Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Blasenmitriss durch Impinging Jets
Schmidtke, M.; Danciu, D.;
Der Gaseintrag durch impinging jets wird mittels Experimenten und CFD-Simulationen untersucht. In den Experimenten wird die Düsenhöhe über dem Waserbecken und die Wassergeschwindigkeit in der Düse variiert. Der Blasenmitriss durch den Wasserstrahl wird mittels einer Hochgeschwindigkeits-Video-Kamera beobachtet. Quantitative Daten zu Blasengrößen so wie Geometrien der Blasenfahne werden durch Bildverarbeitung aus den Videofilmen gewonnen. Zusätzlich wird die Entwicklung zweiphasiger Jets unter Wasser mittels CFD untersucht, unter Verwendung des Euler-Euler Ansatzes. Es wird ein Kriterium für die Eindringtiefe definert, und die simulierten Blasenfahnen werden mit den experimentell beobachteten hinsichtlich der Eindringtiefe verglichen.

The gas entrainment by impinging water jets is studied by the means of experiments and CFD simulations. In the experiments, the nozzle height above the water pool and the water velocity inside the nozzle is varied and the bubble entrainment below the jet is observed with a video camera. Quantitative data for bubble sizes and the geometry of the bubble plume are obtained by image processing. The development of two phase jets under water is also studied with CFD, using the Euler-Eulerian approach. Defining a criterion for an average penetration depth, the simulated plumes are compared with those observed in the experiments.
Keywords: impinging jets, bubble entrainment, gas carryunder, multiphase, penetration depth, plunging
  • Lecture (Conference)
    Jahrestreffen der Fachausschüsse Mehrphasenströmungen und Wärme- und Stoffübertragung, 03.-05.03.2009, Bad Dürkheim, Deutschland

Publ.-Id: 12420 - Permalink

Air entrainment by impinging jets. Experimental identification of the key phenomena and approaches for their modelling.
Schmidtke, M.; Danciu, D.; Lucas, D.;
The gas entrainment by impinging water jets is studied by the means of experiments and CFD simulations. In the experiments, the nozzle height above the water pool and the water velocity inside the nozzle is varied and the bubble entrainment below the jet is observed with a video camera. Quantitative data for bubble sizes and the geometry of the bubble plume are obtained by image processing. The development of two phase jets under water is also studied with CFD, using the Euler-Eulerian approach. Defining a criterion for an average penetration depth, the simulated plumes are compared with those observed in the experiments
Keywords: impinging jets, plunging, gas entrainment, bubble, carryunder, plume, multiphase, CFD
  • Contribution to proceedings
    17th International Conference on Nuclear Engineering ICONE 17, 12.-16.7.2009, Brussels, Belgium
  • Lecture (Conference)
    17th International Conference on Nuclear Engineering ICONE 17, 12.-16.07.2009, Brussels, Belgium

Publ.-Id: 12419 - Permalink

Studies on oxygen concentrations in uranium contaminated biofilms: Comparing electrochemical and fiber-optic sensors
Krawczyk-Bärsch, E.;
Within the framework of ReCosy first comparative investigations of electrochemical and fiber-optic sensors were performed in collaboration with the University Potsdam (UPPC). Fiber-optic sensor measurements in biofilms have some advantages compared to those made by electro-chemical microelectrodes. As described in Beyenal et al. (2000) fiber-optic sensors are immune to environmental changes in pH, salinity, and ionic strength and immune to interference from moisture, carbon dioxide, methane, and other substances. A range of fiber-optic sensor studies were carried out to measure in situ geochemical gradients in biofilms. To our knowledge optical sensors applied to biofilm samples exposed to heavy metals are so far not reported in the literature. In our first collaboration with the UPPC we compared the oxygen concentration profiles obtained by electrochemical and optical microsensors, respectively. Oxygen concentration profiles were measured in the biofilms by electrochemical microsensors of the Clark design (Unisense, Denmark). These Clark-type oxygen microsensors are generally used for microbial ecology studies and contain a guard electrode. They have a tip diameter of 10 µm, a stirring sensitivity of <1–2%, and a response time of <1 s. The used multispecies biofilms (microbial diversity described in Krawczyk-Bärsch et al., 2008) were cultivated in the laboratory under non-sterile conditions in different biofilm reactors. One biofilm reactor was adjusted to a uranium concentration of (1x10-6 M), which is typical for uranium contaminated sites. The data achieved from both sensor methods are directly comparable. Fiber-optic sensor measurements showed high concentrations of oxygen over the total thickness of the biofilms, which were not in contact with uranium. In contrast, biofilms exposed to uranium revealed a much lower oxygen concentration in the bottom parts of the biofilm as described before in Krawczyk-Bärsch et al. (2008). Already at a depth of approximately 400 µm no oxygen was detectable. The comparative studies revealed that depending on the existing environmental conditions during the measurements a decision for the appropriate method is possible. However, further developments, e.g. miniaturization of the sensor equipments, are needed and aimed for within ReCosy.

Beyenal, H. et al. (2000) Appl Opt 39, 3408.
Krawczyk-Bärsch, E. et al. (2008) Geochimica et Cosmochimica Acta 72, 5251–5265
  • Lecture (Conference)
    1st Annual Workshop of the Recosy Project, 10.-12.02.2009, Barcelona, Spain

Publ.-Id: 12418 - Permalink

The influence of charge-transfer complexes on the copolymerization behavior of cyclic maleic acid derivatives with donor monomers
Schmidt-Naake, G.; Drache, M.; Leonhardt, K.;
- wird nachgereicht
  • Macromolecular Chemistry and Physics 199(1998)3, 353-361

Publ.-Id: 12417 - Permalink

First reporting of the scientific-technical outcome of WP 4.2: Chemical and redox behavior of the investigated radionuclides in the different systems through microbial mediated processes
Krawczyk-Bärsch, E.;
Within the framework of ReCosy redox processes in biofilms, grown in-situ in radionuclide contaminated environments, will be studied by oxygen and redox potential microsensors. First in-situ measurement activities have already taken place in a former uranium mine in Saxony (Germany). Since the mining activities had stopped in 1990, the uranium mine has been partially flooded for remediation. This resulted in encroaching release of heavy metals and radionuclides as contaminants in acid, sulphate-rich waters. Huge biofilms with a thickness of more than 10 centimeters are currently growing in drainage channels (so far not flooded) under acid conditions and in the presence of uranium concentrations of approximately 1x10-4 M. Concentration profiles of oxygen were measured in these biofilms in-situ by means of electrochemical microsensors of the Clark design (Unisense, Denmark) with a tip diameter of 10 µm. The sensors were connected to a picoammeter and fixed in a holder on a motor-driven micromanipulator stage, connected with a motor controller, for a precise small-scale positioning and for automated measurements in 50 µm steps in Z-axis. Due to the hetero-geneities of the biofilm, numerous microprofiles were measured at different points of the biofilm. The results revealed a fast decrease of the oxygen concentration in the biofilm profiles. Already at a depth of approximately 2 mm no oxygen was detectable. It can be assumed that the microorganisms of the biofilm battle the toxic effects of aqueous uranium in a similar way as the biofilms described in Krawczyk-Bärsch et al. (2008). The biofilm community is reacting to the exposition of uranium in environmentally relevant concen-trations with an increase of the respiratory activity of the microorganisms. The increased metabolic activity of the microorganisms, as a result of an activation of heavy metal resistance mechanisms, will lead to larger anoxic zones (reducing zones) within the biofilms, which may induce redox processes. In these zones uranium (VI) can be reduced to highly insoluble uranium (IV) through abiotic processes. The precipitations of uranium (IV) solids will result in an increased removal of uranium and immobilisation of uranium from the solution.

Krawczyk-Bärsch, E. et al. (2008) Geochimica et Cosmochimica Acta 72, 5251–5265
  • Lecture (Conference)
    1st Annual Workshop of the Recosy Project, 10.-12.02.2009, Barcelona, Spain
  • Contribution to proceedings
    1st Annual Workshop of the Recosy Project, 10.-12.02.2009, Barcelona, Spain
    Collaborative Project "Redox Phenomena Controlling Systems", Karlsruhe: Forschungszentrum Karlsruhe GmbH, KIT Report FZKA 7466 Dezember 2009, 43-46

Publ.-Id: 12416 - Permalink

Zur Anwendung von Schwerionen und Protonen in der Strahlentherapie
Enghardt, W.;
no abstract available
  • Lecture (others)
    34. Seminar für Mitarbeiter von Landesbehörden, Landesanstalt für Personendosimetrie und Strahlenschutzausbildung Mecklenburg-Vorpommern, 13.11.2008, Berlin, Deutschland

Publ.-Id: 12415 - Permalink

Cell response to laser-accelerated electron beams.
Pawelke, J.;
wird nachgereicht
  • Invited lecture (Conferences)
    N4 Workshop on Radiation Protection Issues, 14.-17.12.2008, Chamonix, France

Publ.-Id: 12414 - Permalink

Neue Entwicklungen im Strahlenschutz in der Forschung.
Pawelke, J.;
wird nachgereicht
  • Invited lecture (Conferences)
    2. Strahlenschutzseminar für Lehrer im Freistaat Sachsen, 18.11.2008, Dresden, Deutschland

Publ.-Id: 12413 - Permalink

Mensch und Strahlung – Wie verstehen wir die Wirkung der zur Krebstherapie eingesetzten Strahlen auf menschliche Zellen?
Pawelke, J.;
wird nachgereicht
  • Lecture (others)
    Lange Nacht der Wissenschaften, 04.07.2008, Dresden, Deutschland

Publ.-Id: 12412 - Permalink

Laser Radiooncology.
Pawelke, J.;
wird nachgereicht
  • Lecture (others)
    3rd Meeting of the Scientific Advisory Board of OncoRay, 28.02.2008, Dresden, Deutschland

Publ.-Id: 12411 - Permalink

Ultra fast electron beam x-ray computed tomography for two-phase flow measurement
Fischer, F.; Hampel, U.;
Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focussing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm × 1.5 mm × 1.5 mm active pixel area. X-ray radiation is produced on a circular water cooled tungsten target. The CT system achieves up to 7000 frames per second with a spatial resolution of 1 millimetre. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in the future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.
Keywords: Two-phase flow, electron beam tomography, CFD code validation

Publ.-Id: 12410 - Permalink

Implications of three dimensional velocity distributions on the generation of magnetic fields in the Von-K\'arm\'an-Sodium dynamo experiment.
Giesecke, A.; Stefani, F.; Gerbeth, G.;
Numerical simulations of the kinematic induction equation have been carried out in a cylindrical domain that resembles the configuration of the VKS dynamo experiment. Primary objective are investigations of non-axisymmetric source terms and their impact on the critical Reynolds number as well as onthe structure of the field geometry.

In case of an axisymmetric velocity distribution the resulting magnetic field is always determined by an azimuthal m=1-mode which is in contradiction to the experimental realization that is dominated by an axisymmetric field.

A simple non-axisymmetric contribution can be parameterized by a localized $\alpha$-effect which arises from the induction action of radially oriented helical outflow between the impeller blades that drive the flow. However, it turns out, that the amplitude of $\alpha$ which is necessary to obtain an axisymmetric field is far above realistic values.

Further potential contributions involve a time dependent non-axisymmetric velocity component in form of azimuthal drifting equatorial vortices as they have been found in water experiments. These structures provide a coupling between different field modes, but the m=1 mode still remains dominant. Resonance effects provide a strong increment of the field growthrate if the vortex drift motion proceeds phase synchronous with a drift of the magnetic field caused by equatorial symmetry braking of the velocity distribution. Presumably this phenomenon is not relevant in the experiment, as the drift of the eigenfield is very small so that resonance would require a much slower vortex drift velocity than it is observed.

