Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31738 Publications
Alteration of magnetic anisotropy of Pt/Co/Pt trilayers by FIB irradiation
Mazalski, P.; Dobrogowski, W.; Sveklo, I.; Maziewski, A.; Fritzsche, M.; Liedke, M. O.; Fassbender, J.ORC; Baczewski, L. T.; Wawro, A.
Investigation of the magnetic thin film structures with the out-of-plane magnetization are important for both fundamental research and applications. In nanostructures with decreasing magnetic film thickness an out-of-plane alignment of magnetization is frequently observed due to increasing contribution of surface anisotropy. It has been shown that ion beam irradiation modifies magnetic properties of such structures [1, 2]. With increasing irradiation dose D of such films the strength of perpendicular anisotropy is suppressed, magnetization rotates towards in-plane alignment or ferromagnetic ordering is converted to the superparamagnetic state. Very recently an oscillatory behaviour of magnetic anisotropy between the in-plane and out-of-plane states driven by an increasing dose of 30 keV Ga+ ion homogenous irradiation, has been observed in the molecular beam epitaxy (MBE) deposited Pt/(Co 3.3 nm)/Pt films [3].
The aim of this work is investigation of local modifications of magnetic properties in MBE grown Mo/Pt(20nm)/(Co3.3nm)/Pt(5nm) films by a focused ion beam (FIB). In the studied as deposited structure magnetization was aligned in the film plane. Numerous spots of the sample (squares 100x100μm² or 50x50μm²) have been locally irradiated with Ga+ ions with energy of 30 keV and different doses D ranging between 2•10^12 and 1•10^16 ions/cm². FIB irradiated spots were probed using polar/longitudinal Kerr effect magnetometry (sensitive to perpendicular/longitudinal magnetization component) and atomic/magnetic force microscopy techniques. Creation of the two out-of-plane magnetization branches upon increasing FIB irradiation dose D was observed, similarly to the effect reported for homogenous irradiation [3].
Presented results seem to be promising for new method for magnetic nanostructure patterning.

[1] C. Chappert et al., Science 280, 1919 (1998).
[2] J. Fassbender et al., J. Magn. Magn. Mat. 320, 579 (2008).
[3] A. Maziewski et al., Phys. Rev. B 85, 054427 (2012).
  • Poster
    Joint European Magnetic Symposia (JEMS 2012), 09.-14.09.2012, Parma, Italien

Publ.-Id: 17126 - Permalink


Application of positron beams to the investigation of memristive materials and diluted magnetic semiconductors
Potzger, K.; Liedke, M.;
After a general introduction to the field of resistive switching and spin electronics and the role of defects therein, recent investigations on the above mentioned topics including positron beams are reviewed. An ongoing project at the Helmholtz Centre Dresden-Rossendorf to further extend such investigations is briefly outlined and expected benefits are mentioned.
Keywords: Resistive switching, memristive materials, diluted magnetic semiconductors, positrons
  • Book chapter
    B.N. Ganguly, G. Brauer: Near-Surfaces Depth Profiling of Solids by Mono-Energetic Positrons, Switzerland: Trans Tech Publishers, 2012, 978-3-03785-524-9, 235-251
    DOI: 10.4028/www.scientific.net/DDF.331.235

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Publ.-Id: 17125 - Permalink


Experiments with strong far-infrared radiation at the free-electron laser
Schneider, H.;
There is no abstract.
  • Lecture (others)
    Kolloquium FB Physik, Universität Marburg, 14.05.2012, Marburg, Deutschland

Publ.-Id: 17124 - Permalink


High-power laser development projects for laser particle acceleration at HZDR
Zeil, K.; Baumann, M.; Beyreuther, E.; Bock, S.; Burris-Mog, T.; Cowan, T. E.; Enghardt, W.; Helbig, U.; Karsch, L.; Kraft, S. D.; Laschinsky, L.; Loeser, M.; Metzkes, J.; Naumburger, D.; Oppelt, M.; Pawelke, J.; Richter, C.; Roeser, F.; Sauerbrey, R.; Schürer, M.; Schramm, U.; Siebold, M.;
Recent developments in the field of laser particle acceleration enable potential applications as, e.g., radiotherapy with laser driven proton beams. Laser driven proton therapy, not only requires sufficiently high proton energies but also a reasonable repetition rate for appropriate control of the dose delivery. In Dresden, this ambitious vision is addressed by close collaborative work at OncoRay (represented by Technical University Dresden and Helmhotz-Zentrum Dresden-Rossendorf (HZDR)) combining expertise in laser plasma physics, accelerator physics, and medicine. A dedicated research building later housing both, a laser driven proton beam delivery system and a conventional proton therapy accelerator for direct comparison in clinical trials is presently under construction.
For the development of a medical high intensity laser prototype to be installed at OncoRay we focus on two major projects in parallel. The first project uses a commercialized Ti:Sapphire based laser concept providing ultra short pulses of tens of femtoseconds at a repetition rate of 10 Hz. With the 150 TW Draco laser the proton acceleration process was investigated in the last three years [1], and a long-term stable and reliable mode of operation was established which has enabled first in vitro cell irradiation studies [2]. The laser system is presently upgraded by an additional amplifier stage and new front end components finally providing high contrast pulses of >500 TW on target at 1 Hz pulse repetition rate. By use of the increased pulse energy and the multiple beam option the proton energy scaling will be investigated and the radiobiological program will be extended to the irradiation of tumors in animals.
Complementary to the ultra short pulse laser approach, the direct diode pumped solid state laser PENELOPE is under development. The status of this energetically more efficient technology providing longer pulse durations at comparable beam power and therefore favoring potentially higher proton acceleration performance than ultra short pulses will be presented.

[1] Zeil, K. et al. New J Phys, 12, 045015, 2010.
[2] Kraft, S. et al. New J Phys 12, 085003 (2010).
  • Invited lecture (Conferences)
    Advanced Accelerator Concepts Workshop, 13.06.2012, Austin, Texas, United States of America

Publ.-Id: 17123 - Permalink


Prompt pre-thermal laser ion sheath acceleration with ultra-short laser pulses
Zeil, K.; Bussmann, M.; Cowan, T. E.; Kluge, T.; Kraft, S.; Metzkes, J.; Schramm, U.;
Recent laser-ion acceleration experiments performed at the 150 TW Draco laser in Dresden, Germany, have demonstrated the importance of a precise understanding of the electron dynamics in solids on an ultra-short time scale. For example, with ultra-short laser pulses a description based purely on the evolution of a thermal electron ensemble, as in standard TNSA models, is not sufficient anymore. Rather, non-thermal effects during the ultra-short intra-pulse phase of laser-electron interaction in solids become important for the acceleration of ions when the laser pulse duration is in the order of only a few 10s of femtoseconds. While the established maximum ion energy scaling in the TNSA regime goes with the square root of the laser intensity, for such ultra short pulse durations the maximum ion energy is found to scale linear with laser intensity [1], motivating the interest in such laser systems.
Investigating the influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution, we present recent advances in the description of the laser interaction with solids, focusing on the implications of intra-pulse non-thermal phenomena on the ion acceleration.
  • Invited lecture (Conferences)
    Advanced Accelerator Concepts Workshop, 12.06.2012, Austin, Texas, United States of America

Publ.-Id: 17122 - Permalink


High magnetic field study of the Gd-Co exchange interactions in GdCo12B6
Isnard, O.; Skourski, Y.; Diop, L. V. B.; Arnold, Z.; Andreev, A. V.; Wosnitza, J.; Iwasa, A.; Kondo, A.; Matsuo, A.; Kindo, K.;
Pulsed magnetic fields up to 68 Tesla have been used to determine the intersublattice coupling strength and its temperature dependence of GdCo12B6 compound. This compound exhibits ferrimagnetic behaviour below 163 ± 2 K. Two antiferromagnetically coupled sublattices cancel out at compensation temperature at about 48 K. They are carrying magnetization of typically 0.42 μB/Co atom and 7 μB/Gd. The intrinsic magnetic properties of the GdCo12B6 compound have been determined by combining low temperature magnetic measurements in both steady and pulsed magnetic field, as well as isofield studies in steady field. At 4.2 K, the magnetization curve of GdCo12B6 is found to reach the full saturation with sum of both sublattice magnetizations for an applied magnetic field of about 68 T. In addition a detailed study is presented in the whole ordered temperature range on the basis of magnetization curves recorded using pulsed magnetic field up to 60 T. This has enabled to investigate the intersublattice coupling strength and its temperature dependence, a value JCo-Gd/kB = −5.3 ± 0.3 K is derived from the magnetization curves whereas one gets much larger value for JCo-Co/kB = 108 K.

