Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34730 Publications

On the T2 deep level in zinc oxide thin films

Schmidt, M.; Karsthof, R.; Schmidt, F.; von Wenckstern, H.; Ellguth, M.; Pickenhain, R.; Grundmann, M.; Brauer, G.

For the majority of deep levels studied in n - type conducting ZnO by means of capacitance spectroscopy only the activation energy and the high temperature limit of the electron capture cross - section are known since these quantities can be evaluated easily from the temperature dependence of the trap’s thermal electron emission rate. We focused on the T2 level occuring in pulsed laser deposition grown ZnO thin films. In order to tune the T2 concentration in the samples, we employed different growth and annealing conditions as well as the implantation of oxygen and zinc ions, respectively. The physical properties of T2 were studied by sophisticated deep level transient spectroscopy and photo - capacitance experiments. These experiments revealed a strong dependence of the thermal activation energy, 185meV < Ea < 280meV, on the concentration of T2 in the sample as well as on the electric field (Poole - Frenkel effect). T2 was found to be preferentially generated under zinc rich conditions as both, the implantation of zinc ions and thermal annealing at low oxygen partial pressures increase its concentration. From photo - capacitance transients the photo - ionisation cross - section spectrum was calculated.

Keywords: T2 deep level in zinc oxide thin films

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM)2011, 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16390
Publ.-Id: 16390


Basic structures of photonic integrated circuits for smart biosensor applications

Germer, S.; Rebohle, L.; Skorupa, W.; Helm, M.

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1, 2]. In fluid media the device is placed beneath the dye-labeled sample exciting the dye. This light emission can be recorded by an external detector. It was shown that the silanization of the device surface was successfully based on the covalent binding of the organosilane [3]. The harmlessness of the silanization method to the integrated light emitters was proved by comparing the electroluminescence spectra of Tb-based MOSLEDs before and after silanization. We further showed that the transparency is maintained. Similarly, the human estrogen receptor hERα could be immobilized effectively on the coated surface [3]. We also discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. This lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

[1] L. Rebohle, C. Cherkouk, S. Prucnal, M. Helm, W. Skorupa, Vacuum 83, 24 (2009)
[2] L. Rebohle, T. Gebel, R.A. Yankov, T. Trautmann, W. Skorupa, J. Sun, G. Gauglitz, R. Frank, Optical Materials 27, 1055 (2005)
[3] C. Cherkouk, L. Rebohle, W. Skorupa, T. Strache, H. Reuther and M. Helm, Journal of Colloid and Interface Science 337, 375 (2009)

Keywords: biosensor; waveguide; silanization; organosilane; photonic crystals

  • Poster
    DOCTORAL STUDENTS CONFERENCE FOR THE DISCUSSION OF OPTICAL CONCEPTS, 21.-25.03.2011, Naumburg (Sachsen), Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16389
Publ.-Id: 16389


Si-based integrated photonic circuits: first approach

Germer, S.; Rebohle, L.; Helm, M.; Skorupa, W.

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1,2]. Now we discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. The guiding of the light depends on the geometry and material composition of the waveguide. First waveguides were fabricated through plasma enhanced chemical vapor deposition (PECVD) and optical photolithography with following etching steps. Afterwards the layer thicknesses were analyzed by ellipsometry and the surface roughness via scanning electron microscopy (SEM). However, the investigation of the different waveguides will be allowed through finite element method (FEM) simulations (COMSOL) and experimentally through a setup for the optical transmission measurement. In summary, this lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

[1] L. Rebohle, C. Cherkouk, S. Prucnal, M. Helm, W. Skorupa, Vacuum 83, 24 (2009)
[2] L. Rebohle, T. Gebel, R.A. Yankov, T. Trautmann, W. Skorupa, J. Sun, G. Gauglitz, R. Frank, Optical Materials 27, 1055 (2005)

Keywords: biosensor; waveguide; photonic crystals

  • Lecture (Conference)
    PhD Seminar HZDR, 26.09.2011, Dresden, Deutschland
  • Poster
    6th PhD seminar, 05.-07.10.2011, Rabenberg, Deutschland
  • Lecture (Conference)
    PhD Seminar HZDR, 07.05.2012, Dresden, Deutschland
  • Lecture (Conference)
    PhD Seminar, 16.09.2013, Dresden, Deutschland
  • Lecture (Conference)
    HZDR PhD Seminar, 07.-09.10.2013, Bautzen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16388
Publ.-Id: 16388


Kelvin probe force microscopy on doped semiconductor nanostructures with local, carrier-depleted space charge regions

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

Failure analysis and optimization of semiconducting devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is the most promising non-contact electrical nanometrology technique to meet the demands of today‘s semiconductor industry. We present its applicability to locally doped silicon structures. Quantitative dopant profiling by means of KPFM measurements is successfully demonstrated on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayers by applying a recently introduced new explanation of the measured KPFM signal [1]. Additionally, the influence of local, carrier-depleted space charge regions and of the electric fields across them is discussed. It is explained how drift and diffusion of injected charge carriers in intrinsic electric fields influence the surface region of the investigated semiconductor and thus may disturb the detected KPFM bias.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Duetschland

Permalink: https://www.hzdr.de/publications/Publ-16387
Publ.-Id: 16387


Positron annihilation at planar defects in oxides

Kuriplach, J.; Brauer, G.; Melikhova, O.

Transition metal oxides are interesting materials with important prospective applications. Planar defects like stacking faults and grain boundaries are often present in such materials and may affect their properties. In particular, it has been recently shown that a zinc oxide (ZnO) single crystal contain a large amount of stacking faults [1]. Furthermore, nanocrystalline materials based on zirconia (ZrO2) are also frequently studied and their characteristics are significantly influenced by grain boundaries [2]. The planar defects just mentioned exhibit free volumes which, in principle, are detectable using positron annihilation spectroscopy. In this contribution, we present a preliminary theoretical study of positron interaction with planar defects in oxides.
First, we examine several stacking faults (SFs) in ZnO, following their structural investigation presented in [3]. It is found that studied SFs represent rather shallow positron traps with the corresponding positron lifetime exceeding the bulk one slightly only. It might be necessary to consider interactions of SFs with other defects (vacancies, impurities) in order to characterize more precisely their effect on materials’ properties, including positron response.
Second, we perform the case study of the Sigma 5 (310) [001] symmetric tilt grain boundary [4,5] in ZrO2. In this case, positrons also localize at the grain boundary, but such localization is affected by the presence of yttrium (Y3+) ions which are often added to zirconia to improve its mechanical properties. The reason is that Y3+ ions influence the charge state of the grain boundary studied.

[1] W. Anwand et al., J. Appl. Phys. 109, 063516 (2011).
[2] J. Čížek et al., Phys. Rev. B 81, 024116 (2010).
[3] Y. Yan et al., Phys. Rev. B 70, 193206 (2004).
[4] Z. Mao et al., J. Am. Ceram. Soc. 85, 1594 (2002).
[5] T. Oyama et al., Phys. Rev. B 71, 224105 (2005).

Keywords: ZnO; stacking faults; positron annihilation

  • Poster
    Tenth International Workshop on Positron and Positronium Chemistry (PPC-10), 05.-09.09.2011, Smolenice Castle, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-16386
Publ.-Id: 16386


Effect of Sintering on Defects in Yttria Stabilised Zirconia

Prochazka, I.; Cizek, J.; Melikhova, O.; Anwand, W.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.

A variable energy slow positron beam was utilised to investigate depth dependent effects of sintering on the tetragonal yttria stabilised zirconia nanopowders. Positron implantation was combined with the determination of Doppler broadened profiles of annihilation radiation. The results are consistent with recent positron lifetime data showing that sintering at elevated temperatures leads to a disappearance of pores and a significant grain growth, which is demonstrated by a strong suppression of positronium formation and a substantial decrease in concentration of open volume defects at triple points, respectively, with increasing sintering temperature. An existence of a subsurface layer of a relatively high content of defects was shown in sintered samples and tentatively attributed to arise from a diffusion of open volume defects from the sample interior toward the surface or from a sintering-induced surface modification.

Keywords: Yttria stabilised zirconia; sintered nanopowders; slow positron implantation spectroscopy

  • Lecture (Conference)
    Tenth International Workshop on Positron and Positronium Chemistry (PPC-10), 05.-09.09.2011, Smolenice Castle, Slovakia
  • Materials Science Forum 733(2013), 236-239
    DOI: 10.4028/www.scientific.net/MSF.733.236

Permalink: https://www.hzdr.de/publications/Publ-16385
Publ.-Id: 16385


Structural Pattern of Cinnamic Acid on Different Substrates Probed by Slow Positron Beam Technique

Ganguly, B. N.; Anwand, W.; Brauer, G.; Wagner, A.

Cinnamic acid (phenyl acrylic acid) is an essential constituent of Cinnamon oil, and is well known for its medicinal values. The compound comprises of hydrogen bonded supra molecular structure due to strong hydrogen bonding between the carboxylic groups and other intermolecular hydrogen bonding as well. On the whole it forms a crystalline layered structure in solid state. In order to study its structural organization and orientation of the molecular functional groups it has been our astute interest if we could form thin layers of these molecules on suitable substrates. Thus, thin layer characteristics of cinnamic acid (CINN) on the two commonly used substrates namely: fused quartz plate and on silicon substrate has been attempted and they were subjected to Doppler broadening of positron annihilation radiation (DB) line shape analysis by slow positron beam on the range of 30 – 1200 eV energy to study the near surface properties. While CINN on quartz substrate showed a periodic pattern (the rippled nature) significant from the point of view of the layer structure, as compared to the pure solid state analysis, the results on the pure silicon substrate were not so regular, it is rather apparent that a strong substrate dependent property was noticed with the layer formation . The cause of this effect was also identified through coincidence DB analysis and another complementary technique XPS in corroboration and shall be presented.
The discussion on the organization of CINN on the quartz substrate as revealed from the DB will be presented.

Keywords: Cinnamic acid; thin layer characteristics; XPS; PAS

  • Poster
    Tenth International Workshop on Positron and Positronium Chemistry (PCC-10), 05.-09.09.2011, Smolenice Castle, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-16384
Publ.-Id: 16384


Bestimmung langlebiger Radionuklide zur Datierung in den Geowissenschaften und der Kosmochemie

Merchel, S.; Rugel, G.; Akhmadaliev, S.

Keywords: accelerator mass spectrometry; AMS; geomorphology

  • Lecture (others)
    Dresdener Geowissenschaftliches Kolloquium, 15.05.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16383
Publ.-Id: 16383


Characterization of quenched-in vacancies in Fe-Al alloys

Cizek, J.; Lukac, F.; Prochazka, I.; Kuzel, R.; Jiraskova, Y.; Janickovic, D.; Anwand, W.; Brauer, G.

Physical and mechanical properties of Fe-Al alloys are strongly influenced by atomic ordering and point defects. In the present work positron lifetime (LT) measurement combined with slow positron implantation spectroscopy (SPIS) were employed for investigation of quenched-in vacancies in Fe-Al alloys with Al content ranging from 18 to 49 at.%. Interpretation of positron annihilation data was performed using ab-inito theoretical calculations of positron parameters. Quenched-in defects were identified as Fe-vacancies.
It was found that the lifetime of positrons trapped at quenched-in defects increases with increasing Al content due to increasing number of Al atoms surrounding vacancies. The concentration of quenched-in vacancies strongly increases with increasing Al content from ~10e-5 in Fe82Al18 (i.e. the alloy with the lowest Al content studied) up to ~ 10e-1 in Fe51Al49 (i.e. the alloy with the highest Al content studied in this work).

Keywords: Fe-Al alloys; vacancies; positron annihilation

  • Lecture (Conference)
    Seventh International Workshop on Positron Studies of Defects (PSD-11), 28.08.-02.09.2011, Delft, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-16382
Publ.-Id: 16382


THEREDA - Thermodynamische Referenzdatenbasis. Abschlussbericht

Altmaier, M.; Brendler, V.; Bube, C.; Marquardt, C.; Moog, H. C.; Richter, A.; Scharge, T.; Voigt, W.; Wilhelm, S.

A long term safety assessment of a repository for radioactive waste requires evidence, that all relevant processes, which might have a significant positive or negative impact on its safety, are known and understood. In the case of brine intrusion into the disposal area, it has to be demonstrated, that the initiated chemical reactions don’t lead to an undue release of radionuclides into the biosphere. The starting point for this is to assess the solubility of contaminants in the solutions interacting with the waste. Solubility estimations can either be based on experimental data determined at conditions closely resembling those in the repository or on thermodynamic calculations.
A so called “thermodynamic database” created from experimental data is the basis for thermodynamic model calculations. Several research institutions in Germany are working on an improvement of the thermodynamic database. This work comprises investigations into fundamental thermodynamic data (such as vapour pressures or solubili-ties) as well as the application of sophisticated analytical or spectroscopic tools, which allow insight into aqueous speciation or structural details of surface complexes as basis for correct chemical and thermodynamic models.
Experience teaches that thermodynamic equilibrium calculations performed by different experts readily become difficult to compare and evaluate. This is only in part due to ill-defined (and -documented!) boundary conditions imposed on the calculations, but is frequently related to the use of different thermodynamic data or different conceptual models underlying them. Further difficulties arise by the fact that thermodynamic data used for a calculation actually are strongly interrelated; modification of an individual value without adapting the dependent values leads to “inconsistent” data. If applied in a calculation, this may lead to erroneous results, often unnoticed by the user.
As a result, in different institutions various databases exist that are appropriate for spe-cific tasks. However, they might lead to different results when they are applied to the same problem. This situation is unacceptable, both from a scientific point of view and considering the special public awareness for the final disposal of radioactive waste.
In 2002, a working group of five institutions was established for the creation of a com-mon thermodynamic database for nuclear waste disposal in deep geological formations (HZDR, GRS, TU BAF, KIT, AF-Consult). The common database was named THEREDA: Thermodynamic Reference Database.
It was agreed that the newly created database should be operated jointly by all members of the working group. In the mean term it is intended, that its usage becomes mandatory for geochemical model calculations for nuclear waste disposal in Germany. Furthermore, it was agreed that the new database should be developed along the guidelines long-term usability, easy access, applicability, internal consistency, comprehensiveness, documentation.
Activities within the time for which this report is valid cover a wide range of aspects. At first, a data model had to be designed from scratch which allows for the storage of thermodynamic data, at the same time facilitating export into code-specific parameter files. Creating the data model emphasis was laid upon its long term usage. Thus, a degree of abstraction was chosen which exceeds todays necessities and allows for future extensions. Technically the databank is implemented on a web server. Programs were created, which permit reading and writing access to the data. From the created webpages programs can be called that produce code specific parameter files ready for download upon specific request by the user.
THEREDA can thus be thought of as a databank in conjunction with a suite of peripheral programs, which aims at administrating, processing and extracting data. The data export is intended for the use in programs that calculate thermodynamic equilibria in aqueous solutions at temperatures which are of potential interest for hydrogeochemical systems in general and solutions containing hazardous contaminants like radionuclides or heavy metals in particular. As such, THEREDA is not designed to hold primary experimental data, neither data concerning any liquid other than aqueous solu-tion, e. g. melts or other substances which are stable under conditions beyond those where aqueous solutions may exist. Emphasis is laid on the correct calculation of ex-perimentally determined solubilities and aqueous speciation. Accompanying the above mentioned activities the working group agreed upon guide-lines which are to be followed upon selection and assessment of data. A system of quality assuring measure was set up; this comprises technical aspects relating to the databank as well as criteria determining how data are to be internally reviewed prior to release (auditing). As an external measure of quality assurance an internet forum was established to feedback questions and requirements from realistic problems into the project. A handbook was written to guide users in the handling of THEREDA (for the time being in german only).
Finally, thermodynamic data were entered. They comprise the system of oceanic salts as well as species and solid phase of a variety of radio-toxic and chemo-toxic ele-ments. This piece of work is on-going. At present, benchmark calculations are prepared. The first release of data will cover the system of oceanic salts (apart from C).

Keywords: THEREDA; thermodynamic reference database; repository; radioactive waste; equlibrium calculations; hydrogeochemical modelling

  • Other report
    Braunschweig: Gesellschaft für Reaktorsicherheit und Strahlenschutz (GRS) mbH, 2011
    876 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16381
Publ.-Id: 16381


A comparative glance into the HAVAR alloy by PAS and TEM methods

May-Tal Beck, S.; Anwand, W.; Wagner, A.; Harush, M.; Eisen, Y.; Beck, A.; Ocherashvili, A.; Hen, O.

The HAVAR alloy was originally developed in the late 1940. It is a high strength, nonmagnetic and corrosion resistant material. One of its applications is in the medical industry, in the process of fluorodeoxyglucose (FDG) production for Positron Emission Tomography (PET). The 18F positron emitting isotope is produced by the reaction 18O(p,n)18F in proton cyclotrons. In Soreq NRC, 25 µm foils of HAVAR are used as a window material for the 18O enriched water targets, contained in Al vessels. With the increasing demand for 18F-FDG, an accelerated production rate is planned, with much higher intense proton beam from the new SARAF accelerator at Soreq NRC [1]. This initiated a research effort to study radiation damage in HAVAR that can predict its radiation hardness in the ~2-4 mA SARAF proton beam.
We measured four 25 µm thick HAVAR samples: cold rolled (CR), cold rolled and heat treated (HT), annealed (AN) and CR irradiated (IR). The latter was a window taken apart from the target 7 years ago after irradiation in the cyclotron to 10MeV protons of total charge 1mA-h. The first three samples were metallurgically characterized by means of Transmission Electron Microscope (TEM). Positron Annihilation Spectroscopy (PAS) measurements were preformed on all four samples. These included Doppler Broadening (DB) and Positron Annihilation Lifetime ( PAL) measurements in the slow positron beam and in the table top lifetime spectrometer at HZDR [2]. We present preliminary results from these PAS measurements, that show clear differences between the four samples. Positron lifetimes of the HAVAR types change between ~80ps for the annealed sample to ~175ps for the irradiated sample. The positron diffusion length changes from (8 ± 1) nm (CR) to (66 ± 1) nm (AN) in these samples. We also compare between the metallurgical characteristics of the different types of HAVAR measured with TEM to PAS results. The PAS measurements show a clear increase of the mean lifetime with the increase of the density of dislocations in the CR sample compared to that of AN HAVAR foils.

