Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35810 Publications

Characterization of a SiC/SiC composite by X-ray diffraction, atomic force microscopy and positron spectroscopies

Brauer, G.; Anwand, W.; Eichhorn, F.; Skorupa, W.; Hofer, C.; Teichert, C.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Coleman, P. G.; Nozawa, T.; Kohyama, A.

A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy, and various positron spectroscopies (slow positron implantation, positron lifetime, re-emission). It is found that beside its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented.

Keywords: SiC/SiC composite; graphite; X-ray diffraction; atomic force microscopy; slow-positron spectroscopy; positron lifetime; positron affinity; positron re-emission

  • Invited lecture (Conferences)
    10th International conference on slow positron beam techniques for solids and surfaces, 19.-25.03.2005, Doha, Qatar
  • Applied Surface Science 252(2006), 3342-3351

Permalink: https://www.hzdr.de/publications/Publ-7254
Publ.-Id: 7254


Evidence of a low quartz structure at the SiO2/Si interface from coincidence Doppler broadening spectroscopy

Brauer, G.; Becvar, F.; Anwand, W.; Skorupa, W.

Results from coincidence Doppler broadening measurements on various Si samples and Brazilian quartz having low quartz structure are presented with the aim to give further strong evidence for the existence of a low quartz structure, but not Si divacancies, at the SiO2/Si interface.

Keywords: slow-positron spectroscopy; coincidence Doppler broadening; silicon; Brazilian quartz; silicon divacancy; SiO2/Si interface

  • Lecture (Conference)
    10th International conference on slow positron beam techniques for solids and surfaces, 19.-25.03.2005, Doha, Qatar
  • Applied Surface Science (2007)

Permalink: https://www.hzdr.de/publications/Publ-7253
Publ.-Id: 7253


Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo Simulations and Target Transformation Factor Analysis

Rossberg, A.; Scheinost, A. C.

We developed a new method for the three-dimensional modeling of Extended X-ray Absorption Fine Structure (EXAFS) spectra, which is suited to extract the local structure of aqueous metal complexes from spectral mixtures of several components. The new method combines two techniques: Monte Carlo simulation and Target Transformation Factor Analysis (TFA). Monte Carlo simulation is used to create random arrangements between the X-ray absorbing metal ion and the ligand atoms, and to calculate the theoretical EXAFS spectrum of each arrangement. The theoretical EXAFS spectrum is then introduced as test spectrum in the TFA procedure, in order to test whether the test spectrum is likely a component of the spectral mixtures or not. This coupled procedure is repeated, until the error in the test spectrum is minimized. The new method is thus able to isolate and refine the structure of complexes from spectral mixtures and to determine their relative concentrations, based solely on an estimate of the ligand structure. The performance of the proposed method was validated using uranium LIII-edge EXAFS spectra of binary mixtures of two uranium(VI) 3,4-dihydoxy benzoic acid complexes.

Keywords: EXAFS; Complexation; Speciation; Factor Analysis; Monte Carlo

Permalink: https://www.hzdr.de/publications/Publ-7252
Publ.-Id: 7252


Superconductivity at Ultralow Temperatures and its Interplay with Nuclear Magnetism

Herrmannsdörfer, T.; Pobell, F.

In this article we will describe experiments at microkelvin temperatures which were performed to give - at least partly - answers to the following questions:

a. will all nonmagnetic metals become superconducting if refrigerated to low enough temperatures,
b. what is the impact of the weakest version of magnetism, nuclear magnetism, on superconductivity.

a. The first question has intrigued low temperature physicists since the discovery of superconductivity by H. Kamerlingh-Onnes in 1911. He wrote already in 1913 “There is left little doubt that if Au and Pt could be obtained absolutely pure, they could also pass into the superconducting state at helium temperatures”. And in 1929 W. Meissner wrote “At present it does not seem unlikely that, opposite to former expectations, all metals will become superconducting at low enough temperature”. One can pose the question in more general terms: “Is the electron-phonon interaction or another possible pairing mechanism in all metals strong enough so that they will eventually become superconducting, if this transition is not hindered by other phenomena, like magnetic properties?” After all, somehow the conduction electrons have to get rid of their entropy when approaching absolute zero, and one way is a transition to a superconducting state.

Looking at the periodic system of the elements, one realizes that superconductivity is rather the rule than the exception. Most metallic elements become superconducting if they show no magnetic order like some 3d- and 4f-elements. Even most insulators, like S or O, if forced into a metallic state by high pressure, eventually enter the superconducting state. When we started our research, there were only two small “islands” in the periodic system of the elements where metals had shown neither a superconducting nor a magnetic transition: some alkali and alkaline-earth metals and the noble and platinum metals (Cu, Ag, Au, Rh, Pd, Pt).

b. Superconductivity in its simplest version - s-wave, singlet pairing of conduction electrons mediated by electron-phonon interaction - is counteracted by magnetic interactions. This has been well demonstrated by the depression of the superconducting transition temperature when magnetic impurities are introduced. The large variety of “magnetic interactions” has varying impacts on superconductivity. The clearest demonstration of its detrimental impact is the vanishing of the superconducting state when a superconducting metal enters a ferromagnetic state. This was demonstrated in 1977 by Matthias et al. for ErRh4B4 and by Ishikawa and Fischer for HoMo8S8.

The weakest known version of magnetism is caused by the interaction of nuclear magnetic moments. Hence, it was a natural question to investigate the impact of nuclear ferromagnetism on superconductivity. This investigation became possible when we had observed a nuclear ferromagnetic transition of the superconductor AuIn2 at 35 µK in 1994. The results of the investigation of the interplay between nuclear ferromagnetism and superconductivity in AuIn2 - some of it are not yet understood - will be described in Sect. 5. Further investigations of the impact of nuclear paramagnetism in AuAl2, Al, Sn, AuIn2, In, Rh, as well as TiH2+x on superconductivity are discussed in Sect. 6. In Sect. 7, a first study of the interplay of hyperfine enhanced nuclear magnetism and superconductivity is presented. Eventually, in Sect. 8, we will summarize our results.

The experiments described in this article have been performed at the Forschungszentrum (formerly: Kernforschungsanlage) Jülich and at the University of Bayreuth

  • Contribution to external collection
    in: Frontiers in Superconducting Materials, Heidelberg: Springer Verlag, 2005, 71

Permalink: https://www.hzdr.de/publications/Publ-7251
Publ.-Id: 7251


High-intensity terahertz radiation from a microstructured large-area photoconductor

Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.

We present a planar large-area photoconducting emitter for impulsive generation of terahertz (THz) radiation. The device consists of an interdigitated electrode metal-semiconductor-metal (MSM) structure which is masked by a second metallization layer isolated from the MSM electrodes. The second layer blocks optical excitation in every second period of the MSM finger structure. Hence charge carriers are excited only in those periods of the MSM structure which exhibit a unidirectional electric field. Constructive interference of the THz emission from accelerated carriers leads to THz electric field amplitudes up to 85 V/cm when excited with fs optical pulses from a Ti:sapphire oscillator with an average power of 100 mW at a bias voltage of 65 V applied to the MSM structure. The proposed device structure has a large potential for large-area high-power THz emitters.

Permalink: https://www.hzdr.de/publications/Publ-7250
Publ.-Id: 7250


11B-NMR studies of weakly ferromagnetic BaB6

Mushkolaj, S.; Gavilano, J. L.; Rau, D.; Ott, H. R.; Bianchi, A.; Fisk, Z.

BaB6 is a weakly ferromagnetic material with a Curie temperature TC well above room temperature. From the results of d.c. magnetization measurements on single crystalline BaB6, the saturation magnetization at low temperatures is 8\times 10-4(\mu B/f.u.), in line with other weak ferromagnets of the hexaboride series. The 11B-NMR spectra measured on a collection of single crystals of BaB6 yield a quadrupolar frequency of 472 KHz, in good agreement with calculated field gradients for this type of materials. The central 11B-NMR transition consists of two partially resolved signals, where the frequency displacement between them is of the order of 10 KHz. One of the signals exhibits a positive, the other a negative frequency shift, both of the order of 50 ppm. Between 7 K and room temperature these shifts do not vary with temperature. The temperature dependence of the spin-lattice relaxation rate T1 -1(T) at the B sites is similar to that of other alkaline-earth hexaborides.

  • Open Access Logo Acta Physica Polonica B 34(2003)22, 1537-1537

Permalink: https://www.hzdr.de/publications/Publ-7249
Publ.-Id: 7249


NMR studies of YbB6

Gavilano, J. L.; Mushkolaj, S.; Rau, D.; Ott, H. R.; Bianchi, A.; Fisk, Z.

We report results of DC-magnetization and 11B-NMR measurements on single crystalline YbB6. The magnetization data at temperatures between 4 and 300 K reveal weak ferromagnetic order with a T C>300 K. It involves very small ordered moments, of the order of 0.002 µB/f.u., representing only a small fraction of the effective paramagnetic moment per formula unit that is indicated by the magnetic susceptibility. The latter can be accounted for by assuming that 2% of all the Yb atoms adopt the Yb+3 configuration. Since almost all the Yb ions adopt the divalent configuration one expects YbB6 to be a poor metal.

Keywords: NMR; Magnetism; Hexaborides

  • Physica B 329-333(2003)Part II, 570-571

Permalink: https://www.hzdr.de/publications/Publ-7248
Publ.-Id: 7248


Atomistic simulation of defects in Si: migration of di- and tri-interstitials

Posselt, M.

The state-of-the-art interpretation of physical processes during post-implantation annealing, such as defect evolution, transient-enhanced dopant diffusion and dopant activation, assumes that ion implantation produces only single vacancies and self-interstitials, and that these are the only mobile intrinsic defects. Theoretical investigations show that both assumptions may be not correct. The talk presents results of comprehensive atomistic simulations on the properties of di- and tri-interstitials. It is focused on the migration of these defects and on the atomic mechanisms of the defect diffusion. The results of the atomistic simulations are compared with experimental data. The fact that the simulations predict a high di-interstitial mobility may lead to a re-interpretation of some experimental results.

Keywords: intrinsic defects; silicon; computer simulation

  • Lecture (others)
    43. Arbeitskreis Punktdefekte, 02.-03.03.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7247
Publ.-Id: 7247


Low-temperature thermal conductivity of CaB6 and EuB6

Gianno, K.; Sologubenko, A. V.; Ott, H. R.; Bianchi, A. D.; Fisk, Z.

The thermal conductivities of stoichiometric CaB6, vacancy-doped Ca1-B6, and EuB6have been measured between 6 and 300 K. All our data may be rather well described across the entire temperature regime covered on the basis of a Debye-type relaxation-time approximation and by assuming the concurring influence of various scattering channels on the mean free path of the phonons. An unusual and strong resonance in the scattering rate of the phonons of all investigated materials is attributed to a strong interaction between acoustic itinerant and localized modes, the latter arising from oscillations of the metal cations around their equilibrium position.

  • Journal of Physics: Condensed Matter 15(2003)40, 6739-6748

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Permalink: https://www.hzdr.de/publications/Publ-7246
Publ.-Id: 7246


Possible Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in CeCoIn5

Bianchi, A.; Movshovich, R.; Capan, C.; Pagliuso, P. G.; Sarrao, J. L.

We report observation of the specific heat anomaly within the superconducting state of the heavy fermion CeCoIn5. It appears in the vicinity of the superconducting critical field H c2, where the superconducting transition changes from second to first order, above 10 T for H || [1 1 0] and H || [1 0 0], and above 4.7 T for H || [0 0 1], and at temperatures on the order of 0.1Tc. We interpret the anomaly within the superconducting state as a signature of a Fulde–Ferrell–Larkin–Ovchinnikov FFLO inhomogeneous superconducting state.

Keywords: FFLO; Heavy fermion; Superconductivity; Unconventional; Inhomogeneous superconducting state

Permalink: https://www.hzdr.de/publications/Publ-7245
Publ.-Id: 7245


FFLO superconducting state in CeCoIn5

Bianchi, A.; Movshovich, R.; Capan, C.; Lacerda, A.; Pagliuso, P. G.; Sarrao, J. L.

We present specific heat data for the heavy fermion superconductor CeCoIn5 close to the upper critical field H c2 for magnetic fields applied along the [1 0 0] crystallographic axis. For fields above 10 T, the superconducting phase transition becomes first-order. In the same field range, we observe a second specific heat anomaly within the superconducting state, which we attribute to a Fulde–Ferrell–Larkin–Ovchinnikov state.

Keywords: Heavy fermion superconductors; Superconductivity phase diagrams; Magnetic field-dependent specific heat

  • Journal of Magnetism and Magnetic Materials 272-76(2004), 140-141

Permalink: https://www.hzdr.de/publications/Publ-7244
Publ.-Id: 7244


Electron-spin domains - Magnetic enhancement of superconductivity

Movshovich, R.; Bianchi, A.; Capan, C.; Jaime, M.; Goodrich, R. G.

Magnetic enhancement of superconductivity

  • Nature (2004)427, 802-802

Permalink: https://www.hzdr.de/publications/Publ-7243
Publ.-Id: 7243


First-order transition from a Kondo insulator to a ferromagnetic metal in single crystalline FeSi1-xGex

Yeo, S.; Nakatsuji, S.; Bianchi, A. D.; Schlottmann, P.; Fisk, Z.; Balicas, L.; Stampe, P.; Kennedy, R. J.

The phase diagram of FeSi1-xGex, obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, x c ≈ 0.25. The gap of the insulating phase strongly decreases with x. The specific heat γ coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si=Ge ligand site

  • Physical Review Letters 91(2003)046401, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7242
Publ.-Id: 7242


Possible Fulde-Ferrell-Larkin-Ovchinnikov superconducting state in CeCoIn5

Bianchi, A.; Movshovich, R.; Capan, C.; Pagliuso, P. G.; Sarrao, J. L.

We report specific heat measurements of the heavy fermion superconductor CeCoIn5 in the vicinity of
the superconducting critical field H c2, with magnetic fields in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first
order for fields above 10 T for H ║ [110] and H ║ [100]. In the same range of magnetic fields, we observe
a second specific heat anomaly within the superconducting state. We interpret this anomaly as a
signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for H ║ [100], with the FFLO state occupying a smaller part of the phase
diagram.

Permalink: https://www.hzdr.de/publications/Publ-7241
Publ.-Id: 7241


Avoided antiferromagnetic order and quantum critical point in CeCoIn5

Bianchi, A.; Movshovich, R.; Vekhter, I.; Pagliuso, P. G.; Sarrao, J. L.

We measured the specific heat and resistivity of heavy fermion CeCoIn5 between the superconducting critical field c2 = 5 T and 9 T, with the field in the [001] direction, and at temperatures down to 50 mK. At 5 T the data show a non-Fermi liquid (NFL) behavior down to the lowest temperatures. At the field above 8 T the data exhibit a crossover from the Fermi liquid to a non-Fermi liquid behavior. We analyzed the scaling properties of the specific heat and compared both the resistivity and the specific heat with the predictions of a spin-fluctuation theory. Our analysis leads us to suggest that the NFL behavior is due to incipient antiferromagnetism (AFM) in CeCoIn5 with the quantum critical point in the vicinity of Hc2. Below Hc2 the AFM phase which competes with the paramagnetic ground state is superseded by the superconducting transition.

