Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33900 Publications

Correlation of structure and conductance in nanowires and nanotubes

Gemming, S.

In nanostructured materials spatial confinement effects lead to structure-dependent deviations from the bulk transport properties. Such modifications may in part be accounted for by classical transport simulations, but a microscopically more detailed and mostly parameter-free picture is obtained from quantum-mechanical density-functional theory (DFT). DFT calculations yield the atom arrangement and electronic structure of nanotubes and nanowires in the electronic ground state. Additionally, an extension by a Green’s function formalism leads to the determination and analysis of electronic transport through contacted nanostructures. A combination of both approaches allows to correlate structural and transport properties of nanostructures. The applicability of this approach will be demonstrated for a mechanically triggered metal-insulator transition in nanowires.
Kibsgaard et al. Nano Lett 8 (2008) 3928; [2] Popov et al. Nano Lett 8 (2008) 4093.

Keywords: nanotubes; nanowires; crystallography; DFT; transition metal chalcogenides; MoS; molybdenum sulfide

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14034
Publ.-Id: 14034


Modeling the morphogenesis of brine channels in sea ice

Kutschan, B.; Morawetz, K.; Gemming, S.

Brine channels are formed in sea ice under certain constraints and represent a habitat of different microorganisms. The complex system depends on a number of various quantities as salinity, density, pH-value or temperature. Each quantity governs the process of brine channel formation. There exists a strong link between bulk salinity and the presence of brine drainage channels in growing ice with respect to both the horizontal and vertical planes. We develop a suitable phenomenological model for the formation of brine channels both referring to the Ginzburg-Landau-theory of phase transitions as well as to the chemical basis of morphogenesis according to Turing. It is possible to conclude from the critical wavenumber on the size of the structure and the critical parameters. The theoretically deduced transition rates have the same magnitude as the experimental values. The model creates channels of similar size as observed experimentally. An extension of the model towards channels with different sizes is possible. The microstructure of ice determines the albedo feedback and plays therefore an important role for large-scale global circulation models (GCMs).

Keywords: structure formation; differential equations; Landau; brine channels; reaction-diffusion system

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland
  • Physical Review E 81(2010), 036106
    DOI: 10.1103/PhysRevE.81.036106
  • Poster
    DPG Frühjahrstagung, 26.03.-30.06.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14033
Publ.-Id: 14033


Low-temperature modelling for degenerate and frustrated Heisenberg systems with anisotropy

Gemming, S.; Schreiber, M.; Kunze, T.; Numazawa, S.

Thermodynamic equilibration of complex systems like spin glasses or (degenerate) anisotropic spin crystals by numerical methods can be challenging due to the presence of multiple minima on the potential energy surface. This problem becomes pronounced especially at low temperature, where the system remains mainly in few states. We employ the anisotropic Heisenberg model in two dimensions to simulate and analyze the domain formation and the domain structure of multiferroic oxides. In particular, we discuss various techniques to improve the low-temperature equilibration behavior by means of a trigonal antiferromagnet with single-ion anisotropy. Furthermore, we present a localized sampling method for the Metropolis algorithm, which increases the acceptance ratio significantly.

Keywords: Monte-Carlo; Heisenberg; frustrated magnetism; Metropolis; importance sampling; multiferroics

  • Poster
    Perspectives in Highly Frustrated Magnetism, 19.-23.04.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14032
Publ.-Id: 14032


Systematic study of the pp -> pp omega reaction

Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Gast, W.; Gillitzer, A.; Gottwald, J.; Jager, H.; Jakob, B.; Jakel, R.; Karsch, L.; Kilian, K.; Koch, H.; Krapp, M.; Kress, J.; Kuhlmann, E.; Lehmann, A.; Marcello, S.; Mauro, S.; Michel, P.; Moller, K.; Morsch, H.; Naumann, L.; Paul, N.; Pizzolotto, C.; Plettner, C.; Reimann, S.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schonmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Steinke, M.; Sun, G.; Teufel, A.; Ullrich, W.; Wagner, G.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.; Wustner, P.; Zupranski, P.

A systematic study of the production of omega-mesons in proton-proton-collisions was carried out in a kinematically complete experiment at three excess energies (epsilon= 92, 128, 173 MeV). Both protons were detected using the large-acceptance COSY-TOF spectrometer at an external beam line at the Cooler Synchrotron COSY at Forschungszentrum J¨ulich. The total cross section, angular distributions of both omega-mesons and protons were measured and presented in various reference frames such as the overall CMS, helicity and Jackson frame. In addition, the orientation of the omega-spin and invariant mass spectra were determined. We observe !-production to take place dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and, additionally, in Sd at epsilon = 173 MeV. No obvious indication of resonant omega-production via N*- resonances was found, as proton angular distributions are almost isotropic and invariant mass spectra are compatible with phase space distributions. A dominant role of 3P1 and 1S0 initial partial waves for omega-production was concluded from the orientation of the decay plane of the !-meson. Although the Jackson angle distributions in the omega-p-Jackson frame are anisotropic we argue that this is not an indication of a resonance but rather a kinematical effect reflecting the anisotropy of the omega angular distribution. The helicity angle distribution in the omega-p-helicity frame shows an anisotropy which probably reflects effects of the omega angular momenta in the final state; this observable may be, in addition to the orientation of the omega decay plane, the most sensitive one to judge the validity of theoretical descriptions of the production process.

Keywords: Nucleon-nucleon interactions; Polarization in interactions and scattering; Other mesons with S=C=0, mass < 2.5 GeV; Nuclear reactions involving few-nucleon systems; Other reactions above meson production thresholds (energies > 400 MeV)

  • European Physical Journal A 44(2010), 7

Permalink: https://www.hzdr.de/publications/Publ-14031
Publ.-Id: 14031


Cobalt(II) "Scorpionate" Complexes as Models for Cobalt-Substituted Zinc Enzymes: Electronic Structure Investigation by High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopy

Krzystek, J.; Swenson, D. C.; Zvyagin, S. A.; Smirnov, D.; Ozarowski, A.; Telser, J.

A series of complexes of formula Tp(R,R')CoL, where Tp(R,R'-) = hydrotris(3-R,5-R'-pyrazol-1-yl)borate ("scorpionate") anion (R = tert-butyl, R' = H, Me, 2'-thienyl (Tn), L = Cl-, NCS-, NCO-, N-3(-)), has been characterized by electronic absorption spectroscopy in the visible and near-infrared (near-IR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR). Reported here are also crystal structures of seven members of the series that have not been reported previously: R' = H, L = NCO-, N-3(-); R' = Me, L = Cl-, NCS-, NCO-, N-3(-); R' = Tn, L = Cl-, NCS-. These include a structure for Tp(t-Bu,me)CoCl different from that previously reported. All of the investigated complexes contain a four-coordinate cobalt(II) ion (3d(7)) with approximate C-3v point group symmetry about the metal ion and exhibit an S = 3/2 high-spin ground state. The use of HFEPR allows extraction of the full set of intrinsic S = 3/2 spin Hamiltonian parameters (D, E, and g values)!The axial zero-field splitting parameter, D, for all investigated Tp(R,R')CoL complexes is always positive, a fact not easily determined by other methods. However, the magnitude of this parameter varies widely: 2.4 cm(-1)<= D<= 12.7 cm(-1), indicating the extreme sensitivity of this parameter to environment. The spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-near-IR spectra to yield ligand-field parameters for these complexes following the angular overlap model (AOM). This description of electronic structure and bonding in pseudotetrahedral cobalt(II) complexes can enhance the understanding of similar sites in metalloproteins, specifically cobalt-substituted zinc enzymes.

  • Journal of the American Chemical Society 132(2010)14, 5241-5253

Permalink: https://www.hzdr.de/publications/Publ-14030
Publ.-Id: 14030


Defects in a nitrogen-implanted ZnO thin film

Schmidt, M.; Ellguth, M.; Schmidt, F.; Lüder, T.; von Wenckstern, H.; Pickenhain, R.; Grundmann, M.; Brauer, G.; Skorupa, W.

Defects in a nitrogen implanted and thermally annealed zinc oxide thin film (n-type conducting) and reference samples were studied. Space charge regions realised by fabrication of semitransparent palladium Schottky contacts enabled the application of capacitance spectroscopic methods and photo - current measurements. We report on the formation of a deep level, in the following labelled TN1. It is 580 meV below the conduction band edge, probably related to nitrogen, and must be distinguished from the well known intrinsic deep level E4 at almost equal energetical depth. Capacitance measurements in combination with optical excitation, conducted at different temperatures, as well as photo-current measurements revealed the existence of two states approximately 60 meV and 100 meV above the valence band edge for the nitrogen implanted sample. These states cause an acceptor compensation degree larger than 0.9. The thermal emission of holes from these states into the valence band was observed by optical deep level transient spectroscopy.

  • Physica Status Solidi (B) 247(2010)5, 1220-1226

Permalink: https://www.hzdr.de/publications/Publ-14029
Publ.-Id: 14029


Numerical and experimental modelling of various MHD induction pumps

Khripchenko, S.; Khalilov, R.; Kolesnichenko, I.; Denisov, S.; Galindo, V.; Gerbeth, G.

This paper considers three variants of MHD induction pumps a centrifugal magnetovortex pump, a transformer type pump with magnetic asymmetry and a travelling field pump All these pumps have a flat channel placed between the poles of one or several ferromagnetic cores inducing an alternating magnetic field directed normally to the channel plane To describe electromagnetic forces generated in the pump channel, a mathematical model is proposed The results of numerical and physical experiments ale presented.

Keywords: mhd induction pumps

  • Magnetohydrodynamics 46(2010)1, 85-97

Permalink: https://www.hzdr.de/publications/Publ-14028
Publ.-Id: 14028


Ion beam induced ferromagnetism in semiconductors

Potzger, K.

Recently, research on diluted magnetic semiconductors (DMS) became very popular due to their large potential in future spintronics devices like spin valves or current-induced magnetic switches. Mostly, transition metal doped classical semiconductors like Si, Ge or GaAs as well as oxides have been investigated. The research faces, however, serious difficulties due to the appearance of tiny magnetic secondary phases, spinodal decomposition or magnetically active defects in the semiconductor induced by the implantation/oversaturation. It was found that those effects lead to ferromagnetic as well as magneto-transport properties which, by mistake, could be interpreted as intrinsic DMS. In this paper, I will focus on the discussion of pitfalls during magnetic and structural analysis, especially on element-specific analysis methods for the identification of the source of the ferromagnetic signal. Moreover, possibilities to overcome those difficulties will be presented.

Keywords: diluted magnetic semiconductors; ion implantation

  • Invited lecture (Conferences)
    International Conference on Nanoscale Magnetism ICNM-2010, 28.09.-02.10.2010, Istanbul, Türkei
  • Invited lecture (Conferences)
    VIII-th International Conference ION 2010, 14.-17.06.2010, Kazimierz Dolny, Polen
  • Invited lecture (Conferences)
    17th International Conference on Ion Beam Modification of Materials (IBMM), 22.-27.08.2010, Montreal, Kanada

Permalink: https://www.hzdr.de/publications/Publ-14027
Publ.-Id: 14027


Untersuchung von Redoxprozessen von Uranyl-Verbindungen mit Flavonoiden

Drewitz, S.

Durch den Uranbergbau entstanden in Sachsen und Thüringen eine Vielzahl von Gruben, Abfallhalden und Absetzanlagen, aus denen beispielsweise über Sickerwasser das Schwermetall in die Umwelt gelangen konnte. Böden wurden kontaminiert und das Actinoid kann von Pflanzen aufgenommen werden. Um Erkenntnisse über die Migration und Wirkung des Urans gewinnen zu können, ist es notwendig die Wechselwirkung mit einzelnen Pflanzenstoffen zu untersuchen.
Im Mittelpunkt dieser Arbeit stand die Untersuchung von in vitro-Wechselwirkungen des in Pflanzen weitverbreiteten Flavonoids Quercetin mit Uranverbindungen. Insbesondere sollte überprüft werden, ob eine Reduktion des Uranyl zu Uran(IV) stattfindet. Im Allgemeinen besitzt vierwertiges Uran gegenüber dem sechswertigen Uran eine sehr geringe Löslichkeit, dies führt zu einer Immobilisierung des Urans.
Zur Charakterisierung des Reduktionsvermögens wurde das Redoxpotential des Polyphenols in Abhängigkeit vom pH-Wert in dem für die nachfolgenden Versuche verwendeten Lösungsmittel (50 % Methanol) bestimmt. Hierbei wurde ein linearer Zusammenhang zwischen pH 3,3 und 8,3 festgestellt: E = (-69 ± 3) mV * pH + (616 ± 7) mV bestimmt gegen Silber-Silberchlorid-Elektrode. Somit weist Quercetin bei steigendem pH-Wert ein zunehmendes Reduktionsvermögen auf.
Es erfolgte zudem die Bestimmung der Stabilitätskonstante des Komplexes zwischen Uran(IV) und Quercetin bei einem pH-Wert von 5,8 in 50 % Methanol im carbonatfreien System unter Inertgasbedingungen (Modellkomplexierung). Die Stabilitätskonstante wurde mittels UV/Vis-Spektroskopie zu log10β1:3:1 = 20,36 ± 0,18 bestimmt. Durch diese starke Komplexbildung wird auch die Löslichkeit der sonst schwerer löslichen Uran(IV)-Spezies erhöht. Dieser Komplex ist zudem stabiler als der Uranyl-Quercetin-Komplex (log10β1:3:1 = 13,8 [1]). Dies bedeutet, dass durch die Komplexbildung eine Erhöhung des Redoxpotentials des Redoxpaares U(VI)│U(IV) vorliegt und somit bei der Koordination des Uranyls mit Quercetin eine Reduktion des Metall-Ions leichter möglich ist.
Es galt weiterhin zu prüfen, ob ein Redoxprozess zwischen Quercetin und Uranyl in vitro bei pH 5,8 bzw. pH 7,0 in 50 % Methanol unter Inertgasbedingungen stattfindet. Eine Reduktion des Uranyl-Ions führt zur Bildung von Uran(IV), der stabilsten reduzierten Oxidationsstufe des Urans. Vierwertiges Uran konnte mittels laserinduzierter photoakustischer Spektroskopie (LIPAS), durch die Komplexbildung mit Arsenazo III bzw. durch die Extraktion mit 2-Thenoyltrifluoraceton (TTA) nachgewiesen werden. Es wurde mithilfe der genannten Methoden bestimmt, dass der Umsatz von Uranyl zu Uran(IV) durch das Reduktionsmittel Quercetin im Prozentbereich liegt.

[1] Viehweger, K. & Geipel, G. (2009) Report FZD-511 p. 41

Keywords: flavonoids; quercetin; uranium(IV); uranyl; reduction

  • Other report
    TU Dresden: Wissenschaftliche Abschlussarbeit (Studiengang Lebensmittelchemie), 2010
    74 Seiten

Permalink: https://www.hzdr.de/publications/Publ-14026
Publ.-Id: 14026


Microstructure, electrical, magnetic, and extraordinary Hall effect studies in Ni:SiO2 nanogranular films synthesized by atom beam sputtering

Kumar, H.; Gosh, S.; Bürger, D.; Zhou, S.; Kabiraj, D.; Avasthi, D. K.; Grötzschel, R.; Schmidt, H.

In this work we report on the synthesis of Ni:SiO2 nanogranular films with different metal fraction 0.10 < x < 0.68 and a homogeneous distribution of Ni particles by atom beam sputtering technique and on the study of their microstructure, electrical transport, magnetic properties, and on the observation of extraordinary Hall effect (EHE). Films with the Ni fraction x above percolation threshold x > 0.58 > xp as revealed by resistivity versus temperature measurements have a large Ni particle size, pronounced ferromagnetic characteristics, and appreciable extraordinary Hall resistivity at 300 K. Furthermore, films above percolation have a relatively low, nearly temperature independent Ohmic resistivity smaller than 10E−3 Ohm cm and may be useful for Hall sensor applications. On the other hand, films below percolation threshold x < 0.54 < xp have a small Ni particle size, superparamagnetic behavior, and do not show EHE at 300 K. However, at 5 K all films show ferromagnetic characteristics with an enhanced EHE.

  • Journal of Applied Physics 107(2010)11, 113913

Permalink: https://www.hzdr.de/publications/Publ-14025
Publ.-Id: 14025


Cluster spin glass behavior in Bi(Fe0.95Co0.05)O3

Xu, Q.; Zhou, S.; Wu, D.; Uhlarz, M.; Tang, Y.; Potzger, K.; Xu, M.; Schmidt, H.

The static and time-dependent magnetic properties of Bi(Fe0.95Co0.05)O3 have been investigated by dc and ac magnetization measurements. Cluster spin glass has been confirmed to be the ground state due to the frustration of the interaction between the ferromagnetic clusters by canted antiferromagnetically arranged Fe spins (Tc > 350 K) and by ferrimagnetically arranged Co and Fe spins (Tc ~ 250 K). Two freezing temperatures Tf of about 260 K and 100 K have been clearly identified from the abrupt change in magnetization relaxation. The higher Tf is related to the canted antiferromagnetically arranged Fe spins, and the lower Tf is related to the ferrimagnetically arranged Co and Fe spins. The cluster spin glass behavior with two freezing temperatures has been confirmed by ac susceptibility measurements.

Permalink: https://www.hzdr.de/publications/Publ-14024
Publ.-Id: 14024


The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge

Zhou, S.; Bürger, D.; Skorupa, W.; Oesterlin, P.; Helm, M.; Schmidt, H.

In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 1018 to 2.1$\times$1020 cm-3, the latter being the highest reported so far. Based on the magneto-transport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.

Keywords: Diluted magnetic semiconductor; Ge; ion implantation

Permalink: https://www.hzdr.de/publications/Publ-14023
Publ.-Id: 14023


Hysteresis in the magnetotransport of manganese-doped germanium: Evidence for carrier-mediated ferromagnetism

Zhou, S.; Bürger, D.; Mücklich, A.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.

We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by pulsed laser annealing. Benefiting from the short time annealing, the hole concentration in Mn-implanted Ge has been increased by two orders of magnitude from 1018 to over 1020 cm−3. Likely due to the high hole concentration, we observe that the longitudinal and Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated ferromagnetism.

Keywords: Diluted magnetic semiconductor; Ge; Ion implantation

Permalink: https://www.hzdr.de/publications/Publ-14022
Publ.-Id: 14022


New high-spin isomer and quasiparticle-vibration coupling in 187Ir

Modamio, V.; Jungclaus, A.; Algora, A.; Bazzacco, D.; Escrig, D.; Fraile, L. M.; Lenzi, S.; Marginean, N.; Martinez, T.; Napoli, D. R.; Schwengner, R.; Ur, C. A.

