Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Studying the constancy of galactic cosmic rays using noble gas and radionuclides data on iron meteorites

Smith, T.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.

The constancy of the galactic cosmic rays (GCR) is a long-standing question in meteorite research. Temporal variations in the GCR intensity might not only sheed light into the origin and evolution of the cosmic rays, it will also compromise systematic studies of the dynamics of small bodies in the solar system using exposure age histograms. Here we present the first results of our study to set-up a consistent exposure ages histogram for iron meteorites, which enables to search for periodic GCR variations. So far, the light noble gases He, Ne, Ar and the cosmogenic radionuclides 10Be, 26Al, and 36Cl have been measured, respectively by mass spectrometry in Bern and at the DREAMS facility [1], in 22 iron meteorites, mostly from group IIIAB. Though, some of the data are still preliminary and further data for 41Ca, 53Mn, and 60Fe are awaited, these data will provide some new information about the distribution of exposure ages among iron meteorites and therefore also on the temporal variability of the GCR.
[1] Akhmadaliev, S. et al. (2012) NIMB 294, 5–10.

Keywords: AMS; cosmic radiation; GCR; meteorite

  • Lecture (Conference)
    Joint meeting “Paneth Kolloquium” and workshop of the DFG special program “The first 10 million years of the solar system” (DFG SPP 1385), 21.-23.10.2013, Nördlingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19245
Publ.-Id: 19245


Magnetic control of Coulomb scattering and terahertz transitions among excitons

Bhattacharyya, J.; Zybell, S.; Eßer, F.; Helm, M.; Schneider, H.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.

Time-resolved terahertz quenching studies of the magnetoexcitonic photoluminescence from GaAs/AlGaAs quantum wells are performed. A microscopic theory is developed to analyze the experiments. Detailed experiment–theory comparisons reveal a remarkable magnetic-field controllability of the Coulomb and terahertz interactions in the excitonic system.

Keywords: exciton dynamics; terahertz; Magneto-excitons

Permalink: https://www.hzdr.de/publications/Publ-19244
Publ.-Id: 19244


Positron emission tomography in pebble beds. part 2: graphite particle deposition and resuspension

Barth, T.; Kulenkampff, J.; Bras, S.; Gründig, M.; Lippmann-Pipke, J.; Hampel, U.

The release of radio-contaminated carbonaceous dust from the pebble bed of a high temperature reactor (HTR) plays a major role for the safety assessment of accidental scenarios. In the present investigation, graphite particle deposition and resuspension in a fluid dynamically scaled HTR pebble bed was studied by means of positron emission tomography (PET). The particle laden turbulent flow in a model pebble bed was generated by an air driven small-scale test facility at ambient conditions. The pebble bed geometry was recorded by a 3D gamma ray computed tomography (CT) scan. Technical graphite dust was radioactively labelled and dispersed into the turbulent flow field of the test facility. The flow scenarios were adapted to study particle deposition and resuspension in succession. Firstly, the radio-labelled graphite particles were dispersed at low fluid velocities to study the multilayer formation during a pure deposition regime. Afterwards, the aerosol generator was switched off and the fan speed was stepwise increased to induce particle resuspension. A time resolved 3D PET-CT overlay provides a complete insight into the particle multilayer formation and removal. Similarities to other particle deposition and resuspension studies in turbulent flows were found.

Permalink: https://www.hzdr.de/publications/Publ-19243
Publ.-Id: 19243


Baseline closure model for dispersed bubbly flow: bubble coalescence and breakup

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

Computational Fluid Dynamics (often abbreviated as CFD) has been becoming one indispensable tool in solving and analyzing of problems that involve fluid flows. Moreover, owing to ever-increasing computer power, the physical scale that can be resolved in a CFD simulation gets smaller and smaller. For example, in a simulation of gas-liquid flows using interface-tracking or interface-capturing methods gas-liquid interfaces can be resolved, where closure models neither for bubble-liquid nor for bubble-bubble are needed. However, the spread of such kind of approaches is retarded by the huge computational consumption. So far it can only be applied to quite small systems, where only a small number of bubbles and thus simple regular interfaces are included.
For problems at engineering or industrial scale, the Euler-Euler or two-fluid model (TFM) is still the most attractive one. However, new issues arise from the complete smearing of gas-liquid interfaces. In a TFM simulation results rely heavily on the applied closure relations, which reconstruct the information of bubble-liquid and bubble-bubble interactions. Furthermore, the effect of all the closures is coupled with each other. As a result, to assess the performance of one certain closure relation, e.g. coalescence and breakup of bubbles, under various flow conditions, a common set of other models should be defined. Otherwise, the wish of generally-applicable closures for TFM will always remain a dream.
On the other hand side, due to a variety of flow regimes and the complicated nature of physics, there exists not yet a consensus set of closure models, even for the simplest case of adiabatic bubbly flow. Rzehak et al. (2013) has taken the first step towards the goal by defining a so-called baseline model, which collects the best or most promising relations from the open literature for adiabatic bubbly flows. It includes bubble forces, bubble-induced turbulence (BIT), and bubble coalescence and breakup. The baseline model provides a common basis for further improvement and development of closure relations.
The focus of the present work is put on the new closures for bubble coalescence and breakup included in the baseline model, which was proposed originally in Liao et al. (2011). In order to guarantee the transferability all important mechanisms that lead to bubble coalescence and breakup are taken into account. In addition, the breakup model avoids successfully uncertainty introduced by separate daughter bubble size distribution functions. These have been believed to be major limitations in most existing models published in the open literature.
One major difficulty encountered in the validation of new bubble coalescence and breakup models is the superposition between coalescence and breakup as well as between multiple mechanisms in the reality. The strategy adopted in the current work is to select validation cases, where only coalescence is most important while the uncertainty brought by breakup is as few as possible. In addition, coalescence due to wake entrainment and eddy capture is negligible. Some test cases that satisfy the criterion approximately are found in the MTLoop experiments for air-water upward vertical pipe flows, which were carried out at the Helmholtz-Zentrum Dresden – Rossendorf a few years ago.
In the simulation, the new closures for bubble coalescence and breakup are implemented in the MUSIG approach (Krepper et al., 2008) provided by ANSYS CFX 14.0. With aid of measured evolution of bubble size distributions along the pipe, the performance of the new model within the baseline model is evaluated for several superficial gas and liquid velocities. The comparison between predictions and measurements demonstrates a promising agreement for all the investigated cases. In addition, considerable improvement against the default closure models available in ANSYS CFX is achieved. Nevertheless, huge validation work is still required to evaluate the breakup model as well as other coalescence mechanisms such as wake entrainment.

Keywords: Dispersed Bubbly Flow; Two-Fluid Model; Bubble Coalescence and Breakup; Kernel Functions; Baseline Closures

  • Lecture (Conference)
    International seminar on Subchannel Analysis, CFD modeling and verification and CHF experiment and benchmarking (ISACC), 03.-04.08.2013, Xian, China

Permalink: https://www.hzdr.de/publications/Publ-19242
Publ.-Id: 19242


New coalescence and breakup kernels for air-water and steam-water pipe flows

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

New coalescence and breakup rate kernel functions are tested in the frame of MUSIG approach for developing bubbly flows inside a vertical pipe. Two test cases are investigated in this work, one from the MTLoop air-water experiment and the other from TOPFLOW steam-water experiment. Both of them demonstrate that consideration of bubble coalescence and breakup can improve predictions considerably. Furthermore, the new models are able to deliver reliable results in both the air-water and steam-water cases without need to adjust the constants, while the widespread model combination predicts too large coalescence and breakup rates. However, there is still a long way to go before a generally-applicable set of constants in the new models is achieved.

Keywords: New Bubble Coalescence and Breakup Kernels; Air-Water; Steam-Water; Vertical Pipe Flows

  • Lecture (Conference)
    5th Population Balance Modeling Conference (PBM2013), 11.-13.09.2013, Bangalore, India
  • Contribution to proceedings
    5th Population Balance Modeling Conference (PBM2013), 11.-13.09.2013, Bangalore, India

Permalink: https://www.hzdr.de/publications/Publ-19241
Publ.-Id: 19241


Effects of inlet condition on flow structure of bubbly flow in rectangular column

Akbar, M. H. B. M.; Hayashi, K.; Tomiyama, A.; Lucas, D.

Experiments on bubbly flows in a rectangular column are carried out to investigate effects of inlet condition on flow structure. An air diffuser having 35 nozzles is used. The inlet gas flow rates from 34 nozzles are uniform and the lift coefficients of bubbles are small at this flow rate, whereas the gas inflow from the remaining one nozzle is varied to change the sign and magnitude of lift coefficients. The main conclusions obtained are as follows: (1) bubbly flow in a bubble column is apt to be heterogeneous even with small non-uniformity in the distribution of gas inflow, (2) when the nozzle causing non-uniform gas inflow is located in the center of the diffuser plate and the inflow distribution is symmetric, heterogeneous structure is formed due to the lift-induced flow instability pointed out by Lucas et al., (3) when the nozzle causing non-uniform gas inflow is located near the side wall of the column and the inflow distribution is asymmetric, heterogeneous structure is induced by the Coanda effect, and (4) a multi-fluid model can predict the effects of non-uniform gas inflow on the formation of heterogeneous structure in bubbly flow.

Keywords: Bubbly flow; Flow instability; Bubble; Bubble column; Multi-fluid model

  • Contribution to proceedings
    8th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, 16.-20.06.2013, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-19240
Publ.-Id: 19240


Characterization of self-damaged (U,Pu)N fuel used in the NIMPHE program

Carvajal-Nunez, U.; Prieur, D.; Janssen, A.; Wiss, T.; Cambriani, A.; Vermorel, E.; Scheinost, A.; Somers, J.

During in-pile, irradiation-induced damage occurs in nuclear fuel and results in a deterioration of its properties, which can affect the margin to melt of the fuel. Damage also occurs in fresh fuel through the self-irradiation process, and thus provides a convenient means to investigate changes in the material. A uranium–plutonium mixed nitride fuel made over 25 years ago, and stored in the ITU archives has been retrieved. Coupling EXAFS and TEM has shown that this material was still well-crystallized. However, an increase of 0.3% of the lattice parameter was found. As shown by the EXAFS, the U–N and Pu–N as well as the metal–metal distances are similarly affected. However, no significant modification of both anion and cation sublattice was found. Although no defect clustering was found by EXAFS, the presence of nanometric helium bubbles was demonstrated by TEM as well as nanometric disordered domains.

Keywords: nuclear fuel; EXAFS

Permalink: https://www.hzdr.de/publications/Publ-19239
Publ.-Id: 19239


Biosorption of heavy metals and nanoparticles by Gram-positive bacteria and cellular components

Suhr, M.; Matys, S.; Viacava Romo, K. E.; Raff, J.; Pollmann, K.

Bacterial isolates from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) possess high affinities to heavy metals e.g. uranium. This binding effect is caused by the components of the bacterial cell wall, mainly affected by surface layer proteins.
In this work we studied the metal uptake of different environmental relevant heavy and noble metals and metaloids as well as nanoparticles by living bacterial cells of a Gram-positive strain and its isolated primary cellular components (e.g. membrane lipids, peptidoglycan, s-layer proteins). This was done via batch experiments and the results were obtained by ICP-MS measurements.
The quartz crystal microbalance with dissipation monitoring was introduced to track the adsorption of biological molecules and to study the metal and nanoparticle interaction with the single cell wall components. With this method it was able to detect the sorption processes on a molecular level in real time and to obtain further information to metal interaction processes and to viscoelastic properties. Partially supporting atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties.

Keywords: Biosorption; bacteria; QCM-D; ICP-MS; s-layer; proteins; lipids; heavy metals; nanoparticles

  • Poster
    8th HZDR PhD Seminar, 07.-09.10.2013, Bautzen, Germany

Permalink: https://www.hzdr.de/publications/Publ-19237
Publ.-Id: 19237


Preliminary investigations on the determination of three-dimensional dose distributions using scintillator blocks and optical tomography

Kroll, F.; Pawelke, J.; Karsch, L.

Purpose: Clinical QA in teletherapy as well as the characterization of experimental radiation sources for future medical applications requires effective methods for measuring three-dimensional (3D) dose distributions generated in a water-equivalent medium. Current dosimeters based on ionization chambers, diodes, thermoluminescence detectors, radiochromic films, or polymer gels exhibit various drawbacks: High quality 3D dose determination is either very sophisticated and expensive or requires high amounts of effort and time for the preparation or read out. New detectors based on scintillator blocks in combination with optical tomography are studied, since they have the potential to facilitate the desired cost-effective, transportable, and long-term stable dosimetry system that is able to determine 3D dose distributions with high spatial resolution in a short time.

Methods: A portable detector prototype was set up based on a plastic scintillator block and four digital cameras. During irradiation the scintillator emits light, which is detected by the fixed cameras. The light distribution is then reconstructed by optical tomography, using maximum-likelihood expectation maximization. The result of the reconstruction approximates the 3D dose distribution. First performance tests of the prototype using laser light were carried out. Irradiation experiments were performed with ionizing radiation, i.e., bremsstrahlung (6 to 21 MV), electrons (6 to 21 MeV), and protons (68 MeV), provided by clinical and research accelerators.

Results: Laser experiments show that the current imaging properties differ from the design specifications: The imaging scale of the optical systems is position dependent, ranging from 0.185 mm/pixel to 0.225 mm/pixel. Nevertheless, the developed dosimetry method is proven to be functional for electron and proton beams. Induced radiation doses of 50 mGy or more made 3D dose reconstructions possible. Taking the imaging properties into account, determined dose profiles are in agreement with reference measurements. An inherent drawback of the scintillator is the nonlinear light output for high stopping-power radiation due to the quenching effect. It impacts the depth dose curves measured with the dosimeter. For single Bragg peak distributions this leads to a peak to plateau ratio of 2.8 instead of 4.5 for the reference ionization chamber measurement. Furthermore, the transmission of the clinical bremsstrahlung beams through the scintillator leads to the saturation of one camera, making dose reconstructions in that case presently not feasible.

Conclusions: It is shown that distributions of scintillation light generated by proton or electron beams can be reconstructed by the dosimetry system within minutes. The quenching apparent for proton irradiation, and the yet not precisely determined position dependency of the imaging scale, require further investigation and corrections. Upgrading the prototype with larger or inorganic scintillators would increase the detectable proton and electron energy range. The presented results show that the determination of 3D dose distributions using scintillator blocks and optical tomography is a promising dosimetry method.

Keywords: biomedical equipment; biomedical optical imaging; bremsstrahlung; cameras; dosimeters; dosimetry; expectation-maximisation algorithm; image reconstruction; ionisation chambers; laser applications in medicine; medical image processing; optical tomography; portable instruments; radiation quenching; radiation therapy; solid scintillation detectors; 3D dosimetry; scintillator; optical tomography; teletherapy

Permalink: https://www.hzdr.de/publications/Publ-19236
Publ.-Id: 19236


Untersuchung von Szintillationsdetektoren für Prompt Gamma Imaging Systeme zur Verifikation der Dosisdeposition in der Protonentherapie

Römer, K.; Petzoldt, J.; Pausch, G.; Rohling, H.; Hertel, N.; Fiedler, F.

Fragestellungen: Bei der Therapie von Tumorpatienten mit Partikelstrahlen ist ein exaktes und promptes Verfahren zur Überwachung der applizierten Dosisverteilung unerlässlich. Ein vielversprechender Ansatz ist die Messung Gammastrahlung, die – im Gegensatz zur Annihilationsstrahlung beim In-Beam-PET – ohne Zeitverzögerung abgestrahlt wird. Das entsprechende Gammaenergiespektrum ist jedoch sehr komplex, hochenergetischer als gängige im Labor zur Verfügung stehende Gammaquellen, und wird mit einer hohen Rate emittiert. Eine mögliche Lösung dieses Problems liefert die Compton Kamera. Jedoch sind diese Systeme sehr komplex und noch weit vom klinischen Einsatz entfernt. Sie erfordern Detektoren mit sehr guter Energieauflösung und spektroskopischer Elektronik. Eine Alternative bietet das Coded Aperture Prinzip. Hier wird eine möglichst stark absorbierende Maske vor dem ortsauflösenden Detektor angebracht, und es erfolgt eine ortsaufgelöste Zählung der Gammaquanten hinter der Maske. Auf eine genaue Energiemessung kann verzichtet werden, so dass die Anforderungen an Detektoren und Elektronik deutlich geringer ist. Kernstück aller Prompt Gamma Imaging Systeme unabhängig vom Messprinzip sind geeignete Detektoren für hochenergetische Gammastrahlung in Kombination mit einer geeigneten Elektronik. Diese Systemkomponenten müssen für den Einsatz unter den Bedingungen einer Partikeltherapie optimiert und charakterisiert werden, wobei Faktoren wie Energiebereich, Energieauflösung, Zählratenfestigkeit und Zeitauflösung entscheidend sind.

Material und Methoden: Standardisierte Proben verschiedener Szintillatormaterialien werden zunächst mit einem Referenz-Photomultiplier gekoppelt und mit klassischer Laborelektronik mit Hilfe radioaktiver Quellen bezüglich Photoelektronen-Ausbeute und Energieauflösung charakterisiert. Die Untersuchung weiterer Proben aus den gleichen Materialien in Abmessungen und Geometrien, die für ortsauflösende Messungen mit Silizuim-Photodetektoren eignen, mit derselben Technik erlaubt es dann, den Einfluß der Detektorgeometrie auf diese Parameter zu ermitteln. Schließlich lässt sich der Einfluss des Photosensors auf Energie-, Orts- und Zeitauflösung quantifizieren, wenn die vorher charakterisierten Proben mit unterschiedlichen, modernen Silizium-Photodetektoren ausgemessen werden. Die gewonnenen Erkenntnisse sollen es gestatten, für den jeweiligen Einsatzfall eine optimale Szintillator-Photosensor-Kombination zu wählen.

Ergebnisse: Erste Szintillatormaterialien wurden mit Hilfe des Referenz-Photomultipiers (XP5500/B von Photonis) hinsichtlich ihrer Photoelektronen-Produktion charakterisiert. NaI(Tl) hat demnach eine Ausbeute von >9000 Photoelektronen pro MeV. GAGG, das eigentlich mehr Licht liefern sollte, dessen Wellenlänge mit 510nm aber für die Effizienz der Photokathode ungünstiger ist, liefert >6000 Photoelektronen pro MeV. Diese nunmehr bekannten Szintillatoren werden dann mit Hilfe des digitalen Silizium-Photomultipliers (dSiPMT) der Firma Philips Digital Photon Counting auf ihre Einsatzmöglichkeit in ortsauflösenden Systemen getestet. Erste Messungen wurden auch mit analogen Silizium-Photomultipliern (SiPMT) oder Avalanche-Photodioden (APD) durchgeführt. Vergleiche mit Geant4 Simulationen zur Nachweiseffizienz und Lichtsammlung werden kurz vorgestellt.

Zusammenfassung: Die bildgebende Messung prompter Gammastrahlung ist ein vielversprechendes Verfahren zur Verifikation von Tumortherapien mit Partikelstrahlung. Entsprechende Messsysteme werden zurzeit entwickelt, benötigen aber maßgeschneiderte Detektoren. Diese Arbeit präsentiert Verfahren und erste Ergebnisse zur Charakterisierung von Szintillationsdetektoren für solche Systeme. Die systematische Untersuchung verschiedener Kristalle mit unterschiedlichen Photosensoren erlaubt dabei die Entkopplung von Material-, Geometrie- und Lichtdetektor-Effekten und damit eine Optimierung der Eigenschaften von Szintillationsdetektoren für die jeweilige Anwendung.

