Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

High-field magnetization and magnetoelasticity of single crystalline HoFe5Al7

Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Skourski, Y.; Arnold, Z.; Zherlitsyn, S.; Wosnitza, J.

Magnetization and ultrasound measurements have been performed in pulsed magnetic fields up to 60 T on a ferrimagnetic HoFe5Al7 single crystal (Curie temperature TC = 216 K, compensation point Tcomp = 65 K) with a tetragonal crystal structure of the ThMn12-type. The compound exhibits a high magnetic anisotropy of the easy-plane type. A large anisotropy is also observed within the basal plane having an easy-magnetization direction along the [110] axis with the spontaneous magnetic moment Ms = 2 μB/f.u. at T = 2 K. Along the easy axis, two first-order field-induced magnetic transitions are observed. At both transitions sharp anomalies in the acoustic properties are found. The critical fields of the transitions depend on temperature in a different manner. Within molecular-field theory and using the high-field magnetization data the Ho-Fe inter-sublattice exchange parameter has been determined to be nHoFe ≈ 4 T/μB. The magnetoelasticity has also been probed by magnetization measurements under hydrostatic pressure. TC decreases with a rate dTC/dp = −10 K/GPa, whereas Tcomp increases with dTcomp/dp = 3.5 K/GPa.

Publ.-Id: 20157

Strongly correlated one-dimensional magnetic behavior of NiTa 2O6

Law, J. M.; Koo, H.-J.; Whangbo, M.-H.; Brücher, E.; Pomjakushin, V.; Kremer, R. K.

The magnetic properties of NiTa2O6 were investigated by magnetic susceptibility, specific heat, electron paramagnetic resonance, neutron powder diffraction, and pulse field magnetization measurements. Accompanying ab initio DFT calculations of the spin-exchange constants complemented and supported our experimental findings that NiTa2O6 must be described as a quasi-1D Heisenberg S=1 spin chain system with a nearest-neighbor only antiferromagnetic spin-exchange interaction of 18.92(2) K. Interchain coupling is by about two orders of magnitude smaller. Electron paramagnetic resonance measurements on Mg1-xNixTa2O6 (x≈1%) polycrystalline samples enabled us to estimate the single-ion zero-field splitting of the S=1 states which amounts to less than 4% of the nearest-neighbor spin-exchange interaction. At 0 T NiTa2O6 undergoes long-range antiferromagnetic ordering at 10.3(1) K evidenced by a λ-type anomaly in the specific heat capacity. On application of a magnetic field the specific heat anomaly is smeared out. We confirmed the magnetic structure by neutron powder diffraction measurements and at 2.00(1) K refined a magnetic moment of 1.93(5) μB per Ni2+ ion. Additionally, we followed the magnetic order parameter as a function of temperature. Last, we found saturation of the magnetic moment at 55.5(5) T with a g factor of 2.14(1), with an additional high field phase above 12.8(1) T. The onset of the new high field phase is not greatly affected by temperature, but rather smears out as one approaches the long-range ordering temperature.

Publ.-Id: 20156

Signature of the topological surface state in the thermoelectric properties of Bi2Te3

Rittweger, F.; Hinsche, N. F.; Zahn, P.; Mertig, I.

We present electronic structure calculations based on density functional theory for the thermoelectric properties of Bi2Te3 films. Conductivity and thermopower are computed in the diffusive limit of transport based on the Boltzmann equation. Bulk and surface contributions to the transport coefficients are separated by a special projection technique. As a result we show clear signatures of the topological surface state in the thermoelectric properties.

Keywords: PACS: 71.15.Mb; 73.50.Lw; 72.20.−i; 03.65.Vf

Publ.-Id: 20154

Building bridges from research to industry: Innovative resource technologies "Made in Germany"

Birtel, S.

Tasks and structure of the Helmholtz Instiute Freiberg, Network, Options for colaboration, introduction of the opti-moly Project in Chile

Keywords: raw materials; strategic metals; Mo recovery

  • Invited lecture (Conferences)
    Länderworkshop und NEtworking Chile- Bergbauigant in der Andenregion, 19.-20.03.2014, Berlin, Germany

Publ.-Id: 20153

Local Ion Irradiation Induced Resistive Threshold and Memory Switching in Nb2O5/NbOx Films

Wylezich, H.; Mähne, H.; Rensberg, J.; Ronning, C.; Zahn, P.; Slesazeck, S.; Mikolajick, T.

Summarizing, metal-insulator-metal devices consisting of one insulating Nb2O5 layer were irradiated with krypton ions to form a metallic NbOx sublayer in order to introduce threshold switching. Two effects were identified that induce this metallic NbOx layer: preferential sputtering at the sample surface and interface mixing at the bottom electrode. These krypton irradiated devices can be operated either as a pure threshold switch or as a combination of both, threshold switch and memory element. The presented fabrication method enables costefficient device manufacturing, since ion irradiation could be structured easily using well established lithography methods. Thus, the threshold switch can be formed in defined areas, e.g. the intersection of top and bottom electrode in cross bar arrays.

Keywords: resistive switching; threshold switching; niobium oxide; ion irradiation

Publ.-Id: 20152

Search for supernova-produced 60Fe in Earth’s microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gomez-Guzman, J. M.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.; Frederichs, T.

The radioisotope 60Fe (T1/2 = (2.62+0.04) Ma [1]) can be produced in copious amounts during different phases of evolution of massive stars. It is possible that 60Fe-rich supernova debris is deposited into solar system reservoirs [2]. Samples from Pacific Ocean sediment were chosen as sample material for this work. Considering an enrichment of the ocean water with 60Fe after deposition of SN material on Earth, all minerals being formed during that time in the sediment will incorporate 60Fe and preserve the original concentration of 60Fe/Fe, except for natural radioactive decay. One particularly interesting reservoir of in situ formed iron-bearing minerals are magnetosomes. Chains of these magnetite crystals are built up by magnetotactic bacteria, who use it similar to a compass needle for magnetotaxis. After cell death, the magnetosome chains can be preserved over geologically significant timescales and represent a very interesting sample material to look for a 60Fe isotope anomaly.
As sample material for this project, two sediment cores from the Eastern Equatorial Pacific (ODP Leg 138, Sites 848 and 851) were chosen. In order to extract iron from 60Fe rich minerals, the chemical CBD extraction procedure was employed. It was carefully calibrated to only dissolve particles of 200 nm diameter. In this way, dilution of 60Fe from iron-bearing grains from other sources (wind, water), which are typically larger, is reduced. A thorough study of the magnetic properties of the samples was also performed [3]. The concentration of 60Fe/Fe was then measured using accelerator mass spectrometry (AMS) at the GAMS setup at the MLL. Its unique ability to separate isobaric background in a gas-filled magnet allows for sensitivities reaching down to 60Fe/Fe ~10-16 and even lower.
At this point, AMS measurements on the smaller one of the two cores have been completed. Measurements of the larger core are underway and are expected to be completed in mid 2014. The 60Fe/Fe concentration determined in core 848 (smaller core) can be seen in Fig. 2. A total of 7 counts of 60Fe have been observed in a depth range corresponding to an age of 2.0 to 2.6 Ma. The signal is above the expected background. Both, this age and the observed average concentration in this range (60Fe/Fe ~1x10-15) agree well with earlier results from a ferromanganese crust [2]. In order to improve statistics and time resolution, the larger core has to be examined as well. In this larger core 851, a total of 12 counts of 60Fe have been detected so far, but measurements have not been completed yet. In addition to measurements of 60Fe, 10Be and 26Al are also currently being measured in the smaller core, to obtain an independent dating, at the DREAMS facility in Dresden.
[1] G. Rugel et al., Phys. Rev. Lett., 103(2009) 072502
[2] K. Knie et al., Phys. Rev. Lett., 93(2004) 171103
[3] P. Ludwig et al., Global Planet. Change 110(2013) 321-339

Keywords: accelerator mass spectrometry; supernova; cosmogenic radionuclide

Publ.-Id: 20151

Search for supernova produced 60Fe in Earth's microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gómez Guzmán, J. M.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.

Nucleosynthesis in massive stars can produce copious amounts of the radioisotope 60Fe (T(1/2)= 2.62 Ma). When those stars end their lives in a supernova, material enriched with nucleosynthesis products can be ejected into the interstellar medium. If such supernova debris is picked up by Earth, it can be incorporated into terrestrial reservoirs. After the discovery of live 60Fe atoms in 2-3 Myr old layers of a Pacific Ocean ferromanganese crust (K. Knie et al., Phys. Rev. Lett., 93(2004) 171103), a confirmation of this signal, as well as a mapping of the signal with high time-resolution is desirable. Another reservoir in which the 60Fe signature should have been incorporated in are the fossils of magnetotactic bacteria in ocean sediment. These bacteria form chains of small magnetite crystals for magnetotaxis. After cell death and sedimentation, these magnetic chains can be preserved even over geologically significant timescales. In order to extract iron from secondary, 60Fe bearing minerals only, a carefully tuned chemical leaching technique was employed. A novel technique to characterize this procedure using magnetic measurements was also developed applied to quantify secondary magnetite in our samples. As sample materials, two sediment cores from the Eastern Equatorial Pacific were obtained and processed. The concentration 60Fe/Fe was then measured with accelerator mass spectrometry at the GAMS setup in Garching. It features a gas-filled magnet, allowing for complete isobar suppression in the case of 60Fe and 60Ni, leading to a sensitivity which can reach even below 60Fe/Fe = 1E-16. Additionally, one of the sediment cores was also analyzed for 10Be and 26Al for independent dating of the samples at the DREAMS facility in Dresden.

Keywords: accelerator mass spectrometry; supernova; cosmogenic radionuclide

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20150

Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution

Schott, J.; Kretzschmar, J.; Acker, M.; Eidner, S.; Kumke, M. U.; Drobot, B.; Barkleit, A.; Taut, S.; Brendler, V.; Stumpf, T.

In the presence of polyborates (detected by 11B-NMR) a weak Eu(III) borate complex formation (lg beta ~ 2, estimated) was observed with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation progress of this solid was investigated by TRLFS in dependence on the total boron concentration: The lower the total boron concentration the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD, solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.

Keywords: europium; borate; complexation; solid; TRLFS; NMR; IR; PARAFAC

Publ.-Id: 20149

Magnetization dynamics of magnetic domain wall imprinted magnetic films

Hamann, C.; Mattheis, R.; Mönch, I.; Fassbender, J.; Schultz, L.; McCord, J.

The influence of micromagnetic objects on the dynamic magnetic excitation in magnetic thin films is studied by imprinting periodic domain wall patterns through selective ion irradiation in exchange biased Ni81Fe 19/IrMn structures. For high domain wall densities an increased precessional frequency is achieved. The zero field resonance of the domain wall state hereby depends directly on the stripe period, showing a pronounced increase with decrease of domain wall spacing. With the abrupt annihilation of magnetic domain walls with an applied bias field a jump-like decrease in precessional frequency takes place. The experimental data and micromagnetic simulations prove that the characteristic collective dynamic mode for the domain wall configurations is attributed to strongly coupled tilted magnetization structure. This is evidenced by an overlapping Néel wall structure for the narrowly spaced imprinted antiparallel unidirectional anisotropy state. The controlled introduction of high density frozen-in micromagnetic objects is a novel way to control the dynamic magnetic properties of continuous magnetic thin films.

Keywords: magnetism; dynamics; domain wall; ion irradiation

Publ.-Id: 20148

3D microstructural model of freckle formation validated using in situ experiments

Karagadde, S.; Yuan, L.; Shevchenko, N.; Eckert, S.; Lee, P. D.

A 3D model of freckle (solute channel) formation at a microstructural level was coupled with in situ x-ray radiography to investigate the mechanisms of freckle initiation and growth. The model predictions for solute partitioning, diffusion and convection were validated via in situ x-ray radiographic measurements in a Ga-25wt%In alloy, showing good agreement. Other key features, such as freckle channel width and critical Rayleigh number, also correlated well.
This validated model was used to investigate freckle formation under a range of solidification conditions. Two distinct stages of freckle onset were observed, identified via the dendrite tip growth and solute profiles. The first stage corresponds to lower flow velocities with large fluctuations; in the second state the velocities stabilize, with established recirculating flows forming solute channels. The influence of imperfections in dendritic morphology, such as grain boundaries and primary spacing variations, upon the critical Rayleigh number were simulated. It was found that that these features initiate freckles. Non-intuitively, converging grain boundaries were observed to have the greatest propensity for freckle formation.

Keywords: Freckle formation; microstructure; solidification defects; solute transport; chimney formation

Publ.-Id: 20147

Forced convection effects on dendritic growth and freckle formation

Shevchenko, N.; Roshchupkina, O.; Sokolova, O.; Eckert, S.

A directional solidification of Ga–25wt%In alloy within a Hele-Shaw cell under the influence of electromagnetically forced melt convection was studied by X-ray radioscopy. The forced convection was produced by a rotating wheel with two parallel disks containing at their inner sides a set of permanent NdFeB magnets with alternating polarisation [1, 2]. The top part of the solidification cell was positioned in the gap between the disks. Rotation speeds of the magnetic wheel were chosen in the range of 30 – 80 revolutions per minute. The melt flows are almost perpendicular with respect to the growth direction of the dendrites (local flow velocities 0.5 - 1.5 mm/s).
The forced convection provoked a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites inhibited the formation of secondary branches completely. The changes of secondary arm spacing depended on the melt flow conditions. The accelerated growth of the secondary arms towards the incoming flow blocked the growth of neighboring primary dendrites leading to a considerable increase in the spacing between the primary trunks. Moreover, the primary trunks show a slight inclination towards the inflow. The flow-induced redistribution of the solute concentration leads to the formation of spacious segregation pattern.

Keywords: forced convection; dendrites; melt flow; microstructure

  • Poster
    E-MRS 2014 Spring Meeting, Symposium V : Effect of natural and forced convection in materials crystallization, 26.-30.05.2014, Lille, France

Publ.-Id: 20146

In situ observation of freckle formation in Ga - In alloys under the influence of melt convection

Shevchenko, N.; Gerbeth, G.; Eckert, S.

The directional bottom-up solidification experiments were carried out using a Ga–25wt%In alloy. A visualization of the solidification process and the main convection pattern in solidifying alloys was obtained by using the X-ray imaging technique [1, 2]. Variations of the temperature gradients applied over the solidification cell induce modifications of the melt flow pattern, which lead to different segregation structures.
Solidifications carried out at low temperature gradients (up to 1 K/mm) revealed a considerable number of perturbations of the growing dendritic network. Stable chimneys occur mainly at positions with initial growth defects or grain boundaries; however, not every initial segregation channel evolves into a stable chimney. The long-term stability of these segregation channels is strongly influenced by the transient nature of the melt convection.
The situation at higher temperature gradients up to 2 K/mm is characterized by a converging flow ahead of the mushy zone coming from the side walls. This leads to a continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a sustaining chimney. This mechanism of chimney formation is different as compared to the case where the development of the segregation channel is linked with any initial growth defect.

Keywords: X-ray imaging; bottom-up solidification; segregation channels; melt convection

  • Invited lecture (Conferences)
    E-MRS 2014 Spring Meeting, Symposium V : Effect of natural and forced convection in materials crystallization, 26.-30.05.2014, Lille, France

Publ.-Id: 20145

Neuroimaging of sigma-1 receptors with positron emission tomography.

Brust, P.

In view of the involvement of sigma-1 receptors in different pathways related to the pathogenesis of various neuropsychiatric diseases and considering the neuroprotective potential of drugs targeting sigma-1 receptors quantitative neuroimaging by positron emission tomography (PET) is regarded as an unique method to investigate sigma-1 receptors in the progress of disease and under therapy. Alterations of sigma-1 receptor densities have been found in psychiatric disorders, neurodegeneration and cancer. Molecular receptor imaging with PET may provide a significant contribution to the understanding of the cross-talk between these receptors and inter- and intracellular signalling systems in these diseases. However the applicability of this imaging approach is still hampered due to lack of suitable radiopharmaceuticals for routine use. Although [11C]SA4503 has been used in human studies for already 10 years its broad clinical applicability is limited. Recent efforts made to develop 18F-labelled PET radiotracers for targeting the sigma-1 receptors in the human brain are presented. The current status of the evaluation of the most favourable radiolabelled compounds, including [18F]fluspidine, in animal models and humans will be discussed. New insights into the function of sigma-1 receptors in human brain will allow a better diagnosis of brain and cancerous diseases and direct a rational development of new therapeutic concepts.

  • Abstract in refereed journal
    Journal of Neurochemistry 130(2014), 13
  • Invited lecture (Conferences)
    12th Meeting of The Asian-Pacific Society for Neurochemistry, 23.-26.08.2014, Kaohsiung, China-Taiwan

Publ.-Id: 20144

Multiple radionuclide study of a recent supernova event in deep-sea sediments with AMS

Feige, J.; Wallner, A.; Bourlès, D.; Fifield, K. L.; Korschinek, G.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

Long-lived radionuclides such as 26Al, 53Mn, and 60Fe are generated in massive stars and ejected into space by stellar winds and explosions. If a star ends its life in a supernova (SN) explosion close to the solar system, a fraction of these elements might be deposited in terrestrial archives. Recent analysis of a ferromanganese crust [1], fossilized bacteria in deep-sea sediments [2] and lunar samples [3] evidence a 60Fe concentration enhancement ~2-3 Myr ago, suggesting to originate from one or more SNe [1].
We expanded this work to a comprehensive and detailed study of a full set of SN-related radionuclides. Detailed depth profiles of 10Be, 26Al, 53Mn and 60Fe concentrations were measured at three different AMS laboratories for ~100 individual samples from four deep-sea sediment cores from the Indian Ocean. In contrast to our 60Fe data, which shows a clear signal without terrestrial background, a possible 26Al signal from a SN event is hidden within a non-negligible terrestrial background production. The major source of 26Al is spallogenic production by cosmic-rays in the Earth's atmosphere.
We obtained isotope ratios 26Al/27Al of ~10-14 with regularly <10% statistical uncertainty [4]. This allowed us to generate for the first time a full history of precise 26Al data over a time period of 2 Myr for two sediment cores revealing an unexpected smooth depth dependence. We took advantage of it and applied the 26Al/27Al ratio as an independent and enhanced dating tool, comparable to 10Be/9Be but without needing stable isotope measurements. Comparative measurements of 10Be/9Be at the DREAMS and VERA facilities show a very good agreement (~5 %).
[1] Knie et al., Phys. Rev. Lett 93, 2004, [2] Ludwig et al., AMS-13, [3] Fimiani et al., LPSC 1659, 2012, [4] Feige et al., EPJWC,63 2013

Keywords: accelerator mass spectrometry; AMS; supernova; radionuclide

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20143

The first three years of DREAMS: Routine operation and developments

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Ziegenrücker, R.

