Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Motion compensated fully 3D list-mode reconstruction

Lougovski, A.; Langner, J.; Beuthien-Baumann, B.; Oehme, L.; Steinbach, J.; van den Hoff, J.
Ziel/Aim:

PET investigations of the brain, e.g. in receptor studies, typically exhibit long acquisition times making them sensitive to patient motion during the data acquisition and leading to potentially significant motion blur of the reconstructed activity distribution. This circumstance makes motion compensation one of the most pressing problems in high resolution PET scanners. We report on our work concerning integration of event-based motion compensation algorithm into a previously developed high resolution fully 3D list-mode reconstruction.

Methodik/Methods:

We integrated motion compensation into our implementation of 3D list-mode Ordered Subsets Expectation Maximization reconstruction (3D LMOSEM). The system matrix elements are computed on-the-fly and are modelled to be proportional to the intersection volume of voxels with Lines Of Response having a finite cross section (TOR: Tube Of Response). Motion information with high temporal resolution is provided by an external infra-red motion tracking system and used by the motion compensation algorithm for suitable spatial transformation of the individual TORs. Scatter correction factors (calculated using Single Scatter Simulation) are reconstructed into a scatter image, which is afterwards used in the forward projection step of the reconstruction together with an image of the delayed events. We have evaluated the new method in phantom and patient studies by comparing it with the previously developed procedure of using standard sinogram-based OSEM-reconstruction after motion pre-correction of the list mode data. The evaluation procedure has been divided into two parts: i) quantitative accuracy and spatial resolution (FWHM comparison) in phantoms and ii) visual evaluation of patient brain studies.

Ergebnisse/Results:

The new method provides a significant improvement of the reconstructed resolution (more than 25%) in comparison to the standard reconstruction of our scanner (Siemens ECAT HR+) while maintaining a high level of quantitative accuracy. Visual evaluation of five F-DOPA and five FDG brain studies showed substantially higher level of details in several brain structures as well as almost complete elimination of motion related artefacts.

Schlussfolgerungen/Conclusions:

The developed reconstruction allows almost complete elimination of motion blurring artefacts in brain studies and provides substantially better resolution than the standard reconstruction of the Siemens HR+ scanner. However, high computational complexity of the algorithm leads to substantial reconstruction times, which currently prevent its use for on-the-fly reconstruction in clinical routine. Further developments are necessary to eliminate this
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A21-A22

Permalink: https://www.hzdr.de/publications/Publ-17083
Publ.-Id: 17083


Gold diffusion into silicon during thermal annealing

Müller, A.-D.; Müller, F.; Wengel, S.; Baumgart, C.; Skorupa, S.; Reuther, H.; Mücklich, A.; Schmidt, H.
Gold was found to diffuse into silicon by a complex mechanism involving a vacancy-controlled interstitial-substitutional equilibrium. We investigated the Au diffusion into silicon using differently thick Au layers on n-Si and thermal annealing in a tube furnace at 800°C for 20 h in an argon atmosphere. After thermal treatment the lateral inhomogeneity in the Au distribution has been probed by Auger electron spectroscopy (AES) scans, Scanning electron microscopy, High resolution transmission electron microscopy (HRTEM), and by Kelvin probe force microscopy (KPFM) measurements [1]. The Au diffusion led to very complex diffusion concentration profiles which deviate from the ideal ones for Au diffusion into dislocation-free silicon. The resulting depth distribution of Au in Si has been determined by AES measurements. The KPFM contrast is independent of the surface topography and reveals different long-range chemical and local electrostatic interaction between the conducting KPFM tip and sample surface. HRTEM on cross-sections prepared from the sample with a nominal 10 and 20 nm thick Au layer reveal different phases of silicide formation.
[1] C. Baumgart, A.-D. Müller, F. Müller, H. Schmidt, phys. stat. sol. (a), 2011, 208, 777-789.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17082
Publ.-Id: 17082


A novel method for in-vivo evaluation of quantification accuracy in PET

Langner, J.; Hofheinz, F.; Schramm, G.; Oehme, L.; Beuthien-Baumann, B.; Lukas, M.; Buchert, R.; Steinbach, J.; van den Hoff, J.
Ziel/Aim:

One of the strengths of PET is the ability to measure regional tracer concentrations, which is the basis of a quantitative evaluation of patient studies. Parameters such as the standardized uptake value (SUV) or transport constants derived from kinetic modeling are commonly used for this purpose. The quantitative accuracy strongly depends on accurate calibration of the scanner, which is commonly performed with suitable phantoms. While this calibration procedure ensures quantitatively correct results in geometrically comparable phantoms, it still leaves questions to be asked regarding its reliability for in-vivo measurements due to different scatter distribution as well as tracer distribution in phantoms compared to patient scans.
It was therefore the aim of our study to investigate the actual in-vivo accuracy of a phantom-based scanner cross-calibration against a well-counter by comparison of the tracer concentration in the patient’s urine as determined by the PET system to the concentration measured in a well-counter.

Methodik/Methods:

In 39 routinely scanned F18-FDG patients on two different PET scanners (EXACT HR+ PET: N=22; Biograph PET/CT: N=17) the bladder region was imaged as the last bed position and urine samples collected immediately after the end of the scan. 3D region-of-interests (ROI) were placed in the bladder by three different observers via a threshold-based delineation method using the ROVER software and image-based activity concentrations were determined. Activity concentration in the urine samples was determined in well-counters which were cross-calibrated against the respective scanner via routine phantom procedures.

Ergebnisse/Results:

Our first results show, that the measured activity concentrations are significantly lower in PET than in the well-counter for all patients and both investigated scanners; PET vs. well-counter ratio: 0.88±0.06 [range: 0.79-1.10] (EXACT HR+), 0.86±0.11 [range: 0.57-1.06] (Biograph).

Schlussfolgerungen/Conclusions:

The presented results suggest, that the commonly used phantom-based scanner calibration is not sufficient to guarantee high quantitative in-vivo accuracy. A possible reason for the observed deviations of up to 43% and the patient and scanner related variations of up to 49% might be an insufficient scatter correction in the manufacturer provided image reconstruction. To further investigate, we are currently acquiring more data sets from a third PET scanner (Gemini-TF PET/CT). We propose to augment standard calibration procedures by measurement of the in-vivo accuracy of the calibration using the described method. Furthermore, we believe that the proposed in-vivo method might also be of value for multi-center studies where monitoring the calibration accuracy for each scanner could be an important benefit and quality control method.
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A77

Permalink: https://www.hzdr.de/publications/Publ-17081
Publ.-Id: 17081


Kelvin probe force microscopy imaging on horizontal locally doped silicon nanowires

Baumgart, C.; Habicht, S.; Feste, S.; Helm, M.; Mantl, S.; Schmidt, H.
Kelvin probe force microscopy (KPFM) [1] has been used for the electrical characterization of silicon nanowires (NWs). Arrays of horizontal Si NWs [2] with widths down to 10 nm have been prepared from a silicon-on-insulator (SOI) starting material. After transferring the NW structures into the Si top layer by conventional top-down approach, the samples have been locally implanted with B and As. Quantitative dopant profiling by means of KPFM is successfully employed to locate the junctions along the B-doped and As-doped Si NWs. In addition, the influence of local intrinsic electric fields [3] is discussed for the investigated SOI structures.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. F. Feste, J. Knoch, S. Habicht, D. Buca, Q.-T. Zhao, S. Mantl, Solid-State Electronics 53, 1257 (2009).
[3] C. Baumgart, A.-D. Müller, F. Müller, and H. Schmidt, Phys. Stat. Sol. A 208, 777 (2011).
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17080
Publ.-Id: 17080


FDG-PET/MR im Rahmen der Primärdiagnostik von Patienten mit Kopf-Hals-Tumoren

Beuthien-Baumann, B.; Platzek, I.; Schneider, M.; Gudziol, V.; Langner, J.; Laniado, M.; Kotzerke, J.; van den Hoff, J.
Ziel/Aim:

Ganzkörper-PET/MR-Geräte kombinieren die metabolische Information der Positronen-Emissions-Tomographie mit dem hohen Weichteilkontrast der Magnet-Resonanz-Tomographie in einem Untersuchungsablauf. Ziel dieser Untersuchung ist es, den möglichen diagnostischen Zugewinn bei der kombinierten Anwendung beider Untersuchungsmodalitäten beim Primärstaging von Patienten mit Kopf-Hals-Tumoren zu untersuchen

Methodik/Methods:

40 Patienten (32 Männer, 8 Frauen, Alter 38 -82 Jahre, mittleres Alter 64 Jahre) mit histologisch gesicherten Kopf-Hals-Tumoren wurden an einem kombinierten PET/MR-Gerät (Philips Ingenuity PET-MR (TOF-PET/ 3T-MRT)) vor geplanter kurativer Operation untersucht (Untersuchungsablauf Kopf/Hals: Schwächungs-MRT; PET:350 MBq F-18-FDG, Start ab ca. 175 min p.i, 6 min /bed.; diagn. MRT: NV16-Spule, T1/T1-KM, T2, STIR). Beurteilt wurden die Detektierbarkeit des Primärtumors und von regionalen Lymphknotenmetastasen getrennt für PET, MRT und deren Kombination im Vergleich zur histologischen Aufarbeitung des Op-Präparates. Zum Ausschluss von Fernmetastasen wurde vor der dedizierten Kopf-Hals-Untersuchung eine konventionelle PET-Untersuchung des Körperstammes 60 min nach Injektion von 350 MBq F-18-FDG (ECAT-EXAT HR+, Siemens/CTI) durchgeführt.

Ergebnisse/Results:

Der Primärtumor war bei 5 Patienten im PET (bei geringer Größe), bei 10 Patienten im MRT (geringe Größe bzw. bei Metallartefakten) nicht abgrenzbar. Bei bisher 26 Patienten konnte ein Vergleich mit der Histologie bzgl. der LK-Metastasen erfolgen. Insgesamt wurden 863 LK histologisch beurteilt, davon waren 56 LK metastatisch befallen. Die Sensitivität und Spezifität hinsichtlich der Detektion von LK-Metastasen für PET und MRT betrug jeweils 69% bzw. 98%, die kombinierte Auswertung von PET-MRT erhöhte die Sensitivität auf 83%. Bei 8 Patienten wurde in der PET-Untersuchung des Körperstammes eine weitere hypernmetabole Läsion mit V.a. Zweittumor bzw. Fernmetastase detektiert.

Schlussfolgerungen/Conclusions:

In dieser vorläufigen Datenauswertung scheint die Kombination von FDG-PET und diagnostischem MRT in einem Untersuchungsablauf die Sensitivität bezüglich der Detektion von LK-Metastasen von Kopf-Hals-Tumoren deutlich zu erhöhen. Primärtumoren können dem Nachweis bei sehr kleiner Ausdehnung sowohl im PET als auch im MRT entgehen. Die MRT-Bildgebung kann, insbesondere im Mundbereich, durch Metallartefakten deutlich beeinträchtigt werden; auch hier bringt die Kombination von PET-MRT einen diagnostischen Zugewinn. Eine PET-Untersuchung des Körperstammes zum Ausschluss von Fernmetastasen oder Zweittumoren erscheint sinnvoll.
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A48

Permalink: https://www.hzdr.de/publications/Publ-17079
Publ.-Id: 17079


Kombinierte PET/MR in der Diagnostik von Skelettmetastasen mit F-18-Natriumfluorid-PET (NaF-PET) und Ganzkörper-MRT (GK-MRT): Erste Erfahrungen

Beuthien-Baumann, B.; Platzek, I.; Langner, J.; Schramm, G.; Oehme, L.; Laniado, M.; van den Hoff, J.; Kotzerke, J.
Ziel/Aim:

Die Skelettszintigraphie mit F-18-NaF-PET weist eine hohe Sensitivität für die Detektion von Skelettmetastasen auf. Voraussetzung für deren Nachweis ist jedoch, dass die Metastase die Knochenmatrix alteriert. Knochenmarkmetastasen, die noch keine Stoffwechselreaktion der Knochenmatrix verursachen, entgehen dem Nachweis der Skelettszintigraphie. Im MRT können Knochenmarkmetastasen mit hoher Sensitivität detektiert werden. Ziel dieser Untersuchung ist es, den möglichen diagnostischen Zugewinn hinsichtlich der Detektion von Knochen- bzw. auch mgl. Knochenmarkmetastasen bei der kombinierten Anwendung der F-18-NaF-PET und einem GK-MRT mit einem Ganzkörper-PET/MR-Gerät zu untersuchen.

Methodik/Methods:

Seit Inbetriebnahme des PET/MR-Gerätes (Philips Ingenuity (TOF-PET/ 3T-MRT)) im Januar 2011 wurden 345 Untersuchungen durchgeführt, davon handelte es sich bei 96 Untersuchungen um Skelettszintigraphien mit F-18-Natriumfluorid mit der Frage nach Skelettmetastasen. Bei 52 Untersuchungen konnte neben dem Schwächungs-MRT und der PET noch ein diagnostisches Ganzkörper-MRT durchgeführt werden. 28 Patientendatensätze gehen in diese vorläufige Datenauswertung ein: 19 Männer, 9 Frauen, mittleres Alter 65 Jahre, 15 Prostata-Karzinome, 5 Mamma-Karzinome, 3 Schilddrüsen-Karzinome, 2 Karzinoide, 1 Bronchial-Karzinom, 1 CUP, 1 Plasmozytom. Injektion von 250 MBq F18-Natriumfluorid, Schwächungs-MRT; Start der Ganzkörper-PET ab 60 min p.i.. MRT: GK-coronar T1 und wenn möglich sagittale STIR der Wirbelsäule.

Ergebnisse/Results:

Qualitativ ergibt die NaF-PET Skelettszintigramme von hoher Qualität. Die coronaren GK-MRT und die sagittalen MRT-Schichten der Wirbelsäule ergänzen die PET mit exzellenten morphologischen Informationen. Metastasenverdächtige Läsionen wurden bei 16/28 Patienten gefunden. Davon bei 9 Patienten ausschließlich im NaF-PET, bei 5 Patienten fanden sich metastasenverdächtige Läsionen ausschließlich im MRT. Die MRT zeigte zusätzliche metastasenverdächtige Läsionen überwiegend im Bereich der Wirbelsäule. Skelettmetastasen im Bereich des Rippenthorax entgingen der GK-MRT auf Grund der coronaren Orientierung. Zusätzliche volldiagnostische MRT-GK-Untersuchungen in Ergänzung zum GK-Skelettszintigramm sind auf Grund des zusätzlichen Zeitbedarfes oft durch den Allgemeinzustand des Patienten limitiert

Schlussfolgerungen/Conclusions:

Die NaF-PET bietet Skelettszintigramme von hoher Bildqualität. In dieser vorläufigen Datenauswertung scheint die Kombination von NaF-PET und diagnostischem GK-MRT in einem Untersuchungsablauf die Nachweiswahrscheinlichkeit kleiner Skelettmetastasen bzw. Knochenmarkmetastasen in der Wirbelsäule zu erhöhen. Eine Optimierung der Untersuchungszeit hinsichtlich der Kombination von PET-und MRT ist erstrebenswert.
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A47-A48

Permalink: https://www.hzdr.de/publications/Publ-17078
Publ.-Id: 17078


Automatisierte volumetrische Abgrenzung heterogener Tumoren in der PET

Hofheinz, F.; Langner, J.; Beuthien-Baumann, B.; Oehme, L.; Steffen, I.; Apostolova, I.; Steinbach, J.; Zöphel, K.; Kotzerke, J.; van den Hoff, J.
Ziel/Aim:

Die akkurate Abgrenzung von Tumoren in der PET gewinnt zunehmend an Bedeutung für die Strahlentherapie sowohl bei der Zielvolumendefinition als auch bei der Bewertung des Therapieansprechens. Für hinreichend homogen anreichernde Tumoren liefern adaptive Schwellwertverfahren, die neben einem Tumor-Referenzwert R (z.B. dem ROI-Maximum) den Untergrund Bg in der Tumorumgebung berücksichtigen, gute Ergebnisse. Der Schwellwert entspricht hierbei einer bestimmten 3D-Isokontur, welche die Tumorabgrenzung definiert. Bei stark heterogenen Tumoren kann es mit adaptiven Schwellwertverfahren jedoch zu merklichen Fehlern bei der Abgrenzung kommen, da die Grenzfläche nicht länger durch eine Isointensitätskontur gegeben ist. Ziel dieser Arbeit war die Entwicklung einer Abgrenzungsmethode, die auch bei stark heterogenen Zielstrukturen einsetzbar ist.

Methodik/Methods:

Die neue Methode (TV) kann als eine Erweiterung der adaptiven Schwellwertverfahren (TK) betrachtet werden, wobei statt eines ortsinvarianten, konstanten Schwellwertes ein voxelabhängiger Schwellwert berechnet wird, indem separat fuer jedes Voxel Bg und R in der Voxelumgebung bestimmt werden. Der absolute Schwellwert für das aktuell betrachtete Voxel ist dann gegeben durch T_abs = T x (R - Bg) + Bg, wobei die Konstante T = 0.39 in Phantommessungen mit homogen gefüllten Kugeln bestimmt wurde.

Der zugrunde liegende Algorithmus ist iterativ und benoetigt als Startwert eine grobe initiale Abgrenzung, welche durch einen benutzerdefinierten Schwellwert erfolgt. Unabhängig für jedes Voxel innerhalb der initialen Abgrenzung werden Bg und R bestimmt. Die zur Untergrundbestimmung genutzte Umgebung des Voxels ist hierbei durch eine Kugel mit Durchmesser 3 x FWHM definiert. Bg ergibt sich als Mittelwert über alle Voxel in dieser Kugel mit einem Mindestabstand zur derzeitigen Schätzung der ROI-Grenzfläche von 1 x FWHM. R ist der Maximalwert innerhalb der Kugel. Durch Anwendung von T_abs für jedes betrachtete Voxel ergibt sich sodann eine erste Schätzung der ROI-Grenze, die Ausgangspunkt des nächsten Iterationsschrittes ist. Iteration erfolgt bis zur Konvergenz des resultierenden ROI-Volumens.

Validierung: 10 klinische Datensätze (5 Bronchial-, 5 Kopf-Hals CA) dienten zur Simulation praxisnaher Bilddaten mit 10 stark heterogenen Tumoren bekannten Volumens (Heterogenität: 35 +/- 8%). Volumenabgrenzung erfolgte mit TK und TR.

Ergebnisse/Results:

Folgende Abweichungen vom wahren Volumen wurden bestimmt: TV: (6.9 +/- 6.6)%, TK: (47.5 +/- 16.8)%. Im Gegensatz zu TK führt TV zu einer sehr guten Reproduktion der wahren Volumina.

Schlussfolgerungen/Conclusions:

In simulierten praxisnahen Datensätzen liefert das neue Verfahren eine deutlich genauere Abgrenzung bei stark heterogenen Zielstrukturen als das konventionelle Verfahren. Die Eignung der Methode für den klinischen Einsatz muss noch näher untersucht werden.
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A20

Permalink: https://www.hzdr.de/publications/Publ-17077
Publ.-Id: 17077


First results of quantitative ASL perfusion measurements on a whole-body PET/MR system

Petr, J.; Bos, A.; Schramm, G.; Langner, J.; Hofheinz, F.; Beuthien-Baumann, B.; Platzek, I.; Kotzerke, J.; Steinbach, J.; van den Hoff, J.
Ziel/Aim:

In the beginning of 2011, a whole-body PET/MR system (Philips Ingenuity TF) became fully operational for patient investigations at our institute. With both imaging modalities, non-invasive quantitative perfusion measurements in the brain are possible. With PET, perfusion can be measured using [O-15]H2O which is considered as the gold standard but requires arterial blood sampling. Alternatively, perfusion values can be derived from arterial spin labeling (ASL) measurements in MR which has the advantage of being completely non-invasive and free of ionizing radiation. The combination of both imaging devices in a hybrid system allows a direct validation of ASL derived perfusion values against the PET measurements. Here, we present our first results of ASL perfusion measurements using the Ingenuity TF PET/MR.

