Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
In-situ conformational analysis of fibrinogen adsorbed on Si surfaces
Tunc, S.; Maitz, M. F.; Steiner, G.; Vázquez, L.; Pham, M. T.; Salzer, R.;
Fibrinogen is a major plasma protein. Previous investigations of structural changes of fibrinogen due to adsorption are mostly based on indirect evidence after its desorption, whereas our measurements were performed on fibrinogen in its adsorbed state. Specific enzyme linked immunosorption experiments showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. AFM investigations revealed the trinodular shape of fibrinogen molecules adsorbed on hydrophilic surfaces, whereas all of the molecules appeared globular on hydrophobic surfaces. The distribution of secondary structures in adsorbed fibrinogen was quantified by in-situ FTIR analysis. Substrates of identical chemical bulk composition but different surface hydrophobicity permit direct comparison among them. Adsorption properties of fibrinogen are different for each degree of hydrophobicity. Although there is some increase of turn structure and decrease of β-sheet structure, the secondary structure of adsorbed fibrinogen on hydrophilic surface turned out to be rather similar to that of the protein in solution phase with a major α-helix content. Hydrophilic surfaces exhibit superior blood compatibility as required for medical applications.
Keywords: Silizium, Protein, Fibrinogen, Adsorption, Konformation, AFM, FTIR
  • Colloids and Surfaces B: Biointerfaces, 42(2005)3-4, 219-225

Publ.-Id: 6569 - Permalink


Experimental Evidence of Si Nanocluster delta-Layer Formation in the Vicinity of Ion-Irradiated SiO2-Si Interfaces
Röntzsch, L.; Heinig, K. H.; Schmidt, B.; Mücklich, A.;
Predictions on formation and self-alignment of Si nanocrystals (NCs) at ion-irradiated SiO2-Si interfaces have been proven by cross-section transmission electron microscopy (TEM). The model is based on ion-mixing of SiO2-Si interfaces resulting in a region of SiOx (x<2). During annealing, the interface restores and in the tail of the mixing profile Si excess precipitates and forms a self-aligned layer
of Si NCs in SiO2. This Si NC delta-layer structure can hardly be observed by conventional TEM techniques due to the very low mass contrast of tiny Si NCs embedded in SiO2. Here, a contrast enhancing method is presented based on alloying of these Si NCs with Ge. For this purpose, a thin Ge layer is embedded into the oxide sufficiently far from the interface mixing range, thus, preventing interference with the Si precipitate formation. During annealing, diffusing Ge monomers attach to the Si NCs, mainly due to the energetically favored Si-Ge bond, resulting in Si1-xGex NCs with an enhanced mass contrast in TEM.
Keywords: SiO2-Si interface; ion irradiation; phase separation; silicon; nanocrystal; self-alignment
  • Poster
    14th International Conference on Ion Beam Modification of Materials, 05.-10.09.2004, Monterey, USA
  • Nuclear Instruments and Methods in Physics Research B 242(2006), 149-151

Publ.-Id: 6565 - Permalink


Renormalization of the Two-Photon Vacuum Polarization and the Self Energy Vacuum Polarization for a Tightly Bound Electron
Zschocke, S.; Plunien, G.; Soff, G.;
The renormalization method of Bogoljubov-Parasuik-Hepp-Zimmermann (BPHZ) is used in order to derive the renormalized energy shift due to the gauge invariant Källén-Sabry diagram of the two-photon vacuum polarization (VPVP) as well as the self energy vacuum polarization S(VP)E beyond the Uehling approximation. It is outlined, that no outer renormalization is required for the two-photon vacuum polarization and that only the inner renormalization has to be accomplished. It is shown that the so-called nongauge invariant sourious term is absent for a wide class of vacuum polarization (VP) diagrams if one applies the widely used sherical expansion of bound and free-electron propagator. This simplifies significantly calculations in bound state quantum electrodynamis. As one result of our paper the use of the BPHZ-approach in bound state QED is established.

Publ.-Id: 6564 - Permalink


An Electromagnetic Undulator for the Far Infrared at ELBE
Dekorsy, T.; Fahmy, K.; Grosse, E.; Michel, P.; Seidel, W.; Wolf, A.; Wünsch, R.;
The parameters of an envisaged undulator at the radiation source ELBE for the production of IR radiation up to 150 microns are presented.
  • Poster
    Poster, 26th Int. Free-Electron Laser Conf. and 11th FEL Users Workshop, Trieste, 29.08.-3.09.2004
  • Open Access LogoContribution to proceedings
    26th International Free-Electron Laser Conference and 11th FEL Users Workshop, 29.08.-03.09.2004, Trieste, Italy
    Proceedings of the 26th International Free-Electron Laser Conference and 11th FEL Users Workshop, 389-391

Publ.-Id: 6563 - Permalink


Ion-induced stress relaxation during the growth of cubic boron nitride thin films
Abendroth, B.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-406

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Publ.-Id: 6560 - Permalink


Modification of magnetic thin films and nanostructures by ion irradiation and implantation
Fassbender, J.ORC
He ion irradiation in an applied magnetic field allows to tailor the magnetic properties of thin films and nanostructures after preparation due to structural phase transformations, interfacial mixing, chemical ordering and magnetic ordering. Some examples for the case of exchange bias films, soft magnetic films and FePt nanoparticles will be demonstrated.
In addition ion implantation can be used for the doping of magnetic materials to modify the Curie temperature, the saturation magnetization or the magnetic damping behavior of ferromagnetic films. First results of these ion implantation studies will be presented.
Keywords: magnetism, magnetic films, nanoparticles, ion irradiation, ion implantation
  • Lecture (others)
    Seminar talk: Hitachi Almaden, San Jose, USA, 08.10.2004

Publ.-Id: 6557 - Permalink


Maßgeschneiderte magnetische Materialien – neue Wege durch Ionenbestrahlung
Fassbender, J.ORC
Aufgrund der reduzierten Dimensionen in ultradünnen magnetischen Schichten und Nanopartikeln hängen die magnetischen Eigenschaf-ten, wie z. B. magnetische Anisotropien und Austauschkopplung, empfindlich von der Grenzflächen- bzw. Oberflächenmorphologie ab. Zusätzlich werden chemisch geordnete intermetallische Verbindungen zunehmend anwendungsrelevant. In beiden vorgenannten Bereichen bietet die Ionenbestrahlung eine exzellente Möglichkeit nach der Prä-paration die magnetischen Eigenschaften gezielt auf einer lokalen Skala zu beeinflussen. Somit lässt sich eine rein magnetische Na-nostrukturierung ohne Veränderung der Oberflächentopographie reali-sieren.
Der Vortrag gibt eine Übersicht über die neuen Möglichkeiten mit Hilfe der Ionenbestrahlung künstliche magnetische Strukturen herzustellen und ordnet diese im Bezug auf deren Anwendungsrelevanz ein.

Keywords: magnetism, ion irradiation
  • Lecture (others)
    Physikalisches Kolloquium TU Dresden

Publ.-Id: 6556 - Permalink


Reflectivity characterization of ion irradiated exchange bias FeMn-FeNi films
Solina, D.; Liedke, M. O.; Tietze, U.; Fassbender, J.ORC; Schreyer, A.
X-ray reflectivity, neutron reflectivity studies and Magneto-Optic Kerr Effect measurements (MOKE) have been carried out on thermally evaporated FeMn-FeNi exchange biased films before and after ion irradiation by helium ions. MOKE shows that ion irradiation reduces the exchange bias characteristics of the samples with increased dose. Modelling of the reflectivity data infers that atoms from the buffer layer are displaced by the ions and imbedded into the substrate material. The correlation between these strong structural modifications by irradiation with the reduction of the exchange bias will be discussed.
Keywords: magnetism, magnetic films, exchange bias, x-ray diffraction, neutron scattering
  • Journal of Magnetism and Magnetics Materials 286(2005), 225

Publ.-Id: 6555 - Permalink


Analysis of theNi81Fe19/Fe50Mn50 exchange bias system with a varying Cu spacer thickness and position for partial decoupling
Liedke, M. O.; Nembach, H.; Hillebrands, B.; Fassbender, J.ORC
In order to study the role of the exchange interaction at and near the interface, Ni81Fe19/Fe50Mn50 bilayers have been studied, which have an intervening layer of varying thickness and position in the antiferromagnetic Fe50Mn50 layer. The role of the intervening layer is to generate partial exchange decoupling. As a result, samples were obtained, where in one in-plane direction the position of the intervening layer varies from the interface to the top surface of the Fe50Mn50 layer at a constant intervening layer thickness, and in the other in-plane direction the intervening layer thickness varies. Two-dimensional maps of the resulting exchange bias field and the coercive field were obtained from magneto-optic Kerr effect magnetometry measurements. The role of the position and strength of the partial decoupling within the antiferromagnetic layer on the exchange bias effect and the coercive field is discussed.
Keywords: magnetism, magnetic films, exchange bias, antiferromagnets, exchange coupling
  • Journal of Magnetism and Magnetic Materials 290-291(2005)1, 588-590

Publ.-Id: 6554 - Permalink


Modified Gilbert Damping due to Exchange Bias in NiFe/FeMn Bilayers
Weber, M.; Nembach, H.; Hillebrands, B.; Fassbender, J.ORC
A picosecond all-optical pump-probe technique is used to investigate magnetization dynamics and magnetic damping behaviour in the Ni81Fe19/Fe50Mn50 exchange bias system. Within the laser excitation the spin temperature is elevated resulting in a collapse of the exchange bias field. Thus, a fast anisotropy field pulse is launched which triggers the magnetization precession. The extracted Gilbert damping increases linearly with the exchange bias field magnitude which can be understood taking local fluctuations of the interfacial exchange coupling as an additional dissipation mechanism into account.
Keywords: magnetism, magnetic films, exhange-bias, magnetic damping, pump-probe, time-resolved
  • Journal of Applied Physics 97(2005), 10A701

Publ.-Id: 6552 - Permalink


Real time temperature dynamics in exchange biased bilayers upon laser excitation
Weber, M.; Nembach, H.; Hillebrands, B.; Fassbender, J.ORC
A hot spin and phonon gas in exchange biased metallic bilayers is induced by an 8.5 ps laser excitation. The spin-lattice temperature dynamics is sensed in real time by the time evolution of the exchange bias field on the picosecond timescale. A calibration with temperature dependent quasistatic Kerr measurements explains a pump pulse induced temperature increase of about 100°C at the interface. Upon photoexcitation the exchange coupling across the interface between the ferromagnetic and antiferromagnetic layer is reduced within the first 10 ps, leading to a reduction of the bias field to about 50% of its initial value. The fast thermal unpinning of the exchange coupling is followed by a heat diffusion dominated recovery with a relaxation time on the order of 160 ps. A heat transport analysis reveals the diffusivity of the studied bilayer system.
Keywords: magnetism, magnetic films, time-resolved MOKE, exchange-bias, pump-probe
  • IEEE Transactions on Magnetics 41(2005)3, 1089-1092

Publ.-Id: 6551 - Permalink


Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high- and low- pressure ion nitriding processes
Ueda, M.; Gomes, G.; Abramof, E.; Reuther, H.;
Ion nitriding is an important surface modification technique used routinely in the advanced technology industries aiming at producing high added value components with increased hardness and wear resistance. To further improve the performance of critical-part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments combining PIII and ion nitriding. In particular, a combination of high-pressure (40 Pa), high-temperature (up to 450 degreesC) glow discharge nitriding with low-pressure (8 x 10(-2) Pa) ion nitriding was implemented. Analysis of the SS304 samples treated by this hybrid method was carried out using the technique of grazing incidence X-ray diffraction (GIXRD) and the results were supported by both normal XRD and AES (Auger electron spectroscopy) measurements. Depending on the particular conditions of the treatment and the depth probed, mixed phases Of gamma(N), and gamma were measured. The improvement in hardness of the obtained surfaces (up to a factor of 2.7) was also in accordance with the results of other analysis.

Publ.-Id: 6550 - Permalink


Surface modification of metal alloys by plasma immersion ion implantation and subsequent plasma nitriding
Kostov, K. G.; Ueda, M.; Lepiensky, A.; Soares, P. C.; Gomes, G. F.; Silva, M. M.; Reuther, H.;
Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersion ion implantation (PIII) is a newly developed technology, which provides ion implantation at moderate energy (10-50 keV), and thereby allowing penetration depths deeper than the surface oxide barrier. The damage caused by ion implantation together with the surface sputtering may create favorable boundary conditions for an efficient subsequent diffusive treatment such as nittiding. Surface modification of aluminum alloy 5052, Ti6A14V alloy and steels (AISI 304 and H13) by a combination of PIII and plasma nitriding (PN) has been investigated. Nitrogen ions were implanted into specimens at 15 W and then ion nitrided at low pressure with bias of - 800 V. Compared to the untreated samples the hardness of Ti6Al4V alloy and AISI 304 steel could be improved significantly. The hardness of H13 steel can be increased by 20+ACU- using a duplex process with 4-h nitriding time. X-ray diffraction (XRD) results have shown some structural modification of the metallic samples and formation of a double-layer structure in AISI 304, treated by PIII and PN. Nitrogen depth profile of the same stainless steel sample, obtained by Auger electron spectroscopy (AES), shows two rather well-defined nitrogen enriched regions with different N contents: high (25-30 at.+ACU-) in a surface layer and medium (similar to 10+ACU-) in a subsurface layer.

