Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Automatisierte Koregistrierung von PET-Ganzkörperaufnahmen mit stückweise starren Transformationen
Hofheinz, F.; Pötzsch, C.; van den Hoff, J.;
Ziel: Im Gegensatz zur intraindividuellen Koregistrierung von PET-Kopfaufnahmen, bei der zumindest die Außenkonturen des Kopfes in verschiedenen Aufnahmen konstant sind, steht man bei der Koregistrierung von PET-Großkörperaufnahmen vor dem Problem, dass sich die zu vergleichenden Datensätez beträchtlich voneinander unterscheiden können. Versucht man alle Unterschiede durch elastische Transformationen zu berücksichtigen, kann es leicht zu Verfälschungen der Bilder kommen. Beschränkt man sich lediglich auf starre Transformationen, gelingt lokal keine gute Anpassung der Intensitäten. Unser Ziel war die Entwicklung einer routinefähigen Methode, die PET-Ganzkörperaufnahmen bestmöglich bei vollständigem Informationserhalt gegeneinander koregistriert. Der Fokus der Entwicklung lag auf der Registrierung von Follow Up Studien. Die Algorithmen sollten über ein benutzerfreundliches graphisches Interface gesteuert werden können.

Methodik: Bei dem von uns verfolgten Ansatz wird eine der beiden Aufnahmen in verschiedene Areale unterteilt. Diese Areale werden dann unabhängig voneinander gegen die andere Studie registriert. Dabei werden nur starre Transformationen verwendet. Die gesamte Transformation ist damit eine stückweise starre Transformation und der stetige Übergang zwischen den Arealen wird durch Interpolation realisiert. Die besten Transformationsparameter werden mit Hilfe einer modifizierten Methode der konjugierten Gradienten gesucht, wobei die Übereinstimmung der Bilder mittels der Korrelation der Voxelintensität und der "Mutual Information" der Bilder bewertet wird.

Bei allen durchgeführten Koregistrierungen konnte eine Verbesserung der Übereinstimmung der PET-Daten erreicht werden. Insbesondere wenn die Areale ganze Organe umschließen, lassen sich auf der Grundlage dieser quasi elastischen Transformation auch starke Unterschiede in den Bildern erfassen und verlustfrei aufeinander abbilden. Die Größe der Areale beeinflusst dabei die Qualität der Ergebnisse. Umfasst ein Areal den gesamten Datensatz, kann nur mit einer mäßigen Güte der Koregistrierung gerechnet werden. Je kleine die Areale umso besser die Resultate. Die Rechenzeiten liegen typischerweise bei zwei bis fünf Minuten. Die Benutzerinteraktion reduziert sich auf die Wahl der interessierenden Areale. Zusätzlich kann der verwendete Algorithmus über Informationen zum Inhalt der Aufnahmen beschleunigt bzw. optimiert werden.

Schlussfolgerungen: Das hier vorgestellte Koregistrierungsprogramm lierfert bei kurzen Rechenzeiten stabile und genaue Ergebnisse und erscheint somit für den Routineeinsatz geeignet.
  • Poster
    Gemeinsame Jahrestagung d. Deutschen,Österreichischen u. Schweizerischen Gesell. f. Nuklearmedizin, 27.-30.04.2005, Basel, Schweiz
  • Abstract in refereed journal
    Nuklearmedizin 44(2005), A162

Publ.-Id: 7384 - Permalink


Annual Report 2004 - Institute of Ion Beam Physics and Materials Research
von Borany, J.; Heera, V.; Helm, M.; Jäger, H.-U.; Möller, W.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-427 2005

Downloads:

Publ.-Id: 7383 - Permalink


Löslichkeitsuntersuchungen an Uran(IV) mittels laserinduzierter Breakdown-Detektion
Opel, K.; Weiß, S.; Hübener, S.; Zänker, H.; Bernhard, G.;
Das Löslichkeitsprodukt von wäßrigem, amorphem Urandioxid UO2•xH2O(am) wurde mit Hilfe der laserinduzierten Breakdown-Detektion (LIBD) bestimmt. Dazu wurden U(VI)-Lösungen bei pH-Werten um 1 elektrochemisch reduziert, das Fortschreiten der Reduktion wurde durch UV-Vis-Spektroskopie und Laserfluoreszenzspektroskopie verfolgt. Die Erhöhung des pH-Wertes erfolgte durch coulometrische Titration der Lösung, die einsetzende Bildung von U(IV)-Kolloiden wurde durch die LIBD detektiert. Der pH-Wert an diesem Punkt lieferte die Grundlage zur Berechnung des Löslichkeitsproduktes. Die Ergebnisse von zwei Titrationen zeigt die folgende Tabelle.

Tabelle: Ergebnisse der coulometrischen Titrationen
[U(IV)]tot/mol•l-1 pHkoll log Ksp°
1,06•10-4 2,57 -54,27
3,37•10-5 2,80 -54,34

Das Löslichkeitsprodukt wurde gemäß folgender Gleichung berechnet:
log Ksp° = [U4+]*[OH-]^4*g(U4+)*g(OH-)^4

Die Berechnung der Aktivitätskoeffizienten erfolgte mit Hilfe der Specific Ion Interaction Theory, die in [1] dargelegt ist. Zur Bestimmung von [OH-] wurden pHkoll und das Ionenprodukt von Wasser herangezogen. Die Berechnung von [U4+] wurde unter Berücksichtigung der unter diesen Bedingungen wichtigen Hydrolysespezies des U(IV) durchgeführt. Der Anteil der einzelnen Spezies wurde über die in [2] aufgeführten Bildungskonstanten der Spezies quantifiziert und von der analytisch bestimmten Gesamtkonzentration des Urans subtrahiert.

Der berechnete Mittelwert des Löslichkeitsproduktes von UO2•xH2O(am) liegt bei log Ksp° = -54,31 und bestätigt Ergebnisse früherer Untersuchungen, bei denen die Reoxidation von U(IV) zu U(VI) wirksam unterbunden wurde [3].

[1] Grenthe, I. et al., Chemical Thermodynamics, Vol. 1. Chemical Thermodynamics of Uranium, 1992, Elsevier, Amsterdam.
[2] Neck, V. et al., Radiochim. Acta 89 (2001) 1.
[3] Rai, D. et al., Radiochim. Acta 79 (1997) 239.
Keywords: uranium, colloids, solubility, LIBD, laser induced breakdown detection
  • Poster
    GDCh-Jahrestagung 2005, 11.-14.09.2005, Düsseldorf, Deutschland
  • Contribution to proceedings
    GDCh-Jahrestagung 2005, Chemie schafft neue Strukturen, 11.-14.09.2005, Düsseldorf, Germany
    Kurzreferate, 3-936028-36-2, 527

Publ.-Id: 7382 - Permalink


Aluminum investment casting with magnetic field control of the mould filling process
Cramer, A.; Eckert, S.; Galindo, V.; Gerbeth, G.; Witke, W.;
From a fluid mechanical point of view, the filling of the mould during aluminum investment casting processes comprises in essence a flow in a U-bend. It is characterized by a high value of the pouring velocity in the early stage, which decreases in the course of the process. This initial high velocity poses distinct problems such as entrapment of bubbles or debris. At present, different types of filters are used for the removal of inclusions, a desired secondary effect of which is a reduction of the melt velocity.
A non-invasive contact-less solution to control the flow of liquid aluminum is the application of a static (DC) magnetic field. Numerical calculations were performed to simulate the filling process and in particular the influence of the field. The free surface problem, which occurs in the riser of the casting unit, was taken into account by a volume-of-fluid method. 3D transient calculations employing the commercial finite-element code FIDAP were carried out for a simplified model system as well as for the real aluminum casting unit. The term for the electromagnetic force was implemented via a user defined subroutine while an additional equation for the electrical potential was solved. End effects owing to the limited size of the magnet poles were taken into account.
In parallel to the simulations, model experiments were performed using the eutectic alloy InGaSn (Tmelt = 10oC). The casting unit was modeled by a perspex pattern, and ultrasonic Doppler veloci­metry was applied for detailed acquisition of velocity data. Such measurements constitute a profound basis for the validation of the numerical simulations. On account of the excellent agreement, an up- scaling towards the realistic aluminium casting process is justified.
Finally, realistic tests with liquid aluminium were performed at an industrial installation. The primarily aimed at influence of the magnetic field, i.e. the attenuation of velocity peaks in the beginning of the process, could be clearly demonstrated. In a second set of experiments, the strength of the DC field was adapted to the process. At start-up, the maximum braking force was applied for a fixed time, followed by a reduction with increasing filling-level of the casting unit. This schedule provided a distinct damping of the peak velocities without the drawback of a significant prolongation in filling time. A remarkable diminishment of defects in the casting product could be achieved.
  • Lecture (Conference)
    International Symposium on Liquid Metal Processing and Casting, 18.-21.09.2005, Santa Fe, New Mexico, United States
  • Contribution to proceedings
    International Symposium on Liquid Metal Processing and Casting, 18.-21.09.2005, Santa Fe, New Mexico, United States
    Proceedings, 0-87170-827-2, 295-303

Publ.-Id: 7381 - Permalink


Bright green electroluminescence from Tb3+ in silicon metal-oxide-semiconductor devices
Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Rebohle, L.; Gebel, T.;
Bright green electroluminescence with luminance up to 2800 cd/m2 is reported from indium-tin-oxide/SiO2:Tb/Si metal-oxide-semiconductor devices. The SiO2:Tb3+ gate oxide was prepared by thermal oxidation followed by Tb+ implantation. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and the annealing temperature. The optimized device shows a high external quantum efficiency of 16 % and a luminous efficiency of 2.1 lm/W. The excitation processes of the strong green electroluminescence are attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent cross-relaxation from 5D3 to 5D4 energy levels. Light emitting devices with micrometer size fabricated by the standard metal-oxide-semiconductor technology are demonstrated
Keywords: Electroluminescence, silicon dioxde, rare earth, terbium
  • Journal of Applied Physics 97(2005)12, 123513

Publ.-Id: 7380 - Permalink


Minimierung der Inter-Observer-Variabilität bei volumetrischen Auswertungen von onkologischen Ganzkörperstudien in der PET
Pötzsch, C.; Hofheinz, F.; van den Hoff, J.;
Ziel: In (1) wurde ein Verfahren vorgestellt, welches zur Eingrenzung, Analyse und quantitativen Auswertung dreidimensionaler Strukturen (VOIs) innerhalb von PET-Bildvolumen dient. Hierbei werden die VOIs halbautomatisch über eine Schwellwertanalyse detektiert und segmentiert. Da der Schwellwert durch den Anwender festgelegt wird, unterliegt das gesamte Verfahren in bestimmtem Umfang der Subjektivität des Anwenders mit entsprechender Konsequenz für die Inter-Observer-Variabilität. Das Ziel dieser Arbeit war es, die vorhandene Schwellwertanalayse so zu modifizieren, dass sie die Volumina von VOIs und hiervon abhängige Größen wie die mittlere Tracerakkumulation/SUVs reproduzierbar bestimmt.

Methodik: Der Anwender muss einen ersten Schwellwert festlegen, der in etwa dem subjektiv als korrekt betrachteten Wert entspricht. Die nähere Umgebung des Volumens definiert den Untergrund und schränkt gleichzeitig den zu betrachtenden Bereich ein. Ausgehend von diesem Hintergrund lassen sich lokale Schwllwerte definieren. Um diese Schwellwerte zu finden, muss das Niveau des Untergrundes ermittelt werden. Dies geschieht über einen Least-Squares-Fit gegen eine 3D-Hyperfläche, welcher mittels multilinearer Regression berechnet wird.

Ergebnisse: Bei den betrachteten Testdatensätzen lieferte die Methode erste viel versprechende Ergebnisse. Untersucht wurden zum einen Studien mit ortinvariante, sowie solche mit stark ortsabhängigem Untergrund. Für einen um 40 Prozentpunkte variierenden Schwellwertbereich wurden die Volumina jeweils mit und ohne Bestimmung des Untergrundes berechnet. Es zeigte sich, dass bei Studien mit ortinvariantem Untergrund die Schwankungsbreite der ermittelten Volumina von 150 Prozent auf 10 Prozent reduziert werdn konnte. Bei Studien mit stark ortsabhängigem Untergrund, z.B. an Organgrenzen, konnte eine Verminderung von 280 Prozent auf 60 Prozent erreicht werden. Hierbei spielt die Höhe des untergrundes in beiden Fällen keine Rolle, solange der Startschwellwert über dem Untergrundniveau liegt.

Schlussfolgerung: Die Methode liefert bei hinreichend ortsinvariantem Untergrund stabile Ergebnisse. Bei stark ortsabhängigem Untergrund sind Erweiterungen nötig. Vorstellbar wäre eien ortsabhängige Gewichtung des Untergrundes im Bereich zwischen Startvolumen und Untergrund, was in weiteren Tests zu untersuchen ist.
  • Lecture (Conference)
    Gemeinsame Jahrestagung d. Deutschen, Österreichischen und Schweizerischen Gesellsschaft für Nuklearmedizin, 27.-30.04.2005, Basel, Swizerland
  • Abstract in refereed journal
    Nuklearmedizin 44(2005), A16

Publ.-Id: 7379 - Permalink


On the dependence on bias voltage of the structural evolution ofmagnetron-sputtered nanocrystalline Cu films during thermal annealing
Schell, N.; Andreasen, K. P.; Bøttiger, J.; Chevallier, J.;
The nanostructural evolution during heat treatments of DC magnetron-sputtered Cu films deposited at different substrate bias voltages was experimentally studied. A growth chamber equipped with two magnetrons and Kapton windows for in-situ X-ray diffraction was mounted on a six-circle goniometer at a synchrotron beam line. Using Bragg–Brentano X-ray diffraction, the grain size,the texture, and the lattice constant were monitored during thermal annealing.Increasing the substrate bias voltage, the grain growth rate lowered, and the change in texture with time became smaller due to a decrease in the defect concentration. Furthermore, the grain size in the as-deposited films decreased with increasing bias voltage. The activation energy for grain growth was, within experimental errors, the see in all the films.
Keywords: Nanocrystalline Cu; Nanostructure; In-situ X-ray diffraction; Magnetron sputtering
  • Thin Solid Films 476(2005)2, 280-287

Publ.-Id: 7378 - Permalink


On 'extraordinary optical transmission' from periodic and random nanostructures
Sharlandjiev, P.; Nazarova, D.; Mednikarov, B.; Pham, M.;
Recently, an enhanced optical transmission (EOT) through 2D periodic arrays of sub-wavelength holes in a metal layer was found. It generated intense theoretical and experimental research, but its physical nature is still not elucidated. In this communication, we report experimental investigations on ID relief gratings, and numerical analysis of the composite structure of randomly distributed dielectric nanoparticles embedded in a thin metallic matrix. We show that EOT is also present in such structures.
  • Journal of Optoelectronics and Advanced Materials 7(2005)1, 309-312

Publ.-Id: 7376 - Permalink


Spectroscopic ellipsometry monitoring of ITO thin film properties evolution during amorphous-to-crystalline transition
Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Kreissig, U.; Möller, W.;
Annealing of thin films of amorphous indium tin oxide (ITO) in vacuum is known to decrease their resistivity. The amorphous-to-crystalline transition is often assumed as the reason for this improvement due to a Sn donor activation, but the physical mechanisms behind the experimental observation are not clear. In present work, the films were studied during heating in vacuum within the temperature range Ta=20-330 °C at a constant rate of 5 °C/min as well as at isothermal annealing at Ta=210 °C. This study is focused on in situ spectroscopic ellipsometry (SE) monitoring of the film properties during annealing. In addition, the films were investigated by in situ four point probe resistivity measurement technique and the in situ X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA). The observed temperature dependences of the ellipsometry parameters and resistivity indicate several stages with features at Ta=110, 150, 280, and 310 °C, in contrast to the more simple two-stage behavior of these characteristics obtained during isothermal annealing. Even in the XRD-amorphous state, the film resistivity significantly decreases with increasing temperature due to a free-electron density enhancement as shown by SE. It is likely caused by the generation of oxygen vacancies, because ERDA showed decrease of the oxygen content in the film on this stage of annealing. A rapid crystallization within the temperature range of 250-280 °C leads to a further decrease of the resistivity due to Sn donor activation. The amorphous-to-crystalline transition is accompanied by a film roughening as it is shown by in situ SE and corroborated by atomic force microscopy.
Keywords: tin-doped indium oxide, in situ spectroscopic ellipsometry, crystallization
  • Poster
    International Conference on Metallurgical Coatings and Thin Films (ICMCTF 2005), 02.-06.05.2005, San Diego, CA, USA

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Publ.-Id: 7375 - Permalink


Disruption of unprecedented B-H...M agostic interactions: An alternative approach for labeling bioactive molecules
Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Pietzsch, H.-J.;
The agostic B-H...Re bond in complexes [Re{kappa(3)-R(mu H)B(tim(Me))(2)}(CO)(3)] (R= H (1), Ph (2), tim(Me) = 2-mercapto-1-methylimidazolyl) is readily cleaved by t-butylisonitrile or cyclohexylisonitrile leading to the mixed-ligand complexes [Re{kappa(2)-Ph(mu-H)B(tim(Me))(2)}(C equivalent to (NBu)-Bu-t)(CO)(3)] (3) and [Re{kappa(2)-H(mu-H)B(tim(Me))(2)}(C equivalent to N-cyclohexyl)(CO)(3)] (4), respectively. Bearing in mind the so-called [2 + 1] mixed ligand approach for the development of target-pecific radiopharmaceuticals, reactions of 1 with isonitriles carrying the (2-methoxyphenyl)piperazine pharmacophore (part of WAY 100635) were also studied and the complexes [Re{kappa(2)-H(mu-H)B(tim(Me))(2)}(C equivalent to N-R'-WAY)(CO)(3)] (R' = butylene (5), pentylene (6) or hexylene (7)) isolated. The novel mixed Re(I) tricarbonyl complexes (3-7) have been characterized by the usual analytical techniques, which included X-ray diffraction analysis in the cases of 3, 4 and 5. The affinity of the complexes 5-7 toward the 5-HT1A receptors was tested in competitive receptor binding assays and the IC50 values found were in the 21.9-66.5 nM range. Complex 7, with the longest spacer length between the isonitrile function and the pharmacophore, has shown an improved selectivity towards the 5-HT1A subtype of receptors when compared with 5 and 6.
  • Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry 35(2005)1, 35-42

Publ.-Id: 7374 - Permalink


Untersuchung der zentralen Verarbeitung trigeminaler Reize
Beuthien-Baumann, B.; Heinke, M.; van den Hoff, J.; Oehme, L.; Will, E.; Kotzerke, J.; Hummel, T.;
Ziel: Wenigstens 5 % der Bevölkerung verlieren im Laufe des Lebens ihren Geruchssinn. Bei diesen Patienten stellt der Nervus trigeminus die einzig verbliebene intranasale chemosensorische Modalität dar. Bisherige Studien beschäftigen sich überwiegend mit olfaktorisch-trigeminalen Mischreizen, zum tieferen Verständnis der Verarbeitung intranasaler trigeminaler Reize fehlt es bisher an Informationen. Ziel dieser Studie ist es zu überprüfen, in wiefern die O-15-H2O-PET für den Nachweis einer gezielten Reizung des N. trigeminus geeignet ist.

