Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Interactions of natural occurring eukaryotic microorganisms with uranium(VI)

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Merroun, M. L.

Despite high uranium concentrations (up to 14 mg L-1) and low pH (2.5 - 3.0) a high biodiversity was detected by culture independent methods in the flooding water of the former uranium mine Königstein (Saxony, Germany). In this study culture dependent methods were used for the isolation of eukaryotic microorganisms from the flooding water. It was possible to isolate different eukaryotic fungi with a glucose riche medium. The results of uranium immobilization tests showed high immobilization rates of about 120 to 160 mg uranium per 1 g dry mass. Flow cytometry experiments with KS5 and DSM 10134 were performed in liquid medium to quantitatively determine the uranium tolerance. In comparison, the isolate KS5 showed a higher uranium tolerance than the reference culture of DSM 10134 on solid as well as in liquid medium. In conclusion, this study indicates that eukaryotic microorganisms within a uranium-contaminated environment could potentially play an important role in the bioremediation of uranium.

Keywords: Bioremediation; Uranium; Königstein; Immobilization

  • Poster
    Petrus PhD Conference 2015, 22.-26.06.2015, Nancy, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-21990
Publ.-Id: 21990


In situ visualisation of dendritic growth in solidifying Ga – In alloys

Shevchenko, N.; Roshchupkina, O.; Grenzer, J.; Baehtz, C.; Eckert, S.

X-ray absorption contrast techniques are an effective tool for investigating solidification processes in opaque metallic alloys. This work is devoted to the in situ visualization of the dendritic growth during the bottom-up solidification of a Ga-25wt%In alloy under natural and forced convections. Many effects of melt flow on the mushy zone structure were observed by standard X-ray radiography with a spatial resolution of 5-10 microns [1, 2]. The flow-induced variations of the local solute concentration result in an unsteady development of the primary dendrites and trigger or inhibit the development of secondary and tertiary arms. Variations of the vertical and lateral temperature gradients induce modifications of the melt flow pattern, which lead to different segregation structures and dendrite morphology.
A more detailed analysis of the particular processes (a detachment of side branches and growth of a dendrite tip) were carried out using synchrotron X-ray radiography with a spatial resolution of less than 1 µm. The synchrotron experiments were performed at the ROBL beam line (BM20, European Synchrotron Radiation Facility, Grenoble) at an energy of 28.5 keV. The combination of synchrotron X-ray radiography and synchrotron X-ray diffraction shows a big potential for orientation analysis of the growing grains and a lattice parameter determination of the solid phase.

Keywords: Directional solidification; melt flows; X-ray radiography; Ga–In alloys

  • Lecture (Conference)
    European Crystallographic Meeting, 23.-28.08.2015, Rovinj, Croatia
  • Abstract in refereed journal
    Acta Crystallographica Section A 71(2015), s156
    DOI: 10.1107/S2053273315097727

Permalink: https://www.hzdr.de/publications/Publ-21989
Publ.-Id: 21989


Detection of melt flow in solidifying metal alloys by X-ray radioscopy

Shevchenko, N.; Roshchupkina, O.; Eckert, S.

X-ray radioscopic methods enable the in-situ real-time observation of solidification processes in metal alloys with a spatial resolution of a few microns. Visualization of bottom up directional solidification of a Ga-25wt%In binary metal alloy contained in a capillary slit container was conducted. The solidification is obviously affected by natural thermo-solutal melt flow patterns. Externally forced melt convection was superimposed by means of a magnetic stirrer in form of a rotating wheel equipped with permanent magnets. The electromagnetic flow provokes a considerable redistribution of the solutal boundary layers around the solidifying dendrites, and influences therewith the formation of the microstructure.
The X-ray radioscopy delivers a two-dimensional projection of the local density in the slit container corresponding to the distribution of the relative brightness P in the acquired images. The relative brightness P allows for an assessment of the local constitution inside the liquid phase. Our analysis of the flow field in the present article follows the Optical Flow approach proposed by Horn and Schunck. [1] The applied algorithm to determine the optical flow from the X-ray images delivers reliable information concerning the velocity field in regions where sufficiently large brightness gradients occurs. The solidification process creates differences of the local composition within the melt leading to characteristic pattern of transmitted light intensity. The analysis of the flow field relies on the monitoring of the temporal variations of characteristic brightness patterns in the liquid phase.
Our results show that melt flow induces various effects on the grain morphology primarily caused by the convective transport of solute. Our observations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting and fragmentation. The manifestation of all phenomena depends on the dendrite orientation, local direction and intensity of the flow. The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. It provokes a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites can inhibit the formation of secondary branches completely. Moreover, the flow changes the inclination angle of the dendrites and the angle between primary trunks and secondary arms.

  • Lecture (Conference)
    3rd International Workshop on Measuring Techniques for Liquid Metal Flows, 15.-17.04.2015, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-21988
Publ.-Id: 21988


Mobility Investigations on Strained 30-nm High-k Metal Gate MOSFETs by Geometrical Magnetoresistance Effect

Beister, J.; Wachowiak, A.; Boschke, R.; Herrmann, T.; Uhlarz, M.; Mikolajick, T.

In this paper, we present mobility investigations of strained nMOS and pMOS short-channel transistors with dimensions down to 30-nm gate length. Using the geometrical magnetoresistance (MR) effect, carrier mobility of electrons and holes in the inversion channel of a recent state-of-the-art CMOS technology is presented from linear to saturation operation conditions. The MR effect allows for a more direct access to the carrier mobility compared with the conventional current/voltage and capacitance/voltage mobility derivation methods, in which series resistance, inversion charge density, and effective channel length are necessary to extract the mobility values of the short-channel devices. In another way, the MR effect can help to disentangle the performance gain of the strained state-of-the art devices to changes in channel mobility or device connection, e.g., series resistance effects.

Permalink: https://www.hzdr.de/publications/Publ-21987
Publ.-Id: 21987


Observation of dendritic growth under the influence of forced convection

Roshchupkina, O.; Shevchenko, N.; Eckert, S.

The directional solidification of Ga–25wt%In alloys within a Hele-Shaw cell was visualized by X-ray radioscopy. The investigations are focused on the impact of melt convection on the dendritic growth. Natural convection occurs during a bottom up solidification because lighter solute is rejected during crystallization. Forced convection was produced by a specific electromagnetic pump. The direction of forced melt flow is almost horizontal at the solidification front. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Forced flow eliminates solutal plumes and damps local fluctuations of solute. A preferential growth of the secondary arms occurs at the upstream side of the dendrites, whereas high solute concentration at the downstream side inhibits the formation of secondary branches.

Keywords: X-ray radioscopy; in situ studies; melt convection; forced convection; dendritic growth

  • Open Access Logo Contribution to proceedings
    Modeling of Casting, Welding and Advanced Solidification Processes, 21.-26.06.2015, Awaji Yumebutai, Japan
    IOP Conference Series: Materials Science and Engineering 84(2015)1, 012080
    DOI: 10.1088/1757-899X/84/1/012080
  • Lecture (Conference)
    Modeling of Casting, Welding and Advanced Solidification Processes, 21.-26.06.2015, Awaji Yumebutai, Japan

Permalink: https://www.hzdr.de/publications/Publ-21986
Publ.-Id: 21986


Visualization of liquid metal bubbly flows using the X-ray radioscopy

Roshchupkina, O.; Shevchenko, N.; Strumpf, E.; Timmel, K.; Eckert, S.

The quality of continuous cast steel is significantly affected by the flow pattern in the mould and submerged entry nozzle (SEN). The flow in continuous casting machines is often a two-phase one because argon is injected to avoid clogging inside the casting nozzle. Moreover, the argon bubbles are supposed to drag alumina particles and transport them towards the slag layer at the free surface. On the other hand, the gas injection leads to highly turbulent and complex two-phase flows, which are difficult to predict by numerical simulations. The injected bubbles have a distinct influence on the flow pattern and may trigger instabilities in the mold, for instance, observations made on real casters showed correlations between gas pressure variations in the SEN and mould meniscus perturbations.

Despite of the considerable number of previous studies mainly performed as numerical simulations and water models the understanding of liquid metal two phase flows remains fragmentary. Many open questions require further investigations, as concerns the formation process of gas bubbles, their distribution and flow regime in the SEN, the size of bubbles entering the mould, the flotation of the gas in the mould, the gas entrapment in the solidifying strand, etc. This situation motivated us to construct a specific model experiment where liquid metal two-phase flows can be investigated under flow conditions which are similar to those in the real continuous casting process.

We present an experimental study in a mockup of the continuous casting process. The two-phase flows in the mould and the SEN were visualized by means of X-ray radioscopy. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously with the low melting, eutectic alloy GaInSn under isothermal conditions. Experimental results will be presented and discussed accompanied by statistical analysis.

Keywords: X-ray radioscopy; two-phase flows; continuous casting

  • Lecture (Conference)
    3rd International Workshop on Measuring Techniques for Liquid Metal Flows, 15.-17.04.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21985
Publ.-Id: 21985


Thin Sample Alloy Solidification in Electromagnetic Driven Convection

Kao, A.; Shevchenko, N.; Roshchupinka, O.; Eckert, S.; Pericleous, K.

During the directional solidification of Ga-In25%wt., density variations in the liquid cause plumes of solute to be ejected from the interface through natural convection. This can lead to the formation of chimneys during solidification and ultimately freckles. The application of external magnetic fields can be used to suppress these plumes. Two magnetic systems are considered. The first is a rotating magnetic wheel, which provides conditions analogous to forced convection at the solidification interface. The forced convection causes preferential growth of secondary branches and the plumes to be transported downstream and back into the bulk. The second is the application of a static magnetic field, which interacts with inherent thermoelectric currents, generating a Lorentz force that drives fluid flow within the inter-dendritic region. However, in the bulk, where there are no thermoelectric currents electromagnetic damping dominates and plumes are stunted.

Using a fully coupled transient numerical model a quantitative analysis of each of these systems has been investigated. Figure 1 shows numerical results of the velocity profiles and dendritic morphology for each of these cases. Comparisons to experiments are given for the cases of natural and forced convection. The experimental setup uses a Hele-Shaw cell with an electric heater and Peltier cooler allowing for control over the thermal gradient and cooling rate.

  • Lecture (Conference)
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France
  • Contribution to proceedings
    8th International Congress on Electromagnetic Processing of Materials (EPM2015), 12.-16.10.2015, Cannes, France

Permalink: https://www.hzdr.de/publications/Publ-21984
Publ.-Id: 21984


Multi Group Geometrical Correction for Coupled Monte Carlo Codes: Multi-Regional Thermal System

Kotlyar, D.; Shwageraus, E.; Fridman, E.

This paper focuses on generating accurate 1-g cross section values that are necessary for evaluation of nuclide densities as a function of burnup for coupled Monte Carlo codes. The proposed method is an alternative to the conventional direct reaction rate tally approach, which requires extensive computational efforts. The method presented here is based on the multi-group (MG) approach, in which pre-generated MG sets are collapsed with MC calculated flux. In our previous studies we showed that generating accurate 1-g cross sections requires their tabulation against the background cross-section (σ0) to account for the self-shielding effect. However, in previous studies, the model that was used to calculate σ0 was simplified by fixing Bell and Dancoff factors. This work demonstrates that 1-g values calculated under the previous simplified model may not agree with the tallied values. Therefore, the original background cross section model was extended by implicitly accounting for the Dancoff and Bell factors. The method developed here reconstructs the correct value of σ0 by utilizing statistical data generated within the MC transport calculation by default. The method does not carry any additional computational burden and it is universally applicable to the analysis of thermal as well as fast reactor systems.

Keywords: Monte Carlo; BGCore; Multi group; one-group cross sections

  • Contribution to proceedings
    Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method 2015, 19.-23.04.2015, Nashville, TN, USA
    Multi Group Geometrical Correction for Coupled Monte Carlo Codes: Multi-Regional Thermal System
  • Lecture (Conference)
    Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method 2015, 19.-23.04.2015, Nashville, TN, USA

Permalink: https://www.hzdr.de/publications/Publ-21983
Publ.-Id: 21983


The effects of natural, forced and thermoelectric magnetohydrodynamic convection during the solidification of thin sample alloys

Kao, A.; Shevchenko, N.; Roshchupinka, O.; Eckert, S.; Pericleous, K.

Using a fully coupled transient 3-dimensional numerical model, the effects of convection on the microstructural evolution of a thin sample of Ga-In25%wt. was predicted. The effects of natural convection, forced convection and thermoelectric magnetohydrodynamics were investigated numerically. A comparison of the numerical results is made to experimental results for natural convection and forced convection. In the case of natural convection, density variations within the liquid cause plumes of solute to be ejected into the bulk. When forced convection is applied observed effects include the suppression of solute plumes, preferential secondary arm growth and an increase in primary arm spacing. These effects were observed both numerically and experimentally. By applying an external magnetic field inter-dendritic flow is generated by thermoelectrically induced Lorentz forces, while bulk flow experiences an electromagnetic damping force. The former causes preferential secondary growth, while the latter slows the formation of solute plumes. This work highlights that the application of external forces can be a valuable tool for tailoring the microstructure and ultimately the macroscopic material properties.

  • Lecture (Conference)
    Modelling of Casting, Welding and Advanced Solidification Processes, 21.-26.06.2015, Awaji island, Hygo, Japan
  • Open Access Logo Contribution to proceedings
    Modelling of Casting, Welding and Advanced Solidification Processes, 21.-26.06.2015, Awaji island, Hygo, Japan
    IOP Conference Series: Materials Science and Engineering 84(2015)1, 012018
    DOI: 10.1088/1757-899X/84/1/012018

Permalink: https://www.hzdr.de/publications/Publ-21982
Publ.-Id: 21982


In situ analysis of dendritic growth and fragmentation in solidifying Ga – In alloys

Shevchenko, N.; Roshchupkina, O.; Eckert, S.

Simultaneous study of solidification phenomena on different length scales (e.g. µm-sized dendrite morphology and mm-sized flow structures) raises a serious problem. Since several years X-ray radioscopy has been proposed and successfully used as an effective tool for in situ real time observations of the dendrite growth, concentration field and flow patterns. The upward directional solidification of Ga-25wt%In alloy within a Hele-Shaw cell was studied by in situ X-ray radioscopy. This work is focused on the investigation of the influence of natural convection on the concentration profiles, dendrite morphology, growth velocities, freckle formation and fragmentation. Additionally, we use the Optical Flow approach proposed by Boden et al. [1] for the estimation of the melt flow ahead of the solidification front.
The ascending plumes and the downward flow of In-rich melt lead to an inhomogeneous horizontal concentration profile along the solidification front. Variations of the vertical and lateral temperature gradients induce modifications of the melt flow pattern, which lead to different segregation structures and dendrite morphology. The dendrite growth velocity is mainly determined by the dynamics of the solute plumes which cause significant fluctuations of solute concentration. Our in situ experiments provide quantitative data on concentration, flow fields, tip velocity, etc. for the verification of actual models of freckle formation [2].
The second part of the study is devoted to the visualization of the fragmentation process in the mushy zone. Numerous events of detachment of secondary arms from the primary trunks occur in the deeper mushy zone. These fragments remain within the inter-dendritic regions. Fragments originating in the upper mushy zone can ascend by convective transport in the plumes and arrive in undercooled regions ahead of the dendritic front. Future work is in progress in order to classify our experimental data with respect to the known fragmentation mechanisms.

  • Poster
    Modelling of Casting, Welding and Advanced Solidification Processes, 21.-26.06.2015, Awaji island, Hygo, Japan

Permalink: https://www.hzdr.de/publications/Publ-21981
Publ.-Id: 21981


X-ray observations showing the effect of fluid flow on dendritic solidification in Ga-In alloys

Shevchenko, N.; Roshchupkina, O.; Eckert, S.

The directional solidification of Ga–25wt%In alloys within a Hele-Shaw cell has been studied by X-ray radioscopy. The investigations have focused on the influence of melt convection on the dendritic growth. Natural convection occurs during a bottom up solidification because a lighter solute is rejected during crystallization. Forced convection has been produced by a specific electromagnetic pump. The direction of forced melt flow is almost horizontal at the solidification front. Melt flow induces various effects on grain morphology caused primarily by convective transport of solute, such as facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Forced flow eliminates solutal plumes and damps local fluctuations of solute. A preferential growth of the secondary arms occurs at the upstream side of the dendrites, whereas high solute concentration at the downstream side inhibits the formation of secondary branches.

Keywords: Fluid flow; solidification; convection; X-ray radiography; in situ observation

  • Invited lecture (Conferences)
    Advances in the Science and Engineering of Casting Solidification: An MPMD Symposium Honoring Doru Michael Stefanescu; 2015 TMS Annual Meeting & Exhibition, 15.-19.03.2015, Orlando, Florida, USA
  • Contribution to proceedings
    Advances in the Science and Engineering of Casting Solidification: An MPMD Symposium Honoring Doru Michael Stefanescu; 2015 TMS Annual Meeting & Exhibition, 15.-19.03.2015, Orlando, Florida, USA

Permalink: https://www.hzdr.de/publications/Publ-21980
Publ.-Id: 21980


Modular Ultrasound Array Doppler Velocimeter with FPGA-based Signal Processing for Real-time Flow Mapping in Liquid Metal

Nauber, R.; Thieme, N.; Beyer, H.; Büttner, L.; Räbiger, D.; Eckert, S.; Czarske, J.

Investigating the complex interaction of conductive fluids and magnetic fields is relevant for a variety of applications from basic research in magnetohydrodynamics (MHD) to modeling industrial processes involving metal melts, such as the crystal growth process in the photovoltaic industry. This enables targeted optimizations of the melt flow and allows to significantly increase the yield and energy effciency of industrial processes. However, experimental studies in this field are often limited by the performance of flow instrumentation for opaque liquids. We present an ultrasound array Doppler velocimeter (UADV) for flow mapping in opaque liquids at room temperature. It is modular and flexible regarding its measurement configuration, for instance it allows capturing two velocity components in two planes (2d - 2c). It uses up to 9 linear arrays with a total element count of 225, driven in a parallelized time division multiplex (TDM) scheme. A FPGA-based signal pre-processing allows to handle the massive data bandwidth of typ. 1.2 GB/s and enables a continuous and near-realtime operation of the measurement system. The capabilities of the UADV system are demonstrated in a basic MHD research experiment with a metal melt (GaInSn) in a cubic container of (67 mm)³. The flow induced by a rotating magnetic field is captured with a temporal resolution of 250 ms for the horizontal and vertical central cross-section of the cube.

Keywords: Flow-Mapping; Ultrasound Doppler Velocimetry; Liquid Metals; Magnetohydrodynamics; Flow Control; FPGA

  • Lecture (Conference)
    International Congress on Ultrasonic, 10.-14.05.2015, Metz, Frankreich
  • Open Access Logo Physics Procedia 70(2015), 537-540
    DOI: 10.1016/j.phpro.2015.08.011

Permalink: https://www.hzdr.de/publications/Publ-21979
Publ.-Id: 21979


Realizing Optical Free-Electron Lasers with Traveling-Wave Thomson-Scattering

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Röser, F.; Schramm, U.; Sauerbrey, R.