Publ.-Id: 6549 - Permalink


Use of low energy and high frequency PBII during thin film diposition to achieve relief of intrinsic stress and microstructural changes
Bilek, M. M. M.; Mckenzie, D. R.; Möller, W.;
In this paper, we describe the use of plasma based ion implantation (PBII) together with physical vapour deposition (PVD) to achieve low intrinsic stress and influence the microstructure of coatings. A model is proposed to explain the physical mechanisms responsible for observed changes in stress. The model is compared with other available models and all are tested against data obtained using a cathodic vacuum arc in background gas to deposit aluminium nitride, titanium nitride and carbon in the presence of high voltage pulsed bias on the substrate. In all three systems, application of PBII resulted in large reductions in intrinsic stress as the voltage and frequency of the pulses was increased. We observed a trade off between applied bias voltage and pulsing frequency. The crystalline systems, aluminium nitride and titanium nitride showed changes in preferred orientation in PBII treated films. An important conclusion of significance to industry is that even relatively low energy (0.5¿5 keV) ion implantation can be effectively employed to achieve stress relief.
Keywords: Intrinsic stress; Plasma immersion ion implantation; Deposition

Publ.-Id: 6548 - Permalink


Stability of the N=50 shell gap in the neutron-rich Rb, Br, Se, and Ge isotones
Zhang, Y. H.; Podolyàk, Z.; de Angelis, G.; Gadea, A.; Ur, C.; Lunardi, S.; Marginean, N.; Rusu, C.; Schwengner, R.; Kröll, T.; Napoli, D. R.; Menegazzo, R.; Bazzacco, D.; Farnea, E.; Lenzi, S.; Martinez, T.; Axiotis, M.; Tonev, D.; Gelletly, W.; Langdown, S.; Regan, P. H.; Valiente Dobon, J. J.; von Oertzen, W.; Rubio, B.; Quintana, B.; Medina, N.; Broda, R.; Bucurescu, D.; Ionescu-Bujor, M.; Iordachescu, A.;
The low- and medium-spin states of the N = 50 neutron-rich, 3787Rb, 3585Br, 3484Se and 3282Ge isotones have been populated in deep-inelastic processes produced by the interaction of 460 MeV 82Se ions with a 192Os target. The subsequent gamma decay has been investigated at the Laboratori Nazionali di Legnaro using the GASP gamma-ray detector array. The comparison of the experimentally observed excited states with shell-model calculations performed with and without neutron degrees of freedom has allowed the investigation of the role of the neutron-core breaking excitations and therefore of the N = 50 shell gap. The inclusion of neutron configurations in the shell-model calculations results in an improved agreement between the experimental and calculated level energies at medium and high spin. These results highlight the considerable contribution of neutron-core particle-hole excitations across the N = 50 shell gap to the level configurations. The overall agreement of the measured excited states with the shell-model predictions is indicative of the persistence of the N = 50 shell gap down to Z = 32.
Keywords: nuclear shell model; gamma-ray spectra; deep inelastic heavy ion reactions; nuclei with mass number 190 to 219; nuclear spin; nuclear energy level transitions; high spin states; nuclei with mass number 59 to 89

Publ.-Id: 6547 - Permalink


Ion Irradiation through SiO2/Si-interfaces: Non-conventional Fabrication of Si Nanocrystals for memory applications
Schmidt, B.; Heinig, K.-H.; Röntzsch, L.; Müller, T.; Stegemann, K.-H.; Votintseva, E.;
Si nanocrystals for multi-dot floating-gate memories have been produced by non-conventional ion beam synthesis (IBS). Due to ion beam mixing irradiation with 1015-1016 Si+ cm-2 at 50-100 keV through 50 nm poly-Si and 15 nm SiO2 on (001)Si results in a considerable Si excess within the oxide. At the upper and lower interfaces of the gate oxide, this ion irradiation forms a metastable SiOx (x < 2) composition. Post-irradiation RTA thermal treatment leads to phase separation into Si and SiO2. Adjacent to the recovering interfaces, narrow SiO2 zones become denuded of excess Si. More distant excess Si precipitates as Si NCs in the gate oxide. MOSFET characteristics in terms of write/erase voltage, duration of the programming time, endurance and retention have been evaluated.
Keywords: nanocluster, ion irradiation, phase separation, non-volatile multi-dot floating-gate memory
  • Lecture (Conference)
    14th Int. Conf. on Ion Beam Modification of Materials (IBMM 2004), September 5-11, 2004, Monterey, California, USA
  • Nuclear Instruments and Methods in Physics Research B 242(2006)1-2, 146-148

Publ.-Id: 6546 - Permalink


Nitrogen Transport in the Primary Circuit of a VVER during a LOCA occurring under Plant Cool-down Conditions
Prasser, H.-M.; Baranyai, G.; Böttger, A.; Ezsöl, G.; Guba, A.; Perneczky, L.; Toth, I.; Zschau, J.;
The paper presents the results of a thermal hydraulic experiment conducted at the PMK-2 test facility in the frame of the IMPAM-VVER project. The test was dedicated to a scenario assuming a loss-of-coolant event dur-ing the cool-down phase of the plant, when neither core flooding tanks nor safety injections systems are available by an automatic action. This may lead to core heat-up in case of a larger LOCA. The assumed break size in the test was 30%. The experiment has shown that an overheat of the fuel rod cladding occurs. Finally, one of four lines of the low pressure ECC injection system is sufficient to handle the situation and to cool down the reactor safely. A speciality of the scenario is the fact that the primary circuit is pressurised with nitrogen. In the course of the transient, non-condensable gas can enter the primary circuit from the pressurizer during the blow-down phase. In order to study the transport of the nitrogen along the primary circuit, the test facility PMK-2 was equipped with a novel type of probe: a local void probe equipped with an integrated micro-thermocouple. The new probes delivered a global picture of the process. Nitrogen coming from the pressurizer after its depletion enters the circuit via the surge line and turns first in the direction of the main coolant flow towards the steam generator and finally towards the break in the cold leg. However, nitrogen is also moving in the opposite direc-tion and reaches the reactor outlet and enters even the upper plenum of the reactor closely after the main circulation pump has stopped. RELAP5 was found to be able to predict the behaviour of the non-condensable gas in the primary circuit. Despite of some delay in the prediction of the time of the appearance of the gaseous phase in the begin of the process, most details of the transient were reproduced by the calculation with a good accuracy.
Keywords: pressurized water reactors, loss-of-coolant transients, VVER, nitrogen transport, void probes, RELAP
  • Kerntechnik 69(2004)4, 167

Publ.-Id: 6545 - Permalink


Long-time operation of a modified Cs sputter ion source 860-C
Friedrich, M.; Tyrroff, H.;
The modified Rossendorf Cs sputter ion source 860-C presented at the SNEAP 2002 [1] was opened in July 2004 for maintenance after 4100 operation hours. The main reason for this first source opening after its installation in July 2002 was a short circuit of the sputter voltage due to material deposition on the cathode insulator. Beside the long lifetime the modification of the source has resulted in a reduced erosion of the spherical ioniser and in a concentrated deposition of the sputtered material on the front side of the additional shielding electrode and on the cathode-shielding electrode. After cleaning all inner source parts can be reused in the ion source.

[1] M. Friedrich and H. Tyrroff, Nucl. Instr. and Meth. B 201 (2003) 645.

Keywords: Ion sources; Negative ions; Electrostatic accelerators
  • Lecture (Conference)
    SNEAP-2004, Hamilton/Ontario, Canada
  • Contribution to external collection
    Proceedings of SNEAP-2004, Hamilton/Ontario, Canada, 2005 (auf CD)

Publ.-Id: 6544 - Permalink


RBS with high depth resolution using small magnetic spectrometers
Grötzschel, R.; Klein, C.; Mäder, M.;
The increasing importance of ultra-thin layers for novel technologies demands quantitative analysis techniques with a depth resolution of atomic monolayers, which can be obtained for RBS and ERDA by magnetic spectrometers.

We operate at the 3 MV Tandetron accelerator a magnetic spectrometer consisting of an UHV scattering chamber and a simple dipole magnet with circular field boundaries (Browne¿Buechner spectrometer). Since in many cases of high resolution ion beam analysis the samples must be prepared in situ in UHV, the chamber with a base vacuum of 4 × 10-10 mbar is equipped with an ion sputter gun and two low rate e-beam evaporators for in situ layer deposition. A RHEED system is used to check the surface reconstruction and monitor the layer growth. Samples are transferred, together with a BN heater, to the precision 5-axes channelling goniometer. The magnet with a mean radius of 0.65 m is mounted vertically and can be positioned either at 35.5° or 144.5°. The backward position offers the advantage of a high mass resolution, but the Rutherford cross sections are a factor of about 100 lower than at the forward angle, which is the preferred position if kinematically possible.

At the 5 MV tandem accelerator a QQDS magnetic spectrometer is being installed. The facilities for in situ sample preparation in UHV are similar. These spectrometers are described in detail and recent applications are discussed.

Publ.-Id: 6542 - Permalink


Electronic structure and mechanical properties of Cr7C3
Music, D.; Kreissig, U.; Mertens, R.; Schneider, J. M.;
We have studied the Dr7C3 phase by means of ab initio calculations and found covalentionic Cr-C-Cr chains in a metallic matrix. Furthermore the structure of thin films, synthesized by Rf magnetron sputtering, is schown to be in good agreement with our theoretical prediction.
  • Physics Letters A 326(2004)5-6, 473-476

Publ.-Id: 6540 - Permalink


Cross-Section Measurement of Charged-Pion Photoproduction from Hydrogen and Deuterium
Zhu, L. Y.; Arrington, J.; Averett, T.; Et, A.;
We have measured the differential cross section for the b3;n࢐c0;-p and b3;n࢐c0;+ reactions at c.m. = 90° in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at E3.3 GeV exhibit a global scaling behavior for both c0;- and c0;+ photoproduction, consistent with the constituent counting rule and the existing c0;+ photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive c0;- to c0;+ photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.

Publ.-Id: 6539 - Permalink


Multiphonon vibrations at high angular momentum in 182Os
Pattison, L. K.; Cullen, D. M.; Smith, J. F.; Et, A.;
Evidence is presented for multiphonon excitations based on a high-spin (25) intrinsic state in the deformed nucleus 182Os. Angular momentum generation by this mode competes with collective rotation. The experimental data are compared with tilted-axis cranking calculations, supporting the vibrational interpretation. However, the lower experimental energies provide evidence that more complex interactions of states are playing a role.

Publ.-Id: 6538 - Permalink


Formation and evolution of sp2 clusters in amorphous carbon networks as predicted by molecular dynamics annealing simulations
Belov, A. Y.; Jäger, H. U.;
A comparative study of clustering of sp2-bonded atoms in the as-deposited and annealed tetrahedral amorphous carbon (ta-C) films is presented. The as-deposited ta-C with a grown-in compressive stress of ~10 GPa is modelled using amorphous networks generated by ion-beam film deposition simulations with a modified hydrocarbon potential of Brenner. The ta-C networks were annealed in the temperature range of 600-1200 K, using molecular-dynamics with the same interatomic potential. The size and type of the sp2 clusters were analysed as a function of the annealing temperature as well as the simulation parameters for the stress and temperature control. An essential finding of this study is that at the density less than 3.0 g/cm3 the structure of ta-C can become unstable with respect to formation of large sp2 clusters. The influence of the sp2 clustering on the film stress is also discussed.
Keywords: tetrahedral amorphous carbon, simulation, thermal stability, microstructure
  • Diamond and Related Materials 14(2005)1014-1018

Publ.-Id: 6537 - Permalink


Precise measurement of the 7Be (p, gamma) 8B S factor
Junghans, A. R.; Mohrmann, E. C.; Snover, K. A.; Et, A.;
We present new measurements of the 7Be(p,gamma)8B cross section from pc.m. = 116 to 2460 keV (where c.m. means center-of-mass), which incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17(0) = 22.1±0.6(expt)±0.6(theor) eV b based on data from pc.m. = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low-energy data. We compare our results to other S17(0) values extracted from both direct [7Be(p,gamma)8B] and indirect (Coulomb-dissociation and heavy-ion reaction) measurements, and show that the results of these three types of experiments are not mutually compatible. We recommend a "best" value, S17(0) = 21.4±0.5(expt)±0.6(theor) eV b, based on the mean of all modern direct measurements below the 1+ resonance. We also present S factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S17(20) = 21.4±0.6(expt)±0.6(theor) eV b, and the recommended value is S17(20) = 20.6±0.5(expt)±0.6(theor) eV b.

Publ.-Id: 6536 - Permalink


Electromagnetic-induced fission of 238U projectile fragments, a test case for the production of spherical super-heavy nuclei
Heinz, A.; Schmidt, K.-H.; Junghans, A. R.; Et, A.;
Isotopic series of 58 neutron-deficient secondary projectiles (205,206At, 205,209Rn, 208,212,217,218Fr, 211,223Ra, 215,226Ac, 221,229Th, 226,k231Pa, 231,234U) were produced by projectile fragmentation using a 1 A GeV 238U beam. Cross sections of fission induced by nuclear and electromagnetic interactions in a secondary lead target were measured. They were found to vary smoothly as a function of proton and neutron number of the fissioning system, also for nuclei with large ground-state shell effects near the 126-neutron shell. No stabilization against fission was observed for these nuclei at low excitation energies. Consequences for the expectations on the production cross sections of super-heavy nuclei are discussed.

Publ.-Id: 6535 - Permalink


Towards strangeness saturation in central heavy ion collisions at high-energies
Cleymans, J.; Kämpfer, B.; Wheaton, S.;
Analyses of the centrality binned identified hadron multiplicities at SPS (Ýa;s = 17 AGeV) and RHIC (Ýa;s = 130 AGeV) within the statistical-thermal model point to strangeness saturation with increasing centrality and energy

Publ.-Id: 6534 - Permalink


Annual Report 2003 - Institute of Nuclear and Hadron Physics
Enghardt, W.; Fahmy, K.; Grosse, E.; Kämpfer, B.; Schneidereit, C.; Wagner, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-401 2004

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Publ.-Id: 6533 - Permalink


Dipole and quadrupole excitations in 88Sr up to 6.8 MeV
Käubler, L.; Schnare, H.; Schwengner, R.; Prade, H.; Dönau, F.; von Brentano, P.; Eberth, J.; Enders, J.; Fitzler, A.; Fransen, C.; Grinberg, M.; Herzberg, R.-D.; Kaiser, H.; von Neumann-Cosel, P.; Pietralla, N.; Richter, A.; Rusev, G.; Stoyanov, C.; Wiedenhöver, I.;
Dipole and quadrupole excitations in the semimagic N=50 Nucleus 88Sr were investigated at the superconducting Darmsatdt linear accelerator S-DALINAC with bremsstrahlung of an endpoint energy of 6.8 MeV. Many new dipole excitations could be identified, and their reduced transition probabilities were determined. The experimental findings are discussed in the context of quasiparticle-phonon-model and shell-model calculations. A breaking of the N=50 core is essential to describe the structure of the observed excitations. The two-phonon quadrupole-octupole Jpi=1- state exhibits unusual features which are presently not understood.
Keywords: Nuclear resonance fluorescence, quasiparticle-phonon model, shell model.