Publ.-Id: 17121 - Permalink


Variation of the intersublattice exchange coupling due to hydrogen absorption in Er2Fe14B: A high-field magnetization study
Tereshina, E. A.; Tereshina, I. S.; Kuzmin, M. D.; Skourski, Y.; Doerr, M.; Chistyakov, O. D.; Telegina, I. V.; Drulis, H.;
Single crystals of a series of hydrides Er2Fe14BHx (x ≤ 2.5) have been produced and studied in pulsed magnetic fields up to 60 T. The magnetization curve of Er2Fe14B in the easy direction [100] features a stepwise anomaly at about 45 T, corresponding to the first-order phase transition. A similar magnetization jump is also present in the curve along [110], but at a higher field, ∼52 T. The [100] data of the parent and hydrogen-charged Er2Fe14BHx with x = 0.25, 1.5, 2.5 were used to deduce the Er-Fe molecular field Hmol as a function of hydrogen content x. After moderate initial decrease, Hmol(x) drops abruptly above x = 1.5. Hydrogenation results in a 12% reduction of the Er-Fe molecular field in Er2Fe14BH2.5 as compared to Er2Fe14B. For reference, influence of hydrogen on Hmol in an Er2Fe17-H system is also presented

Publ.-Id: 17120 - Permalink


Efficient Proton Acceleration with Ultra-short Laser Pulses
Zeil, K.; Bussmann, M.; Cowan, T.; Kluge, T.; Metzkes, J.; Schramm, U.; Kraft, S.;
We present a systematic investigation of ultra-short pulse laser acceleration of protons yielding unprecedented maximum proton energies of 19 MeV using the Ti:Sa based high power laser (150 TW) Draco at the Helmholtz-Zentrum Dresden-Rossendorf. For plain few micron thick foil targets a linear scaling of the maximum proton energy with laser power is observed and attributed to the short acceleration period close to the target rear surface*. The influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution has been investigated. The reliability of the system was improved in order to perform radiobiological studies. Additionally, an increase of laser to proton energy conversion efficiency by use of mass limited Au disks with diameters between 20 µm and 100 µm and sub-micron thickness could have been demonstrated.
  • Poster
    IPAC 2012, 23.-25.05.2012, New Orleans, LA, USA

Publ.-Id: 17119 - Permalink


Direct observation of prompt pre-thermal laser ion sheath acceleration
Zeil, K.; Metzkes, J.; Kluge, T.; Bussmann, M.; Cowan, T. E.; Kraft, S. D.; Sauerbrey, R.; Schramm, U.;
High-intensity laser plasma-based ion accelerators provide unsurpassed field gradients in the megavolt-per-micrometer range. They represent promising candidates for next-generation applications such as ion beam cancer therapy in compact facilities. The weak scaling of maximum ion energies with the square-root of the laser intensity, established for large subpicosecond class laser systems, motivates the search for more efficient acceleration processes. Here we demonstrate that for ultrashort (pulse duration ~ 30 fs) highly relativistic (intensity ~ 10 21 W cm − 2 ) laser pulses, the intra-pulse phase of the proton acceleration process becomes relevant, yielding maximum energies of around 20 MeV. Prominent non-target-normal emission of energetic protons, reflecting an engineered asymmetry in the field distribution of promptly accelerated electrons, is used to identify this pre-thermal phase of the acceleration. The relevant timescale reveals the underlying physics leading to the near-linear intensity scaling observed for 100 TW class table-top laser systems.

Publ.-Id: 17118 - Permalink


Efficient proton acceleration with ultra-short laser pulses
Zeil, K.; Bussmann, M.; Cowan, T. E.; Kluge, T.; Kraft, S. D.; Metzkes, J.; Schramm, U.;
We present a systematic investigation of ultra-short pulse laser acceleration of protons yielding unprecedented maximum proton energies of 19 MeV using the Ti:Sa based high power laser (150 TW) Draco at the Helmholtz-Zentrum Dresden-Rossendorf. For plain few micron thick foil targets a linear scaling of the maximum proton energy with laser power is observed and attributed to the short acceleration period close to the target rear surface [1]. The influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution has been investigated.
Although excellent laser pulse contrast was available slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from target normal towards the laser direction. The change of the emission characteristics are compared to analytical modelling and 2D PIC simulations.
Additionally, an increase of laser to proton energy conversion efficiency by use of mass limited Au disks with diameters between 20 µm and 100 µm and sub-micron thickness could have been demonstrated.
  • Lecture (Conference)
    Laser and Plasma Accelerators Workshop, 22.06.2011, Shanghai, China

Publ.-Id: 17117 - Permalink


Fracture mechanics characterisation of the decommissioned WWER-440 reactor pressure vessel of the NPP Greifswald unit 4
Viehrig, H.-W.; Houska, M.; Altstadt, E.; Valo, M.;
Nuclear power plant operators must demonstrate that the structural integrity of a nuclear reactor pressure vessel (RPV) is assured during routine operations or under postulated accident conditions. The aging of the RPV steels is monitored via surveillance programs. Radiation loading, metallurgical and environmental histories, however, can differ between surveillance and RPV materials. Therefore, the investigation of RPV material from decommissioned NPPs offers the unique opportunity to evaluate the real toughness response.
The Greifswald units representing the first generation of WWER-440/V-230 reactors were shut down after 11 to 15 years of operation and the RPVs represent different material conditions as follows: Irradiated (Unit 4), irradiated and recovery annealed (Units 2 and 3), and irradiated, recovery annealed and re-irradiated (Unit1). The recovery annealing of the RPV was performed at a temperature of 475° for about 150 hours and includes a region covering ±0.70 m above and below the circumferential core weld.
Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The working program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall. The paper presents an overview about test results measured on the trepans taken from the welding seam SN0.1.4. and forged base metal ring 0.3.1. located in the reactor core region of the Greifswald units 1, 2 and 4 RPV. It comprises chemical analysis, microstructure investigations (by means of metallography, electron microscopy and SANS) and mechanical testing (hardness measurements, tensile, Charpy-V), and fracture mechanics testing. The key part of the testing is focussed on the determination of the reference temperature T0 following the ASTM test standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation.
Following results have been determined:
• The recovery annealing of the welding seams and base metal could be confirmed.
• KJc values of the weld metals generally follow the course of the MC though with a large scatter.
• There is a large variation in the T0 values evaluated across the thickness of the multilayered welding seams. The T0 measured on TS oriented SE(B) from different thickness locations of the welding seams strongly depends on the structure along the crack tip.
• A strong scatter of the fracture toughness KJc values of the irradiated (unit 4) and recovery annealed base (unit 1) metal of is observed with clearly more than 2% of the values below the fracture toughness curve for 2% fracture probability.
• It was demonstrated that T0 evaluated according to the SINTAP MC extension represents the brittle fraction of the data sets.
• The application of the Unified Curve concept gave T0 values comparable to the standard MC approach, but the slope of the fracture toughness temperature curve is more shallow for highly embrittled conditions.
• The embrittlement of the unit 4 base and weld metal does not follow the prediction according to the Russian code PNAE G-7-008-86.
Keywords: reactor pressure vessel steel, neutron embrittlement, fracture toughness, Master Curve, integrity assessment, prediction
  • Contribution to proceedings
    12th International Conference “Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", 04.-08.06.2012, St. Petersburg, Russia
    Proceedings of the 12th International Conference “Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", St. Petersburg: Prometey Institute St. Petersburg

Publ.-Id: 17116 - Permalink


New iron(III) nitrate hydrates: Fe(NO3)3•xH2O with x = 4, 5 and 6
Schmidt, H.; Asztalos, A.; Bok, F.; Voigt, W.;
Crystals of the title compounds were grown from their hydrous melts or solutions. The crystal structure of iron(III) trinitrate hexahydrate {hexaaquairon(III) trinitrate, [Fe(H2O)6](NO3)3} is built up from [Fe(H2O)6]2+ octahedra and nitrate anions connected via hydrogen bonds. In iron(III) trinitrate pentahydrate {pentaaquanitratoiron(III) dinitrate, [Fe(NO3)(H2O)5](NO3)2}, one water molecule in the coordination octahedron of the FeIII atom is substituted by an O atom of a nitrate group. Iron(III) trinitrate tetrahydrate {triaquadinitratoiron(III) nitrate monohydrate, [Fe(NO3)2(H2O)3]NO3H2O} represents the first example of a simple iron(III) nitrate with pentagonal–bipyramidal coordination geometry, where two bidentate nitrate anions and one water molecule form a pentagonal plane.

Publ.-Id: 17115 - Permalink


Microbiological analysis of the in situ Bitumen-Nitrate-Opalinus Clay interaction
Moors, H.; Boven, P.; Geissler, A.; Selenska-Pobell, S.; Leys, N.;
Clay formations like the Opalinus Clay are foreseen to serve as the host rock for geological disposal of high- and intermediate-level long-lived radioactive waste in several countries, because of their favourable properties to delay the migration of radionuclides over time. However, bituminized intermediate-level long-lived radioactive waste may physico-chemically perturb the clay barrier properties because in time it will leach substantial amounts of nitrate and organic bitumen degradation products (BDP).
To study the physico-chemical impact of intermediate-level radioactive waste containing bitumen and nitrate, an in situ experiment in the Opalinus Clay (Saint Ursanne, Switzerland) named the Bitumen-Nitrate-Clay interaction (BN) experiment, is being performed at the Mont Terri Rock Laboratory. The in situ equipment of the BN-experiment consists of three separate packed-off intervals, supplied with a filter screen. Each interval is equipped with its own stainless steel water circulation unit. Such water circulation unit contains water sampling containers, circulation pumps and flow meters. One of the circulation units is equipped with an on-line UV spectrophotometer and pH electrode intervals, allowing a continuous monitoring of nitrate, nitrite concentrations, organic carbon level and pH.
In a first series of tests, the microbial and biogeochemical effect of a nitrate and/or acetate perturbation is studied. Acetate is used as it a good representation of BDP. Hereto, nitrate was injected in interval 1 while a mixture of nitrate and acetate is injected in interval 2. As an active microbial community can have a significant impact on the physical and (geo)chemical conditions of the clay surrounding the disposal gallery, microbial analyses were performed on samples taken from the interval solutions before, during and after this first series of tests. Our microbial investigations which included Scanning Electron Microscopy, molecular biology methods, ATP-measurements, and cultivation based techniques of the initial pore water samples, proved the presence and activity of bacteria.
Analysis of the 16S rDNA sequences obtained from the initial interval solutions, i.e. artificial pore water used to fill the intervals and which have been in contact with the surrounding clay for more than six months, indicates similar bacterial communities in all three solutions of the test intervals with the dominant population being Proteobacteria (81.5 – 94.9 %) and Firmicutes (3.4 – 11.1%). Actinobacteria (1.7 and 7.4%) have only been detected in the initial pore water of two intervals.
The first results of the Ribosomal Intergenic Spacer Amplification (RISA) analysis, using universal bacterial primers for 16S rDNA968-983 and 23S rDNA115-130, demonstrate that in both injection tests, i.e. nitrate (interval 1) or nitrate and acetate (interval 2), a strong shift in bacterial communities was induced. Just before the start of these injection tests the pore waters of the two intervals were strongly predominated by different Clostridial species most of them related to Desulfosporosinus species. In addition, smaller populations of Bacteroidetes and Beta– proteobacteria were found as well. Twenty-four hours later, a rapid and strong proliferation of Bacteroidetes, in interval 1, and of Alphaproteobacteria, in intervals 1 and 2, occurred. Specific for interval 1, a stimulation of Beta– and Deltaproteobacteria and a complete masking of the Clostridial groups had occured. In contrast, in interval 2, Gammaproteobacteria were stimulated and some Clostridia continued to persist. This shift may be due to bacterial contamination of the exchanged interval solutions and/or the drastic change of carbon– and/or electron acceptor source.
Keywords: opalinus clay, microbial communities, 16S rDNA retrieval, RISA analyses
  • Poster
    Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, 22.-25.10.2012, Montpellier, France

