Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34800 Publications

Shape evolution of oxidized silicon V-grooves during high dose ion implantation

Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.

The evolution of the shape of oxidized V-grooves on (001) Si under high-dose Ge+ ion irradiation has been studied experimentally as well as theoretically. The shape of the V-grooves changes due to sputtering, re-deposition and swelling. An integro-differential equation has been derived which takes into account these 3 effects. The equation where solved numerically for the experimental conditions. Experimentally, V-grooves where formed by anisotropic etching and dry oxidation. XTEM images of as-oxidized
and as-implanted V-grooves where compared. The theoretically predicted SiO2 layer thickness reduction as well as the predicted surface shape change agree nicely with XTEM images. It is shown that sputtered material accumulates at the bottom of the V-grooves. At the same time implanted species accumulate in the bottom region of V-grooves, which can result in the formation of a very thin wire during subsequent annealing.

  • Nuclear Instruments and Methods in Physics Research B 178: 109-114 MAY 2001

Permalink: https://www.hzdr.de/publications/Publ-3688
Publ.-Id: 3688


Shape evolution of oxidized silicon V-grooves during high dose ion implantation

Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.

The evolution of the shape of oxidized V-grooves on (001) Si under high-dose
Ge+ ion irradiation has been studied experimentally as well as
theoretically. The shape of the V-grooves changes due to sputtering,
re-deposition and swelling. An integro-differential equation has been
derived which takes into account these 3 effects. The equation where solved
numerically for the experimental conditions. Experimentally, V-grooves where
formed by anisotropic etching and dry oxidation. XTEM images of as-oxidized
and as-implanted V-grooves where compared. The theoretically predicted SiO2
layer thickness reduction as well as the predicted surface shape change
agree nicely with XTEM images. It is shown that sputtered material
accumulates at the bottom of the V-grooves. At the same time implanted
species accumulate in the bottom region of V-grooves, which can result in
the formation of a very thin wire during subsequent annealing.

  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Permalink: https://www.hzdr.de/publications/Publ-3687
Publ.-Id: 3687


3D Kinetic Lattice Monte-Carlo Simulations of Ion Erosion of fcc(111) Surfaces

Strobel, M.; Heinig, K.-H.; Michely, T.

In high-dose ion implantation nanoclusters can be formed in a rather well-controlled manner as a function of implantation parameters like ion fluence, ion flux and substrate temperature. According to our current understanding of ion beam synthesis the evolution of nanoclusters is determined by the competition between ballistic and thermodynamic effects. While standard thermodynamics, i.e. the phase transition from a supersaturated solid-solution to second-phase precipitates via homogeneous nucleation and growth, gives a reasonable explanation for a variety of observed nanostructures, under irradiation conditions ballistic processes can modify the phase-ordering kinetics dramatically.
By incorporating collisional mixing with the standard thermodynamical kinetic Monte-Carlo model, analytical predictions of irradiation effects of nanoclusters, e.g. inverse Ostwald ripening, are discussed.

  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Permalink: https://www.hzdr.de/publications/Publ-3686
Publ.-Id: 3686


Ion irradiation of gold inclusions in SiO2: experimental evidence for inverse Ostwald ripening

Rizza, G.; Strobel, M.; Heinig, K.-H.; Bernas, H.

When sub mm size gold inclusions in SiO2 are irradiated with MeV gold ions, a ring of nanometer-size clusters is formed in their immediate vicinity. The size, density and radial distribution of these nanoclusters was determined. Our observations are in agreement with a recent prediction that in a driven system, under appropriate ion beam and temperature conditions, the steady-state solute concentration's dependence on precipitate size may be opposite to that expected from the equilibrium Gibbs-Thomson relation. Kinetic Monte-Carlo simulations account for additional experimental results: the irradiation-induced increase in solute concentration can promote nucleation of additional precipitates around the first ring. The latter finding contradicts the usual assumption that ion beam mixing hinders nucleation..

  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Permalink: https://www.hzdr.de/publications/Publ-3685
Publ.-Id: 3685


Inverse Ostwald ripening under ion irradiation

Heinig, K.-H.; Strobel, M.

The steady-state behavior of plain interfaces and nanoclusters (NCs) under
ion irradiation has been studied analytically as well as by kinetic
Monte-Carlo (MC) simulations. In the two-phase system mixing of A-type atoms
into phase B region leads to a strong increase of the solute concentration
at low irradiation temperatures. For NCs the ion irradiation induced
elevated solute concentration depends on their sizes. The analytical form of
this size dependence is identical to that of NCs in equilibrium, i.e. it is
given by the Gibbs-Thomson relation. However, in contrast to equilibrium,
small NCs have a lower increase in solute concentration than larger ones.
This may result in a dramatically change of the evolution of NC ensembles:
The driven system can get a negative capillarity length for its interfaces
with the consequence of mass transport from large NCs to smaller ones, i.e.
inverse Ostwald ripening is observed. Thus, it is predicted theoretically
that a broad size distribution can be made narrow by ion irradiation. At
conditions not being too far from equilibrium this behavior has been proven
by a computer experiment. The MC simulations predict in addition to the
analytical result that at very high fluxes or low temperatures large NCs can
disintegrate due to the formation of smaller ones by nucleation.

Keywords: Ion irradiation; nanoclusters; non-equilibrium; Ostwald ripening; theory

  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Permalink: https://www.hzdr.de/publications/Publ-3684
Publ.-Id: 3684


Atomistic Study of the Evolution of Nanoclusters in Ion Beam Synthesis

Strobel, M.; Heinig, K.-H.; Möller, W.

Ion implantation is an established tool to synthesize or to modify buried low-dimensional nanostructures (e.g. nanoclusters), which have become the basis of numerous technological applications. According to our current understanding of ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. In this work it is shown, that a sound understanding of the diffusional interaction dynamics of nanoclusters can be achieved by kinetic 3D lattice Monte-Carlo simulations. In particular, the exploitation of the cluster size-concentration dependence (the Gibbs-Thomson relation) under pure thermal or ion irradiation conditions provides a wealth of physical information relevant for ion beam synthesis. Furthermore, evidence is presented, that within a certain parameter window of irradiation conditions collisional mixing induced nucleation of nanoclusters occurs.

Keywords: Ion beam synthesis; nanoclusters; nucleation; Ostwald ripening; collisional mixing; kinetic lattice Monte-Carlo modeling

  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Permalink: https://www.hzdr.de/publications/Publ-3683
Publ.-Id: 3683


Modeling and XPS Study of Pricipitation and Oxidation of Ge in Ge+ implanted SiO2 layers

Borodin, V.; Heinig, K.-H.; Schmidt, B.; Oswald, S.

During annealing at 950oC in an oxidizing ambient, the redistribution of Ge in Ge+ implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM. Sputtering depth profiling in conjunction with the x-ray photoelectron spectroscopy analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.

Keywords: Germanium; oxidation; silicon dioxide; X-ray photoelectron spectroscopy; modeling

  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Permalink: https://www.hzdr.de/publications/Publ-3682
Publ.-Id: 3682


Morphology Evolution during Ion Erosion of fcc(111) Surfaces: A 3D Kinetic Lattice Monte-Carlo Study

Strobel, M.; Heinig, K.-H.; Michely, T.

Ion Erosion ...

  • Lecture (Conference)
    12th Int. Conf. Ion Beam Modifications of Materials (IBMM2000), Canela, Brazil, September 3 - 8, 2000

Permalink: https://www.hzdr.de/publications/Publ-3681
Publ.-Id: 3681


Nanocluster Evolution under Ion Irradiation

Heinig, K.-H.; Strobel, M.; Rizza, G.

An ensemble of nanoclusters embedded in a substrate evolves during thermal annealing by coarsening or Ostwald ripening, and, if the concentration of cluster material is sufficiently high, coalescence.
In this contribution it will be shown that by ion irradiation the evolution of nanoclusters can be modified or even dramatically changed. (i) Ion irradiation increases due to collisional detachments of atoms from clusters the steady-state solubility. Thus, cluster evolution is accelerated or happens at lower temperatures. (ii) Collisional detachment of atoms from nanoclusters is more efficient for large clusters than for small ones. This dependence on cluster size is opposite to that predicted by the Gibbs-Thomson law for thermally activated detachment. The "inverse" behaviour results in "Inverse Ostwald Ripening", i.e. a broad size distribution becomes narrower during annealing under ion irradiation. (iii) Under intense ion irradiation large clusters can evaporate and new nanoclusters will nucleate. A steady-state mean size, which is dependent on ion flux and temperature, can be found.
The new results listed above were predicted by an analytical theory and have been proven by kinetic lattice Monte-Carlo simulations and preliminary experiments.

Keywords: Ion irradiation; nanoclusters; annealing; Ostwald ripening; theory; computer simulation

  • Invited lecture (Conferences)
    12th Int. Conf. Ion Beam Modifications of Materials (IBMM2000), Canela, Brazil, September 3 - 8, 2000 (invited)

Permalink: https://www.hzdr.de/publications/Publ-3680
Publ.-Id: 3680


Synthese und Bearbeitung von Nanostrukturen mit Ionenstrahlen

Heinig, K.-H.

Unter Ionenbestrahlung laufen in der Festkörperoberfläche Prozesse weitab vom thermodynamischen Gleichgewicht ab. Übliche Prozeßabläufe können umgekehrt werden (z.B. inverses Ostwaldreifen), und geordnete Strukturen können sich ausbilden (z.B. wave-ordered-structures). Im Vortrag werden hierzu experimentelle und theoretische Untersuchungen vorgestellt. Es wird u. a. gezeigt, wie Nanocluster in Ordnungszustände gebracht werden können, die für mikroelektronische und mikrooptsche Anwendungen hochinteressant sind.

Keywords: Ionenstrahlsynthese; Nanocluster; Computersimulation; Thermodynamik

  • Lecture (others)
    Friedrich-Schiller Universität Jena, Physikalisch-Astronomische Fakultät, Vortrag am 17. 11. 2000

Permalink: https://www.hzdr.de/publications/Publ-3679
Publ.-Id: 3679


Physico-chemical characterization of seaborgium as oxide hydroxide

Hübener, S.; Taut, S.; Vahle, A.; Dressler, R.; Eichler, B.; Gäggeler, H. W.; Jost, D.; Piguet, D.; Türler, A.; Schädel, M.; Jäger, E.; Brüchle, W.; Schimpf, E.; Kirbach, U.; Trautmann, N.; Yakushev, A.

Seaborgium (element 106) was studied in comparison with tungsten in the O2-H2O(g)/SiO2(s)-system using high-temperature on-line isothermal gas chromatography. The 21-s nuclide 266Sg was produced in the 248Cm + 22Ne reaction at a beam energy of 119 MeV. The reaction products were continuously transported by a He(MoO3)-jet to the chromatography apparatus HITGAS. Group 6 element oxide hy-droxide molecules volatile at temperatures above 1000 K were formed at 1325 K by adding humid oxygen as reactive gas. 266Sg was unambiguously detected after gas chromatographic separation by measuring 266Sg-262Rf mother-daughter a-sf correlations. The experimental results demonstrate the volatility of seaborgium in humid oxygen, presumably as seaborgium oxide hydroxide as typical for both uranium (VI) and the group 6 elements.

Keywords: Seaborgium; group 6 elements; oxide hydroxide; reaction gas chromatography

  • Radiochimica Acta 89 (2001) 737-741

Permalink: https://www.hzdr.de/publications/Publ-3678
Publ.-Id: 3678


Elastic constants of diamond-like amorphous carbon films: the effect of internal stresses

Belov, A.; Jäger, H.-U.

The extreme wear resistance and chemical inertness of tetrahedral, or
diamond-like, amorphous carbon (ta-C) make it a promising material for
wear-resistive mechanical coatings. The unique mechanical behaviour of ta-C
is related to the atomic structure of amorphous carbon and atomic scale
modeling becomes a valuable tool to study both growth mechanisms of ta-C
films and their mechanical properties. Here we report results of atomistic
calculations of elastic constants in ta-C films grown by a realistic
computer simulation of ion-beam deposition. The dependence of the elastic
constants on the ion energy is presented. Similar to the real as-grown
nonequilibrium (not annealed) ta-C films, the simulated structures possess
the high internal compressive stress, which can considerably effect on
elastic constants. An approach employed allows for the stress dependence of
elastic constants to be analysed. We demonstrate the variation of elastic
constants as a function of the internal stress, and therefore the
importance of nonlinear elastic properties in amorphous carbon.

Keywords: tetrahedral amorphous carbon; elastic constants; internal stresses

  • Lecture (Conference)
    E-MRS 2001 SPRING MEETING, June 5-8, 2001, Strasbourg (France), Symposium C: Protective Coatings and Thin Films

Permalink: https://www.hzdr.de/publications/Publ-3677
Publ.-Id: 3677


Structures of technetium and rhenium complexes

Leibnitz, P.; Reck, G.; Pietzsch, H.-J.; Spies, H.

Investigations in the 99mTc chemistry are stimulated by the search for new radiopharmaceuticals for nuclear medical applications. To understand the coordination mode of Tc with various complexing agents, macroscopic studies of technetium coordination chemistry are often performed using the low energy ß-emitting radionuclide 99Tc, which has a much longer half life (t1/2 = 2.12 x 105 years) than 99mTc, in the mg level.
Investigations of Re coordination chemistry are done in conjunction with Tc studies because Re possesses chemical properties similar to those of Tc. For some chemical tasks, Re provides a non-radioactive alternative to work with Tc radioisotopes. In addition, 186Re and 188Re are of great interest to nuclear medicine as they possess nuclear properties favorable for use in therapeutic radiopharmaceuticals.
Our investigations of Tc and Re coordination chemistry are toward this goal. A large series of technetium and rhenium complexes resulted from this studies have been characterized by X-ray crystal structure determinations.
This survey covers the structural investigations performed by P.Leibnitz and G.Reck (BAM) from 1992 till now. It summarizes results obtained in the Rossendorf technetium group and is not intended to compete with the well-written reviews published so far.

Keywords: technetium complexes; rhenium complexes; oxotechnetium(V) complexes; oxorhenium(V) complexes; Tc(III) mixed ligand complexes; Re(III) mixed ligand complexes; X-ray structural analysis

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-311 2001
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-3676
Publ.-Id: 3676


Calculation of intrinsic stresses in amorphous carbon films grown by molecular dynamics simulation: from the atomic to the macroscopic scale

Belov, A.; Jäger, H.-U.

We present a method of calculation and an estimate for the bulk intrinsic stress in nonequilibrium tetrahedral amorphous carbon (ta-C) films grown by a realistic atomic scale simulation of ion-beam deposition. The simulated films have a thickness of a few nanometers and reproduce the important features of the real as grown nonequilibrium (not annealed) structures such as the presence of a steady-state growth region with uniform properties, the large content of sp3 bonded atoms, and the high intrinsic compressive stress, which seriously limits the maximum thickness of films that can be deposited. Using slices from the nearly structurally uniform film region, a 3D periodic model was constructed for the bulk intrinsic stress calculation. Employing empirical interatomic potentials for carbon, atomic stresses as well as the bulk stresses were computed. The obtained value of the compressive stress for the transition from the graphitic-like carbon to ta-C is in a good agreement with experimental data for the stress threshold.

