Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Fe-doped InN layers grown by molecular beam epitaxy
Wang, X.; Liu, S.; Ma, D.; Zheng, X.; Chen, G.; Xu, F.; Tang, N.; Shen, B.; Zhang, P.; Cao, X.; Wang, B.; Huang, S.; Chen, K.; Zhou, S.; Yoshikawa, A.;
Fe-doped InN have been grown by molecular-beam-epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from semi-insulating property of Fe-doped GaN. However, this heavy n-type doping can't be fully explained by Fe-concentration. Further analysis shows that more unintentionally-doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. It shows that Fe-doping is one of good choices to control electron density in InN.
Keywords: Fe-doping, InN, MBE

Publ.-Id: 17870 - Permalink


Copper binding to S100A12: suggested role in oxidative modification of lipids and proteins.
Pietzsch, J.;
kein Abstract verfügbar
  • Poster
    22nd IUBMB & 37th FEBS, 04.-09.09.2012, Sevilla, Spain
  • Abstract in refereed journal
    FEBS journal 279(2012), 200

Publ.-Id: 17869 - Permalink


Protein and non-protein biomarkers in melanoma: a critical update.
Tandler, N.; Mosch, B.; Pietzsch, J.;
Melanoma is the most malignant type of all skin neoplasms. Its worldwide incidence has steadily increased during the past decades, suggesting a probable melanoma ‘epidemic’. Although current clinical, morphologic, and histopathologic methods provide insights into disease behavior and outcome, melanoma is still an unpredictable disease. Once in an advanced stage, it remains a disastrous affliction with scarce therapeutic options. Therefore, significant efforts need to be made in finding informative biomarkers or surrogate markers that could aid or improve early diagnosis of melanoma, its correct staging, the discrimination of other pathological conditions as well as indicate patients’ prognosis or the most appropriate therapeutic regimes. Ideally these markers are secreted into body fluids and easily amenable to the design of non-invasive clinical tests. A critical view on the current debate on serologic protein markers, e.g., lactate dehydrogenase, tyrosinase, and melanoma inhibiting activity, and some selected non-protein markers, e.g., 5-Scysteinyl-dopa and circulating nucleic acids, will be offered and novel innovative approaches currently being explored will be discussed. Special emphasis is put on the S100 family of calcium binding proteins that is more and more emerging as a potentially important group of both molecular key players and biomarkers in the etiology, progression, manifestation, and therapy of neoplastic disorders, including malignant melanoma. Notably, S100B and, possibly, other S100 proteins like S100A4 are assumed to fulfill requirements which make them strong biomarker candidates in melanoma. Moreover, S100 proteins receive attention as possible targets of therapeutic intervention moving closer to clinical impact.
Keywords: Diagnostic markers; Melanomata; Molecular targets; Pigment cells; Prognostic markers; Serological markers; Skin cancer; Stem cell-like markers; S100 proteins; Therapy monitoring

Publ.-Id: 17868 - Permalink


Evaluation of metabolically stabilized 18F-labeled bombesin analogs for imaging GRP receptors in prostate cancer
Richter, S.; Wuest, M.; Krieger, S. S.; Parry, J. J.; Rogers, B.; Bergmann, R. K.; Wuest, F.;
Objectives: According to GLOBOSCAN 2008 the worldwide prostate cancer incidence rates will increase to about 1.7 million new cases per year in 2030. In recent years, bombesin and bombesin analogs have attracted much attention as high affinity and selectivity ligands for the gastrin-releasing peptide (GRP) receptor. The GRP receptor was found to be overexpressed and implicated in a variety of human tumors including prostate cancer. Radiolabeled bombesin and bombesin analogues belong to an interesting class of new diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This study describes the synthesis and radiopharmacological evaluation of a high affinity and metabolically stabilized 18F-labeled bombesin analog for PET imaging of GRP receptors in prostate cancer. Methods: Three modified bombesin analogs bearing an aminovaleric (BBN-1, BBN-2), or an aminooctanoic acid linker (BBN-3) were tested in a competitive binding assay against 125I-[Tyr4]-BBN for their binding to the GRP receptor. A calcium release assay in human prostate cancer cells (PC3) was performed to determine agonistic or antagonistic behaviour. The derivative with the highest affinity to GRP (BBN-2) was selected to be conjugated with the prosthetic labeling agent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) in borate buffer (pH=8.2) for 30 min at 40°C to synthesize the desired 18F-labeled bombesin analog. Tumor-targeting of [18F]BBN-2 was evaluated in PC3 tumor-bearing male nude mice with biodistribution experiments (mean ± SD) and dynamic small animal PET studies. Results: The competitive binding assay revealed IC50-values between 8.7 and 16.7 nM for BBN-1, BBN-2 and BBN-3 against 125I-[Tyr4]-BBN versus 3.0 nM for I-[Tyr4]-BBN. All three stabilized bombesin analogs are GRP receptor antagonists. 18F-labeled [18F]BBN-2 was prepared in 30% radiochemical yield (based upon [18F]SFB) within 80 min including HPLC purification, evaporation of HPLC eluent and formulation in 0.9% saline. The radiochemical purity exceeded 95%, and the specific activity was determined to be 20 GBq/µmol. [18F]BBN-2 showed reasonable metabolic stability in mouse blood resulting in 65% of intact radiolabeled peptide after 60 min p.i.. Uptake of [18F]BBN-2 into PC3 tumors was 2.75±1.82 %ID/g after 5 min and 2.45±1.25 %ID/g after 60 min p.i.. The receptor specificity of [18F]BBN-2 was confirmed by effective blocking of the radiotracers uptake in the presence of non-radioactive BBN-2 resulting in 0.76±0.51 %ID/g at 60 min p.i. (n=4; p<0.05). Dynamic PET imaging resulted in SUV60min values of 0.58 for [18F]BBN-2 versus 0.24 (n=2) for [18F]BBN-2 with BBN-2 pre-dosing in PC3 tumors. Conclusions: The present study showed that 18F-labeled bombesin analog [18F]BBN-2 is a suitable PET radiotracer with favourable metabolic stability for molecular imaging of GRP receptor-positive prostate cancer.
  • Lecture (Conference)
    World Molecular Imaging Congress (WMIC) 2012, 05.-08.09.2012, Dublin, Ireland

Publ.-Id: 17867 - Permalink


Biodistribution of 68Ga-Labeled DOTA-Bisphosphonates
Bergmann, R.; Meckel, M.; Kubicek, V.; Roesch, F.;
Aim: Main indications of oncologic skeletal imaging are metastatic diseases in skeleton, bone pain in patients with known cancer, and primary bone tumors. Benign bone diseases like pediatric/adult back pain, bone viability and Paget's disease are also important indications of skeletal imaging. There are numerous studies with [18F]fluoride PET demonstrating the clinical utility. Similar characteristics show Tc-99m-labeled bisphosphonates. Combining the bone seeking properties, the advantages of PET, and the potential labeling with therapeutic radionuclides we studied DOTA-phosphonates radiolabeled with [68Ga]Ga3+. Methods: The following macrocyclic tetraaza based phosphonate chelators were used BPAMD ((4-{[(bis-phosphonomethyl) carbomoyl]methyl}-7,10-bis-(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl)-acetic acid, BPAPD ((4-{[(bis-phosphonopropyl)carbomoyl]methyl}-7,10-bis-(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl)-acetic acid and BPPED Tetraethyl 10-{[(2,2-bis-phosphonoethyl)hydroxyphosphoryl]methyl}-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid. The DOTA based phosphonate ligands were labeled with [68Ga]GaCl3. The radiochemical purity of the labeled products was >95% determined with radio thin-layer chromatography. The biodistribution and biokinetics were compared with [18F]fluoride and [99mTc]Tc-MDP in Wistar rats using dissection, small animal PET and SPECT. All activity concentration data were calculated as SUV. Results: The compounds were labeled with high yields in ammonium acetate buffer with 68Ga, followed by a purification step using a cation exchange resin. High uptake values were detected for all 68Ga-phosphonates in the femura. The accumulation of [68Ga]BPPED in the bone was the highest and comparable with the uptake of [18F]Fluoride and [99mTc]Tc-MDP. The blood clearance of the [68Ga]BPPED was the fastest with a biexponential kinetics and half-life of 0.4 min and 6.9 min. The [68Ga]BPPED bone to blood ratio was also superior, however, not so large like of [18F]Fluoride and [99mTc]Tc-MDP. Conclusion: The [68Ga]BPPED showed in a preclinical setting excellent characteristics for skeletal imaging. It seems to be also a potential candidate for radionuclide therapy in oncology.
  • Poster
    World Molecular Imaging Congress (WMIC) 2012, 05.-08.09.2012, Dublin, Ireland

Publ.-Id: 17866 - Permalink


Investigations of unstable flows in magnetic fields relevant for industrial applications
Eckert, S.; Gerbeth, G.; Pal, J.; Räbiger, D.; Shevchenko, N.; Timmel, K.; Vogt, T.;
Various types of magnetic fields are applied for electromagnetic flow control in many industrial applications such as metallurgy, casting, crystal growth or electrochemistry. The first part of this paper considers the electromagnetic damping of instabilities by DC magnetic fields (so-called “Electromagnetic Brakes”), which are exploited for casting of steel or aluminum. The magnetic field tends to damp 3D flow perturbations leading to the development of 2D flow structures aligned with the magnetic field direction. However, this effect is not equivalent to a complete damping of turbulent fluctuations as it might be expected at a first glance. The magnetic field application may even enhance local velocity fluctuations in the continuous casting process. This feature that a DC magnetic field may give rise to non-steady, non-isotropic flow structures has to be taking into account for designing of tailored magnetic fields in the continuous casting process.
AC magnetic fields are used in metallurgy and crystal growth for melt stirring or the suppression of instabilities, respectively. The second part of this contribution provides a brief insight into flow phenomena in a liquid metal column resulting from the application of diverse AC magnetic fields, for instance time-modulated or superposed fields.
Keywords: Liquid metal, flow instability, electromagnetic fields, electromagnetic flow control
  • Invited lecture (Conferences)
    European GDR Dynamo & MHD Days 2012, 01.-04.10.2012, Nice, France

Publ.-Id: 17865 - Permalink


Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation
Zhou, S.; Zhang, W.; Shalimov, A.; Wang, Y.; Huang, Z.; Buerger, D.; Mücklich, A.; Zhang, W.; Schmidt, H.; Helm, M.;
The integration of ferromagnetic Mn5Ge3 with the Ge matrix is promising for spin injection in a silicon-compatible geometry. In this paper, we report the preparation of magnetic Mn5Ge3 nanocrystals embedded inside the Ge matrix by Mn ions implantation at elevated temperature. By X-ray diffraction and transmission electron microscopy, we observe crystalline Mn5Ge3 with variable size depending on the Mn ion fluence. The electronic structure of Mn in Mn5Ge3 nanocrystals is 3d6 configuration, the same as in bulk Mn5Ge3. A large positive magnetoresistance has been observed at low temperatures. It can be explained by the conductivity inhomogeneity in the magnetic/semiconductor hybrid system.
Keywords: Magnetic nanocrystals, Ion implantation, Magnetoresistance

Publ.-Id: 17864 - Permalink


Ferromagnetic InMnAs on InAs Prepared by Ion Implantation and Pulsed Laser Annealing
Zhou, S.; Wang, Y.; Jiang, Z.; Weschke, E.; Helm, M.;
Ferromagnetic InMnAs has been prepared by Mn ion implantation and pulsed laser annealing. The InMnAs layer reveals a saturated magnetization of 2.6 µB/Mn at 5 K and a perpendicular magnetic anisotropy. The Curie temperature is determined to be 46 K, which is higher than those in previous reports with similar Mn concentrations. Ferromagnetism is further evidenced by the large magnetic circular dichroism.
Keywords: Ferromagnetic semiconductors, Ion implantation, Pulsed Laser annealing

Publ.-Id: 17862 - Permalink


Depth profile of the tetragonal distortion in thick GaMnAs layers grown on GaAs by Rutherford backscattering/channeling
Zhou, S.; Chen, L.; Shalimov, A.; Zhao, J.; Helm, M.;
We provide a direct measurement of the tetragonal distortion in thick GaMnAs as a function of depth by Rutherford backscattering combining with channeling. The thick GaMnAs film is tetragonally strained and the tetragonal distortion is found to be depth independent. Our finding excludes strain relaxation as the origin of the uniaxial in-plane magnetic anisotropy observed in GaMnAs.
Keywords: Rutherford backscattering/channeling spectrometry

Publ.-Id: 17861 - Permalink


The chemical way to ion irradiation
Faßbender, J.ORC
Local proton irradiation causes a chemical reaction that leads to nanopatterned magnetic media. The technique has strong potential for improving high-density data storage and other types of applications involving nanostructuring of materials.
Keywords: Ion irradiation, ion implantation, magnetism

Publ.-Id: 17860 - Permalink


Topology and origin of effective spin meron pairs in ferromagnetic multilayer elements
Wintz, S.; Bunce, C.; Neudert, A.; Körner, M.; Strache, T.; Buhl, M.; Erbe, A.; Gemming, S.; Raabe, J.; Quitmann, C.; Fassbender, J.ORC
We report on pairs of converging-diverging spin vortices in Co/Rh/NiFe trilayer disks. The lateral magnetization distribution of these effective spin merons is directly imaged by means of element-selective x-ray microscopy. By this method, both the divergence and circulation states of the individual layers are identified to be antisymmetric. Reversal measurements on corresponding continuous films reveal that biquadratic interlayer exchange coupling is the cause for the formation of the effective meron pairs observed. Furthermore their three-dimensional magnetization structure is determined by micromagnetic simulations. It is shown that in order to reduce magnetic surface and volume charges the magnetic induction aligns along a flux-closing torus. This toroidal topology enforces a symmetry break, which links the core polarities to the divergence configuration.
Keywords: spin vortex, spin meron, vortex coupling, interlayer coupling, topology, x-ray microscopy

Publ.-Id: 17859 - Permalink


Library services of the Helmholtz-Zentrum Dresden-Rossendorf
Reschke, E.;
In this slide show some topics of the library services will be presented, for example search for books, for journal articles, to use the SFX Linking service, how to use the licensed datatbasaes from home, publishing services of the library.
Keywords: Online catalogue, interlibrary loan, Linking services, document request, copyright, open access
  • Invited lecture (Conferences)
    7. Doktorandenseminar im IFA Schöneck, 08.-10.10.2012, Schöneck/Vogtl., Germany

Publ.-Id: 17858 - Permalink


Functional arterial spin labeling: Optimal sequence duration for motor activation mapping in clinical practice
Raoult, H.; Ferré, J.-C.; Petr, J.; Bannier, E.; Stamm, A.; Barillot, C.; Gauvrit, J.-Y.;
Purpose: To determine the minimal optimal fASL sequence duration allowing steady and reproducible motor activation mapping.
Materials and methods: Three MRI sessions including fASL and BOLD fMRI sequences were performed on 12 healthy subjects at 3T with a 32-channel coil. The raw 7 min fASL sequence was truncated to obtain six fASL sequences with durations ranging from 1 to 6 min. All the resulting fASL activations were compared between themselves and with both the 7 min fASL and BOLD activations. Quantitative parameters assessed activation location (activated volume, barycenter and distance between barycenters), activation quantification (activation-related cerebral blood flow), and intra-individual reproducibility across fMRI sessions.
The statistical analysis was based on ANOVA and Tukey’s multiple comparisons.
Results: Four min fASL achieved steady location and quantification of activation with the activated volume corresponding to 81% of the 7 min fASL volume and a barycenter located 1.2 mm from the 7 min fASL barycenter and 3.0 mm from the BOLD fMRI barycenter. Four min fASL reproducibility was high and statistically equivalent to 7 min values.
Conclusion: A 4 min fASL sequence is thus a reliable tool for motor activation mapping and suitable for use in clinical practice.

Publ.-Id: 17857 - Permalink


Spectroscopic evidence of NOx formation and band-gap narrowing in N-doped TiO2 films grown by pulsed magnetron sputtering
Gago, R.; Redondo-Cubero, A.; Vinnichenko, M.; Lehmann, J.; Munnik, F.; Palomares, F. J.;
N-containing TiO2 (TiO2:N) films have been grown by reactive pulsed magnetron sputtering (RPMS) with different N2/O2 mixtures and substrate temperatures (Ts) up to 450 °C. In this way, highly-doped films (N between 5 and 8 at.%) have been produced, as derived by elastic recoil detection analysis. The structural properties have been studied by grazing-incidence X-ray diffraction (GIXRD), X-ray absorption near-edge structure (XANES) and X-ray photoemission spectroscopy (XPS). On unheated substrates, the films are X-ray amorphous and N incorporation induces a transformation from rutile-like to highly disordered anatase-like structures. The crystal growth is enhanced by increasing Ts, being the effect larger for doped films. In this way, nearly single-phase (nanocrystalline) anatase TiO2:N films are achieved. The latter can be related to the imprinted anatase-like character by N incorporation observed on unheated substrates. XANES reveals that N sites are preferentially in the form of N2 or NOx (nitrite-like) complexes for growth on unheated and heated substrates, respectively. The dominant formation of NOx structures is corroborated by XPS, together with a small contribution of N at substitutional sites. Spectroscopic ellipsometry shows an effective reduction of the optical band-gap for doped films. A maximum decrease of ~0.3 eV at Ts =450 °C is observed, which correlates with a rigid red-shift of the valence band XPS spectra. The spectroscopic results indicate that band-gap narrowing is due to N interstitials as NOx complexes.