Publ.-Id: 17114 - Permalink


Coherent THz pulses from linear SRF accelerators: Perspectives for naturally synchronized THz pump probe experiments and novel electron beam diagnostic
Gensch, M.;
At the ELBE accelerator at the HZDR a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and for the generation of broad band and narrow bandwidth coherent THz pulses in the frequency range between 0.1 THz – 3 THz. Similar to previous work at the prototype THz pump probe facility at FLASH [1,2] the natural synchronization between light pulses generated by the same electron bunch shall be employed for fully synchronized experiments between narrow and broad band THz pulses. The pulse energies are expected to exceed the 100 microJ limit at scalable repetition rates between 1 and 200 KHz (cw), thereby the coherent THz facility will represent a worldwide unique facility. Besides user experiments the laboratory is also foreseen as a test bed for THz-based electron bunch diagnostics (arrival time, bunch form, …) on cw linear accelerators. The current status of the project and planned experiments are presented.
[1] M. Gensch et. al., The new THz undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[2] U. Fruehling, M. Wieland, M. Gensch et. al., Single-shot Terahertz-field driven Streak camera, Nature Photonics 3 (2009), 523.
[3] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch et. al., Few Femtosecond Timing at 4th Generation X-ray light sources, Nature Photonics 5 (2011), 162."
  • Invited lecture (Conferences)
    Workshop on Terahertz Sources for Time Resolved Studies of Matter, 30.-31.07.2012, Chicago, USA

Publ.-Id: 17113 - Permalink


Age and Genesis of Greisen Mineralization in the Li-Sn(-W) Deposit Zinnwald, Eastern Erzgebirge, Germany
Atanasova, P.; Gutzmer, J.; Seifert, T.; Pfänder, J.;
The Zinnwald greisen-type ore deposit forms part of the Altenberg-Teplice caldera in the eastern part of Saxony, Germany. Flat dipping quartz-zinnwaldite-topaz-fluorite-cassiterite greisen ore bodies and veins are hosted in the uppermost part of the “small intrusion” Zinnwald Li-F-granite stock (cf. Seifert & Kempe, 1994). The current investigation was aimed to provide new insight into the metallogenesis of the deposit and its temporal and genetic relation to the late Variscan magmatic evolution of the Altenberg-Teplice Caldera.
Greisen-type mineralization in Zinnwald is the product of high temperature post-magmatic hydrothermal alteration (i.e., greisenization), which affected and overprinted the uppermost part of the narrow Zinnwald granite stock. Pertrographic and mineral paragenetic evidence is used to illustrate that the genesis of the greisen mineralization is related to the interaction of a felsic igneous protolith with aqueous magmatic fluids, highly enriched in alkali metals, incompatible elements and volatiles, such as F. The chemical and mineralogical effects of greisenization are subdivided into three different stages, reflecting in a logical sequence the predicted physicochemical evolution of a magmatic hydrothermal fluid system.
A model is suggested that predicts upward directed fluid flow explaining the characteristic textural and geochemical alteration patterns within the granite stock, as well as high rare metal contents of the Zinnwald granite and provides a possible solution for the problem of fluid access to the solidified granite cap. This holistic metallogenetic model for the origin of the Zinnwald Li-Sn(-W) deposit integrates available field geological, geochronological, petrological and geochemical data and is largely based on the Burnham (1997) model for porphyry deposits, on the Shcherba (1970) model for greisen deposits, but augmented by peculiarities of greisen-type ore deposits of the Erzgebirge.
Zinnwaldite mica separates from the Zinnwald greisen dated in this study yield an average age of 314.1 ± 1.5 Ma. This age is significantly younger than available intrusion ages of similar A-type granitic intrusions into the Teplice Rhyolite (TR) such as 324 ± 2 Ma Re–Os molybdenite age for the Altenberg granite (Romer et al. 2007). The Ar-Ar age is thought to reflect cooling of the greisen below the closure temperature of zinnwaldite, estimated to be about 373 ± 21°C (closure temperature of biotite, Berger & York 1981). In this case, the Ar-Ar age obtained is a minimum age estimate for Li-Sn(-W) mineralization, known to have formed at temperatures above this closure temperature. Ore formation is regarded as an integral part of the development of the Altenberg-Teplice caldera and associated with the intrusion of peraluminous A-type Li-mica granites in an extensional post-orogenic environment during the later stage of the Variscan Orogeny.
Keywords: Zinnwald, Lithium, Greisen
  • Abstract in refereed journal
    Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften (2012)80, 72-72
  • Lecture (Conference)
    GeoHannover 2012, 01.-03.10.2012, Hannover, Deuschland

Publ.-Id: 17112 - Permalink


(THz based) Electron Bunch Diagnostic at Superconducting Continuous Wave Accelerators
Caglar, K.; Mamidala, V.; Lehnert, U.; Schneider, C.; Seidel, W.; Schlarb, H.; Kuntzsch, M.; Staats, G.; Al-Shemmary, A.; Stojanovic, N.; Geloni, G.; Helm, M.; Michel, M.; Gensch, M.;
At the srf based prototype cw accelerator ELBE a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime and with pC bunch charge and repetition rates of 13 MHz is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and the generation of broad band and narrow bandwidth coherent THz pulses. In this paper we outline ideas for novel online diagnostics of the electron bunch properties (e.g. arrival time and bunch form) based on the time and frequency domain analysis of the emitted coherent THz radiation but also based on direct measurements by e.g. electro-optic sampling. The suitability of ELBE as a testbed for diagnostic of future cw X-ray photon sources (e.g. energy recovery linacs) will be discussed.
  • Poster
    IPAC 2012 - International Particle Accelerator Conference 2012, 21.-25.05.2012, New Orleans, USA

Publ.-Id: 17111 - Permalink


Evaluation of tomographic data
van den Hoff, J.;
kein Abstract verfügbar
  • Book chapter
    R. Salzer: Biomedical Imaging: Principles and Applications, New York: Wiley, 2012, 978-0-470-64847-6, 30-62

Publ.-Id: 17110 - Permalink


Interaction of Uranium(VI) with Bioligands Present in Human Biological Fluids: The Case Study of Urea and Uric Acid
Osman, A. A. A.; Geipel, G.; Bernhard, G.;
The complexation of uranium(VI) with bioligands that found in human biological fluids, viz, urea and uric acid in aqueous solutions has been investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature, I = 0.1 M (NaClO4) and pH (3 for uric acid; 4 for urea). In both complex systems a static quench effect with increasing ligand concentration and no peaks shift upon complexation were observed. With uranium(VI) both ligands formed a fairly weak 1:1 complex with av-erage stability constants of log β110 = 4.67 ± 0.29 for uric acid and log β110 = 3.79 ± 0.15 and 2.12 ± 0.18 for relatively low and relatively high urea concentrations, re-spectively. Application of the newly generated data on the U(VI) speciation modelling in biofluids, e.g., human urine was also discussed.
Keywords: uranium(VI), urea, uric acid, complexation, stability constant, TRLFS, biofluids, speciation modelling

Publ.-Id: 17109 - Permalink


Charakterisierung von Wirt/Gast-Systemen mittels Radiotracertechnik
Stephan, H.;
kein Abstract verfügbar
  • Lecture (Conference)
    Institutsseminar, Freie Universität Berlin, Institut für Chemie und Biochemie, 11.05.2012, Berlin, Deutschland

Publ.-Id: 17108 - Permalink


Coherent THz Radiation from linear accelerators and 4th Generation X-ray Light sources: Status, Challenges and Diagnostic opportunities
Gensch, M.;
The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5], the THz sources furthermore constitute an ideal tool for online diagnostic on the electron bunch form at superconducting linear accelerators. An overview over different THz facility projects will be presented and experimental and diagnostic opportunities as well as challenges will be discussed on the example of recent pilot experiments.

[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys. Lett. 99 (2011), 141117.
  • Invited lecture (Conferences)
    Kolloquium des Physik Fakultät der Universität Siegen, 03.05.2012, Siegen, Germany

Publ.-Id: 17107 - Permalink


Synthesis and characterization of novel tetrahedral copper(I) complexes comprising tridentate PNP-aminodiphosphines and tetradentate PN(X)P-substituted aminodiphosphines (X = O, S)
Peruzzo, V.; Pretzsch, C.; Tisato, F.; Porchia, M.; Refosco, F.; Marzano, C.; Gandin, V.; Schiller, E.; Walther, M.; Pietzsch, H.-J.;
Two series of novel tetrahedral copper(I) complexes comprising tridentate PNP-aminodiphosphines and tetradentate PN(X)P-substituted aminodiphosphines (X = O, S) have been prepared and characterized by conventional physico-chemical techniques. The first series includes ‘3 + 1’-type complexes comprising an aromatic PNP-aminodiphosphine and acetonitrile or triphenylphosphine. In the second series, the central amine function of the PNP-ligand was substituted with functionalized pendant arms containing ether, hydroxyl or thioether groups to enhance the chelation ability of the ligand. Fully coordinated neutral and cationic complexes were isolated. A preliminary study investigating both the labeling of 64Cu with the prototype PN(S)P ligand and the potential cytotoxic activity of the ‘cold’ [Cu(PN(S)P)][BF4] complex is reported.