Publ.-Id: 6531 - Permalink


[Re6Q7O(3,5-Me2PzH)6]Br2*3,5-Me2PzH (Q = S, Se) - new octahedral rhenium cluster complexes with organic ligands: original synthetic approach and unexpected ligand exchange in cluster core
Mironov, Y. V.; Shestopalov, M. A.; Brylev, K. A.; Yarovoi, S. S.; Romanenko, G.; Fedorov, V. E.; Spies, H.; Pietzsch, H.-J.; Stephan, H.; Geipel, G.; Bernhard, G.; Kraus, W.;
Two new octahedral rhenium cluster complexes, [Re6S7O(3,5-Me2PzH)6]Br2*3,5-Me2PzH and [Re6Se7O(3,5-Me2PzH)6]Br2*3,5-Me2PzH, with the organic ligand 3,5-dimethylpyrazole (3,5-Me2PzH) have been synthesized by reaction of rhenium chalcobromides Cs3[Re63-Q7Br)Br6] (Q = S, Se) with molten dimethylpyrazole. During the reaction all six apical bromine ligands of the cluster complexes are substituted by the organic ligand which is coordinated via the aromatic nitrogen N2. Additionally, the inner ligand μ3-Br in the cluster core [Re63-Q7Br)]3+ is substituted by oxygen given cluster cores, [Re63-Q7O)]2+, with mixed chalcogene/oxygen ligands.
Keywords: Rhenium, Cluster compounds, Ligand exchange, Organic ligands, Structure elucidation, Laser Fluorescence Spectroscopy
  • European Journal of Inorganic Chemistry (2005)4, 657-661

Publ.-Id: 6530 - Permalink


Pegylation of 1,4,8,11-Tetraazacyclotetradecane (Cyclam) and its Copper(II) Complexation
Stephan, H.; Geipel, G.; Bernhard, G.; Appelhans, D.; Tabuani, D.; Komber, H.; Voit, B.;
Two novel star-like cyclam derivatives with appended four amino groups and four PEG-arms have been synthesized. The complex formation of cyclam and the cyclam derivatives and with Cu(II) has been studied by UV-Vis and time-resolved laser-induced fluorescence (TRLFS) measurements. The cyclam ligands investigated form 1:1 complexes with Cu(II). Rapid complex formation was found for cyclam and the pegylated derivative. By way of contrast, complete attainment of complexation between Cu(II) and cyclam ligand having external primary amino groups needs approx. 1 hour. By TRLFS measurements a quench effect of the Cu(II) on the fluorescence of the ligand was found. This behaviour was used to determine the complex formation between Cu(II) and the ligands.
  • Tetrahedron Letters 46(2005), 3209-3212

Publ.-Id: 6529 - Permalink


Fluid mixing and flow distribution in the reactor circuit - Part 1: Measurement data base
Rohde, U.; Kliem, S.; Höhne, T.; Karlsson, R.; Hemström, B.; Lillington, J.; Toppila, T.; Elter, J.; Bezrukov, Y.;
Experimental investigations and Computational Fluid Dynamics (CFD) calculations on coolant mixing in Pressurised Water Reactors (PWR) have been performed within the EC project FLOMIX-R. The project aims at describing the mixing phenomena relevant for both safety analysis, particularly in steam line break and boron dilution scenarios, and mixing phenomena of interest for economical operation and the structural integrity. Measurement data from a set of mixing experiments have been gained by using advanced measurement techniques with enhanced resolution in time and space. Slug mixing tests simulating the start-up of the first main circulation pump are performed with two 1:5 scaled facilities: the Rossendorf Coolant Mixing model ROCOM and the Vattenfall test facility. Additional data on slug mixing in a VVER-1000 type reactor have been gained at a 1:5 scaled metal mock-up at EDO Gidropress. Experimental results on buoyancy driven mixing of fluids with density differences have been obtained at ROCOM and the Fortum PTS test facility.
Concerning mixing phenomena of interest for operational issues and thermal fatigue, flow distribution data available from commissioning tests at PWRs and VVER are used together with the data from the ROCOM facility as a basis for the flow distribution studies.
In part 1 of the paper, the experiments performed are described, results of the mixing experiments are shown and discussed. In part 2, efforts on computational fluid dynamics codes validation on selected mixing tests under steady-state flow conditions will be reported about. The application of Best Practice Guidelines in code validation will be demonstrated.
Keywords: nuclear reactor, boron dilution, turbulent mixing, pre-stressed thermal shock, measurement data, wire mesh sensor, test facility
  • Nuclear Engineering and Design, 235(2005), 421-443

Publ.-Id: 6528 - Permalink


PWR Vessel Failure Experiments & Analysis
Sehgal, B. R.; Willschuetz, H.-G.;
For calculations of Lower Head Failure experiments like FOREVER it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model is developed based on a commercial Finite-Element-code. The CFD module is used to calculate the thermodynamics. The resulting temperature field of the vessel wall is applied to the mechanical model. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evaluation of the failure times a damage model is applied.
After pre- and post-test calculations of the ealier FOREVER-experiments, pre-test calculations for the forthcoming experiments were performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios.
After analyzing the results of the calculations, it seems to be advantageous to provide a vessel support, which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it may be advantageous to install a passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

Keywords: Core Melt Down Accident, Temperature Field and Creep Simulation, Accident Mitigation Strategy
  • Lecture (Conference)
    PHARE-Seminar, 13.-17.09.2004, Bulgaria, BG 01.10.01

Publ.-Id: 6527 - Permalink


Lead Corrosion in Soils: A Literature Review
Scheinost, A.;
wird nachgereicht
  • Invited lecture (Conferences)
    International Symposium: Sport Shooting and the Environment - Sustainable Use of Lead Ammunition, 09.-10.09.2004, Rome, Italy

Publ.-Id: 6526 - Permalink


Reduction of the annealing temperature of radiation-induced defects in ion-implanted MOS structures
Kaschieva, S.; Dmitriev, S. N.; Skorupa, W.;
Si-SiO2 structures irradiated with 11-MeV electrons for 10 s and then implanted with B+ ions with an energy of 10 keV at a dose of 1.0×1012 cm-2 through the oxide were annealed at different temperatures. MOS capacitors including such oxide layers were studied by quasi-static C/V and thermally stimulated current (TSC) methods. A comparison of the radiation defect annealing of double-treated (electron-irradiated and ion-implanted) samples and of implanted-only samples was carried out. It is shown that a preceding low-dose high-energy electron irradiation of the samples leads to a lowering of the annealing temperature of radiation defects introduced by ion implantation. After annealing at 500 °C for 15 min, no TSC spectra for the double-treated samples were observed. The spectra of the other samples (which were not previously irradiated) showed that after the same thermal treatment only some of the radiation defects introduced by ion implantation are annealed. The difference between the annealed interface state density of previously electron-irradiated and current MOS structures is also demonstrated. A possible explanation of the results is proposed .

Publ.-Id: 6524 - Permalink


Acoustic and magnetic anomalies near the saturation field of the S=1/2 antiferromagnetic Heisenberg chain studied on a Cu(II) coordination polymer - art. no. 092403
Wolf, B.; Zherlitsyn, S.; Luthi, B.; Et, A.;
By means of magnetic measurements as a function of temperature and magnetic field, the coordination polymer Cu(II)-2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene has been identified as a model system for a homogeneous antiferromagnetic S=1/2 Heisenberg spin chain with a moderate exchange-coupling constant |J| = 21.5 K/kB. Measurements of the longitudinal elastic constant in pulsed fields up to 50 T, i.e., across the saturation field gmu(B)B(S)=2|J|, reveal a pronounced acoustic anomaly near BS at T<|J|kB. We show that this feature is directly related to the shape of the magnetization curve and thus represents a generic property of a one-dimensional S=1/2 Heisenberg antiferromagnet with finite spin-lattice interaction.

Publ.-Id: 6522 - Permalink


Low-dimensional quantum spin systems in pulsed magnetic fields
Wolf, B.; Zherlitsyn, S.; Low, U.; Luthi, B.; Pashchenko, V.; Lang, M.;
Low-dimensional spin systems in high magnetic fields reveal new and unexpected physical phenomena. Typical examples are the distinct plateaus in the magnetization found in quasi- 1d and 2d compounds. Even for the well known case of the quasi-1d homogeneous Heisenberg spin chain or its dimerized variant, unexpected elastic anomalies can be detected in high magnetic fields. Since the exchange constants of these low-dimensional spin systems are of the order of the dominant energy scale, pulse-field experiments are particularly well suited for investigations of the magnetic properties. In this contribution we present and discuss our results for selected low-dimensional compounds such as the homogeneous antiferromagnetic Heisenberg spin chain Cu(II)-bispyrazoldihydroxybenzene, which is a new quasi-1d Cu(II)-coordination polymer, the dimerized spin chain (VO)2P2O7, and the plateau systems SrCU2(BO3)2 and NH4CUCl3.
  • Physica B 346(2004), 19-26

Publ.-Id: 6521 - Permalink


K+- and K--production in heavy-ion collisions at SIS energies
Forster, A.; Böttcher, I.; Grosse, E.;
The production and the propagation of K+- and of K--mesons in heavyion collisions at beam energies of 1 to 2 A GeV have systematically been investigated with the Kaon Spectrometer (KaoS) at the SIS at the GSI. The ratio of the K+-production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. At 1.5 A GeV a comprehensive study of the K+- and of the K--emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K-/K+ ratio is found to be nearly constant as a function of the collision centrality. The spectral slopes and the polar emission patterns are different for K- and K+. These observations indicate that K+-mesons decouple earlier from the reaction zone than K--mesons.
  • Journal of Physics G 30(2004)1, S393-S400

Publ.-Id: 6520 - Permalink


System-size dependence of strangeness saturation
Cleymans, J.; Kämpfer, B.; Steinberg, P.; Wheaton, S.;
The final state in heavy-ion collisions has a higher degree of strangeness saturation than the one produced in collisions between elementary particles such as p-p or p-(p) over bar. A systematic analysis of this phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider and for Au-Au collisions at RHIC and at AGS energies. Strangeness saturation is shown to increase smoothly with the number of participants at AGS, CERN and RHIC energies.
  • Journal of Physics G 30(2004)1, S595-S598

Publ.-Id: 6519 - Permalink


Pinhole interferometry with coherent hard X-rays
Leitenberger, W.; Wendrock, H.; Bischoff, L.; Weitkamp, T.;
This paper discusses the experimental realisation of two types of X-ray interferometer based on pinhole diffraction. In both interferometers the beam splitter was a thin metal foil containing micrometer pinholes to divide the incident X-ray wave into two coherent waves. The interference pattern was studied using an energy-dispersive detector to simultaneously investigate in a large spectral range the diffraction properties of the white synchrotron radiation. For a highly absorbing pinhole mask the interference fringes from the classical Young's double-pinhole experiment were recorded and the degree of coherence of X-rays could be determined. In the case of low absorption of the metal foil at higher X-ray energies (> 15 keV) the interference pattern of a point diffraction interferometer was observed using the same set-up. The spectral refraction index of the metal foil was determined.

Downloads:

Publ.-Id: 6518 - Permalink


Slow highly charged ions for nanoscale surface modifications
Kentsch, U.; Landgraf, S.; Schmidt, M.; Et, A.;
With the Dresden EBIT (electron beam ion trap) a room temperature, compact and long-term stable source of slow highly charged ions (HCIs) has been developed and prepared for small series production. A wide spectrum of ions such as Ar18+, Fe24+ and Xe44+ have been produced and extracted with energies less than q x 10 keV (q - ion charge). At ion-surface interactions the high neutralization energy of the ionic projectiles leads to high power densities of 10(12)-10(13) W/cm(2) at the surface. Thus, these ions can produce nanoscale material modifications and can be used for surface analysis techniques as well. Examples of extracted and magnetically analyzed ion beams are given. Fields of applications of slow highly charged ions are summarized.

Publ.-Id: 6517 - Permalink


Microstructure of beta-FeSi2 buried layers synthesis by ion implantation
Ayache, R.; Richter, E.; Bouabellou, A.;
A buried layer of iron disilicide was synthesized by ion implantation in (111) Si p-type maintained at 500 degreesC using 195 keV Fe ions with a dose of 2 x 10(17) at./cm(2), followed by annealing in a N-2 atmosphere at 850 degreesC for 90 min. The investigation of the phase composition is carried out by Rutherford backscattering spectrometry (RBS), whereas the structural characterization is obtained by means of both X-ray diffraction (XRD) pole figure and cross-sectional transmission electron microscopy (XTEM). The precipitates favor epitaxial growth with respect to (111) Si planes with epitaxial relationships (220) beta-FeSi(2)parallel to(111) Si and/or (202) beta-FeSi(2)parallel to(111) Si. A mixture of beta-FeSi2 and alpha-FeSi2 Silicides is observed in the as-implanted state. After annealing of the samples at 1000 degreesC, the XRD pole figures show the transition from beta-phase to alpha-phase.
  • Nuclear Instruments and Methods in Physics Research B 216(2004), 137-142

Publ.-Id: 6516 - Permalink


Multidimensional cosmological models: Cosmological and astrophysical implications and constraints
Günther, U.; Starobinsky, A.; Zhuk, A.;
  • Physical Review D 69(2004), 044003

Publ.-Id: 6515 - Permalink


Is C-11-choline the most appropriate tracer for prostate cancer?
Zophel, K.; Kotzerke, J.;

Publ.-Id: 6511 - Permalink


Intranuclear cascade plus percolation plus evaporation model applied to the C-12+Au-197 system at 1 GeV/nucleon
Volant, C.; Turzo, K.; Trautmann, W.; Et, A.;
The nucleus-nucleus Liege intranuclear-cascade+percolation+evaporation model has been applied to the C-12+Au-197 data measured by the INDRA-ALADIN collaboration at GSI. After the intranuclear cascade stage, the data are better reproduced when using the Statistical Multiframentation Model as afterburner. Further checks of the model are done on data front the EOS and KAOS collaborations.
  • Nuclear Physics A 734(2004), 545-548

Publ.-Id: 6510 - Permalink


Chemical and nuclear studies of hassium and element 112
Gaggeler, H. W.; Bruchle, W.; Dullmann, C. E.; Et, A.;
  • Nuclear Physics A 734(2004), 208-212

Publ.-Id: 6509 - Permalink


Chemical identification and properties of element 112
Yakushev, A. B.; Zvara, I.; Oganessian, Y. T.; Dmitriev, S. N.; Eichler, B.; Hübener, S.; Sokol, E. A.; Turler, A.; Yeremin, A. V.; Et, A.;
  • Nuclear Physics A 734(2004), 204-207
  • Radiochimica Acta 91(2003)8, 433-439

Publ.-Id: 6508 - Permalink


Magnetic dipole and electric quadrupole rotational structures and chirality in Rh-105
Oliveira, J. R. B.; Cybulska, E. W.; Medina, N. H.; Et, A.;
The Rh-105 nucleus has been studied with the Mo-100(B-11, alpha2ngamma) reaction at 43 MeV incident energy. A rich variety of structures was observed at high and low spins, using gamma-gamma-t and gamma-gamma-particle coincidences and directional correlation ratios. A gamma-vibrational band was observed for the first time in this nucleus. A new structure based on the intruder 1/2(+)[431] proton orbital was identified. Four magnetic dipole bands have also been observed at high spin, three of which have negative parity and have similar characteristics: they are very regular in energy spacing, presenting nearly constant alignments and large values of B(M1)/B(E2) ratios. Two of them are nearly degenerate in excitation energy and could be chiral partners. The pig(9/2)xnuh(11/2)(g(7/2),d(5/2)) configuration is tentatively assigned for these bands, with the angular momenta of the proton and neutron intruders and the collective angular momentum aligning along the three perpendicular axes of the triaxial core, as predicted by tilted axis cranking calculations.
  • Physical Review C 6902(2004)2, 4317

Publ.-Id: 6507 - Permalink


Recent investigations and applications of thin diamond-like carbon (DLC) foils
Liechtenstein, V. K.; Ivkova, T. M.; Olshanski, E. D.; Golser, R.; Kutschera, W.; Steier, P.; Vockenhuber, C.; Repnow, R.; Hahn, R.; Friedrich, M.; Kreissig, U.;
In previous experiments, diamond-like carbon (DLC) foils which are being produced at Kurchatov Institute, have proven well suited as long-lived stripper foils for high-energy heavy-ion tandem accelerators and ultra-thin secondary-electron (SE) emitting foils for TOF spectrometers. This paper presents the recent advances in DLC targetry with main emphasis given to development and applications of ultra thin foils (maximum diameter up to 70 mm) with high uniformity and minimal possible effective thickness, the latter has been evaluated by measurements of both energy loss and angular scattering of heavy ions transmitting through the foils. Comparative lifetimes of DLC stripper foils irradiated with high intensity (150 muA) He+ beams at 2 MeV are reported, which demonstrate the favorable use of DLC foils as supplemental strippers at RFQ linacs. In conclusion, the attractive results of application of ultra-thin DLC foils to TOF detectors for heavy ion AMS as well as to compact tandem accelerators are presented.