Methodik: Es wurden 15 männliche Probanden (Alter 30 - 58 Jahre, mittleres Alter 36) ohne internistische oder neurologische Vorerkrankungen und ohne Erkrankung im HNO-Bereich untersucht. Die PET-Messungen erfolgten an einer dedizierten PET-Kamera (ECAT EXACT HR+). Pro Proband waren 4 dynamische Messungen über 5 min vorgesehen, alternierend Ruhemessungen und Aktivierung nach Applikation von 1,7 GBq O-15-H2O i.v. und mind. 15 min Pause zwischen den Einzelmessungen. Für die Reizung des N. trigeminus wurden per Nasensonde CO2-Pulse (Reizdauer 1 s, Intervall 3 s) in das linke Nasenloch beginnend 20 sec vor Injektion und über den gesamten Messzyklus appliziert. Die Auswertung erfolgte mittels parametrischer Flow-maps, die unter Benutzung einer Standard-Inputfunktion erzeugt wurde. Für den Vergleich Ruhemessung - Aktivierung kam das Softwareprogramm SPM99 zum Einsatz. Die Studie war durch die lokale Ethikkommission und das Bundesamt für Strahlenschutz genehmigt.

Ergebnisse: Bei 12 Probanden konnten je 2 Ruhe- und Aktivierungsmessungen akquiriert werden, bei 3 Probanden konnten auf Grund technischer Schwierigkeiten nur mindestens je 1 Ruhe- und Aktivierungsstudie aufgenommen werden. In der noch andauernden Auswertung zeigt sich in einer ersten Auswertung aller Probandenmessungen eine deutliche Aktivierung im Projektionsfeld des N. trigeminus am Fuse des postzentralen Gyrus, die rechsseitig stärker ausgeprägt ist als in der linken Hemisphäre.

Schlussfolgerung: Nach trigeminaler Reizung der Nasenschleimhaut des linken Nasenloches zeigt sich in einer ersten Auswertung aller Probandenmessungen der H2O-PET eine Perfusionssteigerung im Bereich der postzentralen Projektionsfelder bds. die kontralateral zur Reizung stärker ausgeprägt ist. Die Prüfung der Stabilität der intra-individuellen Aktivierung ist noch Gegenstand der Auswertung.
  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaft für Nuklearmedizin, 27.-30.04.2005, Basel, Swizerland
  • Abstract in refereed journal
    Nuklearmedizin 44(2005)2, A13

Publ.-Id: 7373 - Permalink


Evaluation of F-18 labelled annexin V: apoptosis imaging in mice
Bergmann, R.; Hultsch, C.; Bergmann, S.; Pietzsch, J.; Gunawan, J.; Burchert, W.; van den Hoff, J.;
Apoptosis imaging with PET plays an increasing role in various medical fields like oncology, cardiology, transplant rejection, and inflammation, but the radiotracer distribution in the tis-sues is influenced by various mechanisms. In this study a recombinant annexin-V (courtesy N. Budisa, Max Planck Institute of Biochemistry) derivative and human serum albumin (HSA) were radiolabelled using N-succinimidyl-4-F-18-fluorobenzoate (SFB), and characterized. Mechanism and specificity of both F-18-annexin-V and F-18-HSA biodistribution and accu-mulation were examined in rodents.

Recombinant annexin-V derivative and HSA were radiolabelled using SFB and the products were confirmed by size exclusion chromatography and SDS-PAGE. The radiotracer distribu-tions in animals were studied in rats and mice ex vivo by organ extraction, autoradiography, and in vivo with animal PET. For apoptosis imaging, F-18-annexin-V or F-18-HSA were in-travenously applied in 4 groups of mice that received either intraperitoneal 100 µg Anti-Fas antibody in 200 µL isotonic NaCl or 200 µL isotonic NaCl 2 hours before the radiotracer. The degree of liver apoptosis was characterized by plasma ALAT and ASAT activity measure-ments.

The radiochemical yield was in the range of 10 to 30% (corrected for decay) with a specific activity of more than 20 GBq/µmol. The accumulation of F-18-annexin-V and F-18-HSA, respectively in the apoptotic livers (4 – 16%ID/g) were correlated to the ASAT and increased up to 4 times in comparison to control. The biodistribution of the tracers were comparable except for the renal elimination of F-18-annexin-V, which was up to 3 times higher than of F-18-HSA.
  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaft für Nuklearmedizin, 27.-30.04.2005, Basel, Swizerland
  • Abstract in refereed journal
    Nuklearmedizin 44(2005), A13

Publ.-Id: 7372 - Permalink


Two recipes to stabilize the surface melting in FLASiC structures
Voelskow, M.; Mücklich, A.; Stoemenos, J.; Skorupa, W.;
Due to the lattice misfit between the silicon and the silicon carbide lattices the epitaxial deposition of SiC layers normally results in a highly defected carbide layer. Short time annealing seems to be an effective method to improve the crystal structure of the epitaxial layer using intense light pulses from flash lamps.
From the present point of view the annealing mechanism is based on the rapid melting of a thin silicon interface layer due to the intense light pulse, giving the non molten SiC layer the possibility for relaxation and annealing. Consequently, after the pulse is over and the liquid silicon intermediate layer solidifies epitaxially on the monocrystalline substrate one receives a high temperature annealed epitaxial SiC on silicon structure.
Although the annealing of the SiC layer due to the flash irradiation could be verified by TEM investigations a serious problem remains, connected with the facetted melting of the monocrystalline silicon surface after rapid heating above the melting temperature. Due to the layer by layer crystallisation within the molten pyramides, including a lateral growth component and due to the 5 % higher density of liquid silicon in comparison to solid silicon a surface relief will be formed after the solidification process is completed.
Two techniques were tested to circumvent the deep facetted melting.
The first procedure to homogenize the melting depth is based on the introduction of a so called melt stop layer in a certain depth below the SiC / Si interface. For this purpose carbon admixture which increases the melting temperature of silicon was implanted at a dose of 2*1017cm-2 and a energy of 140 keV through a 30 nm thick SiC layer into silicon, forming a approximately 200 nm thick melt barrier in a depth of 400 nm.
As a further possibility to prevent the facetted melting ion implantation of germanium admixture as a element reducing the melting temperature of silicon was tested.
It could be experimentally shown that both, the introduction of a melt stop layer at any depth behind the Si / SiC interface as well as the modification of the silicon surface, leading to a decrease of the silicon melting temperature, are usefull methods for the homogenization of the melting depth at the bulk silicon surface.
Keywords: flash lamp, annealing, pulse, melting, SiC
  • Lecture (Conference)
    HeT-SiC-05, 26.04.-01.05.2005, Krippen, Deutschland

Publ.-Id: 7371 - Permalink


Uranabfallhalden als Reservoir für Bakterien mit hohem Anwendungspotential für die Bio- und Nanotechnologie
Raff, J.;
Einleitend wird im Rahmen des Vortrags auf Methoden und Ergebnisse zur Bestimmung der bakteriellen Diversität in Uranafallhaden eingegangen. Darauf aufbauend werden Möglichkeiten zur Untersuchung der Wechselwirkungen von Bakterien mit Radionukliden und Schwermetallen aufgezeigt und die Ergebnisse einzelner Analysen vorgestellt. Der letzte Teil umfasst Arbeiten zur Anwendung der Metallbindung in der Biotechnologie und Nanotechnologie.
  • Invited lecture (Conferences)
    Wismut-Kolloquium, 17.-18.05.2005, Jena, Germany
  • Lecture (others)
    Vortrag anlässlich des Besuchs von Mikrobiologie-Studenten der Universität Bayreuth (Prof. Dr. O. Meyer), 27.09.2006, Dresden (Rossendorf), Germany

Publ.-Id: 7370 - Permalink


Tuning magnetic properties locally by ion irradiation and implantation
Fassbender, J.ORC
Recently it has been demonstrated that ion irradiation of ultrathin magnetic films and multilayer structures is a versatile tool to modify the magnetic properties of these systems in laterally confined areas [1–3]. In most cases the modification of the magnetic anisotropy or the different exchange coupling contributions present in multilayered films are due to a post deposition modification of the interface structure. Depending on the enthalpy of mixing light ion irradiation may result in a roughening or a sharpening of the interface on the atomic level. Due to the local nature of the ion-solid interaction these modifications can be restricted to confined areas resulting in magnetically patterned films without a modification of the surface topography.
An alternative route to ion-driven magnetic nanostructures relies on ion implantation. By doping magnetic thin films in a percentage range with Cr or rare earth transition metals either the Curie temperature [4] or the magnetic damping behavior [5] can be adjusted. In combination with focused ion beam techniques magnetic nanostructures can be written directly into the film structure.
In the presentation I will review the current status of these investigations with respect to magnetic nanostructure formation.

[1] C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280, 1919 (1998).
[2] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[3] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[4] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).
[5] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003).
Keywords: magnetism, ion irradiation, ion implantation, magnetic nanostructures, magnetic patterning, anisotropy, exchange-coupling, magnetic damping
  • Lecture (others)
    Seminar, 26.05.2005, Berkeley, USA

Publ.-Id: 7369 - Permalink


Quantitative antimony speciation in shooting-range soils by EXAFS spectroscopy
Scheinost, A.; Rossberg, A.; Vantelon, D.; Xifra, I.; Kretzschmar, R.; Leuz, A.-K.; Johnson, A.;
The Sb speciation in soil samples from Swiss shooting ranges was determined using Sb K-edge Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and advanced statistical data analysis methods (Iterative Transformation Factor Analysis, ITFA). The EXAFS analysis was supported by a spectral data base of 13 Sb minerals and 4 sorption complexes. In spite of a high variability in geology, pH (3.1 – 7.5), Sb concentrations (1000 – 17000 mg/kg) and range history, the spectra of all nine samples could be reconstructed with only two components, indicative of two Sb species. In the first species, Sb is surrounded solely by other Sb atoms at radial distances of 2.90, 3.3.5, 4.30 and 4.51 Å, which are typical for metallic Sb(0). The Sb(0) metal species prevailed in a very acidic (pH 3), organic matter-rich soil. Since no metallic Pb, but Pb2+ bound to soil organic matter was found in this soil by Pb LIII-edge EXAFS spectroscopy, the Pb component of the bullet PbSb alloy may have dissolved more rapidly than the Sb component, leaving metallic Sb behind. In the second species, Sb is coordinated to 6 O atoms at a distance of 1.98 Å, indicative of Sb(V). Iron atoms at radial distances of 3.10 and 3.56 Å are in line with edge-sharing and bidentate corner-sharing linkages between Sb(O,OH)6 and Fe(O,OH)6 octahedra, similar to structural units in the Fe antimonate tripuhyite. This local arrangement, the prevalence of Fe backscatterers and the small coordination numbers suggest formation of clusters of Fe-rich antimonate. This pentavalent Sb species was present in all samples, suggesting that it is the prevailing species after weathering of metallic Sb(0) in oxic soils.

Publ.-Id: 7368 - Permalink


Thermodynamics of Sorption Modeling: Advanced Concepts, Databases and Applicability Tests
Richter, A.;
The lecture summarizes efforts to deliver a chemical base for safety analysis and risk assessment. One major aspect is the substitution of conventional distribution coefficients (Kd values) for the empirical description of sorption processes by surface complexation models (SCM).
The general strategy and examples for current blind predictive capabilities of SCM and the respective database RES3T – the "Rossendorf Expert System for Surface and Sorption Thermodynamics"- are explained.
RES³T is a digitized version of a thermodynamic sorption database as required for the parametrisation of SCM, namely in risk assessment studies.
The approach for the compilation of numerical data includes the collection of the mineral surface characteristics, the selection of reliable data records, the extrapolation to infinite dilution, the normalization to a reference site density and the averaging of selected thermodynamic data records.
The Cu(II) sorption onto goethite and the Np(V) sorption onto hematite were chosen as systems illustrating the blind predictive capabilities. The model predictions represent the experimental values for the adsorbed amount of Cu(II) and Np(V), respectively, expressed as conventional distribution coefficients KD as required by most performance assessment software, are within one order of magnitude or better.
As an example to illustrate the effect of parameter uncertainty in blind predictions the Np(V) sorption onto haematite was selected. The formally large scatter of pK values as extracted from literature is actually not critical. Even the use of inconsistent values from other electrostatic models will yield similar results.
We can conclude, that for well-defined mineral systems, provided a suitable database is accessible, the SCM approach seems to be promising. More realistic (thermodynamic) approaches can and have to amend the KD concept.
Keywords: Sorption, surface complexation models, database, RES3T, blind prediction, uncertainty analysis
  • Lecture (others)
    Seminar, 13.05.2005, Poccatello (Idaho), United States

Publ.-Id: 7367 - Permalink


Review of applied MHD research at Forschungszentrum Rossendorf
Gerbeth, G.;
Based on a classification of the various magnetic field actions on metallic melts, the idea of tailored flow control is presented. Examples will be given for this approach ranging from crystal growth applications, metal casting, electromagnetic levitation, liquid metal two-phase flows to solidification studies. Special emphasis is put on recent developments in velocity measuring techniques for metallic melts as they provide the essential clue for experimental investigations.
  • Invited lecture (Conferences)
    Central Iron & Steel Research Institute (CISRI), 26.05.2005, Beijing, China

Publ.-Id: 7366 - Permalink


Experimental study about gas-liquid metal two-phase flows under the influence of a DC magnetic field
Zhang, C.; Eckert, S.; Gerbeth, G.;
The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC magnetic field was examined. The magnetic field lines were aligned either in longitudinal or in transverse direction. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of about 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4e-13. The liquid metal was in a cylindrical container at rest. The Ultrasound Doppler Velocimetry (UDV) was applied to determine bubble and liquid velocities simultaneously. The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. The measurements revealed a distinct electromagnetic damping of the single bubble wake. Within the whole present parameter range, the bubble Strouhal number was decreased in the longitudinal magnetic field while increased in the transverse magnetic field. On the other hand, the bubble drag coefficient was found to be increased or decreased depending on the bubble size and the magnetic interaction parameter.
In a next step the gas flow rate was increased leading to the formation of weak bubble plumes. The interest was mainly focused on the effect of both longitudinal and transverse magnetic fields on the global flow structure in the container. The UDV results revealed that the velocity field of the liquid phase was completely reorganized by the external DC magnetic field. The magnetic field application does not result exclusively in a plain damping of the recirculating flow. Especially in the case of a transverse magnetic field new flow pattern were observed in both planes parallel and perpendicular to the magnetic field lines. The tendency was found to align and elongate the flow structures along the magnetic field direction. Magnetic damping effects become important with increasing magnetic field strength.
  • Lecture (Conference)
    The 2nd Workshop on Electromagnetic Processing of Materials (Asian-EPM2005), 22.-25.05.2005, Shenyang, China
  • Contribution to proceedings
    The 2nd Workshop on Electromagnetic Processing of Materials (Asian-EPM 2005), 22.-25.05.2005, Shenyang, China, 297-298

Publ.-Id: 7365 - Permalink


Charged hadrons and leptons identification at HADES
Kugler, A.; Agakishiev, H.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Bielcik, J.; Bohmer, J.; Braun-Munzinger, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Frohlich, I.; Garzon, J.; Gernhauser, R.; Golubeva, M.; Gonzales-Dias, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kampfer, B.; Kanaki, K.; Koenig, I.; Koenig, W.; Kolb, B.; Kotte, R.; Kotulic-Bunta, J.; Krucken, R.; Kuhn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lehnert, J.; Maiolino, C.; Markert, J.; Metag, V.; Mousa, J.; Munch, M.; Muntz, C.; Naumann, L.; Novotny, R.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy-Stephan, M.; Rustamov, A.; Sadovski, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Simon, R.; Smoliankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Strobele, H.; Stroth, J.; Sturm, C.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wojcik, T.; Wustenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.;
The HADES spectrometer installed at GSI Darmstadt is devoted to the study of the production of di-lepton pairs from vector meson decays in relativistic nucleus-nucleus collisions, as well as proton- and pion-induced reactions. Extraction of rare lepton pairs in high hadron multiplicity events requires an efficient particle identification (PID). In HADES charged particles momentum is measured by a tracking system surrounding the toroidal super conducting magnet, and velocity and energy loss is provided by a TOF detector. Leptons are identified by a Rich as well as a Shower detector. The particle identification method is using full experimental information from all subdetectors. To demonstrate the method performance, single particle spectra of charged hadrons and leptons from C+C at 2 AGeV will be presented and compared with results of corresponding simulations. The proton and pion yields an m_T and rapidity distributions will be compared with existing data. Very preliminary results of lepton analysis will be shown as well.
  • Open Access LogoActa Physica Slovaca 54(2004)4, 375-384

