance are observed, indicating the carrier mediated nature of the ferromagnetism in GaMnP. According to the micro-Raman spectroscopy data after pulsed laser annealing the implanted layer has been fully recrystallized and the carrier concentration (hole) increases with Mn concentration.
Keywords: Ferromagnetic semiconductors, GaMnP, Ion Implantation, Pulsed laser annealing
  • Lecture (Conference)
    IEEE International Magnetics Conference, 04.-08.05.2014, Dresden, Germany

Publ.-Id: 21000 - Permalink

Possible defect-induced ferromagnetism in Cr doped SiC single crystals
Liu, Y.; Zhou, S.; Wang, G.; Wang, S.; Sun, W.; Chen, X.;
Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.
Keywords: defect-induced ferromagnetism, SiC, Cr doping, semiconductors
  • Poster
    The 19th International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium

Publ.-Id: 20999 - Permalink

Possible defect-induced ferromagnetism in Cr doped SiC single crystals
Liu, Y.; Zhou, S.; Wang, G.; Wang, S.; Sun, W.; Chen, X.;
Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.
Keywords: defect-induced ferromagnetism, SiC, Cr doping, semiconductors
  • Poster
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France

Publ.-Id: 20998 - Permalink

XFM studies of plutonium dispersed in an arid environment
Ikeda-Ohno, A.; Johansen, M. P.; Payne, T. E.; Hotchkis, M. A. C.; Child, D. P.;
The soil particles collected at a former British nuclear test site in Australia were investigated by synchrotron-based X-ray fluorescence microscopy (XFM), in order to determine the chemical speciation of radioactive nuclides retained in the particles. The results demonstrate that the particles contain a high concentration of Pu which derives from the original nuclear bomb material. The outcomes of this study would have a potential impact on the safety and environmental assessment associated with the former nuclear test sites.
Keywords: actinides, plutonium, synchrotron, X-ray fluorescence microscopy, environment, speciation
  • Lecture (Conference)
    12th International Conference on X-Ray Microscopy (XRM 2014), 26.-31.10.2014, Melbourne, Australia

Publ.-Id: 20997 - Permalink

Ferromagnetic InMnAs prepared by Ion implantation and pulsed laser annealing
Yuan, Y.; Wang, Y.; Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.;
Ferromagnetic InMnAs has been previously prepared by low temperature MBE. In this contribution, we present an alternative method what combines Mn ion implantation and pulsed laser annealing to achieve In1-xMnxAs (x = 0.04 and 0.08) [1], and to obtain a remarkably high Curie Temperature (TC) up to 80 K compared to InMnAs with the same Mn concentration as prepared by MBE. The advantage of pulsed laser annealing is its high process temperature within the nano-second range, eliminating n-type defects which can decrease its magnetization and TC. The saturation magnetization is ~2.6μB / Mn by consideration of all implanted Mn ions. The out-of-plane [001] is the easy axis displaying a nearly square like hysteresis loop. Our results suggest that InMnAs prepared by ion implantation and pulsed laser annealing shows a promising prospect to get high TC DMS after optimizing the preparation parameters.
Keywords: Ferromagnetic Semiconductors, Ion Implantation, Pulsed laser annealing
  • Poster
    DPG-Frühjahrstagung, 30.03.-04.04.2014, Dresden, Germany

Publ.-Id: 20996 - Permalink

Local instabilities in magnetized rotational flows: A short-wavelength approach
Kirillov, O.; Stefani, F.; Fukumoto, Y.;
We perform a local stability analysis of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the case of small magnetic Prandtl numbers which applies, e.g., to liquid metal experiments but also to the colder parts of accretion disks. We show that the inductionless versions of MRI that were previously thought to be restricted to comparably steep rotation profiles extend well to the Keplerian case if only the azimuthal field slightly deviates from its current-free (in the fluid) profile. We find an explicit criterion separating the pure azimuthal inductionless magnetorotational instability from the regime where this instability is mixed with the Tayler instability. We further demonstrate that for particular parameter configurations the azimuthal MRI originates as a result of a dissipation-induced instability of the Chandrasekhar's equipartition solution of ideal magnetohydrodynamics.
Keywords: magnetorotational instability, Chandrasekhar's equipartition solution, dissipation-induced instabilities, diffusive instabilities, magnetohydrodynamics

Publ.-Id: 20995 - Permalink

Electronical and structural changes induced by the incorporation of Am into conventional fuels
Prieur, D.; Carvajal-Nunez, U.; Vigier, J.-V.; Somers, J.; Bes, R.; Martin, P.; Lebreton, F.; Caisso, M.; Delahaye, T.; Scheinost, A. C.; Hennig, C.; Pruessmann, T.; Vitova, T.; Kvashnina, K. O.;
241Am is one of the most hazardous actinide isotopes present in the spent fuel Transmutation in fast neutrons reactors :
conversion of highly radioactive elements into short-lived isotopes
Dramatic reduction of the nuclear waste inventory (< 300 years)
Two strategies :
Homogeneous transmutation : Incorporation of MA in low concentration (<5%) to the conventional MOX fuel Am-MOX, Np-MOX, etc.
Heterogeneous transmutation : Incorporation of MA in high concentration (5-30%) in dedicated assemblies at the core periphery
(U,Am)O2, (Pu,Am)O2, etc.
Keywords: Transmutation americium XAFS
  • Lecture (Conference)
    NUMAT 2014, 27.-30.10.2014, Hilton Clearwater, Florida, U.S.A.

Publ.-Id: 20994 - Permalink

Ion beam synthesis of the full spectrum of III-V:Mn ferromagnetic semiconductors
Zhou, S.;
Ferromagnetic semiconductors have been under intensive investigation during the last decade. Until now, III-Mn-V based compound semiconductors are the only well accepted class of materials. The prototype ferromagnetic semiconductor GaMnAs has revealed a variety of unique features induced by the combination of its magnetic and semiconducting properties. To prepare ferromagnetic semiconductors, one needs to dope the host with up to 5-10% Mn, which is far beyond the solid solubility of Mn in III-V compounds. As a non-equilibrium process, ion implantation can introduce enough dopants as required. 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 in the millisecond or nanosecond regime allows the epitaxial growth from a liquid phase. The mature development and commercialization of ion implantation promise the versatility. 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.
[1] D. Bürger, S. Zhou, et al., Phys. Rev. B 81, 115202 (2010).
[2] S. Zhou, et al., Appl. Phys. Lett. 96, 202105 (2010).
[3] S. Zhou, et al., Appl. Phys. Express 5, 093007 (2012).
[4] M. Khalid et al., Phys. Rev. B., 89, 121301(R) (2014).
[5] Y. Yuan, et al, IEEE Tran. Magn., in press (2014).
Keywords: Magnetic semiconductors, Ion implantation
  • Invited lecture (Conferences)
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France
  • Invited lecture (Conferences)
    The Moscow International Symposium on Magnetism 2014, 29.06.-03.07.2014, Moscow, Russia
  • Invited lecture (Conferences)
    X-th International Conference - Ion Implantation and Other Applications of Ions and Electrons, 23.-26.06.2014, Kazimierz Dolny, Poland

Publ.-Id: 20993 - Permalink

Surface protection of titanium and titanium-aluminum alloys against environmental degradation at elevated temperatures
Yankov, R.; von Borany, J.; Munnik, F.; Donchev, A.; Schütze, M.;
Ti and its alloys with Al are a class of lightweight materials, which find extensive use in a number of advanced aerospace, automotive and power generation applications. These materials, however, are limited in applicability by their poor oxidation resistance at elevated temperatures (> 500°C for Ti, and > 750°C for TiAl).
We have developed a technique for protecting the above-mentioned materials against high-temperature environmental degradation (oxidation and embrittlement). In the case of TiAl alloys of an Al content of about 40 to 60 at.% , the technique has involved a single step, i.e. plasma immersion ion implantation (PIII) of fluorine, making use of the so-called “fluorine effect”. Optimum process parameters have been established under which the F-implanted TiAl alloys acquire a stable, adherent and highly protective alumina scale upon subsequent high-temperature oxidation in air. The extent of oxidation protection has been evaluated by testing F-implanted TiAl samples either isothermally or under conditions of thermal cyclic oxidation at temperatures ranging from 900° to 1050°C, and for times as long as 6000 hours. Results from characterization by elastic recoil detection analysis (ERDA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and Rutherford backscattering spectrometry (RBS) have proven the possibility of forming a protective alumina scale on both laboratory coupons and machine components such as jet turbine blades and turbochargers. In the case of Ti and low-Al-content Ti-Al alloys, e.g. Ti3Al, the technique has involved two steps, namely Al enrichment (aluminization) of the material’s near-surface, and introduction of F by PIII to activate the fluorine effect. Under optimized process conditions, the Ti and Ti3Al samples so modified have shown marked environmental stability at temperatures as high as 700°C and for extended oxidation times due to the presence of a protective alumina layer.
Keywords: titanium, titanium aluminides, high-temperature oxidation protection
  • Lecture (Conference)
    28th International Conference on Surface Modification Technologies (SMT), 16.-18.06.2014, Tampere, Finland

Publ.-Id: 20992 - Permalink

Improvement of the resistance of titanium aluminides to environmental embrittlement
Masset, P. J.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R. A.;
Aluminum enriched coatings have been developed for titanium aluminide alloys. It has been shown that Metal Organic Chemical Vapor Deposition (MO-CVD) and Physical Vapor Deposition (PVD) processes combined with fluorination of the coating enables to reduce significantly the embrittlement of TiAl alloys through oxidation. Even after oxidation at 900 °C for 100h, the coatings exhibit suitable adhesion and 90 % of the fracture toughness and ductility of the alloy are maintained.

Publ.-Id: 20991 - Permalink

GGR Biennial Critical Review: Analytical Developments Since 2012
Wiedenbeck, M.; Bédard, P. L.; Bugoi, R.; Horan, M.; Linge, K.; Merchel, S.; Morales, L. F. G.; Savard, D.; Souders, A. K.; Sylvester, P.;
Advances in the chemical, crystallographic and isotopic characterization of geological and environmental materials can often be ascribed to technological improvements in analytical hardware or to innovative approaches to data acquisition and/or its interpretation. This biennial review addresses key laboratory methods that form much of the foundation for analytical geochemistry; again this contribution is presented as a compendium of laboratory techniques. We highlight advances that have appeared since January 2012 and which are of particular significance for the chemical and isotopic characterization of geomaterials. Prominent scientists from the selected analytical fields present publications they judge to be particular noteworthy, providing background information about the method and assessing where further opportunities might be anticipated. In addition to well established technologies such as thermal ionization mass spectrometry and plasma emission spectroscopy, this publication also presents new or rapidly growing methods such as electron backscattered diffraction analysis and atom probe tomography – a very sensitive method providing atomic scale information.
Keywords: ICPMS, laser ablation, mass spectrometry, ICP-AES, microwave plasma source, TIMS, isotopic analysis, geochronology, trace element analysis, calibration, XRF, environmental sampling, AMS, Ion Beam Analysis, radionuclides, SIMS, ion probe, microanalysis, FIB, EBSD, atom probe tomography

Publ.-Id: 20990 - Permalink

Generation of few-group constants with Serpent: Application examples
Fridman, E.;
The purpose of this presentation is to demonstrate the capability of the Serpent Monte Carlo code to generate few-group constants for existing and innovative reactor systems
  • Invited lecture (Conferences)
    PHYSOR 2014, Workshop on new features and capabilities in the Serpent 2 Monte Carlo code, 28.09.-03.10.2014, Kyoto, Japan

Publ.-Id: 20989 - Permalink

Development of new coatings to prevent environmental embrittlement of titanium aluminides
Masset, P.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R.;
Abstract: For temperatures above 750°C, TiAl alloys still show insufficient oxidation resistance and suffer from environmental embrittlement. This work focuses on the surface modification of alloys and development of coatings against environmental embrittlement, as well as on testing of mechanical properties after high temperature oxidation. Aluminum enriched coatings (between 50 and 60 at.%) containing alloying elements, i.e. Cr, Nb, Si, Y, to improve the oxidation behavior and the corrosion resistance have been produced by MO-CVD, CVD, PVD and thermal spraying techniques (HVOF, APS), and have subsequently been chemically modified with halogen elements, notably fluorine. The mechanical properties have been studied by means of 4-point bending and tensile tests on coated samples after 100h oxidation at 900 °C in laboratory air. The CVD process combined with fluorine treatment using plasma immersion implantation (PI³) of F offers the best combination to remedy environmental embrittlement. It has been shown in particular that 90% of the initial fracture strain and fracture stress can be maintained.
Keywords: titanium, titanium aluminides, high-temperature oxidation, protective coatings
  • Lecture (Conference)
    TMS 2014, 143rd Annual Meeting & Exhibition, 16.-20.02.2014, San Diego, United States

Publ.-Id: 20988 - Permalink

Protection of Ti-alloys against high temperature environmental attack by a two step process, aluminization + fluorination
Donchev, A.; Galetz, M.; Schütze, M.; Yankov, R.; Kolitsch, A.;
Ti-alloys cannot be used at elevated temperatures above approximately 600°C in oxidizing environments. They suffer from accelerated oxidation and oxygen uptake in the subsurface zone, which deteriorates the mechanical properties. The addition of Al (usually < 10%) into standard Ti-alloys is not enough to form a protective alumina layer. Aluminization of technical Ti-alloys and formation of intermetallic Al-rich phases (e.g. TiAl3) change the oxidation behavior from fast and non-protective rutile formation to slow growing alumina kinetics, but only for a limited period of time. A subsequent fluorination of the aluminized components gets the fluorine effect to operate. This is away to improve the resistance of technical Ti-alloys against environmental attack, even for longer service times. In this paper the results of high temperature oxidation tests of several untreated and treated Ti-alloys will be presented and their behavior compared.
Keywords: Environmental embrittlement; Fluorine effect; Oxidation
  • Contribution to proceedings
    TMS 2014 143rd TMS Annual Meeting 2014, 16.-20.02.2014, San Diego, United States
    TMS 2014 Supplemental Proceedings, 9781118889725, 79-85
    DOI: 10.1002/9781118889879

Publ.-Id: 20987 - Permalink

Potential Impairment of Core Coolability during LOCA due to Precipitation of Zinc Borate
Pointner, W.; Kryk, H.; Kästner, W.; Austregesilo, H.;
Within the framework of German nuclear safety research, generic experimental investigations were carried out at HZDR and the Hochschule Zittau/Görlitz aiming at the elucidation of physicochemical and thermo hydraulic mechanism of corrosion product formation, which may occur during the sump circulation operation after loss-of-coolant accidents in pressurized water reactors.
The contact of the boric acid containing coolant with hot-dip galvanized steel containment internals causes corrosion of the corresponding materials resulting in dissolution of the zinc coating. As main result of batch experiments, decreasing solubility of zinc corrosion products in boric acid solutions with increasing temperature was found. Thus, the formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up due to its recirculation into hot regions within the cooling circuit. Generic corrosion and deposition experiments at a lab-scale test facility proved that dissolved zinc, formed at low temperatures in boric acid solution by zinc corrosion, may turn into solid deposits of zinc borates when contacting heated zircaloy surfaces during the heating of the coolant. The results obtained at lab-scale were confirmed by generic experiments at semi-technical scale using a 3x3 heating rod configuration including spacer segments as well as a 16x16 (8x8 heated) fuel rod dummy.
Experiments regarding the corrosion kinetics of zinc-coated components were not subject of the study. Therefore, a quantitative transferability of the results to postulated PWR-LOCA is not given so far.
Keywords: pressurized water reactor, loss-off-coolant accident, corrosion, zinc, boric acid, in-vessel effects
  • Lecture (Conference)
    17th WGAMA Meeting, 23.-26.09.2014, Paris, France

Publ.-Id: 20986 - Permalink

Recent developments in surface protection of titanium and titanium-aluminum alloys against environmental degradation at elevated temperatures
Yankov, R.; von Borany, J.; Masset, P. J.; Donchev, A.; Schütze, M.;
Titanium and its alloys with aluminum are lightweight structural materials, which find ever-increasing use in a number of advanced aerospace, automotive and power generation applications. These materials, however, are limited in applicability by their inadequate oxidation resistance at elevated temperatures (> 500°C for Ti, and > 750°C for TiAl).
This talk reviews recent advances in using state-of-the-art techniques for surface engineering of Ti, Ti-base alloys and γ-TiAl intermetallics, with a view to rendering them resistant to high-temperature environmental oxidation and oxygen embrittlement.
The first part of the talk covers the surface modification of Ti and low-Al-content Ti-base alloys by using combined techniques involving either aluminization followed by plasma immersion ion implantation (PIII) of fluorine or formation of a surface barrier coating by magnetron sputter co-deposition of Ti and Al followed by vacuum annealing and PIII of F.
The second part focuses on the direct surface treatment of γ-TiAl by PIII of F. Such type of fluorination enables the F-implanted alloy surface to develop a stable, adherent and highly protective alumina scale upon subsequent oxidation in air at temperatures in excess of 1000°C for extended exposure times.
The last part deals with the fabrication of protective TiAl coatings using a two-step coating scheme. First, an Al-rich TiAl layer is formed on the γ-TiAl alloy by either MO-CVD, PVD or thermal spraying. Then the TiAl layer is treated by PIII of F. The resulting coatings are tested for oxidation resistance, oxygen embrittlement, and retention of mechanical properties. A combination of an Al-rich CVD coating and treatment by PIII of F gives the best results. An example is also given of a thermal barrier coating whose structure comprises, instead of a bond coat, a thin alumina layer formed by PIII of F and subsequent high-T oxidation. The results of these studies have been helpful in understanding the oxidation behavior of the surface-engineered alloys from both a scientific and a technological standpoint.
Keywords: titanium, titanium aluminides, high-temperature oxidation, protective coatings
  • Invited lecture (Conferences)
    Shechtman International Symposium, 29.06.-04.07.2014, Cancun, Mexico