Publ.-Id: 17106 - Permalink


Synthesis, in vitro and in vivo characterization of novel 99mTc-‘4+1’-labeled 5-nitroimidazole derivatives as potential agents for imaging hypoxia
Giglio, J.; Fernández, S.; Pietzsch, H.-J. D.; Dematteis, S.; Moreno, M.; Pacheco, J. P.; Cerecetto, H.; Rey, A.;
The evaluation of oxygenation status of solid tumors is an important field of radiopharmaceutical research. With the aim to develop new potential 99mTc-radiopharmaceuticals for imaging hypoxia, we have synthesized two novel isocyanide derivatives of metronidazole, which has demonstrated high affinity for hypoxic tumors in vitro and in vivo.
Methods: Metronidazole derivatives 4-isocyano-N-[2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl]butanamide (M1) and 1-(4-isocyanobutanoyl)-4-[2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl]piperazine (M2) were synthesized, and labeling was performed through preparation of their corresponding 99mTc-(4+1) complexes, 99mTc-NS3M1 and 99mTc-NS3M2. The structure of the technetium complexes was corroborated by preparation and characterization of the corresponding rhenium complexes. We have studied the main physicochemical properties (stability, lipophilicity and plasma protein binding). Biological behavior in HCT-15 cells both in oxia and in hypoxia was assessed.
Biodistribution in normal mice and in animals bearing induced 3LL Lewis murine lung carcinoma was also studied.
Results: Metronidazole derivatives were successfully synthesized. Labeling with high radiochemical purity was achieved for both ligands.
99mTc complexes were stable in labeling milieu and human plasma. However, presence of the piperazine linker in M2 resulted in higher lipophilicity and protein binding. Although cell uptake in hypoxic conditions was observed for both radiotracers, 99mTc-NS3M2 biodistribution was considered unsuitable for a potential radiopharmaceutical due to high liver uptake and poor blood clearance. However, 99mTc-NS3M1 demonstrated a very favorable in vivo profile both in normal mice and in mice bearing induced tumors.
Conclusion: Selective uptake and retention in tumor together with favorable tumor/muscle ratio make 99mTc-NS3M1 a promising candidate for further evaluation as potential hypoxia imaging agent in tumors.

Publ.-Id: 17105 - Permalink


Brilliant Infrared Light Sources for Micro-Ellipsometric Studies of Organic Thin Films
Gensch, M.;
Micro-ellipsometric studies in the infrared and THz spectral range are of increasing interest in particular for the determination of the optical constants of organic films and multilayers as in these cases the composition, thickness or roughness often vary on micro- and mesoscopic length scales. In cases where the aforementioned properties change across the probed spot, the degree of polarization of the reflected beam is deteriorated and sophisticated models have to be employed to derive the optical constants or other parameters from the determined ellipsometric angles. The achievable spot size in an ellipsometric set-up is now limited by the necessity to perform a specular reflectance measurement with a reasonably defined angle. In the optimal case the infrared radiation can be focused to near diffraction limited spot sizes with opening angles in the incoming beam of less than 7°. In other words such an experiment turns out to be limited by a source property that is typically called brilliance or brightness and makes the technique particularly suited for the use of accelerator based infrared sources such as 3rd generation synchrotron storage rings. The current status of such activities worldwide will be reviewed and discussed on the example of different pilot experiments and an outlook on future developments will be given.
Keywords: Brilliance, Brightness, infrared, THz, polymer brushes, degree of polarization, diffraction limit
  • Book chapter
    K. Hinrichs, K. Eichhorn: Ellipsometry of Functional Organic Surfaces and Films, Berlin: Springer, 2014, 978-3-642-40128-2, 325-336
    DOI: 10.1007/978-3-642-40128-2_16

Publ.-Id: 17104 - Permalink


Coherent THz Radiation from linear accelerators and 4th Generation X-ray Light sources: Status, Challenges and Opportunities
Gensch, M.;
The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges will be discussed on the example of recent pilot experiments.

[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys. Lett. 99 (2011), 141117.
  • Invited lecture (Conferences)
    Kolloquium des Fachbereichs Physik der Freien Unisversität Berlin, 27.04.2012, FU Berlin, Germany

Publ.-Id: 17103 - Permalink


Design, Evaluation, and Comparison of Ghrelin Receptor Agonists and Inverse Agonists as Suitable Radiotracers for PET Imaging
Chollet, C.; Bergmann, R.; Pietzsch, J.; Beck-Sickinger, A. G.;
Ghrelin agonist and inverse agonist radiotracers, suitable for positron emission tomography (PET), were developed to study the behavior of ghrelin receptor ligands in vivo and for further design of druggable peptides. The target peptides were synthesized on solid support and conjugated to the bifunctional chelator 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), which is known to form a stable complex with Ga3+. Complexation with 68Ga could be achieved under mild conditions and led to radiotracers with high radiochemical purity and specific activity. The biological activity of the radiotracers was evaluated in vitro by an inositol phosphate turnover assay. Pharmacokinetic profile and metabolic stability of the 68Ga-NODAGA-radiotracers were investigated by small animal PET in rodent. Ghrelin derived agonists presented very high kidney accumulation, negligible tissue distribution, fast blood clearance, and poor stability in blood. Contrarily, the inverse agonist radiotracer exhibited very high stability in blood, large diffusion in tissues, reasonable kidney and liver metabolism, and slow blood clearance. This pharmacokinetic profile makes the ghrelin inverse agonist motif KwFwLL-CONH2 suitable for further development of radiotracers and a promising lead to design peptide-based therapeutics against obesity.

Publ.-Id: 17102 - Permalink


Irradiation affects cellular properties and Eph receptor expression in human melanoma cells
Mosch, B.; Pietzsch, D.; Pietzsch, J.;
X-ray irradiation influences metastatic properties of tumor cells and, moreover, metastasis and cellular motility can be modified by members of the Eph receptor/ephrin family of receptor tyrosine kinases. We hypothesized that irradiation-induced changes in cellular properties relevant for metastasis in melanoma cells could be mediated by Eph receptor/ephrin signaling. In this pilot study, we analyzed one pre-metastatic (Mel-Juso) and three metastatic human melanoma (Mel-Juso-L3, A375, and A2058) cells lines and predominantly found anti-metastatic effects of X-ray irradiation with impaired cell growth, clonal growth, and motility. Additionally, we observed an irradiation-induced increase in adhesion paralleled by a decrease in migration in Mel-Juso and Mel-Juso-L3 cells and, in part, also in A375 cells. We further demonstrate a decrease of EphA2 both in expression and activity at 7 d after irradiation paralleled by an up-regulation of EphA3. Analyzing downstream signaling after irradiation, we detected decreased Src kinase phosphorylation, but unchanged focal adhesion kinase (FAK) phosphorylation, indicating, in part, irradiation-induced downregulation of signaling via the EphA2-Src-FAK axis in melanoma cells. However, to which extent this finding contributes to the modification of metastasis-relevant cellular properties remains to be elucidated.

Publ.-Id: 17101 - Permalink


Forming-Free Unipolar Resistive Switching in BiFe0.95Co0.05O3 Films
Xu, Q.; Wen, Z.; Shuai, Y.; Wu, D.; Zhou, S.; Schmidt, H.;
We report the forming-free unipolar resistive switching effects in polycrystalline BiFe0.95Co0.05O3 films which were spin-coated on ITO/glass substrates by a chemical solution deposition method. The resistive ratio of the high resistive state (HRS) to the low resistive state (LRS) is more than 2 orders of magnitude. The conduction of the HRS is dominated by the space-charge-limited conduction mechanism, while Ohmic behavior dominates the LRS, which suggests a filamentary conduction mechanism. The oxygen vacancies are considered to play an important role in forming the conducting filaments.
Keywords: Unipolar resistive switching; Multiferroics; Chemical deposition

Publ.-Id: 17100 - Permalink


The impact of salinity on the sorption of selenate onto aged gamma-Al2O3 in the context of salt dome repositories
Franzen, C.; Hering, D.; Jordan, N.;
The radioactive isotope Selenium-79 is a long-lived fission product found in nuclear waste. Due to its long half life of 3.27 ∙ 105 years, it is expected to be one of the isotopes most contributing to the potential radiation dose according to safety assessments of nuclear waste underground repositories. A detailed knowledge of the mobility and bioavailability of selenium is therefore of great importance for a safe disposal of radioactive waste.
One major process controlling selenium mobility and bioavailability is the adsorption onto mineral surfaces of both the engineered and geological barrier. In this context, it is important to understand to what extent this sorption is influenced by different parameters, which are characteristic of deep underground storage of high level and long-lived radioactive waste. These parameters include inter alia the presence of different background salts, which are important with regard to salt domes as potential repositories.
The present study focuses on the impact of ionic strengths due to NaCl, MgCl2 and CaCl2 background electrolytes on the sorption of selenate (SeO42-) onto aged γ-Al2O3. Al2O3 contributes to the formation of clays and other rock forming minerals. Thus and due to its well characterized properties it serves as a model oxide for process understanding.
A combination of macroscopic sorption experiments, electrophoretic mobility and in-situ ATR FT-IR spectroscopy measurements was used to study the interaction of selenate with aged γ-Al2O3 in the presence of NaCl, MgCl2 and CaCl2.
From In-situ ATR FT-IR spectra, a change in the symmetry of the aqueous tetrahedral selenate anion can be derived, which is an evidence for the formation of a surface complex on γ-Al2O3. From batch experiments, we observe that the sorption of selenate is dependent on the ionic strengths and electrolyte composition. Additionally, the sorption decreases with increasing pH.
The isoelectric point (pHIEP) of γ-Al2O3 is located at pH 9.6 for low NaCl background electrolyte concentration (I = 0.1 M). The increase of ionic strength (up to I = 1 M) results in a decrease of the zeta potential for both the acidic and alkaline pH range. However, in the alkaline range the decrease of the zeta potential is more pronounced. Additionally, we observe that the pHIEP is shifted to more alkaline values and finally no charge reversal is found. To what extent these differences influence the sorption of selenate in the alkaline range has to be checked in detail.
Keywords: Sorption, Selenate, Ionic Strength gamma-Al2O3
  • Lecture (Conference)
    EMC2012 - European Mineralogical Conference, 02.-06.09.2012, Frankfurt (Main), Deutschland