[1] L. Weissman et al., "The Status of the SARAF Linac Project", WE102 in Proceedings of Linac 2010, Tsukuba, September 12-17, 2010
[2] W. Anwand, H. - R. Kissener, and G. Brauer, Acta Phys. Pol. A 88, 7 (1995).

Keywords: HAVAR alloy; PET; proton irradiation; defect characterization; Transmission Electron Microscopy; Positron Annihilation Spectroscopy

  • Lecture (Conference)
    Seventh International Workshop on Positron Studies of Defects (PSD-11), 28.08.-02.09.2011, Delft, Niederlande
  • Lecture (Conference)
    26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel

Permalink: https://www.hzdr.de/publications/Publ-16380
Publ.-Id: 16380


Intelligente Sensorpartikel zur Strömungsuntersuchung in Rührbehältern

Reinecke, S.; Pöpping, U.; Hampel, U.

Die räumliche Erfassung relevanter Prozessparameter wird bei einer Vielzahl industrieller Anwendungen durch den begrenzten Zugang zum Prozess erschwert. Beispiele sind Reaktoren mit Rührwerken, Bioreaktoren, Fermenter und Schüttgutbehälter. In solchen Behältern ist die Installation von fest angebrachten Sensoren und Kabelverbindungen oft nicht realisierbar oder unerwünscht. Zudem sind räumlich auflösende Apparate, wie Kameras oder Tomografiemesssysteme, meist nicht anwendbar. Daher bietet die Überwachung der räumlichen Verteilung relevanter Prozessparameter ein hohes Potential für die verbesserte Untersuchung und die Optimierung der Anlagen und Prozesse. Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde ein Konzept autonomer Sensorpartikel entwickelt und getestet. Das Messsystem beinhaltet mehrere autonome Sensorpartikel und eine Basiseinheit.

  • Poster
    10. Dresdner Sensor-Symposium, 05.-07.12.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16379
Publ.-Id: 16379


Defect induced ferromagnetism in 4H-SiC single crystals

Li, L.; Hua, W.; Prucnal, S.; Yao, S.; Shao, L.; Potzger, K.; Zhou, S.

We have demonstrated the feasibility of using ion irradiation to induce ferromagnetism in 4H-SiC. Upon Ne+ ion irradiation to a fluence of 5×1014 /cm2, ferromagnetism is observed up to room temperature, while the virgin sample only shows diamagnetism. Sample characterization by using both Rutherford backscattering/channeling spectrometry and Raman spectroscopy shows defect generation and the partial loss of crystalline structures by ion irradiation. With further increased fluences to reach complete amorphization in SiC, the magnetic moments are still observed. The defect-induced ferromagnetism is stable upon thermal annealing at 1400 °C.

Keywords: Ion irradiation; 4H-SiC; Defect; Ferromagnetism

Permalink: https://www.hzdr.de/publications/Publ-16378
Publ.-Id: 16378


Ultrafast full-angle volumetric X-ray tomography

Bieberle, M.; Stürzel, T.; Menz, H.-J.; Hampel, U.

Ultrafast electron beam X-ray computed tomography has seen considerable progress in the last few years. Beginning with a limited-angle approach, single-plane, dual-plane and multi-plane tomography arrangements have been studied. Based on these proofs of principle, a single-plane full-angle tomography system has been built up and was used to image and analyze various two-phase flow scenarios. Lately, the dual-plane tomography has also been realized as a full-angle setup, which is now able to measure phase distributions as well as velocity profiles within the object of interest.
Now, we present a full-angle volumetric X-ray computed tomography setup, which comprises eight circular X-ray source paths distributed on a vertically expanded target and one ring of 320 detector elements surrounding the target. The resulting reverse cone-beam geometry allows three-dimensional reconstruction of the imaged object volume using Feldkamp-type reconstruction algorithms. The electron beam is guided consecutively along all circular source paths, which takes 500 µs per path, while the detector elements simultaneously measure the X-ray projections with 1 MHz sampling rate. This results in 500 discrete source positions per revolution and a volume rate of 250 s-1.
The performance of the setup has been demonstrated in phantom as well as two-phase flow experiments, which revealed detailed structures and flow dynamics in 3-D.

Keywords: X-ray; computed tomography; ultrafast; 3-D

  • Contribution to proceedings
    6th International Symposium on Industrial Process Tomography (ISPT6), 26.-28.03.2012, Cape Town, South Africa
  • Poster
    6th International Symposium on Industrial Process Tomography (ISPT6), 26.-28.03.2012, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-16377
Publ.-Id: 16377


Study of exclusive one-pion and one-eta production using hadron and dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and 2.2 GeV with HADES

Agakishiev, G.; Alvarez-Pol, H.; Balanda, A.; Bassini, R.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krizek, F.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lapidus, K.; Liu, T.; Maier, L.; Markert, J.; Metag, V.; Michalska, B.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Toia, A.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

We present exclusive measurements of π+, π0 and ω production in pp reactions at 1.25 GeV and 2.2 GeV beam kinetic energy, in hadronic and dielectron channels. Using the former, high statistics invariant mass and angular distributions within the HADES acceptance are obtained for π+ and π0 exclusive production, as well as acceptance corrected distributions, which are compared to a resonance model. The sensitivity of the data to the Δ(1232) production angular distribution and to the contribution of higher lying baryon resonances is shown and an improved parameterization of the data is proposed. Cross sections are extracted especially in the case of pp->ppη at 2.2 GeV (σ=0.142 ± 0.022 mb) for which only old and controversial data existed. Using the dielectron channels, the π0 and η Dalitz decay signals could be reconstructed, with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance corrected helicity angle distributions are found in good agreement with model predictions.

Permalink: https://www.hzdr.de/publications/Publ-16376
Publ.-Id: 16376


Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy

Agakishiev, G.; Alvarez-Pol, H.; Balanda, A.; Bassini, R.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garz´On, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Hennino, T.; Holzmann, R.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krizek, F.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lapidus, K.; Liu, T.; Maier, L.; Markert, J.; Metag, V.; Michalska, B.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Schmah, A.; Schwab, E.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Toia, A.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Wisniowski, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

Data on inclusive dielectron production are presented for the reaction 2.2 GeV p + p measured with the High Acceptance DiElectron Spectrometer (HADES). Our results supplement data obtained formerly in this bombarding energy regime by DLS and HADES. The comparison with the DLS data for the reaction p + p at 2.09 GeV is shown. The reconstructed e+e− distributions are compared with a simulated pair cocktail, which points to an excess yield of invariant masses at around 0.5 GeV/c2. Inclusive cross sections of neutral pion and eta production are obtained as well.

Permalink: https://www.hzdr.de/publications/Publ-16375
Publ.-Id: 16375


Tailoring the magnetism of GaMnAs via defect engineering by energetic ions

Zhou, S.; Li, L.; Chen, L.; Rushforth, A. W.; Fassbender, J.; Helm, M.; Zhao, J.; Campion, R. P.; Gallagher, B. L.; Schmidt, H.

Ion irradiation of semiconductors is a well understood method to tune the carrier concentration in a controlled manner. For dilute magnetic semiconductors (DMS), the free carriers mediate the local magnetic moments and develop the long-range ferromagnetic coupling. Therefore, ion irradiation should provide a tool to engineer the magnetic properties of DMS. In this contribution, we show the possibility of fine tailoring the magnetism of highly conducting virgin GaMnAs films by ion irradiation. With increasing the displacement per atom (ion fluence), the GaMnAs films become more insulating step by step and only paramagnetic at the end. The coercivity can be increased by several times [1]. The approach can be used to tailor GaMnAs films with different coercivities, Curie temperatures (TC) as well as saturation magnetization. On the other hand one can use the approach to understand the conduction and magnetic coupling mechanism [2]. For relatively thick 25nm GaMnAs films with a high TC of 150 K [3] where the electrical gating is difficult due to the large hole concentration, ,we can decrease the hole concentration gradually. We found a linear dependence of Tc with increasing the compensation of holes by ion irradiation. This observation favours a valence band picture of ferromagnetic GaMnAs with high Mn concentrations.
1. L. Li, et al., J. Phys. D 44 099501 (2011);
2. T. E. Winkler, et al., Appl. Phys. Lett. 98, 012103 (2011).
3. Y. Nishitani, et al., Phys. Rev. B 81, 045208 (2010).

Keywords: Diluted magnetic semiconductor; GaMnAs; Ion irradiation

  • Poster
    6th International School and Conference on Spintronics and Quantum Information Technology (SPINTECH6), 01.-05.08.2011, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-16373
Publ.-Id: 16373


Ion implantation and short-time annealing for spintronics

Zhou, S.

Doping of semiconductors is an essential issue for device fabrication. Ion implantation followed by annealing is a well-established method to dope Si and Ge. This approach has been maturely integrated with the IC industry production line. Nowadays, the demands for functional spintronics/photovoltaic materials require a supersaturated doping of semiconductors. For instance, regarding spintronics applications one needs to prepare magnetic semiconductors which are doped with up to 5-10% Mn. As a non-equilibrium process, ion implantation can introduce enough dopants as required. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing in the millisecond or nanosecond regime allows the epitaxial growth from a liquid phase. Shallow dopants in Si and Ge, mainly the elements from the III or V columns of the periodic table, have been successfully built in by ion implantation and pulsed laser annealing [1]. The carrier concentration can reach values as high as 1021 cm-3. Such a platform combining ion implantation and short-time annealing has been established at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [2]. In this contribution, we will give an overview of the platform and particularly of its application in the preparation of Mn doped Ge [3, 4].

Reference:
[1] C. W. White, et al., J. Appl. Phys. 51, 738 (1980).
[2] W. Skorupa, et al., J. Electrochemical Soc. 152, G436 (2005).
[3] S. Zhou, et al., Phys. Rev. 81, 165204 (2010).
[4] S. Zhou, et al., Appl. Phys. Lett. 96, 202105 (2010).

  • Invited lecture (Conferences)
    Seminar at Univ. Jena, 30.06.2011, Jena, Germany
  • Lecture (Conference)
    Workshop „Ionen- und Positronenstrahlen“, 04.-05.07.2011, München, Germany

Permalink: https://www.hzdr.de/publications/Publ-16372
Publ.-Id: 16372


Ion implantation-induced defects in Oxide Dispersion Strengthened (ODS) steel probed by positron annihilation spectroscopy

Anwand, W.; Butterling, M.; Brauer, G.; Wagner, A.; Richter, A.; Chen, C.-L.; Kögler, R.

Oxide Dispersion Strengthened (ODS) steel is a promising candidate for an application in fission and fusion power plants of a new generation because of its advantageous properties as stability and temperature resistance. A microscopic understanding of the physical reasons of the mechanical and thermal properties as well as the behaviour of the material under irradiation is an important pre-condition for such applications. The investigated ODS FeCrAl alloy “PM2000” has been produced in a powder metallurgical way by means of hot isostatic pressing and hot rolling. Neutron-induced damage at ODS steel was simulated by He+ and Fe2+ co-implantation with energies of 2.5 MeV and 400 keV, respectively, and different fluences. The implantation has been carried out with a dual ion beam which enables a simultaneous implantation of both ion types. Thereby the Fe2+ implantation was used for the creation of radiation defects, and He+ was implanted in order to reproduce He bubbles as they are expected to appear by neutron irradiation. The implantation-induced damage was investigated by depth dependent Doppler broadening (DB) measurements using a variable energy slow positron beam. In addition, as-received, deformed and annealed ODS samples were characterized by DB and positron lifetime measurements for comparison.

Keywords: ODS steel; irradiation-induced damage; simultaneous He and Fe implantation; positron annihilation

  • Lecture (Conference)
    Workshop "Ionen- und Positronenstrahlen", 04.-05.07.2011, München/Neubiberg, Deutschland
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16371
Publ.-Id: 16371


Ion irradiation as a controllable approach to study the defect-induced ferromagnetism

Zhou, S.; Potzger, K.; Yang, Z.; Helm, M.; Fassbender, J.

Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators, including TiO2 [1] and ZnO [2-5] (see a review by Coey et al. [6]). This kind of observation challenges the conventional understanding of ferromagnetism, which is rather due to spin-split states or bands. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accidence or by mistake. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in TiO2 [1] and SiC [7]. The saturation magnetization rises and falls with increasing the ion fluence due to the interplay between the amount of defects and the crystalline quality. Using electron spin resonance and positron annihilation spectroscopies, one can determine where the unpaired electrons are located and the concentration of defects. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

Reference:
[1] S. Zhou, et al., Phys. Rev. B 79, 113201 (2009).
[2] S. Zhou, et al., J. Phys. D 41, 105011 (2008).
[3] K. Potzger, et al., Appl. Phys. Lett. 92, 182504 (2008).
[4] S. Zhou, et al., Appl. Phys. Lett. 93, 232507 (2008).
[5] Q. Xu, et al., Appl. Phys. Lett. 92, 082508 (2008).
[6] J. M. D. Coey, et al., New J. Phys. 12, 053025 (2010).
[7] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).

  • Invited lecture (Conferences)
    China-Germany Symposium on "Electronic structure calculations and their application in material science", 08.-11.11.2011, Chengdu, China
  • Poster
    The 56th Magnetism and Magnetic Materials Conference, 30.10.-03.11.2011, Phoenix / Scottsdale, USA
  • Invited lecture (Conferences)
    Invited seminar at the Institute of Solid State Physics, Chinese Academy of Sciences, 13.10.2011, Hefei, China

Permalink: https://www.hzdr.de/publications/Publ-16370
Publ.-Id: 16370


EXAFS and DFT Investigations of Uranyl-Arsenate Complexes in Aqueous Solution

Gezahegne, W. A.; Hennig, C.; Tsushima, S.; Planer-Friedrich, B.; Scheinost, A. C.; Merkel, B. J.

Uranium and arsenic often co-occur in nature, for example, in acid mine drainage waters. Interaction with arsenic is thus important to understand uranium mobility in aqueous solutions. For the present study, EXAFS spectroscopy was used to investigate the formation and identify the structure of aqueous uranyl arsenate species at pH 2. The nearest U−As distance of 3.39 Å, observed in shock-frozen liquid samples, was significantly shorter than that observed in solid uranyl arsenate minerals. The shorter bond length indicated that the solution contained a bidentate-coordinated species, in contrast to the monodentate coordination in solid uranyl arsenate minerals. The U−As coordination number of 1.6 implied that two uranyl arsenate species with U:As ratios of 1:1 and 1:2 formed in nearly equal proportions and that the hydrated uranyl ion was present only as a minor component. The two uranyl arsenate species could not be differentiated spectroscopically, since their U−As distances were equal. A comparison based on DFT modeling indicated for both the 1:1 and the 1:2 species, that the bidentate arsenates were bound to uranium with one of the binding oxygen atoms being protonated. Based on the present spectroscopic study, the two species that will have to be considered in acidic uranium−arsenic-rich solutions are thus
UO2H2AsO4 +, and UO2(H2AsO4)2 0.

Permalink: https://www.hzdr.de/publications/Publ-16369
Publ.-Id: 16369


Identification of defect properties by positron annihilation in Te-doped GaAs after Cu in-diffusion

Elsayed, M.; Krause-Rehberg, R.; Anwand, W.; Butterling, M.; Korff, B.

Positron lifetime measurements and Doppler-broadening spectroscopy were combined to investigate the defect properties during Cu diffusion in Te-doped GaAs. The diffusion of Cu was performed during an annealing step at 1100°C under two different arsenic vapor pressures. The samples were quenched into room temperature water. During a subsequent isochronal annealing experiment, it was found that vacancy clusters were generated and grown, and finally they disappeared. The lifetime results show that, in addition to deep positron traps of vacancy type, positron trapping with a lifetime close to the bulk value of 228 ps occurs. The positron lifetime results give direct evidence of positron localization at shallow traps in GaAs:Te. Due to the Cu contamination during the annealing process, the shallow trap is believed to be the Cu2− Ga double acceptor. The concentration of shallow traps is determined and found to be in good agreement with the concentration determined by Hall measurement. It decreases up to saturation with increasing annealing. The positron binding energy to these negative nonopen volume trap centers is determined to be 79 meV. It is found to be in agreement with the calculated value.Moreover, coincidence Doppler-broadening spectroscopy shows clearly that Cu atoms are bound in the direct vicinity of the observed vacancy-like defects. Theoretical calculations of momentum distribution predicted that one Cu atom incorporated into a Ga site surrounds the observed open-volume defects.

Keywords: positron lifetime and Doppler broadening spectroscopy; Te-doped GaAs; Cu diffusion; defect properties

Permalink: https://www.hzdr.de/publications/Publ-16368
Publ.-Id: 16368


Magneto-optical coupling in ferromagnetic thin films investigated by VMOGE

Mok, K. M.; Scarlat, C.; Kovacs, G. J.; Li, L.; Zviagin, V.; McCord, J.; Helm, M.; Schmidt, H.