  • Physical Review Letters 91(2003)257001, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7240
Publ.-Id: 7240


Magneto-optical Kerr effect in Eu1-xCaxB6

Caimi, G.; Broderick, S.; Ott, H. R.; Degiorgi, L.; Bianchi, A. D.; Fisk, Z.

We have measured the magneto-optical Kerr rotation of ferromagnetic Eu1-xCaxB6 with x=0.2 and 0.4, as well as of YbB6 serving as the nonmagnetic reference material. As previously for EuB6, we could identify a feature at 1 eV in the Kerr response which is related with electronic transitions involving the localized 4 f electron states. The absence of this feature in the data for YbB6 confirms the relevance of the partially occupied 4 f states in shaping the magneto-optical features of Eu-based hexaborides. Disorder by Ca-doping broadens the itinerant charge carrier contribution to the magneto-optical spectra.

  • Physical Review B 69(2004)012406, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7239
Publ.-Id: 7239


Optical evidence for a spin-filter effect in the charge transport of Eu0.6Ca0.4B6

Perucchi, A.; Caimi, G.; Ott, H. R.; Degiorgi, L.; Bianchi, A. D.; Fisk, Z.

We have measured the optical reflectivity R(ω) of Eu0.6Ca0.4B6 as a function of temperature (T) between 1.5 and 300 K and in external magnetic fields (H) up to 7 T. R(ω) increases with decreasing T and increasing H field, but the plasma edge feature does not exhibit the sharp onset and steep slope that is observed in EuB6. The analysis of the H-field dependence of the low-T optical conductivity confirms the previously observed exponential decrease of the electrical resistivity upon increasing bulk magnetization at constant T. The individual exponential magnetization dependences of the plasma frequency and scattering rate are also extracted from the optical data.

  • Physical Review Letters 92(2004)067401, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7238
Publ.-Id: 7238


Weak ferromagnetism in CaB6

Bennett, M. C.; van Lierop, J.; Berkeley, E. M.; Mansfield, J. F.; Henderson, C.; Aronson, M. C.; Young, D. P.; Bianchi, A.; Fisk, Z.; Balakirev, F.; Lacerda, A.

We have combined the results of magnetization and Hall effect measurements to conclude that the ferromagnetic moments of lightly doped CaB6 samples display no systematic variation with electron doping level.
Removal of the surface with acid etching substantially reduces the measured moment, although the Hall constant and resistivity are unaffected, indicating that the ferromagnetism largely resides on and near the sample surface. Electron microprobe experiments reveal that Fe and Ni are found at the edges of facets and growth steps, and on other surface features introduced during growth. Our results indicate that the weak ferromagnetism previously reported in undoped CaB6 is most likely of extrinsic origin.

  • Physical Review B 69(2004)132407, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7237
Publ.-Id: 7237


Transport and thermodynamic properties of Sr3Ru2O7 near the quantum critical point

Zhou, Z. X.; Mccall, S.; Alexander, C. S.; Crow, J. E.; Schlottmann, P.; Bianchi, A.; Capan, C.; Movshovich, R.; Kim, K. H.; Jaime, M.; Harrison, N.; Haas, M. K.; Cava, R. J.; Cao, G.

The specific heat and electrical resistivity of Sr3Ru2O7 single crystals are measured in several magnetic
fields applied along the c axis for temperatures below 2 K and at fields up to 17 T. Near the critical metamagnetic
field at B 1 *~7.8 T, the electronic specific heat divided by temperature increases logarithmically as the
temperature decreases, over a large range of T, before saturating below a certain T* (which is sample dependent),
indicating a crossover from a non-Fermi liquid (NFL) region dominated by quantum critical fluctuations
to a Fermi liquid (FL) region. This crossover from a NFL to a FL state is also observed in the resistivity data
near the critical metamagnetic field for Ic and Bc. The coefficient of electronic specific heat, γ, plotted as a
function of field shows two peaks, consistent with the two metamagnetic transitions observed in magnetization
and magnetic torque measurements. At the lowest temperatures, a Schottky-like upturn with decreasing temperature
is observed. The coefficient of the Schottky anomaly exhibits a field dependence similar to that of γ,
implying an influence by the electrons near the Fermi surface on the Schottky level splitting.

  • Physical Review B 69(2004)140409, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7236
Publ.-Id: 7236


Anisotropy of Thermal Conductivity and Possible Signature of the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn5

Capan, C.; Bianchi, A.; Movshovich, R.; Christianson, A. D.; Malinowski, A.; Hundley, M. F.; Lacerda, A.; Pagliuso, P. G.; Sarrao, J. L.

We have measured the thermal conductivity of the heavy-fermion superconductor CeCoIn5 in the vicinity of the upper critical field, with the magnetic field perpendicular to the c axis. Thermal conductivity displays a discontinuous jump at the superconducting phase boundary below critical temperature T 0≈1 K, indicating a change from a second- to first-order transition and confirming the recent results of specific heat measurements on CeCoIn5. In addition, the thermal conductivity data as a function of field display a kink at a field Hk below the superconducting critical field, which closely coincides with the recently discovered anomaly in specific heat, tentatively identified with the appearance of the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state. Our results indicate that the thermal conductivity is enhanced within the FFLO state, and call for further theoretical investigations of the order parameter’s real-space structure (and, in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.

  • Physical Review B 70(2004)134513, 1-7
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7235
Publ.-Id: 7235


Percolation and the Colossal Magnetoresistance of Eu-Based Hexaboride

Wigger, G. A.; Beeli, C.; Felder, E.; Ott, H. R.; Bianchi, A. D.; Fisk, Z.

Upon substituting Ca for Eu in the local-moment ferromagnet EuB6, the Curie temperature TC
decreases substantially with increasing dilution of the magnetic sublattice and is completely suppressed
for x ≤0:3. The Ca substitution leads to significant changes of the electronic properties across the
Eu x Ca1-x B6 series. Electron microscopy data for x ≈ 0.27 indicate a phase separation into Eu- and
Ca-rich clusters of 5 to 10 nm diameter, leading to percolation-type phenomena in the electrical
transport properties. The related critical concentration x p is approximately 0.3. For x ≈ 0.27, we
observe colossal negative magnetoresistance effects at low temperatures, similar in magnitude as those
reported for manganese oxides.

  • Physical Review Letters 93(2004)147203, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7234
Publ.-Id: 7234


Non-Fermi Liquid behavior in CeIrI5 near a metamagnetic transition

Capan, C.; Bianchi, A.; Ronning, F.; Lacerda, A.; Thompson, J. D.; Pagliuso, P. G.; Sarrao, J. L.; Movshovich, R.

We present a specific heat and resistivity study of CeIrIn5 in magnetic fields up to 17 T and temperature down to 50 mK. Both quantities were measured with the magnetic field parallel to the c axis (H║[001]) and within the a-b plane (H┴[001]). Non-Fermi-liquid (NFL) behavior develops above 12 T for H║[001]. The Fermi-liquid state is much more robust for H║[001] and is suppressed only moderately at the highest applied field. Based on the observed trends and the proximity to a metamagnetic phase transition, which exists at fields above 25 T for H║[001], we suggest that the observed NFL behavior in CeIrIn5 is a consequence of a metamagnetic quantum critical point.

  • Physical Review B 70(2004)180502, 1-4
    DOI: 10.1103

Permalink: https://www.hzdr.de/publications/Publ-7233
Publ.-Id: 7233


First Results from SHIP Experiment

Bagryansky, P. A.; Anikeev, A. V.; Ivanov, A. A.; Lizunov, A. A.; Maximov, V. V.; Murakhtin, S. V.; Stepanov, D. N.; Noack, K.; Prikhodko, V. V.; Solomakhin, A. L.

At present, the GDT facility of the Budker Institute of Nuclear Physics Novosibirsk is being upgraded. The first stage of the upgrade is the Synthesized Hot Ion Plasmoid (SHIP) experiment. It aims, on the one hand, at the investigation of plasmas the parameters of which are expected to appear in the region of high neutron production in a GDT based fusion neutron source as proposed by the Budker Institute and, on the other hand, at the investigation of plasmas the parameters of which have never been achieved before in magnetic mirrors.
The experiment is performed in a small mirror section which is installed at the end of one side of GDT. The magnetic field on axis is in the range of 0.5-20 Tesla and the mirror ratio is 1.2-1.4. The mirror is filled with background plasma streaming in from the central cell. This plasma component is maxwellized and has an electron temperature of about 100 eV. Two neutral beam injectors perpendicularly inject a total current of about 50 Atom Amperes of deuterium neutrals with an energy of 20 keV
as a pulse with a duration of about 1 ms. Ionization of the beams generates the high-energy ion component. The device has been equipped with several diagnostic methods which are successfully used in GDT experiments.
The paper presents first results of plasma parameter measurements in the SHIP experiment.

Keywords: gas dynamik trap; magnetic mirror; GDT facility; SHIP experiment; neutral beam injection; plasma diagnostic

  • Contribution to proceedings
    5th Int. Conf. on Open Magnetic Systems for Plasma Confinement,, 05.-09.07.2004, Novosibirsk, Russia
    Open Magnetic Systems for Plasma Confinement, Dexter, Michigan: Beljan Ltd.
  • Lecture (Conference)
    5th Int. Conference on Open Magnetic Systems for Plasma Confinement, 05.-09.07.2004, Novosibirsk, Russia
  • Fusion Science and Technology 47(2005)1T, 59-62

Permalink: https://www.hzdr.de/publications/Publ-7229
Publ.-Id: 7229


Magnetic domain structure of micro-patterned PtMn/CoFe exchange bias bilayers

Liedke, M. O.; Potzger, K.; Hillebrands, B.; McCord, J.; Rickart, M.; Freitas, P.; Fassbender, J.

Using magnetron sputter deposition a number of glass/Ta 7nm/PtMn 20nm/CoFe 4nm/Ta 4nm samples with large exchange bias field were prepared for magnetic pattering investigations. By means of optical lithography and physical etching several patterns with decreasing lateral sizes of either the elements or the spacing between the elements were prepared. The largest square is 50 x 50 µm2 and the smallest only 1 µm2. The separating lines range from 10 µm to 2 µm width. The magnetic characterization of the samples was done by VSM and MOKE. Kerr microscopy and MFM investigations in an applied magnetic field have been performed in order to get a deeper understanding of the domain pattern. All images show a monodomain magnetization state in zero magnetic field. The shape of the structure itself dose not influence the magnetization direction. The shape anisotropy contribution is thus smaller than the unidirectional anisotropy given by the exchange bias. In addition 5 keV He+ ion irradiation was used to decrease exchange bias field value and thereby modify the ratio between unidirectional and shape anisotropy. The magnetic domain structure is investigated as a function of this ratio.

Keywords: magnetism; exchange bias; magnetization reversal; magnetic force microscopy; Kerr microscopy; magnetic patterning

  • Poster
    The European Conference on Physics of Magnetism'05, 24.-27.06.2005, Poznan, Poland

Permalink: https://www.hzdr.de/publications/Publ-7228
Publ.-Id: 7228


Velocity measurements and concentration field visualizations in natural convection copper electrolysis under magnetic field influence

Weier, T.; Hüller, J.; Gerbeth, G.; Weiss, F.-P.

The effect of magnetic fields on momentum and mass transfer in electrochemical processes has been studied by means of Digital Particle Image Velocimetry (DPIV), shadowgraphy and mean current
density measurements.

Chronoamperometric copper electrolysis was carried out in a small electrolytic cell (29x46x6 mm) made mainly from PMMA. The sidewalls forming the vertical electrodes consist of thin copper plates behind
which permanent magnets could be fixed. The Lorentz force generated from the faradaic currents and the permanent magnets field has been always parallel to the electrodes. Depending on the orientation of the magnets, downwards or upwards directed Lorentz forces could be generated.

The moderate magnetic field of permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. Flow
structures measured by DPIV compare very well with the patterns of the concentration field given by shadography. Steady state limiting current densities as well as initially instationary current density
values can be explained by the corresponding velocity measurements. It will be shown that the interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia

Permalink: https://www.hzdr.de/publications/Publ-7227
Publ.-Id: 7227


Status of the GDT Experiment and Future Plans

Abdrashitov, A.; Abdrashitov, G.; Anikeev, A.; Bagryansky, P.; Beklemishev, A.; Deichuli, P.; Ivanov, A.; Korepanov, S.; Maximov, V.; Murakhtin, S.; Lizunov, A.; Prikhodko, V.; Kapitonov, V.; Kolmogorov, V.; Khilchenko, A.; Mishagin, V.; Savkin, V.; Shoukajev, A.; Shulzhenko, G.; Solomakhin, A.; Sorokin, A.; Stepanov, D.; Stupishin, N.; Tsidulko, Y.; Zouev, A.; Noack, K.; Fiksel, G.; Den Hartog, D.

In recent experiments, on-axis transverse beta exceeding 0.4 in the fast ion turning points near the end mirrors has been achieved in the GDT experiment with 4 MW injection of 15-17 keV deuterium neutral beams at the center of the device. Neither enhanced transverse losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. The measured beta value is close to that needed in the versions of the GDT based 14 MeV neutron source. At the same time, the electron
temperature for given injection power and pulse duration is limited to 100-130 eV. Its further increase is planned after upgrading the injection system and increasing the magnetic field at the center of the device up to 0.3 T. The upgrade of the injection system assumes that the neutral beam power incident on the plasma will be increased up to 9-10 MW and the pulse duration is extended from 1.2 to 5 ms. According to the results
of numerical simulations, for the extended pulse duration
a plasma steady state will be achieved with electron temperature of 250-320 eV depending upon the assumptions on the transverse energy loss rate. Future experiments at the GDT upgrade are discussed in the paper.

Keywords: gasdynamic trap; GDT experiment; neutral beam injection; transverse plasma beta; fusion; neutron source

  • Lecture (Conference)
    5th Internationale Conference on Open Magnetic Systems for Plasma Confinement, 05.-09.07.2004, Novosibirsk, Russia
  • Contribution to proceedings
    5th Internationale Conference on Open Magnetic Systems for Plasma Confinement,, 05.-09.07.2004, Novosibirsk, Russia
    Status of the GDT Experiment and Future Plans, Dexter: Beljan Ltd.
  • Fusion Science and Technology 47(2005)1T, 27-34

Permalink: https://www.hzdr.de/publications/Publ-7226
Publ.-Id: 7226


Irreversible magnetization deep in the vortex-liquid state of a 2D superconductor at high magnetic fields

Maniv, T.; Zhuravlev, V.; Wosnitza, J.; Hagel, J.

The remarkable phenomenon of weak magnetization hysteresis loops, observed recently deep in the vortex-liquid state of a nearly two-dimensional (:213) superconductor at low temperatures and high magnetic fields, is shown to reflect the existence of an unusual vortex-liquid state, consisting of collectively pinned crystallites of easily sliding vortex chains.