The DREAMS (DREsden AMS) facility is based on a state-of-the-art 6 MV accelerator AMS-system [1]. Located at the ion beam centre, the accelerator is also used for ion beam analysis (IBA), material modifications and high-energy ion implantation. Though having no 24/7 availability for AMS, the advantage of a multi-purpose accelerator is the synergy effect with respect to joint technology development and µ-beam IBA for the in-situ identification of elements in problematic cathodes.
Most often measured nuclides are 10Be, 26Al and 36Cl. The majority of samples is prepared on-site [2], 36Cl in a dedicated laboratory for halide targets. About 600 10Be unknowns have been measured for different applications [3]. The mean ratio of processing blanks is as low as 3x10-15 10Be/9Be, even when measuring samples with ratios as high as 10-10–10-11. However, the mean machine blank is generally a factor of four lower. While analysing 150 26Al unknowns, machine blanks are as low as 3x10-15 26Al/27Al. Typical high-energy currents (Al3+) e.g. for the in-house standard are about 300 nA (mean / 1 h).
One of the original ion sources has been modified for reducing long-term memory for volatiles [4] and yet applied to ~100 unknowns of 36Cl [e.g. 5]. Measurements of 41Ca are mainly for nuclear decommissioning [6] and cosmochemistry [5] applications.
The high-energy setup is upgraded with a time-of-flight and energy detector system to perform actinide AMS and Super-SIMS [7].
[1] Akhmadaliev et al., NIMB 294 (2013) 5. [2] Merchel et al., AMS-13. [3] Feige et al., Ludwig et al., Ott et al., Rodrigues et al. & Smith et al., AMS-13. [4] Pavetich et al., NIMB, (2014) 10.1016/j.nimb.2014.02.130 & AMS-13. [5] Ott et al., MAPS, subm. [6] Hampe et al., JRNC 296 (2013) 617. [7] Rugel et al., AMS-13.

Keywords: accelerator mass spectrometry; AMS; radionuclide; SIMS; nuclear decommissioning

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20142

DREAMS come true: Dresden SIMS becomes Super-SIMS

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Renno, A. D.; Wiedenbeck, M.; Ziegenrücker, R.

The DREAMS (DREsden AMS) facility [1,2] has been proven to be very suitable for several kinds of applications [3] based on lighter radionuclides. However, the range of applications shall be broaden by upgrading to a so-called Super-SIMS (SIMS = Secondary Ion Mass Spectrometry). Super-SIMS is a combination of trace element AMS (TEAMS) for the determination of stable elements and isotopes using the spatial-resolution - greater than 3 µm (x,y) and 5 nm (z) - of SIMS. Thus, this ultrasensitive analytical method is best-suited for analysing geological samples within our focus of resource technology.
To realize the DREAMS Super-SIMS, a commercial SIMS (CAMECA IMS 7f-Auto) is used as an ion source and connected to a 6 MV accelerator of highest energy stability. Additionally, the high-energy setup of DREAMS will be equipped with a time-of-flight detector and an energy detection system. By the complete destruction of molecules detection limits some orders of magnitude better than for traditional dynamic SIMS are expected, i.e. ~ 10-9 - 10-12 (see e.g. [4]). A dedicated housing around the source guarantees the requirements for stable ion source operation, i.e. stability of temperature (<1°C/h) and humidity (<10%/h). For reducing vibrations the ion source is installed on a cube shaped block made of gabbro (6.4 t weight; 1.4 m x 1.8 m x 0.86 m size). The whole ion source setup can be set on a negative potential of up to -30 kV to allow for higher transmission.
[1] Akhmadaliev et al., NIMB 294 (2013) 5. [2] Rugel et al. & Pavetich et al., AMS-13. [3] Feige et al., Ludwig et al., Ott et al., Rodrigues et al., Smith et al., AMS-13. [4] Maden, PhD thesis, ETH Zurich 2003.

Keywords: accelerator mass spectrometry; SIMS

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20141

Experimental investigation of high pressure condensation and heat transfer in a single near-horizontal pipe

Geißler, T.; Beyer, M.; Hampel, U.

Wärmeübertragungsvorgänge mit Phasenübergang können genutzt werden, um effizient große Energiemengen zu übertragen. Einen Spezialfall stellt die Kondensation in einem leicht geneigten Rohr dar. Bedingt durch den Einfluss der Gravitation stellt sich eine ausgeprägte azimutale Struktur der Strömung mit dem einhergehenden Wärmeübergang ein. Im Gegensatz zu Kondensationsvorgängen in vertikalen Strukturen existieren für den horizontalen Fall nur integrale Beschreibungsmodelle. Mittels hochaufgelösten Kondensationsexperimenten soll ein Beitrag zur Entwicklung von dreidimensionalen Kondensationsmodellen geleistet werden.

Heat-transfer processes with phase change can be used to efficiently transfer large amounts of energy. A special case is the condensation in a nearly-horizontal pipe. Due to the influence of gravity a pronounced azimuthal structure of the flow with the associated heat transfer occurs. In contrast to condensation processes in vertical structures exist for the horizontal case only integral models. The conducted high-resolution condensation experiments will contribute to the development of three-dimensional condensation models.

Keywords: heat transfer; TOPFLOW; condensation; NOKO; KERENA; x-ray tomography; experiment; high pressure

  • Poster
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-25.03.2014, Fulda, Deutschland

Publ.-Id: 20140

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

Smith, T.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.; Wallner, A.; Fifield, K.; Tims, S.; Korschinek, G.

During their orbit in space, extraterrestrial bodies are exposed to cosmic rays. The interaction between these energetic particles and the meteoroides produce both stable and radioactive cosmogenic nuclides that can be used to study, e.g., the size of the meteorite before ablation in the Earth’s atmosphere and the time the object traveled before falling on Earth (exposure age). For a proper interpretation of such data, especially the ages, the temporal constancy of the cosmic ray intensity has to be proven. Doing so and being interested in timescales in the range of a few hundred million years, we have to rely on iron meteorites because their exposure ages range from a few million to a few billion years.
In this study, we systematically investigate the exposure ages of iron meteorites and search for periodic structures in the age distribution. So far, we have studied 28 iron meteorites for 10Be, 26Al, and 36Cl at the DREsden Accelerator Mass Spectrometry (DREAMS) facility [1] and for the noble gas isotopes of He, Ne, and Ar at the University of Bern. The first 53Mn and 60Fe measurements have already been performed at the Australian National University (ANU) and at the TUM (Munich). Finally, 41Ca measurements at DREAMS to identify long terrestrial residence times influencing the radionuclide concentrations are foreseen for the very near future.
The measurements of additional iron meteorites, which will help improving the statistics of the age distribution as well as extending the list of radionuclides and also extending the study to mineral separates from iron meteorites, are currently ongoing.
[1] Akhmadaliev, S. et al. (2013) NIMB 294, 5.

Keywords: accelerator mass spectrometry; cosmic radiation; meteorite

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20139

Packaging for radiation resistant X-ray detectors

Lohse, T.; Oppermann, M.; Metasch, R.; Zerna, T.; Seilmayer, M.; Wolter, K.-J.

Today non-destructive evaluation techniques become more and more important. Consequently, X-ray detectors are suitable tools to get information about specimens. In comparison to the already established scintillation principle, the direct converting method on the basis of semiconductor materials delivers several advantages. Hence, it is necessary to speed this measurement method and develop appropriate packages for these assemblies. In this paper the method of direct converting X-ray line detectors as well as their packaging and relevant aspects are introduced.

Keywords: X-ray detection; electronics packaging; silicon radiation detectors; measurement method; nondestructive evaluation techniques; radiation resistant X-ray detectors; scintillation principle; semiconductor materials; Absorption; Anodes; Detectors; Integrated circuits; Materials; Packaging; X-ray detectors

  • Contribution to proceedings
    33rd International Spring Seminar on Electronics Technology (ISSE 2010), 12.-16.05.2010, Odrębna 4 04-867 Warsaw, Poland
    33rd International Spring Seminar on Electronics Technology (ISSE 2010): Institute of Electrical and Electronics Engineers, 9781424478491, 138-142

Publ.-Id: 20138

Grundlagenuntersuchungen zur selektiven Trennung sehr feiner Partikelsysteme mittels Flüssig-Flüssig Flotation am System Magnetit-Quarz

Leistner, T.; Müller, M.; Rudolph, M.; Peuker, U. A.

Die Vergrößerung des effizienten Anwendungsbereiches von Sortierprozessen in den Bereich feinster Partikelsysteme (0,1 bis 10 µm) stellt aufgrund der Bedeutung komplexer Partikel-Partikel Wechselwirkungen eine erhebliche Herausforderung für die Forschung dar. Einen möglichen Ansatz in diese Richtung stellt die Flüssig-Flüssig Flotation dar. Bei diesem Heterokoagulationsprozess (ähnlich der Flotation) werden anstelle von Luftblasen feine Tröpfchen einer mit Wasser nicht-mischbaren unpolaren Flüssigkeit zum selektiven Austrag von Feststoffpartikeln eingesetzt. In diesem Beitrag werden erste Ergebnisse einer Grundlagenforschungsstudie zur Anwendbarkeit der Flüssig-Flüssig Flotation für die selektive Trennung im Feinstbereich am Beispiel von Magnetit- und Quarzpartikel (< 10 µm) vorgestellt. Als unpolare Flüssigkeit wird Isooktan eingesetzt. Die selektive Anreicherung der Feststoffpartikel an der Isooktan/Wasser-Grenzfläche bzw. der Transfer in die Isooktan-Phase wird in Abhängigkeit von ausgewählten Prozessparametern, wie dem pH-Wert der wässrigen Suspension sowie der Zugabe von grenzflächenaktiven Substanzen, untersucht und quantitativ dargestellt.

  • Lecture (Conference)
    Jahrestagung 2013 "Aufbereitung und Recycling", 13.-14.11.2013, Freiberg, Deutschland

Publ.-Id: 20137

Photo-neutron reaction cross section for nat-Zr in the end-point bremsstrahlung energies of 12 - 16 and 45 - 70 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; Zaman, M.; Yang, S. C.; Lee, M. W.; Shin, S. G.; Gey, Y.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Goswamia, A.; Cho, M.-H.

The natZr(γ, xn)89-86Zr reaction cross-sections were experimentally determined at the end-point bremsstrahlung energies of 12, 14, 16, 45, 50, 55, 60 and 70 MeV by activation and off-line γ-ray spectrometric technique using the 20 MeV electron linac (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany and 100 MeV electron linac at Pohang Accelerator Laboratory (PAL), Pohang, Korea. The natZr(γ, xn)89-86Zr reaction cross-sections as a function of photon energy were also calculated theoretically using TALYS 1.4 computer code. The flux-weighted average values at the end-point energies of 12-16 and 45-70 MeV were obtained from the literature and the TALYS data based on mono-energetic photon and are found to be in good agreement with the present dat. It was also found that the present data and the flux-weighted literature and theoretical values for the natZr (γ, xn)89-86Zr reaction cross-sections increase from the threshold values to a certain energy, where other reaction channels opens. This indicates the role of excitation energy. However, the increase trend of natZr(γ, xn)89,88Zr reaction cross-sections are sharper from the threshold value up to end-point bremsstrahlung energies of 17-22 MeV compared to the same for natZr(γ, xn)87,86Zr reactions. This is due to the Giant Dipole Resonance (GDR) effect besides the role of excitation energy. After a certain values, the individual natZr (γ, xn) reaction cross sections decrease with increase of bremsstrahlung energy due to opening of other reactions, which indicates portioning of energy in different channels.

Keywords: Photonuclear reactions; photoactivation; electron accelerators; bremsstrahlung; cross sections; statistical-model calculations

Publ.-Id: 20136

From tip to toe – Improvements of the DREAMS facility for the determination of volatile and heavy radionuclides

Pavetich, S.; Akhmadaliev, S.; Arnold, M.; Aumaître, G.; Bourlès, D.; Buchriegler, J.; Fifield, K.; Golser, R.; Keddadouche, K.; Martschini, M.; Merchel, S.; Rugel, G.; Srncik, M.; Steier, P.; Wallner, A.; Ziegenrücker, R.

Since the DREAMS (DREsden Accelerator Mass Spectrometry) facility [1] based on a HVE 6 MV Tandetron went operational in 2011, special effort was immediately devoted to upgrading the system for measurements of volatile elements e.g. Cl, I, and heavy elements e.g. actinides.
In the case of volatile elements, understanding and minimizing the ion source memory effect is a key issue for precise AMS-measurements [2,3]. For this purpose, one of the two original HVE sources was mechanically optimised. The new design has a more open geometry to improve the vacuum level and a modified target loading and positioning system, which allows exchanging the cathode aperture together with each target. To evaluate improvements of these modifications in comparison to other up-to-date AMS facilities [4], the long-term memory effect in the ion sources of VERA [5], ASTER [3] (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and DREAMS [1] have been investigated by measuring samples of natural 35Cl/37Cl-ratio and samples containing highly enriched 35Cl (35Cl/37Cl ~1000). In these measurements the modified DREAMS ion source showed the lowest level of ion source memory effect and typically the fastest recovery [4].
To extend the measurement capabilities to actinides a time-of-flight system based on thin carbon foils and Micro Channel Plates was designed and constructed at DREAMS. For an optimal tuning of the system with low currents special beam diagnostic elements were manufactured. In cooperation with ANU first actinide samples were measured at DREAMS.

[1] S. Akhmadaliev et al., NIMB 294 (2013) 5.
[2] R. Finkel et al., NIMB 294 (2013) 121.
[3] M. Arnold et al., NIMB 294 (2013) 24.
[4] S. Pavetich et al., NIMB, accepted.
[5] M. Martschini et al., NIMB 269 (2011) 3188.

Keywords: Accelerator Mass Spectrometry; Cl-AMS; long-term memory effect; actinide AMS; Time-of-Flight; DREAMS

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France

Publ.-Id: 20135

Development of MMRPC prototype for the NeuLAND detector of the R3B collaboration

Datta Pramanik, U.; Chakraborty, S.; Basu, P.; Basu, J.; Banerjee, P.; Bemmerer, D.; Bose, S.; Chatterjee, S.; Elekes, Z.; Kempe, M.; Leifels, Y.; Panja, J.; Mukherjee, A.; Rahaman, A.; Roy, S.; Simon, H.; Sobiella, M.; Stach, D.; Wagner, A.; Yakorev, D.

A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with active area 40 cm×20 cm has been developed at SINP, Kolkata as a new Time-Of-Flight (TOF) system with timing resolution σt<120ps and position resolution σx∼0.58cm. The intention is to use multilayers of this type together with converter materials as a high energy neutron (1GeV>En>200MeV) TOF system for the R3B collaboration at the FAIR facility. The design of the detector elements is as follows: a double stack MMRPC with float glass plates and two gas gaps of 0.3 mm per stack. The response of this MMRPC has been studied with cosmic muons and γ-raysγ-rays from a standard radioactive source (60Co) in coincidence with fast inorganic scintillators at SINP laboratory. Recently, response of developed MMRPC has been studied using pulsed electron beam at ELBE, FZD. The details of the MMRPC construction , experimental set-up for investigation of its response and first results are presented.

Keywords: Multi-strip Multi-gap Resistive Plate chamber high energy neutron R3B FAIR

Publ.-Id: 20134

Establishment of two complementary in vitro assays for radiocopper complexes achieving reliable and comparable evaluation of in vivo stability

Zarschler, K.; Kubeil, M.; Stephan, H.

The development of novel radiopharmaceuticals for imaging and therapy requires rapid and reproducible in vitro assays to estimate their in vivo stability and dissociation behaviour. In general, these assays should allow an assessment of dissociation of the radiometal from the radiopharmaceuticals. In the past, a series of chemical challenges has been widely used to estimate complex stability under non-physiological and non-radiotracer conditions providing limited information on the potential in vivo stability. In contrast, we herein present two independent in vitro methods to measure the stability of radiocopper complexes under physiologically relevant conditions. To quantify and compare the dissociation behaviour of six well-established 64Cu chelates (TETA, DOTA, NOTA, Cyclam, diamSar and EDTA), we combine a protein challenge experiment considering the stability of the chelates in the presence of human superoxide dismutase with a serum assay measuring the stability of the radiometal complexes against human serum. Unlike HPLC- and TLC-based analytical techniques, we describe the stability assessments by standard gel electrophoretic procedures, which allow a timesaving workflow as well as simultaneous processing and comparative analysis of a variety of copper-containing chelates and conjugates thereof. [64Cu]Cu-diamSar is the most kinetically stable ligand, whereas the acyclic chelate [64Cu]Cu-EDTA underwent an almost complete complex dissociation. Furthermore, kinetic stability studies in human serum carried out for [64Cu]Cu-diamSar revealed no substantial time-dependent influence under commonly used labelling conditions. Both described assays, the protein challenge experiment as well as the serum stability assay, are not restricted to radiocopper, but may be adopted for other radiometal containing chelates. © 2014 The Royal Society of Chemistry.

Publ.-Id: 20133

Transverse wobbling: A collective mode in odd- A triaxial nuclei

Frauendorf, S.; Dönau, F.

The wobbling motion of a triaxial rotor coupled to a high-j quasiparticle is treated semiclassically. Longitudinal and transverse coupling regimes can be distinguished depending on, respectively, whether the quasiparticle angular momentum is oriented parallel or perpendicular to the rotor axis with the largest moment of inertia.
Simple analytical expressions for the wobbling frequency and the electromagnetic E2 and M1 transition probabilities are derived assuming rigid alignment of the quasiparticle with one of the rotor axes and harmonic oscillations (HFA). Transverse wobbling is characterized by a decrease of the wobbling frequency with increasing angular momentum. Two examples for transverse wobbling, 163 Lu and 135 Pr, are studied in the framework of the full triaxial particle-rotor model and the HFA. The signature of transverse wobbling, decreasing wobbling frequency, and enhanced E2 interband transitions, is found in agreement with experiment.

Keywords: Nuclear structure; triaxial particle-rotor model; E2 transitions

Publ.-Id: 20132

Improving AMS-chemistry: Two steps forward, one step back

Merchel, S.; Bourlès, D. L.; Feige, J.; Ludwig, P.; Pavetich, S.; Ritter, A.; Rodrigues, D.; Rugel, G.; Smith, T.; Ziegenrücker, R.

The DREAMS (DREsden AMS) facility consists of a sophisticated 6 MV accelerator system [1], but also provides two chemistry laboratories for external users. One lab is used for preparation of 10Be, 26Al, 41Ca, 53Mn and 60Fe targets. The other one is dedicated to halide targets (36Cl, 129I), thus, any use of Cl- or S-compounds such as HCl or H2SO4 is strictly prohibited.
Separation protocols are applied to calcite- and quartz-rich samples for in-situ projects [2-4]. Atmospheric 10Be has been leached from marine sediments and Mn-nodules for dating purposes [5] and chemistry refined for bigger samples and heavier nuclides (26Al, 53Mn, 60Fe) [6]. After adapting standard protocols [7] introducing simple Mn-separation by delayed hydroxide separation, higher isobar concentrations (53Cr) have been found asking for further cleaning by ion exchange. With intent to speed-up and simplify the separation procedures for ice and meteorite samples [8], difficulties have been arisen e.g. carryover of Ag+-ions into MnO2, and shortly after overcome. Another chemistry challenge probably mastered is the dissolution of meteoritic troilite (FeS) without losing natCl-carrier before equilibrium with 36Cl, plus suppression of massive isobar amounts. Remaining issues also influencing the quality of AMS-data, such as incorrectly measured stable isotope concentrations (9Be, 27Al), are usually underestimated and harder to tackle.
[1] Akhmadaliev et al., NIMB 294 (2013) 5. [2] Merchel et al., Quat. Geo. 22 (2014) 33. [3] Zech et al., Paleo3 369 (2013) 253. [4] Yildirim et al., Tectonics 32 (2013) 1107. [5] Feige et al., Ludwig et al. & Rodrigues et al., AMS-13. [6] Feige et al., EPJ Web Conf. 63 (2013) 03003. [7] Merchel & Herpers, RCA 84 (1999) 215. [8] Smith et al., AMS-13.