Methodik/Methods:

We used multiphase EPISTAR ASL with Look-Locker sampling allowing a multiple inversion time image acquisition every 300 ms starting at 50 ms after the labeling. Crusher gradients were employed to remove signal from vascular blood. Two sequences with flip angles of 30° and 10° were performed to allow real flip-angle and T1 estimation. We performed two separated measurements on a healthy volunteer acquiring 4 slices in the brain with an in-plane pixel size of 3 mm by 3 mm and a slice thickness of 6 mm. The 3-parameter model proposed by Gunther et al. (1) was used to generate a parametric perfusion image and to calculate the cerebral blood flow (CBF).

Ergebnisse/Results:

The perfusion-weighted images showed reasonable signal-to-noise ratio and good contrast between gray and white matter. Gray matter structures were clearly delineated. Preliminary quantitative results are as follows: mean (slice average) CBF was 25 ml/100 g/min, gray matter CBF was 40 ml/100 g/min and white matter CBF was 12 ml/100 g/min. The deduced CBF value for gray matter fit the one given in (2) but are significantly lower than published results obtained with [O-15]H2O.

Schlussfolgerungen/Conclusions:

Our first measurements showed good image quality with the possibility of recognizing gray matter structures across the whole imaged area. The CBF quantification yielded values in partial agreement with the literature. Further work on the ASL quantification model needs to be done before validating the ASL results against [O-15]H2O PET measurements can be performed.

Literatur/References:

(1) Gunther, M., Bock, M., Schad, L. R., Magn. Reson. Med., 46:974-984, 2001.
(2) Petersen, E. T., Mouridsen, K., Golay, X., NeuroImage, 49:104-13, 2010
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A10-A11

Permalink: https://www.hzdr.de/publications/Publ-17076
Publ.-Id: 17076


PT-symmetry, indefinite damping and dissipation-induced instabilities

Kirillov, O.
With perfectly balanced gain and loss, dynamical systems with indefinite damping can obey the exact PT-symmetry being marginally stable with a pure imaginary spectrum. At an exceptional point where the symmetry is spontaneously broken, the stability is lost via passing through a non-semi-simple 1: 1 resonance. In the parameter space of a general dissipative system, marginally stable PT-symmetric ones occupy singularities on the boundary of the asymptotic stability. To observe how the singular surface governs dissipation-induced destabilization of the PT-symmetric system when gain and loss are not matched, an extension of recent experiments with PT-symmetric LRC circuits is proposed
Keywords: PT-symmetry, indefinite damping, stability, dissipation-induced instabilities, modulational instability

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  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-17075
Publ.-Id: 17075


Application of Ex-vessel Neutron Dosimetry Combined with In-core measurements for Correction of Neutron Source Used for RPV Fluence Calculations

Borodkin, P. G.; Borodkin, G. I.; Khrennikov, N. N.; Konheiser, J.
The paper deals with calculational and semi-analytical evaluations of VVER-1000 reactor core neutron source distributions and their influence on measurements and calculations of the integral through-vessel neutron leakage. Neutron activation measurements analyzed in the paper were carried out in ex-vessel air cavity at different NPP units with VVER-1000 during different fuel cycles. Time-integrated neutron source distributions used for DORT calculations were prepared by two different approaches based on a) calculated fuel burn-up (standard routine procedure) and b) in-core measurements by means of SPD & TC (new approach). Taking into account that fuel burn-up distributions in operating VVER may be evaluated now by analytical methods (calculations) only, it is needed to develop new approaches for testing and correction of calculational evaluations of neutron source. Results presented in this paper allow to consider a reverse task of alternative estimation of fuel burnup distributions. The approach proposed is based on adjustment (fitting) of time-integrated neutron source distributions, and hence fuel burn-up patterns in some part of reactor core, on the base of ex-core neutron leakage measurement, neutron-physical calculation and in-core SPD & TC measurement data.
Keywords: VVER-1000; DORT; TRAMO; Neutron activation measurements

Permalink: https://www.hzdr.de/publications/Publ-17074
Publ.-Id: 17074


Möglichkeiten der multimodalen Bildgebung in der Krebsdiagnostik

Stephan, H.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Universität Heidelberg, Institut für Anorganische Chemie, 16.03.2012, Heidelberg, D

Permalink: https://www.hzdr.de/publications/Publ-17072
Publ.-Id: 17072


Synthese und Charakterisierung von Cyclammonopropionsäure-Peptid-Konjugaten

Peschel, L.
kein Abstract verfügbar
  • Bachelor thesis
    FH Zittau/Görlitz, 2012
    64 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17071
Publ.-Id: 17071


Synthese und Charakterisierung asymmetrischer multifunktionaler Cyclam-Liganden mittels Staudinger Ligation

Weißpflog, M.
kein Abstact verfügbar
  • Bachelor thesis
    HTW Dresden, 2012
    68 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17070
Publ.-Id: 17070


Functional nanomaterials for multimodality cancer imaging

Stephan, H.
kein Abstract verfügbar
  • Lecture (others)
    OncoRay-Retreat 2012, 07.-08.03.2012, Dresden, D

Permalink: https://www.hzdr.de/publications/Publ-17069
Publ.-Id: 17069


Extraction Methods

Stephan, H.; Kubeil, M.; Gloe, K.; Gloe, K.
Molecular recognition, binding and transport of different chemical species represents an aspect of supramolecular chemistry that has relevance to a number of areas that include biochemical processes, analytical techniques, recycling and environmental processes as well as aspects of catalysis and medicine. Over the years, a large number of both efficient and selective receptors for cations, anions, salts and zwitterions based on different architectures and binding modes have been developed and studied.
Among the manifold experimental techniques employed for the application of such receptors has been the investigation of the distribution of species between two immiscible solutions, normally an aqueous and an organic phase, under the influence of the receptor in the organic phase. Such a procedure has often allowed characterization of the receptor’s complexation behavior towards individual species as well as enabling an evaluation of its suitability for species monitoring, separation and/or concentration; especially with respect to possible analytical applications as well as for use in extraction and membrane transport processes.
  • Book chapter
    C. A. Schalley (Ed.): Analytical Methods in Supramolecular Chemistry, 2nd, completely revised and enlarged edition, Weinheim: Wiley-VCH, 2012, 978-3-527-32982-3, 105-125

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Permalink: https://www.hzdr.de/publications/Publ-17068
Publ.-Id: 17068


Quantitative accuracy of MR based attenuation correction for PET - first experience with a whole-body PET/MR system

Schramm, G.; Langner, J.; Hofheinz, F.; Beuthien-Baumann, B.; Platzek, I.; Kotzerke, J.; Steinbach, J.; van den Hoff, J.
Ziel/Aim:

Combined whole body PET/MR systems have become commercially available recently. In 2010, one of the first of these systems (Philips Ingenuity TF PET/MR) has been installed at our institute. PET/MR is expected to offer new possibilities, in particular in the field of quantitative bimodal functional imaging (1). Quantitative PET image reconstruction requires attenuation correction (AC) which is commonly based on a direct measurement of photon attenuation using either a transmission scan with a Ge-68 radioactive source in standalone PET (TRAC) or a CT scan in PET/CT systems (CTAC). In PET/MR systems such a measurement cannot be performed. Hence, AC is performed with a software-based approach (MRAC) using dedicated tissue segmentation and tissue type identification (air, lung, soft tissue) of a MR image (2). Here, we report on a first evaluation of the accuracy of the manufacturer provided MRAC in whole body investigations with the Ingenuity TF PET/MR.

Methodik/Methods:

An evaluation of MRAC was performed by a direct comparison of the MR derived attenuation maps with transmission based attenuation maps acquired with a Siemens ECAT Exact HR+ PET system for 10 patients (8m/2f). We compared the pairs of coregistered attenuation maps in a voxel by voxel correlation analysis in the lung and the torso. In order to assess the influence of differences between the two AC methods on the resulting emission images we developed methods allowing to reconstruct PET emission data acquired at the PET/MR using the transmission based attenuation maps from the HR+ PET .

Ergebnisse/Results:

Our correlation analysis has shown that approximately 80% of the voxels in the lung and torso are in quantitative agreement. In one case, the MRAC algorithm failed to correctly detect the lung of the patient. In a further investigation, we observed metal artifacts resulting in distorted MR-derived attenuation maps.

Schlussfolgerungen/Conclusions:

The vendor-provided MRAC algorithm generally yields satisfactory results with respect to soft tissue and air segmentation. However, the algorithm relies on anatomic reference data and thus artifacts can arise if the anatomy of the patient does not fit to the reference. Additionally, metal artifacts can lead to distortion of the MR based attenuation maps.

Literatur/References:

(1) Pichler, B.J. et al., Sem. Nucl. Med., 38:199-208, 2008
(2) Martinez-Möller, A. et al., J. Nucl. Med., 50:520-526, 2009
  • Invited lecture (Conferences)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A79

Permalink: https://www.hzdr.de/publications/Publ-17067
Publ.-Id: 17067


2,3-Diaryl substituted indoles as probes for monitoring cyclooxygenase-2 (COX-2) with PET - radiolabeling, in vitro and in vivo studies

Knieß, T.; Laube, M.; Bergmann, R.; Graf, F.; Steinbach, J.; Pietzsch, J.
Ziel/Aim:

Cyclooxygenase-2 (COX-2) is an enzyme induced during inflammation, but overexpression of COX-2 also has been observed in carcinogenic processes. Non-invasive monitoring and quantitative characterization of functional expression of COX-2 by means of PET would substantially improve understanding of the role of this enzyme during manifestation and progression of inflammatory diseases and cancer.

Methodik/Methods:

Two compounds having a 2,3-diaryl substituted indole scaffold; 3-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-1H-indole 1 and 3-(4-methoxyphenyl)-2-(4-methylsulfonylphenyl)-1H-indole 2, both showing high inhibitory activity for COX-2 (IC50~20nM) served as non-radioactive references. The fluorine-18 radiolabeled tracer [18F]1 was synthesized by nucleophilic substitution of an appropriate trimethylammonium-substituted aromatic precursor with [18F]fluoride and subsequent McMurry cyclization. The carbon-11 radiolabeled probe [11C]2 was formed via a methylation reaction of the corresponding desmethyl precursor with [11C]CH3I. Unstimulated human monocytic leukemia cells (THP-1), phorbol ester stimulated THP-1 macrophages (THP-1M) and human tumor cell lines showing selectively high COX-2 (FaDu, HT-29, A2058) or COX-1 expression (A375) were used to study the overall uptake or cellular association of [18F]1 and [11C]2 in vitro. The stability of [18F]1 was determined by metabolite analysis of arterial blood samples in rats. In vivo kinetics and tumor uptake were investigated by dynamic small animal PET studies on HT-29 tumor bearing mice.

Ergebnisse/Results:

[18F]1 was synthesized in 10% yield (d.c.) in 98% radiochemical purity with a specific activity of 74-91 GBq/µmol. [11C]2 was obtained in 23% yield (d.c.) in 99% radiochemical purity with a specific activity of 79-89 GBq/µmol. The radiotracer cellular uptake in each model used correlated well with the observed COX protein synthesis. Cell models with prominent COX-2 overexpression showed a substantially higher uptake of both [18F]1 and [11C]2 in the order FaDu>HT29>THP-1M>A2058 when compared to COX-1 overexpressing A375 cells. The lowest cellular uptake was observed in THP-1 showing no or very low baseline expression of both COX-1 and COX-2. Metabolite analysis revealed 75% of original compound [18F]1 after 60 min. In contrast to the in vitro results no substantial tumor uptake of [18F]1 on HT-29 tumor bearing mice was detected.

Schlussfolgerungen/Conclusions:

The radiolabeled COX-2 inhibitors [18F]1 and [11C]2 were synthesized in good radiochemical yield and high purity. Cellular studies demonstrated well correlation of the overall radiotracer uptake with COX expression/protein synthesis rate. In vivo investigation did not show any accumulation of [18F]1 in COX-2 overexpressing tumors. Further exploration of new fluorine-18 and carbon-11 radiolabeled COX-2 inhibitors is required and currently under the way.
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, D
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A11-A12

Permalink: https://www.hzdr.de/publications/Publ-17066
Publ.-Id: 17066


A Device for Ultrafast Three-Dimensional X-Ray Computed Tomography with a Scanned Electron Beam

Stürzel, T.; Bieberle, M.; Hampel, U.
A novel tomography device has been realised which enables ultrafast three-dimensional imaging with up to 1000 volumeframes per second. This is achieved by scanning an electron beam over a specially designed annular x-ray transparent target. Its height of 37 mm is also the maximum height of the tomography volume. The maximum experiment diameter is 75 mm. The design of the setup is similar to cone beam tomography which allows image reconstruction based on Feldkamp type algorithms to be used. Various phantom experiments were performed and proved good spatial resolution of up to 1.2 mm at a volume-frame rate of 250 s-1. Eventually, the device was applied to image complex industrial two-phase flows as can be found e.g. in energy and process engineering.
Keywords: ultrafast, x-ray, three-dimensional
  • Lecture (Conference)
    Nuclear Science Symposium and Medical Imaging Conference, 23.-29.10.2011, Valencia, Spain
  • Contribution to proceedings
    Nuclear Science Symposium and Medical Imaging Conference, 23.-29.10.2011, Valencia, Spain
    Proceedings Nuclear Science Symposium and Medical Imaging Conference

Permalink: https://www.hzdr.de/publications/Publ-17065
Publ.-Id: 17065


Vibrational contribution to the thermodynamics of nanosized precipitates: vacancy–copper clusters in bcc-Fe

Talati, M.; Posselt, M.; Bonny, G.; Al-Motasem, A.; Bergner, F.
The effects of lattice vibration on the thermodynamics of nanosized coherent clusters in bcc-Fe consisting of vacancies and/or copper are investigated within the harmonic approximation. A combination of on-lattice simulated annealing based on Metropolis Monte Carlo simulations and off-lattice relaxation by molecular dynamics is applied to obtain the most stable cluster configurations at T = 0 K. The most recent interatomic potential built within the framework of the embedded-atom method for the Fe–Cu system is used. The total free energy of pure bcc-Fe and fcc-Cu as well as the total formation free energy and the total binding free energy of the vacancy–copper clusters are determined for finite temperatures. Our results are compared with the available data from previous investigations performed using many-body interatomic potentials and first-principles methods. For further applications in rate theory and object kinetic Monte Carlo simulations, the vibrational effects evaluated in the present study are included in the previously developed analytical fitting formulae.
Keywords: iron, vacancy-copper clusters, thermodynamics, vibrational contribution

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Publ.-Id: 17064


Magnetization dynamics of buckling domain structures in patterned thin films

Patschurek, C.; Lenz, K.; Strache, T.; Liedke, M. O.; Mönch, I.; Schäfer, R.; Schultz, L.; McCord, J.
The magneto-dynamics of lense shaped thin lm elements where studied using vector network analyzer ferromagnetic resonance (VNA-FMR). An unexpected strong increase of the resonance frequency was found when approaching the switching eld. Using Magnetic Force Microscopy this resonance increase could be ascribed to the formation and evolution of a buckling domain state. The experimental data have been qualitatively reproduced by micromagnetic simulations of a model element. Thereby the role of the external magnetic eld and the buckling wavelength was studied separately. Domain modes with dynamic magnetization modulations parallel and perpendicular to the static magnetization were identied. We derive qualitative arguments based on mageto-static energy considerations that allow for an interpretation of the dynamic response in such low-symmetric magnetization distributions.
Keywords: magnetic domains, magnetization dynamics, Kerr effect, ferromagnetic resonance

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Publ.-Id: 17063


Magnetization reversal of ferromagnetic elements surrounded by a synthetic antiferromagnet

Langer, M.; Neudert, A.; Osten, J.; Körner, M.; Mönch, I.; Mattheis, R.; Fassbender, J.ORC; McCord, J.
We investigated patterning of magnetic thin films by ion implantation. As shown in Ref. 1 by using ion implantation of an exchange coupled Fe/Cr/Fe system one can control the strength and sign of the antiferromagnetic (AF) coupling. Starting with a synthetic AF (SAF) trilayer (Co90Fe10/Ru/Co90Fe10) we used lithographic masks to irradiate spatially restricted areas. By doing this the trilayer structure was intermixed and resulted in ferromagnetic (FM) patterned elements surrounded by a SAF trilayer. At low fields the magnetization in the two Co90Fe10 layers of the SAF is antiparallel to each other and therefore behaves like an environment with a much lower susceptibility than the soft-magnetic Co90Fe10 film. The advantage of patterning by implantation compared to etching is that the magnetic elements don’t have a structural edge which usually is not free from roughness. The boundary of the patterned structures is only a magnetic boundary. Comparing to a previously used method, where we reduced the saturation magnetization locally by implanting Cr ions into a Ni81Fe19 layer [2], the method presented here needs a much lower ion fluence and therefore results in less irradiation damage and sputter losses.

The patterning was done by implanting Co ions with an energy of 80 keV into the following stack structure (deposited by dc-sputtering in an UHV vacuum system onto an oxidized Si wafer): Ta(4nm)/Co90Fe10(10nm)/Ru(1.15nm)/Co90Fe10(10nm)/Ru(3nm). Using optical lithography a mask was formed in photoresist and partly removed. At the used fluence of 5×1015 cm-2 the Co-ions intermixed the two Co90Fe10 layers with the Ru interlayer in the open areas of the mask (shown in Fig. 1 is a simulation of the intermixing during implantation using the Tridyn software package [3]). By this method FM elements were created that are surrounded by an AF-coupled Co90Fe10 bilayer. The magnetization reversal and domain structures were compared to patterned FM Ta(4nm)/Co90Fe10(20nm)/Ru(3nm) where the structures are etched.

Magnetic domain imaging was done using wide-field Kerr microscopy. By analyzing the gray scale intensity of individual stripes the magnetization loops of the FM stripes could be extracted. In the etched 20 µm wide stripes domains with anti-parallel magnetization and 180° domain walls are formed throughout the stripe during hard axis magnetization reversal. In the stripes surrounded by the SAF the magnetization is evolving into a different pattern. Along the FM-SAF interface edge domains evolve that depend on the magnetic field history. Fig. 2 shows the domain states during hard axis reversal for the implanted and etched sample as well as the hysteresis loops for the two different samples. The implanted sample has a smaller coercivity. Therefore even a small misalignment of the magnetic field with the hard axis has a stronger influence than in the etched sample. So in the implanted sample the magnetization in the center of the stripe is turning towards one direction due to the external field but the magnetization at the edge does not flip and is forming an edge domain. This can also explain the different domain size in the two images shown in Fig. 2. The smaller coercivity indicates that there are less pinning sites in the implanted sample compared to the etched stripes.

In narrower stripes with a nominal width of 2 µm Hc and Hk are the same for the etched and implanted stripes. Also here the coercivity is smaller in the implanted sample. The different anisotropy field for the implanted and etched stripes is caused from a different resulting width of the FM stripes for the two different preparation methods (stripe width obtained from AFM/MFM microscopy, not shown here).

To summarize, we used ion implantation to pattern extended magnetic thin films into elements of different sizes without introducing additional structural edges. Only the magnetic behavior is patterned (FM and SAF) and no structural edges are created. By using asymmetric Co90Fe10 thicknesses also patterning into areas of high and low effective saturation magnetization is possible. More examples of the resulting magnetic behavior will be shown during the presentation.

Support by DFG (FA 314/3 and MC 9/7) is gratefully acknowledged
Keywords: magnetic thin film elements, patterned magnetic films, Kerr microscopy, Ion irradiation
  • Poster
    INTERMAG 2012, 10.05.2012, Vancouver, Kanada

Permalink: https://www.hzdr.de/publications/Publ-17062
Publ.-Id: 17062


Tailoring the magnetic damping and anisotropy of Permalloy deposited on GaSb nanocones.