Keywords: Vortices; Lattices; Systems

  • Journal of Physics: Condensed Matter 16(2004)41, 429-435

Permalink: https://www.hzdr.de/publications/Publ-7225
Publ.-Id: 7225


Fermi-surface reconstruction close to a pressure-induced metal-insulator transition

Wosnitza, J.; Hagel, J.; Stockert, O.; Pfleiderer, C.; Schlueter, J. A.; Mohtasham, J.; Gard, G. L.

We report on a detailed investigation of the pressure-dependent structural and electronic properties close to the pres-sure-induced metal-insulator transition of the quasi-two-dimensional organic superconductor beta"-(BEDT-TTF)2SF5CH2CF2SO3, where BEDT-TTF stand for bisethylenedithio-tetrathiafulvalene (or ET for short). Although the pressure-dependent hysteresis of the metal-insulator transition suggests a structural origin, no major crystallo-graphic modifications could be detected by neutron-scattering experiments. Shubnikov-de Haas (SdH) experiments, on the other hand, show that a reconstructed band structure precedes the phase transition to the insulating state. A new SdH frequency with a rather small effective mass appears.

Keywords: organic superconductors; band structure; metal-insulator transition

  • Journal de Physique IV 114(2004), 277-281

Permalink: https://www.hzdr.de/publications/Publ-7223
Publ.-Id: 7223


Transport properties of CeBiPt in magnetic fields up to 60 T

Wosnitza, J.; Hagel, J.; Kozlova, N.; Eckert, D.; Müller, K.-H.; Mielke, C. H.; Goll, G.; Yoshino, T.; Takabatake, T.

Electrical-transport measurements of the semimetal CeBiPt in magnetic fields up to 60 T reveal a drastic change of the electronic band structure. The oscillating Shubnikov-de Haas signal vanishes above about 25 T although the quantum limit is not yet reached. Above this field the magneto resistance rises strongly independent of angle and temperature. These unique features are caused by the Cc 4f electrons as evidenced by the absence of any unconventional behavior in the sister compound LaBiPt.

Keywords: Shubnikov-de Haas effect; Fermi-surface studies; magnetoresistance; CeBiPt; LaBiPt

  • Physica B 346-347(2004), 127-131

Permalink: https://www.hzdr.de/publications/Publ-7222
Publ.-Id: 7222


Neutron-proton pairing in rotating N similar to Z nuclei: dominance of the isovector component

Afanasjev, A.; Frauendorf, S.

Theoretical calculations of rotating N approximate to Z nuclei with A = 58 - 80 within the cranked Nilsson+Strutinsky approach, cranked relativistic mean field and cranked relativistic Hartree+Bogoliubov theories show good agreement with experiment. They point on the presence of the isovector t = 1 np-pairing, but do not show any indications of the isoscalar t = 0 np-pairing.

  • Nuclear Physics A 746(2004), 575C-578C

Permalink: https://www.hzdr.de/publications/Publ-7221
Publ.-Id: 7221


Shell stabilization and the survival of heavy compound nuclei

Heinz, A.; Schmidt, K.; Junghans, A.

Knowledge of the influence of nuclear shell structure on the survival probability of heavy compound nuclei against fission is important for a quantitative understanding of the production rates of spherical super-heavy elements (SHE). Fission probabilities of N = 126 isotones beyond astatine can be used as test cases for the production of spherical super-heavy elements, as those isotones possess a strong shell correction energy and are highly fissile. Here, we report on two new experimental approaches which probe the effect of the closed neutron shell at N = 126 on the competition between fission and particle evaporation using projectile fragmentation and electromagnetic-induced fission of radioactive beams. We conclude that these nuclei lose at least a great part of their stability against fission at low excitation energies and angular momenta-mostly due to the influence of collective contributions in the level density. Implications on the production of spherical SHE will be!
discussed.

  • Nuclear Physics A 746(2004), 483C-486C

Permalink: https://www.hzdr.de/publications/Publ-7220
Publ.-Id: 7220


New determination of the Be-7(p,gamma)B-8 S-factor

Junghans, A.; Mohrmann, E.; Snover, K.; Et, A.

We present new measurements of the Be-7(p,gamma)B-8 cross section from (E) over bar (cm) = 116 to 2460 keV. Our new measurements lead to S-17(0) = 22.1 +/- 0.6(expt) +/- 0.6(theor) eV b based on data from (E) over bar (cm) = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. We compare our results to other S-17(0) values extracted from both direct (Be-7(p, gamma)B-8) and indirect (Coulomb dissociation and heavy-ion reaction) measurements, and show that the results of these 3 types of experiments are not mutually compatible. We recommend a "best" value, S-17(0) = 21.4 +/- 0.5(expt) +/- 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1(+) resonance.

  • Nuclear Physics A 746(2004), 210C-214C

Permalink: https://www.hzdr.de/publications/Publ-7219
Publ.-Id: 7219


Optical characterization of beta-FeSi2 layers formed by ion beam synthesis

Ayache, R.; Bouabellou, A.; Richter, E.

Thin beta-FeSi2 layers have been prepared by ion beam synthesis (IBS) on (111)Si substrates. The obtained samples have been characterized by means of infrared and Raman spectroscopies. The infrared (IR) transmittance spectra show the absorption at 310 cm(-1) as an indication of the initial nucleation of beta-FeSi2 precipitates during the implantation of iron into silicon substrate. The main feature of the photoluminescence (PL) measurements at 12 K in the beta-FeSi2/(111)Si samples annealed at 850 degreesC for 90 min is an intense peak localized at 0.811 eV. This peak is assigned to optical radiative transitions intrinsic to beta-FeSi2. (C) 2004 Elsevier Ltd. All rights reserved.

  • Materials Science in Semiconductor Processing 7(2004)4-6, 463-466

Permalink: https://www.hzdr.de/publications/Publ-7218
Publ.-Id: 7218


Mesoscopic dots as collective terahertz oscillators

Metzner, C.; Stehr, D.

Electrons confined in a flat semiconductor quantum dot with a parabolic in-plane potential act like a collective many-particle oscillator under coherent intraband excitation. We investigate theoretically the properties of these oscillators under a simultaneous scale transformation of the lateral dimensions and the electron occupation number. As the lateral size increases from a few nm (typical for self-assembled dots) to the mesoscopic regime, the physics of the system is changing qualitatively: Quantization effects gradually lose importance against Coulomb interactions and eventually the electron lake in a mesoscopic dot resembles a classical Wigner liquid. This parabolically confined "Wigner lake" behaves to the outside like a form-elastic "superparticle" of high charge. It can be coherently controlled by THz dipole radiation just like a single electron, but with reduced Brownian diffusion in the phonon heat bath. We propose a flexible method to fabricate single mesoscopic!
dots of a controlled shape, Coulomb-coupled groups of dots, and almost arbitrary potential landscapes, using current semiconductor technology. As a first example, the collective modes of two Coulomb-coupled superparticles in neighboring dots are calculated. Also, we consider the possibility of steering a superparticle with shaped laser pulses to follow any complex two-dimensional orbit.

  • Physical Review B 7019(2004)19, 5433-5433

Permalink: https://www.hzdr.de/publications/Publ-7217
Publ.-Id: 7217


Numerical investigation of transition control in low conductive fluids

Albrecht, T.; Grundmann, R.; Mutschke, G.; Gerbeth, G.

We investigate numerically the transition to turbulence in a flat-plate boundary layer controlled by electromagnetic forces. The fluid considered is incompressible, Newtonian and low conductive. Similar to boundary layer suction, when applying a steady, wall-parallel, and streamwise orientated Lorentz force, (as suggested by Gailitis and Lielausis [1] in the early 1960s) the Blasius velocity profile is transformed to an exponential one gaining a critical Reynolds number which is increased by two orders of magnitude.

Two and three dimensional direct numerical simulation (DNS) of both linear and nonlinear stages of the transition process were performed, as well as alinear stability analysis (LSA) of the calculated intermediate velocity profiles. DNS and preliminary LSA results confirm the expected increased stability of the controlled flow. Depending on Lorentz force strength transition to turbulence is delayed or even stopped. Suprisingly, both DNS and LSA results suggest interesting stability characteristics of the intermediate velocity profiles.

In DNS, to initiate transition, small amplitude disturbances are introduced by means of an oscillating body force within a small region near the inflow boundary, forming Tollmien-Schlichting waves (TSW) which grow and decay in uncontrolled case corresponging to linear stability theory. When applying Lorentz force, TSW of all investigated frequencies 0.4 <= F+ <= 3.75 are damped within the computational domain extending over 900 times the inflow displacement thickness d1i. Reynolds number, based on d1i, is 360. The decay rate based on the maximum rms value in wall-normal direction of the streamwise velocity component, is maximum in a region near the onset of control and decreases as the velocity profile approaches the exponential state. This observation could suggest that in the intermediate region there are profiles more stable than the exponential one, although we are aware that from these decay rates one cannot conclude directly the stability of a velocity profile, notably its critical reynolds number. However, our assumption is confirmed by preliminary LSA results where critical Reynolds numbers of intermediate profiles are found to be larger than for the exponential profile.

By three dimensional DNS we show that transition to turbulence can be stopped even in it's late stage. While the evolution of Lambda vorticies from former two dimensional TSW remains almost unchanged, the emerge of Omega vorticies is supressed with increasing Lorentz force strength, thus relaminarizing the flow.

[1] A. Gailitis, O. Lielausis: On a possibility to reduce the hydrodynamic resistance of a plate in an electrolyte. Applied Magnetohydrodynamics, Reports of the Physics Institute Riga, Vol. 12, pp. 143-146, 1961

Keywords: Fluid Mechanics; Magnetohydrodynamics; Stability; Transition; Control

  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 145-148

Permalink: https://www.hzdr.de/publications/Publ-7216
Publ.-Id: 7216


Rossendorf Beamline at ESRF: Biannual Report 2003/2004

Scheinost, A.; Schell, N.

Keywords: EXAFS Synchrotron; radiochemistry; x-ray absorption; diffraction spectroscopy; actinides; materials sciences

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZR-418 2005
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-7215
Publ.-Id: 7215


TRIDYN simulation of target poisoning in reactive sputtering

Rosén, D.; Katardjiev, I.; Berg, S.; Möller, W.

During reactive sputter deposition, target "poisoning", i.e. the formation of a compound layer at the target surface, may reduce the sputter erosion rate substantially and thereby represent a major limitation to achieve high deposition rates. In order to investigate the formation of the poisoned layer, the TRIDYN program has been employed to simulate the processes that take place at the target surface during sputtering at ion energies which are typical for a magnetron discharge, in a typical gas mixture of Ar with a small (<10%) addition of a reactive gas (e.g. oxygen). The bulk of the sputtering results from Ar ion bombardment, while the reactive gas ions contribute to compound formation due to implantation into the subsurface layer. In addition, reactive gas molecules are adsorbed on the surface and react with target metal atoms to add to the formation of the compound layer. Thus, both chemisorption and ion implantation of energetic reactive ions are the two main mechanism! s for the formation of the poisoned layer.TRIDYN simulations have been performed at varying reactive ion to total ion flux ratio, and at varying ion to reactive neutral flux ratio, for fluences which are sufficiently large to achieve a stationary deposition/erosion balance. The results illustrate that the two mechanisms will generate almost identical shapes of the poisoned layer. They also demonstrate the significance of recoil implantation from the chemisorbed layer for the formation of the compound layer. In agreement with experimental findings, the calculated sputter erosion rate of the target is predicted to decrease monotonically as the partial pressure of the reactive gas increases. The shape of the sputter erosion curve hardly changes between conditions dominated by ion implantation or chemisorption. We therefore conclude that ion implantation basically acts as an additional source of reactive atoms to the target surface.

  • Nuclear Instruments and Methods in Physics Research B 228(2005), 193-197

Permalink: https://www.hzdr.de/publications/Publ-7214
Publ.-Id: 7214


Fate of U(VI) Added to a U Mining Waste Sample and the Resulting Changes in the Indigenous Bacterial Community

Geissler, A.; Scheinost, A.; Selenska-Pobell, S.

Background
Bacteria play an important role in biogeochemical transformations and migration of uranium (U) in nature. In order to understand how U(VI) interacts with natural bacterial communities of U mining waste piles a series of microcosm experiments was performed.
Methods
Several portions of a solid sample collected from the U mining waste pile near the city of Johanngeorgenstadt in Germany were supplemented with different amounts of U(VI), starting from the original 40 mg U/kg up to 300 mg/kg.
The solubility of the U originally present and of the added U was assessed by selective sequential extraction (SSE). The composition of bacterial communities present in the original and in the supplemented with U samples was analyzed applying 16S rDNA retrieval by using 43F and 1404R degenerated primers.
Results
SSE analysis demonstrated that in the original sample the main part of uranium was strongly bound in mineral phases. The bacterial community of this sample was predominated by Alphaproteobacteria and by representatives of Holophaga /Acidobacterium phylum.
The bacterial community structure of the sample was noticeable changed by increasing its U content to 100 mg/kg . No Holophaga/Acidobacterium and only a few representatives of Alphaproteobacteria were retrieved in this sample. Instead, a large number of sequences of mainly Gamma-Pseudomonas, and of Arthrobacter sp. were found. The propagation of several populations of Deltaproteobacteria and especially of Geobacter sp. was induced in the sample as well. After 4 weeks of incubation, most of the U added to this sample was still only weakly complexed.
The bacterial community structure of the most contaminated sample, containing 300 mg U/kg, differed significantly from the two samples described above and depended on the aeration conditions during the incubation. In this sample the number of 16S rDNA sequences representing Cytophaga/Flavobacterium /Bacteroides group was extremely high. Arthrobacter sp. populations were also identified but not as strongly predominant.
Conclusions
The addition of U(VI) to a low contaminated U mining waste sample induces significant shifting in the indigenous bacterial populations. The effect of the added U(VI)seems to depend on its amount and on the redox conditions.

  • Contribution to proceedings
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States
  • Lecture (Conference)
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States

Permalink: https://www.hzdr.de/publications/Publ-7213
Publ.-Id: 7213


Microbial Diversity and Activity in Waters of a Siberian Monitoring Well at the Deep-Bore-Hole Radioactive Waste Disposal Site TOMSK-7

Nedelkova, M.; Merroun, M.; Selenska-Pobell, S.