Literatur
[1] G. F. Knoll, “Radiation Measurements”, Eds. John Wiley & Sons, New York, Third Edition, pp. 629-631, 2000.
[2] Z. Guzik, S. Borsuk, K. Traczyk, and M. Plominski, “TUKAN-an 8k pulse-height analyzer and multichannel scaler with a PCI or a USB interface”, IEEE Trans. Nucl. Sci., vol 53, pp. 231-235, 2006.
[3] M. Bertollaccini, S. Cova, and C. Bussolatti, “A technique for absolute measurement of the effective photoelectron per keV yield in scintillation counters”, Proceedings of the Nuclear Electronics Symposium, Versailles, France, 1968.
[4] S. Agostinelli et al., “GEANT4: A simulation toolkit. ”, Nucl. Instrum. Meth., A506:250–303, 2003.
[5] Saint Gobain, Brillance 380 Data Sheet.
[6] C. Plettner et al, “CaF 2 (Eu): An “Old” Scintillator Revisited”, Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE
[7] T. Frach et al, “The digital silicon photomultiplier — Principle of operation and intrinsic detector performance”, Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE, pp.1959,1965, Oct. 24 2009-Nov. 1 2009
[8] T. Kormoll et al, “In-Vivo Dosimetry for Photon Radiotherapy Based on Pair Production”, Nuclear Science, IEEE Transactions on , vol.57, no.3, pp.1125,1131, June 2010

Keywords: proton therapy; in-vivo dosimetry; scintillator

  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP 2013), 18.-21.09.2013, Köln, Deutschland
  • Open Access Logo Abstract in refereed journal
    Medizinische Physik 2013 (2013), 322-323

Permalink: https://www.hzdr.de/publications/Publ-19235
Publ.-Id: 19235


Detectors for monitoring

Fiedler, F.

no abstract available

Keywords: detectors; in-vivo dose monitoring; proton therapy; ion therapy

  • Invited lecture (Conferences)
    ENTERVISION Course: Detectors and electronics, 09.-13.09.2013, Valencia, Spanien

Permalink: https://www.hzdr.de/publications/Publ-19234
Publ.-Id: 19234


Neue bildgebende Systeme für die Partikeltherapie - Ergebnisse des EU-Projektes ENVISION

Fiedler, F.

Einleitung: Die Partikeltherapie ist eine neue und hoch entwickelte Technik der Strahlentherapie bei Krebs. Strahlen geladener Teilchen, also Protonen und Ionen, werden verwendet, um Tumorzellen zu zerstören. Diese Ionenstrahlen deponieren ihre Energie primär am Ende ihres Weges im sogenannten Bragg-Peak. Dadurch gelingt es, eine hohe Koformalität zu erreichen und gesundes Gewebe sowie insbesondere strahlenempfindliche Organe optimal zu schonen. Um jedoch die Vorteile dieser Therapieform vollständig nutzen zu können, ist ein Verfahren erforderlich, welches den Ort der Dosisdeposition verifiziert. Hierfür wurde die Methode der Positronen-Emissions-Tomographie (PET) angewendet, die bei der Bestrahlung entstehende Sekundärteilchen detektiert und damit eine qualitative Bewertung der Dosisapplikation ermöglicht. An mehreren Zentren weltweit wird dieses Verfahren derzeit klinisch angewendet [1-3]. Eine andere, in der Entwicklung befindliche Möglichkeit ist die Einzelphotonentomographie (in-beam SPECT) [4-7], für welch neuartige Detektorkonfigurationen erforderlich sind.
Materialien und Methoden: Um die Instrumente für die Qualitätssicherung in der Partikeltherapie zu verbessern, stellt die Europäische Kommission die Finanzierung für ein 4-Jahres-Projekt, ENVISION - European NoVel Imaging Systems for ION therapy (Grant Agreement Number 241 851), bereit. Das Ziel des Projektes ist die Entwicklung von
(i) Echtzeit-Überwachung der Dosisapplikation;
(ii) quantitativer Bildgebung und präziser Bestimmung der abgegebenen Dosis;
(iii) schnellem Feedback für die optimale Planung der Behandlung;
(iv) der Anwendung des Verfahren auf bewegte Zielvolumina;
(v) Simulationsstudien.
Das Projekt startete Februar 2010 und ist ein Zusammenschluss von 16 führenden europäischen Forschungszentren und Industriepartnern mit einem Budget von 6 Millionen Euro, die Koordination obliegt dem CERN.
Ergebnisse: In Rahmen dieses Projektes wurden Simulationsstudien zur optimalen Auslegung eines für das Dosismonitoring geeigneten Detektors durchgeführt. Sowohl für PET als auch für SPECT wurden mehrere konzeptionell verschiedene Prototypen an den Partnerinstituten aufgebaut und an Bestrahlungsanlagen getestet. Die PET Methode wurde für bewegte Zielvolumina adaptiert und in Phantomexperimenten erfolgreich angewendet. Um die klinische Nutzbarkeit zu verbessern, wurde ein Softwareprototyp zur semiautomatischen Auswertung entwickelt.
Zusammenfassung: ENVISION ermöglichte die Realisierung verschiedener Ansätze und Ideen, existierende Verfahren für das Dosismonitoring zu verbessern und neue Methoden in Prototypen zu überführen. Insbesondere für die neuartigen Verfahren sind weitere Tests und Entwicklungen nötig, um das klinische Potential vollständig abschätzen zu können. Ferner ist die Integration der neuen Verfahren in den klinischen Alltag ein wichtiges Ziel künftiger Arbeiten.
Literatur
[1] W. Enghardt et al.: Nucl. Instr. Meth. A 525 (2004) 284.
[2] T. Nishio et al.: Med. Phys. 33 (2006) 4190.
[3] K. Parodi et al.: Int. J. Radiat. Oncol. Biol. Phys. 68 (2007) 920.
[4] C.H. Min et al.: Appl. Phys. Lett. 89 (2006), 183517.
[5] T. Kormoll et al.: Nucl. Instr. Meth. A 626-627 (2011) 114.
[6] J.C. Polf et al.: Phys. Med. Biol. 54 (2009) N519-27.
[7] J. Smeets et al.: Phys. Med. Biol. 57 (2012) 3371.

Keywords: Partikeltherapie; in-vivo dose monitoring; ENVISION

  • Invited lecture (Conferences)
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP 2013), 18.-21.09.2013, Köln, Deutschland
  • Open Access Logo Abstract in refereed journal
    Medizinische Physik 2013 (2013), 275

Permalink: https://www.hzdr.de/publications/Publ-19233
Publ.-Id: 19233


Tomographic Positron Annihilation Lifetime Spectroscopy

Wagner, A.; Anwand, W.; Butterling, M.; Fiedler, F.; Fritz, F.; Kempe, M.; Cowan, T. E.

Positron annihilation lifetime spectroscopy serves as a perfect tool for studies of open-volume defects in solid materials such as vacancies, vacancy agglomerates, and dislocations. Moreover, structures in porous media can be investigated ranging from 0.3 nm to 30 nm employing the variation of the Positronium lifetime with the pore size. While lifetime measurements close to the material’s surface can be performed at positron-beam installations bulk materials, fluids, bio-materials or composite structures cannot or only destructively accessed by positron beams. Targeting those problems, a new method of non-destructive positron annihilation lifetime spectroscopy has been developed which features even a 3-dimensional tomographic reconstruction of the spatial lifetime distribution.
A beam of intense bremsstrahlung is provided by the superconducting electron linear accelerator ELBE (Electron Linear Accelerator with high Brilliance and low Emittance) at Helmholtz-Zentrum Dresden-Rossendorf which delivers continuous wave electron bunches of less than 10 ps temporal width and an adjustable bunch separation of multiples of 38 ns, average beam currents of up to 1.6 mA, and energies up to 16 MeV. Since the generation of bremsstrahlung and the transport to the sample preserves the sharp timing of the electron beam, positrons generated inside the entire sample volume by pair production feature a sharp start time stamp for lifetime studies. In addition to the existing technique of in-situ production of positrons inside large (cm3) bulk samples using high-energy photons up to 16 MeV from bremsstrahlung production [1], granular position-sensitive photon detectors [2] have been employed.
In the presentation, the detector system [3] will be described and results for experiments using samples with increasing complexity will be presented. The Lu2SiO5:Ce scintillation crystals allow resolving the total energy to 5.1 % (RMS) and the annihilation lifetime to 225 ps (RMS). 3-dimensional annihilation lifetime maps have been created in an offline-analysis employing well-known techniques from PET. Further work concentrates on transferring the analysis to a massively parallel GPU-array.

References
[1] M. Butterling et al., Nucl. Instr. Meth. Phys. Res. B 269(2011) 2623.
[2] http://www.medical.siemens.com, Siemens Medical, ACCEL II HiRez block detector.
[3] A. Wagner et al., Defect and Diffusion Forum 331 (2012) 41.

Keywords: Positron annihilation lifetime spectroscopy; non-destructive 3-dimensional tomographic reconstruction; spatial lifetime distribution; bremsstrahlung; superconducting electron; linear accelerator ELBE

  • Invited lecture (Conferences)
    13th International Workshop on Slow Positron Beam Techniques and Applications, 15.-20.09.2013, München, Deutschland
  • Open Access Logo Journal of Physics: Conference Series 505(2014), 012034
    DOI: 10.1088/1742-6596/505/1/012034

Permalink: https://www.hzdr.de/publications/Publ-19232
Publ.-Id: 19232


Native Cu from the oceanic crust: Isotopic insights into native metal origin

Dekov, V. M.; Rouxel, O.; Asael, D.; Hålenius, U.; Munnik, F.

Ocean drilling has revealed that, although a minor mineral phase, native Cu ubiquitously occurs in the oceanic crust. Cu isotope systematics for native Cu from a set of occurrences from volcanic basement and sediment cover of the oceanic crust drilled at several sites in the Pacific, Atlantic and Indian oceans constrains the sources of Cu and processes that produced Cu0. We propose that both hydrothermally-released Cu and seawater were the sources of Cu at these sites. Phase stability diagrams suggest that Cu0 precipitation is favored only under strictly anoxic, but not sulfidic conditions at circum-neutral pH even at low temperature. In the basaltic basement, dissolution of primary igneous and potentially hydrothermal Cu-sulfides leads to Cu0 precipitation along veins. The restricted Cu-isotope variations (δ65Cu = 0.02 – 0.19‰) similar to host volcanic rocks suggest that Cu0 precipitation occurred under conditions where Cu+-species were dominant, precluding Cu redox fractionation. In contrast, the Cu-isotope variations observed in the Cu0 from sedimentary layers yield larger Cu-isotope fractionation (δ65Cu = 0.41 – 0.95‰) suggesting that Cu0 precipitation involved redox processes during the diagenesis, with potentially seawater as the primary Cu source. We interpret that native Cu precipitation in the basaltic basement is a result of low temperature (20°-65°C) hydrothermal processes under anoxic, but not H2S-rich conditions. Consistent with positive δ65Cu signatures, the sediment cover receives major Cu contribution from hydrogenous (i.e., seawater) sources, although hydrothermal contribution from plume fallout cannot be entirely discarded. In this case, disseminated hydrogenous and/or hydrothermal Cu might be diagenetically remobilized and reprecipitated as Cu0 in reducing microenvironment.

Keywords: Cu-isotopes; Deep-Sea Drilling Project; native Cu; Ocean Drilling Project; oceanic crust alteration

Permalink: https://www.hzdr.de/publications/Publ-19231
Publ.-Id: 19231


Liquid-Solid Mass Transfer in a Tubular Reactor with Solid Foam Packings

Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.

Catalytically active open-cell solid foam packings are promising replacements for conventional randomly packed catalyst particles due to their low pressure drop and high specific surface area. The liquid-solid mass transfer was studied with a modified electrochemical diffusion current method for different packings and flow rates. The effective liquid-solid mass transfer coefficients (Ф • kLS ) were determined at two different axial packing positions. In particular, the effects of gas and liquid superficial velocities and the pre-wetting mode of the packing (‘LEVEC’ and ‘KAN-LIQUID’) were researched. The results reveal that higher liquid superficial velocity increases the liquid-solid mass transfer, while increasing foam pore density lowers the mass transfer rate. The strong multiplicity behavior known from hydrodynamic studies of Mohammed et al. (2013) was not obtained for the liquid-solid mass transfer. However, the type of the liquid distributor providing the initial irrigation pattern has a significant effect on the effective liquid-solid mass transfer coefficient. A new correlation is proposed to predict the effective liquid-solid mass transfer coefficient.

Keywords: solid foam; liquid-solid mass transfer; electrochemical method; pre-wetting mode; packed-bed reactor; multiphase reactor

Permalink: https://www.hzdr.de/publications/Publ-19230
Publ.-Id: 19230


Characterization of narrow bandwidth x-rays from a Laser-Thomson-Backscattering source

Jochmann, A.

A tunable source of intense ultra-short hard X-ray pulses represents a novel tool for the structural analysis of complex systems with unprecedented temporal and spatial resolution. With the simultaneous availability of a high power short-pulse laser system this provides unique opportunities at the forefront of relativistic light–matter interactions. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) we demonstrated the principle of such a light source (PHOENIX – Photon Electron collider for Narrow bandwidth Intense X-Rays) by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating femtosecond laser pulses from the 150 TW Draco Ti:Sapphire laser system. The generated narrowband X-rays are highly collimated and can be reliably adjusted from 12 keV to 20 keV by tuning the electron energy (24–30 MeV). Ensuring the spatial–temporal overlap at the interaction point and suppressing the Bremsstrahlung background a signal to noise ratio of greater than 300 was reached.

Keywords: Laser backscattering; X-ray; Linear accelerator; Inverse Compton; Ultrafast; Thomson scattering

  • Lecture (Conference)
    The 5th International Conference "Channeling 2012", "Charged & Neutral Particles Channeling Phenomena", 23.-28.09.2012, Alghero, Italia

Permalink: https://www.hzdr.de/publications/Publ-19229
Publ.-Id: 19229


Operation of a picosecond narrow-bandwidth Laser-Thomson-backscattering X-ray source

Jochmann, A.; Irman, A.; Lehnert, U.; Couperus, J. P.; Kuntzsch, M.; Trotsenko, S.; Wagner, A.; Debus, A.; Schlenvoigt, H.; Helbig, U.; Bock, S.; Ledingham, K.; Cowan, T.; Sauerbrey, R.; Schramm, U.

A tunable source of intense ultra-short hard X-ray pulses represents a novel tool for the structural analysis of complex systems with unprecedented temporal and spatial resolution. With the simultaneous availability of a high power short-pulse laser system this provides unique opportunities at the forefront of relativistic light–matter interactions. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) we demonstrated the principle of such a light source (PHOENIX – Photon Electron collider for Narrow bandwidth Intense X-Rays) by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating femtosecond laser pulses from the 150 TW Draco Ti:Sapphire laser system. The generated narrowband X-rays are highly collimated and can be reliably adjusted from 12 keV to 20 keV by tuning the electron energy (24–30 MeV). Ensuring the spatial–temporal overlap at the interaction point and suppressing the Bremsstrahlung background a signal to noise ratio of greater than 300 was reached.

Keywords: Laser backscattering; X-ray; Linear accelerator; Inverse Compton; Ultrafast; Thomson scattering

Permalink: https://www.hzdr.de/publications/Publ-19228
Publ.-Id: 19228


Spectral investigations of Laser-wakefield accelerator dynamics and advanced brilliant light sources

Debus, A.; Steiniger, K.; Zarini, O.; Pausch, R.; Widera, R.; Bussmann, M.; Cowan, T.; Schramm, U.; Sauerbrey, R.

In order to improve quality and reproducibility of electron beams by Laser-wakefields acceleration (LWFA) for brilliant X-ray sources, at the HZDR we investigate the radiation emitted by LWFA and the resulting electron beams both in theory and experiment.

Experimentally, we are currently setting up an ultra-broadband, staggered spectrometer system ranging from the UV (200 nm) to the mid-IR (12µm) for analyzing coherent transition radiation from electron bunches to infer bunch durations and temporal structures down to sub-fs resolution at single-shot.

Aiming for a quantitative understanding of spectral signatures emitted by LWFA in arbitrary directions, we have added a Liénard-Wiechert type radiation module to the PIConGPU code for calculating online, spectral "sky-maps", as well as logarithmic spectra from IR to X-ray energies, using all particles of a 3D-PIC simulation.

Towards an optical FEL, either by conventional or LWFA electrons, we discuss design goals and feasibility of Travelling-wave Thomson scattering geometries.

Keywords: Laser-wakefield accelerator; LWFA; brilliant x-ray sources; optical FEL; TWTS; Traveling-wave Thomson scattering; electron bunch duration; coherent transition radiation; CTR; single-shot spectrometer

  • Poster
    Physics and Applications of High Brightness Beams (HBEB) 2013, 25.-28.3.2013, San Juan, Puerto Rico

Permalink: https://www.hzdr.de/publications/Publ-19227
Publ.-Id: 19227


A Spectral Sky Map of Laser Wakefield Acceleration

Debus, A.; Pausch, R.; Widera, R.; Bussmann, M.; Schramm, U.

We present an add-on to our GPU-based 3D particle-in-cell (PIC) code PIConGPU. This add-on allows to compute the radiation far field of all particles in the simulation using Liénard-Wiechert potentials.
With this code it is possible to compute a complete spectral sky map of all the radiation emitted during laser-driven wakefield acceleration of electrons in a plasma. We have implemented the calculation in such a way that it allows us to compute spectra with logarithmic frequency scales from the infrared to the X-ray region. Furthermore, we discuss the techniques involved to implement the algorithm on GPUs and present scaling results on large GPU clusters.

Keywords: particle-in-cell code; PIC; GPU; laser-wakefield accelerators; plasma radiation; Liénard-Wiechert potentials

  • Poster
    GPU Technology Conference 2013, 18.-21.3.2013, San Jose, California, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19226
Publ.-Id: 19226


Simulating radiation from Electron beams to full Laser-plasmas

Debus, A.; Pausch, R.; Steiniger, K.; Hübl, A.; Burau, H.; Widera, R.; Bussmann, M.; Cowan, T.; Jochmann, A.; Couperus, J. P.; Irman, A.; Schramm, U.

We show the results and its numerical analysis using CLARA from the recent Thomson scattering experiment with DRACO and ELBE. Extending the scope to the prediction and analysis of plasma radiation from Laser plasmas, we present PIConGPU with its capability of calculating the radiation from all billions of macro particles in the simulation. This is illustrated with simulation results of Laser-wakefield acceleration and the Kelvin-Helmholtz instability, which was shown to scale up to petaflop performance on the TITAN cluster at Oakridge.

Keywords: Thomson scattering; Liénard-Wiechert potentials; petaflop; HPC; X-ray; Laser-wakefield accelerator; Kelvin-Helmholtz instability; particle-in-cell code

  • Lecture (Conference)
    Laboratory for Laser- and beam-driven plasma Acceleration (LAOLA) Workshop, 28.-29.5.2013, Wismar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19225
Publ.-Id: 19225


Petaflop Plasma Simulations

Debus, A.; Pausch, R.; Widera, R.; Hübl, A.; Burau, H.; Kluge, T.; Schmitt, F.; Juckeland, G.; Nagel, W.; Bernholdt, D. E.; Schuchart, J.; Bussmann, M.; Cowan, T.; Sauerbrey, R.

Current results and performance scalings (strong and weak) are presented from simulating the Kelvin-Helmholtz instability including emitted radiation using PIConGPU on the Oakridge TITAN cluster.

Keywords: plasma radiation; Kelvin-Helmholtz instability; petaflop; HPC; Particle-in-cell code

  • Poster
    Helmholtz International Beamline for Extreme Fields (HIBEF), 02.-5.6.2013, Hamburg, Deutschland
  • Lecture (Conference)
    Helmholtz International Beamline for Extreme Fields (HIBEF), 02.-5.6.2013, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19224
Publ.-Id: 19224


Synthesis of coffinite, USiO4, and structural investigations of the UxTh(1-x)SiO4 solid solutions

Labs, S.; Hennig, C.; Weiss, S.; Curtius, H.; Zaenker, H.; Bosbach, D.

The miscibility behavior of the USiO4 – ThSiO4 system was investigated. The end members and ten solid solutions UxTh(1-x)SiO4 with x = 0.12 – 0.92 were successfully synthesized, without formation of other secondary uranium or thorium phases. Lattice parameters of the solid solutions evidently follow Vegard's Law. Investigation of the local structure with EXAFS reveals small differences between U and Th environment attributed to different atomic radii of the metal atoms but no implications for a miscibility gap. The data provided confirms complete miscibility for the system USiO4 – ThSiO4. The structure of the end members was studied in detail with XRD and discussed with special regard to the oxygen positions and the often neglected Si-O bond length. USiO4 could be obtained without UO2 impurities and the lattice parameters derived from Rietveld refinement as c = 6.2606(3) Å and a = 6.9841(3) Å. The Si-O distance in USiO4 appears to be 1.64 Å, which is more reasonable than earlier reported values.

Keywords: coffinite; thorite; solid solution; structural properties

Permalink: https://www.hzdr.de/publications/Publ-19223
Publ.-Id: 19223


Radiative Particle-in-Cell Simulations: Shedding new Light into the Dynamics of Laser-plasma interactions

Debus, A.; Pausch, R.; Steiniger, K.; Hübl, A.; Burau, H.; Widera, R.; Kluge, T.; Schramm, U.; Cowan, T. E.; Bussmann, M.; Schneider, B.; Grottel, S.; Schmitt, F.; Hönig, W.; Juckeland, G.; Nagel, W.