Ball, D. K.; Fritzsche, M.; Osten, J.; Lenz, K.; Facsko, S.; Mücklich, A.; Fassbender, J.ORC
The fundamental understanding how patterning on the nanometer length scale is affecting the magnetic properties is crucial to improve magnetic devices or recording media [1]. This is even more important when going from 2-dimensional patterns to 3-dimensional structures. Currently, there are still many open questions on this issue. Furthermore, the magnetic properties of these systems like damping and anisotropy need to be investigated. For 2-dimensional arrays this is quite easy. However the third dimension adds a lot of complexity to this issue, especially for micromagnetic simulations, due to the large cell number. Nowadays, there are several methods common practice like lithography and nanoimprinting to obtain patterned surfaces on the nanometer scale. Self-assembled nanostructures are a promising alternative to cover the third dimension.
Applying Ar+-ions with a broad beam ion source at normal incidence one obtains a self-assembled uniform pattern of nanocones on GaSb [2]. Due to the ion erosion the GaSb cones have an amorphous surface layer of a few nanometer. The size is adjustable (aspect ratio = 1) in the range of 10 to 100 nm. The size depends on the ion energy and thus can be selected. The relation between the ion energy and the characteristic length lc is described in [3]. The higher the ion energy is the higher and broader the nanocones can be adjusted. The size distribution is homogeneous within 10% and a short range hexagonal ordering is achieved as well. For the magnetic layers the substrate template was coated by molecular beam epitaxy with a seed layer of 5 nm Cr, followed by a 20 nm Ni80Fe20 and a 3 nm Cr cap layer. In Fig. (1) a transmission electron microscope (TEM) of a magnetically coated sample prepared at an ion energy of 200 eV and a characteristic length lc of about 30 nm. It depicts the film growth on the nanocones.
We investigated the magnetic properties by vector network analyzer ferromagnetic resonance (VNA-FMR). With VNA-FMR one can achieve information about the magneto-static properties like anisotropy and g-factor as well as information about dynamic properties like damping and inhomogeneous linewidth broadening. We measured resonance field and linewidth frequency dependent from 1 to 45 GHz in the polar geometry at θH = 0° [out-of-plane (oop)] and θH = 90° [in-plane (ip)]. In addition the angular-dependent measurements at 15 GHz from θH = - 30° to 195° were analyzed. The results have to be fitted by the FMR resonance equations. The dynamic behavior is shown in Fig. (2a) and (2b). Fig. (2a) shows the Gilbert damping constant α versus the characteristic length lc determined from the frequency dependence. Data for external field directions, i.e. θH = 0° (blue lines / points) and θH = 90° (red lines / points) are shown. The frequency dependence (not shown) evidences that only Gilbert damping contributes to the dynamic properties. The α values for the θH = 90° starts to increase between lc = 34 nm and 51 nm from about 0.010 to 0.034. This is due to the different growth type with increasing nanocone dimension. Whereas the damping for the θH = 0° measurement stays almost constant for all cone sizes with a fitted average value α = 0.006. These resulting damping constants for the measurements in both geometries are comparable to the Permalloy bulk value αbulk = 0.013(4) in literature [4]. The g-factor has been determined to be g = 2.095(4) which is in agreement with the literature value [5]. Fig. (2b) illustrates the behavior of the inhomogeneous linewidth broadening ΔH0 for the two external field directions (blue: θH = 0° / red: θH = 90°). For the oop–geometry ΔH0 is comparable to the bulk value magnitude ΔH0 = 8.6 Oe [4] and almost constant over lc. Along the ip–geometry ΔH0 is significantly higher than for θH = 0°. This can be explained by the superposition of several local resonances around the cone with slightly different resonance fields due to the different local field directions with respect to the cone’s normal. In the oop–geometry no such different resonance fields occur.
Financial support provided by the Deutsche Forschungsgemeinschaft (DFG) via projects DFG FA 314-7.1 and AL 618-6 is gratefully acknowledged.
-----------------------------------------------------------------------------------------------------------------
[1] B. D. Terris et al., J. Magn. Magn. Mater. 41, 10 (2009).
[2] S. Facsko et al., Science 285, 1551 (1999).
[3] S. Facsko et al., Phys. Rev. B 63, 16 (2001).
[4] B. K. Kuanr et al., J. Magn. Magn. Mater. 286, (2005).
[5] D. Markó et al., Appl. Phys. Lett. 96, 022503 (2010).
Keywords: self-assembled nanostructured GaSb surface, anisotropy, damping, remanence
  • Lecture (Conference)
    INTERMAG 2012 Vancover, IEEE International Magnetics Conference, 07.-11.05.2012, Vancouver, Kanada

Permalink: https://www.hzdr.de/publications/Publ-17061
Publ.-Id: 17061


Morphology induced two-magnon scattering in thin NiFe films

Körner, M.; Lenz, K.; Fritzsche, M.; Facsko, S.; Fassbender, J.ORC
When studying magnetization dynamics of thin magnetic films, intrinsic as well as extrinsic spin relaxation processes have to be taken into account. While intrinsic processes, summarized as Gilbert damping, are well known and studied for the last decades, the focus now has shifted to extrinsic contributions. In this context the two-magnon scattering (TMS) is of particular interest. This type of scattering is induced within thin magnetic films by defects and inhomogeneities. It was shown that periodic magnetic patterns can serve as defect structure, e.g. by periodically varying the magnetization saturation using ion beam irradiation combined with periodic sample patterning by electron beam lithography. Due to irradiation of the material a local variation of the magnetic properties can be achieved [1], where the TMS strength is set by the periodicity of the modification. However, directly patterning the material is time consuming and not suitable for large scale manufacturing. Hence a self-organized nanoscale patterning is more favorable. Broad ion beam erosion is a well-established technique for structuring large surface areas. By varying the irradiation parameters, e.g. ion energy, fluence, and incident angle sinusoidally modulated surfaces (ripples) can be created with a periodicity tuneable over a wide range [2]. Growing magnetic materials on these ripples imprints the corrugation to the material and induces by dipolar effects a wavelength dependent uniaxial magnetic anisotropy (UMA). Furthermore the imprinted corrugation can serve as a spin wave scattering center, modifying the two-magnon damping contribution.
Here we present the influence of the substrate surface corrugation on the magnetic damping properties of 30 nm thin Ni80Fe20 (Py) films grown by molecular beam epitaxy at room temperature on rippled Si substrates. Due to ion beam erosion of flat Si as well as natural oxidation of the substrate prior to film deposition, Py films grown on top exhibit a polycrystalline structure that suppresses the intrinsic magneto-crystalline anisotropy almost completely. The in-plane magnetostatic and dynamic properties of these samples were investigated by means of angular and frequency dependent vector network analyzer ferromagnetic resonance (VNA-FMR).
Starting with a planar reference sample the angular together with the frequency dependent linewidth measurements reveal a Gilbert dominated relaxation process, whereby no TMS can be observed. Due to the polycrystalline film structure, only a very weak magnetic anisotropy is observed. This uniaxial magnetic anisotropy (UMA) has a two-fold symmetry and is randomly aligned with respect to the sample edges. Changing to rippled substrates the grown Py film maintains its polycrystalline structure. Depending on the ripple wavelength λ, ranging from 25 nm to 230 nm, an UMA is induced with its easy axis always aligned parallel to the ripple ridges. The strength of the UMA decays with increasing wavelength and is strongest for λ=25 nm. In this case no influence of the corrugation on the damping is observed. This changes drastically for samples with a higher wavelength of λ=230 nm. While the UMA is reduced to the value of the planar reference sample the linewidth measurements now show clear indications for defect induced TMS. This is shown in Fig. 1a, where the peak-to-peak linewidth is plotted as a function of the in-plane magnetic field angle (open circles). Modeling the linewidth results in a Gilbert contribution that is constant for all in-plane field orientations. Additionally an angle dependent TMS contribution is found, which consists of a small four-fold and a dominating two-fold (uniaxial) part. Thereby the direction of minimal linewidth aligns parallel with the ripple ridges, which in turn defines the uniaxial symmetry of the damping. Fig. 1b depicts the frequency dependent measurements parallel (red squares) and perpendicular (green circles) to the ripple ridges. In parallel configuration the damping is purely Gilbert-like, as already observed in the reference measurement. The monotonous increase of the linewidth with applied microwave frequency is instead lost in case of the perpendicular geometry. Here, a preeminent peak is observed with its center at f=10 GHz. Following the description of Barsukov et al. [1] this excessive linewidth increase is a result of defect induced TMS, where the width and frequency position of the peak is determined by the scattering potential, created by the corrugation of the film. The origin and wavelength dependence of these morphology induced linewidth manipulation will be discussed in detail.
We thank I. Barsukov, J. Lindner, and P. Landeros for fruitful discussions. This work is supported by DFG grant no. FA 314/6-1. References: [1] I. Barsukov et al., Phys. Rev. B 84, 140410(R) (2011)
[2] J. Fassbender et al., New J. Phys. 11, 125002 (2009)
  • Lecture (Conference)
    INTERMAG 2012, International Magnetics Conference, 07.-11.05.2012, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-17060
Publ.-Id: 17060


Initial magnetisation angle dependence for microwave oscillation in a metallic spin valve

Fowley, C.; Bernert, K.; Sluka, V.; Fassbender, J.ORC; Deac, A. M.; Rippard, W. H.; Pufall, M. R.; Russek, S. E.
In order for spin transfer torque oscillators to find their way to applications, the problems of obtaining high output power and low frequency linewidth must be solved. To this end differing geometries have been proposed and near zero applied field large high power microwave emission has been obtained [1,2]. One contains an out-of-plane polariser and an in-plane free layer [1], while the other contains an in-plane polariser and an out-of-plane free layer [2]. The former device has the requirement of a third layer in order to read out the magnetoresistance (MR) signal, whereas in the latter device the polariser functions as the reference layer.

[1] Houssameddine, D., et al., Nature Mater. 6, 447 (2007).
[2] Rippard, W. H., et al., Phys. Rev. B 81, 014426 (2010).
Keywords: spin transfer torque, spin transfer oscillators, perpendicular magnetic anisotropy, macrospin approximation
  • Poster
    INTERMAG 2012, International Magnetics Conference, 07.-11.05.2012, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-17059
Publ.-Id: 17059


Frequency-Tunable Magnetic Relaxation in Periodic Nanostructures Tailored by Ion Beam Irradiation

Lenz, K.; Körner, M.; Banholzer, A.; Liedke, M. O.; Grebing, J.; Fassbender, J.ORC; Barsukov, I.; Römer, F. M.; Lindner, J.; Landeros, P.
Tailoring magnetization dynamics in nano structures is a very important field. Here we present, how magnetic hybrid materials can be used to increase the relaxation rate just within several small frequency ranges.

Various elements like Pd, Cr, Ta, as well as several rare-earth elements can be used to modify the magnetic properties of thin ferromagnetic films. They are incorporated either by co-sputtering or ion implantation and are well known to reduce the Curie temperature, saturation magnetization, anisotropy and damping [1,2]. In combination with lithographic masking this allows for magnetic property patterning at the nanoscale [3,4].
In thin ferromagnetic films, the magnetization dynamics are governed by intrinsic effects like Gilbert damping and spin-pumping but also by extrinsic effects like two-magnon scattering [5] due to inevitable defect structures. By lithographic nano patterning or by using ion-eroded, nanoscale periodically modulated substrates (ripples) as templates we are able to artificially create and thus control those defect structures necessary to induce two-magnon scattering.

This preparation procedure is sketched in Fig. 1. First a thin film sample is prepared by molecular beam epitaxy. In our case we use a 30 nm thin Ni80Fe20 (Permalloy=Py) film covered by a 3 nm Cr cap layer. In the second step, using a ~100 nm PMMA resist and electron beam lithography, the periodic stripe pattern is written into the mask over an area of 1x1 mm2 with periodicities of 250 and 400 nm. After development the sample was irradiated with Cr+ ions with a kinetic energy of 5 keV and a fluence of 5x1015 ions/cm2. The Cr ions either get absorbed by the PMMA or penetrate the topmost 8 nm of the sample as depicted in step (iii) of Fig. 1 [4]. This mixes the Cr coming from the ions and the cap layer into the Py layer, hence reducing the saturation magnetization in the irradiated stripe areas. Thus, the modified Py+Cr stripes act as magnetic defects respectively scattering centers.

Broadband ferromagnetic resonance is used to measure the resonance linewidth ΔH for different field directions. From the frequency and angular dependence of ΔH the damping contributions are disentangled like described in Ref. [5]. The frequency-dependent measurements with the external magnetic field aligned parallel to the stripes show a linear increase of ΔH. Therefore the magnetic relaxation is purely Gilbert-like (see Fig. 2a). With the magnetic field aligned perpendicular (Fig. 2b), the frequency dependence exhibits a non-monotonous increase due to two-magnon scattering. There are several distinct peaks (marked by arrows in Fig. 2b). Depending on the stripe periodicity the peak positions shift and the number of visible peaks changes as well.
The conventional model of two-magnon scattering in thin films [5] does not cover this effect. However, the stripe defects resemble a periodic scattering field, which couples the uniform with the final-state magnons in the two-magnon scattering process. The coupling strength and so the FMR linewidth scale with the square of the Fourier transform of the scattering field. Figure 2c shows the corresponding simulated two-magnon scattering strength as function of frequency and stripe periodicity. The black squares ("linescans"), correspond to the FMR linewidth measurements qualitatively very well. Note that a quantitative agreement depends very sensitively on the knowledge of the the static magnetic properties. For spintronic devices it could be very interesting to have a selectively higher damping at certain frequencies---a feature that could be even switched-off simply by changing the external field direction.

In summary, this magnetic hybrid material allows for designing samples where the spin relaxation rate can be easily switched between high and low damping just by slightly varying the frequencies. In contrast to that, with conventional materials only a monotonous increase of damping with frequency is achievable.

This work was supported by the DFG grants FA 314/6-1, FA314/3-2, and SFB491.
  • Poster
    INTERMAG 2012, International Magnetics Conference, 07.-11.05.2012, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-17058
Publ.-Id: 17058


Tailoring perpendicular anisotropy in Co/Pd multilayers by ion irradiation

Osten, J.; Greene, P.; Endo, T.; Iwata, N.; Lenz, K.; Liu, K.; Fassbender, J.ORC
A major obstacle towards the increase in areal magnetic recording density and the decrease in bit size is the retention of thermal stability while maintaining reasonable write fields. Materials with graded magnetic anisotropy are promising candidates to solve this problem.
Here we demonstrate the approach of using post-deposition Ar-ion irradiation to tailor the perpendicular anisotropy in Co/Pd multilayer thin films. The films, with uniform, anisotropy, were synthesized by magnetron sputtering. Based on TRIDYN simulations, different primary ion energies (1-25keV) are chosen to achieve varying penetration depths of the ions creating a depth dependent anisotropy grading. Before and after ion irradiation, MOKE as well as magnetometry measurements were employed to detect the changes of the magnetic properties. Upon ion irradiation, the Co/Pd films exhibit reduced coercivity and remanence with increasing fluence.
Higher ion energies have a more pronounced effect on reducing the perpendicular anisotropy.
Keywords: anisotropy grading perpendicular anisotropy Co/Pd multilayer bit size media
  • Poster
    Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland
  • Poster
    MRS Spring Meeting and Exhibit, 09.-13.04.2012, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-17057
Publ.-Id: 17057


Structure and stability range of a hexanuclear Th(IV) – glycine complex

Hennig, C.; Takao, S.; Takao, K.; Weiss, S.; Kraus, W.; Emmerling, K.; Scheinost, A. C.
A hexanuclear Th(IV) glycine complex was observed by Th L3-edge EXAFS measurements in aqueous solution. Within the stability range of this complex the positively charged hexanuclear species [Th6(µ3-O)4(µ3-OH)4(H2O)6(Gly)6(HGly)6]6+ was preserved in a crystal with the composition [Th6(µ3-O)4(µ3-OH)4(H2O)6(Gly)6(HGly)6]•(NO3)3(ClO4)3(H2O)3. This complex appears as result of a competing reaction between hydrolysis and ligation by glycine. At a pH value below the stability range of the hexanuclear complex, crystals with the composition [Th(H2O)3(HGly)3]•(ClO4)4H2O were obtained from the solution. Three water molecules in the thorium coordination sphere indicate that this complex occurs below the onset of Th(IV) hydrolysis.
Keywords: EXAFS, XRD, formation constant, hexanuclear complex

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Publ.-Id: 17056


Uranium Chemistry in Citric Acid Solution

Steudtner, R.; Müller, K.; Jäckel, E.; Meyer, R.; Schmeide, K.; Günther, A.
For the long-term safety assessment of radioactive waste disposal sites, detailed knowledge on the migration behavior of the different actinides as a function of pH value and redox potential of the solution, concentration of inorganic or organic complex partners and temperature is important. The majority of the studies on the uranium chemistry in presence of carboxylic acids deal with complexation reactions performed at lower pH value and at room temperature. Thermodynamic data of the complexation of U(IV) and U(VI) by citric acid are summarized up to the year 2005 by Hummel et al. [1] and since then comprehensively studied by Bonin et al. [2], Steudtner [3] and Guenther et al. [4]. The photoreduction of U(VI) in citric acid solutions was studied in the presence of visible light by Ohyoshi and Ueno [5]. However, the mechanistic understanding of the basic interaction processes is very fragmentary.
Thus, the study is focused on the mechanism and kinetics of the uranium complexation and redox reactions as a function of carbonate concentration and visible light in citric acid solution. To evaluate the influence of these reaction parameters on the uranium – citric acid – system we used UV-Vis, ATR FT-IR and TRLF spectroscopy. The aqueous complexes of the U(VI) and U(IV) compounds are spectroscopically characterized to gain information on their molecular structures. The knowledge of the spectral properties is indispensable for the interpretation of the spectral changes occurring during the redox reactions. The variation of reaction parameters and the change of different reaction paths strongly influence the redox reactions. The derivation and verification of thermodynamic and kinetic parameters of the complexation and redox processes will improve the safety assessment of nuclear waste disposal sites.
Keywords: Complexation, redox reaction, UV-Vis, ATR FT-IR and TRLF spectroscopy
  • Lecture (Conference)
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17055
Publ.-Id: 17055


Mixing Enhancement in Gas-Stirred Melts by Rotating Magnetic Fields

Vogt, T.; Andruszkiewicz, A.; Eckert, S.; Eckert, K.; Odenbach, S.; Gerbeth, G.
A model experiment of a submerged gas injection system in a cylindrical vessel under the influence of a rotating magnetic field and its effect on liquid metal mixing is presented. Argon gas is injected through a nozzle into a column of the eutectic alloy GaInSn, which is liquid at room temperature. Without a magnetic field the bubble plume in the center region of the cylindrical vessel produces a recirculation zone with high fluid velocities near the free surface while the fluid velocities in the bottom region are rather low. Our measurements revealed the potential of rotating magnetic fields to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid volume. Various periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate.
Keywords: Mixing, rotating magnetic field, bubbles

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Publ.-Id: 17053


Broken magnetic symmetry due to charge-order ferroelectricity discovered in (TMTTF)2X salts by multifrequency ESR

Yasin, S.; Salameh, B.; Rose, E.; Dumm, M.; Krug Von Nidda, H.-A.; Loidl, A.; Ozerov, M.; Untereiner, G.; Montgomery, L.; Dressel, M.
We have investigated the charge-ordered state of the quasi-one-dimensional organic charge-transfer salts (TMTTF)2X (where TMTTF stands for tetramethyltetrathiafulvalene and X = PF6 AsF6, SbF6, and SCN) by performing comprehensive electron-spin-resonance (ESR) experiments at several frequencies for 4 K < T < 300 K. At elevated temperatures all compounds show a linear increase of ΔH(T ). Below the charge-ordering transition TCO important anomalies are observed in both the temperature dependence and the anisotropy of the ESR linewidth. In the case of the centrosymmetric anions PF6, AsF6, and SbF6, the linewidth doubles its periodicity when rotated in a plane normal to the molecule axis; and it exhibits a significant frequency dependence. This enhanced linewidth is caused by anisotropic Zeeman interaction that we identify as a relaxation process in the charge-ordered state where magnetically inequivalent sites are present in adjacent stacks. Thus, charge order not only produces ferroelectricity but also breaks the symmetry of the magnetic degree of freedom in these organic quantum spin chains. For (TMTTF)2SCN charge order coincides with the ordering of the non-centrosymmetric anions; the large contribution of dipolar interaction dominates the relaxation process.