We investigated the magneto-optical coupling in ferromagnetic thin films (Fe, Ni20Fe80, Co, Ni80Fe20, Ni) in the spectral range from 300 to 1100 nm. We performed Mueller matrix ellipsometry measurements in a magnetic field of arbitrary orientation and magnitude up to 400 mT at room temperature with a set-up vector-magneto-optical generalized ellipsometer (VMOGE). We extracted the magneto-optical dielectric tensor of the ferromagnetic thin films under saturated in-plane magnetization conditions. The off-diagonal elements of the magneto-optical dielectric tensor depend on the net spin polarization and the electronic band structure of the magnetized material. For ferromagnetic Fe, Co, and Ni, the converted magneto-optical dielectric tensor agrees well with reported experimental optical conductivity data. With additional measurements on the magnetization of the ferromagnetic thin films, we extracted the magnetic field independent magneto-optical coupling constant Q, which is a useful parameter for characterization of magneto-optical materials.
Reference: K. Mok et al., Phys. Rev. B 84, 094413 (2011)

Keywords: Mueller matrix; generalized ellipsometry; ferromagnet

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Germany
  • Lecture (Conference)
    7th Workshop Ellipsometry, 05.-07.03.2012, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-16367
Publ.-Id: 16367


Magneto-optical dielectric tensor of Co, Fe, Ni, and of NiFe alloys under saturated magnetization conditions

Mok, K. M.; Du, N.; Schmidt, H.

Magneto-optical generalized ellipsometry (MOGE) has become extensively important for characterization the magneto-optical response of single and multilayer materials. We setup a Vector-Magneto-Optical Generalized Ellipsometer (VMOGE) in the spectral range from 250 nm to 1100 nm using an octupole magnet, to perform VMOGE measurements of the Mueller matrix in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. The VMOGE features a new "field orbit" measurement that can be performed without physically moving the sample, which is useful to study magnetic multilayer or nanostructure samples. An optical model based on the 4 x 4 matrix formalism is required to evaluate and fit the experimental Mueller matrix data. Searching the best match model between experimental and calculated VMOGE data, the magneto-optical dielectric tensor of each layer in a multilayer sample system can be determined. In this work, we investigate the magneto-optical properties of the elemental ferromagnets Co, Fe, and Ni, as well as of NiFe alloys. We extracted the wavelength dependence of the magneto-optical dielectric tensor under saturated magnetization conditions.

Keywords: Mueller matrix; generalized ellipsometry; ferromagnet

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.03.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16366
Publ.-Id: 16366


Extension of the wall boiling model by using the MUSIG approach

Krepper, E.; Rzehak, R.

The report describes the capabilities of CFD simulatin wall boiling coupled with a population balance model. For the demonstration DEBORA tests were used. Instead of water at high pressure in the DEBORA tests Dichlorodifluoromethane (R12) was used as the working fluid. Similar conditions in terms of the relevant non-dimensional numbers have been realized. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size.
Essential for the momentum, mass and energy exchange between the phases is an adequate description of the interfacial area or respectively the bubble size. In the present work a population balance approach coupled to a wall boiling model is used, where bubbles are generated at the wall with a certain size that subsequently evolves due to both condensation / evaporation and coalescence / fragmentation processes. The paper shows the potential of this approach which is able to describe the observed bubble size increase caused by bubble coalescence after leaving the wall as well as the change of gas fraction profile from wall to core peaking with increasing inlet temperature respective decreasing liquid subcooling and consequently enhanced vapour generation.

Keywords: CFD; two-phase flow; wall boiling; population balance models; MUSIG

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2011
    HZDR\FWS\2011\08
    33 Seiten
    ISSN: 1437-322X

Permalink: https://www.hzdr.de/publications/Publ-16365
Publ.-Id: 16365


Decomposition kinetics in Ti1-xAlxN coatings as studied by in-situ X-ray diffraction during annealing

Wüstefeld, C.; Rafaja, D.; Dopita, M.; Motylenko, M.; Baehtz, C.; Michotte, C.; Kathrein, M.

The influence of the microstructure of the as-deposited cathodic arc evaporated Ti1-xAlxN coatings and, in particular, the influence of the intrinsic lattice strains on their thermal stability were investigated by insitu synchrotron high temperature glancing angle X-ray diffraction (HT-GAXRD) experiments up to 850 °C. The microstructure of the as-deposited coatings was adjusted by the bias voltage (UB=−40 V, UB=−80 V and UB=−120 V) and by the [Al]/([Ti]+[Al]) ratio (0.4, 0.5 and 0.6) of the used Ti–Al targets. The microstructure evolution during annealing was described in terms of the phase composition of the coatings, the aluminium content, aluminium distribution and residual lattice strains in fcc-(Ti,Al)N. Independent of the deposition parameters ([Al]/([Ti]+[Al]) ratio and bias voltage), all coatings contained a mixture of fcc-(Ti, Al)N, fcc-AlN and w-AlN after annealing at 850 °C. The [Al]/([Ti]+[Al]) ratio was found to control the amount of fcc-(Ti,Al)N, whereas the bias voltage was mainly responsible for the relative amount of fcc-AlN and w- AlN. Finally, the interplay between lattice strains and the kinetics of the spinodal decomposition of fcc-(Ti, Al)N was illustrated.

Keywords: Ti–Al–N Cathodic arc evaporation Thermal stability Microstructure X-ray diffraction Bias voltage

Permalink: https://www.hzdr.de/publications/Publ-16364
Publ.-Id: 16364


In Situ Characterization of Alloy Catalysts for Low-Temperature Graphene Growth

Weatherup, R. S.; Bayer, B. C.; Blume, R.; Ducati, C.; Baehtz, C.; Schlögl, R.; Hofmann, S.

Low-temperature (∼450 °C), scalable chemical vapor deposition of predominantly monolayer (74%) graphene films with an average D/G peak ratio of 0.24 and domain sizes in excess of 220 μm2 is demonstrated via the design of alloy catalysts. The admixture of Au to polycrystalline Ni allows a controlled decrease in graphene nucleation density, highlighting the role of step edges. In situ, time-, and depthresolved X-ray photoelectron spectroscopy and X-ray diffraction reveal the role of subsurface C species and allow a coherent model for graphene formation to be devised.

Keywords: Graphene; chemical vapor deposition (CVD); alloy catalyst; in situ metrology; XPS; XRD

Permalink: https://www.hzdr.de/publications/Publ-16363
Publ.-Id: 16363


Influence of high permeability disks in an axisymmetric model of the Cadarache dynamo experiment

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

Numerical simulations of the kinematic induction equation are performed on a model configuration of the Cadarache von-K\'arm\'an-Sodium dynamo experiment. The effect of a localized axisymmetric distribution of relative permeability mur that represents soft iron material within the conducting fluid flow is investigated. The critical magnetic Reynolds number Rmc for dynamo action of the first non-axisymmetric mode roughly scales like Rmc μ-Rmc ∝ μr -1/2 i.e. the threshold decreases as μr increases. This scaling law suggests a skin effect mechanism in the soft iron disks. More important with regard to the Cadarache dynamo experiment, we observe a purely toroidal axisymmetric mode localized in the high permeability disks which becomes dominant for large μr.
In this limit, the toroidal mode is close to the onset of dynamo action with a (negative) growth-rate that is rather independent of the magnetic Reynolds number. We qualitatively explain this effect by paramagnetic pumping at the fluid/disk interface and propose a simplified model that quantitatively reproduces numerical results.
The decise role of the high permeability disks for the mode selection in the Cadarache dynamo experiment cannot be inferred from computations using idealized pseudo-vacuum boundary conditions (H ✕ n =0).

Keywords: dynamo; VKS; permeability; soft iron

Permalink: https://www.hzdr.de/publications/Publ-16362
Publ.-Id: 16362


Synthese und In-vitro-Charakterisierung neuer Aminobenzovesamicol-Analoga als potentielle Liganden für den vesikulären Acetylcholintransporter im Gehirn

Barthel, C.

  • Thesis / Students' report
    Hochschule Zittau/Görlitz, Fakultät Mathematik/Naturwissenschaften, Fachgruppe Chemie, 2011
    78 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16361
Publ.-Id: 16361


Radiosynthesis, In Vitro and In Vivo Evaluation of a 6-(2-[18F]Fluoroethoxy)-7-methoxy-pyrrolidinylquinazoline for PET Imaging of Phosphodiesterase 10A in Brain

Funke, U.; Deuther-Conrad, W.; Barbar Asskar, G.; Scheunemann, M.; Fischer, S.; Hiller, A.; Briel, D.; Brust, P.

1. Introduction

Phosphodiesterase 10A (PDE10A) is a key enzyme that mediates neural signal transduction by regulating intracellular concentration of the cyclic nucleotides adenosine (cAMP) and guanosine monophosphate (cGMP) and is mainly present in brain. Particularly high PDE10A expression and activity was observed in brain regions of dopaminergic and GABAergic neurotransmission. As these relations are not fully understood and PDE10A hypofunction is supposed to correlate with neuropsychiatric disorders such as schizophrenia, obsessive-compulsive disorders, Parkinson’s disease, and Huntington’s disease, there is an ongoing interest in PDE10A as target for molecular imaging by PET.
For the pharmacological treatment of schizophrenia, a highly PDE10A inhibiting, selective and brain penetrable 6,7-dimethoxy-4-pyrrolidinylquinazoline has been designed (Ki=4 nM [1]). Based on this structure we developed fluorine-18 labeled derivatives as potential PET radiotracers for imaging PDE10A in brain [2]. Herein we report on the radiosynthesis and radiotracer properties of the 6-[18F]fluoroethoxy derivative [18F]2 (Figure 1).

2. Materials & Methods

The non-radioactive reference compound 2 and the 7-tosyloxy precursor 1 were prepared in multi-step syntheses, and 2 was screened for its PDE10A inhibitory potency (Ki=32 nM) as well as selectivity in enzyme activity studies [2]. The automated radiosynthesis of [18F]2 was carried out on a TRACERlabTM FX F-N synthesizer. Aqueous n.c.a. [18F]Fluoride was transferred to MeCN via a Chromafix® 30-PS-HCO3 cartridge, dried azeotropically and converted to its K[18F]F-K2.2.2-carbonate complex. Nucleophilic 18F-for-OTs substitution was performed with ~2 mg of 1 in 750 µL MeCN at 85°C within 15 min. Purification of [18F]2 was carried out by SPE (SepPak®Plus C-18, MeCN), followed by semi-preparative RP-HPLC (e.g. on ReproSil-Pur® C18 AQ, 7 µm; 5010 + 15010 mm, 42% MeCN, 20 mM NH4OAc, 4 mL/min; tR=30.3 min). Formulation of [18F]2 was done by SPE, removal of organic eluent and dissolution in physiological saline.
Radioligand stability (EtOH, MeCN, physiological saline and phosphate buffer solution, 40 and 80°C, 5-120 min) and lipophilicity (logD7.0-7.4, shake-flask) were determined. Further characterization in vitro of [18F]2 included the determination of stability in rat plasma (37°C, 30 and 60 min), PDE10A affinity (KD, PDE10A transfected SF21 cells) and autoradiographic imaging of sagittal female rat brain slices, incubated with [18F]2 alone, together with 2 or highly PDE10A-specific MP-10, respectively. Evaluation in vivo of [18F]2 in female CD-1 mice was carried out by the determination of biodistribution and brain uptake as well as metabolism studies and ex vivo brain autoradiography, with validation of specificity by pre-treatment with MP-10 (1mg/kg at 15 min before radiotracer).

Figure 1. Radiosynthesis of [18F]2 and its binding at a sagittal rat brain slice in vitro.


3. Results

Radiosynthesis of [18F]2 resulted in labeling efficiencies of 76-94%, a radiochemical yield of 41.210.3% (n=6, 2 h, based on [18F]F-), a radiochemical purity of ≥99% and specific activities of 80-1030 GBq/mol. [18F]2 remained stable during heating in organic solvents (97% of [18F]2, 120 min, 80°C), and showed moderate stability in aqueous buffer solutions (95% of [18F]2, 60 min, 40°C) and rat plasma (94% of [18F]2, 60 min, 37°C). A logD7.0-7.4 of ~2.5, was determined, and by homologous competition a KD of 24 nM (n=2) was estimated. By autoradiography in vitro, a heterogeneous distribution of [18F]2 in rat brain was observed (Figure 1), which was partially inhibited by MP-10. Biodistribution studies revealed an initial brain uptake of 1.6%ID/g at 5 min p.i.. Striatal uptake at 60 min p.i. was not inhibited by MP-10, which was confirmed by ex vivo autoradiography. Only 41%, 64% and 20% of the radioactivity measured in plasma, brain and liver, respectively, at 30 min p.i. corresponded to parent radioligand. An evidence for slight defluorination was observed because in femur uptake values increased by 25% at 60 min p.i. after removal of the bone marrow.

4. Discussion/Conclusion

A convenient radiosynthesis and satisfactory radiochemical results, as well as moderate lipophilicity and PDE10A affinity initially indicated [18F]2 to be a suitable radiotracer. However, the heterogeneous but non-displaceable binding of [18F]2 in vitro provides evidence for binding affinity to another target. Reasonable high uptake of [18F]2 in mice brain was found, which was non-specific and non-selective. The radioligand stability in vivo is comparably low and the presence of brain metabolites is inappropriate for molecular imaging.
In conclusion, a structural revision of our pharmaceutical lead is needed to improve the in vivo properties and to develop an applicable radiotracer for neuroimaging of PDE10A with PET.

Research Support: European Regional Development Fund (ERDF).

References: [1] Chappie TA, Humphrey JM, Allen MP et al. [2007] J.Med.Chem. 50: 182-185.
[2] Nieber K, Erdmann S, Briel D et al. [2010] Patent Appl. P1014WO.

  • Poster
    ESRR 2012 - 16th European Symposium on Radiopharmacy and Radiopharmaceuticals, 26.-29.04.2012, Nantes, France

Permalink: https://www.hzdr.de/publications/Publ-16360
Publ.-Id: 16360


Implementation of microbial processes in the performance assessment of spent nuclear fuel repositories

Behrends, T.; Krawczyk-Bärsch, E.; Arnold, T.

Present strategies for the long-term disposal of high-level nuclear wastes are based on the construction of repositories hundreds of meters below the earth surface. Although the surrounding host-rocks are relatively isolated from the light at the earth surface they are by no means lifeless. Microorganisms rule the deep part of the biosphere and it is well established that their activity can alter chemical and physical properties of these environments. Microbial processes can directly and indirectly affect radionuclide migration in multiple ways. Within 6th FP IP FUNMIG the interplay between microbial biofilms and radionuclides and the effect of microbially induced redox transformations of iron on radionuclide mobility have been investigated. For the first time, formation of U(V) as a consequence of microbial U(VI) reduction in a multi-species biofilm was detected in vivo by combining laser fluorescence spectroscopy and confocal laser scanning microscopy. Furthermore, it was demonstrated that addition of U(VI) can lead to increased respiratory activity in a biofilm. Increased respiration in a biofilm can create microenvironments with lower redox potential, and hence induce reduction of radionuclides. Transient mobilisation of uranium was observed in experiments with iron oxides containing adsorbed U(VI) in which the activity of sulphate reducing organisms was mimicked by sulphide addition. Faster reaction of sulphide with iron oxides compared to U(VI) reduction, and decreasing U(VI) adsorption due to the transformation of iron oxides into FeS can explain the observed intermittent U mobilisation. The presented research on microbe-radionuclide interactions performed within FUNMIG addresses only a few aspects of the potential role of microorganisms in the performance assessment of nuclear waste repositories. For this reason, this article provides additionally a cursory overview of microbial processes which were not studied within the FUNMIG project but are relevant in the context of performance assessment. Following aspects are presented: a) the occurrence and metabolic activity of microorganisms of several proposed types of host-rocks b) the potential importance of microorganisms in the near-field of nuclear waste repositories, c) indirect effects of microbial processes on radionuclide mobility in the repository far-field, d) binding of radionuclides to microbial biomass, e) microbial redox transformations of radionuclides, and f) the implementation of microbial processes in reactive transport models for radionuclide migration.

Keywords: microbial processes; radionuclides; repositories

Permalink: https://www.hzdr.de/publications/Publ-16359
Publ.-Id: 16359


Anomalous hysteretic Hall effect in a ferromagnetic, Mn-rich, amorphous Ge:Mn nano-network

Bürger, D.; Zhou, S.; Höwler, M.; Ou, X.; Kovacs, G.; Reuther, H.; Mücklich, A.; Skorupa, W.; Helm, M.; Schmidt, H.

The read out of the magnetization state in magnetic semiconductors by electrical Hall resistance measurements makes it possible to use ferromagnetic semiconductors in nonvolatile memories. In a previous work [1], we fabricated ferromagnetic Ge:Mn by Mn ion implantation and pulsed laser annealing (PLA) and observed hysteretic Hall resistance below 10 K. By applying different PLA conditions we fabricated a percolating, Mn-rich, amorphous Ge:Mn nano-network with hysteretic Hall resistance up to 30K. This nano-network is embedded in crystalline Ge:Mn between 5 nm and 40 nm under the sample surface.
We applied chemical and physical etching to confirm the contribution of the nano-network to the magnetic properties. The nano-network has a significant influence on the correlation between magnetism and anomalous Hall resistance. In the future such nano-networks may be used to spin-polarize free charge carriers in semiconductors at room temperature.
[1] S. Zhou et al., Phys. Rev. B 81, 165204 (2010)

Keywords: percolation; anomalous Hall effect; ferromagnetic semiconductors; pulsed laser annealing

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Deutschland
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16357
Publ.-Id: 16357


Table-top supercomputers for not-quite-table-top radiation source

Bussmann, M.

Laser-driven sources of proton, electron and x-ray beams can provide for new insights into the dynamics of matter on the picosecond to femtosecond time scale. However, for real-world applications such as tumor therapy with laser-driven ion beams or material probing with X-ray Thomson scattering sources our understanding and control of beam properties has to improved. In my talk I will show how modern supercomputing hardware such as GPUs can help us find optimum scenarios for laser-driven radiation sources. Besides showing pretty movies I will focus on the challenges of modern laser plasma simulations and possible ways to overcome them. The talk will conclude with two examples that explore laser matter interaction which illustrate why a pen, some paper and a lot of thinking are always better than all hardware you can possibly buy.