Publ.-Id: 20985 - Permalink

The Use of Plasma Immersion Ion Implantation in the High-Temperature Oxidation Protection of Low-Al-Content Ti-Base Alloys and TiAl Intermetallics
Yankov, R.; von Borany, J.; Pelic, B.; Donchev, A.; Schütze, M.;
Low-Al content Ti-base alloys and TiAl intermetallics are attractive lightweight materials for advanced medium-temperature (500°-750°C) structural applications including components such as jet engine and industrial gas turbine blades, turbocharger rotors and automotive engine valves. However, envisaged service temperatures are in the range of 750° to 1050°C at which these alloys are prone to both destructive oxidation and oxygen embrittlement. Therefore, development of surface-engineering techniques for preventing high-T environmental damage is critical in exploiting the advantages of the TiAl alloys to their fullest extent.
We propose two techniques for protecting candidate Ti-base and TiAl alloys from high-temperature (>750°C) oxidation environments. The first technique involves a single step, namely treating the alloys directly by plasma immersion ion implantation (PIII) of fluorine using a mixture of CH2F2+6.25% Ar as the precursor gas. This technique is applicable to TiAl alloys of an Al content of ~ 45 to 55 at.%. The F implant dose has been found to depend critically on the gas flow rate ratio (GFRR, i.e. CH2F2/Ar) while the resulting F depth profiles show dependence on both the GFRR and the alloy material. Optimum implantation conditions have been established under which the F-implanted alloy surface is able to form a highly protective Al2O3 film upon subsequent oxidation in air. Oxidation resistance has been evaluated by thermal gravimetric analysis (TGA) at temperatures as high as 1050°C for extended exposure times.
The alternative technique is applicable to low-Al-content Ti-base alloys (< 40 at.% Al). It involves the fabrication of a barrier coating in a three-step process, namely formation of a Ti+Al layer by magnetron co-sputtering of Ti and Al followed by vacuum annealing to form a gamma-TiAl coating and, finally, PIII of fluorine. The coating so formed has been shown to prevent further oxidation of the base material at elevated temperatures.
Keywords: Plasma Immersion Ion Implantation, High-Temperature Oxidation, TiAl Intermetallics
  • Poster
    19th International Conference on Ion Beam Modification of Materials (IBMM), 14.-19.09.2014, Leuven, Belgium

Publ.-Id: 20984 - Permalink

Internal Dose Assessment of (-)-18F-Flubatine, Comparing Animal Model Datasets of Mice and Piglets with First-in-Human Results
Sattler, B.; Kranz, M.; Starke, A.; Wilke, S.; Donat, C. K.; Deuther-Conrad, W.; Patt, M.; Schildan, A.; Patt, J.; Smits, R.; Hoepping, A.; Schoenknecht, P.; Steinbach, J.; Brust, P.; Sabri, O.;
(−)-18F-flubatine is a promising tracer for neuroimaging of nicotinic acetylcholine receptors (nAChRs), subtype α4β2, using PET. Radiation doses after intravenous administration of the tracer in mice and piglets were assessed to determine the organ doses (ODs) and the effective dose (ED) to humans. The results were compared with subsequent clinical investigations in human volunteers.
Twenty-seven female CD1 mice (weight ± SD, 28.2 ± 2.1 g) received intravenous injection of 0.75 ± 0.33 MBq of (−)-18F-flubatine. Up to 240 min after injection, 3 animals per time point were sacrificed and the organs harvested, weighed, and counted in a γ counter to determine mass and activity, respectively. Furthermore, whole-body PET scans of 5 female piglets (age ± SD, 44 ± 3 d; weight ± SD, 13.7 ± 1.7 kg) and 3 humans (2 men and 1 woman; age ± SD, 59.6 ± 3.9 y; weight ± SD, 74.3 ± 3.1 kg) were obtained up to 236 min (piglets) and 355 min (humans) after injection of 186.6 ± 7.4 and 353.7 ± 10.2 MBq of (−)-18F-flubatine, respectively, using a PET/CT scanner. The CT was used for delineation of the organs. Exponential curves were fitted to the time–activity-data, and time and mass scales were adapted to the human anatomy. The ODs were calculated using OLINDA/EXM (version 1.0); EDs were calculated with the tissue-weighting factors of ICRP103.
After the injection of (−)-18F-flubatine, there were no adverse or clinically detectable pharmacologic effects in any of the subjects. The highest activities after injection were found in the kidneys, urinary bladder, and liver. The urinary bladder receives the highest OD in all investigated species, followed by the kidneys and the liver for animals and humans, respectively. On the basis of mouse, piglet, and human kinetic data, the projected human ED of (−)-18F-flubatine was estimated to be 12.5 μSv/MBq in mice, 14.7 ± 0.7 μSv/MBq in piglets, and 23.4 ± 0.4 μSv/MBq in humans.
As has been demonstrated for other PET radiotracers, preclinical (i.e., animal-derived) dosimetry underestimates the ED to humans, in the current case of (−)-18F-flubatine by 34%–44%.
Keywords: radiation dosimetry; positron emission tomography; (−)-18F-flubatine; nicotinic receptors; α4β2

Publ.-Id: 20983 - Permalink

Velocity measurements of heavy liquid metal flows by the Ultrasound Doppler method
Franke, S.; Eckert, S.; Gundrum, T.; Gerbeth, G.;
The application of heavy liquid metals as coolant or heat transfer medium in advanced reactor systems demands for a comprehensive knowledge of the flow characteristics. CFD simulations are the main tool to predict the flow behaviour, however, the numerical models have to be validated by experimental data. Flow measurements in hot liquid metals are challenging and the available choice of measuring techniques is rather limited. A great deal of work was done during the last decade to develop suitable measuring principles for applications in metallic melts. The Ultrasound Doppler method can be considered as an attractive technique to obtain real-time velocity profiles in liquid metal flows. Flow measurements in hot metallic melts involve several specific problems, especially the high temperature and the abrasive character of the melt. Furthermore, a sufficient input of acoustic energy into the melt to be measured requires favourable conditions concerning acoustic coupling, transmission and wetting. Moreover, the availability of seeding particles has to be guaranteed to obtain Doppler signals from the fluid. We will present a concept for velocity measurement in a liquid metal channel flow based on high temperature transducer probes in combination with a matched mechanical design of the probe seating. Specific measuring procedure enables us for reliable measurements in a temperature range up to 230°C. The measuring principles are successfully applied at experimental facilities operating with different metal alloys and geometric configurations: At the LIMMCAST (Liquid Metal Model for Continuous Casting) facility of Helmholtz-Zentrum Dresden-Rossendorf we studied the flow profile of a Sn60Bi40 alloy in a circular pipe. Furthermore, the LBE duct flow of the META:LIC loop (Megawatt Target: Lead Bismuth Cooled) at the Institute of Physics in Riga-Salaspils (University of Latvia) was measured. Parametric studies of the velocity profile measurements in the ducts will be presented here. Specific problems arising for the application of the Ultrasound Doppler method in the considered experimental configuration will be discussed.
Keywords: Hot metallic melt flow measurements, Heavy liquid metal coolant, LBE, Ultrasound Doppler velocimetry, LIMMCAST, META:LIC
  • Lecture (Conference)
    SEARCH/MAXSIMA 2014 International Workshop, 07.-10.10.2014, Karlsruhe, Deutschland

Publ.-Id: 20982 - Permalink

Hydrolysis of tetravalent cerium Ce(IV)) - A multi-spectroscopic study on nanocrystalline CeO2 formation
Ikeda-Ohno, A.; Weiss, S.; Tsushima, S.; Hennig, C.;
Because of the flexibility between the tri- and tetravalent oxidation states, cerium (Ce) is known to be the only rare earth element (REE) forming a stable pure stoichiometric dioxide compound (CeO2). Owing to this chemical specificity along with the highest natural abundance of Ce among all REEs, the application of CeO2 has spread over a variety of fields. More recently, CeO2 has been employed as nanoparticles with many technological applications, which include the catalysts for harmful gas treat-ment the water gas shift reaction, electrodes for solid oxide fuel cells and a medical use as an artificial superoxide dismutase. These versatile and still emerging applications of CeO2 still require a simpler and more efficient synthetic strategy, particularly for manufacturing CeO2 nanoparticles.
The hydrolysis of tetravalent cerium (Ce(IV)) is a primary step of many wet syntheses for fabricating CeO2 nanoparticles, although all the reported synthetic methods require additional processes, such as heating, adding organic solvents or calcination, subsequent to the initial hydrolysis step to finally yield CeO2 nanoparticles. This means that understanding of the hydrolysis mechanism of Ce(IV) would be beneficial to developing a new concept for the efficient production of CeO2 nanoparticles. Based on this background, this study focuses on the systematic investigation of the hydrolysis behaviour of Ce(IV) using synchrotron-based X-ray techniques (X-ray absorption spectroscopy (XAS) and high en-ergy X-ray scattering (HEXS)), dynamic light scattering (DLS) and transmission electron microscopy (TEM).
Keywords: cerium, Ce(IV), hydrolysis, nanocrystals, XAS, HEXS, DLS, TEM
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy 2014 (ATAS 2014), 03.-07.11.2014, HZDR Dresden, Germany

Publ.-Id: 20980 - Permalink

Liquid backmixing in an inclined rotating tubular fixed bed reactor - Augmenting liquid residence time via flow regime adjustment
Härting, H.-U.; Berger, R.; Lange, R.; Larachi, F.; Schubert, M.;
The liquid residence time and backmixing in an inclined rotating tubular fixed bed reactor, operated with gas-liquid co-current downflow, are studied experimentally. This novel reactor concept is introduced to extent the process intensification strategies of chemical multiphase reactors. The intermittent catalyst immersion due to rotation induces a continuous refreshment of the liquid at the catalyst surface and enhances the access of the gas phase to the catalyst in the drained section of the fixed bed. Depending on the inclination angle and rotational velocity, different flow regimes are observed. In particular, the flow regimes with stratified gas-liquid flow can be utilized to enhance the performance of the reactor for heterogeneous catalytic reactions.
The backmixing study is based on the method of the imperfect tracer pulse and the propagation of the tracer is measured by low-intrusive wire-mesh sensors. Compared to conventional trickle bed reactors, the liquid residence time and axial dispersion are increased by the inclination and rotation. The effects of reactor inclination angle and rotational velocity as well as of particle size and liquid superficial velocity on the liquid backmixing in the inclined rotating tubular fixed bed reactor are shown in detail.
Keywords: liquid backmixing; residence time; axial dispersion; flow regimes; gas-liquid flow; process intensification

Publ.-Id: 20979 - Permalink

Formation of zinc corrosion products at water-chemical PWR post-LOCA conditions - Physicochemical effects
Kryk, H.; Hoffmann, W.;
During loss-of-coolant accidents (LOCAs) in pressurized water reactors (PWRs), coolant spilling from the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by low pressure injection pumps as part of the emergency core cooling system. The long-term contact of the boric acid containing coolant with hot-dip galvanized steel containment inter-nals (e.g. grating treads, channels, supporting grids of sump strainers) may cause corrosion of the corresponding materials influencing the cooling water chemistry due to dissolution of the zinc coating. Experimental investigations regarding the solubility of Zn corrosion products in boric acid solutions resulted in a decreasing solubility with increasing temperature. Thus, the formation of solid (i.e. particulate) corrosion products cannot be ruled out if the Zn containing coolant is heated up due to its recirculation into hot zones.
During lab-scale experiments, significant amounts of solid corrosion products have been found as deposited layers on hot surfaces as well as in the form of deposits at tubes, fittings and retaining components depending on formation temperature and hydrodynamic conditions. The solid corrosion products were identified as zinc borates. Depending on their forming temperature, different zinc borate compounds may occur having different physicochemical properties.
Although the kinetics of the processes obtained at lab-scale are not transferable to those proceeding during a PWR LOCA due to their dependency on the corroding surface area as well as on the local thermal hydraulics, the results give an insight into physicochemical processes, which might occur in case of zinc corrosion in cooling circuits.
Keywords: loss-of-coolant accident, pressurized water reactor, corrosion, zinc, zinc borate, chemical effects
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2014, 06.-08.05.2014, Frankfurt, Deutschland
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2014, 06.-08.05.2014, Frankfurt, Deutschland

Publ.-Id: 20978 - Permalink

Partikelentstehung und -transport im Kern von Druckwasserreaktoren - Thermo- und fluiddynamische Mechanismen
Renger, S.; Kästner, W.; Alt, S.; Seeliger, A.; Kryk, H.; Hoffmann, W.;
Im Rahmen der Reaktorsicherheitsforschung erfolgten an der Hochschule Zittau/Görlitz in Kooperation mit dem Helmholtz-Zentrum Dresden-Rossendorf experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen und deren Auswirkungen auf thermo-fluiddynamische Prozesse, welche während des Sumpfumwälzbetriebs nach Kühlmittelverluststörfällen in einem Kernkraftwerk ablaufen können, falls in boriertem Kühlmittel (KM) gelöstes Zink in Kernbereiche höherer Temperatur (Hot-Spots) gelangt. Das im KM befindliche Zink kann hierbei im Vorfeld durch die Korrosion feuerverzinkter Bauteile freigesetzt werden.
In den Untersuchungen im halbtechnischen Maßstab wurden die physiko-chemischen Mechanismen und der Temperatureinfluss analysiert. Gleichzeitig wurden Auswirkungen dieser Prozesse auf das thermo-fluiddynamische Verhalten in einer Heizstabkonfiguration (3x3-Anordnung mit für Druckwasserreaktoren (DWR) typischen Zirkaloy-Hüllrohren) mit Abstandshaltern erfasst. Im Fokus der Untersuchungen stand dabei das Verhalten derart zusammengesetzter Fluide an beheizten Konfigurationen, die im Kern von DWR auftreten können.
Die durchgeführten Untersuchungen tragen generischen Charakter und liefern Aussagen zum Löslichkeitsverhalten von Zink in borsäurehaltigem KM sowie zur Bildung fester Korrosionsprodukte und den daraus folgenden Auswirkungen.
Keywords: loss-of-coolant accident, pressurized water reactor, corrosion, zinc, chemical effects
  • Poster
    46. Kraftwerkstechnisches Kolloquium 2014, 14.-15.10.2014, Dresden, Deutschland

Publ.-Id: 20977 - Permalink

Light-Induced Switching of Tunable Single-Molecule Junctions
Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Helm, M.; Gemming, S.; Kerbusch, J.; Scheer, E.; Huhn, T.; Erbe, A.;
A major goal of molecular electronics is the development and implementation of devices such as single-molecular switches. Here, measurements are presented that show the controlled in situ switching of diarylethene molecules from their nonconductive to conductive state in contact to gold nanoelectrodes via controlled light irradiation. Both the conductance and the quantum yield for switching of these molecules are within a range making the molecules suitable for actual devices. The conductance of the molecular junctions in the opened and closed states is characterized and the molecular level E0 , which dominates the current transport in the closed state, and its level broadening Γ are identified. The obtained results show a clear light-induced ring forming isomerization of the single-molecule junctions. Electron withdrawing side-groups lead to a reduction of conductance, but do not influence the efficiency of the switching mechanism. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by electron-withdrawing substituents. This full characterization of a molecular switch operated in a molecular junction is an important step toward the development of real molecular electronics devices.

