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Ultrasensitive determination of long-lived radionuclides by accelerator mass spectrometry for applications from the Earth Sciences and cosmochemistry
Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Renno, A. D.; Rugel, G.; Several Dreams-Users
Concentrations of long-lived radionuclides in man-made material e.g. from decommissioning nuclear installations or unintended release are generally high enough to be directly measured by conventional mass spectrometry, decay counting or radiochemical neutron activation analysis. However, often samples need to be radiochemically processed before measurements to enrich radionuclides, eliminate the matrix and disturbing isobars or nuclides of similar decay characteristics.
Though, if the same radionuclides are produced in terrestrial and extraterrestrial matter by cosmic-ray induced nuclear reactions, concentrations are only in very rare cases measurable by other analytical techniques than accelerator mass spectrometry (AMS) after radiochemical separation. Samples from geomorphology applications can contain radionuclides at the level of several ten thousand atoms per gram mineral e.g. quartz or calcite, thus, asking for processing of 100 g starting material.
Experimental - AMS
For accelerator mass spectrometry negative ions (molecules or elements) are extracted from samples containing long-lived radionuclides (t1/2 > 100 a) in a Cs-sputter ion source. By inserting these ions in a tandem accelerator, they gain MeV-energies. Then by passing through matter (gas or foil) at the positively charged terminal in the middle of the accelerator, the negative ions lose outer electrons and convert into multiple-positively charged ions being then further accelerated towards the exit. Effectively all molecules are destroyed by this stripping process.
Generally, AMS is measuring isotope ratios, i.e., stable isotopes are usually detected in Faraday-cups and radionuclides in ionization chambers. Such a set-up of two mass spectrometers in one, namely the first with negative ions of keV-energy, the second with high-energy positive ions of MeV-energy, and combined with several magnetic and electrostatic analyzers (Fig. 1), allows analyzing isotope ratios as low as 10-16, thus, providing the ultimate detection limit of all mass spectrometry methods.
Figure 1: AMS set-up at DREAMS [1-3].
If using isotopically-enriched carrier such as 35Cl, AMS can also be applied to simultaneously measure stable chlorine by isotope dilution, i.e. ID-AMS.
Very recently, a new AMS facility has been installed at the Ion Beam Centre of the Helmholtz-Zentrum Dresden-Rossendorf: DREsden AMS (DREAMS) [1-3], which is capable of measuring 10Be, 26Al, 36Cl, 41Ca, and 129I (t1/2 = 0.1-16 Ma) as low as 10-14-10-16 (radionuclide/stable nuclide).
In 2013, the DREAMS set-up will be extended for measurements of actinides, and in 2014 for stable elements. Expected detection limits for stable isotope ratios are not as good as for radionuclide AMS, but still some orders of magnitude better than for traditional dynamic secondary ion mass spectrometry (SIMS), i.e. 10-9-10-12.
DREAMS applications are wide-spread e.g. meteoritics, astrophysics, geomorphology, climate research, hydrogeology, resource technology and risk assessment of natural hazards like rock falls.
 S. Merchel et al., GIT Labor-Fachzeitschrift 56(2) (2012) 88-90.
 S. Akhmadaliev et al., Nucl. Instr. Meth. B (2012) in print, doi:10.1016/j.nimb.2012.01.053.
 http://www.dresden-ams.de (Nov. 2012).
Keywords: AMS; radionuclide; cosmogenic; cosmochemistry
24th Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 24), 26.-28.02.2013, Garching, Deutschland
Tuning of the nucleation field in nanowires with perpendicular magnetic anisotropy
Kimling, J.; Gerhardt, T.; Kobs, A.; Vogel, A.; Wintz, S.; Im, M.-Y.; Fischer, P.; Oepen, H. P.; Merkt, U.; Meier, G.
We report on domain nucleation and pinning of domain walls in Co/Pt multilayer nanowires with perpendicular magnetic anisotropy which are patterned using electron-beam lithography, sputter deposition, and lift-off processing. It is found that the nucleation field in these wires can be tuned by changing the geometry of the wire ends. A reduction of the nucleation field by up to 60 percent is achieved when the wire ends are designed as tips. This contrasts with the behavior of soft-magnetic wires for which the domain wall nucleation field increases when they are designed with triangular pointed ends. In order to clarify the origin of the reduced nucleation field observed for Co/Pt nanowires micromagnetic simulations are employed. As result the effect can be attributed to a local reduction of the perpendicular anisotropy caused by shadowing effects of the resist mask during sputter deposition of the multilayer. Related aspects concerning the creation of pinning sites for domain walls are addressed.
Keywords: Co/Pt multilayer; PMA wires; domain wall nucleation; x-ray microscopy
Journal of Applied Physics 113(2013), 163902
Time-resolved electronic capture in germanium doped with hydrogen-like impurity centers
Deßmann, N.; Pavlov, S. G.; Shastin, V. N.; Zhukavin, R. K.; Winnerl, S.; Mittendorff, M.; Hübers, H.-W.
The capture of free holes and electrons in germanium (Ge) doped by gallium (Ga) or antimony (Sb) has been studied by a time-resolved pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. For Ga acceptors the relaxation times decrease with increasing pump power from approximately 3 ns to 1 ns (2 ns and 1 ns for Sb donors, respectively). The results support the development of fast photoconductive detectors in the terahertz region of the spectrum.
Keywords: Time resolved spectroscopy; THz; shallow donors in Ge
Contribution to proceedings
37th International Conference on Infrared, Millimeter and Terahertz Waves, 23.-28.09.2012, Wollogon, Australia
Proceedings of the IEEE 37th International Conference on Infrared, Millimeter and Terahertz Waves, ID:2569425
37th International Conference on Infrared, Millimeter and Terahertz Waves, 23.-28.09.2012, Wollogon, Australia
Anomalous Superconductivity in Gallium Nano-Films embedded in Silicon Wafers
7th PhD Seminar HZDR, 08.-10.10.2012, Schöneck, Deutschland
Anomalous Superconductivity in amorphous 10 nm thin Ga films embedded in Si wafers
3rd EuroMagNET Summer School, Science in High Magnetic Fields, 30.09.-07.10.2012, Rügen, Deutschland
Magnetic and acoustic anomalies of UCu0.95Ge in high magnetic fields
Yasin, S.; Andreev, A. V.; Skourski, Y.; Zvyagin, A. A.; Zherlitsyn, S.; Wosnitza, J.
Magnetic and magneto-acoustic properties of the intermetallic compound UCu0.95Ge with antiferromagnetic ground state have been investigated on single crystals in pulsed magnetic fields up to 64 T. A first-order phase transition has been observed for fields applied along the a and c axis at 61 and 38 T, respectively. In both directions, the magnetization trends to saturate at 1.35 μB per formula unit. These field-induced transitions as well as the antiferromagnetic ordering at TN = 48 K are accompanied by pronounced anomalies in the sound velocity and sound attenuation. Additionally, the acoustic characteristics show some unusual frequency-dependent features which presumably can be related to the dynamics of Cu vacancies . The field-temperature phase diagrams are constructed for both magnetic-field directions. The experimental data are analyzed by use of the mean-field approximation and agree qualitatively with the obtained results.
Quantum Criticality & Novel Phases 2012 (QNCP12), 26.-29.08.2012, Dresden, Deutschland
Spin dynamics of the S = 5/2 2D triangular antiferromagnet Ba3NbFe3Si2O14
Choi, K. Y.; Wang, Z.; Ozarowski, A.; van Tol, J.; Zhou, H. D.; Wiebe, C. R.; Skourski, Y.; Dalal, N. S.
We report pulse-field magnetization, ac susceptibility, and 100 GHz electron spin resonance (ESR) measurements on the S = 5/2 two-dimensional triangular compound Ba3NbFe3Si2O14 with the N´eel temperature TN = 26 K . The magnetization curve shows an almost linear increase up to 60 T with no indication of a one-third magnetization plateau. An unusually large frequency dependence of the ac susceptibility in the temperature range of T = 20–100 K reveals a spin-glass behavior or superparamagnetism, signaling the presence of frustration-related slow magnetic fluctuations. The temperature dependence of the ESR linewidth exhibits two distinct critical regimes; (i) ΔHpp(T) α(T-TN)-p with the exponent p = 0.2(1)–0.2(3) for temperatures above 27 K, and (ii) ΔHpp(T) α(T- T)-p with T=12 K and p = 0.8.(1)–0.8(4) for temperatures between 12 and 27 K. This is interpreted as indicating a dimensional crossover of magnetic interactions and the persistence of short-range correlations with a helically ordered state.
Journal of Physics: Condensed Matter 24(2012), 246001
High-field research at the European XFEL
Cowan, T.; Schramm, U.; Herrmannsdörfer, T.; Weckert, E.; Strempfer, J.; von Zimmermann, M.; Stoehlker, T.
We present an initiative to build up a beamline at the European XFEL. This HELMHOLTZBEAMLINE will establish multi-purpose high-power and ultra-intense lasers as well as high-field magnets at the SASE2 end-station of the European XFEL. It will extend the scope of research that can be carried out at the European XFEL beyond the baseline instruments, especially in the areas of strong-field physics, high energy density science, relativistic laserplasma physics, ultra high-pressure astro- and planetary-physics, dynamic-materials research, and magnetic phenomena in condensed matter. At the European XFEL, an x-ray fluence in a single macropulse (600 microseconds, 2700 micropulses, each with 1E12 photons) will be available to, e.g., map out a full field profile for a magnetic absorption spectroscopy experiment, to probe the electronic or ionic structure in a single micropulse, or to investigate magnet-field driven phase transitions. The high photon fluence at the XFEL will allow for using pulsed-field magnets for a wide range of experimental techniques. The HELMHOLTZBEAMLINE will be used to drive matter to extremes of temperature, density, pressure, field strength, and/or particle irradiation, which can be probed with the XFEL beams; or alternatively to probe XFEL-driven samples with laser-generated particles or radiation. The HELMHOLTZ-BEAMLINE is being proposed for funding from the Helmholtz Association research area Matter, by partners HZDR, DESY and HI-Jena. Over 80 research groups from more than 60 institutions in 15 countries have joined this User Consortium as External Partners.
Workshop on Synchrotron and Neutron Applications of High Magnetic Fields, 17.-19.10.2012, Grenoble, France
On-chip superconductivity above 7 K in microstructured 10 nm thin Ga films embedded in Si wafers
Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Fiedler, J.; Schönemann, R.; Philipp, P.; Bischoff, L.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Helm, M.; Wosnitza, J.
Initiated by the finding of doping-induced ambient-pressure superconductivity in classic group-IV semiconductors, in particular our investigation on Ga-doped Germanium , we have succeeded in preparing an even more promising candidate for superconducting onchip application . Ion implantation has been utilized to introduce a high dose of Ga into silicon wafers capped by 30 nm SiO2. Ga segregation underneath the cover was stimulated by subsequent rapid thermal annealing in a narrow time and temperature window. Extended structural investigations by means of XTEM, EDX, RBS/C, and SIMS confirm a reproducible formation of 10 nm thin amorphous Ga-rich layers. In the normal state these layers reveal a sheet resistance with a negative temperature derivative and an absolute value close to the quantum resistance which is about 6 kOhm. The superconducting onset temperature accounts for up to 10 K while a zero-resistance state coincides with diamagnetic screening below 5 K verified by means of resistivity and dc magnetization measurements. Further, superconductivity remains stable up to remarkable high magnetic fields of more than 8 Tesla and exhibits a distinct critical-field anisotropy manifesting its thin-film character. Homogeneity and scale-independent behavior down to 3 micron have been proven by lateral microstructuring via photolithography rendering critical-current densities higher than 50 kA/cm2. Recently, focussed-ion beam technique has been implemented in order to create Josephson junctions - key elements of the prospective first ever built gallium SQUID.
Invited lecture (Conferences)
M2S 2012 - Materials and Mechanisms of Superconductivity, 29.07.-03.08.2012, Washington, USA
Semimetallic Paramagnetic Nano-Bi2Ir and Superconducting Ferromagnetic Nano-Bi3Ni by Microwave-Assisted Synthesis and Room Temperature Pseudomorphosis
Boldt, R.; Grigas, A.; Heise, M.; Herrmannsdörfer, T.; Isaeva, A.; Kaskel, S.; Köhler, D.; Ruck, M.; Skrotzki, R.; Wosnitza, J.
Uniform nanocrystals of the intermetallic compounds Bi2Ir (diameter ≥ 50 nm) and Bi3Ni (typical size 200x600 nm) were obtained by a microwave-assisted polyol process at 240 °C. The method was also applied to the spatially confined reaction environment in the microporous exo-template SBA-15 resulting in Bi3Ni particles of about 6 nm. Non-crystalline bundles of parallel Bi3Ni nanofibres that have an individual diameter of less than 1 nm were obtained by reductive pseudomorphosis of the subiodide Bi12Ni4I3 at room temperature. Magnetic susceptibility measurements demonstrate coexistence of ferromagnetism and superconductivity in a single phase for the nanostructured Bi3Ni materials. Curie temperature, coercive field, remnant magnetization, saturation moment, diamagnetic screening, and critical field vary with particle size. The crystal structure of Bi2Ir was determined by Rietveld refinement of powder X-ray diffraction data. Bi2Ir crystallizes in the monoclinic arsenopyrite type (space group P21/c), a superstructure of the markasite type, with a = 690.11(1), b = 678.85(1), c = 696.17(1) pm, and β = 116.454(1)°. In contrast to most of the other phases of this type, the Bi2Ir is not a diamagnetic semiconductor but a weakly paramagnetic semimetal. Conductivity measurements down to 4 K and magnetization measurements in a field of μ0H = 10 mT down to 1.8 K give no evidence for a transition into the superconducting state. Bonding analysis shows prevailing contribution of Bi–Bi interactions to the conduction, whereas Bi–Ir bonding is mostly covalent and localized.
Zeitschrift für Anorganische und Allgemeine Chemie 638(2012)12-13, 2035-2043
Nuclear magnetic resonance apparatus for pulsed high magnetic fields
Meier, B.; Kohlrautz, J.; Haase, J.; Braun, M.; Wolff-Fabris, F.; Kampert, E.; Herrmannsdörfer, T.; Wosnitza, J.
A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.
Review of Scientific Instruments 83(2012), 083113
Spin-lattice coupling in the frustrated antiferromagnet ZnCr2Se4 probed by ultrasound
Felea, V.; Yasin, S.; Günther, A.; Deisenhofer, J.; Krug Von Nidda, H.-A.; Zherlitsyn, S.; Tsurkan, V.; Lemmens, P.; Wosnitza, J.; Loidl, A.
Ultrasound and magnetization studies of the frustrated spinel ZnCr2Se4 are performed as a function of temperature and magnetic field up to 14 T. In zero field, the sound velocity and attenuation reveal significant anomalies at the antiferromagnetic transition at TN ≈ 21 K indicating strong spin-lattice coupling. External magnetic fields shift these anomalies to lower temperatures concomitantly with the reduction of the Neel temperature. At 2 K, the sound velocity as a function of magnetic field manifests three pronounced anomalies: a deep minimum at 5.4 T related to an inflection point of the magnetization followed by two plateaus with distinct stiffness at fields above 7 and 10 T. The first plateau is ascribed to a transformation from a tetragonal to a cubic phase, while the second one corresponds to a state with fully polarized magnetization. The evolution of magnetic and structural states is discussed within a H-T phase diagram and compared with related frustrated magnetic spinels with strong spin-lattice coupling.
Physical Review B 86(2012), 104420
Magnetic behaviour of interacting antiferromagnetic nanoparticles
Markovich, V.; Puzniak, R.; Skourski, Y.; Wisniewski, A.; Mogilyanski, D.; Jung, G.; Gorodetsky, G.
Magnetic properties of interacting La0.2Ca0.8MnO3 nanoparticles have been investigated. The field-induced transition from antiferromagnetic (AFM) to ferromagnetic (FM) state in the La0.2Ca0.8MnO3 bulk has been observed at exceptionally high magnetic fields. For large particles, the field-induced transition widens while magnetization progressively decreases. In small particles the transition is almost fully suppressed. The thermoremanence and isothermoremanence curves constitute fingerprints of irreversible magnetization originating from nanoparticle shells. We have ascribed the magnetic behaviour of nanoparticles to a core–shell scenario with two main magnetic contributions; one attributed to the formation of a collective state formed by FM clusters in frustrated coordination at the surfaces of interacting AFM nanoparticles and the other associated with inner core behaviour as a two-dimensional diluted antiferromagnet.
Journal of Physics: Condensed Matter 24(2012), 266001 8pp
Mineralogical and geochemical investigation of seafloor massive sulfides from Panarea Platform (Aeolian Arc, Tyrrhenian Sea)
Dekov, V. M.; Kamenov, G. D.; Abrasheva, M. D.; Capaccioni, B.; Munnik, F.
Panarea seafloor hydrothermal system is associated with a range of mafic to felsic volcanic rocks. The hydrothermal system is active at present and discharges magmatic-hydrothermal fluids and precipitates massive sulfides. The sulfides exhibit multi-stage deposition, evident in the alternation of several mineral generations that follow a general temporal precipitation sequence: marcasite → alunite → opal. Sr-Nd-Pb isotope data indicate that most of the metals in the sulfides are derived predominantly from the Panarea volcanic rocks with some contribution from ambient seawater and/or local sediments. A remarkable feature of these sulfides is their chondrite-normalized rare earth element (REEN) distribution pattern with a pronounced negative Eu anomaly, which has not been observed previously. Our study demonstrates that this REEN pattern reflects the REE fractionation during sulfide deposition. The ionic radius mismatch between Eu2+ (the main form of Eu in reduced, high-temperature hydrothermal fluids) and the only possible site for REE substitution in the marcasite, that of Fe2+, suggests a crystallographic control on the REEN pattern. Apparently, marcasite precipitation can generate a sulfide deposit with a negative Eu anomaly due to discrimination against Eu2+ relative to REE3+ in the Fe2+ crystallographic site.
Keywords: Eu anomaly; hydrothermal; massive sulfide; rare earth elements; Tyrrhenian Sea
Chemical Geology 335(2012), 136-148
Contactless inductive flow tomography: A liquid metal flow measuring technique complementary to UDV
Stefani, F.; Gerbeth, G.; Gundrum, T.; Wondrak, T.