Keywords: laser acceleration; gpu; simulation

  • Lecture (others)
    Trident Seminar, 27.10.2011, Los Alamos, NM, United States of America
  • Lecture (others)
    Seminar Materials Division, 25.10.2011, Livermore, CA, United States of America

Permalink: https://www.hzdr.de/publications/Publ-16356
Publ.-Id: 16356


A scalable implementation of the Particle-in-Cell Algorithm on GPU Clusters

Bussmann, M.; Burau, H.; Widera, R.; Berninger, F.; Hübl, A.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Hönig, W.; Juckeland, G.; Nagel, W.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.; Ragan-Kelley, B.; Verboncoeur, J.

We present PIConGPU, an implementation of the particle-in-cell algorithm for relativistic laser-plasma interactions. PIConGPU is currently used to simulate laser-wakefield acceleration of electrons as a model for strongly anisotropic many-particle systems. We discuss caveats when porting the particle-in-cell algorithm to GPUs and lessons learned from extending the code from a single-GPU version to a multiple-GPU version.

Keywords: pic; particle-in-cell; simulation; gpu

  • Lecture (Conference)
    Workshop Programming of Heterogeneous Systems in Physics, 05.-07.10.2011, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16355
Publ.-Id: 16355


The speciation of curium(III) bound by the Mont Terri opalinus clay isolate Sporomusa sp. and to the Äspö strain Pseudomonas fluorescens

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

It is known that microorganisms exist in host rocks of potential nuclear waste disposals. In this talk, some results will be presented from the current project about the microbial diversity in clay (opalinus clay) and the interactions of dominant microorganisms with actinides. Especially the interactions of two bacteria a Sporomusa sp. clay isolate and a Äspö strain P. fluorescens with curium(III) will be shown and discussed

Keywords: curium(III); TRLFS; bacteria; speciation

  • Lecture (others)
    12. Koordinierungsgespräch HZDR - PSI/LES, 08.-09.12.2011, Paul Scherrer Institut (PSI), Villingen, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-16354
Publ.-Id: 16354


Messung und Simulationen anisotroper Diffusion in Opalinuston

Schikora, J.; Joseph, C.; Kulenkampff, J.; Brendler, V.; Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    PSI-Meeting, 08.-09.12.2011, Villigen, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-16353
Publ.-Id: 16353


Spectral properties of oscillatory and non-oscillatory α2-dynamos.

Giesecke, A.; Stefani, F.; Gerbeth, G.

The eigenvalues and eigenfunctions of a linear α2-dynamo have been computed for different spatial distributions of an isotropic α-effect. Oscillatory solutions are obtained when α exhibits a sign change in the radial direction. The time-dependent solutions arise at so called exceptional points where two stationary modes merge and continue as an oscillatory eigenfunction with conjugate complex eigenvalues. The close proximity of oscillatory and non-oscillatory solutions may serve as the basic ingredient for reversal models that describe abrupt polarity switches of a dipole induced by noise.

Whereas the presence of an inner core with different magnetic diffusivity has remarkable little impact on the character of the dominating dynamo eigenmodes, the introduction of equatorial symmetry breaking considerably changes the geometric character of the solutions. Around the dynamo threshold the leading modes correspond to hemispherical dynamos even when the symmetry breaking is small. This behavior can be explained by the approximate dipole-quadrupole degeneration for the unperturbed problem.

More complicated scenarios may occur in case of more realistic anisotropies of α- and β-effect or through non-linearities caused by the backreaction of the magnetic field (magnetic quenching).

Keywords: dynamo; alpha-effect; mean-field theory; reversal

Permalink: https://www.hzdr.de/publications/Publ-16352
Publ.-Id: 16352


Ionenenergieverteilung während der ZnO-Abscheidung durch Magnetronsputtern: keramisches vs. metallisches Target

Wilde, C.

ad hoc short-notice report. No abstract was necassary

Keywords: ion energy distribution; sputtering; magnetron; mass spectrometry; TCO; AZO

  • Lecture (Conference)
    Transparente leitfähige Oxide - Festkörperphysikalische Grundlagen und Technologie, 16.-17.05.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16351
Publ.-Id: 16351


DC magnetron sputtering of ZnO:Al from metallic and reduced ceramic targets: comparison of ion energy distributions

Wilde, C.; Vinnichenko, M.

Magnetron sputtering is a common technique for deposition of transparent conductive oxides (TCO) such as Al-doped ZnO (AZO). The film growth using either metallic (reactively) or reduced ceramic targets often show different properties and morphology even in case of optimized processes. Therefore it is crucial to understand differences in magnetron plasma leading to such variations of properties.

The energy of ions emitted from the target in these processes is important, because it influences nucleation and the quality of the TCO.
The negative ions with energies high enough to damage the growing film are of special interest.

In this contribution we report results of comparative analysis of ion energy distributions in a broad energy range for DC magnetron sputtering using metallic and ceramic targets. The energy distributions
of low-energy ions show a similar behaviour for both processes, while in case of high-energy negative ions and fragments of them, they are substantially different . Moreover, magnetron plasma in case of metallic target sputtering shows substantially lower fraction of negatively charged ions with high energy. The observed differences indicate the potential of reactive magnetron sputtering to produce AZO films with less damage, and as a result, with improved properties.

Keywords: Sputtering; Magnetron; Ion Energy Distribution; TCO; mass spectrometry

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16350
Publ.-Id: 16350


Fluence calculation and activity determination at the reactor pressure vessel and their Support of VVER reactors

Konheiser, J.; Borodkin, G.; Borodkin, P.

In the first part, Niobium, nickel and technetium isotopes from RPV trepans of the decommissioned NPP Greifswald (VVER-440) have been analyzed. The activities were determined by TRAMO (Monte-Carlo) fluence. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.43 and 0.97. Up to 20 to 40% lesser fluences have been computed for Nickel and Technetium. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.
In the second part, VVER reactor support structures (RSS) and reactor pressure vessel (RPV) welds should be undergone the neutron dosimetry analysis to understand their status of criticality relatively a problem of reactor equipment integrity. DORT synthesis and TRAMO Monte Carlo neutron transport calculations were used for fast neutron fluence rates and reaction rates evaluations. Neutron activation measurements by iron foils in ex-vessel cavity near RPV and RSS points of interest are used for testing calculation results. The study has shown that neutron load parameters of RSS and RPV may be enough reason to require the analyses of the resistance against the brittle fracture of these components.

Keywords: activation; Niobium; nickel; technetium; reactor dosimetry; support structures; VVER-440; VVER-1000

  • Lecture (Conference)
    11. AAA Usergroup Meeting, 05.12.2011, Garching bei München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16349
Publ.-Id: 16349


Dose Controlled Radiobiological Experiments with Ultra-short Pulse Laser Accelerated Proton Pulses - and the future of the Dresden laser lab

Schramm, U.

Kolloquiumsvortrag

  • Lecture (others)
    MLL Kolloquium der TU und LMU München, 01.12.2011, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16348
Publ.-Id: 16348


Spectroscopic investigation of the interaction between uranium(VI) and schiff bases

Lindner, K.; Günther, A.; Bernhard, G.

Presentation of the complexation of Uranium(VI) with selected Schiff bases in methanol investigated by UV/Vis spectroscopy and ATR FT-IR spectroscopy.

Keywords: Uranium(VI); Schiff bases; UV/Vis; ATR FT-IR

  • Poster
    Doktorandenseminar - Kompetenzzentrum Ost für Kerntechnik, 08.12.2011, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16347
Publ.-Id: 16347


The Influence of Temperature and Clay Organics on the Retention Behavior of Opalinus Clay concerning Radionuclides

Schott, J.; Schmeide, K.; Acker, M.; Barkleit, A.; Brendler, V.; Bernhard, G.

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. The sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of this process is essential. Opalinus Clay (OPA) is a complex composed argillaceous rock. This natural occurring clay rock is discussed as host rock formation for nuclear waste repositories. In a repository based on argillaceous rock an initial temperature of around 100°C is expected. But although elevated temperatures are able to influence the sorption behaviour of radionuclides on mineral phases the temperature effect is still investigated insufficiently. Due to the fact that natural organic matter was found in the OPA the influence of organic matter on the radionuclide sorption hast to be investigated. The investigations concentrated on the sorption of Eu(III) and U(VI) on OPA under realistic OPA pore water conditions (OPA pore water medium, pH 7.6, I = 0.4 mol•L-1) up to 50°C. In addition to the temperature dependent investigations the influence of small organic molecules (e.g. lactate, acetate, propionate, tartrate, citrate) on the Eu(III) and U(VI) sorption on OPA was studied up to 50°C.
The Eu(III) sorption is characterized by a strong binding of Eu(III) and the U(VI) sorption is characterized by a weak binding of U(VI) to the clay surface. A significant temperature dependency for the Eu(III) and U(VI) sorption was observed. In the presence of the organic matter the Eu(III) and U(VI) sorption decreases with rising ligand concentration due to a complexation of the metal ions by the ligands in solution. The mobilization of Eu(III) and U(VI) correlates with the complex formation strength of the organic ligands.

Keywords: sorption; Eu(III); U(VI); Opalinus Clay; temperature; organics

  • Lecture (Conference)
    12. Koordinierungsgespräch HZDR-PSI/LES, 08.-09.12.2011, Villigen, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-16346
Publ.-Id: 16346


Photon scattering by nuclei

Grosse, E.; Junghans, A. R.

Most information about the micro-world has been obtained by light microscopy, i.e. observations with photons and our knowledge about the structure of atoms and molecules mainly originates from electromagnetic spectroscopy.

  • Book chapter
    H. Schopper: Landolt-Börnstein - Numerical Data and Funktional Relationships in Science and Technology, Vol. I /25D, Berlin: Springer, 2013, 4-39

Permalink: https://www.hzdr.de/publications/Publ-16345
Publ.-Id: 16345


Description of dipole strength in heavy nuclei in conformity with their quadrupole degrees of freedom

Grosse, E.; Junghans, A. R.; Massarczyk, R.; Schwengner, R.; Schramm, G.

In conformity to new findings about the widespread occurrence of triaxiality arguments are given in favor of a description of the giant dipole resonance in heavy nuclei by the sum of three Lorentzians. This TLO parameterization allows a strict use of resonance widths {\Gamma} in accordance to the theoretically founded power law relation to the resonance energy. No additional variation of {\Gamma} with the photon energy and no violation of the sum rule are necessary to obtain a good agreement to nuclear photo-effect, photon scattering and radiative capture data. Photon strength other than E1 has a small effect, but the influence of the level density on photon emission probabilities needs further investigation.

  • Open Access Logo Contribution to proceedings
    Third International Workshop on Compound Nuclear Reactions and Related Topics, 19.-23.09.2011, Prague, Czech Republic
    EPJ Web of Conferences 21 (2012) 04003

Permalink: https://www.hzdr.de/publications/Publ-16344
Publ.-Id: 16344


Rare-earth plasma extreme ultraviolet sources at 6.5-6.7 nm

Otsuka, T.; Kilbane, D.; White, J.; Higashiguchi, T.; Yugami, N.; Yatagai, T.; Jiang, W.; Endo, A.; Dunne, P.; O'Sullivan, G.

We have demonstrated a laser-produced plasma extreme ultraviolet source operating in the 6.5-6.7 nm region based on rare-earth targets of Gd and Tb coupled with a Mo/B4C multilayer mirror. Multiply charged ions produce strong resonance emission lines, which combine to yield an intense unresolved transition array. The spectra of these resonant lines around 6.7 nm (in-band: 6.7 nm +/-1%) suggest that the in-band emission increases with increased plasma volume by suppressing the plasma hydrodynamic expansion loss at an electron temperature of about 50 eV, resulting in maximized emission.

Permalink: https://www.hzdr.de/publications/Publ-16343
Publ.-Id: 16343


In-Medium Modifications of Scalar Charm Mesons in Nuclear Matter

Hilger, T.; Kaempfer, B.

Employing QCD sum rules the in-medium modifications of scalar charm mesons in a cold nuclear matter environment are estimated. The mass splitting of D* - (D) over bar* is quantified.

Permalink: https://www.hzdr.de/publications/Publ-16342
Publ.-Id: 16342


Determination of 41Ca with LSC and AMS: method development, modifications and applications

Hampe, D.; Gleisberg, B.; Köhler, M.; Akhmadaliev, S.; Rugel, G.; Merchel, S.

The isotope 41Ca is produced by neutron capture of the stable and most abundant calcium nuclide 40Ca in concrete of the bioshield around nuclear reactors. Because of its long half-life (1.04*105 a) the declaration of 41Ca in concrete is often requested for radioactive waste disposal.
The radioanalytical 41Ca determination by liquid scintillation counting (LSC) is still a reasonable option for laboratories involved in decommissioning of nuclear installations despite the emission of only low-energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certificated standard. Besides accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for 41Ca, is increasingly gaining broader accessibility and applicability. Herein, we present a radiochemical separation procedure developed for 41Ca determination with LSC and AMS in varying materials. The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, disturbing radionuclides as 55Fe, 60Co, 90Sr, 137Cs, 152Eu or 241Pu are removed with decontamination factors of 102-104. Quench curves for determining the measurement efficiency are generated with a 41Ca solution gained from the 41Ca/40Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 25-80%, measurement efficiencies of 1-10% and detection limits of 0.05 Bq*g-1 ash and 0.3 Bq*l.1. Aliquot solutions of LSC can be easily converted into CaF2-AMS-targets by successive oxalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on 41Ca results from LSC and AMS for the same material.

Keywords: LSC; accelerator mass spectrometry; nuclear waste disposal

  • Poster
    Ninth International Conference METHODS AND APPLICATIONS OF RADIOANALYTICAL CHEMISTRY (MARC IX), 25.-30.03.2012, Kailua-Kona, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-16340
Publ.-Id: 16340


Using Table-top Supercomputers for Simulating Table-top Radiation Sources

Bussmann, M.; Burau, H.; Widera, R.; Berninger, F.; Hübl, A.; Steiniger, K.; Kluge, T.; Debus, A.; Metzkes, J.; Zeil, K.; Kraft, S.; Jochmann, A.; Schlenvoigt, H. P.; Siebold, M.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Hönig, W.; Juckeland, G.; Nagel, W.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.; Ragan-Kelley, B.; Verboncoeur, J.

Designing laser-driven radiation sources requires realistic simulations, new ideas and good modeling. For inventing a design, a thorough analysis of existing designs is of great help. For planing designs, the fundamentals of the radiation generation process must be well understood. For testing designs, a fast return of results and the possibility to perform surveys of a large landscape of parameters is essential. In my talk I will address all steps in the source design using three examples from our recent research
* Scaling of hot electron energies with laser intensity in laser-solid interaction
* Laser-driven x-ray sources with tunable energy and bandwidth
* Fast computation of laser-plasma interaction with new computation hardware

Keywords: laser particle acceleration

  • Invited lecture (Conferences)
    2nd ELI Beamlines Scientific Challenges Meeting, 05.-06.10.2011, Praha, Česká republika

Permalink: https://www.hzdr.de/publications/Publ-16339
Publ.-Id: 16339


PIConGPU A scalable implementation of the Particle-in-Cell Algorithm for GPU Clusters

Bussmann, M.; Burau, H.; Berninger, F.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Widera, R.; Hönig, W.; Juckeland, G.; Nagel, W.

We present PIConGPU, a performant implementation of the particle-in-cell algorithm for GPUs that is scalable on GPU clusters. PIConGPU is used for fast-response simulations of laser-plasma interaction, including laser wakefield acceleration using the sliding-window technique. We discuss lessons learned from going from the initial two-dimensional PICimplementation to a full 3D implementation, focusing on data storage on the GPU and data communication between GPU nodes in a cluster. We show how communication and data storage can be efficiently hidden from users who want to extend the code by adding new physics so that users can assume to be working in a singledata single-instruction environment without deeper knowledge of GPU programming. As an example we show how the far field of relativistic electrons performing betatron oscillations in a laser-driven wakefield can be calculated from macro-particle trajectories on the GPU and subsequently stored in CPU. First simulation results obtained with PIConGPU are shown to illustrate the advantage of fast response simulations for large parameter scans.

Keywords: gpu; pic; particle-in-cell; simulation

  • Lecture (Conference)
    ICNSP 2011, 07.-09.09.2011, Long Branch, NJ, United States of America

Permalink: https://www.hzdr.de/publications/Publ-16338
Publ.-Id: 16338


A scalable, performant, highly-parallel particle-in-cell code for fast simulations of large laser-plasma experiments

Bussmann, M. H.; Burau, H.; Berninger, F.; Debus, A.; Irman, A.; Jochmann, A.; Hönig, W.; Schmitt, F.; Widera, R.; Juckeland, G.; Nagel, W.; Schramm, U.; Cowan, T. E.

A scalable, performant, highly-parallel Particle-in-Cell code for fast simulations of large Laser-Plasma experiments. Investigating parameters for optimizing laser particle acceleration is a timeconsuming task since realistic simulations of laser plasma interactions using the particle-in-cell technique can require the computation of several hundred million particle trajectories on a grid of several ten million cells. The computational effort needed to investigate the dependence of the performance of new acceleration scenarios on only a few parameters thus normally requires the use of large-scale high-performance computing systems only available at central super computing centres. Thus, parameter scans are usually performed by reducing the system size, the particle density, the computation time and the dimensionality of the problem. Such a scan is then at best complimented by a small number of more realistic large-scale simulations with parameters closer to the experimental parameters. Recently, general purpose graphical processing units (GPGPUs) have entered the stage of high performance computing. This new hardware offers a computational power exceeding that of standard CPU-based computers by several orders of magnitude at much lower investment and maintenance costs. Making good use of this computational power is only possible if the algorithm can run on a massively parallel system consisting of a huge number of independently working processors. However, the memory on a single GPGPU and thus the system size that can be computed on it is limited We present PIConGPU [1], a particle-in-cell algorithm that can run efficiently on a cluster of GPGPU nodes. PIConGPU can run largescale, realistic simulations by mapping the physical system onto many GPGPUs. Thus, the time needed to calculate the evolution of the large system is comparable to the time it takes to compute the small sub-region that can fit on a single GPU and therefore can lead to turnaround times of only a few hours for a hundred thousand time steps and single time steps of under a nanosecond per macro-particle [2].
If computational stability and dispersion is treated appropriately, using GPGPUs to simulate for example laser wakefield acceleration of electrons can greatly enhance the study of large parameter spaces while at the same time using simulation parameters resembling those of the experimental system studied. We focus on real-world examples of using PIConGPU for the simulation of laser electron acceleration scenarios investigated with the DRACO laser system at the Forschungszentrum Dresden-Rossendorf and show how the fast response time of GPGPU-based simulations can open up the path for optimizing experimental parameters.