Publ.-Id: 20976 - Permalink

Simulation of gas-liquid flow in a helical static mixer
Zidouni, F.; Krepper, E.; Rzehak, R.; Rabha, S.; Schubert, M.; Hampel, U.;
CFD simulations using the Euler-Euler approach are performed to model the gas-liquid bubbly flow in a helical static mixer. The model validation work was based on experiments, which are carried out in a column of diameter 0.08 m packed with helical static mixer elements (length 80 mm / diameter 80 mm). Measurements of gas volume fractions, gas velocities and bubble size distributions by in-house developed ultrafast X-ray electron beam tomography were taken at several planes within the mixer elements (Rabha et al. 2014).
The predicted axial and radial gas phase distribution considering different mono-disperse bubble sizes (3, 5.8 and 8 mm) are studied and validated against the experimental results. The dependency of non-drag forces on the bubble size was considered. Consequently, the bubble size dependent effects of the non-drag forces on the flow and on the cross sectional gas volume fraction distribution are shown.
Despite obvious shortcomings of the models for this application, some conclusions on the suitability of certain mixer designs for gas-liquid dispersion may be drawn already. The swirling flows created by the twist and turn of the helical mixer elements, which in turn pushes the lighter phase towards the center of the pipe is well predicted and validated. Further investigations have to consider the bubble size distribution e.g. by a population balance model to accurately predict the dispersion of the gas phase within and downstream the helical static mixer.
Keywords: helical static mixer, dispersion, gas-liquid multiphase flow, Euler-Euler two fluid model, CFD simulation

Publ.-Id: 20975 - Permalink

„Das sagen unsere Kunden/Partner“ für AHK Chile
Birtel, S.;
Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) fokussiert sich auf interdisziplinäre und technologieorientierte Projekte zur energie- und ressourceneffizienten Nutzung von Hochtechnologierohstoffen aber auch die Nutzung von anderen Metallen und ihren Nebenprodukten. Seit 2011 haben die AHK Chile und das ihr angegliederte Kompetenzzentrum für Bergbau und Rohstoffe gemeinsam mit dem HIF sehr erfolgreich mehrere geeignete chilenische Partner aus Industrie und Forschung identifiziert und erste Projektanbahnung unterstützt. Hierzu zählt unter anderem ein BMBF gefördertes Projekt mit der Codelco Tochter IM2. Besuche bei Projektpartnern und Veranstaltungen wie den Deutsch-Chilenischen Wirtschafstagen, dem Länderworkshop Chile der Vereinigung Rohstoffe und Bergbau e.V. oder den Freiberger Innovationstagen bieten gute Gelegenheiten für persönliche Gespräche. Dies wird komplementiert durch einen regelmäßigen E-Mail-Austausch zu aktuellen Entwicklungen. Dabei profitieren die Wissenschaftler des HIF stark vom großen Engagement des Kompetenzzentrums auch in der Begleitung der Projekte.
Keywords: Zusammenarbeit mit AHK Chile
  • Other report
    Santiago: CHAMCHAL AHK Chile, 2014
    21 Seiten

Publ.-Id: 20974 - Permalink

Variability and lower bound of fracture toughness of welds in the ductile to brittle transition regime
Schindler, H.-J.; Kalkhof, D.; Viehrig, H.-W.;
The reference temperature T0 was measured for both T-S and T-L- specimen orientation in 24 layers across the thickness of the beltline weld of a reactor pressure vessel. It turned out to vary in a bandwidth of more than 40K. Because of a high scatter, no clear pattern of T0 as a function of the thickness position could be recognized. A more detailed analysis revealed that the median of KJc was considerably steeper than predicted by the Master-Curve, which leads to a bias of T0 with respect to the testtemperature relative to T0. By a modified evaluation procedure, the scatter of the reference temperature could be significantly reduced, which enabled the global pattern of T0 to be recognized. By comparing the theoretical lower bound to KJc-data of the used specimens with the individual measured KJc a representative T0 that characterizes the overall toughness behaviour of the weld was determined. It turned out to be about 10 K lower than the maximum local T0.
Keywords: reactor pressure vessel, weld metal, fracture toughness, reference temperature

Publ.-Id: 20973 - Permalink

Intra-band dynamics in single InAs/GaAs quantum dots under the influence of strong far-infrared excitation
Stephan, D.; Bhattacharyya, J.; Helm, M.; Huo, Y. H.; Schmidt, O.; Rastelli, A.; Schneider, H.;
Inter-band transitions in single quantum dots (QDs) have received a huge amount of scientific interest in the recent past. However, mostly due to technical challenges in dealing with mid- and far-infrared radiation, intra-band transitions have not been explored quite as thoroughly. In this work, we combine micro-photoluminescence (µPL) on low-density annealed InAs/GaAs QDs with additional excitation at intra-band transition energies by pulsed radiation from a free-electron laser (FEL). This scheme enables the probing of the single-dot response in spite of the large diameter of the FEL focus. The investigation of single QDs eliminates undesirable effects such as inhomogeneous broadening which has been observed in previous studies on QD ensembles1–3. In the time domain, the FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. The subsequent recovery is significantly larger than would be expected for simple redistribution. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse. When investigating at the PL spectrum of a single dot, we observe a marked difference caused by the FEL pulse (Fig. 2), which implies a change of the excitonic state of the QD.
  • Lecture (Conference)
    International Conference on Superlattices, Nanostructures and Nanodevices, 03.-08.08.2014, Savannah, United States of America

Publ.-Id: 20972 - Permalink

Intra-band dynamics in single InAs/GaAs quantum dots probed with a free-electron laser
Stephan, D.; Bhattacharyya, J.; Helm, M.; Huo, Y. H.; Schmidt, O.; Rastelli, A.; Schneider, H.;
Compared to the vast amount of research done in the past on inter-band transitions in single quantum dots (QDs), transitions within the bands have received much less attention. The main reasons for this are most likely the largely non-radiative character of intra-band transitions and the technical difficulties associated with the corresponding mid- and far-infrared radiation. In our contribution, we approach this challenge by combining conventional micro-photoluminescence (µPL) on low-density annealed InAs/GaAs self-assembled QDs with additional excitation at intra-band (i.e. inter-sublevel) transition energies by pulsed radiation from a free-electron laser (FEL). In contrast to previous studies on ensembles of QDs1–3, using single dots eliminates undesirable effects such as inhomogeneous broadening. The FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. This is followed by a pronounced recovery, such that the integrated PL is larger than for a reference transient without FEL excitation. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse.
  • Poster
    8th International Conerence on Quantum Dots, 11.05.-16.10.2014, Pisa, Italia

Publ.-Id: 20971 - Permalink

Optical investigations of GaAsN in high magnetic fields
Eßer, F.; Drachenko, O.; Schneider, H.; Patanè, A.; Hopkinson, M.; Helm, M.;
Introducing a few hundredths of a percent of nitrogen into a GaAs-based semiconductor leads to dramatic changes of the electronic and optical properties of the original material system. This can be used in order to intentionally tune the semiconductors characteristics. In particular the bandgap of semiconductors like GaAs and InGaAs, can be strongly reduced by slight nitrogen incorporation, which is attractive for applications, in particular for detectors or light sources.

Even though a lot of effort has been made on the investigation of the effective mass in GaAsN, it is rather challenging to describe the and stucture and in particular the effective mass of this system. We investigate a series of GaAsN samples and make use of high magnetic fields in combination with THz radiation from a free-electron laser, which provides a unique approach in order to find the source of previous inconsistencies. Cyclotron resonance spectroscopy is probably the most direct way to measure the effective mass, but has never been applied before to GaAsN bulk. We compare the results of this method with those of magneto-photoluminescence (PL), which is more commonly applied to dilute nitrides.

Our cyclotron resonance spectroscopy results indicate that the effective mass is not very much affected by the nitrogen doping, in contrast to previous reports (e.g. [1–4]) based on magneto-PL. In our PL investigations in magnetic fields up to 61 T, the observed blueshift of the PL spectrum indicates a similar increase of the effective mass, as reported before in e.g. [1–4]. We will discuss the significance of the particular method and argue that some assumptions have to be reconsidered.
Keywords: GaAsN, ditute nitrides, effective mass, cyclotron-resonance, magneto-photoluminescence, high magnetic field
  • Poster
    Optical Properties of Individual Nanowires and Quantum Dots in High Magnetic Field, 24.-26.09.2014, Toulouse, France

Publ.-Id: 20969 - Permalink

5 MeV Proton and 15 MeV Electron Radiation Effects Study on 4H-SiC nMOSFET Electrical Parameters
Alexandru, M.; Florentin, M.; Constant, A.; Schmidt, B.; Michel, P.; Godignon, P.;
The impact of proton and electron irradiations on the electrical parameters of 4H-SiC nMOSFETs has been investigated by the time bias stress instability method. This study has allowed observing the effect of holes trapped in the gate oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage, the effective mobility and the maximum drain current were observed. These improvements could be connected with the Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of passivated Carbon atoms is increased, hence improving the SiO2/SiC interface quality.
Keywords: Charge trapping, electron irradiation, mobility, proton irradiation, SiC MOSFET, SiO2/SiC interface, threshold voltage shift, time bias stress instability.

Publ.-Id: 20968 - Permalink

Spin Nernst Angle: Definition and qualitative Estimation for Cu Alloys
Zahn, P.; Gemming, S.;
The spin Nernst effect describes the occurrence of a spin current perpendicular to an applied thermal gradient and the spin quantization axis in a non-magnetic material. To quantify the effect, the spin Nernst angle will be defined in a more general way than in ref. [1]. This allows for a clear separation of the transverse spin current into two opposite contributions proportional to the spin Hall angle and the spin Nernst angle, respectively. Qualitative trends for Cu alloys with 3d, 4d and 5d defects extending a resonant scattering model by Fert and Levy [2] will be presented.
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442) and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2).
Keywords: spin Nernst effect, spin caloric, spin orbit coupling, Cu, dilute alloys, thermoelectrics, spin dependent transport
  • Poster
    Material Science and Engineering conference - MSE 2014, 23.-25.09.2014, Darmstadt, Deutschland

Publ.-Id: 20967 - Permalink

Traveling-Wave Thomson-Scattering for brilliant and efficient optical free-electron lasers
Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Schramm, U.;
In Traveling-Wave Thomson-Scattering (TWTS) a high-power laser pulse is scattered off a relativistic electron pulse to produce radiation from EUV to Angstrom wavelength. TWTS employs a side-scattering geometry where laser and electron propagation direction enclose an angle to become independent of the Rayleigh length limit for the maximum interaction distance in standard head-on Thomson scattering geometries. For optimum spatial overlap in TWTS geometries the laser pulse features a pulse-front tilt. In this way, the electrons interact with all parts of the laser pulse and brilliances as well as photon scattering efficiencies are by orders of magnitude larger than in standard head-on geometries.
Interaction distances in TWTS are long enough for operation of a free-electron laser.
We show how TWTS experiments can be designed, present experimental parameters for TWTS FELs and discuss experimental challenges in their realization.
Keywords: Traveling-Wave, Thomson Scattering, EUV, X-ray, optical FEL
  • Poster
    3rd annual meeting of the LAOLA collaboration, 06.-07.10.2014, Wismar, Deutschland

Publ.-Id: 20966 - Permalink

Adjusting the Forming Step for Resistive Switching in Nb2O5 by Ion Irradiation
Wylezich, H.; Mähne, H.; Heinrich, A.; Slesazeck, S.; Rensberg, J.; Ronning, C.; Zahn, P.; Mikolajick, T.;
Resistive switching devices with Nb2O5 as a switching layer are treated with argon ion irradiation, which generates defects in the oxide layer that support the electroforming step. To distinguish between the effects of layer thinning by sputtering and that of defect generation, devices with different thicknesses of deposited oxide are investigated. It is found that the defect-rich interfaces allow the formation of thick oxides at low forming voltages, and therefore, the effects of the ion irradiation are comparable to the use of reactive electrodes.
Keywords: Resistive switching, Nb2O5, argon, ion irradiation, metal-insulator-metal device, oxide, interfaces, sputtering, electro-forming, forming voltage

Publ.-Id: 20965 - Permalink

A high-yield automated radiosynthesis of the alpha-7 nicotinic receptor radioligand [18F]NS10743
Teodoro, R.; Wenzel, B.; Oh-Nishi, A.; Fischer, S.; Peters, D.; Suhara, T.; Deuther-Conrad, W.; Brust, P.;
[18F]NS10743, a promising and highly competitive α7 nAChR radioligand has been synthesised so far by microwave irradiation using a manual single-mode device followed by a palladium-catalyzed reduction of remaining nitro-precursor for HPLC separation purposes. For further preclinical and clinical use, regulated production of [18F]NS10743 by fully automated radiosynthesis is a crucial requirement. Therefore, we chose a commercial synthesis module and developed the automated radiosynthesis of [18F]NS10743. Besides evaluation of several radiosynthesis procedures, we performed an extensive HPLC study for quantitative separation of [18F]NS10743 from the corresponding nitro precursor. After implementation of the optimised procedure on a TRACERlabTM FX F-N synthesis module, [18F]NS10743 was obtained in high radiochemical purity (≥ 99%) with an overall radiochemical yield of 32.27% (n=3). The specific activities at the end of the synthesis were 571±17 GBq/µmol (n=3).
Keywords: Alpha-7 nicotinic acetylcholine receptor radioligand, Pet WAVE microwave CEM, radiofluorination, automated radiosynthesis, TRACERlabTM FX F-N

Publ.-Id: 20964 - Permalink

Kurzzeit-Spektroskopie an Halbleiter-Quantenstruktren am Freie-Elektronen-Laser FELBE
Winnerl, S.; Mittendorff, M.; Teich, M.; Jacob, R.; Schneider, H.; Helm, M.;
Der mittlere Infrarot- und Terahertz-Bereich bietet Zugang zu einer Vielzahl von faszinierenden Effekten in Halbleiter-Quantenstrukturen, da in diesem Spektralbereich eine Vielzahl von elementaren und kollektiven Anregungen wie z.B. Phononen, Plasmonen und Intersubbandübergängen liegen. Der Freie-Elektronen-Laser FELBE ist durchstimmbar im Bereich von 1 – 80 THz und liefert einen kontinuierlichen Zug von intensiven, schmalbandigen Pikosekundenpulsen, die sich ideal für nichtlineare Spektroskopie und resonante Anregung eignen. Wir zeigen exemplarisch Experimente an zweidimensionalen und nulldimensionalen Systemen und diskutieren sie hinsichtlich spektraler, zeitlicher und räumlicher Auflösung. Insbesondere wird die Ladungsträgerdynamik in selbstorganisierten Halbleiter-Quantenpunkten sowie Spektroskopie an einzelnen Quantenpunkten gezeigt [1-3]. Weiterhin stellen wir Resultate zur Ladungsträgerdynamik in Graphen vor [4,5]. Die Untersuchungen geben wichtige Einblicke in das Verhalten von Ladungsträgern auf kurzen Zeitskalen, insbesondere zu ihrer Phasenkohärenz, ihrer Wechselwirkung untereinander und ihrer Wechselwirkung mit Phononen. Neben der grundlegenden Bedeutung ist die Kenntnis er Kurzzeitdynamik wichtig für die Entwicklung zukünftiger optoelektronischer Bauelemente wie Detektoren, Strahlungsquellen und Elementen zur Informationsspeicherung in Quantencomputern.

[1] E. A. Zibik et al., Nature Mat. 8, 803 (2009).
[2] M. Teich et al., Appl. Phys. Lett. 103, 252110 (2013).
[3] R. Jacob, Nano Lett. 12, 4336 (2012).
[4] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).
[5] M. Mittendorff et al., Nature Phys. (under review).
  • Invited lecture (Conferences)
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014 (SNI 2014), 21.-23.09.2014, Bonn, Deutschland

Publ.-Id: 20963 - Permalink

Anisotropy of absorption bleaching and carrier relaxation in graphene
Winnerl, S.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.;
In the energy region between –1 eV and 1 eV the band structure of graphene is in good approximation described by identical isotropic Dirac cones for electrons and holes, respectively. Therefore, optical properties for interband excitations are typically considered to be isotropic for photon energies below 2 eV. However, our pump-probe experiments at a photon energy of 1.6 eV reveal a pronounced anisotropy in both the excitation characteristics and the subsequent relaxation dynamics. The anisotropy with 2-fold symmetry is induced by the linear polarization of the pump radiation. We compare the experimental results with calculations based on the density matrix formalism and show that optical phonons are mainly responsible for reaching an isotropic carrier distribution.
In the experiments, carried out on multilayer epitaxial graphene, the angle between the polarization of pump and probe beam was varied. Pumping and probing with parallel polarization resulted in two times larger pump-induced transmission as compared to pumping and probing with orthogonal polarization [1]. The initial relaxation after the transmission maximum is faster in the parallel polarization configuration. For time delays larger than 150 fs the induced transmission is similar for the two polarization configurations, indicating that an isotropic carrier distribution is reached. The observed anisotropy in the induced transmission is direct evidence for an anisotropic carrier distribution in k-space. This anisotropy has been predicted by theory [2]. Carriers are preferentially excited in directions perpendicular to the polarization vector of the pump beam. Microscopic modelling, which describes the experimental finding well, allows us to attribute the fast initial relaxation to collinear carrier-carrier scattering. Scattering via optical phonons is mainly responsible for reaching an isotropic distribution.
The results are of fundamental importance as they concern an aspect of the carrier dynamics that has escaped experimental observation so far, despite the large number of publications describing near-infrared pump-probe experiments on graphene. With respect to applications our findings may enable all-optical switches that react differently to pulses of different polarization direction.

[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W.A. de Heer, H. Schneider, and M. Helm, Nano Lett. (2014)
[2] M. Malic, T. Winzer, and A. Knorr, Appl. Phys. Lett. 101, 221115 (2012).
Keywords: Carrier dynamics, ultrafast spectroscopy, graphene
  • Poster
    Graphene Week, 23.-27.06.2014, Goteborg, Sweden

Publ.-Id: 20962 - Permalink

Time-resolved spectroscopy on Landau-quantized graphene revealing strong Auger scattering
Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.;
The carrier dynamics within the system of Landau levels of index n = -1 to n = 0 and n = 1 in graphene is investigated by pump-probe experiments using circularly polarized terahertz radiation. The study, complemented by microscopic modelling, reveals a pronounced carrier redistribution caused by strong Auger scattering.
Keywords: Carrier dyanmics, ultrafast spectroscopy, graphene, Landau quantization, Auger scattering
  • Lecture (Conference)
    4th EOS Topical Meeting on Terahertz Science & Technology (TST 2014), 11.-14.05.2014, Camogli, Italia

Publ.-Id: 20961 - Permalink

THz spectroscopy of solids using a free-electron laser
Helm, M.;
I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss nonlinear experiments on excitons in semiconductor quantum wells and pump-probe studies of the relaxation dynamics in graphene. I will conclude with an outlook on further developments, including the superradiant THz radiation source TELBE.
Keywords: free-electron laser, terahertz, quantum wells, graphene
  • Lecture (others)
    Seminarvortrag am Fritz-Haber-Institut (FHI), Berlin, 20.10.2014, Berlin, Germany

Publ.-Id: 20960 - Permalink

Development of a labeling system for microorganisms based on antimicrobial peptides
Barthen, R.; Mickein, K.; Kutschke, S.; Pollmann, K.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.;
Complex biogeochemical processes are essential in various subsurface ecosystems (like in soils and rock formations), and are relevant for e.g. effective bioleaching of metals from various ores. For an improved mechanistic understanding of biogeochemical processes a non-invasive detection method of present microorganisms in a given geological sample is crucial. Ideally, microorganisms from all kingdoms should be determined in a single step (and may be later differentiated from DNA or cell degradation). Furthermore, microbial responses to changes of the physical or chemical conditions of the system such as flow regime, pH, and nutrient concentrations could be addressed non-invasively.
Our strategy for in-situ identification of microorganism in geological samples is to use labeled antimicrobial peptides (AMPs) as selectively binding agents. In the nuclear medical sciences, this strategy is successfully applied for the identification and visualization of bacterial infections in humans [1]. We aim at tagging the AMPs first with fluorescent dyes, in a later step with the radionuclide 18F for imaging with positron emission tomography (PET).
For our study, AMPs are selected based on their ability to bind to the cells of the tested bacterial strains in sub-lethal concentrations while their sorption to matrix compounds is minimal. We show that AMPs readily interact with microorganisms commonly found in soils such as Pseudomonas fluorescence and Lysinibacillus sphaericus. We aim at labeling the AMPs by means of established, commercial crosslinkers.
In combination with our GeoPET method [2-4] 18F-radiolabeled AMPs were an extremely useful agent for the in-situ visualization of microorganisms also in opaque geological environments. Radiolabeled AMPs could be used for the visualization of growth and dispersal of microbial communities in such environments.
  • Lecture (Conference)
    Gemeinsame Jahrestagung der DGHM und der VAAM, 05.-08.10.2014, Dresden, Deutschland

Publ.-Id: 20959 - Permalink

Population dynamics in graphene Landau levels
Helm, M.; Mittendorff, M.; Winnerl, S.; Wendler, F.; Malic, E.; Knorr, A.;
Population dynamics in graphene Landau levels
Keywords: graphene, Landau levels, population, pump-probe, free-electron laser, Auger scattering
  • Invited lecture (Conferences)
    International Quantum Cascade Lasers School and Workshop 2014, 07.-12.09.2014, Policoro, Italy

Publ.-Id: 20958 - Permalink

A kinetic insight into the formation of neptunium(IV) dioxide NpO2 nanocrystals: a multi-technique study using UV-vis absorption spectroscopy and (high-resolution) transmission electron microscopy
Hübner, R.; Weiss, S.; Hennig, C.; Ikeda-Ohno, A.; Zaenker, H.; Stumpf, T.; Husar, R.;
UV-vis absorption spectroscopy proves itself as an convenient method for in-situ monitoring the formation and growth of waterborne An(IV) nanoparticles. Dilution of pure aqueous Np(CO3)56- species in ultrapure water leads to the dynamic self-assembling of NpO2 nanocrystals, monitored among others at absorbance 742 nm.