Publ.-Id: 17099 - Permalink


Status of the Femtosecond Synchronization System at ELBE
Kuntzsch, M.; Buechner, A.; Gensch, M.; Lehnert, U.; Roeser, F.; Bock, M. K.; Bousonville, M.; Felber, M.; Lamb, T.; Schlarb, H.; Schulz, S.; Sydlo, C.;
The superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf is currently upgraded to enable continuous wave operation with bunch charges of up to 1 nC and durations down to 200 fs (RMS). The new beamline will drive a THz source and an X-ray source based on Thomson scattering. In collaboration with DESY, Hamburg, an optical synchronization system based on a mode locked master laser is currently being set up to ensure timing stability on the few 10 fs level. It allows high temporal resolution pump-probe experiments and new electron beam diagnostics like bunch arrival-time monitors. The synchronization system is assembled in a dedicated laboratory to ensure stable environmental conditions. In this paper the concept of the optical synchronization system is presented and first experience on the link stabilization system, its installation and commissioning is reported.
Keywords: Synchronization ELBE
  • Lecture (Conference)
    Beam Instrumentation Workshop (BIW12), 15.-19.04.2012, Newport News, USA
  • Open Access LogoContribution to proceedings
    Beam Instrumentation Workshop (BIW12), 15.-19.04.2012, Newport News, USA
    Status of the Femtosecond Synchronization System at ELBE

Publ.-Id: 17098 - Permalink


Electrical Evaluation of Ru-W(-N), Ru-Ta(-N) and Ru-Mn films as Cu diffusion barriers
Wojcik, H.; Kaltofen, R.; Merkel, U.; Krien, C.; Strehle, S.; Gluch, J.; Knaut, M.; Wenzel, C.; Preusse, A.; Bartha, J.; Geidel, M.; Adolphi, B.; Neumann, V.; Liske, R.; Munnik, F.;
Co-sputtered Ru–Ta(N), Ru–W(N) and Ru–Mn composites are investigated in terms of their barrier properties against Cu diffusion. A wide range of stoichiometries is analyzed with regard to crystallization, barrier properties, resistivity, Cu adhesion and direct Cu plating behaviour. All films were annealed at 350 °C and 600 °C in forming gas for 1h and subsequently stressed at elevated temperatures and electrical fields (BTS, 250 °C, 2 MV/cm, 30 min). The leakage current was monitored during BTS to observe increased leakage due to Cu diffusion. The Cu ions that eventually have passed the barrier and drifted into the dielectric of the MIS test structure were detected and quantified using the triangular voltage sweep method. The addition of 10% W or Ta into a Ru film already leads to a highly improved barrier performance against Cu diffusion, comparable to TaN, as long as the temperatures involved are kept below 350 °C. Outstanding barriers were identified after 600 °C annealing and subsequent BTS, among them Ru50W50, Ru50Ta50 and Ru95Mn5. However, only Ru90Ta10 and Ru95Mn5 offer an excellent Cu adhesion and the possibility of direct Cu plating.

Publ.-Id: 17097 - Permalink


An automatic method for accurate volume delineation of heterogeneous tumors in PET
Hofheinz, F.; Langner, J.; Beuthien-Baumann, B.; Steffen, I.; Steinbach, J.; Kotzerke, J.; van den Hoff, J.;
Objectives: Accurate volumetric tumor delineation is of increasing importance in radiation treatment planning. Many tumors exhibit only moderate tracer uptake heterogeneity and delineation methods using an adaptive threshold lead to robust results. These methods use a tumor reference value R (e.g. ROI maximum) and the tumor background Bg to compute the volume reproducing threshold. This threshold corresponds to an iso-contour which defines the tumor boundaries. However, the boundaries of strongly heterogeneous tumors can not be described by an iso-contour anymore and therefore conventional threshold methods are not suitable for accurate delineation. The aim of this work is the development and validation of a delineation method for heterogeneous tumors.

Methods: The new method (TV) can be considered as an extension of the adaptive threshold methods (TK), where instead of a single threshold for the whole ROI a local threshold is computed by determining for each voxel Bg and R in the close vicinity of the voxel. The absolute threshold for the considered voxel is then given by T_abs=Tx(R -Bg)+Bg, where T=0.39 was determined with phantom measurements. Validation: 10 clinical datasets (5 patients with lung cancer, 5 with head and neck cancer) were used to generate 10 realistic anthropomorphic software phantoms of strongly heterogeneous tumors with well known volume and boundaries. Volume delineation was performed with TK and TV.

Results: In contrast to TK, TV was able to reproduce the true tumor boundaries accurately. The deviation of the determined volume from the true volume was 6.9+/-6.6% for TV and 47.5+/-16.8% for TK.

Conclusions: In anthropomoric software phantoms the new method leads to promising results and a clear improvement of volume delineation in comparison to conventional background-corrected thresholding. In the next step, the suitability for clinical routine will be further investigated.
  • Poster
    SNM 2012 Annual Meeting, 09.-13.06.2012, Miami Beach, Florida, USA

Publ.-Id: 17096 - Permalink


A novel method for quantitative assessment of irregularity of FDG uptake in head-and-neck carcinoma for prediction of outcome
Apostolova, I.; Steffen, I. G.; Wedel, F.; Hofheinz, F.; Buchert, R.; Brenner, W.;
Objectives: The prognostic value of SUV is unsatisfactory in head-and-neck carcinoma. The aim of the present study was to evaluate a new measure for the irregularity of the tumor`s shape in the FDG image as prognostic factor in this cancer type.

Methods: FDG PET/CT had been performed in 32 patients (61.3±10.1y) with advanced head-and-neck cancer prior to therapy. The FDG image of the primary tumor was segmented using the ROVER 3D segmentation tool based on thresholding at the volume-reproducible intensity threshold after subtraction of local background. The novel irregularity measure (IRREG) is defined as the deviation of the tumor's shape from sphere symmetry, computed as the ratio of the third power of the tumor's surface divided by the second power of its volume. Kaplan-Meier curves with respect to both overall (OAS) and progression-free survival (PFS) were separated by the best discrimination threshold according to ROC analysis and then compared by log-rank tests.

Results: Four patients died during follow-up, 11 experienced tumor progression. Median PFS was 11.3 mo. IRREG was prognostic for OAS (p=0.016), as was the glycolytic volume (GV, p=0.003). Statistical significance for the prediction of PFS was very high for both IRREG (p=0.0003) and GV (p=0.0006). Total mean glycolytic volume was also predictive for PFS, although significance was somewhat lower (p=0.029). Higher tumor irregularity was associated with a higher risk of progression and reduced survival. Pts. with IRREG >2 showed 3-year OAS rate of 58% compared to 92% in pts. with IRREG< 2. Neither SUVmax nor SUVmean was predictive for OAS or PFS.

Conclusions: The irregularity of the pretherapeutic FDG uptake pattern in the primary tumor as quantitatively characterized by the novel measure is predictive for tumor recurrence and survival in patients with head-and-neck carcinoma. The measure should be further evaluated for risk stratification in these patients.
  • Lecture (Conference)
    SNM 2012 Annual Meeting, 09.-13.06.2012, Miami Beach, Florida, USA

Publ.-Id: 17095 - Permalink


Heterogeneity and irregularity of FDG uptake as a prognostic marker for outcome in patients with Ewing sarcoma
Steffen, I.; Apostolova, I.; Schräpler, A.; Nyuyki, F.; Hofheinz, F.; Buchert, R.; Brenner, W.;
Objectives: To determine the prognostic value of FDG-PET for progression-free survival (PFS) and overall survival (OAS) in patients with Ewing sarcoma, we evaluated two novel parameters for tumor heterogeneity and irregularity.

Methods: Twenty-two pts ( age 14.9±8.5) with Ewing Sarcoma (EWS) received FDG-PET for primary staging prior to treatment. Tumor segmentation was performed with ROVER using semi-automatic background detection. Shape irregularity (IRREG) was defined as the deviation of the tumor's shape from sphere symmetry, quantified by the ratio of the third power of the tumor's surface to the second power of its volume. Scale heterogeneity (HETER) was determined using a multiscale variance technique (MSVT) calculating the AUC ratio of heterogeneity-curves based on spatial scales of 8, 16 and 32 mm and varying binarization thresholds. Association of OAS and PFS with heterogeneity parameters (IRREG, HETER) as well as SUVmax was analyzed using Kaplan-Meier (KM) curves. Groups were separated by the best discrimination threshold according to ROC analysis and compared by log-rank test.

Results: Seventeen pts survived with a mean OAS of 58.5 months (min, 18.8 m; max, 97.8 m). Fifteen pts were progression free with a mean PFS of 50.1 month ranging from 2.7 to 91.0 months. KM analysis revealed a 5-year OAS rate of 92% for pts with SUVmax >7 and of 42% in pts with SUVmax ≤ 7 (p=0.012). Pts with HETER >37.5% showed a 5-year OAS rate of 38% compared with 92% in pts with HETER ≤ 37.5% (p=0.004). Higher IRREG> 2.2 was associated with higher 5-year OAS (98% vs. 56%; p=0,049). Higher SUVmax (>7.8) was also associated with higher 5-year PFS rates (91% vs. 62%; p=0.019) whereas neither IRREG nor HETER were predictive for PFS.