The aim of the Contactless Inductive Flow Tomography (CIFT) is the reconstruction of flow structures in metal and semiconductor melts. It relies on the induction of electric currents in moving conductors exposed to magnetic fields. The flow induced deformations of various applied magnetic fields can be measured in the exterior of the melt and utilized for the reconstruction of the velocity field. After a presentation of the principles of CIFT, first applications and possible extensions of the method are discussed and put into the context with traditional measuring techniques such as UDV.
Invited lecture (Conferences)
8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Germany
Contribution to proceedings
8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Germany
Proceedings of the 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, Dresden: HZDR, 101-104
Towards a precession driven dynamo
Stefani, F.; Gundrum, T.; Giesecke, A.; Albrecht, T.; Gerbeth, G.
Precession has been discussed since long as a complementary energy source of planetary dynamos. We present the status of preparations of a large-scale precession-driven dynamo experiment working with liquid sodium. The main focus is laid on the results of a down-scaled water experiment, and on a number of constructional issues of the large machine.
European GDR Dynamo & MHD Days, 01.-04.10.2012, Nice, France
Anisotropic Cascade of Field-Induced Phase Transitions in the Frustrated Spin-Ladder System BiCu2PO6
Kohama, Y.; Wang, S.; Uchida, A.; Prsa, K.; Zvyagin, S.; Skourski, Y.; Mcdonald, R. D.; Balicas, L.; Ronnow, H. M.; Rüegg, C.; Jaime, M.
BiCu2PO6 is a frustrated two-leg spin-ladder compound with a spin gap that can be closed with a magnetic field of approximately 20 T. This quantum phase transition and its related phase diagram as a function of magnetic field and temperature (H, T) are investigated up to 60 T by means of specific heat, magnetocaloric effect, magnetization, and magnetostriction measurements. In contrast to other gapped quantum magnets, BiCu2PO6 undergoes a series of unexpected first- and second-order phase transitions when an external magnetic field is applied along the crystallographic c axis. The application of a magnetic field along the b axis induces two second-order phase transitions. We propose that the anisotropy and complex phase diagram result from the interplay between strong geometrical frustration and spin-orbit interaction necessary for the description of this fascinating magnetic system.
Physical Review Letters 109(2012), 167204
The x-ray magnetic circular dichroism spin sum rule for 3d4 systems: Mn3+ ions in colossal magnetoresistance manganites
Kuepper, K.; Raekers, M.; Taubitz, C.; Uhlarz, M.; Piamonteze, C.; de Groot, F. M. F.; Arenholz, E.; Galakhov, V. R.; Mukovskii, Y. M.; Neumann, M.
The colossal magnetoresistance manganites La0.87±0.02Sr0.12±0.02MnO3+δ, La0.78±0.02Sr0.17±0.02MnO3+δ, and La0.66±0.02Sr0.36±0.02MnO3+ δ (δ close to 0) were investigated by using soft x-ray magnetic circular dichroism (XMCD) and magnetometry. Very good agreement between the values for the average Mn magnetic moments determined with these two methods was achieved by correcting the XMCD spin sum rule results by means of charge transfer multiplet calculations, which also suggest a charge transfer of ~50% for Mn4+ and ~_30% for Mn3+. The magnetic moment was found to be localized at the Mn ions for x = 0.17 and 0.36 at 80 K and for x = 0:12 in the temperature range from 80 to 300 K. We discuss our findings in the light of previously published data, confirming the validity of our approach.
Journal of Physics: Condensed Matter 24(2012), 435602
Astrophysical phenomena in the lab: MHD instabilities in liquid metal experiments
Stefani, F.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Kirillov, O.; Seilmayer, M.
We give an overview about the recent liquid metal experiments on dynamo action and magnetically triggered flow instabilities with relevance to cosmic objetcs like planets, stars, and accretion disks. The prospects for large-scale liquid sodium experiments in the framework of DRESDYN are also discussed.
Invited lecture (Conferences)
Workshop: "Rotation and magnetic fields on the upper main sequence", 05.-06.11.2012, Potsdam, Germany
Exciton dynamics in GaAs quantum wells studied with a free-electron laser
There is no abstract.
Keywords: GaAs quantum well; terahertz free-electron laser; exciton
Invited lecture (Conferences)
The 6th International Symposium on Ultrafast Phenomena and THz Waves (ISUPTW2012), POEM OSA Topical Meeting, 01.-02.11.2012, Wuhan, China
Quantum well infrared photodetectors for dual-band thermal imaging and two-photon detection
There is no Abstract.
Keywords: quantum well infrared photodetector; thermal imaging; GaAs/AlGaAs
Seminar, University of Electronic Science and Technology of China (UESTC), 18.10.2012, Chengdu, China
Status of the Pulsed-Magnet-Development Program at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.; Wustmann, B.; Herrmannsdörfer, T.; Wosnitza, J.
The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which offers to researches a variety of experimental techniques combined with non-destructive pulsed magnetic fields. Recently a new, 9.5 MJ dual-coil magnet has been commissioned. This magnet has achieved magnetic field of 91.4 T in a 16 mm bore and it is available for users now. In this paper, we report on some key upgrades in the magnet design which have led to breaking the 90 T limit at the HLD. Further possible design improvements are discussed. In addition, we share our operational experience obtained with the pulsed magnets.
IEEE Transactions on Applied Superconductivity 22(2012)3
Nanostructured thin manganite films in megagauss magnetic field
Balevicius, S.; Zurauskiene, N.; Stankevic, V.; Kersulis, S.; Plausinaitiene, V.; Abrutis, A.; Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.; Wolff-Fabris, F.
We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77K up to 91.4 T. Moreover, the magnetoresistance behavior at 290K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges.
Applied Physics Letters 101(2012), 092407
Accommodation of multivalent cations in fluorite-type solid solutions: case of Am-bearing UO2
Prieur, D.; Martin, P.; Lebreton, F.; Delahaye, T.; Banerjee, D.; Scheinost, A. C.; Jankowiak, A.
The radiotoxicity of spent nuclear fuel is mainly due to the content of minor actinides, which could be substantially reduced by Partitioning and Transmutation. A possible transmutation method would be to employ americium-bearing uranium oxide materials as blanket fuels in fast neutron reactors. In order to maintain fuel performance and reactor safety, it is mandatory to control the structural homogeneity and oxygen stoichiometry during the sintering process. In this work, U0.85Am0.15O2±x materials, fabricated by a solid state chemistry process, were sintered at 2023 K under three oxygen potentials, i.e. -375, -350 and -325 kJ.mol-1, thereby significantly extending the range of a previous study. By coupling X-ray diffraction and X-ray absorption spectroscopy measurements, it was shown that fluorite solid solutions are obtained whatever the sintering conditions. The presence of U(+V), pointed out in a previous work for oxygen potentials equal to -520 and -450 kJ.mol-1, was confirmed. This result constitutes the first experimental proof of the existence of U(+V) in An-doped UO2 fluorite materials. Considering the now available extended range, the effect of the oxygen potential is discussed in terms of charge distribution and local structure.
Keywords: XAFS; Americium; Partitioning; Transmutation
Journal of Nuclear Materials 434(2013), 7-16
Low electrical resistivity polycrystalline TiO2-based transparent conductive thin films by DC magnetron sputter deposition
Neubert, M.; Vinnichenko, M.; Fiedler, J.; Gebel, T.; Liepack, H.; Kolitsch, A.
Transparent conductive oxides (TCO), mainly In2O3:Sn (ITO), ZnO:Al (AZO) and SnO2:F (FTO) are widely used as transparent electrodes in flat panel displays, thin film solar cells and solid state lighting. The markets for the applications requiring large area electrodes are continuously growing recent years which drives the need for a cost-efficient replacement of conventional TCOs. In addition to a low cost, TiO2 offers unique combination of high refractive index, stability against humidity, the high chemical stability and the non-toxicity. The Nb or Ta doped TiO2 films epitaxially grown on crystalline substrates show electrical and optical properties which are comparable to those of conventional TCOs. However, using expensive crystalline substrates drastically limits applications. It is still a challenge to achieve low electrical resistivity polycrystalline TiO2 films as required for the most applications. Furthermore, it is not possible to get low resistivity in polycrystalline films by direct growth at elevated substrate temperature.
Only a two-step approach containing the deposition of amorphous films followed by annealing in vacuum or hydrogen delivers films with resistivity values in the range of 1·10-3 cm. Even in that case, it is known that electrical, optical and structural properties evolution during crystallization, and crystallization itself, is strongly affected by the Ti/O ratio in the as-deposited films. Achieving required Ti/O ratio remains the main challenge. In order to address this problem, we studied the films formed on glass substrates without heating by DC magnetron sputtering of reduced TiO2-x:Ta ceramic targets followed by vacuum annealing. We achieved oxygen fine-tuning using a MS process in conjunction with a plasma feedback system. The optimum total pressure in combination with O2 fine tuning yielded the films with the best free electron mobility of 8 cm²/Vs. Our approach delivered films with an electrical resistivity in the range of 10-3 W cm, optical transmittance above 80% for 400nm thick films and electrical activation of Ta dopants up to 70% which is substantially higher than that of Al in ZnO. The temperature dependent hall effect measurements show a different behavior of the resistivity vs. temperature with varying film stoichiometry.
Keywords: TCO; TiO2; transparent; conductive; tantalum
4th International Symposium on Transparent Conductive Materials, 21.-26.10.2012, Hersonnisos, Greece
Overview On The Reaction Mechanism And Kinetics Of The Oxidation Of Isobutane And Future Prospects
Willms, T.; Kryk, H.; Hampel, U.
Die Ergebnisse der Literaturrecherche zur Isobutanoxidation werden vorgestellt. Es wird ein ausführlicher Reaktionsmechanismus für die unkatalysierte Oxidation vorgestellt. Außerdem werden einige der ermittelten Reaktionsmodelle vorgestellt und ausgewertet.
Des Weiteren wird die durch Bromwasserstoff katalysierte Variante dieser Reaktion vorgestellt. Sicherheitsaspekte sowie Erkenntnisse zur Stabilität des t-Butylhydroperoxides werden beschrieben und Schlussfolgerungen für das weitere Vorgehen im Rahmen des Projektes gezogen.
2. Dresdener Energie-Allianz-Treffen, 07.11.2012, HZDR, Deutschland
Effect of Ga+ irradiation on the magneto-optic spectra of Pt/Co/Pt sandwiches
Interfacial changes in rf sputtered Pt/Co(2.6 nm)/Pt sandwiches grown onto sapphire (Al2O3) substrates induced by irradiation of 30 keV Ga+ ions at low dose (1014 ions/cm2) have been investigated by magneto-optic polar Kerr rotation (PKR) spectroscopy between 1 and 5 eV. The irradiation resulted in an increase of PKR over the whole spectral range. The measured PKR spectra were compared with those computed from the transfer matrix formalism using known polar Kerr rotation and ellipticity spectra for Co and five CoxPt1−x alloys. The comparison between measured and computed PKR spectra provided an in-depth profile of Co and Pt ion distributions across the sandwich and confirmed that irradiation favors alloying in the vicinity of the two interfaces. These results are in a good agreement with the profile evaluated independently by TRIDYN simulations. Our results evidence an asymmetry in the irradiation effect due to an excess of Pt–Co alloying at the upper interface. Moreover, the observation of a negative PKR peak around 3.2 eV states definitively the presence of a chemically ordered Co0.75Pt0.25 alloy phase inside the irradiated film structure.
Keywords: Magneto-optical Kerr spectroscopy; Pt/Co thin films; Metal and metal alloys; Ion radiation effect
Thin Solid Films 520(2012)24, 7169-7172
Effects of millisecond thermal processing on the properties of ZnO-based transparent conducting materials
Vinnichenko, M.; Hauschild, D.; Krause, M.; Cornelius, S.; Gago, R.; Mücklich, A.; Lissotschenko, V.; Kolitsch, A.
Improvement of the electrical and optical properties of ZnO-based thin films by post-deposition thermal processing at millisecond time scale is an attractive approach to realize low-cost transparent electrodes for different applications. Embedding Ag nanoparticles into ZnO:Al layers can extend functionality of the electrodes by achieving plasmonic light scattering due to spinodal dewetting of the Ag during thermal processing. If applied for preparation of thin film solar cells, both approaches have potential to improve their efficiency without increasing production costs. Nevertheless, this potential remains largely unexplored, partly due to limited understanding of physical mechanisms of the material properties modification during such treatment.
Present study focuses on the investigation of the effects of very rapid thermal processing (vRTP, dwell time of 1 ms) on the ZnO:Al (AZO) and AZO/Ag/AZO film properties using innovative low-cost high power diode laser arrays with microoptically designed line-shaped beam profiles. The method enables treatment of the films on thermally sensitive substrates, because thermal energy is deposited directly in the film, which leads only to partial heating of the substrate. Moreover, it is compatible with in-line growth of the transparent electrodes and is up-scalable to large areas. The properties of the films processed by vRTP and directly grown at elevated substrate temperatures are systematically compared. The AZO films were deposited both by reactive pulsed and non-reactive DC magnetron sputtering (MS). The composite AZO/Ag/AZO films were synthesized using non-reactive DC MS. Only the films grown without substrate heating were subjected to the vRTP.
Even at air ambience, the optimized laser processing of the AZO films results in a decrease of the film electrical resistivity from (1-2)x10-3 to less than 5x10-4 Ω cm. This is accompanied by a substantial increase of the free electron mobility, μe, and density, Ne, and increase of the film transmittance in the visible. Interestingly, the electron mobility values evaluated using Drude term for near-IR spectroscopic ellipsometry data analysis remain higher than the Hall effect values μe both for as deposited and processed films. Both values improve approximately by the same factor due to the laser vRTP. It is known that Hall effect provides information on the electrically connected crystalline grains, while spectroscopic ellipsometry yields intra-grain mobility. Therefore, this result suggests that the AZO film properties improve mainly intra-grain and electrical contact among the grains does not change. This is in agreement with the XRD and X-TEM data showing neither changes in the film morphology nor improvement of the film crystal quality by the vRTP.
The vRTP was observed to cause a substantial decrease of the A1(LO) and E1(LO) disorder-enhanced lines in Raman spectra. Taking into account X-ray absorption near edge structures (XANES) results, annealing of intra-grain oxygen-related point defects is of importance for the AZO electrical properties improvement by vRTP. The as-deposited films having larger amount of defects (according to Raman spectroscopy) improve their optical transmittance to a less extent by laser processing pointing to an importance of the initial state of the film for the results of vRTP.
Using deposition at elevated temperature, the AZO films with better crystal quality but similar electrical and optical properties were achieved only at TS≥250°C. Depositing entire AZO/Ag/AZO stack on heated substrate, the strongest plasmonic resonance was observed in case of TS~450°C. XTEM shows that it is due to the embedded layer of dewetted nano-Ag islands which are ~10 nm thick and have ~60 nm diameter. Achieving similar structures by laser vRTP is in progress.
4th Symposium on Transparent Conductive Materials 2012, 21.-26.10.2012, Chersonissos, Crete, Greece
Crystallization of TiO2:Nb/Ta: effect of the as-deposited film morphology and local order structure
Vinnichenko, M.; Junghähnel, M.; Neubert, M.; Gago, R.; Mücklich, A.; Kolitsch, A.
TiO2-based transparent conductive oxides (TCOs) are of great importance as a cost-efficient, environmentally friendly and chemically inert alternative to conventional TCOs. The two-step process, i.e. growth of amorphous TiO2:Nb (TNO) and TiO2:Ta (TTO) films on glass and their post-deposition annealing provides films with electrical resistivity below 10-3 Ω cm. Further optimization of the growth process and its up-scaling require a deeper understanding of the crystallization process of the TiO2-based amorphous films. Appropriate characterization of the film structure represents a major challenge in this case.
The TNO and TTO films were prepared using two-step process on commercial glass substrates. During the first step, amorphous intermediate material was grown by DC magnetron sputtering of electrically conducting TiO2-x-based ceramic targets. The TNO films were grown using a pilot scale in-line sputtering system with precise adjustment of the O2 flow, fO2, using mass flow controllers. The TTO films were deposited in lab-scale system at higher total pressure and applying a closed-loop feedback system based on plasma emission monitor to tune fO2. The films were subjected to post-deposition thermal annealing in vacuum at TA~450 °C for ~15-60 min. In both cases, it was found that the anatase films with low electrical resistivity (~10-3 Ω cm) and high optical transmittance (>80% in the visible) can be prepared only within very narrow window of fO2 values.
The x-ray amorphous films (those which show no diffraction peaks) upon annealing convert into the films with dramatically different structure and properties depending on the fO2 used during the deposition. In case of fO2
These results show that nanocrystallites of rutile present in amorphous TiO2 matrix work as seeds and induce formation of the undesirable rutile phase during annealing. In order to achieve high-quality TiO2-based TCOs, formation of the seeds has to be avoided, which can be realized by careful adjustment of the Ti/O flux ratio during the intermediate film growth.
1. R.Gago, A.Redondo-Cubero, M.Vinnichenko, and L.Vázquez, Chem. Phys. Lett. 511, 367 (2011).
2. R.Gago, M.Vinnichenko, A.Redondo-Cubero, and L.Vázquez, Plasma Process. Polym. 7, 813 (2010).
4th Symposium on Transparent Conductive Materials 2012, 21.-26.10.2012, Chersonnisos, Crete, Greece
Setup and Fabrication of Cost Effective, Robust Fiber Optical Needle Probes for Application in Multiphase Flows
Bloch, G.; Elfner, J.; Finke, K.; Schleicher, E.; Sattelmayer, T.
A fiber optical probe for detection of void fraction in multiphase flows consisting of silica fibers with core diameters of 200 and 400 µm is presented. Using beam splitter optics with a polarizing filter and a diode laser for illumination, a robust and cost-efective sensor was developed and evaluated in two phase flows with and without phase change. The setup and manufacturing process of the components as well as the post processing of the signals are described in detail.
Keywords: Fiber Optics; Fluid Mechanics; Instruments; Optical Methods; Signal Processing
Contribution to proceedings
21. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", 03.-05.09.2013, München, Bundesrepublik Deutschland
Proceedings der 21. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", Karlsruhe: GALA e.V., 978-3-9805613-9-6, 10-1-10-8
Experimental investigation of stratified two-phase flows in the hot leg of a PWR for CFD validation
Vallée, C.; Lucas, D.; Tomiyama, A.; Murase, M.