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Publ.-Id: 17052


Development of functionalised polyelectrolyte capsules using filamentous Escherichia coli cells

Lederer, F.; Günther, T.; Weinert, U.; Raff, J.; Pollmann, K.
Background: Escherichia coli is one of the best studied microorganisms and finds multiple applications especially as tool in the heterologous production of interesting proteins of other organisms. The heterologous expression of special surface (S-) layer proteins caused the formation of extremely long E. coli cells which leave transparent tubes when they divide into single E. coli cells. Such natural structures are of high value as bio-templates for the development of bio-inorganic composites for many applications. In this study we used genetically modified filamentous Escherichia coli cells as template for the design of polyelectrolyte tubes that can be used as carrier for functional molecules or particles.
Diversity of structures of biogenic materials have the potential to be used to construct inorganic or polymeric superior hybrid materials that reflect the form of the bio-template. Such bio-inspired materials are of great interest in diverse scientific fields like Biology, Chemistry and Material Science and can find application for the construction of functional materials or the bio-inspired synthesis of inorganic nanoparticles.
Results: Genetically modified filamentous E. coli cells were fixed in 2 % glutaraldehyde and coated with alternating six layers of the polyanion polyelectrolyte poly(sodium-4styrenesulfonate) (PSS) and polycation polyelectrolyte poly(allylamine-hydrochloride) (PAH). Afterwards we dissolved the E. coli cells with 1.2 % sodium hypochlorite, thus obtaining hollow polyelectrolyte tubes of 0.7 µm in diameter and 5-50 µm in length. For functionalisation the polyelectrolyte tubes were coated with S-layer protein polymers followed by metallisation with Pd(0) particles. These assemblies were analysed with light microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy.
Conclusion: The thus constructed new material offers possibilities for diverse applications like novel catalysts or metal nanowires for electrical devices. The novelty of this work is the use of filamentous E. coli templates and the use of S-layer proteins in a new material construct.
Keywords: Escherichia coli, S-layer, polyelectrolytes, layer-by-layer (LbL), palladium, SEM, TEM, nanoparticle

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Publ.-Id: 17051


First measurement of proton-induced low-momentum dielectron radiation off cold nuclear matter

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lalik, R.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.
We present data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics measurement of dielectrons radiated from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2\%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e^+e^- invariant mass spectra to elementary p+p data, we observe for e^+e^- momenta P_{ee}<0.8 GeV/c a strong modification of the shape of the spectra, which we attribute to an additional rho-like contribution and a decrease in omega yield. These opposite trends are tentatively interpreted as a strong coupling of the rhomeson to baryonic resonances and an in-medium broadening of the omega spectral function.

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Publ.-Id: 17050


Direct imaging of spin relaxation in stepped alpha-Fe2O3/Ni81Fe19 bilayers using X-Ray PhotoEmission Electron Microscopy

Bali, R.; Marchetto, H.; Barcza, A.; Blamire, M. G.; Dhesi, S. S.
The magnetic domain structure of stepped ferromagnetic Ni81Fe19 films, exchange coupled to antiferromagnetic alpha-Fe2O3, has been studied using PhotoEmission Electron Microscopy combined with X-Ray Magnetic Circular Dichroism. Annealing the alpha-Fe2O3/Ni81Fe19 bilayers in a magnetic eld, applied parallel or perpendicular to the step edges, results in a signifcant increase in the domain size compared to the as-grown bilayer. Subsequent zero-eld annealing induces spin-relaxation along the crystallographic axes of the alpha-Fe2O3. The spin-relaxation process is found to depend on the magnetic field direction during annealing with the domain structure determined by a competition between the step-induced uniaxial anisotropy and the exchange anisotropy.
Keywords: Magnetic Domains, Exchange Bias, Spin Relaxation

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Publ.-Id: 17049


Switching Phase Diagrams and Backhopping in Magnetic Tunnel Junctions (MTJs)

Bernert, K.; Sluka, V.; Fowley, C.; Gan, H.; Fassbender, J.ORC; Deac, A.
A spin-polarized current flowing through a ferromagnet can exert a torque on the local magnetization [1,2]. This phenomenon is currently intensively investigated due to its potential application in magnetic random access memory (MRAM) or in telecommunication devices. Presently, the structure of choice for spin-torque devices includes a magnetic tunnel junction (MTJ) with an MgO barrier, due to their large magnetoresistance signals. However, a key step towards the practical implementation as MRAM elements is the reduction of the critical voltages, in order to keep the size of the selection transistor down and compete with existing technologies [3]. A second issue (but equally important) is the thermal stability of the devices, as data retention for over ten years is required for industrial applications.

The thermal stability of the MgO-MTJs is currently evaluated based on the formalism developed for metallic nanopillars [4]. However, it has been pointed out that based on this formalism, the thermal stability coefficients evaluated for switching starting from different states (parallel or antiparallel) have different values in MgO-MTJs [5]. In addition, magnetic tunnel junctions also exhibit a somewhat obscure behaviour referred to as ‘back-hopping’, whereby reliable switching to the desired state is achieved for applied voltages of the order of the critical voltage, but a larger applied bias induces a telegraph-noise behaviour [6, 7]. Back-hopping is characteristic for MTJs, as it has not been observed in metallic multilayers, and poses serious concerns for designing industrially-competitive MRAM devices.

We evaluate the switching voltages and their temperature dependence by analytically and numerically solving the modified Landau-Lifshitz-Gilbert equation which includes both Slonczewski-like (in-plane) and field-like (out-of-plane) torque terms (equation 1). Here, γ is the gyromagnetic ratio, Heff the effective field (including the anisotropy, demagnetization field and applied field), α the Gilbert damping coefficient, Ms the saturation magnetization and V¬mag the volume of the free layer. and are the coefficients for in-plane and out-of-plane spin-transfer torques, respectively, which can be determined from spin-torque bias dependence measurements [8, 9, 10], and is the vector of the spin polarization (parallel to the pinned layer magnetization).

In metallic spin-valves, the out-of-plane torque has been demonstrated to be about two orders of magnitude lower than the in-plane spin-torque, and can generally be neglected [11], yielding a linear dependence of the switching current on the applied field. In MgO-MTJs, the field-like torque can be of the order of 25% of the in-plane torque [7], and needs to be taken into account. Its quadratic dependence on the applied voltage [9,12] translates into a more complex correlation between the critical bias and the external field, altering the shape of the phase diagram, as demonstrated experimentally [5]. It also offers a potential explanation for the occurrence of back-hopping at a large bias. In addition, it alters the temperature dependence of the critical voltages, which needs to be taken into account when evaluating the thermal stability of such devices.

References:
[1] J. C. Slonczewski, Journal of Magnetism and Magnetic Material 159, L1 (1996)
[2] L. Berger, Physical Review B 54, 9359 (1996)
[3] Z. Diao et al., Journal of Physics: Condensed Matter 19, 165209 (2007)
[4] S. Ikeda et al., Nature Materials 9, 721 (2010)
[5] S.-C. Oh et al., Nature Physics 5, 898 (2009)
[6] J. Z. Sun, J. Appl. Phys. 105, 07D109 (2009)
[7] T. Min et al., J. Appl. Phys. 105, 07D126 (2009)
[8] H. Kubota et al., Nature Phys. 4, 37 (2008)
[9] J. C. Sankey et al., Nature Phys. 4, 67 (2008)
[10] A. Deac et al., Nature Physics 4, 803 (2008)
[11] M. A. Zimmler et al., Phys. Rev. B 70, 184438 (2004)
[12] I. Theodonis et al., Phys. Rev. Lett, 97, 237205 (2006)
Keywords: spin transfer torque, MTJ, phase diagram
  • Lecture (Conference)
    INTERMAG 2012, 10.05.2012, Vancouver, Canada
  • Lecture (Conference)
    The IEEE International Conference on Microwave Magnetics, 26.-29.08.2012, Kaiserslautern, Deutschland
  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS), 24.-28.09.2012, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-17047
Publ.-Id: 17047


Four-quark condensates in open-charm chiral QCD sum rules

Hilger, T.; Buchheim, T.; Kämpfer, B.; Leupold, S.
Recently, in Hilger et al. (2011) [1] QCD sum rules for chiral partners in the open-charm meson sector have been presented at nonzero baryon net density or temperature up to and including mass dimension 5. Referring to this, details concerning the cancelation of infrared divergences are presented and important technical and conceptional ingredients for an incorporation of four-quark condensates beyond factorization and of other mass dimension 6 condensates are collected.

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Microstructural studies of fluorine-implanted titanium aluminides for enhanced environmental durability

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Munnik, F.; Mücklich, A.; Gemming, S.; Alexewicz, A.; Bracht, H.; Rösner, H.; Donchev, A.; Schütze, M.
Titanium aluminides based on the gamma-phase (γ-TiAl) are promising materials for advanced power generation, aerospace and automobile applications. Oxidation-resistance problems, however, limit the maximal service temperature of these alloys to about 700°C. A significant improvement in environmental durability of γ-TiAl up to 1050°C can be achieved by ion-implanting fluorine into the alloy subsurface relying on the so-called halogen effect. Plasma immersion ion implantation (PIII) of F has been employed because of the possibility to process components of complex geometry as well as to inject sufficiently high F doses in relatively short times. In this work, characterization of the microstructure of F-implanted γ-TiAl alloys has been undertaken using cross-sectional transmission electron microscopy in conjunction with energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. Preliminary studies by elastic recoil detection analysis have revealed anomalously broad, high-concentration (up to 60 at. %) F profiles of either Gaussian-like or plateau-like shape extending to much larger depths than those predicted by theory; a phenomenon which cannot be accounted for by standard ion-solid interaction and F diffusion mechanisms. It has been found that the F implant profiles result from a complex amorphiztation/recrystallization (a/c) process, which occurs via the a/c front progressing toward the bulk and giving rise to anomalous F diffusion. The final F distribution is implantation-temperature dependent, with higher temperatures causing partial dynamic annealing of the amorphized TiAl material and profile shrinkage. Long-term pos-implantation oxidation tests have indicated that enhanced oxidation resistance is always associated with Gaussian-type as-implanted fluorine profiles coupled with optimal fluorine doses while flat-topped implant profiles resulting from the implantation of excessively high F doses produce a poorly oxidation-resistant surface. The results of these analyses have been helpful in understanding the behavior of the implanted F from both a basic scientific and a technological standpoint.
Keywords: titanium aluminides, high-temperature oxidation, fluorine diffusion, plasma immersion ion implantation

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Annual Report 2011 - Institute of ion Beam Physics and Materials Research

Cordeiro, A. L.; Fassbender, J.ORC; Heera, V.; Helm, M.
The first year of membership of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in the Helmholtz Association of German Research Centers (HGF) was a year of many changes also for the Institute of Ion Beam Physics and Materials Research (IIM). The transition period, however, is not yet over, since the full integration of the Center into the HGF will only be completed in the next period of the so-called program-oriented funding (POF). This funding scheme addresses the six core research fields identified by the Helmholtz Association (Energy; Earth and Environment; Health; Key Technologies; Structure of Matter; Aeronautics, Space and Transport) to deal with the grand challenges faced by society, science and industry. Since the Institute has strong contributions to both core fields “Key Technologies” and “Structure of Matter”, intense discussions were held amongst the leading scientists of the Institute, across the Institutes of the HZDR, and finally with leading scientists of other Helmholtz centers, to determine the most appropriate classification of the Institute’s research. At the end we decided to establish ourselves in Structure of Matter, the core field in which most of the large-scale photon, neutron and ion facilities in Germany are located. As a consequence, the Ion Beam Center (IBC) of the Institute submitted an application to become a HGF recognized large-scale facility, providing more than 50% of its available beam time to external users. This application perfectly reflects the development of the IBC over more than a decade as a European Union funded infrastructure in the framework of the projects “Center for Application of Ion Beams in Materials Research (AIM)” (1998-2000, 2000-2003, 2006-2010) and subsequently as the coordinator of the integrated infrastructure initiative (I3) “Support of Public and Industrial Research using Ion Beam Technology (SPIRIT)” (2009-2013). Another part of the Institute’s activities is dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. This facility is also open to external users and funded by the European Union.
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-014 2012
    ISSN: 2191-8708

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Publ.-Id: 17044


Superconductivity in Layered Organic Metals

Wosnitza, J.
In this short review, I will give an overview on the current understanding of the superconductivity in quasi-two-dimensional organic metals. Thereby, I will focus on charge-transfer salts based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET for short). In these materials, strong electronic correlations are clearly evident, resulting in unique phase diagrams. The layered crystallographic structure leads to highly anisotropic electronic as well as superconducting properties. The corresponding very high orbital critical field for in-plane magnetic-field alignment allows for the occurrence of the Fulde–Ferrell–Larkin–Ovchinnikov state as evidenced by thermodynamic measurements. The experimental picture on the nature of the superconducting state is still controversial with evidence both for unconventional as well as for BCS-like superconductivity.
Keywords: organic superconductors; electronic structure; superconducting state; Fulde–Ferrell–Larkin–Ovchinnikov state

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Generation of pulsed magnetic fields – stretching the limits—

Zherlitsyn, S.
High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument in condensed-matter physics. Consequently, the demand for ever higher magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), pulsed magnetic fields up to about 90 T are readily available for users. For the generation of such high pulsed magnetic fields a specially designed world-unique capacitor bank has been installed. Operating at a maximum voltage of 24 kV, peak currents of up to 500 kA with a pulsed power of about 5 GW can be supplied. Besides this high-energy (50 MJ) capacitor bank, a number of smaller capacitive pulsed-power generators are designed at the HLD, some of which supply currents beyond 1.5 MA on a microsecond time scale.
  • Invited lecture (Conferences)
    Frühjahrstagung der DPG, 12.-16.03.2012, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17042
Publ.-Id: 17042


A method for model-free partial volume correction in oncological PET

Hofheinz, F.; Langner, J.; Petr, J.; Beuthien-Baumann, B.; Oehme, L.; Steinbach, J.; Kotzerke, J.; van den Hoff, J.
Background
As is well known, limited spatial resolution leads to partial volume effects (PVE) and consequently to limited signal recovery. Determination of the mean activity concentration of a target structure is thus compromised even at target sizes much larger than the reconstructed spatial resolution. This leads to serious size-dependent underestimates of true signal intensity in hot spot imaging. For quantitative PET in general and in the context of therapy assessment in particular it is, therefore, mandatory to perform an adequate partial volume correction (PVC). The goal of our work was to develop and to validate a model-free PVC algorithm for hot spot imaging.
Methods
The algorithm proceeds in two automated steps. Step 1: estimation of the actual object boundary with a threshold based method and determination of the total activity A measured within the enclosed volume V. Step 2: determination of the activity fraction B, which is measured outside the object due to the partial volume effect (spill-out). The PVE corrected mean value is then given by Cmean = (A+B)/V. For validation simulated tumours were used which were derived from real patient data (liver metastases of a colorectal carcinoma and head and neck cancer, respectively). The simulated tumours have characteristics (regarding tumour shape, contrast, noise, etc.) which are very similar to those of the underlying patient data, but the boundaries and tracer accumulation are exactly known. The PVE corrected mean values of 37 simulated tumours were determined and compared with the true mean values.
Results
For the investigated simulated data the proposed approach yields PVE corrected mean values which agree very well with the true values (mean deviation (± s.d.): .(-0.8 ± 2.5)%).
Conclusions
The described method enables accurate quantitative partial volume correction in oncological hot spot imaging.
Keywords: Partial volume effect, Partial volume correction, Recovery correction, PET, Quantification

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Publ.-Id: 17041


Curium(III) citrate speciation in biological systems: An europium(III) assisted spectroscopic and quantum chemical study

Heller, A.; Barkleit, A.; Foerstendorf, H.; Tsushima, S.; Bernhard, G.
Citrate complexes are the dominant binding form of trivalent actinides and lanthanides in human urine at pH < 6. Hence, an accurate prediction of the speciation of these elements in the presence of citric acid is crucial for the understanding of the impact on the metabolism of the human organism and the corresponding health risks. We studied the complexation of Cm(III) and Eu(III), as representatives of trivalent actinides and lanthanides, respectively, in aqueous citrate solution over a wide pH range using time-resolved laser-induced fluorescence spectroscopy. Four distinct citrate complexes were identified and their stability constants were determined for both Cm(III) and Eu(III), which are MHCit0, M(HCitH)HCit2-, M(HCit)23-, and M(Cit)25- (M = Cm, Eu). Additionally, there were also indications for the formation of MCit- complexes. Structural details on the EuHCit and EuCit- complexes were obtained with FT-IR spectroscopy in combination with density functional theory calculations. IR spectroscopic evidence for the deprotonation of the hydroxyl group of the citrate ion in the EuCit- complex is presented, which also revealed that the complexation of the Eu3+ ion takes place not only through the carboxylate groups, like in EuCit0, but additionally via the hydroxylate group. In both EuCit0 and EuCit- the carboxylate binding mode is mono-dentate. Under very low metal : citrate ratio that is typical for human body fluids, the Cm(III) and Eu(III) speciation was found to be strongly pH-dependent. The Cm(III) and Eu(III) citrate complexes dominant in human urine at pH < 6 were identified to be Cm(HCitH)HCit2- and a mixture of Eu(HCitH)HCit2- and EuHCit0. The results specify our previous in vitro study using natural human urine samples.
Keywords: actinoids, lanthanoids, TRLFS, ATR-FT-IR, DFT, heavy metal speciation, biofluids, citric acid
  • Dalton Transactions 41(2012)45, 13969-13983

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Publ.-Id: 17040


Study on severe accidents and countermeasures for VVER-1000 reactors using the integral code ASTEC

Tusheva, P.; Schäfer, F.; Reinke, N.; Altstadt, E.; Kliem, S.
The research field focussing on the investigations and the analyses of severe accidents is an important part of the nuclear safety. To maintain the safety barriers as long as possible and to retain the radioactivity within the airtight premises or the containment, to avoid or mitigate the consequences of such events and to assess the risk, thorough studies are needed. On the one side, it is the aim of the severe accident research to understand the complex phenomena during the in- and ex-vessel phase, involving reactor-physics, thermal-hydraulics, physico-chemical and mechanical processes. On the other side the investigations strive for effective severe accident management measures.