Keywords: tetrahedral amorphous carbon; thin films; intrinsic stress

  • Poster
    E-MRS 2001 SPRING MEETING, June 5-8, 2001, Strasbourg (France), Symposium A: Computational Materials Science Across Time and Length Scales

Permalink: https://www.hzdr.de/publications/Publ-3675
Publ.-Id: 3675


Erwärmung des Reaktordruckbehälters des Blocks 8 des KKW Greifswald bei der Zerlegung mittels Sägetechnik

Mössner, T.; Altstadt, E.; Böhmert, J.; Weiß, R.

Die Arbeit untersucht das Erwärmungsverhalten des Reaktordruckbehälters des Blockes 8 des KKW Greifswald bei der Zerlegung in Ringabschnitte mit einer Bandsäge. Mit dem Programm ANSYS wurde dazu ein thermisches Finite-Elemente-Modell erstellt. Dieses Modell ist an Hand vorhandener Temperaturmessdaten abgeglichen worden. Mit dem abgeglichenen Modell wurden abschließend die auftretenden Maximaltemperaturen für den Sägevorgang ermittelt. Diese liegen bei höchstens 200 °C.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf, FZR-310 Januar 2001
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-3674
Publ.-Id: 3674


Riga Dynamo Experiment

Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.

It is widely believed that almost all magnetic fields in a natural
environment are a result of the dynamo process -- field generation in a
moving nearly homogeneous fluid electroconducting material of celestial
bodies. Such are fields of the Earth, most of the planets, Sun, another
stars and even galaxies. The believe is based on the theory and numerical
simulation. Until very recently no direct laboratory experiment was
supporting this important point. We are not going to model in the laboratory
any particular celestial body. Our aim is to demonstrate the very idea -- by
intense stirring in a large volume of good electroconducting liquid one can
generate a magnetic field. As the working fluid we are using 2 qm of molten
sodium -- the best electroconducting liquid available. The fluid part of
celestial bodies is stirred by thermal and other types of natural
convection. In laboratory circumstances such stirring is much too slow.
Hence we are stirring sodium by an outside forced propeller consuming 150kW
of power. The propeller is producing an axisymmetric swirling flow inside a
prolongated annular vessel. When flowrate reaches 0.6 qmps or so the device
starts to generate magnetic field. The field pattern is nonaxisymmetric and
slowly (1.2 --1.5hz) rotates round symmetry axis. The overall rotation is
superimposed by turbulent fluctuations. The generation process is stable in
operational sense and results are reproducible. We report on two experiments
at the Riga dynamo facility. In November 1999, a slowly growing magnetic
field eigenmode was observed for the first time in a liquid metal
experiment. In July 2000, the magnetic field saturation regime was studied.
We sketch also the underlying theory in order to illuminate the background
of the Riga dynamo experiment.

  • Lecture (Conference)
    Lecture at European Geophysical Society, XXVI General Assembly, Nice (France), March 25-30, 2001

Permalink: https://www.hzdr.de/publications/Publ-3673
Publ.-Id: 3673


Validation of coupled neutron kinetic / thermal-hydraulic codes Part 2: Analysis of a VVER-440 transient (Loviisa-1)

Hämäläinen, A.; Kyrki-Rajamäki, R.; Mittag, S.; Kliem, S.; Weiss, F.-P.; Langenbuch, S.; Danilin, S.; Hadek, J.; Hegyi, G.

Several three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal-hydraulic system codes. Under the auspices of the European Union's Phare programme these codes have been validated against real plant transients by the participants from 7 countries. Two of the collected five transients were chosen for validation of the codes. Part 1 of this article consists of validation against VVER-1000 reactor data. This second part is focussed to validation against measured data of `One turbo-generator load drop experiment' at the Loviisa-1 VVER-440 reactor. The experiment was performed just after plant modernisation and more measured data was available to validation than in normal operation of real plants. Good accuracy of the results was generally achieved comparable to the measurement accuracy. The confidence in the results of the different code systems has increased, and consequences of certain model changes could be evaluated.

  • Annals of Nuclear Energy 29 (2002) 255-269

Permalink: https://www.hzdr.de/publications/Publ-3672
Publ.-Id: 3672


Syntheses and Crystal Structure Determination of hexacoordinated Silicon-Complexes with Dimethylpyridines

Hensen, K.; Kettner, M.; Stumpf, T.; Bolte, M.

Halogensilane, HSiCl3, forms with 3,4-dimethylpyridine in aprotic solvents a crystalline 1:2-compound which is stable at room temperature and readily soluble in CHCl3. Colourless crystals of the dicationic complex, [H2Si(3,4-dimethylpyridine)4]2+ 2Cl-×6 CHCl3 (verified by X-ray structure analysis) are obtained by dismutation of HSiCl3(3,4-di-methylpyridine)2 in CHCl3, within one week at room temperature. 29Si-NMR indicates that SiCl4 is generated as a second product. H2SiCl2 with 2,4-dimethylpyridine as well as MeHSiBr2 with 3,5-dimethylpyridine in aprotic solvents form 1:2-compounds stable at room temperature. X-ray structure analysis in both cases establish neutral-complexes with a hexacoordinated silicon atom.

  • Naturforschung 55b 2000 (901-906)

Permalink: https://www.hzdr.de/publications/Publ-3670
Publ.-Id: 3670


Halogen exchange and expulsion : ligand stabilized dihalogen silicon dications

Hensen, K.; Mayr-Stein, R.; Stumpf, T.; Pickel, P.; Bolte, M.; Fleischer, H.

The first ligand stabilized SiCl22+ dications were synthesed using N-methylimidazole as co-ordinating ligand. The compounds SiCl4, SiBr2Cl2, and SiH2Cl2 form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si-N bonds of about 1.90 C. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought and proceeds with considerable speed even without a catalyst.

  • J. Chem. Soc., Dalton Trans. 2000 (473-477)

Permalink: https://www.hzdr.de/publications/Publ-3669
Publ.-Id: 3669


Template-Directed Self-Assembly of Buried Nanowires and the Pearling Instability

Müller, T.; Heinig, K.-H.; Schmidt, B.

The fabrication of more and more miniaturized electronic and photonic devices relies on new, ingenious methods for the fabrication of spatially controlled nanostructures. Examples are electronic devices based on semiconducting nanowires and photonic devices based on chains of metallic nanoclusters that guide light by coupled surface plasmons. In this contribution a template-directed ion beam synthesis of nanowires and regular nanocluster chains will be presented. As templates, V-grooves etched in (001)Si and subsequently oxidized are used. High fluence Ge+ implantation is carried out into the SiO2 layer at 70 keV. Thereby, the implanted Ge enriches themselves in the V-groove bottom to a critical amount, which may result in nanowire formation by nucleation, growth and coalescence during subsequent thermal treatment. TEM investigations indicate the formation of a nanowire buried in the SiO2 at the V-groove bottom. Kinetic lattice Monte Carlo simulations of the nanowire formation process were performed in order to understand the phase separation mechanism and results are compared to TEM images. Furthermore, it is shown that even ideal nanowires show a instability and form during long-lasting annealing equal-spaced and equal-sized nanoclusters "nanocluster chains" by self-organization.

Keywords: Nanowires; Ion Beam Synthesis; Pearling Instability; Nanocluster Chains

  • Poster
    European Materials Research Society Spring Meeting E-MRS 2001, Strasbourg, France, June 5-8, 2001
  • Material Scince and Engineering C 19 (2002) 209-213
  • Contribution to WWW
    arXiv:cond-mat/0108371 v1 23 Aug 2001

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Permalink: https://www.hzdr.de/publications/Publ-3667
Publ.-Id: 3667


Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers

Spiga, S.; Ferrari, S.; Fanciulli, M.; Schmidt, B.; Heinig, K.-H.; Grötzschel, R.; Mücklich, A.; Pavia, G.

In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed

Keywords: ion beam synthesis; nanoclusters; Tin; Antimony; ion implantation; silicon dioxide; Ostwald ripening; nonvolatile memory device

  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647 (2001)

Permalink: https://www.hzdr.de/publications/Publ-3666
Publ.-Id: 3666


Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers

Spiga, S.; Ferrari, S.; Fanculli, M.; Schmidt, B.; Heinig, K.-H.; Grötzschel, R.; Mücklich, A.; Pavia, G.

In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.

Keywords: ion beam synthesis; nanoclusters; Tin; Antimony; ion implantaion

  • Poster
    Materials Research Society 2000 Fall Meeting, Symp. O "Ion Beam Synthesis and Processing of Advanced Materials" , Boston, USA, Nov. 27-29, 2000
  • Contribution to proceedings
    Mat.Res.Soc.Symp.Proc. Vol. 647 (2001) O11.23 MRS2000 Fall Meeting, Symposium O: "Ion Beam Processing of Advanced Materials", Boston, USA, Nov. 27-29, 2000

Permalink: https://www.hzdr.de/publications/Publ-3665
Publ.-Id: 3665


Understanding ion beam synthesis of nanostructures: Modelling and atomistic simulations

Strobel, M.; Heinig, K.-H.; Möller, W.

Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced, which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient in understanding nanocluster evolution. Various aspects of precipitate evolution during implantation, formation of ordered arrays of nanophase domains by focused ion implantation and compound nanocluster synthesis are discussed.

Keywords: ion beam synthesis; nanostructures; nanoclusters; ion implantation; ion beam mixing; Ostwald ripening; kinetic Monte-Carlo simulation

  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647 (2001)

Permalink: https://www.hzdr.de/publications/Publ-3664
Publ.-Id: 3664


Successful nitriding of austenitic stainless steel: On the diffusion mechanism of nitrogen and on the role of the surface oxide layer.

Parascandola, S.; Möller, W.; Williamson, D. L.

In the first part of this paper we present a quantitative trapping model that includes detrapping to describe the diffusion of nitrogen in austenitic stainless steel during successful nitriding. Calculated nitrogen depth profiles, assuming a diffusion pre-exponential factor D0 = 10-3 cm2/s, a diffusion activation energy Ed = 1.1 eV, and a detrapping activation energy Et2d = 1.45 eV, show good agreement with experimental nitrogen depth profiles
obtained from a sample that has been subsequently nitrided with 14N and 15N. The plausibility of a trapping mechanism is also supported by a number of phenomenological and thermodynamical arguments. In the second part of this paper we present a modelling approach for the evolution of the thickness of the surface oxide layer during successful nitriding. The approach bases on the assumption that the surface oxide layer thickness is completely controlled by the interplay of sputtering and oxidation and differentiates between oxide layer growth limited by diffusion and oxide layer growth limited by the rate of oxygen supply. The applicability of this approach is supported by experimental data obtained by real-time elastic recoil detection analysis during ion nitriding at different combinations of ion energy and oxygen partial pressure.

  • Lecture (Conference)
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan
  • Contribution to proceedings
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-3663
Publ.-Id: 3663


Understanding ion beam synthesis of nanostructures: Modeling and atomistic simulations

Strobel, M.; Heinig, K.-H.; Möller, W.

Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced,
which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient
in understanding nanocluster evolution. Various aspects of
precipitate evolution during implantation, formation of
ordered arrays of nanophase domains by focused ion implantation
and compound nanocluster synthesis are discussed.

Keywords: ion beam synthesis; nanostructures; nanoclusters; ion implantation; ion beam mixing; Ostwald ripening; kinetic Monte-Carlo simulation

  • Invited lecture (Conferences)
    Materials Research Society 2000 Fall Meeting, Symp. O "Ion Beam Synthesis and Processing of Advanced Materials", Nov 27 - Dec 1, 2000, Boston, USA, Invited Talk

Permalink: https://www.hzdr.de/publications/Publ-3662
Publ.-Id: 3662


Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy Ion Collisions

Sturm, C.; Böttcher, I.; Debowski, M.; Förster, A.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Laue, F.; Mang, M.; Naumann, L.; Oeschler, H.; Pühlhofer, F.; Schwab, E.; Senger, P.; Shin, Y.; Speer, J.; Ströbele, H.; Surowka, G.; Uhlig, F.; Wagner, A.; Walus, W.

The production of pions and kaons has been measured in Au+Au collisions at beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.

Keywords: pion kaon Au+Au collisions K+ meson multiplicity nucleon nuclear equation-of-state

  • Physical Review Letters 86 (2001) 39

Permalink: https://www.hzdr.de/publications/Publ-3661
Publ.-Id: 3661


Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation

Heinig, K.-H.; Schmidt, B.; Strobel, M.; Bernas, H.

Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.

Keywords: Nanostructures; ion implantation; Ostwald ripening; nucleation; ion beam mixing; theory; kinetic lattice Monte-Carlo simulation; nonvolatile memory device

  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647(2001) O14.6

Permalink: https://www.hzdr.de/publications/Publ-3660
Publ.-Id: 3660


Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation, (invited talk MRS 2000 Fall Meeting, Boston, USA), Mat. Res. Soc. Proc., vol. 647

Heinig, K.-H.; Schmidt, B.; Strobel, M.; Bernas, H.

Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.

Keywords: nanostructures; nanoclusters; ion implantation; ion irradiation; Ostwald ripening; nucleation; self-organization; nonequilibrium thermodynamics; theory; kinetic lattice Monte-Carlo simulation; nonvolatile memory device

  • Invited lecture (Conferences)
    Materials Research Society 2000 Fall Meeting; Boston (USA), 27.11.-1.12.2000, invited talk
  • Mat.Res.Soc.Proc. 650 (2001) R9.6

Permalink: https://www.hzdr.de/publications/Publ-3659
Publ.-Id: 3659


A toy model for inverse dynamo theory

Stefani, F.; Gerbeth, G.

We consider a simple model of inverse dynamo theory consisting of a spherically symmetric alpha^2-dynamo with unknown radial dependence of alpha. Using an evolutionary strategy, we try to reconstruct this radial dependence of alpha from a finite number of given data, e.g. from a few real or complex eigenvalues and/or from the assumption that the field is confined to the dynamo region. Although for planetary dynamos the direct applicability of our specific model is very limited, the principle of inversion is quite general and might be useful for cosmic dynamos as well as for the emerging laboratory dynamo community.

  • Physics of the Earth and Planetary Interiors 128, No. 1-4 (2001), pp. 109-124

Permalink: https://www.hzdr.de/publications/Publ-3658
Publ.-Id: 3658


Synthesis of S-([18F]fluoromethyl)-(+)-McN5652 as a potential PET radioligand for the serotonin transporter

Zessin, J.; Eskola, O.; Brust, P.; Bergman, J.; Steinbach, J.; Lehikoinen, P.; Solin, O.; Johannsen, B.

The present study describes the synthesis of the [18F]fluoromethyl analogue of (+)-McN5652 ([18F]FMe-McN) as a new potential tracer for the serotonin transporter. In vitro binding studies have shown that FMe-McN displays only slightly lower affinity for the serotonin transporter (Ki=2.3 ± 0.1 nM) than (+)-McN5652 (Ki=0.72 ± 0.2 nM). The radiofluorinated tracer [18F]FMe-McN was prepared by reaction of normethyl (+)-McN5652 with the fluoromethylation agent [18F]bromofluoromethane in an overall radiochemical yield of 5 ± 1% (decay-corrected, related to [18F]fluoride) and with high specific radioactivity (200 - 2000 GBq/µmol at the end of synthesis).