Stratified two-phase flows were investigated in two different models of the hot leg of a pressurised water reactor (PWR) in order to provide experimental data for the development and validation of computational fluid dynamics (CFD) codes. Therefore, the local flow structure was visualised with a high-speed video camera. Moreover, one test section was designed with a rectangular cross-section to achieve optimal observation conditions. The phenomenon of counter-current flow limitation (CCFL) was investigated, which may affect the reflux condenser cooling mode in some accident scenarios.
The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and saturated water at boundary conditions of up to 50 bar and 264°C. The measured CCFL characteristics were compared with similar experimental data and correlations available in the literature. This shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross-sections. Furthermore, the experimental results confirm that the Wallis similarity is appropriate to scale CCFL in the hot leg of a PWR over a wide range of pressure and temperature conditions. Finally, an image processing algorithm was developed to recognise the stratified interface in the camera frames. Subsequently, the interfacial structure along the hot leg was visualised by the representation of the probability distribution of the water level.
Keywords: counter-current flow limitation; CCFL; hot leg; stratified two-phase flow; interfacial structure; image processing
- VGB PowerTech Journal (2012)12, 40-46
- atw - International Journal for Nuclear Power 57(2012), 742-750
Krein space related physics
Physical models with anti-linear symmetries can often be described by differential operators self-adjoint in suitably chosen Krein spaces.
We briefly comment on the spectral properties of some specific operators self-adjoint in Krein spaces and related effects:
- the operator of the hydrodynamic Squire equation, its scaling behavior and mapping to the operator of the Bender-Boettcher model of PT Quantum Mechanics,
- the cusp-type spectral properties in the vicinity of third-order exceptional points (algebraic branch points),
- the unfolding of higher-order exceptional points of the spectrum of Hamiltonians in PT-symmetric Bose-Hubbard models described with the help of Puiseux series expansions and Newton polygon techniques.
Finally, we briefly comment on recent experimental findings in PT-symmetric (i.e. Krein-space related) physics, especially in optical wave-guide systems and microwave cavities.
Keywords: anti-linear symmetries; Krein spaces; spectral singularities; exceptional points; branch points; PT symmetry; PT quantum mechanics; Squire equation; Bose-Hubbard model; Puiseux series expansion; Newton polygon technique; quantum brachistochrone problem; positive operator-valued measures; Naimark dilation; optical wave guides; microwave cavities
Weekly Scientific Seminar of the Department of Applied Functional Analysis, Krakow AGH University of Science and Technology, 21.11.2012, Krakow, Polen
Ultimate detection limits by accelerator-based mass spectrometry
Merchel, S.; Akhmadaliev, S.; Pavetich, S.; Renno, A. D.; Rugel, G.; Ziegenrücker, R.
Accelerator-based analytical methods, mainly accelerator mass spectrometry (AMS) and ion beam analysis (IBA), have been applied to numerous research projects in recent decades. The key element of both methods is a high-energy particle accelerator running at a terminal voltage of 0.2-14 MV.
For AMS negative ions (molecules or elements) are extracted from samples containing long-lived radionuclides (t1/2 >100 a) in a Cs-sputter ion source. By inserting these ions in a tandem accelerator, they gain MeV-energies, and by passing through matter (gas or foil) at the positively charged terminal in the middle of the accelerator, the negative ions lose outer electrons and convert into multiple-positively charged ions being then further accelerated towards the exit. Effectively all molecules are destroyed by this stripping process. Generally, AMS is measuring isotope ratios, i.e., stable isotopes are usually detected in Faraday-cups and radionuclides in ionization chambers. Such a set-up of two mass spectrometers in one, namely the first with negative ions of keV-energy, the second with high-energy positive ions of MeV-energy, and combined with several magnetic and electrostatic analyzers, allows analyzing isotopic ratios as low as 10-16, thus, providing the ultimate detection limit of all mass spectrometry methods. Very recently, a new AMS facility has been installed at the Ion Beam Centre of the Helmholtz-Zentrum Dresden-Rossendorf: DREsden AMS (DREAMS) [1-3].
Probably in 2014, AMS will be also used for the detection of stable element ratios at DREAMS. The most common terms for this are Trace Element AMS (TEAMS, e.g. ) or if the Cs-beam is focused and spatial resolution kept, Accelerator-SIMS or Super-SIMS . However, mainly due to the background e.g. from the ion source, detection limits are expected to be not as low as for “standard” AMS, but still some orders of magnitude better than is the case for traditional dynamic SIMS, i.e. around 10-9-10-12.
References:  S. Merchel et al., GIT Labor-Fachzeitschrift 2012, (2) 56, 88.  S. Akhmadaliev et al., Nucl. Instr. Meth. B 2012, doi:10.1016/j.nimb.2012.01.053.  www.dresden-ams.de.  S. Merchel et al., Geochim. Cosmochim. Acta 2003, 67, 4949.  S. Matteson, Mass Spectrom. Rev. 2008, 27, 470.
Keywords: AMS; Super-SIMS; TEAMS
ANAKON 2013, 04.-07.03.2013, Essen, Deutschland
[68Ga]NS3-RGD and [68Ga] Oxo-DO3A-RGD for imaging αvβ3 integrin expression: synthesis, evaluation, and comparison
Knetsch, P. A.; Petrik, M.; Rangger, C.; Seidel, G.; Pietzsch, H.-J.; Virgolini, I.; Decristoforo, C.; Haubner, R.
68Ga-labeled RGD peptides in combination with PET allow non-invasive determination of αvβ3integrin expression which is highly increased during tumor-induced angiogenesis. The aim of this study was to synthesize and evaluate two RGD peptides containing alternative chelating systems, namely [68Ga]NS3-RGD and [68Ga]Oxo-DO3A-RGD and to compare their in vitro and in vivo properties with [68Ga]DOTA- and [68Ga]NODAGA-RGD.
Syntheses of both radiotracers followed standard SPPS protocols. For in vitro characterization distribution coefficients, protein binding abilities, serum stabilities, and αvβ3 integrin binding affinities were determined. For in vitro tests as well as for the biodistribution assay αvβ3 positive human melanoma M21 and αvβ3 negative M21-L cells were used.
68Ga-labeling of NS3-RGD resulted in good radiochemical purity, whereas HPLC analysis showed two peaks with a ratio of 1:6 for [68Ga]Oxo-DO3A-RGD. Distribution coefficients were −3.4 for [68Ga]Oxo-DO3ARGD and −2.9 for [68Ga]NS3-RGD. Both radiotracers were stable in PBS solution at 37°C for 2h but lack stability in human serum. Protein binding was approximately 40% of the total activity for [68Ga]NS3-RGD and 70% for [68Ga]Oxo-DO3A-RGD, respectively, resulting in high blood pool activities. Biodistribution assays confirmed these findings and showed an additional high uptake in liver and kidneys, especially for [68Ga]NS3-RGD. Furthermore, [68Ga]Oxo-DO3A-RGD showed nearly the same activity concentrations in αvβ3 positive and αvβ3 negative tumors.
[68Ga]Oxo-DO3A-RGD and [68Ga]NS3-RGD have inferior characteristics compared to already existing 68Ga-labeled RGD peptides and thus, both are not suited to image αvβ3 integrin expression. Of all our tested RGD peptides, [68Ga]NODAGA-RGD still possesses the most favorable imaging properties. Moreover this study shows that the use of appropriate chelators to achieve good targeting properties of 68Ga-labeled biomolecules and careful in vitro and in vivo evaluation including comparative studies of different strategies are essential components in designing an effective imaging agent for PET.
Keywords: 68Ga; RGD; αvβ3; Molecular imaging; Angiogenesis
Nuclear Medicine and Biology 40(2013), 65-72
Target water for F-18 production: Recover – Renew – Reuse
Rötering, S.; Franke, K.; Brust, P.; Fischer, S.; Steinbach, J.
Proton irradiation of H2[O-18]O-water is a standard method for F-18 production. Due to the limited availability of O-18 water and increasing costs, its re-use for research purposes gets more and more important. We present two purification methods for the removal of organic contaminants from used target water. The recycled target water is characterized by production yields, radionuclide purity and the use in radiosyntheses.
Oxidation of the organic contaminants in the target water was tested with photo-oxidation (254 nm)  and a chemical method using KMnO4 as oxidation agent validated by gas chromatography, ICP-OES and pycnometry. Target irradiations were done at similar beam parameters (11.7 DAh) at a CYCLONE 18/9 (IBA, target: 2 mL). Radionuclide purity and yield were determined by a well counter (MED) and gamma spectrometry (ORTEC). Produced F-18 was used in nucleophilic substitution reactions.
Both purification methods allow a comparable decrease of organic contaminants from 400 ppm ethanol and 44 ppm acetone to 10 ppm-50 ppm ethanol. The parameters (amount of oxidation agent, temperature, treatment time) for the purification methods were established, allowing comparable irradiation and radiosyntheses as for the original target water. We observed a loss of the production yield (19 %) due to a lower O-18 concentration but no significant influence on the radionuclide purity or radiochemistry.
Both methods enable a multiple cycling of target water for the successful production and application of F-18 for research purposes, whereas photo-oxidation is faster. However, the required amount of F-18 limits the cycling process.
For 83 % O-18 enrichment in H2[O-18]O water after one cycle starting from 87 % we achieved reasonable production yields which allow an efficient economical usage of the target water, including the minimization of the target water contamination in the re-collection process.
1. Gebrauchsmuster DE 29504388 U1, Forschungszentrum Jülich GmbH, 1995
NuklearMedizin 2013, 17.-20.04.2013, Bremen, Deutschland
Abstract in refereed journal
Nuklearmedizin 2(2013)52, V29
Untersuchungen zur Entwicklung eines PET-Tracers für die Phosphodiesterase 10A
Wagner, S.; Scheunemann, M.; Egerland, U.; Fischer, S.; Hoefgen, N.; Brust, P.
Phosphodiesterase 10A (PDE10A) ist ein Schlüsselenzym in der zellulären Signaltransduktion. PDE10A wird hauptsächlich im Striatum exprimiert und spielt vermutlich eine Rolle bei neurologischen Erkrankungen verknüpft mit striataler Hypofunktion wie Schizophrenie. Molekulare Bildgebung mittels PET würde die In-vivo-Untersuchung neurologischer und pathologischer Prozesse in Zusammenhang mit PDE10A und ihrer Expression erlauben. Neuentwickelte Imidazo[1,5-a]chinoxaline zählen als Wirkstoffkandidaten zu einer Gruppe hochpotenter und selektiver PDE10A Inhibitoren (1). Der tricyclische Heterocyclus dient als Leitstruktur für unsere Arbeiten zur Entwicklung eines F-18 markierten Tracers für eine zukünftige PET-Bildgebung der PDE10A.
Zur Darstellung einer Referenzverbindung auf Basis dieser Inhibitoren sollte ein 2-Fluorpyridinbaustein in Position 1 des Imidazo[1,5-a]chinoxalins eingeführt werden. Die 2-Fluorposition, benachbart zum Stickstoff, erlaubt die nukleophile Einführung eines F-18 mit hoher spezifischer Aktivität in der späteren Radiosynthese. Reinheit und Identität der Referenzverbindung wurden mittels NMR, MS und HPLC bestimmt. Die inhibitorische Wirksamkeit auf menschlich rekombinante PDE10A wird zurzeit in Enzym-Assays untersucht.
Der benötigte, bromierte Imidazo[1,5-a]chinoxalinbaustein konnte ausgehend von einem 2,4,6-trisubstituierten Anilin erfolgreich hergestellt werden. In einem konvergenten Syntheseschritt wurde am Ende der Synthesesequenz durch eine Palladium-katalysierte Suzuki-Kupplung ein 2-Fluorpyridinrest eingebaut. Somit konnte eine erste Referenzverbindung erhalten werden.
Ein erstes 2-Fluorpyridinderivat konnte als PDE10A Inhibitorkanditat erfolgreich synthetisiert werden. Folglich ermöglicht die Suzuki-Kupplung den Einbau von 2-Fluorpyridinresten und bietet dadurch einen schnellen Zugang zu strukturell divergenten Inhibitoren und möglichen Präkursoren für die spätere Radiosynthese.
(1) Malamas et. al. J. Med. Chem. 2011,54, 7621-7638
NuklearMedizin2013, 17.-20.04.2013, Bremen, Deutschland
Abstract in refereed journal
Nuklearmedizin 2(2013)52, P24
Y-Ti-O Nanocluster Formation in Bcc Fe Using Dft and Kinetic Monte Carlo Simulations
Murali, D.; Kaur, G.; Jegadeesan, P.; Panigrahi, B. K.; Valsakumar, M. C.; Posselt, M.
Oxide Dispersion Strengthened (ODS) steels are candidate materials for use in nuclear environment as they offer excellent swelling resistance characteristics and enhanced high temperature mechanical properties. ODS steels derive their strength from the dispersion of oxide (Y-Ti-O) nanoclusters in the ferritic matrix. The mechanism of formation, structure, thermal & radiation stability and composition of these nanoclusters are not yet fully understood. We are studying the basic energetic and kinetic properties of solutes and their clusters along with vacancy in bcc Fe using density functional theory and evolution of these nanoclusters using kinetic Monte Carlo simulations. The diffusion coefficients of these solute atoms in bcc Fe have been calculated using Le Claire's nine frequency model. Among these, Y is believed to be rate limiting for the growth of nanoclusters and our calculated diffusion coefficient is found to be three orders of magnitude higher than the experimental one [J. Nucl. Mater. 419, 208 (2011)]. In order to further understand the diffusion behavior of Y in bcc Fe and hence its role in the kinetics of nanocluster formation, we review the Le Claire's diffusion model both in dilute and concentrated limits. Also, in continuation of our previous study of solute atom interaction with vacancy, we discuss our recent results of DFT calculations of solute atom interactions with self-interstitials.
Keywords: ODS; DFT; KMC
Multiscale Materials Modeling (MMM) 2012, 15.-19.10.2012, Singapore, Singapore
On the Role of Cation Interactions in the Reduction Process in Plutonium-Americium Mixed Oxides
Belin, R. C.; Martin, P. M.; Lechelle, J.; Reynaud, M.; Scheinost, A. C.
The oxygen to metal ratio (O/M) is directly related to oxygen potential, which strongly influences the sintering and irradiation performance of nuclear fuels. A better understanding of these two parameters is therefore of major interest. To further ascertain the correlation between O/M ratio and oxygen potential in Am-bearing MOX, several ther-modynamic descriptions are being developed. Despite their differences, they all involve the valence of actinide cations (e.g. U, Pu and Am) as essential parameters. However, as no experimental data on their valence is available, these models rely on assumptions. In the present work, we coupled X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to follow the behaviour of Pu and Am in three hypo-stoichiometric, U-free Pu1-yAmyO2-x compounds. We provide for the first time a quantitative determination of Pu and Am valences, demonstrating that plutonium reduction from Pu4+ to Pu3+ starts only, once americium reduction from Am4+ to Am3+ is completed. This result fills in an important gap in experimental data, thereby improving the thermodynamic description of nuclear fuels. At last, we suggest that the O/M ratio may still evolve at room temperature for high Am content, which is of main concern for the fabrication of Am-loaded MOX and their storage prior to irradiation.
Keywords: plutonium; americium; XAFS
Inorganic Chemistry 52(2013), 2966-2972
Homogeneity testing of natural candidate reference materials for resource technology by three spatially-resolved X-ray methods
Michalak, P. P.; Renno, A. D.; Merchel, S.; Munnik, F.
Quality assurance of natural raw materials (e.g. ores) requires thorough studies on concentration and distribution patterns of technologically relevant trace elements within the mineral matrix at the microscale. Obtaining such a goal is yet only possible with the use of X-ray-based microanalytical methods and a proper set of homogeneous reference materials (RMs).
Three minerals of natural origin: pyrite (FeS2), columbite (FeNb2O6) and sanidine ((K,Na)(Si,Al)4O8) – candidates for RMs for resource technology – have been investigated for their spatial chemical microhomogeneity using three X-ray methods:
- Electron Probe Micro Analysis (EPMA)
- Particle Induced X-ray Emission (PIXE)
- Synchrotron radiation-induced micro-X-ray Fluorescence (Sy-µXRF).
Quantitative (EPMA, PIXE) and qualitative (Sy-µXRF) elemental spatial distribution maps have been obtained for major and trace elements for each mineral. Several trace elements were detected in each of the matrices above the limit of detection (LOD).
EPMA III PIXE III Sy-µXRF
Beam size 2 µm Ø III 3 x 3 µm2 III 5 x 5 µm2
Mapping area 100 µm x 100 µm
Pyrite S, Mn, Fe, Co, Ni, Cu, As, Se, Au III Fe, Ni, Cu, As III S, Fe, Ni, Cu, As
LOD range 20 - 350 µg/g III 9 - 28 µg/g III qualitative
Sanidine Al, Si, K, Ca, Fe, Ba III K, Ca, Fe, Ga, Ge, Rb, Sr, Ba III Al, Si, K, Ca, Fe, Ga, Ge, Rb, Sr, Ba, Pb
LOD range 90 - 450 µg/g III 1 - 517 µg/g III qualitative
Columbite Mg, Al, Ca, Sc, Ti, Mn, Fe, Zr, Nb, Hf, Ta III Ca, Sc, Ti, Mn, Fe, Zr, Nb, Ta, W, U III Sc, Ti, Mn, Fe, Y, Zr, Nb, Ta, W, Th, U
LOD range 40 - 810 µg/g III 24 - 940 µg/g III qualitative
Although all three non-destructive methods are based on X-ray detection, they provide complementary information on chemical composition and microhomogeneity of the tested minerals’ matrices as detection and excitation conditions influencing especially the spectra background and, thus, the LODs.
Most of the elements showed inhomogeneous distribution at the level of 1-3 µm, proving that the selected mineral specimens are not suitable as candidates for RMs. Consequently, artificial minerals are being synthesized and will be investigated by the validated set of X-ray analytical methods to proof their suitability as micro-RMs.
Keywords: reference materials; XRF; PIXE; EPMA
ANAKON 2013, 04.-07.03.2013, Essen, Deutschland
Quantitative comparison of Taylor Flow simulations based on sharp- and diffuse-interface models
Aland, S.; Boden, S.; Hahn, A.; Klingbeil, F.; Weissmann, M.; Weller, S.
A pressure driven flow of elongated bullet-shaped bubbles in a narrow channel is known as Taylor flow or bubble-train flow. This process is of relevance in various applications of chemical engineering.