So far, non-axisymmetric source terms in the induction equation are not able to explain the dominance of the m=0 mode, however it remains still possible that a quite exotic dynamo mechanism is operating which is essentially based on induction terms generated by the azimuthal variation of the permeability introduced by the ferrous impellers.
Keywords: dynamo, alpha-effect, induction, kinematic simulations
  • Lecture (Conference)
    Frontiers in Dynamo Theory, 16.-20.03.2009, Paris, France

Publ.-Id: 12409 - Permalink

Mensch und Strahlung – Forschung an ELBE.
Pawelke, J.;
wird nachgereicht
  • Lecture (others)
    Lehrerfortbildung 2007/2008 im FZD: „Moderne Beschleunigerkonzepte und ihre Anwendung in der Medizin“, 15.02.2008, Dresden, Deutschland

Publ.-Id: 12408 - Permalink

Weltweit erste Zellbestrahlungsexperimente mit laserbeschleunigten Teilchenstrahlen.
Pawelke, J.;
wird nachgereicht
  • Invited lecture (Conferences)
    Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, 21.01.2008, Jena, Deutschland

Publ.-Id: 12407 - Permalink

Therapie von Tumorerkrankungen mit laserbeschleunigten Teilchenstrahlen.
Pawelke, J.;
wird nachgereicht
  • Invited lecture (Conferences)
    OncoRay, Strategie-Meeting, 08.-09.01.2008, Gröditz, Deutschland

Publ.-Id: 12406 - Permalink

Präzisions-Strahlentherapie mit Laser-Ionenbeschleunigern.
Karsch, L.; Messner, L.; Pawelke, J.; Richter, C.; Schüttig, R.;
wird nachgereicht
  • Poster
    Tag der Gesundheitsforschung, 17.02.2008, Dresden, Deutschland

Publ.-Id: 12405 - Permalink

Auf dem Weg zu einer neuen Strahlentherapie mit laserbeschleunigten Teilchen – Erste Experimente mit Elektronen.
Karsch, L.; Hümmerich, J.; Beyreuther, E.; Lessmann, E.; Pawelke, J.; Nicolai, M.; Schlenvoigt, H.;
wird nachgereicht
  • Poster
    OncoRay, Strategie-Meeting, 08.-09.01.2008, Gröditz, Deutschland

Publ.-Id: 12404 - Permalink

Mit laserbeschleunigten Teilchen gegen Tumore – Erste in vitro Experimente an laserbeschleunigten Elektronenstrahlen.
Naumburger, D.; Beyreuther, E.; Enghardt, W.; Karsch, L.; Lessmann, E.; Messner, L.; Nicolai, M.; Pawelke, J.; Richter, C.; Sauerbrey, R.; Schlenvoigt, H.; Baumann, M.;
wird nachgereicht
  • Lecture (Conference)
    11. Jahrestagung der Gesellschaft für Biologische Strahlenforschung (GBS), 06.-08.10.2008, Tübingen, Deutschland
  • Contribution to proceedings
    11. Jahrestagung der Gesellschaft für Biologische Strahlenforschung (GBS), 06.-08.10.2008, Tübingen, Deutschland

Publ.-Id: 12403 - Permalink

Implementation of a High Level Hands-on-Training at an Experimental PET Scanner.
Würschig, T.; Kluge, T.; Enghardt, W.;
The remarkable increase of medical imaging within the last decade demands the implementation of teaching programs for experts and students. Such courses must achieve both the realization of theoretical basics and an understanding of its implementation within real systems. This accounts for positron emission tomography (PET) as well. PET is, among other techniques like computer tomography (CT) or magnetic resonance imaging (MRI), one of the key technologies for biological and medical imaging. To teach and demonstrate the fundamentals of CT and the physical background of PET as well as to illustrate the signal processing of a coincidence measurement and the data processing of multi-parameter, list-mode data sets, the experimental PET scanner PET-TW05 has been developed. It is a simplified but still fully functional scanner consisting of two commercial BGO block-detectors. They are fixed in opposite to each other and can be moved along a linear axis and rotated around the field of view (FOV). The hardware layout and the software performance of the PET-TW05 scanner support the demonstration of important process steps of PET imaging like (i) system calibration, (ii) detector efficiency measurements, (iii) determination of time and spatial resolution of a PET scanner, (iv) list-mode data acquisition, (v) tomographic reconstruction by means of filtered backprojection, (vi) the effect of different filter kernels as well as of time and energy windows on the image quality, (vii) the influence of scatter on the image quality. Furthermore, the principle of time-of-flight PET can be experimentally demonstrated.
Keywords: PET, education, filtered backprojection, BGO block detector, list-mode data acquisition
  • Poster
    IEEE NSS-MIC Nuclear Science Symposium Conference Record M06-147, 19.-25.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    IEEE NSS-MIC Nuclear Science Symposium Conference Record M06-147, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 12402 - Permalink

Considerations on the Biological Effect of Laser Induced Radiation with High Dose Rates.
Khaless, A.; Karsch, L.; Enghardt, W.;
wird nachgereicht
  • Lecture (Conference)
    IEEE NSS-MIC Nuclear Science Symposium Conference Record N51-5, 19.-25.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    IEEE NSS-MIC Nuclear Science Symposium Conference Record N51-5, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 12401 - Permalink

Dosimetric comparison between gated and steady photon and electron beams delivered by the Siemens ONCOR linear accelerator.
Wieczorkowski, L.; Hoinkis, C.; Lehmann, D.; Enghardt, W.;
Objective: The gated irradiation technique is a sophisticated tool for focusing the prescribed dose to periodically moving target volumes while sparing the surrounding healthy tissue. Thus, gated irradiation is predominantly applied to organ motion caused by breathing. The tumour is irradiated in a specific phase of its motion. This requires to switch on and off the beam periodically. The beam-on time may change in a certain range depending on the individual breathing curve, site specific conceptions and the tumour dose conformity required. The latter will be increased for a short beam-on time, however, causing an increase in the number of irradiation cycles for reaching the prescribed dose. Prior to the therapeutic application of gated irradiation, the dose distributions delivered for photons and electrons in steady and gated mode in static phantoms were measured.

Materials: Photon and electron beams were delivered by a Siemens ONCOR Impression linear accelerator. The gating signal was provided by a commercial respiratory gating system based onto a pressure belt feedback mechanism in combination with a respiratory phantom (AZ-733, Anzai Medical). For measurements in stationary phantom linear diode array BMS 96 (Schuster Medizinische Systeme GmbH) was used to measure beam profiles and a solid water phantom (RW3, PTW) with ionization chamber (0.6 cm3 Farmer, PTW) were used to measure the depth dose at different depths. Respiratory frequency were set to 10 and 15 min-1 and beam-on time to 1, 2 and 3 s. Different field sizes (5 × 5, 10 × 10 and 20 × 20 cm2) for 6 and 15 MV photons and 10 × 10 cm2 for 9 and 12 MeV electrons were used.

Results: Depth doses maximum deviation for gated photon and electron beams is up to 0.8 % in comparison to non-gated beams. The maximum deviation between gated and non-gated dose profiles has been found to be less than 3 % and is located in the penumbra region. Deviations are randomized and do not depend on the photon and electron energy. Minor dependence of field size was observed but in most cases, the results for the 10 × 10 cm2 field were more accurate. None respiratory frequency dependence was noticed as well.

Conclusion: To evaluate more realistic cases with respect to therapy the dosimetric and geometric verification using a moving phantom will also been done.
  • Poster
    39. Jahrestagung Deutsche Gesellschaft für Medizinische Physik e.V. Oldenburg, 10.-13.09.2008, Oldenburg, Deutschland

Publ.-Id: 12400 - Permalink

Entwicklung eines bildgeführten Bestrahlungsgerätes für die präzise Tumorbestrahlung an Kleintieren.
Khaless, A.; Thute, P.; Hietschold, V.; Enghardt, W.;
In den letzen Jahren erzielte man große Fortschritte bei der Bildgebung von Kleintieren. Mittlerweile gibt es für fast alle Modalitäten, die für die Bildgebung am Menschen eingesetzt werden, auch Varianten für Nagetiere (microCT, microMRI, microPET). In der Krebsforschung werden diese bildgebenden Verfahren bis jetzt überwiegend bei Tierexperimenten genutzt, die sich mit der Untersuchung von pharmazeutischen Substanzen beschäftigen. Obwohl in der Strahlentherapie am Menschen schon seit einiger Zeit bildgebende Verfahren eingesetzt werden und diese eine immer größere Rolle spielen, um die Therapie präziser und effizienter zu machen, werden diese Entwicklungen nicht am Tiermodell nachvollzogen. Diese Tatsache liegt darin begründet, dass sich die Bestrahlungstechnik für Kleintiere in der experimentellen Strahlentherapie verglichen mit der bei der Humantherapie auf dem Niveau der 1950er Jahre befindet. Während Tumoren beim Menschen mittlerweile hochkonformal, intensitätsmoduliert und stereotaktisch bestrahlt werden, positioniert man Versuchtiere noch unter Stehfeldern mit grober Standardkollimierung. Will man die heutige Präzisionsstrahlentherapie in Tierexperimenten untersuchen, ist es unbedingt erforderlich, mit einem geeigneten Kleintierbestrahlungsgerät die technischen Voraussetzungen dafür zu schaffen.
  • Poster
    39. Jahrestagung Der DGMP, 10.-13.09.2008, Oldenburg, Deutschland

Publ.-Id: 12399 - Permalink

Uranium(IV) colloid in near-neutral solutions: Influences on particle size
Dreissig, I.; Weiss, S.; Zaenker, H.; Bernhard, G.;
Uranium(IV) is only sparingly soluble in near-neutral solutions [1]. As a consequence, uranium is expected to be immobile (deposited) under reducing conditions. However, we found out that under certain conditions U(IV) formes stable colloids which leads to a mobilization of the uranium. The colloids were generated by galvanostatic reduction of a 20 mM UO2(ClO4)2 solution in 1 M NaHCO3. The stock solutions were diluted to 1 mM uranium using solutions of dissolved silicic acid (2 – 5 mM). Then they were neutralized with perchloric acid. Measurement of the scattered light intensity (SLI), photon correlation spectroscopy (PCS) and ultracentrifugation (UC) were carried out.
Typically, the colloids produced did not reach their final particle size immediately but showed a certain growth phase of about one week. This could be seen from both PCS and simple SLI measurements.
It turned out that the highest SLIs occurred in the solutions of the lowest silicate content and vice versa. All samples exhibited an increase in SLI with decreasing pH. Obviously, very small colloidal particles are generated at high pH and/or high silicate concentration and larger ones at low pH and/or low silicate concentration. At the highest initial silicate concentration applied, the colloids were still stable at pH values below 7.
This silicate and pH dependency of U(IV) colloid particle size was also confirmed by our UC results. The smaller the colloids, the longer the time they needed for separation at the given centrifugal acceleration of 170000 x g. After 1 h of UC the supernatants of samples with higher silicate content still contained significantly higher U concentrations than samples with low silicate content. After 5 h UC time the uranium was almost completely removed from all samples, indicating that truly dissolved uranium did not play a significant part in the system, i.e. almost all the U was colloidal.
Keywords: uranium(IV) colloids, photon correlation spectroscopy, light scattering, silicic acid, ultracentrifugation, ultrafiltration
  • Poster
    Goldschmidt2009 - "Challenges to Our Volatile Planet", 21.-26.06.2009, Davos, Switzerland
  • Geochimica et Cosmochimica Acta 73(2009)13, A304 Suppl

Publ.-Id: 12398 - Permalink

Dosimetric comparison between gated and stationary photon and electron beams delivered by the Siemens ONCOR Avant-Garde linear accelerator.
Wieczorkowski, L.; Hoinkis, C.; Lehmann, D.; Enghardt, W.;
Objective: The gated irradiation technique is a sophisticated tool for focusing the prescribed dose to periodically moving target volumes whilst sparing the surrounding healthy tissue. Thus, gated irradiation is predominantly applied to organ motion caused by breathing. The tumour is irradiated in a specific phase of its motion. This requires to switch on and off the beam periodically. The duty cycle may vary in a certain range (about 17 to 75%). It depends on the individual and site specific time dependent elongation and the tumour dose conformity required. Obviously the latter will be increased at a low duty cycle, which, however, increases the number of irradiation cycles for reaching the prescribed dose. Transient effects during switching on and off the beam may influence the dose and its homogeneity. Prior to the therapeutic application of gated irradiation of bronchial carcinoma the dose distributions delivered for photons and electrons in steady and gated mode have been measured.

Methods: Photon and electron beams were delivered by an ONCOR AvantGarde linear accelerator (Siemens). The gating signal was provided by a commercial respiratory gating system based on a pressure belt feedback mechanism (AZ-733, Anzai Medical, Tokyo, Japan) in combination with a respiratory phantom. Lateral profiles of dose were measured by means of a linear diode array BMS 96 (Schuster Medizinische Systeme GmbH, Forchheim, Germany). Depth distributions within a solid water phantom (Piacryl RW3, PTW Freiburg, Germany) and output factors were determined using a Farmer ionization chamber (0.6 cm3) of PTW, Freiburg, Germany. Respiratory frequency values were set to 10 and 15 min-1 (i.e. 6 and 4 s, respectively) and beam-on time values of 1, 2 and 3 s were chosen. Different field sizes (5 × 5, 10 × 10 and 20 × 20 cm2) were used for 6 and 15 MV photons and 10 × 10 cm2 for 9 and 12 MeV electrons. The dose values and output factors of the gated beam delivery have been evaluated relative to those of the constant mode at 50, 100 and 200 MU for photons and 100 and 200 MU for electrons.

Results: Output factors and depth doses maximum deviations for gated photon and electron beams are up to 0.8 % in comparison to non-gated beams. The difference in symmetry and flatness of the dose profiles is less than 3 %. Deviations increase with decreasing beam-on time, decrease with increasing depth, are randomized and do not depend on the photon and electron energy. Minor dependence on the field size was observed but in most cases the results for the 10 × 10 cm2 field were more accurate. None respiratory frequency dependence (i.e. 15 min-1 or 10 min-1) was noticed as well.