Publ.-Id: 7363 - Permalink


Liquid metal flows in AC and DC magnetic fields and its application to casting processes
Gerbeth, G.; Eckert, S.; Galindo, V.; Willers, B.;
Electromagnetic fields provide an attractive tool for a contact-less control of flows in metallurgical and crystal growth processes. The presentation starts with a classification of magnetic field actions on melt flows and with a summary of the recently developed velocity measuring techniques for opaque metallic melts. Emphasis will be given to the Ultrasonic Doppler Velocimetry (UDV) as it provides full profiles of the mean velocity and is applicable even through channel walls.
Based on such experimental and numerical modelling capabilities, we first consider the design and application of various magnetic fields for the inflow control of the mould filling process of aluminum investment casting. This process consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical 3d transient calculations were performed to simulate the filling process and the effect of the magnetic field. In parallel, model experiments with a plexiglas model have been performed using the low melting eutectic GaInSn. UDV was applied to carry out detailed velocity measurements in the model. Those measurements served for the validation of the numerical calculations, thus allowing to scale up the simulations to the realistic aluminium casting process. Tests with molten aluminium have been performed at an industrial investment caster. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly demonstrated. The amplitude of the DC field was tuned during the process as the braking action is only needed during the first part of the process. In this way, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time. Eventually, a remarkable diminishment of defects in the casting products was achieved.
A more active influence on the overall process can be obtained by application of a travelling magnetic field which brakes the flow at the beginning but allows to pump the melt at the end of the filling process. First numerical and experimental results will be presented showing the superimposed stirring action of such an electromagnetic pump besides its integral pumping action. For a homogeneous breaking or pumping a special design of the AC magnetic field is inevitable.
The application of electromagnetically driven flows during solidification improves the quality of casting ingots by promoting the formation of fine, equiaxed grains. However, the lack of detailed knowledge on the transient flow dynamics obstructs the optimisation of solidification processes by electromagnetic flow control and is consequently one of the reasons for the rather empirical application of melt agitation until now. Our results show that the forced convection influences significantly the concentration as well the temperature profile ahead of the solidification front. A flow effect can be supposed both on the presence of free nuclei in the melt and suitable conditions allowing them to grow as equiaxed crystals in competition with the columnar front.
  • Invited lecture (Conferences)
    The 2nd Workshop on Electromagnetic Processing of Materials (Asian-EPM2005), 22.-25.05.2005, Shenyang, China
  • Contribution to proceedings
    The 2nd Workshop on Electromagnetic Processing of Materials (Asian-EPM2005), 22.-25.05.2005, Shenyang, China
    Proceedings, 42-44

Publ.-Id: 7362 - Permalink


Controlling melt convection - an innovation potential for concerted microstructure evolution of Nd-Fe-B alloys
Filip, O.; Hermann, R.; Gerbeth, G.; Priede, J.; Biswas, K.;
The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed forced crucible rotation technique. Samples were subjected to well-defined forced rotation and vibration, respectively, during induction heating and solidification. A concerted microstructure evolution is possible by enhancement or suppression of the melt convection. As a result, the microstructure pattern, mainly the volume fraction of the soft magnetic a-Fe phase, vary strongly with the strength of the internal flow motion. A distinct reduction of the a-Fe volume fraction in samples with strong melt rotation was observed by measuring the magnetic moment. Moreover, the melt flow was studied numerically taking into account the coupled heat and fluid flow fields. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.
  • Lecture (Conference)
    International Conference on Advances in Solidification Processes, 07.-10.06.2005, Stockholm, Sweden
  • Materials Science and Engineering A 413-414(2005), 302-305

Publ.-Id: 7361 - Permalink


Computational study of flow and magnetic field interactions in Riga dynamo
Kenjeres, S.; Renaudier, S.; Hanjalic, K.; Stefani, F.;
Experimental set-ups for magnetohydrodynamic dynamo involve usually complex configurations of fluid flow and magnetic field, designed to achieve the critical magnetic Reynolds number sufficient for magnetic self-excitation, but with minimum energy input and at scales manageable in a laboratory. Computer simulations that could be used to optimize the design and to complement the experiments have, however, been limited to much simplified geometries and flow conditions, which inevitably limit their applicability. In this paper, we report on progress in the coupled finite difference (Maxwell solver)/finite volume (Navier-Stokes solver) computer simulations of the full-scale real Riga dynamo experiment
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    Proceedings 1(2005), 93-96

Publ.-Id: 7360 - Permalink


Unterstützung der ukrainischen Aufsichtsbehörde beim Ausbau der verbesserten betrieblichen KKW-Überwachung (Teil 3)
Beyer, M.; Carl, H.;
In Analogie zu den Systemen für die KKW Saporoshje und Rovno wurden für die drei Blöcke des KKW Südukraine und für den ersten Block des KKW Chmelnitzky technische Systeme zur verbesserten betrieblichen Überwachung eingerichtet. Dazu werden der Aufsichtsbehörde vor Ort und im Krisenzentrum in Kiew einmal pro Minute für jeden Block bis zu 51 sicherheitsrelevante technologische und 16 radiologische Parameter zur Bewertung mittels moderner technischer Ausrüstungen online zur Verfügung gestellt. Die entwickelte Auswertesoftware gestattet die Darstellung der Bewertungsergebnisse in Form von Tabellen, Grafiken und Schemata. Außerdem ermöglicht ein Archivmodus Trendanalysen.
Mit der Integration der für die geschützte Warte gelieferten Ausrüstungen in das am Standort des KKW Saporoshje betriebene Fernüberwachungssystem ist es nunmehr möglich, die wesentlichen sicherheitsrelevanten Parameter des gesamten Standortes auch bei außergewöhnlichen Ereignissen mit Hilfe moderner Technik zu erfassen und zu bewerten.
Keywords: monitoring, ukrainian NPP, nuclear safety
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-429 2005

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Publ.-Id: 7359 - Permalink


A paradigmatic model of Earth's magnetic field reversals
Stefani, F.; Gerbeth, G.; Günther, U.;
The phenomenon of sudden and irregular reversals of the Earth's magnetic field has attracted much interest in the last decades. It is known that the mean reversal rate varies from approximately zero in the Permian and Cretaceous supercrons to approximately 5 per Myr in the present. There is some observational evidence for the facts that the reversals are asymmetric in time and that the overall distribution of the field intensity has a bimodal behaviour. In an attempt to explain these features in a paradigmatic model we investigate a mean-field dynamo model of the alpha^2 type. Field saturation is guaranteed by alpha-quenching, and the influence of noise is taken into account. In order to keep the model simple and to allow for very long simulations, we choose the helical turbulence parameter alpha as spherically symmetric. We show that reversals occur in the vicinity of so-called exceptional points of the spectrum of the dynamo operator, where two real eigenvalues coalesce and continue as a pair of complex conjugate eigenvalues. We describe the reversal mechanism, and all the above mentioned features, in terms of a self-accelerating field decay, followed by the rapid recovery of the field with opposite polarity. We point out that the reversal mechanism can be attributed to the square-root character of exceptional points in the spectrum. Hence it is not restricted to our particular model but should be identifiable also in more realistic models of the Earth dynamo.
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    Proceedings 1(2005), 97-100
  • Magnetohydrodynamics 42(2006)2/3, 123-130

Publ.-Id: 7358 - Permalink


Experimental aspects of contactless inductive flow tomography
Gundrum, T.; Gerbeth, G.; Stefani, F.; Xu, M.;
Exposing a moving electrically conducting fluid to an external magnetic field, one can measure the induced magnetic field in the exteriour of the fluid with the aim to reconstruct the flow field of the fluid. The application of two different external fields represents a certain minimum for the identification of the main topological structure of the flow. After delineating the theory of this measurement method in the framework of the integral equation approach to kinematic MHD, we report on an experiment with a propeller driven flow of InGaSn. In the basic version of this experiment, an axial and a transverse external field are produced by two orthogonal pairs of Helmholtz coils. The externally induced fields are measured by Hall sensors at 49 positions which cover the vessel rather homogeneously. By comparison with ultrasonic Doppler measurements, the method is shown to provide correct and robust results on the main topological structure and the magnitude of the flow. First results of an alternative variant using one homogeneous and one cusp field are presented. The potential advantages of using AC fields instead of DC fields to achieve a better depth resolution and to make the method applicable in rough industrial environments are also indicated.
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    Proceedings 2(2005), 319-322
  • Magnetohydrodynamics 42(2006)2/3, 153-160

Publ.-Id: 7357 - Permalink


Annual Report 2003/04 - Radiation Source ELBE
Lehnert, U.; (Editor)
no abstract available
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-428 2005

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Publ.-Id: 7356 - Permalink


Verhalten des Radiums unter den Bedingungen des Endlagers für radioaktive Abfälle Morsleben
Baraniak, L.; Nebelung, C.;
Mit dem Ziel, die Migration des Radiums im Umfeld des Endlagers Morsleben zu beschreiben, wurde (1) die Löslichkeit des (Ra, Ba)SO4 in den spezifischen Salzlösun-gen (gesättigte NaCl-Lösung, Magnesialauge) bestimmt und (2) die Adsorption des Radiums am Leinetal-Sediment (grauer Salzton) untersucht.
Die Salzlösungen bestanden aus einer 5,35 molaren NaCl-Lösung und einer quinären Lösung mit den Bestandteilen Magnesium (3,8 molar), Kalium (0,8), Natrium (0,4) als Chlorid und Sulfat. Die Lösungen wurden mit den Verfüllmaterialien (Salzbeton und Magnesiabinder) und dem Salzton voräquilibriert.
Die Bestimmung der Löslichkeit wurde nach Einstellung des Löslichkeitsgleich-gewichts (über 360 Tage) durch Bestimmung des 226Ra in der gesättigten Lösung mit-tels Flüssig-Szintillations-Messung durchgeführt. Hierzu wurde zum einen ein Überschuss (226Ra, Ba)SO4 zur Salzlösung gebracht und zum anderen RaCl2-Lösung zugegeben, wobei mit dem in der Lösung vorhandenen Sulfat die Ausfällung des (226Ra, Ba)SO4 erfolgte. Die Gehalte an Barium wurden durch ICP-MS und die des Sulfats durch Ionenchromatografie ermittelt. Die vorkonditionierten Salzlösungen sind zu 95 bis 99% mit BaSO4 gesättigt. Weniger als 5% (Ra, Ba)SO4 lassen sich in diesen Lösungen noch zusätzlich auflösen („mobilisieren“). Die Auflösungen führen zu Ra2+-Konzentrationen im Bereich 1,2∙10-8 bis 4,7∙10-8 mol/l. Die Summenkonzentration von Ba2+ und Ra2+ liegt dann bei 1,1∙10-7 bis 1,3∙10-6 mol/l. Die nach der Ausfällung verbliebenen Ra2+-Konzentrationen sind geringer. Sie liegen im Bereich 1,2∙10-8 bis 4,7∙10-8 mol/l. Durch den Fällvorgang entstandene Übersättigungszustände werden abgebaut. Die hieraus folgenden Löslichkeitsprodukte liegen bei log Ksp,298 = 7,07 ± 0,21 im Falle der Auflösung und bei log Ksp,298 = 7,39 ± 0,21 bei der Ausfällung. Das Löslichkeitsprodukt für unendliche Verdünnung (-10,3 ± 0,1) [1,2] liegt um drei Größenordnungen niedriger.
Die Sorption des Radiums am Salzton wurde an Proben untersucht, die 1,5 bis 2,5 g Salzton in 15 ml Salzlösung enthielten. Die Ausgangskonzentration des Radiums in der flüssigen Phase lag bei 1,3∙10-9 mol/l. Die 226Ra-Konzentration verringerte sich im Zeitraum von etwa 400 Tagen auf 2,7∙10-10 bis 8,6∙10-10 mol/l. Dabei ist die Sorption aus der NaCl-Lösung mit Verteilungskoeffizienten (RS) von 9,6 bis 22,7 ml/g stärker als aus der Magnesialauge, für die RS-Werte von 4,4 bis 7,5 ermittelt wurden. Der Verlauf der Experimente zeigte, dass das Sorptionsgleichgewicht in keinem Falle erreicht war. Es zeigt sich, dass alle Ionenprodukte größer sind als das entsprechende Löslichkeits-produkt, d.h. sowohl die Ausgangslösungen als auch die Lösungen nach der Sorption liegen in jedem Falle im Zustand der Übersättigung vor. Außer der 226Ra-Sorption am Grauen Salzton wurde auch festes (Ra,Ba)SO4 ausgeschieden. Beide Mechanismen tragen im Belastungsfall zur 226Ra-Immobilisierung bei.
[1] Langmuir, D., Riese, A.C.: Geochim. Cosmochim. Acta 49 (1985) 1593.
[2] Paige, C.R. et al.: Geochim. Cosmochim. Acta 62 (1998) 15.

Förderung: BfS-Projekt: Nuklidmigration im Deckgebirge des ERAM, PSP-Nr.: 9M 212230-62.
Keywords: Sorption, Solubility, Radium, Morsleben radioactive waste disposal, near-field migration
  • Poster
    Jahrestagung Fachgruppe Nuclearchemie der GDCh, 12.-14.09.05, Düsseldorf, Deutschland
  • Contribution to proceedings
    GDCh-Jahrestagung 2005, Chemie schafft neue Strukturen, 11.-14.09.2005, Düsseldorf, Deutschland
    Kurzreferate, 3-936028-36-2, 544

Publ.-Id: 7355 - Permalink


Ion-driven magnetic nanostructures
Fassbender, J.ORC; Potzger, K.; Bischoff, L.; Zhou, S.; Talut, G.; Liedke, M. O.; Reuther, H.; Mücklich, A.; Grötzschel, R.
Recently it has been demonstrated that ion irradiation of ultrathin magnetic films and multilayer structures is a versatile tool to modify the magnetic properties of these systems in laterally confined areas [1–3]. In most cases the modification of the magnetic anisotropy or the different exchange coupling contributions present in multilayered films are due to a post deposition modification of the interface structure. Depending on the enthalpy of mixing light ion irradiation may result in a roughening or a sharpening of the interface on the atomic level. Due to the local nature of the ion-solid interaction these modifications can be restricted to confined areas resulting in magnetically patterned films without a modification of the surface topography.
An alternative route to ion-driven magnetic nanostructures relies on ion implantation. By doping magnetic thin films in a percentage range with Cr or rare earth transition metals either the Curie temperature [4] or the magnetic damping behavior [5] can be adjusted. In combination with focused ion beam techniques magnetic nanostructures can be written directly into the film structure. Applications in the area of patterned storage media are evaluated currently.
The third approach makes use of ion beam synthesis of magnetic nanoparticles in a nonmagnetic single crystalline oxide host matrix [6]. Magnetic ions are implanted into the host material which leads to a supersaturation of these ions. During implantation at elevated temperatures or a succeeding annealing step the metallic precipitates grow and form, depending on their size and structure, ferromagnetic nanoparticles.
The current status of these different techniques with respect to magnetic nanostructure formation will be reviewed.
References:
[1] C. Chappert, H. Bernas, J. Ferre, V. Kottler, J.-P. Jamet, Y. Chen, E. Cambril, T. Devolder, F. Rousseaux, V. Mathet, H. Launois, Science 280, 1919 (1998).
[2] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[3] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett., 86, 162502 (2005).
[4] L. Folks, R. E. Fontana, B. A. Gurney, J. R. Childress, S. Maat, J. A. Katine, J. E. E. Baglin, A. J. Kellock, J. Phys. D: Appl. Phys. 36, 2601 (2003).
[5] S. G. Reidy, L. Cheng, W. E. Bailey, Appl. Phys. Lett. 82, 1254 (2003).
[6] C. W. White, S. P. Withrow, J. M. Williams, J. D. Budai, A. Meldrum, K. D. Sorge, J. R. Thompson, L. A. Boatner, J. Appl. Phys. 95, 8160 (2004).
Keywords: magnetism, magnetic nanostructures, ion irradiation, ion implantation, nanostructures, ion beam synthesis, magnetic patterning
  • Invited lecture (Conferences)
    14th International summer school on vacuum, electron and ion technologies, 12.-16.09.2005, Sunny Beach, Bulgaria

Publ.-Id: 7354 - Permalink


Experimental study on the sensitivity and accuracy of electric potential local flow measurements
Cramer, A.; Varshney, K.; Gundrum, T.; Gerbeth, G.;
A measuring system based on potential difference probes is presented which makes possible the determination of very small values of the velocity in liquid metal flows. On the one hand, a large size of the sensor and a high induction of the static measuring field, respectively, and resolution on the other hand has always been a compromise. These opposite demands were countered with state of the art analog instrumentation, and by avoiding meticulously potential sources of error such as induced noise and the even more detrimental thermoelectricity. The present paper instances the flow driven by a rotating magnetic field, in which the scaling of velocity versus strength of the driving electromagnetic force was examined. The measurement of the transition from the Stokes regime to a laminar boundary one demonstrates the obtained improvement of the velocity resolution by about two orders of magnitude.
  • Flow Measurement and Instrumentation 17(2006), 1-11

Publ.-Id: 7352 - Permalink


Formation of Iron-containing Colloids by the Weathering of Phyllite
Zänker, H.; Hüttig, G.; Arnold, T.; Nitsche, H.;
The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to water. Secondary mineral colloids of 10E+1 to 10E+2 nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, aluminosilicates, amorphous Al(OH)3 and gibbsite with possible additions of iron silicates and iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock-water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity.
Keywords: weathering, colloids, phyllite, ferrihydrite, aluminosilicates, aluminum hydroxide, centrifugation, unsaturated zone, mine waste rock piles
  • Aquatic Geochemistry 12(2006)4, 299-325

Publ.-Id: 7351 - Permalink


Flux Effect on the Ion Beam Nitriding of Austenitic Stainless Steel AISI 304L
Abrasonis, G.; Rivière, J. P.; Templier, C.; Pranevičius, L.; Barradas, N.;
The effect of flux and Ar pretreatment during ion beam nitriding of austenitic stainless steel is investigated. The ion energy and temperature were 1.2 keV and 400°C, respectively, the ion current densities were 0.5, 0.67, and 0.83 mA∙cm-2. The nitrogen distribution profiles were measured using nuclear reaction analysis. The obtained nitrogen distribution profiles were analyzed by the means of the nitrided layer thickness evolution due to sputtering and diffusion and the model of trapping-detrapping. Both approaches could fit well the experimental results, however different diffusion coefficients have to be assumed for each current density. In addition, the diffusion coefficients are higher for higher current densities. On the other hand, it is shown that the pretreatment with Ar ion beam at nitriding temperatures produces only a thermal effect without any other influence on the following nitrogen diffusion. The results are discussed in relation with surface and temperature effects and atomic transport mechanisms.
Keywords: nitrogen implantation, stainless steel, diffusion, flux effect
  • Journal of Applied Physics 97(2005)12, 124906

Publ.-Id: 7350 - Permalink


Energiedispersive Untersuchung der Wechselwirkung schneller Neutronen mit Materie - gemeinsamer Abschlussbericht der DFG Projekte GR 1674/2 und FR 575/5
Altstadt, E.; Beckert, C.; Beyer, R.; Freiesleben, H.; Galindo, V.; Greschner, M.; Grosse, E.; Junghans, A.; Klug, J.; Naumann, B.; Schneider, S.; Seidel, K.; Wagner, A.; Weiß, F.-P.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-426 2005