Nowadays, various state-of-the-art spectroscopic techniques (e.g., X-ray spectroscopies, laser-induced and vibrational spectroscopy, etc.) are available to investigate chemical interactions of actinides (An) on a molecular level. Old-fashioned (or conventional) UV-vis absorption spectroscopy is often underestimated as a powerful tool to investigate the chemistry of An, including An(IV) colloids. The present study spotlights the application of UV-vis absorption spectroscopy to studying the colloid system of An(IV). The chemistry of An(IV) in aqueous solution is typical of a small and highly-charged metal ion with a strong hydrolysis tendency leading low solubility, which often result in the underestimation of the migration behavior of An(IV) on the geological disposal of radioactive wastes. The formation mechanisms of An(IV) colloids?, especially under alkaline and near-neutral conditions relevant to the actual environment, are still unexplored even to date. One important issue to be addressed in An(IV) colloid chemistry is the chemical identification of An(IV) colloids. That is, are the colloids formed ill-defined hydroxide precipitate or hydrous oxides, or highly structured clusters/nanoparticles? In order to characterize An(IV) colloids, we investigated in-situ the aggregation of neptunium(IV) colloids formed under ambient aqueous alkaline conditions. The kinetics of the aggregation of Np(IV) colloids and the formation of Np(IV) nanoparticles were tracked by UV-vis absorption spectroscopy, and their morphology and internal structures were further investigated by transmission electron microscopy (TEM). In this study, we demonstrate that UV-vis absorption spectroscopy is an unique and powerful tool for in-situ monitoring of the hydrolysis reaction of Np(IV) and associated colloid/nanoparticle formation. The obtained results will be further discussed by combining with TEM and X-ray absorption spectroscopy.
Keywords: Neptunium, NpO2, hydrolysis, UV vis, TEM, EXAFS, DLS
  • Poster
    ATAS - advanced techniques in actinide spectroscopy, 03.-07.11.2014, Dresden, Deutschland

Publ.-Id: 20957 - Permalink

Intrinsic Formation of Neptunium Nanoparticles in Presence and Absence of Silica: Formation of Np(IV)-silica Colloids and NpO2 Nanocrystals
Husar, R.; Hübner, R.; Hennig, C.; Weiss, S.; Ikeda-Ohno, A.; Zänker, H.; Stumpf, T.;
The chemistry of tetravalent actinides An(IV) in aqueous solution is typical of a small highly-charged metal ion with a strong tendency to hydrolize and therefore a low solubility. Disregarding the formation of clusters, nanoparticles and colloids lead to underestimation of the migration behavior. The reaction mechanisms of formation and growth, especially under alkaline and near-neutral environmental conditions are still unexplored. On the way from aqueous species to nanoparticles two fundamental questions in An(IV) chemistry provoke discussion in literature: 1) are hydrolysis and condensation the driving forces toward nano-scaled solids or 2) are formed aggregates ill-defined complex hydroxides, hydrous oxides or highly structured clusters/nanoparticles? Excluding the presence of other oxidation states then An(IV), we performed in situ investigation of the self organised formation of neptunium(IV) aggregates and nanoparticles from aqueous complex precursor under alkaline conditions. The kinetics of the self-assembling of the nanoparticles, their morphology and internal structures were determined. The influence of silica on the formation of highly coordinated NpO2 structure was proved. In particular, former studies confirmed the formation of amorphous silica-containing U(IV) and Th(IV) colloids. Starting from aqueous neptunium(IV) carbonate complexes, we investigated the behavior after dilution in presence and absence of silica by TEM, EXAFS, UV vis spectroscopy, Ultrafiltration and DLS (dynamic light scattering). The formation of nanoparticles was observed. TEM and diffraction pattern show different morphologies and internal structures in dependence of presence or absence of silica.
Keywords: Neptunium, Np(IV), nanoparticles, colloids, An(IV), hydrolysis, neptunium carbonate complex
  • Poster
    Plutonium Futures 2014 - the science, 07.-12.09.2014, Las Vegas, USA

Publ.-Id: 20956 - Permalink

Der Salzschmelzenreaktor als Transmutationssystem vor dem Hintergrund des Kernenergieausstiegs
Merk, B.;
Salzschmelzenreaktoren besitzen eine lange Historie, zurückgehend auf mehrere Experimente am Oak Ridge Mational Laboratory, die bereits in den 50er und 60er Jahren stattfanden. Das bekannteste hiervon ist das Molten Salt Reactor Experiment (MSRE). Das Konzept des Salzschmelzenreaktors verschwand danach aus dem wissenschaftlichen Fokus. Um die Jahrtausendwende wurde das Konzept dann von russischer und von europäischer Seite wieder aufgegriffen. Zusätzlich wurde das Konzept des Salzschmelzenreaktors im Rahmen des Generation IV International Forums (GIF) als eines der 6 Reaktorkonzepte verankert.
Mit Hinblick auf das Ziel Sustainability des GIF hat sich bereits nach kurzer Zeit eine Verschiebung des Konzeptes für Salzschmelzenreaktoren ergeben. Derzeit untersuchte Reaktoren sind als sogenannte schnelle Systeme ausgelegt und besitzen in im Gegensatz zum MSRE keine Graphitstrukturen innerhalb des Reaktorkerns. Salzschmelzenreaktoren mit schnellem Neutronenspektrum eigenen sich aber nicht nur zur Energieproduktion, sondern sind auch als Transmutationssystem von Interesse und bieten für diesen speziellen Einsatz diverse Vorteile.
Im Vortrag werden die wichtigsten Unterschiede von Reaktoren mit festem Brennstoff (z. B. Sodium Cooled Fast Reactor) und Reaktoren mit flüssigem Brennstoff analysiert und diskutiert. Darauf aufbauend werden die spezifischen Vorteile von Salzschmelzenreaktoren für die Transmutation hergeleitet und die spezifischen Herausforderungen erörtert. Ein besonderer Blick gilt auch den Konsequenzen die sich durch das veränderte Neutronenspektrum, im Vergleich zum MSRE, ergeben.
Abschließend werden ausgewählte neueste wissenschaftliche Ergebnisse zu Salzschmelzenreaktoren vorgestellt. Es wird ein kurzer Einblick in die Ergebnisse der deutschen P&T Studie gegeben und die daraus resultierenden Konsequenzen auf eventuelle zukünftige Forschungsarbeiten zu Salzschmelzenreaktoren beleuchtet.

An overview on the history of molten salt reactors and the projects of the last years is given. The major advantages of molten salt reactors in the view of transmutation are discussed and evaluated in comparison with sodium cooled fast reactors. Finally some scientific highlights are given for the application of molten salt reactors under the bounday conditions of the nuclear ophase out decission in Germany.
Keywords: nuclear, nuclear reactor, molten salt, molten salt reactor, fast reactor, transmutation, nuclear waste management
  • Invited lecture (Conferences)
    Seminar an der RWTH Aachen, 08.07.2014, Aachen, Deutschland

Publ.-Id: 20955 - Permalink

On an optimized neutron shielding for an advanced molten salt fast reactor design
Merk, B.; Konheiser, J.;
The molten salt reactor technology has gained renewed interest. In contrast to the historic molten salt reactors, the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes significantly more challenging than in historic concepts. One very interesting and innovative result of the most recent EURATOM project on molten salt reactors – EVOL – is the fluid flow optimized design of the inner core vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all core internal structures. On the basis of this new geometry a model for neutron physics calculation is presented and applied for a shielding optimization. Based on these results an optimized shielding strategy is developed for the molten salt fast reactor to keep the fluence in the safety related outer vessel below expected limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system has to be significantly increased and will finally be comparable to a sodium cooled fast reac-tor. The HELIOS results are verified against Monte-Carlo calculations with very satisfactory agreement for a deep penetration problem.
Keywords: fast reactor, molten salt reactor, neutron shielding, neutron transport, HELIOS, optimization
  • Contribution to proceedings
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future, 28.09.-03.10.2014, Kyoto, Japan
  • Lecture (Conference)
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future, 28.09.-03.10.2014, Kyoto, Japan

Publ.-Id: 20954 - Permalink

On the use of a molten salt fast reactor for transmutation fulfilling the requests of the nuclear phase out decision
Merk, B.;
The 'Energiewende' in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft Energie and the Bundesministerium für Bildung und Forschung have launched a study in 2012 to answer these questions on a broad scientific basis. A major point during the discussions was the so-called last transmuter problem. This requires special attention in the case of the nuclear phase out, since transmutation of transuranium isotopes is only attractive under the phase out condition when this problem can be solved. Recently, a solution has been proposed, the so-called twofold operation cycle using a molten salt fast reactor.
Based on this proposal a simulation for the burning of the 170t TRUs remaining in Germany after the phase out as efficient as possible. A salt configuration based on the MOSART composition is used which is able to carry the required amount of TRUs for the fertile free operation. The requested number of reactors, the required operation time and the expected TRU leftovers are determined. Finally, a general discussion is added which major R&D topics would have to be envisaged for the realization of P&T in a molten salt fast reactor.
Keywords: nuclear, nuclear reactor, molten salt, molten salt reactor, transmutation, nuclear waste management
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland

Publ.-Id: 20953 - Permalink

Results and conclusions from the German P&T study – a view of the contributing Helmholtz research centres
Merk, B.; Geist, A.; Modolo, G.; Knebel, J.;
The governmental decision for the 'Energiewende' has put some urgent questions on the future of the P&T research. The Bundesministerium für Wirtschaft und Energie and the Bundesministerium für Bildung und Forschung have launched a study managed by acatech in 2012 to answer these questions on a broad scientific basis. The major mandate was to evaluate scientific and technological as well as socio-economic challenges and opportunities of the P&T technology in the view of the phase out decision. The main topics were:
- Starting point and boundary conditions – waste amounts and final disposal strategies
- Definition and description of scenarios – possible ways for transmutation in the view of the phase out, European vs. national
- Technological challenges of P&T – description of the major challenges to be solved on the way to industrial application
- Current status of R&D – discussion of possible transmutation systems, current R&D status of P&T, development gaps, and future research strategy
- Safety aspects – special safety aspects including all steps of the P&T cycle
- International projects & competences in Germany – what is going on around the world and what can be served by the German industry
The socio-scientific, the ecologic, and the economic aspects have been analyzed in parallel using expert interviews, group Delphi, and independent expert opinions on economic, legal, and environmental aspects.
An overview on the results of the study in the view of the contributing Helmholtz research centers (KIT, HZDR, and FZJ) is given. Special focus is put on the political recommendations and the developed research strategy which has been proposed to the ministries. Finally the conclusions of the Helmholtz-Centres regarding their current and future activities are given.
Keywords: nuclear, nuclear waste, nuclear reactors, nuclear waste management, partitioning, transmutation
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutschland

Publ.-Id: 20952 - Permalink

Extraction of valuables from tailings disposals
Leißner, T.; Osbahr, I.; Mütze, T.; Peuker, U. A.;
Mining in the Ore Mountains (Germany) has taken place for hundreds of years and in several stages. Each stage produced its typical tailing. According to the former state of the art of the processing much valuables could not be extracted. This was caused by complex interlocking of the minerals, low grades, or by upgrading processes not sensitive enough for small particle sizes. Thus the processing of these fractions was uneconomically. Modern technical possibilities and rising metal prices bring these tailings disposals into focus for the processing of strategic metals.
Mining disposals can be classified in heaps with coarse, low grade rock, which did not undergo a processing, slags and fly ash from smelting, and tailing disposals from mineral processing. The latter is under investigation to integrate them into a geographic information system. The mineral processing of the material will be part of the database besides information about geographic location, structure, amount of valuables, and details of ownership of the heap.
The tailings disposals are composed of coarse, low grade, interlocked particles from density separation processes, medium size particles, which are tailings from flotation, and fines with liberated valuables, which did not undergo flotation. Therefore mineral processing of these disposals comprises the separation of liberated gangue by classification, beneficiation of locked valuables with density separation, liberation of valuables by grinding, and beneficiation of liberated valuables with flotation. The presented work shows the results concerning the composition of one exemplary heap and results of the classification as well as of the preconcentration tests achieved with material from this heap.
  • Contribution to proceedings
    XXVII Internationl Mineral Processing Congress, 20.-24.10.2014, Santiago, Chile: Gecamin

Publ.-Id: 20951 - Permalink

Hydrodynamics of co-current two-phase flow in an inclined rotating tubular fixed bed reactor – Wetting intermittency via periodic catalyst immersion
Härting, H.-U.; Bieberle, A.; Lange, R.; Larachi, F.; Schubert, M.;
The hydrodynamics of an inclined rotating tubular fixed bed reactor operated with gas–liquid co-current downflow are studied. Reactor inclination is applied to force phase segregation, while the superimposed rotation of the reactor results in a wetting intermittency via periodic catalyst immersion. The fixed bed is clamped to avoid abrasion of the catalyst. The inclined rotating reactor is presented as a new reactor concept for process intensification of heterogeneous catalytic reactions requiring enhanced mass transfer of the gaseous phase and partial catalyst wetting.
Four different flow regimes with stratified, sickle, annular and dispersed flow patterns are determined experimentally by applying a compact gamma-ray computed tomography system. The effects of (i) gas and liquid superficial velocities, (ii) inclination angle and rotational velocity of the reactor and (iii) physico-chemical properties of the liquid phase on the occurrence of the flow regimes are investigated. The results of these investigations are illustrated with flow maps. In addition, pressure drop and liquid saturation depending on the operating conditions are shown.