We present recent results using PIConGPU, a fully relativistic 3D particle-in-cell (PIC) code running on GPU clusters. We extended our code to compute the radiation spectra of all particles in the simulation based on classical Liénard-Wiechert potentials including full coherence and polarisation properties. We discuss implementation, physics tests, scaling and show simulation results of laser-wakefield accelerator and astrophysical plasmas, for which we calculated the angularly resolved spectra ranging from infrared to X-ray wavelengths.

Such an extensive treatment of plasma radiation across billions of macro particles makes it possible to explore temporally resolved plasma radiation spectra on linear and logarithmic photon energy scales over large solid angles ("sky-maps").
This ability of obtaining quantitative spectral data in plasma simulations poses a unique tool for determining the phase space distribution of electrons. Since spectral information is readily accessible in experiments, our results can serve as a valuable input to new diagnostics.

For the petaflop perfomance scaling of PIConGPU on the Oak Ridge TITAN cluster we use a scenario of the Kelvin-Helmholtz instability including radiation. Furthermore, we demonstrate the usefulness of the live 3D visualisation feature of PIConGPU for accessing running simulations.

Keywords: HPC; plasma radiation; particle-in-cell simulation; petaflop; 3D live visualization; Kelvin-Helmholtz instability; Laser-wakefield accelerator

  • Invited lecture (Conferences)
    23rd International Conference on Numerical Simulation of Plasmas (23rd ICNSP), 14.-16.9.2013, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-19222
Publ.-Id: 19222


Interactions of Plutonium with a Typical Isolate from Mont Terri Opalinus Clay

Moll, H.; Lütke, L.; Bachvarova, V.; Cherkouk, A.; Selenska-Pobell, S.; Bernhard, G.

Clay is investigated as one potential host rock for a safe disposal of nuclear waste. In this talk, results will be presented and discussed describing the bacterial diversity in Mont Terri Opalinus clay, the enrichment and cultivation of bacterial clay isolates and the interactions of a specific novel Sporomusa sp. isolate with plutonium.

Keywords: diversity; bacteria; plutonium

  • Lecture (others)
    5. Workshop des Verbundprojekts „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen“, 30.09.-01.10.2013, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19221
Publ.-Id: 19221


Shear induced force on a bubble in a bubble swarm

Ziegenhein, T.

Motivation:
The lift force on a single bubble changes it sign with increasing Eo-Number
Lift formulation, Tomiyama:
𝐹_𝐿𝑖𝑓𝑡= −𝐶_𝐿 𝜌_𝐿 𝛼_𝐺 (𝒗_(𝐵𝑢𝑏.)−𝒗_𝐿𝑖𝑞 ) dv_Liq/𝑑𝑥
𝐶_𝐿≅0.6−0.1𝐸𝑜_𝐻 , 4≤𝐸𝑜_𝐻≤8
Hypothesis: The sign change occur through vortex shedding at the bubble in a shear field

Keywords: bubbly flow; closure models; lift force; bubble column

  • Poster
    HZDR PHD-Seminar, 07.-09.10.2013, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19220
Publ.-Id: 19220


Liquid Metal Experiments for the Visualisation of the Two-phase flow in a Continuous Casting Model

Timmel, K.; Shevchenko, N.; Röder, M.; Eckert, S.; Gerbeth, G.; Anderhuber, M.; Gardin, P.

The quality of continuous casted steel is significantly affected by the flow pattern in the mould and the SEN. The flow in continuous casting machines is often a two-phase one, because argon bubbles are injected into the melt to avoid clogging inside the casting nozzle. Dependent on process parameters, like the liquid and the gas flow rate, such two-phase flows could become rather complex. Obviously, the actual two-phase flow regimes in the SEN are difficult to predict, but, have a distinct influence on the flow pattern and upcoming instabilities in the mould. We present an experimental study concerned with the two-phase flow in a mockup of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing two-phase flows in the mould and the SEN by means of X-ray radioscopy: the X-LIMMCAST (X-ray LIquid Metal Model of continuous CASTing). This setup utilizes the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results about the two-phase flow will be presented here accompanied by statistical analysis on the argon bubbles and a discussion of the advantages and limitations of the X-ray method. The position of the X-ray observation window can be changed, which allows the inspection of regions around the gas injection point at the tip of the stopper rod or the development of the bubbly flow in the mould. The X-ray images reveal complex flow situations, for instance, argon bubbles might be attracted by the wall of the SEN near the inlet forming huge bubbles there. Smaller bubbles are generated at the bottom of the SEN, where high shear flows exist. The bubbles in the mould are entrapped by the liquid metal jet. Bubble coalescence can be observed between the bubbles circulating within the flow rolls below the jet. The tendency to rise towards the mould level increases with growing bubble size.

Keywords: continuous casting; liquid metal model; argon injection; two-phase flow; x-ray imaging

  • Lecture (Conference)
    5th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking - STEELSIM, 10.-12.09.2013, Ostrava, Tschechische Republik
  • Contribution to proceedings
    5th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking - STEELSIM, 10.-12.09.2013, Ostrava, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-19219
Publ.-Id: 19219


The SRF photo injector at ELBE, status of development and operation

Teichert, J.

The production of beams with low emittance as well as high average current is one of the key techniques for future electron accelerators and next generation light sources. The superconducting radio-frequency photo electron source (SRF gun) has the potential to fulfill the requirements for these new accelerators. At the radiation source ELBE an SRF gun has been developed and put into operation. The gun has a 3 ½ cell niobium cavity for 1.3 GHz and uses normal-conducting photo cathodes. Since 2010 the gun has delivered beam into the ELBE linac. Recently a new driver laser with 13 MHz pulse repetition rate allows us to operate the IR free-electron lasers (FEL) with the SRF gun. The successful operation of the SRF gun confirms the general design with an elliptical cavity, superconducting RF choke filter, and normal-conducting photocathodes as well as the proper design of most of the subsystems like couplers and tuners. At present, the main draw-back is the low acceleration gradient of the present cavity, and we expect assembly of the new cavity in an improved cryomodule and its commissioning in 2014

Keywords: SRF gun; photo injector; superconducting RF; photo cathode; ELBE; free-electron laser

  • Lecture (others)
    Seminarvortrag, Brookhaven National Laboratory, ATF, 03.09.2013, Upton, USA

Permalink: https://www.hzdr.de/publications/Publ-19218
Publ.-Id: 19218


Progress of SRF Gun Development and Operation at the ELBE Accelerator

Teichert, J.; Arnold, A.; Buettig, H.; Lehnert, U.; Lu, P.; Michel, P.; Murcek, P.; Schurig, R.; Vennekate, H.; Xiang, R.; Kamps, T.; Rudolph, J.; Kneisel, P.; Will, I.

Superconducting RF photo guns are suitable candidates for electron injectors in future free-electron lasers and energy recovery linacs. For the radiation source ELBE an SRF gun was build and put into operation. During long-term tests, the operation of normal-conducting photocathodes in the superconducting cavity has been successfully demonstrated. At moderate average currents of some hundreds of μA the Cs2Te photocathodes possess excellent lifetime. The gun's acceleration gradient is the key parameters for beam emittance and the maximum achievable bunch charge of the gun. Therefore two new cavities with higher performance were developed, built and treated. The final tests of these cavities are ongoing. An upgraded cryomodule with an integrated superconducting solenoid was built.

Keywords: SRF gun; superconducting RF; photoinjector; ELBE; Nb cavity

  • Lecture (Conference)
    The 53th ICFA Advanced Beam Dynamic Workshop on Energy Recovery Linacs ERL-2013, 09.-13.09.2013, Novosibirsk, Russia
  • Open Access Logo Contribution to proceedings
    The 53th ICFA Advanced Beam Dynamic Workshop on Energy Recovery Linacs ERL-2013, 09.-13.09.2013, Novosibirsk, Russia
    Proceedings of ERL-2013, Novosibirsk, Russia, 2013, Genf: Jacow

Permalink: https://www.hzdr.de/publications/Publ-19217
Publ.-Id: 19217


Dark Current in Superconducting RF Photoinjectors – Measurements and Mitigation

Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Staats, G.; Vennekate, H.; Xiang, R.; Barday, R.; Kamps, T.

Unwanted beam can cause beam losses and may produce acute or chronic damages of the accelerator. Furthermore it can considerably disturb experiments or increase its back-ground. The operation of the superconducting RF photo gun at the ELBE accelerator has delivered the first experimental information on that topic. It was found, that dark current is an important issue, similar to that of normal conducting RF photo injectors. In the presentation the measurement of dark current, its properties and analysis will be shown and we will discuss ways for mitigation, especially the construction of a dark current kicker.

Keywords: SRF gun; superconducting RF; photo injector; dark current; field emission

  • Lecture (Conference)
    The 53th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs ERL-2013, 09.-13.09.2013, Novosibirsk, Russia
  • Open Access Logo Contribution to proceedings
    The 53th ICFA Advanced Beam Dynamic Workshop on Energy Recovery Linacs ERL-2013, 09.-13.09.2013, Novosibirsk, Russia
    Proceedings of ERL-2013, Novosibirsk, Russia, 2013, Genf: Jacow

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-19216
Publ.-Id: 19216


Bildrekonstruktion für Compton-Kameras zur In-vivo-Dosimetrie in der Ionentherapie

Schöne, S.; Rohling, H.; Enghardt, W.; Fiedler, F.

Fragestellungen:
Mit Protonen und Ionen lassen sich tumorkonformere Dosisverteilungen als mit Photonen erzielen [1]. Dieser Vorteil erfordert allerdings eine hohe Präzision der Bestrahlung. Um diese zu gewährleisten, ist eine Kontrolle der bei der Bestrahlung applizierten Dosis wünschenswert. Vorgeschlagene Methoden dafür basieren auf Wechselwirkungen von Ionenstrahl und Gewebe: Zum einen werden Positronenemitter gebildet, die durch Partikel-Therapie Positronen-Emissions-Tomographie (PT-PET) die Bildgebung der bei der Bestrahlung erzeugten Aktivität ermöglichen. Zum anderen kommt es zur Emission prompter Gammastrahlung, welche mit Einzelphotonendetektoren gemessen wird (in-beam-SPECT).

PT-PET ist bereits klinisch etabliert. Aufgrund inhärenter physikalischer Beschränkungen ist es bisher nicht möglich, die applizierte Dosis direkt zu messen. In-beam-SPECT unterliegt nicht diesen Limitierungen; aus diesem Grund sollen die Möglichkeiten der Dosiskontrolle mittels der prompten Gammastrahlung evaluiert werden. Neben anderen Methoden [2] ist zur Messung dieser prompten Gammastrahlung die Compton-Kamera vorgeschlagen worden, welche eine „elektronische Kollimation“ nutzt und damit neue Rekonstruktionsmethoden verlangt.

Material und Methoden:
Die Bildrekonstruktion für Compton-Kameras teilt sich in die Aufgaben der Erstellung eines virtuellen Modells der Kamera in Form einer Systemmatrix (SM) und anschließend der Optimierung eines Emissionsbildes, welches möglichst gut zur aufgenommen Messreihe korreliert. Für Letzteres wurde der Standardalgorithmus MLEM (maximum likelihood expectation expectation maximization) [3] in der Derivation LM-MLEM (Listmode-MLEM) [4] verwendet.

Für die aufwändige Erstellung einer realitätsnahen Systemmatrix wurden sowohl – durch die Kinematik der Compton-Streuung bestimmte – grundsätzlich mögliche Herkunftsorte eines Photons, als auch verschiedene Ereigniswahrscheinlichkeiten – bestimmt durch die jeweiligen Wirkungsquerschnitte – berechnet. Da Messungen mit einem physikalischen System zwangsläufig mit Unsicherheiten behaftet sind, handelt es sich bei den Messwerten um Wahrscheinlichkeitsverteilungen. Daher wurden alle Operatoren zur Verarbeitung von Verteilungen entworfen und implementiert. Zur Reduktion des Platz- und Zeitaufwandes wurden Operationen, soweit wie möglich, analytisch statt numerisch gelöst.
Bei MLEM handelt es sich um ein iteratives Verfahren; der Zugriff auf die SM geschieht mehrfach. Da die Erstellzeit der SM den IO-Aufwand zu ihrer persistenten Ablage übersteigt, wurde ein anpassungsfähiger Cachingmechanismus angewandt.

Ergebnisse:
Die genannten Algorithmen wurden auf experimentelle Messreihen und simulierten Daten angewandt.

Die Abbildungen 1 und 2 zeigen beispielhafte Ergebnisse. Abbildung 1 stellt die Rekonstruktion zweier Aufnahmen einer Punktquelle mit dem Prototyp einer Compton-Kamera [5] dar. Die Rekonstruktionen erreichen dabei Genauigkeiten von rund 6 mm bzw. 10 mm Halbwertsbreite für die zentrierte bzw. nicht-zentrierte Quelle. Abbildung 2 zeigt das Resultat der Rekonstruktion einer simulierten Flächenquelle, deren Strukturen bis zu einem gewissen Grad wiederhergestellt werden konnten.

Es ist ersichtlich, dass auch Quellorte außerhalb der Detektorgröße – hier 2² cm² [ebd.] – rekonstruiert werden können.

Zusammenfassung:
Es wurde gezeigt, dass mit dem vorgestellten Verfahren die Bildgebung, mittels der für den genannten Anwendungszweck entwickelten Compton-Kamera, grundsätzlich möglich ist. Die erfolgreiche Rekonstruktion des Emissionsbildes konnte sowohl an simulierten, als auch gemessenen Aufnahmen gezeigt werden.

  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19215
Publ.-Id: 19215


Dark Current Measurements at the Rossendorf SRF Gun

Xiang, R.; Arnold, A.; Lu, P. N.; Murcek, P.; Teichert, J.; Vennekate, H.; Barday, R.; Kamps, T.; Volkov, V.

In high gradient photo injectors electron field emission creates so-called dark current. The dark current produces beam loss that increases the radiation level, causes damages to the accelerator components, and produces additional background for the users. Field emitted electrons which stay inside the gun, increases RF power consumption and heat load for the superconducting cavities. It is also believed that dark current is the source of local outgassing and plasma formation which can damage sensitive photocathodes. Thus, to understand and control the dark current has become increasingly important for accelerators. In this presentation, we report on dark current measurement at the ELBE SRF Gun at HZDR. The measurements were carried out with the 3.5 cell-cavity SRF gun and Cs2Te photocathodes. We discuss the dark current behavior for different cavity gradients and various solenoid fields. Simulations have been done to understand the experimental results.

Keywords: SRF gun; superconducting rf; electron injector; dark current; field emission

  • Poster
    FEL 2013, 35th International Free-Electron Laser Conference, 26.-30.08.2013, New York, USA
  • Open Access Logo Contribution to proceedings
    FEL 2013, 35th International Free-Electron Laser Conference, 26.-30.08.2013, New York, USA
    Proceedings of FEL 2013, 35th International Free-Electron Laser Conference, New York, USA, 2013: Jacow

Permalink: https://www.hzdr.de/publications/Publ-19214
Publ.-Id: 19214


Ion-guided microstructure evolution of carbon-nickel nanocomposite films during ion beam assisted deposition: 3D sculpting at the nanoscale

Krause, M.; Buljan, M.; Oates, T. W. H.; Mücklich, A.; Fritzsche, M.; Facsko, S.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.; Abrasonis, G.

Ion assistance during film growth provides unique opportunities to influence the microstructure due to energy transfer and imposed directionality. For this study, the carbon:nickel system was chosen as model system. The growth of C:Ni nanocomposites without ion assistance is controlled by the phase separation under kinetic constraints of surface and volume diffusion and by the film growth rate. A systematic study of ion irradiation as a pure energy and momentum transfer agent in the context of surface diffusion assisted phase separations is, however, lacking. Here the influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 50 at.% Ni) thin films will be reported. Two types of ordered nanostructures are identified and characterized: i) tilted columns and ii) compositionally modulated ripples, which are transferred into a periodic three-dimensional nanoparticle array. For i), the tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. For a given composition of the depositing flux, the transition from the columnar growth to the 3D pattern formation regime as a function of the assisting ion energy is demonstrated. The effects of the metal content and the assisting ion current on the self-organized 3D patterns and surface periodicity are studied. The observed microstructures evolution is explained by ion-induced effects.

Keywords: Nanoscale pattern formation; Ion beam assistance; Morphology and microstructure of thin films; Nanocomposites and Nanoparticles

  • Poster
    537th Wilhelm and Else Heraeus Seminar Physics of Ionized and Ion-Assisted PVD: Principles and Current Trends, 26.-28.06.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19213
Publ.-Id: 19213


FEL Operation with the superconducting RF photo gun at ELBE

Teichert, J.; Arnold, A.; Büttig, H.; Justus, M.; Lehnert, U.; Lu, P. N.; Michel, P.; Murcek, P.; Schurig, R.; Seidel, W.; Vennekate, H.; Xiang, R.; Kamps, T.; Rudolph, J.; Will, I.

The superconducting RF photoinjector (SRF gun) operating with a 31/2-cell niobium cavity and Cs2Te photocathodes is installed at the ELBE radiation center. The gun provides beams for ELBE as well as in a separate diagnostics beam line for beam parameter measurements. Since 2012 a new UV driver laser system developed by MBI has been installed for the SRF gun. It delivers CW or burstmode pulses with 13MHz repetition rate or with reduced rates of 500, 200, and 100 kHz at an average UV power of about 1W. The new laser allows the gun to serve as the driver for the infrared FELs at ELBE. In the first successful experiment a 260 µA beam with 3.3 MeV from SRF gun was injected into ELBE, further accelerated in the ELBE superconducting linac modules and then guided to the U100 undulator. First lasing was achieved at the wavelength of 41 µm. The spectrum, detuning curve and further parameters were measured.

Keywords: photoinjector; superconducting rf; free-electron laser; srf gun

  • Lecture (Conference)
    FEL2013, 35th International Free-Electron Laser Conference, 26.-30.08.2013, New York, USA
  • Poster
    FEL 2013, 35th International Free-Electron Laser Conference, 26.-30.08.2013, New York, USA
  • Open Access Logo Contribution to proceedings
    FEL 2013, 35th International Free-Electron Laser Conference, 26.-30.08.2013, New York, USA
    Proceedings of 35th International Free-Electron Laser Conference, New York, USA, 2013, Genf: Jacow

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Permalink: https://www.hzdr.de/publications/Publ-19212
Publ.-Id: 19212


Simultaneous STXM imaging and resistance measurements of trilayer vortices

Banholzer, A.; Wintz, S.; Fowley, C.; Deac, A.; Raabe, J.; Lenz, K.; Lindner, J.; Fassbender, J.

We investigate a trilayer vortex system by simultaneous scanning transmission X-ray microscopy (STXM) and in-situ giant magnetoresistance (GMR) measurements. Our aim is to correlate the magnetic configuration of both magnetic layers with the corresponding magneto-resistance effects.
The sample is a Co/Cu/Ni80Fe20 cylindrical trilayer, with 2 µm diameter [1]. Top and bottom contacts allow to apply a perpendicular DC current to measure the resistance. Simultaneously the magnetic configuration of each element of the disc is imaged using STXM. This is performed at the Paul Scherrer Institute. The vortex core formation in both magnetic layers and the position of the vortex core can be controlled by applying an in-plane external magnetic field. When the cores are at the edge, and the magnetization state resembles that of two in-plane magnetized disks, the GMR is low, as both cores move towards the center. With decreasing field the resistance increases, as the cores move beyond the center and towards the opposite side, the resistance decreases again. We investigate the resistance at different DC currents in dependency on the swept magnetic fields.
REFERENCES
[1] S. Wintz, Appl. Phys. Lett. 98, 232511 (2011)

Keywords: Vortex; STXM

  • Lecture (Conference)
    Joint European Magnetic Symposia (JEMS) 2013, 25.-30.08.2013, Rhodos, Greece

Permalink: https://www.hzdr.de/publications/Publ-19211
Publ.-Id: 19211


Direct Condensation and Entrainment Installation for Steam Experiments TOPFLOW-DENISE: Stratified Steam Condensation Experiments

Seidel, T.; Beyer, M.