Background
Microorganisms strongly influence the migration of radionuclides in the environment. For this reason analysis of natural bacterial and archaeal communities near radioactive wastes deposition sites is of great importance for risk assessments. In this study diversity was studied of the microorganisms indigenous for a monitoring well near the radioactive waste injection site Tomst-7 in Siberia. In addition, interactions of several bacterial isolates from this site with uranium and other metals was investigated.
Methods
Microbial diversity was studied applying the 16S rDNA7F-1513F for bacteria and 16S rDNA21f-958R for archaea. The diversity of the autotrophic bacteria was estimated by direct analysis of different RubisCO gene forms. Oligotrophic bacteria were cultured in low nutrient R2A medium. Interactions of the cultured bacterial isolates with U, Ni, Pb, As, and other metals were studied by using ICP-MS, flow cytometry and X-ray spectroscopic analyses.
Results
Our analyses demonstrated presence of a large number of diverse bacterial and archaeal groups at a depth of about 300m at the Siberian depository site Tomsk-7 where the radioactive wastes were injected. The most predominant bacterial populations were those of Betaproteobacteria mainly from the Rhodocyclus group, of Citophaga/Flavo-bacterium/Bacteroides, and of several novel “Cyanobacteria-like” groups. The RubisCO approach confirmed the Betaproteobacterial predominance in the samples studied.
Bacterial isolates were cultured from the samples belonging to Sphingomonas sp., Brevundimonas sp., Methylobacter sp., and a large microdiverse group of Actinobacteria closely related to Microbacterium oxydans. They tolerated U and other heavy metals in a species- and even strain-specific way. EXAFS analyses demonstrated that the isolates of Microbacterium sp. and of Sphingomonas sp. are complexing U(VI) at pH 4.5 via phosphorus (P) in a form of meta-autunite. The latter was connected to the liberation of inorganic phosphate by these strains due to their exo-phosphatase activity. At lower pH values the U is bound to organic phosphate residues.
Conclusions
The environment around the radioactive waste injection site Tomsk-7 possesses a large variety of microorganisms with a potential to bind and possibly transport radionuclides.

  • Contribution to proceedings
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States
  • Lecture (Conference)
    ISSM 05 + ISEB XVII, 14.-19.08.2005, Jackson Hole, Wyoming, United States

Permalink: https://www.hzdr.de/publications/Publ-7212
Publ.-Id: 7212


Anomalous behaviors of E-1/E-2 deep level defects in 6H silicon carbide

Chen, X.; Ling, C.; Gong, M.; Fung, S.; Beling, C.; Brauer, G.; Anwand, W.; Skorupa, W.

Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7 MeV electron-irradiated n-type 6H-SiC. Similar to others' results, the behaviors of E-1 and E-2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E-1/E-2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E-1/E-2. The activation energy and the capture cross section of this defect are E-C-0.31 eV and sigma similar to 8 x 10(-11) cm(2), respectively.

Keywords: Deep level transient spectroscopy; silicon carbide; electron irradiation

  • Applied Physics Letters 86(2005)3, 31903-31903

Permalink: https://www.hzdr.de/publications/Publ-7211
Publ.-Id: 7211


Experimental results on the effect of wall-parallel Lorentz forces on lift and drag of hydrofoils

Weier, T.; Gerbeth, G.

Lorentz forces on the suction side flow of NACA 0015 and PTL IV hydrofoils is investigated experimentally. Emphasis is placed on separation control. Steady as well as time periodic Lorentz forces will be discussed. Their effect is compared mainly in respect of the attainable increase of the maximum lift and in terms of power consumption.

  • Lecture (Conference)
    2nd International Symposium on Seawater Drag Reduction, 23.-26.05.2005, Busan, South Korea
  • Contribution to proceedings
    2nd International Symposium on Seawater Drag Reduction, 23.-26.05.2005, Busan, South Korea
    Proceedings, 267-281

Permalink: https://www.hzdr.de/publications/Publ-7210
Publ.-Id: 7210


From short-wavelength quantum cascade lasers to impulsive THz emitters

Helm, M.

I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.

Keywords: quantum cascade lasers; THz emitters

  • Lecture (others)
    Seminarvortrag bei THALES Research & Technology, 24.02.2005, Orsay, France

Permalink: https://www.hzdr.de/publications/Publ-7209
Publ.-Id: 7209


Recent developments at the Dresden High Magnetic Field Laboratory

Herrmannsdörfer, T.

Recent developments at the Dresden High Magnetic Field Laboratory

  • Lecture (Conference)
    3rd Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 18.09.2004, Toulouse, France

Permalink: https://www.hzdr.de/publications/Publ-7208
Publ.-Id: 7208


The Dresden High Field Project

Herrmannsdörfer, T.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

Keywords: Dresden High Field Project

  • Invited lecture (Conferences)
    14. Edgar Lüscher Seminar, 03.02.2003, Serneus, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-7205
Publ.-Id: 7205


Synthesis and radiopharmacological evaluation of 2´-(4-fluorophenyl)-21-[18F]fluoro-20-oxo-11β,17α-dihydroxy-pregn-4-eno[3,2-c]pyrazole as potential glucocorticoid receptor ligand for positron emission tomography (PET)

Wüst, F.; Knieß, T.; Kretzschmar, M.; Bergmann, R.

The radiosynthesis and the radiopharmacological evaluation of pyrazolo steroid 2´-(4-fluorophenyl)-21-[18F]fluoro-20-oxo-11β,17α-dihydroxy-pregn-4-eno[3,2-c]pyrazole [18F]-2 is described. The radiolabeling was accomplished in 3 - 4 % decay-corrected radiochemical yield within 80 min at an specific radioactivity of 0.8-1.2 Ci/μmol. Biodistribution studies in male Wistar rats showed an initial brain uptake of 0.25 ± 0.03 % ID/g after 5 min, which remained constant over 60 min. The radiopharmacological evaluation of compound [18F]-2 was completed with autoradiography using rat brain sections and micro-PET imaging.

Keywords: Positron emission tomography; Glucocorticoid receptor; Radiolabeling

  • Bioorganic & Medicinal Chemistry Letters 15(2005), 1303-1306

Permalink: https://www.hzdr.de/publications/Publ-7204
Publ.-Id: 7204


High Field Lab Dresden, progresses

Herrmannsdörfer, T.; Krug, H.

Further developments for the Dresden High Field Laboratory

  • Lecture (Conference)
    2nd Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 24.01.2003, Nijmegen, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-7203
Publ.-Id: 7203


Survey on finite element software with "multiple physics options"

Herrmannsdörfer, T.

In order to design and optimize pulsed field coils, their current leads, and in particular their reinforcement, we currently test commercial Finite Element software of various suppliers. We concentrate on these programs which have implemented so called "multiphysics modules" which are able to solve combined problems as they typically occur in high field techniques: e.g. calculation of the magnetic field from a current distribution along with the resulting Lorentz forces, stresses, dislocations etc.. In detail, we focus on the programs ANSYS, ANSOFT, as well as FEMLAB. We like to give a brief survey of their usefulness, perspectives, and last but not least, of their cost.

Keywords: Novel Multiphysics Finite Element Software

  • Lecture (Conference)
    1st Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 21.06.2002, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7201
Publ.-Id: 7201


High Field Lab Dresden, building

Herrmannsdörfer, T.

In the frame of the high field project Dresden, a new building to be constructed at the research center Rossendorf is in its design phase. The HLD building will be located near the IR-free electron lasers of the superconducting linear accelerator ELBE in order to provide the possibility of IR spectroscopy in high pulsed magnetic fields. Following the present plans, five magnet cells for pulsed magnets, preparation rooms, a lab for superconducting magnets and four labs for accompanying experiments are located around a central room which houses the capacitor bank. In addition, a workshop, stores, and a technical section on one side, as well as the offices for stuff and guests and a control room on the other side are located in separate sections. We present the plans emphasising the ability and the safety items in order to get your feedback.

Keywords: High Field Lab Dresden

  • Lecture (Conference)
    1st Workshop on High Field Techniques of the High Field Labs of Toulouse, Nijmegen and Dresden, 21.06.2002, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7200
Publ.-Id: 7200


Synthesis and biological evaluation of S-[11C]methylated mercaptoimidazolde piperazinyl derivatives as potential radioligands for imaging 5-HT1A receptors by positron emission tomography (PET)

Garcia, R.; Xavier, C.; Paulo, A.; Santos, I.; Knieß, T.; Bergmann, R.; Wüst, F.

The novel 2-mercaptoimidazolde derivatives, 1-[4-((2-methoxyphenyl)-1-piperazinyl)-butyl]-2-mercaptoimidazolde (3) and methyl[4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-mercapto-1-methylimidazol-5-yl)methanamide (8), were efficiently labelled with 11C through methylation of the thioketone function with [11C]methyl iodide. The resulting radioligands 1-[4-((2-methoxyphenyl)-1-piperazinyl))butyl]-2-thio[11C]-methylimidazole ([11C]9) and methyl [4-((2-methoxyphenyl)-1-piperazinyl))butyl] (2-thio[11C]methyl-1-methylimidazol-5-yl)-methanamide ([11C]10) were synthesized in radiochemical yields of 20 - 30 % (decay-corrected, related to [11C]CO2) at a specific radioactivity of 0.2-0.4 Ci/μmol within 40-45 min including HPLC-purification. The radiochemical purity exceeded 99 %. The reference compounds 9 and 10 were tested in a competitive receptor binding assay to determine their affinity toward the 5-HT1A recptor. Both compounds exhibit excellent sub-nanomolar affinities (IC50 = 0.576 ± 0.008 nM (9); IC50 = 0.86 ± 0.02 nM (10)) for the 5-HT1A receptor while displaying a high selectivity towards the 5-HT2A subtype of receptors (IC50 > 480 nM). By contrast, compound 9 also shows substantial binding for the alpha-adrenergic receptor (IC50 = 3.00 ± 0.02 nM) when compared with compound 10 (IC50 = 54.5 ± 0.6 nM). Preliminary biodistribution studies in rats showed an initial brain uptake of 1.14 ± 0.11 and 0.37 ± 0.04 % ID/g after 5 min, which decreased to 0.18 ± 0.04 and 0.16 ± 0.01 % ID/g after 60 min for compounds [11C]9 and [11C]10, respectively. For both compounds, the cerebellum and rest of the brain uptake are very similar at the different time points. Unlike [11C]9, the radioligand [11C]10 has significant uptake and retention in the adrenal glands. Due to their washout from the brain compounds [11C]9 and [11C]10 seem not to be good condidates as radioligands for imaging 5-HT1A receptors by PET.

Keywords: carbon-11; mercaptoimidazoles; 5-HT1A receptors; piperazines; positron emission tomography

  • Journal of Labelled Compounds and Radiopharmaceuticals 48(2005), 301-315

Permalink: https://www.hzdr.de/publications/Publ-7198
Publ.-Id: 7198


Research at High Magnetic Fields in Europe, the New Facility in Dresden

Herrmannsdörfer, T.

In nature, the magnetic field acts as a fundamental thermodynamic property like temperature or pressure. For this, the magnetic field plays a decisive role in many facets of nature, and in consequence, is of importance in several natural sciences. In particular, the understanding of magnetic properties of matter and the interplay of magnetism with other quantities is a challenging field of research. Under extreme conditions, like low temperatures, high pressures, and high magnetic fields, new interesting properties of matter can appear and the understanding of materials properties can crucially be gained.

Further, the manifold magnetic effects in nature and in particular the magnetic properties of matter are a rich source for technological innovations. Historically, there is an immense number of inventions like the compass, electro motor, generator, relay, magnetic brake, levitating train, nuclear magnetic resonance tomograph, hard disk drive, magneto-electric random access memory. Nowadays, in transport, energy production, medicine, communication, data storage, and other areas of daily live, magnetic systems, components, and properties are used in a large variety.

In the last decades, the application of high magnetic fields became a powerful research tool. Especially in solid state physics important discoveries like the integer quantum Hall and fractional quantum Hall effect, both honoured with the Physics Nobel Prize, are based on experiments in very high magnetic fields.

In order to establish a large modern user facility with unique experimental possibilities for science in high magnetic fields and in order to provide an easy access for the high field community in Europe, the Dresden High Field Project has been created. Since 2003 this facility is under construction. In this paper, we give a snapshot on the status and some recent achievements in the course of the project. The Dresden High Field Laboratory for nondestructive pulsed magnetic fields up to 100 T will open its doors as a user facility in January 2007.

Keywords: High Magnetic Fields; Pulsed Fields; Experiments in High Magnetic Fields; User Facility; Megagauss

  • Invited lecture (Conferences)
    12. Internationale Konferenz für Materialwissenschaften und Technologie (Co Mat Tech 2004), 14.-15.10.2004, Trnava, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-7197
Publ.-Id: 7197


The new high magnetic field laboratory at Dresden-Rossendorf

Herrmannsdörfer, T.

A new facility for experiments in pulsed high magnetic fields is under construction at the Forschungszentrum Rossendorf in Dresden, Germany. Its heart will be a modular 50 MJ / 24 kV capacitor bank in a new laboratory. In order to offer a wide spectrum of experimental possibilities, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. Experience in the construction of the pulsed capacitive power supply as well as in the experimental equipment has been gained from a pilot laboratory at the IFW since 1999. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental possibilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible in pulsed fields by connecting the pulsed field lab to the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
The laboratory building will be completed in 2004. The 50 MJ power supply can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and will be tested in 2004 by the 1.44 MJ / 24 kV pilot power supply manufactured at FZR. The user coils as well as the experimental equipment will be installed in 2006, so that the facility can open its doors as a user laboratory in 2007.

* The HLD project has been jointly submitted for funding by the FZR, the Leibniz-Institut für Festkörper- und Werkstoffforschung IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the Technische Universität Dresden. It is jointly funded for installation by the Bundesministerium für Bildung und Forschung of Germany and the Sächsische Ministerium für Wissenschaft und Kunst in the years 2003 to 2006.

Keywords: High Magnetic Fields; Pulsed Fields; Experiments in High Magnetic Fields; User Facility; Megagauss

  • Lecture (Conference)
    Joint European Magnetic Symposium, 05.-10.09.2004, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7196
Publ.-Id: 7196


Van Vleck Paramagnets in High Magnetic Fields

Herrmannsdörfer, T.

We present measurements of the dc magnetization M(B) of van Vleck paramagnets, e.g. PrNi5, at high magnetic fields up to B = 60 T. At low fields up to 10 T, we observe magnetizations which increase linearly with the applied field. Beyond 10 T, the magnetizations start to become nonlinear as the result of the shifts of the energy levels of the crystalline electrical field (CEF) states of the 4f-Pr3+ electrons through the external field. A significant change of slope of the magnetization M(B) as well as of the corresponding susceptibility dM/dB occurs in PrNi5 at B = 20 T which can be explained by a level crossing of the two lowest singlet CEF states. We compare our data to calculations from a point charge model.

  • Poster
    RHMF, 20.-23.07.2003, Toulouse, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-7195
Publ.-Id: 7195


The Dresden High Field Project

Herrmannsdörfer, T.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

  • Poster
    RHMF, 20.-23.07.2003, Toulouse, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-7194
Publ.-Id: 7194


The Pulsed High Magnetic Field Facility in Dresden

Herrmannsdörfer, T.

We are building a user facility for experiments in pulsed high magnetic fields at the Forschungszentrum Rossendorf, Dresden. Based on the experience obtained since 1999 from a pilot pulsed field laboratory with a 1 MJ / 10 kV capacitor bank and magnets for the field range up to 60 T at the IFW, the new large scale facility will be built until 2006. It will comprise a new laboratory building, a 50 MJ / 24 kV capacitor bank, and high performance experimental equipment including various pulsed magnets for the field range up to 100 T / 10 ms. In order to offer a wide spectrum of experimental possibilities, the pulsed field magnets are planned with various bore diameters (up to 50 mm) and various pulse times (10 ms to 1 s). As a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible at high magnetic fields by connecting the pulsed field lab to the free-electron-lasers of the superconducting electron linear accelerator ELBE of the FZR. The german Wissenschaftsrat has recently recommended the Dresden High Field Project without any hesitation. The project is a joint effort of the FZR, the IFW, the Max-Planck-Institut für chemische Physik fester Stoffe, the Max-Planck-Institut für Physik komplexer Systeme, and the Institut für Angewandte Physik of the TU Dresden.