• A new tubular reactor concept for process intensification is introduced.
• Reactor inclination and rotation allow for wetting intermittency via periodic catalyst immersion.
• Flow regimes can be adjusted by reactor inclination and rotation independent of liquid saturation.
• Lower pressure drops can be achieved in comparison to trickle bed reactors.
Keywords: Fixed bed hydrodynamics; Process intensification; Flow regimes; Multiphase flow; Gamma-ray computed tomography

Publ.-Id: 20950 - Permalink

AMNT 2014: Key Topic Reactor Operation, Safety - Report Part 2
Fischer, K. C.; Höhne, T.; Hollands, T.; Schuster, C.; Traichel, A.; Willschütz, H. G.; Wortman, B.;
Report on the following sessions of the Annual Conference on Nuclear Technology held in Frankfurt, 6 to 8 May 2014:
Thermo Dynamics and Fluid Dynamics: Experiments and Backfittings for the Improvement of Safety and Efficiency Safety of Nuclear Installations - Methods, Analyses, Results: In-Vessel Phenomena; Ex-Vessel Phenomena; Standards and Regulations; Hazard and Safety Analysis; and Validation and Uncertainty Analysis.
The other Sessions of the Key Topics "Reactor Operation, Safety", "Competence, Innovation, Regulation" and "Fuel, Decommissioning & Disposal" have been covered in atw 10 (2014) and will be covered in further issues of atw. "
Keywords: Numerical Methods, Models, Codes
  • atw - International Journal for Nuclear Power 59(2014)12, 701-702

Publ.-Id: 20949 - Permalink

Mineral Processing of Lithium-bearing Mica.
Leißner, T.; Rode, S.; Bachmann, K.; Gutzmer, J.; Peuker, U.;
This contribution deals with the mineral processing of Li-silicate greisen-type ores comprising of quartz, topaz and zinnwaldite (lithium-rich mica). The origin of the greisen-type ores processed is the Ore Mountains(Germany) where it is explored as a potential resource for the production of lithium carbonate. The goal is to develop a process chain for the enrichment of zinnwaldite using dry techniques only. As basis for the investigation the process chain, which historically was used to process the greisen focused on cassiterite and wolframite, is taken and modified towards the zinnwaldite.
Starting with crushed material with particle sizes smaller than 35 millimeters, investigations on different approaches to grinding to liberate mica from gangue are carried out. Concentrates of zinnwaldite are then produced by magnetic separation of size fractions. To assess the success of grinding, classification and separation, mineral liberation analysis and atomic absorption spectroscopy are used. The amount of lithium measured in the sample with atomic absorption spectroscopy was used to calculate the content of zinnwaldite based on its known mineral chemistry. Combined with the particle size distributions, product qualities are determined. Altogether, this allows the thorough evaluation of the success of comminution with focus on following steps of concentration.
Keywords: lithium, zinnwaldite, magnetic separation, mineral liberation analysis
  • Lecture (Conference)
    International Mineral Processing Congress, 24.-28.09.2012, New Delhi, India

Publ.-Id: 20948 - Permalink

Recent advances in structural geology, lithogeochemistry and exploration for VHMS deposits, Kristineberg area, Skellefte District, Sweden.
Jansson, N.; Hermansson, T.; Persson, M.; Berglund, A.; Kruuna, A.; Skyttä, P.; Bachmann, K.; Gutzmer, J.; Chmielowski, R.; Weihed, P.;
Kristineberg is the largest mine and VHMS deposit in the Palaeoproterozoic Skellefte District, Sweden. The deposit was discovered in 1918, and it has been mined since 1941. Besides the Kristineberg deposit, several other VHMS deposits have been mined in the Kristineberg area. Despite the long history of mining, significant advances are still being made in terms of exploration and understanding the geological framework of the ore bodies. A key to this success has been persistence in exploration and a combination of local and regional scale geological, geophysical and geochemical surveys. Holistic industry-university collaborative research projects have furthermore played an important role in bringing together geologists and geophysicists from different disciplines to tackle the large-scale geological framework. Among other things, these projects have resulted in the first structural geological 3D model of the Kristineberg area, better age constraints on the formation of the deposits, a regional alteration map as well as ongoing work to model alteration in 3D. This contribution summarizes the results of these investigations and recent exploration.
Keywords: Kristineberg, Skellefte District, VHMS, 3D modelling, Exploration
  • Poster
    12th Biennial SGA Meeting: Mineral deposit research for a high-tech world, 12.-15.08.2013, Uppsala, Sweden

Publ.-Id: 20947 - Permalink

Alteration in the area of the Kristineberg VHMS deposit, Skellefte district, Sweden.
Bachmann, K.; Gutzmer, J.; Persson, M.; Jansson, N.;
The Skellefte district in north-central Sweden is one of the most important mining districts in northern Europe. It contains over 85 pyritic Zn-Cu-Au-Ag massive sulphide deposits of which 21 deposits have been mined since 1924 and 4 are still in operation by Boliden Mineral AB. The most productive deposit, the Kristineberg mine, has been operated by Boliden since 1940 with a current annual production of 670,000 t of polymetallic ore containing 3.0 wt.-% Zn, 0.7 wt.-% Cu, 0.4 wt.-% Pb, 1.9 g/t Au and 47 g/t Ag. Alteration of the volcanic rocks around the Kristineberg deposit is very intense. The main aim of this study has been to describe the alteration intensity and to define alteration trends around the Kristineberg deposit. The success of this approach provides a new exploration tool for future exploration in the Skellefte District where alteration renders the recognition of primary volcanic facies difficult.
Keywords: Kristineberg, Skellefte district, VHMS, alteration
  • Poster
    12th Biennial SGA Meeting: Mineral deposit research for a high-tech world, 12.-15.08.2013, Uppsala, Sweden

Publ.-Id: 20946 - Permalink

Raman spectroscopy – casting (laser) light on microbe – mineral interactions
Kostudis, S.; Kutschke, S.; Pollmann, K.;
Highly efficient and sustainable mining strategies gain importance due to the fact that available resources of base metals like copper but strategic elements such as gallium and molybdenum as well face a steadily decreasing grade. This issue is enhanced by the increased demand and production amounts of those metal compounds. Biohydrometallurgy – the use of microorganisms or related substances in metal extraction - provides the potential of processing low grade ores efficiently. Thus it is applied yet in some gold and uranium mining.
Also due to strategic reasons mining of regional resources such as the European Kupferschiefer come to the fore. Its complex composition including sulphide rich ores, carbonates and organic compounds challenges biotechnological approaches. Nevertheless promising approaches have been reported. We examine heterotrophic bioleaching of copper from Kupferschiefer ores. To investigate the interactions between mineral surface and microorganisms Raman spectroscopy offers a versatile applicability: Identification of minerals and differentiation of microorganisms is nicely provided and is accompanied by imaging opportunities in a two or even three dimensional manner. Thus biofilms, for example, can be analysed with respect to microbial diversity or preferences of minerals during the attaching process.
  • Poster
    Microbiology and Infection, 05.-08.10.2014, Dresden, Deutschland

Publ.-Id: 20945 - Permalink

Evaluation of mineral processing by assessment of liberation and upgrading.
Leißner, T.; Mütze, T.; Bachmann, K.; Rode, S.; Gutzmer, J.; Peuker, U.;
A model is presented to evaluate mineral processing on basis of gangue recovery and valuables recovery. It combines mineralogical limiting curves with upgrading curves in the Fuerstenau diagram. These curves are used to assess mineral liberation and mineral beneficiation compared with the ideal result. Two new parameters (ratio of separation and ratio of liberation) are calculated based on a comparison of areas enclosed by the mineralogical limiting curve, the upgrading curve, the curve representing a total liberation of valuables, and the curve representing a perfect mixture of valuables and gangue.
An assessment of the success of mineral processing is possible using these parameters. The assessment shows whether the quality of a separation product is influenced by the separation process itself or by the achieved liberation of the feed.
A series of experiments on the magnetic separation of a greisen-type ore proves the applicability of this model to mineral processing. SEM-based image analysis and ICP-OES measurements have been used to obtain the necessary data.
Keywords: liberation, upgrading, separation, mineral liberation analysis

Publ.-Id: 20944 - Permalink

Discrimination of hematite and magnetite in finely intergrown natural iron ores by automated mineralogy.
Bachmann, K.; Bartzsch, A.; Gutzmer, J.;
Providing a fast, quantitative characterization of iron ores in terms of liberation, grain sizes and shapes as well as mineral association remains a big challenge. Whilst quantitative mineralogical data are easily attained by QXRD, an automated SEM-EDS based approach is needed for the quantification of relevant microfabric attributes. Two different iron ores were investigated for this study, to illustrate the capabilities and limitations of the latter approach. The first example is a banded-iron formation (BIF) ore from Thabazimbi/RSA, the second ore type studied is a magnetite iron ore from Svappavaaragruvan, c. 50 km east of Kiruna/N-Sweden. The greatest difficulty in the characterization of iron ores is certainly the discrimination between different relevant iron oxides (magnetite, hematite, goethite) that are all of very similar elemental composition – and thus have both very similar backscattered electron (BSE) brightness, as well as almost identical EDS spectra. A principle approach was suggested by Figueroa et al. (2011) by using the Mineral Liberation Analyzer (MLA). The suitability of this method was illustrated on synthetic mixtures. The approach of the present study utilizes the method on thin sections of natural iron ores, which show a fine intergrowth of hematite and magnetite with an unknown composition. For calibration, an in-house magnetite and hematite standard was prepared to further optimize the set-up of the method. A new feature in the MLA suite v.3.1.4 is the capability to define the exact working distance for every single sample separately. Slight variations in the working distance between the different samples and the standard were equalized. The MLA results were compared to bulk chemical data as well as traditional point counting-data by reflected light-microscopy. The results are within a relative error of 5 %. It can be concluded that the method was successfully applied and can be applied to iron ores with complex oxide mineral associations.
  • Poster
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today - Practical Aspects, 22.-24.09.2014, Leoben, Austria

Publ.-Id: 20943 - Permalink

Li isotopes and geochemistry of Li–F–Sn greisen from the Zinnwald deposit.
Bachmann, K.; Seifert, T.; Magna, T.; Neßler, J.;
The Sn–W greisen deposits, located in the eastern part of the Variscan metallogenic Erzgebirge province (zinnwaldite Ar–Ar ages between 313 and 315 Ma), are emplaced in highly metamorphosed and/or igneous rocks and typically are associated with post-collisional Li–F-enriched small granitic intrusions. This metallogenic province traditionally belonged to the major source of economic Sn, Ag, U, W, Co and fluorite–barite deposits for central Europe. The Zinnwald/Cínovec Li–Sn greisen deposit is associated with a unique zinnwaldite–quartz–topaz mineralization hosted by an albitized stock-granite.
Li contents and isotope compositions were measured in host albite granites (n=2), greisens (n=3), and a sample from a flat-dipping vein in the Zinnwald deposit, paralleled by individual mineral phases. All investigated bulk rocks have extreme Li contents reaching from 1,600–2,200 ppm in albite-granite, to 3,400–6,200 ppm in greisen-type rocks and to ~8,000 ppm in a vein-type sample, most likely carried by zinnwaldite (15,000–19,200 ppm) and muscovite (9,500–15,700 ppm) whereas albite and quartz, in particular, have significantly lower Li abundances (560–660 and 33–330 ppm, respectively). The high bulk Li contents are very unusual even for chemically evolved granitic systems with the exception of Li-rich pegmatites. Bulk 7Li values are restricted (–1.0 to 0.3 ‰), consistent with late orogenic granites from a larger area of the Erzgebirge Mts.. Zinnwaldite and muscovite carry isotopically heavy Li relative to the corresponding bulk rocks and, at the same time, muscovite always is slightly heavier than zinnwaldite. 7Li values of quartz become progressively heavier from granites through greisens to a vein sample. Zinnwaldite may represent a late-stage ingress of Li-rich fluids/melts rather than indigenous phase of these lithologies because from mass balance considerations and mineral modes, bulk [Li] and 7Li values cannot easily be reconstructed for either sample of the suite.
  • Poster
    Goldschmidt2014, 08.-14.06.2014, Sacramento, USA

Publ.-Id: 20942 - Permalink

Method for evaluation of upgrading by liberation and separation.
Leißner, T.; Mütze, T.; Anatasova, P.; Bachmann, K.; Peuker, U.;
A method is presented for the evaluation of mineral processing by liberation and upgrading. The method bases on the plot of recovery of valuables versus the recovery of gangue (Fuerstenau upgrading curve). The locking curve of a feed material was plotted together with the upgrading curve in a Fuerstenau diagram. The assessment of liberation and upgrading is done by a comparison of surfaces formed by the curves and some characteristic lines of the diagram. This plot allows the calculation of two new quantitative measures for liberation and upgrading.
Both parameters can be combined to a third parameter describing the quality of the whole technical setup for mineral processing by subtracting the upgrading parameter from the liberation parameter. The third parameter shows a positive value in cases of upgrading determined processes, a negative value in cases of liberation affected processes and about zero for processes affected equally by liberation and upgrading. Thus it is easily possible to distinguish between poor results in the mineral processing caused by insufficient liberation or poor results caused by insufficient upgrading.
Preliminary results from two case studies, performed on two completely different ore types, are very promising illustrating the practical use of such an approach.
  • Lecture (Conference)
    International Mineral Processing Congress, 20.-24.10.2014, Santiago, Chile

Publ.-Id: 20941 - Permalink

WASA-BOSS: ATHLET-CD model for severe accident analysis for a generic KONVOI reactor
Tusheva, P.; Schäfer, F.; Kozmenkov, Y.; Kliem, S.; Hollands, T.; Trometer, A.; Buck, M.;
The work described in this paper is a part of the ongoing joint research project WASA-BOSS, Weiterentwicklung und Anwendung von Severe Accident Codes – Bewertung und Optimierung von Störfallmaßnahmen, aiming at investigation of severe accident scenarios and severe accident management measures in boiling water reactors (BWR) and pressurized water reactors (PWR) [1]. The GRS, IKE and HZDR cooperation is focused on the development of an ATHLET-CD (Analysis of THermal-hydraulics of LEaks and Transients – Core Degradation) code model for a generic PWR of type KONVOI, including investigations of core degradation scenarios and possible accident management. This paper discusses the possible accident management measures (AMM), the ATHLET-CD model as well as the first preliminary simulations for a station blackout (SBO) scenario without and with application of countermeasures.
Keywords: severe accidents, AMM, ATHLET-CD
  • Contribution to proceedings
    Jahrestagung Kerntechnik/Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik/Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Germany
  • atw - International Journal for Nuclear Power 60(2015)7, 442

Publ.-Id: 20940 - Permalink

Multifunctional S-layer proteins as building blocks for hybrid materials
Weinert, U.; Günther, T.; Lehmann, F.; Vogel, M.; Suhr, M.; Matys, S.; Bobeth, C.; Kutschke, S.; Pollmann, K.; Raff, J.;
Nanostructured bio-inorganic hybrid materials are very attractive for technical applications, e.g. nanocatalysts, photocatalytic materials, sensors and filter systems. Self-assembling biomolecules like Surface layer (S-layer) proteins represent a promising tool as hybrid material due to their ability to self-assembly in aqueous solutions and on surfaces. In nature S-layer proteins coat the bacterial and archaeal cells with a highly ordered nanostructure and defined symmetry and fulfill various functions, e.g. protection, binding matrix for exoenzymes and molecular sieves. Isolates, which were taken from a uranium mining waste pile in Saxony, produce S layer proteins to protect themselves from heavy metals and radionuclides. If the S layer proteins are saturated with heavy metals or radio nucleotides, the protein will be rejected and a new one will be produced.

We take advantage of the high affinity to heavy metals to produce hybrid filter materials from micro sieves and S-layers. The so called “S-sieves” will be able to bind heavy and noble metals from aqueous solutions even in low concentration ranges economically.

Another aspect will be the synthesis of Pd, Pt and Au nanoparticles on S-layer proteins. Pd and Au nanoparticles were built in the pores of S-layer proteins. Due to that a surface of nanoparticles of a defined size and regularly arrangement can be constructed. Those surfaces will work as nanocatalysts for many technical applications, e.g. the production of CNTs which has already been demonstrated.

Further work deals with the design of a hybrid materials which will work as photocatalysators for drinking water purification. Especially pharmaceuticals can be disintegrated by radicals. The radicals are formed in sunlight and in presence of the catalytic active ZnO- or TiO2-nanoparticles which are coupled and regularly arranged on S-layer protein interface.

These three examples emphasize the use of S-layer proteins their potential in nanotechnology and will give new prospective in the mentioned techniques.
Keywords: hybrid material, s-layer, nanaoparticles, filter material, nanocatalysts
  • Lecture (Conference)
    Multifunctional S-layer proteins as building blocks for hybrid materials, 23.-25.09.2014, Darmstadt, Deutschland

Publ.-Id: 20939 - Permalink

Bioinspired hybrid nanomaterials based on self-assembling proteins
Weinert, U.; Lederer, F.; Günther, T.; Lehmann, F.; Drobot, B.; Vogel, M.; Pollmann, K.; Raff, J.;
Many microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins (Fig. 1a) bind toxic metals and metalloids and thusly protect the cells from being damaged by these elements. On other cells, S-layers may act for example as immobilization matrix for exoenzymes, as molecular sieve or as ion and molecule trap.
These properties and their ability to self-assemble in suspension, on surfaces and at interfaces qualify S-layers as interesting building blocks for the construction of new bioinspired nanomaterials for different technical applications. Using the two-dimensional protein arrays, different kinds of surfaces can be nanostructured and novel bio-inorganic hybrid materials with multiple functions can be produced.
Currently three materials are in the focus: metal filters, catalysts and sensors (Fig. 1b). Biocomposites made of microsieves and S-layers are under development to selectively recover strategic metals from aqueous solutions. S-layer proteins with immobilized and regularly arranged metals or metal oxides are useful for diverse catalytic applications. Furthermore, S-layer coatings combining highly specific receptors like aptamers and stable fluorescence dyes are very promising for the construction of new biosensors for organics or pharmaceuticals.
Basis for those materials and their industrial application is an effective production of S-layer proteins. The latter is possible by the extraction of the S-layers from growing cells or by heterologous expression of the proteins. In bacteria or yeasts expressed S-layers can be genetically engineered with molecular modifications to further combine the outstanding S layer protein characteristics with additional expedient features. Native as well as engineered S-layer proteins have an application potential going far beyond above mentioned applications ranging from the chemical industry, water and environmental technologies to medicine.
Keywords: nanoparticles, filter material, S-layer, biosensors, nanocatalysts
  • Lecture (Conference)
    Biomaterials - Made in Bioreactors, 26.-28.05.2014, Radebeul, Deutschland

Publ.-Id: 20938 - Permalink

Correct averaging in transmission radiography: analysis of the inverse problem
Hampel, U.; Wagner, M.; Bieberle, M.;
Transmission radiometry is frequently used in industrial measurement processes as a mean to assess the thickness or composition of a material. A common problem encountered in such applications is the so-called dynamic bias error, which results from averaging beam intensities over time while the material distribution changes. We recently reported on a method to overcome the associated measurement error by solving an inverse problem, which in principle restores the exact average attenuation by considering the Poisson statistics of the underlying particle or photon emission process. In this paper we present a detailed analysis of the inverse problem and its optimal regularized numerical solution. As a result we derive an optimal parameter configuration for the inverse problem.