Keywords: accelerator mass spectrometry; cosmogenic radionuclides

  • Lecture (Conference)
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20131

Detectability of proton range shifts in heterogeneous targets with prompt gamma based range monitoring

Priegnitz, M.; Fiedler, F.; Helmbrecht, S.; Janssens, G.; Smeets, J.; Vander Stappen, F.; Enghardt, W.

To make optimal use of the advantages of proton beams in tumor therapy a precise knowledge on their range is required. Recently, a slit camera has been developed using prompt gamma rays emitted during irradiation. First investigations in homogeneous media have shown that the position of the distal falloff of the prompt gamma ray profiles is closely correlated with the Bragg-peak position. Now, heterogeneous targets are under investigation and first results on detectability of range shift as well as range retrieval precision will be presented.

  • Lecture (Conference)
    Dreiländertagung Medizinische Physik - Joint Conference of the SGSMP, DGMP, ÖGMP, 07.-10.09.2014, Zürich, Schweiz
  • Contribution to proceedings
    Dreiländertagung Medizinische Physik - Joint Conference of the SSRMP, DGMP, ÖGMP, 07.-10.09.2014, Zürich, Schweiz
    Abstractbook, 987-3-9816508-5-3, 136-137

Publ.-Id: 20130

Surface speciation of dissolved radionuclides on mineral phases derived from vibrational spectroscopic data

Foerstendorf, H.; Jordan, N.; Heim, K.

A detailed knowledge of the molecular reactions of radionuclides at the aqueous-mineral interface is required for a reliable assessment of their dissemination in the environment. Among numerous spectro-scopic approaches, in situ vibrational spectroscopy has been developed to a powerful tool for the study of surface complexes of heavy metal ions on solid phases. In particular from vibrational data, molecular in-formation can be derived which might be complementary to those obtained from other widely applied techniques, such as X-ray absorption spectroscopy. In this study, a survey of very recent results obtained from sorption reactions of radionuclides, namely U(VI) on iron(hydr)oxides and Se(VI) on metal oxides is given.
A significantly different surface complexation of U(VI) was found for two different iron bearing min-eral phases, that is ferrihydrite and maghemite. As in situ IR spectroscopy allows the investigation of sorption and desorption processes in real time under environmentally relevant conditions, the type of sur-face complexation can be identified by the extent of reversibility of the sorption reactions. Moreover, the evaluation of the formation of ternary U(VI)carbonato surface complexes provides further details of the sorption processes.
The selenate anion (SeVIO42−) preferentially shows relatively weak interactions (physisorption) with mineral phases in the circumneutral pH range. However, the electrostatic interactions of this ion with the mineral surfaces, referred to as outer-sphere complexation, might base on different types of surface com-plexes as shown by vibrational data from surface complexes on different minerals. With respect to the high selectivity of vibrational spectra to molecule symmetry, the results from Se(VI) sorption experiments on different mineral phases clearly demonstrate two different types of outer sphere complexes.

  • Invited lecture (Conferences)
    248th ACS National Meeting & Exposition, 10.-14.08.2014, San Francisco, U.S.A.

Publ.-Id: 20129

Post-irradiation annealing behaviour of neutron-irradiated FeCu, FeMnNi and FeMnNiCu model alloys investigated by means of small-angle neutron scattering

Bergner, F.; Ulbricht, A.; Lindner, P.; Keiderling, U.; Malerba, L.

Neutron irradiation of reactor pressure vessel steels gives rise to the formation of thermodynamically stable and unstable nano-features. The present work is focused on the stability of Cu-, Mn- and Ni-containing solute clusters in model alloys exposed to post-irradiation annealing. Fe0.1Cu, Fe1.2Mn0.7Ni and Fe1.2Mn0.7Ni0.1Cu (wt%) model alloys irradiated up to neutron exposures of 0.1 and 0.19 dpa (displacements per atom) were annealed at stepwise increasing temperatures in the range from 300 °C (i.e. near irradiation temperature) to 500 °C and characterized by means of small-angle neutron scattering (SANS). We have found characteristic differences in the annealing behavior of the alloys. In particular, there is a non-trivial (synergistic-antagonistic) interplay of Mn/Ni and Cu.

Keywords: radiation effects; Fe-based model alloys; SANS; thermal treatment

Publ.-Id: 20128

SiΛvio: A trigger for Λ-hyperons

Münzer, R.; Berger, M.; Fabbietti, L.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Carevic, I.; Charviakova, V.; Crochet, P.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Kienle, P.; Koczon, P.; Kotte, R.; Lebedev, A.; Leifels, Y.; Liu, J. L.; Lopez, X.; Manko, V.; Marton, J.; Matulewicz, T.; Petrovici, M.; Piasecki, K.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Yamazaki, T.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.

As online trigger for events containing Λ hyperons in p+p collisions at 3.1 GeV a silicon-based device has been designed and built. This system has been integrated close to the target region within the FOPI spectrometer at GSI and was also employed as a tracking device to improve the vertex reconstruction of secondary decays. The design of the detector components, read-out, the trigger capability as well as the tracking performance are presented. An enrichment factor of about 14 was achieved for events containing a Λ-hyperon candidate.

Keywords: Si Lambda vio; Lambda-hyperons

Publ.-Id: 20127

Amorphization and recrystallization of single-crystalline hydrogen titanate nanowires by N+ ion irradiation

Behera, A. K.; Facsko, S.; Bandyopadyay, M. K.; Das, S.; Chatterjee, S.

We report the phase transformation of hydrogen titanate (H2Ti3O7) nanowires induced by 50 keV N+ ion irradiation at room temperature with fluencies of 1×1015 ions/cm2 and 1×1016 ions/cm2. By high resolution transmission electron microscopy the internal structure of the ion irradiated nanowires is analyzed. While at lower fluence a transformation from crystalline H2Ti3O7 to amorphous TiO2 is observed, at higher fluence a remarkable crystalline-amorphous TiO2 core-shell structure is formed. At this higher fluence the recrystallization occurs in the core of the nanowire and the outer layer remains amorphized. The phase transformation and formation of core-shell structure is explained using the thermal spike model and non-equilibrium thermodynamics. X-ray Photoelectron Spectroscopy and Raman Scattering reveale further insight into the structure of the nanowires before and after ion irradiation.

Keywords: Nanowires; core-shell structure; ion induced phase transformation

Publ.-Id: 20126

Brain Tumor Imaging with Positron Emission Tomography: Potential Alternatives with New 18F-labelled Radiotracers?

Brust, P.

  • Poster
    20th Annual Blood-Brain Barrier Consortium Meeting in collaboration with the International Brain Barriers Society, 20.-22.03.2014, Sunriver, Oregon, USA

Publ.-Id: 20125

Azimuthal Emission Patterns of K+ and of K- Mesons in Ni+Ni Collisions near the Strangeness Production Threshold

Zinyuk, V.; Kang, T. I.; Leifels, Y.; Herrmann, N.; Hong, B.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Carevic, I.; Crochet, P.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Koczon, P.; Kotte, R.; Lebedev, A.; Le Fèvre, A.; Liu, J. L.; Lopez, X.; Manko, V.; Marton, J.; Matulewicz, T.; Münzer, R.; Petrovici, M.; Piasecki, K.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zmeskal, J.; Bratkovskaya, E.; Hartnack, C.

Azimuthal emission patterns of K ± mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum p T integrated directed and elliptic flow of K + and K − mesons as well as the centrality dependence of p T - differential directed flow of K + mesons are compared to the predictions of hadron string dynamics and isospin quantum molecular dynamics transport models. The data exhibits different propagation patterns of K + and K − mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for K + mesons and attractive for K − mesons.

Publ.-Id: 20124

Ancient and recent exposure history of chondrules from two highly primitive meteorites,

Ott, U.; Merchel, S.; Beyersdorf-Kuis, U.; Akhmadaliev, S.; Pavetich, S.; Rugel, G.; Ziegenrücker, R.

Chondrules may have spent several million years as free-floating particles in the solar nebula [1], and if so, been exposed to an early cosmic ray irradiation. The search for “pre-irradiation” in noble gas isotopic signatures has, thus, been actively pursued recently [2-4]. Results for two highly primitive CR3 chondrites (MET00426 & QUE99177) [5] are intriguing: 1) They are among the most unmetamorphosed meteorites, most likely to have retained any pre-irradiation record. 2) Target elements were determined by Instrumental Neutron Activation Analysis on the same material used for noble gas analysis. 3) QUE99177 shows no hint for having been part of an asteroidal regolith. 4) Chondrules show both higher and lower cosmic ray exposure than identically-shielded matrix samples.
The shortest cosmic ray exposure determined via stable noble gases is an upper limit to the recent cosmic ray exposure age. Further constraints can be obtained via radionuclides such as 10Be, 26Al, 36Cl, which have been analyzed at DREAMS [6,7]. Despite sample masses of only 1.6-1.8 mg for single chondrules, ratios are as high as 1-3x10-12 for 10Be/9Be and 26Al/27Al, and 1x10-13 for 36Cl/35Cl, clearly distinguishable from blanks. Preliminary evaluation shows that the radionuclides are not in saturation. However, since the meteorites are finds from Antarctica, one also has to consider decay during terrestrial residence. To better constrain this, AMS of 41Ca and 53Mn is scheduled at DREAMS and ANU, respectively.
Ref.: [1] Cuzzi, Nat. Geosci. 4 (2011) 219. [2] Eugster et al., MAPS 42 (2007) 1351. [3] Das & Murty, MAPS 44 (2009) 1797. [4] Roth et al., MAPS 46 (2011) 989. [5] Beyersdorf-Kuis et al., 44th LPSC (2013) 1999. [6] Akhmadaliev et al., NIMB 294 (2013) 5. [7] Rugel et al., AMS-13.

Keywords: accelerator mass spectrometry; meteorites; solar system

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20123

Retention of selenium oxyanions at the water-mineral interface in the context of nuclear waste repositories

Franzen, C.; Hering, D.; Jordan, N.; Weiss, S.

The radioactive isotope Selenium-79 is a fission product found in nuclear waste. Due to its long half-life of 3.27 ∙ 105 years and its high mobility, it is expected to be one of the isotopes contributing significantly to the potential radiation dose according to safety assessments of nuclear waste underground repositories. A detailed knowledge of the mobility and bioavailability of selenium in its different oxidation states is therefore of great importance for a safe disposal of radioactive waste.
Adsorption onto mineral surfaces of both the engineered and geological barrier is a major process controlling the retention of the water-soluble selenium oxyanions, selenate (SeVIO42 ) and selenite (SeIVO32 ). In this context, it is important to understand to what extent this sorption is influenced particularly by characteristic parameters as expected in deep underground repositories for high level radioactive waste. These parameters include inter alia the presence of different background salts and elevated temperatures.
In this study, a combination of macroscopic sorption experiments, electrophoretic mobility measurements and in-situ ATR FT-IR spectroscopy was used to study the interaction of SeVIO42 and SeIVO32 with aged γ-Al2O3 in the presence of NaCl and MgCl2 and at elevated temperatures up to 60 °C. In this context, γ-Al2O3 can be considered as model mineral phase for more complex rock and backfill materials associated with a nuclear waste repository.
It could be shown that the retention of both Se(VI) and Se(IV) is affected by all three investigated factors pH, ionic strengths of the solution, and temperature. The increase of each parameter results in a decrease of sorption, with the retention of Se(IV) generally being higher than the one of Se(VI). In-situ ATR FT-IR spectroscopy and electrophoretic mobility measurements evidenced the formation of an outer-sphere surface complex of Se(VI) on γ-Al2O3. Concerning Se(IV), a mixture of inner-sphere and outer-sphere surface complexes could be derived.
Any sorption on mineral surfaces is dominated by the surface charge of the mineral. The impact of salinity and temperature on the variable surface charge of γ−Al2O3 was evaluated by zeta potential measurements using laser Doppler electrophoresis. The isoelectric point (pHIEP) of γ-Al2O3 is located at pH 9.6 with a positively charged surface at lower pH values and a negatively charged surface for higher pH values. Increasing the amount of NaCl in the solution (up to I = 1 M) reduces the zeta potential for both the acidic and alkaline pH range. However, in the alkaline range the decrease of the zeta potential is more pronounced. In the presence of 0.1 M MgCl2, the surface charge of γ-Al2O3 becomes positive throughout the studied pH range (3-11). Above pH 10, a sharp potential decrease occurs due to Mg(OH)2 precipitation. The increase of temperature shifts the pHIEP to lower values and decreases the zeta potential in the acidic range.
These changes in the surface properties of the γ-Al2O3 are consistent to the changes in the sorption behaviour of selenate and selenite.
These results indicate that for geochemical modeling and long-term safety assessments concerning selenium-containing waste it is crucial to include the impact of temperature and ionic strengths effects.

  • Lecture (Conference)
    21st General Meeting of the International Mineralogical Association, 01.-05.09.2014, Johannesburg, South Africa

Publ.-Id: 20122

The German P&T study – results and conclusions in the view of the contributing Helmholtz research centers

Merk, B.; Geist, A.; Modolo, G.; Knebel, J.

The governmental decision to phase out electric energy production in nuclear power plants in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft (ministry of economics) and the Bundesministerium für Bildung und Forschung (ministry of education and research) have launched a study managed by acatech (national academy of science and engineering) in 2012 to answer these questions on a broad scientific basis. The major mandate was to evaluate scientific and technological as well as socio-economic challenges and opportunities of the P&T technology in the view of the phase out decision. The scientific and technological aspects of P&T are analyzed with respect to a possible contribution to the nuclear waste management using the following structure:

  • Starting point and boundary conditions – waste amounts and final disposal strategies
  • Definition and description of scenarios – possible ways for transmutation in the view of the phase out, European vs. national
  • Technological challenges of P&T – description of the major challenges to be solved on the way to industrial application
  • Current status of R&D – discussion of possible transmutation systems, current R&D status of P&T, development gaps, and future research strategy
  • Safety aspects – special safety aspects including all steps of the P&T cycle
  • International projects & competences in Germany – what is going on around the world and what can be served by the German industry
The socio-scientific, the ecologic, and the economic aspects have been analyzed in parallel using expert interviews, group Delphi, and independent expert opinions on economic, legal, and environmental aspects.
An overview on the results of the study in the view of the contributing Helmholtz research centers (KIT, HZDR, and FZJ) will be given with special focus on the political recommendations and the developed research strategy which has been proposed to the ministries.

Keywords: nuclear; nuclear waste; nuclear reactors; nuclear waste management; partitioning; transmutation

  • Open Access Logo Contribution to proceedings
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea
  • Lecture (Conference)
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea

Publ.-Id: 20121

Evaluation of the application of a molten salt fast reactor for transmutation in the frame of the nuclear phase out

Merk, B.; Rohde, R.

The governmental decision to phase out electric energy production in nuclear power plants in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft (ministry of economics) and the Bundesministerium für Bildung und Forschung (ministry of education and research) have launched a study managed by acatech (national academy of science and engineering) in 2012 to answer these questions on a broad scientific basis. One major discussion point was the so-called last transmuter problem which requires much more attention in the case of the nuclear phase out. Transmutation of long lived transuranium isotopes is under the phase out condition only attractive when the last transmuter problem can be solved. A solution for this problem has been proposed in a generic study based on the EVOL molten salt reactor configuration using a twofold operation cycle. It is proposed to operate the fast molten salt reactor for a given time in the transmuter mode feeding the transuranium elements. This operational mode is followed by the deep burn phase where the bred U-233 from the blanket is used as fissile material to burn the last TRU load by more than 90%. The reactor is operated on uranium as fissile material at the end of the deep burn phase which can be forwarded to reactor operation in another country without proliferation concerns as long as it is diluted with U-238 to the required fissile content defined in the non-proliferation guidelines.
Based on this proposal a detailed investigation is presented using the specific German nuclear waste amount and composition in a fertile free salt configuration in the core. A salt configuration based on the MOSART composition is used which is able to carry the required amount of TRUs for the fertile free operation. The transmutation efficiency is evaluated and it is demonstrated that the optimal efficiency of the fertile free configuration can be achieved in the transmuter mode. Following the transmuter mode the nuclide densities are evaluated in the deep burn mode using bred U-233 as fissile material. The remaining TRU amounts are compared during the deep burn mode and evaluated in comparison with the required operation time. The remaining uranium based fissile material configuration is discussed and an estimation is given how many reactors of the EVOL design have to be operated for how many years to burn the remaining German nuclear waste.

Keywords: nuclear; nuclear reactor; molten salt; molten salt reactor; transmutation; nuclear waste management

  • Open Access Logo Contribution to proceedings
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea
  • Poster
    Actinide and Fission Product Partitioning and Transmutation 13th Information Exchange Meeting, 23.-26.09.2014, Seoul, Republic of Korea

Publ.-Id: 20120

Experimental investigation of liquid metal two-phase flows in a continuous casting model

Eckert, S.; Timmel, K.; Shevchenko, N.; Röder, M.; Anderhuber, M.; Gardin, P.

We present an experimental study concerned with the two-phase flow in a mockup of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing two-phase flows in the mould and the SEN by means of X-ray radioscopy. This setup utilizes the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results about the two-phase flow will be presented here accompanied by a discussion of the advantages and limitations of the X-ray method.
The position of the X-ray observation window can be changed, which allows the inspection of regions around the gas injection point at the tip of the stopper rod or the development of the bubbly flow in the mould. The X-ray images reveal complex flow situations, for instance, argon bubbles might be attracted by the wall of the SEN near the inlet forming huge bubbles there. Smaller bubbles are generated at the bottom of the SEN, where high shear flows exist. The bubbles in the mould are entrapped by the liquid metal jet. The tendency to rise towards the mould level increases with growing bubble size.

Keywords: Liquid metal model; two-phase flow; X-ray imaging

  • Lecture (Conference)
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich
  • Contribution to proceedings
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich

Publ.-Id: 20119

Recent activities for experimental modelling and investigation of the steel flow within the limmcast program at HZDR

Eckert, S.; Gerbeth, G.; Shevchenko, N.; Stefani, F.; Timmel, K.; Wondrak, T.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. We present the experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-ups mini-LIMMCAST and X-LIMMCAST will be presented, which work with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. A selection of results will be presented in this paper covering various phenomena occurring in single-phase and two-phase flows.

Keywords: Continuous casting; physical modelling; flow measurements; magnetic field; flow control; electromagnetic brake

  • Lecture (Conference)
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich
  • Contribution to proceedings
    8th European Continuous Casting Conference, 23.-26.06.2014, Graz, Österreich

Publ.-Id: 20118

A compact solution for ion beam therapy with laser accelerated protons

Masood, U.; Bussmann, M.; Cowan, T. E.; Enghardt, W.; Karsch, L.; Kroll, F.; Schramm, U.; Pawelke, J.