Optical free-electron lasers (OFELs) from the EUV to X-ray range can be realized in Traveling-Wave Thomson-Scattering (TWTS)[1,2] by utilizing pulse-front tilted high-power laser pulses as optical undulators.
The interaction distances required to induce microbunching to the electron beam for coherent radiation emission are realized in TWTS with a combination of side-scattering and a tilt of the laser pulse-front, as depicted in fig. 1. In the side-scattering geometry the electron beam and laser pulse directions of motion enclose the interaction angle. The tilt of the laser pulse-front by half of the interaction angle then ensures continuous overlap of electrons and laser while both are propagating in different directions. In this way, the interaction distances realized in TWTS are only limited by the transverse size of the laser and thus by the available laser power and size of available optics.
Our fully analytic theory of TWTS OFELs provides scaling laws for the electron and laser pulse quality requirements for OFEL operation. We show that TWTS OFELs can be realized with state-of-the-art technology in electron accelerators and laser systems if the presented scheme for dispersion control is applied. Thereby the variability of TWTS with respect to the interaction angle is used to control the electron and laser beam quality requirements. Especially the sub-μm transv. emittance beams from laser wakefield accelerators with energy spreads in the percent level can be used for the realization of all-optical FELs with acceleration and interaction distances in the centimeter range. An outlook on 3D simulations of TWTS OFELs using the particle in cell code PIConGPU is given.

Keywords: Thomson-scattering; X-ray; FEL; PIConGPU

  • Invited lecture (Conferences)
    Laser Plasma Acceleration Workshop 2015, 11.-15.05.2015, Guadeloupe, France

Permalink: https://www.hzdr.de/publications/Publ-21978
Publ.-Id: 21978


Realizing all optical free-electron lasers with Traveling-Wave Thomson-Scattering

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Roeser, F.; Schramm, U.

Optical free-electron lasers (OFELs) from the ultra violet to x-ray range can be realized with Traveling-Wave Thomson-Scattering (TWTS). This becomes possible in TWTS by increasing the photon scattering efficiency of standard Thomson scattering geometries more than one order of magnitude by changing the interaction geometry. In TWTS a side-scattering geometry is used where the laser and electron propagation directions enclose the interaction angle $\phi$. Together with a tilt of the laser pulse front the interaction distance is increased in TWTS beyond the limits of head-on Thomson scattering. TWTS implements dispersion control of the laser pulse to compensate for variations of the optical undulator period originating from the pulse-front tilt. Altogether, the combination of side-scattering, pulse-front tilt and dispersion control in TWTS allows for meter-scale interaction distances in which the electron beam becomes microbunched and OFEL operation is achieved. These TWTS OFELs provide transverse coherence as well as brilliances an order of magnitude enhanced over standard head-on Thomson scattering geometries.
We present the scaling laws of TWTS OFELs derived from a fully analytic theory of the electron laser interaction in TWTS scattering geometries. TWTS OFELs can be realized in an all-optical setup with a meter-scale footprint using laser wakefield accelerated electrons featuring both ultralow transverse emittances and large energy spreads.

Keywords: Traveling-Wave; Thomson scattering; X-ray; FEL

  • Poster
    Novel Light Sources from Laser-Plasma Interactions, 20.-24.04.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21977
Publ.-Id: 21977


Realizable Optical Free-Electron Lasers with Traveling-Wave Thomson-Scattering

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Röser, F.; Schramm, U.; Sauerbrey, R.

In Traveling-Wave Thomson-Scattering (TWTS) a high-power laser pulse is scattered off a relativistic electron pulse to realize optical free-electron lasers (OFELs) with a wavelength range from ultraviolet to Angstrom. TWTS employs a side-scattering geometry where laser and electron beam propagation direction enclose an interaction angle to become independent of the Rayleigh length limit for the maximum interaction distance inherent to standard head-on Thomson scattering geometries. For optimum spatial overlap between electrons and laser pulse in TWTS geometries the laser pulse features a pulse-front tilt. In this way, the electrons interact with all parts of the laser pulse and the brilliance of a TWTS light source become by orders of magnitude larger than in standard head-on geometries where spatial overlap between electrons and laser pulse is lost due to defocusing of the laser pulse. OFELs can be operated with TWTS using multi-hundred to petawatt class laser systems with beam diameters in the centimeter range since the interaction distance in TWTS can be controlled with the laser beam diameter in the interaction plane.
We show that interaction distances achieved in TWTS are long enough for microbunching of the electron beam and coherent amplification of the radiation from our 1.5D FEL theory for the interaction of electrons with laser fields in side-scattering geometries.
We give the scaling laws for the design of TWTS OFELs derived from this 1.5D theory and present possible experimental setups for TWTS OFELs using electrons from conventional and laser wakefield accelerators. We put emphasize on how the ultra-low emittance of a laser wakefield accelerator can be exploited to compensate for the one percent level energy spread and how laser pulse dispersion introduced with the pulse-front tilt in TWTS setups can be compensated with an additional pair of gratings in the laser pulse path before the interaction.

Keywords: Traveling-Wave; Thomson scattering; X-ray; FEL

  • Invited lecture (Conferences)
    SPIE Optics + Optoelectronics 2015, 13.-16.04.2015, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-21976
Publ.-Id: 21976


Experimental design of optical free-electron lasers in the Traveling-Wave Thomson-Scattering geometry

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Röser, F.; Schramm, U.; Sauerbrey, R.

Traveling-Wave Thomson-Scattering (TWTS) realizes optical free-electron lasers (OFEL) from the extreme ultraviolet to the X-ray range with existing electron accelerators and high-power laser systems. In TWTS ultrashort laser pulses and relativistic electron bunches are utilized in a side-scattering geometry where laser pulse and electron bunch direction of motion enclose an interaction angle. The laser electric field thereby is the undulator field in which the electrons oscillate and emit radiation during the interaction. When the electrons traverse the laser beam cross-section, TWTS provides continuous overlap of electron bunch and laser pulse by employing a laser pulse-front tilt which compensates the spatial separation of electrons and laser at the beginning and end of the interaction originating from their different propagation directions. The combination of laser pulse-front tilt and side-scattering in TWTS enables interaction lengths long enough to induce microbunching of the electron beam leading to coherent amplification of the emitted radiation and the realization of TWTS OFELs.
We present the scaling laws for the electron beam and laser pulse requirements to operate TWTS OFELs and show with example scenarios that TWTS OFELs can be realized with existing radio-frequency accelerated electrons such as ELBE at HZDR as well as laser-wakefield accelerated electrons. We detail the necessary equipment in a TWTS OFEL experiment and discuss how current experimental limitations affect the design of TWTS OFEL setups.

Keywords: Traveling-wave; Thomson scattering; X-ray; FEL

  • Lecture (Conference)
    DPG Frühjahrstagung Wuppertal 2015, 09.-13.03.2015, Wuppertal, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21975
Publ.-Id: 21975


From Optical Undulators to Optical FELs with Traveling-Wave Thomson-Scattering

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Röser, F.; Schramm, U.; Sauerbrey, R.

No abstract needed

Keywords: Traveling-Wave; Thomson scattering; X-ray; FEL

  • Invited lecture (Conferences)
    Materie und Technologie Kick-Off Meeting, 24.-26.02.2015, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21974
Publ.-Id: 21974


Defect induced magnetism in SiC

Zhou, S.; Wang, Y.; Liu, Y.; Gemming, S.; Helm, M.

Defect-induced magnetism is attracting intensive research interest. It not only challenges the traditional opinions about magnetism, but also has some potential applications in spin-electronics. SiC is a new candidate for the investigation of defect-induced ferromagnetism after graphitic materials and oxides due to its high material purity and crystalline quality [1, 2]. In this contribution, we made a comprehensive investigation on the structural and magnetic properties of ion implanted and neutron irradiated SiC sample. In combination with X-ray absorption spectroscopy and first-principles calculations, we try to understand the mechanism in a microscopic picture.
For neon or xenon ion implanted SiC, we identify a multi-magnetic-phase nature [3]. The magnetization of SiC can be decomposed into paramagnetic, superparamagnetic and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. By combining X-ray magnetic circular dichroism and first-principles calculations, we clarify that p-electrons of the nearest-neighbor carbon atoms around divacancies are mainly responsible for the long-range ferromagnetic coupling [4]. Thus, we provide a correlation between the collective magnetic phenomena and the specific electrons/orbitals.
With the aim to verify if a sample containing defects through its bulk volume can persist ferromagnetic coupling, we applied neutron irradiation to introduce defects into SiC [5]. Besides a weak ferromagnetic contribution, we observe a strong paramagnetism, scaling up with the neutron fluence. The ferromagnetic contribution only occurs in a narrow fluence window or after annealing. We speculate that defect-induced ferromagnetism rather locally appears in particular regions, like surface/interface/grain boundaries.
[1] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011). [2] Y. Wang, et al., Phys. Rev. B 90, 214435 (2014). [3] Y. Wang,et al., Phys. Rev. B 89, 014417 (2014). [4] Y. Wang, et al., Sci. Reports 5, 8999 (2015). [5] Y. Wang, et al., Phys. Rev. B, submitted (2015).

  • Lecture (Conference)
    20th International Conference on Mangetism, 05.-10.07.2015, Barcelona, Spain
  • Lecture (Conference)
    EMRS2016Fall, 19.-22.09.2016, Warsaw, Poland
  • Lecture (Conference)
    DPG-Frühjahrstagung 2016, 06.-11.03.2016, Regensburg, Germany
  • Invited lecture (Conferences)
    Sino-German Symposium on "Defect Engineering in SiC Device Manufacturing – Atomistic Simulations, Characterization and Processing", 10.-14.11.2019, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-21973
Publ.-Id: 21973


Magnetization and X-ray absorption spectroscopy of Mn implanted Ge after flashlamp annealing

Zhou, S.; Wang, Y.; Prucnal, S.; Jiang, Z.; Zhang, W.; Wu, C.; Weschke, E.; Skorupa, W.; Helm, M.

Ge-based diluted magnetic semiconductors have drawn extensive attention over the past decades due to their potential to be applied in spintronic devices and to be integrated with the mainstream Si microelectronics as well. The hole-mediated effect in diluted magnetic semiconductors provides the possibility to realize the control of magnetic properties by the electrical control of free carriers. In this contribution, we will present the magnetic properties and X-ray absorption spectroscopy of Mn implanted Ge annealed by flashlamp.

Keywords: Magnetic thin films and nanostructures

  • Lecture (Conference)
    IEEE International Conference on Magnetics 2015, 11.-15.05.2015, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-21972
Publ.-Id: 21972


Composition and bandgap control of AlxGa1−xN films synthesized by plasma-assisted pulsed laser deposition

Cai, H.; Liang, P.; Hübner, R.; Zhou, S.; Li, Y.; Sun, J.; Xu, N.; Wu, J.

Ternary AlxGa1−xN films with different Al compositions were synthesized on sapphire and Si substrates by pulsed laser co-ablation of a polycrystalline GaAs target and a metallic Al target in nitrogen plasma generated by electron cyclotron resonance discharge of N2 gas. Spectroscopy was used to characterize the synthesis process for the mechanisms responsible for AlxGa1−xN synthesis and film deposition. The synthesized AlxGa1−xN films were evaluated using field emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman scattering spectroscopy, transmission electron microscopy and optical transmission measurements. The AlxGa1−xN films have hexagonal wurtzite structure, which degenerates as the Al composition increases, and show high optical transparency with the absorption edge blue shifted and the bandgap widened with the increasing Al composition. A comparison of the synthesized AlxGa1−xN films with the binary GaN and AlN films synthesized by a similar method reveals their similarity in the structure and the optical properties.

Keywords: AlGaN; PLD

Permalink: https://www.hzdr.de/publications/Publ-21971
Publ.-Id: 21971


lll-V nanocrystal formation in ion-implanted Ge and Si via liquid phase epitaxy during short-time flash lamp annealing

Wutzler, R.; Rebohle, L.; Prucnal, S.; Böttger, R.; Hübner, R.; Facsko, S.; Helm, M.; Skorupa, W.

The integration of III-V compound semiconductors into existing semiconductor technology is a milestone in future development of micro- and opto-electronics. III-V compound semiconductor nanocrystals (NCs) were fabricated in Ge and Si substrates by high-fluence ion implantation and short-time flash lamp annealing (FLA). The III-V NC formation takes place after amorphization due to implantation, followed by recrystallization via millisecond liquid phase epitaxy. Using this approach, GaAs and InAs NCs were fabricated. Whereas this formation process was recently investigated for Si, the case of Ge has not been reported yet but shows remarkable differences. In order to get III-V/Ge and III-V/Si heterojunctions in the form of free-standing III-V NCs on Ge and Si nanocolumns an additional selective etching of Ge and Si was performed using H2O2 and KOH solution, respectively.
Raman spectroscopy measurements confirmed the formation of III-V NCs within the particular, recrystallized matrices. The microstructural properties of the III-V NCs and the distribution of implanted species were investigated by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM), and Auger electron spectroscopy (AES). SEM and TEM images show distinct, crystalline NCs. Conductive atomic force microscopy (c-AFM) was performed to investigate the electrical behavior of the fabricated heterojunctions.

Keywords: Ion implantation; Flash lamp annealing; III-V integration; Liquid phase epitaxy; Silicon; Germanium

  • Lecture (Conference)
    E-MRS Spring Meeting 2015, 11.-15.05.2015, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-21970
Publ.-Id: 21970


Wechselwirkung von Actiniden/Lanthaniden mit Ton, Tonorganika und Mikroorganismen

Schmeide, K.; Fritsch, K.; Lippold, H.; Poetsch, M.; Kulenkampff, J.; Jordan, N.; Moll, H.; Cherkouk, A.

In the talk, the most important results obtained in the project for the system radionuclide/clay organics/clay rock are presented. The influence of salinity and temperature on complexation, sorption as well as diffusion/transport of radionuclides is discussed.

Keywords: Uranium; plutonium; europium; terbium; fulvic acid; propionic acid; microorganisms; montmorillonite; Opalinus Clay; PET

  • Lecture (others)
    Abschlussworkshop des Verbundprojekts "Rückhaltung endlagerrelevanter Radionuklide im natürlichen Tongestein und in salinaren Systemen", 12.-13.05.2015, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21969
Publ.-Id: 21969


Sustainable solutions for restoration & conservation of pipe organs by using Plasma Ion based surface engineering vs. EMA copolymer surface treatment techniques.

Pelic, B.; Skorupa, W.

Pipe organs with their unique sound and beautiful housing are important objects of the cultural heritage. The instrument consists of a number of pipes (flute and reed), which are prone to heavy corrosion attack, resulting in a loss of voice. The atmospheric corrosion of reed (CuZn alloys) and flute pipes (PbSn alloys) is strongly enhanced by traces of volatile organic compounds (VOCs) and the alloy’s instability.
Experiments have been undertaken to explore the improvement of an aqueous corrosion with the high acetic acid concentration (2–5 v/v%) of CuZn and PbSn alloys, by deposition of protective films (Al2O3 and Al) in nano scale using Pulsed laser deposition and Magnetron sputtering. Afterwards, the samples were implanted with N+ ions using plasma immersion ion implantation. Such coating is then able to withstand stresses and vibrations due to sound generation in organ pipes, and it produces a barrier to VOCs and water vapor. Furthermore, for the treatments of new or slightly corroded flute pipes, solution of 4% Paraloid B-72 in toluene has been applied as corrosion inhibitor. The complete and overall application of the PB-72 improved significantly the corrosion resistance of flute pipes. The laboratory corrosion tests were combined with field studies at affected church organs.

Keywords: Plasma immersion ion implantation (PI3); Pulsed laser deposition (PLD); Magnetron sputtering (MS); EMA copolymer (Paraloid B-72); corrosion of organ pipes

  • Lecture (Conference)
    E-MRS Spring Meeting 2015, 11.-15.05.2015, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-21968
Publ.-Id: 21968


Measurement of α-particle quenching in LAB based scintillator in independent small-scale experiments

von Krosigk, B.; Chen, M.; Hans, S.; Junghans, A. R.; Kögler, T.; Kraus, C.; Kuckert, L.; Liu, X.; Nolte, R.; O’Keeffe, H. M.; Wan Chan Tseung, H.; Wilson, J. R.; Wright, A.; Yeh, M.; Zuber, K.

The alpha–particle light response of liquid scintillators based on linear alkylbenzene (LAB) has been measured with three different experimental approaches. In the first approach, alpha–particles were produced in the scintillator via 12C(n,alpha)9Be reactions. In the second approach, the scintillator was loaded with 2% of natSm providing an alpha–emitter, 147Sm, as an internal source. In the third approach, a scintillator flask was deployed into the water–filled SNO+ detector and the radioactive contaminants 222Rn, 218Po and 214Po provided the alpha–particle signal. The behavior of the observed alpha–particle light outputs are in agreement with each case successfully described by Birks’ law. The resulting Birks parameter kB ranges from (0.0066 +- 0.0014) cm/MeV to (0.0076+-0.0003) cm/MeV. In the first approach, the alpha–particle light response was measured simultaneously with the light response of recoil protons produced via neutron–proton elastic scattering. This enabled a first time a direct comparison of kB describing the proton and the alpha–particle response of LAB based scintillator. The observed kB values describing the two light response functions deviate by more than 5 sigma. The presented results are valuable for all current and future detectors, using LAB based scintillator as target, since they depend on an accurate knowledge of the scintillator
response to different particles.

Keywords: Liquid Scintillatiors; Linear Alcyl Benzene

Permalink: https://www.hzdr.de/publications/Publ-21967
Publ.-Id: 21967


Tuning physical properties by introducing defects: Applications in magnetic data storage and sustainable energy materials

Potzger, K.

Structural or chemical defects in materials can have a tremendeous effect on their functunality, e.g. in magnetic data storage or sustainable energy materials. Ion beam techniques are ideal methods for a controlled induction of defects, e.g. in thin films since the defect production rate can be controlled by the ion flux whereas the depth of generated defects can be controlled by means of the ion energy. The analysis of the defects generated, on the other hand, can be performed by means of positron annihaltion spectroscopy, where the positrons are implanted either from a radioactive source or from a free electron laser induced nuclear reaction.
In this tutorial, basic concepts of ion implantation as well as positron annihilation spectroscopy at HZDR will be presented. In addition, the effect of ion irradiation, i.e. defect generation, on the magnetic properties of metal alloys will be explained. We will focus on the potential of ion beams for writing magnetic nano- and microstructures. Moreover, magnetic , defect and structural properties of materials for hydrogen processing will be presented.