The nucleus 187 Ir has been populated up to high spin using the reaction 186 W(7 Li, 6n) at a beam energy of 59 MeV. A comprehensive extension of its level scheme has been proposed comprising 116 newly established excited states connected by 194 transitions which have been observed for the first time. All known rotational bands have been extended up to higher spin and in particular the band crossing region of the h9/2 band has been revised. A number of new intrinsic high-K states has been identified and for some of them multi-quasiparticle configurations have been tentatively assigned. The three-quasiparticle state with spin 29/2- and an excitation energy of 2487 keV is isomeric with a half-live of T1/2 = 1.8(5) µs. On top of this state a rich level scheme reaching up to spin (59/2-) and excitation energies around 7 MeV has been established. Of particular interest is a new structure built on the 31/2-, maximum spin three-quasiparticle state with {11/2-[505]} {11/2+[615],9/2+[624]} configuration at 2755 keV. Arguments have been presented which indicate a vibrational character of these states similar to the proposed vibration-plus-quasiparticle coupling suggested for the structure built on the 11/2- h11/2 proton 1qp state.

Keywords: nuclear structure; gamma-ray spectroscopy; high-spin isomer; vibration-particle coupling

Permalink: https://www.hzdr.de/publications/Publ-14021
Publ.-Id: 14021


Anwendung zeitmodulierter AC-Magnetfelder zur Strömungskontrolle in metallischen Schmelzen

Räbiger, D.; Eckert, S.; Gerbeth, G.

In dieser Arbeit wird die Wirkung des elektromagnetischen Rührens der Restschmelze bei der gerichteten Erstarrung einer Al-Si-Legierung untersucht. Dabei werden neue Methoden zum elektromagnetischen Rühren unter Nutzung eines zeitlich modulierten rotierenden Magnetfeldes (RMF) und eines wandernden Magnetfeldes (TMF) vorgestellt. Beim elektromagnetischen Rühren mit kontinuierlich wirkenden Feldern treten oft strömungsinduzierte Entmischungen im Gefüge auf. Mit der Strategie der Nutzung zeitmodulierter Felder sollen diese bekannten Nachteile vermieden werden. Die Ergebnisse zeigen, dass das Rühren unter Anwendung eines modulierten magnetischen Feldes Möglichkeiten zur effizienten Kontrolle des Strömungsfeldes vor der Erstarrungsfront bietet.

Keywords: Flow control; Electromagnetic stirring; liquid metal

  • Lecture (Conference)
    Symposion zur Simulation metallurgischer Strömungsprozesse an österreichischen und deutschen Universitäten, 16.-19.06.2010, Kirnitzschtal, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14020
Publ.-Id: 14020


Anwendung zeitmodulierter AC-Magnetfelder zum Rühren metallischer Schmelzen während der Erstarrung einer Al-Si-Legierung

Räbiger, D.; Leonhardt, M.; Eckert, S.; Gerbeth, G.

Der Einsatz elektromagnetischer Felder zum Rühren metallischer Schmelzen stellt eine elegante Möglichkeit einer völlig kontaktlosen Strömungskontrolle in erstarrenden Metalllegierungen dar, wobei die Strömungsintensität über die elektrischen Regelgrößen Strom und Frequenz gesteuert werden kann.
Trotz der nachweislichen Verbesserung der Gefügeeigenschaften, wie Kornfeinung und Vergrößerung des equiaxialen Erstarrungsbereiches durch eine intensive Strömung im Bereich der Erstarrungsfront, ist der Einsatz des elektromagnetischen Rührens auch problembehaftet, da die Strömung negative Auswirkungen wie strömungsinduzierte Porosität oder Gefügeinhomogenitäten (z.B. weiße Bänder beim Stahlguss) hervorrufen kann. Diese Nachteile erschweren eine industrielle Anwendung des Verfahrens im Strangguss.
Der Einsatz maßgeschneiderter, zeitmodulierter Magnetfelder bietet die Perspektive, die oben genannten, nachteiligen Effekte zu vermeiden. Mit dem Konzept der maßgeschneiderten Magnetfelder werden geeignete Strömungen erzeugt, welche die für die Herausbildung vorteilhafter Gefüge notwendigen Temperatur- und Konzentrationsfelder in der erstarrenden Schmelze liefern. Dies erfordert jedoch ein genaues Verständnis der Wechselwirkung von Magnetfeld, induzierter Strömung und Erstarrungsvorgang.
In diesem Vortrag wird die Wirkung des elektromagnetischen Rührens der Restschmelze mittels zeitmodulierter Magnetfelder bei der gerichteten Erstarrung einer binären Al-Si-Legierung untersucht. Für eine erfolgreiche Anwendung dieses Verfahrens sind geeignete Kombinationen der Magnetfeldparameter zu ermitteln. Zu diesem Zweck wurden Strömungsmessungen in einer isothermen Modellschmelze unter dem Einfluss modulierter Magnetfelder durchgeführt. Aufbauend auf den gewonnenen Erkenntnissen zur zeitlichen Entwicklung der Strömungsstruktur wurden geeignete Strategien für eine gezielte Beeinflussung der Gefügemerkmale durch den Einsatz maßgeschneiderter Magnetfelder abgeleitet. Die Erstarrungsversuche demonstrieren, dass es möglich ist, mit Hilfe zeitmodulierter magnetischer Felder korngefeinte, equiaxiale Gefüge unter Vermeidung der Herausbildung makroskopischer Gefügeinhomogenitäten herzustellen.
Die Ergebnisse veranschaulichen das große Potenzial des elektromagnetischen Rührens zur Verbesserung der Materialeigenschaften der erstarrten Struktur und einer Optimierung der Prozesskontrolle.

Keywords: Al-Si alloy; Electromagnetic stirring; Rotating magnetic field; Solidification; Columnar to equiaxed transition (CET); Grain refinement

  • Lecture (Conference)
    Tagung Stranggiessen, 15.-17.11.2010, Neu-Ulm, Deutschland
  • Contribution to proceedings
    Tagung Stranggiessen, 15.-17.11.2010, Neu-Ulm, Deutschland
    Stranggießen, Frankfurt: Werkstoff-Informationsgesellschaft mbH, 978-3-88355-384-9, 163-168

Permalink: https://www.hzdr.de/publications/Publ-14019
Publ.-Id: 14019


Terahertz free-electron lasers and their applications for the spectroscopy of solids

Helm, M.

In free-electron lasers (FEL) optical gain and stimulated emission are provided by relativistic electrons, wiggling through a periodic magnetic-field arrangement. Since the emitted wavelength only depends on the energy of the electrons and the magnetic field strength, an in principle arbitrary lasing wavelength may be achieved. Thus FELs are mostly used in spectral ranges, where conventional lasers with reasonably high power hardly exist. This is true, among others, for the long-wavelength infrared and terahertz (THz) range and represents the motivation to build such bulky THz sources.

Here I will discuss the operation principle of an FEL and then describe the THz FEL at FZD in Dresden. This FEL, called FELBE, was first operated in 2004 and covers now a wavelength range of nearly two spectral decades (3-300 µm or 1-100 THz). The key feature which distinguishes FELBE from other FEL user facilities is the possibility of delivering a continuous train of (micro)pulses, made possible by the superconducting accelerator cavities. The FEL thus provides picosecond optical pulses at a repetition rate of 13 MHz.

In order to pinpoint interesting scientific experiments using the FEL, one has to focus on its unique features, which are high peak power (up to 1 MW), high average power (tens of Watts), and short pulses (1-20 ps, depending on the wavelength). These features lend themselves to nonlinear optical experiments, near-field microscopy, and time resolved pump-probe studies, respectively. I will present experiments belonging to each of these three classes, namely

(1) pumping the intra-excitonic 1s-2p transition in semiconductor quantum wells, which leads to THz sideband generation and the observation of the AC Stark effect;
(2) near-field micro-spectroscopy of ferroelectrics, which allows imaging of ferroelectric domains in BaTiO3 purely due to their optical contrast resulting from a slight anisotropy of the dielectric function;
(3) carrier relaxation in semiconductor quantum dots. Here the relaxation time varies by three orders of magnitude (2 ps to 1.5 ns), if the energy level spacing is changed by only a factor of two (30 meV to 15 meV).

Keywords: free electron laser; spectroscopy; terahertz

  • Invited lecture (Conferences)
    THz radiation: generation, detection and applications (Heraeus Seminar), 18.-21.04.2010, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14018
Publ.-Id: 14018


Impulsive terahertz radiation with high electric fields from an amplifier-driven large-area photoconductive antenna

Beck, M.; Schäfer, H.; Klatt, G.; Demsar, J.; Winnerl, S.; Helm, M.; Dekorsy, T.

We report on the generation of impulsive terahertz (THz) radiation with 36 kV/cm vacuum electric field (1.5 mW average thermal power) at 250 kHz repetition rate and a high NIR-to-THz conversion efficiency of 2×10−3. This is achieved by photoexciting biased large-area photoconductive emitter with NIR fs pulses of μJ pulse energy. We demonstrate focussing of the THz beam by tailoring the pulse front of the exciting laser beam without any focussing element for the THz beam. A high dynamic range of 104 signal-to-noise is obtained with an amplifier based system.

Permalink: https://www.hzdr.de/publications/Publ-14017
Publ.-Id: 14017


Biosorption of U(VI) by the green algae Chlorella vulgaris in dependence of pH value and cell activity

Vogel, M.; Günther, A.; Rossberg, A.; Li, B.; Bernhard, G.; Raff, J.

Biosorption of uranium(VI) by the green alga Chlorella vulgaris was studied at varying uranium concentrations from 5 µM to 1 mM, and in the environmentally relevant pH range of 4.4 to 7.0. Living cells bind in a 0.1 mM uranium solution at pH 4.4 within 5 min 14.3 ± 5.5 mg U/g dry biomass and dead cells 28.3 ± 0.6 mg U/g dry biomass which corresponds to 45% and 90% of total uranium in solution, respectively. During 96 h of incubation with uranium initially living cells died off and with 26.6 ± 2.1 mg U/g dry biomass bound similar amounts of uranium compared to dead cells, binding 27.0 ± 0.7 mg U/g dry biomass. In both cases, these amounts correspond to around 85 % of the initially applied uranium. Interestingly, at a lower and more environmentally relevant uranium concentration of 5 µM, living cells firstly bind with 1.3±0.2 mg U/g dry biomass to 1.4±0.1 mg U/g dry biomass almost all uranium within the first 5 min of incubation. But then algal cells again mobilize up to 80% of the bound uranium during ongoing incubation in the time from 48 h to 96 h. The release of metabolism related substances is suggested to cause this mobilization of uranium. As potential leachates for algal-bound uranium oxalate, citrate and ATP were tested and found to be able to mobilize more than 50% of the algal-bound uranium within 24 h. Differences in complexation of uranium by active and inactive algae cells were investigated with a combination of time-resolved laser-induced fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure (EXAFS) spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Obtained results demonstrated an involvement of carboxylic and organic/inorganic phosphate groups in the uranium complexation with varying contributions dependent on cell status, uranium concentration and pH.

Keywords: sorption; uranium(VI); green algae; TRLFS; EXAFS; ATR-FTIR

Permalink: https://www.hzdr.de/publications/Publ-14016
Publ.-Id: 14016


Development of a generalized coalescence and breakup closure for the inhomogeneous MUSIG model

Liao, Y.; Lucas, D.; Krepper, E.; Schmidtke, M.

In the present study we propose new coalescence and breakup closures for the inhomogeneous MUltiple bubble Size Group (MUSIG) model. The major purpose is to consider bubble coalescence and breakup due to different mechanisms in turbulent gas-liquid mixtures and to develop a generally applicable constitutive model for CFD applications. For bubble coalescence the new model includes coalescence due to turbulence, laminar shear, wake entrainment and eddy capture. Bubble breakup mechanisms encompass turbulent fluctuation, laminar shear and interfacial slip velocity. The new model was implemented in the commercial CFD software (CFX-12.0) and applied to the case of turbulent air-water mixtures in a large vertical pipe (DN200). Simulation results for the evolution of bubble size distributions were compared to the standard closure model of Luo and Svendsen (1996), Prince and Blanch (1990) as well as the experimental data of TOPFLOW test facility. Better prediction is accomplished by the proposed new model.

Keywords: new coalescence and breakup closures; the inhomogeneous MUSIG model; upward pipe flow; TOPFLOW facility

Permalink: https://www.hzdr.de/publications/Publ-14015
Publ.-Id: 14015


Influence of two-phase turbulence models on the bubble coalescence and breakup behavior in bubbly pipe flow

Liao, Y.; Lucas, D.; Krepper, E.

In poly-disperse bubbly flows, bubble coalescence and breakup are important local events, which determines the evolution of the flow as well as the transition to slug flow. On the other hand side, the characterization of bubble coalescence and breakup is still one weak point in the CFD simulation of poly-disperse bubbly flows, since the transferability of available models is limited. A generalized model was proposed in our previous work, which takes into account all mechanisms of interest for bubble coalescence and breakup. Turbulence is one major mechanism in a turbulent bubbly flow. In other word, the performance of models for bubble coalescence and breakup relies on the accuracy of turbulence modeling. However, two-phase turbulence modeling is still one open issue.

In the current work, air-water bubbly flow in a vertical pipe (DN200) was investigated. The experimental data were obtained from the TOPFLOW test facility at the Forschungszentrum Dresden-Rossendorf (FZD). The inhomogeneous MUSIG approach in CFD code CFX with a new closure model for bubble coalescence and breakup was used for the simulation. Influence of various two-phase turbulence models was studied. The results of bubble size distribution, radial gas volume fraction, air/water axial velocity, Sauter mean bubble diameter as well as turbulent parameters were compared for each model.
In general, a good agreement with the experimental data has been achieved. The new model for bubble coalescence and breakup was shown as capable of predicting the flow evolution. The influence of two-phase turbulence modeling is considerable. Bubble-induced turbulence can be modeled by additional source term for turbulence transport equations instead of additional viscosity term.

Keywords: Poly-disperse bubbly flow; New model for bubble coalescence and breakup; Two-phase turbulence modeling

  • Contribution to proceedings
    The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8), 10.-14.10.2010, Shanghai, China
  • Lecture (Conference)
    The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-8), 10.-14.10.2010, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-14014
Publ.-Id: 14014


Validierung von Software-Komponenten zur Voraussage der strahleninduzierten Schädigung von RDB-Stahl

Bergner, F.; Birkenheuer, U.; Ulbricht, A.

Die skalenübergreifende Modellierung der strahleninduzierten Schädigung von RDB-Stahl von den Primärschäden auf der atomaren Skala bis zu den Änderungen der mechanischen Eigenschaften auf der Makroskala trägt wesentlich zu einem ver¬besserten Verständnis des Phänomens der Neutronenversprödung bei. Sie kann sich zukünftig zu einem Bestandteil der Sicherheitsbewertung des RDB entwickeln. Der gewählte zweistufige Modellierungsansatz beruht auf der Kopplung eines ratentheoretischen Moduls zur Voraussage der Größenverteilung der strahlen¬induzierten Defekt-Fremdatom-Cluster mit einem Härtungs-Modul zur Voraussage der strahleninduzierten Streckgrenzenerhöhung. Gegenstand der Untersuchungen sind die Weiterentwicklung und Validierung entsprechender Software-Komponenten. Die Validierung erfolgt durch Gegenüberstellung der Berechnungsergebnisse mit Resultaten von Neutronenkleinwinkelstreumessungen und Zugversuchen an neutronenbestrahlten RDB-Stählen.

Der entwickelte ratentheoretische Modul ermöglicht es, die Größe, Konzentration und Zusammensetzung gemischter Cu-Leerstellen-Cluster über die für RDB-Stähle relevanten Größenbereiche von bis zu 10000 Atomen und Zeitbereiche von bis zu mehreren 10 Jahren zu verfolgen. Die Verbindung der Ratentheorie zur Härtungs¬modellierung beruht auf der Übergabe von berechneten mittleren Hindernis¬abständen und -stärken. Die Validierung der numerischen Werkzeuge hat ergeben, dass wesentliche Tendenzen der strahleninduzierten Streckgrenzenerhöhung von Cu-haltigen und Cu-armen RDB-Stählen richtig wiedergegeben werden. Erste Ansätze zur Erfassung des Einflusses des Legierungselements Nickel im Rahmen der Ratentheorie und der Härtungsmodellierung wurden verwirklicht.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-533 2010
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-14013
Publ.-Id: 14013


Experimental data on steam bubble condensation in poly-disperded upward vertical pipe flow

Lucas, D.; Beyer, M.; Szalinski, L.

Experiments were done at the TOPFLOW facility of the Forschungszentrum Dresden-Rossendorf to establish a CFD-grade database on the condensation of steam bubbles injected into sub-cooled upwards vertical pipe flow. Bubble condensation has to be considered in Nuclear Reactor Safety Research, e.g. if sub-cooled boiling or bubble entrainment caused by ECC injection occurs. Bubble size distributions are important, since the condensation rate is proportional to the interfacial area density. To develop and validate closure models for CFD codes experimental data with high resolution in space and time are required. The steam was injected via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Pressure, steam and water flow rates and the sub-cooling were also varied. Measurements are done using wire-mesh sensors and thermocouples. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are available.

Keywords: condensation; phase transfer; bubbles; two-phase flow; CFD

  • Contribution to proceedings
    CFD4NRS-3, International Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, Paper 13.1, 14.-16.09.2010, Washington D.C., USA
  • Lecture (Conference)
    CFD4NRS-3, International Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, 14.-16.09.2010, Washington D.C., USA

Permalink: https://www.hzdr.de/publications/Publ-14012
Publ.-Id: 14012


Pre-test CFD simulations on TOPFLOW-PTS experiments with ANSYS CFX 12.0

Apanasevich, P.; Lucas, D.; Höhne, T.

Pressurized Thermal Shock (PTS) has been identified as one of the most important industrial needs related to nuclear reactor safety. The PTS analysis requires the simulation of the thermal mixing of cold Emergency Core Cooling (ECC) water injected to the cold leg and flowing to the downcomer with the hot coolant, which is present in the primary circuit. The simulation of single-phase and two-phase PTS situations including e.g. stratification of the flow and direct contact condensation is a challenge for CFD methods and requires careful validation against experimental data. In the frame of the NURISP project attempts are made to improve the CFD modelling for two-phase PTS situations. For this purpose, two reference cases with and without mass transfer due the condensation were defined, which are related to the TOPLOW PTS experiments. The present paper focuses on numerical investigations of thermal mixing process in the cold leg and the downcomer using homogeneous and inhomogeneous models for the resolution of momentum equations. Numerical simulations were performed by using the commercial CFD code ANSYS CFX 12.0.