The recent advancements in the eld of laser-driven particle acceleration have made Laser driven Ion Beam Therapy (L-IBT) an attractive alternative to the conventional particle therapy facilities. To bring this emerging technology to clinical application we introduce the Broad Energy Assorted depth-Dose deposition (BEAD) scheme which makes ecient use of the large energy spread and high dose-per-pulse of Laser Accelerated Protons (LAP) and is capable of delivering homogeneous doses to tumors. Furthermore, as a key component of L-IBT solution we present a compact, iso-centric gantry design with 360° rotation capability with an Integrated Shot-to-shot Energy Selection System (ISESS), for efficient transport of LAP with large energy spread to the patient. We show that gantry size could be reduced by a factor of 2-3 compared to conventional gantry systems by utilizing pulsed, air-core magnets.

Keywords: Radiationtherapy; ion beam therapy; laser particle acceleration; beamline; compact gantry; dose distribution

Publ.-Id: 20117

Laborexperimente zur Entstehung und Wirkung kosmischer Magnetfelder

Stefani, F.

Bekanntermaßen entstehen planetare, stellare und galaktische Magnetfelder durch den hydromagnetischen Dynamoeffekt, d.h. durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden. Weniger bekannt ist, dass Magnetfelder auch eine aktive Rolle in der kosmischen Strukturbildung spielen, indem sie Akkretionsscheiben in der Umgebung von Protosternen und Schwarzen Löchern destabilisieren. Der Artikel gibt einen Überblick über die Flüssigmetallexperimente der letzten 15 Jahre, in denen sowohl der Dynamoeffekt als auch die destabilisierende Wirkung von Magnetfeldern auf rotierende Strömungen nachgewiesen worden ist.

  • Praxis der Naturwissenschaften - Physik in der Schule 63(2014)2, 31-37

Publ.-Id: 20116

Terahertz spectroscopy of nanostructures with a free electron laser

Helm, M.

I will start describing the Dresden free-electron laser (FEL) as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in nanostructures. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss experiments studying electronic relaxation processes in semiconductor quantum dots with their totally quantized energy levels, and in graphene with its zero energy gap and linear band dispersion.

Keywords: free electron laser; terahertz; nanostructures; quantum dots; graphene

  • Invited lecture (Conferences)
    Annual BuildMoNa Conference, 04.03.2014, Leipzig, Germany

Publ.-Id: 20115

Ultra-smooth diamond-like carbon coatings with high elasticity deposited at low temperature by direct ion beam deposition

Markwitz, A.; Mohr, B.; Carpeño, D. F.; Hübner, R.

Diamond-like carbon coatings were fabricated under high vacuum at room temperature using a direct ion beam deposition technique based on a penning ion source. Post acceleration and electrostatic scanning were applied to form adhesive and laterally homogenous coatings across 50 mm using ion energies from 3.0 to 10.5 kV. The deposition rate was set to 0.4 nm s-1 to prevent heating of the coating and substrate. Structural, physical and chemical analyses revealed the formation of amorphous atomically flat hydrogenated amorphous carbon (a-C:H) coatings with a sp3 content of typically 20 %. Nanoindentation measurements provided hardness figures of up to 18 GPa combined with high elasticity values of 90 %. Hardness and elasticity values and the sp3 content were measured to be proportional to the ion energy. Furthermore, a growing interface layer was observed with transmission electron microscopy images indicating atomic interlocking between the carbon coating and the silicon substrate. The result highlight the opportunity to produce a-C:H coatings with high elasticity with direct ion deposition at room temperature.

Keywords: diamond-like carbon; amorphous hydrogenated carbon; direct ion beam deposition; room temperature

Publ.-Id: 20114

Optical waveguides in LiTaO3 crystals fabricated by swift C5+ ion irradiation

Liu, G.; He, R.; Akhmadaliev, S.; de Aldana, J.; Zhou, S.; Chen, F.

We report on the optical waveguides, in both planar and ridge configurations, fabricated in LiTaO3 crystal by using carbon (C5+) ions irradiation at energy of 15 MeV. The planar waveguide was produced by direct irradiation of swift C5+ ions, whilst the ridge waveguides were manufactured by using femtosecond laser ablation of the planar layer. The reconstructed refractive index profile of the planar waveguide has showed a barrier-shaped distribution, and the near-field waveguide mode intensity distribution was in good agreement with the calculated modal profile. After thermal annealing at 260 °C in air, the propagation losses of both the planar and ridge waveguides were reduced to 10 dB/cm.

Keywords: Ion irradiation; LiTaO3 crystal; Optical waveguide

Publ.-Id: 20113

Dynamics of marine sediments studied through 10Be

Rodrigues, D.; Arazi, A.; Korschinek, G.; Martí, G. V.; Merchel, S.; Rugel, G.

Marine sediments may originate from the erosion of continental material (containing both cosmogenic 10Be, and 9Be with a ratio around 10-8) that has been carried by rivers to the sea. If the sediments are deposited in zones where a tectonic plate subducts beneath another one, they might follow complex processes, in which part of the sediments are dragged under the plate and the other part is accreted above.

In this work, depth profiles of the 10Be/9Be ratios in marine sediments are being studied near the spot where Nazca, Antarctica and South American tectonic plates join each other.
A preliminary set of seven samples, provided by the Ocean Drill Project [1], were measured at the DREAMS facility [2]; this represents the first measurement of a depth profile near this zone. The isotopic ratios, based on AMS-measurements of 10Be/9Be and determinations of 9Be concentration performed by ICP-MS at HZDR are ranging from 4.9 to 53 x 10-9. Contrary to the expectation they do not decrease with depth, but rise into the interval corresponding to 102 to 145 meters of depth, and from 197 to 256 meters of depth. We show that this result is consistent with a reverse (thrust) fault in the sediments due to the compression pressure exerted by the subduction of the Nazca tectonic plate.

[1] Behrmann et al. Proceedings of the Ocean Drilling Program, Initial Reports, 141, (1992).
[2] Akhmadaliev et al. Nucl. Instr. and Meth. in Physics Research B, 294, 5-10 (2013).

Keywords: accelerator mass spectrometry; cosmogenic nuclide; tectonics

  • Poster
    13th International Conference on Accelerator Mass Spectrometry (AMS-13), 24.-29.08.2014, Aix-en-Provence, France


Publ.-Id: 20112

Hochauflösende Positronen Emissions Tomographie für quantitative, raumzeitliche Prozessvisualisierung in geologischem Material (GeoPET)

Kulenkampff, J.; Lippmann-Pipke, J.

Positronen-Emissions-Tomographie (PET) ist das empfindlichste bildgebende Verfahren der Medizin, um Körperfunktionen in ihrem räumlich-zeitlichen Verlauf sichtbar zu machen. Seit der klinischen Einführung der PET vor etwa 40 Jahren gibt es auch einige Beispiele für den erfolgreichen Einsatz klinischer PET-Scanner in den Geowissenschaften. Explizit wird seit über 10 Jahren die Entwicklung der „GeoPET“-Methode n in der Forschungsstelle Leipzig des HZDR vorangetrieben (Gründig et al., 2007; Kulenkampff et al., 2008; Richter et al., 2000; Richter et al., 2005). Mittels eines kommerziellen hochauflösenden biomedizinischen PET-Scanners (ClearPET) einerseits und ausgereifter Korrektur- und Rekonstruktionsverfahren andererseits haben wir unsere GeoPET-Methode Alleinstellungsmerkmal zur (Transport-)Prozesstomographie in dichtem Medium (z.B. Gesteinen) entwickelt.

PET nutzt die räumliche Detektion der Annihilationsstrahlung (zwei antiparallele Gammas mit jeweils 511 keV), die durch den β+-Zerfall geeigneter Radiotracer entsteht. Beim ClearPET wird die physikalisch maximal mögliche räumliche Auflösung von etwa 1 mm erreicht. Dieser – verglichen mit den Möglichkeiten der Röntgen-CT – geringen räumlichen Auflösung steht die der PET immanente, überragende Empfindlich-keit gegenüber: Die Detektion und Quantifizierung von Tracerkonzentrationen ist auf atomarer Skala möglich: Transport-vorgänge, die sich auf der Nanometerskala abspielen (z.B. gelöste oder nanopartikulär getragene Stoffe) können detektiert und räumlich verortet werden, wenn der Stofftransport eine hinreichende Aktivitäts-konzentration von ca. 0,1 kBq pro Voxel bewirkt (etwa 109 Atome/1 mm³, pikomolar). Diese außergewöhnliche Sensitivität (und Selektivität) ist mit keiner anderen Bildgebungsmodalität erreichbar, insbe-sondere, da wir in repräsentativen Volumen von um 1 L arbeiten, also 106 Voxel. Der Einfluss des Materials – Schwächung und Streuung – ist dabei von zweitrangiger Bedeutung bzw. wird mittels systematischer Verfahren reduziert (Zakhnini et al., 2013).
Sinnvolle Anwendungen liegen in der direkten Visualisierung und Quantifizierung realer chemisch-physikalischer Prozesse (Abb.2a und b). Solche Prozesse können sonst nur über modellhafte Prozess-Simulationen dargestellt werden, indem etwa statistische a-priori-Strukturmodelle oder strukturelle Information aus CT-Bildern oder als Grundlage für LBM- oder FEM-Simulationen genutzt werden (zu letzteren zwei Beispiele in Abb. 3). Bei der direkten Beobachtung chemisch-physikalischer Prozesse in Gesteinen mittels GeoPET zeigen sich regelmäßig Abweichungen von den für Simulationen angenommene Versuchsbedingungen, etwa bezüglich der Homogenität des Probekörpers, der Topologie des Fließpfades oder der Auswirkungen geringster – aber wirkungsvoller – Abweichungen von Idealbedingungen (nicht-Dirac-Injektionsimpulsen, nicht-Punkt-/Linien- oder Flächenhaft homogener Zufuhr von Tracern). Zielparameter sind prozessabhängige, effektive Größen (effektives Transportvolumen, wirksame innere Oberfläche, Geschwindigkeitsverteilung, lokale Retardation), sowie räumlich und tensoriell aufgelöste Dispersions- und Diffusionskoeffizienten.

Die mittels der GeoPET-Methode beobachteten Prozesse können mit Alteration der Struktur durch Auflösung oder Ausfällung einhergehen, welche mit CT oder MRT mit höherer Auflösung, eventuell auch prozessbegleitend-zeitaufgelöst, sichtbar gemacht werden können. Dies entspricht der üblichen Vorgehensweise bei der nuklearmedizinischen PET-CT. Direkte und rückwirkungsfreie ortsaufgelöste Information über das chemische Milieu als Ursache der Alteration kann dagegen nur die PET liefern. Nur hierdurch werden viele bisher deduzierte Parameter direkt messbar und die Ergebnisse von Modellsimulationen verifizierbar.
Begleitend zur Prozessbeobachtung mit der GeoPET wird der Kontrollbereich und das Zyklotron des HZDR in Leipzig zur Produktion von Radiotracern genutzt (siehe z.B. (Mansel et al.)). Hier werden grundlegende geochemische Transport- und Wechselwirkungsstudien durchgeführt, die ebenfalls durch die Anwendung von Radiomarkierungen besonders empfindlich sind, wodurch die geochemische Parametrisierung von Modellen für reaktive Transportvorgänge ermöglicht wird.


Bittner, L., Kulenkampff, J., Gründig, M., Lippmann-Pipke, J. and Enzmann, F., 2014. Direct Observation of Waterglass Impregnation of Fractured Salt Rock with Positron Emission Tomography, International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, BGR, Hannover, Germany.
Gründig, M., Richter, M., Seese, A. and Sabri, O., 2007. Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes. Applied Geochemistry, 22: 2334-2343.
Kulenkampff, J., Gründig, M., Richter, M. and Enzmann, F., 2008. Evaluation of positron emission tomography for visualisation of migration processes in geomaterials. Physics and Chemistry of the Earth, 33: 937-942.
Lippmann-Pipke, J., Kulenkampff, J., Gründig, M. and Richter, M., 2011. Matching PET data with COSMOL Multiphysics simulation results, COMSOL Conference, 26.-28.10.2011, Ludwigsburg, Germany.
Mansel, A., Gruhne, S., Franke, K. and Fischer, S., Production of 85Sr at a 18 MeV-cyclotron and purification for geochemical investigations. Submitted to Applied Radiation and Isotopes, submitted.
Richter, M., Gründig, M. and Butz, T., 2000. Tomographische Radiotracerverfahren zur Untersuchung von Transport- und Sorptionsprozessen in geologischen Schichten. Zeitschrift für Angewandte Geologie, 46(2): 101.
Richter, M., Gründig, M., Zieger, K., Seese, A. and Sabri, O., 2005. Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochimica Acta, 93: 643-651.
Schikora, J., 2012. Simulation of diffusion-adsorption processes in natural geological media by means of COMSOL Multiphysics, Dresden Technical University, Diploma thesis, Dresden, Germany, 95 pp.
Zakhnini, A., Kulenkampff, J., Sauerzapf, S., Pietrzyk, U. and Lippmann-Pipke, J., 2013. Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18F, 124I and 58Co) in Opalinus Clay, anhydrite and quartz. Computers and Geosciences, 57 183-196.

  • Lecture (Conference)
    International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, 06.-07.02.2014, Hannover, Deutschland

Publ.-Id: 20111

Verification of coupled 3D fuel cycle analysis with stable Monte Carlo based code, BGCore, against the nodal diffusion DYN3D code

Kotlyar, D.; Shwageraus, E.; Margulis, M.; Bilodid, Y.; Fridman, E.

Previous studies suggested that different schemes for coupling Monte Carlo (MC) neutron transport with burnup and thermal hydraulic feedbacks may potentially be numerically unstable. This issue can be resolved by application of new Stochastic Implicit Mid-Point (SIMP) methods. In order to assure numerical stability, the new methods do require additional computational effort. The instability issue however, is problem-dependent and does not necessarily occur in all cases. Therefore, blind application of the unconditionally stable coupling schemes, and thus incurring extra computational costs, may not always be necessary. In this paper, we attempt to develop an intelligent diagnostic mechanism, which will monitor numerical stability of the calculations and, if necessary, switch from simple and fast explicit coupling scheme to more computationally expensive but unconditionally stable one. To illustrate this diagnostic mechanism, we performed a coupled burnup and TH analysis of a single BWR fuel assembly. The reference solution was obtained by the state of the art nodal diffusion code – DYN3D. Very good agreement was observed in all neutronic and TH parameters. The results indicate that the developed algorithm can be easily implemented in any MC based code for monitoring of numerical instabilities. The proposed monitoring method has negligible impact on the calculation time even for realistic 3D multi-region full core calculations.

Keywords: Monte Carlo; BGCore; neutronic-burnup-thermal hydraulic coupling; SIMP; stability analysis

  • Contribution to proceedings
    PHYSOR2014, 28.09.-03.10.2014, Kyoto, Japan
    Proceedings of PHYSOR2014

Publ.-Id: 20110

Preclinical Aspects of Nicotinic Acetylcholine Receptor Imaging

Brust, P.; Deuther-Conrad, W.; Donat, C. K.; Barthel, H.; Riss, P.; Paterson, L.; Höpping, A.; Sabri, O.; Cumming, P.

Recent developments in radiochemistry have opened new vistas for investigations of nicotinergic acetylcholine receptors (nAChRs) in living brain by positron emission tomography (PET) and by single photon emission computed tomography (SPECT). In parallel, dedicated instrumentation for molecular imaging in small animals has facilitated preclinical investigations in a number of models in which perturbations in nAChR signalling are implicated, notably Alzheimer’s disease and other neurodegenerative conditions, schizophrenia and other neuropsychiatric disorders, substance abuse and traumatic brain injury. The nAChRs are members of a family of ligand-gated ion channels composed of five subunits, most commonly occurring in the central nervous system as heteropentamers designated α4β2, with lesser amounts of the α7 homopentamer. We present a systematic review of preclinical findings with the diverse nAChR ligands which have been investigated to date. Molecular imaging of the α4β2 nAChR subtype by PET has been successfully achieved by 2-[18F]fluoro-A-85380. Newer agents such as (−)-[18F]flubatine permit quantitation of α4β2 receptors with PET recordings not exceeding 90 min, without the toxicity characteristic of earlier epibatidine derivatives. Imaging studies of α7 nAChRs have been hampered by inadequate pharmacological specificity of available ligands and by the low natural abundance of this receptor subtype in the brain. However, a continued search for optimal ligands is justified by the particular association of α7 nAChRs with aspects of cognitive function. We note that no molecular imaging ligands have been developed for α6-containing nAChRs, despite their importance for the psychopharmacology of nicotine actions in the basal ganglia. Finally, we review the competitive binding model, in which the availability of α4β2 binding sites is altered by competition from endogenous acetylcholine, noting that this approach has yet to be applied for monitoring acetylcholine release in disease models.

  • Book chapter
    Rudi, A.J.O.; Dierckx, A.; Otte, E. F.J.; de Vries, A.; van Waarde: PET and SPECT of Neurobiological Systems, Heidelberg: Springer, 2014, 978-3-642-42013-9, 465-512
    DOI: 10.1007/978-3-642-42014-6

Publ.-Id: 20109

Overview and current status of the PENELOPE project

Siebold, M.

PENELOPE (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) is designed for a pulse energy of 150 J, a repetition rate of 1Hz and a pulse duration of 120 fs after compression. Yb:CaF2 is chosen as gain medium, while each amplifier head consists four He-cooled slabs having a thickness of 5mm and a doping concentration of 1.4mol% Yb3+. The slab diameter of the final 150 J amplifier and its 10 J pre-amplifier is 110 and 55 mm, respectively. A total laser diode peak-power of 1.2 MW is installed for pumping at 980 nm. As front-end a 60 fs Yb:KGW oscillator, a regenerative Yb:CaF2 amplifier and two active mirror Yb:CaF2 multi-pass amplifiers with a pulse energy of 300µJ, 100mJ and 1J are used. The compressor is based on multilayer dielectric (MLD) gratings with a dimension of 94×42cm2, a groove density of 1760 l/mm, a grating distance of 220cm, a hard-clip bandwidth of 50nm, and a output beam diameter of 25cm.

  • Lecture (others)
    Science Palaver talk, 12.02.2014, Jena, Deutschland

Publ.-Id: 20108

High-energy diode-pumped D2O-cooled multi-slab Yb:YAG and Yb:QX-glass lasers

Siebold, M.; Loeser, M.; Harzendorf, G.; Nehring, H.; Tsybin, I.; Röser, F.; Albach, D.; Schramm, U.

We investigated lasing performance of a two-slab Yb:QX glass, a two and a four-slab Yb:YAG laser amplifier which were facet-cooled. As coolant di-Deuterium Oxyde (D2O) flowed between the active slabs while the pump and the laser light were passing through the very low absorbing heavy-water films. A square pump profile with a maximum intensity of 40 kW/cm2 drove the amplifier with a peak fluence of 5.5 J/cm2 at a pulse duration of 6 ns. We demonstrated a maximum pulse energy of 1 J for each gain medium as well as a repetition rate of 10 Hz for Yb:YAG and 1Hz for Yb:QX glass.