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Publ.-Id: 7349 - Permalink


The application of FIB from mass separated alloy LMIS
Bischoff, L.;
During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range ion species other than gallium are needed. Therefore alloy liquid metal ion sources (LMIS) were developed. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMIS`s discussed above have been used for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB is applied for the ion beam synthesis of CoSi2 micro-structures down to 30 nm. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials. Especially this direct patterning was used for the fabrication of various kinds of micro-tools as well as recently for nano-holes in AFM cantilever tips.
Running and future activities will be discussed which are focused to the preparation and investigation of plasmonic structures, like nano-wires and nano-chains in the sub-micron scale down to a few ten nanometers.
Keywords: Focused Ion Beam, Alloy Liquid Metal Ion Source, ExB filter, micro-structures
  • Invited lecture (Conferences)
    nanoFIB 2005 - Advances in Focused Ion Beam Microscopy, 15.04.2005, Oxford, UK

Publ.-Id: 7348 - Permalink


Stability analysis of electromagnetically levitated spherical bodies in 3D coils
Priede, J.; Gerbeth, G.;
Electromagnetic levitation is a well-known technique for container-less processing of molten metals and their alloys. In experiments, the levitated bodies often exhibit various kinds of instabilities. In the simplest case of static instability, a small displacement of the body from its equilibrium position can cause the failure of levitation. In some other cases the levitated bodies are observed to start to oscillate with growing amplitude or rotate with increasing rate that also can result in failure of levitation. This work presents a theoretical study of oscillatory and rotational instabilities of a solid sphere levitated electromagnetically in 3D coil systems. We have developed a combined numerical and analytical approach to analyze the static and dynamic stability of a sphere depending on the AC frequency and configuration of the magnetic system which is modeled by linear current filaments. First, we calculate numerically the magnetic vector potential in a number of points on the surface of the sphere and use Legendre and fast Fourier transforms to find the expansion of the magnetic field in spherical harmonics about the center of the body. Second, the numerically obtained expansion coefficients are substituted into the analytic solution describing the perturbation of the total electromagnetic force depending on both the displacement of the body from its equilibrium position and its velocity of motion. Thus we find the effective electromagnetic stiffness coefficients which characterize the frequency of small-amplitude oscillations of the body. Each equilibrium position is characterized by three mutually orthogonal principal directions of oscillations and three corresponding principal stiffness coefficients which all have to be positive for the equilibrium state to be statically stable. Dynamic instabilities are characterized by critical AC frequencies which, when exceeded, may result either in a spin-up or oscillations with increasing amplitude. The effective electromagnetic friction coefficients which are usually small are found by classical perturbation theory approach. For the spin-up instability we propose a new theoretical model applicable for arbitrary field configurations. This model yields three critical AC frequencies for rotations around three mutually orthogonal principal axis found respectively as eigenvalues and eigenvectors of the effective electromagnetic friction coefficient matrix. Our approach may be useful for analysis and design of electromagnetic levitation systems.
  • Poster
    8th International Symposium on Magnetic Suspension Technology, 26.-28.09.2005, Dresden, Germany

Publ.-Id: 7345 - Permalink


Influence of melt convection on microstructure evolution of Nd-Fe-B alloys using forced crucible rotation technique
Biswas, K.; Hermann, R.; Filip, O.; Werner, J.; Gerbeth, G.; Priede, J.;
The forced crucible rotation technique has been applied to the solidification of Nd-Fe-B alloys. Specially sealed samples were subjected to well-defined forced rotation during induction heating and solidification. The resulting microstructure of the Nd-Fe-B alloys in consideration of melt convection has been investigated using scanning electron probe microscopy. The determination of the α-Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the α-Fe volume fraction in samples with high crucible rotation frequencies. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields.
  • Lecture (Conference)
    Tagung der Deutschen Physikalischen Gesellschaft, 09.03.2005, Berlin, Germany

Publ.-Id: 7344 - Permalink


Computertomographische Untersuchung von Phasenverteilungen in chemischen Rührkesselreaktoren
Boden, S.;
Für die Untersuchung von mehrphasigen Strömungen steht am Forschungszentrum Rossendorf eine Röntgenanlage mit einem zweidimensionalen Bildaufnehmer und einer eindimensionalen schnellen Detektorzeile zur Verfügung. In dieser Arbeit soll die Eignung dieser Anlage zur Bestimmung der lokalen Gasphasenverteilung in einem begasten chemischen Rührkesselreaktor, der aus der Verfahrenstechnik her bekannt ist, untersucht werden. Dazu wird zunächst die Signalcharakteristik des Aufnahmesystems untersucht, um die zu erwartende Genauigkeit der tomographischen Messung beurteilen zu können. Ein Algorithmus für die Rekonstruktion von zwei- und dreidimensionalen Projektionsdaten wurde implementiert. Mit einem Phantom wurde die quantitative Genauigkeit der Bestimmung zeitgemittelter Gaspahsenanteile überprüft. Zur Korrektur der Strahlaufhärtungsartefakte wurde eine Kalibriermethode entwickelt, mit der es möglich ist, die Gasphasenanteile direkt aus den bestimmten Schwächungskoeffizienten zu bestimmen. Es konnte gezeigt werden, dass die quantitative Genauigkeit der Kegelstrahl-Tomographie durch den hohen Anteil an Streustrahlung beeinträchtigt ist. Mit der schnellen Detektorzeile wurden schnell rotierende Objektstrukturen sichtbar gemacht.
Keywords: two-phase flow, x-ray, cone-beam computer tomography
  • Other report
    Dresden: Diplomarbeit Technische Universität Dresden/ Fakultät Elektrotechnik und Informationstechnik, 2004
    82 Seiten

Publ.-Id: 7343 - Permalink


Concepts to determine geochemical heterogeneity within a multi component biofilm by microsensors
Krawczyk-Bärsch, E.; Herrmann, S.; Großmann, K.; Vonau, W.; Arnold, T.;
Bacteria in nature do not usually occur as single individual bacterial cells but rather in large communities of bacteria glued together by Extracellular Polymeric Substances (EPS). Such aggregates are called biofilms. They may significantly influence the transport of heavy metals in the geosphere by changing the geochemical conditions within the biofilm or simply by adsorption onto biological surfaces. For these biofilm studies we generate thick biofilms in a rotating annular bioreactor that provides a well mixed liquid phase, turbulent flow and constant shear fields [1]. For biofilm sampling, removable microscopic slides with affixed mineral platelets are placed in recessed slots on the outside of the inner cylinder. These slides can be removed via a port in the top of the reactor. The nutrient solution includes a bacteria cocktail (Pseudomonas stutzeri, Pseudomonas fluorescens, Flavobacterium aquatile, Bacillusus thuringiensis) was pumped through the reactor at 0.02 mL per minute into the base of the reactor, triggering a circulation from bottom to top at room temperature. After the experiment the mature confluent biofilm was removed from the reactor and the biofilm thickness of approximately 150 µm was determined by using Confocal Scanning Laser Microscopy (CLSM).

To measure the electrochemical conditions such as redox potential and/or pH in situ within the biofilm and in the surrounding bulk solution an experimental setup has been developed. Previous work has been carried out by means of several sensors, mainly focused on the interface basis material/biofilm to investigate microbial induced corrosion [2]. Because of low lateral dimensions for an analytical study of concentration profiles in biofilms only micro sensors with extremly small diameters are applicable. It is essential that the biofilm is not affected by the use of the grooved sensor and that the front surface exclusively acts sensitively. In our experiments an investigation concept is introduced, where the electrochemical micro sensor forms a unit with an integrated micrometer screw (advantage: not rotable spindle). In this way during the measurement the micro sensor can be moved in the biofilm in µm-steps vertically. The sensor systems to determine the redox potential and the pH value consist of indicator electrode and reference electrode, which are arranged sidewise and possess a ceramic diaphragm. The applied redox sensors have been developed in different constructions. On the one hand glass coated Pt sensors with an outer diameter of 300 µm have been constructed; on the other hand we applied micro sensors covered with wax and resin having an outer diameter of 120 µm. In both cases the diameter of the sensitive area amounts to 80 µm.
In our experiments we used the newly constructed micro sensors to determine the redox potentials and pH values within the biofilm generated in the rotating annular bioreactor. In the near future it is planned to develop micro sensors for measuring concentration gradients of other substances such as Cl- and NO3- [3], too.
Keywords: biofilm, microsensors, redox potential
  • Contribution to proceedings
    BioPerspectives 2005, 10.-12.05.05, Wiesbaden, Germany
  • Poster
    BioPerspectives 2005, 10.-12.05.05, Wiesbaden, Deutschland

Publ.-Id: 7342 - Permalink


Atomistic simulation of ion irradiation, ion-beam-induced defect formation and defect migration
Posselt, M.;
Ion implantation and subsequent thermal annealing are the standard processes for the electrical doping of semiconductors. Ion implantation is characterized by fast ballistic processes which lead to the deposition of the implanted atoms and to displacements of the target atoms. After the fast relaxation of the displaced atoms a (meta)stable defect structure is formed. Long-term thermally activated processes, especially during thermal annealing, cause defect reduction, rearrangement, and migration. In my talk I will show that computer simulations on the atomic level are a useful tool for the theoretical description of the different physical processes occurring during ion implantation and thermal annealing. The ballistic processes are simulated by the Crystal-TRIM code which is based on the binary collision approximation (BCA). This code is part of different process simulators. Classical molecular dynamics (MD) simulations are employed to investigate defect migration over a period of 10 - 100 ns. The defect diffusivity as well as the microscopic migration mechanisms are studied. A combination of BCA and MD simulations is used to determine the complex defect morphology after the fast relaxation processes are finished. This method allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion.
Keywords: atomistic computer simulation, ion irradiation, defects, silicon
  • Lecture (others)
    eingeladener Vortrag, 20.04.2005, Bern, Schweiz

Publ.-Id: 7341 - Permalink


High-power short-wavelength quantum cascade lasers
Masselink, W. T.; Semtsiv, M. P.; Dressler, S.; Ziegler, M.; Georgiev, N.; Dekorsy, T.; Helm, M.;
We describe the design and implementation of a broad-gain and low-threshold (Jth = 860 A/cm2 at 8 K) quantum-cascade laser based on strain-compensated In0.73Ga0.27As-AlAs on InP. Laser emission between 3.7 and 4.2 um is achieved because of the very large Gamma-valley conduction band discontinuity with narrow quantum wells, allowing large intersubband energy differences. Furthermore, the design inhibits carrier loss from the upper lasing state into the continuum even at elevated operating temperatures, resulting in room-temperature operation. Laser operation in pulsed mode is achieved up to a temperature of 330 K with maximum single-facet output peak powers of 6 W at 8 K and 240 mW at 296 K. The temperature coefficient T0 is 119K. The 30-period structure exhibits an external differential efficiency of 13 (40% per period) at low temperatures and a maximum wall-plug efficiency of 24%. The lasing transition takes place from several upper states to several lower states, resulting in a relatively broad (300 cm-1) gain spectrum and could allow the design to be used in external tuning configurations.
Keywords: quantum cascade laser, infrared, intersubband
  • Proceedings- SPIE The International Society for Optical Engineering 5738(2005), 13-24
    DOI: 10.1117/12.591738
  • Invited lecture (Conferences)
    Photonics West, 22.-27.01.2005, San Jose, CA, USA

Publ.-Id: 7340 - Permalink


Thermo-mechanical design of a photoneutron source for time-of-flight experiments
Altstadt, E.; Beckert, C.; Galindo, V.; Naumann, B.; Weiss, F.-P.;
At the radiation source ELBE (Electron accelerator producing a quasi-continuous electron beam of high Brilliance and low Emittance) of the FZR a neutron source is being constructed. The electron beam with energies of up to 40 MeV and pulse frequencies of up to 13 MHz is converted into sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator with a small volume. The neutrons are generated by bremsstrahlung photons through (gamma,n)-reactions. The energy deposition of the electron beam in the small neutron radiator is that high that any solid material would melt. Therefore, the neutron radiator consists of liquid lead flowing through a channel of 11.2×11.2 mm² cross section. From the thermal and mechanical point of view molybdenum turned out to be the most suited channel wall (thickness 0.5 mm) material. Depending on the electron energy and current up to 20 kW power will be deposited into a radiator volume of 3 cm³. This heating power is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are in the range of 2 m/s in the radiator section. The electrons escaping from the radiator and the secondary radiation are dumped to a large extent in an aluminum beam dump. To reduce the radiation background in the measuring direction, the neutrons are decoupled from the radiator at an angle of 90° with respect to the impinging electrons.
Particle transport calculations were carried out to determine the volumetric heat generation in the liquid lead, in the channel wall and in the Al beam dump. Subsequent fluiddynamic and thermo-mechanic finite element analyses are performed to proof the mechanical integrity of the radiator channel. It could be shown that the equivalent plastic strain of the radiator channel can be kept sufficiently small, i.e. less than 1 %. Thermal analyses of the water cooled Al beam dump proved, that the maximum temperatures do not exceed 200 °C, thus a sufficient distance from the melting point is maintained.
Keywords: Neutron source, Finite-Element-Method, Thermal Load, Electron Beam
  • Contribution to proceedings
    18th International Conference on Structural Mechanics in Reactor Technology (SMiRT 18), 07.-12.08.2005, Beijing, China
  • Lecture (Conference)
    18th International Conference on Structural Mechanics in Reactor Technology, 07.-12.08.2005, Beijing, China

Publ.-Id: 7339 - Permalink


Detection of U(VI) on the Surface of Altered Depleted Uranium by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS)
Baumann, N.; Arnold, T.; Geipel, G.; Trueman, E.; Black, S.; Read, D.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the surface of a depleted uranium (DU) disc immersed in a Ca-phosphate solution for 182 days. The weathering solution contained 2.49 · 10-3 M calcium and 1.05 · 10-3 M phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that meta-autunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. This secondary U(VI) mineral phase was identified using a fingerprinting procedure by comparing it with TRLFS-spectra from an in-house U(VI) TRLFS database, including U(VI) oxides, U(VI) hydroxides, U(VI) sulphates and U(VI) phosphates. Its TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50 ± 5 ns and 700 ± 25 ns.
Keywords: Depleted uranium, TRLFS, meta-autunite

Publ.-Id: 7338 - Permalink


The potential of ion irradiation for the creation of artificial magnetic structures
Fassbender, J.ORC
Ion irradiation is a versatile tool to modify magnetic properties like anisotropy or exchange coupling in thin magnetic films and multilayers on a local scale. The presentation will review the present status of magnetic anisotropy and domain patterning in amorphous CoFeSiB films and the ion irradiation induced phase transformation in FePt nanoparticle systems.
Keywords: magnetism, ion irradiation, magnetic anisotropy, exchange coupling, phase transformation, magnetic domains
  • Lecture (others)
    Seminarvortrag, 01.06.2005, Argonne, USA

Publ.-Id: 7337 - Permalink


Magnetization Dynamics
Fassbender, J.ORC
Review about the present status regarding magnetization dynamics investigations of magnetic tunnel junctions and exchange bias systems.
Keywords: magnetism, magnetization dynamics, exchange bias, magnetic tunnel junctions, time-resolved, MOKE
  • Lecture (others)
    Evaluierung von Beschichtungs- und Oxidationsverfahren für Tunnel-Schichtsysteme, 19.04.2005, Kahl, Deutschland

Publ.-Id: 7336 - Permalink


CFD-modelling of subcooled boiling and application to simulate a hot channel of a fuel assembly
Krepper, E.; Egorov, Y.;
The paper contributes to the advanced CFD simulation of subcooled boiling in forced convective flows, with special attention given to the momentum transfer between continuous liquid and vapour bubbles. A wall boiling model, implemented in CFX-5 (Egorov, Menter, 2004) and based on the two-fluid approach, is used here together with the state-of-the-art model correlations for the non-drag forces, available in CFX-5. The paper describes the main concepts of modelling mass, heat and momentum transfer between the phases. Published experimental results for flow in a pipe are used for the model validation.
The model is applied to the simulation of subcooled boiling flow in a hot channel of a fuel rod bundle. Influence of mixing vanes, attached to the spacer grids of fuel assembly in order to enhance the heat transfer, is taken into account. The simulation results demonstrate the capability of the model to estimate the effects of geometrical design on the flow physics.
Keywords: CFD, two-fluid model, momentum transition, boiling
  • Lecture (Conference)
    13th International Conference on Nuclear Engineering, ICONE-13, 16.-20.05.2005, Beijing, China
  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 16.-20.05.2005, Beijing, China

Publ.-Id: 7333 - Permalink


Ion implantation in silicon: limits of the +1 model
Kögler, R.;
High energy, high dose Ge ion implantation in silicon results after rapid thermal annealing in a defect structure which shows a stacked structure consisting of sequential layers of vacancy-type defects (cavities) and interstital-type defects (dislocation loops). This structure is in contrast to the predictions of the so called +1 model. The conditions for the formation of such defects and the limits of the +1 model are discussed.
Keywords: Ion implantation, silicon, Ge, +1 model
  • Lecture (Conference)
    43. Arbeitstreffen “Punktdefekte”, 02.-03.03.2005, Dresden, Deutschland

Publ.-Id: 7331 - Permalink


Investigation of gettering effects in CZ-type silicon with SIMS
Krecar, D.; Fuchs, M.; Kögler, R.; Hutter, H.;
Ion implantation is a well-known standard procedure in electronic device technology for precise and controlled introduction of dopants into silicon. However, damage caused by implantation acts as effective gettering zones, collecting unwanted metal impurities. This effect can be applied for "proximity gettering reducing the concentration of impurities in the active device region. In this study the consequences of high-energy ion implantation into silicon and of subsequent annealing were analysed by means of secondary ion mass spectrometry (SIMS). Depth profiles were recorded of such impurities as copper, oxygen and carbon to obtain information about their gettering behaviour. The differences in impurities gettering behaviour were studied as a function of the implanted ions, P and Si, of the implantation dose and annealing time at T=900degreeC. Besides impurities gettering at the mean projected range (Rp) of implanted ions, Rp-effect, defects at around half of the projected ion range, Rp/2-effect, and even in some cases beyond Rp, trans-Rp-effect, have also been found to be effective in gettering of material impurities.
Keywords: Ion implantation
  • Poster
    13th Arbeitstagung Angewandte Oberflächenanalytik (AOFA), 14.-17.09.2004, Dresden, Deutschland