Keywords: Horizontal Stratified Flow; Pressurized Thermal Shock; Direct Contact Condensation; CFD

  • Contribution to proceedings
    CFD4NRS-3, Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, 14.-16.09.2010, Washington D.C., USA
  • Lecture (Conference)
    CFD4NRS-3, Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues. Paper 11.1, 14.-16.09.2010, Washington D.C., USA

Permalink: https://www.hzdr.de/publications/Publ-14011
Publ.-Id: 14011


Evaluation of a multichannel-plate PMT as potential timing detector suitable for positron lifetime measurements

Kosev, K.; Butterling, M.; Anwand, W.; Cowan, T.; Hartmann, A.; Heidel, K.; Jungmann, M.; Krause-Rehberg, R.; Massarczyk, R.; Schilling, K. D.; Schwengner, R.; Wagner, A.

This paper focuses on the evaluation of a multichannel-plate photomultiplier tube (MCP-PMT) as a candidate detector, suitable for positron lifetime studies. Several properties of MCP-PMTs, such as their fast time response, compact size, low susceptibility to magnetic fields, relatively high gain and the low power consumption make them attractive for the positron lifetime spectroscopy. The preliminary tests were performed with the 85001-501 Burle Planacon$^{TM}$ photomultiplier tube assembly. Initial measurements were conducted with a pulsed Picosecond Injection Laser (PiLas) system. The engineering sample of the 85001 exhibits a transit-time-spread (TTS) of 110 ps (FWHM). Further timing experiments showing the suitability of the device as Cherenkov detector are presented. For the first time, a conventional positron lifetime spectrum of Cz-Si probe measured with a spectrometer, where a MCP-PMT detector is incorporated has been demonstrated.

Keywords: multichannel plate detector; photocathode; positron lifetimes

  • Nuclear Instruments and Methods in Physics Research A 624(2010)3, 641-645

Permalink: https://www.hzdr.de/publications/Publ-14010
Publ.-Id: 14010


How to get a new accelerator mass spectrometry (AMS) facility running: The chemistry part

Merchel, S.; Arnold, M.; Aumaître, G.; Bourlès, D.; Braucher, R.

The AMS business is booming: Many low-energy (< 1 MV) facilities, which are fully dedicated for 14C-analysis, are under construction or in funding status. Additionally, medium-energy accelerators such as the British 5 MV-NEC machine at “SUERC” Glasgow, the French 5 MV-HVEE-machine “ASTER” at Aix-en-Provence [2] and the two German 6 MV-HVEE-machines “DREAMS” at Dresden [3] and “Cologne AMS” at Cologne [4] have been recently installed or are still in testing mode in Central Europe. Of course, these bigger machines need not only experienced physicists and technicians to get them running. It also seems to be advisable to have some experienced scientists around, who knows how to prepare AMS targets for 10Be, 26Al, 36Cl, 41Ca, and 129I measurements.
In contrast to the 14C-community, where e.g. round-robin exercises are routine business, the idea of quality assurance and traceable standards has only been brought up lately for the other cosmogenic radionuclides measurable at medium-energy AMS facilities. Thus, world-wide accepted standards issued by metrology institutes are rare: NIST is selling two kinds of 129I/127I-standards, and the Institute for Reference Materials and Measurements (IRMM) provides one set of 41Ca/40Ca solutions having eight different ratios [5]. Unfortunately, the most commonly used 10Be/9Be standard provided by NIST has been recently sold-out and will not be reissued. Other primary standard-type materials (26Al,36Cl), which are not commercially available, have been prepared by diluting certified activities and subsequent analysis within round-robin exercises [6-8]. After production of big quantities of in-house secondary standards for all nuclides (Tab. 1), cross-calibration versus primary standard-type materials has to be performed [2].

Table 1: Primary and secondary AMS standards in use at ASTER and DREAMS.
Primary standards Secondary (in-house) standards
10Be NIST SRM 4325 (sold-out) NIST SRM 4325 (ASTER)
10Be via 9Be(nth,gamma)10Be (DREAMS)
26Al MB04-A,B,C,D [6] SM-Al-10,11,12,13 [2]
36Cl SM-Cl-11,12,13 [7,8] SM-Cl-11,12,13 [7,8]
41Ca IRMM ERM®-AE701 [5] SM-Ca-10,11,12 [2]
--> SM-Ca-P9,11,13 [2]
129I NIST SRM 3231, Level II SM-I-9,10,11,12

Finally, as commercial 9Be contains intrinsic 10Be up to a level of 4x10-14 [9] sophisticated production of in-house carriers, used as machine blanks and for samples, from Be-containing minerals such as Be2SiO4 originating from deep mines, is needed. After production and measurement of all these materials, the AMS facility is ready for routine measurements.

Acknowledgments: We are grateful to U. Herpers & E. Strub for providing 26Al-activity, to A. Wallner & M. Bichler for performing the neutron-irradiation of 9Be, to C. Varajão for providing Be2SiO4 crystals, and to R.C. Finkel, L. Benedetti, W. Möller, HVEE, the FZD-operator- & AMS-team for great cooperation.

References: [1] S. Freeman et al., NIM B 259 (2007) 66. [2] M. Arnold et al., doi: 10.1016/ j.nimb.2010.02.107. [3] Sh. Akhmadaliev et al., this meeting. [4] M. Klein et al., this meeting. [5] C. Hennessy et al., NIM B 229 (2005) 281. [6] S. Merchel, W. Bremser, NIM B 223–224 (2004) 393. [7] S. Merchel et al. Geochim. Cosmochim. Acta 73 (2009) A871. [8] S. Merchel et al., in prep. for NIM B. [9] S. Merchel et al., NIM B 266 (2008) 4921.

Keywords: accelerator mass spectrometry

  • Poster
    10th European Conference on Accelerators in Applied Research and Technology (ECAART 10), 13.-17.09.2010, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-14009
Publ.-Id: 14009


Prokaryotic microorganisms in uranium mining waste piles and their interactions with uranium and other heavy metals

Geißler, A.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    Dissertation
    190 Seiten
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-14008
Publ.-Id: 14008


Lambda-p femtoscopy in collisions of Ar+KCl at 1.76 AGeV

Agakishiev, G.; Balanda, A.; Bassini, R.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Guber, F.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.; Zhou, P.; Zumbruch, P.

Results on Lambda p femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76A~GeV, the reaction Ar+KCl was studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. A high-statistics and high-purity Lambda sample was collected, allowing for the investigation of Lambda p correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the Lambda p emission source. The Lambda p source radius is found slightly smaller than the pp correlation radius for a similar collision system. The present Lambda p radius is significantly smaller than that found for Au+Au/Pb+Pb collisions in the AGS, SPS and RHIC energy domains, but larger than that observed for electroproduction from He. Taking into account all available data, we find the Lambda p source radius to increase almost linearly with the number of participants to the power of one-third.

Permalink: https://www.hzdr.de/publications/Publ-14007
Publ.-Id: 14007


Spektroskopische Charakterisierung eines ternären U(VI)-Carbonato-Humat-Komplexes mittels ATR FT-IR und cryo-TRLFS

Steudtner, R.; Schmeide, K.; Sachs, S.; Müller, K.

Die Komplexierung zwischen Uran(VI) und Huminsäure (HA) in Gegenwart von Carbonat wurde mittels abgeschwächter Totalreflexion Fourier-Transform Infrarotspektroskopie (ATR FT-IR) und zeitaufgelöster laserinduzierter Fluoreszenzspektroskopie bei tiefen Temperaturen untersucht. Die Bildung eines ternären U(VI)-Carbonato-Humat Komplexes konnte spektroskopisch nach gewiesen werden. Die in dieser Arbeit bestimmten Komplexbildungskonstanten von log K(I=0,1M) = 2,69 ± 0,47 (cryo-TRLFS) und log K(I=0,1M) = 3,14 ± 0,70 (ATR FT-IR) zeigen eine sehr gute Übereinstimmung.

Keywords: Uran(VI); Huminsäure; ATR FT-IR; cryo-TRLFS

  • Lecture (Conference)
    Workshop zum Verbundprojekt „Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika“, 13.-14.04.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14006
Publ.-Id: 14006


Measurement of liquid distributions in particle packings: use of wire mesh sensor versus transmission tomographic imaging

Bieberle, A.; Schubert, M.; Da Silva, M. J.; Hampel, U.

The paper compares two different high-resolution imaging techniques for the investigation of the hydrodynamics in a laboratory packed bed reactor operating at different stationary states and with two different particle packings. The wire-mesh sensor offers cross-sectional liquid holdup distribution imaging at ultra high speed of 10,000 frames per second and good spatial resolution. It is therefore a very useful imaging tool for transient and periodic flow conditions. But yet its influence on the flow in a packed bed was never analyzed. Gamma-ray computed tomography uses 662 keV gamma photons to obtain cross-sectional phase distribution images. It offers as well a good spatial resolution of 2 mm and does not influence the flow. But it needs rather long scanning times. As a non-invasive technique gamma-ray tomography has been used as a reference modality to evaluate the wire-mesh sensor measurements. Data from both imaging modalities are compared utilizing different analyzing models and showed good agreement. For the wire mesh sensor only marginal intrusive effects with respect to the flow dynamics were found.

Keywords: wire-mesh sensor; gamma-ray tomography; packed bed reactor

  • Industrial & Engineering Chemistry Research 49(2010)19, 9445-9453
    DOI: 10.1021/ie100900g

Permalink: https://www.hzdr.de/publications/Publ-14005
Publ.-Id: 14005


Möglichkeiten und Potentiale einer modernen Faserstoffherstellung

Tobisch, S.; Krug, D.; Mäbert, M.; Bieberle, A.

Die Herstellung von Holzfaserstoffen im Druckrefiner stellt einen hoch komplexen Prozess dar, dessen Wirkungsweise und entsprechende physikalische Zusammenhänge bisher Zeitpunkt nur in geringem Maße beschrieben sind. Momentan werden Holzfaserstoffe in ausreichender Qualität unter enormem Energieeinsatz produziert, wobei sich jedoch eine gezielte Einstellung und Messung der Faserqualität als schwierig gestaltet. Das Potential, dass die umfassende theoretische Durchdringung des Zerfaserungsprozesses und die sich daraus ergebenden Optimierungsmöglichkeiten hinsichtlich Einstellung einer definierten Faserqualität und Energieeinsparung bietet, wird nicht ausgeschöpft. Die vorliegende Arbeit befasst sich daher mit der Ist-Stand-Analyse des thermomechanischen Faserstoffaufschlusses und macht die Abbildung der thermodynamischen Prozesse, des Materialflusses und der Energieaufnahme während der Zerfaserung möglich.

Keywords: Refiner; Gamma-CT

  • Contribution to proceedings
    14. Holztechnologisches Kolloquium - Werkstoffe aus Holz und Holzverarbeitung im Fokus von Forschung und Entwicklung, 08.-09.04.2010, Dresden, Deutschland
    Möglichkeiten und Potentiale einer modernen Faserstoff-herstellung

Permalink: https://www.hzdr.de/publications/Publ-14004
Publ.-Id: 14004


Untersuchungen zur Am(III)-Komplexierung durch Modellliganden, zur Np(V)-Reduktion durch schwefelhaltige Huminsäuren sowie zur pH-abhängigen U(VI)-Sorption an Opalinuston unter aeroben und anaeroben Bedingungen

Raditzky, B.; Schmeide, K.; Sachs, S.; Joseph, C.; Frost, L.; Bernhard, G.

Im Vortrag werden Ergebnisse zur spektroskopischen Bestimmung von Stabilitätskonstanten für die Am(III)-Komplexierung durch organische Modellliganden sowie zur temperaturabhängigen Untersuchung der U(VI)-Humat-Komplexierung präsentiert. Desweiteren wird der Einflusses von Schwefelfunktionalitäten auf die Np(V)-Reduktion durch Huminsäuren diskutiert. Weiterhin werden neue Erkenntnisse zur pH-abhängigen U(VI)-Sorption an Opalinuston unter anaeroben und aeroben Bedingungen vorgestellt.

Keywords: Actinides; humic substances; complexation; reduction; functional groups; sorption; opalinus clay

  • Lecture (Conference)
    Workshop zum Verbundprojekt „Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika“, 13.-14.04.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-14003
Publ.-Id: 14003


Solar fusion cross sections II: the pp chain and CNO cycles

Adelberger, E. G.; Balantekin, A. B.; Bemmerer, D.; Bertulani, C. A.; Chen, J.-W.; Costantini, H.; Couder, M.; Cyburt, R.; Davids, B.; Freedman, S. J.; Gai, M.; Garcia, A.; Gazit, D.; Gialanella, L.; Greife, U.; Hass, M.; Heeger, K.; Haxton, W. C.; Imbriani, G.; Itahashi, T.; Junghans, A.; Kubodera, K.; Langanke, K.; Leitner, D.; Leitner, M.; Marcucci, L. E.; Motobayashi, T.; Mukhamedzhanov, A.; Nollett, K. M.; Nunes, F. M.; Park, T.-S.; Parker, P. D.; Prati, P.; Ramsey-Musolf, M. J.; Hamish Robertson, R. G.; Schiavilla, R.; Simpson, E. C.; Snover, K. A.; Spitaleri, C.; Strieder, F.; Suemmerer, K.; Trautvetter, H.-P.; Tribble, R. E.; Typel, S.; Uberseder, E.; Vetter, P.; Wiescher, M.; Winslow, L.

We summarize and critically evaluate the available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. We also discuss opportunities for further increasing the precision of key rates, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to Reviews of Modern Physics 70 (1998) 1265.

Permalink: https://www.hzdr.de/publications/Publ-14002
Publ.-Id: 14002


Microcavity enhanced silicon light emitting pn-diode

Potfajova, J.; Schmidt, B.; Helm, M.; Gemming, T.; Benyoucef, M.; Rastelli, A.; Schmidt, O. G.

An electrically driven silicon light emitting diode with two distributed Bragg reflectors is reported. The active material is a Si pn-junction fabricated by boron ion implantation into an n-type silicon-on-insulator wafer. The cavity with a thickness of a few wavelengths is formed by amorphous Si/SiO2 multilayer stacks. A strong narrowing and enhancement of the electroluminescence at a resonant wavelength of lambda=1146 nm is observed with a quality factor of Q=143 and a finesse of F=11.

Keywords: silicon; light emittter; microcavity; electroluminescence; light emitting diodes

Permalink: https://www.hzdr.de/publications/Publ-13999
Publ.-Id: 13999


Wisp-like structures in vertical gas-liquid pipe flow revealed by wire mesh sensor studies

Perez, V. H.; Azzopardi, B. J.; Kaji, R.; Da Silva, M. J.; Beyer, M.; Hampel, U.

A conductance Wire Mesh Sensor system has been employed on a vertical 67 mm diameter pipe with the up flow of air and water mixtures. The measuring system provides time and cross-sectionally resolved information about the spatial distribution of the phases. Statistical information can be extracted and used to identify flow patterns. The fully resolved data has revealed a hitherto unreported structure has been seen in churn flow which could be linked to the wisps in wispy-annular flow.

Keywords: gas-liquid two-phase flow; wire mesh sensor

Permalink: https://www.hzdr.de/publications/Publ-13998
Publ.-Id: 13998


Post Mortem Investigations of Greifswald WWER-440 Reactor Pressure Vessels

Viehrig, H.-W.; Houska, M.; Arora, K. S.; Rindelhardt, U.

Nuclear plant operators must demonstrate that the structural integrity of a nuclear reactor pressure vessel (RPV) is assured during routine operations or under postulated accident conditions. The aging of the RPV steels is controlled with surveillance program results. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response. A chance is given now with the investigation of RPV material from the decommissioned Greifswald NPP (WWER-440/230).
The Greifswald RPVs represent different material conditions such as irradiated, irradiated and annealed and irradiated, annealed and re-irradiated. A region covering ±0.70 m above and below the circumferential core weld was recovery annealed at 475° for about 150 hours. The working program is focused on the characterisation of the RPV steels (base and weld metal) through the RPV wall. It comprises chemical analysis, microstructure investigations (by means of metallography, electron microscopy and SANS) and mechanical testing (hardness measurements, tensile, Charpy-V), and fracture mechanics testing. The key part of the testing is focussed on the determination of the reference temperature T0 following the ASTM test standard E1921-09 to determine the facture toughness, and how it degrades under neutron irradiation.
The paper presents test results measured on trepans of the welding seam and base metal located in the reactor core region. The test results comprise Charpy-V, tensile and fracture toughness parameters. An additional aspect is the comparison of results determined on sub-size Charpy specimens machined of templates taken after the annealing from the uncladded inner RPV wall.

Keywords: nuclear reactor; reactor pressure vessel steel; fracture toughness; Master Curve; integrity assessment

  • Contribution to proceedings
    11th International Conference “Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment, 14.-18.06.2010, St. Petersburg, Russia
    Proceedings of the 11th International Conference Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment, St. Petersburg
  • Lecture (Conference)
    11th International Conference “Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment, 14.-18.06.2010, St. Petersburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-13997
Publ.-Id: 13997


Modified automated synthesis of sodium 2-[18F]fluoroacetate using a TracerlabFXN synthesizer.

Kniess, T.; Richter, S.; Steinbach, J.

1. Introduction:
Prostate cancer is the most frequently diagnosed cancer in men over the age of 40 years in Europe and the USA and its early detection is crucial for prognosis and outcome of the disease. Besides the established radiotracers based on 11C- and 18F-labeled choline [11C]acetate is used for the early detection of prostate cancer and its recurrence. 2-[18F]Fluoroacetate has been proposed as alternative to [11C]acetate offering the advantage of longer half-life which facilitates synthesis, shipping and allowing longer imaging protocols. A few radiosyntheses of the radiotracer have been published in the past, mainly based on trapping of the 2-[18F]fluoroacetate ethylester on C18 cartridges (Oasis HLB), followed by acidic hydrolysis [1-3]. Our approach is the fully automated synthesis of 2-[18F]fluoroacetate with a TracerlabFXN synthesizer including separation of the radiotracer via anion exchange cartridges in alkaline solution.

2. Materials and methods:
The radiolabeling with [18F]fluoride was performed with 2-methanesulfonyl-acetic acid t-butyl-ester as precursor in acetonitrile at 100°C. After hydrolysis with 1M HCl and addition of 1M NaOH the alkaline reaction mixture was diluted with 20mL of water and passed through a combination of two anion exchange cartridges where 2-[18F]fluoroacetate was trapped. The 2-[18F]fluoroacetate was recovered by elution with NaHCO3 and excess [18F]fluoride was removed by alumina N cartridges to provide radiochemical pure sodium 2-[18F]fluoroacetate (radio-TLC, RP18, acetonitrile/water=85/15; Rf=0.59).

3. Results:
The radiosynthesis of sodium 2-[18F]fluoroacetate was accomplished with a TracerlabFXN synthesizer by a fully automated procedure. The purification of the product was performed by anion exchange cartridges and gave the radiotracer in 27-30% yield (decay-corrected) and 99% radiochemical purity within 30 min total synthesis time.