Keywords: (+)-McN5652; [18F]fluoromethyl analogue; [18F]bromofluoromethane; serotonin transporter; positron emission tomography

  • Nuclear Medicine and Biology 28 (2001) 857-863

Permalink: https://www.hzdr.de/publications/Publ-3657
Publ.-Id: 3657


The Rossendorf CYCLONE 18/9 Facility - Four Years Experience in Operation and Maintenance -

Preusche, S.; Füchtner, F.; Steinbach, J.

Our four years experience in operation and maintenance of the PET cyclotron "CYCLONE 18/9" is given. Improvements at the CYCLONE 18/9 are presented as well as results of the routine radionuclide production.

  • Poster
    CYCLONE 18/9 & 10/5 USER COMMUNITY 3. Workshop, February 04 - 06, 2001, Amsterdam, The Netherlands
  • Contribution to proceedings
    CYCLONE 18/9 & 10/5 USER COMMUNITY 3. Workshop, February 04 - 06, 2001, Amsterdam, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-3656
Publ.-Id: 3656


Radio fluorination and positron emission tomography (PET) as a new approach to study the in vivo distribution and elimination of the advanced glycation endproducts Nepsilon-carboxymethyllysine (CML) and Nepsilon-carboxyethyllysine (CEL)

Bergmann, R.; Helling, R.; Heichert, C.; Scheunemann, M.; Mäding, P.; Wittrisch, H.; Johannsen, B.; Henle, T.

After synthesis of fluorine-18 labelled analogues by [18F]fluorobenzoylation at the alpha-amino group, biodistribution and elimination of individual advanced glycation endproducts, namely Nepsilon-carboxymethyllysine and Nepsilon-carboxyethyllysine, was studied in comparison to lysine in rats after intravenous injection using positron emission tomography (PET).
The [18F]radiofluorinated amino acids were fast distributed via the blood, followed by a rapid excretion through the kidneys. Elimination kinetics were similar for both AGEs and lysine. For CML and CEL, but not for lysine, a temporary liver accumulation could be observed, which was not connected with any metabolisation or enterohepatic circulation. No further accumulation in any tissues was observable, indicating that increased tissue levels of CML or CEL, which have been described for certain disorders, are exclusively derived from endogenous origin and should not depend on a dietary intake. Under uremic conditions, however, an impaired kidney function might result in a significant increase of the AGE-load of blood and tissues. PET based on 18F-labelled AGEs proved to be a promising tool to elucidate the physiological fate of post-translationally modified amino acids and to clarify the role of AGEs as possible "glycotoxins".

  • Nahrung/Food 45 (2001) 182-188

Permalink: https://www.hzdr.de/publications/Publ-3655
Publ.-Id: 3655


Biodistribution and catabolism of 18F-labeled neurotensin(8-13) analogs

Bergmann, R.; Scheunemann, M.; Heichert, C.; Mäding, P.; Wittrisch, H.; Kretzschmar, M.; Rodig, H.; Tourwé, D.; Iterbeke, K.; Chavatte, K.; Zips, D.; Reubi, J. C.; Johannsen, B.

4-([18F]fluoro)benzoyl-neurotensin(8-13) (18FB-Arg8-Arg9-Pro10-Tyr11- Ile12-Leu13-OH, 1) and two analogs stabilized in one and two positions (18FB-Arg8Psi(CH2NH)Arg9-Pro10-Tyr11- Ile12-Leu13-OH, 2, 18FB-Arg8Psi(CH2NH)Arg9-Pro10-Tyr11-Tle12-Leu13-OH, 3) were synthesized in a radiochemical yield of 25 - 36% and a specific activity of 5 - 15 GBq/mmol. The peptides were evaluated in vitro and in vivo for their potential to image tumors, overexpressing neurotensin receptor 1 (NTR1) by positron emission tomography (PET). All analogs exhibited in vitro binding affinity in the low nanomolar range to NTR1-expressing human tumors, measured by quantitative receptor autoradiography, HT-29 and WiDr cells, and to sections of tumors derived from these cell lines in mice. The radiotracers were internalized in the cells in vitro, and the fluorinated peptides were able to mobilize intracellular Ca2+ of WiDr cells. In in vivo studies in rats and in mice bearing HT-29 cell tumors, only a moderate uptake of the radioligands into the studied tumors was observed, presumingly due to degradation in vivo and fast elimination by the kidneys. In comparison with the other analogs, the specific tumor uptake expressed as tumor-to-muscle relation was highest for the radioligand 3. The blood clearance of 3 was reduced by co-injection of peptidase inhibitors. The catabolic pathways of the radiofluorinated peptides were elucidated. The results suggest that the high binding affinity to NTR1 and the stabilization against proteolytic degradation are not yet sufficient for tumor imaging by PET.

Keywords: Neurotensin analogs; Positron emission tomography; F-18; Receptor binding; Tumor

  • Nuclear Medicine and Biology 29 (2002) 61-72

Permalink: https://www.hzdr.de/publications/Publ-3654
Publ.-Id: 3654


Evolution of Ion Beam Synthesized Au Nanoclusters in SiO2 under Ion Irradiation

Schmidt, B.; Heinig, K.-H.; Mücklich, A.

The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO2 layer by 330 keV Au+ implantation and subsequent annealing at T = 1000 °C for 1h in dry O2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range Rp(330keV) = 100 nm, having a mean NC size of 5 nm at Rp, and resembling the broad LSW size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions were used in order to tailor their size and size distribution. The high-energy Au+ irradiation were performed at 190...210 °C with a fluence of (0.5...1.0)x1016 cm-2. By the post-irradiation no gold was deposited into the SiO2 layer, the Au+ ions come to rest in the (001)Si substrate at Rp(4.5MeV) = 1 mm. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.

Keywords: Ion beam synthesis; nanucluster; comuter simulation

  • Contribution to proceedings
    Materials Research Society, Symposium Proceedings Ion Beam Synthesis and processing of Advanced Materials Symposium held November 27-29, 2000, Boston, Massachusetts, U.S.A

Permalink: https://www.hzdr.de/publications/Publ-3653
Publ.-Id: 3653


Reflectivity and diffraction study of cross-beam pulsed laser deposited Co/Cu multilayers

Prokert, F.; Noetzel, J.; Schell, N.; Wieser, E.; Matz, W.; Gorbunov, A.

Co/Cu multilayers were prepared by cross-beam pulsed laser deposition and characterised by high-angle X-ray diffraction as well as specular and off-specular reflection. Using synchrotron radiation at the K-edge energy of Co and Cu to enhance the scattering contrast, the study shows that the roughness of these multilayers is well described by the fractal model of self-affine structures. For the pulsed laser deposited layers an extremely large lateral correlation length, xi, of the vertically correlated interfacial roughness is found (xi >1 µm) which exceeds the xi-value of the uncorrelated roughness by about two orders. The interfaces are very jagged (roughness exponent, h, between 0.15 and 0.3). The root mean square roughness, sigma, of the Cu/Co and Co/Cu interfaces are of the same order compared with the values reported for sputtered layers.

Keywords: Surfaces and interfaces; Multilayers; Reflection spec; Surface roughness; X-ray diffraction

  • Thin Solid Films, vol. 394 (1-2), (2001) p.164-173

Permalink: https://www.hzdr.de/publications/Publ-3652
Publ.-Id: 3652


Structure and magnetic properties of Co nanoclusters fabricated by ion beam synthesis in SiO2 films.

Klimenkov, M.; von Borany, J.; Matz, W.; Eckert, D.; Wolf, M.; Müller, K.-H.

Abstract: Co nanoparticles fabricated by ion beam synthesis in SiO2 films were inve-stigated with TEM and SQUID technique. The variation of the thermal treatment enables the formation of Co nanoclusters of different sizes ranging from 2 to 40 nm. Small nanoclusters of about 2-3 nm are amorphous, whereas clusters above 7 nm show the configuration of cubic Co nanocrystals. Measurements of magnetization at tem-peratures between 2 K and 360 K reveal superparamagnetic behaviour for the small nanoclusters up to 3 nm and ferromagnetism for clusters above 7 nm .

Keywords: cobalt nanoclusters; magnetism; transmission electron microscopy; ion implantation

  • Applied Physics A elektron. Publikation vol.73 (2001) DOI 10.1007/s003330100915
  • Appl. Phys. A 74 (2002)571-575 (Druckversion)

Permalink: https://www.hzdr.de/publications/Publ-3651
Publ.-Id: 3651


Development of an Apparatus for Seaborgium Studies by High Temperature Gas Chromatography

Vahle, A.; Hübener, S.; Dressler, R.; Grantz, M.

In preparation for the characterization of Sg as oxide hydroxide a new high temperature gas chromatography apparatus based on the OLGA design was developed. However, the time-consuming recluster step was replaced by direct deposition of species leaving the chromatographic column on metal foils. In test experiments with short-lived Mo isotopes a retention time of 9 s was determined for an isothermal temperature of 1270 K, sufficient to study Sg isotopes.
A model based on the theory of supersonic jet and on simple geometrical considerations reproduces the data of direct condensation experiments quite well.

Keywords: on-line gas chromatography; reaction gas chromatography; direct deposition; molybdenum oxide hydroxide; adsorption

  • Nuclear Instruments and Methods in Physics Research A 481 (2002) 637-645

Permalink: https://www.hzdr.de/publications/Publ-3650
Publ.-Id: 3650


Ion Beam Synthesis of Ge Nanowires

Müller, T.

The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves.
Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations.
In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation.
The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

Keywords: Ion Beam Synthesis; Nanowires; Surface Sputtering; Redeposition; Kinetic Monte Carlo Simulation

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-309 Januar 2001
    ISSN: 1437-322X

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Permalink: https://www.hzdr.de/publications/Publ-3649
Publ.-Id: 3649


Strahlkopplung von Tandetron-Beschleuniger und Ionenimplanter zur Durchführung von Mehrstrahlexperimenten im Forschungszentrum Rossendorf

Tyrroff, H.; Richter, B.; Neumann, W.

Im Sommer 1999 wurde im Forschungszentrum eine Zweistrahlführung in Betrieb genommen. Dieses System gestattet, Ionenarten aus unterschiedlichen Beschleunigern gleichzeitig in die Experimentierstationen zu lenken. In der Doppelimplantationsstation wird die Zweistrahlführung zur Synthese neuartiger Materialien genutzt. In der Analysestation wird die Zweistrahlführung in Kombination mit einem magnetischen Browne-Buechner-Spektrometer eingesetzt, um komplexe und hochgenaue Materialanalysen durchzuführen. Das System überträgt Ionen des gesamten Teilchen- und Energiespektrums von 3-MV-Tandetron-Beschleuniger und 500-kV-Ionenimplanter mit minimalen Intensitätsverlusten zu den Experimenten. Steuerung und Kontrolle von Beschleunigern, Strahlführung und Experiment erfolgen in einem hierarchischen Rechnernetz. Die hier beschriebene Zweistrahlanlage ist Teil eines Projekts zur umfassenden Kopplung von Basisgeräten des Forschungszentrums.

Keywords: Strahlkopplung; Tandetron-Beschleuniger; Ioneneimplanter; Mehrstrahlexperimente; Doppelimplantation; Oberflächenanalyse; ERD; RBS; Browne-Buechner-Spektrometer; Ionenoptik; Emittanz; Optimierung; magnetische Linsen; elektrostatische Linsen; Ablenkmagneten; Strahlenveloppen; Transmission; Energiebereich; Ionenart; Stromdichte; Strahlkontrolle; Testresultate

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-308 Januar 2001
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-3648
Publ.-Id: 3648


Verification of neutron transport calculations for nonstandard pressure vessel surveillance positions in the VVER-1000 Novovoronesh-5

Böhmer, B.; Konheiser, J.; Brodkin, E.; Egorov, A.; Vikhrov, V.; Zaritsky, S.; Polke, E.

Activation measurements results at non-standard surveillance positions of the VVER-1000 Novovoronesh-5 have been used to verify neutron fluence calculations for pe-ripheral reactor regions with large flux gradients. Fluence integrals and activities of irradiated detectors and specimens had been calculated by three laboratories using different transport calculation methods: 2D/1D-SN synthesis, 3D-SN and the Monte Carlo method. The results obtained by different calculations and by activation measurements have been compared. The differences between measured and calculated activities as well as between the different calculation results were reasonable. Possible causes of discrepancies are discussed.

Keywords: neutron embrittlement; neutron fluences; neutron transport calculations; activation measurements

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Proceedings pp. 37-42
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Proceedings pp. 37-42

Permalink: https://www.hzdr.de/publications/Publ-3647
Publ.-Id: 3647


Intersubband Lasers and Detectors

Helm, M.

The term “intersubband transitions” has been coined to describe optical transitions between confined electronic states in semiconductor quantum structures. In this lecture I will discuss the basic underlying physics of intersubband transitions in quantum wells and discuss their recent applications for real optoelectronic devices, as there are the quantum cascade laser (QCL) and the quantum well infrared photodetector (QWIP).

Concerning the physics, the basic concept of intersubband transitions appears extremely simple; yet a detailed understanding of all aspects, such as absorption strength and frequency, polarization dependence and linewidth, requires a careful consideration of band structure, many-body physics and electromagnetism.

The first observation of intersubband absorption was reported in 1974 in Si accumulation layers and 1985 in GaAs quantum wells. Since then, intense research has driven the development of high-sensitivity intersubband infrared detectors and focal-plane arrays, which are now commercially available. Intersubband lasers have been realized in 1994 and are now covering a spectral range from 4 to 17 m. I will discuss the physics and performance of these optoelectronic devices, also in comparison to conventional band-gap detectors and lasers.

Keywords: infrared; laser; detector; intersubband

  • Invited lecture (Conferences)
    Invited talk at the "29th Int. School on the Physics of Semiconducting Compounds", Jaszowiec, Poland, June 2000

Permalink: https://www.hzdr.de/publications/Publ-3646
Publ.-Id: 3646


Miniband absorption in strongly coupled superlattices

Helm, M.

please contact the author

Keywords: superlattice; infrared

  • Lecture (others)
    Seminarvortrag am Paul-Drude-Insitut für Festkörperelektronik (13.11.2000)

Permalink: https://www.hzdr.de/publications/Publ-3645
Publ.-Id: 3645


Infrarotspektroskopie von Halbleiterübergittern

Helm, M.

Ich moechte einen Ueberblick ueber die optischen Eigenschaften von Halbleiteruebergittern im Infrarot- und THz-Spektralbereich geben, die ja im wesentlichen von Inter- und Intraminibanduebergaengen herruehren. Die theoretischen Ueberlegungen werden durch verschiedene experimentelle Resultate illustriert - z.B. Interminibandabsorption und ihre Anwendung zur Analyse der Elektronen Verteilungsfunktion oder thermisches "quenching" der Intraminibandabsorption. Abschliessend diskutiere ich die Erweiterung obiger
Messungen auf Uebergitter mit einem vertikalen elektrischen Feld, d.h. die Untersuchung von Wannier-Stark-Leitern und Bloch-Oszillatoren.

Keywords: superlattice; infrared

  • Lecture (others)
    Seminarvortrag am Institut für Technische Physik der Universität Erlangen (10.11.2000)

Permalink: https://www.hzdr.de/publications/Publ-3644
Publ.-Id: 3644


Elastic Properties of Diamond-Like Amorphous Carbon Films Grown by Computer Simulation of Ion-Beam Deposition Process

Belov, A.; Jäger, H.-U.