  • Invited lecture (Conferences)
    Symposium „Materials under extreme conditions“ während der 67. Physikertagung der DPG, 24.-28.03.2003, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7193
Publ.-Id: 7193


The impact of hyperfine interaction on Cooper pair breaking

Herrmannsdörfer, T.

Since the first experimental finding of a competition between nuclear magnetism and superconductivity in the nuclear ferromagnet AuIn2, investigations have been extended to Al, Sn, Rh, In, AuAl2, and very recently to Pr1-xLaxTe. The experiments have demonstrated that the contribution of nuclear magnetism to Cooper pair breaking is a common phenomenon. Even in a system with tiny nuclear magnetic moments (e.g. Sn), a reduction of the critical field Bc(T) has been detected at ultralow temperatures. In more detail, the observed influences of nuclear magnetism on superconductivity vary strongly with the size of hyperfine coupling, ranging between a tiny reduction of Bc(T) in the case of weak hyperfine coupling (AuAl2) and the complete destruction of superconductivity in the opposite case of strongly coupled and hyperfine enhanced nuclear spin systems (e.g. Pr0.50La0.50Te). The hyperfine interaction appeares to be the dominant mechanism for the nuclear magnetic contribution to Cooper pair breaking.

  • Poster
    International Conference on Ultralow Temperature Physics, 28.-31.08.2002, Kanazawa, Japan

Permalink: https://www.hzdr.de/publications/Publ-7192
Publ.-Id: 7192


Anomalous properties of the heavy fermion compound CeCu6 at ultralow temperatures

Herrmannsdörfer, T.

In the course of our investigation of the heavy fermion compound CeCu6,
we have recently performed measurements of the heat capacity as well as elastic neutron diffraction down to ultralow temperatures. In the last decade, various groups have investigated this compound by means of susceptibility, magnetization, nuclear quadrupole resonance, and thermal expansion as well. There is a strong evidence for a magnetic ordering transition at about 2.5 mK. Here we like to present our latest heat capacity data taken at 0.1 mK ≤ T ≤ 100 K as well as neutron diffraction data taken down to 15 mK. These results give further
hints for magnetic correlation effects in CeCu6.

  • Poster
    International Conference on Ultralow Temperature Physics, 28.-31.08.2002, Kanazawa, Japan

Permalink: https://www.hzdr.de/publications/Publ-7191
Publ.-Id: 7191


Hyperfine Enhanced Nuclear Antiferromagnetism in PrS, PrTe, and PrBi

Herrmannsdörfer, T.

We have investigated the strongly correlated electronic and nuclear magnetic properties of the cubic Van Vleck paramagnets PrS, PrTe, and PrBi by means of SQUID magnetometry at 2 K≤T≤300 K as well as ac susceptometry at ultralow temperatures, 0.06 mK≤T ≤100 mK. We observe magnetic ordering transitions of the hyperfine enhanced magnetic moments of the 141Pr nuclei in all three compounds. Our ac susceptibility data taken at ultralow temperatures point to antiferromagnetic ground states. The observed Neel temperatures, TN(PrS, PrTe, PrBi) = 0.09, 0.60, 1.20 mK, scale with the size of the Van Vleck susceptiblity and related hyperfine enhancement factor respectively. The nuclear fcc spin-5\2 antiferromagnets PrS, PrTe, and PrBi are promising candidates for interesting spin structures. Currently we use the metallurgical possibility to substitute Pr by La and Pb in these compounds in order to study the multiple interplay between electronic magnetism, nuclear magnetism, superconductivity (e.g. in Pr1-xLaxTe), and semiconductivity (e.g. in Pr1-xPbxTe).

  • Invited lecture (Conferences)
    International Conference on Ultralow Temperature Physics, 28.-31.08.2002, Kanazawa, Japan

Permalink: https://www.hzdr.de/publications/Publ-7190
Publ.-Id: 7190


First finding of reentrant superconductivity driven by hyperfine interaction

Herrmannsdörfer, T.

Compared to magnetically doped superconductors described by the theory of Abrikosov and Gorkov, electronic singlet ground state systems can have a much larger critical concentration of magnetic impurities, following the model of Keller and Fulde. The recent study of the superconducting Van Vleck paramagnet La{1-x}PrxTe revealed a critical Pr{3+} concentration x close above 0.50. Surprisingly, in La{0.50}Pr{0.50}Te the superconducting state with Tc = 0.20 K appeares not to be stable down to zero temperature. Instead, a reentrant transition to the normal state likely caused by the hyperfine enhanced magnetic moments of the {141}Pr nuclei occurs at about 0.02 K. Although these moments are not in a magnetically ordered ground state at T = 0.02 K, their contribution to Cooper pair breaking seems to be even stronger than of ferromagnetically ordered but non enhanced nuclear moments in type-I superconducting AuIn2.

  • Poster
    23rd International Conference on Low Temperature Physics, 20.-27.08.2002, Hiroshima, Japan

Permalink: https://www.hzdr.de/publications/Publ-7189
Publ.-Id: 7189


First observation of superconductivity in LaCu6 and possible applications

Herrmannsdörfer, T.

We have measured the ac susceptibility and resistivity of highly pure samples of the intermetallic compound LaCu6 down to ultralow temperatures. We have prepared the samples by arc melting of stoichiometric amounts of 99.99\% La and 99.9999\% Cu in a water-cooled copper crucible under Ar protective atmosphere and analysed them by x-ray diffraction and SQUID magnetometry. At T≤Tc = 0.16 K we observe a superconducting transition. Due to the manifold physical properties of isostructural ReCu6 compounds (e.g. RE = Ce: heavy fermion system, RE = Pr: hyperfine enhanced nuclear spin system, RE = Nd: electronic antiferromagnet), numerous studies of interplay phenomena may become possible in the quasibinary compounds RE1-xLaxCu6, respectively.

  • Poster
    23rd International Conference on Low Temperature Physics, 20.-27.08.2002, Hiroshima, Japan

Permalink: https://www.hzdr.de/publications/Publ-7188
Publ.-Id: 7188


The quantum functional intermetallic compound Pr1-x-yLaxPbyTe

Herrmannsdörfer, T.

The intermetallic compound Pr1-x-yLaxPbyTe shows a wide spectrum of physical phenomena*. Depending on the metallurgical composition as function of x and y, the compound changes its behaviour from nuclear magnetic order to super- or semiconductivity. In addition, there are interesting interplay effects between these ground state phenomena. In consequence, Pr1-x-yLaxPbyTe may serve as an interesting candidate for studies on quantum computing. In this talk, experimental results taken in a wide range of temperature, 0.1 mK ≤ T ≤ 300 K, are presented. Further, effects which arise through the application of high magnetic fields are discussed.

* Whereas several rare earth tellurides undergo magnetic order, in PrTe the crystal electrical field splitting with a singlet ground state leads to Van Vleck paramagnetism. However, the nuclear magnetic moments of Pr are hyperfine enhanced as well as strongly coupled to the conduction electrons in PrTe. In consequence the effective nuclear magnetic moments order antiferromagnetically at 0.6 mK. LaTe is a superconductor with Tc = 5.7 K. The singlet ground state of the Pr ions in Pr1-xLaxTe lead to a large critical Pr concentration x = 0.5 for Cooper pair breaking. Finally, PbTe is a narrow band semiconductor.

Keywords: Quantum Computing; Hyperfine enhanced nuclear magnetism; Quantum functional materials; High Fields; Low Temperature

  • Invited lecture (Conferences)
    InternationalConference on QTSM-QFS, 21.11.2004, Seoul, South Korea

Permalink: https://www.hzdr.de/publications/Publ-7187
Publ.-Id: 7187


Bewertung der Nachhaltigkeit heutiger Technologien der Stromerzeugung - Aggregation der Indikatoren -

Weiß, F.-P.

Die Internationale Länderkommission Kerntechnik (ILK) hat 2004 eine Stellungnahme zur Bewertung der Nachhaltigkeit der Kernenergie und anderer Technologien zur Stromerzeugung vorgelegt.
Die Bewertung beruht u. a. auf der Quantifizierung von Indikatoren, wie etwa die Produktionskosten oder die CO-2-Emission, die verschiedene Nachhaltigkeitsaspekte charakterisieren und der Aggregation dieser Indikatoren zu einem einzigen Nachhaltigkeitskennwert für jede der betrachteten Energieoptionen.
Die Aggregation kann beispielsweise über den Totalkostenansatz oder mit Hilfe der Multikriteriellen Entscheidungsanalyse (MCDA) erfolgen. Die beiden Verfahren führen in der Regel zu unterschiedlicher Nachhaltigkeitsbewertung. Dies liegt zum einen daran, dass einige der Indikatoren finanziell nicht fassbar sind und deshalb im Totalkostenansatz nicht berücksichtigt werden. Zum anderen sind bei der Aggregation mit Hilfe der MCDA Wichtungsfaktoren für Einzelindikatoren und die "Nachhaltigkeitssäulen" Wirtschaft, Umwelt, Gesellschaft festzulegen. Bislang stehen keine Leitlinien für die Fixierung dieser Gewichtungen zur Vefügung. Der Vortrag stellt die genannten Aggregationsverfahren vor und diskuiterit dann Vor- und Nachteile.

  • Invited lecture (Conferences)
    Internationaler ILK-Workshop, 23.02.2005, Frankfurt/Main, Germany

Permalink: https://www.hzdr.de/publications/Publ-7186
Publ.-Id: 7186


The new user facility for high magnetic fields in Dresden, Germany

Herrmannsdörfer, T.

A new facility for experiments in pulsed high magnetic fields (HLD*) is under construction at the Forschungszentrum Rossendorf (FZR) in Dresden, Germany. In order to offer a wide spectrum of experimental capabilities at HLD, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. These magnets will be energized by a modular 50 MJ / 24 kV / 600 kA capacitor bank. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental capabilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 µm will be possible in pulsed fields by connecting the pulsed field lab with the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
Since 1999, we have gained experience in a pilot project by building a 1.0 MJ / 10 kV / 61 T high field laboratory. Funded since 2003, we have already completed our laboratory building and machineshop. In addition, we have planned and started to assemble the 50 MJ power supply which can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and tested using a 1.44 MJ / 24 kV / 37 kA pilot power supply manufactured at FZR. Currently we are starting to order our experimental equipment. Together with the user coils, this equipment will be mainly installed and put into operation during 2006. We are planning to open the doors of our laboratory to users in 2007.

* The HLD project has been jointly submitted for funding by the Forschungszentrum Rossendorf FZR, the Leibniz Institute for Solid State and Materials Research Dresden, the Max Planck Institute for Chemical Physics of Solids, the Max Planck Institute for the Physics of Complex Systems, and the Institute for Solid State Physics of the Dresden Technical University in 1998. It is jointly funded for installation by the Federal Ministry of Education and Research of Germany and the Saxon Ministry of Science and the Fine Arts.

Keywords: High Magnetic Fields; Pulsed Fields; Experiments in High Magnetic Fields; User Facility; Megagauss

  • Invited lecture (Conferences)
    Workshop on the latest Developments in MTNBS, 19.11.2004, Seoul, South Korea

Permalink: https://www.hzdr.de/publications/Publ-7185
Publ.-Id: 7185


The Dresden High Field Project

Herrmannsdörfer, T.

A new facility for experiments in pulsed high magnetic fields up to 1 MegaGauss is under construction at the Forschungszentrum Rossendorf (FZR) in Dresden, Germany. In order to provide a wide spectrum of experimental possibilities, pulsed field coils are planned in the parameter range 60 T, 50 mm, 1s to 100 T, 20 mm, 0.01 s for maximum field, bore, and pulse duration. These field coils will be energized by a modular 50 MJ / 24 kV capacitor bank. Experience in the construction of the pulsed capacitive power supply as well as in the experimental equipment has been gained from a pilot laboratory at the Leibniz-Institut für Festkörper- und Werkstoffforschung, Dresden (IFW) since 1999. The pulsed magnets will be complemented by commercial superconducting magnets for dc fields up to 20 T. Besides many other experimental possibilities, as a unique opportunity, infrared spectroscopy in the wavelength range between 5 and 150 μm will be possible in pulsed fields by connecting the pulsed field lab to the new free-electron-lasers of the neighbouring superconducting electron linear accelerator ELBE of the FZR.
The laboratory building and a workshop hall for coil fabrication will be completed in 2004. The 50 MJ pulsed power supply which is under construction can be partly used in 2005 and will be fully operational by 2006. First pulsed test coils have already been built and will be tested in 2004 by the 1.44 MJ / 24 kV / 40 kA pilot power supply manufactured at FZR. The user coils as well as the experimental equipment will be installed in 2006, so that the facility should open its doors as a user laboratory in 2007.

* The HLD project has been jointly submitted for funding by the Forschungszentrum Rossendorf (FZR), the Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW), the Max-Planck-Institut für chemische Physik fester Stoffe (MPI-CPFS), the Max-Planck-Institut für Physik komplexer Systeme (MP-PKS), and the Institut für Angewandte Physik of the Technische Universität Dresden (TU-DD). It is jointly funded for installation by the Bundesministerium für Bildung und Forschung of Germany and the Sächsische Ministerium für Wissenschaft und Kunst in the years 2003 to 2006.

Keywords: High Magnetic Fields; Pulsed Fields; Experiments in High Magnetic Fields; User Facility; Megagauss

  • Lecture (Conference)
    10. Megagauss-Konferenz MGX, 20.07.2004, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7184
Publ.-Id: 7184


Estimation of field amplitudes during the operation of the 1.5 cell photoelectron RF gun of the PITZ collaboration

Janssen, D.

The present paper discuss the posibility to obtain information about the field flatness of a 1.5 cell normal conducting RF gun cavity during the running of the gun. By measurements of the microwave network parameters at room temperature and by measurement of the passband frequencies in the running regime of the gun it is possible to estimate the perturbation of field flatness, caused by an inhomogeneous temperature distribution.

  • Other report
    Hamburg: DESY, 2005
    7 Seiten

Permalink: https://www.hzdr.de/publications/Publ-7183
Publ.-Id: 7183


[11C]SMe-ADAM, an imaging agent for the brain serotonin transporter: Synthesis, pharmacological characterization and microPET studies in rats

Zessin, J.; Deuther-Conrad, W.; Kretzschmar, M.; Wüst, F.; Pawelke, B.; Brust, P.; Steinbach, J.; Bergmann, R.