4. Discussion/Conclusion:
The modified approach of radiosynthesis and purification delivers sodium 2-[18F]fluoroacetate in high radiochemical purity and good radiochemical yield. The improved radio-TLC method using RP18 plates represents an easy system to distinguish [18F]fluoride from 2-[18F]fluoroacetate. Further optimization of this new method utilising a new precursor and a modified separation system is in progress. The conformation of the process to GMP requirements will be performed in the near future.

References:
[1] Sun LQ, Mori T, Dence CS, Ponde DE, Welch MJ, Furukawa T, Yonekura Y, Fujibayashi Y, [2006], Nucl.Med.Biol., 33:153-158
[2] Ponde DE, Dence CS, Oyama N, Kim J, Tai YC, Laforest R, Siegel BA, Welch MJ, [2007], J.Nucl.Med., 48(3): 420-428
[3] Marik J, Ogasawara A, McNulty BM, Ross J, Flores JE, Gill HS, Tinianow JN, Vanderbilt AN, Nishimura M, Peale F, Pastuskovas C, Greve JM, van Bruggen N, Williams SP, [2009], J.Nucl.Med., 50(6): 982-990

  • Poster
    15th European Symposium on Radiopharmacy and Radiopharmaceuticals (ESRR), 08.-11.04.2010, Edinburgh, Großbritannien
  • Abstract in refereed journal
    Quarterly Journal of Nuclear Medicine and Molecular Imaging 54(2010)S1, 54

Permalink: https://www.hzdr.de/publications/Publ-13996
Publ.-Id: 13996


Dose dependent biological damage of tumour cells by laser-accelerated proton beams

Kraft, S. D.; Richter, C.; Zeil, K.; Baumann, M.; Beyreuther, E.; Bock, S.; Bussmann, M.; Cowan, T. E.; Dammene, Y.; Enghardt, W.; Helbig, U.; Karsch, L.; Kluge, T.; Laschinsky, L.; Lessmann, E.; Metzkes, J.; Naumburger, D.; Sauerbrey, R.; Schürer, M.; Sobiella, M.; Woithe, J.; Schramm, U.; Pawelke, J.

We report on the irradiation of in vitro tumour cells with laser-accelerated proton pulses showing dose dependent biological damage. This experiment, paving the way for future radiobiological studies with laser-accelerated protons, demonstrates for the first time the simultaneous and reliable availability of all components indispensable for systematic radiobiological studies: A laser-plasma accelerator providing stable proton spectra with maximum energy exceeding 15 MeV and applicable doses of a few Gy within few minutes, a beam transport and filtering system, an in-air irradiation site, a dedicated dosimetry system providing both online dose monitoring and a precise absolute dose information applied to the cell sample, and the full infrastructure for analysing radiation induced damage in cells.

Permalink: https://www.hzdr.de/publications/Publ-13995
Publ.-Id: 13995


Theoretical investigations of carbon-based nanocoatings

Kunze, T.; Gemming, S.; Posselt, M.; Erdogan, E.; Seifert, G.

Nanocoatings have the potential to improve the surface characteristics of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. Our research activity focuses on self-lubricating and hard cabon-based nanocoatings (C:TM and taC films) investigated by atomic-scale simulations. We will present morphological as well as tribological properties of the studied systems. Support by the European Union and the Freistaat Sachsen via SAB project 13857/2379 within the ECEMP initiative is gratefully acknowledged.

  • Lecture (Conference)
    Nanocoatings 2010, 28.-31.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13994
Publ.-Id: 13994


Crystalline ripples at the surface of ion eroded strained Si0.8Ge0.2 epilayers

Kanjilal, A.; Prucnal, S.; Minniti, M.; Skorupa, W.; Helm, M.; Facsko, S.

Surface erosion of a strained Si0.8Ge0.2 epilayer by 500 eV Ar+ ions with a fluence of 4 x1017 ions/cm2 and the transformation from crystalline ripples to elongated Ge islands are reported by aligning the beam from 69° to 50° from the surface normal. Crystalline nature and the near surface Ge enrichment in such ripple structures are revealed by transmission electron microscopy. Moreover, ion beam induced decomposition of the SiGe network and the appearance of dislocation bands by suppressing the near-bandgap emission are manifested by u-Raman and photoluminescence studies, respectively.

Keywords: SiGe; ripples; photoluminescence; Raman

  • Journal of Applied Physics 107(2010), 073513

Permalink: https://www.hzdr.de/publications/Publ-13993
Publ.-Id: 13993


Wie flexibel ist die Einwirkzeit von 18F-NaF

May, C.; Beuthien-Baumann, B.; Oehme, L.; Kotzerke, J.

Ziel/Aim:
Bedingt durch die bestehende Knappheit an 99m-Technetium wurden vermehrte Skelettszintigraphien mit 18F-Natriumfluorid (18F-NaF) am PET-Scanner (Siemens HR+) durchgeführt. Es sollte untersucht werden, wie flexibel die Einwirkzeit des 18F-NaF in der Routine gehandhabt werden kann, ohne die Bildqualität negativ zu beeinflussen.

Methodik/Methods:
Der PET-Scan wurde in 3D-Listmode-Technik aufgenommen, 360 MBq 18F-NaF, Emissionsdauer von 4 min pro Bettposition, keine Schwächungskorrektur. Der Abstand von Injektion von 18F-NaF zum Untersuchungssbeginn betrug in der ersten Gruppe 40-60 min, in der 2. Gruppe 60-80 min, in der 3.Gruppe 80-120 min. Bislang wurden 10 Patienten pro Gruppe ausgewertet. Es wurden standardisierte Regions of interest über Lunge und LWK1 (bzw LWK 2 oder BWK 12 gelegt, falls bei LWK 1 eine pathologische Mehranreicherung erkennen ließ) und Quotienten aus Anreicherung in LWK und Lunge gebildet.

Ergebnisse/Results:
Qualitativ konnten alle Patienten ausgewertet werden. Der Mittelwert der Quotienten aus LWK/Lunge betrug für die Gruppe 40-60 min p.i. 2,4; für die Gruppe 60-80 min p.i. 2,3 und für die Gruppe 80-120 min p.i. 3,0. Zwischen Gruppe 1 und 2 bestand hinsichtlich der LWK/Lunge-Quotienten kein wesentlicher Unterschied. Der Mittelwert für die Gruppe 3 lag mit 3,0 etwas höher, unterschied sich jedoch statistisch nicht signifikant von Gruppe 1 und 2.

Schlussfolgerungen/Conclusions:
Nach 40 min ist ohne weiteres eine Aufnahme mit 18F-Fluorid mit guter Bildqualität möglich. Unsere Berechnungen haben ergeben, dass bei einer Einwirkzeit zwischen 40 -80 min keine wesentlichen Qualitätsunterschiede zu erwarten sind. Dadurch fügt sich die Skelettaufnahme am PET flexibel in den Tagesablauf ein. Einen möglichen Gewinn an Bildqualität nach 80-120 min sollte man sich bei adipösen Patienten zu nutze machen.

  • Poster
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A113

Permalink: https://www.hzdr.de/publications/Publ-13992
Publ.-Id: 13992


Wie weit bewegen sich die Schwerpunkte hypoxischer Tumorsubvolumina von HNO-Tumoren unter kombinierter Radiochemotherapie.

Abolmaali, N.; Zöphel, K.; Koch, A.; Haase, R.; Steinbach, J.; Baumann, M.

Ziel/Aim:
Die Berücksichtigung hypoxischer Tumorsubvolumina anhand von FMISO-Daten zur Strahlentherapieplanung ist aufgrund des geringen Signal-zu-Rausch-Verhältnisses schwierig, weil die Konturen nicht eindeutig definiert sind. Ziel dieser Untersuchung war darzustellen, wie weit sich die Schwerpunkte Wie weit wandern die Schwerpunkte hypoxischer Tumorsubvolumina unter kombinierter Radiochemotherapie bewegen.

Methodik/Methods:
14 Patienten (2@, medianes Alter 55 Jahre) mit Plattenepithelkarzinomen des HNO-Traktes wurden vor kombinierter Radiochemotherapie (RCT) mit FDG sowie vor und nach 10Gy, 20Gy und 60Gy unter RCT mit FMISO untersucht (56 Untersuchungen). Mit der Rover-Software (ABX, Radeberg) wurde anhand der co-registrierten Daten Kontrast-basiert in jeder Untersuchung ein hypoxisches Tumorsubvolumen definiert und dessen Schwerpunkt im Koordinatensystem bestimmt. Die Bewegung dieses Schwerpunktes im Raum wurde unter RCT vermessen.

Ergebnisse/Results:
Im Mittel bewegen sich die Tumoren von der ersten zur zweiten Untersuchung um 5.6 mm, von der zweiten zur dritten Untersuchung um 5.5 mm und von der dritten zur vierten Untersuchung um 8 mm. Zwischen erster und vierter Untersuchung bewegten sich die Tumoren um 8.8 mm am weitesten. Die durchschnittliche Verschiebung des Schwerpunktes unter RCT lag bei 6.4 mm.

Schlussfolgerungen/Conclusions:
Unter Berücksichtigung der Registrierungsgenauigkeit von 2 mm und der maximalen Schwerpunktsbewegung von 9 mm erfasst der Strahlentherapieplan am Ende der Therapie das mit FMISO primär geplante Zielvolumen noch vollständig, wenn die üblichen Sicherheitsabstände berücksichtigt werden.

  • Poster
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A80

Permalink: https://www.hzdr.de/publications/Publ-13991
Publ.-Id: 13991


Für die Analyse hypoxischer Tumorvolumina sind 4h-FMISO-Aufnahmen besser geeignet als 2h-FMISO-Aufnahmen.

Abolmaali, N.; Zöphel, K.; Koch, A.; Zips, D.; Steinbach, J.; Baumann, M.

Ziel/Aim:
Die F-18-Misonidazol-PET (FMISO) zur Detektion hypoxischer Tumorsubvolumina weist ein vergleichsweise geringes Signal-zu-Rausch-Verhältnis auf. Üblicherweise werden neben der Dynamik Aufnahmen nach 2h und 4h p.i. angefertigt. Ziel dieser Untersuchung war es zu entscheiden, welche der beiden Spätaufnahmen den besten Kontrast hat und damit am besten für Volumenanalysen geeignet ist.

Methodik/Methods:
25 Patienten (3@, medianes Alter 55 Jahre) mit Plattenepithelkarzinomen des HNO-Traktes wurden vor kombinierter Radiochemotherapie (RCT) mit FDG sowie vor und nach 10Gy, 20Gy und 60Gy unter RCT mit FMISO untersucht (66 Untersuchungen). Mit der Rover-Software (ABX, Radeberg) wurde nach Co-Registrierung der PETs mit dem halbautomatischen Source-to-Background-Algorithmus anhand der FDG-Daten das Tumorgesamtvolumen definiert und in die FMISO kopiert. In diesem Tumorvolumen wurde die MISO-Aktivität bestimmt. Zusätzlich wurde in jeder FMISO ein 5-10 ml großes Referenzvolumen zur Definition des Hintergrundsignals von MISO in der Halsmuskulatur als definiert. Der Kontrast wurde mit dem Verhältnis MISO-Aktivität im Tumor zu MISO-Aktivität im Hintergrund bestimmt. Der statistische Vergleich erfolgte mit dem Wilcoxon-matched-pairs Test.

Ergebnisse/Results:
Der mittlere SUVmax im Tumor nach 2h war 1.9, nach 4h 2.3, der mittlere SUVmean in der Halsmuskulatur nach 2h war 1.2 und nach 4h 1.1. Der Mittelwert±Standardabweichung für den Kontrast nach 2h war 1.33±0.28 und nach 4h 1.41±0.32. Mediane, Minima und Maxima für den Kontrast lagen nach 2h bei 1.29, 0.81 und 2.06 und nach 4h bei 1.38, 0.90 und 2.33. Der Wilcoxon-matched-pairs Test ergab einen hoch signifikanten Unterschied für die Kontraste zwischen diesen beiden Untersuchungszeitpunkten (p = 0.000052).

Schlussfolgerungen/Conclusions:
Für Volumenanalysen von FMISO, z.B. für die Strahlentherapieplanung sind 4h-Daten besser geeignet als 2h-Daten.

  • Poster
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A80

Permalink: https://www.hzdr.de/publications/Publ-13990
Publ.-Id: 13990


> 65 MeV Protons From Laser-Micro-Cone Target Interactions

Gaillard, S. A.; Flippo, K. A.; Gautier, D. C.; Kline, J. L.; Offermann, D.; Workman, J.; Archuleta, F.; Gonzales, R.; Hurry, T.; Johnson, R. P.; Letzring, S.; Montgomery, D. S.; Reid, S.-M.; Shimada, T.; Lockard, T.; Sentoku, Y.; Mucino, J. E.; Lowenstern, M. E.; Gall, B. B.; D’Humières, E.; Cowan, T. E.; Bussman, M.; Kluge, T.; Rassuchine, J.

We have conducted two sets of laser-ion acceleration experiments at the LANL 200 TW Trident short-pulse laser at ~1020 W/cm2 (1 μm, 80-100 J and ~600 fs) at high (>1010) and low (>108) contrast, comparing regular size flat foils (~2 mm by 2 mm), reduced mass targets (200 μm to 500 μm diameter) and new Cu micro-cone targets in three separate geometries (flat-top or pizza-top, funnel, and snub-nose) to elucidate the production of hot electrons [1] and ions in these targets.
Results from the latest experiment show proton energies in excess of ~65 MeV for the pizza-top cones, compared to ~55 MeV for reduced mass targets and ~45 MeV for regular flat foils for high contrast. Data from a Cu Kα 2D imaging crystal, an X-ray single hit CCD, proton beam images on RCF film stacks, and an electron/proton spectrometer are presented and compared, showing the importance of not just generating hot electrons, but in the case of ion acceleration, efficiently propagating these hot electrons to the accelerating “tip”, where they can then be efficiently converted to ion energy, as well as the importance of the micro-cones’ supporting foil size.

  • Lecture (Conference)
    51st Annual Meeting of the APS Division of Plasma Physics, 02.-06.11.2009, Atlanta, USA

Permalink: https://www.hzdr.de/publications/Publ-13989
Publ.-Id: 13989


Verlaufsbeobachtung der Hypoxie anhand von FMISO-Untersuchungen in HNO-Tumoren unter kombinierter Radiochemotherapie.

Abolmaali, N.; Zöphel, K.; Koch, A.; Appold, S.; Steinbach, J.; Baumann, M.

Ziel/Aim:
Zur Optimierung/Individualisierung der Strahlentherapie könnte die Detektion und Berücksichtigung hypoxischer Tumorsubvolumina im Therapieverlauf wichtig sein. Ziel dieser Untersuchung war darzustellen, wie sich in Tumoren die Hypoxie im Vergleich zum nicht im primären Zielvolumen gelegenen Normalgewebe verändert.

Methodik/Methods:
25 Patienten (3@, medianes Alter 55 Jahre) mit Plattenepithelkarzinomen des HNO-Traktes wurden vor kombinierter Radiochemotherapie (RCT) mit FDG sowie vor und nach 10Gy, 20Gy und 60Gy unter RCT mit FMISO untersucht (66 Untersuchungen). Mit der Rover-Software (ABX, Radeberg) wurde nach Co-Registrierung der PETs mit dem halbautomatischen Source-to-Background-Algorithmus anhand der FDG-Daten das Tumorgesamtvolumen definiert und in die FMISO kopiert. In diesem Tumorvolumen wurde die MISO-Aktivität bestimmt. Zusätzlich wurde in jeder FMISO ein 5-10 ml großes Referenzvolumen zur Definition des Hintergrundsignals von MISO in der Halsmuskulatur definiert. Bestimmt wurden im Verlauf der SUVmax, das hypoxische Volumen ("total lesion hypoxia (TLH)" = SUVmean x Volumen) und der Kontrast in Abhängigkeit von der MISO-Aktivität im Hintergrund.

Ergebnisse/Results:
Der gemittelte SUVmax±sd vor, nach 10Gy, nach 20Gy und nach 60Gy lag bei: 2.6±0.6, 2.6±0.7, 2.1±0.6 und 1.6±04. Der SUVmax sank im Mittel auf 64% des Ausgangswertes. Die TLH [ml] vor, nach 10Gy, nach 20Gy und nach 60Gy lag bei: 93.3 ml, 79.6 ml, 77.3 ml und 55.3 ml. Der Kontrast vor, nach 10Gy, nach 20Gy und nach 60Gy lag bei: 1.6±0.3, 1.6±3.9, 1.4±02 und 1.1±0.2. Der Kontrast sank im Mittel auf 71% des Ausgangswertes.

Schlussfolgerungen/Conclusions:
Unter kombinierter Radiochemotherapie sinkt sowohl das Tumorvolumen (erkennbar an den morphologischen CT-Daten) als auch die hypoxische Aktivität der HNO-Tumoren. Da nach 60 Gy der Kontrast in den FMISO-Untersuchungen nahe 1 liegt, lässt sich anhand der aufgenommenen Daten keine Planung für einen Strahlentherapieboost erstellen.

  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A30

Permalink: https://www.hzdr.de/publications/Publ-13988
Publ.-Id: 13988


Vorklinische Abschätzung der Strahlenexposition durch (-)-F-18-NCFHEB, einem neuen PET-Tracer zur Darstellung von zerebralen alpha4beta2 nikotinischen Acetylcholinrezeptoren

Sattler, B.; Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Kendziorra, K.; Starke, A.; Patt, M.; Hesse, S.; Smits, R.; Hoepping, A.; Steinbach, J.; Brust, P.; Sabri, O.

Ziel/Aim:
(-)-F-18-Norchloro-fluoro-homoepibatidin (-)-NCFHEB) ist ein neuer vielversprechender Tracer für die Darstellung von alpha4beta2 nikotinischen Acetylcholinrezeptoren bei neuropsychiatrischen Erkrankungen mit PET. Um die Strahlenexposition durch die Applikation des Tracers abzuschätzen, wurde CD1 Mäusen (-)-NCFHEB appliziert. Es wurden die Biodistribution und die resultierenden Organdosen (OD) sowie die effektive Dosis (ED) bestimmt.

Methodik/Methods:
27 weiblichen CD1 Mäusen (Gewicht: 28,2 ± 2,1g) wurden 0,75± 0,334MBq (-)-F-18-NCFHEB [1] über die V. caudata lateralis appliziert. Nach 5, 15, 30, 45, 60, 90, 120, 180 und 240 min p.i. wurden die Tiere getötet (n=3 pro Zeitpunkt). Die Organe (Hirn, Herz, Lunge, Magen, Dünndarm, Dickdarm, Leber, Nieren, Harnblase, Milz, Thymus, Bauchspeicheldrüse, Nebennieren, Ovarien, Blut, Haut, Muskel, Skelett) wurden isoliert, gewogen und ihr Aktivitätsgehalt in einem g-Counter bestimmt. Die Massen von Skelett und Muskel wurden aus Gewebeproben extrapoliert [2]. Die Zeit- und Massenskalen wurden an die menschlichen Skalen angepasst [3]. Die Aktivitätsanteile in Quellorganen wurden als Fraktionen der injizierten Aktivitätsmenge [%ID] pro Gramm bzw. Organ dargestellt. Mit trapezoiden und exponentiellen Anpassungen an diese Daten wurden Zeit-Aktivitätskurven für jedes Organ bzw. Kompartiment abgeleitet. Die kumulierte Aktivität in den Quellorganen wurden bestimmt und ODs und die ED wurden mit OLINDA abgeschätzt.