This paper is focused on the possibilities for accident management measures in case of severe accidents. The reactor pressure vessel is the last barrier to keep the molten materials inside the reactor, and thus to prevent higher loads to the containment. To assess the behaviour of a nuclear power plant during transient or accident conditions, computer codes are widely used, which have to be validated against experiments or benchmarked against other codes. The analyses performed with the integral code ASTEC cover two accident sequences which could lead to a severe accident: a small break loss of coolant accident and a station blackout. The results have shown that in case of unavailability of major active safety systems the reactor pressure vessel would ultimately fail. The discussed issues concern the main phenomena during the early and late in-vessel phase of the accident, the time to core heat-up, the hydrogen production, the mass of corium in the reactor pressure vessel lower plenum and the failure of the reactor pressure vessel. Additionally, possible operator’s actions and countermeasures in the preventive or mitigative domain are addressed. The presented investigations contribute to the validation of the European integral severe accidents code ASTEC for VVER-1000 type of reactors.
Keywords: Severe accidents, severe accident management, SBLOCA, SBO, primary side depressurization, vessel failure, ASTEC
  • Contribution to proceedings
    AER Symposium 2011, 19.-23.09.2011, Dresden, Germany
  • Lecture (Conference)
    AER Symposium 2011, 19.-23.09.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-17039
Publ.-Id: 17039


Long-term spatiotemporal monitoring of diffusion processes in Opalinus drill cores with GeoPET and parameterization with Comsol Multiphysics

Kulenkampff, J.; Gründig, M.; Schikora, J.; Zakhnini, A.; Lippmann-Pipke, J.
Typically, the assessment of effective diffusion parameters of natural geologic media is conducted by repeated concentration measurements in diffusion cells. They contain small-sized samples which are regarded as 1D-homogeneous “black boxes”. Alternatively, 1D-tracer profiles can be obtained by means of abrasive pealing [1]. These methods have in common that 2D or higher spatial inhomogeneity of structure (and composition) and anisotropy cannot be considered in one and the same sample. In the course of the past decade we established the GeoPET-method allowing the direct, non-destructive, quantitative spatiotemporal visualization of (e.g.) diffusion processes in natural geological media on drill-core scale [2-4]. Here we couple it with the parameterization of heterogeneous and anisotropic effective diffusion parameters by means of inverse modeling with a finite element based numerical model (COMSOL Multiphysics, V4.2a) [5].
Out GeoPET-method is characterized by unrivalled sensitivity and selectivity to positron-emitting radio nuclides (here: PET tracers, Positron Emission Tomography, a nuclear medicine imaging method) in geological systems, without physical and chemical impact on the observed (reactive) transport process, and with adequate spatial and temporal resolution. Requirements for reaching the physical limit of image resolution of nearly 1 mm are a high-resolution PET-camera, like our ClearPET scanner (Raytest), and appropriate correction methods for scatter and attenuation of 511 keV-photons in the dense geological material. The latter are by far more significant than in human
and small animal body tissue (water). For long-term experiments, like diffusion monitoring, unconventional PET-nuclides, like 124I (T1/2 = 4.18 d), 58Co (T1/2 = 71.3 d) and 22Na (T1/2 = 4.602 a), are applied. The sensitivity is in the order of 0.1 kBq per voxel (1.5 mm3), which is limited by the background radiation.
Diffusion experiments were conducted on Opalinus clay drill cores with diameter of 10 cm and a length of 8 cm. These were cast into epoxy resin and a small axial drill hole was filled with 1 ml synthetic Opalinus pore water (OPW), labeled with a PET-nuclide. In first tests we applied 124Iodide.
Over 3 weeks we observed fast tracer propagation in distinct zones of the sample. This we interpret as due to suction into partially unsaturated zones. One sample was re-saturated over 3 months with OPW and then with OPW labeled with 22Na. The diffusion of the PET-tracer was observed for the following cause of 7 months. Then the specific activity fell below the detection threshold.
The quality of the obtained > 20 GeoPET-images is still improvable. Extensive Monte-Carlo simulations of our measurements, considering material dependent scattering cross sections of all occurring nuclear physical effects, have provided us with profound knowledge on the impact of scattering and attenuation on image quality [6]. Typical artifacts and blurring are identified as result of Compton scattering, which affects more than 70% of all recorded coincidences. Skillful selection of energy window and gantry diameter is capable of reducing this value to about 47%. This percentage will further drop significantly once the currently developed, appropriate scatter correction algorithms
are applied. Further, these Monte-Carlo simulations are a potential method for inversion-based image reconstruction [6].
We modeled this experiment with COMSOL Multiphysics ® 4.2a (3D convection-diffusion equation, PDE mode, PARDISO solver) for reproducing the observed spatiotemporal concentration distribution data with the differential equation for anisotropic diffusion and adsorption. By importing GeoPET images from various time steps and applying the Optimization Module (least square fit applying the Levenberg-Marquardt algorithm) to these images we efficiently determined best fit values e.g. of the diffusion tensor. Combined with the parameter sweep operation the sensitivity analysis is performed in parallel and covers the range of literature values for porosity and Kd values for 22Na+ sorption on Opalinus clay [5].
The experimental data could be reproduced quite well, but the obtained parameter values for diffusion parallel and normal to the bedding are slightly larger than reported in [7]. This is in accordance with our observations of an emerging gas bubble in the tracer reservoir. In spite of the long re-saturation period, suction tensions caused by unsaturated clay zones must have significantly influenced the transport regime by an additional advective component.
References
1. Van Loon, L.R. and J. Eikenberg, A high-resolution abrasive method for determining diffusion profiles of sorbing radionuclides in dense argillaceous rocks. Applied Radiation and Isotopes, 2005. 63: p. 11-21.
2. Richter, M., et al., Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochimica Acta, 2005. 93: p. 643-651.
3. Kulenkampff, J., et al., Evaluation of positron emission tomography for visualisation of migration processes in geomaterials. Physics and Chemistry of the Earth, 2008. 33: p. 937-942.
4. Gründig, M., et al., Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes. Applied Geochemistry, 2007. 22: p. 2334-2343.
5. Schikora, J., Simulation of diffusion-adsorption processes in natural geological media by means of COMSOL Multiphysics, in Faculty of mechanical Science and Engineering. 2012, Dresden Technical University: Dresden, Germany. p. 95.
6. Zakhnini, A., et al., Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18F, 124I and 58Co) in Opalinus Clay, anhydrite and quartz. 2012. 2012 (submitted).
7. Gimmi, T. and G. Kosakowski, How mobile are sorbed cations in clay and clay rocks? Environmental Science and Technology, 2011. 45: p. 1443-1449.
  • Lecture (Conference)
    5th International Meeting on "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement", 22.-25.10.2012, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-17038
Publ.-Id: 17038


Determination of the Σ(1385)0/Λ(1405) ratio in p+p collisions at 3.5 GeV

Epple, E.; Fabbietti, L.; Agakishiev, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lang, S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.
The aim of the present analysis is to determine the relative production cross sections of the Λ(1405) and Σ(1385)0 resonances in p+p collisions at Ekin = 3.5 GeV measured with HADES. Upper and lower limits have been determined for the ratio (Σ(1385)0+p+K+)(Λ(1405)+p+K+)=0.76+0.54−0.26. The knowledge of this ratio is an essential input for the analysis of the decay Λ(1405)→Σ±π , where an unambiguous separation of the Λ(1405) and Σ(1385)0 signals is not possible.

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Permalink: https://www.hzdr.de/publications/Publ-17037
Publ.-Id: 17037


Strange baryon resonances in pp collisions measured with HADES

Siebenson, J.; Agakishiev, G.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kozuch, A.; Krása, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lang, S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.
We present an analysis of the hyperons Λ(1405) and Σ(1385)+ for p+p reactions at 3.5 GeV kinetic beam energy. The data were taken with the High Acceptance Di-Electron Spectrometer (HADES). A Λ(1405) signal could be reconstructed in both charged decay channels Λ(1405) → Σ±π. The obtained statistics of the Σ(1385)+ signal allows also differential studies.

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Permalink: https://www.hzdr.de/publications/Publ-17036
Publ.-Id: 17036


Flow structures arising from melt stirring by means of modulated rotating magnetic fields

Räbiger, D.; Eckert, S.; Gerbeth, G.; Franke, S.; Czarske, J.
Electromagnetic stirring during solidification has been proved to be a striking method for achieving a purposeful alteration of the microstructure of casting ingots, such as grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic groth (CET). However, the imposition of a rotating (RMF) or a travelling magnetic field (TMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface. A permanent radial inward (RMF and downward TMF) or outward (upward TMF) flow along the solidification front is responsible for the transport of solute to the axis or the wall of the ingot resulting in typical freckle segregation pattern filled with alloy of eutectic composition. Recent studies have shown, that modulated AC magnetic fields are appropriate to overcome these problems.
We present an experimental study concerning measurements of the flow inside a liquid metal column exposed to a pulsed rotating magnetic field. A novel ultrasound Doppler system was used two measure two-dimensional velocity fields of the secondary flow in the radial-meridional plane. It employs an array of 25 transducer elements allowing a fast electronic traversing with concurrently high spatial and temporal resolution. The measurements revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures. The results demonstrate that the arising flow structure depends sensitively on the frequency of the RMF pulses.
Keywords: Electromagnetic stirring, ultrasound Doppler velocimetry, modulated magnetic field, liquid metal flow
  • Contribution to proceedings
    8th PAMIR International Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo - Corsica, France
  • Lecture (Conference)
    8th PAMIR International Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo - Corsica, France

Permalink: https://www.hzdr.de/publications/Publ-17035
Publ.-Id: 17035


41Ca in Zähnen - ein biologisches Dosimeter für Neutronen

Rugel, G.
Das Wissen über die Parameter eines Strahlungsfeldes ist die Vorraussetzung um Studien zu strahleninduzierten Effekten durchzuführen. Besonders eine Exposition in einem gemischten Neutronen- und Gammastrahlungsfeld stellt eine besondere Herausforderung dar.
Messungen des Radioisotopes Calcium-41 (Halbwertszeit: etwa 100 000 Jahre), das durch eine Neutroneneinfangsreaktion an Calcium-40 in Zahnschmelz produziert wurde, erlauben es, die Fluenz thermischer Neutronen retrospektiv zu bestimmen.
Die verwendete Methode ist die höchstempfindliche Beschleunigermassenspektrometrie (accelerator mass spectrometry, AMS).

Die Messungen an Zahnschmelz wurden an Proben durchgeführt, die von Atombomben-Überlebenden von Hiroshima zur Verfügung gestellt wurden. Die Neutronendosis der gemessenen Zähne beträgt zwischen 10 und 80 mGy und wurde mittels Rechnungen des Dosimetriesystems DS02 zugeordnet. Die Gammadosis in Zahnschmelz wurde bereits aus Messungen der Elektronen-Spin-Resonanz rekonstruiert. Durch die Kombination beider Methoden bietet sich erstmals die Möglichkeit, die Exposition durch ein gemischtes Neutronen- und Gammastrahlungsfeld in ein und demselben biologischen Material retrospektiv zu quantifizieren.

Literatur: A. Wallner et al., Radiation Research 174, 137-145, 2010 und W. Rühm et al., Radiation Research 174, 146-154, 2010.
  • Lecture (Conference)
    Kolloquium der Abteilung 6 der Physikalisch-Technische Bundesanstalt (PTB), 26.04.2012, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17033
Publ.-Id: 17033


Comparison of Different Parallel Implementaions of the 2+1-Dimensional KPZ Model and the 3-Dimensional KMC Model

Kelling, J.; Ódor, G.; Nagy, M. F.; Schulz, H.; Heinig, K.-H.
We show that efficient simulations of the Kardar-Parisi-Zhang interface growth in 2 + 1 dimensions and of the 3-dimensional Kinetic Monte Carlo of thermally activated diffusion can be realized both on GPUs and modern CPUs. In this article we present results of different implementations on GPUs using CUDA and OpenCL and also on CPUs using OpenCL and MPI. We investigate the runtime and scaling behavior on different architectures to find optimal solutions for solving current simulation problems in the field of statistical physics and materials science.

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Permalink: https://www.hzdr.de/publications/Publ-17032
Publ.-Id: 17032


Simplest Homoleptic Metal-Centered Tetrahedrons, [M(OH2)4]2+, in 1- Ethyl-3-methylimidazolium Tetrafluoroborate Ionic Liquid (M = Co, Ni, Cu)

Takao, K.; Tone, Y.; Hennig, C.; Inoue, S.; Tsubomura, T.
Dissolution of a tetrafluoroborate or perchlorate salt of [M(OH2)6]2+ (M = Co, Ni, Cu) in 1-ethyl-3-methylimidazolium tetraluforoborate ionic liquid ([emim]BF4) results in significant solvatochromism and increasing intensity of color. These observations arise from partial dehydration from the octahedral [M(OH2)6]2+ and formation of the tetrahedral [M(OH2)4]2+. This reaction was monitored by the intense absorption band due to the d−d transition in the UV−vis absorption spectrum. The EXAFS investigation clarified the coordination structures around M2+ {[Co(OH2)4]2+, R(Co−O) = 2.17 Å, N = 4.2; [Cu(OH2)4]2+, R(Cu−O) = 2.09 Å, N = 3.8}.
1H and 19F NMR study suggested that both [emim]+ and BF4 − are randomly arranged in the second-coordination sphere of [M(OH2)4]2+.
Keywords: tetrahedral [M(OH2)4]2+ complexes, UV-Vis, EXAFS

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Publ.-Id: 17031


Critical assessment of Cr-rich precipitates in neutron-irradiated Fe-12at%Cr

Bergner, F.; Ulbricht, A.; Wagner, A.; Kuksenko, S.; Pareige, C.; Pareige, P.; Malerba, L.
The composition of solute-enriched clusters and precipitates formed in Fe-Cr alloys as the result of neutron irradiation is an unsolved issue. It is an important issue for several reasons, namely:
• to reach a complete and consistent description of the nanoscale features derived from the application of necessarily several complementary techniques,
• to correctly design and calibrate models addressing the long-term evolution of the nanoscale features,
• to correctly draw conclusions and configure models on the hardening effect of those nanoscale features.
Three sets of data separately reported in the published literature [1-3] have been selected for a critical consideration of the cluster composition in commercial-purity Fe-12at%Cr irradiated at 300°C up to a neutron exposure of 0.6 dpa. The first set of data was derived from the nuclear component of small-angle neutron scattering (SANS) [1]. The second set is based on an atom probe tomography (APT) study [2]. The APT needles were prepared from the bulk of the SANS sample. The third piece of information is adopted from an investigation of the same material by means of positron annihilation spectroscopy (PAS) [3]. The SANS results [1] were found to be consistent with the assumption that the dominant scatterers are α’-phase particles near thermodynamic equilibrium. A composition far from equilibrium was deduced from the APT data [2]. Similar apparent discrepancies were reported in the literature for other systems. In the presentation an effort to overcome the apparent discrepancy will be reported in detail.
The basic weakness of SANS is the integrating and one-parametric nature of the composition-related information hidden in the nuclear scattering contrast. Weaknesses of APT are a possible overestimation of Fe in clusters due to trajectory overlap and the insensitivity to vacancies. In the latter respect, PAS data add a value to the comparison. Other factors will be considered as well. The approach is based on the idea that the measured value of the Porod invariant of nuclear SANS can be directly compared with the corresponding quantity calculated solely from the APT data, namely volume fraction and cluster composition. Careful treatment of all potential factors of uncertainty allows the Fe fraction in the clusters to be estimated.

[1] F. Bergner, A. Ulbricht, C. Heintze, Estimation of the solubility limit of Cr in Fe at 300 °C from small-angle neutron scattering in neutron-irradiated Fe–Cr alloys, Scripta Materialia 61 (2009) 1060–1063.
[2] V. Kuksenko, C. Pareige, C. Genevois, F. Cuvilly, M. Roussel, P. Pareige, Effect of neutron-irradiation on the microstructure of a Fe–12at.%Cr alloy, Journal of Nuclear Materials 415 (2011) 61–66.
[3] M. Lambrecht, L. Malerba, Positron annihilation spectroscopy on binary Fe–Cr alloys and ferritic/martensitic steels after neutron irradiation, Acta Materialia 59 (2011) 6547–6555.
Keywords: Fe-Cr alloys, Atom probe tomography, small-angle neutron scattering
  • Lecture (Conference)
    Joint IAEA - EC Topical meeting on Development of new structural materials for advanced fission and fusion reactor systems, 16.-20.04.2012, JRC Ispra, Italien

Permalink: https://www.hzdr.de/publications/Publ-17030
Publ.-Id: 17030


Intra-excitonic extreme nonlinear optics

Teich, M.; Wagner, M.; Stehr, D.; Schneider, H.; Helm, M.; Chatterjee, S.; Gibbs, H.; Khitrova, G.
A fundamental problem in light-matter interaction is the coupling of an intense, monochromatic electromagnetic wave with a quantum mechanical two-level system. One effect related to this is the Autler-Townes or AC Stark effect. Originally observed and described in molecular spectroscopy the effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level, i.e. the states get ”dressed” by the light-matter interaction. We investigate this effect using a free-electron laser (FEL) driven intra-excitonic transition between the 1s and 2p states in a semiconductor multiple quantum well .We have observed distinct intensity- and wavelengthdependent Rabi sidebands of the heavy-hole hh(1s) exciton line when the FEL was tuned around the 1s-2p transition. We also present measurements at higher electric fields exploring the regime beyond the rotating-wave approximation.
Keywords: Quantum well, Exciton, THz, FEL
  • Lecture (Conference)
    DPG-Frühjahrstagung, Abteilung Kondensierte Materie, 25.-30.03.2012, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-17029
Publ.-Id: 17029


Intraexcitonic coherent optics

Teich, M.; Wagner, M.; Stehr, D.; Schneider, H.; Helm, M.; Chatterjee, S.; Gibbs, H.; Khitrova, G.
A fundamental problem in light-matter interaction is the coupling of an intense, monochromatic electromagnetic wave with a quantum mechanical two-level system. One effect related to this is the Autler-Townes or AC Stark effect. Originally observed and described in molecular spectroscopy the effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level, i.e. the states get ”dressed” by the light-matter interaction. We investigate this effect using a free-electron laser (FEL) driven intra-excitonic transition between the heavy-hole 1s and 2p states in a semiconductor multiple quantum well. We have observed distinct intensity- and wavelength dependent Rabi sidebands of the 1s exciton line when the FEL was tuned around the 1s-2p transition. We also present measurements at higher electric fields exploring the regime beyond the rotating-wave approximation (RWA). Theoretical calculations support the understanding of the underlying processes which is especially interesting for the regime beyond the RWA. Also temperature-dependent measurements have been done and a clear Rabi-sideband behavior is observable up to 200 K where the thermal energy already exceeds the exciton binding energy by a factor of 1.7.
Keywords: Quantum wells, Excitons, THz, FEL
  • Poster
    Free-Electron Lasers: From Fundamentals to Applications, 10.-13.04.2012, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-17028
Publ.-Id: 17028


Experimental evidence for a transient Tayler instability in a cylindrical liquid-metal column

Seilmayer, M.; Stefani, F.; Gundrum, T.; Weier, T.; Gerbeth, G.
In the current-driven, kink-type Tayler instability (TI) a sufficiently strong azimuthal magnetic field becomes unstable against non-axisymmetric perturbations. The TI has been discussed as a possible ingredient of the solar dynamo mechanism and a source of the helical structures in cosmic jets. It is also considered as a size limiting factor for liquid metal batteries. We report on a liquid metal TI experiment using a cylindrical column of the eutectic alloy GaInSn to which electrical currents of up to 8 kA are applied. We present results of external magnetic field measurements that indicate the transient occurrence of the TI in good agreement with numerical predictions. The interference of TI with the competing large scale convection, resulting from Joule heating, is also discussed.
Keywords: Tayler Instability, Liquid Metall

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Permalink: https://www.hzdr.de/publications/Publ-17027
Publ.-Id: 17027


Comparative investigation of the neptunium(V) sorption onto gibbsite by means of ATR FT-IR spectroscopy

Gückel, K.; Foerstendorf, H.; Brendler, V.
The molecular reactions of actinides at the solid-water interface play an important role in the retardation of radionuclides in the environment. Hence, the investigation of the interactions of actinides with metal oxides such as Al(OH)3, Fe(OOH)x, TiO2, or SiO2, serving as model phases for more complex, naturally occurring minerals in aqueous solution, becomes essential for the safety assessment in the near and far field of nuclear repositories. In recent years, the sorption behavior of neptunium (Np) onto synthetic and naturally occurring minerals was insufficiently studied. The majority of these studies provide macroscopic results presenting sorption capacities of the substrates and the effect of selective parameters on the sorption behavior. However, for a better understanding of the sorption mechanisms, structural information on a molecular level of the type of surface complex is still needed.
Comprehensive studies using ATR FT-IR spectroscopy have been carried out to investigate the in situ formation of neptunyl(V) surface complexes on aluminum hydroxide, namely gibbsite. This substrate serves as a model phase for more complex mineral systems, e.g. clay minerals. The surface complexation of Np(V) on amorphous and crystalline gibbsite was studied in detail by a multiplicity of experiments in the presence and absence of atmospherically derived carbonate . In the absence of carbonate, one inner-sphere complex is formed on amorphous gibbsite, whereas no sorption occurs on the crystalline gibbsite. In the presence of carbonate and dependent on the crystal structure, different surface species (inner-, outer-sphere and ternary) were derived from the spectra
Keywords: Neptunium(V), sorption, gibbsite
  • Lecture (Conference)
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-17025
Publ.-Id: 17025


Kinetic Monte Carlo Simulations on Self-organization of Nanostructures Accelerated by Massive Parallelization

Kelling, J.
Modern graphics processing units (GPUs) currently provide the most peek processing performance regarding both cost and energy consumption. This is achieved by mounting large numbers of simple cores rather than a few complex ones. The characteristics that come with this design demand a large degree of data-parallelism from applications. Thus, new approaches are needed for parallelizing tasks that are not by nature data-parallel.
The 3D kinetic lattice Monte Carlo (KLMC) method is a means of performing atomistic simulations of self-organization processes in solids at by far larger scales than those accessible via molecular dynamics (MD). This method has been implemented for GPUs, achieving up to 70 times higher performance than the sequential reference implementation on a single core of a modern CPU. This enables atomistic simulations at even larger scales, even putting space and time scales comparable to the experiment within range.
The new program has been shown to be useful to study the phase separation in large binary systems. This was done with an application for third generation photovoltaics cells in mind which is a subject of a current BMBF project. It was also applied to out-of-equilibrium problems, backing up a theory of inverse Ostwald ripening (IOR) from an angle that was not previously looked at.
  • Diploma thesis
    TU Dresden, 2012
    62 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17024
Publ.-Id: 17024


Magnetism in Ge by ion implantation with Fe and Mn

Reuther, H.; Talut, G.; Mücklich, A.; Stromberg, F.
Previously, ferromagnetic layers of Ge were produced by co-doping with Mn and Fe. While these layers were prepared by molecular beam epitaxy in the present study ion implantation is used for preparation. Implantation conditions were chosen that a maximum doping concentration of 6 atomic % per dopant was achieved. One sample set was implanted at 260 °C, another one at room temperature. Samples were characterized by conversion electron Mössbauer spectroscopy, Auger electron spectroscopy, superconducting quantum interference device magnetometry, transmission electron microscopy, and Rutherford backscattering spectroscopy. Several samples were recovered by flash lamp annealing. Ferromagnetism in Ge may be induced, however, in all cases the origin of the magnetism was not intrinsic but from secondary phases. Such phases were already formed due to implantation at elevated temperature. Implantation at room temperature prevents the formation but let the samples remain non-ferromagnetic. Subsequent short time annealing above a special limit will produce secondary phases or metal rich regions and ferromagnetism, annealing below does not change the magnetic behaviour but let diffusion processes start. Although nearly identical concentration conditions like in the study first mentioned were adjusted the nature of the magnetism is another one. It is hint that the order/disorder state of the magnetic atoms containing layer plays the more important role.