Publ.-Id: 20937 - Permalink

Quantum structure THz photonics and spectroscopy at HZDR
Schneider, H.;
Es gibt kein Abstract.
  • Lecture (others)
    Seminarvortrag, Centre Suisse d'Electronique et Microtechnique SA (CSEM), 19.09.2014, Neuchâtel, Schweiz

Publ.-Id: 20936 - Permalink

Photoinduzierte Dynamik in der ps Zeit- und THz Frequenz-Domäne
Schneider, H.; Schmidt, J.; Teich, M.; Stephan, D.; Fehrenbacher, M.; Franke, C.; Winnerl, S.; Gensch, M.; Seidel, W.; Helm, M.;
Dieser Vortrag stellt die im Rahmen des BmBF-Verbundprojekts PIDID geschaffenen erweiterten Messmöglichkeiten für den Nutzerbetrieb am Freie-Elektronenlaser (FEL) FELBE vor und beschreibt einige exemplarische Experimente. FELBE erlaubt als einziger FEL in Europa einen quasikontinuierlichen Pulsbetrieb, der bei vielen Experimenten zu erheblichen Vorteilen führt im Hinblick auf die Stabilität sowie das Signal-zu-Rauschverhältnis. Aufgrund der Resonatorlänge beträgt die FEL-Pulsrate hierbei 13 MHz (77 ns Pulsabstand). Innerhalb des PIDID-Vorhabens wurden reduzierte Pulsraten (1 kHz bzw. 100 kHz) realisiert, wie sie zur Untersuchung physikalischer Prozesse mit längeren Zeitkonstanten im Bereich µs bis ms benötigt werden. Hierzu wurde ein optischer Schalter aufgebaut, der auf der hohen Reflektivität eines Elektron-Loch-Plasmas beruht, das mittels synchroner optischer Pulse in einem Germaniumkristall angeregt wurde. Des Weiteren wurden ein Fourier-Spektrometer sowie ein Tieftemperatur-Nahfeldmikroskop aufgebaut, die vorwiegend in Teilprojekten der Projektpartner eingesetzt wurden. Im zweiten Teil des Vortrags werden die wichtigsten Messmöglichkeiten an FELBE anhand einiger ausgewählter Experimente dargelegt.
  • Lecture (Conference)
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014 (SNI 2014), 21.-23.09.2014, Bonn, Deutschland

Publ.-Id: 20935 - Permalink

Formation of neptunium(IV)-silica colloids at near-neutral and slightly alkaline pH
Husar, R.; Weiss, S.; Hennig, C.; Hübner, R.; Ikeda-Ohno, A.; Zänker, H.;
The reducing conditions in a nuclear waste repository render neptunium tetravalent. Thus, Np is often assumed to be immobile in the subsurface. However, tetravalent actinides can also become mobile if they occur as colloidal precipitation products. We show that Np(IV) is able to form silica-rich colloids in solutions containing silicic acid at concentrations of both the regions above and below the “mononuclear wall” of silicic acid at 2∙10-3 M (where silicic acid is expected to start polymerization). These Np(IV)-silica colloids have a size of only very few nanometers and can reach significantly higher concentrations than Np(IV) oxyhydroxide colloids. They can be stable in the waterborne form over longer spans of time. In the Np(IV)-silica colloids the actinide-oxygen-actinide bonds are increasingly replaced by actinide-oxygen-silicon bonds due to structural incorporation of Si. Possible implications of the formation of such colloids for environmental scenarios are discussed.
Keywords: Neptunium, Np(IV)-silica colloids, nanoparticles, EXAFS

Publ.-Id: 20934 - Permalink

Low-energy behavior of E2 strength functions
Schwengner, R.;
Electric quadrupole strength functions have been deduced from averages of a large number of E2 transition strengths calculated within the shell model for the nuclides 94Mo and 95Mo. These strength functions are compared with phenomenological approximations as provided by the Reference Input Parameter Library (RIPL) for calculations of reaction rates on the basis of the statistical model. The low-energy behavior of the calculated strength functions differs from the one of the phenomenological E2 strength functions and may be used to improve the input for calculations of reaction rates.
Keywords: Photonuclear reactions, photon strength functions, shell model, transition strengths

Publ.-Id: 20933 - Permalink

Monte-Carlo Simulationen zur Untersuchung der Auswirkungen von Quelländerung im Reaktorkern auf die Excore-Instrumentierung
Konheiser, J.;
Verschiedene Auswirkungen von möglichen Variationen der Kerngeometrie auf die Signalwerte der Excore-Instrumentierung eines Druckwasserreaktors (DWR) werden in dieser Arbeit gezeigt. Zu diesem Zweck werden Neutronenflüsse für mögliche Brennelementanordnungen mit Hilfe stationären Monte Carlo-Berechnungen außerhalb des Reaktors bestimmt. Typische Daten eines deutschen PWR wurden für die Untersuchungen verwendet.
Unterschiede in den Neutronenflüssen der Excore-Instrumentierung von bis zu 4 % wurden bei Änderungen der Abstände von 1 mm zwischen bestimmten Brennelementen, die im Randbereich des Kerns liegen, berechnet.
Der Grund ist eine verbesserte Moderation von Neutronen, die zu einem höheren Leistung bzw. Neutronenfluss im Randbereich des Kerns führt. Die Folge ist ein höherer Neutronenstrom in Richtung der Excore-Instrumentierung. Dieser Effekt ist Abhängigkeit von Zykluszeitpunkt.
Mögliche Wassertemperaturschwankungen von 1K im Ringspalt, die zu Veränderungen der Wasserdichte und somit des Absorptionsvermögens führen, haben dagegen kaum Auswirkungen auf den Neutronenfluss an der Excore-Instrumentierung.

Effects of possible variations of the core geometry on the signal values of excore instrumentation of a pressure water reactor (PWR) are shown in this work. For this purpose, neutron fluxes outside of the reactor are determined for possible arrangements of fuel assemblies by means of stationary Monte Carlo calculations. Typical data of a German PWR were used for the investigations. Differences in the neutron flux of the excore instrumentation of up to 4% were calculated with changes of the pitch from 1 mm between certain fuel assemblies, which lie in the boundary area of the core. The reason is an improved moderation of neutrons, which results in a higher power and neutron flux in the periphery of the core. The result is a higher neutron flux in the direction of excore instrumentation. This effect is a function of cycle time. Possible water temperature fluctuations of 1 K in the downcomer, which leads to changes in water density and thus in the absorbance, have marginal effect on the neutron flux at the excore instrumentation.
Keywords: excore instrumentation, Monte Carlo calculation, pressure water reactor, neutron flux
  • Article, self-published (no contribution to HZDR-Annual report)
    Helmholtz-Zentrum Rossendorf 2014
    56 Seiten

Publ.-Id: 20932 - Permalink

Terahertz spectroscopy of zero- and two-dimensional semiconductor nanostructures with the free-electron laser FELBE
Schneider, H.; Teich, M.; Bhattacharyya, J.; Zybell, S.; Jacob, R.; Winnerl, S.; Helm, M.;
The free-electron laser facility FELBE in Dresden, a unique source of intense, quasi-cw, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes, provides unique research opportunities. In high-quality semiconductor quantum wells, we investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasi-atoms. Tuning FELBE in resonance with the transition between the excitonic 2s and 2p states (at ca. 2 THz) allows us to study the dynamics of intra-excitonic population transfer. Moreover, strong terahertz pumping results in a characteristic Rabi splitting of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect. In semiconductor quantum dots, resonant THz excitation between different sublevels is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where the contrast originates from far-infrared absorption by single electrons. Quantum dots are also known to have very long electronic relaxation times caused by a reduced phase space for optical phonon scattering. We will report on THz four-wave mixing experiments demonstrating that the associated electronic coherence times approximately equal the population relaxation time at low temperatures. This property makes quantum dots promising for quantum optical applications at THz frequencies.
Keywords: free-electrpn laser
  • Lecture (Conference)
    Science@FELs 2014, 15.-17.09.2014, Villigen, Schweiz

Publ.-Id: 20931 - Permalink

QWIP-Based “Ultrafast” Detectors for QCL Research
Schneider, H.;
In this talk, I will summarize two approaches for “ultrafast” QWIP-based detection of mid-infrared signals and cover a few examples for practical applications.
  • Invited lecture (Conferences)
    International Quantum Cascade Laser School and Workshop 2014 (IQCLSW2014), 07.-12.09.2014, Policoro (Matera), Italien

Publ.-Id: 20930 - Permalink

Intrinsic formation of nanocrystalline neptunium dioxide under neutral aqueous conditions relevant to deep geological repositories
Husar, R.; Hübner, R.; Hennig, C.; Martin, P. M.; Chollet, M.; Weiss, S.; Zänker, H.; Stumpf, T.; Ikeda-Ohno, A.;
Nano-sized crystals of neptunium dioxide (NpO2) were prepared successfully based on novel synthetic approach to neutralise a basic Np(IV) carbonate solution. The formation of nanocrystalline NpO2 was monitored by UV/visible absorption and X-ray absorption spectroscopies, and the resultant NpO2 crystals were further characterised by transmission electron microscopy.
Keywords: actinides, neptunium, NpO2, nanocrystals, colloids, formation, UV/visible absorption spectroscopy, X-ray absorption spectroscopy, transmission electron microscopy

Publ.-Id: 20928 - Permalink

Selektive Trennung sehr feiner Partikelsysteme mittels Flüssig/Flüssig-Flotation
Leistner, T.; Müller, M.; Erler, J. V.; Rudolph, M.; Peuker, U. A.;
Die Vergrößerung des effizienten Anwendungsbereiches von Sortierprozessen in den Bereich feinster Partikelsysteme (0,1 – 10 μm) stellt eine erhebliche Herausforderung für die Forschung dar. Ein möglicher Prozessansatz zur Verbesserung des Sortierergebnisses ist die Flüssig/Flüssig-Flotation. In dieser Studie werden Aussagen bezüglich Anwendbarkeit und Prozessverhalten dieses Ansatzes in Abhängigkeit von ausgewählten Prozessparametern an verschiedenen Modellpartikelsystemen präsentiert.
Keywords: Particle-oil-water emulsions; Phase transfer; Surfactant; Two-liquid flotation; Ultrafine particle separation

Publ.-Id: 20927 - Permalink

Efficient and accurate identification of platinum group minerals by a combination of mineral liberation and electron microprobe analysis
Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.;
Identification and accurate characterization of platinum group minerals (PGM) is a very cumbersome procedure due to grain sizes that are mostly below 10 µm and inconspicuous appearance. A novel strategy on finding and quantifying PGM was applied by combining Mineral Liberation Analyzer (MLA) 650F, point logger (JEOL) and a field emission electron probe micro-analyzer (FE-EPMA, JEOL JXA-8530F). Thin sections from a layered intrusion (UG2) in the Bushveld Complex and from two Uralian-Alaskan-type complexes in the Ural Mountains, Russia, were investigated as case studies.
As a first step the PGM are identified, using the Mineral Liberation Analyzer (MLA). The SPL (Sparse Phase Liberation) mode is the best way to find and identify the PGM with high spatial resolution and great accuracy. For this purpose, a series of back-scattered electron images is collected. Within these images, mineral grains are selected that match or exceed a set grey-scale value. These grains are characterized by collecting EDS spectra. Grains identified as PGMs are then marked and coordinates recorded in a format suitable for the EPMA at the point logger. With these coordinates recorded, the sample can be transferred to the microprobe. Despite their small grain sizes the PGM can be retrieved without any difficulties (deviation from the position logged with the point logger is only a few µm). Case studies illustrate that the combination of MLA, point logger and EPMA results in the identification of 4-5 times more PGMs than by careful reflected light microscopy. This is mainly due to the facts that (a) PGM with grain sizes < 5µm are reliably identified and (b) PGM and closely associated base metal sulfides and sulfosalts are well differentiated with the MLA. Furthermore, identification of PGMs remains unaffected by human error and is efficient with respect to the time spent by the mineralogist on a particular sample.
Despite the efficient identification of PGM grains using MLA, the combination with FE-EPMA bears at least one significant advantage. FE-EPMA allows for the accurate determination of mineral chemical composition by WDS, whereas MLA permits only for EDS spot analyses. WDS analyses of PGM by FE-EPMA requires considerable caution, though, due to overlaps of X-rays on both peak and background of almost all PGE and associated elements (e.g. OsMβ on IrMα and AuMβ on HgMα). It is thus necessary to look carefully at every element and to set peak and backgrounds individually for every element. X-ray lines suitable for quantitative analyses (e.g. Mβ instead of Mα) need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction has been developed in order to correct the interferences afterwards. Results obtained in this study attain acceptable totals and atomic proportions, suggesting that the applied corrections are appropriate.
Keywords: Mineral Liberation Analyser, Electron Microprobe, Pointlogger, Platinum Group Minerals, Overlap corrections
  • Contribution to proceedings
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, Practical Aspects, 21.-24.09.2014, Leoben, Österreich
    EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, Antwerp-Wilrijk, Belgien: European Microbeam Analysis Society eV EMAS, 9789082276909, 303-303
  • Poster
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, 21.-24.09.2014, Leoben, Österreich

Publ.-Id: 20926 - Permalink

Abschlussbericht "WTZ Russland - Fluenzberechnungen für Voreilproben beim WWER-440"
Konheiser, J.; Grahn, A.;
Reactor pressure vessels (RPV) are non-restorable equipment and their lifetime may restrict the nuclear power plant-life as a whole. Surveillance specimen programs for RPV materials are among the most important measures of in-service inspection pro-grams that are necessary for realistic and reliable assessment of the RPV residual lifetime. In addition to the chemical composition of the RPV steel, the radiation pa-rameters (neutron and gamma fluences and spectra) have the most important impact on the RPV embrittlement characteristics.
In this work, different geometric positions which have influence on the radiation conditions of the samples are investigated. Thus, the uncertainties can be determined in the fluence values of surveillance specimens. The fluence calculations were carried out by the codes TRAMO and DORT. This study was accompanied by ex-vessel neutron dosimetry experiments at Kola NPP, Unit 3 (VVER-440/213), which provide the basis for validation of calculated neutron fluences. The main neutron-activation monitoring reactions were 54Fe(n,p)54Mn and 58Ni(n,p)58Co. The activity measurements were carried out by “Scientific and Engineering Centre for Nuclear and Radiation Safety (SEC NRS).
Good agreement between the deterministic and stochastic calculation results as well as between the calculations and the ex-vessel measurements was found. The aver-age difference between measured and calculated values is 5%. The influence of the channels for surveillance specimens and the shielding effect of a baffle rib on the monitors and on the Monte-Carlo calculated results was studied.
For the surveillance specimens in the maximum of the flux, an average flux of around 2.45 * 1012 neutrons/cm2 was calculated for the neutron flux E> 0.5 MeV. The differences in the surveillance specimens could be up to 20% depending on the direction to the core. Discrepancies up to 10% can be caused by the change of the position of the capsules in the irradiation channel. Based on these calculations the lead factor of specimens was determined. The maximum fluence of RPV may be achieved after two cycles.
The calculated maximum gamma flux is around 3.4 * 1012 g/cm2s for E> 1.0 MeV and around 8.4 * 1012 g/cm2s for E> 0.5 MeV, with the largest part of the flux (around 97%) from the neutron reactions. The gamma fluxes in the surveillance specimens are two to three times bigger than the neutron fluxes. Nevertheless, the material damage by the gamma radiation is very small, because the dpa (displacement per atom) cross sections of gamma rays are about two to three orders of magnitude smaller.
In order to exclude the possibility of healing effects of the samples due to excessive temperatures, the heat release in the surveillance specimens was determined based on the calculated gamma fluences. The analytic treatment of the heat conduction equation and simplified SS geometries were adopted to calculate the range of tem-peratures to be expected. The temperature increase of 20 K above the inlet coolant temperature was estimated using a conservative approach. Under comparatively re-alistic conditions, the heating was reduced to less than 5 K.
Keywords: Reactor pressure vessels, Surveillance specimen, fluence calculation, neutron-activation monitors
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-053 2014


Publ.-Id: 20925 - Permalink

Tomographic imaging of gas holdup distribution in pressurized bubble columns
Bieberle, A.; Schubert, M.; Rollbusch, P.; Becker, M.; Schleicher, E.; Hampel, U.;
The averaged and radial gas holdup as well as gas phase dynamics and approximate bubble size distribution were studied in a high-pressure bubble column reactor of 4000 mm height and 330 mm diameter. Novel imaging measurement techniques, namely high-resolution gamma-ray computed tomography and wire-mesh sensor, were developed and adapted to the industrial reactor system. The gas phase was nitrogen. Deionized water and cumene were applied as liquid phases. The effect of the superficial gas velocity was studied over a range of 0 to 0.05 m/s at low liquid superficial velocities of 0.008 and 0.018 m/s for operating temperatures and pressures up to 75°C and 18.5 bar, respectively.
Keywords: Bubble column, gas holdup, flow structure, gamma tomography, wire-mesh sensor
  • Contribution to proceedings
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
    Book of Full-Length Manuscripts, 262-267
  • Poster
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
  • Lecture (Conference)
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland

Publ.-Id: 20924 - Permalink

INTRA r³+ Integration und Transfer der r³ Ergebnisse
Dürkoop, A.;
Das Poster präsentiert die Arbeiten im Begleitforschungsprojekt INTRA r³+ zur r³ Fördermaßnahme "Innovative Technologien für Ressourceneffizienz.
  • Poster
    Urban Mining Kongress und r³ Statusseminar 2014, 11.-12.06.2014, Essen, Deutschland

Publ.-Id: 20923 - Permalink

Simultaneous measurement of anisotropic magnetoresistance and observation of magnetic domains by Kerr microscopy
Osten, J.; Lenz, K.; Henschke, A.; Lindner, J.; Fassbender, J.ORC
We report a new instrument, which consists of a Kerr microscope combined with resistance measurements. This setup allows for recording magnetic domains while measuring the anisotropic magnetoresistance (AMR). For this purpose the development of a special sample holder and the extension of the measurement software was needed. The sample holder is equipped with electrical contacts in such a way to apply a current, measure the voltage, and use it in the Kerr microscope. The extension of the measurement software enables one to record resistance and Kerrimages at the same time. This Kerr microscopy combined with the simultaneous measurement of the AMR leads to a better understanding of the AMR behavior.
Keywords: anisotropic magnetoresistance, AMR, magnetic domains, Kerrmicroscope