Keywords: GPU; PIC; particle-in-cell; simulation; parallel

  • Lecture (Conference)
    SPIE Optics + Optoelectronics, 18.-21.04.2011, Praha, Česká republika

Permalink: https://www.hzdr.de/publications/Publ-16337
Publ.-Id: 16337


New direction in Melos obsidian characterization

Eder, F.; Neelmeijer, C.; Pearce, N. J. G.; Sterba, J. H.; Bichler, M.; Merchel, S.

In 2006, Arias et al.[1] chemically characterized a new obsidian source on the island of Melos. This third obsidian source, obsidian blocks inside the volcanoclastic deposits at Agios Ioannes, was claimed to be well distinguishable from the two well-known sources Agia Nychia and Demenegakion.
Following a sampling campaign in 2010, investigations of samples collected from all three Melos obsidian finding spots (Agia Nychia, Demenegakion, Agios Ioannes) were performed by three complementary analytical techniques (Neutron Activation Analysis, Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry, Ion Beam Analysis). Unfortunately, investigations had to be conducted on rubblestones, since the obsidian blocks described by Arias et al. could not be located. The “chemical fingerprint” composed of 43 elements clearly separates the rubblestones into the two known groups of Agia Nychia and Demenegakion. Elevated Sb concentrations already mentioned in Arias et al. could be confirmed but are probably attributed to a local contamination.

References: [1] Arias et al., J. Radioanal. Nucl. Chem. 268 (2006) 371–386.

Keywords: ion beam analysis; archaeometry; PIXE; PIGE

  • Poster
    „Archäometrie und Denkmalpflege 2012“, 28.-31.03.2012, Tübingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16336
Publ.-Id: 16336


Experimental characterisation of the interfacial structure during counter-current flow limitation in a model of the hot leg of a PWR

Vallée, C.; Nariai, T.; Futatsugi, T.; Tomiyama, A.; Lucas, D.; Murase, M.

In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, dedicated experiments were performed in a scaled down model of the Kobe University. The structure of the interface was observed from the side of the channel test section using a high-speed video camera. An algorithm was developed to recognise the stratified interface in the camera frames after background subtraction. The evolution of the water level along the hot leg is analysed in function of the liquid and gas flow rates.

Keywords: counter-current flow limitation; CCFL; hot leg; stratified two-phase flow; interfacial structure; image processing

Permalink: https://www.hzdr.de/publications/Publ-16335
Publ.-Id: 16335


Elektronik für einen Strahllagemonitor (BPM)

Büchner, A.

Die geplante Elektronik für einen neuen Strahllagemonitor (BPM) an ELBE wird vorgestellt. Der neue Strahllagemonitor soll einen wesentlich höheren Dynamikbereich haben und gleichzeitig die alten Differenzstrommonitore (DCM) ablösen. Dazu werden die einzelnen Signale vom Stripline-Monitor aufbereitet, digitalisiert und in einem FPGA verarbeitet. Die Strahllage und der Strahlstrom werden bestimmt und sowohl analog wie auch digital ausgegeben. Die Differenz des Strahlstromes zweier Strahllagemonitore wird gebildet und für das Maschinenschutzsystem überwacht.

Keywords: ELBE; Beam Position Monitor; BPM; Stripline-Monitor; Differential Current Monitor; DCM

  • Invited lecture (Conferences)
    102. Tagung der Studiengruppe elektronische Instrumentierung, 21.-23.03.2011, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16334
Publ.-Id: 16334


Development of a PET ligand for imaging PDE10A in brain - synthesis, potency, metabolism and radiochemistry of a 7-(2-fluoroethoxy)-6-methoxy-quinazoline derivative

Schwan, G.; Funke, U.; Deuther-Conrad, W.; Egerland, U.; Birkemeyer, C.; Scheunemann, M.; Nieber, K.; Sträter, N.; Brust, P.; Briel, D.

The phosphodiesterase (PDE) 10A plays an important role in neurotransmission by regulating intracellular levels of the cyclic nucleotides cAMP and cGMP in dopaminergic neurons. In consequence, PDE10A is associated with dopamine-related central nervous diseases such as Huntington’s disease and schizophrenia. Thus, PDE10A is a promising candidate for drug development with a variety of selective PDE10A inhibitors published during the last decade [1, 2]. The aim of the presented work is the development of a positron emission tomography (PET)
radiotracer for imaging of PDE10A in vivo.
Based on a lead structure (IC50PDE10A = 8 nM), published for therapeutic applications [3], three nonradioactive fluoroalkoxy derivatives (1, 2, 3) were enantioselectively synthesized over 11-14 steps and characterized regarding their potency and selectivity to inhibit PDE10A in a cAMP competition assay. Prolongation of the alkyl chain from 1 to 3 by one methylene group each resulted in decreased inhibitory potency from IC50 = 24 nM over 106 nM to 144 nM. Metabolic stability of 2 was determined in comparison to the lead compound in an in-vitro metabolism assay using rat liver S9-fractions. Metabolites were structurally characterized using ESI-MS-MS coupling techniques.
With regard to radiochemical accessibility, derivative 2 appeared as the most promising candidate for radioligand investigation. Initially, a two-step synthesis of [18F]2, consisting of 18F-labelling of 1,3-bistosyloxyethane and following coupling with phenolic precursor 4, was carried out. For the 18F-fluoroalkylation step labeling yields (LY) of 30-45% were achieved. Consequently, in a one-step procedure the tosylethoxy precursor 5 was used for 18Flabelling, improving LY up to 42-72%. Biodistribution studies in female CD-1 mice revealed high initial brain uptake of [18F]2. However, it was not significantly inhibited by competition with 2 or by pre-treatment with MP-10, a high PDE10A specific inhibitor, indicating lack of specificity in vivo. In conclusion, these results motivate for further structural variation of the lead compound to make it suitable for neuroimaging of PDE10A with PET.
Acknowledgements: We would like to thank J. Ortwein (Institute of Pharmacy, University of Leipzig) and the team of L. Hennig (Institute for Analytical Chemistry, University of Leipzig) for their analytical support. This project was financed by resources of the European Fond for Regional Development (EFRE) and the Free State of Saxony.
References:
1. Chappie et al., Current Opinion in Drug Discovery & Development 2009, 12, 458–467.
2. Kehler and J. P. Kilburn, Expert Opinion on Therapeutic Patents 2009, 19, 1715–1725.
3. Chappie et al., J. Med. Chem. 2006, 50, 182–185.

  • Poster
    Joint Meeting of the Austrian and German Pharmaceutical Science, 20.-23.09.2011, Innsbruck, Österreich

Permalink: https://www.hzdr.de/publications/Publ-16333
Publ.-Id: 16333


Pharmacological and toxicological properties of a novel selective PDE10A ligand

Siegert, F.; Erdmann, S.; Schwan, G.; Scholz, S.; Brust, P.; Sträter, N.; Altenburger, R.; Briel, D.; Nieber, K.

The phosphodiesterase 10A (PDE10A) has an important role in neurotransmission regulating the intracellular cyclic nucleotides especially in dopaminergic neurons. The PDE10A is a promising candidate for drug development and inhibiton of the PDE10A could be an interesting therapeutic stategy for treatment of brain dysfunctions, such as schizophrenia. The present study was designed to examine pharmacological and toxicological properties of a potent and selective brain permeable inhibitor of PDE10A (Ki = 31.9 nM) as nonradioactive derivative for the development of a radiotracer for positron emission tomography (PET).
The lead compound (3006) and the fluoric substituted derivative with prolonged alkyl chain by one methylen group (3039) had no effect on basal intracellular calcium concentration [Ca+]i in human neuroblastoma cells (SH-SY5Y). High concentrations (100 μM) of 3039 but not 3006 increased potassium-induced calcium mobilisation. Electrophysiological investigations on rat brain slices indicated no effect of 3039 or 3006 on postsynaptic membrane parameters and synaptic transmission up to 100 μM. After long-term incubation (48 h) 3039 and 3006 enhanced metabolic activity and reduced LDH-release of SH-SY5Y cells up to 1 μM whereas at high concentration (100 μM) metabolic activity was decreased due to slightly increased cell damage. Using the zebrafish embryo toxicity test mortality was observed at concentration of 100 μM for 3039 and ≥ 1μM for 3006 after incubation of 48 h.
The results suggest a different pharmacological profile of 3039 in comparison to its lead compound 3006 possibly by distinct binding characteristics to the PDE10A enzyme. Both compounds had no toxic effects in concentrations relevant for PET ligands. 3039 seems to be an appropriate candidate for developing a PET probe for studying distribution of PDE10A in vivo.

  • Poster
    Joint Meeting of the Austrian and German Pharmaceutical Science, 20.-23.09.2011, Innsbruck, Österreich

Permalink: https://www.hzdr.de/publications/Publ-16332
Publ.-Id: 16332


Radiolabelling of engineered nanomaterials as a tool for sensitive particle tracking - Cyclotron facility – Radionuclide production

Franke, K.; Hildebrand, H.

Vortrag im Rahmen eines Workshops, kein Abstract vorhanden

  • Lecture (Conference)
    7th annual CYCLEUR workshop on cyclotron research and radio-labelled nanoparticles, 28.-29.11.2011, Ispra, Italia

Permalink: https://www.hzdr.de/publications/Publ-16331
Publ.-Id: 16331


Realistic Integration of Sorption Processes in Long-term Safety Assessments

Schikora, J.

Vortrag für das Kompetenzzentrum OST 2011 in Zittau. Inhalt ist die realitätsnahe Integration von Sorptionsprozessen in Langzeitsicherheitsanalysen. Nach einer kurzen Erläuterung zur Motivation und der Vorstellung des Projektes ESTRAL wird die konzeptionelle Vorgehensweise zur realitätsnahen Integration von Sorptionsprozessen exemplarisch am Standort Gorleben vorgestellt. Für die verwendeten smart-Kd Matrizen werden am Beispiel des oberen Grundwasserleiters anschließend Sensitivitäts- und Unsicherheitsanalysen vorgestellt. Ein Ergebnis dieser Analysen ist die Identifikation von wichtigen Einflussfaktoren. Für den Kd-Wert von U(VI) sind dies zum Beispiel der DIC-Gehalt und die Konzentration an Calciumionen.

  • Lecture (Conference)
    Kompetenzzentrum OST 2011, 08.12.2011, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16330
Publ.-Id: 16330


The Search for Supernova-produced Radionuclides in Terrestrial Deep-sea Archives

Feige, J.; Wallner, A.; Winkler, S. R.; Merchel, S.; Fifield, L. K.; Korschinek, G.; Breitschwerdt, D.

An enhanced concentration of 60Fe was found in a deep ocean's crust in 2004 in a layer corresponding to an age of ~2 Myr. The conrmation of this signal in terrestrial archives as supernovainduced and detection of other supernova-produced radionuclides is of great interest. We will investigate a marine sediment from the South Australian Basin to search for live 26Al, 60Fe, 53Mn, 60Be and the pure r-process element 244Pu. A possible nding of these radionuclides in a sediment core might allow us to improve the time resolution of the signal and thus to link the signal to a supernova event in the solar vicinity ~2 Myr ago. Furthermore, we might get an insight on nucleosynthesis scenarios in massive stars, the condensation into dust grains and transport mechanisms from the supernova-shell into the solar system.

Keywords: intersteller medium; supernova remnants; nucleosynthesis; ISM; accelerator mass spectrometry

  • Open Access Logo Publications of the Astronomical Society of Australia (PASA) 29(2012), 109-114
    DOI: 10.1071/AS11070

Permalink: https://www.hzdr.de/publications/Publ-16329
Publ.-Id: 16329


The Molecular Structure of 1,2:5,6-Di-O-isopropylidene-3-O-toluenesulfonyl-a-D-glucofuranose

Mamat, C.; Peppel, T.; Köckerling, M.

The crystal and molecular structure of 1,2:5,6-Di-O-isopropylidene-3-O-toluenesulfonyl-a-D-glucofuranose is reported. This compound crystallizes from a petroleum ether/ethyl acetate mixture with the chiral orthorhombic space group P212121 with four molecules in the unit cell. The unit cell parameters are: a = 9.7945(7), b = 10.1945(7), and c = 21.306(1), and V = 2127.4(2) Å3. Bond lengths and angles of this tosyl-protected glucofuranose are typical

Permalink: https://www.hzdr.de/publications/Publ-16328
Publ.-Id: 16328


1D-confinement of polyiodides inside single-wall carbon nanotubes

Chorro, M.; Kane, G.; Alvarez, L.; Cambedouzou, J.; Paineau, E.; Rossberg, A.; Kociak, M.; Aznar, R.; Pascarelli, S.; Launois, P.; Bantignies, J. L.

1D-confinement of polyiodides inside single-wall carbon nanotubes (SWCNT) is investigated. Structural arrangement of iodine species as a function of the SWCNT diameters is studied. Evidence for long range one dimensional ordering of the iodine species is shown by x-ray and electron diffraction experiments independently of the tube diameter. The structure of the confined polyiodides is investigated by x-ray absorption spectroscopy. The confinement influences the local arrangement of the chains. Below a critical diameter Φc of 1 nm, long linear polyiodides are evidenced leading to a weaker charge transfer than for nanotube diameter above Φc. A shortening of the polyiodides is exhibited with the increase of the nanotube diameter leading to a more efficient charge transfer. This point reflects the 1D-confinement of the polyiodides inside the nanotubes.

Permalink: https://www.hzdr.de/publications/Publ-16327
Publ.-Id: 16327


Korrekturen für nichtreine und hochenergetische Positronenstrahler in der Kleintierbildgebung unter Verwendung von Monte-Carlo Simulationen

Sauerzapf, S.; Zakhnini, A.; Weber, W.; Pietrzyk, U.; Mix, M.

Ziel/Aim:
Das Isotop I-124 besitzt zusätzlich zum β+-Zerfall γ−Linien, die in sogenannten „falschen“ Koinzidenzen resultieren und eine bildverschlechternde Hintergrundaktivität verursachen. Wegen der maximalen Positronenzerfallsenergie von 2,1MeV besitzt I-124 eine hohe Reichweite, die die Ortsauflösung reduziert. Ziel dieser Arbeit war die Implementation einer Korrektur, die beide Effekte korrigiert.
Methodik/ Methods:
Ausgehend von optimalen Akquisitionseinstellungen wurde eine sinogrammbasierte Hintergrundsubtraktion sowie ein Rekonstruktionsalgorithmus mit Auflösungsrückgewinnung implementiert. Messungen wurden am MicroPET Focus 120 durchgeführt und mit GATE [1] Monte-Carlo (MC) Simulationen für verschiedene Phantome verglichen (Mausvoxelphantom, NEMA Image Quality Phantom (IQ) und ein selbstgebautes Mini-NEMA Schwächungsphantom). Die Bildrekonstruktion erfolgte mit Hilfe eines modifizierten OSEM-Algorithmus aus der STIR Library [2]. Über die MC-Simulationen lassen sich die Anteile der falschen zu wahren Koinzidenzen separieren und bei der Korrektur berücksichtigen. Für die Auflösungsrückgewinnung wurden Punktquellen in verschiedenen Schwächungsmaterialien simuliert und über die Reichweitenhistogramme materialabhängige Faltungskerne berechnet. Diese sind über den Vorwärtsprojektor in den Algorithmus integriert.
Ergebnisse/ Results:
Simulationen und vergleichende Messungen zeigen, dass am MicroPET durch Verkleinerung des Energiefensters von 350-650keV auf 400-550keV eine deutliche Reduktion der störenden Hintergrundaktivität und eine Verbesserung der Bildqualität erzielt werden kann. Die Anteile falscher zu wahrer Koinzidenzen sind außerhalb des Objektes homogen und nicht aktivitätsabhängig: 0,76 (MC: IQ, 90MBq, 50s) bzw. 0,77 (MC: IQ, 9MBq, 70s). Innerhalb existiert ein aktivitätsabhängiger Anteil von 0,29 bzw. 0,18, der über Gauß-Fits in der sinogrammbasierten Hintergrundsubtraktion berücksichtigt wird. Als Resultat ergeben sich quantitativ genauere und kontrastreichere Bilder. Simulationen eines realistischen Mausphantoms mit I-124, Ga-68 und F-18 zeigen, dass der dominante Effekt für die Bildverschlechterung in der Kleintierbildgebung der Auflösungsverlust durch die hohe Positronenzerfallsenergie ist. Die Anwendung der o.g. Entfaltungsmethode verbessert bei I-124 die Ortsauflösung von 4,9mm FWHM vor der Korrektur auf 2,5mm nach der Korrektur (IQ, Insert mit d=5mm, nach 20 Iterationen). Kritisch bei dieser Korrektur ist die genaue Definition des Abbruchkriteriums, da für höhere Iterationen eine Überkorrektur mit Artefakten entsteht.