Publ.-Id: 17856 - Permalink


Nanopatterning dynamics on Si(100) during oblique 40-keV Ar+ erosion with metal codeposition: Morphological and compositional correlation
Redondo-Cubero, A.; Gago, R.; Palomares, F. J.; Mücklich, A.; Vinnichenko, M.; Vazquez, L.;
The formation and dynamics of nanopatterns produced on Si(100) surfaces by 40-keV Ar+ oblique (α = 60◦) bombardment with concurrent Fe codeposition have been studied. Morphological and chemical analysis has been performed by ex situ atomic force microscopy, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and scanning and transmission electron microscopies. During irradiation, Fe atoms incorporated into the target surface react with Si to form silicides, a process enhanced at this medium-ion energy range. The silicides segregate at the nanoscale from the early irradiation stages. As the irradiation proceeds, a ripple pattern is formed without any correlation with silicide segregation. From the comparison with the pattern dynamics reported previously for metal-free conditions, it is demonstrated that the metal incorporation alters both the pattern dynamics and the morphology. Although the pattern formation and dynamics are delayed for decreasing metal content, once ripples emerge, the same qualitative pattern of morphological evolution is observed for different metal content, resulting in an asymptotic saw-tooth-like facetted surface pattern. Despite the medium ion energy employed, the nanopatterning process with concurrent Fe deposition can be explained by those mechanisms proposed for low-ion energy irradiations such as shadowing, height fluctuations, silicide formation and segregation, ensuing composition dependent sputter rate, and ion sculpting effects. In particular, the interplay between the ion irradiation and metal flux geometries, differences in sputtering rates, and the surface pattern morphology produces a dynamic compositional patterning correlated with the evolving morphological one.

Publ.-Id: 17855 - Permalink


Uncertainties in Activity Calculations of different Nuclides in Rector Steels by Neutron Radiation
Konheiser, J.; Ferrari, A.;
Activation processes in a nuclear power plant are mainly due to neutron reactions. The determination of the neutron fluences in the reactor pressure vessel (RPV) is therefore the main task of the reactor dosimetry and the good experience for the activity evaluation has to be used. From 2005 to 2009 trepans were gained from the RPV of decommissioned nuclear power plant in Greifswald for the embrittlement investigation. For the first time, samples could be taken from the inner part of the RPV and activity measurements were performed. Experimental results were obtained for 93Nb, 63Ni and 99Tc. The calculations of the neutron fluences were carried out with the TRAMO Monte Carlo code. Based on these fluence values, the time-dependent activities of different nuclides were estimated. The calculated/experimental (C/E) activity ratios for the selected samples fluctuate between 0.37 and 0.91 for Niobium, while for 63Ni and 99Tc they are approximately between 0.6 and 0.91. The influence of different parameters on the results, for example the boron acid concentration, the thermal data and the local position, are here investigated and discussed.
Keywords: Monte Carlo calculation, decommissioning, neutron fluence calculation, activity calculations
  • Lecture (Conference)
    12th International Conference on Radiation Shielding (ICRS-12) 17th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society (RPSD-2012), 02.-07.09.2012, Nara, Japan

Publ.-Id: 17854 - Permalink


Using statistical measures for automated comparison of in-beam PET data
Kuess, P.; Birkfellner, W.; Enghardt, W.; Helmbrecht, S.; Fiedler, F.; Georg, D.;
Purpose: Positron emission tomography (PET) is considered to be the state of the art technique to monitor particle therapy in vivo. To evaluate the beam delivery the measured PET image is compared to a predicted β +-distribution. Nowadays the range assessment is performed by a group of experts via visual inspection. This procedure is rather time consuming and requires well trained personnel. In this study an approach is presented to support human decisions in an automated and objective way.
Methods: The automated comparison presented uses statistical measures, namely, Pearson’s correlation coefficient (PCC), to detect ion beam range deviations. The study is based on 12 in-beam PET patient data sets recorded at GSI and 70 artificial beam range modifications per data set. The range modifications were 0, 4, 6, and 10 mm water equivalent path length (WEPL) in positive and negative beam directions. The reference image to calculate the PCC was both an unmodified simulation of the activity distribution (Test 1) and a measured in-beam PET image (Test 2). Based on the PCCs sensitivity and specificity were calculated. Additionally the difference between modified and unmodified data sets was investigated using the Wilcoxon rank sum test.
Results: In Test 1 a sensitivity and specificity over 90% was reached for detecting modifications of ±10 and ±6 mm WEPL. Regarding Test 2 a sensitivity and specificity above 80% was obtained for modifications of ±10 and −6 mm WEPL. The limitation of the method was around 4 mm WEPL.
Conclusions: The results demonstrate that the automated comparison using PCC provides similar results in terms of sensitivity and specificity compared to visual inspections of in-beam PET data. Hence the method presented in this study is a promising and effective approach to improve the efficiency in the clinical workflow in terms of particle therapy monitoring by means of PET.
Keywords: in-beam PET, particle therapy monitoring, Pearson’s correlation coefficient

Publ.-Id: 17853 - Permalink


Abiotic reductive immobilization of U6+ by biogenic mackinawite
Veeramani, H.; Scheinost, A. C.; Monsegue, N.; Qafoku, N. P.; Kukkadapu, R.; Newville, M.; Lanzirotti, A.; Pruden, A.; Murayama, M.; Hochella, M.F.;
During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in-situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U6+ reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe1+xS, x = 0 to 0.11) to reduce U6+ abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U6+ indicate the formation of nanoparticulate UO2. This study suggests the relevance of Fe(II) and sulfide bearing biogenic minerals in mediating abiotic U6+ reduction, an alternative pathway in addition to direct enzymatic U6+ reduction.
Keywords: abiotic reduction uranium mackinawite

Publ.-Id: 17852 - Permalink


2-Carbaborane-3-phenyl-1H-indoles—Synthesis via McMurry Reaction and Cyclooxygenase (COX) Inhibition Activity
Laube, M.; Neumann, W.; Scholz, M.; Lönnecke, P.; Crews, B.; Marnett, L. J.; Pietzsch, J.; Kniess, T.; Hey-Hawkins, E.;
Cyclooxygenase-2 (COX-2) inhibitors have been in the focus of medicinal chemistry for years and many compounds exhibiting high selectivity and affinity were developed. As carbaboranes represent interesting pharmacophores as phenyl mimetics in drug development, this paper presents the synthesis of carbaboranyl derivatives of COX-2-selective 2,3-disubstituted indoles. Despite the lability of carbaboranes under reducing conditions, 2-carbaborane-3-phenyl-1H-indoles could be synthesized by McMurry cyclization of the corresponding amides. While the meta-carbaboranyl-substituted derivatives (3a-c) lacked COX inhibition activity, the orthocarbaboranyl analog (3d) was active but showed a selectivity shift towards COX-1.

Publ.-Id: 17851 - Permalink


Microbial life in flooded underground uranium mines in Saxony
Gagell, C.; Arnold, T.; Röske, I.;
First results with regard to microbial life in flooded underground uranium mines in Saxony are presented.
  • Poster
    HZDR Doktorandenseminar, 10.10.2012, Schöneck, Deutschland

Publ.-Id: 17850 - Permalink


Laser-induced spectroscopy - A method for the determination of complexation behaviour of metals by organic ligands
Lindner, K.; Günther, A.; Bernhard, G.;
Presentation of the complexation of Uranium(VI) with selected Schiff bases in methanol investigated by cryo-TRLFS and fs-TRLFS.
Keywords: cryo-TRLFS, fs-TRLFS, Uranium(VI), Schiff Bases
  • Poster
    PhD seminar 2012, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17849 - Permalink


Investigation of the mobility of uranium (VI) in argillaceous rock at higher salinity
Fritsch, K.; Schmeide, K.;
Three types of rock are considered for nuclear waste repositories: salt domes, crystalline rock and argillaceous rock. In this work, clay minerals and natural argillaceous rock are the subject of interest. North German clay deposits have high ionic strength pore water, up to 4 mol L-1. Therefore in the event of container failure, the nuclear waste will be in an environment of high salinity. To study the retention of radionuclides in clays in salinar systems, the experiments in the current project are carried out at high ionic strengths. Previous research(1) at HZDR investigated U(VI) sorption and diffusion at Opalinus clay and kaolinite in natural pore water and sodium perchlorate at low ionic strengths.
Keywords: nuclear waste repositories, uranium sorption, argillaceous rock,clay, uranium
  • Poster
    PhD seminar 2012, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17848 - Permalink


Krein spaces and PT Quantum Mechanics
Günther, U.;
A few basic facts about PT Quantum Mechanics (PTQM) are presented. Specifically, the underlying mathematical structures are briefly sketched, including Krein spaces (Hilbert spaces endowed with indefinite metric structures), J-selfadjointness, spectral singularities and PT phase transitions, the C-operator and the mapping between local PTQM and, in general, nonlocal conventional QM. The features are illustrated by following expamples: PT-symmetric Bose-Hubbard models (which may describe e.g. Bose-Einstein condensates with well balanced particle injection and extraction) and PT-symmetric brachistochrones and tachistochrones. Finally, recent realizations and applications in optical systems and microwave billiards are discussed --- including corresponding experiments.
Keywords: PT quantum mechanics, Krein spaces, spectral singularities, phase transitions, nonlocal quantum mechanics, Bose-Hubbard model, Bose-Einstein condensate, quantum brachistochrone, tachistochrone, optical systems, microwave billiards
  • Invited lecture (Conferences)
    Physics Meeting in Amazonia, 24.-28.09.2012, Belem, Brazil

Publ.-Id: 17847 - Permalink


Stabilization of prolate deformation at high spin in 75Kr
Steinhardt, T.; Eberth, J.; Skoda, S.; Thelen, O.; Schwengner, R.; Dönau, F.; Plettner, C.; Schnare, H.; de Angelis, G.; Napoli, D. R.; Farnea, E.; Gadea, A.; Jungclaus, A.; Lieb, K. P.; Wadsworth, R.;
The neutron-deficient nucleus 75Kr has been studied in two EUROBALL experiments. The analysis yielded a considerably extended level scheme including two newly observed excited high spin bands. The results are interpreted in the framework of the cranked Nilsson-Strutinsky approach. The calculations compare well to the experimentally established level scheme and predict the nucleus to be mainly prolate or triaxially deformed at high spin. Evidence for an oblate-prolate shape coexistence could not be found at high spin.
Keywords: Nuclear structure, gamma-ray spectroscopy, HPGe detectors, EUROBALL; silicon detectors, neutron detectors, cranked Nilsson-Strutinsky model.

Publ.-Id: 17846 - Permalink


Synthesis and characterization of a percolating, ferromagnetic, Mn-rich Ge:Mn nanonet with hysteretic transport properties
Bürger, D.; Zhou, S.; Höwler, M.; Ou, X.; Kovacs, G. J.; Reuther, H.; Mücklich, A.; Skorupa, W.; Helm, M.; Schmidt, H.;
The coupling of the magnetization state with the electrical transport properties of a magnetic semiconductor is one big step to new spintronics devices. The coupling can be proved by SQUID magnetization and Hall resistance measurements. In a previous work we fabricated ferromagnetic Ge:Mn by Mn ion implantation and pulsed laser annealing (PLA) and observed a clear hysteretic Hall resistance correlated with the magnetization below 10 K [1]. Recently, by applying optimized PLA conditions, we fabricated a percolating, Mn-rich Ge:Mn nanonet with hysteretic Hall resistance up to 30 K [2]. This nanonet is embedded in crystalline Ge:Mn between 5 nm and 40 nm under the sample surface. The reason for the formation of the nanonet is a constitutional undercooling of the liquid Ge-Mn-alloy during the recrystallization process using a relatively long pulse length of 300 ns which helped to imprint an optimal temperature profile during PLA [3]. We applied etching to confirm the contribution of the nanonet to the electrical transport properties. In the future such nanonets may be used to spin-polarize free charge carriers in magnetic semiconductors at room temperature. Because the nanonet can be selectively etched, substrates with ordered “nano-channels” can be fabricated which may be also useful in the field of nanoimprint-lithography. [1] S. Zhou et al., Phys. Rev. B 81, 165204 (2010) [2] D. Bürger et al., Appl. Phys. Lett. 100, 012406 (2012) [3] J. Narayan, J. Appl. Phys. 52, 1289 (1981)
Keywords: pulsed laser annealing, pulsed laser melting, ion implantation, Hall resistance, ferromagnetism, constitutional supercooling, nanonet
  • Lecture (Conference)
    E-MRS 2012 Fall Meeting, 17.-21.09.2012, Warschau, Polen

Publ.-Id: 17845 - Permalink


Hydrogen interaction with defects in ZnO
Lukac, F.; Cizek, J.; Vlcek, M.; Prochazka, I.; Vlach, M.; Anwand, W.; Brauer, G.; Traeger, F.; Rogalla, D.; Becker, H.-W.; Wagner, S.; Uchida, H.; Bähtz, C.;
In the present work hydrothermally grown ZnO single crystals were electrochemically charged with hydrogen. The influence of hydrogen on ZnO microstructure was investigated by positron annihilation spectroscopy (PAS) combined with X-ray diffraction (XRD) using synchrotron radiation. Hydrogen concentration in the samples was determined by nuclear reaction analysis (NRA). It was found that a high concentration of hydrogen can be introduced into ZnO by electrochemical loading. At low concentrations absorbed hydrogen causes elastic volume expansion of ZnO crystal. At higher concentration, hydrogen-induced stresses exceed the yield stress in ZnO and plastic deformation of the crystal takes place leading to formation a defected subsurface layer in the crystals.
Keywords: zinc oxide, hydrogen defects, positron annihilation spectroscopy

Publ.-Id: 17844 - Permalink


Synthesis, in silico, in vitro, and in vivo investigation of 5-[11C]methoxy-substituted sunitinib, a tyrosine kinase inhibitor of VEGFR-2
Caballero, J.; Muñoz, C.; Alzate-Morales, J. H.; Cunha, S.; Gano, L.; Bergmann, R.; Steinbach, J.; Kniess, T.;
Sunitinib® (SU11248) is a highly potent tyrosine kinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR). Radiolabeled inhibitors of receptor tyrosine kinases (RTKs) might be useful tools for monitoring RTKs levels in tumor tissue giving valuable information for anti-angiogenic therapy. Herein we report the synthesis of 5-methoxy-sunitinib 5 and its 11C-radiolabeled analogue [11C]-5. The non-radioactive reference compound 5 was prepared by Knoevenagel condensation of 5-methoxy-2-oxindole with the corresponding substituted 5-formyl-1H-pyrrole. A binding constant (Kd) of 20 nM for 5 was determined by competition binding assay against VEGFR-2. In addition, the binding mode of sunitinib® and its 5-methoxy substituted derivative was studied by flexible docking simulations. These studies revealed that the substitution of the fluorine at position 5 of the oxindole scaffold by a methoxy group did not affect the inhibitor orientation, but affected the electrostatic and van der Waals interactions of the ligand with residues near the DFG motif of VEGFR-2. 5-[11C]methoxy-sunitinib ([11C]-5) was synthesized by reaction of the desmethyl precursor with [11C]CH3I in the presence of DMF and NaOH in 17±3% decay-corrected radiochemical yield at a specific activity of 162-205 GBq/µmol (EOS). In vivo stability studies of [11C]-5 in rat blood showed that more than 70% of the injected compound was in blood stream, 60 min after administration.
Keywords: sunitinib®,VEGFR, docking, molecular dynamics, MM-GBSA, carbon-11, radiolabeling

Publ.-Id: 17843 - Permalink


High-field magnetism and magnetoacoustics in uranium intermetallic antiferromagnets
Andreev, A. V.; Skourski, Y.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.;
We report on studies on the magnetic and magnetoacoustic properties of uranium intermetallic antiferromagnets UCo2Si2, UCu0.95Ge, UIrGe and U2Ni2Sn in pulsed magnetic fields up to 60 T, where they undergo metamagnetic transitions. The measurements were performed in the temperature range from 1.4 to 100 K. The magnetic ordering and the metamagnetic transitions are accompanied by pronounced anomalies in the ultrasound velocity and the ultrasound attenuation. All studies were performed on single crystals grown by the Czochralski method in a tri-arc furnace.

Publ.-Id: 17842 - Permalink


Interplay between crystal field splitting and Kondo effect in CeNi9Ge4-xSix
Gold, C.; Gross, P.; Peyker, L.; Eickerling, G.; Simeoni, G. G.; Stockert, O.; Kampert, E.; Wolff-Fabris, F.; Michor, H.; Scheidt, E.-W.;
The pseudo-ternary solid solution CeNi9Ge4-xSix (0 ≤ x ≤ 4) has been investigated by means of x-ray diffraction, magnetic susceptibility, specific heat, electrical resistivity, thermopower and inelastic neutron scattering studies. The isoelectronic substitution of germanium by silicon atoms causes a dramatic change of the relative strength of competing Kondo, RKKY an crystal field (CF) energy scales. The strongest effect is the continuous elevation of the Kondo temperature TK from approximately 3.5 K for CeNi9Ge4 to about 70 K for CeNi9Si4. This increase of the Kondo temperature is attended by a change of the CF level scheme of the Ce ions. The interplay of the different energy scales results in an incipient reduction of the ground state degeneracy from an effectively fourfold degenerate non-magnetic Kondo ground state with unusual non-Fermi-liquid features of CeNi9Ge4 to a lower one, followed by an increase towards a sixfold, fully degenerate ground state multiplet in CeNi9Si4 (TK ~ ΔCF).