1. MOTIVATION
In a hypothetical Small Break Loss of Coolant Accident (SB-LOCA) in a Pressurized Water Reactor (PWR), the Reactor Pressure Vessel wall (RPV) may be exposed to thermal stress, since Emergency Core Cooling Systems (ECCS) injects cold water. The loads on the primary loop and RPV walls are determined by mixing processes with the surrounding hot water and by the condensation of steam on the surface (see Bestion 2010 and Lucas 2005)
For the development and validation of CFD-models, experiments have to meet a high standard of reproducibility, measurement certainty and temporal and local resolution. The pressure tank technology of the TOPFLOW facility allows conducting such experiments at reasonable effort.
2. TOPFLOW-DENISE FACILITY
The Direct Condensation and Entrainment Installation for Steam Experiments (DENISE) is made for CFD-grade condensation experiments at up to 50 bars pressure (see Figure 1). Subcooled water is injected into the DENISE-basin in three different configurations for experimental investigation:
A) Stratified flow
B) Subcooled water Jet
C) steam bubble entrainment with a jet falling on a stratified surface
The experimental facility is equipped with a dense instrumentation. The flow inside is observed and controlled with a high speed camera and an infrared camera, coriolis flow meters and a set of micro thermocouples. The facility is supplied with a 4 MW electrical boiler, saturated water pumps, a 30 kW electrical heater and a 2 MW water cooler.
3. FIRST EXPERIMENTAL SERIES
The first series contains stratified flow experiments comparable to non-adiabatic flow inside hot and cold legs of PWRs. Measurement results can be compared to CFD simulations. Recently 56 experiments have been carried out according to the test matrix in Table 1.
The observed high speed and infrared images from the reference experiment are shown in Figure 2. The surface is slightly wavy and a small increase of water temperature is observable between inlet (left) and outlet (right). Processed data from these measurements, like the temperature plots shown in Figure 3 will provide comparable results for the development and validation of CFD-models.
4. OUTLOOK
Experiments with stratified steam-water surfaces have been carried out in August 2013. They are being analyzed till end of 2013. For the next experiments, a jet injector will be added to the facility and plunging jet experiments with bubble entrainment will be measured. Finally, there will be experiments with a subcooled water jet falling through the steam atmosphere. A special movable thermo sensor will be used to measure temperature profiles inside the jet.

  • Lecture (Conference)
    150 Jahre - Richard Mollier, Internationales Kolloquium zum 150. Geburtstag von Richard Mollier, 21.-23.11.2013, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19210
Publ.-Id: 19210


Lateral spin transfer torque induced magnetic switching at room temperature demonstrated by x-ray microscopy.

Buhl, M.; Erbe, A.; Grebing, J.; Wintz, S.; Raabe, J.; Fassbender, J.

Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nanoelectronic compo- nents. Therefore, new concepts for controlling the state of nanomagnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate re- producible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar. In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM).

Keywords: Magnetic Materials and Devices; Nanosensors and other Devices; Surface Patterning and Imaging

Permalink: https://www.hzdr.de/publications/Publ-19209
Publ.-Id: 19209


Entwicklung von CFD-Modellen für Wandsieden und Entwicklung hochauflösender, schneller Röntgentomographie für die Analyse von Zweiphasenströmungen in Brennstabbündeln

Krepper, E.; Rzehak, R.; Barthel, F.; Franz, R.; Hampel, U.

In einem Verbundprojekt im Rahmen des Programms „Energie 2020+“ gefördert durch das BMBF koordiniert durch das HZDR arbeiteten 4 Universitäten, 2 Forschungszentren und ANSYS zusammen. Der vorliegende Bericht beschreibt die Arbeiten des HZDR, die im Zeitraum September 2009 bis Januar 2013 durchgeführt wurden. Das Vorhaben war auf die Entwicklung und Validierung von CFD-Modellen von unterkühltem Sieden bis zu Filmsieden gerichtet.
Im Bericht werden die entwickelten und verwendeten Modelle dargestellt. Anhand der Nachanalyse von Experimenten wird auf die vorgeschlagene Kalibrierung der Modelle eingegangen. Wichtig ist hierbei eine genauere Beschreibung der Zwischenphasengrenzfläche, die durch Kopplung des Wandsiedemodells mit einem Populationsmodell erreicht werden kann. Anhand der Analyse von Bündelexperimenten konnte gezeigt werden, dass die gemessenen querschnittsgemittelten Messwerte mit einem Satz im Rahmen der Modellunsicherheiten kalibrierter Modellparameter reproduziert werden kann. Für die Berechnung der Verteilungsmuster des Dampfgehaltes im Kanalquerschnitt muss die Modellierung der Turbulenz beachtet werden.
Die experimentellen Arbeiten waren auf die Untersuchung eines Brennelementbündels gerichtet. An einer Versuchsanordnung zu einem Brennelementbündel werden die turbulente einphasige Geschwindigkeit (PIV), der mittlere Gasgehalt (Gamma-Densitometrie) sowie der zeitlich und räumlich aufgelöste Gasgehalt (Hochgeschwindigkeits-Röntgentomographie) gemessen. Letztere Methode wurde in Rossendorf entwickelt.

Keywords: boiling; CFD; bubbly flow; momentum exchange; mass exchange; population balance model; experiments; PIV; gamma densitometry; fast x-ray tomography

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-040 2013
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-19208
Publ.-Id: 19208


Laser assisted Compton scattering of X-ray photons

Seipt, D.; Kämpfer, B.

The Compton scattering of X-ray photons, assisted by a short intense optical laser pulse is discussed. The differential scattering cross section reveals the interesting feature that the main Klein-Nishina line is accompanied by a series of side-lines forming a broad plateau where up to ${\cal O} (10^3)$ laser photons participate simultaneously in a single scattering event. Due to the non-linear mixing of X-ray and laser photons a frequency dependent rotation of the polarization of the final state photons relative to the scattering plane emerges. A consistent description of the scattering process with short laser pulses requires to work with X-ray pulses. An experimental investigation can be accomplished, e.g., at LCLS or the European XFEL in the near future.

Permalink: https://www.hzdr.de/publications/Publ-19207
Publ.-Id: 19207


Magnetic properties of granular CoCrPt:SiO2 thin films deposited on GaSb nanocones

Ball, D. K.; Lenz, K.; Fritzsche, M.; Varvaro, G.; Günther, S.; Krone, P.; Makarov, D.; Mücklich, A.; Facsko, S.; Fassbender, J.; Albrecht, M.

We report on the effect of microstructure on the magnetic properties of granular CoCrPt:SiO2 films with weakly interacting magnetic grains deposited on pre-structured GaSb nanocone templates fabricated by ion erosion technique. By tuning the irradiation conditions, nanocone patterns of different cone size were prepared (from 28 to 120 nm in diameter and 32 to 330 nm high, respectively). The influence of the intergranular exchange coupling was also investigated by varying the SiO2 content from 8 to 12 at.\%. Deposition of CoCrPt:SiO2 on samples with small nanocones leads to a close magnetic grain packing, which results in the formation of extended magnetic domains larger than the average distance between the GaSb cones. In contrast, on larger nanocones, the magnetic coating grows on the side-walls with large separation between neighbouring cones leading to magnetic single-domain regions, which are correlated to the underlying structure. Magnetometry measurements indicate that both remanence and coercivity decrease with increasing cone size and/or SiO2 content due to the combined effect of the angular distribution of the magnetic easy axis of the grains and the intergranular exchange coupling strength.

Keywords: Magnetic granular films; Ion beam erosion; nanocones

Permalink: https://www.hzdr.de/publications/Publ-19206
Publ.-Id: 19206


Origin and enhancement of the 1.3 mu m luminescence from GaAs treated by ion-implantation and flash lamp annealing

Gao, K.; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, S.

GaAs and GaAs based materials have outstanding optoelectronic properties and are widely used as light emitting media in devices. Many approaches have been applied to GaAs to generate luminescence at 0.88, 1.30, 1.55 µm which are transmission windows of optical fibers. In this paper we present the photoluminescence at 1.30 µm from deep level defects in GaAs treated by ion-implantation and flash lamp annealing (FLA). Such emission, which exhibits superior temperature stability, can be obtained from FLA treated virgin GaAs as well as doped GaAs. Indium-doping in GaAs can greatly enhance the luminescence. By photoluminescence, Raman measurements, and positron annihilation spectroscopy, we conclude that the origin of the 1.30 µm emission is from transitions between the VAs-donor and X-acceptor pairs.

Keywords: GaAs; 1.3 µm photoluminescence; ion-implantation; flash lamp annealing

Permalink: https://www.hzdr.de/publications/Publ-19205
Publ.-Id: 19205


Structure and energetics of oxidic nanoclusters in bcc-iron

Posselt, M.; Devaraj, M.

Nanostructured ferritic alloys (NFA) or Oxide Dispersion Strengthened (ODS) steels consist of an iron-based matrix with dispersed nanometer-size oxide particles. Compared to conventional steels these materials exhibit two remarkable properties that are not fully understood yet: (i) Stability: Up to rather high temperatures the number and size of the oxygen-rich nanoparticles do not change significantly. (ii) Tolerance: The nanoclusters act as sinks for transmutation helium, vacancies and self-interstitial. The first property is the reason for the improved creep strength at high temperature, whereas the second property is related to the radiation resistance of these materials. Therefore, NFA or ODS are promising candidates for applications as structural materials in extreme environments, i.e. at high temperature and intense particle irradiation, such as in advanced nuclear fission and fusion reactors.
The detailed structure and composition of the oxidic nanoclusters containing Y, Ti, O along with other minor alloying and impurity elements is still under discussion. In this work simulated annealing (SA) based on the Metropolis Monte Carlo method is used in order to determine the structure of the oxidic nanoclusters with the lowest formation energy. Since cluster sizes up to a few nm are of interest, first-principle methods cannot be used throughout since they are computationally too expensive. In contrast to previous theoretical investigations both pair and triple interactions between the different atomic species are employed in the SA method. The corresponding interaction parameters are obtained from comprehensive first-principle calculations on the structure and energetics of point defects and small clusters. SA is performed for various oxidic clusters and the results are compared with available experimental and theoretical data from literature. The binding energy of the nanoclusters obtained in this work can be used as input parameters of coarse-grained method such as Object Kinetic Monte Carlo simulations and Rate Theory.

Keywords: ODS alloy; oxide nanocluster; structure and energetics; simulated annealing

  • Poster
    EUROMAT 2013, 08.-13.09.2013, Sevilla, Spain
  • Poster
    GETMAT Int. Workshop, 17.-19.09.2013, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19204
Publ.-Id: 19204


Temperature-dependent free formation energies of Y, Ti and O in bcc Fe: A first principles study

Devaraj, M.; Posselt, M.

The dispersion of thermally stable nanosized oxide particles in the ferritic matrix remarkably increases the high temperature mechanical strength of these alloys. These alloys are referred to as Nanostructured ferritic alloys (NFA) or Oxide Dispersion Strengthened (ODS) steels and are potential candidate for use as structural materials in advanced fast breeder and fusion nuclear reactors. NFA possess excellent creep strength compared to conventional ferritic/martensitic steels. These alloys are also found to be highly resistant against long term neutron and radiation fluxes and act as sinks for transmutation helium, vacancies and self-interstitial. The physical mechanisms leading to the formation of these oxide nanoclusters in ferritic matrix is not yet fully understood. The basic properties of these clusters containing Y, Ti, O and vacancies are investigated by Density Functional Theory (DFT). Further, the formation and binding energies obtained from DFT calculations are being used as input for Monte Carlo simulations. In this multiscale approach, the results of calculations crucially depend on the input parameters obtained from DFT calculations. In previous studies only DFT data determined at T=0 have been used as inputs. The main objective of present work is to calculate the temperature-dependent free formation energies of Y, Ti and O point defects in bcc Fe. For this purpose DFT is used to obtain the corresponding vibrational free energies within the framework of the harmonic approximation. The present work is motivated by the assumption that the knowledge of the temperature dependence of free formation and binding energies is very important to understand the thermodynamics of the formation of the oxide nanoclusters at high consolidation temperatures. The results obtained in this work are compared with recent theoretical calculations and discussed in relation to experimental solubility data.

Keywords: iron; foreign atoms; free formation energy; DFT

  • Lecture (Conference)
    EUROMAT 2013, 08.-13.09.2013, Sevilla, Spain

Permalink: https://www.hzdr.de/publications/Publ-19203
Publ.-Id: 19203


Compositionally modulated ripples during composite film growth: three-dimensional pattern formation at the nanoscale

Krause, M.; Buljan, M.; Mücklich, A.; Möller, W.; Fritzsche, M.; Facsko, S.; Heller, R.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.; Abrasonis, G.

Three-dimensional, ion-induced nano-scale pattern formation in the growth mode is studied for a bi-component thin film. C:Ni films were grown by dual ion beam co-sputtering applying an assisting oblique incidence low energy Ar+ ion beam. Their microstructure was determined by scanning electron, atomic force, and transmission electron microscopy, as well as by grazing incidence small angle X-ray scattering. The role of ion-induced collisional effects was investigated by binary collision computer simulations. The formation of compositionally modulated ripples on the C:Ni film surface is demonstrated. They consist of metal enriched topographic crests and carbon enriched valleys. Since the surface is constantly covered by incoming species, this pattern is transferred into the bulk as a periodic array of Ni3C nanoparticles in a carbon matrix. Lateral ripple propagation is shown to be one of the crucial phenomena for the film morphology. The essential experimental features are reproduced by the computer simulations. The results reveal the importance of ion-induced preferential displacements as driving factor for an surface instability, which gives rise to the observed pattern formation. The physical nature of the approach holds potential for the growth of functional nanocomposites with tunable properties independently of the nature of the materials.

Keywords: Nanoscale pattern formation; 3D nanoparticle arrays; Ion beam assisted deposition; Nanocomposites; Thin film morphology

Permalink: https://www.hzdr.de/publications/Publ-19202
Publ.-Id: 19202


Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis

Hannaske, R.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Ferrari, A.; Grosse, E.; Junghans, A. R.; Kempe, M.; Kögler, T.; Kosev, K.; Marta, M.; Massarczyk, R.; Matic, A.; Schilling, K.-D.; Schramm, G.; Schwengner, R.; Wagner, A.; Yakorev, D.

At energies relevant to Big Bang nucleosynthesis there is only scarce experimental data for the reaction p(n,gamma)d. Its reaction rate used in nuclear network calculations relies on theoretical models constrained by nucleon-nucleon scattering data, the capture cross section for thermal neutrons and experimental data of the photodissociation of the deuteron d(gamma,n)p, which as well is investigated sparsely at Big-Bang energies. Large experimental uncertainties make a comparison of measurements with precise theoretical calculations difficult.
We have studied the reaction d(gamma,n)p at the superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf using bremsstrahlung with an endpoint energy of 5.0 MeV. The target consisted of alternating layers of aluminum and deuterated polyethylen. Nuclear-resonance-fluorescence spectroscopy on 27Al with high-purity Germanium detectors allowed us to measure the photon flux at 2.2 and 3.0 MeV. ELBE offers a pulse length of some ps and an adjustable repetition rate making time-of-flight experiments even at a small flight path of 1 m possible. Neutrons with a kinetic energy from 20 to 1400 keV have been measured with six 1-meter-long plastic scintillators read out on two sides by high-gain photomultipliers.
Interactions of the emitted neutrons with components of the experimental setup (target, detectors, collimators, beam dump, walls) have a non-negligible influence and have been simulated using the FLUKA code. In combination with the neutron detection efficiency, which was experimentally determined at Physikalisch-Technische Bundesanstalt Braunschweig, we calculated a time-of-flight-dependent correction factor to the measured neutron spectrum.
We will present the experimental setup, the data analysis, the results of the simulation and the cross section.

Keywords: Big Bang nucleosynthesis; bremsstrahlung; gamma-ray spectroscopy; neutron time-of-flight; nuclear astrophysics; photon scattering; neutron detector; efficiency; FLUKA

  • Lecture (Conference)
    Nuclear Physics in Astrophysics VI, 19.-24.05.2013, Lisbon, Portugal
  • Open Access Logo Journal of Physics: Conference Series 665(2016), 012003
    DOI: 10.1088/1742-6596/665/1/012003

Permalink: https://www.hzdr.de/publications/Publ-19201
Publ.-Id: 19201


Clay mineral characterization and nano-pores evaluation - Arcabuco zone (Colombia)

Palacio, C. A.; Parra Vargas, C. A.; Anwand, W.; Mejía, J. A.; Martínez Ovalle, S. A.

Colombian mining is usually done without any proper scientific methodology, and therefore, without knowing if there is more potential for the mineral resource being mined. For a scientific insight, this work presents the analysis of clay mineral characterization and nano-pores evaluation. The samples were obtained from the Arcabuco zone, a region located in Boyacá-Colombia. The techniques used to identify the minerals, the crystal structure, the chemical composition and the thermal properties were X-ray Diffraction (XRD), Scanning Electron Microscopy and Energy-dispersive X-ray Spectroscopy (SEM - EDX), Thermogravimetry and Differential Thermal Analysis (TG-DTA), Mössbauer Spectroscopy (MS), and finally Positron Annihilation Spectroscopy.
The XRD data were analyzed by means of the Rietveld refinement method, finding phases like Montmorillonite, Quartz, Illite and Kaolinite. These phases were corroborated using the characterization techniques previously described. Positron annihilation data were used to detect and evaluate the size of the nano-pores and to correlate them with the behavior of the dehydration and hydration kinetics in these measurements obtained by TG-DTA.

Keywords: Clay Minerals, Geological environment, Positron Annihilation, Positronium; Open space, nano-pores, Interlayer space, Hydration

  • Lecture (Conference)
    21st Latin American Symposium On Solid State Physics (SLAFES XXI), 30.09.-04.10.2013, Villa de Leyva, Colombia

Permalink: https://www.hzdr.de/publications/Publ-19200
Publ.-Id: 19200


Isotope exchange investigation of nitrogen redistribution in expanded austenite

Christiansen, T. L.; Drouet, M.; Martinaviciusc, A.; Somers, M. A. J.

Sequential plasma and gaseous nitriding of Fe–18Cr–10Ni–3Mo stainless steel at 390 C with 14N and 15N isotopes followed by denitriding in flowing hydrogen was investigated. Redistribution of plasma-inserted nitrogen atoms (15N) by subsequent gaseous nitriding (14N) was observed. Denitriding after plasma- and gaseous nitriding resulted in predominant retraction of 14N, and only a minor amount of 15N. The nitrogen isotope diffusion behaviour is explained by two different states of nitrogen bonding and shortrange ordering between nitrogen and chromium.

Keywords: Nitriding; Nuclear reaction analysis; X-ray diffraction (XRD); Stainless steel

  • Scripta Materialia 69(2013), 582-585

Permalink: https://www.hzdr.de/publications/Publ-19199
Publ.-Id: 19199


Development of Cannabinoid Receptor (CB2R) Ligands for Application in PET Studies - Where to Attach the Radiolabel?

Günther, R.; Moldovan, R.; Lueg, C.; Deuther-Conrad, W.; Wünsch, B.; Brust, P.

The cannabinoid receptors type 2 (CB2R) are involved in many physiological processes but their expression level in healthy and diseased brain has not been unravelled. With positron emission tomography (PET) it is possible to monitor quantitatively very low amounts of compounds labelled with positron emitting isotopes like 18F in living organisms at high spatial resolution. For application in clinical research, such radiotracers have to show high selectivity and affinity to the target protein.
A series of fluorinated N-carbazolyl-oxadiazolyl-propionamides [1] was synthesised and the affinity towards the human CB2R was measured in receptor binding studies. Here, we combine our CB2R receptor model with 3D-QSAR data [2] to support molecular docking studies employing the MOE software (Version 2012.12 Chemical Computing Group Inc. Montreal. http://www.chemcomp.com). The studies revealed that both the primarily investigated compound 2 and the 2-fluoroethyl substituted carbazole derivative 1 (Ki = 3.6 nM) fits well into the binding pocket. Attachment of the fluorine at different positions of the structure does not lead to significantly different poses in accordance with the experimental data. Organ distribution studies on CD1-mice verified our prediction, [4] that [18F]1 and [18F]2 can cross the blood-brain barrier.
[1] Rühl T, Deuther-Conrad W, Fischer S, Günther R, Hennig L, Krautscheid L, Brust P: Cannabinoid Receptor Type 2 (CB2)-Selective N-Aryl-Oxadiazolyl-Propionamides: Synthesis, Radiolabelling, Molecular Modelling and Biological Evaluation. Org Med Chem Lett 2012, 2: 32
[2] Günther R, Brust P: Synergistic approach of structure- based and ligand-based drug design for the development of selective cannabinoid receptor ligands. J Cheminform 2012, 4(Suppl 1): P11
[4] Gerebtzoff G, Seelig A: In Silico Prediction of Blood-Brain Barrier Permeation Using the Calculated Molecular Cross-Sectional Area as Main Parameter. J Chem Inf Model 46 2006, 6: 2638–2650

  • Lecture (Conference)
    9th German Conference on Chemoinformatics 2013, 10.-12.11.2013, Fulda, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Cheminformatics 6(2014)1, O9
    DOI: 10.1186/1758-2946-6-S1-O9

Permalink: https://www.hzdr.de/publications/Publ-19198
Publ.-Id: 19198


Intense green-yellow electroluminescence from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices

Berencen, Y.; Wutzler, R.; Rebohle, L.; Hiller, D.; Ramirez, J. M.; Rodriguez, J. A.; Skorupa, W.; Garrido, B.