Publ.-Id: 6506 - Permalink


Ion beam studies of TiNxOy thin films deposited by reactive magnetron sputtering
Alves, E.; Ramos, A. R.; Barradas, N. P.; Et, A.;
Titanium oxynitride compounds exhibit interesting properties for applications in fields ranging from protective/decorative coatings to solar panels. The properties of TiNxOy are related to the oxide/nitride ratio and can be tailored playing with this ratio. In this work we studied the influence of substrate bias voltage and flow rate of reactive gases (a mixture of N-2 and O-2) on the properties of TiNxOy films. The films were deposited on steel substrates at a constant temperature of 300 degreesC by r.f. reactive magnetron sputtering. The depositions were carried out from a pure Ti target. The composition throughout the entire thickness was determined by Rutherford backscattering spectrometry. To obtain information on the profile of light elements (0, N) and detect the presence of hydrogen on the films, heavy ion elastic recoil detection analysis was performed. The results indicate a nearly constant stoichiometry through the entire analysed depth. The colouration varied from the shiny golden for low oxygen contents (characteristic of TiN films) to dark blue for higher oxygen contents. The electrical resistivity of the samples was obtained at room temperature and the values varied from approximately 120 muOmega cm for a sample with very low oxygen content to values up to 350 muOmega cm, for the highest oxygen contents.
  • Surface & Coatings Technology 180-181(2004), 372-376

Publ.-Id: 6499 - Permalink


Spectroscopic quadrupole moments of high-spin isomers in Pb-193
Balabanski, D.; Ionescu-Bujor, M.; Iordachescu, A.; Et, A.;
The quadrupole interaction of high-spin isomers in Pb-193 implanted into solid Hg cooled at a temperature T=170 K has been investigated by the time-differential perturbed gamma-ray angular-distribution method. Spectroscopic quadrupole moment values of \Q\=0.22(2) eb and 0.45(4) eb have been deduced for the 21/2(-) and 33/2(+) three-neutron states, respectively. A much higher value \Q(s)\=2.84(26) eb has been determined for the 29/2(-) isomer, the band head of a magnetic rotational band.

Publ.-Id: 6495 - Permalink


High-spin states in the vibrational nucleus Cd-114
Jungclaus, A.; Algora, A.; Axiotis, M.; Borge, M. J. G.; Fernandez, M. A.; Gadea, A.; Galindo, E.; Hausmann, M.; Lenzi, S.; Martinez, T.; Napoli, D. R.; Piqueras, I.; Schwengner, R.; Ur, C.;
High-spin states of the neutron-rich vibrational nucleus Cd-114 have been studied using the incomplete fusion reaction Pd-110(Li-7, p2n) and the GASP spectrometer in conjunction with the ISIS Si ball. About 50 new states with excitation energies up to 7 MeV and angular momentum I less than or equal to (18(+)) were observed and for many of them, spin and parity could be firmly assigned. The band-like stuctures in Cd-114 are compared to the corresponding ones in the even-even neighbour Cd-112.

Publ.-Id: 6494 - Permalink


Dissipative continuum model for self-organized pattern formation during ion-beam erosion
Facsko, S.; Bobek, T.; Stahl, A.; Kurz, H.; Dekorsy, T.;
A continuum model, based on the damped Kuramoto-Sivashinsky equation, is shown to reproduce the morphology evolution during ion sputtering quite successfully. In a very narrow range of the damping parameter alpha, the alignment of the structures into hexagonal domains is obtained under normal incidence of ions with striking resemblance to the experimentally observed dot patterns. The origin of this damping factor is discussed.
  • Physical Review B 6915(2004)15, 3412-3412

Publ.-Id: 6493 - Permalink


Gross shell structure at high spin in heavy nuclei
Deleplanque, M. A.; Frauendorf, S.; Pashkevich, V. V.; Chu, S. Y.; Unzhakova, A.;
Experimental nuclear moments of inertia at high spins along the yrast line have been determined for a large number of nuclei. They are found to systematically differ from the rigid-body values. The difference is attributed to shell effects which are well described by a rotating Woods-Saxon potential. The data and quantal calculations are interpreted by means of the semiclassical periodic orbit theory. From this new perspective, features in the moments of inertia as a function of neutron number and spin as well as their relation to the shell energies can be understood. Gross shell effects persist up to the highest angular momenta observed.
  • Physical Review C 6904(2004)4, 4309-4309

Publ.-Id: 6492 - Permalink


Effect of N-2 to C2H2 ratio on r.f. plasma surface treatment of austenitic stainless steel
El-Rahman, A. M.; El-Hossary, F. M.; Fitz, T.; Negm, N. Z.; Prokert, F.; Pham, M. T.; Richter, E.; Möller, W.;
Adding C2H2 gas to nitrogen gas during r.f. plasma processing has significant influence on the properties of 304 austenitic stainless steel. The elemental depth profiles of the compound layer were investigated by glow discharge optical spectroscopy. Different treatment gas compositions of N-2/C2H2 mixtures (0-100% in steps of 10 or 5% in some cases) have been investigated. The total gas pressure during the plasma processing was 8.4 x 10(-2) mbar. The sample temperature was approximately 550 degreesC with an insignificant variation for different gas compositions. A high rate of diffusion of carbonitriding has been obtained without initial sputter removal of the surface oxide layer, which demonstrates that the surface oxide layer does not play a crucial role during r.f. plasma carburizing and carbonitriding of stainless steel. The nitrogen concentration and the compound layer thickness increase, when 10% of C2H2 is added. With further increase in the C2H2 ratio, they decrease again gradually. The carbon depth profiles for the same samples show lower concentration and opposite tendency with respect to the nitrogen content. X-ray diffraction was used to characterize the microstructure of the compound layers. Fe2N, Fe3N, CrN, nitrogen-expanded austenite (gamma(n)) and carbon-expanded austenite (gamma(c)) phases are detected. The relative proportions of the phases are critically dependent on the N-2/C2H2 ratio. Depending on the N-2/C2H2 ratio, the microhardness value increases by a factor between 2 and 6. The carbonitrid layer exhibits a corrosion resistance better than pure nitrided and carburized layers.
  • Surface & Coatings Technology 183(2004)2-3, 268-274

Publ.-Id: 6491 - Permalink


Structure and phase transformations of AISI M2 high-speed tool steel treated by PIII and subsequent compression plasma flows of nitrogen
Uglov, V. V.; Anishchik, V.; Vetushka, A. M.; Rumyanceva, I. N.; Richter, E.;
The effect of 'double' treatment (plasma immersion ion implantation and subsequent compression plasma flows) on microstructure, element and phase composition, as well as on microhardness properties of AISI M2 high-speed tool steel has been studied. Such methods as Auger electron spectrometry (AES), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis and scanning electron microscopy (SEM) allowed us to obtain the data suggesting that under such treatment a martensite-austenite conversion and the formation of a deep (approx. 35 mum) three-layered structure take place. It has been established that transformations of near-surface regions are associated with the complete dissolution of the initial (Fe, Cr)(3)(W, Mo)(3)C carbide (less than or equal to 5-10 mum) and the formation of gamma(N,M) expanded austenite doped with atoms of nitrogen, carbon and alloying metals M=W, Mo, Cr.

Publ.-Id: 6490 - Permalink


Correlation between magnetic properties of CoFe single and CoFe/SiO2multi-layer thin films and their microstructure, texture and internal stress state
Dieter, S.; Pyzalla, A.; Bauer, A.; Schell, N.; McCord, J.; Seemann, K.; Wanderka, N.; Reimers, W.;
CoFe single and multi-layer systems are diposited by a radio-frequency sputter process. Thickness, roughness, morphology, texture and internal stress state of the layers are determined by X-ray reflectometry, transmission electron microscopy, and diffraction methods. The texture and the internal stress of the layers depend strongly on the parameters of the sputter process. The magnetic properties of the layers are determined from hysteresis curve measurements and magneto-optical Kerr microscopy. A strong correlation between the texture, the internal stress and the magnetic properties of the CoFe layers os observed.
Keywords: Reflectometry Microstructure Residual stresses Texture Coercivity Kerr microscopy
  • Zeitschrift für Metallkunde 95/2004 164-175

Publ.-Id: 6489 - Permalink


Exclusive eta production in proton-proton reactions
Balestra, F.; Dressler, R.; u. a.;
Differential cross sections for the exclusive reaction pp-->ppeta observed via the eta-->pi(+)pi(-)pi(0) decay channel have been measured at T-beam=2.15 GeV, 2.50 GeV, and 2.85 GeV (excess energies 324 MeV, 412 MeV, and 554 MeV). The influence of the N(1535)S-11 resonance is clearly seen in the invariant mass and momentum dependent differential cross sections. The extracted resonance parameters are compatible with existing data. No significant evidence for further resonance contributions has been found. In addition, angular distributions of the ppeta final state have been measured. The polar angle distribution of the eta shows an anisotropy with respect to the beam axis for the lowest beam energy, which vanishes for the higher energies. The sign of this
anisotropy is negative and expected to be sensitive to the dominant production mechanism. In contrast, the proton polar angle in the pp rest frame tends to be more strongly aligned along the beam axis with increasing beam energy. The analyzing power A(y) is compatible with zero for all beam energies.
Keywords: meson production

Publ.-Id: 6488 - Permalink


Verlässlichere Prognosen zur Schadstoffausbreitung mit Hilfe einer mineral-spezifischen Sorptionsdatenbank des Forschungszentrums Rossendorf (FZR)
Brendler, V.; Richter, A.; Bernhard, G.;
Anwendungsbereiche der hier vorgestellten thermodynamischen Sorptionsdatenbank RES³T (Rossendorf Expert System for Surface and Sorption Thermodynamics) sind Deponien unterschiedlichster Art und ihre Sickerwässer, aber auch die Sicherung von kontaminierten Militärstandorten und Industrieanlagen. Neben chemo-toxischen Abfällen wird zudem die Lagerung radioaktiver Abfälle adressiert, wobei sowohl das Wirtsgestein als auch das Deckgebirge erfasst wird, und damit nicht nur für ein einziges Endlagerumfeld (z.B. Salzstock) Relevanz besitzt. Und schließlich stellt die Datenbank auch einen Beitrag dar zur Problematik der Stilllegung, Verwahrung oder Rekultivierung von Bergwerken (Uranerz, Kupferschiefer, Steinkohle) und offenen Tagebauen (Steinkohle, Braunkohle). Die avisierten Anwender umfassen Behörden, Gutachter, die WISMUT GmbH, Ingenieurbüros sowie universitäre und außeruniversitäre Forschungseinrichtungen.
Keywords: Sorption, Datenbank, Oberflächenkomplexierung, Schadstoffausbreitung, reaktiver Transport, Sanierung, Endlager, Deponie, Prognose, Actiniden
  • Umwelt-Report (2004), 10-11(Ausgabe Dresden), 56-57(Ausgabe Chemnitz)

Publ.-Id: 6487 - Permalink


Measurement Techniques for Multiphase Flows, Multiphase Flows in Industrial Applications CFX-Germany
Prasser, H.-M.;
keiner
  • Invited lecture (Conferences)
    ANSYS-CFX/FZR Workshop, FZ-Rossendorf 28.-30.04.2003, Invited lecture at Short Course on Multiphase Flows

Publ.-Id: 6484 - Permalink


Excitation function of elliptic flow in Au + Au collisions and the nuclear matter equation of state
Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, L.; Berek, G.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Leifels, Y.; Lopez, X.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; de Schauenburg, B.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stockmeier, M. R.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.-G.; Yushmanov, I.; Zhilin, A.;
We present measurements of the excitation function of elliptic flow at midrapidity in Au + Au collisions at beam energies from 0.09 to 1.49 GeV per nucleon. For the integral flow, we discuss the interplay between collective expansion and spectator shadowing for three centrality classes. A complete excitation function of transverse momentum dependence of elliptiv flow is presented for the first time in this energy range, revealing a rapid change with incident energy below 0.4 AGeV, followed by an almost perfect scaling at the higher energies. The equation of state of compressed nuclear matter is addressed through comparisons to microscopic transport model calculations.
  • Physics Letters B 612(2005), 173

Downloads:

Publ.-Id: 6481 - Permalink


Spectroscopic characterization of the uranium carbonate andersonite Na2Ca[UO2(CO3)3]*6H2O
Amayri, S.; Arnold, T.; Reich, T.; Foerstendorf, H.; Geipel, G.; Bernhard, G.; Massanek, A.;
The uranium carbonate andersonite Na2Ca[UO2(CO3)3]*6H2O was synthesized and identified with classical analytical and spectroscopic methods. The classical methods applied were X-ray powder diffraction (XRD), nitric acid digestion, and Scanning Electron Microcopy combined with Energy-Dispersive Spectroscopy (SEM/EDS). To spectroscopically characterize andersonite, Time-Resolved Laser-induced Fluorescence Spectroscopy (TRLFS), X-ray Photoelectron Spectroscopy (XPS), and Fourier-Transformed InfraRed spectroscopy (FT-IR) were used. Natural and synthetically prepared andersonite samples were characterized with the non-destructive TRLFS by six fluorescence emission bands at 470.6, 486.1, 505.4, 526.7, 549.6, and 573.9 nm. In addition, andersonite was characterized by FT-IR measurements by the appearance of the asymmetric stretching vibration of the uranyl cation (v3 UO22+) at 902 cm-1 with a shoulder at 913 cm-1 and by XPS measurements. The intensity of the measured XPS lines was used to verify the composition of the synthetic andersonite sample. The measured intensity ratios and the calculated atomic ratios agree with the stoichiometry of Na2Ca[UO2(CO3)3]*6H2O. The results of both the qualitative and quantitative XPS analysis confirmed the formation of andersonite. The spectral features of the U 4f electrons and the distinct splitting of the U 6p3/2 electrons can be used to identify the [UO2(CO3)3]4- structural moiety.