Schlussfolgerungen/ Conclusions:
Unter Berücksichtigung von MC-Simulationen wurden Korrekturen für die Bildrekonstruktion von nichtreinen, hochenergetischen Positronenstrahlern erarbeitet. Die Ergebnisse der Simulationen konnten verifiziert und erfolgreich auf reale Daten übertragen werden.

Literatur:
[1]Jan et al. Med. Biol. (56) (2011) 881-901
[2]Thielemans et. al. IEEE NSS & MIC Record 2006

  • Poster
    Die 50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16326
Publ.-Id: 16326


A Simulation study to determine the influence of low-energy bremsstrahlungs photons on the acquisition of very rare coincidence events from Yttrium-90 decay.

Thomas, L.; Sauerzapf, S.; Mix, M.; Zakhnini, A.; Gaens, M.; Axer, M.; Pietrzyk, U.

AIM
In the course of treating liver cancer, frequently SIRT (selective internal radiation therapy) with Yttrium-90 is applied. In order to study the bio-distribution, often SPECT or SPECT/CT imaging is used, based on the detection of low-energy bremstrahlung photons. However, there is also another imaging option, namely through observation of the very rare internal pair production of Y-90, leading to an experimental situation well suited for PET (2). The aim of this study is to study the influence of the low-energy bremsstrahlung photons, which come at relatively high count-rate, but at the same time preserving the PET signal, i.e. the two gammas originating from the e+-e- annihilation, since only 32 out of one million decays of Yttrium-90 happen via internal pair production.

METHODS
The normal decay channel, the emission of therapeutically used electrons with high energy, comes with the production of low energy bremsstrahlung photons. Despite their relatively low energy (only a fraction of 16,6% of such photons exceeds more than 300 keV), the high-count rate could lead to saturation effects (via pulse pile-up) of the PET detector electronics. To absorb these low-energy photons, it was suggested to insert a copper ring into the gantry (1). To analyze a) where or not such a ring is required and b) which material might be best suited, we simulated a Siemens MicroPET Focus 120 and the PET part of a Philips Gemini TOF PET-CT with GATE (2) with different ring materials and a contrast medium filled phantom. Results from simulations were compared with experimental data obtained from measurements under condition comparable to the simulation.

RESULTS
First preliminary results from the simulation showed, that a 0.5 cm thick copper ring absorbs the low-energy bremsstrahlung, while preserving those at higher energy around 511 keV. In contrast, a ring of 0.5 cm of lead also absorbs many of the gammas around 511 keV. However, so far it is not certain, whether such a ring made of copper or lead would be required at all. Further studies are needed, especially with taking into account the signal processing chain as offered by GATE to differentiate further options in improving the detection of very rare signals for PET. Additional measurements might also provide more details of what exactly the PET-images show, because a superposition of the bremsstrahlung photons from interacting electrons with the true coincidence signals cannot be ruled out.
CONCLUSION
Our first results of distributions of simulated and measured events from Y-90 internal pair production look promising. The PET-images show very clear distributions of Y-90, yet need further confirmation, especially studying the influence of pile-up, dead-time effects on the rare coincidence signal.

(1) R Lhommel et al: Eur J Nucl Med Mol Imaging (2009) 36:1696.
(2) S Jan et al: GATE V6. Phys. Med. Biol. (2011) 56 881-901.

  • Poster
    Die 50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16325
Publ.-Id: 16325


Experiments on air entrainment under a vertical circular impinging jet: Measurement of the entrained air quantity

Danciu, D.-V.; Beyer, M.; Lucas, D.

The paper presents an experimental investigation regarding the phenomenon of air entrainment as a result of a jet impinging into a tank filled with water. The main objective of the work consists of gathering information about the concentration of the entrained void fraction, bubble velocities and the entrainment rate. For this purpose, a measuring technique based on wire-mesh sensors was used. For distinct combinations of nozzle exit velocity, jet length and immersion depth, the concentration and distribution of the entrained void fraction, as well as bubble size distributions and velocities were acquired. The corresponding calculated entrainment rate was found to increase linearly with both jet exit velocity and length, and to be smaller than predicted by literature. The experiments aim to provide an extensive database for air entrainment under plunging jets, needed for validation of Computational Fluid Dynamics (CFD) codes.

Keywords: air entrainment; impinging jet; high temporal resolution; experiments; wire-mesh sensor; void fraction; bubble velocities

  • Contribution to proceedings
    6th International Berlin Workshop on Transport Phenomena with Moving Boundaries, 24.-25.11.2011, Berlin, Germany
    Proceedings of the 6th International Berlin Workshop on Transport Phenomena with Moving Boundaries

Permalink: https://www.hzdr.de/publications/Publ-16324
Publ.-Id: 16324


Doping of silicon by ion implantation and annealing

Prucnal, S.

Multicrystalline p-type silicon wafers were used for the implantation of phosphorous. After ion implantation the silicon is strongly disordered or amorphous within the ion range. Therefore subsequent annealing is required to remove the implantation damage and to activate the doping element. The influence of the annealing types (furnace annealing - FA, rapid thermal annealing – RTA and Flash-lamp-annealing – FLA) on the optical and electrical properties of mc-Si solar cell was investigated. FLA offers here an alternative route for the emitter formation at an overall low thermal budget. During FLA, only the wafer surface is heated homogeneously to very high temperatures at ms time scales, resulting in the annealing of the implantation damage and an electrical activation of the phosphorous. However, a variation of the pulse time also allows to modify the degree of annealing of the bulk region to some extent as well, which can have an influence on the gettering behaviour of metallic bulk impurities.

Keywords: mc-Si; solar cells; FLA; PIII

  • Lecture (Conference)
    62th Freiberger Research Conference, 15.-17.06.2011, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-16323
Publ.-Id: 16323


Solar cell emitters fabricated by PIII and flash lamp millisecond annealing

Prucnal, S.; Endler, R.; Henke, D.; Kolitsch, A.; Abendroth, B.; Krockert, K.; König, K.; Möller, H. J.; Skorupa, W.

Cost reduction is the overall goal in the further development of solar cell technologies. Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of Solar Grade (SoG) mc-Si the rigorous control of metal impurities is desirable for solar cell fabrication. The main source of degradation of the photovoltaic effect in p-type mc-Si is iron present as interstitials (Fei) and Fe-B pairs. Processing solar cells at lower temperatures helps reducing the energy cost and in thin film technologies may also facilitate the use of less temperature stable substrates such as normal glass or polymers foils. In the present work a new technique will be presented and explored, which allows the implantation of the doping element by a plasma process and the subsequent annealing by a short time light pulse (Flash Lamp Annealing). Plasma Immersion Ion Implantation (PIII) technique can be used for the emitter formation of solar cells. It is much easier to handle and has the potential for mass production. A dedicated PIII - machine has been built suitable for the implantation of doping impurities into silicon.
The phosphorous implanted and annealed SoG mc-Si wafers were characterised by means of μ-Raman spectroscopy, temperature dependent photoluminescence (PL), surface photo-voltage method (SPV) and four-point probe resistor measurements. It could be demonstrated that FLA at 1000°C for 3 ms even without preheating is sufficient to recrystallize implanted silicon and to electrically activate the phosphorous. The sheet resistance (SR) of FLA samples shows values of about 40 μ/sq. Moreover, the minority carrier diffusion length for the FLA samples is in the range of 80 m. This is up to one order of magnitude higher than that observed from RTA or FA samples.

Keywords: Raman spectroscopy; photoluminescence; FLA; mc-Si

  • Poster
    11th International Workshop on Plasma-Based Ion Implantation & Deposition, 08.-12.09.2011, Harbin, China

Permalink: https://www.hzdr.de/publications/Publ-16322
Publ.-Id: 16322


III-V/Si heterostructures fully integrated into silicon

Prucnal, S.; Facsko, S.; Baumgart, C.; Schmidt, H.; Liedke, M. O.; Mücklich, A.; Zhou, S. Q.; Skorupa, W.

Integration of III-V semiconductors with a silicon technology is crucial for the devices performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of n=4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Keywords: III-V; flash lamp annealing; heterojunction; ion implantation

  • Lecture (Conference)
    Subsecond thermal processing of Advanced Materials 2011 (subtherm-2011), 25.-27.10.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-16321
Publ.-Id: 16321


Millisecond annealing for advanced doping of dirty-silicon solar cells

Prucnal, S.; Abendroth, B.; Krockert, K.; König, K.; Henke, D.; Kolitsch, A.; Möller, H. J.; Skorupa, W.

Cost reduction is the overall goal in the further development of solar cell technologies. Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of Solar Grade (SoG) mc-Si the rigorous control of metal impurities is desirable for solar cell fabrication. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. The influence of different annealing techniques on the optical and electrical properties of mc-Si solar cells was investigated. Flash Lamp Annealing in the ms-range is demonstrated here as a very promising technique for the emitter formation at an overally low thermal budget. It could be presented that FLA at 1000oC for 3 ms even without preheating is sufficient to recrystallize implanted silicon. The sheet resistance (SR) of FLA samples shows values of about 50 Ohm/sq. A specially, the minority carrier diffusion length for the FLA samples is in the range of 80 um without surface passivation. This is up to one order of magnitude higher than that observed from RTA or FA samples. This technology shows great promise to replace the conventional POCl3 –doping.

Keywords: solar cells; PIII; flash lamp annealing; mc-Si

  • Lecture (Conference)
    Subsecond thermal processing of Advanced Materials 2011 (subtherm-2011), 25.-27.10.2011, Dresden, Germany
  • Journal of Applied Physics 111(2012), 123104
    DOI: 10.1063/1.4729812

Permalink: https://www.hzdr.de/publications/Publ-16320
Publ.-Id: 16320


Flash Lamp Annealing vs conventional annealing for mc-silicon solar cell

Prucnal, S.; Abendroth, B.; Krockert, K.; König, K.; Möller, H. J.; Skorupa, W.

Multicrystalline p-type silicon wafers were used for the implantation of phosphorous. After ion implantation the silicon is strongly disordered or amorphous within the ion range. Therefore subsequent annealing is required to remove the implantation damage and to activate the doping element. The influence of the annealing types (furnace annealing - FA, rapid thermal annealing – RTA and Flash-lamp-annealing – FLA) on the optical and electrical properties of mc-Si solar cell was investigated. FLA offers here an alternative route for the emitter formation at an overall low thermal budget. During FLA, only the wafer surface is heated homogeneously to very high temperatures at ms time scales, resulting in the annealing of the implantation damage and an electrical activation of the phosphorous. However, a variation of the pulse time also allows to modify the degree of annealing of the bulk region to some extent as well, which can have an influence on the gettering behaviour of metallic bulk impurities.
The phosphorous implanted and annealed silicon wafers were characterised by means of u-Raman spectroscopy, temperature dependent photoluminescence (PL), surface photo-voltage method (SPV) and four-point probe resistor measurements. The μ-Raman spectroscopy showed that the silicon surface is amorphous after ion implantation. It could be demonstrated that FLA at 1000oC for 3 ms even without preheating is sufficient to recrystallize implanted silicon. The maximum PL intensity (band-to-band transition in silicon) was obtained from samples annealed for 3 ms, at the same time the sheet resistance (SR) of FLA samples shows the value of about 50 Ohm/sq. Moreover, the minority carrier diffusion length for the FLA samples is in the range of 100 um, what is fivefold longer than that observed from RTA or FA samples.

Keywords: solar cells; mc-Si; flash lamp annealing; ion implantation

  • Poster
    E-MRS 2011 SPRING MEETING IUMRS ICAM 2011 & E-MRS / MRS BILATERAL CONFERENCE on ENERGY, 09.-13.05.2011, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-16319
Publ.-Id: 16319


n-InAs/p-Si heterojunction with type-II band alignment

Prucnal, S.; Liedke, M. O.; Schmidt, H.-M.; Baumgart, C.; Shalimov, A.; Reuther, H.; Mücklich, A.; Helm, M.; Skorupa, W.

Crystalline InAs quantum dots (QDs) were successfully synthesized in silicon by hot ion implantation and millisecond flash lamp annealing (FLA). The crystallinity and shape of the InAs quantum dots were proven by high resolution transmission electron microscopy, -Raman spectroscopy and X-ray diffraction (XRD). Selective etching was used to form InAs/Si heterowires. The Kelvin Probe Force Microscope (KPFM) measurements prove the type-II band alignment of n-type InAs QD on p-type silicon nanowires. The Fermi level at the position of the InAs QD lies deep inside the conduction band region of InAs. The measured lateral KPFM bias variation ranges between 0 mV at the edge of the InAs QD and 100 mV at the center of the QD. The lattice parameter and the size of the QDs increases from 6.051 to 6.055 Ǻ and from 40 up to 50 nm with annealing temperature increasing from 1100 up to 1200 oC, respectively. By the proper choice of the preparation conditions such as ion fluence, annealing time and temperature we can synthesize and fully control the size and shape of InAs quantum structures in silicon. The main advantage of this method is its integration with large-scale silicon technology, which allows applying it for Si-based optoelectronic devices.

Keywords: InAs; silicon; heterojunction; flash lamp annealing; ion implantation

  • Lecture (Conference)
    E-MRS 2011 Spring Meeting, 09.-13.05.2011, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-16318
Publ.-Id: 16318


Magnetic anisotropy engineering: Single-crystalline Fe films on ion eroded ripple surfaces

Liedke, M. O.; Körner, M.; Lenz, K.; Grossmann, F.; Facsko, S.; Fassbender, J.

We present a novel method to preselect the direction of an induced in-plane uniaxial magnetic anisotropy (UMA) in thin Fe films on MgO(001). Ion beam sculpturing is used to modulate the MgO(001) surface with quasi-sinusoidal ripples on the nanoscale. The ripple direction determines the orientation of the uniaxial magnetic anisotropy, whereas the intrinsic cubic anisotropy of the Fe film is not affected. Thus, it is possible with a precision of a few degrees to superimpose an in-plane UMA---a level of control not reported so far that can be relevant for example in spintronic applications.

Keywords: Ferromagnetic Resonance; Ripple; MgO; Ion erosion; magnetic anisotropy; self-organization

Permalink: https://www.hzdr.de/publications/Publ-16317
Publ.-Id: 16317


Influence of Hot Implantation on Residual Radiation Damage in Silicon Carbide

Rawski, M.; Zuk, J.; Kulik, M.; Drozdziel, A.; Li, L.; Prucnal, S.; Pyszniak, K.; Turek, M.

Remarkable thermomechanical and electrical properties of silicon carbide (SiC) make this material very
attractive for high-temperature, high-power, and high-frequency applications. Because of very low values of
diffusion coefficient of most impurities in SiC, ion implantation is the best method to selectively introduce
dopants over well-defined depths in SiC. Aluminium is commonly used for creating p-type regions in SiC.
However, post-implantation radiation damage, which strongly deteriorates required electric properties of the
implanted layers, is difficult to anneal even at high temperatures because of remaining residual damage. Therefore
implantation at elevated target temperatures (hot implantation) is nowadays an accepted method to decrease the
level of the residual radiation damage by avoiding ion beam-induced amorphization. The main objective of this
study is to compare the results of the Rutherford backscattering spectroscopy with channeling and micro-Raman
spectroscopy investigations of room temperature and 500 ±C Al+ ion implantation-induced damage in 6H-SiC and
its removal by high temperature (up to 1600 ±C) thermal annealing.

Keywords: ion implantation; SiC; Raman spectroscopy

  • Open Access Logo Acta Physica Polonica A 120(2011), 192

Permalink: https://www.hzdr.de/publications/Publ-16316
Publ.-Id: 16316


Inclusive dielectron spectra in p+p collisions at 3.5 GeV

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chen, J. C.; 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.; 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 the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e+e- pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct ω decays is reconstructed with 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for e+e- invariant masses above 0.2 GeV/c2 and for transverse momenta pt < 1 GeV/c, acceptance corrections are to a large extent model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross sections for light vector mesons. Inclusive production cross sections for π0 and η mesons are also reported. The obtained results will serve as an important reference for the study of vector mesons production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct η decays into the electron-positron channel is obtained.

Permalink: https://www.hzdr.de/publications/Publ-16315
Publ.-Id: 16315


Terahertz nonlinear and coherent effects in semiconductor nanostructures

Helm, M.

The Autler-Townes effect (Rabi splitting) is observed in semiconductor quantum wells, when pumping the intra-excitonic 1s-2p transition with a THz free-electron laser. In a second experiment using time-domain spectroscopy, it is shown that the THz intersubband polarization in a quantum well can be coherently manipulated using a second, phase-locked THz pulse.

Keywords: terahertz; nonlinear; coherent; semiconductor; nanostructure

  • Invited lecture (Conferences)
    International Symposium on Terahertz Nanoscience (TeraNano 2011), 24.-25.11.2011, Osaka, Japan
  • Contribution to proceedings
    International Symposium on Terahertz Nanoscience (TeraNano 2011), 24.-25.11.2011, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-16314
Publ.-Id: 16314


THz science in semiconductor quantum structures

Helm, M.

THz science in semiconductor quantum structures

Keywords: THz; semiconductors; quantum structures

  • Invited lecture (Conferences)
    Nano-Carbon Terahertz Science, 22.11.2011, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-16313
Publ.-Id: 16313


Pairs of diverging-converging spin vortices in biquadratically interlayer exchange coupled elements

Wintz, S.; Bunce, C.; Banholzer, A.; Strache, T.; Körner, M.; Gemming, S.; Erbe, A.; McCord, J.; Raabe, J.; Quitmann, C.; Fassbender, J.