Publ.-Id: 17841 - Permalink


Advanced biotechnology for extraction and recovery of metals
Raff, J.; Lehmann, F.; Moll, H.; Kutschke, S.; Pollmann, K.;
In an era of dwindling resources and rising prices new procedures for the exploitation, beneficiation and recycling of especially industrial relevant metals are in demand. Such elements are essential for modern high tech industry and development of future techno¬logies. Interestingly, nature itself offers promising approaches in these fields. Some organisms are thusly able to mobilize metals not only from ores but also from electrical and electronical equipment waste by bioleaching [Bosecker K. 1997, Brantley et al. 2001, Brandl H. et al. 2001]. Bioleaching is already used for the large scale production of copper especially in ores with low metal content. Furthermore, other species or biomolecules are able to selectively bind and accumulate metals [Pollmann et al. 2006], allowing the con-struction of metal selective filter materials. In addition, some organisms trigger the formation of minerals or are able to form different kinds of biominerals by themselves, representing also a way to separate metals [Wang X. and W.E.G. Müller 2009]. In combination with established physical and chemical processes, such biotechnological approaches have a high potential to improved metal beneficiation and recycling.
Within the biotechnology group at the Helmholtz Institute Freiberg for Resource Technology such new procedures for extracting, treating and recycling metals such as copper or rare earths using microbes are under development. Whereas the bioleaching related research is just at the beginning and the investigation of biomineralization pro¬cesses for metal separation is planned for the future, the group has long-term experience in the investigation of the interaction of metals with biomass and especially in the selective metal binding by proteins and other bioligands. Within radioecological research, bacterial isolates were investigated that possess so called surface-layer (S-layer) proteins, forming a closed protein lattice on many bacteria and archaea protecting the cells from being affected by environ¬mental influences. In case of such bacteria living in highly heavy metals contaminated environments, their S-layers have high metal binding capacity and high stability. Furthermore, they possess different metal binding sites. There are many less specific binding sites, binding large amounts of precious metals such as Pt, Pd and Au as well as radioactive metals such as U. Metals such as Fe, Co, Ni, Cu and Zn are not bound or only in small quantities. In addition, there are several highly specific binding sites, binding Ca, Cm and Eu. First results indicates, that the binding affinity of these metals differs significantly. As the metal binding additionally depends on the pH and differs from metal to metal, S-layer proteins possess a high application potential for the specific separation of industry relevant metals.
Keywords: Biotechnology, biosorption, bioleaching, metals
  • Lecture (Conference)
    GeoHannover 2012, 01.-03.10.2012, Hannover, Deutschland

Publ.-Id: 17840 - Permalink


QCM-D a versatile tool for biosorption processes
Suhr, M.; Drechsel, N.; Günther, T.; Matys, S.; Raff, J.; Pollmann, K.;
Bacterial isolates from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) possess high affinities to heavy metals e.g. uranium. This binding effect is caused by the components of the bacterial cell wall, mainly affected by surface layer proteins.
Aim of this work is to investigate metal interaction processes like biosorption with Gram-positive bacteria and their main cell wall components.
In addition to the standard analytical methods, the quartz crystal microbalance with dissipation monitoring is used to track and control the biological layer formation and metal deposition. This method allows the real time detection of sorption processes on a molecular level and gives further information to viscoelastic properties. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties.
Some selected results of these experiments will be shown on this poster.
Keywords: QCM-D, bacteria, Biosorption, metals, S-layer, lipids, interaction, AFM
  • Poster
    7th Annual Ph.D. seminar, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17839 - Permalink


Do microorganisms influence the transport of radionuclides in Uranium-contaminated underground mines?
Zirnstein, I.; Arnold, T.; Röske, I.;
Microorganisms are ubiquitous, also in extreme environments e.g. in environments with high salinity, in very hot and acid waters or underneath thick slides of ice. In the former uranium mine Königstein exist also an extreme environment, due to the very low pH (2.7), the high concentrations of heavy metals and uranium. Nevertheless microorganisms in form of biofilms exist in a depth of 250 meters in this mine. Since 2010 the underground mine was flooded and is no longer accessible for sampling. For investigations in mine biofilms the microorganisms in the mine water have to be cultivated above ground in flow cells or in a biofilm reactor. The microorganisms in the mine water should grow on special biofilm carriers in the reactor. Our studies may contribute to new remediation measures for heavy metal contaminated mine waters.
  • Lecture (Conference)
    7th PhD Seminar, 08.-10.10.2012, Schöneck, Germany

Publ.-Id: 17838 - Permalink


Biofilms in a Uranium contaminated acid mine drainage environment
Zirnstein, I.; Arnold, T.; Krawczyk-Bärsch, E.; Wobus, A.; Röske, I.;
The Königstein mine is currently in the process of remediation and represents an underground acid mine drainage (AMD) environment. Due to technical leaching with sulphuric acid, the mine water is characterized by low pH, high concentrations of toxic heavy metals and uranium (up to 3×10-4 M). Biofilms in the Königstein mine grew underground in the mine galleries in a depth of 250 m (50 above sea level) either as stalactite-like slime communities (snottites) or as acid streamers in the drainage channels. Previously conducted studies on the bacterial diversity in both biofilm communities showed that beta-proteobacterium affiliated with Ferrovum myxofaciens, also designated “Ferribacter polymyxa” were identified as dominating bacterial species. The eukaryotic diversity of the Königstein biofilms was analysed by molecular methods, i.e. 18S rDNA PCR, cloning and sequencing and by microscopic investigations. It was found that the eukaryotic biofilm communities of the Königstein environment showed a limited number of different heterotrophic species and consist of a variety of lineages belonging to nine major taxa: Ciliates, Flagellates, Amoebae, Heterolobosea, Fungi, Apicomplexa, Stramenopiles, Rotifers and Arthropoda and in addition a large number of uncultured eukaryotes, denoted as acidophilic eukaryotic cluster (AEC).
Since 2010 the underground mine was flooded and is no longer accessible for sampling. For investigations in mine biofilms the microorganisms in the mine water have to be cultivated above ground in flow cells or in a biofilm reactor. The microorganisms in the mine water should grow on special biofilm carriers in the reactor. Our studies may contribute to new remediation measures for heavy metal contaminated mine waters.
  • Poster
    1st Transnational Workshop "GETGEOWEB": Genomics and Transcriptomics in Geobiotechnolgy and White Biotechnology, 29.-30.10.2012, Freiberg, Germany

Publ.-Id: 17837 - Permalink


Optical Excitation of Josephson Plasma Solitons in a Cuprate Superconductor
Dienst, A.; Casandruc, E.; Zhang, L.; Eckstein, M.; Fausti, D.; Hoffmann, M.; Khanna, V.; Dean, N.; Gensch, M.; Winnerl, S.; Seidel, W.; Pyon, S.; Takayama, T.; Takagi, H.; Cavalleri, A.;
Josephson Plasma Waves are linear electromagnetic modes that propagate along the planes of cuprate superconductors, sustained by oscillatory tunnelling supercurrents. These waves exhibit a plasmonic resonance in the GHz , to THz frequency range, depending on the interlayer coupling strength. For strong electromagnetic fields, the supercurrents approach their critical value and the electrodynamics become highly nonlinear , . Josephson Plasma Solitons (JPS) are breather excitations , that emerge in this regime, bound vortex/antivortex pairs that self-localize , , and propagate without dispersion. We experimentally excite such solitons using intense narrowband radiation from an infrared Free Electron Laser, tuned to the 2-THz Josephson Plasma Resonance of La1.84Sr0.16CuO4. The JPS is revealed by the appearance of long-lived transparency window in the spectral region immediately below the plasma resonance, which is opaque to small-amplitude waves. This reshaping of the optical properties originates from Fano-type coupling between probe waves and the JPS. Optical control of solitonic excitations in superconductors opens up possibilities in THz opto-plasmonics or in the manipulation of high-Tc superconductivity.

Publ.-Id: 17836 - Permalink


Das Metallbindungsverhalten von Membranen Gram-positiver Bakterien
Drechsel, N.;
Für das Verständnis von Mobilität und Stabilität von Metallen, wie z.B. Schwermetallen, in der Umwelt, stellt die Untersuchung der Metallsorption einen wichtigen Faktor dar. Für die weiterführende Erforschung von Wechselwirkungsprozessen der Mikroorganis-men und deren Metallbindungseigenschaften ist es notwendig, die Sorption verschie-dener Metalle durch Mikroorganismen und zellulären Bestandteilen zu untersuchen.
In der vorliegenden Bachelorarbeit werden die Wechselwirkungen von umweltrele-vanten Metallen mit biologischen Komponenten untersucht. Dazu dienen die bak-teriellen Haldenisolate Lysinibacillus sphaericus JG-A12 und Lysinibacillus sp. JG-B53. Diese zeigten bereits in vorangegangenen Untersuchungen sehr hohe Metallbindungs-kapazitäten. Für die Sorptionsversuche werden die Schwer- und Edelmetalle Platin, Palladium, Blei, Cadmium, Europium und Gold und das Halbmetall Arsen verwendet. Durch die Einbeziehung von isolierten Zellwandbestandteilen der Gram-positiven Mikroorganismen, wie z.B. S-Layer-Proteine und Membranlipide sollen genauere Kenntnisse der Sorptionseigenschaften der biologischen Komponenten erlangt werden. Als analytische Verfahren werden die ICP-MS und die QCM-D eingesetzt. Durch einen Vergleich der zwei Bakterien werden unterschiedliche Metallselektivitäten aufgedeckt, die in weiteren Forschungsvorhaben und Anwendungsgebieten Einsatz finden können.
Keywords: Biosorption, QCM-D,Bakterien, S-Layer, Lipide, Metalle, Metallinteraktionen
  • Bachelor thesis
    HZDR und Hochschule Mittweida, 2012
    98 Seiten

Publ.-Id: 17835 - Permalink


Electromagnetic dipole strength up to the neutron separation energy from 196Pt(γ,γ′) and 195Pt(n,γ) reactions
Massarczyk, R.; Schramm, G.; Junghans, A. R.; Schwengner, R.; Anders, M.; Belgya, T.; Beyer, R.; Birgersson, E.; Ferrari, A.; Grosse, E.; Hannaske, R.; Kis, Z.; Kögler, T.; Kosev, K.; Marta, M.; Szentmiklosi, L.; Wagner, A.; Weil, J. L.;
The dipole strength in the nucleus 196-Pt was investigated using two different experimental methods. The photon spectrum from the deexcitation of a state after cold neutron capture in 195-Pt is influenced by the dipole strength and nuclear level density in 196-Pt as is also the gamma-ray spectrum from photon scattering on 196-Pt. In a combined analysis of data from the research reactor in Budapest and the bremsstrahlung facility at the ELBE accelerator in Dresden, the GEANT4 code was used to calculate detector response and efficiency. Also the influence of non-nuclear scattered photons was determined and allows us to take into account the continuum of unresolved states. The statistical code gammaDEX was used to estimate branching ratios and compare simulated and experimental spectra. Using information from both experiments it was possible to obtain a temperature parameter of 600\,keV for the constant temperature level density model. For the dipole strength a small extra strength over tail of the Giant Dipole Resonance in the region below the neutron energy separation was found.
Keywords: neutron capture, strength functions, nuclear structure, statistical calculations

Publ.-Id: 17833 - Permalink


From terahertz science and technology to semiconductor quantum structures and back
Helm, M.;
I will give an overview about modern terahertz science and technology and discuss some applications of THz radiation. Then I will present the physics of semiconductor quantum wells and show how such structures can be developed into a so-called quantum cascade laser working in the THz range
Keywords: terahertz, laser, semiconductor
  • Invited lecture (Conferences)
    Lecture at Southeastern University, 18.09.2012, Nanjing, China

Publ.-Id: 17832 - Permalink


Process Monitoring of tracer transport through artificial soil with GeoPET
Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.; Enzmann, F.; Khan, F.; Kersten, M.; Stoll, M.; Ritschel, T.; Totsche, K. U.;
Positron-Emission-Tomography (PET) enables direct and quantitative monitoring of the spatiotemporal distributions of dissolved inert and/or reactive PET-nuclides and PET-nuclide-labelled compounds during their passage through decimeter-scaled material samples. We apply our biomedical PET-scanner (ClearPET, Raytest) exclusively to geomaterial samples and reach the physical limit of spatial resolution of nearly 1 mm with pico-molar sensitivity.
Artificial soil columns (68.5% fine-medium sand, 25.5% coarse silt, 5% Illit, 1% Goethit) have been prepared in Jena. µCT-images have been produced at the Bundesanstalt für Materialforschung und –prüfung (BAM) and analysed in Mainz. They show layering and inhomogeneous water saturation, yet a roughly homogeneous grain distribution. PET-imaging was conducted during flow-through experiments into the upright column, which is perpendicular to the scanner axis.
First flow experiments have been conducted with – presumably – conservative tracers ([18F]KF (decay time 109.77 min) and Eosin). Conventional break-through curves (BTCs) have been recorded both by fluorescence detection of Eosin and with a Gamma Radioactivity Flow-Through Monitor (Gabi Star, Raytest). From the transport process observation by sequential PET-imaging we could derive longitudinal BTCs during the tracer propagation through the column. Further, it could be shown that 18F- was slightly retarded and - more significantly - the effective pore volume was inhomogeneous (preferential transport through the sample).
These experiments will be repeated on newly constructed columns with plastic endplates (instead of the original stainless steel ones) and an optimized dead volume.
To preliminarily conclude, we demonstrated that the combined tomographic information on pore structure and spatio-temporal transport process observation in a soil model column yields an essential gain in information for describing and parameterizing transport processes, compared to input-output experiments. Such measurements represent the experimental control of ab-initio model simulations of conservative and reactive transport, e.g. [64Cu]MCPA), and of the interpretation of conventional input-output transport experiments, conducted by the partners.
Keywords: Reactive Transport, PET, Process Observation
  • Poster
    Annual Meeting DFG Priority Programme SPP1315 "Biogeochemical Interfaces in Soil", 10.-12.10.2012, Dornburg, Deutschland

Publ.-Id: 17830 - Permalink


Verification of the trigonal-geometry diffusion and SP3 models of the code DYN3D
Duerigen, S.; Nikitin, E.; Mittag, S.;
DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of Light-Water Reactors with square and hexagonal fuel assembly geometries, applicable also to innovative reactor concepts. Currently, several versions of the DYN3D code are available including a multi-group diffusion and simplified P3 (SP3) neutron transport option.
In this work, both the diffusion and SP3 method in trigonal geometry are verified by means of fine-mesh homogenized reference solutions. Good agreement is observed for eigenvalues, neutron flux and power distributions. Mesh refinement studies show that the trigonal nodal DYN3D methods converge well to the fine-mesh references. Furthermore, an anisotropic-scattering benchmark problem was chosen to show the advantage of the SP3 method over the diffusion approach.
Keywords: simplified P3, SP3, nodal method, trigonal, triangular, hexagonal, DYN3D, mesh refinement
  • Open Access LogoContribution to proceedings
    22nd SYMPOSIUM of ATOMIC ENERGY RESEARCH (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic
  • Lecture (Conference)
    22nd SYMPOSIUM of ATOMIC ENERGY RESEARCH (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic

Publ.-Id: 17829 - Permalink


Femtosecond Level Synchronization of a Linac Based super-radiant THz Facility
Kuntzsch, M.; Röser, F.; Lehnert, U.; Gensch, M.; Bousonville, M.; Schlarb, H.; Stojanovic, N.; Vilcins-Czvitkovits, S.;
The superconducting radiofrequency (SRF) electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is currently upgraded with an SRF Gun and a femtosecond (fs) electron beamline to enable continuous wave operation with bunch charges of up to 1 nC and bunch durations down to 100 fs (RMS). The new femtosecond electron beamline will be used to drive two coherent THz sources and one X-ray source based on Thomson scattering. The two different THz sources, one narrow bandwidth undulator source and one broad bandwidth coherent transition/diffraction source, are guided into a dedicated THz Laboratory where they can be combined with various fs-laser systems. For the planned THz pump laser probe experiments, synchronization of the external pump-probe lasers on the fs- level is essential. Our approach is based on an optical synchronization system, adapted from a similar system installed at FLASH [*]. That system will be installed in collaboration between DESY and HZDR. In this contribution we will discuss the layout of the synchronization scheme and first ideas for measurements of the arrival time jitter of the THz pulses to evaluate the achieved degree of timing stability.
Keywords: ELBE Synchronization THz
  • Poster
    Free-Electron Laser Conference, 26.-31.08.2012, Nara, Japan

Publ.-Id: 17828 - Permalink


Optical Synchronization at HZDR
Kuntzsch, M.;
The superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf is currently upgraded to enable continuous wave operation with bunch charges of up to 1 nC and durations down to 200 fs (RMS). The new beamline will drive a THz source and an X-ray source based on Thomson scattering. In collaboration with DESY, Hamburg, an optical synchronization system based on a mode locked master laser is currently being set up to ensure timing stability on the few 10 fs level. This talk is giving an overview on different synchronization concepts, the implementation at ELBE and the first comissioning results.
Keywords: ELBE Synchronization
  • Invited lecture (Conferences)
    1st ARD Workshop ST3 “ps-fs Electron and Photon Beams”, 21.-23.08.2012, Hamburg, Germany

Publ.-Id: 17827 - Permalink


Temperature grid sensor for the measurement of spatial temperature distributions
Schäfer, T.; Schubert, M.; Hampel, U.;
This paper presents results of the development and application of a new temperature grid sensor based on the wire-mesh sensor principle. The grid sensor consists of a matrix of 256 Pt1000 platinum chip resistors and an associated electronics that measures the grid resistances with a multiplexing scheme at high speed. The individual sensor elements can be spatially distributed on an object surface and measure transient temperature distributions in real time. The advantage, compared to other temperature field measurement approaches, such as infrared cameras, is that the object under investigation can be thermally insulated and radiation properties of the surface do not play a role for measurement accuracy. The sensor principle is therefore suited for various industrial monitoring applications. Its applicability for surface temperature monitoring has been demonstrated by conduction and analysis of heating and mixing experiments in a vessel.
Keywords: temperature grid sensor; temperature measurement; wire-mesh sensor; thermal surface monitoring

Publ.-Id: 17826 - Permalink


REECOB: 20 Years of Rare Earth Element Calcium Oxoborates Crystal Growth Research
Möckel, R.; Reuther, C.; Götze, J.;
Rare earth element calcium oxoborates (REECOB, REECa4O[BO3]3) represent a group of materials for non-linear optics and with useful piezoelectric properties under high-pressure and high-temperature conditions making it applicable as sensor materials in extreme environments. High-quality crystals with appropriate size are generally grown from a melt by the Czochralski method. This article presents a compilation and comparison of crystal growth parameters and properties of members of the REECOB group from the literature with those of own growth experiments. Recent studies provided new data concerning the melting temperature of REECOB members, such as ca. 1475°C for SmCa4O(BO3)3 (SmCOB). In addition, first data on the change of thermal expansion coefficients of SmCOB are presented and discussed.
Keywords: REECOB, oxoborate, Czochralski