High optical power density of 0.5 mW/cm2, external quantum efficiency of 0.1%, and population inversion of 7% are reported from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices. Electrical and electroluminescence mechanisms in these devices were investigated. The excitation cross section for the 543 nm Tb3+ emission was estimated under electrical pumping, resulting in a value of 8.2E-14 cm2, which is one order of magnitude larger than one reported for Tb3+:SiO2 light emitting devices. These results demonstrate the potentiality of Tb+-implanted silicon nitride material for the development of integrated light sources compatible with Si technology.

Keywords: electroluminescence; MOS devices; Terbium; Si-rich nitride

Permalink: https://www.hzdr.de/publications/Publ-19195
Publ.-Id: 19195


Correlation between efficiency and stability in Er- and Si-implanted MOS light emitting devices

Rebohle, L.; Wutzler, R.; Germer, S.; Helm, M.; Skorupa, W.; Berencén, Y.; Garrido, B.; Hiller, D.

Er-based light emitters, which can be electrically driven and easily integrated into Si-based circuitries, are of great interest for a broad palette of applications, especially in the field of telecommunication and sensing. Among the different approaches Er-implanted MOS devices feature their excellent compatibility to standard CMOS processes and the reproducibility of the implantation process. However, at present such devices do achieve neither the efficiency nor the operation lifetime usually required for such applications.
In this study we compare various designs of Er-implanted MOS devices with respect to their electroluminescence efficiency and electrical operation lifetime. The different designs comprise devices implanted with Er alone or co-implanted with Si and Er, various single and multilayer systems and different host matrices for Er, namely SiO2 or Si-rich Si3N4. Despite the different design parameters, a strong correlation between efficiency and operation lifetime is found. This behavior is explained by the ambivalent role of hot electrons which play a key role both for the efficient excitation of erbium and for the oxide degradation.

Keywords: electroluminescence; MOS devices; Erbium; Si-rich SiO2

  • Lecture (Conference)
    EMRS 2013 Spring Meeting, 27.-31.05.2013, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-19194
Publ.-Id: 19194


Surface exposure dating of the Veliki vrh rock avalanche in Slovenia associated with the 1348 earthquake

Merchel, S.; Mrak, I.; Braucher, R.; Benedetti, L.; Repe, B.; Bourlès, D. L.; Reitner, J. M.

Over 30 samples from bedrock and boulders from theVeliki vrh rock avalanche have been collected for surface exposure dating. The limestone rocks have been radiochemically treated to isolate and determine long-lived 36Cl by accelerator mass spectrometry. It could be shown that the Veliki vrh rock avalanche from the Košuta Mountain (Slovenia) event can be very likely linked to one of the major historical Earth-quakes in Europe happening on the 25th of January 1348. Taken into account independently determined denudation rates, inherited 36Cl originating from pre-exposure at shallow depths (20-55 m) could be calculated. The high amount of inherited 36Cl, i.e. 17-46% of the total 36Cl, makes this site not suitable for a precise determination of the 36Cl production rate as it was originally anticipated. Velikhi vrh is a “classic” rock avalanche of high velocity. The slope failed in the upper part with a translational slide, whereas dynamic fragmentation is the cause for further crushing of the material and the long runout.

Keywords: terrestrial cosmogenic nuclides (TCN); exposure dating; accelerator mass spectrometry, earthquake; rock avalanche; 36Cl; Slovenia

Permalink: https://www.hzdr.de/publications/Publ-19193
Publ.-Id: 19193


Volume-doped cobalt titanates for ethanol sensing: an impedance and X-ray absorption spectroscopy study

Belle, C. J.; Wesch, G. E.; Neumeier, S.; Lozano-Rodríguez, M. J.; Scheinost, A. C.; Simon, U.

The dynamic C2H5OH sensitivity of ilmenite-type cobalt titanates volume-doped by 2 at% Li, Na, K, Sb, La, Sm, Gd, Ho and Pb was systematically studied with respect to exhaust monitoring. Therefore, the p-type semiconducting CoTiO3 materials were characterized as resistive gas sensors via high-throughput impedance spectroscopy toward 5-200 ppm C2H5OH at 300-500 °C. The best performing materials were tested further by time-resolved and long-term measurements whereby the CoTiO3 volume-doped with K exhibited an outstanding overall performance. X-ray absorption spectroscopy on this particular material gave evidence that the local structure around Co and Ti remains unaffected by the doping despite of a slight increase in static disorder. Hence, the effect of K doping does not originate from alteration in the metal-to-oxygen interaction as expected from previous findings

Keywords: EXAFS; Cobalt titanates; sensors

Permalink: https://www.hzdr.de/publications/Publ-19192
Publ.-Id: 19192


Nonlinear Geostatistics for Geometallurgical Optimisation

van den Boogaart, K. G.; Konsulke, S.; Tolosana Delgado, R.

Adaptive mineral processing has to rely on spatially predicted information on primary geometallurgical parameters, like phase composition, size and shape distributions of grains from various phases, portions of value elements in different grain types. Naively, one would predict these parameters geostatistically and select an optimal processing for the predicted structure. This is suboptimal, due to various kinds of nonlinearities in the problem. First, some primary geometallurgical quantities themselves are measured in non-real scales, like compositional or stereologically distorted geometric information. Standard geostatistics has to be replaced by compositional and geometric geostatistics, involving complex transforms and restrictions. Further, only partial and uncertain information is available, introducing a stochastic character to the optimisation problem. Moreover, many response variables leading to costs, outcomes, and eventual effects of later processing depend nonlinearly on the primary geometallurgical parameters, which implies that the final monetary value is not estimated unbiasedly by kriging. Finally unbiased linear prediction (such as kriging) is not the best method of prediction for decision making. The conditional expectation of the monetary values is needed instead. The impact of these problems is explained in this paper with simplified examples and a first approach to a general solution is proposed.

Keywords: geometallurgy; nonlinear geostatistics; adaptive processing

  • Contribution to proceedings
    GeoMet 2013, The second AusIMM International Geometallurgy Conference 2013, 30.09.-2.10.2013, Brisbane, Australia
    Proceedings of GeoMet 2013, 253-258

Permalink: https://www.hzdr.de/publications/Publ-19191
Publ.-Id: 19191


Millennial erosion rates across the Pamir based on 10Be concentrations in fluvial sediments: Dominance of topographic over climatic factors

Fuchs, M. C.; Gloaguen, R.; Merchel, S.; Pohl, E.; Sulaiman, V.; Andermann, C.; Rugel, G.

The understanding of erosion processes is fundamental to study the evolution of actively deforming mountain ranges, whereas the relative contributions tectonic and climatic factors and their feedbacks are debated. The Pamir is peculiar in both, high deformation rates induced by the India-Eurasia collision and its position at the transition between Westerlies and Monsoon. In order to contribute to this debate we quantify basin-wide erosion rates from cosmogenic 10Be concentrations in modern river sediments measured by accelerator mass spectrometry. Sample locations represent the Panj basin at six sites along its trunk stream, and the major, east-west elongated tributary basins at five sites. An average erosion of 0.64 mm/yr for the entire Pamir reveals a rapid landscape evolution.
Erosion rates of tributary sub-basins highlight the strong contrast between the plateau (0.05 mm/yr to 0.16 mm/yr) and the Pamir margins (0.54 mm/yr to 1.45 mm/yr). The intensity of erosion is primarily (R2 of 0.81) correlated to slope steepness (0.75 quartiles) suggesting either tectonic uplift or base level lowering. Multiple linear regression reveals that precipitation may contribute also to the efficiency of erosion (R2 of 0.93) to a lesser extent. Dry conditions and low slopes hinders sediment transport and consequently, erosion on the plateau. The highest erosion coincides with the predominant winter precipitation from the Westerlies. The concentrated discharge during spring and early summer favors pronounced erosion along the north-western Pamir margin by driving the sediment flux out of the basins. The magnitude of erosion in Pamir is similar to rates determined in the south Himalayan escarpment, whereas climatic and tectonic conditions are very different. Millennial erosion does not balance the roughly ten times higher fluvial incision implying a transient landscape. We propose that river captures are responsible for the strong base level drop driving the incision along the Panj and consequently, initiate steep hillslopes that will contribute to high erosion at the Pamir margins. Precipitation may act as limiting factor to hillslope adjustment and consequently to erosion processes.

Keywords: accelerator mass spectrometry; erosion rate; Pamir; cosmogenic nuclides; fluvial sediments

Permalink: https://www.hzdr.de/publications/Publ-19190
Publ.-Id: 19190


Untersuchungen zur Abtrennung von Uranverbindungen aus Grubenwässern

Zabelt, D.

Im Rahmen der vorliegenden Arbeit konnten sowohl erste Ergebnisse zur Abtrennung von Uran(VI)-Spezies aus Grubenwässern der Standorte Königstein und Schlema mittels Membrantrenntechnik, als auch eine Verknüpfung von Speziationsmessung und Modellierung erreicht werden. Die Speziation des gelösten Urans wurde zum einen über direkte Messung mittels TRLFS bestimmt und zum anderen mit einer Gleichgewichtsmodellierung berechnet. Dadurch lassen sich die Speziationen der komplex zusammengesetzten Lösungen mit zusätzlicher Sicherheit bestimmen. Im Vergleich zu bestehenden Untersuchungen, die sich aufgrund der Nichtverfügbarkeit von TRLFS auf sehr einfache synthetische Lösungen beschränken mussten, wurden in dieser Arbeit erste spektroskopische Untersuchungen realer Probenwässer durchgeführt, um eine gesicherte Datenlage für die Membrantrennung liefern zu können.
Ziel der Arbeit war die Untersuchung verschiedener Nanofiltrations- und Umkehrosmosemembranen auf ihre Eignung zur Abtrennung verschiedener Uranverbindungen. Im Rahmen dieser Arbeit sollten die Membranen zunächst anhand des Reinwasserfluxes und Magnesiumsulfat-Rückhaltes charakterisiert werden. Im Anschluss daran fanden Batch- und Cross-Flow-Versuche mit realen Grubenwässern aus Königstein und Schlema statt. Dabei wurden die Rückhalte der Membranen für Uran, sowie die Selektivitäten der Membranen für Uran gegenüber Calcium und Magnesium bestimmt.

  • Bachelor thesis
    Technische Universität Bergakademie Freiberg, 2013
    66 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19189
Publ.-Id: 19189


Spektroskopische Untersuchungen von Uran(VI) und Uran(IV) - Redoxprozesse und Komplexierungsverhalten in Gegenwart organischer Säuren

Jäckel, E.

In dieser Arbeit wird das Verhalten des natürlich auftretenden radioaktiven Isotops Uran-238 gegenüber verschiedenen organischen Säuren, genauer Citronensäure und Oxalsäure, untersucht. Dabei wird auf die Komplexierung sowie auf mögliche Redoxreaktionen in Abhängigkeit vom pH-Wert eingegangen.

  • Bachelor thesis
    Hochschule Zittau/Görlitz, 2013
    93 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19188
Publ.-Id: 19188


Robust Regression with Compositional Response: Applications to Geosciences

Hron, K.; Filzmoser, P.; Templ, M.; van den Boogaart, K. G.; Tolosana-Delgado, R.

Compositional data are multivariate observations describing quantitatively the relative importance or weight of a set of parts on a whole. Compositions frequently occur in geochemistry and they are popularly expressed in relative units, like proportions or percentages (i.e. as data with constant sum constraint 1 or 100, respectively).
The aim of multivariate regression is to quantify relations between a multivariate response and one or more explanatory variables, and to use these identied relations for prediction. The standard theory on linear regression models - the least squares methodology - is appropriate if the data do not include outlying observations, deviating from the main linear trend. Although robust regression tolerates a certain amount of deviating data points, it may lead to distorted results if it is directly applied to compositional data.
The isometric logratio (ilr) transformation is used to develop classical least-squares regression, where a compositional response depends on (non-compositional) explanatory variables. For several reasons it exists no straightforward solution for the robust robust regression problem with compositional response. Similarly as in the classical case, the step from the multivariate to the multiple model is not possible if the response ilr coordinates are not independent. Even more, in the robust case, to regress the response variables separately would result in ignoring the multivariate outliers. An additional challange is the proper choice of the ilr transformation that is crucial for an appropriate interpretation of results. Finally, a simplied approach to implement robust methods to ilr transformed data may produce transformationdependent results, an undesirable characteristic.
A solution is provided by the multivariate least trimmed squares (MLTS) method that fullls all required concepts of robustness for regression with compositional data. The robust regression model with compositional response can be used also for testing on subcompositional independence. Theoretical results are applied to a real-world problem from geosciences.

Keywords: compositional data; robust regression; least trimmed squares

  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, IAMG 2013, 02.-6.9.2013, Madrid, Espana
    Mathematics of Planet Earth, Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences, Lecture Notes in Earth System Science, Heidelberg: Springer, 978-3-642-32407-9, 87-90
    DOI: 10.1007/978-3-642-32408-6

Permalink: https://www.hzdr.de/publications/Publ-19187
Publ.-Id: 19187


Stochastic differential equations with fuzzy drift and diffusion

Sprungk, B.; van den Boogaart, K. G.

A new framework for the fuzzification of stochastic differential equations is presented. It allows for a detailed description of the model uncertainty and the non-predictable stochastic law of natural systems, e.g. in ecosystems even the probability law of the random dynamic changes due to unobservable influences like anthropogenic disturbances or climate variation. The fuzziness of the stochastic system is modelled by a fuzzy set of stochastic differential equations which is identified with a fuzzy set of initial conditions, time-dependent drift and diffusion functions. Using appropriate function spaces the extension principle leads to a consistent theory providing fuzzy solutions in terms of fuzzy sets of processes, fuzzy states, fuzzy moments and fuzzy probabilities.

Keywords: Fuzzy stochastic differential equations; Fuzzy stochastic processes; Model uncertainty

Permalink: https://www.hzdr.de/publications/Publ-19186
Publ.-Id: 19186


Inertial wave dynamics in a rotating liquid metal

Vogt, T.; Raebiger, D.; Eckert, S.

The dynamics of free and forced inertial waves inside cylinders of different aspect ratios A = H0/2R0 are studied experimentally. The liquid metal GaInSn was choosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of AC electromagnetic fields. The ultrasound Doppler velocimetry was used to record the flow structure and the inertial waves. Our experiments demonstrate the capability for selective excitation of different inertial wave modes by deliberate variations of the magnetic field parameters. The application of time-modulated AC fields turned out to be an efficient method for triggering inertial waves. Furthermore, it was found that turbulent fluctuations in a swirling flow driven by a rotating magnetic field are able to provoke one specific inertial wave mode inside the cylinder and that such an inertial wave is able to survive over a distinct time. Experiments at the fundamental resonance have shown that multiple harmonic oscillation modes appeared simultaneously. The measured inertial wave frequencies were compared to the predictions of the linear inviscid theory.

Permalink: https://www.hzdr.de/publications/Publ-19185
Publ.-Id: 19185


Spin-up of a magnetically driven tornado-like vortex

Vogt, T.; Grants, I.; Eckert, S.; Gerbeth, G.

The spin-up of a concentrated vortex in a liquid metal cylinder with a free surface is considered experimentally and numerically. The vortex is driven by two flow-independent magnetic body forces. A continuously applied rotating magnetic field provides source of the angular momentum. A pulse of about one order of magnitude stronger travelling magnetic field drives a converging flow that temporarily focuses this angular momentum towards the axis of the container. A highly concentrated vortex forms that produces a funnel-shaped surface depression. We explore experimentally the duration, the depth and the conditions of formation of this funnel. Additionally, we measure the axial velocity and calculate the axi-symmetric flow field of such transient vortex at a lower force magnitude. The spin-up vortex is similar to the corresponding developed time-averaged turbulent vortex driven by the same magnetic forces (Grants et al. 2008). There are two main differences. First, the maximum swirl concentration condition does not express as a constant ratio of the both driving forces. Second, a much higher degree of swirl concentration is feasible. We explain those differences by a much lower turbulence during the spin-up.

Permalink: https://www.hzdr.de/publications/Publ-19184
Publ.-Id: 19184


Eine Ausleseelektronik für CZT-Detektoren mit dem RENA-3 IC von Nova R&D

Födisch, P.; Lange, B.; Kaever, P.

Vorgestellt wird die Entwicklung einer kompakten Ausleseeinheit für CZT-Detektoren (Cadmiumzinktellurid) für die energieauflösende Spektroskopie von Gammastrahlung. Der von NOVA R&D verfügbare RENA-3 ASIC (Readout Electronics for Nuclear Applications) ist für den direkten Anschluss an die Detektoren vorgesehen und deckt so einen Großteil der analogen Funktionen ab. Im ASIC sind 36 konfigurierbare Eingangskanäle integriert, die mit ladungsempfindlichen Vorverstärkern und analoger Signalverarbeitung (pulse shaping) für CZT-Detektoren optimiert sind. Für die Ansteuerung des ASICs und die Verarbeitung der Ausgangssignale wurde eine digitale, FPGA-basierte Elektronik entwickelt. Die Konfiguration der Hardware wird mittels eines synthetischen Prozessors durch Software im FPGA und auf einem PC unterstützt. Gezeigt werden die Instrumentierung des Prototyps und die Ergebnisse der Kalibrierung des Gesamtsystems durch synthetische Detektorsignale in einer automatisierten Testumgebung. Mit dem entwickelten System werden der Messbereich, die Energieauflösung und das Zeitverhalten des ASICs untersucht und auf die geplante Anwendung mit CZT-Detektoren hin überprüft.

  • Open Access Logo Contribution to proceedings
    104. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2013, 11.-13.03.2013, Jülich, Deutschland, Hamburg: Verlag Deutsches Elektronen-Synchrotron, 978-3-935702-72-0, 135-143

Permalink: https://www.hzdr.de/publications/Publ-19183
Publ.-Id: 19183


High Resolution Energy-Angle Correlation Measurement of Hard X Rays from Laser-Thomson Backscattering

Jochmann, A.; Irman, A.; Bussmann, M.; Couperus, J. P.; Cowan, T. E.; Debus, A. D.; Kuntzsch, M.; Ledingham, K. W. D.; Lehnert, U.; Sauerbrey, R.; Schlenvoigt, H. P.; Seipt, D.; Stöhlker, T.; Thorn, D. B.; Trotsenko, S.; Wagner, A.; Schramm, U.

Thomson backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses but also for the investigation of the complex particle dynamics at the interaction point. For this purpose a complete spectral characterization of a Thomson source powered by a compact linear electron accelerator was performed with unprecedented angular and energy resolution. A rigorous statistical analysis comparing experimental data to 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential gamma-ray sources.

Keywords: Laser Thomson Backscattering Linear Accelerator ELBE X-Ray Emittance

Permalink: https://www.hzdr.de/publications/Publ-19182
Publ.-Id: 19182


Elektrische und strukturelle Eigenschaften von supraleitenden Schichten in Gallium-implantiertem Silizium und Germanium

Fiedler, J.