These spectroscopic methods proved to be suitable to identify in a fingerprinting procedure secondary U(VI) phases in mixtures with other phases or as thin coatings on mineral and rock surfaces. The obtained spectroscopic information are of fundamental importance for uranyl(VI) adsorption studies, since such information are useful to identify the coordination environment and structure of unknown adsorbed uranium(VI) surface species on minerals surfaces.

Keywords: uranium, carbonate, andersonite, synthesis, TRLFS, XPS, FT-IR, spectroscopy

Publ.-Id: 6480 - Permalink


Compressive stress, preferred orientation and film composition in Ti-based coatings developed by plasma immersion ion implantation-assisted deposition
Mukherjee, S.; Prokert, F.; Richter, E.; Moeller, W.;
Plasma immersion ion implantation-assisted deposition has been employed to develop Ti-based coatings in the presence of reactive nitrogen environment. When TiN coatings have been developed on Al alloys, it has been observed that a large compressive stress develops in the coating, which can be reduced when the substrate bias is increased. The formation of stress is attributed to atomic peening effect that densifies a coating, whereas thermal spikes generated at high substrate bias reduce the stress. For TiAl coatings delivered from an alloy plasma source, the Al content decreases with increasing negative substrate bias. This is in agreement with the results of TRIDYN ballistic computer simulations, which confirm that the film composition is significantly influenced by preferential sputtering. The results indicate that time-averaged substrate bias is an ill-defined parameter to describe coating properties deposited by the above technique.
Keywords: Ion implantation; TiN; stress; TRIDYN
  • Surface & Coatings Technology 186(2004), 99-103

Publ.-Id: 6478 - Permalink


Contactless inductive flow tomography
Stefani, F.; Gundrum, T.; Gerbeth, G.;
The three-dimensional velocity field of a propeller driven liquid metal flow is reconstructed by a contactless inductive flow tomography (CIFT). The underlying theory is presented within the framework of an integral equation system that governs the magnetic field distribution in a moving electrically conducting fluid. For small magnetic Reynolds numbers this integral equation system can be cast into a linear inverse problem for the determination of the velocity field from externally measured magnetic fields. A robust reconstruction of the large scale velocity field is already achieved by applying the external magnetic field alternately in two orthogonal directions and measuring the corresponding sets of induced magnetic fields. Kelvin's theorem is exploited to regularize the resulting velocity field by using the kinetic energy of the flow as a regularizing functional. The results of the new technique are shown to be in satisfactory agreement with ultrasonic measurements.

Publ.-Id: 6477 - Permalink


Correlation between bonding structure and microstructure in fullerene-like carbon nitride thin films
Gago, R.; Jiménez, I.; Neidhardt, J.; Abendroth, B.; Caretti, I.; Hultman, L.; Möller, W.;
The bonding structure of highly ordered fullerene-like (FL) carbon nitride (CNx) thin films have been assessed by x-ray absorption near edge spectroscopy (XANES). In particular, samples with different degree of FL character (in terms of graphene plane alignment, extension, and cross-linking) have been analyzed to discern spectral signatures of the microstructure formation. The XANES spectra of FL-CNx films resemble that of graphitic CNx, indicating a sp2 character for C and N atoms. However, the evolution of the FL structure is promoted with the dominance of three-fold N over pyridine-like and cyanide-like bonding environments. In addition, the p*/s* ratio at the C(1s) edge is constant, independent of the change in FL character, while it decreases ~40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp3 hybrids with the development of FL structures and, additionally, that a different spatial localization of p electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could as such explain the outstanding elastic properties of FL-CNx.
  • Physical Review B, 71(2005)12, 5414

Publ.-Id: 6476 - Permalink


Breakdown of Burton-Prime-Slichter approach and lateral solute segregation in radially converging flows
Priede, J.; Gerbeth, G.;
A theoretical study is presented of the effect of a radially converging melt flow on the radial solute segregation in simple solidification models. We show that the classical Burton-Prim-Slichter (BPS) theory describing the effect of a diverging flow on the solute incorporation into the solidifying material breaks down for converging flows. The breakdown is caused by a divergence of the integral defining the effective boundary layer thickness which is the basic concept of the BPS theory. The divergence can formally be avoided by restricting the axial extension of the melt to a layer of finite height. This allows us to obtain radially uniform solutions for the solute distributions which, however, are valid only for weak melt flows with an axial velocity away from the solidification front comparable to the growth rate. There is a critical melt velocity for each growth rate at which the solution passes through a singularity and becomes physically inconsistent for stronger melt flows. Thus, the radially uniform solute distribution becomes incompatible with a converging flow exceeding the growth rate, and a radial segregation sets in. The solute distribution is analysed in detail for a solidification front presented by a disk of finite radius R0 subject to a converging melt flow. We obtain similarity and matched asymptotic solutions showing that the radial solute concentration depends on the radius r as ln1/3(R0/r) and ln(R0/r) close to the rim and at large distances from it, respectively. The converging flow causes a solute pile-up forming a logarithmic concentration peak at the symmetry axis which might be an undesirable feature for crystal growth processes.
  • Journal of Crystal Growth 285(2005), 261-269

Publ.-Id: 6475 - Permalink


Erneuerbare Energien: Das Beispiel Windenergie
Rindelhardt, U.;
Die Nutzung der Windenergie zur Stromerzeugung hat in den letzten Jahren ein beachtliches Niveau erreicht. Im Vortrag wird der gegenwärtige technische Entwicklungsstand vorgestellt. Ferner werden die mit der Aufnahme von großen fluktuierenden Mengen Windstromes im Höchstspannungsnetz auftretenden Probleme und Konsequenzen diskutiert.
Keywords: Windenergie
  • Lecture (others)
    Antrittsvorlesung, Technische Universität Chemnitz, 04.05.2004, Chemnitz, Germany

Publ.-Id: 6474 - Permalink


Grid connected PV systems in Saxony: A ten years review
Hiller, W.; Rindelhardt, U.; Voigtländer, I.;
Even in former East Germany, photovoltaic has being used increasingly for generating electricity. Through weaker buying power the absolute numbers of pv plants are far lower than in the western federal states, but a series of remarkable results was achieved nonetheless. This paper discusses the developments in the federal state Saxony.
It is based on long term results on selected photo-voltaic plants as well as data recorded by the regional electricity supplier Energieversorgung Ostsachsen (ESAG), Dresden, in 2002 and 2003 [1].
Keywords: photovoltaic plants
  • Contribution to proceedings
    EuroSun 2004, 20.-23.06.2004, Freiburg, Germany
    Procedings Vol. 3, 401-407
  • Lecture (Conference)
    EuroSun 2004, 20.03.-23.06.2004, Freiburg, Germany

Publ.-Id: 6472 - Permalink


Regional differences in cerebral blood flow and cerebral ammonia metabolism in patients with cirrhosis
Ahl, B.; Weissenborn, K.; van den Hoff, J.; Fischer-Wasels, D.; Köstler, H.; Hecker, H.; Burchert, W.;
Clinical and histopathological findings hint at regional differences in the brain's sensitivity to metabolic changes in cirrhosis. The aim of the present study was to examine regional differences in cerebral ammonia metabolism in patients with cirrhosis and grade 0-to-I hepatic encephalopathy (HE). 13N-ammonia, 15O-water positron emission tomography (PET) and magnetic resonance imaging (MRI) were performed. Quantitative values of cerebral blood flow (CBF) and the initial cerebral ammonia uptake rate (K1) were derived for several regions of interest from images of the desired parameters after interactive coregistration with the patients' MRI-studies. CBF (mL/mL/min), K1 (mL/mL/min), and the ammonia extraction fraction (K1/CBF) showed marked regional variance with the highest levels in the thalamus, the lenticular nucleus, and the cerebellum. In conclusion, the regional differences in cerebral ammonia uptake correspond to the distribution of histopathological changes in the brain of patients with cirrhosis as well as clinical features of HE, characterized by signs of basal ganglia and cerebellar dysfunction with corresponding signs of functional impairment, especially of the frontal cortex and cingulate gyrus.

Publ.-Id: 6471 - Permalink


UV Raman Spectroscopy of Boron Nitrides
Ferrari, A. C.; Reich, S.; Casiraghi, C.; Arenal De La Concha, R.; Loiseau, A.; Gago, R.; Abendroth, B.; Zhang, W. J.; Chan, C. Y.; Bello., I.; Robertson, J.;
Boron nitride is a remarkable material both for its fundamental properties and for applications [1]. It exists in different polytypes, the sp2 bonded hexagonal and rhombohedral structure and the sp3 cubic and wurzite phases. All phases are high band-gap semiconductors (>5 eV). Cubic boron nitride, c-BN, is of particular interest for its properties similar to diamond [1,2]. Physical or chemical vapor deposition of boron nitride films can often result in the growth of the less dense hexagonal BN (h-BN). BN nanotubes are also very interesting [3]. Their properties, as for carbon nanotubes, can be derived by studying the wrapping of a single layer of h-BN [3]. Boron Carbon Nitrides (BCN) thin films are also useful for hard coating applications and as semiconductors with variable gap [4]. Raman and Infrared spectroscopy are quick and non-destructive tools to assess the properties of materials. Infrared spectroscopy is the most widely used for boron nitrides. It is very sensitive to polar BN bonds. The spectra for c-BN and h-BN show distinct IR features [1]. Raman spectroscopy is rarely used because of its inferior sensitivity, especially in the case of thin films. This is opposite to diamond-like carbons, where Raman spectroscopy is a standard characterization tool [5]. However, Infrared spectroscopy has limitations. The substrate has to be either transparent or not highly reflective. Raman spectroscopy has no requirement on the substrate properties and can simultaneously give informantion on phase composition, crystallinity, size and stress. In order to successfully apply Raman scattering in boron nitrides its low sensitivity has to be overcome. This can be done by measuring the samples with an excitation energy closer to their band gap. Here we measure BN samples by UV Raman spectroscopy at 5.1 and 5.4 eV. This enhances the BN Raman cross-section and paves the way to making UV Raman scattering a standard tool for boron nitrides characterization. We studied the UV Raman spectra of a variety of boron nitride samples ranging from h-BN (bulk and thin film), c-BN (single crystals, thin and thick films), mixed h-BN and c-BN phases and BCN films with varying B, C and N content. The UV Raman spectra of c-BN and h-BN are so intense that a clear measurement of the second order Raman signal is possible. This allows us to probe for the first time non-zone center phonons and validate the predictions of first-principles calculations of BN properties [3,6]. For h-BN, whilst the high-energy optical phonons are in excellent agreement with theory, the ionic interaction was strongly underestimated for lower energies [6]. The first order UV Raman spectra of thin and nano-crystalline films also show the activation of non-zone center phonons and IR modes, such as the 800 cm-1 mode of h-BN. In BCN films the direct signature of BN bonds can be seen, being no more shadowed by the carbon phase.

1. P. B. Mirkarimi, K. F. McCarty, D. L. Mellin, Mat. Sci. Eng. R21, 47 (1997)
2. W. Zhang, S. Matsumoto, Q. Li, I. Bello, S. T. Lee, Adv. Funct. Mat. 12, 250 (2002)
3. L. Wirtz et al. Phys. Rev. B 68, 045425 (2003)
4. R. Gago et al. J. Appl. Phys. 92, 5177 (2002)
5. A.C. Ferrari, J. Robertson, Phys. Rev. B 61, 14095 (2000); 64 075451 (2001)
6. G. Kern, G. Kresse, J. Hafner, Phys. Rev. B 59, 8551 (1999)
  • Lecture (Conference)
    15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides & Silicon Carbide (DIAMOND 2004), 12-17 September 2004, Riva del Garda, Trentino, Italy

Publ.-Id: 6470 - Permalink


Efecto del Ar en películas CNxHy depositadas mediante ECR-CVD
Camero, M.; Gago, R.; Gómez-Aleixandre, C.; Albella, J. M.;
Carbon nitride films have been deposited by ECR-CVD, from Ar/CH4/N2 gas mixtures with different methane concentrations. Infrared Spectroscopy and Elastic Recoil Detection Analysis have been used for films characterisation and Optical Emission Spectroscopy for plasma analysis. Argon concentration in the gas mixture controls the growth rate as well as the composition of the film. In the proposed model, argon plays a key role in the activation of methane molecules. Also, during the growth of the film, two processes may be considered: i) Film formation and ii) Etching of the growing surface. Changing the gas mixture composition affects both processes, which results in films with different composition and structure as well as different deposition rates.
Keywords: Thin films; hydrogenated carbon nitride; ECR-CVD; Argon
  • Boletín de la Sociedad Española de Cerámica y Vidrio 43(2004), 491-493

Publ.-Id: 6469 - Permalink


X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment
Abendroth, B.; Gago, R.; Eichhorn, F.; Möller, W.;
Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2-10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress-release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials.
  • Applied Physics Letters 85(2004)24, 5905-5907

Publ.-Id: 6467 - Permalink


Interaction of nitrogen atoms in expanded austenite formed in pure iron by intense nitrogen plasma pulses
Piekoszewski, J.; Sartowska, B.; Walis, L.; Werner, Z.; Kopcewicz, M.; Prokert, F.; Stanislawski, J.; Kalinowska, J.; Szymczyk, W.;
The paper presents the results of experiments on modification of pure iron by high intense nitrogen pulsed-plasma treatment. The duration of nitrogen plasma pulses is approximately 1 µs, and the energy density amounts to about 5 J/cm2. Such pulses are capable to melt the surface layer of the substrate (1-2 µm) and to introduce a significant concentration of nitrogen into the molten layer. Nuclear reaction analysis (NRA), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) were used for characterisation of the treated samples. The main results of the data analysis are as follows:it has been stated that such treatment leads to gradual transformation of initial alpha-phase into austenitic gamma structure in which expanded austenite gammaN is present. Treatment with 20 pulses results in almost complete transformation and introduces a retained dose of nitrogen estimated as 5.5 x 1017 N/cm2. The susceptibility for expansion of the lattice transformed to austenite in this way is smaller than in the case when the steel subjected to conventional nitriding is orginally of austenite type. The analysis of the ratio of gamma to gammaN as a function of the nitrogen content provides a firm evidence that strong repulsion forces act between the first and the second nearst-neighbour nitrogen atoms in the fcc austenitic structure as a result of nitriding of pure iron by intense nitrogen plasma pulses.
Keywords: alpha-to-gamma phase transformation in iron; expanded austenite; intense nitrogen plasma pulses
  • Nukleonika 49(2004)2, 57-60