Keywords: Laser Amplifiers; Laser cooling; Lasers diode-pumped; Lasers Ytterbium

Publ.-Id: 20107

Towards compositional geochemical potential mapping

Tolosana-Delgado, R.; van den Boogaart, K. G.

Mineral potential mapping aims at defining target zones of future local mineral exploration efforts on the basis of regional geochemical and geological surveys. Geochemical potential mapping typically involves using a small set of elements to predict an anomalous presence of a mineral commodity related with them. In this context it is common to work with logarithmically transformed concentrations of elements. This contribution explores a compositionally compliant approach to potential mapping using geochemical evidences, in which the whole set of components is applied a log-ratio transformation before any potential mapping technique is used. In this way, candidate zones can be identified by its high value in a certain ratio of elements, implying that the important information is a contrast betweeen two or more elements, and not an absolute concentration of one of them. Two different potential mapping techniques are used (a method equivalent to the Fisher rule, and a hierarchical binary logistic regression, both accounting for spatial dependence), with equivalent results.

Keywords: Geostatistics; clr; variation-variograms; centered log-ratio transformation; balance

Publ.-Id: 20106

Astrophysical and experimental implications from the magnetorotational instability of toroidal fields

Rüdiger, G.; Gellert, M.; Schultz, M.; Hollerbach, R.; Stefani, F.

The interaction of differential rotation and toroidal fields that are current-free in the gap between two corotating axially unbounded cylinders is considered. It is shown that non-axisymmetric perturbations are unstable if the rotation rate and Alfven frequency of the field are of the same order, almost independent of the magnetic Prandtl number Pm. For the very steep rotation law Omega proportional to R^2 (the Rayleigh limit) and for small Pm, the threshold values of rotation and field for this azimuthal magnetorotational instability (AMRI) scale with the ordinary Reynolds number and the Hartmann number, respectively. A laboratory experiment with liquid metals like sodium or gallium in a Taylor-Couette container has been designed on the basis of this finding. For fluids with more flat rotation laws, the Reynolds number and the Hartmann number are no longer typical quantities for the instability. For the weakly non-linear system, the numerical values of the kinetic energy and the magnetic energy are derived for magnetic Prandtl numbers <= 1. We find that the magnetic energy grows monotonically with the magnetic Reynolds number Rm, while the kinetic energy grows with Rm/root Pm. The resulting turbulent Schmidt number, as the ratio of the 'eddy' viscosity and the diffusion coefficient of a passive scalar (such as lithium), is of the order of 20 for Pm = 1, but for small Pm it drops to the order of unity. Hence, in a stellar core with fossil fields and steep rotation law, the transport of angular momentum by AMRI is always accompanied by an intense mixing of the plasma, until the rotation becomes rigid.

Publ.-Id: 20105

Numerical Modeling of Bubble Columns Using Experimental Breakup and Coalescence Rates of Bubbles

Azizi, S.; Schubert, M.

The prediction of bubbles size distributions in bubble columns reactors is a great challenge in design and optimization of operating conditions. The implementation of Population Balance Equations (PBE) for bubbly flows into CFD codes allowed better understanding of the hydrodynamic behavior of bubble columns and better quantification of the interfacial area for the estimation of interphase transport phenomena. On the other hand, the complexity of numerical models increased with the introduction of new sub-models for the determination of Bubble Size Distributions (BSD). The formulation of sink and source terms of such PBE is a very controversial issue. These terms depend on assumption on the dominating mechanisms due to turbulence, buoyancy, wake, shear, etc.. However, the unknown physical effects, the variety of constants of Breakup and Coalescence (B&C) kernels as well as their complex coupling with the hydrodynamics of the flow prevent to generalize existing models.
In this work, a new approach will be presented to determine B&C rates in bubble columns using experimental BSD data and hydrodynamic characteristics such as phase fractions at several column heights e.g. obtained by ultrafast X-ray tomography. To calculate the experimental B&C rates, a set of non-linear PBE is solved at each scanning height with the measured hydrodynamic data and statistical equations to consider diameter effect of coalescing bubbles.
The approach was applied to own experimental data and data from literature. Good agreement was found for the numerical simulated BSD and hydrodynamics based on the derived B&C rates compared to experimental data.
For future work, this approach allows to directly validate existing B&C models with different gas and liquid physical properties and operating conditions in order to formulate more generalized B&C models for their implementation in CFD models.

Keywords: Bubble Column; Breakup and Coalescence; Experimental Rates

  • Lecture (Conference)
    Annual Meeting of Computational Fluid Dynamics, Mixing processes and rheology, 24.-25.02.2014, Festung Marienberg Würzburg, Germany

Publ.-Id: 20104

An analytic approach to modeling the optical response of anisotropic nanoparticle arrays at surfaces and interfaces

Persechini, L.; Verre, R.; Mcalinden, N.; Wang, J.; Ranjan, M.; Facsko, S.; Shvets, I.; Mcgilp, J.

Anisotropic nanoparticle (NP) arrays with useful optical properties, such as localized plasmon resonances (LPRs), can be grown by self-assembly on substrates, but these systems often have significant dispersion in NP dimensions and distribution, which makes a numerical approach to modeling the LPRs very difficult. An improved analytic approach to this problem is discussed in detail and applied successfully to NP arrays from three systems that differ in NP metal, shape and distribution, and in substrate and capping layer. The materials and anisotropic NP structures that will produce LPRs in desired spectral regions can be determined using this approach.

Keywords: metallic nanoparticles; plasmonics

Publ.-Id: 20102

Speciation of actinides after plant uptake

Geipel, G.; Viehweger, K.

Besides natural the occurring actinides uranium and thorium the most impact of higher actinides in biological systems is connected to the release of transuranium elements in nuclear accidents as Chernobyl and Fukushima and from scenarios which are seen in the discussion of radioactive waste storage.
In radioactive waste storage sites in the deep underground, however, the first organism which may have contact to actinides are microorganism. In later transport to the earth surface these radionuclides may also access the food chain via several ways of uptake. One of these ways may occur by uptake of actinides by plants.
Nevertheless, the uptake depends on the bioavailability of these elements and therefore also on the speciation or binding form before and after uptake.

It can be stated already here, that some of these radionuclides are much less studied than others. This may be caused by the difficult handling of the radioelements, as they are α-emitting radionuclides and therefore special equipment in the laboratories is necessary as well as regulations of radiation protection have to be considered.

An introduction in the uptake of radionuclides by plants has been given by M. Greger. Besides the description of common uptake mechanisms only few information about actinides is given.
An overview about soil to plant transfer is given by D. Robertson et al. The factors vary very strong depending on plant species, soil and experimental conditions, but compared to Sr isotopes the values for actinides are smaller.

Keywords: Actinides; Speciation; Plants

  • Book chapter
    C. Walther, D.K. Gupta: Radionuclide Contamination and Remediation through Plants, Berlin, Heidelberg: Springer, 2014, 978-3-319-07665-2, 197-214

Publ.-Id: 20101

LC-MS Supported Investigation Of The In Vitro And In Vivo Metabolism Of [18F]Flubatine – A New Radiotracer For Imaging Of α4β2 Nicotinic Acetylcholine Receptors

Ludwig, F.-A.; Fischer, A.; Deuther-Conrad, W.; Donat, C. K.; Smits, B.; Hoepping, A.; Brust, P.; Steinbach, J.

Imaging of brain α4β2 nicotinic acetylcholine receptors (nAChRs), a subtype involved in learning and memory processes, can potentially help to predict prognosis of dementia in neurodegenerative disorders like Alzheimer´s disease (AD). Two [18F]flubatine enantiomers [18F]-1 (derivatives of homoepibatidine) are promising radiotracers for neuroimaging of α4β2-nAChRs [1] and are currently investigated in clinical studies. Therefore, their metabolism was investigated by two different approaches. Initially, (+)- and (−)-1, were incubated with liver microsomes from mouse or human to produce phase I metabolites. After precipitation with acetonitrile, LC-MS/MS studies of the supernatants were performed to compare metabolic stabilities and for structural elucidation of metabolites. Thereafter, (+)-[18F]-1 (~280 MBq) was injected into mice. Liver, plasma and urine samples were taken, precipitated and investigated by radio-HPLC. In order to conclude about chemical identities of the radiometabolites of (+)-[18F]-1, we applied identical chromatographic conditions to both LC-MS and radio-HPLC. LC-MS revealed that both flubatine enantiomers retained a high level of metabolic stability. Furthermore, they were metabolized to higher extent by mouse than by human microsomes. In direct comparison, (+)-1 proved to be more stable than (−)-1. A series of metabolites resulting from oxidation was detected (M0-M6). Presence of each metabolite was species and enantiomer dependent. MS/MS examinations revealed the azabicyclic ring system being exclusively affected by oxidation, namely C- and N-hydroxylation. Using 3-hydroxy flubatine as reference, we identified the radiolabelled derivative (Mc) as one of the metabolites. Correlation with radio-HPLC supports the existence of further radiometabolites resulting from oxidation beside others (Fig. 1). We conclude, that our combined approach offers a useful tool for assignment and finally identification of radiotracer metabolites.

[1] Brust, P. et al. Preclinical Aspects of Nicotinic Acetylcholine Receptor Imaging. In PET and SPECT of Neurobiological Systems; Dierckx, R. A.; Otte, A.; Vries, E. F. de; van Waarde, A.; Luiten, P. G., Eds.; Springer Berlin Heidelberg, 2014; pp 465-512.

  • Poster
    XIII Turku PET Symposium, 24.-27.05.2014, Turku, Finland

Publ.-Id: 20100

Purification Of Used Oxygen-18 Water: Quality Assessment And Re-use

Rötering, S.; Franke, K.; Zessin, J.; Brust, P.; Füchtner, F.; Steinbach, J.; Fischer, S.

Rapid development of PET and the design of larger targets cause a greater need of oxygen-18 enriched water as target material for fluorine-18 production and entail increased costs for oxygen-18 enriched water. This forced us to consider its re-use for research purposes. Used O-18 water is mainly contaminated with metal radionuclides, non-radioactive salts and organic solvents. Here, we present (i) two methods for the removal of organic contaminants, (ii) analytical methods for quality assessment and (iii) findings for irradiation and radiosyntheses using activity produced from re-cycled water. Samples of used target water (1 L containing 44 mg L>sup-1 acetone and 396 mg L>sup-1 ethanol) were treated with UV irradiation (254 nm) [1] or with KMnO4/NaOH at 50°C to reduce the concentration of these contaminants below 50 mg L>sup-1, respectively. Both methods allowed close-to-zero decrease of acetone and decrease of ethanol to 23 ± 20 mg L>sup-1 (n = 8). After vacuum distillation pure re-cycled water was obtained as proven by gamma spectrometry, gas chromatography, ICP-OES, and ion chromatography. Loss of O-18 enrichment (83%, pycnometry) was not observed. A reference study on O-16 water, contaminated by addition of 150 to 200 mg L>sup-1 methanol, ethanol, acetone and acetonitrile, showed a comparable oxidation potential of both methods for methanol, ethanol and acetone (decrease within 48 h below 50 mg L>sup-1). Oxidation of acetonitrile was only achieved with the UV-lamp within 7 days. Re-cycled water and virgin water (Hyox 18 Enriched Water), partly diluted to 83% O-18 enrichment, were irradiated in the Nirtra® Fluor L-target at a CYCLONE 18/9 (iba) with 35 µA and 11.7 µAh. Comparison of produced activities of F-18, N-13 and metal radionuclides confirmed the high quality of the re-cycled water. Compared to undiluted virgin water a loss of the production yield of ~19% was observed. No significant influence on the radionuclide purity or radiochemical reactivity was detected. F-18 obtained from virgin water or re-cycled water irradiation was comparably used for radiosyntheses. Results of automated radiosyntheses (TRACERLAB™ FX-FN) of our new α4β2 nicotinic receptor ligand [18F]flubatine (n=5) and σ1 receptor ligand [18F]fluspidine (n=8) as well as radiosyntheses for development of the α7 nicotinic receptor ligand [18F]NS14490 and 18F-labelled CB2-selective N-aryl-oxdiazolyl-propionamides revealed equivalent yields and unchanged product qualities. The described purification procedures enable a multiple re-cycling of target water for successful F-18 production and application for research purposes with reasonable production yields and efficient economical use of the target water.

[1] DE 29504388 U1, 1995

  • Poster
    XIII Turku PET Symposium, 24.-27.05.2014, Turku, Finland

Publ.-Id: 20099

Uranium(VI) and neptunium(V) retention by clay minerals and natural clay rock – Influence of clay organics, temperature and pore water salinity

Schmeide, K.; Joseph, C.; Fritsch, K.

The long-term disposal of high-level nuclear waste in deep geological formations is discussed worldwide as main strategy for nuclear waste management. In addition to salt and crystalline rock, argillaceous rock has been proposed as potential host rock and backfill material for nuclear waste repositories. This is due to favorable characteristics of clay minerals such as their swelling properties and their large surface areas leading to a low permeability and high retention efficiency toward radionuclides. Sorption and diffusion of safety relevant radionuclides on/in clay rock are important physicochemical processes that have to be studied to contribute to a reliable long-term safety assessment for future nuclear waste repositories.

Clay rock is closely associated with natural organic matter. Low molecular weight organic acids such as acetate, lactate, propionate and formate as well as fulvic and humic acid-like substances can be released from the clay under certain conditions [1]. These organics can influence the migration of radionuclides in the environment by forming soluble complexes or stable colloids. In addition, for the disposal of high-level nuclear waste in clay formations, elevated temperatures of up to 100 °C are expected close to the waste containers resulting from the radioactive decay of the stored radionuclides. Besides that, pore waters of North German clay deposits, considered for underground nuclear waste repositories, show relatively high salinities (2 to 3.5 M). Thus, effects of organic matter, temperature and salinity have to be taken into account for a reliable prediction of radionuclide migration in the geosphere.

Batch sorption studies with clay minerals revealed that the U(VI) sorption onto kaolinite [2] is much higher than the Np(V) sorption [3] in 0.1 M NaClO4. In the presence of humic acid, the actinide sorption is increased in the acidic pH range and decreased in the near-neutral pH range. The influence of ionic strength was studied for U(VI) sorption onto montmorillonite by applying 0.1 to 3 M NaCl and CaCl2 as background electrolytes. It was observed that the ionic strength effect on U(VI) sorption on montmorillonite is very small. In NaCl, a decrease of U(VI) sorption with ionic strength is only observed below pH 6 and up to an ionic strength of 2 M. In CaCl2, U(VI) sorption is at least partly governed by secondary phase formation.

The retention behavior of the natural clay rock Opalinus Clay (Mont Terri, Switzerland) toward U(VI) was studied by means of batch sorption and diffusion experiments. Opalinus Clay is considered as representative host rock of a potential nuclear waste repository in argillaceous rock. For the U(VI) sorption onto Opalinus Clay in synthetic Opalinus Clay pore water (pH = 7.6, I = 0.36 M) at 25 °C, the distribution coefficient, Kd, was determined with 22.2 ± 0.4 L/kg [4]. This shows that the U(VI) sorption is relatively weak under pore water conditions. It is comparable to the Np(V) sorption onto Opalinus Clay (25 ± 5 L/kg [5]). This can be attributed to the predominance of the weakly sorbing Ca2UO2(CO3)3(aq) complex in the Opalinus Clay pore water.

The U(VI) sorption onto Opalinus Clay was also studied in 0.1 M NaClO4 in the pH range 3 to 10. Results of surface complexation modelling [6], applied for blind prediction of pH-dependent U(VI) sorption onto Opalinus Clay, showed that U(VI) may predominantly sorb onto illite and montmorillonite. In addition, U(VI) sorption onto Fe(III) minerals was predicted. U(VI) sorption onto further minerals of the clay (kaolinite, chlorite, quartz, feldspars) is negligible.

With increasing concentration of low molecular weight organic acids (10-5 to 10-2 M), the U(VI) sorption onto Opalinus Clay in pore water decreases due to complex formation in solution. The mobilizing effect of the organics on U(VI) increases in the following sequence: formate < lactate ~ acetate ≤ propionate < tartrate < citrate. In the presence of 1×10-2 M citrate, which has been identified as important ligand in radioactive waste problems, the Kd value for U(VI) amounts to only (1.1 ± 0.3) L/kg. The influence of the organic ligands on the U(VI) sorption onto Opalinus Clay correlates with the stability of the respective U(VI) complexes. In contrast, humic acid (≤ 50 mg/L) does not affect U(VI) sorption [4]. With increasing temperature up to 60 °C, the U(VI) sorption increases both in the absence and in the presence of clay organics.

The U(VI) diffusion in compacted Opalinus Clay was studied in the absence and presence of humic acid at 25 and 60 °C under anaerobic conditions using Opalinus Clay pore water [7]. The effective diffusion and distribution coefficients (De and Kd) determined for U(VI) and humic acid at 25 and 60 °C show that humic acid has no significant influence on the U(VI) diffusion. The diffusion profiles obtained for humic acid in Opalinus Clay at 25 and 60 °C show contributions of at least two different humic acid particle size fractions (< 1 kDa and 10−100 kDa). The smaller humic acid fraction diffused through the whole clay samples at both temperatures within three months whereas the larger humic acid fraction diffused only about 500 µm into the clay. This shows the filtration effect of the compacted clay and also a different sorption affinity of the humic acid size fractions toward Opalinus Clay. At 60 °C, the diffusion profiles of two U(VI) species were observed, which were attributed to a colloidal and an aquatic U(VI) species. The De and Kd value of the aquatic U(VI) species increased with increasing temperature. However, these changes compensated each other, thus, an increase of the temperature to 60 °C did not accelerate the migration of U(VI) through Opalinus Clay.

Under environmentally relevant conditions (pH > 7), U(VI) is only weakly sorbed by the natural clay rock Opalinus Clay. However, since molecular diffusion is the decisive retardation process in clay rock, Opalinus Clay has a good retention potential toward U(VI).

[1] Courdouan, A. et al. (2007) Appl. Geochem. 22, 2926-2939.
[2] Křepelová, A. et al. (2006) Radiochim. Acta 94, 825-833.
[3] Schmeide, K. and Bernhard, G. (2010) Appl. Geochem. 25, 1238-1247.
[4] Joseph, C. et al. (2011) Chem. Geology 284, 240-250.
[5] Wu, T. et al. (2009) Environ. Sci. Technol. 43, 6567-6571.
[6] Joseph, C. et al. (2013) Appl. Geochem. 36, 104-117.
[7] Joseph, C. et al. (2013) Geochim. Cosmochim. Acta 109, 74-89.

Keywords: U(VI); Np(V); Opalinus Clay; clay minerals; adsorption; diffusion; clay organics; humic acid; fulvic acid; temperature

  • Invited lecture (Conferences)
    51st Annual Meeting of the Clay Minerals Society, Texas A&M University, 17.-21.05.2014, College Station, Texas, USA
  • Contribution to proceedings
    51st Annual Meeting of the Clay Minerals Society, Texas A&M University, 17.-21.05.2014, College Station, Texas, USA

Publ.-Id: 20098

Electrical Characterization of Single Molecules via Mechanically Controllable Break Junctions

Wieser, M.; Sendler, T.; Weisbrod, S.; Tang, Z.; Marx, A.; Wolf, J.; Huhn, T.; Scheer, E.; Moresco, F.; Grebing, J.; Erbe, A.