Keywords: Ion Irradiation; magnetism; sustainable energy materials

  • Invited lecture (Conferences)
    50. Zakopane School of Physics Breaking Frontiers: Submicron Structures in Physics and Biology, 18.-23.05.2015, Zakopane, Polen

Permalink: https://www.hzdr.de/publications/Publ-21966
Publ.-Id: 21966


Comparison of LSO and BGO block detectors for prompt gamma imaging in ion beam therapy

Hueso González, F.; Biegun, A. K.; Dendooven, P.; Enghardt, W.; Fiedler, F.; Golnik, C.; Heidel, K.; Kormoll, T.; Petzoldt, J.; Römer, K. E.; Schwengner, R.; Wagner, A.; Pausch, G.

A major weakness of ion beam therapy is the absence of applicable tools for verifying the particle range in clinical routine. The application of the Compton camera concept for the imaging of prompt gamma rays, a by-product of the irradiation correlated to the dose distribution, is a promising approach for range assessment and even two-dimensional in vivo dosimetry. Multiple position sensitive gamma ray detectors arranged in scatter and absorber planes, together with an imaging algorithm, are required to reconstruct the prompt gamma emission density map. Conventional block detectors deployed in Positron Emission Tomography (PET), which are based on Lu2SiO5:Ce (LSO) and Bi4Ge3O12 (BGO) scintillators, are suitable candidates for the Absorber of a Compton camera due to their high density and absorption efficiency even for the prompt Gamma energy range (several MeV). We compare experimentally LSO and BGO block detectors in clinical-like radiation fields in Terms of energy, spatial and time resolution. The high energy range compensates for the low light yield of the BGO material and boosts significantly its performance compared to the PET scenario. Notwithstanding the overall superiority of LSO, BGO catches up in the field of prompt gamma Imaging and can be considered as a competitive alternative to LSO for the absorber plane due to its lower price and the lack of intrinsic radioactivity.

Keywords: Instrumentation for hadron therapy; Detector modelling and simulations; Compton imaging; block detector; prompt gamma; in vivo dosimetry

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-21965
Publ.-Id: 21965


SEM-based automated mineralogy: A fast and effective method for in-situ particle analysis

Osbahr, I.; Heinig, T.; Krause, J.

Scanning electron microscope-based automated mineralogy such as the Mineral Liberation Analyser (MLA) allows several automated procedures based on backscattered electron (BSE) image acquisition and the collection of energy-dispersive X-ray spectra of particles with a specified contrast in the BSE image. The collected spectra are classified with a standard mineral spectra list which has been collected and specified for the samples. Samples should be solid with a polished surface. Different measurement modes are available on the MLA which can deliver extensive sets of information as modal mineralogy, particle- and grain size/shape distribution, liberation, mineral association or intergrowth. SEM-based automated mineralogy is a well-established tool in applied mineralogy and mineral- and metallurgic processing. The features of this method can also be applied in wide areas of research fields including material sciences, geology or environmental sciences.

Keywords: SEM; MLA; automated mineralogy

  • Lecture (Conference)
    ANAKON 2015, 23.-26.03.2015, Graz, Österreich

Permalink: https://www.hzdr.de/publications/Publ-21963
Publ.-Id: 21963


Liquid drainage in inclined packed beds – Accelerating liquid draining time via column tilt

Assima, G. P.; Hamitouche, A.; Schubert, M.; Larachi, F.

The dynamics of liquid drainage in inclined packed beds was studied experimentally using electrical capacitance tomography. The evolution of textural flow regimes and liquid saturation profiles were monitored as a function of bed tilt angle and bed height. Film and droplet textural regimes were discriminated during bed drainage tests. They consisted of a rapid step discharging, virtually at constant flow rate, ca. 80% of the poral dynamic liquid followed by a slower step of partially-saturated pores discharging the remaining 20%. The drainage time was markedly reduced upon tilting the column resulting ultimately in virtually bed-length independent drainage times. Bed inclination reduced the droplet paths to the vessel wall, stimulating migration and coalescence of liquid droplets towards the lowermost area of the column cross-section. This ensured sufficient hydraulic pressure nearby the high-porosity wall area to maintain enhanced liquid outflows. As a prospective process intensification artifice, inclining packed beds way exhibit superior advantage in stimulating drainage of tall vessels especially if emergency circumstances arise.

Keywords: Liquid drainage; static inclined packed bed; electrical capacitance tomography; liquid saturation; film and droplet texture

Permalink: https://www.hzdr.de/publications/Publ-21962
Publ.-Id: 21962


Field-controlled phase diagram from non-collinear magnetic Janus spheres

Steinbach, G.; Nissen, D.; Albrecht, M.; Gemming, S.; Erbe, A.

We show how the non-collinear magnetic arrangement of ferromagnetic Janus particles enables the construction of a rich phase diagram via static self-assembly in two dimensions.
Branched clusters of staggered chains, compact clusters, linear chains and single particles can be formed and interconverted via constant and low-frequency external magnetic fields. The magnetic anisotropy of the presented particles fundamentally adds new possibilities to controlled self-assembly

Keywords: Colloidal particles; soft matter; self assembly; magnetic microstructures

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-21961
Publ.-Id: 21961


Critical evaluation of the small punch test as a screening procedure for mechanical properties

Altstadt, E.; Ge, H. E.; Kuksenko, V.; Serrano, M.; Houska, M.; Lasan, M.; Bruchhausen, M.; Lapetite, J.-M.; Dai, Y.

For quick screening of material properties, it is important to provide simple experimental test techniques to address specific aspects of material properties. Within work package 2 of the Euratom FP7-MATTER project, a small punch test collective exercise was conducted to critically evaluate the potential of this technique for the characterisation of irradiation hardening and embrittlement. The ferritic-martensitic 9%Cr-steel T91 was used. Several data sets were produced for two major specimen geometries by different European laboratories. The reproducibility and scatter of results expressed by coefficient of variation for the total and plastic energy, the elastic-plastic transition load, the maximum load and the displacement at maximum load was analysed. The largest scatter was observed for the elastic-plastic transition load and for the plastic energy. Correlations for the estimation of tensile properties were shown to be device dependent.The estimations of the ductile-to-brittle transition temperatures are in a good agreement in cases of identical main geometrical parameters. The SP tests of neutron irradiated T91 (dose between 2.3 and 4 dpa) showed that the equivalent Charpy transition temperature shifts obtained from SP tests are in very good agreement with KLST based values. Thus the small punch test is an appropriate tool for the screening of the neutron irradiation induced embrittlement. We also observed a significant effect of irradiation on the recalculated yield stress and ultimate tensile strength. In comparison with tensile data, the irradiation induced hardening was underestimated. The small punch test is less appropriate for the screening of hardening (yield stress increase) than it is for embrittlement.

Keywords: Small punch test; ferritic-martensitic steel; ductile-brittle transition temperature; yield stress; neutron irradiation

Permalink: https://www.hzdr.de/publications/Publ-21960
Publ.-Id: 21960


Towards safe long-term operation of reactor pressure vessels

Rouden, J.; Hein, H.; May, J.; Planman, T.; Todeschini, P.; Brumovsky, M.; Ballesteros, A.; Gillemot, F.; Chaouadi, R.; Efsing, P.; Altstadt, E.

This paper summarizes long-term operation conditions in European nuclear power plants. Recommendations for monitoring the radiation embrittlement of reactor pressure vessels during life extension periods (to 60 or 80 years) are presented. The guidelines were developed in the EURATOM FP7 project LONGLIFE. The work performed responds to the need for guidance to treat long term irradiation effects within the ageing management of NPPs, since the standard RPV surveillance programmes were designed for a time period of 40 years. In particular the following issues are addressed: re-use of tested surveillance speciems, transferability of material test reactor results to reactor operation conditions, extension of reactor pressure vessel surveillance programmes, withdrawal schemes for lon-term operation surveillance programmes.

Keywords: Reactor pressure vessel; irradiation embrittlement

  • atw - International Journal for Nuclear Power 60(2015)5, 287-293

Permalink: https://www.hzdr.de/publications/Publ-21959
Publ.-Id: 21959


He stripping for AMS of 236U and other actinides using a 3 MV tandem accelerator

Winkler, S. R.; Steier, P.; Buchriegler, J.; Lachner, J.; Pitters, J.; Priller, A.; Golser, R.

Interest in the long-lived radioisotope 236U (t1/2 = 23.4 million years) has significantly increased recently, due to the emergence of environmental and earth science applications. Presently, only a few (AMS) accelerator mass spectrometry instruments are suited for this measurement. One major limitation is the relatively low total detection efficiency (on the order of 10^4), which is partly caused by a low stripping yield of the positive ion charge state selected after the tandem accelerator. It has been shown that high yield can be achieved using helium as stripper gas for uranium ion energies below 0.35 MeV. Here we investigate the potential of He stripping of U at the 3-MV tandem accelerator VERA. Phenomenological charge state distributions for U and Th are presented for terminal voltages from 1.0 to 1.7 MV. These terminal voltages provide better background rejection than possible below 1 MeV, and are suited to the widely used 1–3 MV workhorses of many accelerator mass spectrometry laboratories. The methods can be applied to other actinides also.

Keywords: Uranium-236; Accelerator mass spectrometry; Actinides; Gas stripping; Time-of-Flight

Permalink: https://www.hzdr.de/publications/Publ-21958
Publ.-Id: 21958


Meißener Deckelvase mit späterer Ergänzung - Protonenstrahl-Analyse beweist die Unterschiede

Neelmeijer, C.; Roscher, R.

Skepsis und die daraus resultierende Frage, ob ein Kunstobjekt vielleicht ergänzt, restauriert oder gar gefälscht ist, sind berechtigt und stellen sich nicht nur dem Kunsthistoriker aus Museen, Sammlern oder interessierten Laien. Die Protonenstrahl-Analyse unterstützt bei der Suche nach der richtigen Antwort. Im Visier: eine Meißener Vase und ihr Deckel. Sowohl die chemischen Zusammensetzungen von Porzellanmassen und Glasuren als auch die Analysen von Pigmenten der Dekore auf Vasenkörper und Deckel beweisen, dass der Deckel nicht original, sondern eine spätere Ergänzung ist.

Keywords: Porzellan/Porcelain; Original/Original; Nachbildung/Replica; Materialanalyse/Material analysis; PIXE; PIGE

  • Restauro 4(2015)

Permalink: https://www.hzdr.de/publications/Publ-21957
Publ.-Id: 21957


Mineralogical and chemical analysis of secondary raw materials – challenges and pitfalls

Dreßler, S.; Bachmann, K.; Renno, A. D.; Scharf, O.; Schaefer, J.

Secondary raw materials (SRM) are becoming increasingly more important in ensuring the stability of critical metal supply. Like for natural raw materials, processing and metallurgical treatment demands a detailed and meticulous geometallurgical characterisation. Unlike municipal solid waste and Waste Electrical and Electronic Equipment (WEEE), ashes, slags, dusts and other industrial residues are "produced" centrally in large quantities. In light of these circumstances, the logistics of supply is simpler. This makes these types of SRM ideal candidates for the extraction of critical metals.
Precise and accurate chemical and mineralogical data, knowledge of distribution of valuable and deleterious elements in the single phases as well as information about homogeneity and grain size distribution of the minerals are crucial for the development of new extraction technologies. Gaining these essential information can be achieved by using SEM-based automated mineralogical analysis. However, the large particle size range, the dominance of very small grain sizes (< 5 µm) and the diversity of phases are challenging for the analysis. Furthermore, in contrast to natural materials the analysis of secondary materials faces the challenge of developing new methods for non-natural extreme combinations of elements and phases. To overcome these challenges we used complementary analytical methods, like XRD and optical microscopy. Two of them, High-Speed PIXE and the “MEGA” instrument are still in the stage of development. Both instruments deliver additional information about trace element distribution.
Nevertheless, in contrast to natural materials the analysis of secondary materials faces the challenge of developing new methods for non-natural extreme combinations of elements and phases. We present initial results of ash and slag samples, like residues of pyrometallurgical recycling of spent lead batteries.

Keywords: Secondary raw materials; SEM-based automated mineralogical analysis

  • Poster
    Geoanalysis 2015, 09.-14.08.2015, Leoben, Österreich

Permalink: https://www.hzdr.de/publications/Publ-21956
Publ.-Id: 21956


Fit-for-purpose analytics for resource technology?

Dreßler, S.; Gurlit, S.; Merchel, S.; Michalak, P. P.; Renno, A. D.; Sazonov, A. M.; Schenk, F.; Sterba, J. H.

Along the value chain (exploration, mining, processing, recycling) generally solid samples of complex matrix and non-stoichiometric composition need to be analysed. Besides spatially-resolved analytics applied to technology development, bulk analytics is mainly used for characterisation of value components.
In the search of the best-suited method, there are important questions to answer at first:
1. What is already known about the sample (matrix, stability, solubility, interferences)?
2. What data are needed (quantitative, semi-quantitative or qualitative)?
3. Are the concentrations of the elements of interest at a major, minor or trace level?
4. How urgently are the data needed and what are the financial restraints?
Here, two different projects are selected to demonstrate a typical search for fit-for-purpose analytics spanning from commonly available Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to more rarely applied Instrumental Neutron Activation Analysis (INAA). These are two examples of primary and secondary raw materials (intermediate goods and waste), which would open possibilities for side products of critical metals, e.g. REE, PGE, Re, Ga.
The first project deals with a natural mineral sample of molybdenite (MoS2) taken from an open pit mine in Kačaran (Armenia) in use for Mo and by-product Re mining. Rhenium is important for catalytic and petrochemical industry, metallurgy, and aviation, e.g. it is used for steel reinforcement in turbine blades for aircrafts [1,2].
The second project focus on secondary raw materials from the non-bauxitic production of aluminium and alumina in Siberia. The analysed materials were taken from different stages of the production process: The final product alumina (Al2O3), waste products like red mud (mainly calcium carbonate and SiO2), sodium salts (e.g. Na2SO4) and anode slag (carbon, Cu-Al alloy, Al) and by-products like wollastonite ceramics (CaSiO3) and soda-potash (K2CO3/Na2CO3).
Of course, there are pros and cons of every analytical method (Total Reflection X-ray Fluorescence (TXRF), ICP-MS, INAA) for different samples yielding to clear conclusions about the best-suited method for future analytical tasks. For example in the case of Re, INAA is identified as method of choice for such kind of analysis due to high sample throughput, an easy and quick sample preparation and a low detection limit (0.26 μg/g).

References:
[1] A. Brumby, M. Verhelst, D. Cheret, Catalysis today. 2005, 106, 166-169.
[2] C. Zhan-Fang, Z. Hong, Q. Zhao-hui, Hydrometallurgy. 2009, 97, 153-157.

Keywords: Resource Technology; raw materials; INAA; Re; aluminium production

  • Poster
    GDCh-Wissenschaftsforum Chemie 2015, 30.08.-02.09.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21955
Publ.-Id: 21955


Herstellung und Reinigung von n.c.a. 88Y am Leipziger Zyklotron Cyclone® 18/9

Mansel, A.; Franke, K.

Die Abteilung „Reaktiver Transport“ der Forschungsstelle Leipzig beschäftigt sich mit dem Migrations-/Sorptionsverhalten von (Schad)stoffen in geologischen Formationen. In aktuellen Projekten werden partikuläre, kolloidale, gelöste und komplexierte, toxische und radiotoxische Stoffe in Batch- und Säulenstudien sowie Extraktionsverfahren für seltene Metalle untersucht. Bei der eingesetzten Radiotracertechnik kommen kurzlebige, nicht kommerziell erhältliche Radionuklide zum Einsatz. Am Leipziger Zyklotron Cyclone® 18/9 neu implementiert ist die 88Y-Herstellung (T1/2 = 106,6 d) durch Protonenbeschuss von Strontium mit natürlicher Isotopenzusammensetzung via 88Sr(p,n)88Y[1-3]. Das Target wird durch Verpressen von ca. 30 mg Strontiumcarbonat in eine Aluminiumhalterung hergestellt. Die Bestrahlung erfolgt bei einem Protonenstrom von 3 µA, einer Strahlzeit von 2 Stunden und einer Projektilenergie von ca. 12 MeV. Die chemische Aufarbeitung des bestrahlten Strontiumcarbonats erfolgte erstmals durch Ionenchromatographie mit LN-Resin-A (TrisKem Int.) aus salpetersaurer Lösung[4-5]. N.c.a. (no-carrier-added) 88Y wird mit einer radiochemischen Ausbeute von 95 % ± 4 % erhalten. Der entwickelte Trennungsgang dient zur Vorbereitung für die Produktion und Aufarbeitung des kurzlebigen Radionuklids 86Y (T1/2 = 14,7 h; Iβ+ = 31,9 %) für die Positronen-Emissions-Tomographie (PET) durch Bestrahlung von isotopenangereichertem 86Sr.

Literatur:
[1] S. A. Kandil, B. Scholten, K. F. Hassan, H. A. Hanafi, S. M. Qaim, J. Radioanal. Nucl. Chem. 2009, 279, 823. [2] K. Kettern, K.-H. Linse, S. Spellerberg, H. H. Coenen, S. M. Qaim, Radiochim. Acta 2002, 90, 845. [3] N. P. van der Meulen, T. N. van der Walt, G. F. Steyn, F. Szelecsenyi, Z. Kovacs, C. M. Perrang, H. M. Raubenheimer, Appl. Radiat. Isot. 2009, 67, 1320. [4] E. P. Horwitz, C. A. A. Bloomquist, J. Inorg. Nucl. Chem. 1975, 37, 425. [5] C. Pin, J. F. S. Zalduegui, Anal. Chim. Acta 1997, 339, 79.

  • Poster
    GDCh Jahrestagung 2015, Fachgruppe Nuklearchemie, 30.08.-02.09.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21952
Publ.-Id: 21952


Efficient Large Scale Simulation of Stochastic Lattice Models on GPUs

Kelling, J.; Ódor, G.; Heinig, K.-H.; Gemming, S.

With growing importance of nano-patterned surfaces and nano-composite materials in many applications from energy technologies to nano-electronics, a thorough understanding of the self-organized evolution of nano-structures needs to be established. Modelling and simulations of such processes can help in this endeavor and provide predictions for the turnout of manufacturing processes.

In this talk GPGPU-enabled implementations of two stochastic lattice models will be discussed, shedding light on the complications which arise when simulations of stochastic processes are to make efficient use of massively parallel GPU architectures.
A single-GPU implementation of the (2+1)-dimensional Roof-Top-model allows very precise large-scale studies of surface growth processes in the Kardar-Parisi-Zhang universality class.[1] Furthermore a multi-GPU enabled version of the 3d kinetic Metropolis lattice Monte-Carlo method[2] provides the capability to study the evolution of nano-structures both towards and out-of-equilibrium at spatio-temporal scales of experiments using only small to medium-sized GPU clusters.