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Permalink: https://www.hzdr.de/publications/Publ-17023
Publ.-Id: 17023


Do elevated temperatures and organic matter influence the U(VI) diffusion through argillaceous rock?

Joseph, C.; van Loon, L. R.; Jakob, A.; Steudtner, R.; Schmeide, K.; Sachs, S.; Bernhard, G.
The suitability of argillaceous rock as host rock and backfill material in a nuclear waste repository is discussed worldwide. In a nuclear waste repository several factors have to be considered for safety assessment. Beside high radiotoxic nuclides, such as neptunium and plutonium, the finally stored high-level radioactive waste will contain also a high amount of uranium, which originates mainly from spent nuclear fuel. 1) Due to radioactive decay of the embedded radionuclides higher temperatures are expected close to the waste containers (argillaceous rock ≤ 100 °C (Brasser et al. 2008)). 2) Argillaceous rock contains also a certain amount of organic matter such as humic acids (Claret et al. 2003), which can be leached by groundwater. Humic acids (HA) have a variety of functional groups, thus, they are able to complex metal ions such as actinides and to form stable colloids. Hence, they can influence the actinide sorption and diffusion. For performance of safety assessment, it is necessary to know, how the migration of the different actinides are influenced by elevated temperatures and the presence of organic matter.
In this study the U(VI) diffusion in the argillaceous rock Opalinus Clay (OPA) from Mont Terri, Switzerland was investigated at 25 and 60 °C both in the absence and presence of HA. As background electrolyte synthetic OPA pore water (Pearson 1998) was applied (pH 7.6, I = 0.36 M). The experimental set-up used for the diffusion experiments at 25 °C and 60 °C is described in Van Loon and Soler (2004) and Joseph et al. (2012), respectively. OPA bore core samples (diameter: 2.55 cm, thickness: 1.1 cm, dry bulk density: ~ 2400 kg/m^3) were placed in four diffusion cells. Each was connected with a tracered source reservoir and a non-tracered receiving reservoir, all reservoirs were filled with OPA pore water. Two cells were tempered at 25 °C (cell 1, cell 2) and 60 °C (cell 3, cell 4), respectively. All experiments were performed under anaerobic conditions (N2, 0 % CO2). The pressure adjusted on the OPA samples amounted to 5 MPa. At first, in all four cells through- and out-diffusion of non-sorbing HTO was studied for determining the transport porosity of the clay samples. The results were in agreement with literature data (Van Loon and Soler 2004). Subsequently, the U(VI) diffusion in OPA was investigated at 25 °C (cell 1) and 60 °C (cell 3). The simultaneous diffusion of U(VI) and HA in OPA was studied at 25 °C (cell 2) and 60 °C (cell 4). Thereby, 233U(VI) (c0 = 1E-6 mol/L) and 14C-labeled HA (c0 = 10 mg/L) were applied as tracers. After three months the experiments were terminated. In all receiving reservoirs no 233U(VI) could be detected. However, diffused HA molecules were found. The diffusion profiles of U(VI) and HA in the OPA samples were determined with the help of the abrasive peeling technique described by Van Loon and Eikenberg (2005). The obtained diffusion profiles were evaluated using the commercial software COMSOL Multiphysics 3.5a (COMSOL 2008).
In Figure 1a the U(VI) diffusion profiles in OPA at 25 and 60 °C in the absence of HA are shown. At 25 °C, the Kd value determined for the interaction of U(VI) with OPA by diffusion experiments clearly confirms the Kd value determined by means of sorption experiments (Joseph et al. 2011). A reduction of U(VI) to U(IV) was excluded. The value for the apparent diffusion coefficient Da of U(VI) was comparable to that of Np(V) determined by Wu et al. (2009). Thus, a similar migration behavior of both actinides through OPA was assumed. At 60 °C, the experimental data could be fitted only by assuming two diffusing U(VI) species resulting in two diffusion profiles. These two species were identified by means of laser-induced fluorescence spectroscopy and scanning electron microscopy with energy dispersive X-ray detector. The aqueous Ca2UO2(CO3)3 complex and so far, a not closer assignable colloidal U(VI) carbonate species were detected. In OPA the colloids diffused only about 500 µm, the aqueous U(VI) species was found up to a depth of about 2.5 mm. At 60 °C, the Kd values for both species were higher than that of U(VI) at 25 °C. Furthermore, the value for the effective diffusion coefficient De for the aqueous U(VI) species was increased. Both values compensate each other to almost equal Da values for U(VI) at 25 and 60 °C (only aqueous U(VI)). This shows, that the migration of U(VI) through OPA was not significantly influenced by the investigated higher temperature.

In Figure 1b the U(VI) diffusion profiles in OPA in the absence and presence of HA at 25 °C are presented. The profiles show, that in the presence of HA U(VI) penetrates the clay less than in the absence of HA. However, considering all the uncertainties a comparison of the respective Kd and De values verifies, that HA has no significant influence on U(VI) diffusion. This confirms the observations made by former batch sorption experiments for the system U(VI) / HA / OPA (Joseph et al. 2011). At 60 °C, also no influence of HA on the U(VI) diffusion was observed.
The study shows, that both investigated factors, an elevated temperature of 60 °C and the presence of HA, have no major influence on U(VI) migration through OPA.

References:
Brasser, T., Droste, J., Müller-Lyda, I., Neles, J.M., Sailer, M., Schmidt, G., Steinhoff, M. 2008. GRS - 247. Öko-Institut and Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), Braunschweig.
Claret, F., Schäfer, T., Bauer, A., Buckau, G. 2003. Sci. Total Environ. 317, 189-200.
COMSOL 2008. Multiphysics 3.5a. Finite-element software package. http://www.comsol.com.
Joseph, C., Schmeide, K., Sachs, S., Brendler, V., Geipel, G., Bernhard, G. 2011. Chem. Geol. 284, 240-250.
Joseph, C., Van Loon, L.R., Jakob, A., Schmeide, K., Sachs, S., Bernhard, G. 2012. Geochim. Cosmochim. Acta, submitted.
Pearson, F.J. 1998. PSI Internal report TM-44-98-07. Paul Scherrer Institut, Villigen PSI, Switzerland.
Van Loon, L.R., Eikenberg, J. 2005. Appl. Radiat. Isot. 63, 11-21.
Van Loon, L.R., Soler, J.M. 2004. PSI-Bericht Nr. 04-03. Paul Scherrer Institut, Villigen, Switzerland.
Wu, T., Amayri, S., Drebert, J., Van Loon, L.R., Reich, T. 2009. Environ. Sci. Technol. 43, 6567-6571.
Keywords: uranium(VI), humic acid, Opalinus Clay, temperature, diffusion
  • Contribution to proceedings
    Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 22.-25.10.2012, Montpellier, France
  • Lecture (Conference)
    Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 22.-25.10.2012, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-17022
Publ.-Id: 17022


Continuous wave ridge waveguide lasers in femtosecond laser micromachined ion irradiated Nd:YAG single crystals

Jia, Y.; Dong, N.; Chen, F.; de Aldana, J. R. V.; Akhmadaliev, S.; Zhou, S.
Ridge waveguides have been fabricated in Nd:YAG single crystal by using femtosecond laser micromachining in an oxygen ion irradiated planar waveguide. The microphotoluminescence features have been found well preserved in the waveguide structures. Continuous wave lasers have been realized at 1.06 µm at room temperature in the ridge waveguide system with a lasing threshold of ~39 mW and a slope efficiency of 35%, which show superior performance to the planar waveguide.
Keywords: Integrated optics devices; Laser materials processing; Waveguides

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Permalink: https://www.hzdr.de/publications/Publ-17021
Publ.-Id: 17021


High-magnetic-field investigation of CoCr2O4

Pronin, A. V.; Uhlarz, M.; Beyer, R.; Fischer, T.; Wosnitza, J.; Gorshunov, B. P.; Komandin, G. A.; Prokhorov, A. S.; Dressel, M.; Bush, A. A.; Torgashev, V. I.
We report on magnetic, optical, and thermodynamic properties of multiferroic CoCr2O4 in magnetic fields up to 14 T. We have found indications of a new phase transition at T* = 5 − 6 K. The phase between T* and the lock-in transition at 15 K is characterized by magnetic irreversibility. At higher fields the irreversibility increases. Heatcapacity measurements confirm the transition at T*, and also show the irreversible behaviour. We construct a field-temperature phase diagram of CoCr2O4. Below the ferrimagnetic transition (94 K), the low-frequency (terahertz) optical response is dominated by a magnetic exchange mode, which shows an anomalous temperature dependence and a softening at the structural transition (26 K).
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17020
Publ.-Id: 17020


Optical investigation of nominally undoped Pr2CuO4 films

Chanda, G.; Pronin, A. V.; Lobo, R. P. S. M.; Wosnitza, J.; Yamamoto, H.; Naito, M.
Superconducting Pr2CuO4 films with T′ structure and Tc beetween 25 and 27 K have been investigated by different optical methods in a wide frequency range (5 – 55000 cm−1) and for temperatures from 2 to 300 K. From the infrared reflectivity spectra, a superconducting gap of 2Δ0 = 17 meV = 7.4 κBTc is estimated. Absolute values of the London penetration depth (ΔL) have been calculated from phase-sensitive teraherz measurements. The zero-temperature limit of (ΔL) is 1.6 µm. The overall temperature dependence of (ΔL)shows a behavior typical for the cuprates. However, a closer look on the penetration depth at low temperatures reveals a flattening of the temperature dependence. We find (ΔL)(T) ∝ Tn with n = 2.8 ± 0.2.
  • Lecture (Conference)
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17019
Publ.-Id: 17019


Magnetic excitations in the diamond spin system Cu3(CO3)2(OH)2 probed by ESR

Kamenskyi, D.; Ozerov, M.; Wolff-Fabris, F.; Wosnitza, J.; Francoual, S.; Zapf, V.; Zvyagin, S.
We report systematic tunable-frequency electron spin resonance (ESR) studies of the natural mineral azurite Cu3(CO3)2(OH)2. This material has a diamond spin-chain structure and exhibits unusual magnetic properties (including a magnetization plateau). ESR experiments have been done at frequencies from 50 to 1000 GHz in magnetic fields up to 51 T. The observed frequency-field dependence of the magnetic excitations clearly indicates the important role of magnetic frustrations in this material, which can be suppressed by high magnetic fields. Our findings are discussed in connection with results of inelastic neutron-scattering experiments.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17018
Publ.-Id: 17018


Angular-dependent specific heat of the fully organic superconductor β′′-(ET)2SF5CH2CF2SO3 - evidence for an FFLO phase

Beyer, R.; Schlueter, J. A.; Wosnitza, J.
Since 1964 predicted, there is no clear-cut experimental proof of the existence of a field-induced superconducting state with finite center of mass momentum (q \neq 0) [1]. In 2007, Lortz et al. reported thermodynamic evidence for a FFLO state in κ-(ET)2Cu(NCS)2 [2], where ET stands for bisethylenedithio-tetrathiafulvalene. They found an emerging sharp double-peak structure in the specific heat, indicating first-order phase transitions at high magnetic fields applied parallel to the superconducting ET layers. Expecting similar novel results for β′′-(ET)2SF5CH2CF2SO3, we performed high-resolution specific-heat measurements for different orientations with very fine steps around perfect parallel alignment. In conclusion, we found an upturn in the field-temperature phase diagram of the superconducting phase beyond the Pauli-Clogston limit and we could observe a double-peak structure above 9.4 Tesla but only by tilting the field 0.2 degree out of the ET sheets.
  • Lecture (Conference)
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17017
Publ.-Id: 17017


ESR studies of the quasi-2D antiferromagnet Cu(Pz)2(ClO4)2

Ozerov, M.; Wosnitza, J.; Čižmár, E.; Xiao, F.; Turnbull, M. M.; Landee, C. P.; Zvyagin, S. A.
We report systematic high-field electron spin resonance (ESR) studies of the quasi-two-dimensional spin- ½ Heisenberg antiferromagnet Cu(pz)2(ClO4)2 (pz denotes pyrazine or C4H4N2). The linewidth and resonance-field temperature dependences of the ESR absorptions in this compound were investigated in the frequency range from 85 to 416 GHz in magnetic fields up to 16 T. A pronounced ESR linewidth anomaly was revealed in the vicinity of TN. This anomaly reflects enhanced critical fluctuations in this compound at the 3D ordering. The experiment revealed a significant change in the linewidth behavior for magnetic fields above 7 T, whose origin will be discussed.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17016
Publ.-Id: 17016


Tantalum incorporation in TiO2 based transparent conductive thin films

Neubert, M.; Vinnichenko, M.; Cornelius, S.; Kolitsch, A.
The growing number of applications of transparent electrodes in optoelectronic devices drives the need for novel cost-efficient transparent conductive materials. The epitaxial films of TiO2 doped with Nb or Ta show electrical resistivity values comparable to those of the best In2O3:Sn and ZnO:Al films. However, it is still challenging to achieve low electrical resistivity in polycrystalline TiO2-based films. In order to address this problem, we studied the films formed on glass substrates without heating by DC magnetron sputtering of reduced TiO2:Ta ceramic targets followed by vacuum annealing. It was crucial to use a plasma feedback system in order to enable a fine tuning of the oxygen supply into Ar and O2 gas mixture during the growth. This approach yielded the films with optical transittance above 85%, electrical resistivity in the range of 10-3  cm and free electron mobility of 8 cm²/Vs. The electrical activation of Ta dopant was above 60% that is substantially higher than that of Al in ZnO.
Keywords: TCO TiO2 titania Ta tantalum transparent conductive oxide
  • Lecture (Conference)
    DPG-Frühjahrstagung, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17015
Publ.-Id: 17015


Investigations on optimization of accident management measures following a station blackout accident in a VVER-1000 pressurized water reactor

Tusheva, P.; Schaefer, F.; Kliem, S.
The reactor safety issues are of primary importance for preserving the health of the population and ensuring no release of radioactivity and fission products into the environment. A part of the nuclear research focuses on improvement of the safety of existing nuclear power plants. Studies, research and efforts are a continuing process at improving the safety and reliability of existing and newly developed nuclear power plants at prevention of a core melt accident.

Station blackout (loss of AC power supply) is one of the dominant accidents taken into consideration at performing accident analysis. In case of multiple failures of safety systems it leads to a severe accident. To prevent an accident to turn into a severe one or to mitigate the consequences, accident management measures must be performed. The present paper outlines possibilities for application and optimization of accident management measures following a station blackout accident. Assessed is the behaviour of the nuclear power plant during a station blackout accident without accident management measures and with application of primary/secondary side oriented accident management measures. Discussed are the possibilities for operators’ intervention and the influence of the performed accident management measures on the course of the accident. Special attention has been paid to the effectiveness of the passive feeding and physical phenomena having an influence on the system behaviour.

The performed simulations show that the effectiveness of the secondary side feeding procedure can be limited due to an early evaporation or flashing effects in the feed water system. The analyzed cases show that the effectiveness of the accident management measures strongly depends on the initiation criteria applied for depressurization of the reactor coolant system.
Keywords: SBO, nuclear power plant behaviour, accident management, accident management measures, passive feeding, flashing effects
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA
  • Lecture (Conference)
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA

Permalink: https://www.hzdr.de/publications/Publ-17014
Publ.-Id: 17014


Radial solidification of Al-Si alloys in the presence of a rotating magnetic field

Travnikov, V.; Nikrityuk, P. A.; Eckert, K.; Räbiger, D.; Odenbach, S.; Eckert, S.
We study the flow during the radial solidification of an Al-7wt pct Si melt inside a cylindrical cavity with cooled side walls which is placed in a rotating magnetic field (RMF). The solidification process is simulated by means of a continuum model which is implemented in a code which solves the axisymmetric Navier-Stokes equations. qwe first analyz the start-up of the buoyancy-driven convection driven by the radial heat flux in absence of the RMF. We show that the initial large vortex breaks up into three smaller ones. The resulting radial temperature profiles are compared with experimental data. Second, we study how the vortex structure is modified by the application of small RMF's.
Keywords: solidification, Al-Si alloys, convection, rotating magnetic field
  • Lecture (Conference)
    Modeling of Casting, Welding and Advanced Solidification Processes 2012 (MCWASP XIII), 17.-22.06.2012, Schladming, Österreich
  • Open Access Logo IOP Conference Series: Materials Science and Engineering 33(2012), 012048
    DOI: 10.1088/1757-899X/33/1/012048

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Permalink: https://www.hzdr.de/publications/Publ-17013
Publ.-Id: 17013


Ultraschall-Array-Geschwindigkeitsmesssystem zur Untersuchung komplexer Flüssigmetallströmungen

Czarske, J.; Büttner, L.; Nauber, R.; Burger, M.; Pätzold, O.; Eckert, S.
Schmelzen von Metallen und Halbleitern besitzen eine hohe industrielle Bedeutung. Als wichtigste Beispiele sind die Stahlherstellung und die Kristallzüchtung zu nennen. Bei allen Prozessen haben die in den Schmelzen auftretenden Strömungsverhältnisse eine großen Einfluss auf die Qualität des Endproduktes. Aufgrund ihrer hohen elektrischen Leitfähigkeit bietet sich die interessante Möglichkeit, diese Strömungen aktiv durch magnetische Felder zu beeinflussen. Da numerische Simulationen komplexe Strömungszustände oftmals nicht zuverlässig nachbilden können, besteht ein großer Bedarf an hochauflösenden Messverfahren. Aufgrund der opaken Fluide sind Ultraschallmesstechniken sehr gut geeignet. Allerdings weisen die aus der Medizintechnik verfügbaren tomographischen Verfahren keine ausreichenden Messeigenschaften, insbesondere für instationäre Strömungen, auf. Vorgestellt wird ein neuartiges Ultraschall-Messsystem, das mit dem Einsatz segmentierter Wandler und deren weitgehendem Parallelbetrieb erstsmals sowohl eine hohe Zeit- als auch eine hohe Ortsauflösung ermöglicht.
Keywords: Messtechnik, Strömungsmessung, Flüssigmetall, Ultraschall-Doppler Methode
  • Lecture (Conference)
    Workshop "Messtechnische Anwendungen von Ultraschall", 18.-20.06.2012, Drübeck, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17012
Publ.-Id: 17012