Atomic-scale calculations were performed for the first time to investigate mechanical
properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition process. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. This investigation showed how the Young's modulus varies as a function of the lateral bulk stress in an amorphous film.

Keywords: amorphous carbon; thin films; computer simulation; molecular dynamics; mechanical properties; empirical potentials

  • Contribution to proceedings
    Materials Research Society Symposium Proceedings 648 (2001) P6.53.1-6

Permalink: https://www.hzdr.de/publications/Publ-3643
Publ.-Id: 3643


RESQUE: Dependence of Test Results from Reconstituted Specimens with Tolerance Deviations and Variation of End Block Materials

Viehrig, H.-W.; Richter, H.; Atkins, T.; van Walle, E.; Scibetta, M.; Valo, M. J.; Wootton, M. R.; Keim, E.; Debaberis, L.; Horsten, M.

This paper continues the presentation of detailed results of the EU-sponsored RESQUE project. Within the RESQUE project it was planned to determine the dependence of Charpy-V test results on tolerance deviations and different end block materials in reconstituted specimens. The conventional Charpy-V parameters - the total impact energy, lateral expansion and shear fracture appearance - are not significantly affected by the effects of oversized dimensional variability. Disturbing load oscillations arise from some of the geometrical deviations. This influences the characteristic yield load, yield deflection and impact energy at load maximum. In comparison to the existing scatter there is no significant effect of the end block material on the main Charpy parameters and the characteristic loads.

Keywords: reactor pressure vessel steel; reconstituted specimens; stud welding; geometrical deviation; Charpy-V test; Charpy-V parameters; transition temperatures

  • Lecture (Conference)
    Small Specimen Test Techniques: Fourth Volume, ASTM STP 1418, M. A. Sokolov, J. D. Landes, and G. E. Lucas, Eds., ASTM International, West Conshohocken, PA, 2002, pp. 477 - 488.
  • Contribution to external collection
    Small Specimen Test Techniques: Fourth Volume, ASTM STP 1418, M. A. Sokolov, J. D. Landes, and G. E. Lucas, Eds., ASTM International, West Conshohocken, PA, 2002, pp. 477 - 488.

Permalink: https://www.hzdr.de/publications/Publ-3642
Publ.-Id: 3642


Dose Rate Calculations from Radioactive Vascular Stents: DPK versus exact MC approach

Gorodkov, S.; Möslang, A.; Vladimirov, P.

Vascular stents activated with radioactive isotopes are planned to be used in clinical practice to prevent restenosis in human coronary arteries after balloon angioplasty. Medical stents are cylindrical meshes and their complex geometry is usually treated for energy dose calculation with approximate dose point kernel(DPK) approach. The important point missed in the DPK approach is the absence of the stent material and, hence, the absence of energy absorption inside the stent. We have performed a comparison between DPK and exact Monte Carlo calculations for some simplified stent models. It appears that DPK approximation significantly overestimates pike dose values especially for the case of gamma-emitting sources. We suggest DPK kernel normalization, which minimizes the difference at relatively far distances, while significant discrepancies near the stent surface still remain.

Keywords: vascular stent; radioactive isotope; medical application; Dose Point Kernel(DPK); Monte Carlo; EGS4

  • Poster
    Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation an Applications, Proceedings of the Monte Carlo 2000 Conference, Lisbon, 23.-26. October 2000, pp 467-472, Springer-Verlag Berlin Heidelberg New York, 2001, ISBN 3-540-41795-8
  • Contribution to proceedings
    Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation an Applications, Proceedings of the Monte Carlo 2000 Conference, Lisbon, 23.-26. October 2000, pp 467-472, Springer-Verlag Berlin Heidelberg New York, 2001, ISBN 3-540-41795-8

Permalink: https://www.hzdr.de/publications/Publ-3641
Publ.-Id: 3641


Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) Study of the Sorption of Cm(III) onto Smectite and Kaolinite

Stumpf, T.; Bauer, A.; Coppin, F.; Kim, I. J.

The surface sorption process of Cm (III) onto smectite and kaolinite was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. We conclude that at low pH Cm(III) is sorbed onto kaolinite and smectite as an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere adsorption onto kaolinite and smectite occurs via the aluminol edge sites. The same evolution of the Cm(III)-clay surface species as a function of pH was observed for both minerals. Starting at a pH ³ 5, we observe the formation of a ºAl-O-Cm2+(H2O)5 surface complex, which is replaced by a second species at higher pH. The second surface complex may be a monodentate ºAl-O-Cm+(OH)(H2O)4 species or bidentate º(Al-O)2-Cm+(H2O)5 species. The Cm(III)/clay surface complexes are characterised by their emission spectra (peak maxima at 598.8 nm and 603.3 nm) and their fluorescence lifetime (both 110±7 µs). An important result for the mobility and bioavailability of radionuclides is that no incorporation of Cm(III) into the bulk clay structure was observed.

  • Environmental Science and Technology

Permalink: https://www.hzdr.de/publications/Publ-3640
Publ.-Id: 3640


Messung der Kondensatfilmdicken in einem dampfdurchströmten horizontalen Rohr

Li, W.; Hicken, E. F.; David, P. H.; Prasser, H.-M.; Baldauf, D.; Zschau, J.

Im Mehrzweck-Thermohydraulik-Versuchsstand NOKO wurde die Wirksamkeit verschiedener passiver Sicherheitssysteme oder deren Komponenten untersucht. Passive Sicherheitssysteme besitzen keine Komponenten, die zur Funktionsfähigkeit Fremdenergie benötigen.
Bei Nachrechnungen der Experimente mit den waagerecht angeordneten Notkondensatorbündeln hatte sich ergeben, dass die verwendeten Rechenprogramme wohl die integral abgeführte Energie gut berechnen können; die lokalen Kondensationsraten auf der Innenseite der Rohre unterschieden sich bei den eingesetzten Programmen beträchtlich voneinander. Daher wurde im Rahmen einer Dissertation die Kondensation von Wasserdampf und eines Wasserdampf-Stickstoff-Gemisches auf der Innenseite eines waagerechten Rohres untersucht. Durch eine entsprechende Instrumentierung war die Dicke des Kondensatfilms sowie dessen Struktur zu ermitteln. In einem besonders instrumentierten Rohr des 2. Notkondensator-Bündels wurden hierzu Nadelsonden eingebaut, deren Eintauchtiefe mit Hilfe von Schrittmotoren verändert werden konnte. Diese beweglichen Nadelsonden wurden im wandnahen Bereich hin und her gefahren, um so die Filmdicke zu registrieren. Zusätzlich waren die Nadelsonden mit Thermoelementen ausgestattet, die gleichzeitig eine Messung der Temperaturverteilung in der Grenzschicht ermöglichten.

Keywords: emergency condenser; passive safety systems; steam condensation; two-phase flow; conductivity probes; heat transfer

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.

Permalink: https://www.hzdr.de/publications/Publ-3638
Publ.-Id: 3638


Spectroscopic Study of Cm(III)Sorption onto γ-Alumina

Stumpf, T.; Rabung, T.; Klenze, R.; Geckeis, H.; Kim, J. I.

The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under Ar atmosphere at ionic strength of 0.1 M NaClO4. pH is varied between 2 and 10 and the metal ion concentration between 2.7.10-7 and 4.5.10-5 mol/L. With increasing pH, two Cm(III)-alumina surface species are identified which are attributed to ºAl-O-Cm2+(H2O)5 and ºAl-O-Cm+(OH)(H2O)4. The two curium-alumina surface complexes are characterised by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110 µs). In the concentration range investigated, the surface complex formation is not dependent upon the metal ion concentration but only on pH. Also the concentration ratio of the two surface species is found to be independent on the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.

Keywords: Curium; Alumina; Surface complexation; TRLFS

  • Journal of Colloid and Interface Science 238, 219-224(2001)

Permalink: https://www.hzdr.de/publications/Publ-3637
Publ.-Id: 3637


Synthesis of Spatially Controlled Nanowires by Ion Implantation in V-Grooves on (001) Si-Surfaces

Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.

The synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxydation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm-2. Ge accumulates within the SiO2 at the bottom of the V-groove which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that the Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalesence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.

Keywords: Ion beam synthesis; nanowires; computer simulation

  • Contribution to proceedings
    Materials Research Society, Symposium Proceedings Ion Beam Synthesis and processing of Advanced Materials Symposium held November 27-29, 2000, Boston, Massachusetts, U.S.A. Mat. Res. Soc. Symp. Proc. vol. 647 (2001) O10.2.1-6

Permalink: https://www.hzdr.de/publications/Publ-3635
Publ.-Id: 3635


Bericht der Herbsttagung der Studiengruppe für elektronische Instrumentierung vom 25. bis 27. September 2000 im Hahn-Meitner-Institut Berlin

Gabriel, F.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-305 November 2000
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-3634
Publ.-Id: 3634


Improving the understanding of ion-beam-induced defect formation and evolution by atomistic computer simulations

Posselt, M.

The morphology of the as-implanted damage in silicon is investigated using a recently developed combination of time-ordered computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations. The method is applied to determine the type and the amount of defects formed within the first nanosecond after ion impact. The depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) produced on average per incident ion are calculated for B+ (15 keV), P+ (5, 10, 20, 30 keV), and As+ (15 keV) implantations. It is shown that the as-implanted defect structure depends not only on the nuclear energy deposition per ion but also explicitly on the ion mass. Therefore for each ion species the damage morphology exhibits characteristic features. For heavy ions the percentage of extended defects is higher than for light ions. In all cases investigated the number of free or isolated interstitials exceeds the amount of free vacancies. The results obtained allow a microscopic interpretation of the phenomenological model for the as-implanted damage employed in conventional BCA simulations in order to describe the dose dependence of the shape of ion range profiles. They can be also applied to get more realistic initial conditions for the simulation of the defect kinetics during post-implantation annealing.

Keywords: ion implantation; computer simulation; defects

  • Invited lecture (Conferences)
    MRS 2000 Fall Meeting, Boston, USA, November 27 - December 1, 2000 (invited talk)
  • Contribution to external collection
    Mat. Res. Soc. Symp. Proc. Vol. 647 (2001) pp. O2.1.1-O2.1.12

Permalink: https://www.hzdr.de/publications/Publ-3632
Publ.-Id: 3632


MHD Turbulence Measurements in a Sodium Channel Flow Exposed to a Transverse Magnetic Field

Eckert, S.; Gerbeth, G.; Witke, W.; Langenbrunner, H.

The influence of a static transverse magnetic field on a turbulent sodium flow in a channel with a
rectangular cross section is investigated. The turbulence has been forced by mechanical means
employing a grid of cylindrical bars. Electric potential probes have been used to determine the
longitudinal component of the liquid velocity. The experiments cover a wide range of the
non-dimensional parameters Hartmann number (Ha < 3000) and the magnetic interaction parameter
(N < 800). Measurements of the turbulence intensity as a function of the magnetic interaction
number N will be presented and discussed. The measured spectra are essentially different from those
predicted according to the theory of two-dimensional turbulence.

Keywords: MHD turbulence; liquid metal channel flow; transverse magnetic field; local velocity; measurements; potential probes; velocity profiles; turbulence intensity; power spectra

  • International Journal of Heat and Fluid Flow, Vol. 22/3, 2001, 358-364

Permalink: https://www.hzdr.de/publications/Publ-3631
Publ.-Id: 3631


On the results of the Riga dynamo experiments

Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.

On 11 November 1999, magnetic field self-excitation was observed for the first time in a hydromagnetic experiment at the Riga dynamo facility. In a second experiment in July 2000, the dynamo behaviour in the kinematic as well as in the saturation regime was studied. We report on the results of both experiments and try to understand the saturation mechanism.

  • Magnetohydrodynamics 37, No. 1/2 (2001) 71-79

Permalink: https://www.hzdr.de/publications/Publ-3630
Publ.-Id: 3630


Ion-nitriding induced plastic deformation in austenitic stainless steel

Grigull, S.; Parascandola, S.

Lattice parameter measurements in ion-nitrided surface layers of austenitic stainless steel have been performed using x-ray microbeam diffraction on samples with different nitrogen contents as a function of depth and grain orientation, respectively. The lattice expansion observed in the layers as a result of nitriding is anisotropic due to the presence of elastic strains, but the austenite (fcc) structure is largely retained. Parallel to the layer–substrate interface the expanded lattice is highly relaxed which is, along with significant changes in the surface morphology, indicative of plastic deformation in the nitrided zone.

  • Journal of Applied Physics 88 (2000) 6925

Permalink: https://www.hzdr.de/publications/Publ-3629
Publ.-Id: 3629


Role of Ion-Beam Processing Time in the Formation and Growth of the High-Nitrogen Phase in Austenitic Stainless Steel

Williamson, D. L.; Wilbur, P. J.; Fickett, F. R.; Parascandola, S.

A systematic series of AISI 316 stainless steel samples has been prepared as a function of exposure time to a nitrogen ion beam. Times from 15 s to 4 h were selected with other conditions maintained as follows: sample temperature = 410oC; accelerating potential = 700 V; beam current density = 2.0 mA/cm2. Compositional, structural, magnetic, and diffusion properties were studied with a combination of x-ray diffraction, backscatter Mössbauer spectroscopy, magnetic force microscopy, surface profilometry, and glow-discharge optical emission spectroscopy. The only N-containing phase detected for all processing times was the high-N-solid-solution phase, γN, and its maximum N content was found to grow rapidly to a saturation value exceeding 30 at.%. A carbon contamination layer, in the form of a C-solid-solution phase, γC, was detected below the γN, and was found to be introduced during the Ar-ion sputter-cleaning/heating step used prior to exposure to the N-ion beam. This C-rich layer is “pushed” ahead of the incoming N. The γN layer thickness growth can be modeled with a simple diffusion-plus-sputtering equation that yields the effective diffusivity and maximum (sputter-limited) γN layer depth for the given processing conditions. The surface roughness increases with processing time. Anisotropy in the lattice expansion for different lattice planes parallel to the sample surface and varying magnetic properties in the different surface grains are observed. This is likely due to a mixture of residual stress and N-composition variation effects. Ferromagnetic maze-like domain structures are observed on the 1 micron size scale.

  • Lecture (Conference)
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan
  • Contribution to proceedings
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-3628
Publ.-Id: 3628


Determination of the hyperfine parameters of a-FeSi2 by angle dependent Mössbauer spectroscopy on single crystals

Reuther, H.; Behr, G.; Teresiak, A.

The hyperfine parameters of the metallic disilicide phase a-FeSi2 at room temperature are determined with high accuracy by conversion electron Mössbauer spectroscopy measurements on a single crystal. It is found that there are two well defined iron environments with different electron densities (isomer shifts 0.202 and 0.257 mm/s, resp.) and different electric field gradients. Both quadrupole splittings are negative (-0.382 and -0.730 mm/s, resp.) and the site occupation for both sites is different.

  • Journal of Physics: Condensed Matter 13 (2001) L225-L229

Permalink: https://www.hzdr.de/publications/Publ-3627
Publ.-Id: 3627


Investigations of natural convection in large pools during the heating up of the secondary side of an emergency condenser

Krepper, E.; Hicken, E.-F.; Jaegers, H.