Zielstellung der Dissertation ist die detaillierte Analyse der Auswirkungen von supraleitenden Galliumausscheidungen auf das elektrische Transportverhalten hochdotierter Silizium- und Germaniumschichten. Dafür wird ein neues Verfahren zur Herstellung von supraleitenden Schichten in kommerziellen Silizium- und Germanium-Wafern mit Hilfe von Ionenimplantation und Kurzzeitausheilung entwickelt. Mittels Ionenimplantation durch eine dünne dielektrische Deckschicht wurden Galliumkonzentrationen weit über der Gleichgewichtslöslichkeit in die Silizium- und Germaniumsubstrate eingebracht. Kurzzeitausheilverfahren wurden verwendet, um die die Umverteilung des Galliums anzuregen. Die resultierende Galliumverteilung wurde analysiert und es konnte ein Modell entwickelt werden, welches die Ursache für die Ausbildung einer 10 nm dünnen Gallium-reichen Schichten an der Deckschicht/Halbleiter-Grenzfläche beschreibt. Übersteigt die Galliumkonzentration an der Grenzfläche den kritischen Wert von 15 at.%, können die Schichten bei Temperaturen unterhalb von 6 – 7 K supraleitend werden und zeigen damit eine ähnlich kritische Temperatur wie bereits untersuchte dünne amorphe Galliumfilme. Es wird somit erstmalig gezeigt, dass Gallium-reiche Ausscheidungen eine mit reinem Gallium vergleichbare kritische Temperatur haben. Der bisher häufig als Funktion der Schichtdicke erforschte Supraleiter-Isolator-Übergang konnte in den Schichten durch die Variation der Ausheilzeit hervorgerufen werden. Der normalleitende Schichtwiderstand ist als entscheidender Parameter für den Phasenübergang anzusehen. Da sich Gallium-reiche Ausscheidungen in Germanium wegen der geringen Differenz in Masse und Elektronenstruktur nur schwer nachweisen lassen, erfolgten die Strukturuntersuchungen hauptsächlich an Siliziumschichten. Die Ergebnisse dieses Modellsystems lassen sich zum großen Teil auf das Verhalten von Gallium in Germanium übertragen. Dieser Vergleich zeigt, dass außer der kritischen Temperatur alle elektrischen Eigenschaften der Gallium-reichen Schichten vom Substratmaterial abhängen. Supraleitung in Gallium-dotiertem Germanium wurde bisher nur bei Temperaturen unterhalb von 1 K beobachtet. Deshalb ist die kritische Temperatur ein geeigneter Parameter, um durch Dotierung hervorgerufene Supraleitung in Germanium von supraleitenden Ausscheidungen zu unterscheiden.

  • Doctoral thesis
    TU Ilmenau, 2013
    126 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19181
Publ.-Id: 19181


Semiconductor spectroscopy using THz free-electron lasers

Helm, M.

I will briefly review the history of THz free-electron lasers (FEL) as versatile sources for semiconductor spectroscopy and present some recent experiments using the FEL in Dresden.

Keywords: free-electron laser; terahertz; semiconductors

  • Invited lecture (Conferences)
    38th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW_THz 2013), 01.-06.09.2013, Mainz, Germany
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW_THz 2013), 01.-06.09.2013, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-19180
Publ.-Id: 19180


Effects of inlet condition on flows structure of bubbly flow in a rectangular column

Akbar, M. H. B. M.; Hayashi, K.; Lucas, D.; Tomiyama, A.

Experiments on bubbly flows in a rectangular column are carried out to investigate effects of inlet condition on flow structure. An air diffuser having 35 nozzles is used. The inlet gas flow rates from 34 nozzles are uniform and the lift coefficients of bubbles are small at this flow rate, whereas the gas inflow from the remaining one nozzle is varied to change the sign and magnitude of lift coefficients. The main conclusions obtained are as follows: (1) bubbly flow in a bubble column is apt to be heterogeneous even with small non-uniformity in the distribution of gas inflow, (2) when the nozzle causing non-uniform gas inflow is located in the center of the diffuser plate and the inflow distribution is symmetric, heterogeneous structure is formed due to the lift-induced flow instability pointed out by Lucas et al., (3) when the nozzle causing non-uniform gas inflow is located near the side wall of the column and the inflow distribution is asymmetric, heterogeneous structure is induced by the Coanda effect, and (4) the effects of inlet condition on flow structure in a bubble column can be predicted using a multi-fluid model.

Keywords: Instability; Bubble; Bubble column; Inlet condition; Lift force; Multi-fluid model

Permalink: https://www.hzdr.de/publications/Publ-19179
Publ.-Id: 19179


New insights into the dynamics of adsorption equilibria of humic matter as revealed by radiotracer studies

Lippold, H.; Lippmann-Pipke, J.

The mobility of contaminants in the subsurface hydrosphere can be governed by their interaction with aquatic humic substances, which may act as carriers. For modelling migration processes, retardation of humic molecules at mineral surfaces must be considered. There is, however, a lack of clarity concerning the reversibility of adsorption of these natural polyelectrolytes. In this work, evidence was provided that a dynamic adsorption equilibrium exists. For this purpose, adsorption of humic substances (purified Aldrich humic acid and an aquatic fulvic acid) onto kaolinite was examined in tracer exchange studies by means of 14C-labelled humic material. In addition, the kinetics of adsorption and desorption were investigated in batch experiments.
Attaining the equilibrium state of adsorption took considerably longer for the humic acid than for the fulvic acid (24 h and 4 h, respectively). In desorption experiments, initiated by diluting the supernatant at constant pH, no net release was observed for both substances within a time frame of 4 weeks. However, when introducing radiolabelled humic or fulvic acid as a tracer into pre-equilibrated adsorption systems in the state of surface saturation, quantitative exchange was found to take place. This indicates that adsorption of humic matter is in fact a reversible process, albeit an exchange time of more than 4 weeks was required for both humic materials. Models for humic-bound contaminant transport (presuming dynamic equilibria) are thus applicable under appropriate conditions.

Permalink: https://www.hzdr.de/publications/Publ-19178
Publ.-Id: 19178


Microbially mediated immobilization of radionuclide in subsurface crystalline rock environments

Krawczyk-Bärsch, E.

In the underground rock characterization facility tunnel ONKALO in Finland, and in the Äspö Hard Rock Laboratory (HRL) in Sweden massive 5–10-mm thick biofilms were observed attached to tunnel walls where groundwater was seeping from bedrock fractures. The main goal of the study was to evaluate the relevance of microbial processes for the immobilization of radionuclides in a deep crystalline repository for high-level radioactive waste. In laboratory experiments the effect of uranium on biofilms was studied on site in the ONKALO tunnel by adding uranium to the fracture water in a self constructed flow cell by using detached biofilm samples. Biofilm specimens collected for transmission electron microscopy studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms as needle-shaped uranyl phosphate minerals, similar to meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O).
Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) from the Äspö HRL were used for laboratory experiments, in which uranium and neptunium, respectively, were added to the BIOS biofilms. The biofilms were submerged in Äspö groundwater in a flow cell under aerobic conditions. The results showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85% and 95%, respectively. Thermodynamic calculation of the theoretical predominant fields of uranium species showed that the formation of an aqueous uranium carbonate species Ca2UO2(CO3)3 was predicted due to the high concentration of carbonate in the groundwater. Under the given pH conditions the uptake of uranium and neptunium in the BIOS biofilm depends predominantly on the high amount of ferrihydrite, which precipitated onto the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea. Consequently, the combination of the biological material and iron oxides created an abundant surface area for bioaccumulation and adsorption of radionuclides.

Keywords: biofilm; uranium; neptunium; nuclear waste repository

  • Invited lecture (Conferences)
    12th Symposium on remediation, 26.-27.09.2013, Jena, Germany

Permalink: https://www.hzdr.de/publications/Publ-19177
Publ.-Id: 19177


Industrial applicability of microbial interaction with metals and metalloids

Suhr, M.; Vogel, M.; Matys, S.; Raff, J.; Pollmann, K.

Many processes in nature are highly efficient and very fast. Therefore it is an obvious idea to screen natural structures and processes for applicability in related industrial processes. Especially microorganisms are known to be highly efficient in what they do. We thusly use microbes or microbial structures for metal removal and metal recovery, the development of novel catalysts and the development of biosensors [1, 2]. In our group we investigated different processes to fix dissolved metals and ecotoxic substances and how they can be used for metal filtering and nanoparticle (NP) synthesis. One scientific topic is the reduction of soluble selenium oxyanion selenit to elemental selenium by Azospirillum brasilense. The formation of hardly soluble Se(0) nanoparticles during this process might be of interest for both bioremediation of selenium contaminated water and for nanotechnology (photovoltaic/ semiconducting industry).
Furthermore, we intensively study self-assembling biomolecules, namely S-layers, which represents the outermost cell envelope of many bacteria and archaea. This highly ordered protein polymers are an attractive matrix to functionalize all kinds of materials. Their surface with its numerous functional groups and their regular distributed pores offers ideal binding and nucleation sites for various metals e.g. gold, palladium and platinum as well as for metal oxide nanoparticles e.g. composed of titanium dioxide or zinc oxide. By reducing bound metals, well defined and regularly arranged nanoparticles were obtained [3, 4]. These nanoparticle lattices can be used as catalysts for organic synthesis like homogeneous and heterogeneous hydrogenation and for metallization of surfaces (Pd-NP), improved photo catalysts with higher degradation rates (TiO2-, ZnO-NP), for defined synthesis of single and multi-walled carbon nanotubes (CNT’s) in case of Pt-NP and the development of bio sensory layer systems (Au-NP).
To increase the efficiency of the resulting nanoparticle lattice, we have introduced adhesion promoter between the technical surfaces and living microorganisms or S-layers by using the layer by layer technique [5]. This results in higher layer stability and a fully covered technical surface.

[1] Raff, J. et al. (2003), Chem. Mat. 15, 240-244.
[2] Sleytr, U.B. et al. (1999), Angew. Chem.-Int. Edit. 38, 1035-1054.
[3] Wahl, R. et al. (2001), Adv. Materials 13, 736-740.
[4] Pollmann, K. et al. (2006), Biotechnol. Adv. 24, 58-68.
[5] Decher, G. et al. (1994), Biosensors & Bioelectronics 9, 677-684.

Keywords: Bioremediation; Sorption; Nanoparticles; Gold; Selen; Bacteria; Microorganisms; Polyelectrolytes

  • Poster
    Engineering Life 2013: Bio-molecular principles for novel methods and materials, 17.-18.09.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19176
Publ.-Id: 19176


Adsorption behavior and heavy metal interaction processes of cellular components of Gram-positive bacteria investigated by QCM-D

Suhr, M.; Matys, S.; Viacava Romo, K. E.; Raff, J.; Pollmann, K.

Sorption processes based on biological materials like biomass itself or cell fragments become more and more attractive for biotechnological applications. In our group we work with isolated bacteria from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) that have high affinities for heavy metals [1]. The metal binding sites are predominantly provided by the bacterial cell wall, mainly by surface layer proteins, but also by other parts of the cell wall e.g. membrane lipids and peptidoglycan. Such biological structures and vital bacterial cells can be used to develop biosorptive materials that are of interest for a broad range of applications. Examples are bioremediation, for a specific and efficient removal and recovery of heavy, precious or actinide metals and as templates for synthesis of bio-based sensory layers or chemical catalysts [2, 3].
In our investigations surface layer proteins (S-layers) are one major research topic. They represent the outermost cell envelope of many eubacteria and archaea forming highly ordered paracrystalline lattices not only on the living cell, but also after isolation on various technical surfaces by self-assembling processes [4]. In previous work these proteins were immobilized in sol-gel ceramics for the successful removal of uranium and chromium [5, 6]. The highly ordered proteins allow a specific metal binding in the pores of the protein lattice. This property can be used for the arrangement of highly structured nanoparticles (e.g. Au, Pd, Pt). Thus investigation of the interaction of isolated cell wall components, like S-layer, peptidoglycan, lipids and secondary cell wall polymers (SCWP) or intact composites with metals and nanoparticles is important. But the deeper understanding of these processes on a molecular level remains challenging. Besides standard analytical methods the quartz crystal microbalance with dissipation monitoring (QCM-D) is used as versatile tool to track and control the biological layer formation, metal interaction and nanoparticle deposition as well as adsorption kinetics. This method allows the real time detection of sorption processes on a molecular level and gives further information of viscoelastic properties, layer stabilities and the total adsorbed mass [7]. Aim of our work is to study metal sorption behavior of cells and single cell wall fragments from Gram-positive bacteria to get more information about multilevel processes in complex natural systems. Therefore it is necessary to examine different immobilization strategies for the used biological components on various technical surfaces [8, 9]. The sorption behavior of metals and nanoparticles with the biological material will be studied by batch experiments and QCM-D [9]. The results were partially evaluated by supporting atomic force microscopy (AFM).

[1] Raff, J., Selenska-Pobell, S. (2006), Nuclear Engineering International 51 (619), 34-36.
[2] Das, N. (2010), Hydrometallurgy 105, 180-189.
[3] Pollmann, K. et al. (2006), Biotechnol. Adv. 24, 58-68.
[4] Sleytr, U. B. et al. (2007), FEMS Microbiology Letters 267(2), 131-144.
[5] Carreo, D. M. et al. (2011), The Canadian Journal of Chemical Engineering 89, 1281-1287.
[6] Raff, J. et al. (2003), Chem. Mater. 15, 240-244.
[7] Lopez, A.E. et al. (2010), Small 6 (3), 396-403.
[8] Günther, T. J., Suhr, M. et al. (2013), submitted.
[9] Suhr, M. et al. (2013), in preparation.

Keywords: Biosorption; Bacteria; S-Layer; Heavy metals; Actinides; Lipids; Bioremediation; Nanoparticles

  • Poster
    International Soft Matter Conference 2013, 15.-19.09.2013, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-19175
Publ.-Id: 19175


Spectroscopic investigations of actinides for ecological risk assessment in the context of nuclear waste disposal

Foerstendorf, H.

In the aftermath of the Fukushima Daiichi incident, the federal government of Germany terminated the civil use of nuclear power within the next decade. Hence, a solution for the long term storage of the nuclear waste from the power plants becomes more and more mandatory. In fact, up to now, the frame conditions for the search of an appropriate repository are still not defined much less accepted by the general public. In this lecture, aspects of the applied research in the field of nuclear waste disposal at the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf, Germany, are introduced. The focus is set on spectroscopic investigations on radionuclides including their speciation in aqueous solution and as well on mineral surfaces. The multi-spectroscopic approach, namely vibrational, X-ray absorption and luminescence spectroscopy, potentially provides complementary information on a molecular scale which is indispensable for the verification of current surface complex modeling calculations for a long term risk assessment of a deep ground waste repository.

  • Lecture (others)
    Seminar of Quantum Beam Science Directorate, JAEA, 30.09.2013, Tokai, Ibaraki, Japan
  • Lecture (others)
    Seminar of Department of Nuclear Engineering, Kyoto University, 02.10.2013, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-19173
Publ.-Id: 19173


Präklinische Fortschritte in der Alpha7-Nikotinrezeptor-PET

Deuther-Conrad, W.

Es ist kein Abstract vorhanden.

  • Invited lecture (Conferences)
    iPET.4 Forschung und Diagnostik, 07.09.2013, Ostrau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19172
Publ.-Id: 19172


1D Two-Fluid Model simulations of Flashing Flows in TOPFLOW Facility

Mikuz, B.; Tiselj, I.; Beyer, M.

The decompression experiment performed at TOPFLOW (acronym for Transient twO Phase FLOW) in 2011 has been reproduced using an in-house code WAHA as well as the latest bestestimate thermohydraulic system code TRACE. The evaporation of liquid water to steam caused by depressurization was simulated in about 8 m long vertical tube with an inner diameter of 195.3 mm. The liquid water was almost saturated at initial pressure value of 6.5 MPa. Simulations successfully reproduced the main features of the experiment’s pressure and temperature history.

Keywords: TOPFLOW; WAHA; TRACE; depressurization

  • Lecture (Conference)
    NENE 2013, 22nd International Conference Nuclear Energy for New Europe, 09.-12.09.2013, Bled, Slovenia
  • Contribution to proceedings
    NENE 2013, 22nd International Conference Nuclear Energy for New Europe, 09.-12.09.2013, Bled, Slovenia
    Proceedings of NENE 2013

Permalink: https://www.hzdr.de/publications/Publ-19171
Publ.-Id: 19171


Fine distributed moderating material with improved thermal stability applied to enhance the feedback effects in SFR cores

Merk, B.

The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effect in sodium cooled fast reactor cores is described. The influence of the moderating material on the fuel assembly geometry, the neutron spectrum, the feedback effects, the power and burnup distribution, and the transmutation performance is given. An overview on possible materials is provided and the relationship between hydrogen content and thermal stability is described. A solution for the problem of the limited thermal stability of primarily proposed hydrogen bearing moderating material ZrH1.6 is developed by the use of Yttrium-mono-hydride. The similarity in the effects reached by ZrH and YH is demonstrated by comparison calculations. The topic is closed by an overview on material properties, manufacturing issues, experience in fast reactors and a comparison of raw material costs.

Keywords: Nuclear; Nuclear reactors; Fast reactors; Innovative reactors; enhanced feedback; moderating material; Yttrium hydride; thermal stability

Permalink: https://www.hzdr.de/publications/Publ-19170
Publ.-Id: 19170


Electron Bunch Diagnostic at the Upgraded ELBE Accelerator: Status and Challenges

Kuntzsch, M.; Findeisen, S.; Gensch, M.; Green, B. W.; Hauser, J.; Kovalev, S.; Lehnert, U.; Michel, P.; Roeser, F.; Schneider, C.; Schurig, R.; Kaya, C.; Al-Shemmary, A.; Bousonville, M.; Czwalinna, M. K.; Golz, T.; Schlarb, H.; Schmidt, B.; Schulz, S.; Stojanovic, N.; Vilcins, S.; Hass, E.

Within the ELBE upgrade towards a Center for High Power Radiation Sources (HSQ), a mono energetic positron, a liquid lead photo neutron source and two new THz sources have been installed at the superconducting electron linac at ELBE. A variety of established as well as newly developed electron beam diagnostics were installed and tested. In this paper we want to present first results achieved with the currently existing prototype beam arrival time and bunch compression monitors (BAM, BCM) as well as one versatile EOS set-up. Based on these future developements and upgrades are discussed.

Keywords: ELBE Bunch Diagnostic

  • Lecture (Conference)
    International Beam Instrumentation Conference IBIC 2013, 16.-19.09.2013, Oxford, United Kingdom
  • Open Access Logo Contribution to proceedings
    International Beam Instrumentation Conference IBIC 2013, 16.-19.09.2013, Oxford, United Kingdom
    Proceedings of IBIC 2013

Permalink: https://www.hzdr.de/publications/Publ-19169
Publ.-Id: 19169


The Structural changes of Y2O3 in ferritic ODS alloys during milling

Hilger, I.; Tegel, M.; Gorley, M. J.; Grant, P. S.; Weißgärber, T.; Kieback, B.

Oxide dispersion strengthened (ODS) ferritic steels are usually fabricated via mechanical alloying and subsequent consolidation via hot extrusion or hot isostatic pressing. During the individual process steps, a complex evolution of the nanoparticle structure is taking place. Powders with different Y2O3 contents were milled and examined by means of X-ray diffraction (XRD) and atom probe tomography (APT). It has been observed that the Y2O3 is fragmented and becomes partially X-ray amorphous upon milling. This effect is due to the grain refinement of Y2O3 during the milling process and not because of its dissociation in the steel matrix.

Keywords: X-ray diffraction; XRD; ODS; ferritic steels; GenIV; dissolution; Y2O3; Atom Probe tomography; amorphous; mechanical alloying; milling

Permalink: https://www.hzdr.de/publications/Publ-19168
Publ.-Id: 19168


Advantages and dynamics features of liquid fueled MSR

Krepel, J.; Fiorina, C.; Kliem, S.

Nuclear reactors operated with liquid fuel may have several remarkable advantages and features. The most developed reactor system in this category is the Molten Salt Reactor (MSR). It represents an old concept, but its properties are qualifying it for the advance utilization: inherent safety, excellent neutron economy, continuous or batch reprocessing possibility. The focus of this paper is to characterize the MSR physics, highlighting its unique advantages and investigating its specific dynamics.

  • Contribution to proceedings
    Conference on Molten Salts in Nuclear Technology, 09.-11.01.2013, Mumbai, India
    Proceedings of the conference on Molten Salts in Nuclear Technology CMSNT-2013, Mumbai

Permalink: https://www.hzdr.de/publications/Publ-19167
Publ.-Id: 19167


Fuel cycle advantages and dynamics features of liquid fueled MSR

Krepel, J.; Hombourger, B.; Fiorina, C.; Mikityuk, K.; Rohde, U.; Kliem, S.; Pautz, A.

Nuclear reactors operated with liquid fuel may have several remarkable advantages and features. The most developed reactor system in this category is the Molten Salt Reactor. It represents an old concept, but its properties are qualifying it for the advanced utilization: inherent safety, excellent neutron economy, continuous or batch reprocessing possibility without fuel fabrication. The focus has currently moved from the graphite moderated MSR studied in the past towards the fast MSR. The aim of this study is to characterize the MSR physics, highlighting its unique fuel cycle advantages using ERANOS-based EQL3D procedure and investigating its specific dynamics features by the dedicated DYN3D-MSR code.

Permalink: https://www.hzdr.de/publications/Publ-19166
Publ.-Id: 19166


RIA Fuel Codes Benchmark Volume 1

OECD / NEA, Committee On The Safety Of Nuclear Installations, Working Group On Fuel Safety; Holt, L.