Molecular electronics has been a field of big interest for the last years. Using the technique of mechanically controllable break junctions we characterize different organic molecules, e.g. 1,4-Diethoxy-2,5-bis(4-sulfanyl-phenylethynyl)-benzene (PEEB) and switchable molecular wires, dissolved in an organic non-polar solvent. IV-curves taken from the molecules connected to single gold atom contacts show the expected tunneling behavior described by the single-level model: weak coupling of the molecules to the gold atoms implies an off-resonant tunneling process and a transport through a single channel. Varying the end-groups of the molecules leads to a different transport behavior. Figure 1 shows a 2D histogram of IV-curves of PEEB with amino end-groups. Based on the single-level transport model the analysis of the current-voltage characteristics delivers the energy of the molecular level and the coupling between electrode and molecule. It also indicates a reliable contact of the molecules to the gold atoms. A further goal is the investigation of an electric gate effect on the transport behavior through the molecules.

Keywords: Molecular Electronics; Electronic Transport

  • Poster
    IHRS NANONET Annual Workshop 2013, 10.10.2013, Dresden, Deutschland

Publ.-Id: 20097

Electrical Characterization of Single Organic Molecules via Mechanically Controllable Break Junctions

Sendler, T.; Wieser, M.; Liu, S.-P.; Weisbrod, S.; Tang, Z.; Marx, A.; Wolf, J.; Huhn, T.; Scheer, E.; Moresco, F.; Grebing, J.; Erbe, A.

Molecular electronics has been of big interest for the last years. To allow an electrical characterization of single molecules a reliable contact to gold atoms is required. We ensure this by using single organic molecules with a plain structure, in particular 1,4-Diethoxy-2,5-bis (4-sulfanyl-phenylethynyl)-benzene and single stranded DNA fragments, dissolved in an organic non-polar solvent. For measurements we use the technique of mechanically controllable break junctions. IV-curves taken from single molecules connected to single gold atom contacts show the expected tunneling behavior, from which we gain the energy of the molecular level and the coupling between electrode and molecule.

Keywords: Molecular Electronics; Electronic Transport

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 20096

Direct Determination of Exchange Parameters in Cs2CuBr4 and Cs2CuCl4: High-Field Electron-Spin-Resonance Studies

Zvyagin, S. A.; Kamenskyi, D.; Ozerov, M.; Wosnitza, J.; Ikeda, M.; Fujita, T.; Hagiwara, M.; Smirnov, A. I.; Soldatov, T. A.; Shapiro, A. Y.; Krzystek, J.; Hu, R.; Ryu, H.; Petrovic, C.; Zhitomirsky, M. E.

Spin-1/2 Heisenberg antiferromagnets Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures are studied by means of electron spin resonance spectroscopy in magnetic fields up to the saturation field and above. In the magnetically saturated phase, quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their Exchange parameters. The viability of the proposed method was proven by applying it to Cs2CuCl4, yielding J/kB = 4.7(2) K, J'/kB = 1.42(7) K, [J'/J ≃ 0.30] and revealing good agreement with inelastic neutronscattering results. For the isostructural Cs2CuBr4, we obtain J/kB = 14.9(7) K, J'/kB = 6.1(3) K, [J'/J ≃ 0.41], providing exact and conclusive information on the exchange couplings in this frustrated spin system.

Publ.-Id: 20095

Radiation Thermometry—Sources of Uncertainty During Contactless Temperature Measurement

Reichel, D.; Schumann, T.; Skorupa, W.; Lerch, W.; Gelpey, J.

Short Time Annealing on a microsecond to nanosecond scale presents new challenges to temperature measurement. Pyrometers are widely used owing to their commercial availability, short response time, easy handling and contactless operation. However, they hold a source for considerable measurement errors. False readings are easily gained producing large errors during temperature measurement.
This chapter intends to give the reader an overview on characteristic features associated with Radiation Thermometry in a broader sense and more specifically with Pyrometry.

Keywords: short time annealing; temperature measurement; pyrometry; flash lamps

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 211-228
    DOI: 10.1007/978-3-319-03131-6_12

Publ.-Id: 20094

Hydrophobicity of Minerals Determined by Atomic Force Microscopy – A Tool for Flotation Research

Rudolph, M.; Peuker, U. A.

The mineral separation process flotation is fundamentally relying on hydrophobic interactions, which are still not entirely understood and heavily discussed in literature. We introduce the various possibilities to determine hydrophobic properties of mineral surfaces in water using the concept of colloidal probe atomic force microscopy. We base our method on the most accepted theories of the hydrophobic effect of hydrophobic surfaces in water, which consider nanoscopic gas layers to be responsible for the long range interactions. Finally, we correlate the hydrophobic parameters with microflotation experiments for magnetite and quartz surfaces.

Keywords: Atomic Force Microscopy; Colloidal Probe; Flotation; Hydrophobic Interactions; Nanobubbles

Publ.-Id: 20093

All-optical helicity dependent magnetic switching in an artificial zero moment magnet

Schubert, C.; Hassdenteufel, A.; Matthes, P.; Schmidt, J.; Helm, M.; Bratschitsch, R.; Albrecht, M.

Low remanent magnetization as key prerequisite for the ability of helicity dependent all-optical magnetic switching (AOS) is demonstrated for an artificial zero moment magnet. A heterostructure consisting of two amorphous ferrimagnetic Tb36Fe64 and Tb19Fe81 alloy layers is designed to yield a zero remanent net magnetization at room temperature by means of an antiparallel interfacial exchange coupling of the dominant magnetic moments. The canceling layer magnetizations provide vanishing demagnetization fields and the ability of AOS. Contrary to this, no all-optical switching is observed for single Tb36Fe64 and Tb19Fe81 films. This study provides further evidence that the ability for all-optical magnetic switching is correlated to the remanent sample magnetization and thus to the difference in magnetic moment of the rare-earth and transition-metal sublattices.

Keywords: optical switching; magnetic switching; magnetic film

Publ.-Id: 20092

TCR/CD3 activation and co-stimulation combined in one T cell retargeting system improve anti-tumor immunity

Cartellieri, M.; Arndt, C.; Feldmann, A.; von Bonin, M.; Ewen, E.-M.; Koristka, S.; Michalk, I.; Stamova, S.; Berndt, N.; Gocht, A.; Bornhäuser, M.; Ehninger, G.; Schmitz, M.; Bachmann, M.

We have recently described a novel modular targeting platform for T cell recruitment that not only efficiently replaces but also is superior to conventional T cell-engaging bispecific antibodies as it allows for the flexible targeting of several antigens and the delivery of co-stimulatory ligands to malignant lesions, thereby enhancing the antitumor potential of redirected T cells.

Keywords: acute myeloid leukemia; CD33; CD137; co-stimulatory ligands; immunotherapy; modular targeting system; single-chain bispecific antibodies; T-cell retargeting

Publ.-Id: 20091

III-V/Si on silicon-on-insulator platform for hybrid nanoelectronics

Prucnal, S.; Zhou, S.; Ou, X.; Facsko, S.; Liedke, M. O.; Bregolin, F.; Liedke, B.; Grebing, J.; Fritzsche, M.; Hübner, R.; Mücklich, A.; Rebohle, L.; Helm, M.; Turek, M.; Drozdziel, A.; Skorupa, W.

The unique properties of SOI wafers enable the integration of heterogeneous materials with distinct functionalities in different layers. In particular, III-V compound semiconductors are very attractive for low-noise and high-speed electronic and photonic components integrated on a single chip. We have developed a CMOS compatible and fully integrated solution for the integration of III-V compound semiconductors with silicon technology for optoelectronic applications. InAs compound semiconductor nanostructures are synthesized in SOI wafers using the combined ion beam implantation and millisecond liquid-phase epitaxial growth. Optoelectronic and microstructural investigations carried out on implanted, annealed and selectively etched samples confirm the formation of high-quality III-V compound semiconductor nanostructures.

Keywords: Ion Implantation; Flash Lamp Annealing; InAs; SOI; heterojunction

  • Journal of Applied Physics 115(2014), 074306
    Online First (2014) DOI: 10.1063/1.4865875

Publ.-Id: 20090

Zero-field spin-transfer oscillators combining in-plane and out-of-plane magnetized layers

Fowley, C.; Sluka, V.; Bernert, K.; Lindner, J.; Fassbender, J.; Rippard, W. H.; Pufall, M. R.; Russek, S. E.; Deac, A. M.

Excited magnetization dynamics in a spin-valve device consisting of an in-plane polarizer and an out-of-plane free layer were studied numerically. In the case where the free layer is assumed to lack any in-plane anisotropy components, a finite external field is required to generate steady-state dynamics, in agreement with previous reports. We demonstrate that this constraint can be removed and precession can be stabilized in zero applied field by introducing an additional in-plane anisotropy axis. Moreover, the in-plane anisotropy offers an additional degree of freedom for tuning the frequency response of the device.

Keywords: spin transfer torque; spin valve; spin transfer oscillator; magnetisation dynamics; zero-field oscillator; perpendicular magnetic anisitropy

  • Applied Physics Express 7(2014)4, 043001
    DOI: 10.7567/APEX.7.043001
  • Poster
    Intermag Beijing 2015, 11.-15.05.2015, Beijing, China

Publ.-Id: 20089

Environmental fate of TiO2 nanoparticles

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

Vortrag im Rahmen des IRE STATUS-SEMINAR 2013 „Nuclear Safety Research – From Reactors to Disposal“ 11. - 13.12.2013 in Dresden
Präsentation von Ergebnissen aus den Projekten NanoTrack und QNano

  • Lecture (Conference)
    STATUS-SEMINAR 2013 „Nuclear Safety Research – From Reactors to Disposal“, 11.-13.12.2013, Rossendorf, Deutschland

Publ.-Id: 20088

In-medium QCD sum rules for D mesons: A projection method for higher order contributions

Buchheim, T.; Hilger, T.; Kämpfer, B.

D mesons serve as excellent probes of hot and/or dense strongly interacting matter. They can provide insight into the restoration of chiral symmetry. The chiral condensate as well as other chirally odd condensates, such as certain four-quark condensates, are linked to order parameters of spontaneous chiral symmetry breaking. Thus, the evaluation of these higher order condensate contributions in the framework of QCD sum rules is of high interest. We present a general method for projecting Lorentz indices of ground state expectation values providing a crucial step towards a comprehensive calculation of higher order corrections to the operator product expansion of hadrons, especially D mesons, in a strongly interacting medium.

Publ.-Id: 20086

Evaluation of PET quantification accuracy in vivo - Comparison of measured FDG concentration in the bladder with urine samples / In-vivo-Evaluation der Quantifizierungsgenauigkeit der PET - Vergleich der gemessenen FDG-Konzentration in der Blase mit Urinproben

Maus, J.; Hofheinz, F.; Schramm, G.; Oehme, L.; Beuthien-Baumann, B.; Lukas, M.; Buchert, R.; Steinbach, J.; Kotzerke, J.; van den Hoff, J.

Quantitative positron emission tomography (PET) requires accurate scanner calibration, which is commonly performed using phantoms. It is not clear to what extent this procedure ensures quantitatively correct results in vivo, since certain conditions differ between phantom and patient scans.
Aim: We, therefore, have evaluated the actual quantification accuracy in vivo of PET under clinical routine conditions.
Patients, methods: We determined the activity concentration in the bladder in patients undergoing routine [18F]FDG whole body investigations with three different PET scanners (Siemens ECAT EXACT HR+ PET: n = 21; Siemens Biograph 16 PET/CT: n = 16; Philips Gemini-TF PET/CT: n = 19). Urine samples were collected immediately after scan. Activity concentration in the samples was determined in well counters cross-calibrated against the respective scanner. The PET (bladder) to well counter (urine sample) activity concentration ratio was determined.
Results: Activity concentration in the bladder (PET) was systematically lower than in the urine samples (well counter). The patient-averaged PET to well counter ratios for the investigated scanners are (mean ± SEM): 0.881 ± 0.015 (ECAT HR+), 0.898 ± 0.024 (Biograph 16), 0.932 ± 0.024 (Gemini-TF). These values correspond to underestimates by PET of 11.9%, 10.2%, and 6.8%, respectively.
Conclusions: The investigated PET systems consistently underestimate activity concentration in the bladder. The comparison of urine samples with PET scans of the bladder is a straightforward means for in vivo evaluation of the expectable quantification accuracy. The method might be interesting for multi-center trials, for additional quality assurance in PET and for investigation of PET/MR systems for which clear proof of sufficient quantitative accuracy in vivo is still missing.

Für die Bestimmung quantitativer Parameter mittels Positronenemissionstomo graphie (PET) ist eine genaue Kalibrierung des PET-Scanners mit Hilfe geeigneter Phantommessungen notwendig. Auf Grund der offensichtlichen Unterschiede zwischen Phantom- und Patientenmessungen bestehen jedoch Unsicherheiten im Bezug auf die In- vivo- Genauigkeit einer solchen phantom-basierten Kalibrierung. Ziel dieser Studie war es daher die Genauigkeit
einer solchen Kalibrierung mittels klinischer Routinemessungen in vivo zu evaluieren.
Patienten, Methoden: Wir bestimmten die Aktivitätskonzentration in der Blase bei Patienten die an unterschiedlichen PET-Scannern eine [18F]FDG-Ganzkörperuntersuchung erhielten (Siemens ECAT EXACT HR+ PET: n = 21; Siemens Biograph 16 PET/CT: n = 16; Philips Gemini-TF PET/CT: n = 19). Unmittelbar nach Messung der Blasenregion gaben alle Patienten Urinproben ab. Die Aktivitätskonzentration der Urinproben wurde mit Hilfe eines kreuzkalibrierten Bohrlochzählers bestimmt. Im Anschluss wurde das Verhältnis zwischen Aktivitätskonzentration PET (Blase) zu Bohrlochzähler (Urinprobe) berechnet.
Ergebnisse: Die Aktivitätskonzentration in der Blase (PET) war systematisch niedriger als die der Urinproben (Bohrlochzähler). Das über die jeweiligen Patienten gemittelte Verhältnis zwischen PET und Bohrlochzähler war für die untersuchten Scanner (Mittelwert ± SEM): 0,881 ± 0,015 (ECAT HR+), 0,898 ± 0,024 (Biograph 16), 0,932 ± 0,024 (Gemini-TF). Diese Werte entsprechen Unterschätzungen der Aktivitätskonzentration durch die PET von jeweils 11,9%, 10,2% und 6,8%.
Schlussfolgerungen: Die untersuchten PETSysteme unterschätzen die Aktivitätskonzentration in der Blase. Der direkte Vergleich von Urinproben und PET-Bildern der Blase stellt eine einfache Art der In-vivo-Evaluation der zu erwartenden Quantifizierungsgenauigkeit eines PET-Scanners dar. Die vorgestellte Methode kann für Multicenterstudien, für eine zusätzliche Qualitätssicherung in der PET sowie für eine Untersuchung von PET/MRSystemen
interessant sein, für die es hinsichtlich einer ausreichenden Quantifizierungsgenauigkeit in vivo noch keine belastbaren Zahlen gibt.

Keywords: PET; quantification; accuracy; in vivo; multicenter; QA; PET; Quantifizierung; Genauigkeit; in vivo; Multicenter; QA

Publ.-Id: 20085

Influence of speciation during membrane treatment of uranium contaminated water

Hoyer, M.; Zabelt, D.; Steudtner, R.; Brendler, V.; Haseneder, R.; Repke, J.

Membrane treatment can be used to selectively remove chemical species from effluents. However, speciation depends on different chemical factors such as inorganic and organic reaction partners, tem-perature, and pH, complicating a deeper understanding of underlying mechanisms. In this study the potential of membrane separation for selective uranium removal was assessed. Speciation for complex chemical conditions in two real water samples was determined independently by predictive speciation modelling, and direct measurement using cryo-TRLFS (time-resolved laser-induced fluorescence spectroscopy). Different nanofiltration membranes and reverse osmosis membranes were characterized for their potential rejection, and pure water flux. The best performing membrane was then employed in cross-flow experiments and reached retentions over 99 % and U/Na-selectivities of 200. Uranium retentions showed a low dependency on feed uranium speciation. Continuing research is necessary for an exact determination of separation mechanisms for each membrane.

Keywords: Separation; Water treatment; uranium; speciation; spectroscopy; membranes; retention; selectivity; modelling

Publ.-Id: 20084

Assessment of accident management measures on early in-vessel station blackout sequence at VVER-1000 pressurized water reactors

Tusheva, P.; Schäfer, F.; Reinke, N.; Kamenov, A.; Mladenov, I.; Kamenov, K.; Kliem, S.

In the process of elaboration and evaluation of severe accident management guidelines, the assessment of the accident management measures and procedures plays an important role. This paper investigates the early in-vessel phase accident progression of a hypothetical station blackout scenario for a generic VVER-1000 pressurized water reactor. The study focuses on the following accident management measures: primary side depressurization with passive safety systems injection, secondary side depressurization with passive feeding from the feedwater system, and a combination of the both procedures. The analyses have been done with the mechanistic computer code ATHLET. The simulations give in-depth analyses of the reactor system behaviour, assessment of the time margins till heating up of the reactor core and insights into physical phenomena which can influence the passive feeding procedures for cooling of the reactor core. The simulation results show that such accident management measures can significantly prolong the time till core degradation. Maximum delay for core heat up can be achieved by sequentially realization of the secondary and primary side bleed and feed strategies. Due to reversed heat transfer in the steam generators or caused by the depressurization itself a part of the injected water is evaporated. Evaporation or flashing in the feedwater system can lead to an intermittent water injection, thus reducing the effectiveness of the feeding procedure.

Keywords: VVER-1000 reactor; severe accidents; station blackout; accident management measures; flashing

Publ.-Id: 20083

The Ion Beam Center at the HZDR, nanocomposite growth with ions, and cluster tool setting up

Krause, M.

The talk will first emphasize the role of the Ion Beam Center as large scale facility within our research center. Recent results of ion-assisted growth of carbon:metal nanocomposite thin films will be shown in the second part. In the third part of the talk the concept and the current state of the setting up of the cluster tool at the Ion Beam Center will be presented. Examples for possible in situ experiments are given. They include the layer exchange in carbon: nickel double layers, the growth mechanism of carbon on metals at different temperatures, the thermal stability and graphitization of carbon: metal films, and the graphitization of carbon implanted in metals.

  • Lecture (others)
    Seminar at Abengoa Research, 12.02.2014, Seville, Spain

Publ.-Id: 20082

Medium effects in proton-induced K0 production at 3.5 GeV

Agakishiev, G.; Arnold, O.; Balanda, A.; Belver, D.; Belyaev, A. V.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Göbe, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kornakov, G.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.; Gaitanos, T.; Weil, J.

We present the analysis of the inclusive K0 production in p+p and p+Nb collisions measured with the HADES detector at a beam kinetic energy of 3.5 GeV. Data are compared to the GiBUU transport model. The data support the presence of a repulsive momentum-dependent kaon potential as predicted by the Chiral Perturbation Theory (ChPT). For the kaon at rest and at normal nuclear density, the ChPT potential amounts to 35 MeV. A detailed tuning of the kaon production cross sections implemented in the model has been carried out to reproduce the experimental data measured in p+p collisions. The uncertainties in the parameters of the model were examined with respect to the sensitivity of experimental results from p+Nb collisions to the in-medium kaon potential.