In this paper, we describe a typical simplified experimental setting, with surface tension, density and viscosity as prescribed input parameters. We compare a sharp interface model based on a moving grid aligned with the bubble boundary (ALE coordinates) and a diffuse interface model where the bubble shape is implicitly given by a phase-field function.
Four independent implementations based on the two modeling approaches are introduced and described briefly. Besides the simulation of the bubble shapes, we compare some resulting quantities such as pressure difference and film widths within the implementations and to existing analytical and experimental results. The simulations were conducted in 2D and 3D (rotationally symmetric).
Good accordance of the results indicate the applicability and usability of all approaches. Differences between the models and their implementations are visible but in no contradiction to theoretical results.
Keywords: Free surface flow; Multiphase flow; Finite Element Method; Taylor bubbles; Arbitrary Lagrangian Eulerian method; Phase field
International Journal for Numerical Methods in Fluids 73(2013)4, 344-361
Actinide Computational Study at HZDR: Overview and Outlook
no abstract for this lecture
International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Germany
Bakterien sind Bergarbeiter
Bakterien sind zwar sehr klein, aber ihre Rolle für verschiedene Stoffkreisläufe in der Natur und damit für das Leben auf unserem Planeten ist elementar. Darüber hinaus verfügen sie noch über viele weitere sehr bemerkenswerte Fähigkeiten, die man sich in technischen Prozessen zunutze machen kann. So haben Bakterien verschiedene Entgiftungsstrategien entwickelt, die ihnen zum Beispiel ein Überleben in einer stark metallhaltigen, also eher lebensfeindlichen Umgebung ermöglichen. Die zugrunde liegenden Prozesse lassen sich für die (Rück-) Gewinnung von Spurenmetallen und damit zur Sicherung von Rohstoffen für die Industrie nutzen. Der Vortrag gibt einen Überblick über die Leistungen von Bakterien und stellt dazu aktuelle und geplante Forschungsprojekte am Helmholtz-Institut Freiberg für Ressourcentechnologie vor.
Nacht der Wissenschaft, 08.06.2012, Freiberg, Deutschland
Abgeschaut aus der Natur: Biobasierte Nanoverbundmaterialien für die Wasserbehandlung
Bakterielle S-Layer lassen sich aufgrund ihrer strukturellen und biochemsichen Eigenschaften vorteilhaft als Template zur Herstellung hochreaktiver nanostrukturierter Beschichtungen für sehr unterschiedliche technische Anwendungen nutzen. Gerade auch in der Wasserpraxis ergeben sich für derartige Biokompositmaterialien zahlreiche Anwendungen. Aufbauend auf den natürlichen Funktionen bakterieller S-Layer werden am Helmholtz-Zentrum Dresden-Rossendorf verschiedenen S-Layer basierte Materialien entwickelt. Im Fokus stehen gegenwärtig Materialien zur metallselektiven Bindung gelöster Metalle zur Entfernung von Schadstoffen oder zur Rückgewinnugn von Wertstoffen wie auch Materialien zur Detektion und dem Abbau organischer Schadstoffen in Wasser.
Keywords: S-layer; nanotechnology; filter; sensor; catalyst; water treatment
Invited lecture (Conferences)
nANO meets water IV, 08.11.2012, Oberhausen, Deutschland
Importance of configurational contributions to the free energy of nanoclusters
An effective simulation method based on the Wang-Landau Monte Carlo algorithm is used in order to demonstrate the significance of the configurational contributions to the free energy of embedded nanoclusters. Starting from the most stable cluster configuration the simulation provides all geometrically different, but simply connected and sufficiently compact configurations of a nanocluster of a given size and the respective formation energies. The knowledge of these data allows the calculation of the free formation and free binding energy of the cluster at . The method is applied to coherent Cu clusters in bcc-Fe. It is shown that even at moderate temperatures the configurational contributions to the free formation and binding energy must not be neglected. The dependence of the monomer free binding energy on clusters size is found to change significantly with increasing temperature which has a considerable effect on the pathway of cluster evolution. Therefore, present investigations provide an essential contribution to the improvement of the input parameters for object kinetic Monte Carlo simulations and rate theory used in multi-scale simulations of the nanostructure evolution. The calculation scheme developed in this work is rather general and applicable to many types of embedded nanoclusters. Compared to the method of overlapping distributions hitherto used in some cases to determine the configurational part of the free energy the new method has major advantages. Various tests are performed in order verify the presented approach and to compare with the results of the other calculation procedure. A roadmap is proposed to include the vibrational contributions to the free energy of the clusters within the framework of the method employed in this work.
Keywords: free energy; nanoclusters; Metropolis Monte Carlo simulations; Wang-Landau Monte Carlo simulations
AIP Advances 3(2013), 072137
Control over Janus micromotors by the strength of a magnetic field
Baraban, L.; Makarov, D.; Schmidt, O.; Cuniberti, G.; Leiderer, P.; Erbe, A.
For transportation of molecules or biological cells using artificial motors, the control over their motion, i.e. direction and speed of transfer, is important. Here, we demonstrate that modification of the velocity and orientation of a magnetic Janus particle can be efficiently controlled by tuning the strength of an applied magnetic field. Interestingly, by keeping the same orientation of the magnetic field but changing its magnitude not only velocity of capped particles can be altered but even their direction of motion can be reversed.
Keywords: microparticles; colloidal model systems; micro engines
Nanoscale 5(2013), 1332-1336
Contacting metallic nanoparticles on transparent substrates
We demonstrate reliable contacting of single nanoparticles in metallic junctions. The junctions are prepared using electron beam lithography and investigated by means of transmission electron microscopy and electrical transport measurements. The size, shape and crystalline structure of the particles can be clearly identified in our junctions. These properties are then related to low temperature measurements of the conductance of these devices. Due to the weak coupling of the metallic electrodes to the particles, Coulomb Blockade effects are found in these junctions.
Keywords: Nanoparticles; single electron transistor; transmission electron microscopy
Physica Status Solidi (A) 210(2013)7, 1311-1315
Atomic-level simulations of materials properties and processes
Posselt, M.; Kunze, T.; Al-Motasem, A.
Computer simulations using classical interatomic potentials are an efficient tool to study and understand materials properties and to investigate processes of materials modification on the atomic level. In this manner length and time scales can be considered which are often hardly accessible by experiments. In the talk two applications of atomistic simulations are discussed. The focus is on nanoclusters in structural materials for nuclear fission reactors as well as on friction and wear of nanocoatings.
Subjects of the first example are structure, energetics and thermodynamics of coherent nanoclusters in bcc-Fe containing vacancies, Cu and Ni. These precipitates are formed during neutron irradiation of reactor pressure vessel steel and can cause hardening and embrittlement. For clusters up to a size of 200 monomers (i.e. vacancies, Cu or Ni atoms) the most stable configurations at T=0 and the related formation and binding energies are determined by simulated annealing combined with Metropolis Monte Carlo simulations on a rigid lattice and subsequent off-lattice relaxation. In the case of Cu clusters the temperature-dependent free formation and free binding energies are calculated by the Wang-Landau Monte Carlo method using a rigid lattice model.
The second example concerns the study of basic processes of friction and wear in hydrogen-free tetrahedrally coordinated (or diamond-like) amorphous carbon (ta-C) films. These nanocoatings have a great potential to improve the surface properties of materials and components used in car production. First, the structure and the properties of the films determined by the simulations are compared with experimental data. Second, the atomic-level processes occuring during the friction between two ta-C interfaces are discussed. Particular attention is paid to the formation of the tribolayer and to triboreactions.
Keywords: Atomic-level simulations; materials properties; processes in materials
Talk at Department of Physics, Beihang University, 22.10.2012, Beijing, China
Free energy of embedded nanoclusters: Role of the configurational contributions
Diffusion and reaction processes during thermal treatment or particle irradiation can cause the formation of nanoclusters embedded in the host material. This modification often leads to the change of materials properties. Coarse-grained methods such as object kinetic Monte Carlo simulations and rate theory are well suited to simulate the nanocluster evolution on time and length scales easily accessible by experiments. However, these methods need a number of input parameters. One of the most important is the free binding energy of a monomer to a cluster which can be hardly obtained by measurements but can be provided by atomistic simulations. This quantity is calculated using the free formation energy of the clusters which consists not only of the formation energy but also of vibrational and configurational contributions. The present work is focused on the evaluation of the configurational part of the free formation energy. As characteristic examples coherent nanoclusters in bcc-Fe containing Cu and Ni are considered. First-principle data from literature are used to describe the interactions between the atoms. In a first step the most stable cluster configurations at T=0 are determined by Metropolis Monte Carlo simulations and their formation and binding energies are calculated. Second, a modified Wang-Landau Monte Carlo method is employed in order to determine the contribution of all possible geometrical configurations of nanoclusters to the free formation energy. Finally, the total and monomer free binding energies are calculated. It is shown that the configurational contributions to the free energy cannot be neglected if the cluster formation energy is relatively low. The calculation scheme applied in this work can be extended to other types of embedded nanoclusters in solids. Further investigations are required in order to estimate the vibrational contribution to the free energy and to perform a comparison with the configurational part.
Keywords: nanoclusters; free energy; Metropolis Monte Carlo simulations; Wang-Landau Monte Carlo simulations; Cu clusters in bcc-Fe
MMM 2012 - 6th International Conference on Multiscale Materials Modeling, 15.-19.10.2012, Singapore, Singapore
Long-term, on-site borehole monitoring of gases released from an “active” fault system at 3.6km depth, TauTona Gold Mine, South Africa
Lippmann-Pipke, J.; Erzinger, J.; Zimmer, M.; Kujawa, C.; Boettcher, M. S.; van Heerden, E.; Bester, A.; Cason, E.; Reches, Z.
Fluid transport and seismicity are interrelated. Fluids can trigger earthquakes and seismic activity can release fluids from rock formations. The study of this relationship requires direct and near-field observations at focal depth. The international DAFSAM-NELSAM*-projects focus on building the earthquake laboratory in deep gold mines in South Africa. Our DAFGAS-project (Drilling Active Faults - Gas Analytical System) aims to quantify the gases released during seismic events.
One motivation for the project is to investigate the hypothesis that released fluids might be a nutrient supply for microbial ecosystems in active fault zones. Extensive underground activities started in 2004 with establishing a 25 m2 cubby within the Pretorius fault zone at 3.6 km depth for the save installation of comprehensive technical equipment.
For DAFGAS, subsequently two different gas analytical units were installed to measure gases collected in a 40m long borehole crossing the fault. The DAFGAS Team and our collaborators overcame numerous technical problems. Since 2007 a dedicated air-conditioned box protects a mass spectrometer, pumps, a PC, a radon detector and electronics from the harsh underground environment. Since 2009 gas sensitive sensors and a data logger replace the spectrometer and the PC.
In parallel the NELSAM project has installed 9 seismometers in a narrow network surrounding the gas collection system. The accelerometers and geophones record mining activities (e.g. drilling and ore-production blasts) as well as tens of mining-induced earthquakes (magnitude = -4) on and around the Pretorius Fault each day.
Data from three years is presented: Borehole temperature at 40m increased by about 0.8 °C/year to 52.3 °C; different scales of pressure variations on surface (869±5) mbar (three-week mean, maximal and minimal daily mean) and below surface (1130±15) mbar are explained by the barometric formula. The major gas concentrations are constant and air-like with 78 % N2, 21 % O2, 1 % Ar, while the trace gas components CO2, CH4, He and H2 show most interesting trends and variations on weekly, daily, hourly and on the minute-by-minute basis. They are interpreted by means of time series and cross correlation analysis. He, CH4, CO2 and H2 fluxes positively correlate with mining induced seismic activity. The CO2 flux additionally correlates with air pressure. Gas flow rates of H2 and CO2 from the formation into the borehole are calculated for periods with and without mining activity. In passive times they amount to =(1 and 3)*10-7 mol/min and increase to (7.3±0.7)*10-7 and (4.5±0.6)*10-6 mol/min during times of mining induced seismic activity, respectively. The installed gas sensitive electrodes (O2, CO2, CH4 and H2) are clearly more suitable for the underground environment than the mass spectrometer. Their sensitivity is currently only sufficient for H2 and CO2 measurements, however.
*) Drilling Active Faults Laboratory in South African Mines - Natural Earthquake Laboratory in South African Mines
GeoFuture Workshop, 28.-29.11.2012, Potsdam, Deutschland
Mikrobielle Diversität im Tongestein (Opalinus-Ton) und Wechselwirkung dominanter Mikroorganismen mit Actiniden – Vorhaben BMWi 0210618
Moll, H.; Lütke, L.; Bachvarova, V.; Geissler, A.; Krawczyk-Bärsch, E.; Selenska-Pobell, S.; Bernhard, G.
Microorganisms exist in host rocks of potential nuclear waste disposals. In this talk, results will be presented from the current project about the microbial diversity in Mont Terri Opalinus clay and the interactions of dominant microorganisms with actinides. Especially the bacterial diversity investigations and the actinide (U, Cm, Pu) interactions with the novel Opalinus clay isolate Sporomusa sp. will be shown and discussed.
Keywords: curium; uranium; plutonium; TRLFS; bacteria; speciation
10. Projektstatusgespräch zu BMWi- und BMBF-geförderten FuE-Projekten der Endlagerforschung und der Nuklearen Sicherheitsforschung, 13.-14.11.2012, Karlsruhe, Deutschland
Irradiation system for pre-clinical studies with laser accelerated electrons
Schürer, M.; Baumann, M.; Beyreuther, E.; Brüchner, K.; Enghardt, W.; Kaluza, M.; Karsch, L.; Laschinksy, L.; Lessmann, E.; Nicolai, M.; Oppelt, M.; Reuter, M.; Richter, C.; Sävert, A.; Schnell, M.; Woithe, J.; Pawelke, J.
In recent years, the new technology of laser based particle acceleration was developed at such a rate that medical application for cancer therapy could become feasible. Promising more compact and economic proton and ion accelerators the laser technology however results in specific properties, like ultra-short (~ps) and ultra-intensive particle beam pulses. The clinical applicability of such new beam qualities requires comprehensive translational research from basic investigations to cell and animal experiments, finally followed by clinical trials. For the first time, the new laser based irradiation technology was established for animal experiments by the German joint research project “onCOOPtics”. A complete irradiation facility for laser accelerated electrons was developed, set up, commissioned, tested and applied for radiobiological tumour irradiation experiments under usage of a mouse model at the high intensity laser system JETI. The integration of a magnet and a collimator system resulted in an optimized beam transport and efficient electron energy filtration. Moreover, a specific irradiation and dosimetry setup was integrated allowing for the formation of irradiation fields, the real-time control of beam parameters and dose delivery to the tumour. For an accurate and reproducible positioning of the tumour in the irradiation field the mice were fixed in a movable box and the tumour position was online verified by means of a CCD camera system. The combination of both, the advanced laser accelerator system and the newly implemented irradiation and dosimetry setup allowed the successful performance of systematic radiobiological studies over months. Moreover, the practicability and easy handling of the system results in a reasonable duration of about 15 min for the whole procedure of mouse preparation, positioning and irradiation. In conclusion, the successful establishment of all technical requirements for and the performance of systematic animal studies with laser accelerated electrons mark an important step towards the clinical application of laser accelerated particle beams.
Biomedical Engineering / Biomedizinische Technik 57(2012), 62-65
BMT 2012 - Tagung der Biomedizinischen Technik in Jena, 16.-19.09.2012, Jena, Deutschland
Hydrolysis of Tetravalent Cerium for a Simple Route to Nanocrystalline Cerium Dioxide: An In Situ Spectroscopic Study of Nanocrystal Evolution
Ikeda-Ohno, A.; Hennig, C.; Weiss, S.; Yaita, T.; Bernhard, G.
Despite the rapid developments in recent nanocrystal research and their expanding applications, the evolution mechanism of nanocrystals remains veiled for the most part due to the lack of appropriate analytical techniques. Here we demonstrate one promising multi-spectroscopic approach for the in situ investigation of nanocrystal evolution. That is, the formation of nanocrystalline cerium dioxide (NC-CeO2) has been probed by dynamic light scattering (DLS), X-ray absorption spectroscopy (XAS) and highenergy X-ray scattering (HEXS). The obtained results indicate that the fine colloidal particles of NC-CeO2 are formed in an acidic aqueous solution simply through the hydrolysis of the initial precursor of small oligomer CeIV species. This information on how NCCeO2 evolves is fundamental to simplifying and alleviating the synthetic strategy for NC-CeO2 production.
Keywords: cerium; hydrolysis; lanthanides; nanomaterials; X-ray spectroscopy
Chemistry - A European Journal 19(2013), 7348-7360
Characterization of a solid Eu-borate species by TRLFS
Schott, J.; Acker, M.; Barkleit, A.; Taut, S.; Brendler, V.
Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers. The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution.
At pH 6 the formation of a Eu borate solid species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.
Keywords: lanthanides; actinides; europium; boric acid; borates; polyborates
BMWi-Verbundprojekttreffen „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen„, 29.-30.10.2012, Garching, Deutschland
Flüssigmetallbatterien als preiswerte stationäre Speicher - Strömungsmechanische Aspekte
Weier, T.; Stefani, F.; Seilmayer, M.; Weber, N.; Gundrum, T.; Gerbeth, G.
Flüssigmetallbatterien, d.h. elektrochemische Hochtemperaturbatterien mit vollständig flüssigem Inventar, werden derzeit als preiswerte Regelenergiespeicher diskutiert. Das ursprünglich auf kleinere Zellen als Bestandteil thermisch regenerierbarer Systeme gerichtete Konzept soll auf Zellen mit Grundflächen im Quadratmeterbereich übertragen werden.
Eine elektrochemische Zelle mit vollständig flüssigem Inventar hat eine Reihe von Vorteilen: bei gut abgestimmten Dichten von Elektrolyt und aktiven Materialien ist die Batterie selbstassemblierend, eine stabile Dichteschichtung bildet sich aus. Die strukturlosen (flüssigen) Elektroden sind für Alterungserscheinungen unanfällig, versprechen somit gute Zyklierbarkeit, die Kinetik an den flüssig-flüssig Phasengrenzen und die Diffusionsprozesse sind vergleichsweise schnell, was hohe Stromdichten ermöglicht. Als aktive Materialien können breit und ökonomisch verfügbare Ausgangsstoffe eingesetzt werden. Natrium-Schwefel und Natrium-Nickelchlorid Zellen teilen eine Reihe der obengenannten Vorteile, erfordern wegen der komplexen Konstruktion jedoch ein beträchtliches Investitionsvolumen. Die Ausnutzung positiver Skaleneffekte ist ein wichtiges Mittel zur Kostensenkung und die einfache Skalierbarkeit eine der grundlegenden Annahmen bei der Entwicklung von Flüssigmetallbatterien.