Natural convection is a basic principle for a lot of industrial processes. As an example for the investigation of natural convection phenomena, the paper describes investigations of a passive heat removal system in advanced designs of nuclear power plants. The SWR-1000 concept of Siemens AG includes emergency condensers. In the Research Centre Jülich at the NOKO test facility experiments were performed, to investigate the heat transfer capability under different operation modes. In the last time experiments with detailed instrumentation of thermocouples on the secondary side were performed, to investigate the heating up phenomena in the pool. The paper describes simulations performed in the FZ-Rossendorf using the CFD-code CFX-4 of AEA-Technology and comparisons to the experiments.

Keywords: natural convection; experiments; cfd-simulations

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden 15-17 Mai 2001, Tagungsband S. 99-102
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden 15-17 Mai 2001, Tagungsband S. 99-102

Permalink: https://www.hzdr.de/publications/Publ-3626
Publ.-Id: 3626


A semi-analytical model for the description of coolant mixing inside the KONVOI reactor pressure vessel during pump start-up

Kliem, S.; Prasser, H.-M.

The coolant mixing in the downcomer and the lower plenum during pump start-up has been investigated experimentally at the ROCOM test facility. This facility is a 1:5 linearly scaled model of the KONVOI reactor pressure vessel. Transfer functions for a semi-analytical model have been derived from these experiments. The comparison of the model with further experiments and a computational fluid dynamics calculation is presented.

Keywords: Coolant mixing; pump start-up

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsbericht, S. 107-112
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsbericht, S. 107-112

Permalink: https://www.hzdr.de/publications/Publ-3625
Publ.-Id: 3625


Beziehungen zwischen Mikrostruktur und Zähigkeitseigenschaften von neutronenbestrahlten WWER-Reaktordruckbehälterstählen

Ulbricht, A.; Böhmert, J.; Viehrig, H.-W.

An 7 Chargen von Druckbehälterstählen russischer Herkunft wurden SANS-Unter-
suchungen im unbestrahlten Zustand, nach Bestrahlung im Reaktor WWER-2
Rheinsberg und nach einer 100-h-Ausheilglühung bei 475 °C durchgeführt. Bestrah-
lung erzeugt in jedem Fall eine erhöhte Kleinwinkelstreuintensität. Die Analyse ihrer
Streuvektorabhängigkeit führt auf Strukturdefekte mit einem mittleren Radius von
ca. 1 nm und einem chargenabhängig variierenden Volumenanteil von 0,03 - 0,71 %. Der Volumenanteil korreliert tendenziell mit der Verschiebung der Sprödbruchüber-
gangstemperatur.

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, Germany, 15.-17. Mai 2001, S. 697-700
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, Germany, 15.-17. Mai 2001, S. 697-700

Permalink: https://www.hzdr.de/publications/Publ-3624
Publ.-Id: 3624


Verification of the code ATHLET by post-test analysis of two experiments performed at the integral test facility CCTF

Schäfer, F.; Krepper, E.

In the framework of the external validation of the thermo-hydraulic code ATHLET Mod 1.2 Cycle A, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the japanese test facility CCTF. The experiments C2-04/62 and C2-19/79 simulate a double end break in the cold leg of the PWR with ECC injection into the cold leg and with combined ECC injection into the hot and cold legs. The evaluation of the calculated results shows, that the main phenomena can be calculated in a good agreement with the experiment. Especially the behaviour of the quench front and the core cooling are calculated very well.

Keywords: ATHLET; code validation; experiments

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, Dresden, May 15-17 2001, p. 87-90
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, Dresden, May 15-17 2001, p. 87-90

Permalink: https://www.hzdr.de/publications/Publ-3623
Publ.-Id: 3623


The hydrolysis of uranium(VI) investigated using EXAFS and 17O-NMR

Moll, H.; Reich, T.; Szabó, Z.

The hydrolysis of uranium(VI) has been the subject of extensive studies since 50 years because uranyl forms strong comlexes with OH- in solution. A comprehensive discussion and review of the thermodynamic data is published in [1]. We investigated the structure of UO22+ as a function of pH with the aid of U LIII-edge EXAFS spectroscopy. The experiments were carried out at beamline BM20. The equipment allows excellent XAS measurements up to high k-values, 17.5 Å-1 in our case.
The speciation of uranium(VI) at a total concentration of 0.05 M in slightly acidic (pH: 3 to 4) solutions is dominated by the two polynuclear complexes (UO2)2(OH)22+ and (UO2)3(OH)5+. Sample A is an example from this pH region, where (UO2)3(OH)5+ is the dominant species. Structure investigations of these polymeric cations in solution at such uranium concentrations are rare. The formation of polynuclear complexes is clearly confirmed by the U-U interaction at 3.81 Å (Figure 1). Approximately 5 oxygen atoms are coordinated in the equatorial plane at 2.41 Å.
In the following pH region from 6 to 11, the U(VI) speciation is dominated by the precipitation of schoepite phases, UO2(OH)2xH2O (sample B). A longer U-U distance of 3.87 Å was measured. Similar U bond lengths of Ë 3.9 Å were found in schoepite phases. Their structure consists of a network of UO2(OH)2 sheets, where the uranyl centers are connected via a double OH bridge.
In the alkaline pH region (sample C and D), monomeric uranium species are formed. As compared to our previous study [2], we were able to extend the k-space region from 15 Å-1 in [2] up to 17.5 Å-1 and thereby to increase the accuracy. The EXAFS measurements confirm the speciation calculations indicating that UO2(OH)42- is the major species at 0.5 M tetramethylammonium hydroxide (TMA-OH). There are two trends in the EXAFS data, the U-Oaxial bond length increases 1.79, 1.81, and 1.83 Å moving from pH 4.1 to 13.7, while the average U-Oequatorial bond length decreases, 2.41, 2.34, 2.26 Å, respectively. This indicates a stronger bonding of equatorial OH groups with increasing pH. Clark et al. have presented spectroscopic evidence for the formation of a penta-hydroxide complex at high TMA-OH concentrations, however with no information about the equilibrium constant [3]. We have tested the hypothesis of Clark et. al. using 17O-NMR spectroscopy with 17O-enriched "yl" oxygens. The spectrum recorded at 258 K (Figure 2) shows only one peak for UO2(OH)42- in 1 M TMA-OH. However, when increasing the hydroxide concentration to 3 M two peaks were obtained, one with the same shift as in the 1 M TMA-OH solution, 1132.2 ppm, the other at 1135.8 ppm presumably due to UO2(OH)53- (Figure 2). To conclude, the complex UO2(OH)42- has a very broad range of existence in strongly alkaline solution. At very high total concentrations of hydroxide [> 1 M TMA-OH], an additional OH- ligand may coordinate in an associative reaction.

  • Contribution to external collection
    ESRF Highlights 2000, 21-22 (2001)

Permalink: https://www.hzdr.de/publications/Publ-3622
Publ.-Id: 3622


Copper gettering in silicon at half of the projected ion range induced by helium implantation

Peeva, A.; Fichtner, P. F. P.; Da Silva, D.; Behar, M.; Koegler, R.; Skorupa, W.

Damage has been observed in keV He + ion-implanted Si away from the projected ion range Rp, mainly around Rp/2. Cu gettering has been used for the detection of irradiation defects which are formed during rapid thermal annealing (RTA) of 800°C/10 min. The transmission electron microscopy (TEM) micrographs show no visible defects at Rp/2. The Cu gettering peak at Rp/2 is well known for MeV-ion-implanted and annealed Si (Rp/2 effect). In this study the corresponding effect is observed for low energy implantation of a light ion like He. The mechanism of the cavity formation when He is implanted into silicon and its influence to the implantation induced point defects recombination during subsequent annealing is discussed.

Keywords: Gettering; Ion Implantation; Defects; Helium; Cavities

  • Journal of Applied Physics 91 (2002) 69

Permalink: https://www.hzdr.de/publications/Publ-3621
Publ.-Id: 3621


The Colloid Chemistry of Acid Rock Drainage Solution from an Abandoned Zn-Pb-Ag Mine

Zänker, H.; Moll, H.; Richter, W.; Brendler, V.; Hennig, C.; Reich, T.; Kluge, A.; Hüttig, G.

Acid rock drainage (ARD) solution from an abandoned ore mine (pH 2.7, sulfate concentration 411 mMol/L, Fe concentration 93.5 mMol/L) was investigated by photon correlation spectroscopy, centrifugation, filtration, ultrafiltration, scanning electron microscopy, ICP-MS, AAS, ion chromatography, TOC analysis and X-ray absorption fine structure (EXAFS) spectroscopy. A colloid concentration of $ 1 g/L was found. The prevailing particle size was < 5 nm. The most probable mineralogical composition of the colloidal particles is a mixture of hydronium jarosite and schwertmannite. Conclusions as to the type of binding of arsenic onto the particles are drawn.

Keywords: Key words: acid rock drainage; colloids; iron hydroxy sulfates; arsenic

  • Applied Geochemistry 17 (2002) 633-648

Permalink: https://www.hzdr.de/publications/Publ-3620
Publ.-Id: 3620


The Modeling of Fuel Rod Behaviour under RIA Conditions in the Code DYN3D

Rohde, U.

A description of the fuel rod behaviour and heat transfer model used in the code DYN3D for the simulation of reactivity initiated accidents (RIA) is given. The model comprises a detailed description of the heat transfer in the gas gap between fuel and cladding by conduction, radiation and fuel-cladding contact. The gas gap behaviour is modeled in a mechanistic way taking into account transient changes of the gas gap parameters based on given conditions for the steady state. Thermal, elastic and plastic deformations of fuel and cladding are taken into account. Metal-water reaction of the cladding material in the high temperature region is considered. The cladding-coolant heat transfer regime map covers the region from one-phase liquid convection to dispersed flow with superheated steam.
For the validation of the model, experiments on fuel rod behaviour during RIAs performed in Russian and Japanese pulsed ressearch reactors with shortened probes of fresh fuel rods are calculated. Comparisons between calculated and measured results are shown and discussed. Numerical studies concerning the fuel rod behaviour under RIA conditions in power reactors are reported about. It is demonstrated, that the fuel rod behaviour at high pressure and mass flow rate in power reactors is different from the behaviour at low pressure and stagnant flow conditions in the experiments. It is shown that the mechanisms of fuel rod failure known from the literature can be qualitatively reproduced by the DYN3D fuel rod model.

Keywords: nuclear reactors; reactivity initiated accidents; fuel rod behaviour; heat transfer; validation; pulsed research reactors

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, Deutschland, 15.-17.5.2001, Tagungsband S. 339-344, Inforum Verlags- und Verwaltungsgesellschaft mbH, Bonn 2001
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, Deutschland, 15.-17.5.2001, Tagungsband S. 339-344, Inforum Verlags- und Verwaltungsgesellschaft mbH, Bonn 2001

Permalink: https://www.hzdr.de/publications/Publ-3619
Publ.-Id: 3619


Boundary Layer Control by Means of Wall Parallel Lorentz Forces

Weier, T.; Fey, U.; Gerbeth, G.; Mutschke, G.; Lielausis, O.; Platacis, E.

Lorentz forces can be used to control the near wall flow of low conducting liquids like sea-water. To achieve force densities strong enough to modify the flow, both magnetic and electric fields have to be applied to the fluid. Here, wall parallel Lorentz forces in streamwise direction were used to influence the velocity profile of a flat plate boundary layer as well as the flow around a symmetric hydrofoil. Velocity measurements inside the boundary layer and direct force measurements are given for the flat plate.
At moderate force strength, the mean velocity profile is characterized by a momentum thickness smaller than in the unforced case, whereas at high enough Hartmann numbers a wall jet develops. Additionally, a turbulent, but approximately non-growing boundary layer has been observed. The effect of a suction-side, streamwise Lorentz force on a NACA-0017-like hydrofoil is quantified by means of force balance measurements. Depending on the angle of attack, two different effects are observed. (1) At small angles of incidence, a moderate increase in lift due to additional circulation is observed. Simultaneously, a decrease in drag of the hydrofoil is caused by the momentum added. (2) At higher angles of attack, where the unforced hydrof oil would normally stall, a more pronounced lift increase and a corresponding drag reduction are observed due to separation prevention.

  • Magnetohydrodynamics, Vol. 37, No. 1/2, 177-186, 2001

Permalink: https://www.hzdr.de/publications/Publ-3618
Publ.-Id: 3618


Post-test analysis of two accident management experiments performed at the Bethsy test facility using the code ATHLET

Schäfer, F.; Krepper, E.; Weiß, F.-P.

In the framework of the external validation of the thermal-hydraulic code ATHLET Mod 1.1 Cycle D, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the french integral test facility BETHSY. During the experiment 5.2 C the complete loss of steam generator feedwater was simulated. The depressurization of the primary circuit and high pressure injection is assumed as an emergency measure. During the experiment 9.3 the break of a steam generator U-tube is simulated. The failure of the high pressure injection is assumed. As accident management measures, the depressurization of the steam generator secondary sides and finally of the primary circuit by opening of the pressurizer valve was investigated. The results show, that the code ATHLET is able to describe the complex scenario in good accordance with the experiment. For both tests the safety related statement could be reproduced.

Keywords: accident-management; codes; simulations

  • Lecture (Conference)
    ICONE - Ninth International Conference on Nuclear Engineering, Nice, France, April 8-12 2001, Track 7 (407.pdf on CD-ROM)
  • Contribution to proceedings
    ICONE - Ninth International Conference on Nuclear Engineering, Nice, France, April 8-12 2001, Track 7 (407.pdf on CD-ROM)

Permalink: https://www.hzdr.de/publications/Publ-3617
Publ.-Id: 3617


Evolution of Ion Beam Synthesized Au Nanoclusters in SiO2 under Ion Irradiation

Schmidt, B.; Heinig, K.-H.; Mücklich, A.

Au nanoclusters have been synthesized in a 500 nm thick SiO2 layer on (001)Si by 330 keV Au+ implantation of 2x1016 cm-2 and subsequent annealing at T = 1000 °C for 1h in dry oxygen. XTEM images show arround the projected ion range Rp = 100 nm a layer of crystalline Au clusters. At Rp the Au clusters have a mean size of 5 nm and a broad size distribution resembling approximately the LSW distribution of diffusion controlled Ostwald ripening. The Au nanoclusters were subsequently irradiated by 4.5 MeV Au+ ions with a fluence of (0.5...1.0)x1016 cm-2 at 190...210 °C . The high energy Au+ ions come to rest at a depth of 1 µm, i.e. in the Si substrate far below the Au nanoclusters and even below the SiO2 layer. The high energy Au+ irradiation causes a strong decrease of the mean size and of the width of the size distribution of Au nanoclusters. The observed Au nanocluster evolution under ion irradiation agrees qualitatively with recent theoretical predictions and kinitic lattice Monte-Carlo simulations.

Keywords: Nanocluster; Ion beam synthesis; Ostwald ripening

  • Poster
    Proceedings MRS 2000 Fall Meeting, Boston, USA, 27.11.-01.12.2000
  • Contribution to proceedings
    Proceedings MRS 2000 Fall Meeting, Boston, USA, 27.11.-01.12.2000

Permalink: https://www.hzdr.de/publications/Publ-3616
Publ.-Id: 3616


Synthesis of Spatially Controlled Nanostructures by Ion Implantation in V-Grooves on (001) Si Surfaces

Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.

The synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxydation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm-2. Ge accumulates within the SiO2 at the bottom of the V-groove which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalesence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.