Publ.-Id: 6466 - Permalink


Materials analysis in archaeometrical studies - The cases of ceramics pigments and of gold objects
Constantinescu, B.; Bugoi, R.; Cojocaru, V.; Grambole, D.; Herrmann, F.; Popovici, D.;
The scientific analysis of archaeological objects ideally requires the availability of methods, which are simultaneously non-destructive, fast, universal, versatile, sensitive and multielemental. Analyses of source materials combined with analyses of the objects could distinguish from pieces produced in different regions. Our purpose is to help archaeologists to identify objects provenance (workshops, technologies, mines) and to explain different commercial, military and political aspects. We used 241Am source based XRF (X-ray Fluorescence), 3 MeV protons induced PIXE (Particle Induced X-ray Emission), 11 MeV proton activation analysis (PAA) and 3 MeV protons micro-PIXE methods. The above mentioned methods are complementary and they work better together. Some results on pigments from Cucuteni Neolithical and Iznik Medieval ceramics, especially the case of black (Manganese) and blue (Cobalt) colours are presented. We also report a study on ancient Dacian gold coins. The method used were XRF and PAA. Three groups of coins with different composition were found, corresponding to simple, complex and no monogram pieces. Possible historical conclusions are discussed. Finally, micro-PIXE results on some ancient gold objects from Romanian Pietrosa hoard are reported.
Keywords: XRF, PIXE, PAA, microPIXE, ceramics, pigments, gold
  • Rom. Journ. Phys. 48 (2003) 347-354

Publ.-Id: 6465 - Permalink


Synthesis and biological evaluation of silylated mixed-ligand 99mTc complexes with the [PNS/S] donor atom set
Fernandes, C.; Knieß, T.; Gano, L.; Seifert, S.; Spies, H.; Santos, I.;
New oxotechnetium compleses of general formula [99mTc(O)(PNS)(S(CH2)nOSiR3] (4-6) were synthesized by direct reduction of [[99mTcO4]- with stannous chloride, in the presence of the tridentate heterofunctionalized phosphine H2PNS and of the monodentate silylated thiols [HS(CH2)nOSiR3] (n=2, R=Ph (1); n=3, R=Ph (2); n=3, R=Et (3)). The mixed-ligand rhenium and technetium complexes of general formula [M(O)(PNS)(S(CH2)nOH] (n=2: M=99mTc, (7), M=Re, (7a); n=3: M=99m, (8), M=Re, (8a)) were also prepared. All the 99mTc complexes were obtained with high radiochemical purity (> 95 %), after purification by HPCL, and were characterized by comparison of their HPLC profiles with the ones obtained for the corresponding Re compounds. The silylated compounds 4-6 are stable in phosphate saline buffer (PBS) pH 7.4; rat plasma, human serum and whole blood, and do not bind to plasmatic proteins, and also do not challenge with glutathione. The biological behavior of [99mTc(O)(PNS)(S(CH2)nOH] (7, 8) and [99mTc(O)(PNS)(S(CH2)nOSiR3] (4-6) was studied. The effect of the pH on the cleavage of the O-Si bond in complexes 4-6 was also evaluated.
Keywords: Mixed-ligand complexes; 99mTc; Biological evaluation

Publ.-Id: 6464 - Permalink


Study of a liquid metal field ion emitter for the production of Si ions
Aidinis, C. J.; Bischoff, L.; Mair, G. L. R.; Londos, C. A.; Ganetsos, T.; Akhmadaliev, C.;
The study of AuSi liquid metal alloy ion sources (LMAIs) for the production of Si ions is not new. However, the present work encompasses in a concise form almost all fundamental aspects of source behaviour, in particular of a Au82Si18 source. A key finding, manifested in the behaviour of the ion extraction voltage with temperature, is the abnormal behaviour of the surface tension coefficient of the alloy with temperature. An important deduction, however, concerns the mechanisms responsible for the creation of doubly charged ions: reasons of self-consistency suggest that while Si++ is directly field-evaporated, Au++ must form by the post-ionization of Au+. (C) 2004 Elsevier B.V. All rights reserved.
Keywords: liquid metal alloy ion sources, temperature, doubly charged ions, field-evaporation, post-ionization

Publ.-Id: 6463 - Permalink


Calcium dipicolinate induced germination of Bacillus spores embedded in thin silica layers: novel perspectives for the usage of biocers
Matys, S.; Raff, J.; Soltmann, U.; Selenska-Pobell, S.; Böttcher, H.; Pompe, W.;
The germination rate of sol-gel immobilized spores of B. sphaericus JG-A12 in thin silica layers is 5-8 fold enhanced after pre-incubation with an 1:1 chelate of calcium and dipicolinic acid. This germination potential is conserved during long-time storage of 2.5 years.

Publ.-Id: 6462 - Permalink


Cyclopentadienyl tricarbonyl complexes of 99mTC for the in vivo imaging of the serotonin 5-HT1A receptor in the brain
Saidi, M.; Kretzschmar, M.; Seifert, S.; Bergmann, R.; Pietzsch, H.-J.;
The present interest in the 5-HT1A receptor is due to its implicated role in several major neuropsychiatric disorders such as depression, eating disorders and anxiety. For the diagnosis of these pathophysiological processes it is important to have radioligands in hand able to specifically bind on the 5-HT1A receptor in order to allow brain imaging. Due to the optimal radiation properties of 99mTc there is a considerable interest in the development of 99mTc radiopharmaceuticals for imaging serotonergic CNS receptors using single-photon emission tomography (SPET) [1,2].
Here we introduce two cyclopentadienyl technetium tricarbonyl conjugates of piperidine derivatives which show high accumulation of radioactivity in brain areas rich in 5-HT1A receptors. The complexes have been synthesized starting from the ferrocene complexes N-(alkyl)piperidino-4-[bispentahaptocyclopentadenyl)iron]carboxylate (with alkyl = methyl, isopropyl) [3]. Their chemical identity was confirmed by chromato-graphic methods and electrospray mass spectrometry.
The in vivo uptake of the 99mTc ligands in the whole rat brain and into brain regions was investigated. To determine the pharmacological specificity and selectivity, a group of rats was pretreated with several receptor ligands. The evaluation was carried out by quantitative digital ex vivo autoradiography.
Furthermore, we report the in vitro receptor affinity and biodistribution of the two candidates in order to demonstrate the suitability of the concept and to elucidate the influence of the building blocks on the biobehaviour of the complexes.
  • Invited lecture (Conferences)
    2. International Symposium on Bioorganometallic Chemistry (ISBOMC04), 14.-19.07.2004, Zürich, Swizerland
  • Journal of Organometallic Chemistry 689(2004)25, 4739-4744
    DOI: 10.1016/j.jorganchem.2004.09.004

Publ.-Id: 6461 - Permalink


Labelling of biomolecules using organometallic Tc(III) and Re(III) mixed-ligand complexes
Schiller, E.; Kraus, W.; Seifert, S.; Pawelke, B.; Bergmann, R.; Spies, H.; Pietzsch, H.-J.;
Trigonal-bipyramidal Tc(III) and Re(III) mixed-ligand complexes of the general formula [MIII(L1)(L2)] (M = Tc, Re; L1 = 2,2‘,2“-nitrilotris-(ethanethiol) NS3 or NS3-COOH; L2 = isocyanide or phosphine) are stable against ligand exchange with cysteine or glutathione and in vitro incubations with plasma as well as whole blood of rats. Therefore, such complexes represent an interesting tool concerning the possibilities of designing biologically relevant 99mTc or 188Re labelled compounds. The introduction of a carboxyl group into the tetradentate ligand and/or the monodentate ligand enables the conjugation of biomolecules as well as fine-tuning of lipophilicity. Improved methods for n.c.a. preparations will be presented. To avoid formation of reduced-hydrolysed species of both metals the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand (NS3) or its carboxyl derivative (NS3-COOH) and the monodentate phosphine or isocyanide to the so-called ‘4+1’ complexes. The isocyanides are used in form of their copper(I) complexes, [Cu(CN-R)4]Cl. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of 188Re isocyanide complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labelling of interesting molecules. The stability of various 99mTc and 188Re complexes will be discussed. The described approach allows the functionalization of a biomolecule with the tripodal as well as the monodentate ligand. The isocyanides and phosphines offer the possibility to vary the length and type of spacer for coupling the biomolecule.
  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals, 09.-12.09.2004, Danzig, Poland
  • Invited lecture (Conferences)
    Meeting der COST ACTION B12 "Radiotracers for in vivo assessment of biological function", 21.05.2004, Lissabon, Portugal

Publ.-Id: 6460 - Permalink


Synthesis and biological evaluation of a new type of technetium-labelled fatty acids for myocardial metabolism imaging
Walther, M.; Jung, C. M.; Bergmann, R.; Pietzsch, J.; Rode, K.; Stehr, S.; Heintz, A.; Wunderlich, G.; Kraus, W.; Pietzsch, H.-J.; Kropp, J.; Deussen, A.; Spies, H.;
Introduction: In an effort to develop technetium-labelled fatty acid analogues for myocardial metabolism imaging rhenium model complexes and their 99mTc analogues were synthesized according to the '4+1' mixed-ligand approach and investigated in vitro and in vivo.

Materials and Methods: The rhenium model complexes were completely characterised by NMR, IR, MS, EA and the geometrical impact of the chelate unit on the integrity of the fatty acid head structure was determined by single crystal X-ray analyses. To estimate the diagnostic value of the 99mTc-labelled fatty acids the compounds were investigated using the isolated constant-flow-perfused guinea pig heart model (see presentation A. Heintz et al.), in cell-uptake experiments and in biodistribution studies using male Wistar rats (5 - 6 weeks old, body weight 151 ± 15 g).

Results: The new fatty acid tracers contain the metal core in the oxidation states +3, well-wrapped in a trigonal-bipyramidal coordination moiety which is attached at the omega-position of a fatty acid chain. This structural feature is considered to be a good imitate of the well-established iodinated phenyl fatty acid. The formation of the rhenium models was accomplished by ligand exchange reactions using different pre-formed rhenium precursors. Noticable heart uptake of the 99mTc tracers being in the order of 2 % ID/g 5´p.i. and accompanied by a good heart to blood ratio of 8.6 confirms the remarkably results of the perfused heart experiments. A significant time-dependent cell uptake in HepG2 cells is shown for two representatives.

Conclusion: Further species such as mice and guinea pigs will be involved to characterise in vivo patterns of those derivatives, that show high extraction rates in the isolated constant-flow-perfused guinea pig heart model. While the tracers are superior to other described Tc-fatty acid imitates with regard to good heart to blood ratios, heart to liver ratio has to be improved. For this, chemical modifications will be performed at the chelating part as well as at the alkyl chain.
  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals 2004, 09.-12.09.2004, Danzig, Poland

Publ.-Id: 6458 - Permalink


Myocardial extraction of a new type of technetium-labeled fatty acids
Heintz, A.; Stehr, S. N.; Wunderlich, G.; Walther, M.; Jung, C. M.; Bergmann, R.; Pietzsch, J.; Rode, K.; Kraus, W.; Pietzsch, H.-J.; Kropp, J.; Spies, H.; Deussen, A.;
Introduction: Newly developed technetium-labeled fatty acid analogues are promising agents for myocardial metabolism imaging. We tested the myocardial extraction of 99mTc analogues of rhenium model complexes synthesized according to the '4+1' mixed-ligand approach (see presentation M. Walther et al.) in a guinea pig heart LANGENDORFF model

Materials and Methods: Firstly 30 min of steady state perfusion with 10 ml/min of normotherm Krebs-Henseleit-Buffer enriched with 0,1 % albumin was performed. Isolated guinea pig heart were then perfused with fatty acid tracers for 180 seconds in a 1:100 ratio. The venous effluate was collected in intervals of 15 s for 225 s following the start of tracer infusion. Perfusion was stopped, the heart was dissected into atria and ventricle compartments and γ-activity was measured. Eight new (C11, C12, C15, C10S, C11S, C12S, C14S, C16S) and for known control substances (123I-IPPA, 123I-BMIPP, 99mTc-MIBI, 99mTc-DTPA) were tested in this model (n=3-5).

Results: All eight substances showed acceptable extractions rates. Especially experiments with the C11 (39.8 %), but also C12 (14.8 %)and C11S (17.1 %) fatty acid analogues showed excellent results.

Conclusion: When compared with extraction rates for IPPA determined with the same set-up, extraction for the C11 and 11S compounds is 3 fold and 1.3 fold, respectively. These results confirm our hypothesis that the "4+1" Tc(III) chelate unit is promising tool for the Tc-labelling of fatty acids. Further experiments with different species are planned to elucidate exact myocardial uptake mechanisms.
  • Poster
    European Symposium on Radiopharmacy and Radiopharmaceutical 2004, Danzig, 09.-12.09.2004

Publ.-Id: 6457 - Permalink


Design of a photoneutron source for time-of-flight experiments at the radiation source ELBE
Altstadt, E.; Beckert, C.; Freiesleben, H.; Galindo, V.; Grosse, E.; Junghans, A.; Naumann, B.; Weiss, F.-P.;
The new radiation source ELBE at Research Center Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to 1 mA at energies between 12 MeV and 40 MeV can be delivered with a wide variability in the electron pulse structure. The maximum pulse frequency is 13 MHz with a pulse width less than 10 ps. The small emittance of the electron beam permits the irradiation of very small volumes. These main beam parameters led to the idea to convert the intense picosecond electron pulses into sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and to produce neutrons by bremsstrahlung photons through (gamma,n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n,p), (n,alpha) and (n,f) with a time-of-flight arrangement with a short flight path of only a few meters, it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons which would broaden the neutron pulses. It is the primary physics objective of this neutron source to determine neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select radiation hard materials, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. In addition, the distribution of fragments can be analyzed which are produced by neutron-induced transmutation of long-lived radioactive nuclides. Furthermore experiments can be performed which address problems of nuclear astrophysics.
The energy deposition of the electron beam in the small neutron radiator is that high that any solid material would melt. Therefore, the neutron radiator consists of liquid lead flowing through a channel of 11.2×11.2 mm² cross section. From the thermal and mechanical point of view molybdenum turned out to be the most suited channel wall (thickness 0.5 mm) material. Depending on the electron energy and current up to 20 kW power will be deposited into a radiator volume of 3 cm³. This heating power is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are in the range of 2 m/s in the radiator section. The electrons that are not stopped in the radiator and the secondary radiation are dumped in an aluminum beam dump. To reduce the radiation background in the measuring direction, the neutrons are decoupled from the radiator at an angle of 90° with respect to the impinging electrons. Particle transport calculations were carried out using the Monte Carlo codes MCNP and FLUKA. These calculations predict a neutron source strength of 7.88e+12 and 2.67e+13 n/s for electron energies between 20 and 40 MeV. At the measuring place 362 cm away from the radiator, neutron fluxes of 1.7e+7 n/(cm² s) will be obtained. The mentioned time-of-flight distance allows for an energy resolution better than 1%. The maximum usable neutron energy is about 7 MeV.