Spin structures have been a relevant topic of magnetism research for many years. In particular, magnetic vortices have attracted much at- tention, due to their non-trivial topology and the various dynamic modes they exhibit. A magnetic vortex consists of a planar, flux- closing magnetization curl that turns out of the plane in the central nanoscopic core. For a single layer structure, the curl’s radial components typically cancel each other out. Recent investigations show that this holds also true for multilayer vortex systems comprising bilinear interlayer exchange coupling (IEC). In this contribution we report on pairs of diverging-converging spin vortices occurring in biquadratically coupled systems. Using magnetic x-ray microscopy we directly observe that the individual vortices of such pairs possess a residual radial magnetization component. From this ∇M𝑥𝑦 ̸= 0, an additional perpendicular magnetization divergence ∇M𝑧 is analytically deduced. We compare our continuous model with discrete micromagnetic simulations.

Keywords: magnetism; vortex; multilayer; coupling; interlayer; biquadratic; exchange

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2012, 25.-30.03.2012, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-16312
Publ.-Id: 16312


Imaging of the brain serotonin transporters (SERT) with 18F-labelled fluoromethyl-McN5652 and PET in humans

Hesse, S.; Brust, P.; Mäding, P.; Becker, G.-A.; Seese, A.; Patt, M.; Sorger, D.; Zessin, J.; Sacher, J.; Lobsien, D.; Habermann, B.; Meyer, P. M.; Füchtner, F.; Luthardt, J.; Bresch, A.; Steinbach, J.; Sabri, O.

Purpose [1134 C]DASB is currently the most frequently applied highly selective radiotracer for visualisation and quantification of central SERT. Its use, however, is hampered by the short half life of carbon-11, the moderate cortical test retest reliability, and the lack for quantifying endogenous serotonin. Labelling with fluorine-18 allows in principle for longer acquisition times for kinetic analysis in brain tissue and may provide higher sensitivity. The aim of our study was to firstly apply in human the new highly SERT-selective fluorine-18 labelled fluoromethyl analogue of (+)-McN5652 ((+)-[1840 F]FMe-McN5652) and to evaluate its potential for SERT quantification.
Methods
The PET data of five healthy volunteers (3 male, 2 female, age 39 ± 10 years) coregistered with individual MRI were semi-quantitatively assessed by volume-of-interest analysis using the software package PMOD. Rate constants and distribution volume ratios (DVR) were calculated using a 2-tissue compartment model and arterial input function measurement were corrected for metabolites/plasma data. Standardized uptake region-to-cerebellum ratios as measure of specific radiotracer accumulation were compared with those of a [1146 C]DASB-PET data set of healthy subjects (10 male, 11 female, 38 ± 8 years).
Results
The 2-tissue compartment model provided adequate fits to the data. Estimates of total distribution volume (VT) demonstrated good identifiability based on coefficient of variation (COV) for the volumes of interest (VOIs) in SERT-rich and also for cortical areas (COV VT < 10%).
Compared with [11C]DASB-PET, there was a tendency to lower mean values in (+)-[1851 F]FMe-McN5652 PET, however, the standard deviation was also somewhat lower. Altogether, cerebral (+)-[1853 F]FMe-McN5652 uptake corresponds well with the known SERT distribution also in humans.
Conclusion
The results showed also that (+)-[1855 F]FMe-McN5652 is suitable for in vivo quantification of SERT with PET. Because of the long half-life of fluorine-18, a widespread application within a satellite concept seems feasible.

Keywords: Serotonin receptor; Positron emission tomography; PET; 18F

Permalink: https://www.hzdr.de/publications/Publ-16309
Publ.-Id: 16309


Development of radioligands for α7-nAChR imaging with positron emission tomography

Brust, P.; Peters, D.; Deuther-Conrad, W.

Molecular imaging of brain structures by highly sensitive non-invasive techniques offers unique possibilities in the understanding of physiological and pathological processes in the central nervous system. In particular, the quantitative analysis by positron emission tomography (PET) of α7 nicotinic acetylcholine receptors ( α7 nAChR), which are involved in different signalling pathways in the brain, is assumed to provide important information on the relation between receptor dysfunction and the pathogeneses of neuropsychiatric brain diseases, but the applicability of this imaging approach is still hampered due to insufficient imaging agents. This paper presents the recent efforts made to develop PET radiotracers targeting α7 nAChR as well as the current state of the evaluation of the most promising radiolabelled compounds in animal models and humans.

Permalink: https://www.hzdr.de/publications/Publ-16308
Publ.-Id: 16308


Synthesis, radiofluorination and pharmacological evaluation of fluoromethyl substituted spirocyclic PET tracers for labeling of σ1 receptors in the central nervous system and comparison with longer homologues

Maisonial, A.; Grosse Maestrup, E.; Wiese, C.; Hiller, A.; Schepmann, D.; Deuther-Conrad, W.; Fischer, S.; Brust, P.; Wünsch, B.

The spirocyclic s1 receptor ligand 1 (1’-benzyl-3-(fluoromethyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]) was prepared in four steps starting from methoxy derivative 5. Due to its high s1 affinity (Ki = 0.74 nM) and selectivity against several other relevant targets, 1 was investigated as 18F-labeled PET tracer and its biological properties were compared with those of homologous fluoroalkyl derivatives 2-4. The fluoromethyl derivative 1 was faster metabolized in vitro than homologues 2-4. In contrast to the radiosynthesis of [18F]2-4, the nucleophilic substitution of the tosylate 15 using the K[18F]F-K222-carbonate complex required heating to 150 °C in DMSO to achieve high labeling efficiencies. Whereas radiometabolites of [18F]2-4 were not detected in vivo in the brain of mice, two radiometabolites of [18F]1 were found. Analysis of ex vivo autoradiography images provided rather low target-to-nontarget ratio for [18F]1 compared with [18F]2-4. [18F]1 showed a fast uptake in the brain, which decreased continuously over time. The brain-to-plasma ratio of the radiotracer [18F]1 was only exceeded by the fluoroethyl tracer [18F]2.

Permalink: https://www.hzdr.de/publications/Publ-16307
Publ.-Id: 16307


Spektroskopische Untersuchungen zum Verhalten von Neptunium und Uran in der Geosphäre

Müller, K.

The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces.
Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral - water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes.
For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3^-, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system.
The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered.
A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important.
A significant different surface complexation is observed for Al2O3. The formation of innerspheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested.
The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces.
In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2 ^+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 - 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes.
The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.

  • Invited lecture (Conferences)
    Jahresveranstaltung "Woman in Nuclear", 24.-25.11.2011, Biblis, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16306
Publ.-Id: 16306


α4β2 nicotinic acetylcholine receptor PET to study the cholinergic function in patients with MCl and Alzheimer’s disease

Sabri, O.; Brust, P.; Barthel, H.

Einleitung
In Alzheimer’s disease (AD), there is growing evidence for the brain nicotinic acetylcholine receptors (nAChRs) being reduced at very early disease stages (in transgenic Tg2576 mice even earlier than beta-amyloid plaque deposition [Int J Devl Neurosci 2003]) and for this reduction being strongly associated with cognitive decline. Our group aims at developing and testing new nAChR positron emission tomography (PET) tracers with the goal to improve early dementia diagnosis.
Methode
We tested A85380, an 18F-labeled PET tracer which binds to the α4β2-subunit of the nAChR, and could show that nAChRs are highly significantly reduced in brain areas affected by AD-pathology in patients with early AD (correlating significantly with impaired cognition), and even in subjects with MCI who later progressed to AD [Eur J Nucl Med Mol Imaging 2011]. Using A85380, however, PET imaging of up to seven hours is required. This limitation encouraged to search for better suited tracers to be used as biomarkers in clinical routine. As a result we developed the 18F-labeled epibatidine derivative NCFHEB [Synapse 2008]. The first-in-man study testing this tracer in AD-patients and healthy controls (HCs) is ongoing. First results show that this tracer might allow imaging of nAChRs in a 20 minutes scan within 90 minutes and a significantly lower tracer binding in AD-patients compared to HCs.
Diskussion/Ergebnisse
Taken together, we were successful in the implementation of PET to image nAChRs in dementia. Our PET results support the concept of the nicotinic system being involved at early AD stages, providing motivation to further develop PET imaging for early AD diagnosis, prognosis, and therapy control.

  • Lecture (Conference)
    DGPPN Kongress 2011, 23.-26.11.2011, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16305
Publ.-Id: 16305


Synthesis of an 18F-labeled cyclin-dependent kinase-2 inhibitor

Svensson, F.; Kniess, T.; Bergmann, R.; Pietzsch, J.; Wuest, F.

The radiosynthesis of N-(5-(((5-(tert-butyl)oxazol-2-yl)methyl)thio)thiazol-2-yl)-4-[18F]fluoro-benzamide [18F]2 as a potential radiotracer for molecular imaging of cyclin-dependent kinase-2 (CDK-2) expression in vivo by positron emission tomography is described. Two different synthesis routes were envisaged. The first approach followed direct radiofluorination of respective nitro- and trimethylammonium substituted benzamides as labeling precursors with no-carrier-added (n.c.a.) [18F]fluoride. A second synthesis route was based on the acylation reaction of 2-aminothiazole derivative with labeling agent [18F] SFB. Direct radiofluorination afforded 18F-labeled CDK-2 inhibitor in very low yields of 1%–3%, whereas acylation reaction with [18F]SFB gave 18 F-labeled CDK-2 inhibitor [18 F]2 in high yields of up to 85% based upon [18 F]SFB during the optimization experiments. Large scale preparation afforded radiotracer [18 F]2 in isolated radiochemical yields of 37%–44% (n=3, decay-corrected) after HPLC purification within 75 min based upon [18 F]SFB. This corresponds to a decay-corrected radiochemical yield of 13%–16% based upon [18F]fluoride. The radiochemical purity exceeded 95% and the specific activity was determined to be 20 GBq/mmol.

Keywords: cyclin-dependent kinase 2; fluorine-18; radiofluorination; [18F]SFB

  • Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 769-774
    DOI: 10.1002/jlcr.1922

Permalink: https://www.hzdr.de/publications/Publ-16304
Publ.-Id: 16304


Cyclin-Dependent Kinases (Cdk) as Targets for Cancer Therapy and Imaging

Graf, F.; Wuest, F.; Pietzsch, J.

kein Abstract verfügbar

  • Open Access Logo Book chapter
    Gali-Muhtasib H: Advances in Cancer Therapy, Croatia: Rijeka: InTech, 2011, 978-953-307-703-1, 265-288

Permalink: https://www.hzdr.de/publications/Publ-16302
Publ.-Id: 16302


Combined approach of microsensor and EF-TEM/EELS studies to study the speciation of uranium in biofilms and in the surrounding bulk solution

Krawczyk-Bärsch, E.; Lünsdorf, H.; Pedersen, K.; Arnold, T.; Bok, F.; Steudtner, R.; Lehtinen, A.; Brendler, V.

The effects of a microbial habitat (biofilm) on the transport behavior of uranium in a simulated incident in an underground repository were studied by pH and Eh microelectrodes and energy-filtered transmission electron microscopy (EF-TEM), and electron energy-loss spectroscopy (EELS). Biofilm samples were collected in the underground rock characterization facility tunnel ONKALO (Finland) and positioned in a rectangular flow cell for immobilization experiments by adding uranium to the bulk solution to a final uranium concentration of 4.25 × 10–5 M. The bulk solution was pumped through the flow cell in a closed circuit, simulating in situ conditions on the tunnel wall. The use of microelectrode with a tip diameter of 10 µm to measure pH and Eh in the biofilm proved to be essential to indicate that the biofilm has formed its own microenvironment. EF-TEM and EELS studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms by the formation of metabolically mediated uranyl phosphate, similar to Autunite. In contrast, time resolved laser fluorescence spectroscopy (TRLFS) in the bulk solution identified aqueous uranium carbonate species, likely (Ca2UO2[CO3]3), formed due to the high concentration of carbonate. The results were further confirmed by thermodynamic calculations of the predominant field of uranium species, formed in the bulk solution.
Our combined approach clearly showed that uranium was removed from solution and immobilized exclusively in biofilm microorganisms. In contrast, the aqueous uranyl carbonates species, formed in the bulk solution, may contribute to the migration of U(VI) and consequently to environmental hazard.

Keywords: biofilm; uranium; microelectrodes; EF-TEM

  • Lecture (Conference)
    marc ix - Methods & Application of Radioanalytical Chemistry, 25.-30.03.2012, Kailua-Kona, USA

Permalink: https://www.hzdr.de/publications/Publ-16301
Publ.-Id: 16301


Radiation field characterization and shielding studies for the ELI Beamlines Facility

Ferrari, A.; Amato, E.; Margarone, D.; Cowan, T.; Rus, B.

The ELI (Extreme Light Infrastructure) Beamlines Facility in the Czech Republic, which is planned to complete the installation in 2015, is one of the four pillars of the ELI european project. Several laser beamlines with ultrahigh intensities and ultrashort pulses are foreseen, offering versatile radiation sources in an unprecedented energy range: laser-driven particle beams are expected to range between 1 GeV and 50 GeV for electrons and from 100 MeV up to 3 GeV for protons. The number of particles delivered per laser shot is estimated to be 109-1010 for the electron beams and 1010-1012 for the proton beams.
The high energy and current values of the produced particles, together with the potentiality to operate at 10 Hz laser repetition rate, require an accurate study of the primary and secondary radiation fields to optimize appropriate shielding solutions: this is a key issue to minimize prompt and residual doses in order to protect the personnel, reduce the radiation damage of electronic devices and avoid strong limitations in the operational time.
A general shielding study for the 10 PW (0.016 Hz) and 2 PW (10 Hz) laser beamlines is presented here. Starting from analytical calculations, as well as from dedicated simulations, the main electron and proton fields produced in the laser-matter interaction have been described and used to characterize the "source terms" in full simulations with the Monte Carlo code FLUKA. The secondary radiation fields have been then analyzed to assess a proper shielding. The results of this study and the proposed solutions for the beam dumps of the high energy beamlines are presented, together with a cross-check analysis performed with the Monte Carlo code GEANT4.

Keywords: particle acceleration from laser-matter interaction; shielding; Monte Carlo; radiation protection

Permalink: https://www.hzdr.de/publications/Publ-16300
Publ.-Id: 16300


Layer by Layer investigation on the magneto-transport properties of ferromagnetic Ge:Mn prepared by pulsed laser

Bürger, D.; Zhou, S.; Höwler, M.; Kovacs, G.; Reuther, H.; Skorupa, W.; Helm, M.; Schmidt, H.

The fabrication of ferromagnetic semiconductors is one big step to realize spintronic devices. Beside GaAs:Mn also Ge:Mn is a very interesting material system [1-2].
Moreover, the lattice inversion symmetry of Ge leads to weak spin-orbit interaction and enhanced spin-lifetime and spin-diffusion lengths of more than 100 μ m. This is shown in Ge nanowires at 4.2 K [3].
Also a spin diffusion up to 225 K could be shown in weakly n-doped Ge [4].
In a previous work we investigated ferromagnetism in Ge:Mn thin films. Hysteretic Hall resistance after Mn implantation and short-time pulsed laser annealing (PLA) has been observed [5].
Similar to low temperature molecular beam epitaxy [1], the clustering of Mn inside the material has to be prevented. Especially after PLA, the Mn segregation leads to the formation of a Mn enriched surface layer. In our work, we performed layer by layer magneto-transport measurements after different etching steps. The hysteretic properties are vanishing after removing the segregated Mn-rich phases. In conclusion, we think that the observed hysteretic Hall resistance may have its origin in the scattering of spin-polarized holes on these Mn-rich phases. Such hysteretic transport properties have not yet been reported for Ge with embedded Mn-rich clusters. The vanishing hysteresis at 30 K and above can be interpreted by the increasing decoherence between the individual Mn rich clusters or/and the reduced magnetization of the clusters itself.
[1] M. Jamet et al., Nature Materials 5, 653 (2006) [2] Y.D. Park et al., Science 295, 651 (2002) [3] E. S. Liu et al., Nano Letters 10, 3297 (2010) [4] Y. Zhou et al. arXiv:1103.5095v1 (2011) [5] S. Zhou et al., Phys. Rev. B 81, 165204 (2010)

Keywords: implantation; segregation; pulsed laser annealing; ferromagnetic semiconductor

  • Poster
    56th annual conference on magnetis and magnetic materials, 30.10.-03.11.2011, Scottsdale, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-16299
Publ.-Id: 16299


Depth-resolved magnetotransport properties of ferromagnetic Ge:Mn

Bürger, D.; Zhou, S.; Höwler, M.; Kovacs, G.; Reuther, H.; Skorupa, W.; Helm, M.; Schmidt, H.

The fabrication of ferromagnetic semiconductors is one big step to realize spintronic devices. Beside GaAs:Mn also Ge:Mn is a very interesting material system [1-2]. Moreover, the lattice inversion symmetry of Ge leads to weak spin-orbit interaction and enhanced spin-lifetime and spin-diffusion lengths of more than 100 µm. This is shown in Ge nanowires at 4.2 K [3]. Also a spin diffusion up to 225 K could be shown in weakly n-doped Ge [4]. We investigated ferromagnetism in Ge:Mn thin films [5]. Hysteretic Hall resistance after Mn implantation and short-time pulsed laser annealing (PLA) has been observed. Similar to low temperature molecular beam epitaxy [1], the inhomogenous distribution of Mn inside the material has to be prevented. Especially after PLA, the Mn segregation leads to the formation of a Mn enriched surface layer. In our work, we performed layer-by-layer etching of ferromagnetic Ge:Mn and subsequent depth-resolved magnetotransport measurements. The hysteretic properties are vanishing after removing the segregated Mn-rich phases. In conclusion, we think that the hysteretic Hall resistance may have its origin in the scattering of spin-polarized holes on these Mn-rich phases. The vanishing hysteresis at 30 K can be interpreted by the increasing spin decoherence between the individual Mn rich clusters or/and the reduced magnetization of the clusters itself at increased temperature.