Keywords: Ion beam synthesis; nanowires; Ostwald ripening

  • Lecture (Conference)
    Proceedings MRS 2000 Fall Meeting, Boston, USA, 27.11.-01.12.2000

Permalink: https://www.hzdr.de/publications/Publ-3615
Publ.-Id: 3615


Model for radial gas fraction profiles in vertical pipe flow

Lucas, D.; Krepper, E.; Prasser, H.-M.

One-dimensional codes are frequently used for the simulation of two phase flow in the field of design, optimization and safety analysis of nuclear and chemical plants. Most of the correlations used by these codes e.g. for pressure drop or heat and mass transfer are valid only for a given flow regime. Steady flow maps are not able to predict the flow pattern in case of transient flows. Recently attempts were made to solve this problem by the introduction of additional equations for the bubble density or corresponding parameters like bubble diameter, bubble volume or interfacial area. Bubble coalescence and break-up rates, which form the source terms in these equations, are determined by local events. That means, they depend on local parameters of turbulence as well as on the local bubble size distribution.

Experimental and theoretical investigations for vertical pipes have shown, that the probability of radial residence of a bubble strongly depends on their diameter. Whereas smaller bubbles tend to move towards the wall, large bubbles are preferably found in the centre of the tube. For the water-air system at ambient conditions a change of the maximum in the radial profiles was found to occur at a bubble diameter of about 5 - 6 mm. This change is very important for the development of the flow.

A one-dimensional model is presented, which predicts the radial volume fraction profiles from a given bubble size distribution. It bases on the assumption of an equilibrium of the forces acting on a bubble perpendicularly to the flow path (non drag forces). For the prediction of the flow pattern this model could be used within an procedure together with appropriate models for local bubble coalescence and break-up.

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsband, S. 83-86
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsband, S. 83-86

Permalink: https://www.hzdr.de/publications/Publ-3614
Publ.-Id: 3614


Stability analysis of the flow inside an electromagnetically levitated drop

Shatrov, V.; Galindo, V.; Gerbeth, G.

The stability of the flow driven by the electromagnetic force of a HF levitation coil inside a drop is studied numerically using a spectral code. In the uniform or almost uniform external alternating magnetic field the first instability of the flow is three-dimensional with an azimuthal wave number of m = 3. The corresponding critical Reynolds number varies from 108 to 81 for various skin depth.

  • Magnetohydrodynamics, Vol. 37, No. 1/2, pp 45-54, 2001

Permalink: https://www.hzdr.de/publications/Publ-3613
Publ.-Id: 3613


Positron Annihilation Spectroscopy

Brauer, G.

The practical application of positron annihilation spectroscopies to SiC, i.e. conventional positron lifetime and Doppler broadening measurements as well as slow positron implantation studies, will be demonstrated and discussed. It will be shown how to finally obtain materials characteristics which are of general interest, i.e. well beyond the ordinary positron annihilation parameters. As a second example, some results from the investigation of Pt layers on alumina will be presented.

Keywords: positron annihilation; defects; SiC; Pt; thin films

  • Lecture (others)
    Seminar am Lehrstuhl für Tieftemperaturphysik, Karlsuniversität Prag, Prag, 04.12.2000

Permalink: https://www.hzdr.de/publications/Publ-3612
Publ.-Id: 3612


Innovative Maßnahmen zur Vermeidung von Druckstößen und Kavitationsschlägen

Dudlik, A.; Hagemann, O.; Fahlenkamp, H.; Prasser, H.-M.

Druckstöße und Kavitationsschläge in Rohrleitungen entstehen immer dann, wenn die Strömungsgeschwindigkeit schnell geändert wird. Als Folgen kann man an Rohrleitungs-systemen laute Schläge, von den Halterungen springende Leitungen bis hin zu Leitungsrissen beobachten. In dem Beitrag werden nach einer Aufstellung bekannter Maßnahmen und Diskussion deren Einsatzgrenzen zwei neue, von Fraunhofer UMSICHT und dem Forschungszentrum Rossendorf entwickelte Verfahren zur Vermeidung unerwünschter Drücke in Rohrleitungen, insbesondere von Druckstößen und Kavitationsschlägen, vorgestellt. Durch Anordnung einer Hilfsarmatur hinter der eigentlichen Absperrarmatur ist eine Schnellabsperrung der Rohrleitung ohne Kavitationsschläge möglich. Der Einsatz von Rückschlagklappen stellt hierbei eine kostengünstige Variante dar. Die Kavitationsschläge hinter der Absperrarmatur werden vollständig unterdrückt. Darüber hinaus wird ein neues passives Sicherheitssystem (ABS-Armatur) zur Verhinderung von Druckstößen vorgestellt. Hierbei wirkt der Leitungsdruck stromaufwärts der Absperrarmatur auf ein Scheibenbremssystem, das die Schließbewegung der Armatur beim Ansteigen des Leitungsdruck unterbricht. Sinkt der Druck wieder ab, so wird der Schließvorgang fortgesetzt. Durch Kombination beider neuer Verfahren können sowohl der Druckanstieg stromaufwärts der Armatur als auch die Kollabierung von Kavitationsblasen stromabwärts der Armatur sicher vermieden werden. Durch diese innovativen Maßnahmen kann der Systemdruck in der Rohrleitung niemals unerwünschte Beträge annehmen. Einzeln für sich sowohl als auch in Kombination stellen beide Verfahren passive Sicherheitssysteme für Rohrleitungen dar.

Keywords: Schnellschlussarmaturen; Druckstöße; Kavitationsschläge; passive Sicherheitstechnik

  • 3R international 39 (2000) 11, S. 673-677.

Permalink: https://www.hzdr.de/publications/Publ-3610
Publ.-Id: 3610


Evolution of the Two-Phase Flow in a Vertical Tube - Decomposition of Gas Fraction Profiles according to Bubble Size Classes using Wire-Mesh Sensors

Prasser, H.-M.; Krepper, E.; Lucas, D.

The wire-mesh sensor developed by the Forschungszentrum Rossendorf produces sequences of instantaneous gas fraction distributions in a cross section with a time resolution of 1200 frames per second and a spatial resolution of about 2-3 mm. At moderate flow velocities (up to 1-2 m/s), bubble size distributions can be obtained, since each individual bubble is mapped in several successive distributions. The method was used to study the evolution of the bubble size distribution in a vertical two-phase flow. For this purpose, the sensor was placed downstream of an air injector, the distance between air injection and sensor was varied. The bubble identification algorithm allows to select bubbles of a given range of the effective diameter and to calculate partial gas fraction profiles for this diameter range. In this way, the different behaviour of small and large bubbles in respect to the action of the lift force was observed in a mixture of small and large bubbles.

Keywords: two-phase flow; gas-liquid flow; bubble size measurement; gas fraction measurement; flow pattern; wire-mesh sensors

  • International Journal of Thermal Sciences 41 (2002) pp. 17-28.

Permalink: https://www.hzdr.de/publications/Publ-3609
Publ.-Id: 3609


PET radiopharmaceutical production - a unit of preparation and quality control

Füchtner, F.; Steinbach, J.; Johannsen, B.

The view on the production of radiopharmaceuticals for human use in Positron Emission Tomography (PET) has been changing considerably during the last few years. PET has developed from an elitist research method only to a tool covering the research purpose as well the clinical application.
Accordingly, the radioactive substances which have been applied as radiotracers underwent a transformation to radiopharmaceuticals. This is accompanied by the transfer of the pharmaceutical legislation to PET radiopharmaceuticals. Consequently, Marketing and Manufacturing Authorisation becomes more and more important for the production of PET radiopharmaceuticals. To get the manufacturing Authorisation the manufacturer has to apply the guidelines of Good Manufacturing Practise (GMP) by consideration of monographs in pharmacopoeia.
In the lecture, the translation of the GMP regulations to the manufacturing conditions of PET radiopharmaceuticals is presented. This is illustrated by the example of the Rossendorf PET-Centre.

  • Lecture (others)
    Sixth TESLA Workshop: Positron Emission Tomography at the Cyclotron Center of the Slovak Republic, Castá-Papiernicka, Slovak Republic, November 24-25, 2000

Permalink: https://www.hzdr.de/publications/Publ-3608
Publ.-Id: 3608


Integrated Transport Code Sytem for Multicomponent High-ß Plasmas in the Gas Dynamic Trap

Karpushov, A. N.; Anikeev, A. V.; Noack, K.; Strogalova, S. L.

The Budker Institute Novosibirsk made the proposal for a high-power 14 MeV neutron source on the base of a gas dynamic trap (GDT). The GDT is an axisymmetric open trap with a high mirror ratio confining a collisional plasma. To be able to calculate the dynamics of the particle fields appearing inside the existing experimental GDT device of the Budker Institute, and later, inside the neutron source an Integrated Transport Code System (ITCS) is under development. It is to consider the full dependencies of the transport phenomena on space, time, energy and angle variables as well as the interactions between the fields. The paper briefly describes the theoretical and numerical models of the code system and illustrates its first application to calculate the particle fields inside the experimental GDT facility.

Keywords: plasma; fusion; neutron source; gas dynamic trap; mirror; theoretical methods; numerical methods; code system

  • Poster
    EPS 27th Conference on Controlled Fusion and Plasma Physics, Budapest, Hungary, 12-16 June 2000, Poster P3.019, Proceedings will be published
  • Contribution to proceedings
    EPS 27th Conference on Controlled Fusion and Plasma Physics, Budapest, Hungary, 12-16 June 2000, Poster P3.019, Proceedings will be published

Permalink: https://www.hzdr.de/publications/Publ-3607
Publ.-Id: 3607


Actinide elements

Hübener, S.

This encyclopedia article is a comprehensive overview of the actinide elements. Subdivided in the sections
- Discovery, Occurrence, and Synthesis of the Actinides,
- Radioactivity and Nuclear Reactions of Actinides,
- Applications of Actinides,
- Actinide Metals,
- Actinide Ions, and
- Actinide Compounds and Complexes
the current knowledge of the actinide elements that is generally accepted within the field is presented.

  • Book (Authorship)
    The Encyclopedia of Physical Science and Technology - Third Edition, Academic Press

Permalink: https://www.hzdr.de/publications/Publ-3606
Publ.-Id: 3606


CHT'01 validation exercise: Natural convection in an air filled cavity

Krepper, E.

The paper presents calculations of a benchmark problem using the CFD code CFX-4 and the comparison with published experiments. The benchmark comprises the calculation of natural convection in a air-filled cavity with differentially heated walls. The experiments were performed for different orientations of the heated and cooled faces. The calculated Nusselt numbers correspond quite well to the experimental results. The steady state problem was approached by transient calculations. Not for each test case a stable final solution was found. In those cases the correspondent time averaged values were close to the experiment.

Keywords: natural convection; cfd-benchmark; experiments; CFX-4 calculations

  • Lecture (Conference)
    Int. Conf. on "Advances in computational heat transfer", Palm Cove, Australien Mai 2001, Proc. Vol. 2, pp. 1351-1356
  • Contribution to external collection
    Int. Conf. on "Advances in computational heat transfer", Palm Cove, Australien Mai 2001, Proc. Vol. 2, pp. 1351-1356

Permalink: https://www.hzdr.de/publications/Publ-3605
Publ.-Id: 3605


Modeling of radial gas fraction profiles for bubble flow in vertical pipes

Lucas, D.; Krepper, E.; Prasser, H.-M.

The paper presents a method for the prediction of local bubble size distributions from a given bubble size distribution for the entire cross section. The method bases on the assumption of the equilibrium of the forces acting on a bubble perpendicularly to the flow direction. Assuming a large number of bubble size classes radial distributions are calculated separately for all bubble classes. The sum of these distributions is the radial profile of the gas fraction. The results of the model are compared with experimental data for a number of gas and liquid volume flow rates. The experiments were performed at a vertical test loop (inner diameter 50 mm) in FZ-Rossendorf using a wire mesh sensor. The sensor enables the determination of void distributions in the cross section of the loop. A special evaluation procedure supplies bubble size distributions as well as local distributions of bubbles within a predefined interval of bubble sizes. There is a good agreement between experimental and calculated data. In particular the change from wall peaking to core peaking is well predicted.

Keywords: flow; two-phase; simulations

  • Lecture (Conference)
    Ninth International Conference On Nuclear Engineering - ICONE-9, Nice, France, April 8-12, 2001, Conference-CD, Paper 279
  • Contribution to proceedings
    Ninth International Conference On Nuclear Engineering - ICONE-9, Nice, France, April 8-12, 2001, Conference-CD, Paper 279

Permalink: https://www.hzdr.de/publications/Publ-3603
Publ.-Id: 3603


Simulation of subcooled flow instability for high flux research reactors using the extended code ATHLET

Hainoun, A.; Schaffrath, A.

Considering the specific features of high flux research reactors given by both high heat flux and high flow velocity, the ATHLET condensation model especially in subcooled flow conditions has been extended and a new correlation of critical heat flux (CHF) is implemented. To validate the extended program, the Thermal-Hydraulic Test Loop (THTL) of Oak Ridge National Laboratory (ORNL) was modeled with ATHELT and an extensive series of experiments concerning the onset of thermohydraulic flow instability (OFI) in subcooled boiling regime were calculated

  • Nuclear Engineering and Design 207 (2001) 2, 163-180

Permalink: https://www.hzdr.de/publications/Publ-3602
Publ.-Id: 3602


4-[18-F]Fluorbenzoyl-carboxymethyllysin (18-FB-CML) - ein neuer potentieller PET-Tracer für Probenecid-sensitive organische Anionentransporter

Bergmann, R.; Helling, R.; Heichert, C.; Wittrisch, H.; Hinz, R.; Steinbach, J.; Johannsen, B.

Ziel:
Verschiedene Probenecid-sensitive multispezifische organische Anionentransporter sind in Leber, Niere und Dünndarm an der aktiven Ausscheidung von organischen Anionen beteiligt und werden mit der Medikamentenresistenz bei Chemotherapie in Zusammenhang gebracht. Deshalb wurde als potentieller Radiotracer auf der Basis des anionischen Stoffwechselendproduktes, Carboxymethyllysin und zum Vergleich Carboxyethyllysin und Lysin, mit 18-F markiert und in vitro und in vivo charakterisiert.
Methodik: [N-Alpha-4-[18-F]FB-N-Epsilon-Carboymethyllysin (18-FB-CML), N-Alpha-4-[18-F]FB-N-Epsilon-Carboxyethyllysin (18-FB-CEL) und N-Alpha-4-[18-F]FB-Lysin (18-FB-Lys) wurden mit [18-F]N-Succinimidyl-4-fluorbenzoat unter Trägerzusatz synthetisiert, die in vivo Stabilität mit HPLC und die Bioverteilung und -Kinetik durch Organenentnahme und PET (dynamisch, 30 Aufnahmen, 0-120 min, ECAT HR+) an Ratten charakterisiert.
Ergebnisse:
Alle drei Tracer werden renal (>20 %ID, 5 min p.i., >85 %ID 2 h p.i.) ausgeschieden. Die vorübergehende Akkumulation von 18-FB-CML und 18-FB-CEL in der Niere und der Leber wird durch Probenecid (10 min vor Tracerinjektion, 5 mg/kg Körpergewicht) zu mehr als 50 % gegenüber der Kontrollgruppe gehemmt (5 min p.i.). Unter Probenecid werden auch 2 h p.i. weniger als 50 % der Radioaktivität der Kontrolle in Leber und im Darm gefunden. 18-FB-CML und 18-FB-CEL werden nicht metabolisiert. Durch Probenecid wird in der Leber K1 (18-FB-CML) von 0.42 1/min auf 0.05 1/min verringert.
Schlussfolgerungen:
Die Stabilität von 18-FB-CML in vivo, die Möglichkeit der Hemmung der Akkumulation in Leber, Darm und Niere durch Probenecid, die Halbwertszeit von 18-F, die einfache Biokinetik und die fehlende Chiralität, lassen 18-FB-CML als PET-Tracer für Probenecid-sensitive organische Anionentransporter geeignet erscheinen.