Publ.-Id: 20081

Associate K0 production in p+p collisions at 3.5 GeV: The role of Δ(1232)++

Agakishiev, G.; Arnold, O.; Balanda, A.; Belver, D.; Belyaev, A. V.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Göbe, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kornakov, G.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.

An exclusive analysis of the 4-body final states Λ+p+π +K0 and Σ0+p+π++K0 measured with HADES for p+p collisions at a beam kinetic energy of 3.5 GeV is presented. The analysis uses various phase space variables, such as missing mass and invariant mass distributions, in the four particle event selection (p, π+, π+, π-) to find cross sections of the different production channels, contributions of the intermediate resonances Δ++ and Σ(1385)+ and corresponding angular distributions. A dominant resonant production is seen, where the reaction Λ+Δ+++K0 has an about ten times higher cross section (29.45 ±0.08 +1.67 -1.46 ±2.06 μb) than the analougous non-resonant reaction (2.57 ±0.02 +0.21 -1.98 ±0.18 μb). A similiar result is obtained in the corresponding Σ 0 channels with 9.26 ±0.05 +1.41 -0.31 ±0.65 μb in the resonant and 1.35 ±0.02 +0.10 -1.35 ±0.09 μb in the non-resonant

Publ.-Id: 20080

Ab-initio investigation of carbides and of CNT junctions at finite temperature and under stress.

Kelling, J.; Gemming, S.

With the presented work we lay the foundation for ab-initio studies of contacted carbon nanotubes with both metal and metal--carbide leads. We Focus on applying the frozen phonon method on top density-functional-theory calculations for electronic the system. Here we show our ab-initio results on the elastic and electronic properties of Al4C3 and the metastable Ni3C.

Furthermore we present an alternative non-perturbative approach to calculating the quantum conductance in CNT/molecular junctions at finite temperature. Strictly employing the Born--Oppenheimer approximation, we aim to calculate the influence of phonons on the conductance of such a system by averaging over a representative sample drawn from snapshots of thermal fluctuation of the lattice.

  • Poster
    NanoNet Workshop, 10.10.2013, Rossendorf, Deutschland

Publ.-Id: 20079

Millisecond-range liquid-phase processing of silicon-based hetero-nanostructures

Prucnal, S.; Skorupa, W.

The downscaling and stressor technology of Si based devices is extending the performance of the silicon channel to its limits. Further downsizing of CMOS devices below 16 nm will need to solve some of the practical limits caused by one of the integration issues, such as chip performance, cost of development and production, power dissipation, reliability, etc. One solution for the performance progress which can overcome the downsizing limit in silicon technology is the integration of different functional optoelectronic elements within one chip.
We have realized a compact, CMOS compatible and fully integrated solution for the integration of III-V compound semiconductors with silicon technology for optoelectronic applications. The III-V nanostructured semiconductors are synthesized in either silicon or SOI wafers using the combined ion implantation and millisecond flash lamp annealing (FLA) techniques [1]. The FLA appears to be the most suitable one for this purpose. The energy budget introduced to the sample during FLA is sufficient to recrystallize silicon amorphized during implantation and to form III-V nanocrystals (NCs). In this paper we will present research results of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs and InP) formed in silicon and on SOI wafers. The influence of the annealing conditions and the lattice mismatch between III-V semiconductors and silicon on the shape of the III-V quantum dots will be examined. The annealing is performed at temperatures by far exceeding the melting point of bulk compound semiconductors, which leads to the formation of III-V nanostructures due to liquid phase epitaxy and enhances the probability for the incorporation of silicon atoms into III-V NCs. Silicon atoms are commonly used as n-type dopants in most III-V semiconductors. Therefore, liquid phase processing leads to the formation of heavily n-type doped single crystalline III-V nanostructures on silicon. If we consider that the synthesized NCs are n-type, by using a p-type silicon substrate a heterojunction can be formed between the III-V NCs and p-type Si. Conventional selective etching has been used to form the n-III-V/p-Si heterojunction. Current-voltage measurements confirm the heterojunction diode formation between n-type III-V quantum dots and p-type Si. The main advantage of our method is its ability to be integrated into large-scale silicon technology, which also allows applying it to Si-based optoelectronic devices.

Keywords: liquid phase epitaxy; Flash Lamp Annealing; ion implantation; compound semiconductors; silicon

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 189-210
    DOI: 10.1007/978-3-319-03131-6_11

Publ.-Id: 20078

Effect of solvent exchange on the stability of sterically functionalized magnetite nanoparticles in poly(methyl methacrylate)-solutions and resulting spray dried composites

Bremerstein, T.; Rudolph, M.; Peuker, U. A.

In this study highly filled nanoparticle-polymer-composites consisting of the polymer poly(methyl methacrylate) and magnetite nanoparticles are synthesized via the solution and spray drying method. The synthesis process is carried out for two different solvents, dichloromethane and ethyl acetate, and the resulting suspensions and composites are compared to each other. The preparation of the composites consists of the following steps: First the magnetite nanoparticles are precipitated in an aqueous phase. In the next step the nanoparticles are coated with ricinoleic acid for stabilization and are transferred to the organic solvent dichloromethane. In a rotating evaporator the solvent dichloromethane is exchanged with ethyl acetate. Finally, the nanoparticles in the respective solvent and dissolved polymer are mixed and spray dried.
The stability of the nanoparticle suspensions is characterized using thermogravimetric and photometric analyses. The specific surface of spray dried composites is determined via BET measurements and the distribution of the nanoparticles is assessed with BSE-SEM imaging and laser diffraction.
The stability of the nanoparticles is independent of the examined solvents. Both solvents provide a homogeneous distribution of nanoparticles in the composite at high filler concentrations.

Keywords: Polymer nanocomposites; Spray drying; Magnetite nanoparticles; Solvent; Ethyl acetate; Dichloromethane

Publ.-Id: 20077

High Conversion Th-U233 fuel for current generation of PWRs: Part II – 3D full core analysis

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

This study explores a possibility of designing a high conversion (HC) Th-U233 core for current generation of Pressurized Water Reactors (PWRs). Increasing the conversion ratio in existing PWRs can potentially improve the utilization of natural resources, through the exploitation of vast thorium reserves and reduction in natural uranium demand.
HC can be achieved through the use of heterogeneous seed-blanket (SB) Th-U233 fuel assembly design, where the supercritical seed works as a neutron supplier, while the subcritical blanket acts as U233 breeder. One of the main challenges associated with the heterogeneous SB fuel assembly designs is significant power imbalance between the seed and blanket regions caused by the high concentration of fissile material in the seed region and consequently requiring a substantial reduction in the core average power density.
The main objectives of the current work are: 1) to design a high conversion SB Th-U233 fuel assembly which is directly retrofittable into existing PWRs without introducing significant modifications into the core and plant design; 2) to estimate the reasonably achievable core power density level at which reactor safety is not compromised by performing 3D coupled neutronic and thermal-hydraulic (T-H) analysis of a typical PWR core fully loaded with HC Th-U233 SB fuel.
Part II of the paper reports on the steady-state whole core analysis of 100% Th-U233 fueled PWR. The results of this study demonstrate the principal feasibility of operating a self-sustainable Th-U233 PWR core at power density of 60 W/cc in three-batch annual fuel cycle without exceeding the main safety limits.

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

Publ.-Id: 20076

High Conversion Th-U233 fuel for current generation of PWRs: Part I – assembly level analysis

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

This study explores a possibility of designing a high conversion (HC) Th-U233 core for current generation of Pressurized Water Reactors (PWRs). Increasing the conversion ratio in existing PWRs can potentially improve the utilization of natural resources, through the exploitation of vast thorium reserves and reduction in natural uranium demand.
HC can be achieved through the use of heterogeneous seed-blanket (SB) Th-U233 fuel assembly design where the supercritical seed works as a neutron supplier, while the subcritical blanket acts as U233 breeder. One of the main challenges associated with the heterogeneous SB fuel assembly designs is a significant power imbalance between the seed and blanket regions caused by the concentration of fissile material primarily in the seed zone and consequently requiring a substantial reduction in the core average power density.
The main objectives of the current work are: 1) to design a high conversion SB Th-U233 fuel assembly which is directly retrofittable into existing PWRs without introducing significant modifications into the core and plant design; 2) to estimate the reasonably achievable core power density level at which reactor safety is not compromised by performing 3D coupled neutronic and thermal-hydraulic (T-H) analysis of a typical PWR core fully loaded with HC Th-U233 SB fuel.
Part I of the paper presents the results of the assembly-level parametric study aiming at the selection of a number of SB fuel assembly configurations for the following whole-core analysis. The assembly configurations are selected according to their potential to satisfy the specified fuel cycle requirements and comply with the T-H safety limits.
The results of the 3D full core analysis are reported in Part II of the paper.

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

Publ.-Id: 20075

Infrared spectroscopy on lipid–protein interactions: what crystals don't tell

Fahmy, K.

Membrane proteins fulfil vital functions in cellular signalling and ion exchange across cell membranes. Their function originates in well defined structural transitions of transmembrane and extramembraneous protein domains. The latter experience aqueous and hydrophobic solvation forces, respectively. We have used time-resolved FTIR spectroscopy coupled to static fluorescence measurements to study how this solvation balance at the membrane water interface affects membrane protein structure. Transmembrane peptides derived from rhodopsin, a prototypical G protein-coupled receptor (GPCRs), exhibit solvent-accessible stretches which couple protonation and hydration to local helical structure: protonation of a conserved cytosolic site in helix 3 (Glu-134) causes side chain partitioning at the water lipid interface [1]. Vice versa, the side chain charge affects structural transitions that are induced by transients (seconds) of interfacial water potential. These local processes depend on the hydrophobic context of the amino acid sequence. Opsin mutants containing amino acid replacements of the same carboxyl side chain also exhibit altered responses of their structure to water potential. The data indicate that the conserved carboxyl in helix 3 of GPCRs is a protonation-controlled hydration site that regulates the partial entry of water at the protein lipid interface, thereby contributing to the free enthalpy difference between active and inactive structures of the receptor.

Keywords: infrared spectroscopy; membrane protein; lipid

  • Invited lecture (Conferences)
    564. WE-Heraeus-Seminar: Physical Approaches to Membrane Proteins, 25.-28.05.2014, Bad Honnef, Deutschland

Publ.-Id: 20074

Experimental and Theoretical Approaches to Redox Innocence of Ligands in Uranyl Complexes: What is Formal Oxidation State of Uranium in Reductant of Uranyl(VI)?

Takao, K.; Tsushima, S.; Ogura, T.; Tsubomura, T.; Ikeda, Y.

Redox behavior of [UO2(gha)DMSO]−/0 couple (gha = glyoxal bis(2-hydroxanil)ate, DMSO = dimethyl sulfoxide) in DMSO solution was investigated by cyclic voltammetry and UV-vis-NIR spectroelectrochemical technique, as well as density functional theory (DFT) calculations. [UO2(gha)DMSO] was found to be formed via one-electron reduction of UO2(gha)DMSO without any successive reactions. The observed absorption spectrum of [UO2(gha)DMSO], however, has clearly different characteristics from those of uranyl(V) complexes reported so far. Detailed analysis of molecular orbitals and spin density of the redox couple showed that the gha2− ligand in UO2(gha)DMSO is reduced to gha●3− to give [UO2(gha)DMSO] and the formal oxidation state of U remains unchanged from +6. In contrast, the additional DFT calculations confirmed that the redox reaction certainly occurs at the U center in other uranyl(V/VI) redox couples we found previously. The non-innocence of the Schiff base ligand in the [UO2(gha)DMSO]−/0 is due to the lower energy level of LUMO in this ligand relative to those of U 5f orbitals. This is the first example of the non-innocent ligand system in the coordination chemistry of uranyl(VI).

  • Inorganic Chemistry 53(2014)11, 5772-5780
    Online First (2014) DOI: 10.1021/ic5006314

Publ.-Id: 20073

Simulation of multilayer particle resuspension in an obstructed channel flow

Lecrivain, G.; Vitsas, A.; Boudouvis, A. G.; Hampel, U.

The present work deals with the multilayer resuspension of solid aerosol particles off a multilayer deposit exposed to a sudden gas flow increase. The heavy detachment of particles spans a wide range of industrial and non-industrial applications. It is used extensively in applications dealing with the resuspension of dust by wind, the resuspension of particles in ventilation ducts and the resuspension of radioactive graphite particles in high temperature reactors. A new numerical approach is suggested to simulate the particle resuspension off a multilayer deposit initially at rest in the cavity of horizontal obstructed turbulent channel flow. The present resuspension model is based on alternating iterations of a Large Eddy Simulation (LES) for the gas flow and a Discrete Element Method (DEM) for the particle detachment. The combination of LES and DEM simulates the effect of a sudden increase in the turbulent gas flow on the topology of the granular interface, i.e. the surface separating the multilayer deposit from the turbulent gas phase. After tuning two parameters of a simple cluster re-entrainment criterion, results show good agreements with experimental data performed on-site. Both the shape and the wall roughness of the granular interface are predicted with a good level of accuracy. Findings from this study also confirm that the friction velocity is a major resuspension agent.

Publ.-Id: 20071

Low-cost and large-area electronics, roll-to-roll processing and beyond

Wiesenhütter, K.; Skorupa, W.

In the following chapter, the authors conduct a literature survey of current advances in state-of-the-art low-cost, flexible electronics. A new emerging trend in the design of modern semiconductor devices dedicated to scaling-up, rather than reducing, their dimensions is presented. To realize volume manufacturing, alternative semiconductor materials with superior performance, fabricated by innovative processing methods, are essential. This review provides readers with a general overview of the material and technology evolution in the area of macroelectronics. Herein, the term macroelectronics (MEs) refers to electronic systems that can cover a large area of flexible media. In stark contrast to well-established micro- and nano-scale semiconductor devices, where property improvement is associated with downscaling the dimensions of the functional elements, in macroelectronic systems their overall size defines the ultimate performance (Sun and Rogers in Adv. Mater. 19:1897–1916, 2007). The major challenges of large-scale production are discussed. Particular Attention has been focused on describing advanced, short-term heat treatment approaches, which offer a range of advantages compared to conventional annealing methods. There is no doubt that large-area, flexible electronic systems constitute an important research topic for the semiconductor industry. The ability to fabricate highly efficient macroelectronics by inexpensive processes will have a significant impact on a range of diverse technology sectors. A new era “towards semiconductor volume manufacturing. . .” has begun.
The chapter is organized in three main sections. The candidate materials for flexible, large-area electronics (LAEs) are discussed in Sect. 14.1. Given the Limitation of this chapter, only selected groups of the semiconductors are presented. The target materials are Si-based inorganic thin-films and their intriguing, organic competitors. The general attributes of the materials suitable for macroelectronics are revised. The challenges associated with volume manufacturing with emphasis on the evolution of the heating technologies are demonstrated in Sect. 14.2. The final conclusions along with the authors’ considerations on the LAEs’ perspectives are given in Sect. 14.3.

Keywords: large-area semiconductor manufacturing; low-cost and flexible electronics; laser and flash lamp annealing; millisecond annealing; plastic foils; roll-to-roll processing; organic semiconductors

  • Book chapter
    Wolfgang Skorupa, Heidemarie Schmidt: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 271-295
    DOI: 10.1007/978-3-319-03131-6

Publ.-Id: 20067

Mapping of Hydrophobic Interactions for Investigating the Floatability of Mineral Using Atomic Force Microscopy and Raman Spectroscopy

Rudolph, M.

The novel method of measuring the floatability of individual mineral phases on an ore cross section is presented. Combining atomic force microscopy with Raman spectroscopy can make use of hydrophobic effects to evaluate the hydrophobization of surfaces, a crucial microprocess of flotation. This paper presents comparative results of classic microflotation experiments and the new method looking at pure mineral samples of magnetite and quartz using simple anionic and cationic collectors. The mapping capabilities and identification of mineral phases with Raman spectroscopy is presented for a silicate type or from southern Sweden containing the mineral eudialyte rich in heavy rare earth elements. We show theoretically and experimentally the different possibilities to determine hydrophobic effects using force spectroscopy and the colloidal probe technique with a hydrophobic colloid attached to the cantilever of an atomic force microscope. This novel concept shall not only be a plain research tool but should help to simplify the investigation of the right flotation reagent and thus optimize flotation processes.

Keywords: AFM; Raman; Nanobubbles; Hydrophobic Interactions; Minerals

  • Lecture (Conference)
    Conference in Minerals Engineering 2014, 04.-05.02.2014, Lulea, Sverige

Publ.-Id: 20066

Reconstitution of the P-type ATPase CopA into Nanodiscs: a platform for molecular spectroscopy

Fischermeier, E.; Sayed, A.; Pospisil, P.; Hof, M.; Fahmy, K.

Reconstitution of membrane proteins in a native-like lipidic environment is crucial for the in vitro determination of their structural and functional properties. Nanoscale protein-bounded planar lipid bilayers, so-called Nanodiscs1, provide a versatile novel model membrane system into which membrane proteins can be incorporated in a monodisperse and active form being accessible from both sides of the membrane. They exhibit less scatter than liposomes and bicelles and are soluble in aqueous solution. We succeeded in the reconstitution of the evolutionary conserved P-type ATPase CopA from Legionella pneumophila into Nanodiscs, which is a key player in copper homeostasis throughout all kingdoms of life2. This provides us with an excellent platform for spectroscopic studies of the allosteric couplings that are associated with ATP-powered copper transport in this enzyme in fully controllable lipidic environments. Our current focus lies on the real-time observation of the allosteric coupling of the cytosolic nucleotide-binding domain to the intramembranous conserved copper-binding CPC-motif (cysteine‒prolin‒cysteine) in transmembrane helix 4. Moreover, the CopA‒Nanodisc system allows addressing specifically the influence of the lipid environment in the catalytic cycle. We are particularly interested in the role of water entry into the transmembrane region at specific catalytic intermediates. To this end, we use cysteine-reactive fluorophores as molecular probes for the physical environment of the copper-binding CPC-motif. Comparison between mutated versions of the CPC-motif enables a detailed view of structural transitions in the transmembrane part of the enzyme evoked by allosteric coupling. The biochemical platform represented by the Nanodiscs also opens new routes for the analysis of structural dynamics by time-resolved fluorescence spectroscopy. Our presented data on the copper-binding site hydration can be interpreted in the context of conformational changes proposed from crystal structures of CopA3.

1. T.H. Bayburt, S.G. Sligar. FEBS Lett. 2010, 584, 1721–1727.
2. J.M. Argüello, E. Eren, M. González-Guerrero. Biometals, 2007, 20, 233–248.
3. M. Andersson, D. Mattle, O. Sitsel, T. Klymchuk, A.M. Nielsen, L.B. Møller, S.H. White, P. Nissen, P. Gourdon. Nat. Struct. Mol. Biol. 2013, 21, 43–50.

  • Poster
    Physics and Biological Systems 2014, 24.-27.07.2014, Gif-sur-Yvette, Frankreich

Publ.-Id: 20065

Actinyl(V/VI) complexes at water-mineral interfaces investigated by vibrational spectroscopy and complementary techniques.