Publ.-Id: 17825 - Permalink


Investigation of the Eu(III)-B(OH)3-Organic System
Schott, J.; Barkleit, A.; Acker, M.; Brendler, V.;
Borates and organic matter (humic and fulvic acids, small organic molecules) are ubiquitous compounds in the environment (rocks, soils, natural waters).
Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers.
The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution.
For boric acid (B(OH)3) no and for polyborates weak complexation properties concerning Eu(III) are observed.
The complexation between Eu(III) and salicylate is influenced by boric acid due to the formation of a borate ester.
Furthermore at pH 6 the formation of a solid Eu borate species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.
Keywords: lanthanides, actinides, europium, boric acid, borates, polyborates
  • Poster
    Annual Ph.D. seminar, 08.-10.10.2012, Schöneck, Deutschland

Publ.-Id: 17824 - Permalink


Broadband, diode pumped Yb:SiO2 multicomponent glass laser
Loeser, M.; Röser, F.; Reichelt, A.; Siebold, M.; Grimm, S.; Litzkendorf, D.; Schwuchow, A.; Kirchhof, J.; Schramm, U.;
Fabrication, spectroscopic properties, and laser performance of a Yb:SiO2 multicomponent glass have been investigated in this paper. The glass system composed of SiO2, Al2O3, and La2O3 excels in terms of a high thermal stress resistance compared to other laser glasses. The laser experiments were conducted with a 3.4 mm thick and 0.9 mol. % Y2O3 doped sample. A maximum slope efficiency of 51%, a maximum optical to optical efficiency of 42%, and a tuning range from 1010–1090 nm was realized. Due to the promising laser properties and a straightforward fabrication technique it may well qualify as an alternative gain medium in high-energy, ultrashort pulse laser systems.
Keywords: Lasers, diode-pumped; Lasers, solid-state; Lasers, tunable; Rare earth and transition metal solid-state lasers; Laser materials; Lasers, ytterbium
  • Optics Letters 37(2012)19, 4029-4031

Publ.-Id: 17823 - Permalink


Hades experiments: investigation of hadron in-medium properties
Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; 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.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lalik, R.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; 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.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
Hadron modications in nuclear matter are discussed in connection to chiral symmetry restoration and/or hadronic many body eects. Experiments with photon, proton and heavy ion beams are used to probe properties of hadrons embedded in nuclear matter at different temperatures and densities. Most of the information has been gathered for the light vector mesons ρ, ω and φ. HADES is a second generation experiment operating at GSI with the main aim to study in-medium mass modication by means of dielectron production at SIS18/Bevelac energy range. Large acceptance and excellent particle identication capabilities allows also for measurement of strangeness production. These abilities combined with the variety of beams provided by the SIS18 allows for characterization of properties of the dense baryonic matter properties created in heavy ion collisions at these energies. A review of recent experimental results obtained by HADES is presented, with main emphasis on hadron properties in nuclear matter.

Publ.-Id: 17822 - Permalink


High rate deposition of amorphous hydrogenated carbon films by hollow cathode arc PECVD
Zimmermann, B.; Fietzke, F.; Klostermann, H.; Lehmann, J.; Munnik, F.; Möller, W.;
Amorphous hydrogenated carbon films (a-C:H) are of increasing importance in science and applications. However, most deposition techniques applied suffer from a low deposition rate. In this paper, a high rate process based on hollow cathode arc PECVD is presented. A magnetically enhanced hollow cathode arc plasma has been used to activate the precursor acetylene. The argon-acetylene plasma has been characterized by energy-resolved mass spectrometry revealing a large variety of dissociation and polymerization products as well as their kinetic energy distributions, which are related to the spatial distribution of ion generation. A-C:H layers have been deposited on flat substrates with rates of up to 1 µm/min. Depending on the deposition conditions, polymeric, graphitic, and diamond-like carbon films with a nanoindentation hardness of 18.2 GPa have been produced and analyzed by Raman spectroscopy and scanning electron microscopy. In order to obtain the film composition, elastic recoil detection analysis and Rutherford backscattering spectrometry have been applied.
Keywords: hollow cathode arc, plasma diagnostics, amorphous hydrogenated carbon, diamond-like carbon, plasma-enhanced chemical vapor deposition, elastic recoil detection analysis

Publ.-Id: 17821 - Permalink


Investigation of upward cocurrent gas-liquid pipe flow using ultrafast X-ray tomography and wire-mesh sensor
Zhang, Z.; Bieberle, M.; Barthel, F.; Szalinski, L.; Hampel, U.;
Ultrafast X-ray tomography and wire-mesh sensor as two high-speed imaging modalities were applied to study upward gas-liquid flow in a vertical pipe of 50 mm inner diameter. High speed scanning of the flow cross-section was performed with 2500 frames per second with both modalities. Sequences of two-dimensional distributions of local gas fraction were acquired and further analyzed. Radial profiles of time averaged gas fraction distributions show a good agreement for both imaging techniques. Furthermore radial gas velocity profiles were obtained from a temporal cross-correlation of the image data of both measurement techniques and also bubble size distributions from binarized image data were compared.
Keywords: gas-liquid flow, ultrafast X-ray tomography, wire-mesh sensor

Publ.-Id: 17820 - Permalink


Insider 6 / 2012
Weigl, A.;
Mitarbeiterzeitung des HZDR
Keywords: HZDR in-house paper
  • Communication & Media Relations
    Mitarbeiterzeitung 31.07.2012
    8 Seiten

Publ.-Id: 17819 - Permalink


Kelvin probe force microscopy for characterizing functionalized semiconductor surfaces for nano and biotechnologies
Baumgart, C.; Habicht, S.; Feste, S.; Helm, M.; Müller, A.-D.; Schmidt, H.;
Kelvin probe force microscopy (KPFM) is one of the most promising non-contact electrical nanometrology technique to characterize functionalized semiconductor. We present its applicability to determine surface-near electrostatic forces in locally doped silicon structures. Those electrostatic forces may be used to position and control nano and biomaterials on doped semiconductor carriers. Furthermore, quantitative dopant profiling by means of KPFM measurements [1] is successfully demonstrated on a conventional static random access memory (SRAM) cell, on cross-sectionally prepared Si epilayers, and on arrays of horizontal Si nanowires [2] by applying a recently introduced new explanation of the measured KPFM signal. Additionally, the influence of local, carrier-depleted space charge regions and of the electric fields across them is discussed. It is explained how drift and diffusion of injected charge carriers in intrinsic electric fields influence the surface-near electrostatic forces [3]. Surface-near electrostatic forces may be enhanced above pn junctions and KPFM is successfully employed to locate pn junctions in doped silicon structures, e.g. along the B-doped and As-doped Si nanowires. [1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B, 80, 085305 (2009). [2] S. F. Feste, J. Knoch, S. Habicht, D. Buca, Q.-T. Zhao, S. Mantl, Solid-State Electronics, 53, 1257 (2009). [3] C. Baumgart, A.-D. Müller, F. Müller, and H. Schmidt, Phys. Stat. Sol. A, 208, 777 (2011) (editor’s choice).
  • Lecture (Conference)
    E-MRS Fall Meeting 2012, 17.-21.09.2012, Warsaw, Poland

Publ.-Id: 17818 - Permalink


Optical probing of TNSA acceleration conditions
Metzkes, J.; Zeil, K.; Kluge, T.; Kraft, S. D.; Bussmann, M.; Cowan, T. E.; Schramm, U.;
Laser-plasma based accelerators, where a high intensity laser interacts with a solid target, represent a promising concept for compact and cost-efficient ion sources.
As the acceleration takes place on ultra-fast timescales and very small spatial scales of only a few µm, information about the acceleration processes in the plasma are generally derived indirectly, e.g. through particle or radiation diagnostics. Optical probing techniques however can give direct access to the plasma dynamics on the fs to ps timescale.
In this poster we will present pump-probe experiments performed at the high-intensity laser DRACO at the HZDR, Germany. Seeking information about the conditions of the critical density surface in the plasma, we simply image the probe reflected from the target surface without doing tomography. The curvature of the reflecting critical surface translates into characteristic angular patterns in the reflected probe beam which can be traced back to the original surface shape using a ray-tracing model of the experiment.
In our experiments, the pump beam was the 150 TW DRACO beam with a pulse length of 30 fs and a central wavelength of 800 nm. The probe beam was derived from the mean beam, frequency doubled, and had a pulse duration of ~100fs. Both beams were synchronized and the probe could be delayed with respect to the main beam with a resolution of ~200 fs. The imaging of the probe was performed with a large-aperture objective yielding a high spatial resolution of ~2µm.
As a result, we compared the critical surface deformation and dynamics for different target materials (metal and silicon) and target shapes, observing a strong influence of the lateral target size.
  • Poster
    32nd European Conference on Laser Interaction with Matter (ECLIM 2012), 10.-14.09.2012, Warschau, Polen

Publ.-Id: 17817 - Permalink


Time resolved FT-IR difference spectroscopy of vibrational control experiments on bacteriorhodopsin
Bauer, C.; Gensch, M.; Heberle, J.;
Our goal is to investigate how photoreactions of proteins can be controlled by intense THz radiation tuned in resonance to specific vibrational modes, in analogy to coherent control experiments conducted by femtosecond (fs) NIR laser pulses [1]. For this we combine a time-resolved IR difference spectroscopic setup with uniquely intense, tunable narrow bandwidth THz radiation at the picosecond (ps) beamline of the THz free electron laser FELBE [2].
  • Poster
    Jahrestagung der Deutschen Gesellschaft für Biophysik (DGfB), 24.-29.09.2012, Göttingen, Deutschland

Publ.-Id: 17816 - Permalink


Direct observation of prompt pre-thermal laser ion sheath acceleration
Metzkes, J.; Zeil, K.; Kluge, T.; Bussmann, M.; Cowan, T.; Kraft, S.; Sauerbrey, R.; Schramm, U.;
High-intensity laser-plasma ion generation is promising as a compact, low-cost proton source for applications like ion beam therapy. Using a femtosecond table-top laser system, we study the intra-pulse phase of the laser driven proton acceleration and show that protons efficiently gain energy in these early times [1].

In recent laser-ion acceleration experiments performed at the 150 TW Draco laser in Dresden, Germany, we have demonstrated the importance of a precise understanding of the electron dynamics in solids on an ultra-short time scale. For example, with ultra-short laser pulses a description based purely on the evolution of a thermal electron ensemble, as in standard TNSA models, is not sufficient anymore. Rather, non-thermal effects during the ultra-short intra-pulse phase of laser-electron interaction in solids become important for the acceleration of ions when the laser pulse duration is in the order of only a few 10s of femtoseconds. While the established maximum ion energy scaling in the TNSA regime goes with the square root of the laser intensity, for such ultra short pulse durations the maximum ion energy is found to scale linear with laser intensity [2], motivating the interest in such laser systems.
Investigating the influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution, we present recent advances in the description of the laser interaction with solids, focusing on the implications of intra-pulse non-thermal phenomena on the ion acceleration.

References

1. K. Zeil, J. Metzkes, T. Kluge, M. Bussmann, T.E. Cowan, S. D. Kraft, R. Sauerbrey and U. Schramm, Direct observation of prompt pre-thermal laser ion sheath acceleration, Nature Communications 3 (874), 2012

2. K. Zeil, S. D. Kraft, S. Bock, M. Bussmann, T.E. Cowan, T. Kluge, J. Metzkes, T. Richter, R. Sauerbrey and U. Schramm, Scaling of proton energies in ultrashort pulse laser plasma acceleration, New Journal of Physics 12 (045015), 2010
  • Lecture (Conference)
    32nd European Conference on Laser Interaction with Matter (ECLIM 2012), 10.-14.09.2012, Warschau, Polen
  • Lecture (Conference)
    SPIE Optics + Optoelectronics 2013, 15.-18.04.2013, Prague, Czech Republic

Publ.-Id: 17815 - Permalink


Segmentierung von Gasblasen aus Röntgentomographiedaten von zweiphasigen Rohrströmungen
Banowski, M.; Bieberle, M.; Wagner, M.; Lucas, D.; Hoppe, D.; Harnisch, J.; Hampel, U.;
In der Präsentation wird das bildgebende Messverfahren „ultraschnelle Röntgentomographie“ vorgestellt sowie die Versuchsanlage TOPFLOW kurz erläutert. Die verschiedenen, zur Segmentierung von Gasblasen entwickelten und getesteten Algorithmen werden ebenfalls vorgestellt und deren Ergebnisse anhand von Phantommessungen qualitativ und quantitativ verglichen. Die jeweiligen Vor- und Nachteile der Algorithmen werden beispielhaft gezeigt und mögliche weitere Lösungsansätze diskutiert.
Keywords: two-phase, measuring technique, X-ray, tomography, pipe flow, bubble detection
  • Lecture (Conference)
    DBV-Workshop - Workshop für Digitale Bildverarbeitung, 04.09.2012, Zittau, Deutschland

Publ.-Id: 17814 - Permalink


Ion mass and energy distributions in the DC magnetron sputtering of AZO from metallic and ceramic targets
Wilde, C.; Cornelius, S.; Vinnichenko, M.;
technique to fabricate transparent conductive oxides. Especially in large-scale solar cell production a combination of good electrical and optical properties along with low production costs is of crucial importance. AZO can be sputter-deposited reactively (i.e. with addition of O2) using a metallic target or non-reactively using a ceramic target. On the one hand, non reactive processes are easy to control and they provide high-quality films with high reproducibility, but on the other hand, ceramic Al-doped ZnO targets are much more expensive compared to the metallic ones. Therefore, the understanding of differences between these two techniques is of vital importance for the improvement of process control, stability and, finally, properties of reactively sputtered AZO, especially in large-scale fabrication. In this contribution we report results of systematic comparison of ion mass and energy distributions in magnetron plasma using reactive and non reactive DC process of AZO film growth. The measurements were performed with the orifice of mass-spectrometer facing the magnetron target race track. We present the results of comparison in a broad range of particles’ energy for different deposition conditions with a main focus on high energetic ions and fragments. It is shown that in case of sputtering of ceramic target the ratio of high to low energetic ions is substantially higher than that of metallic target. The contribution from high energetic particle fragments is also more pronounced in that case. Therefore, from point of ion energy distributions, a well established reactive process has a potential to provide better properties for AZO layer.
Keywords: AZO TCO mass spectrometry ion energy distribution DC magnetron sputtering
  • Poster
    13th International Conference on Plasma Surface Engineering (PSE 2012), 09.-14.09.2012, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 17813 - Permalink


Resonance production in p+p, p+A and A+A collisions measured with HADES
Lorenz, M.; Agakishiev, G.; Behnke, C.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; 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.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lalik, R.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; 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.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.;
The knowledge of baryonic resonance properties and production cross sections plays an important role for the extraction and understanding of medium modications of mesons in hot and/or dense nuclear matter. We present and discuss systematics on dielectron and strangeness production obtained with HADES on p+p, p+A and A+A collisions in the few GeV energy regime with respect to these resonances.