Publ.-Id: 7330 - Permalink


Computertomografie für Mehrphasenströmungen
Hampel, U.;
Der Vortrag gibt einen Überblick über die Anwendung der Computertomografie mit Röntgen- und Gammastrahlung bei der Untersuchung von Mehrphasenströmungen in hydrodynamischen Maschinen sowie thermohydraulischen und verfahrenstechnischen Anlagen.
  • Invited lecture (Conferences)
    Ehrenkolloquium an der Hochschule Zittau/Görlitz, 15.04.2005, Zittau, Germany

Publ.-Id: 7328 - Permalink


Application of the Master Curve approach on WWER-440 reactor pressure vessel steel of the nuclear power plant Greifswald unit 8
Viehrig, H.-W.; Wallin, K.; Murasov, M.;
The Master Curve (MC) approach of defining reference transition temperature, T0, has been standardized in ASTM Standard Test Method E 1921. This approach has been gaining acceptance in the codes for reactor pressure vessel (RPV) integrity assessment throughout the world. T0 is calculated from a data set of J-integral based fracture toughness values measured in the lower ductile-to-brittle transition region. This direct measurement approach is preferred over the correlative and indirect methods used in the past to assess irradiated RPV integrity. The basic MC approach for analysis of fracture test results is intended for macroscopically homogeneous steels with a body centred (ferritic) structure only. In reality, the steels in question are seldom fully macroscopically homogeneous.
The fracture toughness values measured on Charpy size SE(B) specimens of base metal from the Greifswald Unit 8 RPV show a large scatter. The basic MC evaluation following ASTM E1921 supplies a MC with many fracture toughness values which lie below the 1% fracture probability line. Thus, some inhomogeneity may still exist in the data set. In this paper, new comparatively simple extensions of the MC are applied on these fracture toughness data. The structural integrity assessment procedure SINTAP contains a lower tail modification of the MC analysis. A random estimation method describes the fracture toughness distribution following a Gaussian distribution with infinite quality steps oscillating around a normal distribution. With the application of the SINTAP modification and the random estimation higher reference temperatures were estimated in comparison to the basic MC approach according to ASTM E1921.
Keywords: cleavage fracture toughness, Master Curve approach, reactor pressure vessel steel, maximum likelihood,reference temperature
  • Lecture (Conference)
    The 4th International Conference “Safety Assurance of Nuclear Power Plants with WWER”, 22.05.2005, Podolsk, Russia

Publ.-Id: 7327 - Permalink


188Re complexes based on novel chelators derived from dimercaptosuccinic acid
Pietzsch, H.-J.; Heinrich, T.; Kraus, W.; Seifert, S.; Spies, H.;
This work is part of our efforts to develop chelating agents for stable binding and easy conjugation of 188Re to biologically interesting structures. Keeping in mind the high in vivo stability of [188ReO(DMSA)2]- [1] we want to exploit this coordination system for the design of 188ReO(V) chelates which are stable towards re-oxidation to perrhenate and towards ligand exchange under all conditions of radiopharmaceutical procedures and applications.
The new type of tetradentate ligand has been synthesized by bridging two molecules of dimercapto-succinic acid (DMSA) with an alkylene triamine chain. The resulting stereo-isomeric tetrathiolato S4 ligand 1 forms five-coordinate oxorhenium(V) complexes by ligand exchange reaction of NBu4[ReOCl4] in methanol. Without addition of base the compounds will be isolated as “betain”, [ReO(S4)], with the protonated nitrogen of the bridge as internal “counter ion”.
The activated BFCA 2 enables easy linking of biomolecules containing a terminal amino group. Prototypic model conjugates with tripeptides have been identified in non-radioactive form by electrospray mass spectrometry.
The 188Re labelling procedure runs fast, in good yields and under mild conditions, making the new complexes interesting as a further access to stable 188Re radio-therapeutics.
  • Lecture (Conference)
    „Radiotracers for In vivo Assessment of Biological Function New Directions“, 22.-23.04.2005, Warschau, Poland

Publ.-Id: 7326 - Permalink


Novel Computational Chemistry for Molecular Design of Radioactive Metal Complexes
Yoshizuka, K.; Pietzsch, H.-J.; Seifert, S.; Stephan, H.;
We are now developing a novel molecular modelling of Re and Tc complexes combined with the molecular mechanics and the molecular dynamics for estimating the partition coefficient of these complexes between water and 1-octanol (LogP). The MM potential parameters developing with MOMEC program were fitted to all relevant X-ray crystal structures of [TcO(DMSA)2]- and [ReO(DMSA)2]- (DMSA: dimercaptosuccinic acid). The MM potential parameters were transferred to that in the MD program, MASPHYC. The MD simulations also indicate that a quantitative structure property relationship (QSPR) is obtained, which relates the internal energy difference between the Tc/Re-DMSA complexes in water phase and that in 1-octanol phase with experimental LogP value.
  • Lecture (Conference)
    International Solvent Extraction Conference, 19.-23.09.2005, Beijing, China
  • Contribution to proceedings
    International Solvent Extraction Conference, ISEC, 19.-23.09.2005, Beijing, China
    Proceedings of the International Solvent Extraction Conference, 424-428

Publ.-Id: 7325 - Permalink


Dilepton analysis in the HADES spectrometer for C+C at 2 A GeV
Bielcik, J.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bellia, G.; Böhmer, M.; Boyard, J.; Braun-Munzinger, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Djeridi, R.; Dohrmann, F.; Duran, I.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kotte, R.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lehnert, J.; Maiolino, C.; Markert, J.; Metag, V.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Novotny, R.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Pant, L. M.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Pvrzygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Simon, R.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zovinec, D.; Zumbruch, P.; Hades Collaboration;
The high-acceptance dielectron spectrometer (HADES) has become operational at GSI Darmstadt. The primary physics programme is to study in-medium changes of light vector mesons via their e+e- decays. The methods of dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 A GeV are presented. In the signal reconstruction, particularly important is the reduction of the huge combinatorial background arising from e+e- combinations of leptons from gamma conversion in materials with other leptons in the collision. The purity of the dilepton signal is determined by using GEANT simulations with the full HADES geometry and a realistic detector response.

Publ.-Id: 7324 - Permalink


Doping magnetic materials - tunable properties due to Cr ion implantation
Fassbender, J.ORC; McCord, J.; Mattheis, R.; Potzger, K.; Mücklich, A.; von Borany, J.
Various magnetic properties like the saturation magnetization, the Curie temperature, the coercivity and the magnetic damping behavior can easily be modified by means of ion irradiation and implantation. In combination with focused ion beam techniques even a pure magnetic patterning without changing the surface topography becomes feasible. A magnetic domain pattern can be imprinted by using ion irradiation in an applied magnetic field. Thus doping of magnetic materials opens a route to a new class of artificial magnetic materials with adjustable magnetic properties.
Here, as an example, we report on the tailoring of the magnetic properties of Permalloy (20 nm Ni81Fe19) by means of 30 keV Cr implantation. Due to the doping the Curie temperature of the Permalloy film decreases with the implantation fluence and drops below room temperature at an averaged Cr concentration of about 7 at-%. Also the saturation magnetization and the uniaxial anisotropy decrease. However the magnetic damping behavior of Cr implanted Permalloy films is strongly enhanced which is due to a combination of structural changes and alloying effects in the thin film. In order to clarify the basic mechanism for the enhancement the chemical and structural contributions to the magnetic damping parameter are separated by a comparison to results of 30 keV Ni implantation.
Keywords: magnetism, ion implantation, magnetic anisotropy, Curie temperature, magnetization dynamics
  • Poster
    348. Heraeus-Seminar "Ions at Surfaces: Patterns and Processes", 19.-23.06.2005, Bad Honnef, Deutschland

Publ.-Id: 7323 - Permalink


Magnetic anisotropy and domain patterning by means of ion irradiation
McCord, J.; Fassbender, J.ORC; Frommberger, M.; Liedke, M. O.; Quandt, E.; Schultz, L.
The control of magnetic properties and anisotropy in ferromagnetic thin films is of importance for many applications in spin electronics. Usually the uniaxial anisotropy in ferromagnetic alloys is set by applying a magnetic in-plane field during thin film deposition or adjusted by magnetic field annealing. In addition to temperature treatment, the alteration of magnetic properties in magnetic thin films by ion irradiation has gained increasing attention in recent years. However, most of the experiments focus on magnetic sandwiches or multilayers, where the magnetic properties depend strongly on the interface structure [1].
Here, we describe how to modify and tune the magnetic anisotropy axis and strength in single layer amorphous FeCoSiB soft magnetic films by ion irradiation with Co- and He-ions locally. Depending on the fluence and field angle during irradiation the uniaxial anisotropy can be realigned in the case of He-ion irradiation [2]. For Cobalt-implantation an increase of uniaxial anisotropy field with increasing fluence by more than a factor of two relative to the as-deposited anisotropy value (from Hk  15 Oe to Hk  40 Oe) is found. The ion treatment is used to “anneal” the films locally and thus to tailor the magnetic properties laterally. Periodic magnetic structures, consisting of regions of alternating anisotropy axis and strength, are generated using photo-lithographic processing. For that reason the films are partially masked with photo resist, patterned by optical lithography, and then irradiated with ions. Depending on the processing conditions and the size of the magnetic patterning, varying from mm in size down to sub-micrometer patterns, different kind of magnetic structures develop. The magnetization is modulated in accordance with the induced lateral anisotropy distribution. However, the domain walls do not align with the boundaries of the structures. Different types of periodic but rather complicated domain patterns are generated under different applied field conditions. The local change of magnetic properties due to the mixed anisotropy is limited by the micromagnetic feature size, not by the structural feature size. By structuring with a feature size smaller than the magnetic length scales, materials with novel magnetic properties are designed.

References
[1] J. Fassbender, D. Ravelosona, and Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M.O. Liedke, M. Frommberger,
E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
Keywords: magnetism, ion irradiation, magnetic anisotropy, magnetic domains, amorphous films, Kerr microscopy
  • Poster
    348. Heraeus-Seminar "Ions at Surfaces: Patterns and Processes, 19.-23.06.2005, Bad Honnef, Deutschland

Publ.-Id: 7322 - Permalink


Asymmetric polarity reversals, bimodal field distribution, and coherence resonance in a spherically symmetric mean-field dynamo model
Stefani, F.; Gerbeth, G.;
Using a mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha which is algebraically quenched and disturbed by additional noise, the basic features of geomagnetic polarity reversals are shown to be generic consequences of the dynamo action in the vicinity of exceptional points of the spectrum. This simple paradigmatic model yields long periods of constant polarity which are interrupted by self-accelerating field decays leading to asymmetric polarity reversals. It shows the recently discovered bimodal field distribution, and it gives a natural explanation of the correlation between polarity persistence time and field strength. The dependence of the persistence time on the noise shows typical features of coherence resonance.

Publ.-Id: 7321 - Permalink


Field-tuned quantum critical point in CeCoIn5 near the superconducting upper critical field
Ronning, F.; Capan, C.; Bianchi, A.; Movshovich, R.; Lacerda, A.; Hundley, M.; Thompson, J.; Pagliuso, P.; Sarrao, J.;
We report a systematic study of high-magnetic-field specific heat and resistivity in single crystals of CeCoIn5 for the field oriented in the basal plane (H parallel to ab)of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T-2 law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H parallel to c), the emergent picture is that of a magnetic-field-tuned quantum critical point which exists in the vicinity of the superconducting H-c2(0) despite a variation of a factor of 2.4 in H-c2(0) for different field orientations. This suggests that an underlying physical reason exists for the superconducting H-c2(0) to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi-liquid ground state with increasing magnetic field is more!
gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in plane. Together with the close proximity of the quantum critical point and H-c2(0) in CeCoIn5 for both field orientations, the anisotropy in the recovery of the Fermi-liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical.
Keywords: UNCONVENTIONAL SUPERCONDUCTIVITY; HIGH-PRESSURE
  • Physical Review B 71(2005), 104528

Publ.-Id: 7320 - Permalink


RBS/Channeling-Messungen mit dem Mikrostrahl zur Untersuchung der Strahlenschaden-Akkumulation in Silizium durch Ionen-Implantation
Grambole, D.; Herrmann, F.; Dagkaldiran, Ü.; Meijer, J.;
Um die bisherigen Untersuchungen zur Strahlenschaden-Akkumulation in Silizium durch Ionen-Implantation auf sehr hohe Ionenstromdichten zu erweitern, wurden (100) Si-Proben mit 600 keV Si+ -Ionen mit einer Stromdichte von 360 µA/cm² (2.2 x 1015 Si/s/cm²) bei Substrattemperaturen von 50°C bis 400°C bis zu einer Fluenz von 1018 Si/cm² implantiert. Die Implantation erfolgte mit dem Bochumer supraleitenden Ionenprojektor [J. Meijer, A. Stephan, Microelec. Eng. 41/42 (1998) 257]. Die Schädigung des Si-Kristalls in den implantierten Flächen von 185 µm Durchmesser wurde mit Hilfe der RBS/Channeling-Methode (3 MeV He-Ionen) an der Rossendorfer Mikrosonde untersucht. Für diese Messungen wurde eine zweite Messkammer mit einem 4-Achsen-Goniometer hinter der sonst zur Ionenstrahlanalytik genutzten Messkammer installiert. Die beobachtete deutliche Abhängigkeit der Strahlenschaden-Akkumulation bis hin zur kompletten Amorphisierung der bestrahlten Schicht von der Substrattemperatur und Fluenz wird diskutiert.
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und - technologie", 11.-12.04.2005, Leipzig, Deutschland

Publ.-Id: 7319 - Permalink


Natural circulation and stability performance of BWRs (NACUSP)
Aguirre, C.; Caruge, D.; Castrillo, F.; Dominicus, G.; Geutjes, A. J.; Saldo, V.; van der Hagen, T. H. J. J.; Hennig, D.; Huggenberger, M.; Ketelaar, K. C. J.; Manera, A.; Munoz-Cobo, J. L.; Prasser, H.-M.; Rohde, U.; Royer, E.; Yadigaroglu, G.;
From the beginning of BWR technology it was realized that a BWR can become unstable under particular circumstances caused by a feedback between the thermal-hydraulics and the neutronics. This instability can result in oscillations of the power and the flow rate, which is an unwanted phenomenon.

The NACUSP project addresses the stability issues in current and future BWRs by expanding the basic understanding through well structured testing and analyses of experimental data, by analyses of existing operational stability data from three different European reactors (Forsmark, Leibstadt, Cofrentes), by applying this knowledge via efficient models and validated computer codes to operating reactors and reactor designs, and by developing general guidelines for reactor operation and design on how to avoid BWR instabilities.
In order to cover the parameter range as efficiently as possible, four existing, sophisticated thermohydraulic test facilities (CLOTAIRE, DESIRE, CIRCUS and PANDA) have been selected. To extrapolate from small-scale separate-effect testing conditions to full-scale integral reactor conditions one needs to rely on the performance of computer codes (MONA, ATHLET , RAMONA-3(-5), LAPUR-V, DWOS, FLICA, SAPHYR, RELAP5/MOD3,TRAC-BF1). For specific items CFD codes are applied as well. Within NACUSP a linear stability analysis tool is developed.
Four of the three experimental facilities within the project have yielded a large, unique database.
Natural-circulation and stability characteristics at nominal pressure were collected from extensive experiments at the DESIRE facility. Low-pressure characteristics were measured at the PANDA (large scale) and the CIRCUS (small scale) facility.
The phenomena encountered (flow rate and stability trends, the occurrence of flashing induced oscillations) can be explained from basic physical models and are now well understood.
Several thermal-hydraulic codes have been benchmarked—some successfully, others with limited success—against these data.
The CLOTAIRE (nominal pressure, large scale) facility has been modified and is now ready for experiments.
Nuclear power plant data from three BWRs (Cofrentes, Forsmark and Leibstadt) have been collected. A very complete set of reactor data was obtained from measurements at the Leibstadt BWR during cycle-19. During this test, which was performed within the NACUSP project, safe reactor operation was demonstrated at extreme conditions, covering the entire power-flow map.
State-of-the-art, coupled thermal-hydraulic—neutronics codes are being benchmarked on these data.
The development of an easy to use, rapid and efficient analytical tool for parametric studies on BWR stability is in progress.
The last year of NACUSP will be devoted to finalising the before mentioned activities and to use the tools developed and the experience obtained for developing general guidelines for designing and operating BWRs.
Keywords: natural circulation, BWR, instability
  • Nuclear Engineering and Design (2005)235, 401-409

Publ.-Id: 7318 - Permalink


Experiments on the magnetic damping of an inductively stirred liquid metal flow
Bojarevics, A.; Cramer, A.; Gelfgat, Y.; Gerbeth, G.;
This work is concerned with the stabilisation of both the bulk liquid metal flow and the free surface shape in inductively heated melts. Steady magnetic fields of different orientation were used to damp fluctuations generated by an external alternating magnetic field as it is typical for an induction heater. This superposition of a driving alternating with a braking steady magnetic field was investigated experimentally at a low temperature isothermal model utilising a rectangular fluid volume in an induction--furnace--like setup fed by a current of intermediate frequency. Local velocity measurements in the liquid metal revealed quite different damping characteristics for steady fields aligned either normal or parallel to the melt surface.
  • Experiments in Fluids 40(2006)2, 257-266

Publ.-Id: 7317 - Permalink


Annual Report 2004 - Institute of Bioinorganic and Radiopharmaceutical Chemistry
van den Hoff, J.; Seifert, S.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-424 2005

Downloads:

Publ.-Id: 7316 - Permalink


TRLFS with fs-Lasers – a tool to study interactions of actinides with organic ligands
Geipel, G.; Vulpius, D.; Bernhard, G.;
Due to the sensitive detection of light fluorescence properties often are used to study the interaction of metal ions with various ligands. Several actinides as UO2++, Am3+ and Cm3+ show intense fluorescence properties and can be detected at very low concentrations. However, for neptunium and plutonium fluorescence properties are not known up to now. Nevertheless many organic ligands present in the environment as humic substances and wood degradation products fluorescence after excitation. To study the interaction of non-fluorescent actinides with these organic ligands fs-laser pulses were used for excitation. The light emitted from the ligand is observed by ICCD-cameras in a picosecond to nanosecond time scale. Using this TRLFS system the interaction of Np(V) with several small organic ligands was studied. As examples results will be presented for the interaction of Np(V) with 2,3-dihydroxybenzoic acid and 4-hydroxy-3-methoxybenzoic acid. For the interaction of uranyl with 2,3-dihydroxybenzoic acid a complex formation with the phenolic OH groups was found. In the case of Np(V) the interaction is very different. At pH values below 5.0 only the interaction with the carboxylic group can be observed and the interaction with the phenolic group starts at higher pH. This results in a 2:1 complex. Studies of the complex formation of Np(V) with 4-hydroxy-3-methoxybenzoic acid at pH 6 showed also a 2:1 complex, demonstrating the Np(V) interaction with the carboxylic group and the phenolic OH group.
Nevertheless the fluorescence spectra did not show in any case a single component spectrum. This may be connected to other reactions of the non-complexed ligand. Therefore the influence of excited state reactions of the ligand will be discussed.
Keywords: Fluorescence, complex formation, organic ligands
  • Contribution to proceedings
    Asia-Pacific Symposium on Radiochemistry, 17.-21.10.2005, Beijing, China
  • Lecture (Conference)
    APSORC 2005, 17.-21.10.2005, Beijing, China

Publ.-Id: 7315 - Permalink


Observation of negative-parity high-spin states of 68As
Stefanova, E. A.; Lieb, K. P.; Stefanescu, I.; de Angelis, G.; Curien, D.; Eberth, J.; Farnea, E.; Gadea, A.; Gersch, G.; Jungclaus, A.; Martinez, T.; Schwengner, R.; Steinhardt, T.; Warr, N.; Weisshaar, D.; Wyss, R.;
The neutron-deficient nucleus 68AS was populated at high spin in two experiments using the reaction 40Ca(32S, 3pn) at beam energies of 105 and 95 MeV. A self-supporting and a gold backed, highly enriched 40Ca target were used. Gamma rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The 68As level scheme was considerably extended, especially at negative parity and many previous spin-parity assignments were confirmed or rejected. The total-Routhian-surface (TRS) calculation find shape coexistence and γ softness for the negative- and positive-parity states, respectively
  • European Physical Journal A 24(2005), 1-4

Publ.-Id: 7314 - Permalink


Approaches for Silicon Based Light Emitters
Helm, M.;
The realization of an efficient Si based light emitter or even a laser would be a breakthrough for micro- and optoelectronics, since it would allow for full integration of optical functionality on a chip. Being an indirect semiconductor, Si is an inherently bad light emitter, yet recently some remarkable progress has occurred. Light emitting devices based on Si pn junctions, Si MOS structures doped with rare earth elements, or containing Si nanoclusters have been demonstrated. I will present our work in some of these areas.