Müller, K.; Foerstendorf, H.; Steudtner, R.; Rossberg, A.

For the long-term safety assessment of nuclear waste repositories, neptunium and uranium are two of the most environmentally relevant components of nuclear waste to be considered. Hence, great attention is attracted to their geochemistry and migration behavior. Among the various geochemical processes, the migration of radioactive contaminants in the environment is strongly affected by molecular reactions in aqueous solution and at the solid-water interface, e.g. complexation with organic/inorganic ligands, sorption onto mineral phases, surface precipitation, and colloid formation. A detailed description of these interactions on a molecular level is required for a reliable modeling of the contaminants dissemination in the environment.
In the past decade, vibrational spectroscopy has been developed to a powerful tool for the study of dissolved complexes of heavy metal ions with a variety of inorganic and organic ligands and surface complexes on solid phases. In particular, a combined approach of in situ vibrational, time-resolved laser fluorescence and X-ray absorption spectroscopy potentially provides comprehensive molecular information. A survey of very recent spectroscopic results obtained from geochemical reactions of radionuclides, namely Np(V) and U(VI), is given.

  • Lecture (others)
    Institutskolloquium, 28.02.2014, Umea, Schweden

Publ.-Id: 20064

An attempt to simulate multilayer particle resuspension in a cavity

Lecrivain, G.; Vitsas, A.; Hampel, U.

The present work deals with particle re-entrainment from a multilayer deposit exposed to a sudden flow increase. An early model is suggested to simulate the multilayer remobilisation of solid aerosol particles. The work is decomposed in two parts: 1. an algorithm is first developed for the virtual reconstruction of the multilayer deposit given its porosity and 2. particle detachment off the deposit is coupled with computational fluid mechanics. Experimental observations have shown that the clustering effect plays an important role in multilayer resuspension. Particle aggregates, and not individual particles, tend to reenter the turbulent flow. A cluster identification procedure is therefore suggested to work out resuspendable particle clusters. The condition of cluster dislocation is based on a force-balance model. The cluster detachment off the multilayer deposit occurs whenever the aerodynamic force overcomes the adhesive force. The turbulent flow was computed with a large eddy simulation. The numerical results showed satisfactory agreement with experimental data. Findings from that study showed that the wall shear stress is a main resuspension agent. Results have a direct impact for the safety assessment of gas-cooled high temperature reactor, in which the remobilisation of radioactive graphite particles occurs.

  • Contribution to proceedings
    International Workshop on Thermal Hydraulics of Innovative Nuclear Systems, 20.-22.01.2014, Modena, Italy

Publ.-Id: 20063

Three-dimensional simulation of multilayer particle deposition in an obstructed channel flow

Lecrivain, G.; Barry, L.; Hampel, U.

A large variety of systems are subject to slow and lengthy processes of solid aerosol particle deposition in turbulent flows. As a result of a long exposure to deposition, a multilayer particle bed eventually forms over time. Notable examples are the formation of multilayer deposits in ventilation ducts, in nuclear reactors or on earth surfaces subject to atmospheric sedimentation. Simulations are of great importance to predict the multilayer deposition of solid aerosol particles. Theoretical models are quite limited since their complexity rapidly increases when the flow becomes turbulent and the surface geometry complex. The present study proposes a new three-dimensional approach to reproduce the growth of a multilayer deposit in a turbulent obstructed channel flow at Reynolds number Re = 10, 000. Computational Fluid Dynamics and Computational Granular Dynamics are brought together to simulate four hours of real deposition. A detached eddy simulation is employed to predict particle deposition while self-organised criticality is employed to reproduce the slow growth of the multilayer deposit. The three dimensional shape of the multilayer deposit matches remarkably well the experimental data.

Publ.-Id: 20062

Spear-anvil point-contact spectroscopy in pulsed magnetic fields

Arnold, F.; Yager, B.; Kampert, E.; Putzke, C.; Nyeki, J.; Saunders, J.

We describe a new design and experimental technique for point-contact spectroscopy in non-destructive pulsed magnetic fields up to 70 T. Point-contact spectroscopy uses a quasi-dc four-point measurement of the current and voltage across a spear-anvil point-contact. The contact resistance could be adjusted over three orders of magnitude by a built-in fine pitch threaded screw. The first measurements using this set-up were performed on both single-crystalline and exfoliated graphite samples in a 150ms, pulse length 70 T coil at 4.2K and reproduced the well known point-contact spectrum of graphite and showed evidence for a developing high field excitation above 35 T, the onset field of the charge-density wave instability in graphite.

Publ.-Id: 20061

Pu interaction with bacterial isolates from Mont Terri Opalinus Clay

Moll, H.; Lütke, L.; Cherkouk, A.; Bernhard, G.

For the long-term safety assessment of a nuclear waste repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay) and how these microorganisms can influence the performance of a repository. The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock for nuclear waste disposal (1). It is well known that indigenous bacteria in such underground environments can affect the speciation and the mobility of actinides (2-4).
In this study, the unknown interaction between Pu and Sporomusa sp. MT-2.99 and Paenibacillus sp. MT-2.2 cells were explored in aqueous solution at pH 6. Both bacteria were isolated from Mont Terri Opalinus clay core samples. The time-dependent Pu concentrations measured in the supernatants were successfully fitted with bi-exponential decay functions. The time-dependent Pu oxidation state distributions were successfully fitted by using mono-exponential decay or growth functions.
To conclude, a moderate to strong impact of Sporomusa sp. and Paenibacillus sp. cells on the Pu speciation was observed. Differences in the Pu interaction process of both strains for instance depend on the presence or absence of an electron donor were detected and will be discussed in detail.

1. M. Thury, P. Bossart, “The Mont Terri Rock Laboratory, a new international research project in a Mesozoic shale formation, in Switzerland” Eng. Geol., 52, 347-359 (1999).
2. J.R. Lloyd, G.M. Gadd, “The Geomicrobiology of Radionuclides” Geomicrobiol. J., 28, 383-386. (2011).
3. L. Lütke, H. Moll, V. Bachvarova, S. Selenska-Pobell, G. Bernhard, “The U(VI) speciation influenced by a novel Paenibacillus isolate from Mont Terri Opalinus clay” Dalton Trans., 42, 6979-6988 (2013).
4. M.P. Neu, G.A. Icopini, H. Boukhalfa, “Plutonium speciation affected by environmental bacteria” Radiochim. Acta, 93, 705-714 (2005).

Keywords: plutonium; Mont Terri; Opalinus Clay; Sporomusa sp; Paenibacillus sp; solvent extractions

  • Contribution to proceedings
    Plutonium Futures - The Science 2014, 07.-12.09.2014, Las Vegas, USA
  • Lecture (Conference)
    Plutonium Futures - The Science 2014, 07.-12.09.2014, Las Vegas, USA

Publ.-Id: 20060

Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions

Skorupa, W.; Schmidt, H.; (Editors)

The thermal processing of materials ranges from few femtoseconds by Swift Heavy Ion Implantation to about one second using advanced Rapid Thermal Annealing. This book offers after an historical excursus selected contributions on fundamental and applied aspects of thermal processing of classical elemental semiconductors and other advanced materials including nanostructures with novel optoelectronic, magnetic, and superconducting properties. Special emphasis is given on the diffusion and segregation of impurity atoms during thermal treatment. A broad range of examples describes the solid phase and/or liquid phase processing of elemental and compound semiconductors, dielectric composites and organic materials.

Keywords: Activation of Dopants; Annealing by Swift Heavy Ions; Epitaxial Growth of Silicon; Explosive Crystallisation; Flash Lamp Annealing; Pulsed Laser Annealing; Radiation Thermometry; Sub-second Annealing; Thermal Processing of Materials; Thermal Spike-induced Nanostructuring

  • Book (Editorship)
    Cham, Heidelberg, New York, Dordrecht, London: Springer International Publishing Switzerland, 2014
    321 Seiten
    ISBN: 978-3-319-03130-9

Publ.-Id: 20059

Anisotropy of excitation and relaxation of photogenerated charge carriers in graphene

Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.; Schneider, H.; Helm, M.; Winnerl, S.

We present pump-probe experiments on graphene, which reveal a pronounced dependence of the pump-induced transmission on the angle between pump and probe polarization. It reflects a strong anisotropy of the pump-induced occupation of photogenerated carriers in momentum space. Within 150 fs after excitation an isotropic carrier distribution is established. The experiments are well described by microscopic modelling, which identify carrier-phonon scattering to be the main relaxation mechanism giving rise to an isotropic carrier distribution.

Keywords: graphene; carrier-dynamics; anisotropy; collinear scattering

Publ.-Id: 20058

Response of a microbial community, present in the borehole water of the in situ BN-experiment of Mont Terri, towards components leaching from the matrix of Bituminized intermediate-level long-lived radioactive waste.

Moors, H.; Cherkouk, A.; Mysara, M.; Bleyen, N.; Boven, P.; Selenska-Pobell, S.; Leys, N.

Clay formations (e.g. Opalinus Clay in Switzerland) are intended to serve as a host rock for the geological disposal of high- and intermediate-level long-lived radioactive waste in several European countries. Besides radionuclides, waste form like bituminized intermediate-level long-lived radioactive waste, harbour large amounts of additional components (e.g. organics, NaNO3 and CaSO4) which could perturb the beneficial physico-chemical barrier properties of the clay. To study the fate of leaching nitrate and organics in a clay formation, an in situ experiment, called Bitumen-Nitrate-Clay interaction (BN) experiment, was installed in the Opalinus Clay. The BN experiment aims to clarify the biochemical and chemical processes that could potentially be introduced by this nitrate and organic plume within the host clay formation.
As an active microbial community can have a significant contribution on the physical and (geo)chemical conditions of the surrounding clay, microbial analyses were performed. Our microbial investigation indicates that the present microbial community responds, and at the same time contributes, to the changing properties of the clay rock. As soon as nitrate becomes available a shift towards nitrate reduction appears. If in parallel easily oxidizable organics are introduced, like acetate, the community composition does not alter that much but the nitrate reduction rate is increased.

  • Poster
    IGDTP-Geodisposal 2014, 24.-26.06.2014, Manchester, United Kingdom

Publ.-Id: 20057

Strategische Rohstoffe - Risikovorsorge

Kausch, P.; Bertau, M.; Gutzmer, J.; Matschullat, J.; (Editors)

Teil 1: Rohstoffwirtschaft
Teil 2: Primäre Rohstoffe
Teil 3: Sekundäre Rohstoffe und Recycling
Teil 4: Verarbeitung und Produkte

Keywords: Bergbau; Lagerstätten; Lithium; Recycling; Risikomanagement; Rohstoffstrategie; Seltene Erden; Supply chain; Verhüttung

  • Book (Editorship)
    Berlin Heidelberg: Springer, 2014
    300 Seiten
    ISBN: 978-3-642-39703-5

Publ.-Id: 20056

The origin of conductivity in ion-irradiated diamond-like carbon – Phase transformation and atomic ordering

Philipp, P.; Bischoff, L.; Treske, U.; Schmidt, B.; Fiedler, J.; Hübner, R.; Klein, F.; Koitzsch, A.; Mühl, T.

We present recent progress in the field of ion-implanted diamond-like carbon thin films. The phase transformation mechanism from an insulating sp3 matrix into a well-conducting sp2-rich graphite-like carbon phase by means of focused ion beam irradiation is investigated. The resistivity decrease is compared for the implantation of different ion species at 30 keV. It is shown that the sp3-to-sp2-conversion saturates at an Ga+ ion fluence of approximately 1 x 1015 cm-2. Nevertheless, further ion irradiation yields a continued drop of the film resistivity. Raman spectroscopy and transmission electron microscopy analysis show that ion-induced ordering proceeds at high fluences above the sp3-to-sp2-conversion saturation. This ordering can be considered as a microstructural transformation into a more graphite-like arrangement. We show that the increase of atomic ordering correlates with the local energy density deposited during the ion impact and furthermore, the resistivity lowering correlates with the degree of graphitization. The ion-induced phase transformation of diamond-like carbon layers is thus proposed to comprise a rehybridization stage (sp3-to-sp2-conversion), driven by nuclear collisions, and a rearrangement stage (graphitic ordering) that is thermally driven by the ion impact.

Keywords: diamond-like carbon; phase transformation; atomic ordering; focused ion beam; nanostructures

Publ.-Id: 20054

The magnetic flywheel flow meter: Theoretical and experimental contributions

Buchenau, D.; Galindo, V.; Eckert, S.

The development of contactless flow meters is an important issue for monitoring and controlling of processes in different application fields, like metallurgy, liquid metal casting, or cooling systems for nuclear reactors and transmutation machines. Shercliff described in his book “The Theory of Electromagnetic Flow Measurement, Cambridge University Press, 1962” a simple and robust device for contact-less measurements of liquid metal flow rates which is known as magnetic flywheel. The sensor consists of several permanent magnets attached on a rotatable soft iron plate. This arrangement will be placed closely to the liquid metal flow to be measured, so that the field of the permanent magnets penetrates into the fluid volume. The flywheel will be accelerated by a Lorentz force arising from the interaction between the magnetic field and the moving liquid. Steady rotation rates of the flywheel can be taken as a measure for the mean flow rate inside the fluid channel. The present paper provides a detailed theoretical description of the sensor in order to gain a better insight into the functional principle of the magnetic flywheel. Theoretical predictions are confirmed by corresponding laboratory experiments. For that purpose, a laboratory model of such a flow meter was built and tested on a GaInSn-loop under various test conditions.

Keywords: Magnetic Flywheel; J. A. Shercliff; flow rate; liquid metal; rotation rate

Publ.-Id: 20053

Rare Earth Doped Metal-Oxide-Semiconductor Structures: A Promising Material System or a Dead End of Optoelectronic Evolution?

Rebohle, L.; Berencén, Y.; Braun, M.; Garrido, B.; Hiller, D.; Liu, B.; Ramírez, J. M.; Sun, J. M.; Wutzler, R.; Helm, M.; Skorupa, W.

The suitability of rare earth doped metal-oxide-semiconductor structures for optoelectronic applications is investigated. To do so, several Tb- and Er-doped devices with different designs and fabricated by different methods are compared among each other with respect to their electroluminescence (EL) properties. In detail, the investigated devices show EL power efficiencies between 2×10-4 and 2×10-3 which, taken individually for Tb and Er, have a linear dependence on the EL decay time for low and medium injection current densities. The excited fraction of Er ions is significantly higher than that of Tb ions and achieves a maximum value of 50% (with a maximum uncertainty factor of 2.25) under optimum conditions.

Keywords: Electroluminescence; rare earth; MOS structure; decay time

  • Invited lecture (Conferences)
    225th ECS Meeting, 11.-15.05.2014, Orlando, United States
  • Contribution to proceedings
    225th ECS Meeting, 11.-15.05.2014, Orlando, United States
    Nanoscale Luminescent Materials 3: Electrochemical Society (ECS), 978-1-60768-520-3, 175-185
    DOI: 10.1149/06105.0175ecst

Publ.-Id: 20052

Energetics, structure, and composition of nanoclusters in Oxide Dispersion Strenghtened Fe-Cr alloys

Posselt, M.; Murali, D.; Panigrahi, B. K.

Extensive first-principle calculations on embedded clusters containing few O, Y, Ti, and Cr atoms as well as vacancies are performed to obtain interaction parameters to be applied in Metropolis Monte Carlo simulations, within the framework of a rigid lattice model. A novel description using both pair and triple parameters is shown to be more precise than the commonly used pair parameterization. Simulated annealing provides comprehensive data on the energetics, structure and stoichiometry of nm-size clusters at . Additionally, Metropolis Monte Carlo simulations are carried out at high temperature in order to investigate the dependence of nanocluster composition on temperature. The absolute value of the binding energy per O atom unit increases with cluster size and approaches a constant for large clusters. The presence of Ti and/or vacancies increases the value of this quantity. In alloys without vacancies clusters show a planar structure, whereas the presence of vacancies leads to three-dimensional configurations. Cr is not part of the nanoclusters, except for alloys without Ti but with vacancies. In the latter case clusters consist of a core containing O, vacancies, as well as Y and a Cr shell, which was also observed experimentally. A good agreement between the existing experimental data on the ratios (Y+Ti):O, Y:Ti, (Y+Cr):O, and Y:Cr, and the simulation results is found. The comparison of experimental data with those obtained by simulations demonstrates that the assumption of nanoclusters consisting of nonstoichiometric oxides that are essentially coherent with the bcc lattice of the Fe-Cr matrix leads to reasonable results.

Keywords: Nanoclusters; ODS ferritic steel, Atomistic modeling; First-principle calculations; Monte Carlo techniques

Publ.-Id: 20051

Cost effectiveness of modified fractionation radiotherapy versus conventional radiotherapy for unresected non-small-cell lung cancer patients

Ramaekers, B. L.; Joore, M. A.; Lueza, B.; Bonastre, J.; Mauguen, A.; Pignon, J. P.; Le Pechoux, C.; de Ruysscher, D. K.; Grutters, J. P.; Arriagada, R.; Bae, K.; Ball, D.; Baumann, M.; Behrendt, K.; Belani, C. P.; Beresford, J.; Bishop, J.; Bonner, J. A.; Choy, H.; Dahlberg, S. E.; et al.; (MAR-LC Collaborative group)

Introduction: Modified fractionation radiotherapy (RT), delivering multiple fractions per day or shortening the overall treatment time, improves overall survival for non-small-cell lung cancer (NSCLC) patients compared with conventional fractionation RT (CRT). However, its cost effectiveness is unknown. Therefore, we aimed to examine and compare the cost effectiveness of different modified RT schemes and CRT in the curative treatment of unresected NSCLC patients. Methods: A probabilistic Markov model was developed based on individual patient data from the meta-analysis of radiotherapy in lung cancer (N = 2000). Dutch health care costs, quality-adjusted life years (QALYs), and net monetary benefits (NMBs) were compared between two accelerated schemes (very accelerated RT [VART] and moderately accelerated RT [MART]), two hyperfractionated schemes (using an identical (HRTI) or higher (HRTH) total treatment dose than CRT) and CRT. Results: All modified fractionations were more effective and costlier than CRT (1.12 QALYs, €24,360). VART and MART were most effective (1.30 and 1.32 QALYs) and cost €25,746 and €26,208, respectively. HRTI and HRTH yielded less QALYs than the accelerated schemes (1.27 and 1.14 QALYs), and cost €26,199 and €29,683, respectively. MART had the highest NMB (€79,322; 95% confidence interval [CI], €35,478-€133,648) and was the most cost-effective treatment followed by VART (€78,347; 95% CI, €64,635-€92,526). CRT had an NMB of €65,125 (95% CI, €54,663-€75,537). MART had the highest probability of being cost effective (43%), followed by VART (31%), HRTI (24%), HRTH (2%), and CRT (0%). Conclusion: Implementing accelerated RT is almost certainly more efficient than current practice CRT and should be recommended as standard RT for the curative treatment of unresected NSCLC patients not receiving concurrent chemo-radiotherapy. Copyright © 2013 by the International Association for the Study of Lung Cancer.

Keywords: Cost-benefit analysis; Dose fractionation; Markov chain; Non-small-cell lung cancer; Radiotherapy

Publ.-Id: 20050

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