[1] J. Kelling, G. Ódor Extremely large-scale simulation of a Kardar-Parisi-Zhang model using graphics cards, Physical Review E 84, 061150 (2011)
[1] J. Kelling, G. Ódor, F. Nagy, H. Schulz, K. Heinig Comparison of different parallel implementations of the 2+1-dimensional KPZ model and the 3-dimensional KMC model, The European Physical Journal - Special Topics 210, 175-187 (2012)

  • Lecture (others)
    Seminar Topical Problems, 06.05.2015, Chemnitz, Deutschland
  • Invited lecture (Conferences)
    GPU Day 2015 - The Future of Many-Core Computing in Science, 20.-21.05.2015, Budapest, Hungary
  • Lecture (others)
    Seminar, 18.11.2015, Coventry, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-21951
Publ.-Id: 21951


Effect of rotating magnetic field on the microstructures and physical properties of Al-Cu-Co ternary eutectic alloy

Cadirli, E.; Kaya, H.; Räbiger, D.; Eckert, S.; Gündüz, M.

The solidification microstructures and physical properties of Al-Cu-Co ternary eutectic alloy were studied in a rotating magnetic field (RMF). The RMF-driven flow was the key factor causing grain refinement and uniformity of solidification microstructures. The temperature distributions during solidification were recorded under the conditions with and without RMF. The dependence of the eutectic spacing (λ) the microhardness (HV), tensile strength (σt) and compressive strength (σc) on the RMF were investigated. Electrical resistivity (ρ) measurements of the studied alloy were also performed by using the four-point probe method and the dependence of the resistivity on temperature and RMF were determined. Besides, the enthalpy (ΔH) and the specific heat (Cp) values were determined by the DSC analysis. Important changes were found in the microstructure, microhardness, tensile strength, compressive strength and electrical resistivity of the studied alloy with increasing RMF.

Keywords: rotating magnetic field; microstructure; microhardness; tensile strength; compressive strength; electrical resistivity

Permalink: https://www.hzdr.de/publications/Publ-21950
Publ.-Id: 21950


Terahertz response of patterned epitaxial graphene

Sorger, C.; Preu, S.; Schmidt, J.; Winnerl, S.; Bludov, Y. V.; Peres, N. M. R.; Vasilevskiy, M. I.; Weber, H. B.

We study the interaction between polarized terahertz (THz) radiation and micro-structured large-area graphene in transmission geometry. In order to efficiently couple the radiation into the two-dimensional material, a lateral periodic patterning of a closed graphene sheet by intercalation doping into stripes is chosen. We observe unequal transmittance of the radiation polarized parallel and perpendicular to the stripes. The relative contrast, partly enhanced by Fabry-Perot oscillations reaches 20 %. The effect even increases up to 50% when removing graphene stripes in analogy to a wire grid polarizer. The polarization dependence is analyzed in a large frequency range from <80 GHz to 3 THz, including the plasmon-polariton resonance. The results are in excellent agreement with theoretical calculations based on the electronic energy spectrum of graphene and the electrodynamics of the patterned structure.

Keywords: Graphene; plasmonics

Permalink: https://www.hzdr.de/publications/Publ-21949
Publ.-Id: 21949


Lifetime-limited, subnanosecond terahertz germanium photoconductive detectors

Deßmann, N.; Pavlov, S. G.; Pohl, A.; Abrosimov, N. V.; Winnerl, S.; Mittendorff, M.; Zhukavin, R. K.; Tsyplenkov, V. V.; Shengurov, D. V.; Shastin, V. N.; Hübers, H.-W.

The recombination times of photo-excited free charge carriers in heavily doped and highly compensated germanium are studied by a time-resolved pump-probe experiment at a frequency of 3THz. The dominant dopant in the germanium samples is either antimony (n-Ge:Ga:Sb) or gallium (p-Ge:Sb:Ga) with compensating doping levels close to 100%. The recombination time of the free charge carriers measured by our pump-probe technique varies between 30 and 300 ps. It decreases with increasing pump pulse energy and increasing compensation due to high concentrations of Coulomb recombination centers. The recombination times at low pump powers are up to ten times shorter than those previously obtained for low-compensated n-Ge:Sb and p-Ge:Ga. The photoconductive detector made from this material shows the response time is in the order of its recombination time.

Keywords: photoconductive detector; THz detector; fast detector

Permalink: https://www.hzdr.de/publications/Publ-21948
Publ.-Id: 21948


SIKELOR - Silicon kerf loss recycling

Cramer, A.; Eckert, S.; Lombardi, I.; Dughiero, F.; Forzan, M.; Bojarevics, V.; Pericleous, K.; Kroschk, M.; Steinbach, H.

During slicing silicon block casts to wafers, about 50 % of the valuable material is lost into saw dust. The objective of the EU project SIKELOR is to process such silicon waste in an industrially viable and resource-friendly manner. To be competitive to virgin feedstock, maximum cumulative recycling costs of 10 $/kg are imposed as the economic goal.

Keywords: Ressources; solar silicon; recycling; electromagnetic processing of materials

  • Contribution to proceedings
    8th International Workshop on Crystalline Silicon for Solar Cells, 05.-08.05.2015, Bamberg, Deutschland
    Book of extended abstracts
  • Poster
    8th International Workshop on Crystalline Silicon for Solar Cells, 05.-08.05.2015, Bamberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21947
Publ.-Id: 21947


Ion bombardment and light irradiation driven modifications of magnetic nanostructures

Maziewski, A.; Kisielewski, J.; Kurant, Z.; Mazalski, P.; Sveklo, I.; Tahir, N.; Jakubowski, M.; Wojciechowski, T.; Wawro, A.; Fassbender, J.; Stobiecki, F.

Much attention is paid to magnetic nanostructures due to their intrigiung properties and different applications. Appearance of perpendicular magnetic anisotropy (PMA) when a magnetic layer thickness is decreased and a giant magneto-resistance effect are the most interesting effects. Tuning the magnetic domain sizes in a broad range (several orders of magnitude) by changing PMA, the geometrical parameters of the nanostructure, as well as by an applied external magnetic field is observed, see the review [1]. Patterned nanostructures with PMA are prospective for e.g.: mass memories together with magnetic ratchet memories, magnetic field sensors, spin wave applications.
A decrease of PMA as a result of the ion irradiation of the metallic ultrathin films, has been usually reported [2]. However we have recently shown that, Ga+ ion irradiation drives creation of the out-of-plane magnetization states, dependent on the ion fluence [3,4]. Irradiation with Ga+, Ar+, He+ ions results in an increase of magnetooptical effects and changes the coercivity field. We have also found that femtosecond light pulses induce: (i) reversible PMA changes which can be used to trigger magnetization oscillations [4] and (ii) irreversible PMA modifications [5] due to creation of out-of-plane magnetization states for low and high light power densities, respectively. Ion/light irradiation affecting magnetic and magnetooptical properties of nanostructures is a promising approach for new patterning purposes. Such desired modifications can be realized with fluence/energy densities lower than that reqired for the nanostructure surface etching. Moreover, using e.g. focused ion beam technique, lateral patterning can be performed with a nanometer precision. New metamaterials such as magnonic and magnetophotonic crystals or controllable transport of magnetic beads can be created in this way.


Acknowledgements
This work was supported by: National Science Center in Poland under the project HARMONIA Nr 2012/06/M/ST3/00475 and Foundation for Polish Science under the SYMPHONY project (Polish Science Team Programme, European Regional Development Fund, OPIE 2007–2013.

References
[1] A. Maziewski, et al., Phys. Status Solidi A, 211, 1005 (2014).
[2] H. Bernas (Ed.), Materials Science with Ion Beams, Vol. 116 (Springer-Verlag, Berlin, Berlin, 2010).
[3] A. Maziewski, et al., Phys. Rev. B 85, 054427 (2012).
[4] M. Sakamaki et al., Phys. Rev. B 86, 024418 (2012).
[4] J. Kisielewski, et al., Phys. Rev. B 85 (2012) 184429.
[5] J. Kisielewski, et al., Journal of Applied Physics 115, 053906 (2014).

Keywords: Ion bombardment and light irradiation driven modifications of magnetic nanostructures

  • Lecture (Conference)
    7th Polish Conference on Nanotechnology, 25.06.2015, Poznan, Poland

Permalink: https://www.hzdr.de/publications/Publ-21946
Publ.-Id: 21946


Ultrathin films: Light and ions irradiations induced changes of magnetic properties

Kisielewski, J.; Kisielewski, M.; Kurant, Z.; Mazalski, P.; Stupakiewicz, A.; Sveklo, I.; Tekielak, M.; Wawro, A.; Fassbender, J.; Maziewski, A.

When decreasing ultrathin film thickness d, an increase of the perpendicular magnetic anisotropy (PMA) occurs, resulting in the magnetization reorientation phase transition (RPT) from the in-plane to out-of-plane magnetization state below the critical thickness dRPT. The results of combined experimental, analytical, and micromagnetic simulations studies on the evolution of magnetization states and processes in ultrathin films and multilayered systems [1] will be presented. Possibilities of tuning the magnetic domain sizes in a broad range (of several orders of magnitude) by changing the geometrical parameters of the nanostructure, as well as by an applied external magnetic field will be discussed. Transitions between two- and three-dimensional magnetization distributions will be shown.
As a result of the ion irradiation of the metallic ultrathin films, a decrease of PMA was usually reported [2]. Contrariwise, Ga+ ion irradiation driven creation of the out-of-plane magnetization states, dependent on ion fluence, have been found [3]. Similarly, femtosecond light pulses of high energy density may also induce irreversible enhancement of PMA [4], while low energy density pulses can be used to trigger the magnetization oscillations, via reversible thermal changes of the magnetic anisotropy [5].
1. A. Maziewski, J. Fassbender, J. Kisielewski, M. Kisielewski, Z. Kurant, P. Mazalski, F. Stobiecki, A. Stupakiewicz, I.Sveklo, M.Tekielak, A.Wawro, and V. Zablotskii, Magnetization states and magnetization processes in nanostructures: From a single layer to multilayers, Phys. Status Solidi A, 211, 1005 (2014).
2. H. Bernas (Ed.), Materials Science with Ion Beams, Vol. 116 (Springer-Verlag, Berlin, Berlin, 2010).
3. A. Maziewski, P. Mazalski, Z. Kurant, M. O. Liedke, J. McCord, J. Fassbender, J. Ferré, A. Mougin, A. Wawro, L. T. Baczewski, A. Rogalev, F. Wilhelm, and T. Gemming, Tailoring of magnetism in Pt/Co/Pt ultrathin films by ion irradiation, Phys. Rev. B 85, 054427 (2012).
4. J. Kisielewski, W. Dobrogowski, Z. Kurant, A. Stupakiewicz, M. Tekielak, A. Kirilyuk, A. Kimel, Th. Rasing, L. T.Baczewski, A. Wawro, K. Balin, J. Szade, and A. Maziewski, Irreversible modification of magnetic properties of Pt/Co/Pt ultrathin films by femtosecond laser pulses, Journal of Applied Physics 115, 053906 (2014),
5. J. Kisielewski, A. Kirilyuk, A. Stupakiewicz, A. Maziewski, A. Kimel, Th. Rasing, L. T. Baczewski, and A. Wawro, Laser-induced manipulation of magnetic anisotropy and magnetization precession in an ultrathin cobalt wedge, Phys. Rev. B 85 (2012) 184429.

Keywords: Ultrathin films: Light and ions irradiations induced changes of magnetic properties

  • Lecture (Conference)
    50. Zakopane School of Physics Breaking Frontiers: Submicron Structures in Physics and Biology, 18.05.2015, Zakopane, Poland

Permalink: https://www.hzdr.de/publications/Publ-21945
Publ.-Id: 21945


Synthese und Evaluierung von [18F]NS14490 für die Bildgebung von α7 nikotinischen Acetylcholinrezeptoren im Gehirn mit Positronen-Emissions-Tomographie

Rötering, S.

Neurodegenerative Erkrankungen werden mit Veränderungen der Expressionsdichte α7 nikotinischer Acetylcholinrezeptoren in Verbindung gebracht. Dieser Rezeptor ist folglich ein interessantes Target für die molekulare Bildgebung mit Positronen-Emissions-Tomographie (PET). In der vorliegenden Arbeit werden die Synthese sowie eine Evaluierung von [18F]NS14490, ([18F]2-(1,4-Diazabicyclo[3.2.2]nonan-4-yl)-5-(1-(2-fluoroethyl)-1H-indol-6-yl)-1,3,4-oxadiazol) als neuer, potentieller Radioligand vorgestellt. Für die Radiosynthese wurden zwei Strategien verfolgt: Zum einen wurde Ethylenglykolditosylat mit [18F]Fluorethyltosylat umgesetzt und anschließend mit NS14540, einem am Indolstickstoffatom unsubstituierten Derivat zu [18F]NS14490 umgesetzt. Gleichzeitig wurden synthetisierte Präkursoren für eine direkte Radiofluorierung eingesetzt. Nach umfangreichen Arbeiten zur Isolierung und Reinigung des Radioliganden mit semipräparativer HPLC und Festphasenextraktion sowie der Formulierung folgten Untersuchungen zur Stabiltität des Radioliganden in Puffersystemem bei pH = 7 und in Schweineplasma, die Bestimmung der Lipophilie und erste Versuche zur Extraktion aus Schweineplasma.
Die In-vivo-Evaluierung des Radioliganden setzt sich aus der Bestimmung der Anreicherung des Radioliganden im Gehirn von Mäusen und Schweinen sowie der Metabolitenanalyse von Plasmaproben und Hirnhomogenaten (Maus) und in der Metabolitenanalyse von Plasmaproben (Schwein) während dynamischer PET-Aufnahmen zusammen. Der Radioligand hatte im Plasma in Mäusen eine höhere Stabilität als in Schweinen und lag im Mäusehirn nahezu unmetabolisiert vor.
Der 2. Teil dieser Arbeit beschäftigt sich mit der Aufbereitung von bestrahltem [18O]H2O zur Wiederverwendung bei der Produktion von [18F]F. 1 Liter bestrahltes [18O]H2O wurde durch Oxidation organischer Lösungsmittel mit KMnO4 und NaOH bei 50 °C oder durch Bestrahlung mit 254 nm sowie anschließender Tieftemperatur-Vakuumdestillation zur Abtrennung von Rückständen aufbereitet. Die Charakterisierung des [18O]Wassers zeigte nur geringe Restkontaminationen durch Ionen (unterer mg-l−1-Bereich) und eine nahezu abreicherungsfreie Aufbereitung. Die Durchführung von Modellexperimenten mit künstlich kontaminierten [16O]H2O gab Hinweise auf eine fast quantitative Rückgewinnung des Wassers.
Die Bestrahlung von aufbereitetem [18O]H2O und der Vergleich der Produktionsaktivitäten mit (verdünntem) [18O]Originalwasser sowie der unproblematische Einsatz des [18F]F in radiochemischen Synthesen unterstreichen die Qualität des Aufbereitungsprozesses.

Keywords: 18Fluor; α7 nikotinische Acetylcholinrezeptoren; Präkursoren; Aufbereitung von [18O]Wasser; Positronen-Emissions-Tomographie

  • Doctoral thesis
    Universität Leipzig, Fakultät für Chemie und Mineralogie, 2015
    Mentor: Prof. Dr. Thorsten Berg
    158 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21944
Publ.-Id: 21944


On the accuracy of wire-mesh sensors in dependence of bubble sizes and liquid flow rates

Nuryadin, S.; Ignaczak, M.; Lucas, D.; Deendarlianto

An experimental study to assess the accuracy of wire-mesh sensors in dependence of bubble sizes and flow rates has been performed in a 50 mm x 50 mm transparent rectangular channel. The liquid superficial velocities were ranging from 0 m/s up to 0.62 m/s with the obtained bubble size ranging from 3 mm to 7 mm. A single wire-mesh sensor with 16 x 16 electrode wires was used with a temporal and spatial resolution of 10 kHz and 3.1 mm (lateral distance between two wires), respectively. Single bubbles with known bubble size, subsequently called reference bubble size, was injected into the test section via bubble injector approx. 25 cm upstream of the wire-mesh sensor. The bubble size measurement by using wire-mesh sensor cannot be obtained directly since it requires the information of bubble velocity which is not available only by installing a single sensor. Therefore, a stereoscopic observation was conducted to obtain the bubble velocity by tracking the successive frames as well as to study the intrusiveness of the sensor. This configuration gave an advantage that the registered bubble will be assigned with its real approach velocity and a better agreement is expected. As the result, a direct comparison of all individual bubbles with the reference bubble size showed an agreement within ±10%. However, a deceleration effect was found for low superficial and observed to disappear as the liquid superficial velocity increased then vanish at observed JL = 0.62 m/s.

Keywords: wire-mesh sensor; bubble size; bubble velocity; bubble flow

Permalink: https://www.hzdr.de/publications/Publ-21943
Publ.-Id: 21943


Magnetic anisotropy and magnetic Phase transitions in RFe5Al7

Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Skourski, Y.; Mushnikov, N. V.; Rosenfeld, E. V.; Zherlitsyn, S.; Wosnitza, J.

RFe5Al7 (R – Gd, Tb, Dy, Ho, Er and Tm) single crystals have been studied by measurements of magnetization, sound propagation (in static and pulsed magnetic fields up to 60 T) and specific heat. Fundamental magnetic properties have been determined and compared for all these materials. RFe5Al7 are highly anisotropic ferrimagnets. Spontaneous and field-induced magnetic phase transitions of anisotropic and exchange nature have been observed in RFe5Al7. Strong magnetoelastic interactions are manifested by pronounced acoustic anomalies at the phase transformations. The detected magnetization jumps provide important information on the R–Fe inter-sublattice exchange interactions.

Permalink: https://www.hzdr.de/publications/Publ-21942
Publ.-Id: 21942


Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

Salazar Mejia, C.; Ghorbani Zavareh, M.; Nayak, A. K.; Skourski, Y.; Wosnitza, J.; Felser, C.; Nicklas, M.

The present pulsed high-magnetic-field study on Ni50Mn35In15 gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.

Permalink: https://www.hzdr.de/publications/Publ-21941
Publ.-Id: 21941


Uncertainty Analysis of an Interfacial Area Reconstruction Algorithm and its application to Two Group Interfacial Area Transport Equation Validation

Dave, A.; Manera, A.; Beyer, M.; Lucas, D.; Prasser, H.-M.