We have fabricated Si light emitting pn diodes (LED) by high-dose boron implantation into n-type Si. The free-exciton electroluminescence (EL) increases with temperature, reaching wall-plug efficiencies of more than 0.1% at room temperature. A model which is based on excitons localized near nanoscale boron doping spikes can explain the EL dependence on current and temperature as well as an electrical bistability occurring at low temperature. We have integrated such structures into a microcavity with a buried metallic CoSi2 bottom mirror and a Si/SiO2 Bragg mirror on top, representing the first electrically driven resonant-cavity LED based on silicon. This resonant-cavity LED exhibits significant spectral narrowing, consistent with the quality of the cavity.

A second class of devices are metal-oxide-semiconductor (MOS) structures, which are implanted with various rare-earth elements. Here the emission results from 4f intrashell transitions, impact excited by hot electrons in the oxide. The most widely studied example is the Er3+ ion emitting at the telecom wavelength of 1.54 microns. We have also fabricated a Gd doped MOS structure, which emits in the deep UV at 316 nm. This is, to our knowledge, the first Si based UV light emitter, with many potential applications in areas such as bio-sensing. Finally we demonstrate a bright-green MOS light emitter based on Tb ions implanted into the oxide, which could find applications in low-cost micro-displays.
Keywords: silicon light emitter, rare earth, electroluminescence
  • Invited lecture (Conferences)
    8th German-Vietnamese Seminar on Physics and Engineering (GVS-8), 03.-09.04.2005, Erlangen, Deutschland

Publ.-Id: 7313 - Permalink


Effects of Mg, Ca, Sr and Ba on Geochemical Uranyl Speciation
Geipel, G.; Bernhard, G.;
The uranyl tricarbonato complex is one of the most important uranyl species under environmental conditions. The tendency to form stable metal-uranyl tricarbonato complexes was found particularly for the interaction with alkaline earth elements. However, under comparable chemical conditions the formation of these complexes is very different. While magnesium tends mainly to the formation of a MgUO2(CO3)32+ - complex, in the case of calcium the Ca2UO2(CO3)3(aq.) complex is the most stable and the formation of the CaUO2(CO3)32+ - complex is very limited. In the corresponding systems with strontium as well as for barium only the MeUO2(CO3)32+ - complex is formed. The stability constants of the MeUO2(CO3)32+ - complexes increase in the series Mg, Ca , Sr and Ba. The formation of Me2UO2(CO3)3 – complexes for Mg, Sr and Ba occurs only in a small concentration range and the formed complexes tends to precipitate. The Me2UO2(CO3)3 – complexes for Mg and Ca form stable minerals as bayleyite and liebigite. However several other mineral modifications as zellerite, fontanite, sharpite and rabbittite underline the geochemical importance of this class of compounds.
Analogous phenomena can be expected in the alkaline earth uranyl phosphate systems and first results will be presented.
Keywords: Uranium, Carbonate, Speciation
  • Contribution to proceedings
    PACIFICHEM 2005, 15.-20.12.2005, Honolulu, United States
  • Invited lecture (Conferences)
    PACIFICHEM 2005, 15.-20.12.2005, Honolulu, United States

Publ.-Id: 7312 - Permalink


Photothermal beam deflection (PTBD) spectroscopy using an FEL as a pump source
Foerstendorf, H.; Seidel, W.; Glotin, F.; Prazeres, R.; Ortega, J. M.;
The PTBD technique is based on the theory of photothermal spectroscopy which describes the conversion of absorbed energy of a light beam incident on a sample into heat by nonradiative de-excitation processes [1]. The distribution of this induced, exponentially decaying, thermal field is given by the solution of the heat equation with a source term of a Gaussian beam [2]. In typical PTBD experiments the magnitude of the signal is proportional to the slope of the induced displacement of the sample surface. Additionally, it can be shown that there is a direct proportionality between the observed signal and the absorption coefficient of the material under investigation [2]. Therefore, a direct access to absorption spectra is provided [3]. In PTBD spectroscopy generating and detection of thermal waves occur generally in the sub-millimeter length scale. Therefore, PTBD provides spatial information about the surface of the sample and permits imaging and/or microspectrometry.
We investigated distinct patterns of O+-implanted and untreated regions at the surface of germanium substrates serving as model systems. This was achieved by special stainless steal masks in front of the substrate during the implantation processes. The different areas of the surfaces can be distinguished by optical absorption (i.e. the amplitude of the deflection signal) at λ = 11.6 µm of the germaniumoxide produced during ion implantation.
The dimensions of the masks were fully recovered by recording one dimensional absorption profiles of the substrate’s surfaces using a high resolution positioning system. Since the minimum dimensions of the implanted pattern was 30 µm the spatial resolution obtained is near the diffraction limit of the infrared pump beam.

References
[1] A. Rosencwaig and A. Gersho, J. Appl. Phys. 47 (1976) 64.
[2] M.A. Olmstead et al., Appl. Phys. A 32 (1983) 141.
[3] W. Seidel et al., Eur. Phys. J - Appl. Phys. 25 (2004) 39.
  • Poster
    WIRMS 2005 Int. Workshop on Infrared Microscopy and Spectroscopy with Accelerator Based Sources, 26.-30.06.2005, Rathen, Deutschland

Publ.-Id: 7311 - Permalink


Velocity measurements and concentration field visualizations in natural convection copper electrolysis under magnetic field influence
Weier, T.; Hüller, J.; Gerbeth, G.; Weiss, F.-P.;
The effect of magnetic fields on momentum and mass transfer in electrochemical processes has been studied by means of Digital Particle Image Velocimetry (DPIV), shadowgraphy and mean current density measurements.

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

The moderate magnetic field of permanent magnets placed behind the electrodes, although its action is limited to the vicinity of the electrodes, is able to promote convection in the whole cell. Flow structures measured by DPIV compare very well with the patterns of the concentration field given by shadography. Steady state limiting current densities as well as initially instationary current density values can be explained by the corresponding velocity measurements. It will be shown that the interplay of Lorentz and buoyancy forces is substantial for the resulting flow structure.
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference Fundamental and Applied MHD, 27.06.-01.07.2005, Rigas Jurmala, Latvia
    Proceedings 2(2005), 143-146

Publ.-Id: 7310 - Permalink


Reactive transport codes applied to gypsum dissolution in a laboratory column experiment with focus on sensitivity of model concepts and data uncertainty
Pfingsten, W.; Mibus, J.; Küchler, R.;
Experimentally determined kinetic gypsum dissolution by pure water has been used as a data set to investigate different model concepts for mineral dissolution integrated into the four different couple codes. All concepts include a kinetic approach, but with different detail of parameter dependency. In the case of gypsum dissolution, only those concepts, which include an explicit dependency on the actual gypsum mineral surface area, gave good agreement with the measurements. Concepts which do not include such a dependency could not reproduce the measurements. More complex rate equations were necessary to describe the experiments. Nevertheless, the accessible mineral surface area, which decreases during the dissolution, was not directly measurable in the experiment and is so far a model parameter, albeit the one which reproduced measured Ca2+ in solution. Solution chemistry measurements forced the kinetic dissolution model to include a temporal evolving accessible mineral surface area to correctly describe the dissolution experiment.
Keywords: gypsum dissolution, coupled codes, column experiment, code comparison, mineral surface area, reaction rates
  • Contribution to proceedings
    Fifth International Conference on Calibration and Reliability in Groundwater Modelling, 06.-09.06.2005, Scheveningen, Netherlands
    Reactive transport codes applied to gypsum dissolution in a laboratory column experiment with focus
  • Lecture (Conference)
    Fifth International Conference on Calibration and Reliability in Groundwater Modelling, 06.-09.06.2005, Scheveningen, Netherlands

Publ.-Id: 7309 - Permalink


Reactor cell calculations with the codes HELIOS, MCNP and TransRay and comparison of the results
Beckert, C.; Koch, R.;
The DYN3D code allowing to calculate the whole reactor core of light water reactors and its transient behaviour has been developed at the Forschungszentrum Rossendorf (FZR). It treats the three-dimensional (3d) neutron kinetics with a two-group diffusion approximation using the nodal method for assemblies with quadratic and hexagonal geometry. As input data DYN3D needs two-group cross sections for the neutrons, which are averaged over each node. These cross sections are generated using the 2d-code-system HELIOS. The necessity to calculate these two-group cross sections three-dimensionally was evaluated with the Monte-Carlo code MCNP and the 2d- and 3d-cell-code TransRay, which has been specially developed for that purpose at FZR. TransRay uses the same solution method as employed by HELIOS. The following reactor cells were investigated: A partially inserted control rod and void (or moderator with a lower density respectively) around a fuel rod as a model for a steam bubble in the moderator region. In general it could be concluded, that a three-dimensional data generation of averaged two-group cross sections is rather necessary for reactor cells with steam bubbles than for reactor cells with absorbers.
Keywords: cross section, neutron transport, HELIOS, MCNP, TransRay, ray-tracing
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
    CD-ROM
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany

Publ.-Id: 7308 - Permalink


Module efficiencies and performance measurements: Summary of a 10 years measuring program
Rindelhardt, U.; Futterschneider, H.;
Since 1994 a photovoltaic test field has been operated at Forschungszentrum Rossendorf near Dresden. It consists of about 15 modules (mono- and polycrystalline Si, a-Si:H and CIS) from different suppliers, which were mounted in a plane with an inclination of 30 degrees and directed to south. The module power and the module temperature were measured every minute. The 10-minute-mean-values were stored together with the corresponding irradiance data. The main results of this comprehensive program will be reported.
Keywords: photovoltaic, performance
  • Contribution to proceedings
    20th European Photovoltaic Solar Energy Conference and Exhibition, 06.-10.06.2005, Barcelona, Spain, 3-936338-19-1
  • Poster
    20th European Photovoltaic Solar Energy Conference and Exhibition, 06.-10.06.2005, Barcelona, Spain

Publ.-Id: 7307 - Permalink


Die Erholung der Talsperrenökosysteme von der atmosphärischen Versauerung 1. Trends ausgewählter chemischer Kriterien
Ulrich, K.-U.;
Aufgrund des enormen Ausstoßes an Schwefeldioxid und Stickoxiden sowie des kalkarmen Grundgesteins von Erzgebirge und Vogtland litten zahlreiche sächsische Staugewässer spätestens seit Anfang der 1970er Jahre unter dem Phänomen der atmosphärischen Versauerung. Dies betraf auch einige Trinkwassertalsperren. Nach der Wiedervereinigung wurden weder Kosten noch Aufwand gescheut, um geeignete Technologien zur Aufbereitung des weichen, sauren Rohwassers zu entwickeln, die Wasserwerke zu modernisieren und auf die Einhaltung der geforderten Grenzwerte einzustellen. Innerhalb des letzten Jahrzehnts verringerten sich vor allem die Schwefeldioxid-Emissionen beträchtlich. Der Literatur zufolge gibt es große regionale Unterschiede bei der Erholung der Oberflächengewässer von der atmosphärischen Versauerung. Entsprechende Trends sind in einigen deutschen Mittelgebirgen oft nur schwach ausgeprägt oder überhaupt nicht nachweisbar. Dies begründet die Motivation, den Datenbestand der Landestalsperrenverwaltung Sachsen am Beispiel von sieben versauerten Talsperren und 22 Zuflüssen hinsichtlich der Trends ausgewählter wasserchemischer Parameter für 11 Jahre (1993-2003) statistisch mit dem Seasonal Kendall Test auszuwerten und zu vergleichen.
Der Vortrag stellt die wesentlichen Ergebnisse im Kontext mit der regionalen Entwicklung der Emissions- und Depositionssituation und vor dem Hintergrund der forstlichen Bodenschutzkalkung in Südsachsen dar. Als Hauptfaktor für den in 85% der untersuchten Gewässer signifikanten Konzentrationsrückgang von Protonen und Sulfat wird die Abnahme der Depositionsraten mindestens um Faktor 3 angesehen. In etwa 20% der Gewässer, bei denen die insgesamt applizierte Dolomitdosis im Einzugsgebiet 7 t ha-1 überschritt, fanden sich steigende Trends der Calcium- und/oder Magnesiumkonzentration, die jedoch nicht signifikant waren. Der direkte Beitrag der Bodenschutzkalkung zur Entsäuerung und nachhaltigen Erhöhung des Pufferungsvermögens der Oberflächengewässer wird als relativ gering eingeschätzt. Der starke Konzentrationsrückgang von Protonen und damit einhergehend von toxischen Aluminiumspezies bildet die Grundlage für eine Wiederbesiedelung der Gewässer durch säureempfindliche Organismen.
Keywords: acidification reversal, drinking-water reservoir, hydrochemistry, atmospheric emissions, acidic deposition, forest soil liming, sulfur, aluminum, recovery
  • Invited lecture (Conferences)
    Wassergüteberatung des Referats für Wassergütebewirtschaftung, 13.04.2005, Bad Gottleuba, Germany

Publ.-Id: 7306 - Permalink


Ion beam synthesis of 3C–(Si1–xC1–y)Gex+y solid solutions
Weih, P.; Stauden, T.; Ecke, G.; Shokhovets, S.; Zgheib, C.; Voelskow, M.; Skorupa, W.; Ambacher, O.; Pezoldt, J.;
In the present study cubic 3C–(Si1–xC1–y)Gex+y solid solutions were created by using ion beam synthesis. 3C–SiC thin layers grown on on-axis Si (111) substrates by Molecular Beam Epitaxy were implanted with Ge in order to incorporate Ge atoms in the Silicon Carbide lattice. Two series of experiments were carried out. The implantation energy was chosen to be 140 keV and 200 keV and the implantation dose 1 × 1017 cm–2 and 4.7 × 1016 cm–2 respectively. The samples were annealed under rapid thermal annealing conditions in the temperature range between 800 °C and 1300 °C. X-ray diffraction measurements indicate an enlargement of the lattice constant. The observed higher absorption in the implanted layers could be a sign of a band gap reduction as a consequence of Ge incorporation.
  • Physica Status Solidi (A) 202(2005)4, 545-549

Publ.-Id: 7305 - Permalink


Two-phase flow simulations in the FZ Rossendorf using CFX-5
Krepper, E.; Lucas, D.; Prasser, H.-M.; Shi, J.-M.; Rohde, U.;
To qualify CFD codes for gas-liquid two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubbly flow this particularly concerns the forces acting on the bubbles as well as bubble coalescence and break-up. Besides the drag forces describing the momentum exchange in flow direction, the non drag forces acting perpendicular to the flow direction play an important role for the development of the flow structure. The presentation describes the two phase flow test facilities in the Forschungszentrum Rossendorf, the applied measurement technique and the modelling efforts simulating the momentum exchange between the phases by means of a two-fluid model. The simulation of a rectangular bubble column and a hot channel in a nuclear reactor fuel assembly are presented as application examples.
Keywords: two-phase flow measurements, two-phase flow CFD calculations, Euler/Euler two fluid approach, momentum exchange non drag forces, wall boiling
  • Contribution to proceedings
    11th Workshop on Two Phase Flow Predictions, 05.-08.04.2005, Merseburg, Germany
  • Lecture (Conference)
    11th Workshop on Two Phase Flow Predictions, 05.-08.04.2005, Merseburg, Germany

Publ.-Id: 7304 - Permalink


Die Strahlungsquelle ELBE im Forschungszentrum Rossendorf Konzept und erste Betriebserfahrungen
Michel, P.;
Der Elektronenbeschleuniger ELBE (Elektronenbeschleuniger mit hoher Brillanz und geringer Emittanz) [1] im Forschungszentrum Rossendorf wird nach seiner endgültigen Fertigstellung elektromagnetische Strahlung, Neutronen, Positronen sowie Elektronen für die Forschung liefern. Die Vielfalt und die hervorragenden Eigenschaften dieser Sekundärstrahlung machen ELBE zum zentralen und verbindenden Großgerät der Institute im Forschungszentrum Rossendorf. Ein 40 MeV, 1mA Elektronenbeschleuniger dient als Treiber für die verschiedenen Arten von Sekundärstrahlung.
  • Lecture (Conference)
    SEI - Herbsttagung (Studiengruppe für Elektronische Instrumentierung), 27.-29.09.2004, Forschungszentrum Rossendorf, Dresden, Germany
  • Contribution to proceedings
    Herbsttagung der SEI Studiengruppe für Elektronische Instrumentierung, 27.-29.09.2004, FZ Rossendorf, Dresden, Germany
    Bericht der Herbsttagung der Studiengruppe für Elektronische Instrumentierung, Berlin: HMI-B 600, ISSN 0936 - 0891, 2-8
  • Contribution to WWW
    http://www.hmi.de/bereiche/I/DS/sei/archiv/2004-09/vortrag/michel_text.pdf