N,N-Dimethyl-2-(2-amino-4-methylthiophenylthio)benzylamine (SMe-ADAM, 1) was found to be a highly potent and selective inhibitor of the serotonin transporter (SERT). This compound was labelled with carbon-11 by methylation of the S-desmethyl precursor 10 with [11C]methyl iodide to obtain the potential positron emission tomography radiotracer [11C]SMe-ADAM. Radiochemical yield was 27  5 % and the specific radioactivity was 26 – 40 GBq/µmol at the end of synthesis . Ex vivo and in vivo biodistribution experiments in rats demonstrated a rapid accumulation of the radiotracer in brain regions known to be rich in SERT, such as the thalamus/hypothalamus region (3.59 ± 0.41 %ID/g at 5 min after injection). This is the highest brain uptake ever reported for this type of radiotracer in rats. The specific uptake reached a thalamus to cerebellum ratio of 6.74 ± 0.95 at 60 min post injection. The [11C]SMe-ADAM uptake in the thalamus was significantly decreased by pre-treatment with fluoxetine to 45 ± 9 % of the control values. Furthermore, no metabolites of [11C]SMe-ADAM could be detected in the SERT rich regions of the rat brain. It is concluded that [11C]SMe-ADAM may be a suitable PET ligand for SERT imaging in the living brain.

Keywords: [11C]SMe-ADAM; [11C]methyl iodide; serotonin transporter; microPET

  • Nuclear Medicine and Biology 33(2006)1, 53-63

Permalink: https://www.hzdr.de/publications/Publ-7181
Publ.-Id: 7181


Motion of single gas bubbles rising in a liquid metal exposed to a DC magnetic field

Zhang, C.; Eckert, S.; Gerbeth, G.

The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Within the present interaction number range (N < 2), the applied magnetic field can either increase or decrease the bubble drag coefficient depending on the bubble size and the magnetic interaction parameter. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddy structures in the wake. In case of the longitudinal magnetic field the Strouhal number St decreases with increasing magnetic interaction parameter.

Keywords: Single bubble; Liquid metal; Magnetic field; Terminal velocity; Drag coefficient; Bubble wake; Ultrasound Doppler Velocimetry

  • Poster
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 195-198

Permalink: https://www.hzdr.de/publications/Publ-7178
Publ.-Id: 7178


Flow structures during solidification of metallic alloys affected by a rotating magnetic field

Willers, B.; Nikritjuk, P. A.; Eckert, K.; Eckert, S.

In order to improve the microstructure of casting ingots a rotating magnetic field (RMF) is widely used to stir the liquid phase during solidification. Usually, the interaction between the solidification process and the RMF driven flow has been discussed only in terms of the flow pattern well-known from the laminar, isothermal case being a superposition of a primary swirling flow in azimuthal direction and a secondary flow occurring as a double vortex in the r-z plane. Effects arising from the propagation of the solidification front, the extension of the mush zone or the spin-up of the flow at higher cooling rates are almost not taken into account. We present experimental and numerical investigations concerning the influence of a RMF driven flow on the momentum, heat and mass transfer within a binary Sn-Pb alloys solidified directionally.
Solidification experiments were carried out using a Sn-15wt%Pb alloy in a cylindrical mold positioned on a water-cooled copper chill. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification. The temperature field was monitored using thermocouples. The set-up was enclosed by an inductor providing the RMF. The Taylor numbers Ta were varied between 10e5 and 10e8.
The continuum formulation based model has been adopted for numerical simulations using the following assumptions: all transport properties, such as thermal and electrical conductivity or viscosity, are assumed to be constant; the density of solid phase equals the density of liquid phase; the phases are in local thermodynamic equilibrium; the velocity of solid phase in the upper part of the mushy zone is equal to the velocity of the liquid phase. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution for the time-averaged Lorentz force for a finite cylinder. The resulting set of eqiuations is discretized by an implicit finite-volume, finite-difference based method, and solved by using the SIMPLE algorithm.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case.

Keywords: solidification; Pb-Sn alloy; Fluid flow; Electromagnetic stirring; Rotating magnetic field

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Riga, Latvia
    Proceedings 2(2005), 269-272

Permalink: https://www.hzdr.de/publications/Publ-7177
Publ.-Id: 7177


Synthesis and Binding Properties of Dendritic Oxybathophenanthroline Ligands towards Copper(II)

Stephan, H.; Geipel, G.; Bernhard, G.; Comba, P.; Rajaraman, G.; Hahn, U.; Vögtle, F.

Dendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7-bis(4´-hydroxyphenyl)-1,10-phenanthroline with the corresponding Fréchet-type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid-liquid extraction using the radioisotope 64Cu and time-resolved laser-induced fluorescence (TRLFS) measurements in organic media proving the formation of 1:3 complexes (Cu : dendritic ligand). The stability of the copper complexes is mainly determined by the 1,10-phenanthroline core element. The stability constants of the 1:3 complexes were found to be in the order of log K ~ 16 in CHCl3. On the other hand, increasing generation of the dendritic Fréchet-type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands.

Permalink: https://www.hzdr.de/publications/Publ-7176
Publ.-Id: 7176


A study on the mixing behaviour of different density liquids in a stirred tank reactor by passive and reactive tracers

Hessel, G.; Hristov, H. V.; Kryk, H.; Prasser, H.-M.; Schmitt, W.

Mixing in stirred vessels of different density liquids is common operation in the process industry. The hydrodynamic behaviour of such a system could be crucial for the overall process performance. The aim of this work is to numerically predict the dynamics of the mixing process of initially stratified system of two different density liquids. Stratified conditions could occur in the stirred vessel, especially in the case of impeller malfunctioning, i.e. impeller breakdown. This effect might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses were performed for a non-baffled stirred vessel reactor, mechanically agitated by the Pfaudler impeller. The two main cases of passive and reactive tracer mixing behaviour were numerically predicted by the means of the CFD software CFX 5.7. In both cases the system of two miscible liquids with different densities was dynamically predicted in 3D from an initially stratified to a complete mixing condition. The full 3D simulation was applied in order to capture the flow instabilities associated with the impeller blade passage, especially pronounced in the first few seconds after the impeller start. In order to study the effect of the free surface deformation on the mixing process, the gas phase was also involved into the system via the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. In the case of the reactive tracer mixing, the alkali was diluted in the lighter liquid. The simulations were performed on different grids in order to obtain grid independent results.
The accuracy of the numerical simulations was evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one which were initially stratified were brought into motion by the rotating impeller. In the case of the passive tracer mixing, the alcoholic phase was coloured by blue dye whereas in the case of the reactive mixing a phenolphthalein indicator was applied. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The mixing of different initial lighter phase concentrations was visually investigated to obtain the colour calibration curve. The numerical predictions were evaluated against several locations, close to vessel central line and wall, for which the optical distortion was minimal.

  • Lecture (Conference)
    GVC/DECHEMA Jahrestagung, 06.-08.09.2005, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 77(2005)8, 1057-1058

Permalink: https://www.hzdr.de/publications/Publ-7175
Publ.-Id: 7175


Untersuchungen zur sicheren Prozessführung von Grignard-Reaktionen

Hessel, G.; Kryk, H.; Schmitt, W.; Tefera, N.

Die Grignard-Chemie erlebt eine Renaissance bei der industriellen Herstellung neuer pharmazeutischer Wirkstoffe, Lebensmitteladditive und Feinchemikalien. Sicherheitsprobleme können aufgrund der sehr großen Exothermie und der hohen Reaktivität der Grignard-Reagenz beim Scale-up in den großtechnischen Maßstab auftreten. Die Hauptgefahrenquelle ist das spontane Starten der Grignard-Reaktion, wenn bereits eine kritische Menge an organischem Halogenid akkumuliert ist, und dann die durchgehende Startreaktion durch den starken Druckanstieg zur Stofffreisetzung führt. Die genaue Bestimmung der reaktionstechnischen Prozessparameter zur Auslegung des Kühlsystems für das Produktions-Betriebsregime wird an einem ge-schlossenen Reaktionskalorimeter mit integriertem in-situ FTIR-Spektrometer für eine industrielle Grignard-Reaktion beschrieben. Weiterhin werden Möglichkeiten zur Detektion des Reaktionsstarts und zur Verfolgung der Halogenid-Akkumulation vorgestellt. Durch den Einsatz der in-situ FTIR-Spektroskopie läßt sich einerseits der Re-aktionsstart eindeutig detektieren, andererseits können sowohl der Verbrauch des organischen Halogenids als auch der Aufbau der Grignard-Reagenz in Echtzeit überwacht werden. Neben den Online-Konzentrationsmessungen können an einem geschlossenen Rührkesselreaktor auch die steilen Anstiege der Reaktortemperatur und des Druckes sowie die Wärmebilanz zum Nachweis des Reaktionsstarts genutzt werden. Durch Online-Konzentrationsmessungen und/oder Wärmebilanzmessungen ist es außerdem möglich, das Einschlafen der Hauptreaktion durch Verunreinigungen zu erkennen und das spätere Wiederstarten zu verhindern. Darüber hinaus konnte nachgewiesen werden, daß im geschlossenen Reaktionskalorimeter die reaktionstechnischen Parameter, wie Induktionszeit, Dauer des Startprozesses und Reaktionsenthalpie, wesentlich genauer als im offenen Reaktor gemessenen werden können. Ferner werden Untersuchungen dieser Grignard-Reaktion im adiabatischen Reaktionskalorimeter (PhiTecII) diskutiert, das auch zur Dimensionierung von Notentlastungssystemen dienen kann.

  • Lecture (Conference)
    GVC/DECHEMA Jahrestagung 2005, 06.-08.09.2005, Wiesbaden, Germany
  • Abstract in refereed journal
    Chemie Ingenieur Technik 77(2005)8, 1123-1123

Permalink: https://www.hzdr.de/publications/Publ-7174
Publ.-Id: 7174


The influence of the density difference on the mixing process in mechanically agitated reactor

Hessel, G.; Hristov, H. V.; Kryk, H.; Prasser, H.-M.; Schmitt, W.

A non-baffled stirred vessel reactor was investigated computationally with CFX-5 numerical package. The mixing of two miscible liquids with different densities was dynamically predicted from an initially stratified to a complete mixing condition. Although for a non-baffled vessel an axi-symmetric behaviour can be expected, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. Additionally, the gas phase was involved into the simulations to investigate the effect of the free surface deformation on the mixing process. The two-phase gas-liquid interactions were modelled using the free surface model. The different density liquids were comprised into the liquid phase by the means of the multicomponent model. The grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Furthermore, the available turbulence models were considered to obtain the closest possible match with the experimental observations. In such a way, the stirred vessel hydrodynamics was dynamically calculated in 3-D in order to study the effect of the density difference.
The numerical simulations were evaluated experimentally using video visualisation technique. The lighter (alcoholic) coloured component and the heavier (water) transparent one, which were initially stratified, were brought into motion by the means of the rotating impeller and the mixing process was captured by digital camcorder and subsequently the images were digitally processed. Several points, close to vessel central line and wall, for which the optical distortion was minimal were considered for evaluation of the numerical predictions.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred vessel reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation. Such so called idealised conditions, however, also might occur in the stirred vessel, especially in the case of impeller malfunctioning. In case of impeller stoppage, i.e. breakdown, different density liquids present in the vessel might get stratified. This effect might prove to be of significant importance, especially in the case of reacting liquids for large-scale reactors operating in the industry.

  • Contribution to proceedings
    Conference on Computational Fluid Dynamics in Chemical Reaction Engineering IV, 19.-24.06.2005, Barga, Italy
    CD-ROM
  • Lecture (Conference)
    Conference on Computational Fluid Dynamics in Chemical Reaction Engineering IV, 19.-24.06.2005, Barga, Italy

Permalink: https://www.hzdr.de/publications/Publ-7173
Publ.-Id: 7173


Sonne in der Schule: Betriebsergebnisse aus den Programmen in Bayern, Sachsen und Norddeutschland

Becker, G.; Schiebelsberger, B.; Rindelhardt, U.; Weber, W.

Seit 10 Jahren wird in Deutschland das Programm "Sonne in der Schule" durchgeführt. An mehr als 1000 Schulen wurden dabei netzgekoppelte Photovoltaik-Anlagen errichtet. Im Beitrag werden die erreichten Betriebsergebnisse dieser Anlagen dargestellt. Darüber hinaus wird auf die Nutzung der Anlagen im Unterricht eingegangen.

Keywords: Photovoltaik-Anlagen

  • Poster
    20. Symposium Photovoltaische Solarenergie, 09.-11.03.2005, Staffelstein, Deutschland
  • Contribution to proceedings
    20. Symposium Photovoltaische Solarenergie, 09.-11.03.2005, Staffelstein, Germany

Permalink: https://www.hzdr.de/publications/Publ-7172
Publ.-Id: 7172


Athermal germanium migration in strained silicon layers during junction formation with solid-phase epitaxial regrowth

Vandervorst, W.; Janssens, T.; Brijs, B.; Delhougne, R.; Loo, R.; Caymax, M.; Pawlak, B. J.; Posselt, M.

The formation of a thin strained Si layer on top of a strain-relaxed SiGe buffer is a recent approach to improve the drive current of complementary metal-oxide-semiconductor devices by inducing strain within the transistor channel. At the same time, advanced process technologies require junction formation processes with minimal diffusion and very high dopant activation. Solid-phase epitaxial regrowth is a low temperature process based on preamorphization and subsequent regrowth leading to highly activated and shallow junctions. In this letter, we investigate the stability of the thin strained Si layer, during solid-phase epitaxial regrowth process by monitoring the Ge redistribution/strain after the preamorphization step (without any anneal) and after the thermal regrowth process.

Keywords: strained silicon; germanium; silicon germanium; junction formation; athermal migration

  • Applied Physics Letters 86(2005), 081915

Permalink: https://www.hzdr.de/publications/Publ-7168
Publ.-Id: 7168


Wire-mesh sensors and tomography methods developed by FZR

Prasser, H.-M.

The Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, has developed electrode-mesh sensors, which allow the measurement of the electrical conductivity distribution in a flow duct. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. This allows to obtain bubble size distributions as well as bubble-size resolved gas fraction profiles beside the visualisation and the calculation of profiles of the time-averaged void fraction. The sensor is widely used to study the evolution of the flow pattern in an upwards air-water flow. The experiments aim at closure equations describing forces acting on bubbles as well as coalescence and fragmentation frequencies for the implementation in CFD-codes. Some other prominent examples of the application of wire-mesh sensors were given, like (1) boiling water reactor stability studies, (2) the visualization of cavitation at fast-acting cut-off valves, (3) the visualization of the flow structure behind a closing globe valve, and finally (4) mixing studies in single-phase flow at the ROCOM test facility in Rossendorf, which are aimed at the mixing of deborated slugs during boron dilution transients.

Second subject of the paper is radiation tomography. A gamma-tomography setup for imaging a periodically changing density field is described. It is based on a time-resolved acquisition of the detector signals. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture, as well as to a hydraulic clutch (coupling). In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz.

Keywords: Wire-mesh sensor; X-ray tomography; gamma tomography; gas-liquid flow

  • Invited lecture (Conferences)
    Seminar, 29.11.2004, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-7167
Publ.-Id: 7167


Irrtümer über Kernenergie

Prasser, H.-M.