Conclusions: Surprisingly, in EWS higher initial SUVmax was significantly correlated with a higher OAS and PFS. Scale heterogeneity seems to be a new promising parameter for prediction of outcome based on FDG-PET in EWS.
  • Lecture (Conference)
    SNM 2012 Annual Meeting, 09.-13.06.2012, Miami Beach, Florida, USA

Publ.-Id: 17094 - Permalink


The prognostic value of a novel irregularity measure of FDG uptake in sarcomas
Apostolova, I.; Steffen, I. G.; Schräpler, A.; Hofheinz, F.; Buchert, R.; Brenner, W.;
Ziel/Aim:

In sarcoma patients it is important to estimate the prognosis at the time of diagnosis, particularly to define patients at high risk. FDG PET is widely used for this purpose. Heterogeneity of FDG uptake in the tumor has been shown to be a useful characteristic for grading and prediction of outcome in patients with various sarcoma types, independent of the SUV. Here we propose and evaluate a novel measure for the irregularity of the tumor`s shape in the FDG image with respect to its predictive power in sarcoma patients.

Methodik/Methods:

The retrospective analysis included 56 sarcoma patients with different histological background: 17 patients with osteosarcoma (OS), 22 with Ewing sarcoma (EW) and 17 with various different sarcoma types (VS). Whole-body FDG-PET had been performed prior to therapy in all patients. The tumors were segmented fully automatically using the ROVER 3D segmentation tool which is based on thresholding at the volume-reproducible intensity threshold after subtraction of the local background. SUVmax, SUVmean were determined in addition to the novel measure of spatial irregularity (IRREG) of the primary tumor. IRREG is defined as the deviation of the tumor's shape from sphere symmetry, which can be computed as the third power of the tumor's surface devided by the second power of its volume. IRREG is normalized to 1 for a spherical lesion. Kaplan-Meier curves were obtained for IRREG, SUVmax and SUVmean with respect to both overall (OAS) and progression-free survival (PFS). Survival and PFS curves were separated by the best discrimination threshold according to ROC analysis and then compared by log-rank tests.

Ergebnisse/Results:

Median follow-up in all patients was 37.2 months. Sixteen patients died, 24 further patients experienced tumor progression. Median PFS was 29.5 months. SUVmax / SUVmean were higher in OS (median 12.5/4.9) than in EW (7.5/3.6, Wilcoxon p=0.002/0.096, Holm-adjusted) and VS (7.8/3.5, p=0.001/0.066). Median IRREG was smaller in OS (1.7) than in EW (2.9, p=0.002), it was intermediate in VS (2.3). Kaplan-Meier analysis revealed prognostic power of IRREG with respect to OAS in all patient groups with highest statistical significance in OS (p=0.0001, 0.049 and 0.031 in OS, EW and VS, respectively). Higher pretherapeutic IRREG was associated with shorter OAS, i.e. high risk, in OS, whereas it was associated with low risk in EW and VS. SUVmax and SUVmean were not predictive for OAS in OS and VS, but in EW only (high risk at SUVmax≤7.0, p=0.012, and SUVmean≤3.3, p=0.004). In OS, IRREG provided prognostic power also with respect to PFS (p=0.015). SUVmean was predictive for PFS in both OS (p=0.016) and EW (p=0.019), SUVmax in EW only (p=0.019).

Schlussfolgerungen/Conclusions:

The novel irregularity measure is promising for the identification of high risk sarcomas. It appears to provide better prognostic power than SUV, particularly in osteosarcomas.
  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 26.-29.04.2012, Bremen, DE
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A100

Publ.-Id: 17093 - Permalink


Radionuclide sorption studies of Co, Cs and Sr onto soils from an Australian legacy radioactive waste site
Gückel, K.; Comarmond, M. J.; Payne, T. E.; Chong, E.; Mokher-Shahin, L.;
This paper discusses results of radionuclide sorption studies on a soil profile taken from a low level radioactive waste site in South Eastern Australia, known as the Little Forest Burial Ground. Low level radioactive waste was buried at this site in a series of shallow trenches in the 1960s, and the site has an on-going environmental monitoring program. This site has been the focus of a field study in recent years and an extensive core-drilling program was undertaken in 2009. Measurable amounts of Co-60, Sr-90, Cs-137 and traces of actinides have been observed at this legacy waste site in some soils, groundwater and vegetation samples taken in close proximity to the disposal area.

The sorption of Co, Cs and Sr has been studied at four depth intervals from one corehole located near the trenches using radioactive tracers and a batch sorption method to assess the key site characteristics governing contaminant release and transport. The studies were conducted on bulk samples (< 1 mm) with a mass loading of 10 g/L, ionic strength of 0.01 M (NaCl) in the presence of air. Strong sorption was observed for Cs over the entire pH range studied, whereas the sorption of Co and Sr on the soils was pH dependent with sorption edges between pH 3 and pH 6. Distribution coefficients (Kd values) for Cs sorption were similar for each soil over the entire pH range, with variations of less than one order of magnitude between samples. However, the Kd values for Sr and Co sorption varied over two and three orders of magnitude, respectively, over the pH range studied.

The four soil samples were mineralogically characterised and the BET surface areas and cation exchange capacities (CEC) determined. The bulk mineralogy of the soils was found to be similar with quartz, kaolinite and interstratified illite/smectite to be the main mineralogical phases. Most soils also contained iron oxides and anatase as minor minerals. The BET surface areas of the bulk samples varied from 27 m2/g to 47 m2/g and no strong correlation of surface area with sorption was observed. For the bulk samples, those with the higher clay fraction had the highest CEC, with CEC ranging between 10 and 24 cmol/kg. The CEC of the clay fractions were significantly higher, ranging from 21 to 34 cmol/kg and 34 to 55 cmol/kg for the < 2 µm and < 0.2 µm fractions, respectively. Further studies to elucidate the role of the various minerals with respect to sorption are in progress.
  • Lecture (Conference)
    12th South Pacific Environmental Radioactivity Association Conference, 16.-19.10.2012, Sydney, Australien

Publ.-Id: 17092 - Permalink


The simplified P3 approach on a trigonal geometry of the nodal reactor code DYN3D
Duerigen, S.; Fridman, E.;
DYN3D is a three-dimensional nodal code for steady-state and transient analyses of Light Water Reactors applicable for square and hexagonal fuel assembly geometries. Several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option. The multi-group SP3 method based on a trigonal geometry was developed recently. This method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement. In this paper, the theoretical background for the SP3 method is briefly described. The consistency of the implementation of the trigonal SP3 methodology in DYN3D is demonstrated by means of a simplified VVER-440 core test example. The corresponding few-group homogenized cross sections and reference solutions were produced by the Monte Carlo code Serpent. The DYN3D results are in good agreement with the reference solutions.
  • Kerntechnik 4(2012), 226-229

Publ.-Id: 17091 - Permalink


Prediction of outcome in sarcoma patients based on spatial heterogeneity of F18-FDG uptake using a multiscale variance technique
Steffen, I. G.; Apostolova, I.; Schräpler, A.; Brenner, W.; Buchert, R.; Hofheinz, F.;
Ziel/Aim:

Spatial heterogeneity of tracer uptake in the tumor is a promising predictor of patient outcome in various tumor entities. Different definitions have been proposed for spatial heterogeneity of tracer uptake. However, as heterogeneity is a very complex characteristic, the most appropriate mathematical approach for quantitative description of heterogeneity has still to be determined. Here we propose the use of a multiscale variance technique (MSVT) that provides a vector of heterogeneity values at different spatial scales (distances). The technique is widely used for the characterization of geographical data (maps). The prognostic value of spatial heterogeneity based on MSVT was evaluated in sarcoma patients with F18-FDG-PET for initial staging.

Methodik/Methods:

In total 51 sarcoma patients (29 m, median age 15 y, range 2-61 y) were included retrospectively. Histological subtypes were 19 Ewing sarcomas (EWS), 16 osteosarcomas (OS) and 16 sarcomas with other subtypes (MS). The primary tumor was segmented fully automatically using the ROVER 3D segmentation tool which is based on thresholding at the volume-reproducible intensity threshold after subtraction of the local background. For the computation of heterogeneity, SUV values were first binarized at a given threshold. Then MSVT was used to compute heterogeneity at the following spatial scales: 8mm, 16mm, 32mm. For each scale, heterogeneity was plotted as function of the binarization threshold. The area under the curve (AUC) from SUVmin to SUVmax was computed. The AUC ratio of heterogeneity (HR) at 8mm to 16mm was used for the univariate analysis presented here. The best threshold for discrimination between survivors and non-survivors was determined by ROC analysis. Overall survival rates between the resulting groups were compared by Kaplan-Meier curves and log-rank tests.

Ergebnisse/Results:

36 patients (15 EWS, 14 OS, 7 MS) survived till the end of the follow-up ranging from 9.1 to 97.8 months (median 46.5 months). Overall survival of non-survivors ranged from 2.7 to 49.6 months (median 16.3 months). The highest HR was observed in the group of miscellaneous sarcomas (median 44.6, IQR 38.5-53.6) followed by osteosarcomas (median 43.6, IQR 35.3-46.0) and Ewing sarcomas (median 34.4, IQR, 31.2-39.6) (Kruskal-Wallis p<0.05). HR was significantly higher in non-survivors (median, 39.6; IQR, 14.6) than in survivors (median 36.3, IQR 31.5-44.8, Mann-Whitney p<0.05) with a threshold of 38.3 in ROC analysis (p<0.05). Kaplan-Meier-analysis revealed a higher overall 5-year-survival rate of 85.6% in patients with HR≤38.3 compared to 37.7% in patients with HR>38.3 (log-rank-test p<0.01). Significantly different distribution of survival rates was also observed in subgroups of EWS (p<0.05) and OS (p<0.05), but not in MS (p=0.23).