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Publ.-Id: 7303 - Permalink


Die Strahlungsquelle ELBE im Forschungszentrum Rossendorf
Michel, P.;
Die Strahlungsquelle ELBE (Elektronenbeschleuniger mit hoher Brillanz und niedriger Emittanz) im Forschungszentrum Rossendorf wird nach ihrer vollständigen Inbetriebnahme ein breites Spektrum von Sekundärstrahlung für die Forschung liefern. Im elektromagnetischen Bereich werden an ELBE intensive und polarisierte Bremsstrahlung (Maximalenergie 20 MeV), monochromatische Röntgenstrahlung (10-100 keV) und Infrarotstrahlung aus Freie-Elektronen-Lasern (6-400 meV) produziert. Darüber hinaus werden gepulste Neutronen und monoenergetische Positronen als Sekundärteilchenstrahlen und ein direkter Elektronenstrahl mit hoher Strahlleistung bis zu 40kW zur Verfügung stehen. Als Treiber für die Sekundärstrahlungserzeugung dient ein supraleitender Hochfrequenzelektronenbeschleuniger mit einer Maximalenergie von 40 MeV und einem mittleren Strahlstrom von 1 mA. ELBE wurde im Rahmen einer Projektgruppe des FZR konzipiert und aufgebaut. Die vollständige Inbetriebnahme soll im Jahre 2005 abgeschlossen sein. Mit ELBE steht dem Forschungszentrum Rossendorf und der Forschungsgemeinschaft insgesamt ein leistungsfähiges und modernes Instrument zu Verfügung. Das breite Spektrum von Strahlung und die exzellenten Strahleigenschaften eröffnen einer Vielzahl von Forschungsrichtungen, experimentellen Techniken und technologischen Anwendungen neue Möglichkeiten. Derzeit sind beispielsweise Experimente zur Untersuchung der Kernstruktur, der biologischen Wirksamkeit von Röntgenstrahlung, der Dynamik von metallischen Mehrphasenströmungen, von Halbleiter-, Festkörper- und Quantenstrukturen sowie von nuklearen Prozessen in Fusionsreaktormaterialien geplant. Der Vortrag soll die Parameter und die potentiellen Möglichkeiten der Strahlungsquelle ELBE aufzeigen und für weitere Anwendungen werben.
  • Contribution to WWW
    P. Michel et al., DACH-Jahrestagung, Zerstörungsfreie Materialprüfung, ZfP in Forschung, Entwicklung und Anwendung, Kurzfassungen der Vorträge und Plakatbeiträge, Vortrag 50, Sitzung E3, 17. – 19.05.2004, Salzburg, Austria: http://www.dgzfp.de/tagungen/Jahrestagung/Salzburg/KuFa2004.pdf
  • Lecture (Conference)
    DACH-Jahrestagung, Zerstörungsfreie Materialprüfung ZfP in Forschung, Entwicklung und Anwendung, 17.-19.05.2004, Salzburg, Austria

Publ.-Id: 7302 - Permalink


Diagnostics at the ELBE Bremsstrahlung Facility
Michel, P.; Evtushenko, P.; Lehnert, U.; Schurig, R.; Teichert, J.; Schilling, K.-D.;
The ELBE (Electron Linear accelerator with high Brilliance and low Emittance) machine is currently under transition from commissioning to regular user operation. The linac produces an up to 40 MeV, 1 mA (CW) electron beam which is used to generate various kinds of secondary radiation. While IR-FEL and X-ray facilities are still under construction, comprehensive nuclear physics experiments at the bremsstrahlung facility have been conducted. Both, to meet the experimentor’s demands on beam quality, stability and reproducibility and to ensure a safe operation of the machine, several diagnostic elements, such as backward OTR viewers, radiator temperature diagnostics, stripline detectors to monitor the beam incidence angle on the radiator and a four-quadrant loss monitor were developed, installed and tested. These elements are described and results are presented in this paper.
  • Poster
    11th Beam Instrumentation Workshop, 03.-06.05.2004, Knoxville, TN, USA
  • Contribution to proceedings
    Eleventh Beam Instrumentation Workshop 2004, 03.-06.05.2004, Knoxville, Tennessee, USA
    Beam Instrumentation Workshop 2004, Melville, N. Y., USA: American Institute of Physics, 0-7354-0214-0, 128-132

Publ.-Id: 7301 - Permalink


The ELBE accelerator and the SRF Gun project
Teichert, J.;
leider nicht vorhanden
  • Lecture (Conference)
    EUROFEL Kick - Off Meeting 2005, 17.-18.01.2005, Hamburg, Germany

Publ.-Id: 7300 - Permalink


Speciation of Uranium in Environmental Relevant Compartments
Bernhard, G.;
In the past, the chemistry of uranium was focused on its mining and milling for production of high pure uranium compounds as initial matter of reactor fuel elements for energy production and breeding of plutonium for weapons production. In this sense, the recovery of uranium and plutonium from the used reactor fuel elements was also technical realized. The increasing input of uranium into bio-sphere by mining and milling and industrial processes like production of cement, fossil fuels, and fertilizers has led to the realization of the importance of uranium environmental chemistry. For a better assessment of radiotoxicity and transport along the food chain knowledge about the chemistry of uranium is needed in all involved compartments.
  • Lecture (Conference)
    Asia-Pacific Symposium on Radiochemistry, 17.-21.10.2005, Beijing, China
  • Contribution to proceedings
    Asia-Pacific Symposium on Radiochemistry, 17.-21.10.2005, Beijing, China

Publ.-Id: 7299 - Permalink


Interfacial Reactions of Uranium Related to Geology and Biology
Bernhard, G.;
The increasing input of uranium into bio-sphere by mining and milling an dindustrial processes like production of cement, using fossile fuels, and fertilizers has led to the realization of the importance of environmental chemistry of uranium. Detailed knowledge of the nature of uranium complexes formed on the interfaces of relevant geo- and bio-systems is an essential prerequisite to describe the migration behavior in the environment. Our investigations are focused on surface complexation of uranium on phyllite and its mineral constituents like chlorite, muscovite, albite and quartz. Weathering of iron containing chlorite forms ferrihydrite as a secondary phase on the mineral surface. Results showed that the formed ferrihydrite is dominating the surface complexation. Furthermmore, the changing of uranium speciation on the surface layer will be discussed in dependence on different weathering conditions, the presence of humic acids, and the formation of biofilms on the surface. Bacteria are ubiquitous in nature and can influence the uranium transport by mobilization or immobilization. Formation of biofilms can immobilize uranium by increasing the sorption. On the other hand the formation of bio-colloids can promote the uranium transport. In dependence on the living mechanism, bacteria have different structure of the outer cell membrane and can express a wide variety of complexing ligands with various functionalities. Results about binding of uranium on cell surfaces of selected bacterial strains will be presented. For uranium speciation determination various laser spectroscopic methods and X-ray absorption spectroscopy were used. For localization of uranium on the surfaces sensitive microscopic techniques were helpful.
  • Invited lecture (Conferences)
    Pacifichem 2005, 15.-20.12.2005, Honolulu, United States
  • Contribution to proceedings
    PACIFICHEM 2005, 15.-20.12.2005, Honolulu, United States

Publ.-Id: 7298 - Permalink


Oberflächenmodifizierung durch Ionenstrahlbehandlung – Charakterisierung mittels Elektronen
Reuther, H.;
Oberflächenmodifizierung durch Ionenstrahlbehandlung – Charakterisierung mittels Elektronen
  • Lecture (others)
    Institutsseminar, 20.04.2005, Dresden, Deutschland

Publ.-Id: 7297 - Permalink


Electromagnetically driven convection applied during solidification of Pb-Sn alloys
Eckert, S.; Willers, B.; Nikritjuk, P. A.; Eckert, K.; Michel, U.; Zouhar, G.;
Many references from the cast metal literature consider the application of sonic vibrations, mechanical or electromagnetic stirring as a tool to promote the formation of fine, equiaxed grains during solidification. In this paper experimental and numerical investigations will be presented concerning the influence of a flow driven by a rotating magnetic field (RMF) on the momentum, heat and mass transfer within binary Sn-Pb alloys solidified directionally.
Our results show that the forced convection influences significantly the concentration as well the temperature profile ahead of the solidification front. The convective transport of solute reduces the thickness of the solutal boundary layer and increases the constitutional supercooling. The RMF-application provokes a distinct grain refinement for all considered alloy compositions and equiaxed growth has shown to be encouraged. A flow effect can be supposed both on the presence of nuclei in the melt and suitable conditions allowing them to grow in competition with the columnar front.
Keywords: solidification, Pb-Sn alloys, convection, rotating magnetic field
  • Lecture (Conference)
    Material Science &Technology 2005, 25.-28.09.05, Pittsburgh, United States

Publ.-Id: 7296 - Permalink


Application of a rotating magnetic field during directional solidification of Pb-Sn alloys: Consequences on the CET
Willers, B.; Eckert, S.; Nikritjuk, P. A.; Eckert, K.; Michel, U.; Zouhar, G.;
Many references from the cast metal literature are known discussing the effect of melt convection during the early stages of solidification on the grain structure. The application of mechanical or electromagnetic stirring, ultrasonic or sonic vibrations promotes the formation of fine, equiaxed grains. In this paper experimental and numerical investigations will be presented concerning the influence of a flow driven by a rotating magnetic field (RMF) on the momentum, heat and mass transfer within binary Sn-Pb alloys solidified directionally. The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow during solidification.
The continuum formulation based model has been adopted for numerical simulations. The mushy region is modeled using a mixture viscosity formulation. The Lorentz force in the Navier-Stokes equation has been calculated by means of an analytical solution given by for a finite cylinder.
Our results show that the velocity field undergoes distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case. The forced convection causes distinct modifications of the temperature and concentration field such as a reduction of the temperature gradient ahead of the solidification front and a shift of the mixture concentration towards the eutectic concentration on the axis of the ingots. Without electromagnetic stirring the alloy solidifies solely in form of dendrites aligned parallel to the heat flow direction. In contrast, a transition from a columnar to an equiaxed growth (CET) is observed if the solidifying ingot is exposed to an RMF. The position of the CET is shifted downwards by increasing the field strength.
Keywords: solidification, Pb-Sn alloys, convection, rotating magnetic field
  • Lecture (Conference)
    International Conference on Advances in Solidification Processes, 07.-10.06.05, Stockholm, Sweden
  • Materials Science and Engineering A 413-414(2005), 211-216

Publ.-Id: 7295 - Permalink


Technology Challenges for SRF Guns as ERL Sources in View of Rossendorf work
Janssen, D.; Büttig, H.; Evtushenko, P.; Lehnert, U.; Michel, P.; Möller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Xiang, R.; Stephan, J.; Lehmann, W.-D.; Kamps, T.; Lipka, D.; Volkov, V.; Will, I.;
After discussing the demands on ERL injectors for different projects, we will discuss the technological challenges and the obtained solutions for different parts of the SRF gun. The first point is the shape of the gun cavity and the tuning system. An essential parameter is the length of the first cell, which is determined by the condition, that the field strength at the cathode has a maximal value at the moment of electron emission. If the cavity consists of different cells, as the 3 ½ cell cavity of the Rossendorf gun, two independent tuning systems are necessary. An essential point is the installation of a normal conducting cathode inside a superconducting cavity. The cathode must be isolated by a vacuum gap, it must be alignable and exchangeable from outside of the cryostat and on has to cool down it to LN2 temperature. The next point of discussion is the RF choke filter, which prevents the leakage of RF power, caused by the coaxial between the cathode and the cavity. Different solutions will be shown. In order to focus the beam and to avoid the increasing of transverse emittance a static magnetic field is applied immediately after the cathode in normal conducting RF guns. For a superconducting cavity three possibilities exist to reach the same effect: The first is to put a solenoid after the cavity and outside the cryostat. The second one is the so called RF focussing, where near the cathode a radial component of the RF field is created, which focus the beam. The most elegant way is to put an additional magnetic RF mode into the cavity. It is shown, that for emittance compensation the phase of this mode is not relevant and the amplitude is inside the limit, given by the maximal surface field strength. Especially for high current guns the input of RF power could be a problem. We will show the limits of the RF coupler in the current Rossendorf project and discuss the idea of a coaxial input of RF power from the cathode side of the gun, where the coaxial between the cathode and the cavity is the main part of the RF input coupler. In the last point we discuss the experimental results obtained in Rossendorf and present the status of the current project.
  • Nuclear Instruments and Methods in Physics Research A 557(2006), 80-86
    DOI: 10.1016/j.nima.2005.10.120
  • Invited lecture (Conferences)
    32nd Advanced ICFA Beam Dynamics Workshop on Energy Recovering Linacs ERL 2005, 19.-23.03.2005, Newport News, USA

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Publ.-Id: 7294 - Permalink


Status of superconducting module development suitable for cw operation: ELBE cryostats
Teichert, J.; Büttig, H.; Michel, P.; Lehnert, U.; Schneider, C.; Möller, K.; Büchner, A.; Gabriel, F.; Stephan, J.; Winter, A.;
For the ELBE electron linear accelerator a superconducting accerating module was developed and is now in routine operation. The cryostat contains two TESLA cavities (1.3 GHz) and is designed for cw operation with an accelerating gradient of 10 MV/m and a maximum average beam current of 1 mA. For the power RF two 10 kW klystrons are used. Special tuners, power couplers, low level rf control, cryogenic control systems and safety systems were developed. We will discuss engineering design, operation parameters and our experience with the module.
  • Nuclear Instruments and Methods in Physics Research A 557(2006), 239-242
    DOI: PII: S0168-9002(5)02000-0
  • Invited lecture (Conferences)
    32nd Advanced ICFA Beam Dynamics Workshop on Energy Recovering Linacs ERL 2005, 19.-23.03.2005, Newport News, USA

Publ.-Id: 7293 - Permalink


Tailoring magnetic properties of permalloy by means of Cr implantation
Fassbender, J.ORC; McCord, J.; Mattheis, R.; Potzger, K.; Mücklich, A.; von Borany, J.
As an example, we report on the tailoring of the magnetic properties of Permalloy (20 nm Ni81Fe19) by means of 30 keV Cr implantation. Due to the doping the Curie temperature of the Permalloy film decreases with the implantation fluence and drops below room temperature at an averaged Cr concentration of about 7 at-%. Also the saturation magnetization and the uniaxial anisotropy decrease. However the magnetic damping behavior of Cr implanted Permalloy films is strongly enhanced which is due to a combination of structural changes and alloying effects in the thin film. In order to clarify the basic mechanism for the enhancement the chemical and structural contributions to the magnetic damping parameter are separated by a comparison to results of 30 keV Ni implantation.
Keywords: magnetism, ion implantation, magnetization dynamics, tuning magnetic properties, Curie temperature, magnetic anisotropy
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und -technologie", 11.-12.04.2005, Leipzig, Deutschland

Publ.-Id: 7292 - Permalink


Magnetic Anisotropy and Domain Pattering of Amorphous Films by He-ion Irraddiation
McCord, J.; Fassbender, J.ORC; Frommberger, M.; Liedke, M. O.; Quandt, E.; Schultz, L.
The alteration of magnetic properties in magnetic thin films by ion radiation has gained increasing attention in recent years. Here, we present data on the local alteration of the magnetic anisotropy axis in amorphous soft magnetic FeCoBSi films by He-ion irradiation in an applied magnetic in-plane field. Sputtered CoFeSiB (thickness 30 nm) were irradiated with 5 keV He-ions. A magnetic field of 600 Oe was applied during irradiation aligned orthogonal to the initial easy axis of anisotropy. Above a critical fluence an alignment of anisotropy in the applied field direction is observed by MOKE magnetometry and complementary domain observation by Kerr microscopy. Using irradiation together with photolithography the films were irradiated locally, thus resulting in anisotropypatterned
structures. Domain patterns in different elements with varying
angles of anisotropy and edge orientation, separating regions of different anisotropy alignment, are shown. The influence of the patterning on the (still) full film reversal is discussed in detail.
Keywords: magnetism, ion irradiation, magnetic anisotropy, domains, patterning
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und -technologie", 11.-12.04.2005, Leipzig, Deutschland

Publ.-Id: 7291 - Permalink


Bildung von Goldpartikeln und Molekularbiologie von S-Layern
Pollmann, K.; Merroun, M.; Selenska-Pobell, S.;
Zellen des Bakterienstammes Bacillus sphaericus JG-A12 sind in der Lage, Au(III) an ihre Zelloberfläche, vermutlich durch ihre S-layer, zu binden. Nach Zugabe eines Reduktionsmittels wird Au(III) zu Au(0) reduziert. Die Bildung von Goldnanopartikeln wurde mittels EXAFS, TEM und EDX-Analyse nachgewiesen.
Molekularbiologische Analysen der metallbindenden S-layer wiesen die Existenz von zwei unterschiedlichen S-layer-Genen nach. Sowohl das funktionale Gen als auch das stumme Gen wurde sequenziert. Zudem wurde ein neuartiges Insertionselement identifiziert, welches interessanterweise ein stummes S-layer-Gen enthält.
  • Lecture (others)
    SMWK-Projekttreffen, 31.03.2005, Dresden, Germany

Publ.-Id: 7290 - Permalink


First Lasing at the ELBE mid-IR FEL
Michel, P.; Evtushenko, P.; Lehnert, U.; Dekorsy, T.; Gabriel, F.; Grosse, E.; Helm, M.; Krenz, M.; Seidel, W.; Wohlfarth, D.; Wolf, A.; Wünsch, R.;
First lasing of the mid infrared FEL at ELBE was achieved on May 7, 2004. The Radiation Source ELBE at the Forschungszentrum Rossendorf in Dresden is currently under transition from commissioning to regular user operation. Presently the electron linac produces an up to 18 MeV, 1 mA (cw) electron beam which is alotted to generate various kinds of secondary radiation. After the successful commissioning of the bremsstrahlung and channeling-X-ray facilities during 2003 stable lasing has now been observed in the IR range (15 to 22 μm). The oscillator FEL is equipped with two planar undulator units, both consisting of 34 hybrid permanent magnet periods of 27.3 mm (Krms = 0.3 - 0.8). The distance between the two parts is variable and the gaps can be adjusted and tapered independently. At 19.6 µm an optical power of 3W was out-coupled in a macro pulse of 0.6 ms duration using an electron beam energy of 16.1 MeV and an energy spread of less than 100 keV; the micropulse charge was 50 pC and its width slightly above 1ps. With the installation of a second acceleration module for additional 20 MeV smaller wavelengths will become available in the near future.
  • Lecture (Conference)
    26th International Free Electron Laser Conference FEL 2004, 29.08.-03.09.2004, Trieste, Italy
  • Contribution to proceedings
    26th International Free Electron Laser Conference and 11th FEL Users Workshop, 29.08.-03.09.2004, Trieste, Italy
    Proceedings of the 26th International Free Electron Laser Conference and 11th FEL Users Workshop, MOAIS04, Trieste: Graphart ts, 88-87992-02-9 (CD), 88-87992-02-9 (Book), 8-13