Conclusion: All this measurements were performed in a stationary phantom and they are acceptable for clinical applications. To evaluate more realistic cases with respect to therapy the geometric and dosimetric verification in moving phantoms will be done.
  • Poster
    14. Jahreskongress der Deutschen Gesellschaft für Radioonkologie 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik „Der Wiener Kongress“ Radioonkologie-Medizin.Physik-Strahlenbiologie, 01.-04.05.2008, Wien, Österreich
  • Contribution to proceedings
    14. Jahreskongress der Deutschen Gesellschaft für Radioonkologie 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik „Der Wiener Kongress“, 01.-04.05.2008, Wien, Österreich
    Strahlentherapie und Onkologie 2008;184 (Sondernr 1): 1–165 DOI 10.1007/s00066-008-1001-9, München: Verlag Urban & Vogel, 124

Publ.-Id: 12397 - Permalink

Der supraleitende Fotoelektronen-Injektor an ELBE (SRF-Gun)
Arnold, A.; Teichert, J.; Murcek, P.; Xiang, R.;
no abstract available
  • Lecture (others)
    FZD-Seminar, Institut für Strahlenphysik, 17.12.2008, Dresden, Deutschland

Publ.-Id: 12395 - Permalink

A high-brightness superconducting photo-electron injector
Arnold, A.;
  • Lecture (others)
    Abteilungsseminar der Universität Rostock am Institut für allgemeine Elektrotechnik/Theoretische Elektrotechnik, 09.04.2008, Rostock, Deutschland

Publ.-Id: 12393 - Permalink

A high-brightniess superconducting photo-electorn injector for future FEL's
Arnold, A.; Büttig, H.; Teichert, J.; Janssen, D.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Xiang, R.;
Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. While the concepts of DC- and NC-guns are well proofed, the SRF gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the right photocathode type, its life time and possible cavity contamination. But in combination with SRF linacs, the SRF guns will be the best solution for high average currents and continuous wave operation.
The contribution will give an overview on the technical concept, the proposed performance, and the current status of the leading superconducting rf gun project developed in Dresden-Rossendorf. At the moment the cryomodule and a diagnostic beamline are installed next to the ELBE superconducting linear accelerator. During the first commissioning and test period the gun is operated in parallel to the existing dc thermionic gun, but at the end of 2008 it will be used to improve the beam quality of the ELBE accelerator significantly.
The first beam, using a copper cathode, was imaged on the screens on 12th November 2007. The UV-laser with an output power of 400mW at 100kHz rep. rate produced a beam current of 40nA and a corresponding bunch charge of 0.5pC. At next the commissioning of the diagnostic beamline, to measure all important beam parameters, will be finished and first high current tests using a Cs2Te-Cathode will be done.
  • Lecture (Conference)
    DPG Frühjahrstagung, 03.-07.03.2008, Freiburg, Deutschland


Publ.-Id: 12391 - Permalink

Rossendorf SRF-Gun Cavity Characteristics
Arnold, A.; Teichert, J.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Wiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is finished. This new injector is placed next to the existing thermionic gun of the superconducting linear accelerator called ELBE. In the next shutdown a connection between this accelerator and the SRF-Gun will provide the improved beam parameters for the users. At the moment the commissioning is fully under way.
The contribution will present important results concerning cavity commissioning like measurements of: Q vs. E, microphonics, Lorentz detuning, tuner parameters, spectra HOM excitation spectra and the field distribution calculated from measured fundamental mode passband. The results will be used to improve the existing cavity design.
  • Poster
    Workshop on Sources of Polarized Electrons and High Brightness Electron Beams, 01.-03.10.2008, Newport News, USA
  • Contribution to proceedings
    SPIN PHYSICS: 18th International Spin Physics Symposium, 06.-11.11.2008, Charlottesville, Virginia, USA
    AIP Conference Proceedings, Volume 1149,, Melville/NY, 978-0-7354-0686-5, 1125-1132
  • Poster
    First DITANET School on Beam Diagnostics, 30.03.-03.04.2009, London, UK


Publ.-Id: 12390 - Permalink

Experiences on NC Cathodes and Choke Filters
Arnold, A.; Teichert, J.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
  • Invited lecture (Conferences)
    CW Source Workshop at BESSY, 08.-10.09.2008, Berlin, Deutschland

Publ.-Id: 12389 - Permalink

Verbessert die IMRT die Möglichkeit einer Dosiseskalation bis 78 Gy für Patienten mit einem nichtkleinzelligen Bronchialkarzinom (NSCLC)?
Appold, S.; Evers, C.; Gillham, C.; Pönisch, F.; Enghardt, W.; Abolmaali, N.; Zöphel, K.; Hölscher, T.; Kotzerke, J.; Herrmann, T.; Baumann, M.; Zips, D.;
Hintergrund: In einer früheren Planungsstudie an Patienten mit NSCLC wurde untersucht, ob mittels einer FDG-PET/CT während einer fraktionierten Strahlentherapie eine Verkleinerung des Zielvolumens und damit eine Dosiseskalation der Dosis über 66 Gy möglich ist. Es zeigte sich, dass die Tumorvolumina während der Therapie abnahmen. Doch bei 6/10 Patienten war eine Therapie mit einer Dosis von 78 Gy selbst dann nicht möglich, wenn das Bestrahlungsvolumen nach 66 Gy auf die Tumorausdehnung des PET/CT 5-6 Wochen nach Beginn der RT (PET/CT w5-6) reduziert wurde (Radiother Oncol, in press). In der vorliegenden Untersuchung soll geprüft werden, ob eine optimierte inverse Therapieplanung für eine intensitätsmodulierte Strahlentherapie (IMRT) zu einer Reduktion der Normalgewebsbelastung führt und in diesen Fällen eine Dosiseskalation bis 78 Gy ermöglicht.

Patienten und Methodik: 10 Patienten mit einem NSCLC im Stadium III wurden in Bestrahlungsposition vor und während einer fraktionierten Strahlentherapie (66 Gy in 33 Fraktionen) mittels FDG-PET/CT (Biograph 16) untersucht. Die Konturierung des GTV in PET und CT erfolgte durch den Strahlentherapeuten (GC) und wurde durch einen Radiologen (NA) bzw. Nuklearmediziner (KZ) überprüft. Das PTV ergab sich durch einen Sicherheitsabstand von 1,5 cm um das GTV-PET/CT ohne prophylaktische Bestrahlung des Mediastinums. Die Strahlentherapie wurde mit einer Zieldosis von 78 Gy (Bestrahlung auf das Ausgangsvolumen oder Feldverkleinerung ab 66 Gy auf PTV-PET/CT w5-6) geplant (Pinnacle, Phillips). Die Vorgaben für die Normalgewebsbelastung waren:
Myelon max. 45 Gy , mittlere Lungendosis (MLD) £20 Gy, Lungenvolumen 20 Gy (V20) £37%, Ösophagusvolumen 60 Gy (V60) £30 %, Herzbelastung 1/3 £60 Gy, 2/3 £50 Gy und 3/3 £40 Gy. Für 6/10 Patienten, bei denen diese Vorgaben mit 3D-konformaler Planung nicht eingehalten werden konnten (5/10 Pat. V60 >30%; 3/10 Pat. V20>37% bzw. MLD>20 Gy), wurde eine IMRT geplant. Hierbei sollten die Minima im CTV (GTV+7 mm) ³95% sein, eine geringe Unterdosierung im PTV wurde akzeptiert.

Ergebnisse: Eine Reduktion der Belastung kritischer Organe (Lunge, Ösophagus) konnte bei 5 der 6 Patienten durch eine IMRT-Planung erreicht werden. Allerdings führte nur in 2 Fällen die IMRT zu einer Unterschreitung der vorgegebenen Dosisgrenzen und ermöglichte damit eine Dosiseskalation bis 78 Gy. Eine Reduktion des Bestrahlungsvolumens nach 66 Gy brachte dabei keinen entscheidenden Vorteil. Bei einem Patienten war eine inverse Planung mit einer akzeptablen Dosisverteilung nicht möglich. In 5/6 Fällen führte die IMRT-Planung zu einer inhomogeneren Erfassung des PTV und CTV mit geringen Minima im PTV.
Schlussfolgerung: In ausgewählten Fällen kann für Patienten mit NSCLC, für die mittels konventioneller Planung das Risiko der Normalgewebstoxizität zu hoch ist, durch eine IMRT-Planung eine Dosiseskalation bis 78 Gy möglich werden. Gefördert durch das BMBF (03ZIK042)
  • Poster
    14. Jahreskongress der Deutschen Gesellschaft für Radioonkologie 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik „Der Wiener Kongress“, 01.-04.05.2008, Wien, Österreich
  • Contribution to proceedings
    14. Jahreskongress der Deutschen Gesellschaft für Radioonkologie 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik „Der Wiener Kongress“, 01.-04.05.2008, Wien, Österreich
    Strahlentheraphie und Onkolologie 2008;184 (Sondernr 1): 1–165, München: Verlag Urban & Vogel

Publ.-Id: 12388 - Permalink

Overview on the most advanced SRF-Gun Projects in the world
Arnold, A.; Teichert, J.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
  • Invited lecture (Conferences)
    CW Source Workshop at BESSY, 08.-10.09.2008, Berlin, Deutschland

Publ.-Id: 12387 - Permalink

Commissioning results of the superconducting photoinjector for ELBE at FZ Dresden-Rossendorf
Teichert, J.; Arnold, A.; Büttig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.;
  • Invited lecture (Conferences)
    CARE 2008 Annual Meeting, 02.-05.12.2008, Geneva, Schweiz

Publ.-Id: 12386 - Permalink

Attenuation correction of four dimensional (4D) PET using phase-correlated 4D-computed tomography.
Pönisch, F.; Richter, C.; Just, U.; Enghardt, W.;
The image quality in a conventional positron emission tomography (PET)/computed tomography (CT) scanner is degraded by respiratory motion because of erroneous attenuation correction when three-dimensional image acquisition is used. To overcome this problem, time-resolved data acquisition (4D) is required. For this, a Siemens Biograph 16 PET/CT scanner has been modified and its normal capability has been extended to a true 4D-PET/4D-CT imaging device including phase-correlated attenuation correction. To verify the correct functionality of this device, experiments on a respiratory motion phantom that allowed movement in two dimensions have been performed. The measurements showed good spatial correlation as well as good time synchronization between the PET and CT data. Furthermore, the motion pattern of the phantom and the shape of the activity distribution have been examined, and the volume of the reconstructed PET images has been analyzed. The results demonstrate the feasibility of such a procedure, and we therefore recommend that 4D-PET data should be reconstructed using 4D-CT data, which can be acquired on the same machine.

Publ.-Id: 12384 - Permalink

First Test of a Turnkey 1.3 Ghz 30 kW IOT - Based Power Amplifier at ELBE
Büttig, H.; Erber, J.; Justus, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Bedau, J.; Dupire, P.; Gonella, O.;
Bruker BioSpin has developed a turnkey IOT-based RF-power amplifier in cooperation with CPI within a very short time of six months.
In the framework of a co-operation between Bruker, CPI and FZD (ELBE) first successfully tests were carried out to study the behaviour of the new amplifier at the superconducting linac ELBE. The results obtained and presented are used to optimize the design.
Keywords: turnkey IOT-based RF-power amplifier
  • Poster
    24. Linear Acc. Conference, 29.09.-03.10.2008, Victoria, Canada

Publ.-Id: 12382 - Permalink

Gain Deterioration at particular wavelengths in a partially waveguided FEL
Lehnert, U.; Staats, G.; Wünsch, R.;
abstract available
  • Poster
    30th annual International Conference on Free Electron Laser, 24.-29.8.2008, Gyeongju, Republic of Korea
  • Contribution to proceedings
    30th annual International Conference on Free Electron Laser, 24.-29.8.2008, Gyeongju, Republic of Korea

Publ.-Id: 12381 - Permalink

Design of the Nijmegen High-Resolution FIR-FEL
Lehnert, U.; Jongma, R.; Dunkel, K.; Piel, C.; van der Meer, A.; Michel, P.; Wuensch, R.; van der Zande, W.; van der Geer, K.; van der Slot, P.;
abstract available
  • Contribution to proceedings
    30th International (FEL) Conference on Free Electron Laser, 24.-29.8.2008, Gyeongju, Republic of Korea

Publ.-Id: 12380 - Permalink

The New Superconducting RF Photoinjector – a High-Average Current & High-Brightness Gun
Teichert, J.;
The paper reports on the first operation results of the Rossendorf superconducting RF photo electron gun (SRF gun). Developed in a collaboration with BESSY, DESY, and MBI and within the frame of European CARE project, the SRF gun is now installed at the superconducting electron accelerator ELBE. In November 2007 the first beam was produced. In 2008 the gun was operated with Cs2Te photo cathodes and RF and electron beam parameter measurements were carried out.
Keywords: RF photo electron gun electron accelerator ELBE
  • Lecture (Conference)
    The Second Workshop on High Average Power & High Brightness Beams, 14.-16.1.2009, Los Angeles, USA

Publ.-Id: 12379 - Permalink

Die supraleitenden Fotoelektronen-Injektor an ELBE (SRF-Gun)
Xiang, R.; Murcek, P.; Arnold, A.; Teichert, J.;
  • Lecture (others)
    FWKE Seminar, 17.12.2008, Dresden, Deutschlnad

Publ.-Id: 12378 - Permalink

Status Report on the Report on the Radiation Source ELBE User Facility and the NEw Superconducting Photoelectron Injector
Teichert, J.;
  • Lecture (others)
    SFB Seminar, 12.12.2008, Darmstadt, Deutschland

Publ.-Id: 12377 - Permalink

The Superconducting RF Photoinjector at ELBE - First Operational Experience
Teichert, J.; Arnold, A.; Büttig, H.; Michel, P.; Justus, M.; Lehnert, U.; Schamlott, A.; Xiang, R.; Schneider, C.; Schurig, R.;
A RF photo injector with a superconducting cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. This new and promising injector type allows CW operation and has the potential for the production of high-brightness electron beams. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed. In November 2007 the first beam was produced. Results of the beam parameter measurements with Cs2Te photo cathodes are presented.
Keywords: RF photo injector high brightness electron beams
  • Lecture (Conference)
    The Superconducting RF Photoinjector at ELBE – First Operational Experience, 01.-03.10.2008, Newport News, USA