  • Lecture (Conference)
    39. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 25.-28.4.2001 in Hamburg
  • Abstract in refereed journal
    Nuklearmedizin 40 (2001) A24

Permalink: https://www.hzdr.de/publications/Publ-3601
Publ.-Id: 3601


Neptunium(V) Complexation by Various Humic Acids in Solution Studied by EXAFS and NIR Spectroscopy

Pompe, S.; Schmeide, K.; Reich, T.; Hennig, C.; Rossberg, A.; Geipel, G.; Brendler, V.; Heise, K. H.; Bernhard, G.

The structure of Np(V) humic acid (HA) complexes at pH 7 was studied by EXAFS. For the first time, the influence of phenolic OH groups on the complexation of HA and Np(V) in the neutral pH range was investigated using a modified natural HA with blocked phenolic OH groups and Bio-Rex70, a cation exchange resin having carboxyl groups as proton exchanging sites. Near-infrared (NIR) spectroscopic measurements verified the formation of Np(V) humates under the applied conditions. Coordination numbers and bond distances were determined for the axial and equatorial coordination shells of neptunium. These were compared to structural parameters of Np(V) hydrates and carboxylates.

Keywords: Humic Acid; Complexation; Neptunium; Np(V); EXAFS; NIR Spectroscopy; Structure

  • Contribution to proceedings
    Proceedings of the 2nd NEA and Euroconference Workshop on Speciation, Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources. Grenoble, France, 10.-12.09.2000, p. 277-284.

Permalink: https://www.hzdr.de/publications/Publ-3600
Publ.-Id: 3600


Nanocluster Based Memories

von Borany, J.

The talk starts with a short survey of the concepts for non-volatile memories designed for nanoelectronics. Among different approaches memories based on the charge storage in small semiconductor quantum dots are of particular interest, as they offer an opportunity for integration in the present CMOS-technology. Following this route the "Nanocrystal Memory" - which was first introduced by IBM in 1996 - is discussed in detail regarding its working principle and the corresponding technological challenges. One of the critical points is the fabrication of a shallow band of small semiconductors in the gate oxide of a FET very close, but well separated to the Si/SiO2-interface. Different deposition and ion beam techniques have been successfully applied to realize small Si or Ge nanoclusters with a typical size of 2-5 nm and a density between 10E11…10E12 cm-2. One very promising technique is the ion beam synthesis of nanoclusters, which is mainly applied in the Forschungszentrum Rossendorf. Microstructural investigations have shown, that IBS enables the fabrication of delta-like nanocluster bands, which fulfill very well the requirements for a "nanocrystal" memory. Electrical investigations revealed, that cluster containing thin SiO2 films show a remarkable storage effect even at room temperature, which are characterized by the shift of flatband or threshold voltage of MOS- or FET-structures, respectively. Despite these successful results main questions are still open, so that hopes and challenges are close together.

  • Lecture (others)
    Japanese-German Symposium "Strategies in Nanotechnology", October 30-31, 2000, Berlin; organized by the Community of German Competence Centers for Nanotechnology

Permalink: https://www.hzdr.de/publications/Publ-3599
Publ.-Id: 3599


18-F-markierte Neurotensinderivate zur Tumordarstellung: Bioverteilung, -kinetik und Katabolismus

Bergmann, R.; Wittrisch, H.; Heichert, C.; Kretzschmar, M.; Rodig, H.; Mäding, P.; Steinbach, J.; Reubi, J.-C.; Johannsen, B.

Ziel:
Entwicklung 18-F-markierter Neurotensinderivate zur Darstellung von hochaffinen Neurotensinrezeptoren (NTR1), die in humanen duktalen Pankreaskarzinomen mit hoher Inzidenz überexprimiert werden, dagegen bei chronischer Pankreatitis oder im normalen Pankreas nicht vorkommen (1).
Methodik:
4-[18-F]Fluorbenzoyl-NT(8-13) [1], 4-[18-F]FB-ArgPsi(CH2-NH)Arg-Pro-Tyr-Ile-Leu [2] und 4-[18-F]FB-ArgPsi(CH2-NH)Arg-Pro-Tle-Leu [3] und weitere Modellpeptide wurden synthetisiert, in vitro mittels Rezeptor Autoradiographie an NTR-exprimierenden humanen Adenokarzinomen und in vivo an humanen (Adenokarzinomzellen) HT-29 und WiDr tumortragenden Mäusen charakterisiert.
Ergebnisse:
Die Tracer binden in vitro, ex vivo und in vivo an NTR1 von tumortragenden Mäusen. Alle Substanzen werden in vitro internalisiert und mobilisieren intrazellulär Ca2+. Die Tracer unterscheiden sich in vivo in ihrer proteolytischen Stabilität und ihren Residenzzeiten im Blut. Die moderate Tumoraufnahme begründet sich in unterschiedlicher Bindungsaffinität der Peptide zum NTR1 im proteolytischen Abbau und rezeptorunabhängiger Aufnahme der entstanden 18-F-markierten Kataboliten in Tumor und Muskel. Alle radioaktiven Spaltprodukte wurden identifiziert.

Ligand....IC50± SEM (nM).........Tumor/Muskel Verhältnis (MW±SEM)
..............(humane Ca)...............................(HT-29 Tumor Maus)

...............................................Kontrolle...............NT(8-13)..........Spez..........P..
.......................................................................(5mg/kg KG)........Bindung
NT..........0.86±0.10 (6)........... ......-..........................-...................-.................-
1............0.42±0.05 (6)..........7,27±0,45 (5)........6,89±0,19 (4).........0,38........>0.01
2............0.91±0.20 (6)..........4,68±1,28 (4)........2,12±0,97 (4).........2.56........<0.01
3..............4.1±0.60 (6)..........2,63±0,83 (5)........1,25±0,23 (5).........1.38........<0.005

Schlussfolgerungen:
Es wird ein Schema des Abbaus der 18-F-markierten Peptide vorgeschlagen. Die untersuchten Tracer dienen als Leitsubstanzen für die Entwicklung neuer 18-F-markierter Peptidderivate mit höherer proteolytischen Stabilität bei Erhaltung der Bindungsaffinität zum humanen NTR1 für PET von Pankreastumoren.
(1) Reubi et al., Gut 1998;42:, 546-50

  • Lecture (Conference)
    39. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin vom 25.-28. April 2001 in Hamburg
  • Abstract in refereed journal
    Nuklearmedizin 40 (2001) A22

Permalink: https://www.hzdr.de/publications/Publ-3598
Publ.-Id: 3598


Identifizierung und Quantifizierung der Abbauprodukte 18F-markierter Neurotensinderivate

Wittrisch, H.; Bergmann, R.; Heichert, C.; Fischer, K.; Mäding, P.; Johannsen, B.

Ziel:
Entwicklung einer schnellen Untersuchungsmethode zur Identifizierung und Quantifizierung von radioaktiv markierten Peptiden am Beispiel des Neurotensins (NT). Neurotensinrezeptoren (NTR1) werden in humanen duktalen Pankreaskarzinomen mit hoher Inzidenz überexprimiert. 18F-markierten NT-Derivate sollen als Tracer zur hochaffinen Darstellung von NTR1 mittels PET eingesetzt werden.

Methodik:
Zur Ermittlung der in vitro Stabilität wurden 4-[18F]FB-NT(8-13) (1), 4-[18F]FB-[Arg8Psi(CH2-NH)Arg9]-NT(8-13) (2) und 4-[18F]FB-[Arg8Psi(CH2-NH)Arg9]-NT(8-13) (3) in Rattenblut bzw. -plasmsa bei 37°C über 8 Stunden inkubiert. Die in vivo Untersuchungen wurden an Wistar-Ratten durchgeführt, denen nach Injektion der jeweiligen Verbindung (spezifische Aktivität 5-15 GBq/mmol) über einen Zeitraum von 2 Stunden in regelmäßigen Abständen aterielles Blut entnommen wurde. Die erhaltenen Proben wurden aufgearbeitet und die vorhandenen Abbauprodukte mittels RP-HPLC getrennt. Zur Identifizierung der Katabolite wurde das Eluat fraktioniert und die Fraktionen massenspektrometrisch untersucht.

Ergebnisse:
Es wurden signifikante Unterschiede in der Stabilität der verwendeten Verbindungen erhalten. In vitro konnte ein proteolytischer Abbau nur für (1) und (2) nachgewiesen werden. Dagegen war (3) unter den gewählten Bedingungen stabil. In vivo wurden deutliche Unterschiede bei den Residenzzeiten der Verbindungen beobachtet. (1) und (2) waren bereits 5 min p.i. nicht mehr nachweisbar. Dagegen wurden für (3) 24 min p.i. noch 50 % der Ausgangsverbindung beobachtet. Als Abbauprodukte der Verbindung (1) wurden sowohl in vitro als auch in vivo 4-[18F]FB-Arg-Arg und 4-[18F]FB-Arg ermittelt. Die Katabolite von (2) sind dagegen 4-18F]FB-[Arg8Psi(CH2-NH)Arg9]-Pro-Tyr und 4-[18F]FB-[Arg8Psi(CH2-NH)Arg9]-Pro. Bei (3) wurde nur 4-[18F]FB-[Arg8Psi(CH2-NH)Arg9]-Pro als Abbauprodukt nachgewiesen.

Schlußfolgerungen:
Mit der verwendeten Untersuchungsmethode konnten die Katabolite der untersuchten Neurotensinderivate getrennt werden. Durch die Identifizierung und Quantifizierung der Abbauprodukte wurden wichtige Informationen über die protolytischer Stabilität der Peptidbindungen in den einzelnen Verbindungen erhalten, die beim Design neuer 18F-markierter Neurotensinderivate mit höherer protolytischer Stabilität von entscheidender Bedeutung sind.

  • Lecture (Conference)
    39. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin vom 25.-28. April 2001 in Hamburg
  • Abstract in refereed journal
    Nuklearmedizin 40 (2001) A23

Permalink: https://www.hzdr.de/publications/Publ-3597
Publ.-Id: 3597


186/188Re-markierte Stents zur Prävention von Restenose

Noll, B.; Muschik, P.; Dinkelborg, L.; Tepe, G.; Johannsen, B.

Ziel:
Intraluminale Betabestrahlung nach Ballonangioplastie führt zu einer Erniedrigung der neointimalen Proliferation. Eine erfolgversprechende Variante stellt der Einsatz radioaktiv markierter Stents dar (1,2). In der Studie wird die technische Durchführbarkeit der 186/188Re-Markierung vaskulärer Stents und deren biologischer Effekt zur Inhibition der neointimalen Proliferation im Tiermodell getestet.

Methodik:
Palmaz Stents werden in einem "kitlike"-Verfahren mit 186/188Re markiert und die Markierungsbedingungen, die Stentoberfläche, die Aktivitätsverteilung, die Thrombogenität sowie die in-vitro Stabilität untersucht. Die markierten Stents und Kontroll Stents werden nach Fütterung einer 0.5%igen Cholesterindiät und Ballonangioplastie in die infrarenalen Aorta von Neuseeland-Kaninchen implantiert. Es erfolgten szintigraphi-sche Messungen zu unterschiedlichen Zeiten und nach 6 Wochen wurden die Gefäße immunhistologisch untersucht.

Ergebnisse:
In Abhängigkeit von der Markierungszeit und der vorgelegten Aktivität gelingt es, definierte Aktivitätsmengen stabil und reproduzierbar auf die Stentoberfläche zu fixieren. In-vitro Untersuchungen in isotonischer Kochsalzlösung und Humanblut beweisen, dass nach 72 Std. Inkubation bei 37°C >95 % der abgeschiedenen 186/188Re Aktivität am Stent gebunden bleiben. Thrombogenitätsuntersuchungen an markierten Stents ergaben keine Veränderungen im Vergleich zu den unbehandelten Vergleichs-stents. Die Implantation der Stents war bei allen Tieren erfolgreich, nach 14 Tagen verblieben mehr als 90 % des aufgebrachten Rheniums auf der Stentoberläche. Die Neointimafläche ließ sich von 2,2±0,2 mm bei den Kontrollstents auf 0 mm bei den markierten Stents reduzieren.

Schlußfolgerungen:
Es ist gelungen, Palmaz Stents reproduzierbar mit 186Re und 188Re zu markieren, wobei die aufgebrachte Aktivität in einem weiten Bereich variiert werden kann. Es wird eine hohe in-vitro und auch in-vivo-Stabilität erreicht, die Stents sind nicht trombogen. Innerhalb von 6 Wochen ließ sich die neointimale Proliferation komplett unterbinden.

1) Fishell et al., Circulation 1994; 90: 2956-2963
(2) Waksman et al., Circulation 1998; 98: I-651:3721

  • Lecture (Conference)
    39. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin vom 25.-28. April 2001 in Hamburg
  • Abstract in refereed journal
    Nuklearmedizin 40 (2001) A23

Permalink: https://www.hzdr.de/publications/Publ-3596
Publ.-Id: 3596


Methodische Grundlagen für die Tomographie durch gefilterte Rückprojektion an einer Axialpumpe

Hoppe, D.

Ein zweiphasiges, aus einer gashaltigen Flüssigkeit bestehendes Medium wird in einer Axialpumpe von einem propellerartigen Laufrad senkrecht zur Drehachse die ses Laufrades transportiert. Die Wechselwirkung zwischen der Gasphase und dem Laufrad soll unter Verwendung von Gamma-Strahlung mittels Tomographie unter sucht werden. Dabei ist für die Rekonstruktion des Objektbildes das Prinzip der so genannten gefilterten Rückprojektion vorgesehen. Die methodischen Grundlagen für die Nutzung dieses Prinzips unter den vorgesehenen geometrischen und meßtech nischen Bedingungen sind Gegenstand dieser Arbeit.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-306 November 2000
    ISSN: 1437-322X

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-3595
Publ.-Id: 3595


Ion beam synthesis of shallow Ge nanocluster bands in thin SiO2 films for non-volatile memory applications

von Borany, J.; Gebel, T.; Heinig, K.-H.; Klimenkov, M.; Stegemann, K.-H.; Thees, H.-J.; Wittmaack, M.

Ion beam synthesis has been applied to fabricate semiconductor (Si, Ge) nanoclusters in thin gate SiO2 films for non-volatile memory applications. The cluster size (2-3 nm), the cluster density (>5x10E11 cm-2) and the short distance to the Si/SiO2 fulfill main requirements for a cluster related memory cell. The charge storage have been clearly established at MOS and transistor structures by the shift of the flatband or threshold voltage, respectively. Typical programming windows are in the order of 1-2 V and the endurance is > 10E6 w/e-cycles. Differences of Si- and Ge-cluster containing SiO2 films with respect to the retention behaviour are finally discussed.