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Publ.-Id: 7288 - Permalink


Crystallization of amorphous-Si films by flash lamp annealing
Pecz, B.; Dobos, L.; Panknin, D.; Skorupa, W.; Lioutas, C.; Vouroutzis, N.;
The crystallization of amorphous silicon films deposited on glass, using the flash lamp annealing process was realized and studied. The duration of the flash is 20 ms, about two orders of magnitude shorter than the standard rapid thermal annealing process. The a-Si films deposited on Coming glass were irradiated with different energy densities and crystallized exhibiting grains with a mean size up to 6 mum. In order to reduce the strain due to the thermal gradient, the samples were preheated from the backside. The ability of the FLA process to eliminate the ingrain defects in already crystallized poly-Si films at 600 degreesC is also demonstrated.
  • Applied Surface Science 242(2005)1-2, 185-191

Publ.-Id: 7286 - Permalink


Programmes and Projects-examples of management in a German Research Institute
Joehnk, P.;
- The Scientific System of Germany
. among: the Research Centre Rossendorf, Dresden
- The Current Change-Management Process
. Management of Programmes
. Management of Projects
- Tools for Management Assistance
- Controlling: Performance and Success Evaluation
- Summary
Keywords: -
  • Invited lecture (Conferences)
    Instituto nationale per la fizica della materia, 15.03.2005, Trieste, Italiy

Publ.-Id: 7285 - Permalink


Suppression of Modes in the Random Phase Approximation
Dönau, F.;
A general but simple method is proposed to eliminate the quantum fluctuations generated by selected one-body operators in the excitation spectrum of a discrete random phase approximation (RPA) Hamiltonian. This method provides an outstanding tool for the removal of the contaminating spurious effects originated from symetry violations. It can be also applied as a mode filter for analyzing RPA response functions.
  • Physical Review Letters 94(2005), 092503

Publ.-Id: 7284 - Permalink


Texture development during growth of Ti1-xAlxN thin films studied by in-situ x-ray diffraction
Beckers, M.; Schell, N.; Martins, R. M. S.; Möller, W.;
Ti1-xAlxN coatings are of common use for a vast variety of applications. For each of them, controlling the microstructure is crucial because it determines usefulness, performance and lifetime. Thus, literature on the relationship between deposition parameters, microstructure, and performance of Ti1-xAlxN coatings is large. However, little is known regarding the atomistic mechanisms for these observed relationships. Our approach in understanding those mechanisms is in-situ x-ray diffraction during the growth of Ti1-xAlxN films using a deposition chamber installed at the Rossendorf beam line BM20 at the European Synchrotron Radiation Facility in Grenoble, France. All films were deposited by reactive co-sputtering from Ti and Al targets; one series at constant x = 0.06 varying substrate temperature, bias voltage, and nitrogen partial pressure and thus growth rate. In another series, x was systematically varied from 0 to 0.73 while keeping all other parameters constant. Values of x < 0.15 and high deposition rates lead to a typical cross-over behavior between initial (002) and final (111) preferred orientation. Reducing the deposition rate leads to (002) preferred orientation practically independent of film thickness and substrate temperature. Yet, suppressing collisionally-induced atomic N on the sample surface by applying a positive bias voltage, brings back a (111) preferred orientation. Those observations are consistent with proposed atomistic models. Keeping the deposition rates low, (111) preferred orientation can also be induced by increasing x above 0.15, which in the presence of atomic N can be explained by its higher adatom mobility. Increasing x towards the AlN segregation threshold at x = 0.60 leads to hard nano-composite TiAlN/AlN structures, and pushing x further to 0.73 leads to highly stressed AlN with an a-axis off-plane texture.
Keywords: Texture development, nucleation and growth, Ti-Al-N, sputter deposition, in-situ x-ray diffraction
  • Contribution to proceedings
    International Conference on Metallurgical Coatings and Thin Films, 02.-06.05.2005, San Diego, U.S.A.

Publ.-Id: 7283 - Permalink


In-situ x-ray diffraction studies concerning the influence of Al concentration on the texture development during sputter deposition of Ti-Al-N thin films
Beckers, M.; Schell, N.; Martins, R. M. S.; Mücklich, A.; Möller, W.;
In-situ x-ray diffraction was employed during the growth of thin Ti1-xAlxN films, using a deposition chamber installed at a synchrotron radiation beamline. The films were deposited by reactive co-sputtering from Ti and Al targets. At constant x ~ 0.06, substrate temperature, bias voltage, and nitrogen partial pressure, and thus growth rate, was varied. Further, x was systematically varied from 0 to 0.73 while keeping all the other parameters constant. x < 0.15 and high deposition rates of ~ 1 Å/s lead to the typical crossover behavior between initial (001) and final (111) off-plane preferred orientation. Reducing the deposition rate to < 0.5 Å/s leads to a reversed behavior with a clear (001) preferred orientation above a film thickness of 600 Å which is essentially independent of the substrate temperature. Keeping the deposition rate low, the (111) preferred orientation can be recovered for x > 0.15, which can be explained by the higher adatom mobility of Al compared to Ti in the presence of atomic nitrogen. Increasing x towards the AlN segregation threshold at x ~ 0.60 leads to hard nano-composite nc-TiAlN/AlN structures, and x > 0.73 finally leads to dominant AlN with an a-axis off-plane texture.
Keywords: Texture development, nucleation and growth, Ti-Al-N, sputter deposition, in-situ x-ray diffraction
  • Journal of Vacuum Science & Technology A 23(2005)5, 1384-1391

Publ.-Id: 7282 - Permalink


The influence of the growth rate on the preferred orientation of magnetron sputtered Ti-Al-N thin films studied by in-situ x-ray diffraction
Beckers, M.; Schell, N.; Martins, R. M. S.; Mücklich, A.; Möller, W.;
In-situ x-ray diffraction has been used to characterize the growth and microstructure of wear protective Ti1-xAlxN thin films. The films were deposited onto oxidized Si(100) wafers in a sputter chamber mounted onto a six-circle goniometer located at a synchrotron radiation beamline. Off-plane and in-plane x-ray diffraction data were recorded in-situ during growth, in order to follow the development of microstructure and preferred orientation as a function of film thickness. The measurements were supplemented by ex-situ cross-sectional transmission electron microscopy analyses. The films were deposited by reactive co-sputtering from metallic Ti and Al targets in Ar/N2 gas mixtures at substrate temperatures of 150 °C and 300 °C, substrate bias voltages of -30 V and +10 V, and deposition rates between 0.9 Å/s and 0.3 Å/s. The film composition was changed between pure TiN and Ti0.91Al0.09N. Films deposited at higher deposition rates show columnar structure with competitive growth between (001) and (111) crystalline orientation, which slowly evolves into a (111) preferred orientation containing inter- and intracolumn porosities. Reducing the deposition rate to 0.3 Å/s leads to an almost complete (001) preferred orientation with reduced surface roughness, practically independent of the deposition temperature. As the stress state of the films remains low for both deposition rates, it is suggested that the ion-to-neutral arrival rate (JI/JTi+Al) determines the texture development rather than the stress. This is corroborated by applying a positive substrate bias, which, by suppressing ion impingement, leads back to an evolving (111) preferred orientation.
Keywords: Texture development, nucleation and growth, Ti-Al-N, sputter deposition, in-situ x-ray diffraction
  • Journal of Applied Physics 98(2005)4, 44901
  • ESRF Newsletter 42(2005), 20-21

Publ.-Id: 7281 - Permalink


Identifikation elastoplastischer und schädigungsmechanischer Materialparameter aus dem Small Punch Test
Abendroth, M.;
Der Small Punch Test (SPT) ist ein Kleinstprobenversuch, bei dem kleine scheibenförmige Proben in einem Miniaturtiefziehversuch bis zum Versagen belastet werden. Dabei wird eine charakteristische Kraft-Verschiebungs-Kurve für den Druckstempel ermittelt, welche Informationen über das Verformungs- und Versagensverhalten des verwendeten Probenmaterials enthält. Es wird eine den speziellen Anforderungen entsprechende Messapparatur vorgestellt, die es ermöglicht, die Kraft-Verschiebungs-Kurve zu ermitteln und auf optischem Wege den Versagenszeitpunkt der Probe zu bestimmen. Es wird ein Finite Elemente Modell des Small Punch Test benutzt, in dem ein schädigungsmechanisches Materialmodell implementiert ist, um für verschiedene Materialparametersätze die zu erwartenden Kraft-Verschiebungs-Kurven zu berechnen. Mit Hilfe der simulierten Kraft-Verschiebungs-Kurven und den dazugehörigen Materialparametern werden neuronale Netze trainiert, die in einem Lernprozess einen verallgemeinerten Zusammenhang zwischen Materialparametern und Kraft-Verschiebungs-Kurven herstellen. Dieser Zusammenhang kann entweder die approximierte Lösung des inversen Randwertproblems sein, die es ermöglicht aus einer experimentell ermittelten Kraft-Verschiebungs-Kurve des SPT direkt die gesuchten Materialparameter zu bestimmen. Es kann aber auch das Randwertproblem selbst approximiert werden, um in einem Optimierungsverfahren die Materialparameter zu bestimmen, für die sich eine optimale Übereinstimmung zwischen Simulation und Experiment ergeben würde. Beide Techniken werden an verschiedenen duktilen metallischen Werkstoffen getestet. Mit den ermittelten Materialparametern werden Zug- und Bruchmechanikproben simuliert, wobei nicht nur die Materialparameter verifiziert werden, sondern es auch gelingt, für einige Werkstoffe bruchmechanische Kennwerte vorherzusagen.
Keywords: small punch test, damage mechanics, fracture mechanics, parameter identification, neural networks
  • Book (Authorship)
    Freiberg: Freiberger Forschungshefte, Technische Universität Bergakademie Freiberg, 2005
    165 Seiten

Publ.-Id: 7280 - Permalink


Wavelet analysis of EXAFS data
Funke, H.; Chukalina, M.; Scheinost, A.;
- wird nachgereicht
  • Lecture (others)
    Seminarvortrag, 17.03.2005, Zürich, Switzerland

Publ.-Id: 7278 - Permalink


Isotopically resolved residues frorn the fragmentation of projectiles with largely different N/Z - the isospin-thermometer method
Henzlova, D.; Audouin, L.; Benlliure, J.; Botvina, A.; Boudard, A.; Casarejos, E.; Ducret, J.; Enqvist, T.; Got, L.; Heinz, A.; Henzl, V.; Junghans, A.; Jurado, B.; Kelic, A.; Krasa, A.; Kurtukian, T.; Leray, S.; Napolitani, P.; Ordonez, M.; Pereira, J.; Pleskac, R.; Rejmund, F.; Ricciardi, M.; Schmidt, K.; Schmitt, C.; Stephan, C.; Villagrasa, C.; Volant, C.; Wagner, A.; Yordanov, O.;
The mean N-over-Z (Z) ratio of residues produced in the fragmentation of Xe-136 (N/Z = 1.519), Xe-124 (N/Z = 1.296) in comparison with Fe-56 (N/Z = 1.154) is investigated over the full range of Z. The final residues from the Xe-136 projectile keep a memory on the initial N/Z. The idea to trace back the excitation energy of the fragment entering evaporation via direct exploration of the N/Z evolution in the evaporation process is investigated and applied to the data. The freeze-out temperature is deduced, which is consistent with the investigations of light and intermediate-mass fragments (IMF) in other experiments.
  • Nuclear Physics A 749(2005), 110c-113c

Publ.-Id: 7277 - Permalink


Investigation of the creation of Fe nanoparticles in MgO by ion beam synthesis
Reuther, H.; Potzger, K.; Zhou, S.; Mücklich, A.; Eichhorn, F.;
Recently, the investigation of metallic nanoparticles embedded in dielectric oxides has become a topic in magnetic data storage development. Especially the creation of high density data storage devices due to ion beam synthesis of magnetically, highly anisotropic FePt nanoparticles in sapphire yielded promising results. On the other hand, pure Fe-nanoparticles have been created in sapphire, Y-stabilized ZrO2 or MgO. The motivation for the latter includes the search for magneto-optically active surfaces as well as pronounced magnetoresistance.
For doping MgO single crystals with Fe, ion implantation is a promising technique. First extensive studies were performed by Perez et al. who investigated the annealing behaviour of samples implanted with different doses of 57Fe at different energies with conversion electron Mössbauer spectroscopy (CEMS) [1]. They obtained up to 20 % of the implanted iron atoms in a-Fe precipitates while the remaining Fe-atoms were found to be in different Fe2+ and Fe3+ charge states.

In this paper, we propose a method for the creation of large fractions of a-Fe nanoparticles (up to 60%). MgO(001) single crystals were implanted with of 6x1016 cm-2 ions of the Mössbauer isotope 57Fe at 100 keV. The implantation temperature was varied from room temperature up to 800 °C. Moreover, post annealing was investigated. Samples were characterized by CEMS, RBS, TEM and XRD. We found that the temperature during the implantation plays the important role for the formation of the Fe0 state while post annealing results in the preferential formation of Fe oxidation states, mainly Fe3+ states. The largest fraction of iron with Fe0 state was obtained at implantation temperatures between 600 and 800 °C.

[1] A. Perez, G. Marest, B.D. Sawicka, J.A. Sawicki, T. Tyliszczak, Phys. Rev. B, 28, 1227 (1983)
  • Lecture (Conference)
    International Conference on the Applications of the Mössbauer Effect, 05.-09.09.2005, Montpellier, France

Publ.-Id: 7276 - Permalink


Efficient silicon based light emitters
Helm, M.; Sun, J. M.; Potfajova, J.; Dekorsy, T.; Schmidt, B.; Skorupa, W.;
Recent progress on electrically driven silicon based light emitters is reviewed, with emphasis on our work on light emitting pn diodes (LED) and MOS devices doped with rare-earth elements. The LEDs were fabricated by high-dose boron implantation, producing nanoscale modifications in the material. The electroluminescence (EL) efficiency increases with temperature, reaching 0.1% (wall plug efficiency) at room temperature for optimized conditions. Such devices were integrated into a microcavity. In the MOS devices the oxide was implanted with various rare-earth elements, resulting in strong EL in the visible (Tb) and ultraviolet (Gd). External quantum efficiencies in excess of 10% are reported.
Keywords: silicon, light emitting diode, electroluminescence, rare earth, microcavity
  • Microelectronics Journal 36(2005), 957-962

Publ.-Id: 7275 - Permalink


Efficient silicon based light emitters
Helm, M.;
Recently remarkable progress has occurred in the variety and efficiency of silicon based light emitters, based on Si pn junctions, Si MOS structures doped with rare earth elements, or containing Si nanoclusters. I will present our work in some of these areas.

We have fabricated Si light emitting diodes (LED) by high-dose boron implantation into n-type Si. The free-exciton electroluminescence (EL) increases with temperature, reaching wall-plug efficiencies of more than 0.1% at room temperature. A model which is based on excitons localized near nanoscale boron doping spikes can explain the EL dependence on current and temperature. We have integrated such structures into a microcavity with a buried metallic CoSi2 bottom mirror and a Si/SiO2 Bragg mirror on top. This resonant-cavity LED exhibits significant spectral narrowing, consistent with the quality of the cavity.

We also have fabricated light emitting Si MOS structures which were implanted with various rare-earth elements, from the well known Er3+ emitting at the telecom wavelength of 1.54 microns, to Gd3+, which emits in the deep UV at 316 nm. This is, to our knowledge, the first Si based UV light emitter, with many potential applications in areas such as bio-sensing.
Keywords: silicon, light emitting diode, rare earth, electroluminescence, microcavity
  • Invited lecture (Conferences)
    4th Workshop on Semiconductor Nanodevices and Nanostructured Materials (NANOSEMIMAT-4), 09.-13.03.2005, Sao Pedro, SP, Brazil

Publ.-Id: 7274 - Permalink


Krein space related physics: PT-symmetric Quantum Mechanics, MHD α²-dynamos, planar Couette flows, ...
Günther, U.; Stefani, F.; Znojil, M.;
Operator theoretic structures are discussed which underlie PT-symmetric Quantum Mechanics (PTSQM), the spherically symmetric α²-dynamo of magnetohydrodynamics (MHD) and the plane Couette flow of hydrodynamics (described by the Squire equation). Mathematically, the three types of models are closely related as spectral problems in Krein spaces − Hilbert spaces with an indefinite metric structure.
In contrast to the purely real spectrum of self-adjoint operators in "usual" Hilbert spaces, the spectrum of self-adjoint operators in Krein spaces consists, in general, of two types of spectral sectors: sectors with purely real eigenvalues and other sectors with pairwise complex conjugate eigenvalues. Transitions between different sectors occur at exceptional points of square root branching type. Knowing the boundaries of the sectors in parameter space one would know, e.g., the boundaries of the physical sectors of PTSQM (with exact/unbroken PT-symmetry) or of the oscillatory regimes of α²-dynamos.
The underlying Krein space related structure of the different physical setups indicates a possible fruitful interplay of these models in handling their technical and conceptual aspects on a unified footing. We make some aspects of such an interplay explicit and demonstrate its usefulness on the example of a PT-symmetric interpolation model and the Squire equation of hydrodynamics. This allows us to gain a deeper insight into the specifics of the Herbst limit.

The talk is based on material from math-ph/0501069 (which is to appear in J. Math. Phys.) and extends it.
Keywords: MHD dynamos, PT-symmetric Quantum Mechanics, Squire equation, Krein spaces, exceptional points, Herbst limit
  • Invited lecture (Conferences)
    3rd International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 20.-22.06.2005, Istanbul, Turkey

Publ.-Id: 7273 - Permalink


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