Wire mesh sensors (WMS) are state of the art devices that allow high resolution (in space and time) measurement of 2D void fraction distribution in any two-phase flow regime. Data using WMS have been recorded at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Lucas et al., 2010; Beyer et al., 2008; Prasser et al., 2003) for a wide combination of superficial gas and liquid velocities, providing an excellent database for advances in two-phase flow modeling.
In two-phase flow, the interfacial area plays an integral role in coupling the mass, momentum and energy transport equations of the liquid and gas phase. While current models used in best-estimate thermal-hydraulic codes (e.g. RELAP5, TRACE, TRACG, etc.) are still based on algebraic correlations for the estimation of the interfacial area in different flow regimes, interfacial area transport equations (IATE) have been proposed to predict the dynamic propagation in space and time of interfacial area (Ishii 2010). IATE models are still under development and the HZDR WMS experimental data provide an excellent basis for the validation and further advance of these models. The current paper is focused on the uncertainty analysis of algorithms used to reconstruct interfacial area densities from the void-fraction voxel data measured using WMS and their application towards validation efforts of two-group IATE models.
In previous research efforts, a surface triangularization algorithm has been developed in order to estimate the surface area of individual bubbles recorded with the WMS, and estimate the interfacial area in the given flow condition. In the present paper, synthetically generated bubbles are used to assess the algorithm’s accuracy. As the interfacial area of the synthetic bubbles are defined by user inputs, the error introduced by the algorithm can be quantitatively obtained. The accuracy of interfacial area measurements is characterized for different bubbles sizes and shapes, and for different WMS acquisition frequencies. It is found that while convex shapes are successfully analyzed by the reconstruction algorithm, some difficulties are faced with bubbles presenting internal cavities.
Utilizing the experimental HZDR database, the performance of the current two-group IATE model is evaluated. While the qualitative propagation of interfacial area is predicted sufficiently well, there is a discrepancy in magnitude between the model’s prediction and the experimental results. Overall, the study suggests that differences exist in the incidence of interaction mechanisms between small and large diameter pipes and further efforts are needed in order to extend the range of validity of current IATE models.

Keywords: Wire mesh sensor; two-phase flow; interfacial area transport equation

  • Invited lecture (Conferences)
    Japan-U.S. Seminar on Two-Phase Flow Dynamics, 10.-15.05.2015, West Lafayette, USA
  • Nuclear Engineering and Design 310(2016), 620-637
    DOI: 10.1016/j.nucengdes.2016.10.038

Permalink: https://www.hzdr.de/publications/Publ-21940
Publ.-Id: 21940


Upbend and M1 scissors mode in in neutron-rich nuclei - consequences for r-process (n,γ) reaction rates

Larsen, A. C.; Goriely, S.; Bernstein, L. A.; Bleuel, D. L.; Bracco, A.; Brown, B. A.; Camera, F.; Eriksen, T. K.; Frauendorf, S.; Giacoppo, F.; Guttormsen, M.; Görgen, A.; Harissopulos, S.; Leoni, S.; Liddick, S. N.; Naqvi, F.; Nyhus, H. T.; Rose, S. J.; Renstrøm, T.; Schwengner, R.; Siem, S.; Spyrou, A.; Tveten, G. M.; Voinov, A. V.; Wiedeking, M.

An enhanced probability for low-energy -emission (upbend, E < 3 MeV) at high excitation energies has been observed for several light and medium-mass nuclei close to the valley of stability. Also the M1 scissors mode seen in deformed nuclei increases the γ-decay probability for low-energy γ-rays (E < 2­ - 3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. The experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutron-rich, mid-mass nuclei including the scissors mode are shown.

Keywords: Electromagnetic strength functions; low-energy enhancement; scissors mode; neutron-capture rates; r-process

Permalink: https://www.hzdr.de/publications/Publ-21939
Publ.-Id: 21939


Ultrafast X-ray computed tomography for phase distribution and velocity measurements in multiphase flows

Bieberle, M.; Wagner, M.; Barthel, F.; Rabha, S.; Banowski, M.; Hampel, U.

Various flow measurement and visualization techniques are based on optical and laser-based methods. However, in many multiphase flow situations, e.g. at higher interfacial density or in flows with internals, the optical access is no longer given. Radiation based methods are in principle able to penetrate most of these systems, but are normally too slow to capture the dynamics of the flow. With ultrafast X-ray tomography a flow visualization and measurement technique has been developed, which is able to recover the dynamic phase distributions in various multiphase flow scenarios. The high imaging rate is achieved by deflecting an electron beam along a circular target, where a moving X-ray spot is generated. Tomographic projections are gathered simultaneously by a static detector ring with fast read-out. Thus, no components of the X-ray tomography system have to be rotated mechanically. The reconstructed tomography slices represent the non-superimposed phase distribution within a cross-section as a function of time. Up to 8,000 fps can be achieved in single plane mode. For velocity measurements, a second set of X-ray target and detector ring arranged at a small axial distance can be included to form the so-called dual plane mode. Although the alternating scanning of both planes reduces the frame rate by a factor of two, the benefit of combining the information from both planes to retrieve velocity information arises directly. There are different ways to extract velocity information from the two stacks of slice image data. Cross-correlation techniques offer the opportunity to retrieve time averaged as well as time resolved local or global velocities of the disperse phase. Some systems also allow the determination of single bubble or particle velocities, provided that they can be identified as the same object in both planes.

Keywords: ultrafast; X-ray CT; multiphase flows; velocity; phase distribution

  • Contribution to proceedings
    10th Pacific Symposium on Flow Visualization and Image Processing, 15.-18.06.2015, Napoli, Italia
    Proceedings of 10th Pacific Symposium on Flow Visualization and Image Processing
  • Lecture (Conference)
    10th Pacific Symposium on Flow Visualization and Image Processing, 15.-18.06.2015, Napoli, Italia

Permalink: https://www.hzdr.de/publications/Publ-21938
Publ.-Id: 21938


Environmental risks induced by elevated thorium contents in the complex rare earth elements deposit Strange Lake, Québec (Canada): Mineralogical investigations

Brombacher, L. C.; Kempe, U.; Möckel, R.; Heide, G.; Gutzmer, J.

The Strange Lake pluton is situated on the northern border between Québec and Labrador in northeastern Canada. The ore-body, located within a complex peralkaline granite-hosted system of pegmatites and aplites, contains elevated concentrations of both LREE and the highly coveted HREE, as well as other HFSE (high field strength elements, such as Zr, Nb, Y, Ti, and Th). The REE mineralization, however, is extremely complex and the elements of interest are variably distributed between various “exotic” minerals from different mineral classes that may also contain considerable amounts of unwanted impurities such as thorium, uranium and beryllium. Naturally occurring radioactive materials (NORM) like Th may be concentrated during beneficiation, thus constituting a serious hazard to the workers and the environment. In order to limit transportation and storage of hazardous material during production, it is of the company’s interest to separate these deleterious constituents early in or at best in advance to the extraction process. This study focuses on the characterization of the mineral phases that primarily host thorium for early recognition. Combined chemical and structural analyses indicate that there is one particular mineral phase in which Th is present in highly elevated concentrations. This mineral is best described as a metamict Th-silicate occurring in isolated, rounded grains enclosed in quartz. Further studies are required to indicate if this mineral can be separated early during minerals processing from the ore without considerable loss of valuable REE.

Keywords: rare earth elements; peralkaline complex; exotic minerals; thorium mineralogy

  • Contribution to proceedings
    Problems of use of natural resources - International forum of young scientists, 22.-24.04.2015, St. Petersburg, Russland
    Environmental risks induced by elevated thorium contents in the complex rare earth elements deposit Strange Lake, Québec (Canada): Mineralogical investigations, 978-5-94511-723-8

Permalink: https://www.hzdr.de/publications/Publ-21937
Publ.-Id: 21937


Improving external beam radiotherapy by combination with internal irradiation.

Dietrich, A.; Koi, L.; Zöphel, K.; Sihver, W.; Kotzerke, J.; Baumann, M.; Krause, M.

The efficacy of external beam radiotherapy (EBRT) is dose dependent, but the dose that can be applied to solid tumour lesions is limited by the sensitivity of the surrounding tissue. The combination of EBRT with systemically applied radioimmunotherapy (RIT) is a promising approach to increase efficacy of radiotherapy. Toxicities of both treatment modalities of this combination of internal and external radiotherapy (CIERT) are not additive, as different organs at risk are in target. However, advantages of both single treatments are combined, for example, precise high dose delivery to the bulk tumour via standard EBRT, which can be increased by addition of RIT, and potential targeting of micrometastases by RIT. Eventually, theragnostic radionuclide pairs can be used to predict uptake of the radiotherapeutic drug prior to and during therapy and find individual patients who may benefit from this treatment. This review aims to highlight the outcome of pre-clinical studies on CIERT and resultant questions for translation into the clinic. Few clinical data are available until now and reasons as well as challenges for clinical implementation are discussed.

Permalink: https://www.hzdr.de/publications/Publ-21936
Publ.-Id: 21936


Production of no-carrier-added 135La at an 18 MeV cyclotron and its purification for investigations at a concentration range down to 10-15 mol/L

Mansel, A.; Franke, K.

The production of non-commercially available 135La by proton irradiation of an isotopically enriched [135Ba]BaCO3 target at a cyclotron is described. The purification of the radionuclide was performed by a La-selective resin. 135La was separated in no-carrier-added (n.c.a) form in a nitric acid solution with a radiochemical yield of 83% ± 5% and a total activity per batch of 43 MBq ± 3 MBq. The enriched [135Ba]Ba was recycled to the carbonate form with a recovery of 90% ± 3%. On the basis of a detection limit of 1 Bq/ml, solutions of n.c.a. 135La could be measured down to the 10-15 mol/l concentration range.

Keywords: Lanthanum-135; Isotopically enriched Barium-135 target; Proton induced nuclear reaction; Chemical separation; LN-Resin-A

Permalink: https://www.hzdr.de/publications/Publ-21935
Publ.-Id: 21935


Co-doping GaMnP with Zinc and Carbon

Hentschel, H.; Khalid, M.; Yuan, Y.; Helm, M.; Zhou, S.

Spintronics appears to be a new and exciting field of technology, but there is still a lag of suitable materials. In principle magnetic semiconductors (DMS) would be an excellent choice, but even their highest reached Curie temperature (Tc) in GaMnAs is still too low for practical usage. Ferromagnetism in DMS is suggested to be holes according to the Zener-Model. Therefore, it is expected to increase Tc by adding additional holes, e.g. co-doping. But there is a high risk to induce more defects, especially interstitial Mn atoms. Indeed, previous investigation revealed a lower Tc in carbon codoped GaMnAs [1]. Ion Implantation followed by laser annealing might overcome this problem. We choose ferromagnetic GaMnP since it shows insulating behavior [2]. Co-doping with shallow acceptors may lead to a more pronounced change in the conductivity of GaMnP. The samples were investigated with SQUID-VSM and Hall-Effect measurement. First results do not show an increase in Tc. Structural analysis is in progress to check if more defects appear upon carbon codoping.
[1] G. M. Schott, et al., Appl. Phys. Lett. 85, 4678 (2004).
[2] M. A. Scarpulla, et al., Phys. Rev. Lett., 95, 207204 (2005).

Keywords: DMS; Co-Doping; GaMnP

  • Lecture (Conference)
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21934
Publ.-Id: 21934


Carbon p Electron Ferromagnetism in SiC Single Crystal

Wang, Y.; Liu, Y.; Wang, G.; Anwand, W.; Jenkins, C. A.; Arenholz, E.; Munnik, F.; Gordan, O. D.; Salvan, G.; Zahn, D. R. T.; Chen, X.; Gemming, S.; Helm, M.; Zhou, S.

Defect induced ferromagnetism has been reported in wide-bandgap semiconductors as well as in carbon-based materials, when defects are introduced in an appropriate way. It is desirable to establish a direct relation between such ferromagnetism and defects. Here, we succeed to reveal the origin of defect-induced ferromagnetism using SiC by X-ray magnetic circular dichroism (XMCD). In addition, the theoretical model is calculated by first-principles theory. We show that the long-range ferromagnetic coupling is due to the p electrons of the nearest-neighbor carbon atoms around VSiVC divacancies. Thus, the ferromagnetism is traced down to its microscopic, electronic origin.

Keywords: XMCD; defect-induced ferromagnetism; SiC

  • Lecture (Conference)
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-21933
Publ.-Id: 21933


The PARIS cluster coupled to the BaFPro electronic module: data analysis from the NRF experiment at the γELBE facility

Wasilewska, B.; Bednarczyk, P.; Boiano, C.; Brambilla, S.; Camera, F.; Ciemala, M.; Dorvaux, O.; Giaz, A.; Jastrzab, M.; Kihel, S.; Kmiecik, M.; Maj, A.; Matea, I.; Massarczyk, R.; Mazumdar, I.; Mentana, A.; Napiorkowski, P.; Sowicki, B.; Schwengner, R.; Riboldi, S.; Zieblinski, M.

The first cluster of the constructed PARIS calorimeter was assembled and tested at the ELBE facility at HZDR, Dresden, Germany. The experiment was aimed at the evaluation of the performance of each detector separately as well as the whole PARIS cluster with discrete gamma-ray energies seen by the PARIS ranging up to 8.9 MeV. As the detectors use phoswich configuration, with 2'' x 2'' x 2'' LaBr3 (Ce) crystal coupled to 2'' x 2'' x 6'' NaI(Tl) one, great care must be taken during the data analysis process to obtain the best possible values for energy resolution. Two algorithms for data transformation from matrices created with slow vs fast pulse shaping to energy spectra were tested from which one was chosen for further analysis. An algorithm for adding back energies of -rays scattered inside the cluster was prepared, as well. Energy resolution for gamma-rays in 2­8 MeV range was estimated and is presented in this paper.

Keywords: LaBr3 detectors; NaI detectors; bremsstrahlung

Permalink: https://www.hzdr.de/publications/Publ-21931
Publ.-Id: 21931


Influence of calcium onto the sorption of uranium(VI) in the far-field of nuclear waste repositories

Richter, C.

Sorption of uranium(VI) onto orthoclase and muscovite, representing feldspars and micas as important components of the earth crust, was investigated in presence and absence of calcium under aerobic conditions. Batch experiments accompanied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) were performed. A reduction of the U(VI) sorption by calcium at pH ≥ 8 due to the formation of the Ca2UO2(CO3)3 complex was observed. An evaluation of the spectroscopic results by PARAFAC indicates the formation of three surface species ≡SiO2UO20, ≡SiO2UO2OH– and ≡SiO2UO2OHCO33–. The results improve the basis for a mechanistic modeling of the sorption onto orthoclase and muscovite, which is important for long-term safety analysis of waste repositories.

  • Lecture (Conference)
    Petrus PhD Conference 2015, 22.-26.06.2015, Nancy, France

Permalink: https://www.hzdr.de/publications/Publ-21930
Publ.-Id: 21930


Synthesis and Biodistribution Studies of 3H- and 64Cu-labeled Dendritic Polyglycerol and Dendritic Polyglycerol Sulfate

Pant, K.; Gröger, D.; Bergmann, R.; Pietzsch, J.; Steinbach, J.; Graham, B.; Spiccia, L.; Berthon, F.; Czarny, B.; Devel, L.; Dive, V.; Stephan, H.; Haag, R.

Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-inflammatory activity in vivo and thus represents a promising candidate for therapeutic and diagnostic applications. To investigate the in vivo pharmacokinetics in detail, dPGS with a molecular weight of ca. 10 kDa was radiolabeled with 3H and 64Cu, and evaluated by performing biodistribution studies and small animal positron emission tomography (PET). 3H-labeling was accomplished by an oxidation-reduction process with sodium periodate and [3H]-borohydride. 64Cu-labeling was achieved by conjugation of isothiocyanate- or maleimide-functionalized copper(II)-chelating ligands based on 1,4-bis(2-pyridinylmethyl)-1,4,7-triazacyclononane (DMPTACN) to an amino functionalized dPGS scaffold, followed by reaction with an aqueous solution containing 64CuCl2. Independent biodistribution by radioimaging and PET imaging studies with healthy mice and rats showed that the neutral dPG was quantitatively renally eliminated, whereas the polysulfated analogs accumulated mainly in the liver and spleen. Small amounts of the dPGS derivatives were slowly excreted via the kidneys. The degree of uptake by the reticuloendothelial system (RES) was similar for dPGS with 40% or 85% sulfation, and surface modification of the scaffold with the DMPTACN chelator did not appear to significantly affect the biodistribution profile. On the basis of our data, the applicability of bioactive dPGS as a therapeutic agent might be limited due to organ accumulation even after 3 weeks. The inert characteristics and clearance of the neutral polymer, however, underlines the potential of dPG as a multifunctional scaffold for various nanomedical applications.

Permalink: https://www.hzdr.de/publications/Publ-21929
Publ.-Id: 21929


Bibliotheksservices für Mitarbeiter des VKTA

Reschke, E.

VKTA-MitarbietrInnen sind externe Bibliotheksbenutzer. Im Vortrag werden die für externe Benutzer verfügbaren Bibliotheks- und Informationsservices vorgestellt.

Keywords: Library; Information services; Research Portal; eJournals; eBooks; Data bases

  • Lecture (others)
    VKTA-Leitungskreissitzung, 28.04.2015, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21928
Publ.-Id: 21928


K*(892)+ production in proton-proton collisions at Ebeam=3.5 GeV

Agakishiev, G.; Arnold, O.; Balanda, A.; Belver, D.; Belyaev, A. V.; Berger-Chen, J. C.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Chernenko, S.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Göbel, K.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kornakov, G.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Ladygin, V.; Lalik, R.; Lang, S.; Lapidus, K.; Lebedev, A.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, V.; Wagner, T.; Weber, M.; Wendisch, C.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.

Results on the K*(892)+ production in proton-proton collisions at a beam energy of E = 3.5 GeV, which is hitherto the lowest energy at which this mesonic resonance has been observed in nucleon-nucleon reactions, are presented. The data are interpreted with a two-channel model that includes the 3-body production of K*(892)+ associated with the Λ- or Σ-hyperon. The relative contributions of both channels are estimated. Besides the total cross section σ(p + p -> K*(892)+ + X) = 9.5 +- 0.9 +1.1-0.9 +- 0.7 μb, that adds a new data point to the excitation function of the K*(892)+ production in the region of the low excess energy, transverse momenta and angular spectra are extracted and compared with the predictions of the two-channel model. The spin characteristics of K*(892)+ are discussed as well in terms of the spin-alignment.

Permalink: https://www.hzdr.de/publications/Publ-21927
Publ.-Id: 21927


A novel inclined rotating tubular fixed bed reactor concept for enhancement of reaction rates and adjustment of flow regimes

Härting, H.-U.; Lange, R.; Larachi, F.; Schubert, M.