Publ.-Id: 12375 - Permalink

Commissioning Results of the Superconducting Photo-Injector at ELBE
Teichert, J.; Büttig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Arnold, A.; Schurig, R.; Staats, G.; Büchner, A.; Staufenbiel, F.; Xiang, R.; Will, I.; Kamps, T.; Klemz, G.; Matheisen, A.;
  • Contribution to proceedings
    11th biennial European Particle Accelerator Conference EPAC'08,, 23.-27.6.2008, Genoa, Italy, Proceeding 2755

Publ.-Id: 12374 - Permalink

Current-voltage characteristics of metal-oxide-semiconductor devices containing Ge or Si nanocrystals in thin gate oxides
Beyer, V.; von Borany, J.; Klimenkov, M.; Müller, T.;
Current-voltage characteristics were measured, electrically modeled, and calculated for gate oxides, which contain nanocrystals (NCs) in different distributions, sizes, and densities. Ge and Si NCs were synthesized embedded in separate thin SiO2 layers by ion implantation at different fluences and subsequent annealing. It was found that the currents through the NC containing thin gate oxides are strongly related to the NCs’ location and are not driven by ion implantation induced oxide defects. Charging of the NCs determines the internal electrical fields, which is confirmed by simultaneous current and capacitance measurements. Depending on the implanted fluence the Ge NCs were mainly detected in the oxide center or close to the Si/SiO2 interface. The Si NCs were fabricated in the oxide center sandwiched between two oxide regions denuded of NCs. The processes of Si NC formation, growth and dissolution are discussed by means of kinetic lattice Monte Carlo simulations.
Keywords: nanocrystal, Si, Ge, ion implantation, leakage current, kinetic lattice Monte Carlo simulation, memory device
  • Journal of Applied Physics 106(2009), 064505

Publ.-Id: 12373 - Permalink

High-field splitting of the cyclotron resonance absorption in strained p-InGaAs/GaAs quantum wells
Drachenko, O.; Kozlov, D. V.; Aleshkin, V.; Gavrilenko, V. I.; Maremyanin, K. V.; Ikonnikov, A. V.; Zvonkov, B. N.; Goiran, M.; Leotin, J.; Fasching, G.; Winnerl, S.; Schneider, H.; Wosnitza, J.; Helm, M.;
We report a systematic study of the cyclotron resonance (CR) absorption of two-dimensional holes in strained InGaAs/GaAs quantum wells (QWs) in the quantum limit. The energies of the CR transitions are traced as a function of magnetic field up to 55 T. A remarkable CR line splitting was evidenced when the resonant field exceeds 20 T. We analyze our data with a 4x4 Luttinger Hamiltonian including strain and QW potentials using two different methods to calculate Luttinger parameters for ternary alloys. We found excellent agreement with the experiment when linear interpolation of the Luttinger parameters is used.
Keywords: Cyclotron resonance, high magnetic field, p-type, strain, InGaAs, GaAs, free electron laser, FEL, effective mass, Luttinger parameter, splitting

Publ.-Id: 12372 - Permalink

Field-controlled magnetic order in the quantum spin-ladder system (Hpip)2CuBr4
Thielemann, B.; Rüegg, C.; Kiefer, K.; Rønnow, H. M.; Normand, B.; Bouillot, P.; Kollath, C.; Orignac, E.; Citro, R.; Giamarchi, T.; Läuchli, A. M.; Biner, D.; Krämer, K. W.; Wolff-Fabris, F.; Zapf, V. S.; Jaime, M.; Stahn, J.; Christensen, N. B.; Grenier, B.; Mcmorrow, D. F.; Mesot, J.;
Neutron diffraction is used to investigate the field-induced, antiferromagnetically ordered state in the two-leg spin-ladder material (Hpip)2CuBr4. This “classical” phase, a consequence of weak interladder coupling, is nevertheless highly unconventional: its properties are influenced strongly by the spin Luttinger-liquid state of the ladder subunits. We determine directly the order parameter (transverse magnetization), the ordering temperature, the spin structure, and the critical exponents around the transition. We introduce a minimal microscopic model for the interladder coupling and calculate the quantum fluctuation corrections to the mean-field interaction.
  • Physical Review B 79(2009), 020408(R)

Publ.-Id: 12371 - Permalink

Medizinische Strahlenphysik in Dresden
Kunath, D.;
Vortrag über die Struktur und Forschungs-Schwerpunkte von OncoRay
  • Lecture (Conference)
    Seminar "Netzwerke für die Medizinische Physik in der Strahlentherapie", 13.-14.02.2009, Heidelberg, Deutschland

Publ.-Id: 12370 - Permalink

Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
Was sind Magnetfelder? Wo findet man sie? Wie erzeugt man sie und zu was sind sie nutze? Antworten auf diese Fragen sollen in dem Vortrag durch Vorstellung der weltweiten Bestrebungen, immer höhere Magnetfelder zu erreichen, gegeben werden. Ähnlich wie z. B. Druck und Temperatur haben magnetische Felder einen tief greifenden Einfluss auf den Zustand und Zustandsänderungen der Materie. Untersuchungen von Materialien in hohen Magnetfeldern sind daher mittlerweile Standard und eine Vielzahl von Anwendungen in unserem täglichen Leben sind ohne Magnetfeldeffekte undenkbar. In der Forschung wird der stetig wachsende Bedarf an möglichst großen Magnetfeldstärken durch Hochfeldlaboratorien abgedeckt. In dem neu aufgebauten Hochfeld-Magnetlabor Dresden sollen demnächst gepulste Magnetfelder bis zu 100 Tesla erzeugt werden. Erste Hochfeldmagnete sind in Betrieb und seit 2007 hat neben der Eigenforschung der Nutzerbetrieb begonnen. Der momentane Status des Labors, die Schwierigkeiten, die zur Erzeugung so hoher Magnetfelder überwunden werden müssen, und exemplarische wissenschaftliche Ergebnisse aus Hochfeldstudien sollen vorgestellt werden.
  • Invited lecture (Conferences)
    Universität Ulm, 09.02.2009, Ulm, Deutschland

Publ.-Id: 12369 - Permalink

Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
hat nicht vorgelegen
  • Lecture (others)
    Eröffnungsvortrag zum Tag des offenen Labors des Forschungszentrum Dresden-Rossendorf, 24.05.2008, Dresden, Deutschland

Publ.-Id: 12368 - Permalink

Window Coupler Test Stand at ELBE
Staats, G.; Buechner, A.; Büttig, H.; Michel, P.; Schurig, R.; Teichert, J.; Winter, A.;
abstract available
  • Lecture (Conference)
    TTC 2008, 14.-17.1.2008, Hamburg, Deutschland

Publ.-Id: 12366 - Permalink

Tunable-frequency ESR as a tool to study magnetic excitations in highly-correlated electron systems
Zvyagin, S.;
In this presentation I will talk about recent development of the high-field Electron Spin Resonance program at the Dresden High Magnetic Field Laboratory (HLD) in Rossendorf. A unique feature of the facility is a combination of an extraordinary broad frequency range, 9 GHz - 100 THz (quasi-continuously covered by a number of tunable-frequency radiation sources, including THz-range free-electron laser FELBE) and high magnetic fields (up to 60 T). The talk will be illustrated by tunable-frequency ESR results obtained in sine-Gordon chain material Cu-PM and BEC candidate NiCl2-4SC(NH22 (known as DTN).
  • Invited lecture (Conferences)
    Invited talk at the University of Florida, 18.11.2008, Gainesville, Florida, USA

Publ.-Id: 12365 - Permalink

Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
hat nicht vorgelegen
  • Lecture (others)
    Vorlesung in der Reihe "Physik am Samstag" der Fachrichtung Physik der TU Dresden, 13.12.2008, Dresden, Deutschland

Publ.-Id: 12364 - Permalink

Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
hat nicht vorgelegen
  • Lecture (others)
    Helmholtzabend am Forschungszentrum Dresden-Rossendorf, 05.09.2008, Dresden, Deutschland

Publ.-Id: 12363 - Permalink

Force-free and contactless sensor for electromagnetic flowrate measurements
Priede, J.; Buchenau, D.; Gerbeth, G.;
We present a novel design of a contactless flowmeter using a single cylindrical permanent magnet magnetised perpendicularly to its axis, about which it can freely rotate, and placed close to a duct with a liquid metal flow. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. The equilibrium rotation rate, which is attained at a vanishing net electromagnetic torque on the magnet, depends only on the flowrate and the geometry of the system while it is independent of the electromagnetic torque itself. A laboratory model of such a flowmeter has been built and tested at a liquid metal flow.
  • Magnetohydrodynamics 45(2009)3, 451-458

Publ.-Id: 12361 - Permalink

Design, Synthese und Anwendungsmöglichkeiten radiomarkierter Verbindungen
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Universität Duisburg-Essen, Institut für Organische Chemie, 05.02.2009, Essen, Deutschland

Publ.-Id: 12360 - Permalink

Role of D(E)RY motif in switching mechanism of G protein-coupled receptors studied by ITC
Eichler, S.; Fahmy, K.;
Membrane proteins, especially GPCRs (G-protein coupled receptors), play a fundamental role in many physiological processes. Their function is based on the ability to switch between different structures. Due to the low dielectricity of the lipidic environment, side chain charges contribute to the energetics of such transitions much more than in purely aqueous environment.
Our aim is to understand the functional implication of charged amino acids in the conformational control of membrane-spanning protein domains.
We used Isothermal Titration Calorimetry (ITC) to study proton uptake from the buffer by the class-defining and highly conserved D(E)RY motif in a synthetic peptide derived from rhodopsin transmembrane (TM) helix 3. By adding a negatively charged molecule (SDS) the pKA of the peptide is expected to be shifted and proton uptake from the buffer by glutamic acid in the D(E)RY motif is assumed to occur depending on pH. Thus the heat of buffer ionization depending on pH and buffer ionization enthalpy is measured according to Baker and Murphy. First experiments in phosphate buffer at pH 4.8 showed promising results, i.e. a titration curve with stoichiometry around 1:1 (SDS:peptide) and ∆H in good agreement to buffer ionization heat of phosphate buffer. However the buffer ionization heat of phosphate buffer is comparatively low and so are other buffers at that pH. Thus these results were not sufficiently reproducible and following experiments were performed at pH 6 and 8 with Imidazole buffer, PIPES and TRIS. These results were good reproducible but no buffer ionization could be shown. A pKA shift in our model peptide introduced by an additional charge (SDS) could not be proved by means of ITC. Thus, there is no evidence for breakage of the internal Glu-Arg salt bridge by competition with an Arg-sulfate interaction.
Keywords: GPCR, D(E)RY motif, Isothermal Titration Calorimetry
  • Poster
    18. Ulm-Freiberger Kalorimetrietage, 18.-20.03.2009, Freiberg, Deutschland

Publ.-Id: 12359 - Permalink

Instability of the melt flow in VGF growth with a traveling magnetic field
Grants, I.; Klyukin, A.; Gerbeth, G.;
The linear instability of a thermally stratified melt flow in the VGF configuration driven by a traveling magnetic field (TMF) is considered numerically and experimentally. The dependency of the instability threshold on the governing parameters is found for several cuts through the parameter space covering a wide range of possible applications. In a first approximation the linear instability occurs when the dimensionless TMF forcing parameter reaches the magnitude of the Grashof number. This is particularly true in a medium-sized crucible where the first instability is axisymmetric and sub-critical. As the Grashof number increases the flow develops self-similar boundary layers and the instability becomes three-dimensional. The instability originates in the bottom boundary layer where the convection tends to suppress the imposed temperature gradient in the central part of the melt zone. It is shown that the TMF may serve as a tool to control the phase interface shape without causing flow instationarity when the crucible diameter exceeds a certain value. This value is estimated to be around 5-6 cm for GaAs. The flow stays stable if the TMF is used for a reversal of the meridional flow with the aim to remove a possible dopant concentration peak on the axis.
  • Journal of Crystal Growth 311(2009)17, 4255-4264

Publ.-Id: 12358 - Permalink

Growth and Electrical Properties of the (Si/Ge)-on-Insulator Structures Formed by Ion Implantation and Subsequent Hydrogen-Assisted Transfer
Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.;
Systematic features of endotaxial growth of intermediate germanium layers at the bonding interface
in the silicon-on-insulator structure consisting of buried SiO2 layer implanted with Ge+ ions are studied in relation to the annealing temperature. On the basis of the results for high-resolution electron microscopy and thermodynamic analysis of the Si/Ge/SiO2 system it is assumed that the endotaxial growth of the Ge layer occurs via formation of a melt due to enhanced segregation and accumulation of Ge at the Si/SiO
interface. Effect of germanium at the bonding interface on the Hall mobility of holes in silicon layers with nanometer-scale thickness is studied. It is found that the structures including the top silicon layer with the thickness 3–20 nm and incorporating germanium feature the hole mobility that exceeds by a factor of 2–3 the hole mobility in corresponding Ge-free silicon-on-insulator structures.
Keywords: Si/Ge, Electrical Properties, Ion Implantation, Hydrogen Transfer
  • Semiconductors 43(2009)1, 52-56
  • Fizika i Tekhnika Poluprovodnikov 43(2009)1, 58-63