LMFR instrumentation development

Eckert, S.; Buchenau, D.; Gerbeth, G.; Stefani, F.; Wondrak, T.
The safe and reliable operation of liquid metal systems requires corresponding measuring systems and control units, both for the liquid metal single-phase flow as well as for bubble-laden liquid metal two-phase flows. However, velocity measurements in opaque liquid metal flows still represent a challenging task as commercial measuring systems are not available for such fluids.
The paper reports on established methods and new developments in the field of measuring techniques for liquid metal flows. The presentation is focussed on measurements of the flow rate and the local velocity field as well as on the characterization of liquid metal two-phase flows. During the last two decades considerable effort was spent by miscellaneous researcher groups to provide new solutions for measurements of flow fields in liquid metals. This paper intends to summarize different approaches and tempts to account on perspectives, particularly in view of some recent developments (ultrasonic techniques, magnetic tomography).
Keywords: liquid metal cooled fast reactor, instrumentation, flow rate measurements, velocity measurements, inductive tomography, ultrasound Doppler method
  • Lecture (Conference)
    International Workshop on Innovative Nuclear Reactors, 17.-20.04.2012, Pisa, Italy

Permalink: https://www.hzdr.de/publications/Publ-17011
Publ.-Id: 17011


Two concepts of introducing thin-film superconductivity in Ge and Si by use of Ga-ion implantation

Skrotzki, R.; Herrmannsdörfer, T.; Fiedler, J.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Helm, M.; Wosnitza, J.
We report on two unconventional routes of embedding superconducting nanolayers in a semiconducting environment. Ion implantation and subsequent annealing have been used for preparation of superconducting thin-films of Ga-doped germanium (Ge:Ga) [1] as well as 10 nm thin amorphous Ga-rich layers in silicon (Si:Ga) [2]. Structural investigations by means of XTEM, EDX, RBS/C, and SIMS have been performed in addition to low-temperature electrical transport and magnetization measurements. Regarding Ge:Ga, we unravel the evolution of Tc with charge-charrier concentration while for Si:Ga recently implemented microstructuring renders critical-current densities or more than 50 kA/cm2. Combined with a superconducting onset at around 10 K, this calls for onchip application in novel heterostructured devices.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17010
Publ.-Id: 17010


Ultrasound investigations of intrinsic and extrinsic nonstationary field-driven processes in spin ice

Erfanifam, S.; Zherlitsyn, S.; Wosnitza, J.; Moessner, R.; Petrenko, O. A.; Balakrishnan, G.; Zvyagin, A. A.
The elastic properties of spin-ice material Dy2Ti2O7 has been studied for different longitudinal and transverse acoustic-modes in a temperature range from 20 mK to 300 K and magnetic fields applied along various crystallographic directions. The sound velocity and the sound attenuation exhibit a number of anomalies versus magnetic field at temperatures below the ”freezing” temperature of approximately 500 mK. Most notable are peaks in the sound velocity, which exhibit two distinct regimes: an intrinsic (extrinsic) one in which the data collapse for different field-sweep rates when plotted as function of field strength (time). The intrinsic regime involves the release of Zeeman energy from spins, the extrinsic one, transfer of energy out of the sample. Additionally a sharp drop in the sound velocity can be seen at B = 1.25 T. This can indicate a 1st-order phase transition from the low-density to the high-density monopole state. We discuss our observations in context of the emergent quasiparticles which govern the low-temperature dynamics of the spin-ice.
  • Poster
    Frühjahrstagung der DPG, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17009
Publ.-Id: 17009


High field magnetism and magnetoacoustics in UCu0.95Ge

Zvyagin, A. A.; Yasin, S.; Skourski, Y.; Andreev, A. V.; Zherlitsyn, S.; Wosnitza, J.
Studies of magnetic and magneto-acoustic characteristics of the intermetallic compound UCu0.95Ge with antiferromagnetic ground state have been performed on single crystals in pulsed magnetic fields up to 64 T applied along the main axes. Along the a axis, a first-order phase transition has been observed at 61 T. For the field applied along the c axis, the first-order phase transition occurs at a much lower magnetic field (38 T). In both directions, the magnetization trends to saturate at 1.35 µB per formula unit. These field-induced transitions as well as the spontaneous transition at the magnetic ordering at TN = 48 K are accompanied by pronounced anomalies in the sound velocity and sound attenuation. The field-temperature phase diagrams are constructed for both directions of the magnetic field. The results of our theoretical analysis within the framework of the mean-field approximation qualitatively agree with the observed behavior of magnetic and magneto-acoustic characteristics of UCu0.95Ge.

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Permalink: https://www.hzdr.de/publications/Publ-17008
Publ.-Id: 17008


Numerical modeling of bubble-driven liquid metal flows with external static magnetic field

Miao, X.; Lucas, D.; Ren, Z.; Eckert, S.; Gerbeth, G.
Three-dimensional numerical simulations are presented considering the impact of a steady magnetic field on a bubble-driven liquid metal flow inside a cylinder. The injection of moderate gas flow rates through a single orifice at the bottom of the fluid vessel results in the formation of a bubble plume. The magnetic field is applied in either vertical or horizontal direction. The calculations were performed by means of the commercial software package CFX using the Euler-Euler multiphase model and the RANS-SST turbulence model. The non-isotropic nature of MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical models are validated with recent experimental results (Zhang et al., 2007b). The comparison between the numerical simulations and the experimental findings shows a good agreement. The calculations are able to reproduce a striking feature of a horizontal magnetic field found in the range of moderate Hartmann numbers revealing that such a steady transverse magnetic field may destabilize the flow and cause distinct oscillations of the liquid velocity.
Keywords: Liquid metal, Bubble-driven flow, DC magnetic field, Multiphase model

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Permalink: https://www.hzdr.de/publications/Publ-17007
Publ.-Id: 17007


An optimized protocol for the radiosynthesis of (–)-[F-18]flubatine permits its application as a new PET radioligand for neuroimaging of alpha4beta2-nAChRs

Fischer, S.; Hiller, A.; Hoepping, A.; Smits, R.; Funke, U.; Sabri, O.; Steinbach, J.; Brust, P.
Objectives:
The alpha4beta2 subtype of nicotinic acetylcholine receptors (nAChRs) is involved in various neurodegenerative diseases. (–)-[F-18]flubatine is a new and promising PET tracer for neuroimaging of alpha4beta2-nAChRs and is currently investigated in a first study in humans. The original radiosynthesis of (–)-[F-18]flubatine was based on the bromo precursor and afforded the product in low yields (~2-3%). Here we present a new high yield radiosynthesis strategy based on an optimised leaving group/ protecting group assembly.

Methods:
A small library of precursors was synthesized containing –Cl, –NO2 and trimethylammonium (TMA) triflate and iodide as leaving groups and ethylcarbamate, Fmoc, Trityl, as well as Boc as protecting groups. [F-18]flubatine, was prepared via a two-step radiosynthesis. In the first step the nucleophilic radiofluorination was investigated. The radiolabelled product was then deprotected to yield the final radiotracer.

Results:
The best radiochemical results were obtained with a TMA iodide precursor containing a Bocprotecting group. Radiolabelling afforded the protected product in yields of 90±5%, with a RCY 70±5% (n=25) and a specific activity >350 GBq/Hmol. The complete deprotection of the Boc-PG succeeded with 1M HCl at 90°C within 5 min. TMA iodide precursors with other PGs led to lower labelling yields and several by-products after deprotection. Analytical and semipreparative HPLC separation protocols were developed using RP18-AQ phases and (–)-[F-18]flubatine was isolated in very high purity. The final product is stable in diluted HCl, NaOH and K2CO3 solutions as well as under physiological conditions.

Conclusions:
An optimized radiosynthesis of (–)-[F-18]flubatine was developed which will allow for an easy and automated radiotracer production applicable for human studies.

Research Support:
The project was supported by the German Federal Ministry of Education and Research (01EZ0820).
  • Lecture (Conference)
    SNM 2012 Annual Meeting, 09.-13.06.2012, Miami, Florida, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 53(2012)1, 130

Permalink: https://www.hzdr.de/publications/Publ-17006
Publ.-Id: 17006


THz-range free-electron laser ESR sprectroscopy: techniques and applications in high magnetic fields

Ozerov, M.
  • Poster
    503. WE-Heraeus-Seminar on Free-Electron Lasers: from Fundamentals to Applications, 11.-13.04.2012, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17005
Publ.-Id: 17005


Wann ist denn das passiert? – Ko(s)mische Strahlung und einstürzende Berge

Merchel, S.
eingeladener Vortrag ohne Abstract
Keywords: accelerator mass spectrometry, geomorphology
  • Lecture (others)
    TU Dresden, Ringvorlesung im Studium generale / öffentliche Vorträge, Sommersemester 2012, 19.04.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17004
Publ.-Id: 17004


Spatially-resolved analysis of natural minerals as carriers of high-tech metals and Rare Earth Elements: comparison of EPMA, PIXE and Sy-µXRF

Michalak, P. P.; Munnik, F.; Radtke, M.; Buzanich, G.; Reinholz, U.; Riesemeier, H.; Merchel, S.; Renno, A. D.
The assessment of supply risk of high technology elements requires quality assurance of their natural carriers such as ores. One path to achieve this goal is through the use of reference materials (RMs). Providing reliable data on elemental concentrations at the µg/g level and on their spatial distribution is achieved by employing spatially-resolved micro-analytical methods.
In order to produce synthetic RMs with optimized chemical composition, three natural mineral analogues (sanidine, pyrite, columbite) have been tested for chemical homogeneity with three methods based on X-ray detection: EPMA (Electron Probe Micro Analyzer), Sy-µXRF (Synchrotron radiation-induced X-ray Fluorescence) and PIXE. EPMA analyses were carried out at the TU Bergakademie Freiberg using an accelerating voltage of 20 keV and a beam size of 2 µm. Sy-µXRF measurements were performed at the hard X-ray beamline “BAMline” at the synchrotron facility BESSY in Berlin. Samples were exposed in atmosphere to monochromatic X-rays of 20 keV focused with a compound refractive lens to 3x3 µm2 or 5x7.4 µm2. PIXE data were obtained using a 3 MeV proton beam of about 5x5 µm2 from a 3 MV tandem accelerator at the HZDR, Dresden.
Quantitative (EPMA, PIXE) and qualitative (Sy-µXRF) elemental distribution maps have been obtained for major, minor and trace elements for each scan. At least five trace elements were detected in each of the matrices, showing irregular distribution patterns. Compared to PIXE, Sy-µXRF spectra were characterized by lower peak to background ratios, thus, better detection limits could be achieved and more trace elements identified, such as Ge and Pb in sanidine, Mn and Ti in columbite, and Zn and Se in pyrite.
Compared to EPMA and PIXE, only Sy-µXRF seems to be thorough and robust enough for swift homogeneity testing for trace elements distribution in light, medium-heavy matrices, thus, proving to be an invaluable method in quality assurance of synthetic candidate RMs.
Keywords: ion beam analysis, reference materials, PIXE, XRF, synchrotron
  • Poster
    13th International Conference on Nuclear Microprobe Technology & Applications (ICNMTA), 22.-27.07.2012, Lisbon, Portugal

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Permalink: https://www.hzdr.de/publications/Publ-17003
Publ.-Id: 17003


Switching voltages and back-hopping in magnetic tunnel junctions with different geometries

Bernert, K.; Sluka, V.; Fowley, C.; Fassbender, J.ORC; Deac, A. M.
A spin-polarized current flowing through a ferromagnet can exert a torque on the local magnetization [1,2]. This phenomenon is currently intensively investigated due to its potential application in magnetic random access memory (MRAM) or in telecommunication devices. Presently, the structure of choice for spin-torque devices includes a magnetic tunnel junction (MTJ) with an MgO barrier, due to their large magnetoresistance signals. However, a key step towards the practical implementation as MRAM elements is the reduction of the critical voltages, in order to keep the size of the selection transistor down and compete with existing technologies [3]. In addition, magnetic tunnel junctions also exhibit a somewhat obscure behaviour referred to as ‘back-hopping’, whereby reliable switching to the desired state is achieved for applied voltages of the order of the critical voltage, but a larger applied bias induces a telegraph-noise behaviour [4, 5]. Back-hopping is characteristic for MTJs, as it has not been observed in metallic multilayers, and poses concerns for designing industrially-competitive MRAM devices.

We evaluate the switching voltages and their temperature dependence by analytically and numerically solving the modified Landau-Lifshitz-Gilbert equation which includes both Slonczewski-like (in-plane) and field-like (out-of-plane) torque terms for different geometries. Its quadratic dependence on the applied voltage [6] translates into a more complex correlation between the critical bias and the external field, altering the shape of the phase diagram. It also explains back-hopping at a large bias for specific geometries, in agreement with experimental results.

References:
[1] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)
[2] L. Berger, Phys. Rev. B 54, 9359 (1996)
[3] Z. Diao et al., J. Phys. D: Cond. Mat. 19, 165209 (2007)
[4] J. Z. Sun, J. Appl. Phys. 105, 07D109 (2009)
[5] T. Min et al., J. Appl. Phys. 105, 07D126 (2009)
[6] C. Heiliger and M. Stiles, Phys. Rev. Lett. 100, 186805 (2008)
Keywords: spin-transfer torque, magnetic tunnel junction, magnetic random access memory
  • Invited lecture (Conferences)
    Third Nordic Workshop on Spintronics and Nanomagnetism (NordicSpin 2012), 22.-25.04.2012, Varberg, Sweden
  • Invited lecture (Conferences)
    Spin Caloritronics 4, 02.-06.06.2012, Sendai, Japan
  • Invited lecture (Conferences)
    Magnetism and Magnetic Nanomaterials, MMN’2012, 04.-06.09.2012, Bourmedes, Algeria

Permalink: https://www.hzdr.de/publications/Publ-17002
Publ.-Id: 17002


Injection and detection of spin in a semiconductor by tunneling via interface states

Jansen, R.; Deac, A. M.; Saito, H.; Yuasa, S.
Injection and detection of spin accumulation in a semiconductor having localized states at the interface is evaluated. Spin transport from a ferromagnetic contact by sequential, two-step tunneling via interface states is treated not in itself, but in parallelwith direct tunneling. The spin accumulation dμch induced in the semiconductor channel is not suppressed, as previously argued, but genuinely enhanced by the additional spin current via interface states. Spin detection with a ferromagnetic contact yields a weighted average of dμch and the spin accumulation dμls in the localized states. In the regime where dμls/dμch is largest, the detected spin signal is insensitive to dμls and the ferromagnet probes the spin accumulation in the semiconductor channel.
Keywords: semiconductor, spin injection, spin detection, interface states

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Publ.-Id: 17001


Probing Electron-Induced Bond Cleavage at the Single-Molecule Level Using DNA Origami Templates

Keller, A.; Bald, I.; Rotaru, A.; Cauët, E.; Gothelf, K. V.; Besenbacher, F.
Low-energy electrons (LEEs) play an important role in nanolithography, atmospheric chemistry, and DNA radiation damage. Previously, the cleavage of specific chemical bonds triggered by LEEs has been demonstrated in a variety of small organic molecules such as halogenated benzenes and DNA nucleobases. Here we present a strategy that allows for the first time to visualize the electron-induced dissociation of single chemical bonds within complex, but well-defined self-assembled DNA nanostructures. We employ atomic force microscopy to image and quantify LEE-induced bond dissociations within specifically designed oligonucleotide targets that are attached to DNA origami templates. In this way, we use a highly selective approach to compare the efficiency of the electron-induced dissociation of a single disulfide bond with the more complex cleavage of the DNA backbone within a TT dinucleotide sequence. This novel technique enables the fast and parallel determination of DNA strand break yields with unprecedented control over the DNA’s primary and secondary structure. Thus the detailed investigation of DNA radiation damage in its most natural environment, e.g., DNA nucleosomes constituting the chromatin, now becomes feasible.
Keywords: DNA origami, Low-energy electrons, Atomic force microscopy, DNA radiation damage, ab initio calculations
  • ACS Nano 6(2012)5, 4392-4399
    DOI: 10.1021/nn3010747
  • Poster
    Electron Controlled Chemical Lithography 2012 Meeting, 18.-22.05.2012, Stykkishólmur, Iceland

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Permalink: https://www.hzdr.de/publications/Publ-17000
Publ.-Id: 17000


Applocation of new closure models for bubble coalescence and breakup to steam-water vertical pipe flow

Liao, Y.; Lucas, D.; Krepper, E.
The new closure models for bubble coalescence and breakup proposed in our previous work (Liao and Lucas, 2011) are tested in the case of condensing steam-water pipe flows. Steady-state CFD calculations are performed with the commercial CFD solver CFX12.1. The predicted evolution of cross-section averaged bubble size distribution and gas volume fraction along the pipe is compared with the measured one provided by the TOPFLOW facility (Lucas et al., 2010). It is shown that for cases with small initial bubble size and low gas volume fraction, bubble coalescence and breakup is nearly negligible and the change of bubble size is mainly due to condensation. Nevertheless, with the increase of initial bubble size or gas volume fraction bubble coalescence and breakup become important phenomena. The performance of the new closure models and the standard ones available in CFX is investigated for two examples of such a case. It is shown that both sets of the models give an overestimation of breakup rate, especially the standard ones. Furthermore, the results are found to be dependent sensitively on the inlet liquid temperatures, which might exceed the accuracy of the measurements. In addition, inter-phase heat transfer models have a significant impact on the results.
Keywords: condensation, steam-water, sub-cooling, coalescence and breakup, interphase heat transfer
  • Open Access Logo Contribution to proceedings
    CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
    Proceedings of CFD4NRS - 4
  • Lecture (Conference)
    CFD4NRS-4 - The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology - OECD/NEA and IAEA Workshop, 10.-12.09.2012, Daejeon, Korea
  • Nuclear Engineering and Design 279(2014), 126-136
    DOI: 10.1016/j.nucengdes.2014.02.015

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Permalink: https://www.hzdr.de/publications/Publ-16999
Publ.-Id: 16999


Electromagnetic dipole strength of 136Ba below the neutron separation energy

Massarczyk, R.; Schwengner, R.; Dönau, F.; Litvinova, E.; Rusev, G.; Beyer, R.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kelley, J. H.; Kögler, T.; Kosev, K.; Kwan, E.; Marta, M.; Matic, A.; Nair, C.; Raut, R.; Schilling, K. D.; Schramm, G.; Stach, D.; Tonchev, A. P.; Tornow, W.; Trompler, E.; Yakorev, D.; Wagner, A.
The electromagnetic dipole strength of the nucleus 136Ba has been investigated at two facilities. At the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf, two measurements were performed with electron energies of 7.0 and 11.4 MeV. Photon scattering on the same nucleus has been investigated at the HI$gS facility of the Triangle Universities Nuclear Laboratory.
The GEANT4 code has been used to determine detector response and non-nuclear scattered events. Thus it is possible to account for the dipole strength in the quasi-continuum of unresolvable transitions. A statistical code was used to simulate inelastic transitions and to determine the branching ratios of transitions to the ground-state. The resulting photo-absorption cross section is compared to QRPA and RQTBA calculations.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function

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Publ.-Id: 16998


Superconducting Gallium implanted Germanium

Fiedler, J.; Heera, V.
Superconductivity in doped semiconductors is of increasing interest in both, fundamental research and applied physics. We report on superconducting Ge layers fabricated by Ga ion implantation and subse-quent flash lamp annealing. A brief introduction to alternative preparation methods and the physics of superconducting semiconductors is given, too. The microstructure of and the electrical transport in the Ga doped Ge layers are investigated in detail. Finally, it is demonstrated that increasing the Ga concentration and the thermal budget of annealing leads to Ga segregation. In this case superconducting properties similar to that of amorphous Ga films are obtained.
Keywords: carrier density; clusters; cover layer; diffusion; dopant; flash lamp annealing; gallium; germanium; Hall; implantation; metal-insulator-transition; nanocrystalline; oxygen; rapid thermal annealing; resistance; sem-iconductor; superconducting; surface
  • Book chapter
    Heidemarie Schmidt, Wolfgang Skorupa: Subsecond Annealing of Advanced Materials: Annealing by Lasers, Flash Lamps and Swift Heavy Ions (Springer Series in Materials Science), Switzerland: Springer, 2014, 978-3-319-03130-9, 57-78
    DOI: 10.1007/978-3-319-03131-6_4