Ergebnisse/Results:
Die Harnblase erhält die höchste OD mit 104,0 μSv/MBq, gefolgt von den Nieren (24,2 μSv/MBq), dem Uterus (14,1 μSv/MBq), der Leber (14,0 μSv/MBq) und der Bauchspeicheldrüse (14,0 μSv/MBq). Den höchsten Beitrag zur ED leistet die Harnblase (5,2μSv/MBq) gefolgt von den Ovarien (2,1μSv/MBq), dem Dickdarm (1,5μSv/MBq) und dem roten Knochenmark (1,3 μSv/MBq). Mit diesen Daten ergibt sich die ED durch i.v. Applikation von (-)-F-18-NCFHEB zu 14,2 μSv/MBq.

Schlussfolgerungen/Conclusions:
Die ED durch i.v. Applikation von etwa 370 MBq (-)-F-18-NCFHEB am Menschen ergibt sich zu 5,3 mSv. Dies liegt im Bereich der Strahlenexposition, welche durch andere F-18-markierte Radioliganden erzeugt wird. Diese vorklinischen inkorporationsdosimetrischen Ergebnisse bestärken die weitere Entwicklung von (-)-F-18-NCFHEB in klinischen Studienphasen am Menschen und seine weitere Entwicklung als klinischer Hirn-PET-Tracer.

Literatur/References:
[1] Brust P et. al.: In vivo measurement of nicotinic acetylcholine receptors with [18F]norchloro-fluoro-homoepibatidine (NCFHEB). Synapse 62, 205-218.
[2] Lindstedt SL, Schaeffer PJ.: Use of allometry in predicting anatomical and physiological parameters of mammals Laboratory Animals (2002) 36, 1–19
[3] Stabin MJ: Fundamentals of Nuclear Medicine Dosimetry, Springer 2008, ISBN 978-0-387-74578-7, 237P Diese Studie wird durch das Bundesministerium für Bildung und Forschung unterstützt. (Nr. 01EZ0820)

  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A66

Permalink: https://www.hzdr.de/publications/Publ-13987
Publ.-Id: 13987


Proton, Electron and K-Alpha Emission from Micro-Scale Copper Cone Targets

Gaillard, S. A.; Flippo, K. A.; Gautier, D. C.; Kline, J. L.; Offermann, D.; Workman, J.; Archuleta, F.; Gonzales, R.; Hurry, T.; Johnson, R. P.; Letzring, S.; Montgomery, D. S.; Reid, S.-M.; Shimada, T.; Lockard, T.; Sentoku, Y.; D'Humieres, E.; Cowan, T. E.; Bussmann, M.; Kluge, T.; Rassuchine, J.; Mucino, J. E.; Lowenstern, M. E.

Fast ignition fusion requires transporting a large amount of energy into the compressed ICF capsule in a short period of time. One metthod for efficiently transporting laser energy into a compressed fusion capsule is to use a cone situated near or in the capsule, decreasing the distance to the core, improing laser conversion efficiency and concentrating charged particle flow. Results from recent experiments performed at the LANL 200 TW Trident short-pulse laser at ~1020 W/cm² (80-100 J and ~600 fs) are presented.

Keywords: Cone; Laser; LANL; Trident; Record; Proton; Protons; Energy; Fusion; Acceleration

  • Lecture (Conference)
    IFSA09, 06.-11.09.2009, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-13986
Publ.-Id: 13986


Erste in-vivo Applikation eines Fluor-18 markierten Serotonin-Transporter-(SERT)-Markers für die PET

Hesse, S.; Brust, P.; Mäding, P.; Bresch, A.; Zessin, J.; Becker, G. A.; Seese, A.; Habermann, B.; Patt, M.; Meyer, P. M.; Luthardt, J.; Steinbach, J.; Sabri, O.

Ziel/Aim:
Die zentralen SERT lassen sich mittels SPECT-Radiotracern in SERT-reichen Gehirnarealen und mit PET-Markern wie [11C]DASB hochselektiv im gesamten Gehirn darstellen. Die kortikale Test-Retest-Reliabilität von [11C]DASB PET ist lediglich moderat, eine Quantifizierung endogenen Serotonins gelingt mit dieser Methode nicht. Möglicherweise können Tracer mit längerlebigen Nukliden diese Mängel beseitigen helfen. Ziel unserer Studie war die erstmalige Applikation eines Fluor-18-markierten SERT-Radiotracers im Menschen.

Methodik/Methods:
In Anlehnung an (1) wurde die Synthese von [18F]FMe-McN 5652 unter GMP-Bedingungen in einem modifizierten Synthesemodul "TRACERlab FxF-N” als 2-Stufen-2-Topf-Reaktion adaptiert: Stufe 1: Synthese von [18F]Fluormethylbromid durch nukleophile [18F]Fluorierung von Dibrommethan und nachfolgende Reinigung mittels Silicagel-Kartuschen (2). Stufe 2: [18F]Fluormethylierung eines entsprechenden Thiolat-Präkursors. Da [18F]FMe-McN 5652 in wässriger Lösung nicht stabil ist, wurde eine HPLC-Reinigung unter Verwendung eines ethanolischen Eluenten entwickelt, in deren Produktfraktion der Tracer stabil ist. Die PET-Datensätze, erhoben bei 5 gesunden Probanden (2 weiblich, Alter 39±10 Jahre) als dynamische Akquisition über 120 Min. nach i.v. 90-Sek.-Bolusinjektion von 298±57 MBq [18F]FMe-McN 5652 sowie statische Aufnahmen über 30 Min, wurden mit dem individuellen MRT koregistriert (PMOD) und mittels VOI analysiert (Target-/Background-Ratios, TB-R, Background=Zerebellum).

Ergebnisse/Results:
Die TB-R für den frontalen Kortex (FC) betragen 1,02±0,04 für rechts und 1,01±0,03 für links, für die Kaudatuskopfregion (Kaud) 1,46±0,16 (rechts) und 1,50±0,15 (links) und für die RaphÈ-Region 2,04±0,11. Vergleichsweise finden sich bei gesunden Probanden, die mittels [11C]DASB-PET untersucht wurden (N=21, 11 weiblich, 38±8 Jahre), entsprechende TB-R von 1,10±0,07 (FC rechts, t-Test: n.s.), 1,08±0,78 (FC links, n.s.), 2,14±0,21 (Kaud rechts, n.s.), 2,06±0,19 (Kaud links, n.s.) und 2,23±0,39 (RaphÈ, n.s.) bei insgesamt visuell besserer Bildqualität des neuen Tracers.

Schlussfolgerungen/Conclusions:
Die zerebrale [18F]FMe-McN 5652-Aufnahme entspricht der Verteilung der SERT auch beim Menschen, so dass der Radiotracer einen geeigneten Marker für SERT darstellen könnte. Trotz der tendenziell geringeren TB-R im Vergleich mit den [11C]DASB-PET-Daten könnte sich die geringere Standardabweichung bei der Untersuchung der Test-Retest-Reliabilität mit größeren Fallzahlen als Vorteil erweisen. Zudem soll mit Verdrängungsstudien die Sensivitität des neuen Markers, insbesondere in den kortikalen Arealen und hinsichtlich der Quantifizierung endogenen Serotonins, eingeschätzt werden.

Literatur/References:
(1) Zessin J, Eskola O, Brust P et al. Nucl Med Biol 2001; 28: 857-863.
(2) Iwata R, Pascali C, Bogni A et al. Appl Radiat Isot 2002; 57: 347-352

  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A34
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D

Permalink: https://www.hzdr.de/publications/Publ-13985
Publ.-Id: 13985


Ein neues stabilisiertes Cu-64 markiertes Neurotensin-Analogon zur in vivo Bildgebung von Neurotensin-Rezeptoren

Bergmann, R.; Brans, L.; Tourwe, D.; Schlottig, K.; Pietzsch, J.

Ziel/Aim:
Neurotensin (NT) und seine Rezeptoren werden in verschiedenen humanen Tumoren (Brust-, Prostata-, Lungen-, duktale Pankreas- und Hypophysentumore) überexprimiert, insbesondere stehen sie im Zusammenhang mit der Tumorprogression und dem Übergang zu aggressiveren Tumorphänotypen. Deshalb kommt der quantitativen in vivo-Bildgebung der funktionellen Neurotensin-Rezeptor-Expression, sowohl in der Forschung, als auch in Diagnostik und Therapie besondere Bedeutung zu. Deshalb sollte ein in vivo stabiles Neurotensin-Analogon entwickelt werden, das sowohl zur Bildgebung, als auch für therapeutische Zwecke eingesetzt werden kann.

Methodik/Methods:
Durch manuelle Festphasensynthese auf Merrifield-Resin mit anschließender DOTA-Konjugation wurde DOTA-ArgΨ(CH2NH)ArgProDmtTleLeu-OH synthetisiert. Die Markierung des Peptides (3 pmol) mit Cu-64 erfolgte in Ammoniumacetat-Lösung 0,1 M, pH 5.5 über 15 min bei 50&inf;C. Der IC50 wurde an HT-29-Zellen bestimmt. Zellaufnahme und Internalisierung wurden an HT-29- und PC3-Zellen untersucht. Die Bioverteilung des Radiotracers wurde bei HT-29- tumortragenden NMRI-Nacktmäusen sowohl durch Organentnahme (je 4 Tiere pro Zeitpunkt), als auch mit Kleintier-PET (insgesamt 8 Tiere) untersucht. Die Dynamik der Metabolisierung wurde bei Ratten bestimmt.

Ergebnisse/Results:
Die Bindungsaffinität des Peptides an HT-29-Membranen, mit Neurotensin-Rezeptor 1 betrug 7 nM (4-12 nM, 95% Konfidenzintervall). Das Peptid konnte mit einer radiochemischen Reinheit größer 92% in einem Schritt mit Cu-64 markiert werden. Nach einmaliger intravenöser Injektion stieg die Konzentration im Tumor schnell an (0,8±0,1 SUV, 5 min p.i.) und verringerte sich dann auf 0,3±0,1 SUV (60 min p.i.). Daraus ergaben sich Tumor zu Organ-Verhältnisse von 2,8±0,7 im Blut, 5,2±0,9 im Muskel, 4,2±0,6 im Pankreas, 0,6±0,5 in Leber und 0,4±0,4 in Nieren. Das Peptid wurde schnell von den Nieren (3,7±0,6 SUV, 5 min p.i.; 0,8±0,1 SUV 60 min p.i. ) aufgenommen und in den Urin (60±6%ID im Urin nach 1 h) eliminiert . In der PET konnten die xenotransplantierten Tumore deutlich dargestellt werden. Bei gleichzeitiger Injektion von Neurotensin verringerte sich die Tumoraufnahme des Tracers auf 27% der Kontrolle. Nach 1 h lagen noch 33% der Aktivität im Blutplasma der Ratte als Originalsubstanz vor.

Schlussfolgerungen/Conclusions:
Das Cu-64-Neurotensin-Analogon erlaubt auf Grund seiner Stabilität, Affinität und Spezifität die bildgebende Darstellung der funktionellen Expression von Neurotensin-Rezeptoren in vivo. Die Daten lassen erwarten, dass ähnliche Ergebnisse auch mit Radionukliden für SPECT (In-111) oder therapeutische Anwendungen (Cu-67, Lu-177, Y-90) erreicht werden können.

Literatur/References:
Das Projekt wurde partiell durch das EU-Projekt GIPIO (Grant Agreement Nr. 223057) gefördert.

  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A17

Permalink: https://www.hzdr.de/publications/Publ-13983
Publ.-Id: 13983


Markierung und Stabilität von DOTA Mikrosphären markiert mit Ga-68, Y-90 und Lu-177

Wunderlich, G.; Schiller, E.; Bergmann, R.; Pietzsch, H.-J.; Kotzerke, J.

Ziel/Aim:
Intraarteriell applizierbare Partikel, markiert mit therapeutisch wirksamen Radionukliden (Y-90, Lu-177, Re-188) sind eine Alternative zur Behandlung von Lebertumoren und Lebermetastasen. Ga-68 markierte Partikel könnten zur Blutflussdarstellung und zur Lungenperfusion verwendet werden. In unserer Untersuchung verwendeten wir 20μm HSA Mikrosphären (MS). Es wurde untersucht, unter welchen Bedingungen sich DOTA modifizierte MS markieren lassen und wie stabil die Markierungen in vitro und in vivo sind.

Methodik/Methods:
Markiert wurde 1mg MS in 0,5M Azetatpuffer bei pH5, Reaktion 15min bei 95&inf;C unter Schütteln mit 0,1-0,5GBq Ga-68, 0,1-7,2GBq Y-90 und 1,8GBq Lu-177. Die Ausbeuten und die in vitro Stabilität wurden mit ITLC und nach Zentrifugieren bestimmt. Nach Zugabe von 1ml 0,1M DTPA Lösung (Challenge), 20mg Ascorbinsäure (Radikalfänger) und Stehenlassen der Suspension bestimmten wir die in vitro Stabilität der Produkte nach einigen Stunden bis Tagen in Gegenwart von DTPA/Ascorbinsäure bzw. Plasma und die in vivo Stabilität der Y-90 DOTA-MS nach intravenöser Injektion in Wistar-Ratten.

Ergebnisse/Results:
Die Markierungsausbeuten betrugen bei allen Nukliden >90%. Zur Bestimmung der in vitro Stabilitäten wurde das Produkt zentrifugiert und der Überstand abgenommen und/oder nach Aufschütteln eine Dünnschichtchromatografie durchgeführt. Nach 3h Inkubation in Humanplasma wurde 5% Ga-68 im Überstand gefunden. Nach Ascorbinsäurezugabe zum Reaktionsansatz fanden sich 18% freies Lu-177 nach 7d. Bei Y-90 DOTA MS wurden in Gegenwart von Ascorbinsäure bei Markierungen im GBq-Bereich im Überstand der Partikelsuspension unmittelbar nach Markierung bereits >10% der Radioaktivität nachgewiesen. Dabei handelt es sich wahrscheinlich um Y-90 DOTA-Thioharnstoffderivate, die vermutlich in Folge von Radiolyse und erhöhter Temperatur von den Partikeln abgespalten werden. Die Halbwertszeit von Y-90 DOTA-MS in der Lunge nach i.v. Injektion der Partikel in Wistarratten beträgt 3,5d.

Schlussfolgerungen/Conclusions:
Die Stabilität der Ga-68 markierten MS ist ausreichend für in vivo Anwendungen. Y-90 markierte Albumin-MS sind radiolytisch instabil und werden in vivo relativ rasch abgebaut. Sie sind deshalb kein Alternative zu den Re-188 markierten MS, die wir regelmäßig zur i.a. Therapie verwenden [1]. Dementsprechend ist auch eine Lu-177 Markierung dieser biologisch abbaubaren Partikeln nicht sinnvoll.

Literatur/References:
1] Wunderlich, G., Drews, A., Kotzerke, J. A kit for labelling of Re-188 HSA Mikrosphären for therapeutic use in nuclear medicine. Appl Radiat Isot 62 (2005) 915-918

  • Poster
    48. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 21.-24.04.2010, Leipzig, D
  • Abstract in refereed journal
    Nuklearmedizin 49(2010)2, A77

Permalink: https://www.hzdr.de/publications/Publ-13982
Publ.-Id: 13982


Modification of GaAs by Mn ion implantation towards semiconductor spintronic thin films

Bürger, D.; Zhou, S.; Pandey, M.; Grenzer, J.; Roshchupkina, O.; Anwand, W.; Reuther, H.; Gottschalch, V.; Helm, M.; Schmidt, H.

Ferromagnetic semiconductors with high Curie temperatures and large coercivity are very promising materials for spintronic applications. An approach to fabricate ferromagnetic GaMnAs is Mn ion implantation into GaAs followed by pulsed laser annealing (PLA) [1]. Magnetic Mn ions which occupy the Ga sublattice sites form acceptor centers and pro-vide free holes for the mediation of the parallel align-ment of the magnetic moments of the Mn ions. For a strong ferromagnetic interaction, activation of the Mn acceptor dopants over their thermodynamic equilib-rium solubility is necessary. Long time, rapid thermal, and also flash lamp annealing processes take too long to realize a large enough free hole concentration by activation of Mn acceptor dopants. From a thermody-namical point of view, the PLA process is beside the more expensive LT-MBE process the best route to fabricate oversaturated ferromagnetic GaMnAs.
We investigated the influence of the implanted Mn concentration and PLA conditions on the structural and magnetic properties of GaMnAs thin films. We per-formed heatflow calculations to visualize the fast tem-peratue quenching during the PLA process [2]. Using SQUID magnetometry, we reveal a strong decrease of the saturation magnetization with increasing number of laser pulses during PLA (Fig. 1). However, the crystal-line quality is improved after several laser pulses. This has been verified by RBS (Fig. 2) and XRD measure-ments. The decrease of saturation magnetization after several laser pulses may be caused by the continuous Mn cluster formation during each PLA cycle.
[1] M. A. Scarpulla. et al. APL 82 (2003) 1251
[2] D. Bürger et al. PRB 81 115202 (2010)

  • Poster
    Ion Beam Workshop, 29.-31.03.2010, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13981
Publ.-Id: 13981


Thermodynamical limits of diluted magnetic semiconductors

Bürger, D.; Seeger, M.; Zhou, S.; Helm, M.; Schmidt, H.

The incorporation of transition metals dopants in semiconductors over their solubility limit is the main challenge for the fabrication of diluted ferromagnetic semiconductors. Dietl et al. [1] calculated the Curie temperatures for various semiconductors doped with 5 at% Mn. A lot of experimental effort was focused on the fabrication of diluted magnetic semiconductors. Unfortunately, such metastable alloys try to reach their thermodynamical equilibrium by the diffusion of the incorporated dopants. The equilibrium state at room temperature for semiconductors with a low solubility of magnetic dopant atoms is characterized by unwanted secondary phases. We present the results from combined random walk simulations and heatflow calculations and explain the successful fabrication of GaAs:Mn and the impossibility to produce Si:Mn. The clustering process is simulated under the assumption that neighbouring magnetic atoms stick together. This is a general approach for the growth of clusters in supersaturated materials [2]. With the knowledge of the diffusion coefficient our modelling can be used to predict the thermodynamical limit at room temperature and the producibility by pulsed laser annealing of diluted magnetic semiconductors.
[1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000)
[2] P. Meakin, Fractals, scaling and growth far from equilibrium (Cambridge University Press, 1998)

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13980
Publ.-Id: 13980


Experimental study of the N-14(p, gamma)O-15 reaction at high and low energies

Marta, M.