Der Vortrag plädiert für einen Mix aus Atomenergie und erneuerbaren Energien, um die Versorgung für die Zukunft sicher zu stellen. Kernkraftwerke sind ebenso wirtschaftlich, wie heute die Energiegewinnung aus fossilen Brennstoffen, jedoch mit wesentlich geringeren Stoffströmen verbunden: Der Ertrag aus der Spaltung von einem Kilogramm Uran 235 oder Plutonium 239 entspricht dem aus der Verbrennung von rund 2800 Tonnen Steinkohle. Dies ist die Stärke der Kernenergie, denn dadurch ist sie die einzige Primärenergiequelle, bei der die Abfälle vollständig erfasst und geordnet entsorgt werden können. Unrealistisch ist die Vorstellung, Deutschland könne seinen Energiebedarf bis 2050 zur Hälfte aus regenerativen Quellen decken. Speichermöglichkeiten sind begrenzt, weshalb bei idealen Witterungsbedingungen Überkapazitäten auftreten würden, die nicht verwertet werden könnten. Bei einer Flaute oder bedecktem Himmel wiederum müsste Strom importiert oder beispielsweise aus fossilen Kraftwerken eingespeist werden. Beides würde den ohnehin schon hohen Strompreis aus diesen Quellen in unvertretbare Höhen treiben. Weiterhin betrachtet werden die Verfügbarkeit von Spaltmaterial, der erreichte Stand bei der Sicherheit der Kernkraftwerke sowie die Endlagerproblematik.

Keywords: nuclear energy; energy strategy; nuclear safety; nuclear waste disposal; nuclear fuel

  • Lecture (others)
    Thematischer Abend, 19.11.2004, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-7166
Publ.-Id: 7166


Kernkraft - eine Energiequelle der Zukunft - auch für Deutschland

Prasser, H.-M.

Gefährlich, riskant, umweltschädigend, gesundheitsschädlich, unverantwortbar, unwirtschaftlich, unsozial, nicht nachhaltig - das sind Adjektive, mit der die Nutzung der Kernenergie zur Stromversorgung häufig belegt wird. Tatsächlich tragen die Kernkraftwerke jedoch stabil zur kostengünstigen Stromversorgung bei. In Deutschland haben sie einen Anteil von 30 %, in einigen Ländern mehr. Unter dem Eindruck spürbar anwachsender Brennstoffpreise bei den fossilen Energieträgern und immer deutlicher werdender Folgen der Klimaveränderungen mehren sich die Stimmen, die eine Renaissance der Kernenergie für notwendig halten. In einer solchen Situation ist es wichtig, die Potenzen der Energiegewinnung durch Kernspaltung zu kennen und die wichtigsten Behauptungen der Kernenergiegegner kritisch zu hinterfragen. Speziell für Deutschland wird ein Blick auf die gängigen Konzeptionen zur Energiestrategie der nächsten 50 Jahre geworfen. Letztendlich wird der Schluss gezogen, dass langfristig ein Umsteuern auf einen Mix aus nuklearen und regenerativen Energiequellen erfolgen muss, um zu einer nachhaltigen und ökonomisch, sozial und ökologisch vertretbaren Energieversorgung zu gelangen.

Keywords: nuclear energy; sustainability; energy strategy; acceptance of nuclear energy

  • Lecture (others)
    Industrieclub Sachsen, 05.10.2004, Dresden, Schloss Eckberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-7165
Publ.-Id: 7165


Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe

Shi, J.-M.; Burns, A.; Prasser, H.-M.

The turbulence of the liquid phase has a signi cant dispersion e ect on the migration of bubbles in a vertical ow. Based on a double averaging approach and by adopting the Favre averaged velocity, a generalized model, called the Favre Averaged Drag (FAD) Model, was developed for the turbulent dispersion force for Eulerian simulations of multiphase ows [Burns et al., 2004]. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the inter phase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation makes the sense of the double averaging approach straightforward. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will signi cantly increase the computational e ciency. We also provide validation and evaluation for this model by numerical and experimental investigations of bubbly ows in a vertical pipe. The experimental data were obtained by using the wire-mesh sensor technique. The computations were carried out by applying poly-dispersed models. The emphasis is to examine the model applicability under various ow conditions including bubbly ows with a wall peak and a core peak of the gas volume fraction, ows in the transition region between them, and in the nely dispersed ow regime. The e ect of the drag force model on the turbulent dispersion force was also examined.

Keywords: Turbulent dispersion force; non-drag force model; bubbly flow; CFD

  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 15.-20.05.2005, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-7163
Publ.-Id: 7163


DYN1D-MSR dynamics code for molten salt reactors

Krepel, J.; Rohde, U.; Grundmann, U.; Weiss, F.-P.

This paper reports about the DYN1D-MSR code development and dynamics studies of the molten salt reactors (MSR) – one of the ‘Generation IV International Forum’ concepts. In this forum the graphite-moderated channel type MSR based on the previous Oak Ridge National Laboratory research is considered.
The liquid molten salt serves as a fuel and coolant, simultaneously and causes two physical peculiarities: the fission energy is released predominantly directly into the coolant and the delayed neutrons precursors are drifted by the fuel flow. The drift causes the spread of delayed neutrons distribution to the non-core parts of primary circuit and it can lead to a reactivity loss or gain in the case of fuel flow acceleration or deceleration, respectively. Therefore, specific 3D tool based on in house code DYN3D was developed in FZR. The code DYN3D-MSR is based on the solution of two-group neutron diffusion equation by the help of a nodal expansion method and it includes models of delayed neutrons drift and specific MSR heat release distribution.
In this paper the development and verification of 1D version DYN1D-MSR of the code is described. The code has been validated with the experimental data gained from the molten salt reactor experiment performed in the Oak Ridge and after the validation it was applied to several typical transients (overcooling of fuel at the core inlet, reactivity insertion, and the fuel pump trip).

Keywords: MSR; Molten; Salt; Reactor; Dynamics; DYN3D; DYN1D-MSR; liquid; fuel

Permalink: https://www.hzdr.de/publications/Publ-7162
Publ.-Id: 7162


Thermo-mechanical FE-modelling of in-vessel retention

Willschuetz, H.-G.; Altstadt, E.

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. At the Institute of Safety Research of the FZR a finite element model has been developed simulating the thermal processes and the viscoplastic behaviour of the vessel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal hydraulic and the mechanical calculations are sequentially and recursively coupled. The model is capable of evaluating fracture time and fracture position of a vessel with an internally heated melt pool. The model was applied to pre-and post test calculations for the FOREVER test series of the KTH Stockholm. First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments.

Keywords: Finite-Element-Model; In-vessel melt retention; Light Water Reactor; Creep; Convection; Fracture

  • Lecture (Conference)
    SARNET - First Annual Review Meeting, 15.02.2005, Köln, Germany

Permalink: https://www.hzdr.de/publications/Publ-7161
Publ.-Id: 7161


Links of SARNET with the ISTC program - presentation of the contact expert group of severe accident management

Altstadt, E.

General information on the ISTC program are given. The working procedures of the CEG-SAM are explained and the currently running ISTC projects related to SAM are presented in brief.

Keywords: Severe accident management; International Science and Technology Center (ISTC)

  • Invited lecture (Conferences)
    SARNET - First Annual Review Meeting of Corium Topic, 15.02.2004, Köln, Germany

Permalink: https://www.hzdr.de/publications/Publ-7160
Publ.-Id: 7160


Studies of the Interaction Behavior of Humic Acids with Actinides in the Environment

Sachs, S.; Schmeide, K.; Geipel, G.; Mibus, J.; Bernhard, G.

Due to their abilities for complex and colloid formation as well as their redox properties, humic acids influence the migration of actinides in the environment. Therefore, risk assessments, related to the behavior of actinides in the environment, require basic knowledge on the interaction of humic acids with metal ions. Thus, the interaction of humic acids with actinides is studied, e.g., the Np(V)-humic acid-complexation and the redox stability of uranium(VI) humate complexes, applying synthetic and natural humic acids.

Keywords: Humic Acids; Model Substances, Actinides; Complexation; Migration; Redox Processes

  • Poster
    8. German-American Frontiers of Engineering Symposium, 04.-07.05.2005, Potsdam, Germany

Permalink: https://www.hzdr.de/publications/Publ-7159
Publ.-Id: 7159


First analysis of anisotropic flow with Lee-Yang zeroes

Bastid, N.; Andronic, A.; Barret, V.; Basrak, Z.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Gobbi, A.; 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.; Mangiarotti, A.; Manko, V.; Merschmeyer, M.; Moisa, D.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolarkiewicz, M. M.; Smolyankin, V.; Soliwoda, I. J.; Stockmeier, M. R.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Yushmanov, I.; Zhilin, A.

We report on the first analysis of directed and elliptic flow with the new method of Lee-Yang zeroes. Experimental data are presented for Ru+Ru reactions at 1.69A GeV measured with the FOPI detector at SIS/GSI. The results obtained with several methods, based on the event-plane reconstruction, on Lee-Yang zeroes, and on multi-particle cumulants (up th 5th order) applied for the first time at SIS energies, are compared. They show conclusive evidence that azimuthal correlations between nucleons and composite particles at this energy are largely dominated by anisotropic flow.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-7158
Publ.-Id: 7158


Turbulent dispersion force -- physics, model derivation and evaluation --

Shi, J.-M.; Frank, T.; Burns, A.

Turbulence dispersion has a significant dispersion effect on the migration of bubbles in a vertical flow. Based on a double averaging approach and by adopting the Favre averged velocity, we developed the Favre Averaged Drag (FAD) turbulent dispersion force model for Eulerian simulations of multiphase flows. The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the interphase drag and the volume fractions. In this work, a new model derivation from the two-way coupled Lagrangian formulation is provided. This derivation explains the physical mechanism and makes the sense of the double averaging approach straightford. Moreover, the new derivation provides a theoretical foundation for applying the FAD model to the Lagrangian solver, which will significantly increase the computational efficiency.

We also provide a systematic model evaluation based on numerical simulations of bubbly flows in a vertical pipe using both mono- and poly-dispersed flow models. The numerical results for the radial distribution of the gas concentration were compared with the experimental data measured by using the wire-mesh sensor technique. The results confirm that the bubble size and the liquid flow Reynolds number have a strong effect on the turbulent dispersion as is shown in the model derivation.

Keywords: turbulent dispersion; bubbly flow; CFD; model

  • Lecture (Conference)
    FZR-ANSYS CFX Workshop on Multiphase Flow, 29.-30.06.2004, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-7157
Publ.-Id: 7157


Uranyl Complexation in Fluorinated Acids (HF, HBF4, HPF6, HTf2N): ACombined Experimental and Theoretical Study

Gaillard, C.; El Azzi, A.; Billard, I.; Bolvin, H.; Hennig, C.

The aim of this work is to characterize the complexation ability of F-, BF4 -, PF6 -, and Tf2N- toward uranyl ions in aqueous solution. These anions were chosen as they represent the anionic part of the most studied roomtemperature ionic liquids. Time-resolved emission spectroscopy and X-ray absorption spectroscopy were used to retrieve structural data on the complexes formed. The results obtained were compared with computational data.
Tf2N- does not complex uranyl, even at high concentration. Other fluorinated acids form inner-sphere complexes with U(VI), in a monodentate fashion in the case of BF4 and PF6.

  • Inorganic Chemistry 44(2005), 852-861

Permalink: https://www.hzdr.de/publications/Publ-7155
Publ.-Id: 7155


Predictive Atomistic Computer Simulations on Synthesis and Stability of Single-crystalline Nanowires

Röntzsch, L.; Heinig, K.-H.

In this contribution, results of predictive atomistic computer simulations are presented which describe the ion beam synthesis of single-crystalline CoSi2 nanowires (NWs) embedded in Si. In order to simulate the Co implantation, the binary collision codes TRIDYN and TRIM were adapted to the particular experimental situation of a finely focused Co ion beam of a few tens of nanometers in width. The resulting 3D implantation profile serves as input for a kinetic lattice Monte-Carlo code by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are described.
Due to the systems tendency towards a reduction of interfacial free energy (Rayleigh instability), it will be demonstrated that the orientation of the Co implantation profile to the Si matrix influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the CoSi2(111)/Si(111) interface, faceting forces occur if the Co implantation profile is not aligned with the Si-[011] direction. Thus, intentional misalignment is a possible way to a controlled decay of the NW into a chain of monodisperse and equidistant nanoclusters which is applicable as plasmon waveguide.

Keywords: nanowire; CoSi2; Rayleigh instability; faceting; kinetic Monte-Carlo

  • Poster
    342. WE-Heraeus Seminar "Science and Technology of Inorganic Nanowires", 13.-16.02.2005, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7154
Publ.-Id: 7154


X-ray Tomography

Hampel, U.

The presentation discusses the application of X-ray micro-tomography to the measurement of size, shape and porosity of polymer particles.

Keywords: X-ray; micro-tomography; polymer processing

  • Invited lecture (Conferences)
    DPI PO Day, 10.02.2005, Enschede, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-7153
Publ.-Id: 7153


Application of computer tomography in microelectronic packaging

Speck, M.; Wolter, K.-J.; Danczak, M.; Daniel, D.

In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.

Keywords: computer tomography; nondestructive testing; microelectronic packaging; limited angle tomography

  • Contribution to proceedings
    9th International Symposium on NDE for Health Monitoring and Diagnostics, 15.-17.03.2004, San Diego, United States
    5392(2004), 194-202
  • Lecture (Conference)
    9th International Symposium on NDE for Health Monitoring and Diagnostics, 15.-17.03.2004, San Diego, United States

Permalink: https://www.hzdr.de/publications/Publ-7152
Publ.-Id: 7152


Optical measurement of nasal swellings

Hampel, U.; Schleicher, E.; Wüstenberg, E. G.; Hüttenbrink, K.-B.

We introduce a new method to noninvasively and continuously measure the swelling process of the nasal mucosa. Thereby we use light of different wavelengths in the near infrared range which is transilluminated through the nasal tissue and whose extinction is recorded as a function of time. From the temporal and spectral extinction data we are able to extract characteristic parameters that describe the swelling process quantitatively by means of a regression type parameter estimation algorithm. Furthermore, we show the capability of the method to quantify hemoglobin saturation in the surplus blood volume and introduce a bilateral measurement approach that allows us to examine the swelling process in both nasal cavities simultaneously. The method has been applied to the nasal allergen provocation test and verified on a limited number of volunteers.

Keywords: allergy diagnostics; nasal provocation test; optical sensor; NIR spectroscopy

  • IEEE Transactions on Biomedical Engineering 51(2004)9, 1673-1679

Permalink: https://www.hzdr.de/publications/Publ-7151
Publ.-Id: 7151


X-ray computed tomography for experimental investigations of multi-phase flows

Hampel, U.

The presentation discusses the application of conventional X-ray CT, X-ray cone beam CT and ultrafast limited angle X-ray CT to the measurement of phase distributions in multiphase flow problems.