Publ.-Id: 12357 - Permalink

Evidence for an FFLO state in layered organic superconductors
Wosnitza, J.;
In the so-called FFLO state, named after Fulde, Ferrell, Larkin, and Ovchinnikov, the superconducting state can survive even at high magnetic fields above the Pauli paramagnetic limit. The quasi-two-dimensional (2D) organic superconductors have been suggested as good candidates for exhibiting the FFLO state. When applying the magnetic field exactly parallel to the conducting layers the orbital pair breaking is greatly suppressed and the Pauli limit is reached. We performed high-resolution specific-heat and torque-magnetization experiments in magnetic fields up to 28 T for different 2D organic superconductors. In a very narrow region close to parallel orientation we observe additional anomalies below the upper critical field signalling the existence of an additional superconducting phase. The specific-heat data for kappa-(BEDT-TTF)2Cu(NCS)2 with Tc = 9.1 K show that the superconducting transition becomes first order for fields above 21 T indicating that the Pauli limit is reached. Below about 3 K, the upper critical field increases sharply and a second first-order transition appears within the superconducting phase. Our results give strong evidence for the realization of the FFLO state in organic superconductors.
  • Invited lecture (Conferences)
    10th German-Japanese Symposium "Collective Quantum Phenomena in Correlated Condensed Matter Systems", 28.09.-01.10.2008, Ringberg Castle, Rottach-Egern, Deutschland

Publ.-Id: 12356 - Permalink

Magnetic quantum oscillations in strongly correlated metals - experimental data meet theoretical predicitons
Wosnitza, J.;
hat nicht vorgelegen
  • Invited lecture (Conferences)
    DFT Meets Experiment & 7th Tutorial Hand-on-FPLO, Workshop at the IFW Dresden, 25.-28.08.2008, Dresden, Deutschland

Publ.-Id: 12355 - Permalink

Calorimetric Evidence for an FFLO superconducting state in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2
Wosnitza, J.;
hat nicht vorgelegen
  • Invited lecture (Conferences)
    The 63rd Calorimetry Conference, 02.-06.07.2008, Jersey City, New Jersey, USA

Publ.-Id: 12354 - Permalink

Amorphous clusters in Co implanted ZnO induced by boron pre-implantation
Potzger, K.; Shalimov, A.; Zhou, S.; Schmidt, H.; Mücklich, A.; Helm, M.; Fassbender, J.ORC; Arenholz, M.; Liberati, E.
We demonstrate the formation of superparamagnetic/ferromagnetic regions within ZnO(0001) single crystals sequentially implanted with B and Co. While the pre-implantation with B plays a minor role for the electrical transport properties, its presence leads to the formation of amorphous phases. Moreover, B acts strongly reducing on the implanted Co. Thus, the origin of the ferromagnetic ordering in local clusters with large Co concentration are itinerant d-electrons as in the case of metallic Co. The amorphous Co-based phases are non-detectable by common X-ray diffraction.
Keywords: ZnO, DMS, Ion implantation
  • Journal of Applied Physics 105(2009)12, 123917

Publ.-Id: 12353 - Permalink

Static and dynamic magnetization processes in magnetic property patterned thin films
McCord, J.; Hamann, C.; Martin, N.; Mönch, I.; Kaltofen, R.; Schultz, L.; Strache, T.; Fassbender, J.ORC; Mattheis, R.
The control of the effective magnetic anisotropy, saturation magnetization as well as the dynamic magnetic properties in ferromagnetic thin films is of significant importance for most applications in spin electronics. Usually, the magnetic anisotropy, e.g. uniaxial anisotropy or unidirectional anisotropy (exchange bias), in ferromagnetic single or multi-layers is initialized by applying a magnetic field during film deposition or by a magnetic field anneal, which results in an anisotropy aligned along the applied field direction. The saturation magnetization is mainly determined by the film's composition. Whereas anisotropy and saturation magnetization together determine the precessional frequency of the films, the magnetic damping parameter cannot easily be varied in a controlled way.

We demonstrate different ways to pattern soft magnetic magnetic films in terms of laterally varying magnetic properties [1]. In distinction from conventionally patterned systems, the magnetic behavior of these hybrid property films is strongly influenced by the direct exchange interaction across the (now) magnetic property element's borders. Therefore, the effects are directly correlated with the magnetic feature size. Below a critical magnetic feature size, a transition from a magnetic two-phase material to an effective magnetic meta material occurs. This makes them in some sense comparable to magnetic multilayer structures. However, the lateral 'layers' permit access to spatially resolved characterization methods.

Different samples of anisotropy [1,2], exchange bias [1,3], and saturation magnetization [4] modulated thin films are prepared by local oxidation, introducing local stress variation [5], or local ion irradiation. The magnetization reversal processes in the two-phase materials exhibit unique features, some of them so far only known from magnetic multilayer samples. The main emphasis is on the role of magnetic domain formation and domain wall effects in stripe-like magnetic hybrid structures on the overall magnetization properties. Quasi-cubic anisotropies and bi-directional anisotropies, as well as lateral exchange spring behavior are derived from hysteresis loop measurements and magnetic domain imaging. Effects from the introduced quasi-domains, which are related to the domain wall structure and the corresponding wall interaction, will be discussed. In addition, data regarding the influence of pattern density on precessional frequency and effective damping parameter will be shown.

The presented paths of film preparation provide additional degrees of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films. Some of the presented methods allow for a local setting of magnetic properties without irreversible structural and magnetic alterations.

Financial support from the Deutsche Forschungsgemeinschaft DFG is highly acknowledged.

[1] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320, 579 (2008)
[2] J. McCord, I. Mönch et al., J. Phys. D: Appl. Phys., accepted (2009)
[3] C. Hamann, I. Mönch et al., J. Appl. Phys. 104, 13926 (2008)
[4] J. McCord, L. Schultz et al., Adv. Mat. 20, 2009 (2008)
[5] N. Martin, J. McCord et al., Appl. Phys. Lett., accepted (2009)
Keywords: magnetism, ion irradiation, ion implantation, magnetic domains, magnetization processes, property patterning
  • Invited lecture (Conferences)
    International Magnetics Conference, 04.-08.05.2009, Sacramento, USA

Publ.-Id: 12352 - Permalink

Engineering surfaces, interfaces and structural phases to tailor magnetic properties
Fassbender, J.ORC
Surfaces and interfaces play an important role in order to determine the overall properties of ultrathin magnetic films and multilayers. In particular, the morphology and roughness of the surface and the sharpness of mutual interfaces between magnetic and non-magnetic thin films are crucial. All these parameters are easily accessible by means of ion irradiation [1,2], ion implantation [2,3] and ion erosion approaches [4]. Also structural phase transitions can be accompanied by magnetic ones [5] which allow the creation of nanomagnets in the sub-100 nm regime [6]. In this talk I am going to present a survey of ion beam modifications of magnetic materials with special emphasis on the basic phenomena including some technological applications. Supported by DFG FA 314/3-1, FA 314/6-1 and FA 314/7-1.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mat. 320, 579 (2008).
[3] J. McCord, L. Schultz, J. Fassbender, Adv. Mater. 20, 2090 (2008).
[4] M. O. Liedke et al., Phys. Rev. B 75, 220407(R) (2007).
[5] J. Fassbender et al., Phys. Rev. B 77, 174413 (2008).
[6] E. Menendez et al., Small, in press.
Keywords: magnetism, ion irradiation, ion implantation, interface, phase transition
  • Invited lecture (Conferences)
    Gaede-Preis-Vortrag auf der Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12351 - Permalink

Atembewegungskorrektur von listmode-basierten Ganzkörperuntersuchungen mit dem PET-Scanner ECAT Exact HR+
Mölle, H.; Langner, J.; Beuthien-Baumann, B.; Hofheinz, F.; Will, E.; van den Hoff, J.;
Die Messzeit bei Ganzkörperuntersuchungen (GKU) am PET-Scanner ECAT Exact HR+ beträgt 6-8 Minuten pro Bettposition. Atembewegungen des Patienten sind während einer solchen Aufnahme unvermeidbar, woraus unter anderem eine lageabhängige Beeinträchtigung der Tumorabbildung resultiert. Hieraus ergibt sich insbesondere eine Verfälschung quantitativer Parameter wie des SUV und des scheinbaren Tumorvolumens, die unter anderen im Rahmen der Therapieresponse und Follow-up Untersuchungen von Bedeutung sind. Daher ist es wünschenswert die atmungsbedingte Unschärfe bei GKU in der klinischen Routine zu korrigieren.

Es wurden Methoden für die Durchführung listmode-basierter GKU implementiert (Akquisition der Listmodedaten für jede Bettposition, Steuerung des Bettvorschubs, Eintrag der Datensätze in die ECAT-Datenbank). Das Verfahren wurde bisher bei 32 klinischen Untersuchungen eingesetzt. Gleichzeitig erfassten Infrarot-Tracking-Kameras die Brustkorbbewegung der Patienten. Anhand der Bewegungsamplitude erfolgte die Einteilung der Listmodedaten in einzelne Atemphasen (Gates). Mit Hilfe eines Atembewegungsmodells, das die Atembewegung im inneren des Körpers vereinfacht modelliert, wurden alle Atemphasen auf eine einzige Atemphase abgebildet.

Erstmals konnten listmode-basierte GKU (6-8 Bettpositionen) mit gleichzeitiger Atembewegungserfassung am PET-Scanner ECAT Exact HR+ in der klinischen Routine durchgeführt werden. Dadurch wird eine Atembewegungskorrektur bei GKU ermöglicht. Um die Größe der Korrektur zu prüfen, wurde die Organbewegung der Patienten bestimmt. Vorläufige Ergebnisse zeigen eine mittlere transaxiale Bewegung der Niere von 0.93 ± 0.43 cm. Die Bewegung war so groß, dass bei den meisten Patienten eine Korrektur sowohl im Bereich des Thorax als auch im Abdomen notwendig ist. Die bewegungskorrigierten GKU enthalten nur noch minimale Bewegungen, wodurch eine bessere Quantifizierung des Tumorvolumens und des SUV im Tumor möglich ist.

Die hier vorgestellte Methode der Atembewegungskorrektur bei GKU mit dem PETScanner ECAT Exact HR+ führt zu einer deutlichen Verbesserung der Bildqualität. Die Bewegungskorrektur erfolgt weitestgehend automatisch, wodurch ein Einsatz in der klinischen Routine problemlos möglich ist.
  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A21

Publ.-Id: 12350 - Permalink

Atomistic simulation of amorphous germanium and its solid phase epitaxial recrystallization
Posselt, M.; Gabriel, A.;
Amorphous Ge and its recrystallization are investigated by molecular dynamics simulations using a Stillinger-Weber-type interatomic potential. Unlike previously used parametrizations of this potential the parameter set employed in this work yields a reasonable description of all condensed phases of Ge. The preparation of amorphous Ge is performed by cooling from the molten state. Structural and thermal properties of the amorphous phase such as the pair correlation function, the atomic density as well as the melting temperature are calculated and a good agreement with experimental data is found. In order to obtain the initial atomic configuration for the simulation of recrystallization of amorphous Ge, a simulation cell that contains an amorphous and a crystalline layer is carefully prepared by melting a part of a primarily crystalline simulation cell and by cooling the liquid in a similar manner as in the preparation of bulk amorphous Ge. The recrystallization is simulated in the temperature range between 600 and 950 K. The simulation cell is built in such a manner that the main regrowth direction is parallel to [100]. Using an efficient characterization method the configuration of the current amorphous-crystalline interface, its average position with respect to the [100] direction and its roughness given by the rms deviation of this position are determined throughout the simulations. Consistently with former models for Si it is found that recrystallization of amorphous Ge occurs mainly at small {111} facets and is characterized by a sequential local rearrangement of atomic bonds and positions. In very good agreement with experiments the dependence of the velocity of solid phase epitaxial recrystallization on temperature can be approximated by a straight line in an Arrhenius plot. However, the absolute value of the velocity is too high compared to the experimental data. The main reason for this discrepancy may be the overestimation of the flexibility of atomic bonds by the present interatomic potential which leads to an underestimation of the activation energy. Similar to the state of the art in atomistic simulations of solid phase epitaxial regrowth in Si, there is not yet a suitable interatomic potential which allows a consistent quantitative modeling of both the condensed phases and the solid phase epitaxial recrystallization.
Keywords: solid phase epitaxy, atomistic simulation, germanium
  • Physical Review B 80(2009), 045202

Publ.-Id: 12349 - Permalink

Boron activation and diffusion in silicon and strained silicon-on-insulator by rapid thermal and flash lamp annealing
Lanzerath, F.; Buca, D.; Trinkaus, H.; Goryll, M.; Mantl, S.; Knoch, J.; Breuer, U.; Skorupa, W.; Ghyselen, B.;
We present experimental results on the activation and diffusion behaviors of boron in silicon-on-insulator and strained silicon-on-insulator using standard rapid thermal processing treatments as well as flash lamp annealing. After boron implantation at different doses and at a low energy of 1 keV, samples were annealed to activate the dopants, and secondary ion mass spectrometry and Hall measurements were carried out to determine boron diffusion and the amount of activated dopants, respectively. In contrast to rapid thermal annealing, flash lamp annealing enables the activation without significant diffusion of dopants. In addition, we investigated the effect of coating the samples with antireflection layers to increase the absorbed energy during flash annealing. As a result, the activation was increased significantly to values comparable with the activation obtained with standard annealing. Furthermore, the relation between the observed boron diffusion and activation as a function of the implantation and annealing parameters is discussed in terms of the kinetics of the defects involved in these processes.
Keywords: silicon-on-insulator, strained silicon-on-insulator, flash lamp annealing, rapid thermal annealing, Boron implantation, electrical activation
  • Journal of Applied Physics 104(2008), 044908-1-044908-7