Publ.-Id: 17812 - Permalink


Dipole strength on the tail of the giant dipole resonance
Schwengner, R.;
http://www.hzdr.de/FWK/MITARB/rs/Tours2012-Schwengner.pdf
Keywords: Photon scattering, bremsstrahlung, monoenergetic polarized gamma rays, photoabsorption, dipole strength, reaction rates, statistical models, RPA, QPM.
  • Invited lecture (Conferences)
    VIII. Tours Symposium on Nuclear Physics and Astrophysics, 02.-07.09.2012, Black Forest, Deutschland

Publ.-Id: 17811 - Permalink


Morphology induced two-magnon scattering in thin NiFe films
Körner, M.; Lenz, K.; Fritzsche, M.; Facsko, S.; Fassbender, J.ORC
When studying magnetization dynamics of thin magnetic films, intrinsic as well as extrinsic spin relaxation processes have to be taken into account. While intrinsic processes, summarized as Gilbert damping, are well known and studied for the last decades, the focus now has shifted to extrinsic contributions. In this context the two-magnon scattering (TMS) is of particular interest. This type of scattering is induced within thin magnetic films by defects and inhomogeneities. It was shown that periodic magnetic patterns can serve as defect structure, e.g. by periodically varying the magnetization saturation using ion beam irradiation combined with periodic sample patterning by electron beam lithography. Due to irradiation of the material a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the periodicity of the modification. However, directly patterning the material is time consuming and not suitable for large scale manufacturing. Hence a self-organized nanoscale patterning is more favorable. Broad ion beam erosion is a well-established technique for structuring large surface areas. By varying the irradiation parameters, e.g. ion energy, fluence, and incident angle sinusoidally modulated surfaces (ripples) can be created with a periodicity tuneable over a wide range [2]. Growing magnetic materials on these ripples imprints the corrugation to the material and induces by dipolar effects a wavelength dependent uniaxial magnetic anisotropy (UMA). Furthermore the imprinted corrugation can serve as a spin wave scattering center, modifying the two-magnon damping contribution. Here we present the influence of the substrate surface corrugation on the magnetic damping properties of 30 nm thin Ni80Fe20 (Py) films grown by molecular beam epitaxy at room temperature on rippled Si substrates. Due to ion beam erosion of flat Si as well as natural oxidation of the substrate prior to film deposition, Py films grown on top exhibit a polycrystalline structure that suppresses the intrinsic magneto-crystalline anisotropy almost completely. The in-plane magnetostatic and dynamic properties of these samples were investigated by means of angular and frequency dependent vector network analyzer ferromagnetic resonance (VNA-FMR).
Starting with a planar reference sample the angular together with the frequency dependent linewidth measurements reveal a Gilbert dominated relaxation process, whereby no TMS can be observed. Due to the polycrystalline film structure, only a very weak magnetic anisotropy is observed. This uniaxial magnetic anisotropy (UMA) has a two-fold symmetry and is randomly aligned with respect to the sample edges. Changing to rippled substrates the grown Py film maintains its polycrystalline structure. Depending on the ripple wavelength λ, ranging from 25 nm to 230 nm, an UMA is induced with its easy axis always aligned parallel to the ripple ridges. The strength of the UMA decays with increasing wavelength and is strongest for λ=25 nm. In this case no influence of the corrugation on the damping is observed. This changes drastically for samples with a higher wavelength of λ=230 nm. While the UMA is reduced to the value of the planar reference sample the linewidth measurements now show clear indications for defect induced TMS. This is shown in Fig. 1a, where the peak-to-peak linewidth is plotted as a function of the in-plane magnetic field angle (open circles). Modeling the linewidth results in a Gilbert contribution that is constant for all in-plane field orientations. Additionally an angle dependent TMS contribution is found, which consists of a small four-fold and a dominating two-fold (uniaxial) part. Thereby the direction of minimal linewidth aligns parallel with the ripple ridges, which in turn defines the uniaxial symmetry of the damping. Fig. 1b depicts the frequency dependent measurements parallel (red squares) and perpendicular (green circles) to the ripple ridges. In parallel configuration the damping is purely Gilbert-like, as already observed in the reference measurement. The monotonous increase of the linewidth with applied microwave frequency is instead lost in case of the perpendicular geometry. Here, a preeminent peak is observed with its center at f=10 GHz. Following the description of Barsukov et al. [1] this excessive linewidth increase is a result of defect induced TMS, where the width and frequency position of the peak is determined by the scattering potential, created by the corrugation of the film. The origin and wavelength dependence of these morphology induced linewidth manipulation will be discussed in detail.
We thank I. Barsukov, J. Lindner, and P. Landeros for fruitful discussions. This work is supported
by DFG grant no. FA 314/6-1.
1) I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)
2) J. Fassbender et al., New J. Phys. 11, 125002 (2009)
  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012, 24.-28.09.2012, Shanghai, China

Publ.-Id: 17810 - Permalink


Frequency dependence of spin relaxation in periodic systems
Körner, M.; Barsukov, I.; Römer, F. M.; Lenz, K.; Meckenstock, R.; Hemken To Krax, S.; Banholzer, A.; Grebing, J.; Lindner, J.; Farle, M.; Fassbender, J.ORC
In the presence of a periodic scattering potential the spin relaxation in ultrathin ferromagnets is not a monotonous function of the frequency. The spin relaxation rate is found to substantially increase at characteristic frequencies related to the periodicity of the magnon scattering potential (see Fig. 1). This is experimentally confirmed in Ni80Fe20 thin films by artificially introducing different scattering periodicities [1]. The lateral struvturing of the thin film is achieved by Cr+ ion implantation with at an energy of 5 keV and a fluence of 5 × 10E15 ions/cm2 through a 100 nm thick polymethyl methacrylate (PMMA) resist covering the whole sample area. Electron beam lithography was used to fabricate 1 mm long-stripes of width s0 and spacing s1 (i.e., with periodicity l = s0 + s1) within the PMMA resist so that the surface becomes Cr-implanted in a stripewise manner. Frequency dependent Ferromagnetic resonance spectroscopy reveals that the magnetic damping may be increased at specific frequencies by a factor of up to 100%.
This work is supported by the DFG, SFB 491, Grants No. FA 314/6-1 and No. FA 314/3-2.
[1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)
  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012, 24.-28.09.2012, Shanghai, China

Publ.-Id: 17809 - Permalink


Magnonic Crystals By Means Of Patterned Ion Implantation
Fassbender, J.ORC; Körner, M.; Lenz, K.; Strache, T.; Banholzer, A.; Grebin, J.; Lindner, J.; Barsukov, I.; Römer, F.; Meckenstock, R.; Hemken To Krax, S.; Farle, M.; McCord, J.; Mönch, I.; Mattheis, R.
Ion implantation is a standard process in semiconductor tech¬nology. However, since a doping of metals typically does not have such a tremendous effect as compared to semiconductors ion implantation in metals to achieve a desired electrical, optical or magnetic property is much less explored. A combination of litho-graphy and ion implantation to achieve a lateral ion implantation pattern is a novel route to design and construct artificial materials like photonic or magnonic crystal which rely on the local band gap or spin wave dispersion engineering [1].
The contribution will provide an overview over the different physical mechanisms which allow modifying and tailoring the dynamical magnetic properties, i. e., magnetic damping even in an anisotropic fashion, aiming at the creation of new functional materials. In one example [2] it is demonstrated that the mag¬netic damping parameter in a ferromagnetic/antiferromag¬ne¬tic/ferro¬magnetic trilayer stack can be continuously and spatially varied between two extremal values (see Fig. 1). In a second example [3] the creation of a lateral magnetization pattern by ion implantation gives rise to additional and anisotropic relaxation channels. Potential areas of application are magnonic crystals and band-stop filters in the GHz range.

Acknowledgement: This work was supported by Deutsche Forschungsgemeinschaft SFB491, FA 314/3, FA314/6-1 and MC 9/7.

[1] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[2] J. McCord, T. Strache, I. Mönch, R. Mattheis, J. Fassbender, Phys. Rev. B 83, 224407 (2011).
[3] I. Barsukov, F. M. Römer, R. Meckenstock, K. Lenz, J. Lindner, S. Hemken to Krax, A. Banholzer, M. Körner, J. Grebing, J. Fassbender, M. Farle, Phys. Rev. B 84, 140410(R) (2011).
Keywords: ion irradiation, ion implantation, magnetic films, modification, magnonics, dynamics
  • Lecture (Conference)
    18th International Conference on Ion Beam Modification of Materials (IBMM2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17808 - Permalink


Tailoring perpendicular anisotropy in Co/Pd multilayers by ion irradiation
Osten, J.; Greene, P.; Ende, T.; Iwata, N.; Lenz, K.; Liu, K.; Fassbender, J.ORC
A major obstacle towards the increase in areal magnetic recording density and the decrease in bit size is the retention of thermal stability while maintaining reasonable write fields. Materials with graded magnetic anisotropy are promising candidates to solve this problem. Here we demonstrate the approach of using post-deposition ion irradiation to tailor the perpendicular anisotropy in Co/Pd multilayer thin films. The films, with uniform as well as graded perpendicular anisotropy, were synthesized by magnetron sputtering. Based on TRIDYN simulations, different primary ion energies are chosen to achieve varying penetration depths of the ions creating a depth dependent anisotropy grading. Before and after ion irradiation, MOKE as well as magnetometry measurements were employed to detect the changes of the magnetic properties. In the irradiated layer of the film domain nucleation is promoted (Fig. 1). Upon ion irradiation, the Co/Pd films exhibit reduced coercivity and remanence with increasing energies. Higher ion energies have a more pronounced effect on reducing the perpendicular anisotropy. The archived anisotropy grading also depends on the original film stack.
Keywords: ion irradiation, magnetism, magnetic recording, thermal stability, graded media
  • Poster
    18th International Conference on Ion Beam Modification of Materials (IBMM 2012), 02.-07.09.2012, Qingdao, China

Publ.-Id: 17807 - Permalink


Self-consistent isotopic comparative method used to determine dependence of secondary-yields on oxygen concentration in Si-O system up to 33%
Dupuy, J. C.; Prudon, G.; Dubois, C.; Kögler, R.; Akhmadaliev, S.; Perrat-Mabilon, A.;
Yields of B+,O+,Si+, B-, O-, and Si- versus oxygen concentration were determined in Si under Ar+ bombardment using the isotopic comparative method (ICM). Samples containing a near-uniform low concentration of 18O and a Gaussian-like profile of 16O with high concentration were fabricated by multi-energy ion implantation. ICM allows to determine the oxygen concentration profile by secondary-ion mass spectrometry. The ion yield can be measured as a function of the oxygen concentration up to 33 at%. Whatever the charge of the secondary ions, all relative ion yields are enhanced with increasing oxygen concentration. Very strong matrix effects due to oxygen are found for B+ (>100), whereas moderate or slight matrix effects are found for Si+ and O- (>10) and for Si-, B-, and O+ (<4). Relative ion yields of B+ and Si+ differ versus oxygen, whereas they are identical for B- and Si-. The relative ionization probability versus oxygen for Si+ agrees very well with the results of William´s group.
Keywords: SIMS, matrix effect, ion yield, silicon-oxygen system, ICM

Publ.-Id: 17806 - Permalink


Zeitaufgelöste (4D) Rekonstruktion von in-beam PET Daten für das Dosismonitoring bei der Bestrahlung bewegter Zielvolumina in der Ionentherapie
Laube, K.; Bert, C.; Fiedler, F.; Helmbrecht, S.; Priegnitz, M.; Saito, N.; Enghardt, W.;
no abstract available
Keywords: in-beam PET, moving targets, ion beam therapy
  • Lecture (Conference)
    43. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik e. V. (DGMP), 26.-29.09.2012, Jena, Deutschland

Publ.-Id: 17805 - Permalink


Time resolved (4D) reconstruction of in-beam PET data for the dose monitoring of intra-fractionally moving target volumes in ion beam therapy
Laube, K.; Bert, C.; Fiedler, F.; Helmbrecht, S.; Parodi, K.; Priegnitz, M.; Saito, N.; Enghardt, W.;
In-beam positron emission tomography (PET) with a double-head PET scanner has been successfully applied for the in situ dose monitoring of about 440 patients with static tumour entities within a pilot project at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. For future treatment of intra-fractionally moving tumours, mainly located in the lung or liver, a dose monitoring is highly desired since complex beam delivery strategies and continuous respiration-related density changes in the irradiated tissue increase the risk for dose errors. Conventional three-dimensional (3D) in-beam PET measurements taken from moving structures would result in a reproduction of a blurred activity distribution and would, therefore, impede correct dose verification. An implemented motion compensated (4D) reconstruction routine based on the existing 3D Maximum Likelihood Expectation Maximization (MLEM) algorithm has been tested by phantom experiments performed at the GSI facility. Homogeneous polymethyl methacrylate (PMMA) phantoms of dedicated geometries have been irradiated with 12C pencil beams and in-beam PET data acquisition was performed throughout irradiation and additional time beyond to gain better statistics. Motion mitigation techniques of rescanning, gating or tracking have been used for a homogeneous dose deposition in the PMMA targets which performed a one-dimensional cos2- or cos4-shaped motion perpendicular to the beam direction. 4D reconstruction results have been compared to static reference measurements and to reconstruction results without consideration of the
target motion. Evaluation outcome with respect to the conservation of lateral and distal gradients in the reconstructed activity distributions will be shown at the workshop. Furthermore, the acquisition of required input parameters from the accelerator, the motion acquisition and the motion compensation systems and the data handling before reconstruction, like the temporal synchronization of all signals, as well as the necessary improvements for clinical usage of the 4D in-beam PET dose monitoring will be discussed.
Keywords: in-beam PET, moving targets, ion beam therapy, reconstruction
  • Lecture (Conference)
    Tomography, data processing and image reconstruction for medicine and engineering, 10.-12.09.2012, Dresden, Deutschland

Publ.-Id: 17804 - Permalink


Generalizations of Matérn's hard-core point processes
Teichmann, J.; Ballani, F.; van den Boogaart, K. G.;
Matérn’s hard-core processes are valuable point process models in spatial statistics. In order to extend their field of application, Matérn’s original models are generalized here, both as point processes and particle processes. The thinning rule uses a distancedependent probability function, which controls deletion of points close together. For this general setting, explicit formulas for first- and second-order characteristics can be given. Two examples from materials science illustrate the application of the models.
Keywords: Point process, marked Poisson process, Matérn hard-core process, dependent thinning, independent thinning, pair correlation function

Publ.-Id: 17803 - Permalink


Entwicklung und Synthese von [18F]Flubatine für die Visualisierung von α4β2 nikotinischen Acetylcholinrezeptoren (nAChRs)
Smits, R.; Hoepping, A.; Fischer, S.; Hiller, A.; Funke, U.; Deuther-Conrad, W.; Steinbach, J.; Sabri, O.; Brust, P.;
Ziel: Bei Patienten mit Alzheimer-Demenz (AD) ist die Verfügbarkeit nikotinischer Acetylcholinrezeptoren (nAChR), insbesondere des α4β2 Subtyps im Gehirn reduziert [1]. Die Visualisierung dieser Rezeptoren könnte zu einer frühzeitigen Diagnose der AD beitragen. Die zur Zeit zur Verfügung stehenden Radioliganden haben entweder eine unzureichende Affinität zum Rezeptor oder weisen eine sehr langsame Bindungskinetik auf. Der neue Ligand [18F]Flubatine bietet wesentliche Vorteile. Beide Enantiomere besitzen eine hohe in vitro Affinität [2] und zeigen eine schnelle cerebrale Bindungskinetik in der Maus [3] und im Schwein [4]. Erste humane PET-Studien bestätigen eine hohe Aufnahme im Thalamus, eine geringe unspezifische Bindung und das Erreichen des Bindungsgleichgewichtes in weniger als zwei Stunden. Für die Durchführung von klinischen Studien und für eine potentielle routinemäßige Anwendung war es notwendig, die bestehende Präkursorsynthese zu optimieren. Ein neuer enantiomerenreiner Präkursor soll eine einfache, robuste und effiziente Radiosynthese erlauben, mit dem Ziel der Automatisierung der Tracerproduktion. Zu diesem Zweck wurden eine kleine Bibliothek von Präkursoren mit verschiedenen Schutzgruppen und Abgangsgruppen synthetisiert und getestet.

Methodik: Als Startmaterial für die Synthese der neuen Präkursoren diente das Cbz-geschützte 8-Aza-bicyclo[3.2.1]oct-6-en-3-on, das nach literaturbekannten Verfahren dargestellt wurde. Nach einer reduktiven Heck-Reaktion zur Einführung des Pyridylrestes konnte die C3-Ketofunktion in einer dreistufigen Sequenz deoxygeniert werden. Die Abspaltung der Cbz-Schutzgruppe lieferte den [18F]Flubatine-Standard, dessen Racematspaltung mittels chiraler HPLC gelang. Im Anschluss wurden verschiedene Schutzgruppen und Fluchtgruppen eingeführt, deren [18F]-Markierung untersucht und optimiert wurde. Die Radiomarkierung der verschiedenen Präkursoren erfolgte über ein zweistufiges Verfahren bestehend aus trägerfreier, nucleophiler Radiofluorierung und Abspaltung der Schutzgruppe.

Ergebnisse: Die besten Resultate wurden mit dem Boc-geschützten Trimethylammonium-Präkursor erzielt. Die Ausbeute der unter Phasentransfer-Bedingungen durchgeführten Radiomarkierung betrug 90±5%. Nach Abspaltung der Schutzgruppe mit 1N HCl und Aufreinigung mittels semipräparativer HPLC konnte enantiomerenreines [18F]Flubatine in einer radiochemischen Ausbeute von 70±5% und einer spezifischen Aktivität >750 GBq/µmol erhalten werden.