The 14N(p,gamma)15O reaction controls the rate of the hydrogen burning CNO cycle. The solar CNO neutrino flux which may be detected e.g. in Borexino and SNO+ can in principle be used to measure the carbon and nitrogen abundance at the center of the Sun, thus addressing the "solar abundance problem". However this requires more precise nuclear data. Updated results from the experimental study performed at the LUNA facility (Gran Sasso National Laboratories, Italy) in the energy range E_p = 0.36 - 0.4 MeV and from the high-current FZD Tandetron (Dresden) in the range E_p = 0.6 - 2.0 MeV are presented.

Keywords: Nuclear astrophysics; CNO cycle; TiN solid target; Tandetron; LUNA; Clover detector

  • Lecture (Conference)
    15th Workshop on Nuclear Astrophysics, 22.-27.03.2010, Schlöß Ringberg, Tegernsee, Deutschland
  • Lecture (Conference)
    International School of Nuclear Physics (32nd Course), 16.-24.09.2010, Erice (Sicily), Italy
  • Progress in Particle and Nuclear Physics 66(2011)2, 303-308
    DOI: 10.1016/j.ppnp.2011.01.025

Permalink: https://www.hzdr.de/publications/Publ-13978
Publ.-Id: 13978


Updated 14N(p,gamma)15O data from LUNA

Marta, M.; Bemmerer, D.; Caciolli, A.; Bonetti, R.; Broggini, C.; Confortola, F.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Imbriani, G.; Junker, M.; Lemut, A.; Limata, B.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Alvarez, C. R.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.

The 14N(p,gamma)15O reaction controls the rate of the hydrogen burning CNO cycle. By detecting solar CNO neutrinos (e.g. in Borexino, SNO+) one can in principle measure directly the carbon and nitrogen abundance at the center of the Sun. However this requires more precise nuclear data. Updated experimental results on capture to various excited states (as well as to the ground state) in 15O are shown, together with improved branching ratios obtained for the E_p = 278 keV resonance.

Keywords: Nuclear astrophysics; LUNA; CNO cycle; Clover detector; TiN solid target

  • Lecture (Conference)
    Frühjahrstagung des DPG - Fachverbands Hadronen und Kerne, 15.-19.03.2010, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13977
Publ.-Id: 13977


A possible accelerator laboratory in the Dresden Felsenkeller

Zuber, K.; Bemmerer, D.; Szücs, T.

The field of underground accelerator physics to study rare nuclear reaction events has greatly expanded over the last decade. Consequently, there is an increasing need to put ion accelerators in underground laboratories, making use of overlying rock to suppress cosmic-ray induced background. Here we show data from a feasibility study on such a laboratory in the Dresden Felsenkeller.

  • Poster
    Astroteilchenphysik in Deutschland: Status und Perspektiven, 25.-26.02.2010, Zeuthen, Deutschland
  • Poster
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Deutschland
  • Poster
    Nuclei in the Cosmos XI, 18.-23.07.2010, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13976
Publ.-Id: 13976


An actively vetoed Clover Gamma-detector for nuclear astrophysics at LUNA

Szücs, T.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Confortola, F.; Corvisiero, P.; Elekes, Z.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Lemut, A.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.

An escape-suppressed, composite high-purity germanium detector of the Clover type has been installed at the Laboratory for Underground Nuclear Astrophysics (LUNA) facility, deep underground in the Gran Sasso Laboratory, Italy. The laboratory gamma-ray background of the Clover detector has been studied underground at LUNA and, for comparison, also in an overground laboratory. Spectra have been recorded both for the single segments and for the virtual detector formed by online addition of all four segments. The effect of the escape-suppression shield has been studied as well. Despite their generally higher intrinsic background, escape-suppressed detectors are found to be well suited for underground nuclear astrophysics studies. As an example for the advantage of using a composite detector deep underground, the weak ground state branching of the Ep = 223 keV resonance in the 24Mg(p,gamma)25Al reaction is determined with improved precision.

Permalink: https://www.hzdr.de/publications/Publ-13975
Publ.-Id: 13975


MRPC prototypes for NeuLAND tested using the single electron mode of ELBE/Dresden

Yakorev, D.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Caesar, C.; Ciobanu, M.; Elekes, Z.; Elvers, M.; Hehner, J.; Heil, M.; Kempe, M.; Maroussov, V.; Nusair, O.; Reifarth, R.; Simon, H.; Stach, D.; Wagner, A.; Zilges, A.; Zuber, K.

The NeuLAND detector at the R$^3$B experiment at the future FAIR facility in Darmstadt aims to detect fast neutrons (0.2-1.0\,GeV) with high time and spatial resolutions ($\sigma_{\rm t}$$<$100\,ps, $\sigma_{\rm x,y,z}$$<$1\,cm). The detector will consist of about 60 subsequent MRPC stacks containing a 4\,mm thick anode made of iron converter material, with an additional 4\,mm of converter material between two stacks. The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPC's.

Prototypes for the NeuLAND detector have been built at FZD and GSI and then studied using the 32\,MeV pulsed electron beam at the superconducting electron accelerator ELBE in Dresden, Germany. Owing to the new, single-electron per bunch mode of operation, a rapid validation of the design criteria ($\geq$90\% efficiency for minimum ionizing particles, $\sigma$ $\leq$ 100\,ps time resolution) was possible.

Tested properties of the prototypes include glass thickness, spacing of the central anode, and a comparison of single-ended and differential readout. Tested frontend electronics schemes include FOPI (single-ended), PADI-based (both single-ended and differential mode tested), and ALICE (differential). --- Supported by BMBF (06DR9058I) and GSI FuE.

  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13974
Publ.-Id: 13974


Experiment zur ^{14}N(p,gamma)^{15}O--Reaktion bei 0.6-2.0\,MeV

Bemmerer, D.; Beyer, R.; Broggini, C.; Caciolli, A.; Erhard, M.; Fülöp, Z.; Grosse, E.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menegazzo, R.; Nair, C.; Schwengner, R.; Szücs, T.; Trompler, E.; Wagner, A.; Yakorev, D.

Die Rate des Bethe-Weizsäcker-Zyklus des Wasserstoffbrennens wird von der langsamsten Reaktion, ^{14}N(p,gamma)^{15}O, bestimmt. Diese Reaktion ist kürzlich u.a. bei LUNA im Energiebereich unterhalb 0.5\,MeV gründlich neu untersucht worden. Allerdings spielen auch höherenergetische Daten eine Rolle bei der Extrapolation des Wirkungsquerschnitts zu extrem niedrigen, unmessbaren Energien. Die Reaktion wurde jetzt am FZD-Tandetron im Energiebereich von 0.6-2.0\,MeV neu untersucht. --- Unterstützt von der Herbert-Quandt-Stiftung (Stipendium f\"ur T.S.) und der Europäischen Union (FP6 AIM RITA 025646).

  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung der Fachverbände 2010, 15.-19.03.2010, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13973
Publ.-Id: 13973


NeuLAND: MRPC-based time-of-flight detector for 1 GeV neutrons

Bemmerer, D.; Elekes, Z.; Kempe, M.; Stach, D.; Wagner, A.; Yakorev, D.; Aumann, T.; Boretzky, K.; Caesar, C.; Ciobanu, M.; Hehner, J.; Heil, M.; Nusair, O.; Reifarth, R.; Simon, H.; Rossi, D.; Kratz, J. V.; Elvers, M.; Maroussov, V.; Zilges, A.

The NeuLAND detector at the R$^3$B experiment at the future FAIR facility in Darmstadt aims to detect fast neutrons (0.2-1.0\,GeV) with high time and spatial resolutions ($\sigma_{\rm t}$$<$100\,ps, $\sigma_{\rm x,y,z}$$<$1\,cm). The detector will consist of about 60 subsequent MRPC stacks containing a 4\,mm thick anode made of iron converter material, with an additional 4\,mm of converter material between two stacks. The secondary charged particles stemming from hadronic interactions of the high energetic neutrons in the converter will be detected in the MRPC's.

As part of the ongoing development effort, a number of prototypes for this detector have been developed and built at GSI, FZD, and SINP. By testing some prototypes from GSI and FZD in experiments with picosecond electrons at ELBE (Dresden, Germany) and with 175 MeV quasi-monochromatic neutrons at TSL (Uppsala, Sweden) it was shown that the working principle is sound.

  • Lecture (Conference)
    X. Workshop on Resistive Plate Chambers and Related Detectors, 09.-12.02.2010, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13972
Publ.-Id: 13972


Nuclear Physics Underground

Bemmerer, D.

Precisely known nuclear cross sections are an essential ingredient for the modeling of nuclear processes in our Sun, in stars, and in the Big Bang. Uncertainties due to theoretical extrapolations can be avoided if experimental data are available directly at astrophysically relevant energies. Since such energies are typically far below the Coulomb barrier, this entails cross section measurements in the picobarn range.

The Laboratory for Underground Nuclear Astrophysics (LUNA) inside the Gran Sasso mountain in Italy takes up this challenge by combining accelerator-based experiments with low-background measurement techniques. Using this approach, in recent years several reactions relevant to hydrogen burning have been studied, e.g. $^3$He($\alpha$,$\gamma$)$^7$Be and $^{14}$N(p,$\gamma$)$^{15}$O. The implications of the data range from an independent lower limit on the age of the universe to a precise solar thermometer.

Based on this progress, currently there are efforts in several countries to construct new underground accelerators. The exciting science that can be probed with these new facilities will be highlighted.

  • Invited lecture (Conferences)
    VIII Latin American Symposium on Nuclear Physics and Applications, 15.-19.12.2009, Santiago, Chile
  • Contribution to proceedings
    VIII Latin American Symposium on Nuclear Physics and Applications, 15.-19.12.2009, Santiago, Chile
    AIP conference proceedings 1265: VIII Latin American Symposium on Nuclear Physics and Applications, College Park, Maryland: American Institute of Physics, 121-128
  • Lecture (Conference)
    Seminar Nukleare Astrophysik, 11.01.2010, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13971
Publ.-Id: 13971


Determination of redox processes in biofilms from acidic waters

Krawczyk-Bärsch, E.

First studies have been carried out in stalactite-like biofilms from the uranium mine Königstein (Germany), where the mining activities had been stopped in 1990 and the uranium mine has been partially flooded for remediation. In the acidic, sulphate-rich waters with high concentration of heavy metals and radionuclides (uranium) as contaminants, biofilms are formed and occur as gelatinous filaments, and as stalactite-like snotites. The analyses of the bacterial diversity of these biofilms showed a dominance of Ferrovum myxofaciens, an acidophilic, autotrophic, iron oxidizing bacteria, which belongs to the Betaproteobacteria. Ferrous iron is oxidized strongly catalyzed by Fe(II)-oxidizing bacteria with the consequence of producing oxidizing conditions within the biofilm with high oxygen concentration. Fiber-optic oxgyen microprofiles, carried out in these snotites are in a good agreement with electro-chemical measurements. The oxygen concentration is decreasing slowly from the edge versus center of the snotite biofilm. Electrochemical redox potential micoprofilings were carried out in these snottite-biofilms by a miniaturized platinum redox electrode with a tip diameter of 10 µm, too. In the bulk solution a redox potential of 728 mV +- 9.5 mV was measured in comparison to an increased redox potential of 834.5 mV +- 10.21 mV within the snottite-biofilm. We guess that the different geochemical conditions are due to the oxidation of ferrous iron catalyzed by Fe(II) oxidizing bacteria and that they will have an influence on the uranium speciations. A pH-Eh diagram for the U-S-O-H-C system at 15 °C was constructed using the geochemical speciation code “Geochemist´s Workbench” Version 8.0.8 / ACT2 Version 8.0.8 and the most recent NEA database for Uranyl Silicates and solid Uranates (Guillaumont et al., 2003), supplemented with solubility data for Uranophane (Nguyen et al., 1992) and CaU2O7.3H2O(s) (Altmaier et al., 2006) and the analytical data of the bulk water for the calculation of the field stability boundaries of different uranium species. The plotting of the measured pH and Eh values into this diagram showed that the theoretical stability fields of U species are defined in areas characterized by higher pH or lower Eh. The measured values indicate that aqueous Uranium(VI) Sulfate Complexations were formed in the biofilm as well as in the bulk solution. Only the changing of the local conditions (e.g. closure of the underground galleries) will lead to substantial changes and the formation of solid uranium(IV) species.

Keywords: Biofilm; uranium; redox potential; sensor measurements

  • Lecture (Conference)
    2nd Annual Workshop of ReCosy, 16.-19.03.2010, Larnaca, Cyprus

Permalink: https://www.hzdr.de/publications/Publ-13970
Publ.-Id: 13970


Electrochemical and fiber-optic oxygen sensor measurements in uranium contaminated biofilms - a collaboration with UPPC

Krawczyk-Bärsch, E.; Arnold, T.; Steinbrück, D.; Kumke, M.

To compare the applicability of an electrochemical and a laser-based fiber-optical microsensor for oxygen determination in biofilm samples, microprofiling measurements in uranium free biofilms and in biofilms exposed to ecologically relevant uranium concentration were performed. For our studies we used a commercial available Clark-type microelectrode and a custom fiber-optic instrument, which was optimized for tip probes < 10 µm (optodes) by use of a diode laser and the so-called two frequency phase modulation technique, to mask interfering background fluorescence.
The data obtained from both microsensor methods in uranium free and uranium contaminated biofilms were in good agreement. Fiber-optic and electrochemical microsensor measurements showed high concentrations of oxygen over the total thickness of the uranium free biofilms. In contrast, biofilms exposed to uranium revealed a much lower oxygen concentration in the upper layers of the biofilm. At a biofilm depth of approximately 750 µm no oxygen was detectable at all.

Keywords: Electrochemical microsensor; fiber-optic sensor; biofilms; uranium

  • Lecture (Conference)
    2nd Annual Workshop of ReCosy, 16.-19.03.2010, Larnaca, Cyprus

Permalink: https://www.hzdr.de/publications/Publ-13969
Publ.-Id: 13969


Characterization of Xe ion-induced rippled structures on Si (001) in the medium ion energy range

Hanisch, A.; Biermanns, A.; Grenzer, J.; Pietsch, U.

Ion-beam eroded self-organized nanostructures on semiconductors offer new ways for the fabrication of high density memory and optoelectronic devices. It is known that wavelength and amplitude of noble gas ion-induced rippled structures tune with the ion energy and the fluence depending on the energy range, ion type and substrate. The linear theory by Makeev [1] predicts a linear dependence of the ion energy on the wavelength for low temperatures. For Ar+ and Xe+ it was observed by different groups [2] that the wavelength grows with increasing fluence after being constant up to an onset fluence and before saturation. In this coarsening regime power-law or exponential behavior of the wavelength with the fluence was monitored. So far, investigations for Xe ions on silicon surfaces mainly concentrated on energies below 1keV. We found a linear dependence of both the ion energy and the fluence on the wavelength and amplitude of rippled structures over a wide range of the Xe+ ion energy between 5 and 70keV. Moreover, we estimated the ratio of wavelength to amplitude to be constant meaning a shape stability when a threshold fluence of 2x1017cm−2 was exceeded.

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13968
Publ.-Id: 13968


Ion-beam synthesis of InSb nanocrystals within the buried SiO2 layer of silicon-on-insulator structure

Tyschenko, I. E.; Cherkov, A. G.; Voelskow, M.; Popov, V. P.

A strong decrease of the carrier mobility of the nanometer thick silicon films imposes limitation on the application of SOI structures in the current silicon planar CMOS technology. The formation of heterostructures-on-insulator is a way to increase carrier mobility in the nanometer scale layers.

Keywords: SOI; InSb

  • Poster
    IIT 2010, 01.-07.06.2010, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-13967
Publ.-Id: 13967


Doping of germanium by ion implantation and flash lamp annealing

Wündisch, C.; Posselt, M.; Schmidt, B.; Heera, V.; Mücklich, A.; Skorupa, W.; Clarysse, T.; Simoen, E.; Hortenbach, H.

In the past the lack of stable native germanium oxide for surface passivation and gate dielectrics as well as the inability to epitaxially grow sufficiently thick defect-free germanium layers on silicon hindered the integration of germanium into the mainstream Si-based technology. Recent developments, such as high-k dielectrics and germanium-on-insulator substrates have made germanium a promising candidate for future high mobility devices. Therefore electrical doping of germanium by ion implantation and subsequent annealing has drawn a renewed interest. Investigations on the formation of ultra shallow junctions by ion beam processing have shown that p+-doping using B yields junctions that meet the requirements for the 22 nm technology node, whereas the formation of n+-junctions by P or As is complicated by the high diffusivity and the low solubility of the dopants. Recently, the concentration-dependent diffusion of n-dopants like P, As and Sb has been explored, and it has been found that doubly negatively charged vacancies are the mobile species responsible for the migration of the dopant atoms. The application of conventional rapid thermal annealing (RTA) with durations of some seconds and temperatures above about 500 °C leads to the activation of the n-dopants but their fast concentration-dependent diffusion can generally not be prevented. On the other hand it has been shown that both the diffusion and the activation of the dopants does not depend significantly on the implantation damage, i.e. using the defect engineering schemes known from Si technology seems not to be promising. Therefore, in order to control junction depth and dopant activation ultra-short annealing by flash lamps or lasers are currently under investigation.
The present work deals with the application of millisecond flash lamp annealing (FLA) to samples containing an implanted surface layer of about 100 nm thickness. P or As ions were implanted at an energy of 30 or 90 keV, respectively, and a fluence of 3x1015 cm-2. The investigations are focused on solid phase epitaxial recrystallization, dopant redistribution and dopant activation. The dependence of these effects on the heat transfer to the sample during FLA as well as on pre-amorphization and pre-annealing treatment is discussed. The results are compared to typical data achievable by RTA. Different characterization methods were employed. Channeling Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy (XTEM) were used to monitor the recrystallization of the amorphous layers formed during implantation. The depth distributions of P and As were measured by secondary ion mass spectrometry. In order to determine the sheet resistance variable probe spacing and micro four point probe measurements were utilized. Selected samples were studied by XTEM to search for precipitates and end-of-range defects. While in RTA the concentration dependent dopant diffusion hinders the formation of ultra-shallow n+ layers, FLA does not cause any diffusion. The maximum activation obtained by FLA is about 6x1019 and 2x1019 cm-3 for P and As, respectively. This is about 3-4 times higher than under typical RTA conditions. However, the activation and the sheet resistance achieved by FLA do not yet fulfill the ITRS requirements for the 22 nm technology node. Possible mechanisms responsible for dopant deactivation are discussed.