Schlussfolgerungen/Conclusions:

MSVT based spatial heterogeneity is promising for outcome prediction based on F18-FDG-PET in sarcoma. Studies with enlarged patient numbers using multivariate statistical models with adjustment of confounders are necessary for further evaluation of the potential of MSVT.
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A98-A99
  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 26.-29.04.2012, Bremen, Deutschland

Publ.-Id: 17090 - Permalink


Irregularity of pretherapeutic tumor FDG uptake as prognostic factor in head and neck carcinoma
Apostolova, I.; Wedel, F.; Steffen, I. G.; Schreiter, N.; Marnitz, S.; Hofheinz, F.; Buchert, R.; Brenner, W.;
Ziel/Aim:

FDG PET is widely used for diagnosis, staging, and therapy monitoring in patients with head and neck carcinoma. Quantitative analysis of FDG uptake in the tumor has the potential to complement visual reading for improvement of diagnostic accuracy. However, the prognostic value of SUV-based and some more sophisticated (semi-)quantitative measures is unsatisfactory in this cancer type. The aim of the present study was to propose and evaluate a new histogram-based measure of the irregularity of FDG uptake in the tumor as prognostic factor in head-and-neck carcinoma.

Methodik/Methods:

The retrospective analysis included 32 pts with head and neck tumor in whom whole-body FDG-PET/CT had been performed for primary staging (n=26) or recurrence diagnosis (n=6). All patients underwent therapy after PET/CT. The FDG image of the primary tumor was segmented fully automatically using the ROVER 3D segmentation tool which is based on thresholding at the volume-reproducible intensity threshold after subtraction of the local background. SUVmax, SUVmean, glycolytic volume (GV) and total mean glycolytic volume (MGV) were determined in addition to the novel measure of irregularity IRREG in the ROI. IRREG is defined as the deviation of the ROI's symmetry from a sphere symmetry, which can be computed as the third power of the ROI's surface divided by the second power of the ROI's volume. IRREG is normalized in such a way that for a spherical ROI IRREG is 1. Kaplan-Meier curves were obtained for all tested parameters with respect to both progression-free (PFS) and overall survival (OAS). Survival and PFS curves were separated by the best discrimination threshold by ROC analysis and compared by log-rank tests.

Ergebnisse/Results:

Four patients died during the follow-up, 11 further patients experienced tumor progression. Median PFS was 12.5 months. Median SUVmax/mean over the whole group was 10.9/5.9. Median glycolytic volumes were 16.0 ml and 85.6 ml for GV and MGV, respectively. Kaplan-Meier analysis revealed prognosticpower with respect to OAS for IRREG (p=0.016) and both glycolytic volumes (GV: p=0.0025, MGV: p=0.08). Statistical significance for the prediction of PFS was very high for IRREG (p=0.0003) and GV (p=0.0006), somewhat smaller for MGV (p=0.043). Higher tumor irregularity was associated with high risk with respect to both recurrence and survival. The SUV measures were not predictive, neither for OAS nor PFS.

Schlussfolgerungen/Conclusions:

The irregularity of FDG uptake of the primary tumor in the baseline FDG-PET as measured by the novel irregularity measure is predictive for tumor recurrence and survival in patients with head and neck carcinoma. Therefore, the irregularity measure is a promising marker for risk stratification in these patients. Reliable analysis of the independent contribution to risk stratification over other parameters such as the glycolytic volume requires further studies with larger patient samples.
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A99
  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 26.-29.04.2012, Bremen, Deutschland

Publ.-Id: 17089 - Permalink


Metabolisches Volumen von Lungenkarzinomen - Vergleich mit dem Goldstandard, der Pathologie
Schäfer, A.; Kim, Y. J.; Mai, S.; Schäfers, H. J.; Bohnenberger, H.; Hofheinz, F.; Farmakis, G.; Khreish, F.; Hellwig, D.; Bohle, R. M.; Kirsch, C. M.; Grgic, A.;
Ziel/Aim:

F-18-FDG-PET und -PET/CT werden zur Bestimmung des metabolisch aktiven Tumorgewebes im Staging und Follow-up des nicht-kleinzelligen Lungenkarzinoms (NSCLC) und zunehmend auch für die Bestrahlungsplanung eingesetzt. Zur Konturierung des PET-Volumens wurde ein kontrastorientierter Algorithmus vorgeschlagen, der eine optimierte Beziehung zwischen dem wahren Volumen einer Aktivitätsanreicherung in der FDG-PET und dem Schwellwert SUV beinhaltet. Der Algorithmus wurde aus Phantommessungen entwickelt und mit CT-Daten von Patienten validiert (1). Ziel der vorliegenden Arbeit ist die Validierung des Algorithmus im Vergleich zum Goldstandard, der Pathologie.

Methodik/Methods:

Die prospektive Studie umfasste 15 Patienten (65±7 Jahre, 10m) mit histologisch gesichertem NSCLC und einem Tumorvolumen > 3 ml. Für alle Patienten wurde zeitnah nach der PET die Lobektomie des betroffenen Lappens durchgeführt. Die nativen Präparate wurden in standardisierter Form lamelliert und digitale Makrofotografien jeweils sämtlicher Tumorscheiben zur Volumenermittlung erstellt. Das Volumen der nativen Tumorschnitte (TV) wurde mithilfe der Software ImageJ (Open Source) berechnet. Die Konturierung der PET-Volumina mittels kontrastorientiertem Algorithmus erfolgte mit der Software ROVER (ABX, Radeberg). Zum besseren Vergleich wurden hypothetische Kugeldurchmesser aus den Tumorvolumina berechnet. Zur Beurteilung der Unterschiede der Volumina bzw. der Durchmesser (D) wurden die Varianzanalyse (ANOVA) sowie die Bland-Altman Analyse durchgeführt. Des Weiteren wurden die Lokalisation (L) der Tumore (Ober- vs. Unterlappen), Kontakt (K) zum Mediastinum/Hilus sowie histologischer Tumortyp (H) in der Analyse berücksichtigt.

Ergebnisse/Results:

Die Volumina der Tumoren in der Pathologie betrugen zwischen 3 ml und 177 ml. Die mittels kontrastorientiertem Algorithmus konturierten PET-Volumina zeigten eine gute Übereinstimmung mit den Volumina der makropathologischen Analyse (r=0,99, p<0,001). Alle Tumorvolumina wurden in der PET überschätzt (mittlere Abweichung: 37,1%, range: 6 - 102 %). Die maximalen Abweichungen der Durchmesser der PET mit denjenigen der Pathologie betrugen im Mittel 3,1 mm (range: 0,2-7 mm). Die Abweichung vom D der Pathologie war signifikant unterschiedlich (p<0,01) zwischen den zentralen (Abweichung von 5,0 mm, n=8) und den intrapulmonalen Tumoren (Abweichung von 1,4 mm, n=7).

Schlussfolgerungen/Conclusions:

Die Konturierung von PET-Volumina mittels kontrast-orientiertem Algorithmus zeigt eine gute Übereinstimmung mit der Pathologie. Die Abhängigkeit der Ergebnisse von der Tumorlokalisation zeigt, dass eine Weiterentwicklung des Algorithmus unter Berücksichtigung von Atemgating sinnvoll ist.
  • Lecture (Conference)
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin (DGN), 26.-29.04.2012, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A19-A20

Publ.-Id: 17087 - Permalink


Open Access - Publizieren im Helmholtz-Zentrum Dresden-Rossendorf
Reschke, E.;
Im Rahmen des Frühjahrstreffen der EU-Referenten der Helmholtz-Gemeinschaft im Helmholtz-Zentrum Dresden-Rossendorf am 08.u. 09.Mai 2012 werden die HZDR-Aktivitäten zu OPen Access dargestellt.
Keywords: Open Access, Open Data, Helmholtz-Zentrum Dresden Rossendorf, HZDR, Bibliothek, HORIZON 2020, EU Open Access Pilot; Special Clause 39
  • Invited lecture (Conferences)
    Frühjahrstreffen EU Referenten der Helmholtz-Gemeinschaft, 08.05.2012, Dresden, Deutschland

Publ.-Id: 17086 - Permalink


Usefulness of voxel-wise Pearson correlation coefficient for reproducibility and repeatability measurements in PET
Haase, R.; Zöphel, K.; Andreeff, M.; Steinbach, J.; Kotzerke, J.; Abolmaali, N.;
Ziel/Aim:

In the field of molecular imaging using Positron Emission Tomography (PET), a method for measuring reproducibility or repeatability of serial PET is discussed continuously. For example the limited reproducibility of [18F]fluoromisonidazole PET measurements was shown using voxel-wise Pearson correlation coefficient (PCC) (1). But the applied method may not be suitable for this purpose (2). The argumentation follows the statement of Westgard and Hunt (3): “The correlation coefficient [...] is of no practical use in the statistical analysis of comparison data.” This investigation focuses on visualizing the usefulness of the PCC method.

Methodik/Methods:

A PET phantom was used to gather 3D volumetric PET data sets. The phantom consists of a cylinder filled with [18F]fluorodeoxyglucose. It contains four wax spheres partly made of [68Ga]gallium-chloride and two glass spheres filled with a [68Ga]gallium-chloride solution. After scanning this phantom in a clinical PET/CT scanner (Biograph16, Siemens, Germany) for 10 hours several 3D data sets were reconstructed showing the phantom at different contrast levels. PCC was then measured in pairs of high- and low-contrast data sets and in several sub volumes of the phantom: a) at the centre and b) at the boundary of all spheres, c) in the cylinder, d) on the cylinder-air boundary and e) in the air.

Ergebnisse/Results:

Even though all objects appear reproducible by visual interpretation, PCC inside the glass spheres, in the cylinder and in the air (0.13<0.91) was always lower than in wax spheres showing inhomogeneous activity distribution (0.92<1). PCC at object boundaries and in the wax spheres always indicated strong correlation (0.83 < PCC < 1). PCC in all target spheres was higher in high-contrast data sets compared to low-contrast data sets.