Publ.-Id: 20922 - Permalink

Working with hierarchical databases in R to model geometallurgical data
Matos Camacho, S.; van den Boogaart, K. G.;
For the demands of geometallurgy a vast amount of data in multifaceted shape is needed. There are high resolution images from the MLA, data tables with information on the chemistry of some mineral phases, statistics on the distribution of the grain size, and so on. This data needs to be stored in a database, which reflects the often hierarchical structure of it and is flexible enough to be extended with almost any potential occurring information. We provide a MySQL template for such a database. Finding the desired data there can be a tough task, since queries might be highly complex and confusing. Therefore, we developed an easy accessible R interface for accessing this database.
Keywords: R, geometallurgy, MySQL
  • Lecture (Conference)
    16th Annual Conference of the International Association for Mathematical Geosciences, 17.-20.10.2014, New Delhi, India
  • Contribution to proceedings
    16th Annual Conference of the International Association for Mathematical Geosciences, 17.-20.10.2014, New Delhi, India
    Geostatistical and Geospatial Approaches for the Characterization of Natural Resources in the Environment: Challenges,Processes and Strategies Geostatistical, New Delhi: Capital Publishing Company, 978-93-81891-25-4, 341-343

Publ.-Id: 20921 - Permalink

Evidence for Deposition of Interstellar Material on the Lunar Surface
Fimiani, L.; Cook, D. L.; Faestermann, T.; Gómez Guzmán, J. M.; Hain, K.; Herzog, G. F.; Knie, K.; Korschinek, G.; Ligon, B.; Ludwig, P.; Park, J.; Reedy, R. C.; Rugel, G.;
Astronomical observations indicate that one or more supernovae (SN) ocurred in the vicinity of our solar system in the recent past (~10Myr) [1,2]. One possible indication of the arrival of SN (or perhaps AGB) debris locally was the detection of 60Fe/Fe (T1/2 = 2.62 Myr [3]) excesses in a ferroman-ganese crust from the Pacific Ocean [4,5]. Another indication came from the Moon. In a previous study [6] we reported a 60Fe/Fe depth profile constructed with 2 samples of the Apollo 12 core 12025, 4 samples of the Apollo 15 core 15008, 2 samples known as ‘skim’, ‘scoop’ and ‘under boulder’ soil collected near the shade of a small boulder in Station 9 during the Apollo 16 mission (shaded samples), and 5 samples of the deep drill core 60007/6, sampled during the same mission. We complete the previous work by reporting new measurements of 53Mn (T1/2 = 3.7 Myr [7]) in the same samples, including deeper samples of the 12025 core, and by using those measurements for a critical assessment of the 60Fe results. We also determined the activities of 60Fe and 53Mn of 7 samples from 4 iron meteorites; these activities were used to establish reference levels for local production due to galactic cosmic rays.
Keywords: supernova, Fe-60, Mn-53
  • Poster
    45th Lunar and Planetary Science Conference, 17.-21.03.2014, Houston, USA

Publ.-Id: 20920 - Permalink

Development of a micro reactor for the isobutane oxidation as a multiphase process
Willms, T.; Kryk, H.; Wiezorek, M.; Hampel, U.;
The partial oxidation of liquid isobutane to tertiary butyl hydroperoxide (TBHP) is currently conducted on an industrial scale with bubble columns at a selectivity of 60% and a maximum conversion of 25%. In this process, liquid isobutane is converted with oxygen at high temperatures (130 to 140°C) and pressures (25 to 37 Bar) at high residence times of 10 to 12 hours. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“ a micro reactor has been built and used to investigate this reaction for the first time as a continuous two-phase process in a broad range of flow rates, temperatures (120 to 150°C) and pressures (25 to 100 bar). For the improvement of the selectivity of the industrial process the influence of the residence time, hydrodynamics, initiator, additives and pressure on the reaction is studied. To realize a large range of residence times, flow rates in the range of 15 µl/min to 188 µl/min for isobutane and in the range of 0.1 up to 1.5 ml/min for oxygen were realized, using different capillary lengths which lie between 20 and 100 m. To charac¬terize the isobutane flow, preliminary measurements of the system isobutane – nitrogen were performed in a glass capillary. As the target product and initiator TBHP is sensitive to most metals, the micro reactor and further parts of the lab facility have been coated. To assure reasonable results of the hydrodynamic and kinetic studies, it was also important to realize a flow without pulsation by large pressure fluctuations. Therefore, the pressure is controlled by a gas pressure valve after a gas-liquid separation. The oxidation is followed by taking samples and analysis of the liquid reaction mixture by means of a GC-MS-System. In the frame of the presentation the challenges of the reactor construction and their solutions are discussed.
Keywords: Micro reactor, process intensification, isobutane oxidation
  • Lecture (Conference)
    4th European Conference on Microfluidics, 10.-12.12.2014, Limerick, Ireland

Publ.-Id: 20919 - Permalink

Towards Laser Driven Particle Therapy: from in vitro studies to human tumor irradiation on mice
Beyreuther, E.; Baumann, M.; Brüchner, K.; Hartmann, J.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Oppelt, M.; Reuter, M.; Richter, C.; Sävert, A.; Schürer, M.; Schnell, M.; Woithe, J.; Pawelke, J.;
The novel technology of particle acceleration by high intensity lasers promises more compact and cost effective ion sources as well as electron beams of very high energy for radiotherapeutic application. However, compared to conventional beams, laser-driven acceleration results in different beam properties like ultra-short and very intensive pulses, inherent pulse-to-pulse fluctuations, low pulse repetition rate, large beam divergence and broad energy distribution. In consequence, the future medical application of these particle beams requires not only a high power laser system but also new technical solutions for dose delivery and quality assurance as well as comprehensive research on the radiobiological consequences of ultra-short radiation pulses with high pulse dose.
During the last years the laser-driven technology was developed at such a rate that cell samples and small animals can be irradiated. Within the joint research project “onCOOPtics” extensive in vitro dose response studies were already performed comparing the radiobiological effects of laser driven electron and proton beams to their conventional equivalents. As overall result, the obtained dose-effect relationships for human tumor and human normal tissue cells reveal no difference between conventional and laser-driven beams. In a second translational step, in vivo experiments were recently established at the laser system JETI. Although the experiments were motivated by future proton trials, first attempts were performed with laser accelerated electrons, since the homogeneous delivery of prescribed doses to a 3D target volume is easier for electrons than for protons. Tumor irradiation was realized for the murine sarcoma KHT and the human squamous cell carcinoma FaDu grown on nude mice ear. Doses of up to 14 Gy were applied and the radiation induced tumor growth delay was investigated and later on compared to those obtained after similar treatment at a conventional electron Linac. Moreover, the successful performance of such an experiment campaign over a period of several weeks underlines the stability and reproducibility of all implemented methods and setup components. Further experiments with laser accelerated protons are in progress.
The work was supported by the German Federal Ministry of Education and Research
(BMBF), grant nos. 03ZIK445 and 03Z1N511.
  • Lecture (Conference)
    41st Annual Meeting of the European Radiation Research Society, 14.-19.09.2014, Kallithea/Rhodos, Greece
  • Poster
    Space Radiation and Heavy Ions in Therapy Symposium 2015, incl. 15th Workshop on Ion Beams in Biology and Medicine (IBIBAM), 22.-24.05.2015, Osaka, Japan

Publ.-Id: 20918 - Permalink

Ultrafast Terahertz-induced Magnetization Dynamics Studied on a Nanometer Length Scale by Coherent XUV Free-electron Laser Radiation.
Berntsen, M. H.; Müller, L.; Schleitzer, S.; Steinke, I.; Lehmkühler, F.; Schroer, M. A.; Ricci, A.; Al-Shemmary, A.; Stojanovic, N.; Golz, T.; Fischer, B.; Bagschik, K.; Bach, J.; Beyersdorff, B.; Winkler, G.; Frömter, R.; Gensch, M.; Oepen, H. P.; Gutt, C.; Grübel, G.;
Free-electron lasers (FELs), with their high photon flux, short pulse lengths, and coherent radiation, are ideal tools for studying complex materials, simultaneously on sub-picosecond time and on nanometer length scales. In particular, by exploiting the magneto-dichroic transitions at the L or M edges of Fe, Co, Ni or Gd, temporal and spatial studies of magnetic systems can be performed.
Infrared-pump–XUV-probe experiments performed at a FEL have revealed that the optically induced demagnetization in magnetic maze-domain structured Co/Pt samples is also accompanied by a spatial response. In this, and other studies using optical (IR) pumping, the magnetization is manipulated by heating of the spin system, i.e. through ultrafast electronic excitations.
Using terahertz (THz) radiation for pumping gives a unique possibility to investigate the influence of ultra-short pulses of strong magnetic fields on the magnetization dynamics since the THz photons do not generate direct electronic heating and because the THz phase can couple directly to the magnetic moments. Hence, the use of THz radiation could bring one a step closer to being able to control magnetism on ultrafast time scales.
  • Poster
    Science at FEL´s, 15.-17.09.2014, Villigen, Schweiz

Publ.-Id: 20917 - Permalink

Geometallurgy of REE deposits - state of the art
Renno, A. D.; Gutzmer, J.; Birtel, S.; Atanasova, P.; Bachmann, K.; Matos Camacho, S.; Schulz, B.; Kern, M.; Krause, J.; Munnik, F.;
Review of the most recent activities of the Helmholtz-Institute Freiberg for Resource Technology in the field of geometallurgy of REE deposits
Keywords: geometallurgy, REE
  • Invited lecture (Conferences)
    Geology to Metallurgy of Critical Rare Earths, 24.-25.03.2014, Penryn, UK

Publ.-Id: 20916 - Permalink

Terahertz Radiation driven Dynamics of Magnetic Domain Structures probed by coherent Free-Electron Laser Light
Müller, L.; Gutt, C.; Gruebel, G.; Golz, T.; Stojanovic, N.; Gensch, M.;
The new free-electron laser (FEL) sources provide radiation with unprecedented parameters in terms of ultrashort pulse length, high photon flux, and coherence. These properties make FELs ideal tools for studying ultrafast dynamics in matter on a previously inaccessible level.
Tuning the FEL photon energy resonantly to the magneto-dichroic transition of cobalt at 59.6 eV (equivalent to a wavelength of 20.8 nm) yields magnetic scattering contrast from a thin cobalt/platinum multilayer sample via the X-ray magnetic dichroism effect. Due to their magnetic anisotropy, these samples show domains magnetized in the out-of-plane direction with a typical domain width of 80 nm. For our transmission small-angle X-ray scattering (SAXS) geometry the magnetic scattering signal, therefore, originates from circular dichroism only.
After magnetic scattering of resonantly tuned XUV radiation from magnetic domains systems was proven feasible at FELs, ultrafast demagnetization, discovered initially by Beaurepaire in 1996, was for the first time measured in a mesoscopic magnetic domain systems at FLASH in Hamburg in an IR pump – FEL probe type of experiment. An ultrafast spatial response was found to accompany the demagnetization process.
In a later experimental approach, magnetic domain systems were pumped using THz radiation and probed by SAXS using XUV radiation from the FEL source. The 10-cycle THz pulse is produced by an additional electromagnetic undulator available at FLASH and therefore allows for measurements with minimal time jitter. In our experimental configuration, the THz magnetic field in the sample plane was ~ 20 mT. For samples in their close-to-equilibrium maze-domain configuration no change in form or strength of the scattering pattern was observed. However, when putting the sample in a static magnetic field of a few 10 mT, the magnetic domains are partially aligned along the magnetic field resulting in an anisotropic scattering pattern. We find that, in dependence of the pump-probe delay time, this anisotropy changes on time scales of a few picoseconds (Fig. 2). This experiment shows that THz radiation can affect magnetic domain systems directly which can be of great interest for future FEL experiments concentrating on THz control of magnetism.
  • Poster
    Intermag 2014, 04.-08.05.2014, Dresden, Germany

Publ.-Id: 20915 - Permalink

High-Speed PIXE – a new tool for Automated Mineralogy using a Color X-Ray Camera
Renno, A. D.; Buchriegler, J.; Dressler, S.; Hanf, D.; Merchel, S.; Munnik, F.; Nowak, S.; Scharf, O.; Ziegenrücker, R.;
Methods of automated mineralogy form the analytical backbone of geometallurgy. Most of them exploit the combined imaging and analytical capabilities of optical and scanning electron microscopes. Typical results are „phase maps“ either derived from the distribution of major elements or determined directly. The effective application of such methods for strategic metals which are won as by-products from other metal ores or secondary raw materials is handicapped by the restricted possibilities to determine the spatial distribution of such trace elements like In, Ga, Ge or the rare earth elements (REE). The recently commissioned High-Speed PIXE (Particle Induced X-Ray Emission) setup at the Helmholtz-Institute Freiberg for Resource Technologies will overcome these limitations by using the advantages of PIXE over traditional electron beam based methods like the better peak-background ratio. We use the SLcam® Colour X-ray Camera - a novel pnCCD pixel detector (264×264=69696 pixel) combined with a polycapillary X-ray optics (Scharf et al., 2011) as detector for element specific X-ray radiation. This design allows us the simultaneous determination of trace element distributions on a 12 × 12 mm2 area with a lateral resolution better than 100 μm. First results of geometallurgical applications of this method are presented.
Keywords: PIXE, High-Speed PIXE
  • Lecture (Conference)
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft (DMG) 2014, 21.-24.09.2014, Jena, Deutschland

Publ.-Id: 20914 - Permalink

High field THz sources operating at 100 kHz Repetition rates: Challenges and Opportunities
Gensch, M.;
Picosecond long transients of electric and magnetic fields in combination with repetition rates in the few 100 kHz to even MHz regime is crucial to understand several recently observed fascinating nonequilibrium phenomena driven by THz excitations. A new class of compact accelerator based THz sources based on super-radiant amplification of radiation from ultra-short electron bunches allows to generate high field THz pulses at unprecedented repetition rates. First measurements at a prototype facility proof the feasibility of the approach and demonstrate already parameters which exceeds laser-based sources by more than 2 orders of magnitude. Results from first pilot experiments aiming at investigating THz driven magnetization dynamics in MnGa, NiO and YIG are discussed and an outlook into the opportunities for High-field THz science at the future TELBE user facility is given.
  • Invited lecture (Conferences)
    Seminar of the Stanford Institute for Materials and Energy Sciences, 12.09.2014, Stanford / SLAC, USA

Publ.-Id: 20913 - Permalink

High-Speed PIXE: Automated Mineralogy using a Color X-Ray Camera
Renno, A. D.; Buchriegler, J.; Hanf, D.; Munnik, F.; Nowak, S.; Scharf, O.; Ziegenrücker, R.;
Methods of automated mineralogy form the analytical backbone of geometallurgy. Most of them exploit the combined imaging and analytical capabilities of optical and scanning electron microscopes. Typical results are „phase maps“ either derived from the distribution of major elements or determined directly. The effective application of such methods for strategic metals which are won as by-products from other metal ores is handicapped by the restricted possibilities to determine the spatial distribution of such trace elements like In, Ga, Ge or the rare earth elements (REE). The recently comissioned High-Speed PIXE (Particle Induced X-Ray Emission) setup at the Helmholtz-Institute Freiberg for Resource Technologies will overcome these limitations.
We use the SLcam® X-ray Color Camera - a novel pnCCD Pixel detector (264 x 264 = 69696 Pixel) combined with a polycapillary X-ray optic (Scharf et al., 2011) as the detector for the element specific X-ray radiation. This design allows us the simultaneous determination of the trace element distribution on a 12 * 12 mm2 area with a lateral
resolution of about 50 μm. First results of geometallurgical applications of this method are presented.
Keywords: PIXE, High-Speed PIXE
  • Lecture (Conference)
    21st General Meeting of the International Mineralogical Association, 01.-05.09.2014, Sandton, South Africa

Publ.-Id: 20912 - Permalink

Electron Microprobe Analysis of REE in Eudialyte Group Minerals: Challenges and Solutions
Atanasova, P.; Krause, J.; Möckel, R.; Osbahr, I.; Gutzmer, J.;
Alkaline complexes containing eudialyte group minerals (EGM) comprise one of the most promising sources for future rare earth element (REE) supply. Complex mineral chemistry and crystal structure of EGM pose particular challenges for resource analytics and ore characterisation. A combination of qualitative scanning electron microscope (SEM)-based image analysis and quantitative analytical methods like electron microprobe (EPMA) is required. For this purpose polished thick sections are first mapped by the mineral liberation analyzer (MLA) to effectively identify the ore-bearing minerals and mineral associations. Backscattered electron images (BSE images) indicate varying BSE contrast within the EGM crystals. In order to determine the assumed elemental variations, element distribution maps of main (e.g., Zr, Si, Al) and minor (e.g., Ce, Y) elements are obtained by EPMA. These maps illustrate variable and complex zonation patterns within the EGM crystals. Based on the element distribution maps, quantitative analyses are then performed with a field emission electron microprobe JEOL JXA 8530F.
The accurate quantification of the chemical composition of EGM is complicated by both mineralogical and X-ray-specific challenges. These include: 1) structural and chemical variability of EGM composition (e.g., [1-3]); 2) mutual interferences of X-ray lines from major and trace elements, in particular REE elements [4]; 3) the diffusive volatility of light anions as F and Cl and cations such as K and Na; 4) particular instability of EGM under the electron beam.
A novel analytical approach has been developed to account for the above mentioned analytical challenges. Additionally, loss on ignition und differential scanning calorimetry data has been applied to constrain the content and composition of volatiles in the EGM structure. All correction for the overlapping of X-ray lines is processed offline. Preliminary results demonstrate that the parameters mentioned above need to be considered and carefully optimized to perform accurate quantitative analyses on the chemical composition of EGM with the electron microprobe.
Keywords: Electron Mikroprobe, EPMA, rare earth elements, eudialyte
  • Poster
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today - Practical Aspects, 22.-24.09.2014, Leoben, Austria