Schlussfolgerungen: Die Radiosynthese von [18F]Flubatine konnte durch den Einsatz des neuen, enantiomerenreinen Präkursors entscheidend verbessert werden und ermöglicht eine automatisierte Produktion zur klinischen Evaluierung des Radioliganden.
  • Lecture (Conference)
    20. Jahrestagung der AG Radiochemie/Radiopharmazie der DGN, 04.-06.10.2012, Bad Honnef, Deutschland

Publ.-Id: 17802 - Permalink


Severe accident research in the core degradation area: An example of effective international cooperation between the European Union (EU) and the Commonwealth of Independent States (CIS) by the International Science and Technology Center
Bottomleya, D.; Stuckert, J.; Hofmann, P.; Tocheny, L.; Hugon, M.; Journeau, C.; Clément, B.; Weber, S.; Guentay, S.; Hozer, Z.; Herranz, L.; Schumm, A.; Oriolo, F.; Altstadt, E.; Krause, M.; Fischer, M.; Khabensky, V. B.; Bechta, S. V.; Veshchunov, M. S.; Palagin, A. V.; Kiselev, A. E.; Nalivaev, V. I.; Goryachev, A. V.; Zhdanov, V.; Baklanov, V.;
The International Science and Technology Center (ISTC) was set up in Moscow to support nonproliferation of sensitive knowledge and technologies in biological, chemical and nuclear domains by engaging scientists in peaceful research programmes with a broad international cooperation. The paper has two following objectives:
1) to describe the organization of complex, international, experimental and analytical research of material processes under extreme conditions similar to those of severe accidents in nuclear reactors and,
2) to inform briefly about some results of these studies.
The main forms of ISTC activity are Research Projects and Supporting Programs. In the Research Projects informal contact expert groups (CEGs) were set up by ISTC to improve coordination between adjacent projects and to encourage international collaboration. The European Commission was the first to use this. The CEG members – experts from the national institutes and industry – evaluated and managed the projects’ scientific results from initial stage of proposal formulation until the final reporting. They were often involved directly in the project’s details by joining the Steering Committees of the project. The Contact Expert Group for Severe Accidents and Management (CEG-SAM) is one of these groups, five project groups from this area from the total of 30 funded projects during 10 years of activity are detailed to demonstrate this: (1) QUENCH-VVER from RIAR, Dimitrovgrad and IBRAE, Moscow, and PARAMETER projects (SF1–SF4) from LUCH, Podolsk and IBRAE, Moscow; these concerned a detailed study of bundle quenching from high temperature; (2) Reactor Core Degradation; a modelling project simulating the fuel
rod degradation and loss of geometry from IBRAE, Moscow; (3) METCOR projects from NITI, St. Petersburg on the interaction of core melt with reactor vessel steel; (4) INVECOR project, NNE Kurchatov City, Kazakhstan; this is a large-scale facility to examine the vessel steel retention of 60 kg corium during the decay heat; and finally, (5) CORPHAD and PRECOS projects, NITI, St. Petersburg undertook a systematic examination of refractory ceramics relevant to in-vessel and ex-vessel coria, particularly examining poorly characterised, limited data or experimentally difficult systems.
Keywords: Severe accident management, core melt down, nuclear reactors, in-vessel melt retention

Publ.-Id: 17801 - Permalink


Impact of 5-lipoxygenase inhibitors on the spatiotemporal distribution of inflammatory cells and neuronal COX-2 expression following experimental traumatic brain injury in rats
Härtig, W.; Michalski, D.; Seeger, G.; Voigt, C.; Donat, C. K.; Dulin, J.; Kacza, J.; Meixensberger, J.; Arendt, T.; Schuhmann, M. U.;
Inflammation induced by traumatic brain injury (TBI) is considered as contributor to neuronal death with poor outcome. Although anti-inflammatory strategies were beneficial in experimental TBI, clinical translations mostly failed, probably caused by the complexity of involved cells and mediators. We recently showed in a rat model of controlled cortical impact (CCI) that leukotriene inhibitors (LIs) attenuate contusion growth and improve neuronal survival. This study focuses on spatiotemporal characteristics of macrophages and granulocytes, typically involved in inflammatory processes, and neuronal COX-2 expression. Further, effects of LIs (Boscari/MK-886) were evaluated by quantifying CD68+, CD43+ and COX-2+ cells 24 and 72 h post-CCI in the parietal cortex (PC), CA3 region (CA3r), dentate gyrus (DG) and visual/auditory cortex (v/aC). Correlations were applied to identify inter-cellular relationships. At 24 h, untreated animals showed granulocytes in all regions investigated, decreasing towards 72 h. In contrast, macrophages increased from 24 to 72 h post-CCI in the PC and v/aC. COX-2+ neurones showed no temporal dynamics, except of an increase in the CA3r towards 72 h. Treatment reduced granulocytes at 24 h in the pericontusional penumbra and hippocampus, and reduced macrophages at 72 h in the PC and v/aC. COX-2 expression remained unaffected by LIs, except of time-specific reactions in the DG (increase/decrease at 24/72 h). Interrelations confirmed concomitant cellular reactions beyond initial trauma site. In conclusion, LIs attenuated the cellular inflammatory response following CCI and therefore become attractive as potential treatment strategy. Future studies should clarify region-specific effects and feasible time windows for applying LIs after CCI.
Keywords: Traumatic brain injury, Neuronal death, Macrophage, Granulocyte, COX-2

Publ.-Id: 17800 - Permalink


Reconstruction of Gebel Kamil’s irradiation history
Merchel, S.; Akhmadaliev, S.; Fimiani, L.; Haubold, R.; Herrmann, S.; Korschinek, G.; Ott, U.; Pavetich, S.; Rugel, G.;
Data of the lighter cosmogenic radionuclides 10Be, 26Al, 36Cl, and 41Ca are now easily attainable at the accelerator mass spectrometry facility DREAMS [1]. Accompanied by the heavier radionuclides 53Mn and 60Fe, which are measured at the 14 MV tandem at Munich, and stable noble gas nuclides from MPI Mainz, complete and unique exposure histories of extraterrestrial material can be reconstructed.
One of the first meteorites investigated by this team is Gebel Kamil, an ungrouped Ni-rich ataxite that produced an impact crater (Ø: 45 m) in southern Egypt. Two neighboured shrapnel (S) samples and two from the only individual (I) fragment (~83 kg) have been analysed. Comparison with Monte-Carlo calculations of production rates indicate that Gebel Kamil was exposed as a meteoroid body of >120 cm radius. Samples I originate from a moderate shielding of 18-25 cm, whereas samples S are from a deeper position of 53-65 cm. Most reliable 36Cl-36Ar ages of I and S are ~450 Ma calculated after [3].
Ackn.: L. Folco (meteorite) & accelerator crews (support AMS). Ref.: [1] Akhmadaliev et al. (2012) NIMB, in print. [2] Folco et al., Science 329 (2010) 804. [3] Ammon et al., MAPS 44 (2009) 485.
Keywords: cosmogenic, AMS, meteorite
  • Lecture (Conference)
    Joint meeting “Paneth Kolloquium”, “The first 10 million years of the solar system” (DFG SPP 1385) & “MEMIN” (DFG FOR 887), 09.-12.10.2012, Nördlingen, Duetschland

Publ.-Id: 17799 - Permalink


Growth mode and texture development in Ni-Ti shape memory alloy (SMA) films during co-sputtering deposition – An in situ synchrotron radiation study
Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.;
In-situ X-ray scattering measurements were carried out during Ni-Ti shape memory alloy film processing at the Rossendorf Beamline (BM20-ESRF). The experiments performed with a two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the beamline enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth. The results show that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. Amorphous SiO2 and TiN buffer layers were used to successfully control their crystallographic orientations. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented. The control of texture is an important achievement since it has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition of graded Ni-Ti films by deliberately changing the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, provided significant data for the optimisation of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). This is a plus for the miniaturization of Ni–Ti films based devices in the field of micro-electro-mechanical systems since no consideration has to be paid to a resetting spring.
  • Poster
    MPA 2012 – 6th International Meeting on Developments in Materials, Processes and Applications of Emerging Technologies, 02.-04.07.2012, Alvor, Portugal

Publ.-Id: 17798 - Permalink


Terahertz nonlinear optics of excitons in quantum wells using a free-electron laser
Helm, M.; Keywords: terahertz, quantum well, free electron laser, exciton
  • Invited lecture (Conferences)
    Viennese Symposium on Heterostructures, 07.09.2012, Wien, Österreich

Publ.-Id: 17797 - Permalink


Modification of Ni-Ti surface composition and morphology by plasma immersion ion implantation for biomedical applications
Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Schell, N.; Carmezim, M. J.; Silva, T. M.; Fernandes, J. C. S.;
The shape memory effect and superelasticity of Ni-Ti (Nitinol) make it very attractive for biomedical applications. The Ni-Ti alloy (~ 50.4 at.% Ni) selected for this work is austenitic (superelastic) at body temperature. In the frame of the AIM-74 and SPIRIT-77 projects, plasma immersion ion implantation (PIII) has been employed to modify and improve the superficial region of the alloy. The formation of titanium oxynitride (TiNxOy) was achieved by ion implantation of nitrogen. A Ti-rich oxide layer was obtained during the experiments carried out with oxygen. Thus, the parameters to obtain a Ni-depleted surface, which serves as a barrier to out-diffusion of Ni ions from the bulk material, have been successfully established. Furthermore, nanostructured Ni-Ti surfaces have been produced. Synchrotron radiation-based X-ray diffraction data acquired in transmission mode show that the PIII technique only changes the structure of the Ni-Ti alloy top layer preserving superelastic behaviour at body temperature (PIII experiments carried out without intentional heating of the substrate holder). Techniques like thermal oxidation and nitriding also lead to an improved corrosion resistance and Ni-depleted Ni-Ti surface but require high processing temperatures leading to modification of the phase transformation characteristics and loss of specific mechanical properties.
  • Lecture (Conference)
    MPA 2012 - 6th International Meeting on Developments in Materials, Processes and Applications of Emering Technologies, 02.-04.07.2012, Alvor, Portugal

Publ.-Id: 17796 - Permalink


Supernova Dust in Terrestrial Deep-Sea Archives
Feige, J.; Wallner, A.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Winkler, S. R.;
The long-lived radionuclides 26Al, 53Mn and 60Fe are produced in the late burning phases and during a supernova explosion of a massive star. These nuclides are then ejected into space, condensed into dust and, if the supernova occurs in a close distance to the solar system, might be able to reach the Earth. An indication for a close-by supernova in the past, deduced from a signal about 2 Myr ago, has already been identified in a ferromanganese crust [1]. Deep-sea sediments, with higher accumulation rates, provide a higher time resolution and allows therefore a more precise dating of the signal.
Here, samples of two sediment cores originating from the Indian Ocean are analyzed to search for supernova signals. Currently, the only method sensitive enough to detect these signals is accelerator mass spectrometry. Additionally to the supernova-produced nuclides, 10Be, which is constantly produced by cosmic rays in the Earth's atmosphere, is measured to date the sediment cores. First 10Be and 26Al data are presented and discussed.
[1] Knie, K., et al. (2004), Phys. Rev. Lett. 93, 17.
Keywords: supernovae, AMS, radionuclide
  • Poster
    Joint meeting “Paneth Kolloquium”, “The first 10 million years of the solar system” (DFG SPP 1385) & “MEMIN” (DFG FOR 887), 09.-12.10.2012, Nördlingen, Deutschland

Publ.-Id: 17795 - Permalink


Radiosynthesis of racemic and enantiomerically pure (–)-[18F]flubatine – A promising PET radiotracer for neuroimaging of α4β2 nicotinic acetylcholine receptors
Fischer, S.; Hiller, A.; Smits, R.; Hoepping, A.; Funke, U.; Wenzel, B.; Cumming, P.; Sabri, O.; Steinbach, J.; Brust, P.;
(–)-[18F]flubatine is a promising agent for visualization by PET of cerebral α4β2 nicotinic acetylcholine receptors (nAChRs), which are implicated in psychiatric and neurodegenerative disorders. Here, we describe a substantially improved two-step radiosynthesis strategy for (–)-[18F]flubatine, based on the nucleophilic radiofluorination of an enantiomerically pure precursor followed by deprotection of the intermediate. An extensive leaving group/protecting group library of precursors was tested. Application of a trimethylammonium-iodide precursor with a Boc protecting group provided the best results: Labeling efficiencies of 80-95%, RCY of 60±5%, radiochemical purity of >98%, and a specific activity of >350 GBq/µmol. The radiosynthesis is easily transferable to an automated synthesis module.
Keywords: Fluorine-18, Positron emission tomography, Neuroimaging, α4β2 nicotinic acetylcholine receptors, α4β2 ligands, Radiosynthesis, Leaving groups, Protecting groups

Publ.-Id: 17794 - Permalink


PET/MR for therapy response evaluation in malignant lymphoma: initial experience
Platzek, I.; Beuthien-Baumann, B.; Langner, J.; Popp, M.; Schramm, G.; Ordemann, R.; Laniado, M.; Kotzerke, J.; van den Hoff, J.;
Object: To evaluate the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with 18fluoro-2-deoxyglucose (FDG) for therapy response evaluation of malignant lymphoma.
Materials and methods: Nine patients with malignant lymphoma who underwent FDG-PET/MR before and after chemotherapy were included in this retrospective study. Average time between the two scans was 70 days. The scans were evaluated independently by two nuclear medicine physicians. The Ann Arbor classification was used to describe lymphoma stage. Furthermore, the readers also rated PET image quality using a five point scale. Weighted kappa was used to calculate interrater agreement.
Results: The initial scan showed foci of increased FDG uptake in all patients, with Ann Arbor stage varying between I and IV. In the follow-up examination, all but one patient showed complete response to chemotherapy. PET image quality was rated as very good or excellent for all scans. Interrater agreement was excellent regarding Ann Arbor stage (kappa = 0.97) and good regarding image quality (kappa = 0.41). Conclusion PET/MR shows promising initial results for therapy response evaluation in lymphoma patients.
Keywords: PET; MRI; Lymphoma

Publ.-Id: 17793 - Permalink


PET/MR in head and neck cancer: initial experience
Platzek, I.; Beuthien-Baumann, B.; Schneider, M.; Gudziol, V.; Langner, J.; Schramm, G.; Laniado, M.; Kotzerke, J.; van den Hoff, J.;
Purpose: To evaluate the feasibility of PET/MRI (positron emission tomography/magnetic resonance imaging) with FDG (18F-fluorodeoxyglucose) for initial staging of head and neck cancer.
Methods: The study group comprised 20 patients (16 men, 4 women) aged between 52 and 81 years (median 64 years) with histologically proven squamous cell carcinoma of the head and neck region. The patients underwent a PET scan on a conventional scanner and a subsequent PET/MRI examination on a whole-body hybrid system. FDG was administered intravenously prior to the conventional PET scan (267–395 MBq FDG, 348 MBq on average). The maximum standardized uptake values (SUVmax) of the tumour and of both cerebellar hemispheres were determined for both PET datasets. The numbers of lymph nodes with increased FDG uptake were compared between the two PET datasets.
Results: No MRI-induced artefacts where observed in the PET images. The tumour was detected by PET/MRI in 17 of the 20 patients, by PET in 16 and by MRI in 14. The PET/MRI examination yielded significantly higher SUVmax than the conventional PET scanner for both the tumour (p<0.0001) and the cerebellum (p00.0009). The number of lymph nodes with increased FDG uptake detected using the PET dataset from the PET/MRI system was significantly higher the number detected by the stand-alone PET system (64 vs. 39, p00.001).
Conclusion: The current study demonstrated that PET/MRI of the whole head and neck region is feasible with a wholebody PET/MRI system without impairment of PET or MR image quality.
Keywords: PET/MRI; Head and neck cancer

Publ.-Id: 17792 - Permalink


Intraband carrier dynamics in quantum dots and quantum wells
Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Hopkinson, M.; Wilson, L. R.; Andrews, A. M.; Strasser, G.; Helm, M.; Schneider, H.;
Optical properties of self assembled quantum dots (QDs) have dominant inhomogeneous broadening due to the distribution of size and composition of the QDs in the ensemble. The carrier dynamics in such systems is affected by the neighboring dots due to interdot diffusion of carriers. In this work we investigate the intraband relaxation mechanisms in the QDs. We performed time-resolved photoluminescence (PL) quenching measurements on InAs/GaAs self assembled QDs. The samples were excited by near infrared laser pulses and the time and wavelength resolved PL was measured by a streak camera. During the decay of the PL, a THz pulse from a free electron laser, tuned to the intersublevel transition energy of the QDs, was made incident on the sample. This THz pulse induced quenching of the PL, shown by the dip in Fig.1, by re-exciting carriers to higher levels within the QDs. These carriers eventually relaxed back to the ground state (s-state) resulting in the recovery of the s-state PL intensity. Thus, the recovery of the PL was directly related to carrier relaxation dynamics in the QDs. The mechanisms involved were (i) ISL relaxation, where the excited carriers in the QDs directly fell back into the s-state of the same dot and (ii) transfer to adjacent dots via the wetting layer by multiphoton absorption or tunneling. To distinguish these two effects we performed measurements on two samples grown simultaneously but post-growth annealed at different temperatures resulting in different ISL relaxation times of 60 ps and 1.5 ns. From rate equation model fit of the measured data we found that the recovery time of the quenched PL was independent of the ISL relaxation times. This implied that the carrier relaxation within the dots was dominated by mechanisms other than ISL transition. Comparison of the amount of recovered PL signals for different emission energies showed that there was loss of carriers at higher PL energies, as showed in Fig.1(a), and gain of carriers after recovery for lower emission energies [Fig.1(b)]. This indicates carrier transfer among adjacent QDs. Therefore, even for quite low QD densities (4 x 10^10 cm-2 for our samples), interdot carrier transfer plays an important role in intraband carrier relaxation in self assembled QDs.
Keywords: Photoluminescence quenching, FEL, Intraband transition, quantum dots, quantum well
  • Lecture (Conference)
    International conference on superlattices, nanostructures and nanodevices, 22.-27.07.2012, Dresden, Germany

Publ.-Id: 17791 - Permalink


Alpha self-irradiation effect on the local structure of the U0.85Am0.15O2+x solid solution
Prieur, D.; Martin, P. M.; Lebreton, F.; Delahaye, T.; Jankowiak, A.; Laval, J.-P.; Scheinost, A. C.; Dehaudt, P.; Blanchart, P.;
Uranium–americium mixed oxides are promising fuels for achieving an efficient Am recycling. Previous studies on U0.85Am0.15O27x materials showed that the high a activity of 241Am induces pellet swelling which is a major issue for cladding materials design. In this context, X-ray Diffraction and X-ray Absorption Spectroscopy measurements were used to study self-irradiation effects on U0.85Am0.15O27x local structure and to correlate these results with those obtained at the macroscopic scale. For a cumulative a decay dose equal to 0.28 dpa, it was shown that non-defective fluorite solid solutions were achieved and therefore, that the fluorite structure is stable for the studied doses. In addition, both interatomic distance and lattice parameter expansions were observed, which only partially explains the macroscopic swelling. As expected, an increase of the structural disorder with self-irradiation was also observed.
Keywords: XAFS self-irradiation nuclear fuel nuclear waste Am

Publ.-Id: 17790 - Permalink


Moderating material to compensate the drawback of high minor actinide containing transmutation fuel on the feedback effects in SFR cores
Merk, B.;
The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effecting SFRs is described. The drawback on the feedback effects due to the introduction of minor actinides into SFR fuel is analyzed. The possibility of compensation of the effect of the minor actinides on the feedback effects by the use of fine distributed moderating material is demonstrated. The consequences of the introduction of fine distributed moderating material into fuel assemblies with fuel configurations foreseen for minor actinide transmutation is analyzed and the positive effects on the transmutation efficiency are shown. Finally, the possible increase of the Americium content to improve the transmutation efficiency is discussed, the limit value of Americium is determined and the possibilities given by an increase of the Hydrogen content are analyzed.
Keywords: enhanced feedback, transmutation, fast reactror, Americium, Curium