Publ.-Id: 12348 - Permalink

Ion beam analysis (IBA) and accelerator mass spectrometry (AMS) with the new 6 MV accelerator at FZ Dresden-Rossendorf
Neelmeijer, C.; Grambole, D.; Grötzschel, R.; Merchel, S.; Munnik, F.;
Since more than 30 years IBA is performed at the Forschungszentrum Dresden-Rossendorf (FZD) for the determination of element distributions. Due to continuous upgrades of the different experimental set-ups, we are able to routinely perform:
• Rutherford Backscattering Spectrometry (RBS) & Channeling (C-RBS)
• Nuclear Reaction Analysis (NRA)
• Elastic Recoil Detection Analysis (ERDA)
• Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE)
Most of our applications lie within material sciences. We are able to measure non-destructively “all natural” elements, i.e. H to U; most elements with lateral, some in 3-D resolution with the following typical parameters (matrix- and analyte-depending):
• depth resolution: 0.5-30 nm
• depth range: nm-µm
• lateral resolution: few µm
• usual mapping area: 2x2 mm2
• maximum sample size: 3x10 cm2 (vacuum) & “unlimited” (external beam)
• detection limits: ~10 µg/g (H); 500 µg/g – 1% (He-F); 10-100 µg/g (Na-U)
In summer 2009, our 5 MV van-de-Graaff accelerator will be replaced by a 6 MV Tandetron model [1], which is even more sophisticated than the lately installed 5 MV one in France [2]. The new accelerator will need less maintenance allowing more beam time. It might be also possible to expand from two to three 8-hour-shifts a day with the new fully automatic system. The main scientific advantages are an increased depth range by a factor of two for ERDA and improved detection limits for NRA. The high energy resolution also provides the ion optical requirements for a MeV-ion nanoprobe for selective in vivo-irradiation of cell nuclei at the nanometre-scale.
In addition, the machine will have special equipment for AMS [3]. There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses (e.g. isobars), are nearly completely eliminated. Thus, AMS provides much lower detection limits compared to conventional mass spectrometry (isotope ratios: 10-10-10-15).
In contrast to common low-energy AMS facilities, which have mainly specialized in radiocarbon analyses, the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV. Especially in environmental and geosciences, the determination of long-lived (t1/2 > 0.3 Ma) cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last decades [4]. Using these nuclides dating of e.g. volcanic eruptions, rock avalanches, earth quakes, and glacier movements is possible.
References: [1] A. Gottdang et al., Nucl. Instr. and Meth. B 2002, 190, 177. [2] M.G. Klein et al., Nucl. Instr. and Meth. B 2008, 266, 1828. [3] [4] J.C. Gosse and F.M. Phillips, Quat. Sci. Rev. 2001, 20, 1475.
Keywords: ion beam analysis, accelerator mass spectrometry
  • Poster
    GDCh-Wissenschaftsforum Chemie 2009, 30.08.-02.09.2009, Frankfurt am Main, Deutschland

Publ.-Id: 12347 - Permalink

Radio-induced alteration in cordierite – Implications for petrology, gemmology and materials science
Krickl, R.; Nasdala, L.; Grambole, D.; Kaindl, R.;
Cordierite is a common metamorphic and magmatic mineral, which is used as petrologic tool for reconstructing the history of its host rock. Further applications include cordierite gemstones and the use of synthetic analogs in ceramics. Cordierite is stable over a wide temperature and pressure range and relatively resistant to chemical alteration; however, its properties can be significantly changed upon the impact of external irradiation.
In the course of a comprehensive study, natural radiohaloes in cordierite (a widespread feature caused by the impact of alpha-particles originating from radioactive inclusions) as well as artificial analogs produced by implantation of 8.8 MeV He2+ ions were investigated using modern micro-techniques. Additional irradiation experiments were performed using O6+ ions, electrons and gamma-rays.
Ion irradiation causes yellow colouration that is strongly pleochroic, and fades at higher doses. The possibility of radiation-treatment for enhancing the quality of gem-cordierite is discussed. While samples remain crystalline up to doses of 1016 He2+ /cm², the same material is fully amorphised when irradiated with the same dose of 30 MeV O6+ ions. These different observations may help to estimate the performance assessment of cordierite-ceramics in radiated environments.
A most important result concerning the petrological use of cordierite is the radio-induced transformation of channel constituents: Inside the irradiated areas the vibrational bands of CO2 decrease in intensity, whereas two new bands appear at 2135 cm-1 (both IR and Raman; cf. Nasdala et al., 2006) and 1550 cm-1 (Raman only). They are assigned to stretching vibrations of carbon monoxide and molecular oxygen, respectively, thus indicating a radio-chemical transformation 2CO2 → 2CO + O2 in alpha-irradiated cordierite. This study yields the first spectroscopic evidence for the irradiation-induced formation of molecular oxygen in cordierite. Polarised vibrational spectra of oriented samples give evidence that not only CO2 but also CO and O2 are preferentially oriented parallel [100], most probably being located at the Ch0 position in the large channel cavities. Carbon monoxide and O2 molecules seem to coexist in artificially irradiated cordierite without any sign of back reaction. Investigations on natural CO2 -bearing cordierite from different localities show that the 2CO2 → 2CO + O2 transformation is ubiquitous in radiohaloes.
Up to date, the detection of CO in cordierite has solely been ascribed to a reducing environment during crystal formation (Khomeko & Langer, 2005). In contrast, this present study shows that CO can also be produced by the action of radioactivity. This, as well as the production of radiogenic O2 , has to be taken into account in reconstructing palaeofluid compositions from molecules trapped in the structural channels of cordierite.

Khomenko VM, Langer K (2005): Carbon oxides in cordierite channels: Determination of CO2 isotopic species and CO by single crystal IR spectroscopy. Am Mineral 90: 1913-1917
Nasdala L, Wildner M, Wirth R, Groschopf N, Pal DC, Möller A (2006): Alpha particle haloes in chlorite and cordierite. Mineral Petrol 86: 1-27
  • Poster
    General Assembly 2009 of the European Geosciences Union (EGU), 19.-24.04.2009, Vienna, Austria
  • Open Access LogoAbstract in refereed journal
    Geophysical Research Abstracts 11(2009), EGU2009-2657-2

Publ.-Id: 12346 - Permalink

Binding Form of Uranium in Environmental Relevant Compartments
Bernhard, G.; Geipel, G.;
wird nachgereicht
  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SEISS-08), 21.-29.11.2008, Kolkata, India

Publ.-Id: 12345 - Permalink

Chemistry of Actinides
Bernhard, G.; Geipel, G.;
wird nachgereicht
  • Invited lecture (Conferences)
    School cum Workshop on Trace Element Speciation (SElS-08), 24.-28.11.2008, Kolkata, India

Publ.-Id: 12344 - Permalink

Subsecond melt processing for achieving SiGe surface layers
Voelskow, M.; Kanjilal, A.; Skorupa, W.;
High dose germanium (Ge) ion implantation in silicon (Si) substrate in combination with flash lamp irradiation was used to produce a thin SiGe surface layer. Due to the reduced melting temperature of the SiGe alloys, the possibility to form an undesirable facetted liquid/solid interface, well known for pulse melting in the millisecond time regime, was found to decrease significantly using ion beam implantation technique. The formation of a dislocation network in the surface SiGe layer and strain were evidenced by transmission electron microscopy and -Raman spectroscopy measurements, respectively.
Keywords: SiGe, FLA, RBS, Raman spectroscopy


Publ.-Id: 12343 - Permalink

Planned experiment on 40Ca(alpha,gamma)44Ti in Dresden
Bemmerer, D.;
The 40Ca(alpha,gamma)44Ti nuclear reaction is important for the production of 44Ti in the alpha-rich freezeout in supernovae. The decay of 44Ti has been observed in several staellite-based gamma observatories for the Cas A supernova remnant, but surprisingly not in other cases. A new 40Ca(alpha,gamma)44Ti cross section measurement planned in Dresden is briefly described in the talk. The irradiations are to be performed at the FZD 3 MV Tandetron. Besides in-beam gamma-spectrometry and accelerator mass spectrometry, the main detection method will be an activation measurement. The weak activated 44Ti samples will be counted in the Felsenkeller underground low-level counting facility.
  • Invited lecture (Conferences)
    Research Day "44Ti" of the Excellence cluster "Origin and structure of the universe", 15.01.2009, München, Deutschland

Publ.-Id: 12342 - Permalink

Comparison of two dedicated 'in beam' PET systems via simultaneous imaging of 12C-induced β+-activity
Attanasi, F.; Belcari, N.; Del Guerra, A.; Enghardt, W.; Moehrs, S.; Parodi, K.; Rosso, V.; Vecchio, S.;
The selective energy deposition of hadrontherapy has led to a growing interest in quality assurance techniques such as ‘in-beam’ PET. Due to the current lack of commercial solutions, dedicated detectors need to be developed. In this paper, we compare the performances of two different ‘in-beam’ PET systems which were simultaneously operated during and after lowenergy carbon ion irradiation of PMMA phantoms at GSI Darmstadt. The results highlight advantages and drawbacks of a novel in-beam PET prototype against a long-term clinically operated tomograph for ion therapy monitoring.
  • Physics in Medicine and Biology 54(2008), n29-n35

Publ.-Id: 12341 - Permalink

Direct measurement of the 15N(p,gamma)16O total cross section at novae energies
Bemmerer, D.; Caciolli, A.; Bonetti, R.; Broggini, C.; Confortola, F.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Junker, M.; Limata, B.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Alvarez, C. R.; Somorjai, E.; Straniero, O.;
The 15N(p,gamma)16O reaction controls the passage of nucleosynthetic material from the first to the second carbon-nitrogen-oxygen (CNO) cycle. A direct measurement of the total 15N(p,gamma)16O cross section at energies corresponding to hydrogen burning in novae is presented here. Data have been taken at 90-230 keV center-of-mass energy using a windowless gas target filled with nitrogen of natural isotopic composition and a bismuth germanate summing detector. The cross section is found to be a factor two lower than previously believed.
Keywords: Nuclear astrophysics; Nova burning, CNO cycle; gas target; BGO detector; LUNA

Publ.-Id: 12340 - Permalink

First 4D in-beam PET measurement for beam tracking of a moving phantom with a scanned carbon ion beam
Parodi, K.; Saito, N.; Richter, C.; Chaudhri, N.; Enghardt, W.; Rietzel, E.; Bert, C.;
More than 10 years of clinical operation of in-beam PET at GSI Darmstadt have proven its positive impact on quality assurance of carbon ion therapy, mostly for head-and-neck sites. Due to the promise of ion beam therapy for indications such as lung and liver tumors which are influenced by respiratory motion we started to investigate the potential of time-resolved, 4D in-beam PET. 4D in-beam PET is expected to facilitate in-vivo assessment of tumor miss or unwanted involvement of nearby critical structures in the presence of organ motion. In a first experiment performed at GSI, in-beam PET was used in combination with beam tracking. A homogeneous PMMA phantom was placed in the center of the field of view of the PET camera and moved parallel to the two detector heads (left-right in beam's eye view, amplitude: 3 cm peak-to-peak, period: ~ 3 s). Dose was delivered by beam tracking as a two-dimensionally spread-out Bragg-peak of 5 x 5 cm2 extension, centered at a depth of 10 cm in the central plane of the phantom. The dynamic PET acquisition was performed during the 6 min of beam delivery and for 25 min after irradiation. The data stream was synchronized with the time course of the dynamic beam application and with the phantom motion. Additional 18 min of decay were acquired with the activated phantom kept steady, for comparison with a separate measurement of the same treatment field without motion. Reconstruction of the data taken with a steady phantom yielded comparable activation patterns for beam tracking and stationary irradiation. 4D PET reconstruction is currently in progress. Motion phase sorted data as well as results for imaging performance in dependence on the amount of reconstructed events will be presented. First conclusions on the feasibility of in-beam PET for monitoring ion treatment of moving targets will be discussed.
  • Lecture (Conference)
    IEEE MIC 2008, 19.-25.10.2008, Dresden, Deutschland
  • Contribution to proceedings
    IEEE Dresden 2008, 19.-25.10.2008, Dresden, Deutschland
    IEEE Conference Report

Publ.-Id: 12339 - Permalink

Phasenkorrelierte Schwächungskorrektur von 4D-PET mit Hilfe von 4D-CT
Richter, C.; Just, U.; Pönisch, F.; Enghardt, W.;
kein Abstract vorhanden
  • Poster
    OncoRay Retreat 2008, 08.-09.01.2008, Gröditz, Deutschland

Publ.-Id: 12338 - Permalink

Phase-Correlated Attenuation Correction (PC-AC) for 4D-PET/4D-CT
Richter, C.;
  • Lecture (others)
    3rd Meeting of the Scientific Advisory Board of OncoRay, 28.02.2008, Dresden, Deutschland