The inclined rotating tubular fixed bed reactor has been introduced recently as a novel reactor concept for multiphase processes, especially for heterogeneously catalyzed gas–liquid reactions with a mass transfer limitation of the gas phase (Härting et al., 2015; DOI: http://dx.doi.org/10.1016/j.ces.2015.02.008). It is based on the adjustment of a beneficial gas–liquid distribution in the cross section of the fixed bed that allows for complete utilization of the fixed bed accompanied by periodic wetting and draining of the catalyst.
The hydrodynamics in gas–liquid co-current downflow are studied by applying a compact gamma-ray computed tomography system for different organic liquids and gas phase properties as well as various fixed bed packing materials. Four different flow regimes with stratified, sickle, annular and dispersed flow patterns are identified. Pressure drop and liquid saturation are presented as a function of reactor inclination and rotation.
Inclination of the reactor is applied to force phase separation and the superimposed rotation of the clamped fixed bed results in a favorable wetting intermittency via periodic catalyst immersion. A significant rate enhancement of the hydrogenation of alpha-methylstyrene to cumene under severe limitations of the mass transfer of the gas phase is observed in the novel reactor concept at separated flow conditions. In addition, the potential for an efficient quenching of hotspots for exothermic reactions is demonstrated.

Keywords: Heterogeneous catalysis; Hydrogenation; Process intensification; Multiphase flow; Reactor inclination; Rotating fixed bed

Permalink: https://www.hzdr.de/publications/Publ-21926
Publ.-Id: 21926


Triadic resonances in numerical simulations of a precessing cylinder

Giesecke, A.

In the framework of the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) a next generation dynamo experiment is under construction at the Helmholtz-Zentrum Dresden-Rossendorf. In this experiment a fluid flow of liquid sodium in a cylindrical container, solely driven by precession, is considered as a possible source for magnetic field generation.

Precession has long been discussed as a complementary energy source for driving the geodynamo, and dynamo action generated by precession driven flows has been found in various numerical simulations in a sphere, ellipsoid, cube and cylinder. In the current study we perform hydrodynamic simulations of the three-dimensional non-linear Navier-Stokes equation in cylindrical geometry including weakly precessional forcing. The main focus is put on the development of the non-axisymmetric time-dependent instabilities that could be responsible for dynamo action like triadic resonances.

Our simulations reveal clear triads at aspect ratios and frequencies close to predictions from the linear inviscid theory with an amplitude below the forced m=1 mode so that most of the flow energy remains in the fundamental forced mode. Next step will be kinematic simulations in order to test the ability of the triades to provide for dynamo action.

Keywords: dynamo

  • Lecture (Conference)
    Stellar and Planetary Dynamos, 26.-29.05.2015, Goettingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-21925
Publ.-Id: 21925


Low-remanence criterion for helicity-dependent all-optical magnetic switching in ferrimagnets

Hassdenteufel, A.; Schmidt, J.; Schubert, C.; Hebler, B.; Helm, M.; Albrecht, M.; Bratschitsch, R.

We demonstrate that a low-remanent sample magnetization MR is crucial for all-optical magnetic switching (AOS) in ferrimagnets and ferrimagnet heterostructures. MR may be devised by the composition of the material. However, it can also be controlled in situ by changing the sample temperature because it affects MR. We show that increasing the lattice temperature by laser pulses or a simple heating resistor enables AOS in a ferrimagnetic Tb-Fe film, which does not exhibit AOS at room temperature. We reconcile earlier contradicting results for AOS in heated and cooled magnetic films by applying the low-remanence criterion. It also applies to other existing rare-earth transition-metal (RE-TM) alloys, such as GdFeCo or Tb-Co, to ferrimagnet heterostructures, and to RE-free synthetic ferrimagnets.

Keywords: remanence; all optical magnetic switching; helicity aos

Permalink: https://www.hzdr.de/publications/Publ-21924
Publ.-Id: 21924


Nanoscale modulated magnetization patterns for reproducible configurational and switchable static and dynamic properties films

McCord, J.; Trützschler, J.; Langer, M.; Mattheis, R.; Fassbender, J.

Domain wall (DW) imprinting in spatially varying magnetic property thin films is a novel method to obtain thin films with new effective magnetic characteristics ranging from static to dynamic applications. In order to generate such effective material systems, light ion irradiation is an advantageous method allowing for, e. g. laterally modified exchange bias (EB) directions, making the imprinting of artificial magnetic DW patterns possible. The magnetically hybrid structures with different unidirectional anisotropy directions are unique as, e.g. a domain pattern and domain walls can be imprinted directly into the magnetic material. A reproducible nucleation and positioning of magnetic domain walls in a high density arrangement is achieved. In dependence of the applied magnetic field amplitude, the system allows for an additional defined adjustment of the magnetic configuration with varying effective magnetic anisotropy.
Extended Ni19Fe81(50nm)/Ir23Mn77(7nm) thin films with an initial unidirectional anisotropy are patterned by local He-ion irradiation in the presence of a magnetic field, which is aligned perpendicular to the initial unidirectional anisotropy, and by which hybrid magnetization patterns with two different types of modulated directions of EB are obtained. The stripe width of the patterned thin films is varied down to 500 nm by one order of magnitude, being well below the distance of the magnetic Néel wall tails. The influence of the overlapping DW structures on the effective static and dynamic magnetization properties of the thin films are investigated by complementary inductive static and dynamic methods, magneto-resistive measurement techniques, by magneto-optical microscopy, and are as well supported by matching micromagnetic simulations. By this, a complete picture of spatial and temporal evolution of magnetization is derived.
In a zig-zag or head-to-tail configuration a folded magnetization forms (Fig.1), in which the magnetization is modulated along the magnetic net direction perpendicular to the stripes. In an alternating head-to-head/tail-to-tail configuration charged DWs form, favoring a modulated magnetization with low angle head-to-head and tail-to-tail configurations. In all cases the remanent magnetization along the net-magnetization of the films increases with decreasing feature size. The fixed position of the artificial DWs leads to pronounced two staged quasi-static magnetization reversal and, accordingly, different dynamic magneto-static modes are excited in the magnetic meta-material (Fig. 2).
We show that precessional frequencies of magnetic thin films can be directly influenced by means of high density DW imprinting (up to 104 DWs/sample). The static and dynamic magnetic response is tuned by imprinting periodic DW patterns with overlapping DW structures through selective ion irradiation. Mode coupling via dynamic magnetic charges in the periodically modulated magnetization patterns is directly provoked by adjusting the micromagnetic interface density. At the transition from the saturated magnetic phase to the domain wall phase the permeability spectra exhibit a pronounced discontinuous jump in the dynamic response, making an abrupt switch between two different dynamic states achievable. We show that the controlled introduction of micromagnetic DW objects is a unique way to tailor the effective magnetic properties of magnetic thin films. Dependencies of magnetic field angle, stripe-width and orientation of EB will be discussed.

Funding from the German Science Foundation DFG through (MC9/7-2; FA314/3-2) and the Heisenberg programme of the DFG (MC9/9-1) is highly acknowledged.

Keywords: Domain Walls; Exchange Bias; Ion Irradiation

  • Lecture (Conference)
    Intermag 2015, 11.-15.05.2015, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-21923
Publ.-Id: 21923


Über die Lorentzkraft-getriebene dreidimensionale Strömung um eine magnetische Kugel in einem elektrischen Feld

Weier, T.; Landgraf, S.; Cierpka, C.

Im Hinblick auf die in Deutschland beschlossene Energiewende ist die effiziente Energiespeicherung für die Netzstabilität enorm wichtig. Insbesondere für die Langzeitspeicherung gibt es zur Nutzung chemischer Energieträger, vor allem von Wasserstoff und Methanol auf Wasserstoffbasis, kaum Alternativen. Die notwendigen Prozessketten sind jedoch beim Strom-zu-Strom-Wirkungsgrad alternativen Speichertechniken deutlich unterlegen. Bei der Wasserstoffelektrolyse entstehen Wasserstoff- und Sauerstoffblasen. Diese verringern die Leitfähigkeit des Elektrolyten sowie die effektive Elektrodenoberfläche, was die Effizienz limitiert. Eine signifikante Effizienzsteigerung der Wasserstoffelektrolyse wird daher durch gezielt beschleunigtes Abtragen der Wasserstoffblasen von den Elektrodenoberflächen erwartet. In diesem Zusammenhang wurde in der jüngsten Vergangenheit die Beeinflussung der wandnahen Konvektionsströmung durch elektromagnetische Volumenkräfte, d.h. Lorentzkräfte, untersucht. Dazu stand bisher der makroskopische Einfluss der Lorentzkraft auf die Gesamtströmung im Vordergrund der Arbeit. Für eine genaue Analyse der durch die Volumenkräfte hervorgerufenen Effekte muss das Geschwindigkeitsfeld in der flüssigen Phase – insbesondere um die Gasblase – vermessen werden. Im vorliegenden Beitrag werden nominell parallele elektrische und magnetische Felder betrachtet. Da die Gasblasen nicht elektrisch leitend sind, werden die elektrischen Feldlinien abgelenkt und durch das Kreuzprodukt aus magnetischer Flussdichte und elektrischer Feldstärke entsteht eine Volumenkraft in unmittelbarer Umgebung der Blase. Da die Strömung um eine reale Einzelblase (d ~ 50 mum) messtechnisch schwer zu erfassen ist, sollen die grundlegenden Phänomene an einem größeren Modell untersucht werden.
Die sich einstellende Drehströmung wurde mittels der 2D2C Particle Image Velocimetry in mehreren Ebenen charakterisiert. Anschließend wurde die dreidimensionale Strömung mittels der 3D3C Astigmatism Particle Tracking Velocimetry zeitaufgelöst vermessen, um Partikeltrajektorien im Volumen zu verfolgen. Im finalen Beitrag wird die sich einstellende Strömung anhand der 2D2C/3D3C Ergebnisse neben der Darstellung der beiden Messverfahren ausführlich diskutiert.

Keywords: Lorentzkraft; Elektrolyse; Astigmatsim Particle Tracking Velocimetry; Particle Image Velocimetry

  • Lecture (Conference)
    Lasermethoden in der Strömungsmesstechnik, 08.-10.09.2015, Dresden, Deutschland
  • Contribution to proceedings
    Lasermethoden in der Strömungsmesstechnik, 08.-10.09.2015, Dresden, Deutschland
    Proceedings der 23. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", 978-3-9816764-1-9, 18-1-18-8

Permalink: https://www.hzdr.de/publications/Publ-21922
Publ.-Id: 21922


A step closer to the CW high brilliant beam with SRF gun II

Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.; Lu, P.; Vennekate, H.

In order to achieve CW electron beam with a high average current up to 1 mA and a very low emittance of 1 um, an improved superconducting photoinjector (SRF Gun II) has been installed and commissioned at HZDR since 2014. This new gun replaces the first 3.5-cell SRF gun at the SC Linac ELBE. The RF performance of the niobium cavity has been evaluated, the transverse and longitudinal beam parameters for low charge bunches have been measured, and the first beam has been guided into the ELBE beam line. The results agree with the simulation very well. The photocathode transfer system has been installed for the first high current beam test planned in 2015. In this contribution the results of the commissioning and the first beam parameters will be presented in detail.

  • Poster
    6th International Particle Accelerator Conference (IPAC'15), 03.-08.05.2015, Richmond, USA
  • Open Access Logo Contribution to proceedings
    6th International Particle Accelerator Conference (IPAC'15), 03.-08.05.2015, Richmond, USA
    Proceedings of IPAC'15, CERN: JACoW

Permalink: https://www.hzdr.de/publications/Publ-21921
Publ.-Id: 21921


Photocathodes for High Brightness Photo Injectors

Xiang, R.; Teichert, J.

The development of the photo-injector has become a significant technology for the future light sources and the electron-ion collider. There are a lot of opportunities to improve the electron source quality, also for the photocathodes. Especially for the high average power gun producing up to mA level of average current, the searching for the better photocathodes is a principal technical challenge. The photocathodes used in the electron gun require four important aspects: high efficiency, long life time, small transverse emittance and prompt time response. The quantum efficiency (QE) needs to be made more reliable, and the cathode material must be more robust. Thus there is a strong motivation to push the cathode R&D: one hand is to modify the present cathodes; the other hand is to search new materials.
In this presentation, we focus on the photocathode research for high brightness gun, DC or RF/SRF guns. There are several types of cathodes, such as the metallic photocathodes, the semiconductor photocathodes, and the recent superconducting (SC) cathodes and the new plasma-enhanced cathodes. The “conventional” normal conducting (NC) metallic photocathodes, such as Cu or Mg, are most robust for RF guns, but their QEs are pitifully very low, mostly on the level of 10-5. The semiconductor photocathodes, alkali antimonides, III-V GaAs(Cs), Cs2Te, have the best QE up to 1~10% but critical working environment is required. Among them, Cs2Te is relative robust and can be used in most of RF/SRF guns. And Cs2KSb achieves the highest current record 65mA in Cornell DC gun. The SC photocathodes consisting of Nb and Pb have been well investigated but the drive laser requirement is more challenging.

  • Lecture (Conference)
    LA³NET: The Laser Applications at Accelerators Conference 2015, 25.-27.03.2015, Mallorca, Spain
  • Open Access Logo Physics Procedia 77(2015), 58-65
    DOI: 10.1016/j.phpro.2015.11.010

Permalink: https://www.hzdr.de/publications/Publ-21920
Publ.-Id: 21920


Status and running experience of the SRF gun at HZDR

Xiang, R.; Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.

In order to achieve a high average current up to 1 mA with a low emittance of 1 mm
mrad at 77 pC, an improved SRF gun has been installed and commissioned at HZDR since 2014. This new gun replaces the first 3.5-cell SRF gun at the superconducting linear accelerator ELBE which had been in operation since 2007. The new gun has been tested first with a Cu photocathode. The RF performance of the niobium cavity has been evaluated, the transverse and longitudinal beam parameters for low charge bunches have been measured, and the first beam has been guided into the ELBE beamline. The photocathode transfer system is also installed for the first high current beam test in 2015. In this contribution the status of the gun and the results of this first measurement period will be presented in detail.

  • Lecture (Conference)
    DPG Frühjahrstagung 2015, 09.-13.03.2015, Wuppertal, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21919
Publ.-Id: 21919


The Tayler instability at low magnetic Prandtl numbers: between chiral symmetry breaking and helicity oscillations

Weber, N.; Galindo, V.; Stefani, F.; Weier, T.

The Tayler instability is a kink-type, current driven instability that plays an important role in plasma physics but might also be relevant in liquid metal applications with high electrical currents. In the framework of the Tayler-Spruit dynamo model of stellar magnetic field generation, the question of spontaneous helical (chiral) symmetry breaking during the saturation of the Tayler instability has received considerable interest. Focusing on fluids with low magnetic Prandtl numbers, for which the quasistatic approximation can be applied, we utilize an integro-differential equation approach in order to investigate the saturation mechanism of the Tayler instability. Both the exponential growth phase and the saturated phase are analyzed in terms of the action of the α and β effects of mean-field magnetohydrodynamics. In the exponential growth phase we always find a spontaneous chiral symmetry breaking which, however, disappears in the saturated phase. For higher degrees of supercriticality, we observe helicity oscillations in the saturated regime. For Lundquist numbers in the order of one we also obtain chiral symmetry breaking of the saturated magnetic field.

Keywords: Tayler instability; chiral symmetry breaking; helicity oscillation; Tayler Spruit dynamo

Permalink: https://www.hzdr.de/publications/Publ-21917
Publ.-Id: 21917


Validation of high-resolution gamma-ray computed tomography for quantitative gas holdup measurements in centrifugal pumps

Bieberle, A.; Schäfer, T.; Neumann, M.; Hampel, U.

In this paper, the capability of high-resolution gamma-ray computed tomography (HireCT) for quantitative gas-liquid phase distribution measurements in fluid machines is experimentally investigated. The object of interest thereby is an industrial centrifugal pump, which operates under two-phase flow conditions. The HireCT-System comprises a collimated 137Cs isotopic source, a radiation detector arc with a multi-channel signal processing unit, and a rotary unit enabling CT scans of objects with diameters of up to 700 mm. The accuracy of gas holdup measurement was validated on a sophisticated modular test mockup replicating defined gas-liquid distributions, which are expectable in impeller chambers of industrial centrifugal pumps under two-phase operation. Stationary as well as rotation-synchronized CT scanning techniques have been analyzed, which are both used to obtain sharply resolved gas phase distributions in rotating structures as well as non-rotating zones. A measuring accuracy of better than 1% for various distributed static gas holdups in the rotating frame has been verified with the modular test mockup using HireCT.

Keywords: Two-phase flow; gamma-ray computed tomography; gas holdup and centrifugal pump

Permalink: https://www.hzdr.de/publications/Publ-21916
Publ.-Id: 21916


Investigations of the interactions of subsurface living microorganisms with uranium

Gerber, U.; Krawczyk-Bärsch, E.; Anrold, T.

Actually the former uranium mine Königstein (Saxony, Germany) is in process of controlled flooding. Despite the high uranium concentrations of up to 14 mg/L and the low pH of 3,0 a high biodiversity was detected within this flooding water. Microorganisms are very important for bioremediation of uranium contaminated environments from activities such as uranium mining and extraction or fuel fabrication. Due to their ability to interact with radionuclides and heavy metals microorganisms could help to clean up the contaminated water in Königstein. With a culture dependent method it was possible to isolate different microorganisms from the flooding water. Tolerance tests displayed high resistances to uranium of these natural isolates. Furthermore uranium immobilization experiments show high rates of uranium binding to the cells. Some of the isolates are able to remove nearly 100% of the initial added uranium. TEM analysis showed two different interaction mechanisms, biosorption to the cell membrane and bioaccumulation within the cell.

Keywords: Uranium immobilization; Bioremediation; Königstein

  • Lecture (others)
    3. Workshop – TransAqua, 20.-21.04.2015, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21915
Publ.-Id: 21915


Lithological control on gas hydrate saturation as revealed by signal classification of NMR logging data

Bauer, K.; Kulenkampff, J.; Henninges, J.; Spangenberg, E.

In this paper, nuclear magnetic resonance (NMR) downhole logging data are analyzed with a new strategy to study gas hydrate-bearing sediments in the Mackenzie Delta (NW Canada). In NMR logging, T2 distribution curves are usually used to determine single-valued parameters such as apparent total porosity or hydrocarbon saturation. Our approach analyzes the entire T2 distribution curves as quasi-continuous signals to characterize the rock formation. We apply self-organizing maps, a neural network clustering technique, to sub-divide the data set of NMR curves into classes with a similar and distinctive signal shape. The method includes (1) preparation of data vectors, (2) unsupervised learning, (3) cluster definition, and (4) classification and depth mapping of all NMR signals. Each signal class thus represents a specific pore size distribution which can be interpreted in terms of distinct lithologies and reservoir types. A key step in the interpretation strategy is to reconcile the NMR classes with other log data not considered in the clustering analysis, such as gamma ray, hydrate saturation and other logs. Our results defined six main lithologies within the target zone. Gas hydrate layers were recognized by their low signal amplitudes for all relaxation times. Most important, two sub-types of hydrate-bearing shaly sands were identified. They show distinct NMR signals and differ in hydrate saturation and gamma ray values. An inverse linear relationship between hydrate saturation and clay content was concluded. Finally, from the interpretations of the classified NMR signals we infer a non-cementing, pore-filling growth habit for the gas hydrates.