Keywords: implantation; pulsed laser annealing; segregation; manganese; magnetic semiconductor

  • Lecture (Conference)
    Subtherm 2011, 24.-27.10.2011, Dresden, Deutschland
  • Poster
    Subtherm 2011, 24.-27.11.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-16298
Publ.-Id: 16298


Dielectric function and magneto-optical Voigt constant of Cu2O: A combined spectroscopic ellipsometry and polar magneto-optical Kerr spectroscopy study

Haidu, F.; Fronk, M.; Gordan, D. O.; Scarlat, C.; Salvan, G.; Zahn, R. T. D.

Cuprous oxide is a highly interesting material for the emerging field of transparent oxide electronics. In this work the energy dispersion of the dielectric function of Cu2O bulk material is revised by spectroscopic ellipsometry measurements in an extended spectral range from 0.73 to 10 eV. For the first time, the magneto-optical Kerr effect was measured in the spectral range from 1.7 to 5.5 eV and the magneto-optical Voigt constant of Cu2O was obtained by numerical calculations from the magneto-optical Kerr effect spectra and the dielectric function.

Permalink: https://www.hzdr.de/publications/Publ-16297
Publ.-Id: 16297


Radiosynthesis and Radiotracer Properties of a 7-(2-[F-18]Fluoroethoxy)-6-methoxy-pyrrolidinylquinazoline for Imaging of Phosphodiesterase 10A with PET

Funke, U.; Deuther-Conrad, W.; Schwan, G.; Maisonial, A.; Scheunemann, M.; Fischer, S.; Hiller, A.; Briel, D.; Brust, P.

Phosphodiesterase 10A (PDE10A) is a key enzyme of intracellular signal transduction which is involved in the regulation of neurotransmission. The molecular imaging of PDE10A by PET is expected to allow a better understanding of physiological and pathological processes related to PDE10A expression and function in brain. The aim of this study was to develop a new 18F-labeled PDE10A ligand based on a 6,7-dimethoxy-4-pyrrolidinylquinazoline and to evaluate its properties in biodistribution studies. Nucleophilic substitution of the 7-tosyloxy-analogue led to the 7-[18F]fluoroethoxy-derivative [18F]IV with high PDE10A affinity (KD,PDE10A=14 nM), radiochemical yields of 25±9% (n=9), high radiochemical purity of ≥99% and specific activities of 110-1100 GBq/mol. [18F]IV entered rapidly into the brain of female CD-1 mice with a peak uptake of 2.3%ID/g in striatum at 5 min p.i.. High metabolic stability in brain was observed. However, blocking studies revealed no target specific accumulation of [18F]IV. Therefore, successful imaging of PDE10A using 18F-labeled 6,7-dialkoxyquinazoline derivatives requires further structural optimization.

Keywords: PDE10A; Quinazoline; Fluorine-18; Positron emission tomography; PET

Permalink: https://www.hzdr.de/publications/Publ-16296
Publ.-Id: 16296


Alpha7 nicotinic acetylcholine receptors as a potential target for imaging of brain disorders with Positron Emission Tomography

Brust, P.; Knudsen, G. M.; Mikkelsen, J. D.; Ettrup, A.; Deuther-Conrad, W.; Peters, D.

Molecular imaging of brain structures by non-invasive techniques offers unique possibilities in the understanding of physiological and pathological processes in the central nervous system. In particular, the quantitative analysis by positron emission tomography (PET) of alpha7 nicotinic acetylcholine receptors (α7nAChR) could provide important information on the relation between receptor dysfunction and the pathogeneses of neurodegenerative brain diseases. However, the applicability of PET for α7nAChR imaging is still hampered by a lack of validated radiotracer for human use.
As radiotracers for imaging α7nAChR, 18F- and 11C-labelled 1,4-diazabicyclo-[3.2.2]nonane derivatives (NS10743 and NS14492) were developed and investigated for in vivo imaging characteristics. Brain autoradiography and organ distribution in mice showed specific accumulation of [18F]NS10743 in α7nAChR expressing brain substructures and peripheral organs. In pigs [18F]NS10743 readily entered the brain (peak SUV ~2.5), with the highest uptake in α7nAChR expressing brain regions such as the colliculi, thalamus, temporal lobe, and hippocampus. Pretreatment followed by constant infusion of NS6740, a selective α7nAChR antagonist, significantly reduced the specific binding of [18F]NS10743 in receptor-dense regions of pigs.
[11C]NS14492, a radioligand of similar high affinity and selectivity in vitro, also showed high uptake in the pig brain (peak SUV ~2.2) with a distribution pattern in accordance with α7nAChR expression. Homologous blocking or pretreatment with the α7nAChR partial agonist SSR180711 both reduced distribution volumes of [11C]NS14492 in all examined regions in a dose-dependent manner.
In conclusion, because of their high brain uptake and regional distribution in accordance with α7nAChR expression pattern in the pig brain, 1,4-diazabicyclo-[3.2.2]nonane derivatives are promising PET radioligands for in vivo mapping and quantitative imaging of α7nAChR. Furthermore, in vivo in pigs the PET radioligand brain binding can be dose-dependently blocked by α7nAChR antagonists.

  • Invited lecture (Conferences)
    28th CINP Congress, 03.-07.06.2012, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-16293
Publ.-Id: 16293


Sublattice-specific ordering of ZnO layers during the heteroepitaxial growth at different temperatures

Redondo-Cubero, A.; Vinnichenko, M.; Krause, M.; Mücklich, A.; Mun˜Oz, E.; Kolitsch, A.; Gago, R.

The effect of the substrate temperature on the sublattice ordering in ZnO layers grown by reactive pulsed magnetron sputtering on sapphire has been investigated by different techniques. The improvement of the crystal quality and heteroepitaxial growth at relatively low temperatures (550 °C) is verified by X-ray diffraction, high-resolution transmission electron microscopy, Rutherford backscattering spectrometry in channeling mode (RBS/C), and Raman spectroscopy. Sublattice-resolved analysis by resonant RBS/C and Raman spectroscopy reveals that the progressive transition to the single crystal phase is accomplished in a faster way for Zn- than for O-sublattice. This behavior is attributed to the preferential annealing of defects in the Zn sublattice at low temperatures when compared to those of the O sublattice.

Keywords: ZnO; reactive pulsed magnetron sputtering; defects; structure

Permalink: https://www.hzdr.de/publications/Publ-16292
Publ.-Id: 16292


Kernkraftwerk Krümmel – Berechnung der Fluidlasten in der Kondensationskammer bei luftarmer Kondensation mit einem Randelemente-Verfahren

Wagner, M.; Estorf, M.

Im Fall eines Frischdampfleitungsbruchs wird Dampf über die Kondensationsrohre in die Kondensationskammer gepresst. Dabei ergeben sich an den in die Wasservorlage eintauchenden Rohrenden Dampfblasen, die sich zyklisch erweitern und wieder kollabieren. Bei geringem Anteil nicht kondensierbaren Gases führt der Kollaps der Blasen zu starken Druckstößen, welche die Wände der Kondensationskammer belasten. Die physikalischen Zusammenhänge des intermittierenden Blasenkollapses sowie die den Vorgang beeinflussenden Parameter sind in umfangreichen Experimenten untersucht. Die auftretenden Drücke auf der Behälterwand wurden in Testbehältern experimentell ermittelt, statistisch ausgewertet und in konservativer Weise für die Spezifikation der entsprechenden Lasten am Sicherheitsbehälter des KKK verwendet. Dazu erfolgte eine potentialtheoretische Skalierung des Druckes aufgrund der berechneten Lösung der Potentialgleichung auf Basis einer vereinfachten abgewickelten, rechteckigen Geometrie der Wasservorlage.
Der vorliegende Bericht bewertet diese mit vereinfachter Geometrie erzeugte Lösung der Potentialgleichung anhand einer genaueren Berechnung des Behälterpotentials für die tatsächliche 3-dimensionale Geometrie. Die Potentialgleichung wird hier mit einer Randelemente-Methode gelöst. Anschließend werden mit Hilfe von Monte-Carlo-Rechnungen die Einflüsse der unterschiedlich stark auftretenden Druckamplituden sowie der Asynchronität der Kondensationsereignisse auf die zu erwartenden Lasten ermittelt.

Keywords: condensation chamber; pressure distribution; potential equation; boundray element method

  • Other report
    Institutsbericht: HZDR\FWS\2011\07, 2011
    28 Seiten

Permalink: https://www.hzdr.de/publications/Publ-16291
Publ.-Id: 16291


Ion-implantation induced nano distortion layer and its influence on nonlinear optical properties of ZnO single crystals

Zheng, C. C.; Xu, S. J.; Ning, J. Q.; Chen, Y. N.; Lu, X. H.; Ling, C.-C.; Che, C. M.; Gao, G. Y.; Hao, J. H.; Brauer, G.; Anwand, W.

Second harmonic generation (SHG) and X-ray diffraction rocking curves of high-quality ZnO single crystals implanted by different ions (He, Cu, and Zn) were investigated. Interestingly, it was found that both He-and Zn-implanted samples show a convinced increment in SHG efficiency while the Cu-implanted one does not. X-ray diffraction rocking curves of the samples show satellite structures, and the simulations firmly reveal the formation of quasi-interfaces inside He-and Zn-implanted crystals. These quasi-interfaces lead to SHG improvement in the two samples. Polarization dependence of SHG of the samples on the excitation light also evidences this conclusion.

  • Journal of Applied Physics 110(2011)8, 083102

Permalink: https://www.hzdr.de/publications/Publ-16290
Publ.-Id: 16290


Mid-infrared pump-related electric-field domains in GaAs/(Al,Ga)As quantum-cascade structures for terahertz lasing without population inversion

Giehler, M.; Wienold, M.; Schrottke, L.; Hey, R.; Grahn, H. T.; Pavlov, S. G.; Hübers, H.-W.; Winnerl, S.; Schneider, H.

We investigate the effect of mid-infrared (MIR) pumping on the transport properties of GaAs/(Al,Ga)As terahertz (THz) quantum lasers (TQLs), which rely on quantum coherence effects of intersubband transitions. Aiming at THz lasing at elevated temperatures, we extend the concept of THz gain with and without population inversion of a single, MIR-pumped, electrically driven THz stage proposed by Waldmueller et al. [Phys. Rev. Lett. 99, 117401 (2007)] to an entire TQL. However, experiments using a CO2 as well as a free-electron laser and numerical simulations show that this resonant MIR pumping causes a negative differential conductivity (NDC) in addition to the NDC caused by sequential tunneling. Lasing of these TQLs is prevented by the formation of electric-field domains below the resonance field strength for gain of each single THz stage.

Keywords: quantum cascade laer; intersubband transition; GaAs/AlGaAs; free-electron laser

Permalink: https://www.hzdr.de/publications/Publ-16289
Publ.-Id: 16289


High-field terahertz investigations on semiconductor quantum structures

Schneider, H.

This seminar reviews our recent experimental studies involving terahertz (THz) and mid-infrared radiation from the free-electron laser facility FELBE in Dresden, Germany. As examples for linear measurements, cyclotron resonance spectroscopy and aperture-less near-field microscopy will be addressed. Applications of nonlinear THz spectroscopy include pump-probe experiments in graphene, and nonlinear THz two-photon intersubband excitation in semiconductor quantum wells. The final part of my talk will concentrate on two-color THz spectroscopy, in particular THz sideband generation and coherent dynamics of excitons dressed by strong THz beams.

Keywords: terahertz THz spectroscopy; free-electron laser; semiconductor quantum well; two-photon transition; excitons

  • Lecture (others)
    Seminar, Hebrew University of Jerusalem, 09.11.2011, Jerusalem, Israel

Permalink: https://www.hzdr.de/publications/Publ-16288
Publ.-Id: 16288


Paradoxical transitions to instabilities in hydromagnetic Couette-Taylor flows

Kirillov, O. N.; Pelinovsky, D. E.; Schneider, G.

By methods of modern spectral analysis, we rigorously find distributions of eigenvalues of linearized operators associated with an ideal hydromagnetic Couette-Taylor flow. Transition to instability in the limit of vanishing magnetic field has a discontinuous change compared to the Rayleigh stability criterion for hydrodynamical flows, which is known as the Velikhov-Chandrasekhar paradox.

Keywords: Magnetorotational instability; boundary eigenvalue problem; eigencurves; Velikhov-Chandrasekhar paradox

Permalink: https://www.hzdr.de/publications/Publ-16287
Publ.-Id: 16287


Enhancements of high-resolution gamma-ray computed tomography

Bieberle, A.; Berger, R.; Nehring, H.; Hampel, U.

Recently, we developed a transportable high-resolution gamma-ray computed tomography (GCT) measurement system for the investigation of phase distributions in multi-phase flows in technical apparatus. The GCT measurement system contains a collimated isotopic source (137Cs), a radiation detector arc and an external signal processing as well as thermal stabilisation unit. For tomographic scans radiographic projections are obtained from different angular positions by rotating either the measuring ensemble or the object of interest. To improve the mechanical and thermal handling of the existing radiation measurement electronics, in a first step a new modular signal processing board was developed. It implements variable gain amplifier stages, gamma photon counters as well as data transfer and communication to a standard PC into the detector arc. Furthermore, the new developed electronics allows various arrangements of multiple detector modules. In a second step the thermal stabilisation system was integrated into the detector arc. Two 30 W (thermal power) Peltier elements directly placed onto the top side of the detector base plate undertake the task of thermal stabilisation. Into the back side of the base plate, a spatially optimised channel is milled in which a fluid, driven by an integrated centrifugal pump, realises a homogeneous temperature distribution. Thus, the heat losses of the active electronics that are connected to the base plate can be efficiently dissipated, which is the key for a good measuring repeat accuracy. The functionality of the thermal stabilisation design was proven by an IR camera.

Keywords: Gamma-ray tomography; multiple detector module

  • Contribution to proceedings
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa
    Proceedings of 6th International Symposium on Process Tomography
  • Lecture (Conference)
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-16286
Publ.-Id: 16286


Radio-coloration of Diamond

Nasdala, L.; Grambole, D.; Harris, J. W.; Schulze, D. J.; Hofmeister, W.

This study investigated the green and orangy brown spots that commonly occur on the surface of rough diamonds and which are caused by external irradiation by helium ions in the form of alpha particles. These ions are believed to be generated by the decay of radionudides in radioactive minerals that were located close to a diamond in irs geologic past. Helium ions generated in the U- and Th-decay chains have energies in the 4.0-8.8 MeV range; their travel distances in diamond arc up tO 29 1-1m. Depending on rhe sizes (mostly unknown) of rhe radiation sources and their proximity to the diamond's surface, helium irradiation typically results in blurred round spots with green color. These spots are usually deformed semi-spheres with fuzzy boundaries. With moderate-temperature heating, the green radio-coloration turns orange-brown. Raman measurements revealed that these richly colored green and brown spots represent elevated levels of radiation dan1age. The same observation was made on spots produced by the irradiarion of diamond plates with 8.8 MeV He ions in a tandem accelerator, foUowed by annealing experiments. The transformation from green to brown was accompanied by relatively low degrees of structural reconstitution.
Our experiments showed that irradiation with about l x l 016 He ions per cm2 is needed to produce strong radio-coloration. This in rum leads us to conclude that radio-coloration on the surface of natural stones must be a long-tenn process: A typical spot has a size on the order of 1,000 fU112, requiring about 1 x 1011 helium ions. If the helium irradiation emanated, for instance, from a 5 fUll uraninirecrysral {>80wr.% U), it would rake more than 10 million years to accumulate l x 1011 helium ions in the neighboring diamond In the case of a lO fUll zircon crysra1 containing 1,000 ppm of uraniurn, that same alpha dose would require more than 2 billion years, which seems implausible. Therefore, radio-coloration is likely due to the action of small grains of strongly radioactive phases that lay adjacent to the diamond for at least several million years.

  • Abstract in refereed journal
    Gems & Gemology 47(2011), 105-106

Permalink: https://www.hzdr.de/publications/Publ-16285
Publ.-Id: 16285


ELBE Timing System

Kuntzsch, M.

German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications

Keywords: ELBE Timing System

  • Lecture (Conference)
    German-Turkish Workshop on Superconducting Accelerators for FEL and Bremsstrahlung Applications, 31.01.-03.02.2011, Antalya, Turkey

Permalink: https://www.hzdr.de/publications/Publ-16284
Publ.-Id: 16284


Concept of Femtosecond Timing and Synchronization Scheme at ELBE

Kuntzsch, M.; Buechner, A.; Gensch, M.; Jochmann, A.; Kirschke, T.; Lehner, U.; Roeser, F.; Bock, M. K.; Bousonville, M.; Felber, M.; Lamb, T.; Schlarb, H.; Schulz, S.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf is undergoing an extension to offer capacity for various applications. The extension includes the setup of a THz-beamline with a dedicated laboratory and a beamline for electron-beam - high-power laser interaction. The current synchronization scheme offers stability on the picoseconds level. For pump-probe experiments using optical lasers, the desired synchronization between the pump and the probe pulse should be on the femtosecond scale. In the future there will be an optical synchronization system with a pulsed fiber laser as an optical reference. The laser pulses will be distributed over stabilized fiber links to the remote stations. It is planned to install EOM-based beam arrival time monitors (BAMs) in order to monitor the bunch jitter and to establish a beam-based feedback to reduce the jitter. Besides that, the timing system has to be revised to generate triggers for experiments with low repetition rate, two electron guns (thermionic DC, superconducting RF) and several lasers. The Poster will show the possible layout of the future Timing and Synchronization System at ELBE.

Keywords: Synchronization Timing ELBE

  • Open Access Logo Contribution to proceedings
    International Particle Accelerator Conference, 04.-09.09.2011, San Sebastian, Spain
    Concept of Femtosecond Timing and Synchronization Scheme at ELBE
  • Poster
    International Particle Accelerator Conference, 04.-09.09.2011, San Sebastian, Spain

Permalink: https://www.hzdr.de/publications/Publ-16283
Publ.-Id: 16283


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