Hohe Stromdichten und große Phasengrenzflächen resultieren jedoch in erheblichen Zellströmen. Diese generieren Magnetfelder und mithin beträchtliche elektromagnetische Kräfte. Das flüssige Inventar der Zelle kann auf diese elektromagnetischen Einwirkungen mit Instabilitäten reagieren. Eine dieser Instabilitäten ist die Tayler-Instabilität. Sie führt zu einer starken Strömung im Zellvolumen, die in der Lage ist, die Dichteschichtung zu destabilisieren. In der Folge käme es zu einem Direktkontakt der Elektroden und einem Versagen der Zelle. Der Tayler-Instabilität lässt sich durch konstruktive Maßnahmen begegnen, die in der Lage sind, die gewünschte Skalierbarkeit zu gewährleisten. Sie werden im Vortrag diskutiert.
Keywords: liquid metal batteries; energy storage; Tayler instability
Sächsisches Forum für Brennstoffzellen und Energiespeicher, 23.10.2012, Leipzig, Deutschland
OECD PKL2 Project – Final Report on the ROCOM Tests
Kliem, S.; Franz, R.
In the frame of the OECD PKL 2 Project the Test G3.1 was conducted at the PKL test facility. This test was dedicated to the investigation of a fast cool down transient. The transient was initiated by a main steam line break. One of the main objectives of this test was the creation of an experimental data base for the qualification of thermal hydraulic codes against Pressurized Thermal Shock (PTS) and re-criticality aspects. The results of this test are documented in (Dennhardt, 2011). Roughly this test can be divided into two main phases. After opening of the leak on the secondary side of one steam generator, the increased heat transfer leads to an overcooling of the corresponding loop. This overcooling continues till the full evaporation of the steam generator. In the second phase of the transient the emergency core cooling (ECC) system is activated injecting highly borated cold water into the cold legs of two loops.
To investigate in more detail the thermal hydraulic behavior in both phases inside the reactor pressure vessel (RPV) complementary tests on the coolant mixing were conducted at the ROCOM (ROssendorf COolant Mixing) test facility. Experimental results at the RPV inlet derived from the Test G3.1 were used as boundary conditions for the ROCOM tests.
Altogether five ROCOM tests have been conducted within the OECD PKL2 Project. The tests ROCOM 1.1, 2.1 and 2.2 were dedicated to the overcooling phase of the related transient while the tests ROCOM 1.2 and 1.3 are dealing with the ECC injection phase of the transient.
Article, self-published (no contribution to HZDR-Annual report)
Forschungszentrum Rossendorf 2012
ISSN: 2191-8708, eISSN: 2191-8716
Entwicklung einer Version des Reaktordynamikcodes DYN3D für Hochtemperaturreaktoren
Rohde, U.; Apanasevich, P.; Baier, S.; Duerigen, S.; Fridman, E.; Grahn, A.; Kliem, S.; Merk, B.
Basierend auf dem Reaktordynamikcode DYN3D für LWR, wurde die Codeversion DYN3D-HTR für das Blockkonzept eines graphit-moderierten, helium-gekühlten Hochtemperaturreaktors entwickelt. Diese Entwicklung umfasst die:
- methodische Weiterentwicklung der 3D stationären Neutronenflussberechnung für hexagonale Geometrie (HTR-Brennelement-Blöcke),
- Generierung von Wirkungsquerschnittsdaten unter Berücksichtigung der doppelten Heterogenität,
- Modellierung der Wärmeleitung und des Wärmetransports in der Graphitmatrix.
Keywords: High temperature reactor; neutron transport; cross sections; heat conduction; CFD; transients
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-023 2012
ISSN: 2191-8708, eISSN: 2191-8716
Leitlinie für die Hirnperfusions-SPECT mit Tc-99m Radiopharmaka / Hirnperfusions-SPECT with 99mTc-labelled Radiopharmaceuticals DGN-Guidance (S1 Guideline)
Kranert, T.; Menzel, C.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Krause, B. J.; Kuwert, T.; Sabri, O.; Schreckenberger, M.; Tatsch, K.; Grünwald, F.
This paper describes the guideline for perfusion brain imaging with SPECT-technique published by the Association of the Scientific Medical Societies in Germany (AWMF).The purpose of this guideline is to provide practical assistance for indication, examination procedures, findings and their interpretation also reflecting the present state of the art.
Information and instruction are given regarding indication, preparation of the patients and examination procedures of brain perfusion SPECT, including preparation and quality control of the tracer as well as the radiation dosimetry, technical performance of image acquisition with the gamma-camera and image processing. Also advices for interpretation of findings are given. In addition, possible pitfalls are described.
- Nuklearmedizin 5(2013)52, 157-162
Contribution to WWW
AWMF online - Das Portal der wissenschaftlichen Medizin: http://www.awmf.org/leitlinien/detail/ll/031-016.html
Experimental database on steam-water flow with phase transfer in a vertical pipe
Lucas, D.; Beyer, M.; Szalinski, L.
The evolution of steam-water flow with an initial sub-cooling along an 8 m long pipe with an inner diameter of about 200 mm was measured to obtain a database suitable for the qualification of CFD-codes on poly-dispersed flows with phase transfer. Phase transfer has to be considered in Nuclear Reactor Safety Research, e.g. in case of sub-cooled boiling or bubble entrainment caused by Emergency Core Cooling (ECC) injection. Bubble size distributions are important, since the phase transfer rate is proportional to the interfacial area density. To develop and validate closure models for CFD codes experimental data with high resolution in space and time are required. The experiments were conducted at the TOPFLOW facility of the Helmholtz-Zentrum Dresden-Rossendorf. Steam was injected into upwards flowing sub-cooled water via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Pressure, steam and water flow rates and the sub-cooling were also varied. Measurements are done using wire-mesh sensors and thermocouples. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are available.
Keywords: two-phase flow; pipe flow; bubbles; experiment; phase transfer; condensation; CFD
Nuclear Engineering and Design 265(2013), 1113-1123
Special issue on quantum physics with non-Hermitian operators
Bender, C.; Fring, A.; Günther, U.; Jones, H.; (Editors)
The main motivation behind the call for this special issue was to gather recent results, developments and open problems in quantum physics with non-Hermitian operators. There have been previous special issues in this journal and elsewhere on this subject. The intention of this issue is to reflect the current state of this rapidly-developing field. It has therefore been open to all contributions containing new results on non-Hermitian theories that are explicitly PT-symmetric and/or pseudo-Hermitian or quasi-Hermitian. In the last decade these types of systems have proved to be viable self-consistent physical theories with well defined unitary time-evolution and real spectra. As the large number of responses demonstrates, this is a rapidly evolving field of research.
A consensus has been reached regarding most of the fundamental problems, and the general ideas and techniques are now readily being employed in many areas of physics. Nonetheless, this issue still contains some treatments of a more general nature regarding the spectral analysis of these models, in particular, the physics of the exceptional points, the breaking of the PT-symmetry, an interpretation of negative energies and the consistent implementation of the WKB analysis. This issue also contains a treatment of a scattering theory associated with these types of systems, weak measurements, coherent states, decoherence, unbounded metric operators and the inclusion of domain issues to obtain well defined self-adjoint theories. Contributions in the form of applications of the general ideas include: studies of classical shock-waves and tunnelling, supersymmetric models, spin chain models, models with ring structure, random matrix models, the Pauli equation, the nonlinear Schrödinger equation, quasi-exactly solvable models, integrable models such as the Calogero model, Bose–Einstein condensates, thermodynamics, nonlinear oligomers, quantum catastrophes, the Landau–Zener problem and pseudo-Fermions. Applications close to experimental realization are proposed in optics, including short light pulse models, waveguides and laser systems, and also in electronics.
Keywords: non-Hermitian operators; PT-symmetry; pseudo-Hermiticity; quasi-Hermiticity; exceptional points; Bose-Einstein condensate; shock waves; WKB analysis; Calogero model; spin chains; nonlinear oligomers; pseudo-fermions; waveguides; spectral properties; PT phase transition
Journal of Physics A 45(2012)44, 440301
In vivo imaging of lysyl oxidase by fluorine-18 labelled substrate-based radiotracers
Kuchar, M.; Lenk, J.; Bergmann, R.; Wodtke, R.; Mosch, B.; Steinbach, J.; Pietzsch, J.; Löser, R.
The ability of solid tumours to invade surrounding tissues and, in consequence, to metastasise to distant organs is mediated by bidirectional molecular interactions between tumour cells and the extracellular matrix [1,2]. Recently, the copper-dependent amine oxidase lysyl oxidase (LOX, EC 126.96.36.199) could be identified as one of the key players in these processes . Therefore, the development of molecular probes that enable the imaging of this enzyme in vivo by positron emission tomography (PET) was in the focus of this study.
As the enzyme is catalysing the oxidative crosslinking of lysine side chains in collagen and other extracellular proteins, the design of radiotracers based on substrates seemed to be promising. Thus, the N-terminal telopeptide of the alpha1-chain of type I collagen containing the key sequence Asp-Glu-Lys-Ser  and peptides derived from this were chosen to be functionalised with fluorine-18 at their N-termini. To achieve this, a method was developed that allows the site-selective 18F-fluorobenzoylation of peptides . The metabolic stability and biodistribution of these potential radiotracers was investigated in male wistar rats.
To estimate the potential of the different lysine-containing peptides for crosslinking with collagen in vivo, their interaction with bovine atelocollagen was investigated by surface plasmon resonance (SPR) experiments.
A panel of tumour cell lines was screened for expression of the enzyme.
The presence of LOX could be confirmed for the human breast cancer cell-lines MDA-MB-231, MCF-7 and the melanoma cell line A375 by RT-PCR as well as western blots. Based on the human A375 cell line, an animal model was established consisting of nude mice bearing tumours derived from these cells. Expression of LOX in the developed tumours was proven by immunohistochemical methods and western blots.
The developed labelling method for site-selective radiolabelling of peptides allowed to obtain the 18F-fluorobenzoylated telopeptide in high radiochemical yields and purities. All peptides show good stability in vivo and even no metabolites could be detected for the cyclopeptide. The biodistribution studies indicate no organ enrichment and fast renal elimination. For the first time, the telopeptide-collagen interaction could be studied quantitatively, indicating dissociation constants in the high micromolar range.
Despite unfavourable pharmokinetics due to fast blood clearance, the compounds show the potential to reflect the LOX acticity in vivo, as concluded from PET imaging experiments with nude mice bearing A375 tumours.
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3rd Annual Symposium "Physics of Cancer", 01.-03.11.2012, Leipzig, Deutschland
Validation of the RELAP5 code for the modeling of flashing-induced instabilities under natural circulation conditions using experimental data from the CIRCUS test facility
Rohde, U.; Kozmenkov, Y.
This paper reports on the use of the RELAP5 code for the simulation of flashing-induced instabilities in natural circulation systems. The RELAP 5 code is used for the simulation of transient processes in the Russian RUTA reactor concept operating at atmospheric pressure with forced convection of coolant. However, during transient processes, natural circulation with flashing-induced instabilities might occur. The RELAP5 code is validated against measurement data from natural circulation experiments performed within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of a typical natural-circulation-cooled BWR. It was shown that the RELAP5 code is able to model all relevant phenomena related to flashing induced instabilities. The magnitude and frequency of the oscillations were reproduced in a good agreement with the measurement data. The close correspondence to the experiments was reached by detailed modeling of all components of the CIRCUS facility including the heat exchanger, the buffer vessel and the steam dome at the top of the facility.
In the second part of the presentation, the impact of the modeling of subcooled boiling on natural circulation instability is considered. A transient with failure of all primary circulation pumps (initial event) and the failure of reactor SCRAM for the RUTA facility using the coupled neutron kinetics/thermo-hydaulic code systems DYN3D/ATHLET and DYN3D/RELAP5 was simulated. The predictions for initial and final reactor states given by the codes are in good agreement. However, the process of transition between these two states shows a qualitative difference. The DYN3D/RELAP5 code predicts unstable transient behavior of the reactor, while in the DYN3D/ATHLET simulation a smooth change of reactor parameters is observed during the whole accident. It was found that the different stability behavior is due to differences between the subcooled boiling models of the ATHLET and RELAP5 codes.
Despite the different performance of RUTA in the DYN3D/ATHLET and DYN3D/RELAP5 simulations of the accident the obtained results confirm a high intrinsic safety level for this reactor concept. In both compared calculations the allowed safety margins have not been reached. However, further validation of the subcooled boiling models on experiments at low pressure is necessary.
Keywords: boiling water reactor; natural circulation; instability; low pressure; flashing; experimental facility; subcooled boiling
Scientific Workshop on Reactor Dynamics and Safety 2012, 13.-14.09.2012, Dresden, Deutschland
Application of the method of uncertainty and sensitivity evaluation to results of PWR LBLOCA analysis calculated with the code ATHLET
Rohde, U.; Kozmenkov, Y.
Usually, safety analyses are based on the traditional conservative deterministic approach. However, the conservative approach does not allow evaluating the accuracy of results and their deviations from the real values. An alternative approach to reactor safety analyses uses best estimate computer codes together with quantification of uncertainties in model and plant parameters. Uncertainties in the results of safety analysis calculations are related to model uncertainties as well as deficiencies of knowledge of reactor initial conditions.
The German Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) has developed an approach to uncertainty analysis based on the Wilks’ theorem. According to that theorem, the number of calculations to be performed to get a probabilistic estimation of an output parameter with certain coverage at a certain confidence level (e.g., 95%/95%) does not depend on the number of statistically independent input uncertain parameters.
An important part of the analysis is devoted to the selection of the uncertain parameters and definition of the probability distributions and intervals of parameter variation. The variations should cover all parameters which are necessary to describe all phenomena relevant for the considered scenario. The parameter selection is based on a Phenomena Identification and Ranking Table (PIRT) elaborated based on engineering judgment.
In this paper, the results of an uncertainty and sensitivity analysis for a Large Break LOCA scenario for a generic German PWR of the Konvoi design are reported about. The accident was performed using the system code ATHLET Mod 2.2 Cycle A. 47 uncertain parameters were statistically varied, among them 32 model parameters, 7 plant initial state parameters and 7 core parameters. The EXEL-integrated software SUSA developed by GRS is used for generation of the uncertainty parameter vectors, their incorporation into ATHLET input files and for the result analysis. Investigation of the sensitivity of the output parameter (peak cladding temperature) from the uncertain input parameters reveals the most relevant parameters.
Results of this reference uncertainty analysis and a related sensitivity analysis are presented in this report.
Keywords: large break LOCA; uncertainty analysis; sensitivity analysis
22nd Symposium of Atomic Energy Research (AER) on VVER reactor physics and reactor safety, 01.-05.10.2012, Pruhonice, Czech Republic
Radiolabelling of engineered silver and titania nanoparticles as a tool for sensitive detection of nanoparticle release from surface coatings
Hildebrand, H.; Franke, K.; Gibson, N.; Cydzik, I.; Simonelli, F.; Bulgheroni, A.; Holzwarth, U.; Bilz, E.; Freyer, A.
Engineered nanoparticles (NPs) such as silver and titania are widely used in consumer products e.g. as functional additives in surface coatings. Due to aging or abrasion of these nanocomposites, particle release becomes likely and further transport e.g. in environmental systems could be assumed. Figure 1 shows results from a worst-case scenario study where NP release was enforced due to the use of a quite labile surface coating and photooxidative degradation of the nanocomposite catalysed by TiO2 anatase NPs. For conventional, more stable nanocomposites, accurate and sensitive detection and quantification of NP release is still a challenge due to the fact that released fractions might be small but nevertheless significant. The application of radiotracers provides the excellent option of “visibility”, traceability and quantification of NPs in complex media. Therefore, different radiolabelling strategies for engineered nanopowders (TiO2 P 25, Evonic Industries, dp = 21 nm; Ag0, Sigma Aldrich, dp < 100 nm) were established using a diffusive introduction of 110mAg radionuclides (t1/2 = 250 d) into Ag0-NPs (Hildebrand & Franke, 2012) and 44Ti radionuclides (t1/2 = 63 a) into TiO2-NPs through a low-temperature annealing procedure. Another radiolabelling strategy is the direct activation of Ag0 and TiO2 nanopowders that was done via proton irradiation using a Scanditronix MC40 cyclotron (Abbas et al. 2010, Holzwarth et al. 2012).
Both methods were tested with respect to labelling yield, achievable activity concentration, pH-dependent stability of the labelling and the influence on NP properties. Results obtained show an appropriate selection of radiolabeling methods suitable for different experimental conditions for NP release studies.
Figure 1: Time-dependent degradation of a polyacrylate TiO2 nanocomposite by UV-A-irradiation (intensity ~ 15 mW/cm2) ;A) original, B) after 2 days (50.000x); C) 4 days, D) 8 days, E) 16 days (75.000x); SEM micrographs: Leibniz Institute for Surface Modification.
Abbas K, Cydzik I, Del Torchio R, Farina M, Forti E, Gibson N, Holzwarth U, Simonelli F, Kreyling W (2010) J Nanopart Res 12:2435–2443.
Holzwarth U, Bulgheroni A, Gibson N, Kozempel J, Cotogno G, Abbas K, Simonelli F, Cydzik I (2012) J Nanopart Res 14:880
Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.
Keywords: engineered nanoparticles; radiolabelling; titania; silver
NanoSAFE'12, 13.-15.11.2012, Grenoble, France
Time-resolved photoluminescence quenching by intra-excitonic transitions in presence of external magnetic field
Bhattacharyya, J.; Zybell, S.; Helm, M.; Schneider, H.; Andrews, A. M.; Strasser, G.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Chatterjee, S.; Kira, M.; Koch, S. W.
We present our experimental results on the excitation and manipulation of intra-excitonic transitions in semiconductor quantum wells. We performed time resolved photoluminescence (PL) quenching measurements on a GaAs/AlGaAs multiple QW sample. The excitons were generated by near infrared pulsed laser excitation and intraexcitonic 1s-2p transition was induced by THz laser pulses resonant to the 1s-2p energy separation. We used the free electron laser at Helmholtz-Zentrum Dresden-Rossendorf as the THz source. Due to the population transfer from the 1s to the 2p, the PL intensity at 1s energy decreased abruptly during the incidence of the THz pulse. Such quenching of PL has been reported earlier for intersubband excitations .