Publ.-Id: 12337 - Permalink

On the multivariate nature of brain metabolic impairment in Alzheimer's disease
Salmon, E.; Kerrouche, N.; Perani, D.; Lekeu, F.; Holthoff, V.; Beuthien-Baumann, B.; Sorbi, S.; Lemaire, C.; Herholz, K.;
We used principal component analysis to decompose functional images of patients with AD in orthogonal ensembles of brain regions with maximal metabolic covariance. Three principal components explained 38% of the total variance in a large sample of FDG-PET images obtained in 225 AD patients. One functional ensemble (PC2) included limbic structures from Papez's circuit (medial temporal regions, posterior and anterior cingulate cortex, thalamus); its disruption in AD patients was related to episodic memory impairment. Another principal component (PC1) illustrated major metabolic variance in posterior cerebral cortices, and patients’ scores were correlated to instrumental functions (language and visuospatial abilities). PC3 comprised frontal, parietal, temporal and posteromedial (posterior cingulate and precuneus) cortices, and patients’ scores were related to executive dysfunction and global cognitive impairment. The three main metabolic covariance networks converged in the posterior cingulate area that showed complex relationships with medial temporal structures within each PC. Individual AD scores were distributed as a continuum along PC axes: an individual combination of scores would determine specific clinical symptoms in each patient.
Keywords: Alzheimer; Dementia; PET; Brain imaging; Multivariate; PCA

Publ.-Id: 12336 - Permalink

Magnetic Structure of RuSr2GdCu2O8 Determined by Resonant X-Ray Diffraction
Bohnenbuck, B.; Zegkinoglou, I.; Strempfer, J.; Nelson, C. S.; Wu, H.-H.; Schüßler-Langeheine, C.; Reehuis, M.; Schierle, E.; Leininger, P.; Herrmannsdörfer, T.; Lang, J. C.; Srajer, G.; Lin, C. T.; Keimer, B.;
X-ray diffraction with photon energies near the Ru L2-absorption edge was used to detect resonant
reflections characteristic of a G-type superstructure in RuSr2GdCu2O8 single crystals. A polarization
analysis confirms that these reflections are due to magnetic order of Ru moments, and the azimuthal-angle
dependence of the scattering amplitude reveals that the moments lie along a low-symmetry axis with
substantial components parallel and perpendicular to the RuO2 layers. Complemented by susceptibility
data and a symmetry analysis of the magnetic structure, these results reconcile many of the apparently
contradictory findings reported in the literature
  • Physical Review Letters 102(2009), 037205

Publ.-Id: 12335 - Permalink

Magnetic field control of the pouring process in aluminium investment casting
Gerbeth, G.; Eckert, S.; Galindo, V.; Willers, B.; Hewelt, U.; Hornung, B.;
The mould filling process of aluminium investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical 3d transient calculations were performed to simulate the filling process and the effect of the magnetic field. In parallel, model experiments with a plexiglas model have been performed using the low melting eutectic GaInSn. Ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. These measurements served for the validation of the numerical calculations, thus allowing to scale up the simulations to the realistic aluminium casting process.
The developed DC field system has been tested under industrial conditions. The amplitude of the DC field was tuned during the process as the braking action is only needed during the first part of the process. In this way, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time. A multitude of investment casting units have been produced showing a significant diminishment of defects due to the magnetic field control of the pouring process.
  • Contribution to proceedings
    11th International Conference on Aluminium Alloys, 22.-26.09.2008, Aachen, Germany
    Aluminium Alloys, Eds.: J. Hirsch, B. Skrotzki, G. Gottstein: Wiley-VCH, 427-433
  • Lecture (Conference)
    11th International Conference on Aluminium Alloys, 22.-26.09.2008, Aachen, Germany

Publ.-Id: 12334 - Permalink

Synthesis and cyclooxygenase inhibition of various (aryl-1,2,3-triazole-1-yl)-methanesulfonylphenyl derivatives
Wuest, F.; Tang, X.; Knieß, T.; Pietzsch, J.; Suresh, M.;
A series of 1,4- and 1,5-diaryl substituted 1,2,3-triazoles was synthesized by either Cu(I)-catalyzed or Ru(II)-catalyzed 1,3-dipolar cycloaddition reactions between 1-azido-4-methane-sulfonylbenzene 9 and a panel of various para-substituted phenyl acetylenes (4-H, 4-Me, 4-OMe, 4-NMe2, 4-Cl, 4-F). All compounds were used in in vitro cyclooxygenase (COX) assays to determine the combined electronic and steric effects upon COX-1 and COX-2 inhibitory potency and selectivity. Structure-activity relationship studies showed that compounds having a vicinal diaryl substitution pattern showed more potent COX-2 inhibition (IC50 = 0.03–0.36 µM) compared to their corresponding 1,3-diaryl-substituted counterparts (IC50 = 0.15 to >10.0 µM). In both series, compounds possessing an electron-withdrawing group (Cl and F) at the para-position of one of the aryl rings displayed higher COX-2 inhibition potency and selectivity as determined for compounds containing electron-donating groups (Me, OMe, NMe2). The obtained data show, that the central carbocyclic or heterocyclic ring system as found in many COX-2 inhibitors can be replaced by a central 1,2,3-triazole unit without losing COX-2 inhibition potency and selectivity. The high COX-2 inhibition potency of some 1,2,3-triazoles having a vicinal diaryl substitution pattern along with their ease in synthesis through versatile Ru(II)-catalyzed click chemistry make this class of compounds interesting candidates for further design and synthesis of highly selective and potent COX-2 inhibitors.
Keywords: Click chemistry, Cyclooxygenase-1 and -2 inhibitors, Triazoles

Publ.-Id: 12332 - Permalink

Co-localization of hypoxia and perfusion markers with parameters of glucose metabolism in human tumour xenografts
Yaromina, A.; Zips, D.; Quennet, V.; Meyer, S.; Shakirin, G.; Mueller-Klieser, W.; Baumann, M.;
Tumour hypoxia measured by biochemical markers such as pimonidazole and parameters of the glucose metabolism such as lactate concentration have been shown to correlate with outcome after fractionated radiotherapy in experimental and clinical tumours and might serve as potential candidates for treatment individualization. High resolution imaging of tumour pathophysiology allows to study not only average values per tumour but also to investigate the spatial variations in hypoxia, perfusion, and energy metabolism. To examine relationships between hypoxia marker pimonidazole, perfusion marker Hoechst and the parameters of metabolic micromilieu such as glucose and lactate at the microregional level serial histological sections were explored for co-localization in 3 different human squamous cell carcinomas (hSCC) growing in nude mice
Keywords: hypoxia, hSCC, pefusion
  • Poster
    International Workshop "Radiation and Multidrug Resistance Mediated via the Tumor Microenvironment", 09.-10.02.2009, Dresden, Germany

Publ.-Id: 12331 - Permalink

Anwendung zeitmodulierter Magnetfelder zur Strömungskontrolle während der gerichteten Erstarrung metallischer Legierungen
Eckert, S.; Nikrityuk, P. A.; Räbiger, D.; Willers, B.; Eckert, K.;
In dieser Arbeit wird die Wirkung des elektromagnetischen Rührens der Restschmelze bei der gerichteten Erstarrung einer Al-Si-Legierung untersucht. Dabei wird eine neue Methode zum elektromagnetischen Rühren unter Nutzung eines rotierenden Magnetfeldes (RMF) und eines wandernden Magnetfeldes (TMF) vorgeschlagen, bei der beide Felder einzeln aufeinanderfolgend in Form von Rechteckpulsen angewandt werden. Beim konventionellen elektromagnetischen Rühren mit kontinuierlich wirkenden Feldern treten oft strömungsinduzierte Entmischungen im Gefüge auf. Mit der Strategie der Nutzung zeitmodulierter Felder sollen diese bekannten Nachteile vermieden werden. Die Ergebnisse zeigen, dass das Rühren unter Anwendung eines modulierten magnetischen Feldes Möglichkeiten zur Beeinflussung des Erstarrungsgefüges durch eine effiziente Kontrolle des Strömungsfeldes vor der Erstarrungsfront bietet. Eine erfolgreiche Anwendung erfordert eine dem jeweiligen Prozess angepasste Optimierung der Magnetfeldparameter.
Keywords: solidification, electromagnetic stirring, rotating magnetic field, traveling magnetic field, macrosegregation
  • Berg- und hüttenmännische Monatshefte 154(2009)3, 117-120

Publ.-Id: 12330 - Permalink

Coprecipitation of Arsenate with Metal Oxides. 3. Nature, Mineralogy, and Reactivity of Iron(III)-Aluminum Precipitates.
Violante, A.; Pigna, M.; Del Gaudio, S.; Cozzolino, V.; Banerjee, D.;
Coprecipitation involving arsenic with aluminum or iron has been studied because this technique is considered particularly efficient for removal of this toxic element from polluted waters. Coprecipitation of arsenic with mixed iron-aluminum solutions has received scant attention. In this work we studied
(i) the mineralogy, surface properties, and chemical composition of mixed iron-aluminum oxides formed at initial Fe/Al molar ratio of 1.0 in the absence or presence of arsenate [As/Fe+Al molar ratio (R) of 0, 0.01, or 0.1] and at pH 4.0, 7.0, and 10.0 and aged for 30 and 210 days at 50 °C and
(ii) the removal of arsenate from the coprecipitates after addition of phosphate. The amounts of short-range ordered precipitates (ferrihydrite, aluminous ferrihydrite and/or poorly crystalline boehmite) were greater than those found in iron and aluminum systems (studied in previous works), due to the capacity of both aluminum and arsenate to retard or inhibit the transformation of the initially formed precipitates into well-crystallized oxides (gibbsite, bayerite, and hematite). As a consequence, the surface areas of the iron-aluminum oxides formed in the absence or presence of arsenate were usually much larger than those of aluminum or iron oxides formed under the same conditions. Arsenate was found to be associated mainly into short-rangeorderedmaterials. Chemicalcompositionofallsamples was affected by pH, initial R, and aging. Phosphate sorption was facilitated by the presence of short-range ordered materials, mainly those richer in aluminum, but was inhibited by arsenate present in the samples. The quantities of arsenate replaced by phosphate, expressed as percentages of its total amount present in the samples, were particularly low, ranging from 10% to 26%. A comparison of the desorption of arsenate by phosphate from aluminum-arsenate and iron-arsenate (studied in previous works) and iron-aluminum-arsenate coprecipitates evidenced that phosphate has a greater capacity to desorb arsenate from aluminum than iron sites.
Keywords: Arsenic, XPS, Coprecipitate

Publ.-Id: 12329 - Permalink

Was tut ein Medizinphysikexperte? Der Masterstudiengang „Medical Radiation Sciences“ an der medizinischen Fakultät“
Enghardt, W.;
Was tut ein Medizinphysikexperte? Der Masterstudiengang „Medical Radiation Sciences“ an der medizinischen Fakultät“
  • Invited lecture (Conferences)
    Uni-Tag der TU Dresden, 31.05.2008, Dresden, Deutschland

Publ.-Id: 12328 - Permalink

Neue Anwendungen ionisierender Strahlen in der Medizin
Enghardt, W.;
1. Motivation für neue Therapiestrahlen
2. Physikalische Eigenschaften von Ionenstrahlen
3. Biologische Eigenschaften von Ionenstrahlen
4. Technologische Umsetzung
5. Klinische Ergebnisse
  • Invited lecture (Conferences)
    1. Strahlenschutzseminar für Führungskräfte in Sachsen, 13.10.2008, Dresden, Deutschland

Publ.-Id: 12327 - Permalink

Erste dosimetrische und strahlenbiologische Experimente an Laser beschleunigten Elektronenstrahlen
Enghardt, W.;
1. Laser Beschleuniger für die Strahlentherapie
2. Das Verbundprojekt onCOOPtics (Jena – Dresden)
3. Dosimetrie Laser beschleunigten Elektronenstrahlen
4. Strahlenbiologische Experimente
  • Invited lecture (Conferences)
    Radioonkologisches Kolloquium, 02.04.2008, München, Deutschland

Publ.-Id: 12326 - Permalink

Der Masterstudiengang „Medical Radiation Sciences“und die Ausbildung von MPE an der medizinischen Fakultät der TU Dresden
Enghardt, W.;
Der Masterstudiengang „Medical Radiation Sciences“und die Ausbildung von MPE an der medizinischen Fakultät der TU Dresden
  • Invited lecture (Conferences)
    39. Wissenschaftliche Jahrestagung der DGMP 2008 Medizinische Physik, 13.09.2008, Oldenburg, Deutschland

Publ.-Id: 12324 - Permalink

Monitoring of Hadron Therapy by means of PET Techniques
Enghardt, W.;
1. PET and hadron therapy (PT-PET)
2. Clinical implementation
3. Results and conclusions
  • Invited lecture (Conferences)
    ESTRO 27, 16.09.2008, Göteborg, Schweden

Publ.-Id: 12323 - Permalink

Erfahrungen zum und künftige Anforderungen an das Verhältnis zwischen großen Forschungseinrichtungen und dem Rechnungshof
Joehnk, P.;
Neues Steuerungsmodell in der Wissenschaft und die Rolle der Rechnungshöfe
  • Invited lecture (Conferences)
    Veranstaltung des ZWM Wissenschaftsmanagement Speyer, 29.-30.01.2009, Berlin, Germany