Keywords: X-ray tomography; multiphase flows

  • Contribution to proceedings
    Multi-phase Flow: Simulation, Experiment and Applications, ANSYS-CFX / FZR workshop, 28.-30.06.2004, Dresden, BRD

Permalink: https://www.hzdr.de/publications/Publ-7150
Publ.-Id: 7150


K6H2[TiW11CoO40]×13H2O, with a monotitanoundecatungstocobaltate(II) anion

Kraus, W.; Stephan, H.; Röllich, A.; Matéjka, Z.; Reck, G.

Hexapotassium dihydrogen monotitanoundecatungstocobaltate(II) tridecahydrate, K6H2[TiW11CoO40]×13H2O, crystallizes from aqueous solution in the cubic space group P43m. The structure was refined as an inversion twin. The [TiW11CoO40]8- anion has a Keggin structure with one W-atom site occupied by titanium and a central tetrahedral CoO4 group.

  • Open Access Logo Acta Crystallographica Section E 61(2005), i35-i37

Permalink: https://www.hzdr.de/publications/Publ-7149
Publ.-Id: 7149


New concepts for short-wavelength quantum cascade lasers and few-cycle THz emitters

Helm, M.

I will discuss two recent advances related to semiconductor light sources in the infrared and THz regions. One example is a quantum cascade laser operating at a wavelength shorter than 4 microns above room temperature with high peak power. It is based on strained InGaAs/InAlAs on InP, with the addition of high barriers of pure AlAs for better confinement and strain compensation. In a novel few-cycle THz emitter we try to combine the advantages of the high electric bias field in photoconductive antennas with a large active area. This is achieved with an interdigitated electrode structure, partially covered in order to mask one field polarity. As a result no destructive interference of the emitted THz wave occurs, which allows upscaling of the device area.

Keywords: THz emitter; quantum cascade laser

  • Invited lecture (Conferences)
    Japan-Germany Colloquium 2005: Semiconductor Physics and Technology, 14.-16.02.2005, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7148
Publ.-Id: 7148


Study of the Influence of Humic Acid on the U(VI) Sorption onto Kaolinite

Krepelova, A.; Sachs, S.; Reich, T.; Rossberg, A.; Bernhard, G.

Humic acids (HA) comprise an important part of natural organic materials. Due to their interactions with organic and inorganic pollutants produced by human activity, they play a significant role in biochemical cycles of ecosystems. By the formation of soluble anionic complexes with the range of more or less toxic metals, including radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of their impact on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study the influence of HA on the U(VI) sorption onto kaolinite was studied. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled HA) and kaolinite (KGa-1b).
Three kinds of batch experiments were performed under different experimental conditions: HA sorption in the absence of U(VI), U(VI) sorption in the absence and U(VI) sorption in the presence of HA. The sorption curves have shown that the U(VI) sorption on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 8.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system (Fig.1).
We performed EXAFS measurements with U(VI)-HA-kaolinite sorbates in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA [1] to obtain information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.

Keywords: Humic Acid; Uranium; Sorption; EXAFS; Kaolinite

  • Lecture (Conference)
    GDCh Jahrestagung 2005, 11.-14.09.2005, Düsseldorf, Germany
  • Contribution to proceedings
    GDCh - Jahrestagung 2005, Chemie schafft neue Strukturen, 11.-14.09.2005, Düsseldorf, Germany
    Kurzreferate, 3-936028-36-2, 500

Permalink: https://www.hzdr.de/publications/Publ-7147
Publ.-Id: 7147


Interpretation of TOF-SIMS depth profiles from ultrashallow high-K dielectric stacks assisted by hybrid collisional computer simulation

Ignatova, V. A.; Möller, W.; Conard, T.; Vandervorst, W.; Gijbels, R.

The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration, and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF-SIMS depth profiling of ZrO2/SiO2/Si high-k dielectric stacks with thicknesses of the SiO2 interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between experiment and computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e. atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O.

  • Applied Physics A 81(2005)1, 71-77

Permalink: https://www.hzdr.de/publications/Publ-7146
Publ.-Id: 7146


Uncertainty and sensitivity analysis for the modeling of transients with interaction of thermal hydraulics and neutron kinetics

Kliem, S.; Mittag, S.; Weiß, F.-P.; Langenbuch, S.

The GRS methodology to assess the uncertainty of the calculation results of computer simulation codes was applied to the coupled code system DYN3D/ATHLET, consisting of a 3D neutron kinetic core model and a thermal hydraulic system code. It was used to make a statistical analysis of the result parameters from the output data of the DYN3D/ATHLET-calculation. A number of variation calculations with randomly distributed input parameters within given boundaries was carried out. On that basis, time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations.

  • Lecture (Conference)
    11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    Proceedings CDROM paper 461

Permalink: https://www.hzdr.de/publications/Publ-7145
Publ.-Id: 7145


Polarization effects at the Uranium L1 and L3 edges – Theory and Applications

Hennig, C.

The polarization dependence of U L1 edge EXAFS spectra is relatively simple because the photoelectron is excited from ground state (l = 0) to one excited state (l = 1). By contrast, the polarization dependence is more complicated at the L2 and L3 edges were the photoelectron is excited from p ground state into final states s (l = 0) and d (l = 2). The EXAFS expression of L2 and L3 edges comprises here pure s, pure d and coupled s-d states. The polarization effect at the U L1 and L3 edges was investigated using a single crystal of Ca[UO2PO4]2•6H2O. The high symmetry in the equatorial shell allows to compare successful the measurements with the theory. In a second part two types of applications will be discussed. It will be shown, that powder samples have a texture which can lead to an erroneous determination of coordination numbers. A use of the magic angle allows to avoid this problem. A second example will be discussed where the polarization dependency can be used to determine the orientation of actinyl ions sorbed at mineral surfaces.

  • Lecture (Conference)
    Actinides 2005, 04.-08.07.2005, Manchester, Great Britain
  • Contribution to proceedings
    Actinides 2005, 03.-09.07.2005, Manchester, Great Britain
    Recent Advances in Actinide Science, Editors: May, I., Alvares, R., Bryan, N.: The Royal Society of Chemistry 2006, 0-85404-678-X, 716-718

Permalink: https://www.hzdr.de/publications/Publ-7144
Publ.-Id: 7144


Ion irradiation in exchange bias systems

Fassbender, J.

Lecture on the present status of ion irradiation in exchange bias systems.

Keywords: magnetism; ion irradiation; exchange bias

  • Invited lecture (Conferences)
    EU-RTN-Meeting Nexbias, 17.-18.02.2005, Kaiserslautern, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7141
Publ.-Id: 7141


Uranium speciation in 30-year old Freital mine tailings: An EXAFS, μ-XRD, and μ-XRF Study

Scheinost, A.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.

Risk assessments of actinide-contaminated soils and sediments require detailed knowledge of actinide speciation and its long-term kinetics. Former Saxonian mine tailings, which have been covered but else left undisturbed, are ideally suited to study changes in uranium speciation over timescales of decades. We investigated the major uranium species in two samples from buried mine tailings using a combination of Synchrotron-based microfocus-techniques (μ-XRF, μ-XRD with micrometer resolution), bulk EXAFS spectroscopy, and chemical extractions.
In sample F1 (5 m depth, oxic, pH 8, U=440 mg/kg, high Ca, S, Pb, Cu, Zn concentrations), uranium is diffusely distributed among aggregates of layer silicates (muscovite, illite and kaolinite). The chemical extractions and EXAFS results confirm that uranium is sorbed to these minerals, but is not incorporated into their crystal structure. Sorption is also in line with the high pH and low carbonate concentrations in pore water. In sample F3 (12 m depth, oxic, pH 4, U=430 mg/kg), the combination of μ-XRF and μ-XRD enabled us to identify several U(IV) and U(VI) containing minerals like coffinite, uraninite, uranyl hydroxide, and vanuralite. Only a minor part of U is sorbed to layer silicates as confirmed by chemical extractions and EXAFS spectroscopy.
At smaller depth (F1, 5 m), sulfuric acid from the ore extraction procedure was completely neutralized by the construction waste used as cover material, resulting in precipitation of jarosite and gypsum. Even 30 years after the ore extraction, uranium remains highly soluble. At greater depth (F3, 12 m), the low pH from ore extraction was conserved. The presence of U(IV) minerals suggest either precipitation of secondary (IV) minerals due to microbial redox activity, or incomplete dissolution of primary (IV) minerals due to ore processing inefficiency of these older sediments. The U(IV) minerals were recalcitrant during chemical extractions, suggesting low uranium solubility even at oxic redox conditions. The results demonstrate a very high variability of uranium speciation and hence potential mobility, which seems to depend on geochemical parameters and site history, but shows little influence of time.

  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Lecture (Conference)
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Permalink: https://www.hzdr.de/publications/Publ-7140
Publ.-Id: 7140


Dilepton Analysis in the HADES Spectrometer for C+C at 2 AGeV

Otwinowski, J.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Atkin, E.; Balanda, A.; Bellia, G.; Belver, D.; Bielcik, J.; Böhmer, M.; Bokemeyer, H.; Boyard, J.; Braun-Munzinger, P.; Chepurnov, V.; Chernenko, S.; Christ, T.; Coniglione, R.; Daues, H.; Diaz, J.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Emelianov, V.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hehner, J.; Heinz, T.; Hennino, T.; Hlavac, S.; Hoffmann, J.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kopf, U.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Kutukian-Nieto, T.; Lang, S.; Lehnert, J.; Maiolino, C.; Marin, J.; Markert, J.; Mishin, Y.; Montes, N.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, J.; Ott, W.; Pachmayer, Y.; Panebrasev, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Pvrzygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Rodrigez Pieto, G.; Roy-Stephan, M.; Rustamov, A.; Sabin, F. J.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Schroeder, C.; Schwab, E.; Senger, P.; Simon, R.; Smolyankin, V.; Smykov, L.; Spataro, S.; Stelzer, H.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Titov, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vazquez, A.; Volkov, Y.; Wagner, V.; Walus, W.; Wang, Y.; Winkler, S.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.

The light meson dilepton identification in the HADES detection system is based on an invariant mass reconstruction of their decay into e+e- pairs. Methods of the dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 AGeV are presented in this paper. In the signal reconstruction particularly important is the reduction of the huge combinatorial background arising from wrong combinations of electrons and positrons into un-like sign pairs. A purity of the dilepton signal is determined by using GEANT simulation with the full HADES geometry and a realistic detector response.

  • Contribution to proceedings
    XLII International Winter Meeting on Nuclear Physics ON NUCLEAR PHYSICS, 25.01.-01.02.2004, Bormio, Italy
    Ricerca Scientifica ed Educazione Permanente Supplemento, 180-189

Permalink: https://www.hzdr.de/publications/Publ-7138
Publ.-Id: 7138


FELBE - a new facility providing coherent radiation for infrared spectroscopic investigations in actinide research

Foerstendorf, H.; Seidel, W.; Bernhard, G.

FELBE is an acronym for the free-electron laser (FEL) at the Electron Linear accelerator with high Brilliance and Low Emittance (ELBE) located at the Forschungszentrum Rossendorf in Dresden, Germany. This FEL is a source of pulsed, coherent light which is continuously tunable over the infrared wavelength range from 5 to 25 µm. This will be enlarged to about 150 µm in late 2006.
At the FELBE facility a laboratory suitable for radiochemistry research was installed. This lab is classified as a controlled zone for investigations of certain radionuclides obeying to all aspects of radiation protection. The maximum activity of the investigated radioactive samples can add up to 105 times of the admissible limit. A glove box provides the possibility to perform experiments on sensitive samples which have to be kept in an inert gas atmosphere.
The time structure of the pulsed FEL beam is related to the frequency of the electron pulses of the accelerator which offers a 13 MHz repetition rate in macropulses of a few 100 μs at up to 25 Hz. A continuous 13 MHz regime is also available as well as single pulse selection down to a frequency of 1 Hz. The energy of the infrared pulses is up to 1 µJ/pulse depending on the wavelength.
The FELBE facility is a member in the Integrated Infrastructure Initiative (I3) on synchrotron and free-electron laser science (IA SFS) within the 6th framework programme of the EU. With this grant, external users of FELBE can be financially supported ("transnational access").
In our first experiment we use the FEL beam for investigation of mineral surfaces by Phototermal Beam Deflection (PTBD) spectroscopy. The PTBD technique is based on the theory of photothermal spectroscopy which describes the conversion of absorbed energy of a light beam incident on a sample into heat by nonradiative de-excitation processes. In typical PTBD experiments the magnitude signal is proportional to the slope of the induced displacement of the sample surface. There is a direct proportionality between the observed signal and the absorption coefficient of the material under investigation which provides a direct access to infrared absorption spectra with a very low detection limit is provided.
Furthermore, the PTBD technique is capable to gain spatial information (microspectrometry) of the sample’s surface since generation and detection of the thermal wave occurs generally in the submillimeter length scale. This may result in a microspectrometric technique for determining the distribution e.g. of sorbed metal species on mineral surfaces.

  • Contribution to proceedings
    Migration 2005, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 18.-23.09.2005, Avignon, France

Permalink: https://www.hzdr.de/publications/Publ-7137
Publ.-Id: 7137


Characterization of the Binding Mechanisms of Uranium to Different Isolated Bacteria in Function of pH

Merroun, M.; Nedelkova, M.; Raff, J.; Roßberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.

The mining and processing of uranium during the last decades for nuclear fuel and nuclear weapon production resulted in generation of significant amounts of radioactive wastes. The mobility of this radionuclide is controlled by its interactions with ions, minerals and microorganisms present in nature. As a consequence of their small size and diverse metabolic activities, bacteria are able to interact intimately with uranium and other metal ions present in their environment. Assessment of the potential hazard posed by the presence of uranyl-bacterial complexes, as well as the development and application of accurate contaminant transport models, requires an understanding of the speciation of uranium associated with bacteria. This paper summarizes the effect of pH on the speciation of uranium bound by about fifteen bacterial strains isolated from uranium mining wastes. Microbiological methods in combination with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared (IR) spectroscopy, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were applied. EXAFS analysis showed that the cells of the most bacterial strains studied precipitate U(VI) as m-autunite-like phase at pH 4.5, probably due to the release of the inorganic phosphate from the cells as result of the acidic phosphatase activity. However, at pH 2 uranium formed complexes with organically bound phosphates of the cell surface. At pH 3, both organic and inorganic phosphate uranyl species occur together. No structural differences of the uranium complexes formed by three types of Acidithiobacillus ferrooxidans at above mentioned pH values were found, indicating the implication of organic phosphate moieties in the complexation. However, in the case of B. sphaericus JG-A12 the uranium bonding was consistent with the formation of complexes with organic bound phosphate and carboxylate groups of the cell surface. We applied Iterative Target Test Factor Analysis to determine the speciation at different pH values quantitatively from the EXAFS spectra. Transmission electron microscopy and energy dispersive X-ray analysis revealed species and even strain-specific extracellular and/or intracellular uranium accumulations to varying degrees. Different hypothesis explaining the different coordination chemistry of uranium to bacteria in function of the pH of the uranium solution in terms of solubility of m-autunite and/or microbial activity will be discussed.

  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Permalink: https://www.hzdr.de/publications/Publ-7136
Publ.-Id: 7136


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