Interestingly, a simultaneous increase in the PL is observed around the 2p energy. Since radiative recombination is forbidden for the 2p state the enhancement of the PL intensity at higher energy is attributed to emission from the 2s excitonic state, which is nearly degenerate with the 2p state. This implies an appreciable transfer of carriers from 2p to 2s state. This has been predicted in theory  and is explained to result from Coulomb scattering. Time resolved measurements allowed us to estimate the time-constants related to the carrier dynamics involved in this 2p-2s transfer. We were also able to control the 2s-2p carrier transfer by an external magnetic field. The energy separations between excitonic levels increase with increasing magnetic field . We employ this effect to reduce the 2p-2s carrier transfer observed as a decrease in the THz induced 2s emission. We can practically switch off this transfer by a magnetic field of about 2.5 T. We will also present a comparison of the experimental data with a microscopic theory which includes Coulomb induced excitonic scattering.
1) S. Zybell, et. al., Appl. Phys. Lett. 99, 041103 (2011)
2) M. Kira, et. al. Phys. Rev. Lett. 93, 076402 (2004)
3) H. A. Nickel, et. al. Phys. Rev. B 62, 2773 (2000)
Keywords: Magneto-photoluminescence; free electron laser; intraexcitonic transitions
11th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, 23.-27.09.2012, Stuttgart, Germany
Investigation of the life cycle of nanoparticles by means of [44,45Ti]TiO2 and [110mAg]Ag0 – Research project NanoTrack
Hildebrand, H.; Franke, K.; Freyer, A.; Bilz, E.; Mehnert, R.; Mai, E.; Isaacson, C.; Schirmer, K.; Ammann, A.; Sigg, L.
Production and application of nanocomposites such as functional surface coatings have significantly increased in recent years. Nanoparticle (NPs) coatings are used in a wide array of applications ranging from self-cleaning and scratch resistant surfaces to biocidal coatings. The current database for risk evaluation of NPs containing surface coatings (e.g. TiO2, Ag0) is still insufficient. Tools are currently lacking with which to assess the impact of TiO2 and Ag0 NPs. Radiolabeling of the NPs provides a method to sensitively detect NPs and is feasible for qualitative and quantitative fate and effects determination. With this detection method, evaluation of NPs fate during aging and abrasion of nanocomposites, estimation of release rates, transport of NPs in the environment and up-take and effects with organisms can be studied in great detail.
The joint research project NanoTrack uses model surface coatings in an acrylate-based formulation containing TiO2 (d = 21 nm, P25, Evonik Industries) and Ag0 NPs (d < 100 nm, Sigma Aldrich). Coatings were produced by application of 25 µm thick nanocomposite layers (thickness of wet coat) on a substrate followed by curing and later weathered under laboratory standard test conditions. Due to the low resistivity of this model system, the organic matrix of the surface coating was severely degraded and nanoparticles were partly released. Scanning electron microscopy showed that mostly aggregates and agglomerates of NPs were released and only a small fraction of primary NPs can be expected to be discharged. Nevertheless, further environmental processes can also lead to disaggregation and stabilization of smaller NPs composites.
Current studies on the environmental fate and effects of nanoparticles are limited by our inability to detect and quantify nanoparticles in complex environmental test systems and radiolabeling nanoparticles may provide a solution to this limitation. Isotopic labeling was carried out via a low-temperature diffusive implementation of radionuclides resulting in [44Ti]TiO2 and [110mAg]Ag0 NPs (Hildebrand & Franke, 2012). Chemical composition, particle size distributions and morphology of the radiolabeled NPs remained unaltered compared to the original material. Upon suspension in various test solutions, [44Ti] from TiO2 and [110mAg] from Ag0 NPs did not leach from the NPs and remained within the lattice framework of the NPs. Within the project, interactions of the NPs with environmental geological media (such as humic acids or sediments) and transport in flow through systems are under study.
Another important aspect is the ecotoxicological impact of the released NPs. In case of entry of the NPs in aquatic systems, interactions with living organisms become very likely. Biofilms are considered as potential receptor of industrial nanoparticles in the environment and as an important part of aquatic ecosystems it is not yet known if these NPs may end up in higher organisms via the food chain transfer. Systematic studies of NPs behavior in aquatic systems are carried out to gain knowledge of their fate and transport and potential risks for ecosystems.
The integrated examination of NPs in surface coatings in terms of production, aging and abrasion, NP release and their fate and transport in the environment provides a data base for risk assessment and validation or possibly adaptation of new nanocomposite production.
Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.
Keywords: radiolabeling; nanoparticles; titania; silver; life cycle assessment
NanoSAFE'12, 13.-15.11.2012, Grenoble, France
Properties of Ga implanted germanium and silicon
Fiedler, J.; Heera, V.; Skrotzki, R.; Herrmannsdörfer, T.; Voelskow, M.; Mücklich, A.; Skorupa, W.; Gobsch, G.; Helm, M.
Struktur und Eigenschaften dielektrischer Schichten für die Optik, 07.11.2012, Jena, Deutschland
Advanced Technologies for Bacterial Cell Encapsulation for Water Treatment
Vogel, M.; Lehrer, T.; Green, M.; Zussman, E.; Avrahami, R.; Kumar, D.; Tarre, S.; Raff, J.; Pollmann, K.
Encapsulation of whole bacterial cells using advanced technologies for water treatment is the objective of this cooperative research project. The use of electrospun polymeric microtubes by the Technion group and sol-gel ceramics by the Helmholtz-Zentrum Dresden-Rossendorf group are being investigated to encapsulate whole bacteria cells for two test cases, 1) encapsulation of Pseudomonas sp. ADP for atrazine (herbicide) removal, and 2) encapsulation of cell isolates of Bacillus spec. B5T for toxic metal removal. The project will advance new bacterial immobilization technologies for more efficient and cost effective bioremediation processes.
Keywords: encapsulation; water treatment
German-Israeli Cooperation in Water Technology Research: 12th Status Seminar 2012, 17.-18.10.2012, Haifa, Israel
Capability of nonlinear ultrasonic methods to monitor radiation damage in reactor pressure vessel steels
Matlack, K.; Wall, J.; Kim, J. Y.; Qu, J.; Jacobs, L. J.; Viehrig, H.-W.
Nonlinear ultrasonic methods have the potential to monitor increasing levels of irradiation damage in reactor pressure vessel (RPV) steels. Currently, there is no nondestructive evaluation method to monitor irradiation damage in RPV steels, so monitoring of structural material state relies on models and can result in costly and unnecessary shut-downs. Previous research shows that nonlinear ultrasonic methods are able to characterize irradiation damage since they are sensitive to microstructural changes such as dislocations and precipitates. Irradiation causes these microstructural changes in RPV steels, eventually resulting in embrittlement of the material. This embrittlement leaves the component susceptible to brittle fracture and irradiation-assisted stress corrosion cracking. In this work, the nonlinear ultrasonic parameter was measured on steel samples of typical RPV material with increasing levels of neutron fluence. A fixture was designed enabling a quick and intuitive set up for measurements. Results show that the nonlinear ultrasonic parameter can characterize increasing levels of fluence up to a certain level. Implications of these results in terms of future in situ monitoring of RPV steel components in nuclear reactors are discussed.
Keywords: Nonlinear ultrasound; Nondestructive evaluation; Irradiation damage; Reactor pressure vessel steel
NuMat 2012: The Nuclear Materials Conference, 22.-25.10.2012, Osaka, Japan
Wechselwirkungsstudien von Radionukliden mit makrozyklischen, multifunktionalen Chelatliganden
The aim of the present work was to investigate the extraction behaviour of various lower rim substituted calixarenes towards environmentally relevant radionuclides.
Extraction experiments were performed in a chloroform/water system and analysed by means of radiotracer technique. For 85Sr a carboxy-modified and for 56Co, 64Cu and 65Zn a salicylic-modified calixarene were found to be potent extracting agents under alkaline conditions. Depending on pH, the extractions are partially reversible. The experiments can be efficiently transferred to natural water samples.
Das Ziel der vorliegenden Masterarbeit war die Untersuchung des Extraktionsverhaltens diverser lower rim-modifizierter Calixarene bezüglich umweltrelevanter Radionuklide.
Die Extraktionsexperimente wurden in einem Chloroform/Wasser-System durchgeführt und mit Hilfe der Radiotracertechnik verfolgt. Unter alkalischen Bedingungen konnten für 85Sr ein Carbonyl-modifiziertes, und für 56Co, 64Cu und 65Zn ein salicyclidenartiges Calixaren als potente Chelatbildner eingestuft werden. Die Extraktionen sind, in Abhängigkeit vom pH-Wert, teilweise reversibel. Auf natürliche Wasserproben lassen sich die getätigten Experimente erfolgreich übertragen.
Universität Leipzig / HZDR, 2012
On the Use of a Molten Salt Fast Reactor to Apply an Idealized Transmutation Scenario for the Nuclear Phase Out
Merk, B.; Rohde, U.; Glivici-Cotruţă, V.; Scholl, S.
In the view of transmutation, molten salt fast reactors (MSFRs) offer certain advantages compared to solid fuelled reactor types. In the first part these advantages are discussed in comparison with the sodium cooled fast reactor technology, and the research challenges are analyzed. In the second part cycle studies for the MSFR are given for different configurations – a core with U-238 fertile, a fertile free core, and a core with Th-232 as a fertile material. For all cases, the transmutation potential is determined, and a significant improvement in the transmutation performance for the case with thorium as a fertile material is demonstrated. The time evolution of different important isotopes is analyzed. In the third part a strategy for the optimization of the transmutation efficiency is developed. The final aim is dictated by the phase out decision of the German government, which requests to put the focus on the determination of the maximal transmutation efficiency and on an as much as possible reduced left over of transuranium elements at the end of the reactor life. This minimal left over is achieved by a second deep burning phase. There the U-233, which is bred in the blanket of the core, is used as feed. It is demonstrated, that transmutation rates up to more than 90% can be reached, while the production of undesired high elements like californium is very limited. Additionally, the adaptations needed for the simulation of a MSFR, and the used tool HELIOS 1.10 are described.
Keywords: molten salt reactor; molten salt; fast reactor; nuclear power; nuclear reactor; partitioning & transmutation; transmutation; thorium; uranium; fertile free core; HELIOS
PLOS ONE 9(2014)4, e92776
Gammadensitometrische Gasgehaltsmessungen an einem beheizten Rohrbündel
Franz, R.; Sprewitz, U.; Hampel, U.
Im Rahmen eines vom Bundesministerium für Bildung und Forschung geförderten Projektes (Förderkennzeichen 02NUK010A) wurden an einem senkrechten, mit Flüssigkeit umströmten und beheizten Stabbündel gammadensitometrische Gasgehaltsmessungen durchgeführt. Es wurden zwei Messpositionen, zwei Volumenstromraten des umströmenden Fluides, zwei Unterkühlungswerte und elf Wärmestromdichten zur Messung gewählt. Der Bericht umfasst die Beschreibung des Versuchsstandes, die Messmethodik, Ergebnisse und deren Interpretation. Im Detail wird ebenfalls die Messunsicherheit bewertet.
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-028 2012
ISSN: 2191-8708, eISSN: 2191-8716
Assessment of spectral history influence on PWR and WWER core
Bilodid, Y.; Ovdiienko, I.; Mittag, S.; Kuchin, A.; Khalimonchuk, V.; Leremenko, M.
The few-group cross section libraries, used by reactor dynamics codes, are affected by the spectral history effect a dependence of fuel cross sections not only on burnup, but also on local spectral conditions during burnup. Neglecting this effect leads to an additional component of error in neutron-physical characteristics. Two solution approaches to this problem implemented in the reactor dynamic code DYN3D are described and compared in this paper: a cross section correction method based on Pu-239 concentration and separate cross sections treatment for each axial layer of reactor core. Steady-state and burnup characteristics of a PWR and a WWER-1000 cores, calculated by DYN3D with and without cross section corrections, are compared. An impact of the correction on transient calculations is studied for a control rod ejection example. Studies have shown a significant influence of spectral history on axial power and burnup distributions as well as on calculated cycle length. Two different correction methods have shown similar major effects.
Keywords: cross section library; history effects; spectral history; burnup; DYN3D
- Kerntechnik 77(2012)4, 278-285
OLDAPS – Obsidian Least Destructive Analysis Provenancing System
Eder, F. M.; Neelmeijer, C.; Pearce, N. J. G.; Sterba, J. H.; Bichler, M.; Merchel, S.
The natural volcanic glass obsidian is one of the classical objects of archaeometric analyses. Reliable provenancing by means of the highly specific chemical composition, the “chemical fingerprint”, can provide information about trading routes, extension of territory, long-distance contacts and the mobility of prehistoric people.
Since the pioneer work of Cann and Renfrew in 1964  various analytical methods have been employed on obsidian samples in order to locate their provenance. The existing data already offers important knowledge about long-distance interactions between prehistoric human populations. However, most applied techniques just show a small part of the element spectrum. Latest studies showed that published results gained by different analytical methods are not consistent due to systematic errors [2-3].
Therefore, the application of three complementary analytical techniques on the same set of raw material samples allows both a better characterization of obsidian sources and a comparison and validation of analytical results. The aim of this multi-methodical approach is to apply in particular:
- Ion Beam Analysis (IBA) comprising of Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE),
- Instrumental Neutron Activation Analysis (INAA),
- Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)
to detect a maximum element spectrum and to compare element concentrations determined with at least two analytical techniques. This approach should check the accuracy and reliability of analytical results and should show a maximum of compositional differences between European obsidian sources to reveal the most characteristic “chemical fingerprint” composed of more than 40 elements.
These investigations are part of a new multi-methodical analytical database called the “Obsidian Least Destructive Analysis Provenancing System” (OLDAPS). This novel scientific approach for provenancing obsidian artefacts found in archaeological contexts contributes to both conservation and prehistoric research by ensuring a minimum of destruction to gain a maximum of information. Besides, it enables to assess analytical accuracies of our archaeometric elemental analyses.
For this study, IBA, INAA and LA-ICP-MS measurements have been applied to the most relevant obsidian sources in central and southern Europe. IBA studies have been carried out using the external 4 MeV proton beam of the 6 MV Tandem accelerator of the Ion Beam Centre of HZDR. INAA investigations have been performed in the TRIGA Mark II 250 kW research reactor of the Atominstitut in Vienna. LA-ICP-MS measurements have been taken with the Thermo Element 2 ICP-MS coupled to an ArF gas Excimer laser system at the Aberystwyth University.
 J.R. Cann, C. Renfrew, Proc. Prehist. Soc. 30, (1964) 111-131.
 R.G.V. Hancock, T. Carter, J. Archaeol. Sci. 37, (2010) 243–250.
 G. Poupeau et al., J. Archaeol. Sci. 37, (2010) 2705-2720.
Keywords: PIXE; PIGE; archaeometry
13th International Conference on Particle Induced X-ray Emission and its Analytical Applications (PIXE), 03.-08.03.2013, Gramado, Brazil
Vergleich komplementärer „Fingerprint“-Techniken an europäischen Obsidianvorkommen
Eder, F. M.; Neelmeijer, C.; Pearce, N. J. G.; Sterba, J. H.; Bichler, M.; Merchel, S.
Obsidian ist ein natürliches, vulkanisches Glas, welches bei geeigneter Bearbeitung die Herstellung von sehr scharfen Werkzeugen und Waffen ermöglicht. Auf Grund dieser Eigenschaft war Obsidian einer der begehrtesten und daher weitest verbreiteten Rohstoffe in prähistorischen Kulturkreisen. Die Herkunftsbestimmung von Obsidianen, liefert somit Kenntnisse über ur- und frühgeschichtliche Handelsbeziehungen. Zur Charakterisierung von Obsidianen wird der sogenannte „chemische Fingerprint“ herangezogen, welcher die Bestimmung signifikanter Unterschiede in den Elementzusammensetzungen ermöglicht.
Seit der Pionierarbeit von Cann und Renfrew 1964  wurden zahlreiche Analysen mit den unterschiedlichsten Methoden durchgeführt. Die existierende Datenbasis hat bereits wichtige Erkenntnisse über die Verbreitung des Obsidians erbracht, wobei in den häufigsten Fällen nur Teile des Elementspektrums bestimmt wurden. Neueste Untersuchungen haben aufgezeigt, dass bei publizierten Herkunftsbestimmungen mit unterschiedlichen Methoden aufgrund systematischer Fehler nicht direkt vergleichbare Daten produziert wurden [2, 3].
Eine kombinierte Anwendung derAnalysemethoden:
- Instrumentelle Neutronenaktivierungsanalyse (INAA), durchgeführt am TRIGA Mk II Forschungsreaktor des Atominstituts der TU Wien
- Kombinierte externe Ionenstrahlanalytik: Particle Induced X-ray Emission (PIXE) und Particle Induced Gamma-ray Emission (PIGE), ausgeführt am 6 MV Tandembeschleuniger des HZDR
- Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) Messungen, durchgeführt an der Aberystwyth University, Wales, UK
Mit Hilfe dieser Analyseverfahren wurde eine methodenübergreifenden Datensammlung von Obsidian-vorkommen aus dem europäischen Raum erstellt. Diese Vorgehensweise liefert ein größtmögliches Elementspektrum aus mehr als 40 Elementen und enthüllt die signifikantesten Elemente zur Obsidiancharakterisierung (siehe Abb. 1).
Abbildung 1: Elementspektrum von Obsidian aus Demenegakion und Agia Nychia (Melos, Griechenland). Die Kombination von INAA-, PIXE & PIGE- und LA-ICP-MS-Daten liefert einen maximalen „chemischen Fingerprint“ von 41 Elementen. Die Normierung auf eine interne Obsidian-Referenzprobe aus Hrafntinnuhryggur (Island) ermöglicht eine eindeutige Unterscheidung der beiden Vorkommen in den Konzentrationen von Ca, Ti, Sc, Fe und Co.
Die unmittelbare Vergleichbarkeit der Resultate unter Berücksichtigung der jeweiligen Messunsicherheit ist essentiell für die Entscheidung, welche analytische Methode auf weitere archäologische Artefakte angewendet werden soll, um bei möglichst geringem Eingriff die aussagekräftigsten Informationen zu liefern.