Keywords: neutron, source, photoneutron, flux, pulsed, radiator, time-of-flight, cross section
  • Lecture (Conference)
    12th International Conference on Nuclear Engineering ICONE-12, 25.-29.04.2004 Washington D.C., United States
  • Contribution to proceedings
    12th International Conference on Nuclear Engineering ICONE-12, Washington D.C., USA, April 25-29, 2004, Proceedings on CD-ROM paper 49456

Publ.-Id: 6456 - Permalink


Evaluation and ranking of restoration strategies for radioactively contaminated sites
Zeevaert, T.; Bousher, A.; Brendler, V.; Hedemann Jensen, P.; Nordlinder, S.;
An international project, whose aim was the development of a transparent and robust method for evaluating and ranking restoration strategies for radioactively contaminated sites (RESTRAT), was carried out under the Fourth Framework of the Nuclear Fission Safety Programme of the EU. The evaluation and ranking procedure used was based on the principles of justification and optimisation for radiation protection. A multi-attribute utility analysis was applied to allow for the inclusion of radiological health effects, economic costs and social factors. Values of these attributes were converted into utility values by applying linear utility functions and weighting factors, derived from scaling constants and expert judgement. The uncertainties and variabilities associated with these utility functions and weighting factors were dealt with by a probabilistic approach which utilised a Latin Hypercube Sampling technique. Potentially relevant restoration techniques were identified and their characteristics determined through a literature review. The methodology developed by this project has been illustrated by application to representative examples of different categories of contaminated sites; a waste disposal site, a uranium tailing site and a contaminated freshwater river.
Keywords: Restoration; Radioactivity; Ranking; Evaluation; Optimisation
  • Journal of Environmental Radioactivity 56 (1-2), 33-50 (2001)

Publ.-Id: 6455 - Permalink


First attempt to chemically identify element 112
Yakushev, A. B.; Buklanov, G. V.; Chelnokov, M. L.; Chepigin, V. I.; Dmitriev, S. N.; Gorshkov, V. A.; Hübener, S.; Lebedev, V. Y.; Malyshev, O. N.; Oganessian, Y. T.;
The first attempt to chemically identify one of the recently discovered long-lived isotopes of superheavy elements, namely 283112 (3 min, SF), made at FLNR, Dubna is reported. The nuclide was produced by fusion of accelerated 48Ca with a target of natural U, which contained some Nd to simultaneously produce also short-lived Hg nuclides. According to test experiments with Hg, the expected lighter homologue of element 112, both elements can be isolated from the products of the bombardment in metallic state, and transported from the target in flowing He gas to a detection system, where spontaneous fission and alpha decays 49-s 185Hg) were registered using PIPS detectors. The surface of the detectors was covered with a thin layer of Au or Pd which ensured the detection of Hg with high efficiency due to its chemisorption on these surfaces. While about three SF events could be expected, not a single one was detected at an upper limit for the production cross section of about one picobarn. This may point to a "Rn-like" rather than "Hg-like" behavior of element 112. A new experiment is planned, in which both a "Rn-like" and a "Hg-like" species could be detected.
  • Radiochimica Acta 89 (11-12), 743 (2001)

Publ.-Id: 6454 - Permalink


A theoretical study of uranyl hydroxide monomeric and dimeric complexes
Tsushima, S.; Reich, T.;
Structures of uranyl hydroxide monomeric UO2(OH)20, and dimeric (UO2)2(OH)22+ were studied by hybrid density functional theoretical calculations. It was found out that both the monomeric ortho-UO2(OH)20 and dimeric (UO2)2(OH)22+ complexes have bent O=U=O angles (~170°). This is attributed to significant donation from the equatorial OH ligands to the uranyl moiety. It was also found that the ortho- and meta-UO2(OH)2(H2O)30 complexes lie very close in energy, and that both isomers may exist in normal aqueous media.
  • Chemical Physics Letters 347 (1-3), 127-132 (2001)

Publ.-Id: 6453 - Permalink


Hydrogen-induced defects in bulk niobium
Cizek, J.; Prochazka, I.; Becvar, F.; Kuzel, R.; Cieslar, R.; Brauer, G.; Anwand, W.; Kirchheim, R.; Pundt, A.;
Our aim in the present work was to investigate changes of the defect structure of bulk niobium induced by hydrogen loading. The evolution of the microstructure with increasing hydrogen concentration was studied by x-ray diffraction and two complementary techniques of positron annihilation spectroscopies (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with the measurement of the Doppler broadening, in defect-free Nb (99.9%) and Nb containing a remarkable number of dislocations. These samples were electrochemically loaded with hydrogen up to xH=0.06 [H/Nb], i.e. in the alpha-phase region, and it was found that the defect density increases with hydrogen concentration in both Nb samples. This means that hydrogen-induced defects are created in the Nb samples. A comparison of PAS results with theoretical calculations revealed that vacancy-hydrogen complexes are introduced into the samples due to hydrogen loading. Most probably these are vacancies surrounded by 4 hydrogen atoms.
Keywords: PACS number(s): 78.70.Bj, 61.72.-y

Publ.-Id: 6452 - Permalink


Spectroscopic Study of Cm(III) Sorption onto -Alumina
Stumpf, T.; Rabung, T.; Klenze, R.; Geckeis, H.; Kim, J. I.;
The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under an Ar atmosphere at an ionic strength of 0.1 M NaClO4. The pH is varied between 2 and 10 and the metal ion concentration between 2.7×10−8 and 4.5×10−5 mol/L. With increasing pH, two Cm(III)–alumina surface species are identified which are attributed to≡Al–O–Cm2+(H2O)5 and≡Al–O–Cm+(OH)(H2O)4. The two curium–alumina surface complexes are characterized by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110s). In the concentration range investigated, the surface complex formation is not dependent on the metal ion concentration but only on the pH. Additionally, the concentration ratio of the two surface species is found to be independent of the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.
  • Journal of Colloid and Interface Science 238 (1), 219-224 (2001)

Publ.-Id: 6451 - Permalink


EXAFS as a tool for bond-length determination in the environment of heavy atoms
Hennig, C.; Reich, T.; Funke, H.; Rossberg, A.; Rutsch, M.; Bernhard, G.;
Single crystal X-ray diffraction measurements are complicated in the presence of heavy atoms. In these cases the structure factors are mainly influenced by the heavy catterers and the error in determination of atomic coordinates increases for light atoms. The difficulties grow if the unit cell dimensions or the space group symmetry remain uncertain. If the structure model is similar to the correct structure, it is difficult to find an independent criterion for the accuracy of the bond-length determination. We demonstrate that extended X-ray absorption fine structure (EXAFS) spectroscopy is a useful tool for the investigation of local bond lengths in the environment of heavy atoms.
Keywords: heavy atoms, uranyl arsenate, EXAFS, XRD
  • Journal of Synchrotron Radiation 8 (2), 695-697 (2001)
  • Zeitschrift für Kristallographie (2000)17, 81

Publ.-Id: 6450 - Permalink


A climatology of 7Be at four high-altitude stations at the Alps and the Northern Apennines
Gerasopoulos, E.; Zanis, P.; Stohl, A.; Zerefos, C. S.; Papastefanou, C.; Ringer, W.; Tobler, L.; Hübener, S.; Gäggeler, H. W.; Kanter, H. J.; Tositti, L.; Sandrini, S.;
The 7Be activity concentrations measured from 1996 to 1998 at four high-altitude stations, Jungfraujoch—Switzerland, Zugspitze—Germany, Sonnblick—Austria and Mt. Cimone—Italy, were analyzed in combination with a set of, meteorological and atmospheric parameters such as the tropopause height, relative and specific humidity and also in conjunction with 3D back-trajectories in order to investigate the climatological features of 7Be. A frequency distribution analysis on 7Be activity concentrations revealed the existence of two concentration classes around 1.5 and 6 mBq m−3 and a transition class between the two modes of the distribution at 3–4 mBq m−3. Cross-correlation analysis performed between 7Be and a number of meteorological and atmospheric parameters at the first three stations showed a strong negative correlation with relative humidity (−0.56, −0.51, −0.41) indicating the importance of wet scavenging as a controlling mechanism. Also, the positive correlation with the height of 3-days back-trajectories and tropopause height (+0.49/+0.43, +0.59/+0.36, +0.44/+0.38) shows that downward transport from the upper or middle to lower troposphere within anticyclonic conditions plays also an important role. Trajectory statistics showed that low 7Be concentrations typically originate from lower-altitude subtropical ocean areas, while high concentrations arrive from the north and high altitudes, as is characteristic for stratospheric intrusions. Although the 7Be activity concentrations are highly episodic, the monthly means indicate an annual cycle with a late-summer maximum at all stations. The correlation coefficients calculated for monthly means of the 7Be and atmospheric data suggest that the main predictor controlling the seasonality of the 7Be concentrations is tropopause height (+0.76, +0.56, +0.60), reflecting more vertical transport from upper tropospheric levels into the lower troposphere during the warm season than during the cold season.
Keywords: 7Be; Alps; Climatology; Stratospheric intrusions; Surface ozone
  • Atmospheric Environment 35 (36), 6347-6360 (2001)

Publ.-Id: 6449 - Permalink


Synthesis of [1,2-14C]trichloroacetic acid
Bubner, M.; Fuksová, K.; Matucha, M.; Heise, K. H.; Bernhard, G.;
A growing interest in the phytotoxic effects of trichloroacetic acid (TCA) has led us to develop a small-scale (<1 mmol) one-pot synthesis of [1,2-14C]TCA with >70% yield and specific activity of 3.7 GBq/mmol
Keywords: [1,2-14C]trichloroacetic acid; one-pot synthesis
  • Journal of Labelled Compounds and Radipharmaceuticals 44 (11), 811-814 (2001)

Publ.-Id: 6448 - Permalink


Uranyl Surface Speciation on Silica Particles Studied by Time-Resolved Laser-Induced Fluorescence Spectroscopy
Gabriel, U.; Charlet, L.; Schläpfer, C. W.; Vial, J. C.; Brachmann, A.; Geipel, G.;
The sorption of uranyl ions onto amorphous silica has been studied in the presence of atmospheric CO2 by laser-induced time-resolved fluorescence spectroscopy at trace concentrations (1.0 and 0.1 M). Two fluorescent uranyl surface complexes have been identified in the pH range 4 to 9. Both complexes could be differentiated by lifetimes (170±25 s at low pH and 360±50 s at high pH) and fluorescence emission spectra. Within the constant capacitance model framework they are described by mononuclear (1 : 1) complexes with release of two and three protons, respectively. When fluorescence data were compared to wet chemistry sorption data, a third “silent” ternary uranyl–silica–carbonate surface complex had to be postulated to account partly for adsorption between pH 8.0 and 9.0. Three independent data sets led therefore to the identification of three surface complexes, postulated as &tbond;SiO2UO2°,&tbond;SiO2UO2OH-, and &tbond;SiO2UO2OHCO33-.
  • Journal of Colloid and Interface Science 239, 358-369 (2001)

Publ.-Id: 6447 - Permalink


FTIR Studies of Phytochrome Photoreactions Reveal the C=O Bands of the Chromophore: Consequences for Its Protonation States, Conformation, and Protein Interaction
Foerstendorf, H.; Benda, C.; Gärtner, W.; Storf, M.; Scheer, H.; Siebert, F.;
The molecular changes of phytochrome during red far-red and reverse photoreactions have been monitored by static infrared difference spectroscopy using the recombinant 65 kDa N-terminal fragment assembled with a chromophore chemically modified at ring D or with a chromophore isotopically labeled with 18O at the carbonyl group of ring A. This allows the identification of the C=O stretching vibrations of rings D and A. We exclude the formation of an iminoether in Pfr. The positions of both these modes show that the chromophore always remains protonated. The upshift of the C=O stretch of ring D in the first photoproducts is explained by a twisted methine bridge connecting rings C and D. The changes in the vibrational pattern during the red far-red conversion show that the backreaction is not just the reversal of the forward reaction. The infrared difference spectra of the fragment deviate very little from those of the full-length protein. The differences which are related to the lack of the C-terminal half of the protein constituting the signaling domain are possibly important for the understanding of the signaling mechanism.
  • Biochemistry 40, 14952-14959 (2001)

Publ.-Id: 6446 - Permalink


Sorption behavior of U(VI) on phyllite: experiments and modeling
Arnold, T.; Zorn, T.; Zänker, H.; Bernhard, G.; Nitsche, H.;

The sorption of U(VI) onto low-grade metamorphic rock phyllite was modeled with the diffuse double layer model (DDLM) using the primary mineralogical constituents of phyllite, i.e. quartz, chlorite, muscovite, and albite, as input components, and as additional component, the poorly ordered Fe oxide hydroxide mineral, ferrihydrite. Ferrihydrite forms during the batch sorption experiment as a weathering product of chlorite. In this process, Fe(II), leached from the chlorite, oxidizes to Fe(III), hydrolyses and precipitates as ferrihydrite. The formation of ferrihydrite during the batch sorption experiment was identified by Mössbauer spectroscopy, showing a 2.8% increase of Fe(III) in the phyllite powder. The ferrihydrite was present as Fe nanoparticles or agglomerates with diameters ranging from 6 to 25 nm, with indications for even smaller particles. These Fe colloids were detected in centrifugation experiments of a ground phyllite suspension using various centrifugal forces.

The basis for the successful interpretation of the experimental sorption data of uranyl(VI) on phyllite were: (1) the determination of surface complex formation constants of uranyl with quartz, chlorite, muscovite, albite, and ferrihydrite in individual batch sorption experiments, (2) the determination of surface acidity constants of quartz, chlorite, muscovite, and albite obtained from separate acid–base titration, (3) the determination of surface site densities of quartz, chlorite, muscovite, and albite evaluated independently of each other with adsorption isotherms, and (4) the quantification of the secondary phase ferrihydrite, which formed during the batch sorption experiments with phyllite. The surface complex formation constants and the protolysis constants were optimized by using the experimentally obtained data sets and the computer code FITEQL. Surface site densities were evaluated from adsorption isotherms at pH 6.5.