Keywords: germanium; electrical doping; annealing

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 29.-31.03.2010, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-13966
Publ.-Id: 13966


Novel Functionalised Nanoparticles for Application in the Imaging of Cancer

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    DAAD Alumni Meeting ”Tackling the future” , 26.-28.03.2010, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-13965
Publ.-Id: 13965


Tumor imaging using 64Cu-labeled peptides

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Seminar, Bio21 Institute, School of Chemistry, University of Melbourne , 25.03.2010, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-13964
Publ.-Id: 13964


Is there a real need to develop new chelating systems for radioisotopes?

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Seminar, School of Chemistry, Monash University , 22.03.2010, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-13963
Publ.-Id: 13963


Induction of atherogenic changes in vascular endothelial cells by radiation: role of the receptor for advanced glycation endproducts

Pietzsch, J.

kein Abstract verfügbar

  • Poster
    Inflammation 2010, 27.-30.01.2010, Luxembourg, Luxembourg
  • Contribution to proceedings
    Inflammation 2010, 27.-30.01.2010, Luxembourg, Luxembourg
    Inflammatory cell signaling mechanisms as therapeutic targets. (Ed. Diederich M). Fondation de Recherche Cancer et Sang, Luxembourg 2010, 114

Permalink: https://www.hzdr.de/publications/Publ-13962
Publ.-Id: 13962


Influence of novel selective cyclooxygenase-2 (COX-2) inhibitors on low density lipoprotein oxidation

Pietzsch, J.; Pietzsch, F.-J.; Laube, M.; Bergmann, R.; Wuest, F.; Steinbach, J.; Kniess, T.

kein Abstract verfügbar

  • Poster
    Inflammation 2010, 27.-30.01.2010, Luxembourg, Luxembourg
  • Contribution to proceedings
    Inflammation 2010, 27.-30.01.2010, Luxembourg, Luxembourg
    Inflammatory cell signaling mechanisms as therapeutic targets (Ed. Diederich M). Fondation de Recherche Cancer et Sang, Luxembourg 2010, 210

Permalink: https://www.hzdr.de/publications/Publ-13961
Publ.-Id: 13961


Magnetic Properties of the quasi-2D S=1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6

Ozerov, M.; Cizmár, E.; Zvyagin, S. A.; Beyer, R.; Uhlarz, M.; Skourski, Y.; Manson, J. L.; Schlueter, J. A.; Wosnitza, J.

We report on ESR, magnetization, and specific-heat studies of [Cu(pyz)2(HF2)]PF6 single crystals, identified as a quasi-twodimensional spin-1/2 Heisenberg antiferromagnet. Our measurements revealed Jinter/Jintrainter,Jintra, J are the interplane, intraplane and mean exchange interactions, respectively, and A is the anisotropy constant. It is argued that the magnetic properties of this material are strongly affected by two-dimensional spin fluctuations, despite of the onset of 3D long-range magnetic ordering at TN ≈ 4.4 K. The temperature-field phase diagram and ESR magnetic excitation spectrum in the 3D ordered phase of [Cu(pyz)2(HF2)]PF6 will be discussed in detail.

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13960
Publ.-Id: 13960


Chiral symmetry, di-electrons and charm

Kämpfer, B.; Hilger, T.; Schade, H.; Schulze, R.; Wolf, G.

We survey some prospects of identifying furhter in-medium modifications of hadrons in a strongly interacting medium with respect to ongoing experiment series of the HADES Collaboration and planned experiments of the CBM Collaboration at FAIR. Di-electrons, strange and charm mesons are considered and their potential for signalling imprints of chiral restoration is highlighted.

  • Contribution to proceedings
    XLVIII International Winter Meeting on Nuclear Physics in Memorian of Ileana Iori, 25.-29.01.2010, Bormio, Italy
    PoS(BORMIO2010)045

Permalink: https://www.hzdr.de/publications/Publ-13959
Publ.-Id: 13959


Optical conductivity of LuNi2B2C in the terahertz range

Fischer, T.; Pronin, A. V.; Wosnitza, J.; Niemeier, T.; Holzapfel, B.

Using a backward-wave-oscillator-based setup in a Mach-Zehnder interferometer arrangement, we have measured the temperature and frequency-dependent transmission and phase-shift spectra of LuNi2B2C films on MgO substrates in the range 200 GHz - 1.4 THz. From the measured spectra, we have directly calculated the complex optical conductivity. We observe a clear signature of the superconducting energy gap in the spectra. In the talk, a comparison of the experimentally obtained spectra with theoretical predictions for a multi-band superconductor will be given.

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13958
Publ.-Id: 13958


ESR Studies of the Quantum Spin Dimer System Ba3Cr2O8

Kamenskyi, D.; Wosnitza, J.; Zvyagin, S. A.; Krzystek, J.; Aczel, A. A.; Dabkowska, H. A.; Luke, G. M.

Ba3Cr2O8 is a system of three-dimensionally coupled dimers, exhibiting a field-induced phase transition from a quantum-disordered to a long-range antiferromagnetically ordered state at Hc1 = 12.5 T. We report tunable-frequency electron spin resonance (ESR) studies of Ba3Cr2O8 single crystals performed in a frequency range between 50 and 700 GHz in fields up to 25 T (applied along the c axis). Two gaps in the magnetic excitation spectrum, Δ1 = 564 GHz and Δ2 = 400 GHz, were observed directly, confirming the spin-singlet ground state of Ba3Cr2O8 below Hc1. The observation of singlet-triplet ESR transitions, which are normally forbidden in spin-1/2 dimer systems by selection rules, indicates the break-down of the axial symmetry in this compound. Details of the ESR excitation spectrum of Ba3Cr2O8 across different regions of its phase diagram will be discussed.

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13957
Publ.-Id: 13957


Annual Report 2009 - Institute of Radiochemistry

Bernhard, G.; Foerstendorf, H.; Richter, A.; Viehweger, K.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-530 2010
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-13956
Publ.-Id: 13956


Schlussbericht zum BMBF-Vorhaben "Entwicklung und Erprobung neuer Instrumente zur Bildung von Verwertung- und Transfernetzen" NanoFoto - Neue Wege zur verwertungsorientierten Netzwerkbildung in der Nanobiotechnologie

Raff, J.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-529 2010
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-13955
Publ.-Id: 13955


Effect of Gallium Doping on Superconductivity in Germanium

Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Fiedler, J.; Helm, M.; Wosnitza, J.

We report recent discoveries of superconductivity in Ga-doped germanium fabricated by ion implantation and subsequent flash-lamp or oven annealing. Tuning the preparation parameters allows for varying both charge-carrier and Ga concentration in the resulting roughly 100 nm thin nano- or single-crystalline layers. Transport measurements on systematically prepared samples reveal that besides a needed charge-carrier concentration of more than 0.4 atom%, superconductivity occurs to be sensitive on the implanted Ga content which may also be attributed to a change in the phonon properties. Onset transition temperatures up to 1.4 K have been found for almost 10 atom% Ga. Further, we observe in-plane critical fields exceeding 1 T and being close to the Pauli-Clogston limit. An exceptionally low Cooper-pair density of around 1015 cm−3 turns out the extreme type-II character of superconductivity. Finally, our work adds to our previous report [1] and may help to understand superconductivity in doped elemental semiconductors in general.

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13954
Publ.-Id: 13954


Magnetic field effects in electrochemical reactions

Mutschke, G.; Koschichow, D.; Peipmann, R.; Bund, A.; Fröhlich, J.; Weier, T.; Tschulik, K.; Uhlemann, M.

Today's available strong magnets allow to study distinct magnetic effects in various electrochemical systems. Lorentz forces and also magnetic gradient forces can be utilized to tailor convection and mass transfer in electrolytic cells, thereby influencing for example the morphology and the structure of the electrodeposits. The presentation will give an overview on recent results of numerical simulations and experimental findings in lab-scale electrochemical systems and will discuss potential applications. Whereas Lorentz forces are often known to enhance mass transfer, new results show that the convection pattern found in simple geometries can already be quite complex. A deeper understanding is required for improved applications. Recently, also magnetic gradient forces gained attention, e.g. for their potential in preparing micro-structured deposits. A detailed discussion of recent results will give further insight. Finally, new investigations of cyclic operation modes or time-dependent magnetic fields are presented which allow for a broad range of new phenomena.

Keywords: magnetoelectrochemistry; Lorentz force

  • Invited lecture (Conferences)
    Pacifichem 2010, 15.-20.12.2010, Honolulu, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-13953
Publ.-Id: 13953


Neue (UO2)2+-Komplexe von Bis(2-hydroxyaryl)imin-Liganden: Synthese, Struktur und Extraktionseigenschaften

Gloe, K.; Tanh Jeazet, H. B.; Doert, T.; Gloe, K.; Geipel, G.; Bernhard, G.

Die Koordinationschemie von Uran(VI) hat in den letzten Jahren vielfältiges Interesse gefunden. Ursachen dafür sind sowohl dessen Bedeutung im Rahmen der Kernenergiegewinnung als auch Probleme bei der Aufarbeitung sowie Lagerung von verbrauchten Kernbrennstoffen. Weitere Fragestellungen beziehen sich auf die Umweltrelevanz von U(VI) als Folge seiner natürlichen Verbreitung sowie bergbaulicher Altlasten. Schließlich werden auch potentielle Anwendungsoptionen von spezifischen Komplexverbindungen des Urans diskutiert.
Wir haben einige Imin-Liganden synthetisiert und drei neue Komplexverbindungen mit UO2(NO3)2 strukturell charakterisiert. Zum Vergleich wurden auch die strukturanalogen Aminderivate in die Untersuchungen einbezogen. Extraktionsexperimente mit den genannten Liganden zeigen differenzierte Extraktionseigenschaften gegenüber U(VI) mit einer ausgeprägten Selektivität gegenüber Eu(III).

Keywords: Extraction study; Imine-ligand; radioactive waste; uranium

  • Lecture (Conference)
    Jahrestreffen des Fachausschusses Extraktion., 18.-19.03.2010, Kaiserslautern, Germany

Permalink: https://www.hzdr.de/publications/Publ-13952
Publ.-Id: 13952


Quantitative Kelvin probe force microscopy imaging on locally doped semiconductors

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.

Kelvin probe force microscopy (KPFM) is used for the nanoscale characterization of semiconductors. Quantitative dopant profiling by means of KPFM measurements is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions after Mn implantation [2].
In addition, it will be shown that due to surface state formation and charge trapping in a thin native oxide layer the Kelvin bias probed above differently doped regions strongly depends on the measurement frequency [3]. Therefore, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, H. Schmidt, submitted.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

  • Lecture (Conference)
    International Conference on Functional Nanocoatings 2010, 28.-31.03.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13951
Publ.-Id: 13951


Self-organization during the growth of phase-separated nanostructured thin films

Abrasonis, G.

Control over the morphology and spatial correlations at the nanoscale is one of the major challenge of the nowadays nanoscience and nanotechnology. Bottom-up approaches to nanostructured material synthesis are based on self-organization processes to precisely define ordered nanostructures on a large scale. Self-organization occurs via the interplay between two factors - an external constraint acting on internal system processes. During the thin film growth this is translated into the interplay between thermodynamic driving forces and kinetic constraints. In this talk I will summarize the recent research activities of our group on the phase separation during the growth of carbontransition metal thin films. Different processes can be ’switched off/on’ by external control of the experimental parameters such as temperature, substrate type, matrix/dispersed phase chemical affinity or incoming particle energy. This results in a large variety of lateral or vertical composition modulations, such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays. Such self-organization process is versatile as different carbontransition metal systems show this effect. The observed tendencies will be discussed on the basis of the interplay of thermal and energetic ion induced phenomena.

  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-13950
Publ.-Id: 13950


Actinide Redox Speciation and Structure Analysis in Aqueous and Nonaqueous Solutions

Hennig, C.

Actinide redox chemistry plays a crucial role in nuclear technology like fuel reprocessing and nuclear waste disposal aspects including predicting of actinide mobility in the environment. Hydrolysis and complex formation of the early actinides are strongly related with their redox behavior in aqueous and nonaqueous solutions. We are interested in understanding the complexation of actinide compounds under controlled redox conditions in presence of inorganic oxo ligands and organic ligands with carboxylic groups.
This study is mainly focused on the use of EXAFS spectroscopy in combination with other supporting methods. The information from EXAFS spectroscopy is restricted to a pair distribution function providing coordination numbers and distances of the next neighbors. Two pathways were used to relate this information to the spatial arrangement of the ligands: (i) EXAFS was combined with DFT calculations which introduce constraints of molecular characteristics [1], and (ii) individual solution species were preserved in crystal structures and determined with single crystal diffraction. EXAFS was used subsequently to quantify differences or identify agreement between the coordination of complex structures in solution and solid state [2-4]. EXAFS is furthermore not very sensitive to differentiate between individual solution species, especially in not a single sample. This problem was solved in the following manner: (i) combination of EXAFS with other more species sensitive techniques, e.g. like UV-Vis spectroscopy [5] and (ii) by using sample series with broad variation of species distribution and subsequent application of statistical analysis techniques to separate the scattering contribution of individual solution species [6]. Finally, we investigated the correlation between the formal redox potential and the stability range of solution species [7].

[1] Hennig et al. The sulfate coordination of Np(IV), Np(V) and Np(VI) in aqueous solution. Inorg. Chem. 48 (2009) 5350-5360.
[2] Hennig et al. Comparative investigation of the solution species [U(CO3)5]6 and the crystal structure of Na6[U(CO3)5]•12H2O. Dalton Trans. 39 (2010) 3744–3750.
[3] Takao et al. First hexanuclear UIV and ThIV formate complexes – structure and stability range in solution. Eur. J. Inorg. Chem. (2009) 4771-4775.
[4] Hennig et al. Coordination of a uranium(IV) monomer in aqueous solution and in solid state. Inorg. Chem. 47 (2008) 1634-1638.
[5] Hennig et al. The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution. Radiochim. Acta 96 (2008) 607-611.
[6] Hennig et al. Species distribution and coordination of uranyl chloro complexes in acetonitrile. Inorg. Chem. 47 (2008) 2987-2993.
[7] Takao et al. Complex formation and molecular structure of neptunyl(VI) and –(V) acetates. Inorg. Chem. 48 (2009) 8803-8810.

Keywords: Actinides; redox chemistry; EXAFS; UV-Vis; DFT; XRD

  • Contribution to proceedings
    APS users meeting 2010, 03.-05.05.2010, Argonne/Illinois, USA
    APS users meeting 2010 - Celebrating 20 Years of Groundbreaking Science, 48-48
  • Invited lecture (Conferences)
    APS users Meeting, 03.-05.05.2010, Argonne, USA

Permalink: https://www.hzdr.de/publications/Publ-13949
Publ.-Id: 13949


Prediction of polydisperse steam bubble condensation in sub-cooled water using the Inhomogeneous MUSIG model

Lifante, C.; Frank, T.; Burns, A. D.; Lucas, D.; Krepper, E.

The aim of this paper is to present the validation of a new methodology implemented in ANSYS CFX (ANSYS, 2009), that extends the standard capabilities of the inhomogeneous MUltiple-SIze Group model (MUSIG) by additionally accounting for bubble size changes due to heat and mass transfer. Bubble condensation plays an important role in sub-cooled boiling or steam injection into pools among many other applications of interest in the Nuclear Reactor Safety (NRS) area and other engineering areas. Since the mass transfer rate between phases is proportional to the interfacial area density, a polydisperse modelling approach considering different bubble sizes is of main importance, because an accurate prediction of the bubble diameter distribution is required.
The standard MUSIG approach is an inhomogeneous one with respect to bubble velocities, which combines the size classes into different so-called velocity groups to precisely capture the different behaviour of the bubbles depending on their size. In the framework of collaboration between ANSYS and the Forschungszentrum Dresden-Rossendorf (FZD) an extension of the MUSIG model was developed, which allows to take into account the effect of mass transfer due to evaporation and condensation on the bubble size distribution changes in addition to breakup and coalescence effects.
After the successful verification of the model, the next step was the validation of the new developed model against experimental data. For this purpose an experiment was chosen, which was investigated in detail at the TOPFLOW test facility at FZD. It consists of a steam bubble condensation case at 2MPa pressure in 3.9K sub-cooled water at a large diameter (DN200) vertical pipe. Sub-cooled water flows into the 195.3 mm wide and 8 m height pipe, were steam is injected at z=0.0 m and is recondensing. The experimental results are published in (Lucas, et al., 2007). Using a wire-mesh sensor technique the main characteristics of the two-phase flow were measured, i.e. radial steam volume fraction distribution and bubble
diameter distribution at different heights and cross-sections.
ANSYS CFX 12.0 was used for the numerical prediction. A 60 degrees pipe sector was modelled in order to save computational time, discretized into a mesh containing about 260.000 elements refined towards the pipe wall and towards the location of the steam injection nozzles. Interfacial forces due to drag, lift, turbulent dispersion and wall lubrication force were considered. The numerical results were compared to the experimental data. The agreement is highly satisfactory, proving the capability of the new MUSIG model extension to accurately predict such complex two-phase flow.

Keywords: CFD; water/steam flow; MUSIG; polydisperse flow; phase change

  • Contribution to proceedings
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05.-04.06.2010, Tampa, FL, USA
    paper 5.6.4
  • Lecture (Conference)
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05.-04.06.2010, Tampa, FL, USA

Permalink: https://www.hzdr.de/publications/Publ-13948
Publ.-Id: 13948


Analysis of developing gas/liquid two-phase flows

Tselishcheva, E. A.; Podowski, M. Z.; Antal, S. P.; Post Guillen, D.; Beyer, M.; Lucas, D.

The objective of this work has been to study the mechanisms governing flow and phase distributions in developing gas/liquid two phase flows in general, and the evolution of different size bubbles in an adiabatic vertical pipe in particular. Flow regimes from bubbly to churn-turbulent have been accounted for. The main emphasis of the work has been on the modeling of various interfacial forces between the dispersed bubbles and the continuous liquid, as well as of bubble/bubble interactions (coalescence and breakup).
The proposed modeling concept uses a complete set of transport equations for each field, such as the continuous liquid and dispersed bubble fields. The overall model has been implemented in a state-of-the-art computational multiphase fluid dynamics code, NPHASE–CMFD. This three-dimensional four-field model, including the continuous liquid field and three dispersed gas fields representing bubbles of different sizes, has been carefully tested for numerical convergence and accuracy, and then validated against the TOPFLOW experimental results.
The NPHASE-CMFD simulations were aimed at demonstrating the capability of the proposed modeling concepts to predict the evolution of bubble concentration from channel inlet to near-equilibrium (fully-developed) conditions downstream. Along with several interfacial closure laws, the effect of elevation on air density has also been included in the model.