 J.R. Cann, C. Renfrew, Proc. Prehist. Soc. 30 (1964) 111-132.
 R.G.V. Hancock, T. Carter, J. Archaeol. Sci. 37 (2010) 243–250.
 G. Poupeau et al., J. Archaeol. Sci. 37 (2010) 2705-2720.
Keywords: PIXE; PIGE; archaeometry; LA-ICP-MS
24th Seminar Activation Analysis and Gamma-Spectroscopy (SAAGAS 24), 26.-28.02.2013, Garching, Deutschland
U(VI)-Sorption und -Diffusion an/in Tonmineralen und Opalinuston – Einfluss von pH, Ionenstärke und Organika
Joseph, C.; Fritsch, K.; Steudtner, R.; Schmeide, K.
Tongestein wird als potentielles Wirtsgestein für ein Endlager für radioaktive Abfälle diskutiert. Im Vortrag werden dazu folgende Untersuchungen vorgestellt: Reinigung und Charakterisierung (CEC, BET, ICP-MS) der Tonminerale Illit und Montmorillonit; U(VI)-Sorption an Illit in Abhängigkeit vom pH-Wert mit dazugehöriger PHREEQC-Modellierung, Einfluss des Ca2+ auf die U(VI)-Speziation; U(VI)-Sorption an Montmorillonit in Abhängigkeit vom pH-Wert und der Ionenstärke; aktueller Stand der U(VI)-Diffusion in Ab- und Anwesenheit von Citronensäure.
Keywords: illite; montmorillonite; sorption; uranium(VI); diffusion; Opalinus Clay; citric acid; ionic strength
3. Workshop des Verbundprojekts „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen“, 29.-30.10.2012, München, Deutschland
Ultrasensitive Detection of Actinides by Accelerator Mass Spectrometry
Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.
Accelerator mass spectrometry (AMS) represents an ultrasensitive technique for quantifying long-lived radionuclides. The new AMS facility DREAMS (DREsden AMS) see fig. 1 will broaden the spectrum of measurable radionuclides like 10Be, 26Al, 36Cl, 41Ca  to actinides with the setup of a new time-of-flight (TOF) beam line.
AMS is capable of quantifying isotope ratios, i.e. stable nuclides are usually measured in Faraday-cups while radionuclides are counted by detectors like an ionization chamber. In comparison to α-spectrometry a relative simple chemical sample preparation can be applied and isotopes like 239Pu and 240Pu can be distinguished at the detector. AMS determines ratios as low as 10-16, thus, providing the lowest detection limit of all mass spectrometry methods . For long half-lives it is also more sensitive than decay counting techniques.
We expect about 100 events in the detector for samples containing an amount of about 104 to 106 atoms of the radionuclide in the ion source. As an example the sensitivity limit for a 236U/U ratio is about 10-12 .
This high sensitivity allows many applications from nuclear forensics, radiation protection, environmental monitoring to astrophysics. Isotopes measured by AMS are e.g. 236U, 237Np, 239,240,241,242,244Pu .
This setup will be also used in the future analyzing geological samples with high lateral resolution – without chemical sample preparation - a so called Super-SIMS – a combination of a SIMS (Secondary Ion Mass Spectrometry) with an accelerator.
 Akhmadaliev, S. et al. (2012) Nucl. Instr. and Meth. in Phys. Res. B, 6 pages, doi: 10.1016/j.nimb.2012.01.053.
 Fifield, L.K. (2008) Quaternary Geochronology 3, 276-290.
 Steier, P. et al. (2010) Nucl. Instr. and Meth. in Phys. Res. B 268,1045-1049
International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland
Radiation response of the overlay cladding from the decommissioned WWER-440 Greifswald unit 4 reactor pressure vessel
Viehrig, H.-W.; Altstadt, E.; Houska, M.
Results of tensile and crack extension testing conducted on irradiated austenitic overlay cladding material of WWER 440 reactor pressure vessels are presented. The specimens were sampled from three trepans originating from the decommissioned WWER-440 reactor pressure vessel of the nuclear power plant Greifswald Unit 4. Crack extension curves were measured with Charpy size SE(B) specimens using the unloading compliance technique according to ASTM E1820-11 at different temperatures. Crack initiation fracture toughness values JQ and KJQ are determined with the crack extension curves. The highest KJQ values were found in the temperature range from 20 to 75 °C. A significant scatter was observed in the initiation values. The reasons are seen in the scatter of the estimation of very low crack extensions and crack jumps caused by regions of low tearing strength in the overlay cladding. The comparison of the measured KJQ values and conservatively estimated stress intensity factors at an assumed surface crack shows that the cladding would remain intact during pressurized thermal shock transient.
Keywords: reactor pressure vessel; overlay cladding; ductile tearing; fracture toughness; integrity assessment
Nuclear Engineering and Design 286(2015), 227-236
Forcing of out-of-plane magnetic anisotropy in ultrathin Co films by ion irradiation
Ga+, He+ irradiated sapphire/Pt/Co(dCo)/Pt(dPt) ultrathin films were studied using polar Kerr effect in wide ranges of both cobalt dCo and platinum dPt thicknesses as well as ions fluences F. Ga+, He+ irradiation induce: creation of two branches with increased magnetic anisotropy and enhancement of Kerr rotation angle. Ga+ irradiation induces creation of two branches of out-of-plane magnetization state.
12th Joint MMM/Intermag Conference, 14.-18.01.2013, Chicago, Illinois, USA
Precise nuclear physics for the sun
For many centuries, the study of the Sun has been an important testbed for understanding stars that are further away. One of the first astronomical observations Galileo Galilei made in 1612 with the newly invented telescope concerned the sunspots, and in 1814, Joseph von Fraunhofer employed his new spectroscope to discover the absorption lines in the solar spectrum that are now named after him.
Even though more refined and new modes of observation are now available than in the days of Galileo and Fraunhofer, the study of the Sun is still high on the agenda of contemporary science, due to three guiding interests.
The first is connected to the ages-old human striving to understand the structure of the larger world surrounding us. Modern telescopes, some of them even based outside the Earth’s atmosphere in space, have succeeded in observing astronomical objects that are billions of lightyears away. However, for practical reasons precision data that are important for understanding stars can still only be gained from the Sun. In a sense, the observations of far-away astronomical objects thus call for a more precise study of the closeby, of the Sun, for their interpretation.
The second interest stems from the human desire to understand the essence of the world, in particular the elementary particles of which it consists. Large accelerators have been constructed to produce and collide these particles. However, man-made machines can never be as luminous as the Sun when it comes to producing particles. Solar neutrinos have thus served not only as an astronomical tool to understand the Sun’s inner workings, but their behavior on the way from the Sun to the Earth is also being studied with the aim to understand their nature and interactions.
The third interest is strictly connected to life on Earth. A multitude of research has shown that even relatively slight changes in the Earth’s climate may strongly affect the living conditions in a number of densely populated areas, mainly near the ocean shore and in arid regions. Thus, great effort is expended on the study of greenhouse gases in the Earth’s atmosphere. Also the Sun, via the solar irradiance and via the effects of the so-called solar wind of magnetic particles on the Earth’s atmosphere, may affect the climate. There is no proof linking solar effects to short-term changes in the Earth’s climate. However, such effects cannot be excluded, either, making it necessary to study the Sun.
The experiments summarized in the present work contribute to the present-day study of our Sun by repeating, in the laboratory, some of the nuclear processes that take place in the core of the Sun. They aim to improve the precision of the nuclear cross section data that lay the foundation of the model of the nuclear reactions generating energy and producing neutrinos in the Sun.
In order to reach this goal, low-energy nuclear physics experiments are performed. Wherever possible, the data are taken in a low-background, underground environment. There is only one underground accelerator facility in the world, the Laboratory Underground for Nuclear Astrophysics (LUNA) 0.4MV accelerator in the Gran Sasso laboratory in Italy. Much of the research described here is based on experiments at LUNA. Background and feasibility studies shown here lay the base for future, higher-energy underground accelerators. Finally, it is shown that such a device can even be placed in a shallow-underground facility such as the Dresden Felsenkeller without great loss of sensitivity.
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-024 2012
ISSN: 2191-8708, eISSN: 2191-8716
Quantitative dopant profiling in semiconductors: A new approach to Kelvin probe force microscopy
Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.
Keywords: semiconducting devices; doping profile; Kelvin probe force microscopy; KPFM
Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-026 2012
ISSN: 2191-8708, eISSN: 2191-8716
Fine distributed moderating material to enhance feedback coefficients in lead cooled fast reactor experiment
Recently, the use of moderating materials in fuel assemblies for Sodium cooled fast reactors (SFRs) has been investigated and published in several papers (Annals of Nuclear Energy 38, 5, Annals of Nuclear Energy 38, 11 (2011)). Especially the fine distribution of the moderating material has shown very promising results for the enhancement of the feedback coefficients in Sodium cooled fast reactors. The validity of the HELIOS results has been demonstrated in a comparison with MCNP and the transferability of the effect to full core calculations has been shown.
In a new attempt, it will be demonstrated, that the concept of enhanced feedback coefficients is transferable to lead cooled fast reactors (LFRs). The demonstration is based on a test for the configuration of the zero power experimental setup GUINEVERE in the VENUS facility at SCK•CEN in Mol/Belgium, since this experiment could serve for a first real experimental test to confirm the simulations. The calculations are based on the preliminary design of the fuel assemblies of the currently running subcritical experiments at GUINEVERE. The effect of the moderating material on the neutron spectrum, on the kinf, and on the fuel temperature feedback of the zero power facility is shown, discussed and compared to SFRs. The thermal stability of the hydrogen bearing compound is of paramount importance for the use of moderating material in a LFR. An insight will be given into the relationship of the hydrogen content of the compound and the resulting thermal stability. Thermal stability of the moderating material up to more than 1300°C can be ensured by the use of Yttrium-mono-hydride as moderating material.
Over all it is demonstrated, that the use of fine distributed moderating material has the potential to open the stage for designable feedback coefficients not only in sodium cooled fast reactors, but also in lead cooled fast reactors. An important point is that the enhanced feedback effects can be achieved without creating a major influence on the operational parameters and core coolability.
Keywords: Lead Cooled Fast Reactor; Fast Reactor; Enhanced Feedback Effects; Moderating Material; Yttriumhydride; GUINEVERE
Contribution to proceedings
2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
Proceedings of ICAPP'13
2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
The molten salt fast reactor as transmutation system in the view of the nuclear phase-out
Merk, B.; Rohde, U.; Scholl, S.
The basic development and design of a molten salt reactor with fast neutron spectrum (Molten Salt Fast Reactor – MSFR) is the target of the EVOL project in FP7. The MSFR offers certain advantages in the view of transmutation compared to solid fuelled reactor types. In the first part, these advantages will be discussed in a comparison with the sodium cooled fast reactor technology and the research challenges will be analyzed.
In the second part, a strategy for the optimization of the transmutation efficiency is developed, based on the findings of a former study, for different configurations – core with U-238 fertile, a fertile free core and a core with Th-232 as fertile material. The study has identified advantageous use of Thorium as fertile material. The final aim of this study is dictated by the phase out decision of the German government. Transmutation in the German view thus is focused on the determination of the maximal transmutation efficiency and on an as much as possible reduced left over of transuranium elements (TRUs) in the end of reactor life core. This is a prerequisite, since there is no future reactor foreseen and the reminders have to be put into a final repository. This minimal left over is achieved by a two step operation, first a TRU burning phase with continuous feed in a salt configuration with Thorium as fertile material, second a deep burning phase utilizing the U-233 bred in the blanket of the core as feed. In the calculation results, the time evolution of different important isotopes will be analyzed for both phases. It will be demonstrated, that transmutation rates up to more than 90% can be reached, while the production of undesired high elements like Californium is very limited. Based on these results a rough approximation will be given on the required number of reactors for the transmutation of the German TRU stockpile and the left over will estimated. Additionally, the used tool HELIOS 1.10 and the adaptations needed for the simulation of a MSFR will be described.
Keywords: Transmutation; Molten Salt Reactor; Molten Salt Reactor; Thoruim; Nuclear Phase Out
Contribution to proceedings
2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
Proceedings of ICAPP'13
2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
Acceleratorbased super-radiant coherent THz sources: Challenges and Opportunities
The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators . A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th generation X-ray light sources such as FLASH [2,3,and 4] and LCLS . This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges ranging.
 G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
 M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
 U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
 F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light
sources, Nat. Photon. 5 (2011), 162.
 D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent
transition radiation, Appl. Phys. Lett. 99 (2011), 141117.
Invited lecture (Conferences)
Seminar des Fritz Haber Instituts, 22.10.2012, Berlin, Deutschland
Temperature stable 1.3 um emission from GaAs
Prucnal, S.; Gao, K.; Anwand, W.; Helm, M.; Skorupa, W.; Zhou, S.
Gallium arsenide has outstanding performance in optical communication devices for light source purposes. Different approaches have been done to realize the luminescence from GaAs matching the transmission window of optical fibers. Here we present the realization of quasi- temperature independent photoluminescence at around 1.3 um from millisecond-range thermally treated GaAs. It is shown that the VAs donor and X acceptor pairs are responsible for the 1.3 um emission. The influence of the flash-lamp-annealing on the donor-acceptor pair (DAP) formation in the nitrogen and manganese doped and un-doped semi-insulating GaAs wafers were investigated. The concentration of DAP and the 1.3 um emission can be easily tuned by controlling doping and annealing conditions.
Keywords: Optical communications; Optical properties; Photoluminescence; Ion Implantation; GaAs; Flash Lamp Annealing
- Optics Express 20(2012), 26075-26081
A 3D-QSAR Model for Cannabinoid Receptor (CB2) Ligands Derived from Aligned Pharmacophors
Günther, R.; Deuther-Conrad, W.; Moldovan, R.; Fischer, S.; Brust, P.
Cannabinoid (CB) receptors have gained much attention as markers for various brain tumours and potential therapeutic targets of neuropathic pain and mood disorders. Two CB receptors have been cloned and described: CB1, predominantly expressed in the brain and CB2, primarily found in the peripheral system but also in brain. The CB2 receptor is suggested to be involved in various neurodegenerative diseases, such as Alzheimer's or Parkinson's disease . Early and non-invasive diagnosis and therapy monitoring of such diseases is desired. Positron-Emission-Tomography (PET) allows imaging of functional processes in living humans. For this, compounds with positron emitting labels like 18F are used. Due to the high sensitivity of PET, such radiotracers must bind to the target protein with high selectivity.
Here, we utilise AutoGPA  implemented in the modelling suite MOE (Chemical Computing Group Inc., Montreal) to compute grid potentials build upon a 3D-QSAR model derived from a library of CB2 selective N-Aryl-oxadiazolylpropionamides.
Since a proper alignment of the molecules prior the analysis is crucial to the successful application of these models in further studies, the molecules were aligned based on their pharmacophore features. The obtained model delivers also knowledge of the 3D-structure of the binding site, which, in turn, can be used to refine 3D-models of the CB2 receptor. The steric and electrostatic contour maps are applied for identification of regions suitable for labelling with 18F, the most preferred PET radionuclide.
 Scotter EL, Abood ME, Glass M: The Endocannabinoid System as a Target for the Treatment of Neurodegenerative Disease. Br J Pharmacol 2010, 160:480-498
 Asakawa N, Kobayashi S, Goto J, Hirayama N: AutoGPA: A novel 3D-QSAR method based on grid potential analysis and pharmacophore alignment. Poster presentation at 10th InCoB - 1st ISCB Asia Joint Conference (InCoB2011/ISCB-Asia 2011); Kuala Lumpur, Malaysia
8th German Conference on Chemoinformatics (GCC2012), 11.-13.11.2012, Goslar, Deutschland
BIOTEC Forum "Bioinformatics and Computational Biology", 06.-07.12.2012, Dresden, Deutschland
The generalized two phase flow CFD model (GENTOP)
Lucas, D.; Hänsch, S.; Krepper, E.; Höhne, T.
In recent years many attempts were done to qualify CFD codes for multiphase flows. There is a clear progress e.g. for simulating dispersed bubbly or droplet flows on the one hand and stratified flows with large interfaces on the other hand. However many multiphase flows occurring in nature and technical applications are characterized by transitions between dispersed and continuous morphologies. Examples are bubble entrainment caused by plunging jets or by rolling waves. With presently available CFD-codes such transitions can be simulated only for some idealized cases. Simulations applying the multi-fluid model which is frequently applied for simulations on large technical systems provide some results for such transitions but they are rather caused by numerical effects than on physical basis. For this reason a new concept basing on the multi-fluid model and combining the previously developed MUSIG (Multi size bubble group model) and AIAD (Algebraic Interfacial Area Density) approaches was developed. It can be considered as a two-phase, three-field approach which includes a continuous liquid phase, one or more dispersed gas phases and a continuous gas phase. Transitions between dispersed and continuous gas phases are reflected by coalescence and breakup models. The paper presents the GENTOP concepts and simulations demonstrating the capabilities of the concept.
6th Japanese - European Two-Phase Flow Group Meeting, 23.-27.09.2012, Kumamoto, Japan
Validation of models for bubbly flows and cap flows using one-group and two-group average bubble number density
Yeoh, G. H.; Cheung, S. C. P.; Tu, J. Y.; Lucas, D.; Krepper, E.
Gas-liquid flows with wide range of bubble sizes are commonly encountered in many nuclear gas-liquid flow systems. In tracking the changes of gas volume fraction and bubble size distribution under complex flow conditions, numerical studies have been performed to validate predictions of the onegroup and two-group approaches against experimental measurements for upward gas-liquid flows in vertical pipes. These experiments have been strategically chosen because of particular flow conditions yielding specific trends of bubble size evolution, which provided the necessary means of carrying out thorough assessments of bubble coalescence and break-up kernels. Predictions of one-group approach for bubbly flows were in good agreement with experimental data. Predictions of two-group approach for bubbly and cap flows were in reasonable agreement with experimental data; additional insights into the appropriate bubble interaction mechanisms are still required for cap flows. Nevertheless, the encouraging results demonstrated the capability of both approaches in capturing the dynamical changes of bubbles size due to bubble interactions and the transition from “wall peak” to “core peak” gas volume fraction profiles caused by the presence of small and large bubbles.
Contribution to proceedings
CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
Numerical simulation and modeling of a laboratory MWD mud siren pressure pulse propagation in fluid filled pipe
Namuq, M. A.; Reich, M.; Al-Zoubi, A.