Schlussfolgerungen/Conclusions:

The fact that PCC is higher in volumes where activity gradients are located compared to homogeneously distributed volumes indicates that this method is not applicable to measure repeatability or reproducibility of PET measurements. PCC describes a combination of image properties like presence of signal gradients, signal homogeneity, noise and other imaging related effects.

Literatur/References:

1. Nehmeh SA, Lee NY, Schröder H, et. Al. (2008) Reproducibility of intratumor distribution of (18)F-fluoromisonidazole in head and neck cancer. Int J Radiat Oncol Biol Phys. 70(1):235-42.
2. Schwartz J, Humm JL, Gonen M, et. Al. (2011) Repeatability of SUV measurements in serial PET. Med Phys. 38(5):2629-38.
3. Westgard JO, Hunt MR. (1973) Use and interpretation of common statistical tests in method-comparison studies. Clin Chem. 19(1):49-57.
  • Poster
    50. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.04.2012, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 51(2012), A92-A93

Publ.-Id: 17084 - Permalink


Motion compensated fully 3D list-mode reconstruction
Lougovski, A.; Langner, J.; Beuthien-Baumann, B.; Oehme, L.; Steinbach, J.; van den Hoff, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Publ.-Id: 17083 - Permalink


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

Publ.-Id: 17082 - Permalink


A novel method for in-vivo evaluation of quantification accuracy in PET
Langner, J.; Hofheinz, F.; Schramm, G.; Oehme, L.; Beuthien-Baumann, B.; Lukas, M.; Buchert, R.; Steinbach, J.; van den Hoff, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Publ.-Id: 17081 - Permalink


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

Publ.-Id: 17080 - Permalink


FDG-PET/MR im Rahmen der Primärdiagnostik von Patienten mit Kopf-Hals-Tumoren
Beuthien-Baumann, B.; Platzek, I.; Schneider, M.; Gudziol, V.; Langner, J.; Laniado, M.; Kotzerke, J.; van den Hoff, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Publ.-Id: 17079 - Permalink


Kombinierte PET/MR in der Diagnostik von Skelettmetastasen mit F-18-Natriumfluorid-PET (NaF-PET) und Ganzkörper-MRT (GK-MRT): Erste Erfahrungen
Beuthien-Baumann, B.; Platzek, I.; Langner, J.; Schramm, G.; Oehme, L.; Laniado, M.; van den Hoff, J.; Kotzerke, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Publ.-Id: 17078 - Permalink


Automatisierte volumetrische Abgrenzung heterogener Tumoren in der PET
Hofheinz, F.; Langner, J.; Beuthien-Baumann, B.; Oehme, L.; Steffen, I.; Apostolova, I.; Steinbach, J.; Zöphel, K.; Kotzerke, J.; van den Hoff, J.;
Ziel/Aim:

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

Methodik/Methods:

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

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

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Publ.-Id: 17077 - Permalink


First results of quantitative ASL perfusion measurements on a whole-body PET/MR system
Petr, J.; Bos, A.; Schramm, G.; Langner, J.; Hofheinz, F.; Beuthien-Baumann, B.; Platzek, I.; Kotzerke, J.; Steinbach, J.; van den Hoff, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Literatur/References:

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

Publ.-Id: 17076 - Permalink


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

Publ.-Id: 17075 - Permalink


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

Publ.-Id: 17074 - Permalink


Möglichkeiten der multimodalen Bildgebung in der Krebsdiagnostik
Stephan, H.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Universität Heidelberg, Institut für Anorganische Chemie, 16.03.2012, Heidelberg, D

Publ.-Id: 17072 - Permalink


Synthese und Charakterisierung von Cyclammonopropionsäure-Peptid-Konjugaten
Peschel, L.;
kein Abstract verfügbar
  • Bachelor thesis
    FH Zittau/Görlitz, 2012
    64 Seiten

Publ.-Id: 17071 - Permalink


Synthese und Charakterisierung asymmetrischer multifunktionaler Cyclam-Liganden mittels Staudinger Ligation
Weißpflog, M.;
kein Abstact verfügbar
  • Bachelor thesis
    HTW Dresden, 2012
    68 Seiten

Publ.-Id: 17070 - Permalink


Functional nanomaterials for multimodality cancer imaging
Stephan, H.;
kein Abstract verfügbar
  • Lecture (others)
    OncoRay-Retreat 2012, 07.-08.03.2012, Dresden, D

Publ.-Id: 17069 - Permalink


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

Downloads:

Publ.-Id: 17068 - Permalink


Quantitative accuracy of MR based attenuation correction for PET - first experience with a whole-body PET/MR system
Schramm, G.; Langner, J.; Hofheinz, F.; Beuthien-Baumann, B.; Platzek, I.; Kotzerke, J.; Steinbach, J.; van den Hoff, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Literatur/References:

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

Publ.-Id: 17067 - Permalink


2,3-Diaryl substituted indoles as probes for monitoring cyclooxygenase-2 (COX-2) with PET - radiolabeling, in vitro and in vivo studies
Knieß, T.; Laube, M.; Bergmann, R.; Graf, F.; Steinbach, J.; Pietzsch, J.;
Ziel/Aim:

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

Methodik/Methods:

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

Ergebnisse/Results:

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

Schlussfolgerungen/Conclusions:

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

Publ.-Id: 17066 - Permalink


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

Publ.-Id: 17065 - Permalink


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

Publ.-Id: 17064 - Permalink


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

Publ.-Id: 17063 - Permalink


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

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

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

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

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

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

Publ.-Id: 17062 - Permalink


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

Publ.-Id: 17061 - Permalink


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

Publ.-Id: 17060 - Permalink


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

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

Publ.-Id: 17059 - Permalink


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

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

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

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

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

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

Publ.-Id: 17058 - Permalink


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

Publ.-Id: 17057 - Permalink


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

Publ.-Id: 17056 - Permalink


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

Publ.-Id: 17055 - Permalink


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

Publ.-Id: 17053 - Permalink


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

Publ.-Id: 17052 - Permalink


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

Publ.-Id: 17051 - Permalink


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

Publ.-Id: 17050 - Permalink


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

Publ.-Id: 17049 - Permalink


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

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

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

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

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

Publ.-Id: 17047 - Permalink


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

Publ.-Id: 17046 - Permalink


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

Publ.-Id: 17045 - Permalink


Annual Report 2011 - Institute of ion Beam Physics and Materials Research
Cordeiro, A. L.; Fassbender, J.ORC; Heera, V.; Helm, M.
The first year of membership of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in the Helmholtz Association of German Research Centers (HGF) was a year of many changes also for the Institute of Ion Beam Physics and Materials Research (IIM). The transition period, however, is not yet over, since the full integration of the Center into the HGF will only be completed in the next period of the so-called program-oriented funding (POF). This funding scheme addresses the six core research fields identified by the Helmholtz Association (Energy; Earth and Environment; Health; Key Technologies; Structure of Matter; Aeronautics, Space and Transport) to deal with the grand challenges faced by society, science and industry. Since the Institute has strong contributions to both core fields “Key Technologies” and “Structure of Matter”, intense discussions were held amongst the leading scientists of the Institute, across the Institutes of the HZDR, and finally with leading scientists of other Helmholtz centers, to determine the most appropriate classification of the Institute’s research. At the end we decided to establish ourselves in Structure of Matter, the core field in which most of the large-scale photon, neutron and ion facilities in Germany are located. As a consequence, the Ion Beam Center (IBC) of the Institute submitted an application to become a HGF recognized large-scale facility, providing more than 50% of its available beam time to external users. This application perfectly reflects the development of the IBC over more than a decade as a European Union funded infrastructure in the framework of the projects “Center for Application of Ion Beams in Materials Research (AIM)” (1998-2000, 2000-2003, 2006-2010) and subsequently as the coordinator of the integrated infrastructure initiative (I3) “Support of Public and Industrial Research using Ion Beam Technology (SPIRIT)” (2009-2013). Another part of the Institute’s activities is dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. This facility is also open to external users and funded by the European Union.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-014 2012
    ISSN: 2191-8708

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Publ.-Id: 17044 - Permalink


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

Publ.-Id: 17043 - Permalink


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

Publ.-Id: 17042 - Permalink


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

Publ.-Id: 17041 - Permalink


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

Publ.-Id: 17040 - Permalink


Study on severe accidents and countermeasures for VVER-1000 reactors using the integral code ASTEC
Tusheva, P.; Schäfer, F.; Reinke, N.; Altstadt, E.; Kliem, S.;
The research field focussing on the investigations and the analyses of severe accidents is an important part of the nuclear safety. To maintain the safety barriers as long as possible and to retain the radioactivity within the airtight premises or the containment, to avoid or mitigate the consequences of such events and to assess the risk, thorough studies are needed. On the one side, it is the aim of the severe accident research to understand the complex phenomena during the in- and ex-vessel phase, involving reactor-physics, thermal-hydraulics, physico-chemical and mechanical processes. On the other side the investigations strive for effective severe accident management measures.

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

Publ.-Id: 17039 - Permalink


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

Publ.-Id: 17038 - Permalink


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

Publ.-Id: 17037 - Permalink


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

Publ.-Id: 17036 - Permalink


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

Publ.-Id: 17035 - Permalink


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

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

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

Publ.-Id: 17033 - Permalink


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

Publ.-Id: 17032 - Permalink


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

Publ.-Id: 17031 - Permalink


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

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

Publ.-Id: 17030 - Permalink


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

Publ.-Id: 17029 - Permalink


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

Publ.-Id: 17028 - Permalink


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

Publ.-Id: 17027 - Permalink


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

Publ.-Id: 17025 - Permalink


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

Publ.-Id: 17024 - Permalink


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

Publ.-Id: 17023 - Permalink


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

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

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

Publ.-Id: 17022 - Permalink


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

Publ.-Id: 17021 - Permalink


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

Publ.-Id: 17020 - Permalink


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