Keywords: gas hydrates; NMR logging; self-organizing maps; shaliness; Mackenzie Delta

Permalink: https://www.hzdr.de/publications/Publ-21914
Publ.-Id: 21914


Investigations of the interactions of subsurface living microorganisms with uranium

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Kothe, E.

Actually the former uranium mine Königstein (Saxony, Germany) is in process of controlled flooding. Despite the high uranium concentrations of up to 14 mg/L and the low pH of 3,0 a high biodiversity was detected within this flooding water. Microorganisms are very important for bioremediation of uranium contaminated environments from activities such as uranium mining and extraction or fuel fabrication. Due to their ability to interact with radionuclides and heavy metals microorganisms could help to clean up the contaminated water in Königstein. With a culture dependent method it was possible to isolate different microorganisms from the flooding water. Tolerance tests displayed high resistances to uranium of these natural isolates. Furthermore uranium immobilization experiments show high rates of uranium binding to the cells. Some of the isolates are able to remove nearly 100% of the initial added uranium. TEM analysis showed two different interaction mechanisms, biosorption to the cell membrane and bioaccumulation within the cell.

Keywords: Uranium immobilization; Bioremediation; Königstein

  • Lecture (Conference)
    2. Projektstatusgespräch zu BMBF-geförderten Forschungs- und Entwicklungsvorhaben auf dem Gebiet der "Nuklearen Sicherheits- und Entsorgungsforschung sowie Strahlenforschung", 25.-26.03.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21913
Publ.-Id: 21913


Structural and electrical properties of sulfur doped Si by ion implantation

Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Skorupa, W.; Helm, M.; Zhou, S.

Hydoping Si with chalcogens is one of the effective approaches to form an intermediate band (IB). This IB material is a candidate of infrared photodetectors and intermediate band solar cells. However, the chalcogens have relatively low solid solubility limit in Si. We prepared sulfur doped silicon to above the Mott insulator concentration by ion implantation followed by pulsed laser annealing. The degree of crystalline lattice recovery in implanted layers and the lattice location of sulfur in Si were analyzed by Rutherford backscattering spectrometry / Channeling. Our results show that S atoms are occupying substitutional lattice sites in Si. We also observe an insulator-to-metal transition in silicon hyperdoped with sulfur to concentrations well above the maximum solubility limit of about 3×1016 cm-3[1]. Analyzing temperature-dependent conductivity data, we find that a transition from insulating to metallic conduction occurs at a peak sulfur concentration of around 1×1021 cm-3.

Keywords: Hydoping; sulfur; insulator-to-metal transition; lattice location

  • Lecture (Conference)
    DPG 2015 Spring Meeting, 15.-20.03.2015, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-21912
Publ.-Id: 21912


A review of graphite beneficiation techniques

Chehreh Chelgani, S.; Rudolph, M.; Kratzsch, R.; Sandmann, D.

Graphite as a naturally occurring crystalline carbon is required for many different applications such as batteries, refractories, electrical products, pencils, etc. Many new graphite deposits are currently being extracted to help meet the growing demand. It is among the list of critical raw materials by the European Union. Graphite ore is mostly beneficiated using flotation separation techniques. The increasing demand for high grade graphite products with up to 99.99% carbon has led to develop various methods to remove impurities even to ppm range. This paper considers separation and purification techniques that are currently employed for graphite mineral beneficiation and identifies areas in need of further research.

Keywords: Graphite; Liberation; Flotation; Leaching; Roasting; Microwave; Kish

Permalink: https://www.hzdr.de/publications/Publ-21911
Publ.-Id: 21911


Radiosynthesis of a [18F]-quinuclidine 1,2,3-thiazole derivative as PET radioligand for neuroimaging of the α7 nicotinic acetylcholine receptor

Sarasamkan, J.; Fischer, S.; Scheunemann, M.; Brust, P.; Vajragupta, O.

Aim
The α7 nicotinic acetylcholine receptor (α7nAChR) is well recognized as a key receptor involved in memory formation and cognition which implicates its involvement in the pathophysiology of neurodegenerative disorders. Currently, this receptor subtype is one of the most attractive targets for neuroimaging to monitor the etiology and progression of brain diseases such as schizophrenia and Alzheimer’s disease (AD). Therefore, a new PET radioligand selective to α7nAChR was developed in this study. The structure of the developed ligand is based on a novel potent and selective α7nAChR agonist, 3-(4-hydroxyphenyl-1,2,3-triazol-1-yl) quinuclidine (QND8) which demonstrated cognitive enhancement in mice [1].
Materials and methods
The structure of the radioligand (18F-QND) was modified from QND8 by replacing the hydroxyl (OH) group with fluorine. After synthesis of the starting quinuclidine azide and aryl alkyne, F-QND and its precursor were synthesized by copper-catalyzed azide-alkyne cycloaddition (CuAAC) or click chemistry. Their structures were confirmed by 1H-NMR, 13C-NMR and mass spectrometry (MS). 18F-QND was radiolabeled by nucleophilic substitution of the nitro precursor. Altered amounts of kryptofix and various conditions (solvent and temperature) were chosen to improve the radiolabeling yield. The radiolabeled compound was separated and purified by chromatography. The radiochemical yield and radiochemical purity were analyzed by radio-thin layer chromatography and radio-high performance liquid chromatography. Non-radioactive references were used to confirm the stereochemistry of the nitro-precursor and F-QND.
Results
The chemical yields of the nitro-precursor (NO2-QND) and the reference standard (F-QND) were 21% and 11%, respectively, with purity higher than 95%. The radiolabeling yield of 18F-QND was 7% with radiochemical purity > 98% and specific activity of 65 GBq/µmol. The stereochemistry study approved that both compounds were optically active. Therefore, the developed radiochemical processes can be applied for the radiosynthesis of further 18F-QND-derivatives.
Conclusion
Radiosynthesis of 18F-QND was accomplished by nucleophilic substitution of the phenyl-nitro compound. However, at high temperature racemization currently cannot be excluded.
References
1. Chalon S, Guilloteau D, PIN F, Routier S, Suzenet F, Vercouillie J. Centre National De La Recherche Scientifique (C.N.R.S). Patent WO2012143526A1, Oct. 6, 2012.

  • Poster
    EANM 2015 - Annual Congress of the European Association of Nuclear Medicine, 10.-14.10.2015, Hamburg, Deutschland
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 42(2015), 279

Permalink: https://www.hzdr.de/publications/Publ-21910
Publ.-Id: 21910


Robust increase of the translocator protein 18 kDa (TSPO), demonstrated with radiotracer [123I]CLINDE, in an adult rat model of Traumatic Brain Injury

Donat, C. K.; Gaber, K.; Meixensberger, J.; Brust, P.; Pinborg, L. H.; Mikkelsen, J. D.

Question
Traumatic brain injury (TBI) can result in long-term disability, but the mechanisms are not fully elucidated. Neuroinflammation is part of these secondary injury mechanisms, and is therefore regarded as a potential target for treatment and diagnostics employing molecular imaging techniques. TSPO, a protein in the mitochondrial membrane, is robustly upregulated in response to injury and neuroinflammation, making it a marker. We therefore hypothesize that TSPO is time-dependently upregulated after TBI. This was investigated in a rat model of TBI, employing the TSPO-selective and clinically relevant radioligand [123I]CLINDE.
Methods
Adult male Sprague-Dawley rats were randomized into four groups (survival time: 6, 24, 72 h and 28 d). Animals were anaesthetized and subjected to either sham injury, craniotomy or mild-to-moderate (2 mm impact depth at 4 m/sec) controlled cortical impact injury (CCI). Drug/surgery-naïve animals were included in the study. Frozen coronal sections were cut and TSPO binding was assessed in the vicinity of the injury (M1 motor cortex, 3.5 mm posterior and +4.0 mm lateral to bregma) with in vitro autoradiography.
Results
Binding of [123I]CLINDE was nearly uniform and displaceable (10 µMol/L PK1195) in the brains of naïve and sham-operated animals.
At 24 h, injured animals exhibited a significant increase in binding in the whole ipsilateral hemisphere (49%) and the ipsilateral M1 cortex (201%). Interestingly, CCI also resulted in an elevated binding in the contralateral M1 cortex (38%). [123I]CLINDE binding was maximally increased at 72 h after CCI in the whole ipsilateral hemisphere (368 %) and M1 cortex (1076%). Again, TBI significantly increased binding in the contralateral whole hemisphere (29%) and M1 cortex (32%).
Craniotomy, without TBI, produced a significant increase in TSPO at 24 h in the ipsilateral M1 cortex (42%) and at 72h in the ipsilateral hemisphere (232%) and M1 cortex (598%). At 6 h and 28 d, [123I]CLINDE binding was not significantly different between the groups.
Conclusions
[123I]CLINDE binding, reflecting TSPO, was significantly increased after experimental TBI, which corresponds to the time-course of the inflammatory response. This makes [123I]CLINDE a suitable radiotracer for the assessment brain injury in TBI and the monitoring of anti-inflammatory (pharmaco)therapies.

  • Poster
    60th Annual Meeting of the German Society for Neuropathology and Neuroanatomy, 26.-28.08.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21909
Publ.-Id: 21909


Low-energy magnetic radiation: Deviations from GOE

Frauendorf, S.; Schwengner, R.; Wimmer, K.

A pronounced spike at low energy in the strength function for magnetic radiation (LEMAR) is found by means of Shell Model calculations, which explains the experimentally observed enhancement of the dipole strength. LEMAR originates from statistical low-energy M1-transitions between many excited complex states. Re-coupling of the proton and neutron high-j orbitals generates the strong magnetic radiation. LEMAR is closely related to Magnetic Rotation. LEMAR is predicted for nuclides participating in the r-process of element synthesis and is expected to change the reaction rates. An exponential decrease of the strength function and a power law for the size distribution of the B(M1) values are found, which strongly deviate from the ones of the GOE of random matrices, which is commonly used to represent complex compound states.

Keywords: Magnetic dipole radiation; nuclearstructure; nuclear shell model; Gaussian Orthogonal Ensemble

Permalink: https://www.hzdr.de/publications/Publ-21908
Publ.-Id: 21908


Operational Experience at ELBE

Michel, P.; Lehnert, U.; Seidel, W.

The ELBE center for high power radiation sources is the largest user facility in the Helmholtz-Zentrum Dresden-Rossendorf. The facility is based on a 36 MeV superconducting RF Linac which can be operated up to 1.6 mA in cw mode. The electron beam is used to generate secondary radiation, such as infrared light (Free Electron Lasers), coherent THz radiation, MeV-Bremsstrahlung, fast neutrons and positrons for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations. Two high power laser systems (500 TW Ti:Sa laser, 2 PW diode pumped laser) are under construction for laser acceleration experiments and X-ray generation by Thomson scattering. The FELs are in operation since 2004 (mid-IR FEL, 4-22µm) and 2006 (far-IF FEL, 20-250µm). The fundamental features of the ELBE IR FELs, the FEL instrumentation and advanced beam diagnostics for the photon beam are described. During ten years of user operation experiences and statistical data were collected.

Keywords: ELBE; FEL; FELBE; operational Experience

  • Contribution to proceedings
    SPIE, Advances in X-ray Free-Electron Lasers Instrumentation, 13.-16.04.2015, Prague, Czechia
    Proceedings of SPIE 9512
    DOI: 10.1117/12.2181503
  • Lecture (Conference)
    SPIE, Advances in X-ray Free-Electron Lasers Instrumentation, 13.-16.04.2015, Prague, Czechia

Permalink: https://www.hzdr.de/publications/Publ-21906
Publ.-Id: 21906


Use of AC magnetic fields for flow control in solidifying metallic alloys

Räbiger, D.; Vogt, T.; Gerbeth, G.; Eckert, S.

AC magnetic fields unlock an enormous potential to realize a variety of flow structures in molten metals, which makes the electromagnetic stirring attractive for controlling the melt flow during solidification. We present an experimental study concerning the solidification of AlSi alloys exposed to a pulsed rotating magnetic field. Isothermal flow measurements were carried out in order to understand the flow structures resulting from the application of time-modulated magnetic fields. These investigations revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures. An intense melt flow with periodic reversals of the flow direction at the solidification front can be created by a suitable choice of the magnetic field parameters. Such resonant states of the flow pattern have been proven to provide beneficial conditions for solidification processes. Optimized flow conditions realized in a solidifying melt result in a significant grain refinement without provoking the formation of harmful segregation freckles.

  • Lecture (Conference)
    TMS 2016 145th ANNUAL MEETING & EXHIBITION, 15.-19.03.2015, Orlando, USA

Permalink: https://www.hzdr.de/publications/Publ-21905
Publ.-Id: 21905


Melt flow and grain refinement in Al-Si alloys solidified under the influence of applied electric currents

Räbiger, D.; Zhang, Y.; Galindo, V.; Franke, S.; Eckert, S.

The application of electric currents during solidification can cause grain refinement in metallic alloys. However, the knowledge about the mechanisms underlying the decrease in grain size remains fragmentary. This study considers the solidification of Al Si alloys under the influence of electric currents for the configuration of two parallel electrodes at the free surface. Solidification experiments were performed under the influence of both direct currents (DC) and rectangular electric current pulses (ECP). The interaction between the applied current and its own induced magnetic field causes a Lorentz force which produces an electro-vortex flow. Numerical simulations were conducted to calculate the Lorentz force, the Joule heating and the induced melt flow. The numerical predictions were confirmed by isothermal flow measurements in eutectic GaInSn. The results demonstrate that the grain refining effect observed in our experiments can be ascribed solely to the forced melt flow driven by the Lorentz force.

Keywords: Grain refinement; Al-Si alloys; External electric field

  • Lecture (Conference)
    TMS 2015 144th ANNUAL MEETING & EXHIBITION, 15.03.-19.04.2015, Orlando, USA
  • Contribution to proceedings
    TMS 2016 145th ANNUAL MEETING & EXHIBITION, 15.-19.03.2015, Orlando, USA
    TMS 2016 145th ANNUAL MEETING & EXHIBITION - COLLECTED PROCEEDINGS
    DOI: 10.1002/9781119093466.ch5

Permalink: https://www.hzdr.de/publications/Publ-21904
Publ.-Id: 21904


Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge

Jain, R.; Seder-Colomina, M.; Jordan, N.; Dessi, P.; Cosmidis, J.; van Hullebusch, E. D.; Weiss, S.; Farges, F.; Lens, P. N. L.

Selenite containing wastewaters can be treated in activated sludge systems, where the total selenium is removed from the wastewater by the formation of elemental selenium nanoparticles, which are trapped in the biomass. No studies have been carried out so far on the characterization of selenium fed activated sludge flocs, which is important for the development of this novel selenium removal process. This study showed that more than 93% of the trapped selenium in activated sludge flocs is in the form of elemental selenium, both as amorphous/ monoclinic selenium nanospheres and trigonal selenium nanorods. The entrapment of the elemental selenium nanoparticles in the selenium fed activated sludge flocs leads to faster settling rates, higher hydrophilicity and poorer dewaterability compared to the control activated sludge (i.e. not fed with selenite). The selenium fed activated sludge showed a less negative surface charge density as compared to control activated sludge. The presence of trapped elemental selenium nanoparticles further affected the spatial distribution of Al and Mg in the activated sludge flocs. This study demonstrated that the formation and subsequent trapping of elemental selenium nanoparticles in the activated sludge flocs affects their physicochemical properties.

Keywords: selenium; nanoparticles; activated sludge; physicochemical; settleability; surface charge

Permalink: https://www.hzdr.de/publications/Publ-21902
Publ.-Id: 21902


Electron Probe Microanalysis of REE in Eudialyte Group Minerals: Challenges and Solutions

Atanasova, P.; Krause, J.; Moeckel, R.; Osbahr, I.; Gutzmer, J.

The accurate quantification of the chemical composition of eudialyte group minerals with the electron probe microanalyzer is complicated by both mineralogical and X-ray-specific challenges. These include structural and chemical variability, mutual interferences of X-ray lines, in particular of the rare earth elements, diffusive volatility of light anions and cations and instability of eudialyte group minerals under the electron beam.
A novel analytical approach has been developed to overcome these analytical challenges. The effect of diffusive volatility and beam damage is shown to be minimal when a square of 20x20 µm is scanned with a beam diameter of 6 µm at the fastest possible speed, while measuring elements critical to electron beam exposure early in the measurement sequence. Appropriate reference materials are selected for calibration considering their volatile content and composition, and supplementary offline overlap correction is performed using individual calibration factors. Preliminary results indicate good agreement with data from laser ablation inductively coupled plasma mass spectrometry demonstrating that a quantitative mineral chemical analysis of eudialyte group minerals by electron probe microanalysis is possible once all the parameters mentioned above are accounted for.

Keywords: Rare earth elements; eudialyte; electron probe microanalyzer; electron microprobe; beam conditions; diffusive volatility; interferences; reference material

Permalink: https://www.hzdr.de/publications/Publ-21901
Publ.-Id: 21901


Optical ridge waveguides in Yb:YAG laser crystal produced by combination of swift carbon ion irradiation and femtosecond laser ablation

Cheng, Y.; Lv, J.; Akhmadaliev, S.; Hernández-Palmero, I.; Romero, C.; Vázquez De Aldana, J. R.; Zhou, S.; Chen, F.

We report on the fabrication of optical ridge waveguides in ytterbium-doped yttrium aluminum garnet (Yb:YAG) single crystal by applying swift C5+ ion irradiation and the followed femtosecond laser ablation. The planar waveguide layer is first produced by C5+ ion irradiation and the laser ablation is used to microstructure the planar waveguide surface to construct ridge structures. The lowest propagation loss of the ridge waveguide has been determined to be ~2.1 dB/cm. From the confocal micro-fluorescence and micro-Raman spectra obtained from the waveguide regions, the intensities, positions and widths of the emission-line peaks had no obvious changes with respect to those from the bulks, which indicate that C5+ ion irradiation does not affect the bulk-related properties of the Yb:YAG crystal significantly in the waveguide regions. The results obtained in this work suggest potential applications of the Yb:YAG ridge waveguides as integrated laser sources.

Keywords: Optical ridge waveguides; Swift ion irradiation; Femtosecond laser ablation

Permalink: https://www.hzdr.de/publications/Publ-21900
Publ.-Id: 21900


Experimentelle Untersuchung zur Strömungsbeeinflussung mittels elektromagnetischer Bremsen beim kontinuierlichen Strangguss von Stahl

Timmel, K.