Reactivity-initiated accident (RIA) fuel rod codes have been developed for a significant period of time and they all have shown their ability to reproduce some experimental results with a certain degree of adequacy. However, they sometimes rely on different specific modeling assumptions the influence of which on the final results of the calculations is difficult to evaluate.

A conclusion from the 2009 CSNI workshop on RIA was that RIA fuel rod codes are now heavily used, within the industry as well as the technical safety organizations (TSOs), in the process of setting up and assessing revised safety criteria for the RIA design basis accident.

It is then very important to master the use of such codes for reactor accident studies, particularly those involving safety analyses. It is essential to identify and understand real accident conditions that deviate from those of experiments. As a conclusion of the workshop, it was recommended that a benchmark between these codes be organized in order to give a sound basis for their comparison and assessment.

In order to maximize the benefits from this exercise, it was decided to use a consistent set of four experiments on very similar highly irradiated fuel rods tested under different experimental conditions:

- low temperature, low pressure, stagnant water coolant, very short power pulse (NSRR VA-1),
- high temperature, medium pressure, stagnant water coolant, very short power pulse (NSRR VA-3),
- high temperature, low pressure, flowing sodium coolant, larger power pulse (CABRI CIP0-1),
- high temperature, high pressure, flowing water coolant, medium width power pulse (CABRI CIP3-1).

Each of these four sibling rods are of identical fuel design and cladding material. Each experienced essentially the same pre-test irradiation history. For most practical purposes, the experiments are identical except for test conditions. The intent was to examine the so-called “temperature” effect (i.e. how to transpose results from experiments at low temperature to reactor conditions at high temperature?) in various RIA test programs.

The participation to the benchmark has been very important: 17 organizations representing 14 countries provided solutions for some or all the cases that were defined. In terms of computer codes used, the spectrum was also large as solutions were provided with FALCON, FEMAXI coupled to TRACE, FRAPTRAN, RANNS, RAPTA, SCANAIR, TESPAROD and TRANSURANUS.

The first noticeable fact is that, nearly all the participants used code that rely on simplified geometrical representation usually referred to as 1.5D codes. Although some 3D calculations may be done (one example was shown by one participant), it appears that given the conclusions below, the detailed geometrical description is not a priority. Rather, it looks more important at this stage to put the efforts and continue working on physical modeling.

During the benchmark, one source of differences between the results of the participants was identified to be due to the way input data, in particular the power pulse, are interpreted within the different codes. It is recommended that the code developers carefully examine the way the input data are used because this source of difference, that appeared to be significant, should be completely removed.

It was not possible during this benchmark to assess the influence of the initial state (resulting from base irradiation) of the fuel on the behavior during RIA. Nevertheless, this would be an important thing to do in the future in order to evaluate how much it accounts for on the scatter of the results.

With respect to the thermal behavior, the general conclusion is that the differences in the evaluation of fuel temperatures remain limited, although significant in some cases. The situation is very different for the cladding temperatures that exhibited considerable scatter, in particular for the cases when water boiling occurs. The film boiling heat transfer model was responsible for large differences between the calculations.

With respect to mechanical behavior, when compared to the (known) results of an experiment that involved only PCMI, the predictions of the cladding hoop strain from the different participants appeared acceptable, even though there was a factor of 2 between the highest and the lowest calculations. The conclusion is not as favorable for a case for which both the experimental results are unknown and water boiling is predicted to appear because then a factor of 10 on the hoop strain between the calculations was exhibited. This is due for a large part to the differences on the cladding temperatures.

In this benchmark, the fission gas release evaluations were also compared. The ratio of the maximum to the minimum values appears to be roughly 2, which is estimated to be relatively moderate given the complexity of fission gas release processes.

Finally, failure predictions that may appear as the ultimate goal of fuel code dedicated to the behavior under RIA conditions were compared. When looking at predictions in terms of enthalpy at failure, which is of interest in practical reactor applications, typical variations between calculations were found to be within a +/- 50 % range. Although major causes of the differences were identified, it is recommended to perform more systematic sensitivity and uncertainty analyses in a new phase of the benchmark to further assess the significance of the results produced.

It has been possible to evaluate the so-called user effect for the FRAPTRAN and SCANAIR codes. For both of them, it was found to be very limited on the cases of this benchmark, nearly negligible if compared to the differences between the results of the different codes. To generalize this conclusion would require more case to be studied.

The broader objective of the benchmark was to assess the possibility of evaluating the “temperature effect” that can be stated as: is it realistic to use the RIA fuel codes to transpose results, in particular enthalpy at failure, from experiments performed at low temperature to typical reactor conditions? Based on the conclusions formulated above, it appears obvious that it should be done with caution given the scatter that exists between the predictions of the different codes mainly due to the different approaches used to assess the rod failure level.

  • Other report
    Paris: OECD / NEA, 2013
    56 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19165
Publ.-Id: 19165


Development of a General Coupling Interface for the Fuel Performance Code TRANSURANUS Tested with the Reactor Dynamic Code DYN3D

Holt, L.; Rohde, U.; Seidl, M.; Schubert, A.; van Uffelen, P.

Several institutions plan to couple the fuel performance code TRANSURANUS developed by the European Institute for Transuranium Elements with their own codes. One of these codes is the reactor dynamic code DYN3D maintained by the Helmholtz-Zentrum Dresden - Rossendorf. DYN3D was developed originally for VVER type reactors and was extended later to western type reactors. Usually, the fuel rod behavior is modeled in thermal hydraulics and neutronic codes in a simplified manner. The main idea of this coupling is to describe the fuel rod behavior in the frame of core safety analysis in a more detailed way, e.g. including the influence of the high burn-up structure, geometry changes and fission gas release. It allows to take benefit from the improved computational power and software achieved over the last two decades.

The coupling interface was developed in a general way from the beginning. Thence it can be easily used also by other codes for a coupling with TRANSURANUS. The user can choose between a one-way as well as a two-way online coupling option. For a one-way online coupling, DYN3D provides only the time-dependent rod power and thermal hydraulics conditions to TRANSURANUS, but the fuel performance code doesn’t transfer any variable back to DYN3D. In a two-way online coupling, TRANSURANUS in addition transfers parameters like fuel temperature and cladding temperature back to DYN3D. This list of variables can be extended easily by geometric and further variables of interest.

First results of the code system DYN3D-TRANSURANUS will be presented for a control rod ejection transient in a modern western type reactor. Pre-analyses show already that a detailed fuel rod behavior modeling will influence the thermal hydraulics and thence also the neutronics due to the Doppler reactivity effect of the fuel temperature. The coupled code system has therefore a potential to improve the assessment of safety criteria. The developed code system DYN3D-TRANSURANUS can be used also for VVER type reactors. For this purpose, only the DYN3D and TRANSURANUS input files have to be modified.

  • Contribution to proceedings
    10th International Conference on WWER Fuel Performance, Modelling and Experimental Support, 07.-14.09.2013, Sandanski, Bulgaria
    Proceedings of 10th International Conference on WWER Fuel Performance, Modelling and Experimental Support
  • Lecture (Conference)
    10th International Conference on WWER Fuel Performance, Modelling and Experimental Support, 07.-14.09.2013, Sandanski, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-19164
Publ.-Id: 19164


Kurzzeittemperung zur Herstellung TiO2-basierter TCOs

Neubert, M.; Vinnichenko, M.; Gemming, S.; Gebel, T.; Liepack, H.; Kolitsch, A.

Die vielfältigen Anwendungen transparenter leitfähiger Oxide (TCO), wie zum Beispiel in Flachbildschirmen, Solarzellen und der Beleuchtungstechnik erfordern die Entwicklung neuartiger TCO-Materialien. Darüber hinaus ist der Einsatz der etablierten TCOs, wie Indiumzinnoxid (ITO) oder Fluor dotiertes Zinnoxid (FTO) zukünftig nur bedingt fortzuführen. Die Verwendung von ITO ist aufgrund des kontinuierlich steigenden Indiumpreises sehr kostenintensiv, während der Einsatz von FTO-Dünnschichten aufgrund des hochgradig toxischen Herstellungsprozesses weltweit umstritten ist. Es konnte gezeigt werden, dass Titandioxid dotiert mit Tantal (TTO) vergleichbare elektrische und optische Eigenschaften, verglichen mit den etablierten TCOs aufweist. Eine wesentliche Herausforderung besteht allerdings darin, TTO-Dünnschichten mittels eines industrienahen kostengünstigen Prozess abzuscheiden. Diese Problemstellung wurde gelöst, indem TTO-Schichten mittels eines 2-stufigen Prozesses, bestehend aus Sputterabscheidung und anschließender Blitzlampentemperung, hergestellt wurden. Die dabei erreichten spezifischen Widerstände im Bereich von 0,001 Ohmcm entsprechen denen, bei Nutzung konventioneller Ofentemperung und sind für zahlreiche Anwendung ausreichend.

Keywords: transparent conductive oxide; TCO; tantalum; titania; titanium dioxide

  • Lecture (Conference)
    Workshop "Transparente leitfähige Materialien (TCO / TCM) – Festkörperphysikalische Grundlagen und Technologien", 04.-05.06.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19163
Publ.-Id: 19163


Nuclear deformation and neutron excess as competing effects for dipole strength in the pygmy region

Massarczyk, R.; Schwengner, R.; Dönau, F.; Frauendorf, S.; Anders, M.; Bemmerer, D.; Beyer, R.; Bhatia, C.; Birgersson, E.; Butterling, M.; Elekes, Z.; Ferrari, A.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kelley, J. H.; Kögler, T.; Matic, A.; Menzel, M. L.; Müller, S.; Reinhardt, T. P.; Röder, M.; Rusev, G.; Schilling, K. D.; Schmidt, K.; Schramm, G.; Tonchev, A. P.; Tornow, W.; Wagner, A.; Gooden, M. E.

The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A = 124, 128, 132 and 134 in nuclear resonance fluorescence experiments using the ELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIgS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.

Keywords: nuclear resonance flourescene; dipole strength; pygmy strength; statistical analysis; photo-nuclear reactions

Permalink: https://www.hzdr.de/publications/Publ-19162
Publ.-Id: 19162


Wave optical description of the Traveling-Wave Thomson-Scattering optical undulator field and its application to the TWTS-FEL

Steiniger, K.; Widera, R.; Pausch, R.; Debus, A.; Bussmann, M.; Schramm, U.

We show that X-ray optical free-electron lasers (OFELs) can be realized using Traveling-Wave Thomson-Scattering (TWTS).
In TWTS pulse front tilted laser pulses are scattered off relativistic electron bunches in a side-scattering geometry.
The pulse-front tilt guarantees overlap between laser and electrons over distances in the meter range while both are traveling in different directions.
An interaction distance of 90 cm is obtained in a setup were 590 MeV electrons scatter off a petawatt class laser incident under an angle of 4.5°.
The amplification of the 1.5 Å radiation saturates at the end of the interaction.
In order to account for spatial and temporal dispersion introduced with the pulse front tilt, we develop an exact three-dimensional analytical description of TWTS pulses that can be used in three-dimensional simulations of the radiation amplification process.
The wave-optical formulation of the TWTS pulse includes dispersion to all orders and provides a general description of laser pulses diffracted at VLS gratings.

Keywords: traveling-wave; thomson scattering; optical FEL; VLS grating

  • Contribution to proceedings
    1st European Advanced Accelerator Concepts, 02.-06.06.2013, La Biodola, Isola d'Elba, Italy
    Proceedings of the 1st European Advanced Accelerator Concepts, Amsterdam: Elsevier, 147-152
    DOI: 10.1016/j.nima.2013.10.091
  • Nuclear Instruments and Methods in Physics Research A 740(2014), 147-152
    DOI: 10.1016/j.nima.2013.10.091

Permalink: https://www.hzdr.de/publications/Publ-19161
Publ.-Id: 19161


Excitation of the Delta(1232) isobar in deuteron charge exchange on hydrogen at 1.6, 1.8, and 2.3 GeV

Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Imambekov, O.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H. J.; Steffens, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Uzikov, Y.; Valdau, Y.; Wilkin, C.

The charge-exchange break-up of polarised deuterons pol{d}p -> {pp}n, where the final {pp} diproton system has a very low excitation energy and hence is mainly in the 1S0 state, is a powerful tool to probe the spin-flip terms in the proton-neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Delta(1232) isobar in the pol{d}p -> {pp}X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A_{xx} and A_{yy}, have been extracted in terms of the momentum transfer to the diproton or the invariant mass Mx of the unobserved system X. The unpolarised cross section in the high Mx region is well described in a model that includes only direct excitation of the Delta isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low Mx, even when Delta excitation in the projectile deuteron is included in the calculation. Furthermore, direct Delta production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

Permalink: https://www.hzdr.de/publications/Publ-19160
Publ.-Id: 19160


First measurements of spin correlations in the np -> d pi0 reaction

Shmakova, V.; Mchedlishvili, D.; Dymov, S.; Azaryan, T.; Barsov, S.; Chiladze, D.; Engels, R.; Gebel, R.; Gou, B.; Grigoryev, K.; Hartmann, M.; Kacharava, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Kurbatov, V.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Merzliakov, S.; Mikirtytchiants, M.; Mikirtytchiants, S.; Nioradze, M.; Ohm, H.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Tsirkov, D.; Uzikov, Y.; Valdau, Y.; Wilkin, C.

The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related pp-> d pi^+ reaction, though the present results cover also the small-angle region, which was largely absent from these data.

Permalink: https://www.hzdr.de/publications/Publ-19159
Publ.-Id: 19159


Terahertz interlevel spectroscopy of quantum well excitons

Schneider, H.; Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Helm, M.

According to the proceedings of the first conference on intersubband transitions in quantum wells (ITQW), which took place in 1991 in Cargèse [1], research on this topic in the early 90s concentrated mostly on mid-infrared detectors (quantum well infrared photodetectors, QWIPs) for applications in thermal imaging. The following reasons make ITQW quite interesting for infrared optoelectronics: (a) III-V semiconductor technology supply a mature technological basis, (b) spectral properties of ITQW are determined basically by layer thicknesses and not by material bandgaps, and (c) theoretically engineered layer structures enable novel device concepts and huge resonant optical nonlinearities [2]. In 1994, the invention of the quantum cascade laser (QCL) [3] has marked the birth of another exciting research field and paved the way for a wide range of new applications for ITQW. Later on, both the QWIP and QCL concepts have been applied to longer wavelengths beyond the Reststrahlen band [4,5], thus giving rise to important devices in the emerging field of terahertz (THz) technology.
Going from the 2D quantum well (QW) system to 1D quantum wires, and even 0D quantum dots (QD), there has been a long debate whether device performance, in particular at high operation temperatures, will become superior due to the restricted phase space for electron scattering. Most importantly, a phonon bottleneck has been predicted [6], which gave rise to the expectation that quantum dot infrared photodetectors (QDIP) [7] and QD-based QCLs could exhibit improved device properties. Even though the formation of a "true" phonon bottleneck is prevented by polaron effects, very long relaxation times up to ~ 1 ns have in fact been observed for intersublevel transitions in n-type QD systems at appropriate transition energies [8]. Nevertheless, the performance of QD-based infrared devices is limited as yet mainly by technological difficulties to realize QD ensembles with sufficient homogeneity, spatial density, and, in particular, optimized QD shape.
Besides QD and QW, yet another interesting system is the quantum well exciton (QWE), which is caused by the Coulomb attraction between a – usually photogenerated – electron and hole inside a QW. This results in a hydrogen-like quasi atom with discrete bound states. In contrast to ITQW, interlevel transitions in QWEs have their dipole matrix elements in the QW plane, such that optical transitions between QWE levels occur under normal incidence. Since QWE can move freely in the QW, the center-of-mass momentum gives rise to a 2D continuum, which is in close analogy to the in-plane dispersion of QW subbands. Being a two-particle molecule, the QWE exhibits more complex physics than an electron in a QW or QD, including angular momentum as a new degree of freedom, finite recombination lifetime, and various optically active (bright) or inactive (dark) exciton states. For possible applications, an intriguing property of QWE is the opportunity of controlling near-infrared (NIR) interband processes (eV range) via intra-exciton transitions (few meV range) between bright and dark exciton states [9-11].
This talk will focus on the internal dynamics of quantum well excitons, which are excited into higher levels using a THz free-electron laser, by monitoring intra-exciton relaxation via time-resolved interband photoluminescence.
Acknowledgements – The authors thank E. Rosencher for initiating the ITQW conference series. We are also indebted to L. Schneebeli, C. N. Böttge, B. Breddermann, S. Chatterjee, M. Kira, and S. W. Koch (U. Marburg, Germany) for fruitful discussions and collaboration, to A.M. Andrews and G. Strasser (TU Vienna) for sample growth, and to P. Michel, W. Seidel (HZDR Dresden) and the ELBE team for their dedicated support.
References
[1] E. Rosencher, B. Vinter, B. F. Levine, Eds., "Intersubband Transitions in Quantum Wells", NATO ASI, Series B: Physics, Vol. 188 (Plenum Press, New York, 1992).
[2] E. Rosencher, A. Fiore, B. Vinter, V. Berger, Ph. Bois, J. Nagle, "Quantum Engineering of Optical Nonlinearities ", Science 271, 168 (1995).
[3] J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, A. Y. Cho, "Quantum Cascade Laser", Science 264, 553 (1994).
[4] H. C. Liu, C. Y. Song, A. J. SpringThorpe, J. C. Cao, "Terahertz quantum-well photodetector", Appl. Phys. Lett. 84, 4068 (2004).
[5] R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, F. Rossi, "Terahertz semiconductor heterostructure laser", Nature 417, 156 (2002).
[6] U. Bockelmann and G. Bastard, "Phonon scattering and energy relaxation in two-, one-, and zero-dimensional electron gases" Phys. Rev. B 42, 8947 (1990).
[7] H. C. Liu, M. Gao, J. McCaffrey, Z. R. Wasilewski, S. Fafard, "Quantum dot infrared photodetectors", Appl. Phys. Lett. 78, 79 (2001).
[8] E. A. Zibik, T. Grange, B. A. Carpenter, N. E. Porter, R. Ferreira, G. Bastard, D. Stehr, S.Winnerl, M. Helm, H. Y. Liu, M. S. Skolnick, L. R. Wilson, "Long lifetimes of quantum-dot intersublevel transitions in the terahertz range", Nature Mat. 8, 803 - 807 (2009).
[9] M. Kira and S. W. Koch, "Exciton-Population Inversion and Terahertz Gain in Semiconductors Excited to Resonance", Phys. Rev. Lett. 93, 076402 (2004).
[10] W. D. Rice, J. Kono, S. Zybell, S. Winnerl, J. Bhattacharyya, H. Schneider, M. Helm, B. Ewers, A. Chernikov, M. Koch, S. Chatterjee, G. Khitrova, H. M. Gibbs, L. Schneebeli, B. Breddermann, M. Kira, S. W. Koch, "Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells", Phys. Rev. Lett. 110, 137404 (2013).
[11] J. Bhattacharyya, M. Wagner, S. Zybell, S. Winnerl, D. Stehr, M. Helm, H. Schneider, "Simultaneous time and wavelength resolved spectroscopy under two-color near infrared and terahertz excitation", Rev. Sci. Instr. 82, 103107 (2011).

Keywords: Terahertz free-electron laser; semiconductor quantum wells; excitons; Coulomb scattering

  • Invited lecture (Conferences)
    The 12th International Conference on Intersubband Transitions in Quantum Wells - ITQW 2013, 15.-20.09.2013, Bolton Landing, NY, USA

Permalink: https://www.hzdr.de/publications/Publ-19158
Publ.-Id: 19158


THz free-electron laser spectroscopy of magnetoexcitons in semiconductor quantum wells

Bhattacharyya, J.; Zybell, S.; Eßer, F.; Winnerl, S.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.; Helm, M.; Schneider, H.

Transitions between the 1s and 2p levels of the fundamental heavy-hole exciton in GaAs quantum wells, followed by scattering into the 2s state, are investigated by resonant THz excitations using a free-electron laser. We report on the external control of this intra-excitonic population transfer by an external magnetic field.

Keywords: terahertz free electron laser; semiconductor quantum wells; exciton; interlevel transition

  • Invited lecture (Conferences)
    The 38th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665864

Permalink: https://www.hzdr.de/publications/Publ-19157
Publ.-Id: 19157


Spectroscopy of low-dimensional semiconductors with a terahertz free-electron laser

Schneider, H.