Publ.-Id: 17789 - Permalink


Thermal stability of moderating material used to enhance the feedback coefficients in SFR cores
Merk, B.;
Recently, the use of moderating materials in fuel assemblies for Sodium cooled fast reactors has been investigated and published in several papers (e. g. Annals of Nuclear Energy 38, 5, Annals of Nuclear Energy 38, 11 (2011)). Especially the fine distribution of the moderating material in a layer inside the fuel rod or inside the wire spacer has shown very promising results for the enhancement of the feedback coefficients. Additionally, this arrangement is very attractive since it causes only a very limited influence on the safety relevant fuel assembly structure and on the operational parameters. A detailed investigation on the use of moderating material for transmutation fuels has proven that a compensation of the negative influence on the feedback coefficients caused by the Minor Actinides is possible. The critics on the limited thermal stability of the suggested ZrH based moderating material has been a major issue in the discussion of all up to now published publications. In this work the problem will be solved with the help of t change of the hydrogen bearing metal compound. In a first step an overview on possible metal materials will be given and properties as well as manufacturing issues will be discussed. Additionally, an insight will be given into the relationship of the hydrogen content of the compound and the resulting thermal stability. Based on this relation the reasons for the choice of Yttrium are described. In a second step the transferability of the old results gained for ZrH will be proven by a detailed comparison of different important reactor physical parameters for cases using identical amounts of ZrH and YH.
Thermal stability of the moderating material up to more than 1300°C can be ensured by the use of Yttrium-mono-hydride as moderating material. The topic will be closed by a survey on the existing operation experience with YH in fast reactors and a comparison of the raw material costs for Zirconium and Yttrium.
Keywords: fast reactor, enhanced feedback effects, moderating material, Yttrium hydride, thermal stability
  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), 04.-07.03.2013, Paris, France
  • Lecture (Conference)
    International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), 04.-07.03.2013, Paris, France

Publ.-Id: 17788 - Permalink


The Molten Salt Fast Reactor as Transmutation System
Merk, B.; Rohde, U.; Scholl, S.;
The basic development and design of a molten salt reactor with fast neutron spectrum (Molten Salt Fast Reactor – MSFR) is the target of the EVOL project in FP7. The MSFR offers certain advantages in the view of transmutation compared to solid fuelled reactor types. In the first part, these advantages will be discussed in a comparison with the sodium cooled fast reactor technology and the research challenges will be analyzed. In the second part, cycle studies for the MSFR, based on the EVOL benchmark design, will be given for different configurations – core with U-238 fertile, a fertile free core and a core with Th-232 as fertile material. For all cases, the transmutation potential will be determined and a significant improvement in the transmutation performance for the case with Th as fertile will be demonstrated. The time evolution of different important isotopes will be analyzed. Additionally, the used tool HELIOS 1.10 and the adaptations needed for the simulation of a MSFR will be described.
Keywords: molten salt fast reactor, molten salt reactor, fast reactor, transmutation
  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), 04.-07.03.2013, Paris, France
  • Lecture (Conference)
    International Conference on Fast Reactors and Related Fuel Cycles: Safe Technologies and Sustainable Scenarios (FR13), 04.-07.03.2013, Paris, France

Publ.-Id: 17786 - Permalink


Progress in fast reactor operation and new trends to increased inherent safety
Merk, B.; Stanculescu, A.; Chellapandi, P.; Hill, R.;
The reasons for the renewed interest in fast reactors and an overview of the progress in sodium cooled fast reactor operation and design in the last ten years is given. The relevance of feedback effects for safe reactor design is described, and a new method for the enhancement of feedback effects in fast reactors is proposed. The excellent operational performance of sodium cooled fast reactors in this period is highlighted as a sound basis for the development of new fast reactors. Experimental reactors demonstrating the inherent safety of advanced sodium cooled fast reactor designs are described and the potential safety improvements resulting from the use of fine distributed moderating material are demonstrated. Finally, the fast reactor specifics are analysed with regard to the Fukushima accident.
Keywords: fast reactor history, fast reactor technology , enhanced feedback, inherent safety

Publ.-Id: 17785 - Permalink


Sorption of Se(VI) and Se(IV) oxyanions onto maghemite: a macroscopic and spectroscopic study
Jordan, N.; Ritter, A.; Foerstendorf, H.; Scheinost, A. C.; Heim, K.; Weiß, S.; Brendler, V.;
79Se, a long-lived (t1/2 ~ 3.27 × 105 years) and radiotoxic fission product, was identified by safety performance assessments to be one of the most contributing isotopes to the total radioactivity that could be potentially released to the biosphere. Selenium has a quite complex speciation, with four main oxidation states, depending on both the pH and the redox potential of the surrounding environment. Sorption of selenium oxyanions onto mineral surfaces (iron, alumina, titanium oxides and clays) has been extensively investigated based on batch experiments and spectroscopic studies. However, the sorption processes of selenium oxyanions onto maghemite was not explicitly studied before and thus the potential ability of maghemite to significantly retard selenium migration in the environment is therefore still unknown. Maghemite was identified as a corrosion product of steel waste canisters and iron archaeological analogues, and is also a ubiquitous mineral in the environment.
In this work, we investigated in detail the sorption of selenium(VI) and selenium(IV) onto maghemite (γ-Fe2O3), for the first time. The effect of pH and ionic strength was studied by batch experiments. Sorption of both oxyanions onto maghemite was found to decrease with increasing pH. An increase of the ionic strength (from 0.01 M to 0.1 M) impacted the sorption of selenium(VI), while it had no significant effect for selenium(IV) uptake. Electrophoretic mobility measurements revealed that the isoelectric point (pHIEP) of maghemite was shifted to lower pH values upon selenium(IV) sorption, while it was not significantly modified upon selenium(VI) sorption. By combining EXAFS and in situ ATR FT-IR spectroscopic measurements, the formation of inner-sphere complexes during selenium(IV) sorption onto maghemite was observed. Selenium(VI) sorption proceeded via the formation of predominant outer-sphere complexes (together with a small amount of inner-sphere complexes).
Keywords: selenium; sorption; EXAFS; IR; maghemite
  • Lecture (Conference)
    Selen2012 - Selenium in geological, hydrological and biological systems, 08.-09.10.2012, Karlsruhe, Germany

Publ.-Id: 17784 - Permalink


Inertial wave observations in liquid metal by means of ultrasound Doppler velocimetry
Räbiger, D.; Vogt, T.; Franke, S.; Eckert, S.; Gerbeth, G.; Czarske, J.;
This experimental study considers the transient flow inside a liquid metal column exposed to a pulsed rotating magnetic field. To measure two-dimensional velocity fields of the secondary flow in the radial-meridional plane a novel ultrasound Doppler system was used. A linear ultrasound transducer array equipped with 25 transducer elements is used to measure the flow field in a square plane of 67 x 67 mm². The application of advanced processing techniques like a simultaneous excitation of multiple transducer elements and a segmented array technique enable high data acquisition rates as well as a high spatial resolution. The measurements revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures.
Keywords: Ultrasound Doppler method, flow field measurements, electromagnetic stirring, rotating magnetic field, inertial waves, flow control
  • Lecture (Conference)
    ISUD8 - 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland
  • Contribution to proceedings
    ISUD8 - 8th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 19.-21.09.2012, Dresden, Deutschland

Publ.-Id: 17783 - Permalink


Magnetic properties of Co/Pd multilayers films deposited on GaSb nanocones
Ball, D. K.; Günther, S.; Fritzsche, M.; Lenz, K.; Varvaro, G.; Makarov, D.; Mücklich, A.; Facsko, S.; Fassbender, J.ORC; Albrecht, M.
The magnetic properties of ferromagnetic thin films fabricated on nanostructured templates is strongly affected by the surface morphology. Low energy ion irradiation of GaSb yields to a self organized hexagonal pattern that can serve as templates for subsequent deposition of magnetic films.
In this respect, curvature effects and influence of pattern symmetry result in a substantial modification of the magnetization reversal behavior of individual magnetic nanostructures and their assemblies.
Curvature-driven changes can be beneficial to reduce the switching field, which is advantageous for magnetic data storage applications, especially for the recording concept known as bit patterned media (BPM). In the BPM concept, an individual bit will be stored in a single magnetic nanostructure. Candidates for a recording layer are films with strong out-of-plane magnetic anisotropy (Ku) such as hard magnetic FePt alloys and [Co/Pd(Pt)]n multilayers.
Here, we aim at the fabrication of arrays of magnetic [Co/Pd]n multilayers on top of selfassembled nanocone templates created on GaSb(100) single crystal using a Ar+ ion erosion technique. By tailoring the irradiation conditions, the self-organized assemblies of nanocones were modified in size and periodicity. Due to the self-organization, large patterned areas can be fabricated which is challenging using e-beam lithography.
Macroscopic magnetic measurements performed using vector-VSM magnetometry (vVSM) indicate that all samples possess the magnetic easy axis perpendicular to the cone surface. The remanence as well as the coercivity decreases with increasing cone size, as the letter leads to a larger angular spread of easy axis following the morphology of the pattern. Additionally, MFM characterization shows that in the case of small cone structures the underlying cone pattern results in a pinning of magnetic domain walls on cone locations as there is a clear correlation between the morphology and positions of magnetic domain walls. For larger cone sizes, exchange decoupled magnetic caps are achieved with single domain areas confined to the cones apexes.
  • Poster
    Joint European Magnetic Symposia (JEMS 2012), 09.-14.09.2012, Parma, Italien

Publ.-Id: 17782 - Permalink


NMR Investigations of the intra- and intermolecular exchange phenomena of the 3,5-dimethylpyrazolylsilane ClSi(pz*) and related compounds
Bitto, F.; Kretzschmar, J.; Brendler, E.; Kroke, E.;
Chlorine substituted 3,5-dimethylpyrazolyl (pz*) silanes exhibit interesting inter- and intramolecular exchange phenomena. Intermolecular reactions involving Si-N vs. Si-Cl dismutation cause equilibria between the three species Cl2Si(pz*)2, ClSi(pz*)3 (main component) and Si(pz*)4. Intramolecular exchange is interpreted as a “dangling” of the pz*-moieties in every pyrazolyl silane molecule itself.[1] These phenomena were investigated with one and two dimensional NMR spectroscopic methods at variable temperatures. The “dangling” of the pz*-moieties is slowed down with decreasing temperature and are best visible in the spectra recorded at -40°C. The use of 1H-29Si-HMBC spectroscopy (heteronuclear multiple bond correlation) allows to assign the olefinic protons to the corresponding silicon species. In the EXSY (exchange spectroscopy) spectra the exchange between the pz*-methyl groups and the NOE (nuclear overhauser effect) correlation between the methyl groups and the olefinic protons are observed at the same time in one spectrum. The data obtained with EXSY and HMBC-spectroscopy in combination with variable temperature 1H NMR allows qualitative conclusions concerning the rate of exchange and the dependence on the silicon corresponding species.

[1] F. Bitto, J. Wagler, E. Kroke, Eur. J. Inorg. Chem. 2012, in press, doi:10.1002/ejic.201101409.
Keywords: NMR spectroscopy; H,Si-HMBC; H,H-NOESY, H,H-EXSY; 3,5-dimethylpyrazolyl silanes
  • Poster
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prag, Tschechische Republik

Publ.-Id: 17781 - Permalink


Dual-beam irradiation of friction stir spot welding of nanostructured ferritic oxide dispersion strengthened alloy
Chen, C.-L.; Richter, A.; Kögler, R.; Wu, L.-T.;
Friction stir spot welding (FSSW) is a very promising technique for the joining of oxide dispersion strengthened (ODS) materials without oxide particle agglomeration and loss in mechanical properties in the weld zone. Heating and severe plastic deformation can significantly alter the originally as-received material. The local microstructure determines the weld mechanical properties, which are analyzed by nanointendation. The FSSW region consists of three different zones: the base material, the thermo-mechanically affected zone and the heat affected zone. Irradiation of the FSSW area was performed with a Fe+/He+ dual ion beam. Hardness changes within the welding zones and variation with irradiation damage are discussed.
Keywords: Nanostructured material, oxide dispersion strengthened (ODS) alloys, friction stir welding, nanoindentation, irradiation damage

Publ.-Id: 17780 - Permalink


Neutronic analysis of SFR core with HELIOS-2, SERPENT, and DYN3D codes
Rachamin, R.; Wemple, C.; Fridman, E.;
In this study, HELIOS-2 deterministic transport code and Serpent Monte-Carlo (MC) reactor physics code were considered as tools for preparation of few-group constants for sodium cooled fast reactor (SFR) analysis. Initially, applicability of the mainly LWR-oriented HELIOS-2 code to the modeling of SFR lattices was investigated and recommendations for methodological modifications were given. At the next stage the methodology for few-group cross section generation for fuel and non-multiplying regions of SFR core was proposed. Afterward, few-group constants produced by HELIOS-2 and Serpent employing the proposed methodology were used by nodal diffusion code DYN3D for the analysis of a reference SFR core. Finally, the DYN3D results were verified against the full core Serpent MC solution. The full core DYN3D results obtained using few-group constants produced by Serpent agreed very well with that of the reference full core MC simulations. The use of HELIOS-2 based few-group constants led to somewhat reduced agreement between reference MC and DYN3D results. The implementation of the suggested modifications to the HELIOS-2 methodology can potentially improve its modeling accuracy for SFR lattices.
Keywords: HELIOS-2, Serpent, Monte Carlo, DYN3D, few-group cross section generation, sodium cooled fast reactor

Publ.-Id: 17779 - Permalink


AMS Measurements of Supernova-Produced Radionuclides in Deep-Sea Sediment Cores
Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, L. K.; Korschinek, G.; Rugel, G.;
Accelerator Mass Spectrometry (AMS) provides the highest sensitivity for measurements of long-lived radionuclides with half-lives in the order of million years. We will apply this method to search for live supernova (SN)-produced radionuclides on Earth.
An indication to recent SN activity in our solar neighborhood is the existence of a thin, hot cavity in the local interstellar medium, embedding our solar system. This so called superbubble, the Local Bubble, was produced by multiple SN explosions, starting ~14 Myr ago. Nuclides, which are synthesized in massive stars and during their explosions, are then entrained in the SN shell and may be transported to the solar system, if such an event happens within a short distance.
Two deep-sea sediment cores originating from the Indian Ocean have been selected to search for the SN-produced radionuclides 26Al, 53Mn, 60Fe and 244Pu in the time range of 2-3 Myr. We aim to measure these isotopes at different laboratories with high time resolution with the goal to confirm a previously found SN signal in a ferromanganese crust from the Pacific Ocean.
Keywords: supernovae, radionuclide, AMS, sediments
  • Poster
    62. Jahrestagung der Österreichischen Physikalischen Gesellschaft, 18.-21.09.2012, Graz, Österreich

Publ.-Id: 17778 - Permalink


The Search for Supernova-Produced Radionuclides in Deep-Sea Sediments with AMS
Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, K. L.; Korschinek, G.;
We will search for supernova-produced radionuclides in deep-sea sediment cores originating from the Indian Ocean. We aim to measure the long-lived radionuclides 26Al (t1/2 = 0.7 Myr), 60Fe (t1/2 = 2.6 Myr), 53Mn (t1/2 = 3.7 Myr) and 244Pu (t1/2= 80 Myr) at different laboratories in sediment samples with high time resolution.
A positive signal will also confirm a previous finding of an enhanced 60Fe content in a ferromanganese crust [1]. The above mentioned radionuclides are commonly synthesized in massive stars and ejected by supernova (SN) explosions. If such a SN event happens in the solar vicinity, the expanding SN envelope might hit the solar system and leave certain traces in terrestrial archives. An indication to recent SN activity is the existence of a cavity consisting of thin, hot gas in the local interstellar medium, embedding our solar system. This superbubble, called the Local Bubble, was presumably produced by 14-20 SN explosions starting 14 Myr ago [2].
Because SNe and their ejecta are a site for dust formation, there might be a chance of finding such radionuclides in dust particles deposited in such terrestrial archives, like deep-sea sediments. The measurements will be carried out with accelerator mass spectrometry (AMS) utilizing laboratories with the highest sensitivities for these long-lived radionuclides.
[1] K. Knie, et al., Physical Review Letters 93, 17 (2004).
[2] B. Fuchs et al., Monthly Notices of the Royal Astronomical Society 373, 993-1003 (2006).
Keywords: supernovae, AMS, radionuclide, sediments
  • Poster
    496. Wilhelm und Else Heraeus-Seminar - Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland

Publ.-Id: 17777 - Permalink


Supernova-Dust in Deep-Sea Sediment Cores
Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, L. K.; Korschinek, G.; Rugel, G.;
Because supernovae (SNe) and their ejecta are a site for dust formation, there might be a chance of finding supernova-produced radionuclides in dust particles deposited in terrestrial archives, like deepsea sediments. Measurements will be carried out with Accelerator Mass Spectrometry (AMS), which provides the highest sensitivity for measurements of long-lived radionuclides with half-lifes in the order of million years.
An indication to recent SN activity in our solar neighborhood is the existence of a thin, hot cavity in the local insterstellar medium, embedding our solar system. This so called superbubble, the Local Bubble, was produced by multiple SN explosions, starting ~14 Myr ago (Fuchs et al. 2006). Nuclides, which are synthesized in massive stars and during their explosions, are then entrained in the SN shell, condensed into dust, and may be transported to the solar system and thus into Earth archives, if such an event happens within a short distance.
Two deep-sea sediment cores originating from the Indian Ocean have been selected to search for the SN-produced radionuclides 26Al, 53Mn, 60Fe and 244Pu in the time range of 2-3 Myr. We aim to measure these isotopes at different laboratories with high time resolution with the goal to confirm a previously found SN signal in a ferromanganese crust from the Pacific Ocean (Knie et al. 2004),
Keywords: supernovae, AMS, radionuclide, sediments
  • Poster
    International conference of the European Science Foundation EuroGENESIS CoDustMas network action, 05.-08.11.2012, Ascona, Schweiz