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Permalink: https://www.hzdr.de/publications/Publ-16997
Publ.-Id: 16997


Ridge waveguide lasers in Nd:GGG crystals produced by swift carbon ion irradiation and femtosecond laser ablation

Jia, Y.; Dong, N.; Chen, F.; de Aldana, J. R. V.; Akhmadaliev, S.; Zhou, S.
We report on the fabrication of ridge waveguide in Nd:GGG crystal by using swift C5+ ion irradiation and femtosecond laser ablation. At room temperature continuous wave laser oscillation at wavelength of ~1063 nm has been realized through the optical pump at 808 nm with a slope efficiency of 41.8% and the pump threshold is 71.6 mW.
Keywords: Integrated optics devices, Laser materials processing, Waveguides

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Publ.-Id: 16996


AMS within Eurogenesis: Nanodiamonds and SN-signatures

Wallner, A.; Feige, J.; Fifield, K.; Korschinek, G.; Melber, K.; Merchel, S.; Ott, U.; Paul, M.; Rugel, G.; Steier, P.; Tims, S.; Vockenhuber, C.
CoDustMas is a Collaborative Research Project (CRP) of Eurogenesis, one of the EUROCORES programmes of the European Science Foundation. This international network aims at understanding the crucial role that supernovae (SNe) play in the formation of cosmic dust. Specifically, this CRP will study the synthesis of dust grains in core-collapse supernovae; isotopic signatures in dust grains; and mixing, evolution and transport of dust in supernova remnants.
Applying accelerator mass spectrometry (AMS) two aspects are tackled. First, the measurement of trace element isotope ratios in presolar nanodiamonds isolated from primitive meteorites, e.g. the ratios of Pt isotopes to extract r-process nucleosynthesis signatures. Recent results demonstrate the applicability of AMS for determining stable Pt isotope signatures in diamonds extracted from Allende. These AMS data may indicate a small 198Pt anomaly; its significance and new approaches will be discussed.
The second aspect relates to the search for live SN-produced radionuclides in terrestrial deep-sea archives. In particular, the focus is on isotopes with half-lives of the order of million years. We continue this search by investigating, with high time resolution, two deep-sea sediment cores from the Indian Ocean for a possible signal of the SN-candidates 26Al, 53Mn, 60Fe, and potentially 244Pu.
Keywords: accelerator mass sepctrometry, AMS, Pt, supernova, radionuclide
  • Lecture (Conference)
    XII International Symposium on Nuclei in the Cosmos, 05.-10.08.2012, Cairns, Australia

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Permalink: https://www.hzdr.de/publications/Publ-16995
Publ.-Id: 16995


Dipole Strength in 86Kr up to Neutron Separation

Massarczyk, R.; Schwengner, R.; Junghans, A. R.; Wagner, A.
For the rst time a high-pressure gas target has been investigated at the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The experiment was carried out at electron beam energies of 7 and 12MeV in order to study dipole excitations up to an energy region up to the neutron separation. The talk will present data analysis and simulations methods of the experiments in Rossendorf. GEANT4 simulations were performed to subtract the atomic background from the measured spectrum and deduce the intensity of the resonantly scattered gamma-rays. Also the response functions for the high-purity germanium detectors were simulated by GEANT4, which allows us to deduce the intensity of unresolvable peaks due to decreasing level-spacing. Considering also the transitions from states in the quasicontinuum, simulations of gamma-ray cascades were carried out with a new code to estimate branching ratios. As a result the photoabsorption cross section obtained from transitions to the ground state is calculated. The data will be presented in the context of further photon-scattering experiments performed in Rossendorf on the stable isotopes at the closed neutron shell N = 50.
Keywords: Photon scattering, nuclear spectroscopy, nuclear structure, gamma strength function
  • Lecture (Conference)
    3rd Workshop on Level Density and Gamma Strength, 23.-27.05.2011, Oslo, Norway

Permalink: https://www.hzdr.de/publications/Publ-16994
Publ.-Id: 16994


Cross-Section Measurements of the 86Kr(gamma,n) Reaction to Probe the s-Process Branching at 85Kr

Raut, R.; Banu, A.; Iliadis, C.; Kelley, J. H.; Rusev, G.; Schwengner, R.; Tonchev, A. P.; Tornow, W.
For the first time, cross-section measurements were carried out for the 86 Kr(gamma,n) reaction in order to probe the s-process branching point nucleus 85Kr. The branching point nuclei in the s-process path are of importance in testing and constraining the nucleosynthesis models. Cross-section measurement for the photoneutron reaction on the neighbouring stable isotope is carried out to deduce the aforesaid neutron capture cross-section, as has been adopted in the present case of 85Kr branching point. The cross-section results from the 86 Kr(gamma,n) reaction were compared with the statistical model calculations using TALYS code.
Keywords: Monoenergetic gamma rays, photodisintegration, neutron detection, cross section, s-process, waiting point, statistical models.

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Permalink: https://www.hzdr.de/publications/Publ-16991
Publ.-Id: 16991


Study of hadron properties in cold nuclear matter with HADES

Tlusty, P.; Agakishiev, G.; Belver, D.; Belyaev, A.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Cabanelas, P.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Krása, A.; Krizek, F.; Kuc, H.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michel, J.; Müntz, C.; Münzer, R.; Naumann, L.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Traxler, M.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.
Results of a study of dielectron and pion production in p + Nb collisions at incident proton beam energy 3.5 GeV are presented. The data are taken by the High Acceptance Di-Electron Spectrometer (HADES) at GSI Darmstadt.
The dielectron invariant mass distributions are compared to data from elementary p+p reactions at the same beam energy. At this energy above the light vector meson production threshold, the omega peak is clearly identified. The collected statistics and high acceptance for pair momenta within the interval 50-2000 MeV/c allow for a study of momentum dependence of the omega yield and spectral shape. The strongest medium modification in the line shape is expected for low momenta mesons decaying inside the nuclear matter. Comparing the measured p+Nb data with the p+p reference experiment results, the signifficant change in yield of low momenta dielectron pairs in the vector meson mass region is observed.
Data on charged pi meson emission, which are related to neutral pions representing a dominant contribution to the dielectron yield, are shown as well. They contribute to the results from systematic studies of the pion production in the proton-nucleus collisions, which point to a transition of the pion source from simple NN collisions to emission of thermalized pions from a fireball, when increasing the atomic number of the target nucleus. The data also serve as a reliable tool for normalization of the dielectron data.
  • Open Access Logo Proceedings of Science (2012), Pos(Bormio2012)019

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Permalink: https://www.hzdr.de/publications/Publ-16990
Publ.-Id: 16990


Detection of Laser-accelerated ions at the DRACO laser

Kraft, S.
In the last years, the detection schemes for laser-accelerated ion beams had to be developed much further. In the beginning, experiments where mainly performed on laser facilities with a few shots a day and online diagnostics such as film stacks where sufficient in order to characterize the ion beam. Nowadays many experiments are carried out at high power lasers with repetition rates on the order of 10 Hz and thus the need of on line detectors has grown significantly.
In this talk, the ion accelerator at the 100 TW laser DRACO in Dresden are described. Already implemented detectors such as MCPs and scintillators as well as desirable devices for future measurements are described.
  • Invited lecture (Conferences)
    Industry meets Academia: Beam Monitoring Instrumentation and Quality Assurance, 10.-11.11.2011, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16989
Publ.-Id: 16989


20 kW Upgrade of the ELBE 1.3 GHz CW RF-System with BRUKER 10kW Solid State Amplifiers

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.
Summary:
With the expansion of the radiation source ELBE, a centre for high power radiation sources is being built between 2009 and 2014 at the Helmholtz Zentrum Dresden Rossendorf. One part of this program is to increase the beam current of the ELBE LINAC. In January 2012 each of the 10kW CW klystrons used to operate the superconducting cavities of ELBE since 2001 had been replaced by a pair of 10kW solid state amplifiers.The talk gives an overview on the new RF-system of ELBE and its performance.
Keywords: Superconducting LINAC, 1.3GHz RF-System, Solid State RF-Power Amplifiers, 10kW RF Power, 10 kW RF SSPA, Turnkey SSPA, ELBE-RF System, ELBE-UPGRADE, HSQ
  • Lecture (others)
    Eingeladener Vortrag KEK Tsukuba/Japan, 17.04.2012, KEK, Tsukuba, Japan

Permalink: https://www.hzdr.de/publications/Publ-16988
Publ.-Id: 16988


Present and future laser driven proton therapy program in Dresden

Kraft, S.
  • Lecture (Conference)
    Coulomb ’11: Optical Acceleration of Ions and Perspective for Biomedicine, 04.-05.11.2011, Bologna, Italien

Permalink: https://www.hzdr.de/publications/Publ-16987
Publ.-Id: 16987


Nanocavity formation and hardness increase by dual ion beam irradiation of oxide dispersion strengthened FeCrAl alloy

Kögler, R.; Anwand, W.; Richter, A.; Butterling, M.; Ou, X.; Wagner, A.; Chen, C.-L.
Open volume defects generated by ion implantation into oxide dispersion strengthened (ODS) alloy and the related hardness were investigated by positron annihilation spectroscopy and nanoindentation measurements, respectively. Synchronized dual beam implantation of Fe and He ions was performed at room temperature and at moderately enhanced temperature of 300°C. For room temperature implantation a significant hardness increase after irradiation is observed which is more distinctive in heat treated than in as-received ODS alloy. There is also a difference between the simultaneous and sequential implantation mode as the hardening effect for the simultaneously implanted ODS alloy is stronger than for sequential implantation.
The comparison of hardness profiles and of the corresponding open volume profiles shows a qualitative agreement between the open volume defects generated on the nanoscopic scale and the macroscopic hardness characteristics.
Open volume defects are drastically reduced for performing the simultaneous dual beam irradiation at 300°C which is a more realistic temperature under application aspects. Few remaining defects are clusters of 3-4 vacancies in connection with Y oxide nanoparticles. These defects completely disappear in a shallow layer at the surface. The results are in agreement with hardness measurements showing little hardness increase after irradiation at 300°C.
Suitable characteristics of ODS alloy for nuclear applications and the close correlation between He-related open volume defects and the hardness characteristics are verified.
Keywords: Radiation hardness, ion implantation, ODS alloy, positron annihilation spectrometry, nanointendation

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Permalink: https://www.hzdr.de/publications/Publ-16986
Publ.-Id: 16986


Ansätze zur Bestimmung heterogener Diffusionsparameter auf Bohrkernskala mit Hilfe von Na-22-PET-Diffusionsmessungen und Modellsimulationen

Kulenkampff, J.; Schikora, J.; Zakhnini, A.; Gründig, M.; Lippmann-Pipke, J.
  • Lecture (others)
    2. Actinidenverbundtreffen "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 03.-04.04.2012, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16985
Publ.-Id: 16985


Für den Laboreinsatz optimierte Kalibrationsmethode für pH-Elektroden bei hohen Ionenstärken

Fritsch, K.
Eine vereinfachte Auswertemethode für die Elektrodenkalibration bei hohen Ionenstärken unter Beachtung der Kw-Korrektur wird vorgestellt.
Keywords: pH measurements, electrode calibration, high ionic strength
  • Lecture (others)
    2. Workshop des Verbundprojekts „Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen“, 04.04.12, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16984
Publ.-Id: 16984


Monte Carlo simulations of GeoPET experiments: 3D images of tracer distributions (18F, 124I and 58Co) in Opalinus Clay, anhydrite and quartz

Zakhnini, A.; Kulenkampff, J.; Sauerzapf, S.; Pietrzyk, U.; Lippmann-Pipke, J.
Understanding conservative flow and reactive tracer transport processes in soils and rock formations requires quantitative visualization methods in 3D+t. After a decade of research and development we established the GeoPET as a non-destructive method with unrivalled sensitivity and selectivity, without physical and chemical impact, and with due spatial and temporal resolution by applying Positron Emission Tomography (PET), a nuclear medicine imaging method, to dense rock material. Requirements for reaching the physical limit of image resolution of nearly 1 mm are a high-resolution PET- camera, like our ClearPET scanner (Raytest), and appropriate correction methods for scatter and attenuation of 511 keV - photons in the dense geological material, which are by far more significant than in human and small animal body tissue (water).
Here we present data from Monte Carlo simulations, considering all involved nuclear physical processes of the measurement with the ClearPET-system, that allows us to quantify the sensitivity of the method and the scatter fractions in geological media as function of material (quartz, Opalinus clay and anhydrite compared to water), PET isotope (18F, 58Co and 124I), and system parameters. Comparison of simulated data with measured images indicates the limits of the method and provides procedures for image quality improvement, including a scatter correction method by subtracting projections of simulated scattered coincidences from experimental data sets prior to image reconstruction with an iterative reconstruction process.
Keywords: Monte Carlo Simulation, PET, radiotracer, radiation, process monitoring

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Permalink: https://www.hzdr.de/publications/Publ-16983
Publ.-Id: 16983


Magnetic Frustration in a Quantum Spin Chain: The Case of Linarite PbCuSO4(OH)2

Willenberg, B.; Schäpers, M.; Rule, K. C.; Süllow, S.; Reehuis, M.; Ryll, H.; Klemke, B.; Kiefer, K.; Schottenhamel, W.; Büchner, B.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Wosnitza, J.; Wolter, A. U. B.
We present a combined neutron diffraction and bulk thermodynamic study of the natural mineral linarite PbCuSO4(OH)2, this way establishing the nature of the ground-state magnetic order. An incommensurate magnetic ordering with a propagation vector k = (0, 0.186, 1/2) was found below TN = 2.8 K in a zero magnetic field. The analysis of the neutron diffraction data yields an elliptical helical structure, where one component (0.638 µB) is in the monoclinic ac plane forming an angle with the a axis of 27(2)°, while the other component (0.833 µB) points along the b axis. From a detailed thermodynamic study of bulk linarite in magnetic fields up to 12 T, applied along the chain direction, a very rich magnetic phase diagram is established, with multiple field-induced phases, and possibly short-range-order effects occurring in high fields. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. Long-range magnetic order is brought about by interchain coupling 1 order of magnitude smaller than the intrachain coupling.

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Permalink: https://www.hzdr.de/publications/Publ-16981
Publ.-Id: 16981


Vorstellung und Bewertung des Beitrags zur Erreichung des Meilensteins im Projekt Nanopharm

Vogel, M.
Vorstellung der wissenschaftlichen Arbeiten und erzielten Ergebnisse im Projekt NanoPharm - Teilprojekt: Herstellung und Charakterisierung von photokatalytischen S-Layer Nanokompositen, welche zur Erreichung des Meilensteins beitragen.
  • Lecture (others)
    Meilenstein-Treffen zum Projekt Nanopharm, 19.04.2012, Köthen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16979
Publ.-Id: 16979


Untersuchung der 40Ca(alpha,gamma)44Ti-Reaktion bei E_alpha ~ 3.5 MeV

Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Dietz, M.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A.; Marta, M.; Menzel, M.-L.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.
Das radioaktive Nuklid Titan-44 wird Modellrechnungen zufolge in Kernkollaps-Supernovae erzeugt. Die Gammastrahlung aus seinem Zerfall kann als Werkzeug zum Test von Supernova-Modellen genutzt werden, weil sie zumindest für einen Supernova-Überrest durch satellitengestützte Gamma-Teleskope nachweisbar ist. Zur Interpretation dieser Messungen ist eine genaue Kenntnis der Kernreaktionsraten für die Erzeugung und Zerstörung von Titan-44 erforderlich. Die 40Ca(alpha,gamma)44Ti-Reaktion dominiert die Erzeugung von Titan-44. Ihre Rate wird je nach Temperatur von mehreren Resonanzen dominiert. Die Stärken der Resonanzen bei 3.5 - 3.7 MeV alpha-Energie werden am Dresdner 3MV Tandetron sowohl mittels in-beam Gamma-Spektrometrie als auch durch eine Aktivierungsmessung im Felsenkeller-Niederniveaumesslabor bestimmt. Gefördert von der EU (FP7-SPIRIT 227012) und der DFG (BE 4100/2-1).
Keywords: Titan-44, 44Ti, 40Ca(alpha,gamma)44Ti, 40Ca(a,g)44Ti, Kernkollaps-Supernovae, Supernova, Kernreaktionsraten, Resonanzstärken, Gamma-Spektrometrie, Felsenkeller-Niederniveaumesslabor
  • Lecture (Conference)
    DPG Frühjahrstagung 2012, 19.-23.03.2012, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16978
Publ.-Id: 16978


Towards a study of the 22Ne(p,g)23Na reaction at LUNA

Menzel, M.-L.; Bemmerer, D.
The 22Ne(p,g)23Na reaction takes part in the so called neon-sodium-cycle of hydrogen burning. This cycle is important at higher temperature than those experienced in the sun and plays a role in explosive hydrogen burning in an astrophysical nova. In addition, this reaction possibly depletes the supply of 22Ne in the accreting white dwarf preceeding a supernova of type Ia. The rate of this reaction depends on the strengths of several resonances in the energy range of the LUNA 0.4 MV accelerator which have never been observed in direct experiments. A related study is under preparation at LUNA. The poster will show the experimental set-up and planned measurement strategy.
Keywords: 22 Neon, 23 Natrium, LUNA
  • Poster
    Heraeus-Seminar on Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland
  • Lecture (Conference)
    Heraeus-Seminar on Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16977
Publ.-Id: 16977


Late Pleistocene glaciation in the Gissar Range, Tajikistan, based on 10Be surface exposure dating

Zech, R.; Röhringer, I.; Sosin, P.; Kabgov, H.; Akhmadaliev, S.; Merchel, S.; Zech, W.
Mountain glaciers are sensitive indicators for climate change, mainly summer temperature and precipitation. Glacial chronologies from Central Asia have therefore been suggested to provide valuable information about past changes in temperature, as well as precipitation and related changes in atmospheric circulation. However, available age control is still sparse. Here we present a glacial chronology for the Gissar Range, Tajikistan, based on thirteen 10Be surface exposure ages. Prominent moraine lobes document glacial advances in phase with the global last glacial maximum (LGM) during marine isotope stage (MIS) 2. Rapid and significant deglaciation occurred already at ~20 ka as inferred from recessional stages. An older and slightly more extensive glaciation could be dated to MIS 4, whereas the timing of the most extensive glaciation remains speculative. In contrast to the glacial chronologies from the nearby, more arid Pamir and Tien Shan, where MIS 3 and MIS 5 moraines likely document past periods with increased precipitation, glaciers in the more humid Gissar Range predominantly recorded past changes in temperature and summer insolation.
Keywords: cosmogenic nuclides; Quaternary; paleoclimate; Central Asia; accelerator mass spectrometry

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Permalink: https://www.hzdr.de/publications/Publ-16976
Publ.-Id: 16976


Electronic andmagneticstudiesof k-(BEDT-TTF)2Hg(SCN)2Cl

Yasin, S.; Rose, E.; Drichko, N.; Dressel, M.; Schlueter, J. A.; Zhilyaeva, E. I.; Torunova, S.; Lyubovskaya, R. N.
DC resistivity and electron spin resonance (ESR) measurements have been performed on the two-dimensionalorganicconductor k-(BEDT-TTF)2Hg(SCN)2Cl. Due to electronic correlations, the compound undergoes a transition from a metallic to an insulating state at TMI= 34 K.The ESR parameters exhibit a drastic change below Tafm=27K that evidences a magnetic phase transition. Int his low-temperature state, we observe the characteristics of antiferromagnetic resonances in the angular dependence of the g-value.

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Permalink: https://www.hzdr.de/publications/Publ-16975
Publ.-Id: 16975


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