Publ.-Id: 12322 - Permalink

The detector system for measurement of multiple cosmic muons in the central detector of KASCADE
Bozdog, H.; Elzer, M.; Gils, H.; Haungs, A.; Herm, F.; Koepernik, H.; Kohler, K.; Kretschmer, M.; Leibrock, H.; Mathes, H.; Petcu, M.; Proehl, D.; Rebel, H.; Wentz, J.; Wolf, A.; Zagromski, S.;
A detector system for directional and time correlation measurements of multiple cosmic muons has been set up within the extensive air shower experiment KASCADE. The system consists of two layers (129 m(2) area each) of position-sensitive multiwire proportional chambers (MWPC) triggered by a layer of segmented plastic scintillation counters placed upon an iron/concrete shielding above the MWPCs. Operation conditions and performance of the MWPCs have been studied by means of a prototype arrangement consisting of a stack of four detectors and two trigger layers. Results of the detailed prototype studies are presented and discussed. In particular, it has been found that for the present purposes an operation with a commonly used argon-methane gas mixture instead of previously used argon-isobutane leads to an excellent performance. The chambers are integrated into the KASCADE experiment as described and are in continuous operation since 1996. Some typical measurements with the full detector assembly are used to illustrate which features of extensive air showers can be studied. (C) 2001 Elsevier Science B.V. All rights reserved.
Keywords: multiwire proportional chambers; data processing; extensive air showers; cosmic muons; extensive air showers
  • Nuclear Instruments and Methods in Physics Research A 465(2001)2-3, 455-471

Publ.-Id: 12321 - Permalink

In-beam PET for moving targets in particle therapy
Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.;
no abstract available
Keywords: in-beam PET, moving targets, ion therapy
  • Poster
    OncoRay, Retreat, 14.-15.01.2009, Bautzen, Deutschland

Publ.-Id: 12320 - Permalink

PET-CT Co-Registrierung for In-Beam PET
Fiedler, F.; Sobiella, M.; Enghardt, W.;
no abstract available
Keywords: in-beam PET
  • Poster
    Oncoray, Retreat, 14.-15.01.2009, Bautzen, Deutschland

Publ.-Id: 12319 - Permalink

In-beam PET for ion therapy monitoring
Fiedler, F.;
no abstract available
Keywords: in-beam PET
  • Lecture (others)
    Oncoray-Meeting, 03.06.2008, Dresden, Deutschland

Publ.-Id: 12318 - Permalink

Local setting of magnetic anisotropy in amorphous films by Co ion implantation
McCord, J.; Mönch, I.; Fassbender, J.ORC; Gerber, A.; Quandt, E.
The local setting of magnetic anisotropy by low fluence Co ion implantation in amorphous magnetic thin films is demonstrated. For a wide range of ion fluences no structural changes occur and the adjustment of anisotropy is reversible. A quantitative relationship between the anisotropy change and the atomic displacements is found. Magnetic domain investigations of the purely magnetically patterned stripes reveal an effective quasi-cubic anisotropy below a critical width for orthogonal magnetic anisotropy alignment. The method of ion-annealing allows for a local setting of anisotropy without irreversible structural and magnetic alterations.
Keywords: magnetism, ion implantation, amorphous films, patterning, anisotropy

Publ.-Id: 12317 - Permalink

Local stress engineering of magnetic anisotropy in soft magnetic thin films
Martin, N.; McCord, J.; Gerber, A.; Strache, T.; Gemming, T.; Mönch, I.; Farag, N.; Schäfer, R.; Fassbender, J.ORC; Quandt, E.; Schultz, L.
The magnetic anisotropy of amorphous thin films was modified laterally by masked ion irradiation without alteration of the intrinsic magnetic properties. The changes were introduced by local ion implantation in a protection layer, causing additional stress-induced magnetic anisotropy in the magnetostrictive layer. The underlying local variation of magnetic anisotropy was modelled and confirmed experimentally. The described method, relying purely on magneto-elastics, introduces a new path to the alteration of magnetic properties subsequent to magnetic film preparation. With the use of the resulting artificial magnetization patterns it is possible to tailor the ferromagnetic thin film structure used in magneto-electronic applications.
Keywords: magnetism, ion irradiation, amorphous films, magneto-elastic, patterning

Publ.-Id: 12316 - Permalink

Künstliche magnetische Materialien durch Nanostrukturierung
Fassbender, J.ORC
Nanostrukturierte magnetische Materialien wurden in den letzten 15 Jahren intensiv untersucht. In den allermeisten Fällen handelte es sich dabei um magnetische Inseln die mittels Lithographietechniken auf einem unmagnetischen Substrat hergestellt wurden. Eine völlig neuartige Klasse von Materialien entsteht, wenn anstelle einer topographischen eine rein magnetische Strukturierung verwendet wird. Dies geschieht durch lokale Modifikation der Oberflächenrauhigkeit oder Grenzflächenschärfe bei Vielfachschichtsystemen. Derartige Modifikationen können leicht mittels Ionenbestrahlung [1], Ionenimplantation [2,3] oder Ionenstrahlerosion [4] erzielt werden. Alternativ können auch strukturelle Phasenübergänge, die mit magnetischen Phasenübergängen einhergehen realisiert werden [5], die die Erzeugung magnetischer Nanostrukturen im sub-100 nm Bereich zulassen [6]. Der Vortrag gibt einen Überblick über die auftretenden physikalischen Phänomene unter Einbezug einiger Anwendungsbeispiele.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Applied Physics 37, R179 (2004).
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
[3] J. McCord, L. Schultz, J. Fassbender, Advanced Materials 20, 2090 (2008).
[4] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Phys. Rev. B 75, 220407(R) (2007).
[5] J. Fassbender, M. O. Liedke, T. Strache, W. Möller, E. Menendez, J. Sort, K. V. Rao, S. C. Deevi, J. Nogues, Phys. Rev. B 77, 174430 (2008).
[6] E. Menendez, J. Sort, M. O. Liedke, J. Fassbender, T. Gemming, A. Weber, L. J. Heydermann, S. Surinach, K. V. Rao, S. C. Deevi, M. D. Baro, J. Nogues, Small 5, 229 (2009).
Keywords: magnetism, ion irradiation, implantation, patterning, nano, ion erosion
  • Invited lecture (Conferences)
    Kolloquiumsvortrag, Universität Mainz, 16.02.2009, Mainz, Deutschland

Publ.-Id: 12315 - Permalink

Superconductivity in heavily Ga-doped Ge
Heera, V.; Herrmannsdörfer, T.; Heinig, K.-H.; Ignatchik, O.; Mücklich, A.; Posselt, M.; Schmidt, B.; Skrotzki, R.; Skorupa, W.; Uhlarz, M.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.;
Recently, superconductivity was detected in heavily boron doped group IV semiconductors like diamond (cB=2.8 at%, TC=4 K) [1] and silicon (cB=1.2 at%, TC=0.34 K) [2]. These unexpected results initiated a new debate about the possibility and the mechanism of superconductivity in doped semiconductors. Theoretical calculations, based on the classical electron-phonon coupling mechanism, demonstrated that critical temperatures in diamond can clearly exceed 1 K for acceptor concentrations higher than 5 at% [3]. However, unrealistic high doping concentrations are predicted for observable superconductivity in Si or even Ge. It was an open question whether superconductivity can be achieved in doped Ge.
In order to fabricate group IV semiconductors with acceptor concentrations much higher than their equilibrium solid solubility exotic doping methods like high-pressure-high-temperature synthesis [1] or gas immersion laser doping [2] were applied. We used a more conventional doping process consisting of high dose implantation and 3 ms flash lamp or 60 s rapid thermal annealing in order to form Ge layers with Ga concentrations up to 6 at%. According to Hall effect measurements the hole concentrations are in the range between 0.3x1021 and 1.4x1021 cm-3. Superconductivity was found in the Ga-doped Ge samples below critical temperatures between 0.1 and 0.5 K in dependence on the annealing conditions.

[1] E. A. Ekimov et al., Nature 428 (2004) 542
[2] E. Bustarret et al., Nature 444 (2006) 465
[3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67 (2006) 552
Keywords: Ga doped Ge, Ga implantation, flash lamp annealing, Hall effect measurements, superconductivity
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-08.04.2009, Jena, Deutschland

Publ.-Id: 12314 - Permalink

Synthesis, Modification and Applications of Ge Nanoclusters Embedded in SiO2 Films
von Borany, J.; Beyer, V.; Heinig, K.-H.; Mücklich, A.; Schmidt, B.; Skorupa, W.;
Due to their quantum confinement properties and the large surface-to-volume-ratio, semiconductor and metal nanoparticles embedded in a matrix play a significant role for new functional materials. Among them, Si, Ge, or SiC nanoclusters (-or crystals) are of particular interest for future (opto)electronic devices due to the full compatibility with semiconductor technology.
The contribution focus on recent studies on Ge nanoparticles embedded in dielectric films (mainly SiO2). Based on phase separation of supersaturated solid solutions, Ge nanocluster have been fabricated using ion beam synthesis or magnetron sputtering techniques. The size, density, density and position of the Ge nanocrystals can be varied in a technological relevant way by the degree of supersaturation and the spatial distribution of the Ge. Moreover, subsequent thermal or ion-beam processing enables to tailor nanocluster properties like shape, size or composition. Taking into account the ion beam interaction at interfaces, the generation of delta-like nanocluster bands has been successfully demonstrated. For Ge nanocrystals formation, relatively low process temperatures (< 950°C) are characteristic, but careful processing remains necessary to avoid Ge loss in thin films due to the formation of volatile GeO components. Some conceivable (opto)electronic applications of Ge nanoclusters will be discussed more in detail. Thin gate oxides containing ion beam synthesized Ge nanoclusters have been applied to study “non-volatile” me¬mory with low-field programming (< 5 MV/cm) capability. The violet luminescence in Ge doped SiO2 films was investigated with respect to their possible use to fabricate luminescence or opto-coupling devices. Finally, nanocluster films offer a new interesting approach for light absorption in bandgap engineered absorber materials designed for next generation solar cells.
Keywords: Ion beam synthesis, Ge nanoclusters, Nanocrystal memory, Bandgap engineering, Photovoltaics
  • Invited lecture (Conferences)
    The IUMRS International Conference in Asia 2008 (IUMRS-ICA2008), Session M "Innovative Material Technologies Utilizing Ion Beams", 08.-13.12.2008, Nagoya, Japan

Publ.-Id: 12313 - Permalink

Evidence of a thermally stimulated charge transfer mechanism and interface defect formation in metal-oxide-semiconductor structures with germanium nanocrystals
Beyer, R.; von Borany, J.;
The trapping of charge carriers and the mechanism of the charge transfer were examined in metal-oxide-semiconductor structures with germanium nanocrystals embedded in a 20 nm silicondioxide layer. The nanoclusters were generated by ion beam synthesis. Capacitance-voltage (C-V) measurements exhibit a hysteresis loop due to the charge trapping and detrapping. Effective oxide trap densities were derived and could be related to the nanoclusters. A strong temperature dependence of the C-V loop indicates, that a thermally stimulated process is involved in the charge transfer between the clusters and the interface, thus ruling out direct tunneling. The application of deep level transient spectroscopy revealed a large amount of interface states in the Ge implanted samples, including a distinct trap state at 0.32 eV above the valence band edge with a concentration up to 2e13 /(cm²eV), which is much likely involved in the emission of carriers from cluster related states in a two stage process.
Keywords: Ion beam synthesis, Ge nanocrystals, CV characteristics

Publ.-Id: 12312 - Permalink

X rays from relaxation of slow highly charged ions hitting thin metallic foils: emission depth and time
PešIć, Z. D.; Vikor, G.; Schuch, R.;
Nanotechnological devices are reaching the size of few molecules and there is a quest for new nanoscale materials. It has been prompted already in the eighties that the high potential energy carried by highly charged ions (HCIs) might be exploited for surface modifications . For example, the use of potential sputtering for nanostructuring would avoid unwanted damage caused by fast ions. Therefore, the knowledge of the exact time and depth scale for the energy deposition is essential.
Apart from the work reported in, there are very few direct experimental determinations of the relaxation time in the bulk. Recently, we introduced a method to determine the relaxation time of the innermost vacancies for highly ionized heavy ions moving through the bulk . The method compares the intensities of photons emitted through the front and back-side of a thin metal foil. Using foils with known thickness and x-ray absorption cross-sections, we obtained directly the mean x-ray emission depth, and thereafter the mean relaxation time.
The experiment was performed at the Manne Siegbahn Laboratory in Stockholm. Two Si(Li) detectors were used to measure X-rays emitted following the impact of 8.5xq keV and 23.5xq keV Pbq+ ions (q=53-58) on thin Ta foils oriented 45o relative to the ion-beam direction. This geometry allowed simultaneous detection of photons that escape through the back and the front surface of the foil.
The difference of the intensities of front- and back-side x-ray spectra is caused by different path lengths through the absorbing material (Ta foil) as well as by different detection efficiencies of the two Si(Li) detectors. The fitting procedure is illustrated in Fig.1, clearly showing that it is necessary to correct both spectra for the proper absorption by the Ta foil.
The experimental results of the emission depth are combined with a trajectory simulation to obtain the slowing down of the ion in the solid, to get the range and to convert the length scale to a time scale. We found that the relaxation time ranges from 30-60 fs.
The extracted mean relaxation time is compared with the prediction of the rate-equations model that incorporates radiative and non-radiative transitions, combined with a molecular orbital (MO) calculation for the Pb-Ta collision system which gives the projectile levels that are filled in close collisions with target atoms. The calculated mean relaxation time is found to be in fair agreement with the experimental results.
  • Invited lecture (Conferences)
    IISC-17, 17th International Workshop on Inelastic Ion-Surface Collisions, 21.-26.09.2008, Porquerolles, France

Publ.-Id: 12311 - Permalink

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