Publ.-Id: 17776 - Permalink


AMS within CoDustMas: Nanodiamonds and SN-signatures
Wallner, A.; Vockenhuber, C.; Güttler, D.; Feige, J.; Fifield, L. K.; Korschinek, G.; Melber, K.; Merchel, S.; Ott, U.; Paul, M.; Rugel, G.; Steier, P.; Tims, S.;
Via accelerator mass spectrometry (AMS) two relevant aspects to dust formation and evolution are studied in the laboratory: First, the measurement of trace element isotope ratios in presolar nanodiamonds isolated from meteorites, e.g. isotope ratios of stable Pt isotopes to extract r-process nucleosynthesis signatures. Recent experiments demonstrate the applicability of AMS for measuring Pt isotope signatures in material from the Allende meteorite [1,2]. The second aspect relates to the search for live supernova (SN)-produced radionuclides in terrestrial deep-sea archives [3-5]. In particular, we focus on longer-lived isotopes with half-lives of the order of million years. Previous time-resolved measurements of a deep-sea manganese crust identified a clear 60Fe enrichment about 2.5 Ma in the past [6]. This anomaly is interpreted as evidence for a nearby SN. With improved time resolution we continue this search by investigating two deep-sea sediment cores from the Indian Ocean for a possible signal of the SN-candidates 26Al, 53Mn, 60Fe, and potentially 244Pu [7].
An overview of the technique of AMS will be given and its potential for such studies and some selected applications will be discussed. In particular, the experimental proof of r-process scenarios via the direct observation of nuclides generated in the r-process such as the significance of new data for Pt isotope ratios measured in nanodiamonds will be presented and new technical approaches will be detailed [1,2]. We will exemplify the high sensitivity of AMS via the search of r-process 244Pu complementing the recent finding of live 60Fe in a manganese crust.
References: [1] U. Ott et al. PASA 29 (2012) 90; [2] A. Wallner et al. NIMB (2012); [3] J. Ellis et al., AstrophysJ. 470 (1996) 1227; [4] G. Korschinek et al., Radiocarbon 38 (1996) 68; [5] M. Paul et al., J.Radioanal.Nucl.Chem. 272, (2007) 243; [6] K. Knie et al. PRL 93 (2004) 171103; [7] J. Feige et al. PASA 29 (2012) 109.
Keywords: AMS, supernova, radionuclide, presolar grains, nanodiamonds, deep-sea sediments, meteorite
  • Poster
    International conference of the European Science Foundation EuroGENESIS CoDustMas network action, 05.-08.11.2012, Ascona, Schweiz

Publ.-Id: 17775 - Permalink


Evidences for a more restricted Icelandic Ice cap re-advance after the Bølling warming period
Meriaux, A.-S.; Delunel, R.; Merchel, S.; Finkel, R. C.;
Moraines dated north of Vatnajökull by cosmogenic surface exposure dating show that the Icelandic Ice cap (IIS) was less extended during the Younger Dryas than previously suggested. The data imply that this glacial advance was more complex and restricted in some glacial valleys in NE Iceland. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about their onshore characteristics and rates of recession during the warmer Holocene periods. This is especially the case in the NE of Iceland where volcanic activity and major outburst floods (jökulhlaups) have removed a large amount of morphological evidences of past ice margins. Our study aimed at filling this chronological gap of the IIS inland during the late Quaternary deglaciation by dating past preserved ice margins using 36Cl and 3He cosmogenic nuclides. We studied moraines and outwash located 44 km, 48 km and 60 km north of Vatnajökull, between the Jökulsà à Fjöllum and Jökulsà à Brú, the main northern glacial river systems draining the icecap. Preliminary 36Cl ages of the northernmost moraine at Skessugardur, 60 km north of present-day IIS and 65 km away from the coastline, indicate that the minimum exposure ages derived from Ca-rich plagioclases range from 11.0 ± 1.2 ka to 13.4 ± 1.4 ka with an average at 12.2 ± 1.0 ka (±1 sigma=6), using the local Icelandic production rates for Ca spallation of Licciardi et al. (2008). These ages are close to the Younger Dryas at a time when the Icelandic Ice Sheet is thought to have re-advanced further north toward the coastline. Overall, our results call for a revision of our understanding of the IIS deglaciation history and provide new tie-points for the calibration of the IIS models.
References: Licciardi et al., EPSL 267 (2008) 365–377.
Keywords: Ice sheets, Quaternary geochronology, Cosmogenic-nuclide exposure dating, AMS, TCN, radionuclide
  • Poster
    American Geophysical Union, Fall Meeting 2012, 03.-07.12.2012, San Francisco, USA

Publ.-Id: 17774 - Permalink


Decadal to Millennial scale erosion rates in the Nepal Himalayas
Andermann, C.; Bonnet, S.; Gloaguen, R.; Crave, A.; Merchel, S.; Braucher, R.; Bourlès, D. L.;
On a sub-millennial time scale the spatial distribution of erosion is controlled to first order by tectonics, relief, and possibly precipitation, and secondly by vegetation, lithology, temperature and human activity. The Himalayas form a very distinct orographic barrier with a pronounced rainfall gradient from the South to the North and have a very rugged terrain, causing highly dynamic surface processes and fast erosion rates. Thus, the Himalayas provide an ideal site of investigation to study erosion and constrain its controlling factors. In this contribution we present an integrated comparison of mean catchment erosion rates, calculated from in-situ produced 10Be cosmogenic isotope concentration in river sands (representative for millennial time scales) and suspended sediment measurements (integrating the annual to decadal time spans). We discuss erosion rates and patterns in the context of precipitation-landscape features of the studied catchments. The samples cover all major rivers, and several minor tributaries of the Narayani watershed (30,000 km2) in central Nepal. They represent all lithologies, topographic units and climate regimes across the Himalayan range. The erosion rates, both from cosmogenic nuclide analysis and suspended sediment measurements, range from 0.1 to 4 mm/yr. These agree well between the two methods and also with already published data for the major outlet stations at the Himalayan front. However, in the Middle and High Himalayas the cosmogenic erosion rates are significantly higher than those from suspended sediment measurements. While on the short term (intra-annual) a clear relation between precipitation and erosion can be observed, the cosmogenic erosion rates show no clear dependency with the basin wide precipitation pattern. Furthermore, no relation could be observed with the dominant lithological units and the degree of glaciation.
Our observations confirm the overall established relationship between erosion rates, relief and slope, showing clearly that topography exerts a predominant control on spatial erosion rates on the millennial timescale. However, we observe a different relationship between main stream basins (> 250 km2) and small tributary basins (< 250 km2). Small basins show in general lower erosion rates than larger basins for respectively the same topographic characteristics.
Keywords: Hydrology, Erosion, Geomorphological geochronology, hillslope, AMS, TCN, radionuclide
  • Poster
    American Geophysical Union, Fall Meeting 2012., 03.-07.12.2012, San Francisco, USA

Publ.-Id: 17773 - Permalink


Ion-irradiation induced damage in FeCr alloys characterized by nanoindentation
Heintze, C.; Bergner, F.; Hernández-Mayoral, M.;
Self-ion irradiation in combination with nanoindentation offers the possibility to characterize irradiation damage in a broad range of irradiation temperature and fluence. Nanoindentation results are reported for binary FeCr alloys of commercial purity with nominal chromium contents of 2.5, 9 and 12 at%. The irradiation conditions considered include irradiations at room temperature, 300°C and 500°C. Special features of this work are roughly rectangular damage profiles produced by multi-step irradiations with different ion energies and exploitation of the load dependence of hardness for indentation loads in the range of 2 to 500 mN. The effects of Cr content, fluence and irradiation temperature are discussed. Irradiation-induced changes of the microstructure were characterized by means of transmission electron microscopy (TEM). Hardening features and their contribution to the observed irradiation-induced hardness changes will be discussed in the framework of a tentative two-feature hardening model. Small-angle neutron scattering (SANS) data reported for neutron-irradiated conditions of the same alloys will be taken into account.
Keywords: Self-ion irradiation, nanoindentation, TEM, irradiation hardening, FeCr alloys
  • Invited lecture (Conferences)
    CAARI 2012 - 22nd International Conference on the Application of Accelerators in Research and Industry, 05.-10.08.2012, Fort Worth, USA

Publ.-Id: 17772 - Permalink


Complexation behaviour of U(VI) and Eu(III) with Schiff Bases investigated by laserinduced spectroscopy
Lindner, K.; Günther, A.; Bernhard, G.;
Actinides and lanthanides play an increasing important role in present time. Actinides can be released into the natural environment especially from mining areas by weathering, erosion and anthropogenic activities as well as by nuclear incidents and thus represents a hazard potential for humans. Lantha-nides occur in nature rarely, but they are significant in the glass and ceramics industries, metallurgy and the cracking of petroleum. New supramolecular complexing agents with N, O, S donor function are developed to separate the metals of the d- and f-block and enriched rare earths. Schiff Bases are essential basic components of these new organic ligands. In this study the complexation of uranium(VI) and europium(III) with the Schiff bases N-benzylideneaniline (NBA), 2-(2-hydroxybenzyliden-amino)phenol (HBAP) and alpha-(4-hydroxyphenyl-imino)-p-cresol (HPIC) was investigated in methanolic solution using time-resolved laserinduced fluorescence spectroscopy (TRLFS) at room and cryogenic temperature and in the case of the uranium(VI)-Schiff bases systems by applying of TRLFS with ultrashort laser pulses (fs-TRLFS).
The measurements of the uranyl luminescence in alcoholic solution at room temperature show strong quenching effects by solvent. These quenching effects could be minimized by measurements at cryogenic temperature (153 K). There is a decrease in fluorescence of the uranium(VI) with the addition of the Schiff Base. A wavelength shift can not be observed, which indicate that the complex seems not to fluoresce.
The europium(III) fluorescence at room temperature is not affected by the methanol. But it turns out that the europium(III) in methanol solution forms an asymmetric complex in comparison to the Eu(III)-water complex. The europium(III) fluorescence decrease with addition of Schiff Base. The observed splitting of the peaks indicates that two different europium(III) species exist in the system.
The fs-TRLFS as a sensitive speciation technique was used to determine the luminescence properties of formed complexes in the uranium(VI)-NBA, uranium(VI)-HBAP and uranium(VI)-HPIC systems. The emission signals show hypsochromic, bathochromic or hypsochromic shifts in comparison to the emission maxima of the uncomplexed ligand. The intensity of the ligand fluorescence increase with the increasing uranium(VI) concentration. The fs-TRLFS investigation opens up the possibilities for the determination of very short-lived complex species via the fluores-cence of the organic compounds by delocalized p-electron systems. Corresponding to the first analyses of the time resolved measurements the luminescence lifetimes of the free ligand and the uranium(VI) complex species are in the range from 2-4 ns. Through the change of the emission properties of organic ligands or metals can be observed the complexation with uranium(VI) and europium(III) and calculated corresponding complex formation constants.
Keywords: fs-TRLFS, Cryo TRLFS, uranium(VI), europium(III), Schiff Bases
  • Poster
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.11.-07.12.2012, Dresden, Deutschland

Publ.-Id: 17771 - Permalink


Lower head failure
Altstadt, E.;
During a severe accident in a pressurized water reactor with core melt, the reactor pressure vessel integrity may be threatened by the relocation of molten corium into the lower head and the formation of a molten pool.This book section describes the thermal and mechanical phenomena in the reactor pressure vessel.
Keywords: Reactor pressure vessel failure, core melt down, in-vessel melt retention, nuclear reactor
  • Book chapter
    Bal Raj Sehgal: Nuclear Safety in Light Water Reactors: Severe Accident Phenomenology, Amsterdam etc.: Academic Press Elsevier, 2012, 978-0-12-3888446-6, 145-155

Publ.-Id: 17770 - Permalink


Combination of spectroscopic methods for the identification of U(VI) spezies formed by selected bacteria, algae and fungi
Günther, A.; Vogel, M.; Roßberg, A.; Raff, J.; Bernhard, G.;
Microorganisms like bacteria, algae and fungi have a significant influence on the immobilization, mo-bilization and transport of radionuclides like uranium and other heavy metals in the biological and geological environment via the soil and water path. To understand the mechanisms of uptake, trans-port, deposition, degradation and the behavior of actinides in different biological and geological sys-tems structural knowledge about the formed actinides species are of great importance and are essential for a reliable assessment of these processes.
Arthrobacter (bacteria), Chlorella vulgaris (green algae) and Schizophyllum commune (fungi) bind significant amounts of uranium(VI) in the pH range from 4 to 7 and contact time of two days. Trans-mission electron microscopy and scanning electron microscopy investigations showed mainly interac-tions of uranium with parts of cell walls of the selected biomass. By investigations of transparent fun-gal cells were identified additionally uranium containing accumulates inside originally living cells.For the determination of the functionalities, which are important for the binding and mobilization or immobilization of uranium, the interaction of uranium(VI) with metabolic active bacterial, algal and fungal cells was investigated by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and X-ray absorption fine structure spectroscopy (EXAFS). The measured luminescence spectra of uranyl containing cell species of all investigated organisms show bathochromic shifts of the uranyl emission bands in comparison to the corresponding emission signals of the uranyl species in the initial solution independent of the uranium concentration and the pH value of the solution. The com-parison of the obtained biomass spectra with luminescence properties of uranyl model compounds demonstrated the carboxylic and organic/inorganic phosphate groups are responsible for uranium binding on the biomass with varying contributions dependent on the microbial biomass, cell status and uranium concentration in the initial sorption solution. The dominant interaction of uranium(VI) with organic/inorganic phosphate groups could be verified by corresponding EXAFS investigations.
Keywords: Bacteria, algae, fungi, uranium, TRLFS, EXAFS
  • Poster
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland

Publ.-Id: 17769 - Permalink


Transient magneto-photoluminescence quenching by intra-excitonic THz absorption
Bhattacharyya, J.; Zybell, S.; Helm, M.; Andrews, A. M.; Strasser, G.; Schneider, H.;
Optical properties of III-V semiconductor heterostructures are strongly influenced by excitons. With increasing carrier confinement, as in quantum wells and quantum dots, the exciton binding energy increases. This results in distinct features in absorption and emission spectra arising from the excitonic transitions and recombinations. The temporal behavior of the optical properties of these systems is also influenced by the exciton dynamics. Recently, there has been an increasing interest on the study of intraexcitonic transitions. The energy separations of the excitonic states (1s, 2s, 2p, and so on) fall in the terahertz (THz) frequency range. Intense and tunable THz sources like free electron lasers have been used to probe these transitions. However, most experiments like optically detected magnetic resonance measurements, were done in the time integrated mode and the intraexcitonic carrier dynamics could not be probed.
Here we present our work on time resolved measurements of photoluminescence (PL) quenching in presence of a varying external magnetic field. We performed measurements on GaAs/AlGaAs multiple quantum well sample with a narrow PL line width (2 meV) associated with the 1s heavy-hole exciton. THz pulses from a free electron laser were used to induce intraexcitonic transitions resulting in the quenching of the PL. The quench manifested itself as a dip in the PL transient during the incidence of the THz pulse and the depth of the dip was proportional to the THz absorption. The intraexcitonic transition energies were tuned using an external magnetic field. Excitonic 1s-2p and cyclotron resonances appeared as maxima in the plot of the dip depth vs. magnetic field. Time resolved measurement enabled us to investigate the relaxation dynamics of the 2p state which does not undergo radiative recombination and thus cannot be observed directly in the PL spectra. The carriers excited to the 2p state, by the THz pulse, eventually relaxed back to the 1s-state resulting in the gradual recovery of the 1s PL intensity after the quench. Some of the carriers in the 2p state however got scattered to the 2s state resulting in the enhancement of the 2s emission during the incidence of the THz pulse. This is a direct consequence of intraexcitonic carrier transfer between the 2p and 2s states. From magnetic field dependence of the THz induced 2s emission intensity we showed the possibility of externally controlling intraexcitonic transitions.
Keywords: excitons, terahertz, GaAs quantum wells, transient photoluminescence
  • Poster
    ICPS2012 - 31st International Conference on the Physics of Semiconductors, 29.07.-03.08.2012, Zürich, Schweiz

Publ.-Id: 17766 - Permalink


Untersuchungen zur magnetfeldkontrollierten Auftriebskonvektion in einem Czochralski-Tiegel
Cramer, A.; Pal, J.; Gerbeth, G.;
Die Untersuchungen zur physikalischen Modellierung der Strömung in einer Czochralski-Geometrie umfassen Ultraschall-Doppler Geschwindigkeits- und Temperaturmessungen, Letztere mit dünnen, und damit hinreichend schnell ansprechenden, Thermoelementen. Um ähnliche Wärmetransporteigenschaften, wie sie bspw. bei der Züchtung von Siliziumkristallen vorliegen, zu haben, wurde die niedrig-schmelzende ternäre Legierung GaInSn eingesetzt. Die kleine Prandtlzahl Pr « 1 dieses de facto Standard-Modellfluids für derartige Untersuchungen liegt im Bereich der Halbleiterschmelzen und sorgt für die Dominanz von Wärmeleitung über konvektiven Transport. Das Strömungsfeld zeigt eine komplexe nicht achsen­sym­metrische Topologie. Reine Moden mit einer bestimmten azimuthalen Wellenzahl, über die in der Literatur oftmals berichtet wird, wurden nicht gefunden. Vielmehr manifestiert sich die Konvektionsstruktur in der Überlagerung der achsen­symmetrischen (azimuthale Wellenzahl m = 0) mit einer monozellulären (m = 1) Mode. Die Temperaturmessungen zeigen, dass die in vielen anderen Arbeiten gefundene Dämpfung der unerwünschten auftriebsinduzierten Tempe­ra­tur­fluk­tu­ationen durch Anwendung eines rotierenden Magnetfeldes nicht reproduziert werden können.
Keywords: Crystal growth, Czochralski technique, electromagnetic flow control, damping of turbulence, rotating magnetic field
  • Lecture (Conference)
    Elektroprozesstechnik, 06.-07.09.2012, Ilmenau-Heyda, Deutschland
  • Contribution to proceedings
    Elektroprozesstechnik, 06.-07.09.2012, Ilmenau-Heyda, Deutschland
    Tagungsband Elektroprozesstechnik 2012

Publ.-Id: 17765 - Permalink


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