This talk reviews recent experimental studies which we carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices. In high-quality semiconductor quantum wells, we investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasi-atoms. Tuning the FEL in resonance with the transtion between the excitonic 2s and 2p states (at about 2 THz) allows us to study the dynamics of intra-excitonic population transfer. Moreover, strong terahertz pumping results in a characteristic Rabi splitting of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect. In semiconductor quantum dots, resonant THz excitation between different sublevels is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where far-infrared absorption by single electrons produces sufficient contrast to map individual quantum dots. In graphene, FEL-based pump-probe spectroscopy reveals different relaxation times for excitation energies above and below the optical phonons. At even smaller photon energies, this two-dimensional semiconductor material exhibits a transition from induced transmission to induced absorption, which is indicative for possible applications as an optical modulator.

Keywords: Terahertz spectroscopy; quantum well; quantum dot; exciton

  • Invited lecture (Conferences)
    9th National Conference on Nanoscience and Nanotechnology (NanoTR-9), 14.-28.07.2013, Ataturk University, Erzurum Province, Turkey

Permalink: https://www.hzdr.de/publications/Publ-19156
Publ.-Id: 19156


In vivo comparison of DOTA based 68Ga-labelled bisphosphonates for bone imaging in non-tumour models

Meckel, M.; Fellner, M.; Thieme, N.; Bergmann, R.; Kubicek, V.; Rösch, F.

Bone metastases are a class of cancerous metastases that result from the invasion of a tumor into bone. The solid mass which forms inside the bone is often associated with a constant dull ache and severe spikes in pain, which greatly reduce the quality of life of the patient. Numerous 99mTc-labeled bisphosphonate functionalised complexes are well established tracers for bone metastases imaging. The objective of this research was to evaluate the pharmacokinetics and behaviour of three DOTA based bisphosphonate functionalised ligands (BPAMD, BPAPD and BPPED), using both 68Ga μ-PET in vivo imaging and ex vivo biodistribution studies in healthy Wistar rats. The compounds were labelled with 68Ga in high yields using an ammonium acetate buffer, and subsequently purified using a cation exchange resin. High bone uptake values were observed for all 68Ga-labelled bisphosphonates at 60 minutes p.i. The highest uptake was observed for [68Ga]BPPED (2.6 ± 0.3% ID/g) which compares favourably with that of [99mTc]MDP (2.7 ± 0.1 ID/g) and [18F]fluoride (2.4 ± 0.2% ID/g). The 68Ga-labelled DOTA-bisphosphonates showed rapid clearance from the blood and renal system, as well as low binding to soft tissue, resulting in a high bone to blood ratio (9.9 at 60 minutes p.i. for [68Ga]BPPED, for example). Although further studies are required to assess their performance in tumor models, the results obtained suggest that these ligands could be useful both in imaging (68Ga) and therapeutic treatment (177Lu) of bone metastases.

Keywords: Bone metastases; 68Ga; PET; 177Lu; DOTA; Bisphosphonates

Permalink: https://www.hzdr.de/publications/Publ-19155
Publ.-Id: 19155


Synthesis and radiopharmacological evaluation of a high-affinity and metabolically stabilized 18F-labeled bombesin analogue for molecular imaging of gastrin-releasing peptide receptor-expressing prostate cancer

Richter, S.; Wuest, M.; Krieger, S. S.; Rogers, B. E.; Friebe, M.; Bergmann, R.; Wuest, F.

Introduction: Bombesin (BBN) and BBN analogues have attracted much attention as high-affinity ligands for selective targeting of the gastrin-releasing peptide (GRP) receptor. GRP receptors are overexpressed in a variety of human cancers including prostate cancer. Radiolabeled BBN derivatives are promising diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This study describes the synthesis and radiopharmacological evaluation of various metabolically stabilized fluorobenzoylated bombesin analogues (BBN-1, BBN-2, BBN-3).

Methods: Three fluorobenzoylated BBN analogues containing an aminovaleric (BBN-1, BBN-2), or an aminooctanoic acid linker (BBN-3) were tested in a competitive binding assay against 125I-[Tyr4]-BBN for their binding potency to the GRP receptor. Intracellular calcium release in human prostate cancer cells (PC3) was measured to determine agonistic or antagonistic profiles of fluorobenzoylated BBN derivatives. Bombesin derivative BBN-2 displayed the highest inhibitory potency toward GRP receptor (IC50 = 8.7 ± 2.2 nM) and was subsequently selected for radiolabeling with fluorine-18 (18F) through acylation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). The radiopharmacological profile of 18F-labeled bombesin [18F]BBN-2 was evaluated in PC3 tumor-bearing NMRI nude mice involving metabolic stability studies, biodistribution experiments and dynamic small-animal PET studies.

Results: All fluorobenzoylated BBN derivatives displayed high inhibitory potency toward the GRP receptor (IC50 = 8.7–16.7 nM), and all compounds exhibited antagonistic profiles as determined in an intracellular calcium release assay. The 18F-labeled BBN analogue [18F]BBN-2 was obtained in 30% decay-corrected radiochemical yield with high radiochemical purity N95% after semi-preparative HPLC purification. [18F]BBN-2 showed high metabolic stability in vivo with 65% of the radiolabeled peptide remaining intact after 60 min p.i. in mouse plasma. Biodistribution experiments and dynamic small-animal PET studies demonstrated high
tumor uptake of [18F]BBN-2 in PC3 xenografts (2.75 ± 1.82 %ID/g after 5 min and 2.45 ± 1.25 %ID/g after 60 min p.i.). Specificity of radiotracer uptake in PC3 tumors was confirmed by blocking experiments.

Conclusion: The present study demonstrates that 18F-labeled BBN analogue [18F]BBN-2 is a suitable PET radiotracer with favorable metabolic stability in vivo for molecular imaging of GRP receptor-positive
prostate cancer.

Keywords: 18F; Bombesin (BBN); Gastrin-releasing peptide (GRP) receptor; Prostate cancer; N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB); Positron emission tomography (PET)

Permalink: https://www.hzdr.de/publications/Publ-19154
Publ.-Id: 19154


Quantitative Structure Property Relationship of logP for Radiopharmaceutical Technetium and Rhenium Complexes by using Molecular Dynamics Calculations

Yoshizuka, K.; Pietzsch, H.-J.; Seifert, S.; Stephan, H.

We have developed a novel molecular modelling technique for radiopharmaceutical Tc and Re complexes combined with molecular mechanics (MM) and molecular dynamics (MD) for estimating the partition coefficient of these complexes between water and l-octanol (logP). The field force parameters developed with a MM program, "MOMEC" were fitted to all relevant X-ray crystal structures of [99mTcO(DMSA)2]- and [188ReO(DMSA)2]- (DMSA: dimercaptosuccinic acid). The force field parameters were transferred to those in a MD program, "Material Explorer". The MD simulations also indicate that a quantitative structure property relationship (QSPR) was optained, which relates the internal energy difference between the Tc/Re-DMSA derivatives in the water phase and that in l-octanol phase with the experimental logP value.

  • Open Access Logo Solvent Extraction Research and Development 20(2013), 15-27

Permalink: https://www.hzdr.de/publications/Publ-19153
Publ.-Id: 19153


Depth-resolved transport measurements and atom-probe tomography of heterogeneous, superconducting Ge:Ga films

Heera, V.; Fiedler, J.; Naumann, M.; Skrotzki, R.; Kölling, S.; Wilde, L.; Herrmannsdörfer, T.; Skorupa, W.; Wosnitza, J.; Helm, M.

Ge films with a mean Ga content of about 8 at.% and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change of the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters up to 10,000 atoms. Since no percolating Ga cluster exists, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect.

Keywords: Ga ion implantation; flash-lamp annealing; superconducting Ge:Ga; inhomogeneous superconductor; hole doping; Ga cluster

Permalink: https://www.hzdr.de/publications/Publ-19152
Publ.-Id: 19152


PET-Bildgebung von α7 Nikotinrezeptoren: Einfacher Zugang zu einem Markierungsvorläufer für [18F]NS14490

Scheunemann, M.; Rötering, S.; Fischer, S.; Hiller, A.; Peters, D.; Steinbach, J.; Deuther-Conrad, W.; Brust, P.

Das 1-(2-Fluorethylindol-6-yl)-oxadiazolylamin NS14490 ist ein hoch affiner α7-Subtyp-spezifischer Ligand für den nikotinischen Acetylcholinrezeptor (nAChR, Ki,α7 = 2,5 nM), für dessen 18F-markierte Form wir ein Syntheseverfahren entwickelt haben [1]. Das Potential dieses neuen Radiotracers für die molekulare PET-Bildgebung von α7 nAChR bei neurodegenerativen und Tumorerkrankungen wird gegenwärtig von uns untersucht.
Da die Herstellung des zur Radiosynthese von [18F]NS14490 benötigten Tosylates 1 nach einer ursprünglich verfolgten Methode [1], ausgehend vom N-unsubstituierten NS14490-Derivat unbefriedigende Ergebnisse erbrachte, wurde ein verbessertes Syntheseverfahren aus dem Ester 3 über eine 6-stufige Sequenz, mit BOP-Kupplung zu 7 als Schlüsselschritt [2] entwickelt, das eine Gesamtausbeute von 32% ermöglichte. Die Darstellung von [18F]NS14490 erfolgt mit [18F]Fluorid [18O(p,n)18F-Reaktion am Cyclone 18/9, Leipzig] in Gegenwart von Kryptofix K2.2.2 in einem Schritt aus 1. Die Isolierung und Reinigung des Radiotracers (radiochemisch ≥95%) ist umfassend optimiert und erfolgt durch semipräparative RP-HPLC mit anschließender Festphasenextraktion (RCA: 36%, spezifische Aktivität: 150 GBq/μmol, Synthesedauer: 2-2,5 h).
Weiterführende In-vitro- und In-vivo-Studien, insbesondere zur Hirn-Aufnahme und zur Selektivität der Bindung von [18F]NS14490 an α7 nAChR im Gehirn belegen die potentielle Eignung des Radioliganden für die molekularen Bildgebung [1].
(Unterstützt durch die Deutsche Forschungsgemeinschaft, Ref. DE1165/2-1)
Literatur:
[1] S. Rötering et al. Bioorg. Med. Chem. (im Druck). [2] C. G. Levins et al. Org. Lett. 2008, 10, 1755.

  • Lecture (Conference)
    GDCh Wissenschaftsforum Chemie, 01.-04.09.2013, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19151
Publ.-Id: 19151


Hydrogen-induced microstructural changes of Pd films

Cizek, J.; Melikhova, O.; Vlcek, M.; Lukac, F.; Vlach, M.; Prochazka, I.; Anwand, W.; Brauer, G.; Mücklich, A.; Wagner, S.; Uchida, H.; Pundt, A.

The development of the microstructure in nanocrystalline, polycrystalline and epitaxial Pd films loaded with hydrogen is investigated. Structural changes in Pd films loaded with hydrogen were characterized by positron annihilation spectroscopy combined with electron microscopy and X-ray diffraction. It was found that hydrogen charging causes plastic deformation which leads to an increase of the defect density in all Pd films studied. Moreover, the formation of buckles was observed in nanocrystalline and polycrystalline Pd films loaded above a certain critical hydrogen concentration. Buckling leads to detachment of the film from the substrate and this is accompanied with in-plane stress relaxation and plastic deformation of the film.

Keywords: Palladium films; Hydrogen; Positron annihilation spectroscopy; X-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-19149
Publ.-Id: 19149


Electron transfer processes at the mineral/water interface in the context of anoxic radioactive waste disposal

Scheinost, A.C.

Se, Pu in the context of radioactive waste disposal
FeII-driven interfacial redox reactions
Se interfacial redox reactions
Pu interfacial redox reactions

Keywords: EXAFS; XAFS; redox

  • Invited lecture (Conferences)
    Goldschmidt 2013, Workshop: Redox-active Minerals: Properties, Reactions and Applications in Clean Technologies, 25.-30.08.2013, Florence, Italy

Permalink: https://www.hzdr.de/publications/Publ-19148
Publ.-Id: 19148


Dynamic behavior of selected PET tracers in embryonated chicken eggs

Gebhardt, P.; Würbach, L.; Heidrich, A.; Heinrich, L.; Walther, M.; Opfermann, T.; Sørensen, B.; Saluz, H. P.

Positron emission tomography/computer tomography (PET/CT) is an established method in the preclinical research of small animal disease models and in the clinical diagnosis of cancer. It combines the functional information of the positron-emitting biomarker with the anatomical data from the CT image, thereby allowing for the 4D in vivo investigation of biological processes of interest. Recently, the bone growth of chicken embryos was monitored using [18F]fluoride as a bone-seeking tracer. We are interested to investigate additional PET/CT tracers in embryonated chicken eggs as in vivo model system. The properties of 18F-, 68Ga-labelled tracers and 64Cu-chloride were studied in catheterised eggs via small animal microPET/CT. [18F]FDG was primarily absorbed at sites of bone growth. 64Cu chloride and a 68Ga-labelled amyloid-fibril-binding antibody accumulated in the liver, while 68Ga-albumin desferrioxamine conjugate was rapidly cleared. The method potentially can be utilised to monitor biological processes in chicken eggs.

Permalink: https://www.hzdr.de/publications/Publ-19147
Publ.-Id: 19147


Low Energy Proton Radiation Impact on 4H-SiC nMOSFET Electrical Parameters

Florentin, M.; Alexandru, M.; Constant, A.; Schmidt, B.; Godignon, P.

In this work, the effect of 180 keV proton radiation in lateral 4H-SiC nMOSFETs with rapid thermally processed (RTP) gate oxides is investigated before and after radiation. Comparison with non-irradiated (NI) samples allows the study of hole trap effects in the oxide and of generated interface traps. It has been observed that for the two lower fluences, the threshold voltage (VTH) shifts toward lower values, reaching a minimum for a fluence of 5x1012 cm-2. The effective channel mobility (µEFF) and the maximum drain current (IDSAT_MAX) reach maximum values for 5x1012 cm-2 as well; the µEFF gets 6 times superior, while the IDSAT_MAX doubles in accordance with the NI sample values.

Keywords: SiC; low energy proton irradiation; threshold voltage shift; channel mobility

  • Lecture (Conference)
    International Conference on Silicon Carbide and Related Materials, 29.09.-04.10.2013, Phoenix Seagaia Resort, Miyazaki, Japan

Permalink: https://www.hzdr.de/publications/Publ-19146
Publ.-Id: 19146


5MeV Proton and 15MeV Electron Radiation Effects Study on 4H-SiC nMOSFET Electrical Parameters

Alexandru, M.; Florentin, M.; Constant, A.; Schmidt, B.; Michel, P.; Godignon, P.

The impact of proton and electron irradiation on the electrical parameters of 4H-SiC nMOSFETs has been
investigated by using time bias stress instability method. This study has allowed observing the effect of holes trapped in the
oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage,
the effective mobility and the maximum drain current were observed. These amendments could be connected with the
Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These
atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of
passivated Carbon atoms is increasing, hence the interface quality getting improved.

Keywords: Charge Trapping; Electron Irradiation; Mobility; Proton irradiation; SiC MOSFET; SiO2/SiC Interface; Time Bias Stress Instability; Threshold Voltage Shift

  • Lecture (Conference)
    Radiation Effects on Components and Systems 2013, 23.-27.09.2013, Oxford, England

Permalink: https://www.hzdr.de/publications/Publ-19145
Publ.-Id: 19145


10 MeV Proton Irradiation Effect on 4H-SiC nMOSFET Electrical Parameters

Florentin, M.; Alexandru, M.; Constant, A.; Schmidt, B.; Godignon, P.

This work presents the 10 MeV proton irradiation effects on 4H-SiC MOSFETs at different fluences. MOSFETs main electrical parameters, such as the channel mobility (µEFF), threshold voltage (VTH), transconductance (gm) and subthreshold current, were analyzed using the time bias stress instability (BSI) technique. Applying this method allowed us to study the effect of carrier interaction with proton induced defects (traps), whether in the bulk or at the interface. Improvements, such as VTH stabilization in time and a significant increase of the µEFF at high fluencies, have been noticed. We assume that this behavior is connected with the atomic diffusion from the SiO2/SiC interface, towards the epilayer during proton irradiation. These atoms, mainly Nitrogen, may create other bonds by occupying various vacancies coming from Silicon and Carbon’s dangling bond. Therefore, by increasing the number of passivated Carbon atoms, we show that high irradiation proton could be a way to improve the SiO2/SiC interface quality.

Keywords: Silicon carbide; MOSFET devices; proton irradiation

  • Lecture (Conference)
    HeteroSiC-WASMPE, 17.-19.07.2013, Nice, France
  • Materials Science Forum 806(2015), 121-125

Permalink: https://www.hzdr.de/publications/Publ-19144
Publ.-Id: 19144


Deceleration of Ar9+ ions within a tapered glass capillary

Kreller, M.; Zschornack, G.; Kentsch, U.

We report experimental studies of the deceleration of Ar9+ ions within a single tapered glass capillary with an inlet diameter of 1 mm, an outlet diameter of 0.15 mm and a length of 45 mm. In the experiments we have chosen an incident ion energy of q x 8.5 keV (q – ion charge state). The influence of the deceleration potential between entrance and exit of the glass capillary on the intensity of the transmitted ion beam was measured. We detected a transmission of the ion beam up to a deceleration potential of 7 kV. Hence, the ion beam was decelerated and compressed to a diameter of 150 µm without using any additional decelerating lens systems.

Keywords: Ion guiding; Highly charged ion; Tapered macro-capillary; Ion beam deceleration

Permalink: https://www.hzdr.de/publications/Publ-19143
Publ.-Id: 19143


Quantitative imaging of the magnetic configuration of modulated nanostructures by electron holography

Körner, M.; Röder, F.; Lenz, K.; Fritzsche, M.; Lindner, J.; Lichte, H.; Fassbender, J.

Regarding magnetic nanostructures, dipolar stray fields start to evolve with ongoing miniaturization, that grossly alter the magnetic properties. Besides, these fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals.
Hence, a detailed knowledge of the magnetic configuration under geometric confinements on the nanoscale is mandatory.
We present a study of the magnetic fields arising from thin Permalloy films deposited on periodically modulated surfaces (ripples).
These ripples were prepared using a self-organized ion beam erosion process generating modulations on the nanoscale.
Cross-sectional transmission electron holography nowadays offers the necessary sensitivity and nanoscale lateral resolution to probe the magnetic configuration of such rippled films quantitatively.
The imaging allows for an absolute analysis of the local magnetization inside the film as well as the accompanying stray fields outside.
In addition, the evolving stray fields above the sample's surface were investigated by magnetic force microscopy.

Permalink: https://www.hzdr.de/publications/Publ-19142
Publ.-Id: 19142


Two-Magnon Scattering in the Transition from Periodical Perturbations to Magnonic Crystals

Lenz, K.; Körner, M.; Gallardo, R. A.; Banholzer, A.; Facsko, S.; Lindner, J.; Landeros, P.; Fassbender, J.

Two-magnon scattering is a well-known effect e.g. in ferromagnetic resonance (FMR) experiments leading to a linewidth broadening. Available theory so far was based on random defects acting as a dipolar scattering potential. Recently it was shown by Landeros and Mills [1] that this theory can be extended to handle two-magnon scattering in periodically perturbed films, which can be easily created by lithographical patterning. These perturbed films are the intermediate step towards full magnonic crystals.
The extended model allows for analytically calculating the resonance response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments [2,3]. The scattering potential of the defects builds up due to the dipolar stray fields at the edges of the defects. Within the perturbation theory this leads on the one hand to a shift of the resonance peak and on the other hand also to a splitting of the uniform resonance mode. Both effects are clearly visible in the FMR experiments. The mode splitting due to the two-magnon scattering finally is also responsible for the opening of magnonic band gaps in the dispersion relation of magnonic crystals. The splitting can be tailored by the geometric and magnetic sample parameters. Experimental data for magnetically patterned stripe samples as well as for ripple samples [3] is presented and compared to calculations by the analytical model (see e.g. Fig. 1).
This work was supported by the DFG grants FA 314/6-1, FA314/3-2.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, K. Lenz, A. Banholzer, M. Körner, J. Lindner, J. Fassbender, P. Landeros, Phys Rev. B (2013) submitted
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner, P. Landeros, J. Fassbender, Phys. Rev. B (2013) submitted

Keywords: magnonic crystals; two-magnon scattering

  • Poster
    3rd international conference on magnonics 2013, 04.-08.08.2013, Varberg, Schweden

Permalink: https://www.hzdr.de/publications/Publ-19141
Publ.-Id: 19141


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