The uranyl(VI) sorption onto phyllite was accurately modeled with these newly determined constants and parameters of the main mineralogical constituents of phyllite and the secondary mineralization phase ferrihydrite. The modeling indicated that uranyl sorption to ferrihydrite clearly dominates uranyl sorption, showing the great importance of secondary iron phases for sorption studies.

Keywords: Surface complexation modeling; Quartz; Chlorite; Muscovite; Albite; Ferrihydrite
  • Journal of Contaminant Hydrology, Vol: 47, Issue: 2-4, pp. 219-23, February, 2001

Publ.-Id: 6444 - Permalink


Ermüdungsrissausbreitung in Aluminiumlegierungen – Datenbasis und Anwendungen im Rahmen des Damage-Toleranz-Konzeptes
Bergner, F.; Thieme, M.; Zouhar, G.; Franke, R.;
Aluminiumknetlegierungen haben sich seit langem im Bereich der Außenhaut des Rumpfes und der Tragflächen von Verkehrsflugzeugen bewährt. Klassische Vertreter sind die hochfeste Legierung 7075 T6 sowie die als schädigungstolerant geltende Legierung 2024 T3. In den letzten Jahren hat sich vor dem Hintergrund des Erfordernisses der Gewichtsreduzierung sowie der Einführung neuer Bauweisen und Fertigungsverfahren der Blick auf ein breiteres Spektrum von Aluminiumlegierungen geöffnet. Für eine fundierte Bewertung dieser Legierungen werden zuverlässige Materialdaten benötigt, wobei im Rahmen des Schädigungs-Toleranz-Konzeptes die Ermüdungsrissausbreitung von besonderem Interesse ist. Unglücklicherweise sind zuverlässige Rissaubreitungsdaten nicht ohne weiteres aus der Literatur beschaffbar. Eine diesbezügliche Studie [Sinclair und Pieri, On obtaining fatigue crack growth parameters from the literature, Int. J. Fatigue 12 (1990) 57-62] kam zu dem ernüchternden Urteil, dass für nominell gleiche Werkstoffe die Streubreite der Literaturangaben deren praktischen Nutzen ernsthaft in Frage stellt. Folgerichtig kommt der Angabe der Messbedingungen sowie der Bekanntgabe der Originalmessdaten große Bedeutung zu.

Im vergangenen Jahrzehnt wurde in einem breit angelegten Versuchsprogramm eine neue Datenbasis mit Ergeb-nissen von Ermüdungsrissausbreitungsmessungen aufgestellt. Die Datenbasis beruht weitgehend auf Messungen mit konstanter Spannungsamplitude (Spannungsverhältnis R=0,1) an mittenangerissenen Proben (Probenbreite 160 mm) aus gewalzten dünnen Blechen (Blechdicke 1,5 bis 3 mm) unterschiedlicher Aluminiumknetlegierungen. Der Riss-fortschritt wurde lichtoptisch gemessen, die Auswertung erfolgte im Rahmen der linear-elastischen Bruchmechanik gemäß Norm ASTM E647. Die Datenbasis enthält neben den Originalmesswerten (Risslänge a, Lastspielzahl N) und den berechneten Werten der Rissausbreitungskurve (Rissausbreitungsrate da/dN über der Schwingbreite des Spannungsintensitätsfaktors DK) auch Zugversuchskennwerte und Restfestigkeiten. Sofern die Materialmenge ausreichte, wurden für jeden Werkstoffzustand in den Orientierungen längs bzw. quer zur Walzrichtung mindestens je fünf Zugversuche und fünf Rissausbreitungsversuche durchgeführt. Für ausgewählte Aluminiumlegierungen wurde auch das Spannungsverhältnis (R=0,5) oder das Umgebungsmedium (3,5%ige NaCl-Lösung) variiert. Speziell für die Aluminiumlegierung 6013 T6 erfolgten Messungen in 3,5%iger NaCl-Lösung im Frequenzbereich von 4 mHz bis 40 Hz.

Ziel des Beitrages ist es, die Datenbasis einem breiteren Interessentenkreis bekannt und zugänglich zu machen. Sie enthält unter anderem Ermüdungsrissausbreitungsdaten für jeweils mehrere 2000er (Hauptlegierungselement Cu), 6000er (Hauptlegierungselemente Mg und Si) und 7000er (Hauptlegierungselement Zn) Aluminiumknetlegierungen im kalt- sowie im warmausgelagerten Zustand. An ausgewählten Beispielen soll gezeigt werden, wie die Materialdaten zur vergleichenden Bewertung der einzelnen Werkstoffe herangezogen werden können. Sofern die Belastungsbedingungen (konstante Spannungsamplitude, Spannungsverhältnis) eine Übertragung auf ein Bauteil zulassen, können durch Integration der Ermüdungsrissausbreitungskurven Restlebensdauern für das betreffende Bauteil abgeschätzt und geeignete Inspektionsintervalle festgelegt werden.
  • Lecture (Conference)
    Deutscher Luft- und Raumfahrtkongress, 20.-23.09.2004, Dresden, Germany
  • Contribution to external collection
    Jahrbuch 2004 der Deutschen Gesellschaft für Luft- und Raumfahrt, ISSN 0070-4083, Bonn: DGLR, 2004, S. 81-90.

Publ.-Id: 6443 - Permalink


Synthesis of 4-([18F]fluoromethyl)-2-chlorophenylisothiocyanate: A novel bifunctional 18F-labelling agent
Wüst, F.; Müller, M.; Bergmann, R.;
The one-step radiosynthesis of 4-([18F]fluoromethyl)-2-chlorophenylisothiocyanate 18F-7 as a novel bifunctional 18F-labelling agent is described. Optimised reaction conditions in a remotely controlled synthesis module gave isothiocyanate 18F-7 in radiochemical yields of 45 % (decay-corrected) within 40 min and high radiochemical purity of > 95 % after solid-phase-extraction. Coupling of compound 18F-7 with the primary amine benzylamine as a model reaction afforded the corresponding ((4-[18F]fluoromethyl)-2-chloro-phenyl)-benzyl thiourea 18F-8 in a high radiochemical yield of > 90 %. Stability studies of thiourea 18F-8 in terms of radiodefluorination showed appreciable buffer stability at pH 7.4, whereas significant radiodefluorination was observed when 18F-8 was incubated in buffers af pH 3.6 and pH 9.4. Preliminary dynamic PET studies with thiourea 18F-8 in male Wistar rats showed high bone accumulation, indicative of high in vivo radiodefluorination.
  • Radiochimica Acta 92(2004)4-6, 349-353

Publ.-Id: 6442 - Permalink


EXAFS structural analysis of aqueous uranium(VI) complexes with lignin degradation products
Reich, T.; Roßberg, A.; Baraniak, L.; Hennig, C.; Bernhard, G.; Nitsche, H.;
Uranium LIII-edge extended X-ray absorption fine structure (EXAFS) analysis was carried out on aqueous uranium(VI) complexes with monomeric intermediates of the natural wood-degradation process such as protocatechuic acid (3,4-dihydroxybenzoic acid), catechol (2-hydroxyphenol), pyrogallol (1,2,3-trihydroxybenzol), and vanillic acid (4-hydroxy-3-methoxybenzoic acid). The structural parameters of the 1:1 complexes with protocatechuic acid and vanillic acid in weakly acidic solution indicate that the carboxylic group coordinates the uranyl cation in a bidentate mode in the equatorial plane. Based on the identical structural parameters observed for protocatechuic acid, catechol and pyrogallol in alkaline media, we conclude that the coordination with uranium occurs via the neighboring OH groups of the phenols under formation of a five-membered ring.
  • Radiochimica Acta 88, 593-597 (2000)

Publ.-Id: 6441 - Permalink


Soluble humic substances from in situ precipitated microcrystalline calcium carbonate, internal sediment, and spar cement in a Cretaceous carbonate mud-mound
Neuweiler, F.; Rutsch, M.; Geipel, G.; Reimer, A.; Heise, K. H.;
Albian carbonate mud-mound limestones exposed near Iraneta, northern Spain, show a fabric- and particle-specific fluorescence. Intense fluorescence is restricted to in situ precipitated microcrystalline (automicritic) fabrics, calcified demosponges, and coralline sponges. Intermediate intensity derives from micritized bioclasts, pellets, and a rim of marine bladed cement. Most invertebrate skeletons, late-diagenetic equant cement, and crosscutting zones of dolomitization are weakly to nonfluorescent. Internal microcrystalline sediment (allomicrite) and red algae debris have variable fluorescence. Correlation between rock fluorescence and soluble humic substances was evaluated from 3 g of automicrite, allomicrite, and cement. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) with ultra-short pulses on two extracrystalline fractions (NaOH-soluble) and two intracrystalline fractions (HCl-soluble and NaOH-soluble) showed that most of the soluble humic substances of automicrite are within the crystals; but conversely, are significantly enriched on outer surfaces of allomicrite. Spar cement is close to detection limits. Fluorescence lifetimes are in the range of 0.5–2 ns and 3.5–6 ns. We conclude that precipitation of automicrite took place during oxidative organic matter diagenesis, i.e., during condensation reactions of degradation products of marine biopolymers. By contrast, allomicrite formed by skeletal breakdown followed by ingestion, organic coating, and reingestion during deposit feeding. A humic-substance–based model of marine polymer gels represents a new approach for the understanding of ancient polygenetic carbonate muds, so typical of Phanerozoic mud-mounds in deeper water settings.
  • Geology 28, 851-854 (2000)

Publ.-Id: 6440 - Permalink


Solution coordination chemistry of uranium in the binary UO22+}-SO42- and the ternary UO22+-SO42--OH- system
Moll, H.; Reich, T.; Hennig, C.; Roßberg, A.; Szabó, Z.; Grenthe, I.;
The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and 17O-NMR spectroscopy. Uranium LIII edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Å. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Å. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22+ + SO42- ⇔ UO2SO4 (k1), (2) U*O22+ + UO2SO4 ⇔ U*O2SO4 + UO22+ (k2), (3) UO22+ + UO2(SO4)22- ⇔ 2 UO2SO4 (k3), and (4) UO2SO4 + SO42- ⇔ UO2(SO4)22- (k4). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their 17O chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.
  • Radiochimica Acta 88, 559-566 (2000)

Publ.-Id: 6439 - Permalink


Spectroscopic properties of uranium(VI) minerals studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)
Geipel, G.; Bernhard, G.; Rutsch, M.; Brendler, V.; Nitsche, H.;
We studied the fluorescence properties of 120 uranium minerals in order to provide a data base of potential secondary solids that may form in the flooding process of defunct uranium mines. This data base may provide a link of the fluorescence spectra of the minerals to solution spectra containing so far unknown tertiary and quaternary solution complexes in environmental uranium(VI)-containing waters. In our initial effort to establish the data base, we are focusing on phosphate- and arsenate-containing uranium(VI) minerals. Except for chernikovite [(H3O)2(UO2)2(PO4)2 · 6H2O], these minerals show intensive fluorescence emissions bands with a bathochromic shift of up to 18 nm compared to the fluorescence of the uranyl ion in solution. We found hypsochromic shifts of the fluorescence emission for the uranyl phosphates and bathochromic shifts for the uranyl arsenates. The band spacing of the fluorescence emissions from the 20502 cm-1 level are comparable to the vibrational frequency available from IR-data. Using these data we estimated the axial U-O bond lengths. The decrease of the vibration frequency from 813 cm-1 (saleiite, [Mg(UO2)2(PO4)2 · 10(H2O)]) to 794 cm-1 (uranocircite, [Ba(UO2)2(PO4)2 · 12(H2O)]) is related to a slight increase of the U-O bond length by 3 pm. In both series, the fluorescence lifetime decreases with decreasing crystal water. This is different compared to solution spectra where the lifetime increases as water is displaced from the inner coordination shell. Comparing the fluorescence data of the mineral troegerite [H2(UO2)2(AsO4)2 · 8(H2O)] with the fluorescence spectra of uranyl arsenate solutions, we identified one of the three uranyl arsenate complexes in solution as HUO2(AsO4)(aq.).batch experiment at anoxic conditions proved that pyrite can immobilise U(VI).
  • Radiochimica Acta 88, 757-762 (2000)

Publ.-Id: 6438 - Permalink


The MHD α²-dynamo, Z2-graded pseudo-Hermiticity, level crossings, and exceptional points of branching type
Günther, U.; Stefani, F.; Gerbeth, G.;
The spectral branching behavior of the 2×2 operator matrix of the magneto-hydrodynamic α²-dynamo is analyzed numerically. Some qualitative aspects of level crossings are briefly discussed with the help of a simple toy model which is based on a Z2-graded-pseudo-Hermitian 2×2 matrix. The considered issues comprise: the underlying SU(1,1) symmetry and the Krein space structure of the system, exceptional points of branching type and diabolic points, as well as the algebraic and geometric multiplicity of corresponding degenerate eigenvalues.
  • Czechoslovak Journal of Physics 54(2004), 1075-1089

Publ.-Id: 6437 - Permalink


Chemical characterization of bohrium (element 107)
Eichler, R.; Brüchle, W.; Dressler, R.; Düllmann, C. E.; Eichler, B.; Gäggeler, H. W.; Gregorich, K. E.; Hoffmann, D. C.; Hübener, S.; Jost, D. T.; Kirbach, U. W.; Laue, C. A.; Lavanchy, V. M.; Nitsche, H.; Patin, J. B.; Piguet, D.; Schädel, M.; Shaughnessy, D. A.; Strellis, D. A.; Taut, S.; Tobler, L.; Tsyganov, Y. S.; Türler, A.; Vahle, A.; Wilk, P. A.; Yakushev, A. B.;
The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected1-3: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties. The synthesis of increasingly heavy elements4-6, now including that of elements 114, 116 and 118, allows the investigation of this effect, provided sufficiently long-lived isotopes for chemical characterization are available7. In the case of elements 104 and 105, for example, relativistic effects interrupt characteristic trends in the chemical properties of the elements constituting the corresponding columns of the periodic table8, whereas element 106 behaves in accordance with the expected periodicity9-12. Here we report the chemical separation and characterization of six atoms of element 107 (bohrium, Bh), in the form of its oxychloride. We find that this compound is less volatile than the oxychlorides of the lighter elements of group VII, thus confirming relativistic calculations13 that predict the behaviour of bohrium, like that of element 106, to coincide with that expected on the basis of its position in the periodic table.
  • Nature 407, 63-65 (2000)

Publ.-Id: 6435 - Permalink


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