Keywords: ion beam synthesis; nanoclusters; nanoelectronics; non-volatile memories

  • Poster
    Poster presented at IEEE Intern. Conference on Industrial Electronics (IECON 2000), Oct. 22-28, 2000, Nagoya, Japan; Proceedings, pp. 1900-1904, ed. by the IEEE Industrial Electronics Society
  • Contribution to proceedings
    Poster presented at IEEE Intern. Conference on Industrial Electronics (IECON 2000), Oct. 22-28, 2000, Nagoya, Japan; Proceedings, pp. 1900-1904, ed. by the IEEE Industrial Electronics Society

Permalink: https://www.hzdr.de/publications/Publ-3594
Publ.-Id: 3594


The Riga dynamo experiment

Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.

Cosmic magnetic fields, including the magnetic field of the Earth, are produced by the homogeneous dynamo effect in moving electrically conducting fluids. We sketch the history of the underlying theory and comment on previous attempts to realize homogeneous dynamos in laboratory. For the main part, we report on two series of experiments carried out at the Riga dynamo facility. In November 1999 a slowly growing magnetic field eigenmode was observed for the first time in a liquid metal experiment. In July 2000, the magnetic field saturation regime was studied and a number of interesting back-reaction effects were observed. A preliminary interpretation of the measured data is also presented.

  • Surveys in Geophysics 24 (2003) 247-267

Permalink: https://www.hzdr.de/publications/Publ-3593
Publ.-Id: 3593


PET-Radiopharmaka: Stand und Perspektiven

Steinbach, J.

  • Lecture (Conference)
    7. Jahrestagung, Berlin-Brandenburgische Gesellschaft für Nuklearmedizin e.V., Brielow, 11.11.2000

Permalink: https://www.hzdr.de/publications/Publ-3592
Publ.-Id: 3592


Trägerarme Markierung aromatischer Verbindungen mit C-11 und F-18

Steinbach, J.

  • Lecture (others)
    Institutsseminar, Institut für Nuklearchemie, Forschungszentrum Jülich, 28.05.2000

Permalink: https://www.hzdr.de/publications/Publ-3591
Publ.-Id: 3591


Lipophilicity and pKa measurements of technetium and rhenium complexes as potential radiopharmaceuticals by using RP-HPLC

Berger, R.; Spies, H.; Friebe, M.; Johannsen, B.

99mTc is the most widely used radionuclide for nuclear medicine diagnostics. Efforts are made to design this unphysiological element for targeting specifically organs and cells. In this respect, lipophilic properties are of importance. We studied lipophilicity on a series of "3+1" mixed ligand oxoTc and -Re complexes with an [S-(CH2)2-E-(CH2)2-S] chelate unit [E = O, S, N-Me, N-Et] and a thiol ligand with various residues [alkyl, aryl; (CH2)2-NMe2, -NEt2,-NBu2, -piperidinyl, -morpholinyl].
The lipophilicity/pH profiles were determined by RP-HPLC. A Perkin-Elmer HPLC Model 1022 equipped with a UV/VIS detector (254 nm) and a PRP-1 column (Hamilton, 250 x 4.1 mm, 10mm) was employed [mobile phase: isocratic eluent acetonitrile / buffer (volume ratio 3:1; pH range: 1.5 - 11); flow rate: 1.5 ml/min].
The lipophilicity determination is based on the linear relationship between the chromato-graphic retention (log k') and log D/P and results in DHPLC/PHPLC values. Aniline, benzene, and brombenzene were used as internal standards. The pKa values were estimated from the turning point of sigmoidal curves and were corrected by using a calibration curve of amine standards since the measurements are performed in organic/aqueous solutions.
For amine group containing complexes (R2), that are used as models of neuroreceptor affine tracers, the influence of lipophilicity and/or pKa on brain uptake was studied. High brain uptake relates with low pKa, so that the highest uptake was found for morpholino-bearing complexes (0.9-2.0 % injected dose per rat brain, <5 min p.i.; pKa 7.1-7.6). The log PHPLC values for Tc complexes are higher than for the corresponding Re complexes.

  • Poster
    LogP2000, The Second Lipophilicity Symposium: "Lipophilicity in Drug Disposition: Practical and Computational Approaches to Molecular Properties Related to Drug Permeation, Disposition and Metabolism" Lausanne, March 5-9, 2000
  • Contribution to proceedings
    LogP2000, The Second Lipophilicity Symposium: "Lipophilicity in Drug Disposition: Practical and Computational Approaches to Molecular Properties Related to Drug Permeation, Disposition and Metabolism" Lausanne, March 5-9, 2000

Permalink: https://www.hzdr.de/publications/Publ-3590
Publ.-Id: 3590


Monte Carlo Simulations of Neutral Gas and Fast Ion Dynamics in GDT Experiments

Noack, K.

The Budker Institute of Nuclear Physics Novosibirsk proposed a highly intense 14 MeV neutron source on the base of a gas dynamic trap (GDT). The GDT is an axisymmetric mirror plasma device. In case of the complete effectiveness at the necessary parameters this type of neutron source promises several advantages in comparison to other proposals. Its actual disadvantage is the incomplete data basis which does not yet allow a reliable interpolation of its feasibility. To close this gap is the goal of the experimental and computational research presently being under way. Here the Monte Carlo codes TUBE for the hydrogen gas and MCFIT for the fast ions which have been developed by Forschungszentrum Rossendorf in collaboration with the Budker Institute take an important part. The paper shortly describes the MCFIT code, compares some numerical with measured results and draws certain conclusions.

Keywords: neutron source; gas dynamic trap; mirror plasma device; neutral gas; fast ions; monte carlo method

  • Lecture (Conference)
    Monte Carlo 2000, International Conference on Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation and Applications, October 23-26, 2000 - Lisbon, Portugal; Proc. will be published by Springer-Verlag
  • Contribution to proceedings
    Monte Carlo 2000, International Conference on Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation and Applications, October 23-26, 2000 - Lisbon, Portugal; Proc. will be published by Springer-Verlag

Permalink: https://www.hzdr.de/publications/Publ-3589
Publ.-Id: 3589


Reactivity of Technetium(I) Thioether Carbonyl Complexes towards Histidine - An EXAFS Study in Solution

Seifert, S.; Künstler, J.-U.; Gupta, A.; Funke, H.; Reich, T.; Pietzsch, H.-J.; Alberto, R.; Johannsen, B.

Technetium(I) thioether carbonyl complexes and their reaction products with histidine were prepared and characterized by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy , various chromatographic and electrophoretic methods and electrospray mass spectrometry. Their behaviour in aqueous solutions was studied on the carrier-added (99Tc) and the no-carrier-added (99mTc) levels. HPLC and electrophoretic studies show the identity of reaction products at both concentration levels. Technetium(I) carbonyl complexes containing a bidentate dithioether ligand, [Tc(CO)3Cl(S-S)], as well as a tridentate carboxylato thioether ligand, [Tc(CO)3(S-S-O)], undergo a ligand exchange reaction with histidine and form the complex [Tc(CO)3His]. EXAFS measurements were performed to estimate structural parameters of the dissolved technetium(I) carbonyl complexes and their reaction products after the challenge experiments. The calculated bond lengths and coordination numbers are in accordance with the expected values and confirm the ligand exchange reactions.

  • Inorganica Chimica Acta 322 (2001) 79-86

Permalink: https://www.hzdr.de/publications/Publ-3588
Publ.-Id: 3588


An Integrated Transport Code System for the Calculation of Multi-Component, High-ß Plasmas in the Gas Dynamic Trap

Anikeev, A.; Karpushov, A.; Collatz, S.; Noack, K.; Otto, G.; Strogalova, S.

The Budker Institute Novosibirsk made a proposal for a highly intense neutron source on the base of a gas dynamic trap. It is mainly intended for fusion material irradiation. The gas dynamic trap is an axisymmetric open system with a high mirror ratio for the confinement of a collision dominated plasma and a high-energetic ion component which is fed by an oblique neutral beam injection. In addition to research at the experimental facility of the Budker Institute an Integrated Transport Code System is under development in collaboration with the Forschungszentrum Rossendorf. It is to calculate the relevant physical effects connected with the target plasma, fast ions, neutral gas and the neutrons appearing inside the central cell of the device. The paper briefly describes the functions of the main modules and reports on the first exercise devoted to the planned upgrade of the facility.

Keywords: Neutron Source; Fusion; Materials; Gas Dynamic Trap; Plasma; Mirror; Target Plasma; Fast Ions; Neutral Gas; Transport Code System

  • Lecture (Conference)
    3rd International Conference on Open Magnetic Systems for Plasma Confinement, July 3-6, 2000, Tsukuba, Japan; Proc. published in Transactions of Fusion Technology, Vol 39, p. 183 (2001)
  • Contribution to proceedings
    3rd International Conference on Open Magnetic Systems for Plasma Confinement, July 3-6, 2000, Tsukuba, Japan; Proc. published in Transactions of Fusion Technology, Vol 39, p. 183 (2001)

Permalink: https://www.hzdr.de/publications/Publ-3587
Publ.-Id: 3587


TOPFLOW - eine neue Mehrzweck-Thermohydraulik-Versuchsanlage zur Untersuchung stationärer und transienter Zweiphasenströmungen

Schaffrath, A.; Krüssenberg, A.-K.; Weiß, F.-P.; Carl, H.

Am Institut für Sicherheitsforschung (FWS) des Forschungszentrums Rossendorf (FZR) e.V. wird die Mehrzweckthermohydraulikversuchsanlage TOPFLOW (Transient Two Phase Flow Test Facility) zur Untersuchung stationärer und transienter Phänomene in Zweiphasenströmungen sowie zur Entwicklung und Validierung der in Computational Fluiddynamic (CFD) Codes enthaltenen Modelle aufgebaut. Die Versuchsanlage soll im Rahmen des Kompetenzerhaltungsprogramms Kerntechnik von dem Kompetenzzentrum Sachsen bestehend aus der Technischen Universität Dresden, der Hochschule für Technik, Wirtschaft und Soziales Zittau/Görlitz (FH) sowie dem Forschungszentrum Rossendorf e.V. betrieben werden.

Keywords: TOPFLOW; stationäre und transiente Zweiphasenströmungen; Strömungsformen in vertikalen Rohrleitungen

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsbericht S. 125-131
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsbericht S. 125-131

Permalink: https://www.hzdr.de/publications/Publ-3585
Publ.-Id: 3585


Production of a0+- mesons in the reaction pp to da0+

Müller, H.

We investigate the reaction pp to da0 + at COSY and SIS energies together with accompanying background reactions and inclusive particle yields. The a0 + is considered as a usual quark model state with two decay channels a0 + to K+K0 and a0 + to pi+ eta. Cross sections for a0 + production as well as for the corresponding nonresonant channels pp to dK+K0 and pp to dpi+eta are compared. Especially in case of the final channel dpi+eta high statistics measurements are necessary to extract the a0 + signal from the nonresonant background.

  • The European Physical Journal A 11, 113-119 (2001)

Permalink: https://www.hzdr.de/publications/Publ-3584
Publ.-Id: 3584


Investigation of Co/Cu/NiFe-Multilayers by X-Ray Reflectometry and Diffraction

Hecker, M.; Tietjen, D.; Prokert, F.; Schell, N.; Schneider, C. M.

Structural properties of sputtered multilayers with different Co-, Cu- and NeFe- sequences of about 2nm individual layer thickness were investigated by means of synchrotron radiation techniques. Correlations between the layer combination and structural parameters such as layer thickness and rms interface roughness derived from specular scans were obtained, whereas the lateral characteristics of the interface morphology investigated by diffuse scattering were found to be similar for all multilayers. Wide angle diffraction measurements yielded lattice plane information, e.g. size-strain effects due to profile broadening and predominating <111> fibre textures.

Keywords: Reflectometry; synchrotron radiation; multilayers; GMR-effects

  • Mikrochim. Acta 133, 239-241 (2000)

Permalink: https://www.hzdr.de/publications/Publ-3583
Publ.-Id: 3583


Particle excitations and rotational modes in Nuclei with A = 70 -90

Schwengner, R.; Schnare, H.; Borcan, C.; Dönau, F.; Käubler, L.

In nuclei in the mass region of $A \approx 70 - 90$ a variety of phenomena
is observed which are based on single-particle and collective motion of the
nucleons. We discuss the properties of Br and Rb isotopes with neutron numbers
of 38 - 48. In light Br isotopes ($N$ = 37, 38) rotational bands have been
observed up to spins of 65/2 and rotational frequencies of 1.8 MeV. Both
features can be described in terms of the cranked Nilsson-Strutinsky formalism.
In Rb nuclei with $N$ = 45, 47 we found regular magnetic dipole bands
evolving at high spin whereas the low-spin structure of those less deformed
nuclei is irregular. These magnetic dipole bands represent magnetic rotation,
a new rotational mode predicted by the tilted-axis cranking model.
In nuclei at $N$ = 48 we found small collectivity in low-spin states and
multiplets based on multi-particle excitations at high spin. These properties
are interpreted in terms of the shell-model.

Keywords: Nuclear structure; particle excitations; rotational modes; gamma spectrometer GASP and EUROBALL; cranking model; titlted-axis craniking model; shell model

  • Contribution to external collection
    XIII. International School on Nuclear Physics, Neutron Physics and Nuclear Energy, Varna, Bulgaria, 27.9. - 3.10. 1999, Bg NS Transactions, Vol. 5, No. 1, (2000), 136-144

Permalink: https://www.hzdr.de/publications/Publ-3582
Publ.-Id: 3582


Pre-Test Calculations for the EC-FOREVER-2-Experiment

Willschütz, H.-G.; Altstadt, E.; Weiss, F.-P.; Sehgal, B. R.

Assuming the hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower plenum of a Light Water Reactor (LWR) leads to the question about the behaviour of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
To get an improved understanding and knowledge of the melt pool convection and the vessel creep and possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments (Failure Of REactor VEssel Retention) are currently underway at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm (Sehgal, 1999). These experiments are simulating the behaviour of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurization scenario. The geometrical scale of the experiments is 1:10 compared to a common LWR.
During the first series of experiments the creep behaviour (FOREVER-C) of the vessel under the thermal attack of the melt pool and varying internal pressure loads is investigated. It is intended to enforce the creep process until vessel failure.
Due to the multi axial creep deformation of the vessel with a non-uniform temperature field these experiments are on the one hand an excellent source of data to validate numerical creep models which are developed on the basis of uniaxial creep tests. On the other hand the results of pre-test calculations can be used to optimize the experimental procedure and can help to make on-site decisions during the experiment.
Therefore an axisymmetric Finite Element (FE) model is developed based on the multi-purpose code ANSYS/Multiphysics®. Using the Computational Fluid Dynamics (CFD) module the temperature field within the melt pool and within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a creep model which takes into account large temperature, stress and strain variations.

Keywords: Scaled Light Water Reactor Experiments; Core Melt Down; Finite Element Model; Creep and Damage Model; Pre-Test Calculations

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, May 15-17, 2001, Tagungsband S.187-192
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, May 15-17, 2001, Tagungsband S.187-192

Permalink: https://www.hzdr.de/publications/Publ-3581
Publ.-Id: 3581


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