This article presents modeling and numerical simulations of a laboratory mud siren pressure pulse propagation in a water filled pipeline. The unsteady flow behavior is simulated and modeled with ANSYS CFX11 (Computational Fluid Dynamics (CFD) commercial code). Time domain simulations were performed for three different carrier frequencies of the mud siren, and the results were also analyzed in frequency using a Fast Fourier Transformation code in MATLAB. The estimated results from the model are compared with real experimental data in both time and frequency domain in order to validate the model. A pretty good agreement is obtained between the predicated and measured pressure pulses at different locations along the pipeline for all experimental runs.
- Oil Gas European Magazine 38(2012)3, 125-131
Microscopic observation of aerosol particle deposition in turbulent channel flows
Barth, T.; Lécrivain, G.; Lehmann, A.; Preuss, J.
The transport behaviour of carbonaceous dust in the primary circuit of a High Temperature Reactor (HTR) plays an important role in the safety assessment during a Design Basis Accident (DBA). Carbonaceous dust is formed mainly due to friction between graphite fuel elements (Kissane, 2009). In a pebble bed reactor the dust forms due to abrasion of graphite material between the pebbles. During reactor operation it is a safety issue to precisely predict the dust deposition and the corresponding resuspension rate of particles released into the containment during a DBA.
Deposition of aerosol particles has been investigated e.g. by Sippola & Nazaroff (2004). These experiments have been performed in steel ducts at Reynolds numbers and with particle relaxation times observed in a HTR. Their results follow the “v-shaped” curve of the non-dimensional deposition velocity against particle relaxation time and show a dependency on flow speed, particle size and orientation of the duct.
More recently, an Euler-Lagrange CFD simulation of particle deposition in a turbulent square duct flow has been performed by Lecrivain (2012). It was found that the friction velocity significantly influences the particle deposition velocities.
Deposition experiments of liquid and solid particles in a fully developed horizontal turbulent square duct flow are performed to further study the deposition behaviour of aerosol particles. The oil liquid particles (DEHS) are generated by a condensational aerosol generator (TOPAS, SLG 270). The aerodynamic particle size distribution and the particle number concentration of the suspended particles are determined by isokinetic sampling using an Aerodynamic Particle Sizer Spectrometer (TSI. APS 3321). The particle size distributions are fairly monodisperse for particles with daero = [1.5, 2.5, 3.5, 4.5] µm. The solid aerosol particles are microspheres (AkzoNobel, Expancel DU, d50 = 6.5 µm) and are injected into the flow field by means of a solid aerosol generator (TOPAS, SAG 410). The particle mass flow rate and the particle concentration are precisely adjusted by the feed rate of the SAG. The particle size distribution of the airborne particles is measured by means of Scanning Electron Microscopy (SEM). The size distributions gained by the APS and the SEM analysis are used to calibrate the size distributions obtained by an optical microscope.
A commercial light microscope equipped with a CMOS camera is mounted underneath the test section of the channel. It is focused on the inside surface of the channel floor which consists of a glass plate coated with indium tin oxide to remove electrostatic charges. This allows a time-resolved in situ observation of the particle deposition processes. A standard LED light source illuminates the microscope’s 6 x 4 mm² field of view and the CMOS camera records the scatter light of the wall deposited particles. The measurement uncertainty for particles larger than 2 µm is assumed to be 24%.
Figure 1 illustrates the time averaged deposition velocities for varying friction velocities. The CFD results of Lecrivain (2012) and Sipolla & Nazaroff (2004) are also plotted for comparison purposes. In the particle relaxation time range τ+ = 0.001..10 the deposition velocity increases with decreasing friction velocity. which is also observed elsewhere. It is assumed that the effect of gravitational settling leads to an increase of deposition velocity for decreasing flow speed. The results of this study also capture this tendency. Nevertheless, the scatter in the data has to be further investigated.
Keywords: Turbulent flow; particle deposition; microscopic observation; isokinetic sampling; spectrometry
European Aerosol Conference 2012, 02.-07.09.2012, Granada, Spanien
Effect of the Lagrangian integral time scale estimation on particle deposition
Lecrivain, G.; Barth, T.; Hampel, U.
In a high temperature pebble-bed reactor, carbonaceous dust is conveyed by the cooling carrier phase and eventually deposits in the primary circuit of the reactor. In hypothetical severe accident, a dose of radioactive graphite dust may escape the system boundaries. The accurate prediction of transport and deposition of graphite particles is therefore a key primary safety issue.The numerical prediction of carbonaceous dust transport and deposition in turbulent flows is a key safety issue. Most particle tracking procedures make use of the Lagrangian integral time scale to reproduce the turbulent dispersion of the discrete phase. In the present Lagrangian particle tracking procedure, the effect of the Lagrangian integral time scale near the wall is thoroughly investigated.
Keywords: nuclear aerosols; deposition velocity; numerical simulation; CFD
European Aerosol Conference 2012, 02.-07.09.2012, Granada, Spain
Simulation of particle deposition and layer formation between periodic steps
Lecrivain, G.; Drapeau-Martin, S.; Reiche, M.; Barth, T.; Hampel, U.
In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 8,000. Particles in the size range d = 1...100µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site
Keywords: Particle deposition; particle dispersion; graphite particles; dust layer build-up; turbulent flow; obstructed channel flow
13th Workshop on two-phase flows, 17.-20.09.2012, Halle, Deutschland
Selective Extraction of 85Sr2+ with modified Calixarenes in a liquid-liquid system
Poetsch, M.; Mansel, A.; Schnorr, R.; Haupt, S.; Kersting, B.
90Sr is a long-lived radionuclide (T1/2 = 28.6 a), which is produced as a by-product in nuclear power plants in the decay chain of uranium. In case of release in the biosphere, it can be concentrated in aquatic systems or in soil. It follows the food chain from environment to fauna and human. Due to its chemically similarity to calcium, it can be incorporated in bones. Stable isotopes of strontium might not be harmful, but radioactive analogues can lead to bone disorders and diseases, including leukaemia .
Calixarenes represent an important class of supramolecules having various applications, e.g. in the recovery of nuclear fission products of uranium, like cesium or strontium. We synthesised and structurally analysed calixarene-based extractants as shown in Fig. 1 in order to investigate their binding ability towards strontium in liquid-liquid extraction systems.
An aqueous phase was traced using the short-lived radionuclide 85Sr (T1/2 = 64.9 d), which was produced and purified at the in-house 18 MeV-cyclotron . To quantify the extraction behaviour of the calixarenes, the remaining amounts of 85Sr in the aqueous phases after the extraction, were recorded using gamma spectrometry. We systematically investigated the influence of various experimental parameters. Figure 1 shows extraction behaviour of various calixarene derivatives depending on the pH of the aqueous strontium phase. Under alkaline conditions of the aqueous strontium phase, extraction yields of >(90±4)% were obtained for calixarenes derivatives having carbonyl binding sites. Furthermore, the competition of inorganic and organic impurities to the extraction performance was studied. The impurities are in naturally occurring concentrations of ions like sodium, calcium, acetate or tartaric acid as groundwater ingredients. By simulating a synthetic groundwater, extraction of strontium was per-formed in yields up to (86±6)%.
In further experiments, the calixarene-strontium complex is going to be analysed spectroscopically with the aim to investigate the complex formation behaviour.
The authors gratefully thank the German Federal Ministry of Education and Research (BMBF) for financial support of this study (project no. 02NUK014).
 Wallova, G., N. Kandler, and G. Wallner, Monitoring of radionuclides in soil and bone samples from Austria. Journal of Environmental Radioactivity, 2012. 107: p. 44-50.
 Otho, K., Review of the extraction behavior of metal cations with calixarene derivatives. Solvent Extraction Research and Development, 2010. 17: p. 1-18.
 Mansel, A., et al., Production of 85Sr at a 18 MeV-cyclotron and purification for geochemical investigations, 2012. (submitted)
Keywords: calixarene radio strontium liquid-liquid extraction complex
Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland
CMOS integrated antenna-coupled field-effect-transistors for the detection of radiation from 0.2 to 4.3 THz
Boppel, S.; Lisauskas, A.; Mundt, M.; Seliuta, D.; Minkevičius, L.; Kašalynas, I.; Valušis, G.; Krozer, V.; Mittendorff, M.; Winnerl, S.; Roskos, H. G.
Using 150-nm CMOS process technology, various patch antenna coupled detectors have been implemented with different antenna resonance frequencies spanning from 0.2 to 4.3 THz.. These devices employ self-mixing in n-channel field-effect transistors and operate well above the transistors’ cutoff frequency. Detector designs are based on a novel concept which couples the signal to the drain, which facilitates detection also at electronic frequencies applicable to e. g. device calibration. The theoretical description of device operation by Dyakonov and Shur is extended to include the new boundary conditions and any gate bias. Additionally device impedance, responsivity and noise equivalent power are considered. The different transport regimes (i.e. quasi-stationary (QS), distributed resistive and plasmonic mixing) and their transitions are theoretically discussed and experimentally accessed. Responsivity values of 1344 V/W at 585 GHz, 90 V/W at 3.1 THz and 11 V/W at 4.3 THz are reported. At 0.585 THz we report the optical noise-equivalent-power (NEP) of 13 pW/√Hz at optimum gate bias and at 3.1 THz of 163 pW/√Hz. Under ideal 0.585 THz coupling conditions and room temperature operation, a NEP as low as 2 pW/√Hz is predicted. All values are normalized to the physical antenna area.
Keywords: Submillimeter wave detectors; Terahertz detectors; patch antennas; CMOS; terahertz direct detection; distributed resistive self-mixing; plasmonic detection
IEEE Transactions on Microwave Theory and Techniques 60(2012)12, 3834-3843
Universal phase relation between longitudinal and transverse fields observed in focused terahertz beams
Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.
We directly observe longitudinal electromagnetic fields in focused freely propagating terahertz beams of radial and linear polarization. Employing electro-optic detection, which is phase sensitive, allows one to selectively detect longitudinal and transverse field components. A phase shift of pi/2 between transverse and longitudinal field components is revealed. This phase shift is of universal nature, as it does not depend on the mode, frequency and focusing conditions. We show that the universal phase relation is a direct consequence of the divergence-free nature of electromagnetic waves in vacuum. In the experiments we observe the phase shift of pi/2 for all frequency components of single-cycle THz radiation pulses of both radial and linear polarization. Additionally we show that the longitudinal field of a radially polarized THz beam has a smaller spot size as compared to the transverse field of a linearly polarized beam that is focused under the same conditions. For field-sensitive measurements this property can be exploited even for moderate focusing conditions. Furthermore the phase-sensitive detection of longitudinal electromagnetic fields opens up new possibilities to study their interaction with electronic excitations in semiconductor nanostructures.
Keywords: longitudinal electromagnetic fields; terahertz vector beams; Bessel Gauss beams; radially polarized beams
New Journal of Physics 14(2012), 103049
Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior
Winnerl, S.; Göttfert, F.; Mittendorff, M.; Schneider, H.; Helm, M.; Winzer, T.; Malic, E.; Knorr, A.; Orlita, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.
We present the results of pump-probe experiments on multilayer graphene samples performed in a wide spectral range, namely from the near-infrared (photon energy 1.5 eV) to the terahertz (photon energy 8 meV) spectral range. In the near infrared, exciting carriers and probing at higher photon energies provides direct evidence for a hot carrier distribution. Furthermore spectroscopic signatures of the highly doped graphene layers at the interface to SiC are observed in the near-infrared range. In the mid-infrared range, the various relaxation mechanisms, in particular scattering via optical phonons and Auger-type processes, are identified by comparing the experimental results to microscopic modelling. Changes from induced transmission to induced absorption are attributed to probing above or below the Fermi edge of the graphene layers. This effect occurs for certain photon energies in the near infrared range, where it is related to highly doped graphene layers at the interface to SiC, and in the far infrared range for the quasi-intrinsic graphene layers. In addition to the relaxation dynamics, the saturation of pump-induced bleaching of graphene is studied. Here a quadratic dependence of the saturation fluence on the pump photon energy in the infrared spectral range is revealed.
Keywords: relaxation dynamics in graphene; ultrafast spectroscopy on graphene; graphene saturable absorber
Journal of Physics: Condensed Matter 25(2013), 054202
Large area photoconductive THz emitter for 1.55 µm excitation based on an InGaAs heterostructure
Mittendorff, M.; Xu, M.; Dietz, R. J. B.; Künzel, H.; Sartorius, B.; Schneider, H.; Helm, M.; Winnerl, S.
We present scalable large area terahertz (THz) emitters based on a nanoscale multilayer InGaAs/InAlAs heterostructure and a microstructured electrode pattern. The emitters are designed for pump lasers working at the telecommunication wavelength of 1.55µm. Electric THz fields of more than 2.5 V/cm are reached with moderate pump powers of 80 mW, the corresponding spectrum extends up to 3 THz. The saturation characteristics have been investigated for different pump laser spot sizes. For small pump powers of less than 50 mW the emitted THz field is nearly independent of the spot size, for higher pump powers and small spot sizes a clear saturation of the generated THz pulse can be observed. Hence the usage of scalable emitters is especially promising for high power fibre laser systems. The spectral content of the generated radiation is nearly independent of the parameters spot size, pump power, and bias voltage, which allows for stable operation in spectroscopic applications.
Keywords: photoconductive THz emitter; 1.55 µm excitation; InGaAs-based THz emitter
Nanotechnology 24(2013)21, 214007
Influence of intergranular exchange coupling on the magnetization dynamics of CoCrPt:SiO2 granular media
We investigate the effect of Co+ irradiation on the magnetization dynamics of CoCrPt:SiO2 granular media. Increasing irradiation levels reduce the saturation magnetization and effective anisotropy, which decrease the intrinsic magnetization precession frequency. Furthermore, increasing intergranular exchange coupling results in a qualitative change in the behavior of the magnetic material from a collection of individual grains to a homogeneous thin film, as evidenced in both the switching behavior and dynamics. The frequency change cannot be explained by single crystal macrospin modeling, and can only be reproduced by the inclusion of the dipolar effects and anisotropy distribution inherent in a granular medium.
Keywords: ion irradiation; ion implantation; magnetism; magnetic storage
Journal of Applied Physics 112(2012), 033918
GPGPU for Kinetic Lattice Monte Carlo Simulations
Kinetic lattice Monte Carlo (KLMC) methods have for long been applied successfully for the atomistic large scale simulations of processes like annealing or ion beam treatment as well as for the study of scaling phenomena. Increasing the size of simulated systems is indispensable to get closer to the experiment as well as obtaining more accurate numerical estimates. In a time of stagnating sequential performance in computers parallelization is the only way to reach this goal. We have successfully taken on the implementation of two different methods for GPUs. In this talk I will outline the potential of general purpose processing on GPUs (GPGPU) for KLMC methods alongside presenting some of our key results.
CCoE Seminar, 11.10.2012, TU-Dresden WIL/A317, Deutschland
GGR Biennial Critical Review: Analytical Developments Since 2010
Wiedenbeck, M.; Bugoi, R.; Duke, M. J. M.; Dunai, T.; Enzweiler, J.; Horan, M.; Jochum, K. P.; Linge, K.; Košler, J.; Merchel, S.; Morales, L.; Nasdala, L.; Stalder, R.; Sylvester, P.; Weis, U.; Zoubir, A.
Advances in the chemical and isotopic characterisation of geological and environmental materials can often be ascribed to technological improvements in analytical hardware. Equally, the creation of novel methods of data acquisition and interpretation, including access to better reference materials, can also be crucial components enabling important breakthroughs. This biennial review highlights key advances in either instrumentation or data acquisition and treatment which have appeared since January 2010. This review is based on the assessments by scientists prominent in each of the given analytical fields; it is not intended as an exhaustive summary, but rather provides insight from experts of the most significant advances and trends in their given field of expertise. In contrast to earlier reviews, this presentation has been formulated into a unified work, providing a single source covering a broad spectrum of geoanalytical techniques. Additionally, some themes that were not previously emphasised, in particular TIMS, accelerator-based methods and vibrational spectroscopy, are also presented in detail.
Keywords: TIMS; isotopic analysis; geochronology; ICP-MS; laser ablation; mass spectrometry; ICP-AES; calibration; environmental sampling; FIB; 3D imaging; SIMS; particle search; AMS; Ion Beam Analysis; radionuclides; Raman; FTIR; neutron activation; INAA; reference materials; microanalysis
Geostandards and Geoanalytical Research 36(2012)4, 337-398
Investigation of bacterial survival strategies in metalliferous environments: Molecular biological studies on S-layer proteins
Lederer, F.; Raff, J.; Pollmann, K.
Generally, heavy metal contamination of the environment is a result of either natural events like volcanic emissions or human activities such as mining processes. High concentrations of heavy metals are toxic to the majority of organisms. However, several bacteria exhibit surprising strategies to survive in metalliferous environments. These strategies are attractive for novel bio-based resource technologies. Their understanding is the purpose of our research.
Lysinibacillus sphaericus JG-B53, an isolate from the uranium mining waste pile Haberland, was studied using genome sequencing analyses in order to identify strain intrinsic survival strategies like surface (S) layer proteins with metal specific binding affinities and metal specific transporter proteins. Using the Next generation sequencing technology and bioinformatic analyses of the whole genome sequence of L. sphaericus JG-B53 with the Genomics Workbench (CLC bio) we identified 15 putative S-layer protein genes and 3 metal ion exporter protein genes for metals that occur in the natural habitat of Lysinibacillus sphaericus JG-B53. Their characteristics were analysed with multiple gene and protein analyzing programs. The protein expression was analyzed using cDNA analyses (Lederer, 2012; Lederer et al, 2013) .
Future studies will analyse recombinant S-layer proteins regarding their lattice symmetry and metal binding affinities.
Lederer FL 2012. Genetic characterization, heterologous expression and application of S-layer proteins from the bacterial isolates Lysinibacillus sphaericus JG-B53 and Lysinibacillus sphaericus JG-A12. PhD Thesis, University of Rostock.
Lederer FL, Weinert U, Günther T, Raff J, Pollmann K. 2013. Identification of survival strategies of Lysinibacillus sphaericus JG-B53 in heavy metal and radionuclide contaminated soil. In preparation.
GETGEOWEB - Genomic and Transcriptomic in Geobiotechnology and White Biotechnology, 29.-30.10.2012, Freiberg, Germany
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