Keywords: gas/liquid two phas flow; NPHASE-CMFD; interfacial forces; bubble/bubble interaction; coalescence; breakup; TOPFLOW

  • Contribution to proceedings
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05.-04.06.2010, Tampa, USA
    Analysis of developing gas/liquid two-phase flows
  • Lecture (Conference)
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05.-04.06.2010, Tampa, USA

Permalink: https://www.hzdr.de/publications/Publ-13947
Publ.-Id: 13947


A simple design for a continuous magnetically guided positron beam - and - news from the EPOS project

Krause-Rehberg, R.; Jungmann, M.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Krille, A.; Wagner, A.; Kosev, K.; Cowan, T.

In the first part of the contribution, a rather simple design of a conventional, magnetically guided, continuous positron beam will be presented. The moderator is a tungsten mesh and the energy selection is realized using a bent tube. The sample is on ground potential. Further details will be presented during the talk.
In the second part of the talk, the recent progress of the EPOS project at the Research Center Dresden-Rossendorf will be demonstrated. EPOS consists of a pulsed monoenergetic positron beam (MePS), a conventional lifetime/Doppler spectrometer (CoPS), and a setup for gamma-induced positron annihilation spectroscopy (GiPS). While CoPS and GiPS systems are available for user operation, the MePS system is still under construction. First positrons were moderated and fed into the positron lab. At the moment, the chopper/buncher/accelerator system is under construction.

Keywords: positron annihilation; continuous magnetically guided positron beam; pulsed monoenergetic positron beam

  • Invited lecture (Conferences)
    International Workshop on Advanced Positron Beam Technology for Material Science, 15.-18.03.2010, Algiers, Algeria

Permalink: https://www.hzdr.de/publications/Publ-13946
Publ.-Id: 13946


Positron study of ion-cutting process in GaN

Guittoum, A.; Moutanabbir, O.; Jungmann, M.; Butterling, M.; Krause-Rehberg, R.; Anwand, W.; Egger, W.; Sperr, P.

We report on the nature of vacancy complexes and voids involved in H ion-induced splitting of free standing fs-GaN. The fs-GaN wafers were subjected to room temperature implantation with 50 keV H ions at a fluence of 2x1017 H cm-2. After implantation, the wafers were annealed at different temperatures ranging from 100 to 600 °C. Variable energy Doppler broadening spectroscopy (VEDBS) was used in order to probe open-volume defects and their thermoevolution. Pulsed low energy positron lifetime spectroscopy (PLEPLS) was employed to qualitively characterize H ion-induced vacancy complexes and to observe their subtle changes during the thermally activated splitting of GaN thin layer. The decomposition of the lifetime spectra of as-implanted and annealed samples up to a temperature of 450 °C resulted in the detection of two vacancy defects: divacancies (260-282 ps) and vacancy clusters (470-650 ps). With increasing temperature, we have noted in addition the existence of other kind of vacancy-type defects, namely, monovacancies (220-236 ps) and a long lifetime which is attributed to positronium. From the values of positronium lifetime equal to 1 ns, 2.2 ns and 3.8 ns, it was possible to estimate the corresponding wall spacing according to the Tao-Eldrup model to be 0.2 nm to 0.4 nm. The fact that positron annihilation spectroscopy can give information about the wall spacing in GaN, leads us to say that this technique is able to predict the phenomenon of splitting in wide band gap semiconductors.

Keywords: ion-cutting; GaN; positron annihilation spectroscopy

  • Invited lecture (Conferences)
    International Workshop on Advanced Positron Beam Technology for Material Science - APSB 2010, 15.-18.03.2010, Algiers, Algeria

Permalink: https://www.hzdr.de/publications/Publ-13945
Publ.-Id: 13945


Electromagnetic induction in non-uniform domains

Giesecke, A.; Nore, C.; Luddens, F.; Stefani, F.; Leorat, J.; Guermond, J.-L.; Gerbeth, G.

Kinematic simulations of the induction equation are carried out for different setups suitable for the von-Karman-Sodium (VKS) dynamo experiment. Material properties of the flow driving impellers are considered by means of high conducting and high permeability disks that are present in a cylindrical volume filled with a conducting fluid. Two entirely different numerical codes are mutually validated by showing quantitative agreement on Ohmic decay and kinematic dynamo problems using various configurations and physical parameters. Field geometry and growth rates are strongly modified by the material properties of the disks even if the high permeability/high conductivity material is localized within a quite thin region. In contrast the influence of external boundary conditions remains small.

Utilizing a VKS like mean fluid flow and high permeability disks yields a reduction of the critical magnetic Reynolds number for the onset of dynamo action of the simplest non-axisymmetric field mode. However this decrease is not sufficient to become relevant in the VKS experiment. Furthermore, the reduction of Rm_c is essentially influenced by tiny changes in the flow configuration so that the result is not very robust against small modifications of setup and properties of turbulence.

Keywords: Magnetohydrodynamics; Ohmic decay; kinematic Dynamo; Permeability; VKS dynamo

Permalink: https://www.hzdr.de/publications/Publ-13944
Publ.-Id: 13944


Velocity fields under impinging jets with gas entrainment

Danciu, D.-V.; Zidouni Kendil, F.; Mishra, A.; Schmidtke, M.; Lucas, D.; Hampel, U.

Particle Image Velocimetry (PIV) is a powerful measurement technique, suitable for the study of complex flow fields encountered in single- or two-phase flow phenomena. Air entrainment is a widely studied phenomenon, which is encountered in multiple industrial applications, as well as in nature. Results from the successful application of PIV to both impinging region and recirculation zone are presented. Both instantaneous and time-averaged flow fields were obtained. The turbulent kinetic energy is estimated from the averaged velocity fields in the recirculation zone. Simulations of the phenomenon are performed with ANSYS-CFX. The turbulence was modelled using the k-epsilon model. Experimental results were compared with the simulation and showed good agreement.

Keywords: gas entrainment; particle image velocimetry; liquid velocity fields; simulation

  • Lecture (Conference)
    7th International Conference on Multiphase Flow ICMF 2010, 30.05.-04.06.2010, Tampa, USA
  • Contribution to proceedings
    7th International Conference on Multiphase Flow, ICMF 2010, 30.05-04.06.2010, Tampa,USA, 30.05.-04.06.2010, Tampa, USA
    International Conference on Multiphase Flow

Permalink: https://www.hzdr.de/publications/Publ-13943
Publ.-Id: 13943


The 9th International Conference on Research in High Magnetic Fields in Retrospective View

Wosnitza, J.; Herrmannsdörfer, T.; Wolff-Fabris, F.

es hat kein Abstract vorgelegen

  • Journal of Low Temperature Physics 159(2010), 1-2

Permalink: https://www.hzdr.de/publications/Publ-13942
Publ.-Id: 13942


Superconducting Phase Diagram of Rh17S15

Uhlarz, M.; Ignatchik, O.; Wosnitza, J.; Naren, H. R.; Thamizhavel, A.; Ramakrishnan, S.

We report on measurements of the magnetization up to 7 T, of the specific heat and electrical resistivity in fields up to 14 T, and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh17S15. Our data allow us to complement the superconducting phase diagram. The existence of narrow 4 d-band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the moderately high electronic contribution to the specific heat of about 107 mJ/molK2, favoring the existence of a strong superconducting interaction. This fact, and the remarkably high upper critical field (exceeding the simple Pauli limit by a factor of two), give evidence of the uncommon nature of the superconductivity in Rh17S15.

  • Journal of Low Temperature Physics 159(2010), 176-179

Permalink: https://www.hzdr.de/publications/Publ-13941
Publ.-Id: 13941


Magneto-Acoustic Faraday Effect in Tb3Ga5O12

Sytcheva, A.; Löw, U.; Yasin, S.; Wosnitza, J.; Zherlitsyn, S.; Goto, T.; Wyder, P.; Lüthi, B.

The transverse acoustic wave propagating along the [100] axis of the cubic paramagnet Tb3Ga5O12 (TGG) exhibits amplitude oscillations as a function of magnetic field applied in the direction of propagation. This magneto-acoustic Faraday effect shows a linear frequency dependence contrary to theoretical expectation which demands a quadratic frequency dependence. The c44 mode demonstrates also a strong softening of 6% up to 19 T, the magnetic field where an energy level of the CEF triplet branch starts to cross the quasi-doublet branch. This softening has the same origin, the magneto-elastic coupling, as the anomalies in the temperature dependence of the elastic constants and the magneto-acoustic Faraday effect.

  • Journal of Low Temperature Physics 159(2010), 126-129

Permalink: https://www.hzdr.de/publications/Publ-13940
Publ.-Id: 13940


Magnetoacoustics of the Low-Dimensional Quantum Antiferromagnet Cs2CuCl4 with Spin Frustration

Sytcheva, A.; Chiatti, O.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, A. A.; Coldea, R.; Tylczynski, Z.

We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice spin-1/2 antiferromagnet Cs2CuCl4 (TN = 0.6 K), in external magnetic fields up to 14 T, applied along the b axis, and at temperatures down to 300 mK. The results are analyzed with a quasi-two-dimensional hard-core boson theory based on exchange-striction coupling. There is a good qualitative agreement between theoretical and experimental results.

  • Journal of Low Temperature Physics 159(2010), 109-113

Permalink: https://www.hzdr.de/publications/Publ-13939
Publ.-Id: 13939


Microminiature Hall Probes for Applications at Pulsed Magnetic Fields up to 87 Tesla

Mironov, O. A.; Zherlitsyn, S.; Uhlarz, M.; Skourski, Y.; Palewski, T.; Wosnitza, J.

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area from 90 × 90 μm down to 20 × 20 μm and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. MHPs were intensively tested in static (up to 14 T) and pulsed magnetic fields and shown to be appropriate for various applications in the temperature range 2–300 K and in pulsed magnetic fields up to 87 T. The latest version of these probes, with overall cross-section thickness-width dimensions of 150 × 750 μm, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged or unpackaged sensors.

  • Journal of Low Temperature Physics 159(2010), 315-318

Permalink: https://www.hzdr.de/publications/Publ-13938
Publ.-Id: 13938


Upper Critical Field Measurements up to 60 T in Arsenic Deficient LaO0.9F0.1FeAs1−δ: Pauli Limiting Behavior at High Fields vs. Improved Superconductivity at Low Fields

Fuchs, G.; Drechsler, S.-L.; Kozlova, N.; Freudenberger, J.; Bartkowiak, M.; Wosnitza, J.; Behr, G.; Nenkov, K.; Büchner, B.; Schultz, L.

We report resistivity and upper critical field Bc2(T ) data for As-deficient LaO0.9F0.1FeAs1−δ in a wide temperature and field range up to 60 T. These disordered samples exhibit a slightly enhanced superconducting transition at Tc = 29 K and a significantly enlarged slope dBc2/dT = −5.4 T/K near Tc which contrasts with a flattening of Bc2(T ) starting near 23 K above 30 T. This flattening is interpreted as Pauli limiting behavior (PLB) with Bc2(0) ≈ 63 T. We compare our results with Bc2(T )-data reported in the literature for clean and disordered samples. Whereas clean samples show no PLB for fields below 60 to 70 T, the hitherto unexplained flattening of Bc2(T ) for applied fields H || ab observed for several disordered closely related systems is interpreted also as a manifestation of PLB. Consequences of our results are discussed in terms of disorder effects within the frame of conventional and unconventional superconductivity.

  • Journal of Low Temperature Physics 159(2010), 164-167

Permalink: https://www.hzdr.de/publications/Publ-13937
Publ.-Id: 13937


High-Field Magnetization Study of [Cu(pyz)2(HF2)]PF6: An S = 1:2 Quasi-two-dimensional Heisenberg Magnet

Cizmar, E.; Ozerov, M.; Skourski, Y.; Zvyagin, S. A.; Schlueter, J. A.; Manson, J. L.; Wosnitza, J.

We report on pulsed-field magnetization studies of the quasi-two-dimensional spin system [Cu(pyz)2(HF2)]PF6. The magnetization saturates at BabC = 37.5 T and BcC= 33.8 T for in-plane and out-of-plane orientations of the applied magnetic field, respectively. In addition, the angular dependence of the g-factor studied by electron-spin resonance reveals orbital overlap in the ab plane suggesting a quasi-two-dimensional square-lattice network of Cu spins. It is argued that the high-field behavior is governed by the two-dimensional nature of the spin correlations due to the large anisotropy of the exchange couplings.

  • Journal of Low Temperature Physics 159(2010), 92-95

Permalink: https://www.hzdr.de/publications/Publ-13936
Publ.-Id: 13936


A High Resolution, Broad Energy Acceptance Spectrometer for Laser Wake-field Acceleration Experiments

Sears, C. M. S.; Benavides Cuevas, S.; Schramm, U.; Schmid, K.; Buck, A.; Habs, D.; Krausz, F.; Veisz, L.

Laser wake¯eld experiments present a unique challenge in measuring the resulting electron energy properties due to the large energy range of interest, typically several 100 MeV, and the large electron beam divergence and pointing jitter >1 mrad. In many experiments the energy resolution and accuracy are limited by the convolved transverse spot size and pointing jitter of the beam. In this paper we present an electron energy spectrometer consisting of two magnets designed speci¯cally for laser wake¯eld experiments. In the primary magnet the ¯eld is produced by permanent magnets while a second electromagnet can be used for electron energies above 75 MeV. The spectrometer has an acceptance of 2.5-400 MeV (Emax=Emin > 100) with a resolution of better than 1% rms for electron energies above 25 MeV. This high resolution is achieved by refocusing electrons in the energy plane and without any post-processing image deconvolution. Finally, the spectrometer employs two complimentary detection mechanisms: 1) absolutely calibrated scintillation screens imaged by cameras outside the vacuum chamber, and 2) an array of scintillating ¯bers coupled to a low-noise CCD.

Keywords: Laser plasma electron acceleration; magnetic spectrometer; scintillating fiber array

Permalink: https://www.hzdr.de/publications/Publ-13935
Publ.-Id: 13935


Radionuclide Geomicrobiology of the Deep Biosphere

Anderson, C.; Johnsson, A.; Moll, H.; Pedersen, K.

This review summarizes research into interactions between microorganisms and radionuclides under conditions typical of a repository for high-level radioactive waste in deep hard rock environments at a depth of approximately 500 m. The cell-radionuclide interactions of strains of Pseudomonas species (i.e., Shewanella putrefaciens and Desulfovibrio aespoeensis) with Cm, Pm, and Pu were investigated in vitro and the results were found to agree with literature data. Siderophores are capable of binding actinides strongly and need to be considered in terms of radionuclide mobility in the subsurface. Siderophores and other bioligands were found to have a generally very strong mobilizing effect on Am, Cm, Fe, Np, Pm, Pu, Th, and U. Where reduced groundwater enters an aerobic environment, such as a large open fracture or fracture zone (e.g., in tunnels), there is the possibility of rapid aerobic bacterial metabolism, microbial proliferation, biofilm development, and iron oxide formation. In these environments, the stalk-forming bacterium Gallionella may act as a scaffold for iron oxide precipitation on biological material. In situ work in the Äspö Hard Rock Laboratory tunnel indicated that the concentrations of biological iron oxides, lanthanides, and actinides correlated positively with Gallionella biomass, a finding that compares well to literature data. In deep oligotrophic subsurface granitic rock environments, fracture biofilms reach a threshold of approximately 2-5 x 106 cells/cm2. The cells in these biofilms are spatially distinct and are surrounded by an extracellular polysaccharide matrix that constitutes up to 60% of the total organic carbon. Calcium-rich amorphous masses are associated with this base layer of cells and organic exudates. In situ, these biofilms have been found to influence the adsorption and immobilization of Am, Np, Pm, Th, and U. This review demonstrates that microorganisms can influence, and sometimes even control, the migration behavior of radionuclides in deep geological environments typical of future sites for radioactive waste repositories.

Keywords: Radionuclides; Geomicrobiology; Deep biosphere

Permalink: https://www.hzdr.de/publications/Publ-13934
Publ.-Id: 13934


Some nuclear reactor safety related aspects of plunging jets

Krepper, E.; Weiss, F.-P.; Alt, S.; Kratzsch, A.; Renger, S.; Kästner, W.

Plunging jets play an important role in nuclear reactor safety research. In the present paper the case of the strainer clogging issue is considered. Entrained air caused by a plunging jet has an influence of the liquid flow field and on the fibre transport in the sump. In the paper the amount of entrained air is given as an inlet boundary condition according to correlations in the literature and confirmed by own experiments. The influence of entrained air on the fibre deposition pattern at the bottom of a tank and on the mixing procedure for the case of temperature differences between jet and tank water are investigated by CFD calculations and compared to experiments.
The presented work is part of a joint research project performed in cooperation between the University of Applied Science Zittau/Görlitz and Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow in Zittau and the development of CFD models for its simulation in Rossendorf (Krepper et al. 2008).

Keywords: fibres; experiments; cfd; multiphase flow

  • Contribution to proceedings
    18th International Conference on Nuclear Engineering, ICONE18, 17.-21.05.2010, Xi'an, China
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering, ICONE18, 17.-21.05.2010, Xi’an, China

Permalink: https://www.hzdr.de/publications/Publ-13933
Publ.-Id: 13933


Quantum Transport and Cyclotron Resonance Study of Ge/SiGe Quantum Wells in High Magnetic Fields

Miura, N.; Kozlova, N. V.; Dörr, K.; Freudenberger, J.; Schultz, L.; Drachenko, O.; Sawano, K.; Shiraki, Y.

Shubnikov-de Haas oscillation and cyclotron resonance were studied for high mobility p-type Ge channels in strained Ge/Si1-x Ge (x) quantum wells, using pulsed high magnetic fields up to 50 T. Fine quantum oscillations were observed in rho (xx) . Reflecting the complex Landau level structure in the nearly degenerate valence bands, the Fourier transform of the oscillatory spectra consists of several peaks. Cyclotron resonance was measured at photon energies between 10 and 17 meV. Two well-defined resonance peaks were observed in two samples with different x, resulting in different strains. A large non-parabolicity and large strain dependence of the effective masses were observed.

Keywords: Ge/SiGe quantum well; Magneto-spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-13932
Publ.-Id: 13932


Cyclotron Resonance of Extremely Conductive 2D Holes in High Ge Content Strained Heterostructures

Mironov, O. A.; Goiran, M.; Galibert, J.; Kozlov, D. V.; Ikonnikov, A. V.; Spirin, K. E.; Gavrilenko, V. I.; Isella, G.; Kummer, M.; von Känel, H.; Drachenko, O.; Helm, M.; Wosnitza, J.; Morris, R. J. H.; Leadley, D. R.

Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels.

Keywords: Cyclotron resonance; Ge; SiGe; Landau Levels

Permalink: https://www.hzdr.de/publications/Publ-13931
Publ.-Id: 13931


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