Publ.-Id: 20910 - Permalink

Regression with compositional response having unobserved components or below detection limit values
van den Boogaart, K. G.; Tolosana-Delgado, R.; Templ, M.;
The typical way to deal with zeros and missing values in compositional data sets is to impute them with a reasonable value, and then the desired statistical model is estimated with the imputed data set, e.g., a regression model. This contribution aims at presenting alternative approaches to this problem within the framework of Bayesian regression with a compositional response. In the first step, a compositional data set with missing data is considered to follow a normal distribution on the simplex, which mean value is given as an Aitchison affine linear combination of some fully observed explanatory variables. Both the coefficients of this linear combination and the missing values can be estimated with standard Gibbs sampling techniques. In the second step, a normally distributed additive error is considered superimposed on the compositional response, and values are taken as ‘below the detection limit’ (BDL) if they are ‘too small’ in comparison with the additive standard deviation of each variable. Within this framework, the regression parameters and all missing values (including BDL) can be estimated with a Metropolis-Hastings algorithm. Both methods estimate the regression coefficients without need of any preliminary imputation step, and adequately propagate the uncertainty derived from the fact that the missing values and BDL are not actually observed, something imputation methods cannot achieve.
Keywords: Bayesian regression; compositional regression; missing values; nondetects; MCMC

Publ.-Id: 20909 - Permalink

Commissioning Results of the 2nd 3.5 cell SRF Gun for ELBE
Arnold, A.; Freitag, M.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.; Ciovati, G.; Turlington, L.;
As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation, it turned out that the specified performance has not been achieved. However, to demonstrate the full potential of this new type of electron source, a second and slightly modified SRF gun II was built in collaboration with Thomas Jefferson National Accelerator Facility (TJNAF). We will report on commissioning and first results of the new gun, which includes in particular the characterization of the most important RF properties as well as their comparison with previous vertical test results.
Keywords: superconducting, radio frequency, electron, injector, SRF gun
  • Open Access LogoContribution to proceedings
    27th Linear Accelerator Conference, LINAC14, 31.08.-05.09.2014, Genf, Schweiz
  • Poster
    27th Linear Accelerator Conference, LINAC14, 31.08.-05.09.2014, Genf, Schweitz

Publ.-Id: 20908 - Permalink

Uranium(VI) Binding Forms in Selected Human Body Fluids: Thermodynamic Calculations versus Spectroscopic Measurements
Osman, A. A. A.; Geipel, G.; Barkleit, A.; Bernhard, G.;
Human exposure to uranium increasingly becomes a subject of interest in many scientific disciplines such as environmental medicine, toxicology, and radiation protection. Knowledge about uranium chemical binding forms (speciation) in natural body fluids can be of great importance not only to understand its biokinetics, but also relevant for risk assessment and for designing decorporation therapy in the case of accidental overexposure. In this study, thermodynamic calculations of uranium speciation in relevant simulated and original body fluids were compared with spectroscopic data after ex-situ uranium addition. For the first time, experimental data on U(VI) speciation in natural body fluids (saliva, sweat, urine) was obtained by means of cryogenic time-resolved laser-induced fluorescence spectroscopy (cryo-TRLFS) at 153 K. By using the time dependency of fluorescence decay and the band positions of the emission spectra, various uranyl complexes were demonstrated in the studied samples. The variations of the body fluids in terms of chemical composition, pH, and ionic strength resulted in different binding forms of U(VI). The speciation of U(VI) in saliva and in urine was affected by the presence of bioorganic ligands, whereas in sweat, the distribution depends mainly on inorganic ligands. We also elucidated the role of biological buffers, i.e., phosphate (H2PO4-/HPO42-) on U(VI) distribution, and the system Ca2+/UO22+/PO43- was discussed in detail in both saliva and urine. The theoretical speciation calculations of the main U(VI) species in the investigated body fluids were significantly consistent with the spectroscopic data. Laser fluorescence spectroscopy showed success and reliability for direct determination of U(VI) in such biological matrices with the possibility for further improvement.
Keywords: uranium, speciation, saliva, sweat, urine

Publ.-Id: 20907 - Permalink

Simulation Studies for Prompt Gamma Imaging and Prompt Gamma Timing
Rohling, H.; Golnik, C.; Müller, A.; Pausch, G.; Schöne, S.; Kormoll, T.; Enghardt, W.; Fiedler, F.;
kein Abstract verfügbar.
  • Poster
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.09.2014, Dresden, Deutschland
  • Poster
    Workshop: "Precision, Speed und Flexibility: New radiation detection methods for ion beam radiotherapy", 23.-25.09.2014, Heidelberg, Deutschland

Publ.-Id: 20906 - Permalink

Migrating ignimbrite flare-ups in the Central Andes - Implications for crustal evolution based on chemical, geochronological and GIS-based volumetric data
Brandmeier, M.; Wörner, G.;
Temporal and compositional patterns of Neogene ignimbrite magmatism in the Central Andes were analyzed using GIS and geostatistical modeling. We compiled a comprehensive ignimbrite data base and digitized 203 individual ignimbrite sheets, for which geochemical, isotopic (partly), and geochronological data are available from the literature and own data. Composition, timing, volumes and sources of erupted ignimbrite deposits are constrained and magma volumes through space and time are calculated for five segments of the Central Andes.
The total erupted ignimbrite magma volume of 31,000 km3 for the past 30 Ma is distributed as follows: 2,400 km3 for Southern Peru, 2,700 km3 for Southernmost Peru, 8,400 km3 for the Altiplano, 14,200 km3 for the Northern Puna and 3,100 km3 for the Southern Puna segments. Average magmatic addition per Ma and km arc for ignimbrites range between 20 to 30 km3. This is similar to the basaltic “base”-flux for arc magmatism and suggests that ignimbrite flare-ups do not represent orders of magnitude increased magma production rates but are rather punctuated, short-lived well events separated in space and time. There is a clear N-S “younging” of eruption ages and ignimbrite pulses. Major pulses occurred at 19-24 Ma (e.g. Oxaya, Nazca Group), 13-14 Ma (e.g. Huaylillas ignimbrites), 6-10 Ma (Altiplano and Puna ignimbrites, e.g. Vilama ignimbrite) and 3-6 Ma (e.g. Atana, Los Frailes, Toconao). Small and younger ignimbrites (0-3 Ma, e.g. Lauca-Perez, Purico) do not follow this pattern. We propose that large-volume ignimbrite eruptions occurred in the wake of subduction of the Juan-Fernandez ridge on the Nazca Plate that passed below the Central Andes from N to S during the past 25 Ma. Low angle subduction caused compression and fluid release is followed by massive inflow and melting of asthenospheric mantle when the slab steepened again after the passing of the ridge. This in turn caused massive melting within the crust aided by advective heat transport. Differences in chemcial and isotopic composition of the large-volume ignimbrites are related to changes in crustal thickness, and different “preconditioning” during the Anden orogeny. Isotope data and whole rock compositional data suggest a higher degree of crustal assimilation for the younger Altiplano ignimbrites in the S compared to the older (22-19 Ma) ignimbrites in the North. REE compositions for large-volume ignimbrites reflect changes in crustal thickness with a "transition" at ca. 13-9 Ma that can be related to accelerated crustal shortening at that time (Oncken et al., 2006).
Total volumes for the northern segments and the Northern Puna are similar. However, calderas and intra-caldera ignimbrite volumes in the north are less well constrained due to the lower level of study, higher ages and higher degrees of incision and erosion. In any case, there is no “single” ignimbrite flare up in the Central Andes with one regionally and temporally restricted event of high-magma flux and bath-olith construction (de Silva and Gosnold, 2007). Instead, we suggest a more dynamic scenario, with “flare ups” moving from N to S across the Central Andes during the past 25 Ma. Our database aids to better constrain numerical models of Andean geodynamic processes.
deSilva, S., Gosnold, W.D. (2007) Episodic construction of batholiths: Insights from the spatiotemporal development of an ignimbrite flare-up. J. Volcanol. Geotherm. Res. 167: 320-335
Oncken, O. et al. (2006), Deformation of the Central Andean Upper Plate System-Facts, Fiction, and Constraints for Plateau Models, in Oncken, O. et. al., eds., The Andes: Frontiers in Earth Sciences, Springer Berlin Heidelberg: 3-27.
  • Contribution to proceedings
    GeoFrankfurt 2014, 21.-24.09.2014, Frankfurt, Germany

Publ.-Id: 20905 - Permalink

Assessments of boundary conditions and requirements for Rare Earth Underground Mining due to presence of NORMs
Barakos, G.; Mischo, H.; Gutzmer, J.;
Rare earths contain NORMs, such as uranium, thorium and their progeny, like radium and radon. The varying concentrations of NORMs are quite often significant enough to result in occupational and environmental radiation exposures during the mining, milling and processing procedures of rare earths and compounds. Ventilation is the primary technique of controlling ambient concentrations of radon. Fresh air volume flow rates, the distribution of airflow within the mine and the radon emanation rate are primary factors affecting such concentrations. In this paper, it is attempted to determine the factors that may result in radiation risks and evaluate the boundary conditions that will contribute to the restriction or even elimination of radon progeny, with a goal to use the evaluations in order to build an overall assessment tool.
Keywords: Rare Earth Elements, NORMs, Radon, Thoron, Underground Mining, Occupational Safety
  • Open Access LogoContribution to proceedings
    ERES 2014 - 1st International Conference on European Rare Earth Resources, 04.-07.09.2014, Milos Island, Greece
    ERES 2014 - 1st International Conference on European Rare Earth Resources, Imerovigli, Santorini GR‐84700: Heliotopos Conferences Ltd., 978‐960‐6746‐15‐4

Publ.-Id: 20904 - Permalink

Simulation of aerosol particle deposition and resuspension in high temperature reactors
Lecrivain, G.; Hampel, U.;
In a high temperature pebble-bed reactor core where thousands of pebbles are amassed, the friction between the outer graphite layer of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the cooling carrier phase in the primary circuit of the high temperature reactor. Depending on the gas velocity, the solid aerosol particles can either attach to the wall surfaces or be re-entrained in the turbulent flow. Two numerical models developed for the prediction of particle attachment and detachment are presented.
  • Invited lecture (Conferences)
    Seminar / Commissariat à l’énergie atomique / Invited lecture, 20.06.2014, Saclay, France

Publ.-Id: 20903 - Permalink

Simulation of aerosol particle deposition in a high temperature reactor
Lecrivain, G.; Hampel, U.; Hurtado, A.;
In a high temperature pebble-bed reactor core where thousands of pebbles are amassed, the friction between the outer graphite layer of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the cooling carrier phase in the primary circuit of the high temperature reactor. Depending on the gas velocity, the solid aerosol particles can either attach to the wall surfaces or be re-entrained in the turbulent flow. Two numerical models developed for the prediction of particle attachment and detachment are presented.
  • Contribution to proceedings
    Workshop des CFD-Kompetenzverbunds / German CFD Network, 19.-20.03.2014, Garching, Germany
    Proceedings of the German CFD Network

Publ.-Id: 20902 - Permalink

Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - physicochemical effects
Kryk, H.; Hoffmann, W.; Kästner, W.; Alt, S.; Seeliger, A.; Renger, S.;
Within the framework of the reactor safety research, generic experimental investigations were carried out aiming at the physicochemical background of possible zinc corrosion product formation, which may occur inside the reactor pressure vessel during the sump circulation operation after loss-of-coolant accidents in pressurized water reactors. The contact of the boric acid containing coolant with hot-dip galvanized steel containment internals causes corrosion of the corresponding materials resulting in dissolution of the zinc coat. A retrograde solubility of zinc corrosion products with increasing temperature was observed during batch experiments of zinc corrosion in boric acid containing coolants. Thus, the formation and deposition of solid corrosion products cannot be ruled out if the coolant containing dissolved zinc is heated up during its recirculation into hot regions within the emergency cooling circuit (e.g. hot-spots in the core). Corrosion experiments at a lab-scale test facility, which included formation of corrosion products at a single heated cladding tube, proved that dissolved zinc, formed at low temperatures in boric acid solution by zinc corrosion, turns into solid deposits of zinc borates when contacting heated zircaloy surfaces during the heating of the coolant. Moreover, the temperature of formation influences the chemical composition of the zinc borates and thus the deposition and mobilization behavior of the products.
Keywords: pressurized water reactor, loss-of-coolant accident, corrosion, zinc, boric acid, in-vessel effects

Publ.-Id: 20901 - Permalink

Surface and Material Analytics based on Dresden-EBIS Platform Technology
Schmidt, M.; König, J.; Bischoff, L.; Pilz, W.; Zschornack, G.;
Nowadays widely used mass spectrometry systems utilize energetic ions hitting a sample and sputter material from the surface of a specimen. The generated secondary ions are separated and detected with high mass resolution to determine the target materials constitution. Based on this principle, we present an alternative approach implementing a compact Electron Beam Ion Source (EBIS) in combination with a Liquid Metal Ion Source (LMIS).
An LMIS can deliver heavy elements which generate high sputter yields on a target surface. More than 90% of this sputtered material consists of mono- and polyatomic neutrals. These particles are able to penetrate the magnetic field of an EBIS and they will be ionized within the electron beam.
A broad spectrum of singly up to highly charged ions can be extracted depending on the operation conditions. Polyatomic ions will decay during the charge-up process. A standard bending magnet or a Wien filter is used to separate the different ion species due to their mass-to-charge ratio. Using different charge states of ions as it is common with EBIS it is also possible to resolve interferring charge-to-mass ratios of only singly charged ions.
Different setups for the realization of feeding the electron beam with sputtered atoms of solids will be presented and discussed. As an example the analysis of a copper surface is used to show high-resolution spectra with low background noise. Individual copper isotopes and clusters with different isotope compositions can be resolved at equal atomic numbers.
These results are a first step for the development of a new compact low-cost and high-resolution mass spectrometry system. In a more general context, the described technique demonstrates an efficient method for feeding an EBIS with atoms of nearly all solid elements from various solid target materials. The new straightforward design of the presented setup should be of high interest for a broad range of applications in materials research as well as for applications connected to analyzing the biosphere, hydrosphere, lithosphere, cosmosphere and technosphere.
Keywords: Electron Beam Ion Source, LMIS, Sputter yield, Mass Spectra
  • Lecture (Conference)
    International Symposium Electron Beam Ion Sources and Traps, EBIST 2014, 18.-21.05.2014, East Lansing, Michigan, USA
  • Contribution to proceedings
    12th International Symposium on Electron Beam Ion Sources and Traps (EBIST'14), 18.-21.05.2014, East Lansing, Michigan, USA
    AIP Conference Proceedings 88(2015), 1640: AIP, 88-93
    DOI: 10.1063/1.4905403

Publ.-Id: 20900 - Permalink

Development and characterization of new liquid metal ion sources
Bischoff, L.; Pilz, W.; Tajmar, M.;
In the last decades liquid metal ion sources (LMIS) working in focused ion beam (FIB) systems became an irrecoverable instrument in research and industry [1]. Sample preparation, local ion implantation and ion analysis are the main application topics. Most of the systems are equipped with a gallium LMIS. But, modern trends in nanotechnology require more extended properties like variable ion species for local doping, non-contaminating milling at higher rates or the application of focused cluster beams for surface modifications [2]. LMIS are also used for space propulsion as precision thrusters to provide ultrastable attitude and orbit control for satellites called Field-Emission- Electric-Propulsion [3].
In this contribution the basics of LMIS operation, the measurement of the main parameters and so the characterization of this type of ion sources will be presented. Moreover, the application of new source concepts including prototypes will be shown. At present about half of the periodic table can be provided as single or double charged ions as well as heavy cluster ions up to five atoms per ion by alloy LMIS. This provokes the interest to apply such sources not only in focused ion beam systems but also in high energy single-end ion accelerators. A first concept for an injector module to adapt a high current LMIS with integrated mass separation to a high energy ion beam system will be presented and discussed.

The authors would like to thank BMBF for financial support under Projekt 05K130DC: "Verbundprojekt 05K2013 – Ioneninduzierte Materialanalyse/-modifizierung: Modifizierung und in-situ Analyse von Materialien durch mittelenergetische Ionenbestrahlung. TP 1: Ultraschwere Ionen und deren Nutzung an HZDR-Beschleunigern."

[1] L. Bischoff, R. Böttger, P. Philipp and B. Schmidt, Nanostructures by mass-separated FIB, Book chapter in “FIB Nanostructures” in “Lecture Notes in Nanoscale Science and Technology” ed. Z. Wang, Peking, Berlin: Springer, 2013, Vol. 20, 465.
[2] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz, Nucl. Instr. and Meth. B 2012, 272 198.
[3] M. Tajmar, I. Vasiljevich and W. Grienauer, Ultramicroscopy 2010, 111, 1.
Keywords: Liquid metal ion source, cluster, single-end ion accelerators
  • Lecture (Conference)
    Workshop Ionenstrahlen & Nanostrukturen, 20.-22.07.2014, Paderborn, Deutschland

Publ.-Id: 20899 - Permalink

A new algorithm for segmentation of ultrafast X-ray tomographed gas-liquid flows
Banowski, M.; Lucas, D.; Szalinski, L.;
The ultrafast electron beam X-ray computed tomography was developed during the last years to obtain detailed data on two-phase flows. In a recent study we investigated different gas-liquid flow regimes in a vertical pipe at the Transient Two-phase Flow test facility (TOPFLOW). The study includes experiments on gas-liquid flows with varied superficial velocities for both phases and different flow directions. The obtained data is required for understanding fundamental physics of two-phase flow phenomena and for the development and validation of CFD- codes.
To extract quantitative data from the reconstructed three-dimensional data array, a new segmentation algorithm was developed, due the results of existing segmentation algorithms aren’t satisfyingly. The originality of this new algorithm bases on a stepwise creation of new bubbles using pixel agglomeration in shrinking steps without defining markers or starting points. The results were compared with threshold and gradient methods using two different bubble phantoms and real two-phase flow measurements. The new algorithm shows the best qualitative and quantitative results.
Keywords: X-ray; computed tomography; gas-liquid flow; bubbles; segmentation

Publ.-Id: 20898 - Permalink

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