Beim kontinuierlichen Stranggießen von Stahl werden elektromagnetische Felder zur Strömungsbeeinflussung eingesetzt. In dieser Arbeit wird die Wirkung eines statischen Magnetfeldes auf die Kokillenströmung in einem Modellexperiment untersucht. Das statische Magnetfeld strukturiert die Strömung um, kann lokal die Strömungsgeschwindigkeiten erhöhen und verändert die Ausbildung und Anzahl der für Brammenkokillen typischen großskaligen Wirbel. Es zeigt sich weiterhin, dass die elektrische Leitfähigkeit der Kokillenwände einen entscheidenden Einfluss auf die Wirkung einer elektromagnetischen Bremse hat. Unter isolierenden Wänden werden räumliche Oszillationen des Flüssigmetallstrahles initiiert und es bildet sich zwischen den beiden Kokillenhälften eine asymmetrische Strömung aus. Leitfähige Wände verhindern die Oszillationen und die Kokillenströmung ist symmetrisch. Eine eindeutige bremsende Wirkung der elektromagnetischen Bremse auf den Durchfluss konnte jedoch in beiden Fällen nicht festgestellt werden.

Keywords: Continuous Casting of steel; liquid metal model; electro-magnetic brake; Ultrasonic-Doppler-Velocimetry

  • Doctoral thesis
    TU Bergakademie Freiberg, 2014
    Mentor: Prof. Dr.-Ing. Rüdiger Schwarze
    196 Seiten
  • Book (Authorship)
    Freiberg: Verlag der TU Bergakademie Freiberg, 2015
    240 Seiten

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-21899
Publ.-Id: 21899


Ferromagnetic and paramagnetic magnetization of implanted GaN:Ho,Tb,Sm,Tm films

Maryško, M.; Hejtmánek, J.; Laguta, V.; Sofer, Z.; Sedmidubský, D.; Šimek, P.; Veselý, M.; Mikulics, M.; Buchal, C.; Macková, A.; Malínský, P.; Wilhelm, R. A.

The SQUID magnetic measurements were performed on the GaN films prepared by metal-organic vapour phase epitaxy and implanted by Tb3+, Tm3+, Sm3+, and Ho3+ ions. The sapphire substrate was checked by the electron paramagnetic resonance method which showed a content of Cr3+ and Fe3+ impurities. The samples 5 × 5 mm2 were positioned in the classical straws and within an estimated accuracy of 10−6 emu, no ferromagnetic moment was detected in the temperature region of 2–300 K. The paramagnetic magnetization was studied for parallel and perpendicular orientation. In the case of GaN:Tb sample, at T = 2 K, a pronounced anisotropy with the easy axis perpendicular to the film was observed which can be explained by the lowest quasi-doublet state of the non-Kramers Tb3+ ion. The Weiss temperature deduced from the susceptibility data using the Curie-Weiss (C-W) law was found to depend substantially on the magnetic field.

Permalink: https://www.hzdr.de/publications/Publ-21898
Publ.-Id: 21898


The inclined rotating tubular fixed bed reactor for process intensification of heterogeneous catalytic multiphase reactions

Härting, H.-U.; Lange, R.; Schubert, M.

The inclined rotating tubular fixed bed reactor has been introduced recently as a new concept for the implementation of multiphase processes, in particular for hetero-geneously catalysed gas-liquid reactions. Commonly applied trickle bed reactors (TBR) suffer from liquid maldistribution and low mass and heat transfer rates and have therefore been subject to process intensification: periodic liquid flow rate modulation at the reactor inlet was introduced, which leads to elevated space time yields in comparison to steady-state operation. However, the beneficial effects decay rapidly along the reactor length and maldistribution is not effectively curbed.
To fully utilise the positive effects of such modulation strategy, the new reactor concept is operated inclined against the vertical and rotated permanently. This operation mode ensures a wetting intermittency via periodic immersion of the whole catalyst packing, which is clamped between retaining grids. Furthermore, it allows adjusting different flow regimes, i.e. stratified flow or annular flow.
The new reactor concept enables also tuning the liquid residence time at constant gas and liquid flow rates. The wetting intermittency results in a complete utilization of the catalyst on the reactor scale and in thinner liquid films at the catalyst surface, which enhances the accessibility of the active sites for the gaseous reactants. The latter is proven by an increased space time yield compared to conventional TBR operation for the hydrogenation of α-methylstyrene to cumene.
In this presentation, the performance of the new reactor concept will be assessed based on reactive studies. Furthermore, the results will be discussed with respect to the prevailing flow regimes investigated via gamma-ray computed tomography, as well as liquid residence time and axial dispersion obtained by a stimulus-response technique using embedded wire mesh sensors.

Keywords: Hydrogenation; Heterogeneous Catalysis; Multiphase Flow; Flow Regimes

  • Lecture (Conference)
    ESCRE 2015 - European Symposium on Chemical Reaction Engineering, 27.-30.10.2015, Fürstenfeldbruck, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21897
Publ.-Id: 21897


Bacterial Diversity in Clay and Actinide Interactions with Bacterial Isolates in Relation to Nuclear Waste Disposal

Moll, H.; Lütke, L.; Cherkouk, A.

One potential source of radionuclides in the environment could be the accidental release from nuclear waste disposal sites. Hence the long-term safety of nuclear waste in a deep geological repository is an important issue in our society. Microorganisms indigenous to potential host rocks are able to influence the speciation and therefore the mobility of radionuclides and their retardation both by direct and indirect pathways. They can as well affect the conditions in a geologic repository (e.g., by gas generation or canister corrosion). The focus of this chapter lies on the influence of indigenous microbes on the speciation of Rn. Therefore, for the safety assessment of such a repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay and salt) and if these microorganisms can influence the speciation of released Rn. Hence, dominant bacterial strains from potential host rocks for future nuclear waste deposition have to be investigated regarding their interaction mechanisms with soluble actinide (An) ions. This chapter will cover the following research areas. Gained knowledge concerning the bacterial diversity in e.g., Mont Terri Opalinus Clay by applying direct molecular culture-independent retrievals and cultivation experiments will be presented. Their influence on the geo-chemical behavior of selected An (e.g., uranium, and curium) will be highlighted. These investigations contribute to a better understanding of microbial interactions of An on a molecular level for an improved prediction of the safety of a planned nuclear waste repository.

Keywords: bacterial diversity; bacteria; complexation; uranium; curium; Sporomusa sp; Paenibacillus sp; TRLFS; potentiometry

  • Book chapter
    Clemens Walther, Dharmendra K. Gupta: Radionuclides in the Environment - Influence of chemical speciation and plant uptake on radionuclide migration, Heidelberg: Springer, 2015, 978-3-319-22171-7, 209-229
    DOI: 10.1007/978-3-319-22171-7_12

Permalink: https://www.hzdr.de/publications/Publ-21896
Publ.-Id: 21896


Helium Ion Microscopy

Hlawacek, G.; Gölzhäuser, A.

This book covers the fundamentals of Helium Ion Microscopy (HIM) including the Gas Field Ion Source (GFIS), column and contrast formation. It also provides first hand information on nanofabrication and high resolution imaging. Relevant theoretical models and the existing simulation approaches are discussed in an extra section. The structure of the book allows the novice to get acquainted with the specifics of the technique needed to understand the more applied chapters in the second half of the volume. The expert reader will find a complete reference of the technique covering all important applications in several chapters written by the leading experts in the field. This includes imaging of biological samples, resist and precursor based nanofabrication, applications in semiconductor industry, using Helium as well as Neon and many more. The fundamental part allows the regular HIM user to deepen his understanding of the method. A final chapter by Bill Ward, one of the pioneers of HIM, covering the historical developments leading to the existing tool complements the content.

Keywords: Helium Ion Microscopy; Focused ion beam; high resolution imaging; nano-fabrication; gas field ion source

  • Book (Editorship)
    Heidelberg: Springer International Publishing Switzerland, 2016
    526 Seiten
    ISBN: 9783319419886

Permalink: https://www.hzdr.de/publications/Publ-21895
Publ.-Id: 21895


Speciation studies of uranyl(VI) using an advanced combination of theoretical and luminescence spectroscopic methods

Drobot, B.; Tsushima, S.; Steudtner, R.; Raff, J.; Geipel, G.; Brendler, V.

Speciation constitutes the basis for actinide complexation studies. These systems can be very complex and challenging especially because of the polynuclear species. An advanced combination of theoretical and experimental methods is proposed here. Continuous wave (CW) and time-resolved laser-induced fluorescence spectroscopy (TRLFS) data of uranyl(VI) hydrolysis were analyzed using parallel factor analysis (PARAFAC). Distribution patterns of five major species were thereby derived under a fixed uranyl concentration (10-5 M) over a wide pH range from 2 to 11. UV (180 nm to 370 nm) excitation spectra were extracted for individual species. Time-dependent density functional theory (TD-DFT) calculations revealed ligand excitation (water, hydroxo, oxo) in this region and ligand-to-metal charge transfer (LMCT) responsible for luminescence. Thus excitation in the UV is extreme ligand sensitive and highly specific. Combining findings from PARAFAC and DFT the aquo complex (1:0) and four hydroxo complexes (1:1, 3:5, 3:7 and 1:3) were identified and characterized.

  • Lecture (Conference)
    Anakon 2015, 23.-26.03.2015, Graz, Östereich

Permalink: https://www.hzdr.de/publications/Publ-21894
Publ.-Id: 21894


Synthesis, 18F-radiolabelling and biological characterization of novel fluoroalkylated triazine derivatives for in vivo imaging of phosphodiesterase 2A in brain via positron emission tomography

Schröder, S.; Wenzel, B.; Deuther-Conrad, W.; Teodoro, R.; Egerland, U.; Kranz, M.; Scheunemann, M.; Höfgen, N.; Steinbach, J.; Brust, P.

Phosphodiesterase 2A (PDE2A) is highly and specifically expressed in particular brain regions affected by neurological disorders and in certain tumors. Development of a specific PDE2A radioligand enables molecular imaging of the PDE2A protein via positron emission tomography (PET). Herein we report on the syntheses of three novel fluoroalkylated triazine derivatives (TA2-4) and on the evaluation of their effect on the enzymatic activity of human PDE2A. The most potent PDE2A inhibitors were 18F-radiolabelled ([1818F]TA4) and investigated regarding their potential as PET radioligands for imaging of PDE2A in mouse brain. In vitro autoradiography on rat brain showed region-specific distribution of [18F]TA3 and [18F]TA4, which is consistent with the expression pattern of PDE2A protein. Metabolism studies of both [18/F]TA3 and [18F]TA4 in mice discovered a significant accumulation of two major radiometabolites of each radioligand in brain as investigated by micellar radio-chromatography. Small-animal PET/MR studies in mice using [18F]TA3 revealed a constantly increasing uptake of activity in the non-target region cerebellum, which may be caused by the accumulation of brain penetrating radiometabolites. Hence, [18F]TA3 and [18F]TA4 are exclusively suitable for in vitro investigation of PDE2A. Nevertheless, further structural modification of these promising radioligands might result in metabolically stable derivatives.

Keywords: PDE2A; Alzheimer´s disease; PET imaging in brain; micellar HPLC

Permalink: https://www.hzdr.de/publications/Publ-21893
Publ.-Id: 21893


Quantifying 3D tracer velocity and porosity on core scale from 3D GeoPET image sequences

Eichelbaum, S.; Lippmann-Pipke, J.; Korn, N.; Kulenkampff, J.

Flow and transport simulations in geomaterials are commonly conducted on high-resolution tomograms (µCT) of the pore structure or stochastical models that are calibrated with measured integral quantities, like break through curves (BTC). Yet, there existed virtually no method for experimental verification of the simulated velocity distribution results.
Positron emission tomography (PET) has unrivaled sensitivity and robustness for non-destructive quantitative spatio-temporal measurement of tracer concentrations in body tissue. We empowered PET for its applicability in opaque/geological media (GeoPET). Thus it is the appropriate method for experimental verification and calibration of computer simulations of pore-scale transport by means of the observed propagation of a tracer pulse, cPET(x,y,z,t).
As a principal concept, velocity and residence time distributions, as well as the tortuous pathway topology, principally can be derived directly from cPET(x,y,z,t). However, the fundamental experimental limit of finite signal to noise ratios is manifested in apparently intermittent propagation pathways, with gaps in zones where the concentration cPET falls below the significance threshold. This hampers the direct parameter estimation of velocity, v(x,y,z), and porosity distribution n(x,y,z) from cPET(x,y,z,t).

This issue is overcome to some extent by introduction of causality (continuity) into the here presented evaluation algorithm.

Likely Topics in math & comp. sciences
1) Space-Time Processes
2) Image Analysis
3) Numerical Modelling and Numerical Simulation
4) Inverse Problem solving
5) other computer sciences methods

Likely Geoscience topics:
1) Water: sea, surface and subsurface

  • Lecture (Conference)
    IAMG 2015, The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21892
Publ.-Id: 21892


Electrical Conductance of DNA Oligomers — A Review of Experimental Results

Erbe, A.

the publication has no abstract

Keywords: DNA; molecular electronics

  • Book chapter
    Eugen Stulz and Guido Clever: DNA in supramolecular chemistry and nanotechnology, Chichester UK: John Wiley & Sons Limited, 2015, 978-1-118-69686-6, 94-101

Permalink: https://www.hzdr.de/publications/Publ-21891
Publ.-Id: 21891


Magnetic and structural studies of as grown and hydrogenated Mg2Fe based thin films

Trinh, T. T.; Liedke, M. O.; Anwand, W.; Wagner, A.; Yildirim, O.; Cornelius, S.; Grenzer, J.; Ehrler, J.; Dam, B.; Asano, K.; Potzger, K.

Due to chemochromism, Mg2Me (Me=Fe, Co, Ni) based alloys are low-cost and rare-earth-free candidates for switchable mirrors upon hydrogen loading. In order to understand the basic physical properties of Mg2Fe based thin films and its hydride, as-sputtered as well as hydrogen loaded films have been investigated using magnetometry, X-ray diffraction, 4-point probe sheet resistance technique and positron annihilation spectroscopy (PAS). The interplay of hydrogen loading, the magnetic moment, and structural properties like the sizes and chemical decoration of open volume defects in thin films detected by PAS will be presented.

Keywords: Positron; Defects; Superparamagnetism; Mg2Fe; X-Ray; RBS

  • Poster
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21890
Publ.-Id: 21890


Method for constructing a mineralogical composition from a measured sample of single components

Konsulke, S.; Hopfe, S.; Tolosana-Delgado, R.; Matos Camacho, S.; van den Boogaart, K. G.

Our aim is to infer the mineral composition from the chemical composition of a material. Several difficulties occur: Different mineral compositions can lead to the same chemical composition. Not all chemical compositions can be reached by compositions of certain minerals, while e.g. due to measurement errors impossible chemical compositions will typically be observed. In principle the dependency between mineral composition and chemical composition is linear. Inversion of the linear system however often leads to negative portions for some mineral components. Only the first problem is properly solved by state of the art linear end member calculation methods (see e.g. Tolosana et al. 2011).
Our algorithm computes the set of all mineral compositions leading to the chemical composition maximizing the likelihood of the observed concentrations. The measurement error for the chemical components are modelled as independent normal distributions with mean zero and standard deviation given by the measurement error reported by the lab. For any given mineral composition, the chemical composition can thus be computed by stoichiometric calculations and Maximum log-likelihood is than a weighted least squares problem. The parameter space is however constraint to the possible mineral compositions. The problem is transformed into a quadratic programming problem with linear equality and inequality constraints with a unique solution for the chemical composition. From this unique solution we can than compute all possible mineral compositions leading to the corresponding chemical composition by enumerating the corners of the simplex of equally fitting solutions.
As an example we will discuss a sample of waste material consisting of Rare Earth Elements (REE), since recycling of waste materials is getting more and more important. Rare Earth Elements (REE) are used in mostly all new technologies and until now, there is no environmentally friendly recycling-process for fluorescent phosphor. For the development of a suitable recycling method, it is important to know the composition of the materials. Due to company secrecy, in some cases only rough informations about the composition of the material can be found. In the case of fluorescent phosphor, which is collected during the recycling-process of energy saving bulbs, only the type of the dye but not the precise composition is known. Because of different restrictions in the analytical methods and the complex composition, only the elemental concentrations with relatively high measurement errors can be measured.

Keywords: End-Member Problems; Rare Earth Elements; fluorescent phosphor

  • Lecture (Conference)
    The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
    Proceedings of IAMG 2015, 978-3-00-050337-5

Permalink: https://www.hzdr.de/publications/Publ-21889
Publ.-Id: 21889


Short-lived positron emitters in beam-on PET imaging during proton therapy

Dendooven, P.; Buitenhuis, H. J. T.; Diblen, F.; Heeres, P. N.; Biegun, A. K.; Fiedler, F.; van Goethem, M.-J.; van der Graaf, E. R.; Brandenburg, S.

The only method for in-vivo dose delivery verification in proton beam radiotherapy in clinical use today is positron emission tomography (PET) of the positron emitters produced in the patient during irradiation. PET imaging during irradiation maximizes the number of detected counts and minimizes biological washout. In such a scenario, also short-lived positron emitters will be observed. We determined which short-lived positron emitters are relevant by measuring their production in the stopping of 55 MeV protons in water, carbon, phosphorus and calcium. The most copiously produced short-lived nuclides and their production rates relative to the relevant long-lived nuclides are: 12N (T1/2 = 11 ms) on carbon (9% of 11C), 29P (T1/2 = 4.1 s) on phosphorus (20% of 30P) and 38mK (T1/2 = 0.92 s) on calcium (113% of 38gK). No short-lived nuclides are produced on water. The production on PMMA and 4 tissue materials is calculated from the experimental results. The number of decays, integrated over an irradiation, is calculated as function of the duration of the irradiation. For an irradiation in (carbon-rich) adipose tissue, 12N dominates the PET image up to an irradiation duration of 70 s. On bone tissue, 12N dominates over 15O during the first 8-15 s (depending on the carbon-to-oxygen ratio). The short-lived nuclides created on phosphorus and calcium provide 2.5 times more decays than the long-lived ones during a 70 s irradiation. Bone tissue will thus be better visible in in-beam PET compared to PET imaging after an irradiation. 12N needs to be considered in PET imaging during proton beam irradiations as its large positron range blurring may noticeably degrade image quality. Investigations into the energy-dependent production of 12N, 29P and 38mK and their effect on the quality of in-vivo treatment verification in proton therapy with PET imaging are urgently needed.

Keywords: PET; dose monitoring; short lived isotopes

Permalink: https://www.hzdr.de/publications/Publ-21888
Publ.-Id: 21888


Spin-transfer effects in MgO-based tunnel junctions with an out-of-plane free layer and in-plane polarizer: static states and steady-state precession

Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Deac, A. M.

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications. In particular, it has recently been demonstrated that STNOs utilizing an in-plane (IP) magnetized polarizer and out-of-plane (OOP) magnetized free layer allow for the full parallel (P)-to-antiparallel (AP) resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based MTJs under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence. These results have so far been interpreted based on the formalism for metallic devices, including the spin-torque angular dependence. Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based MTJs with an IP polarizer and an OOP free layer. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation for a nano-pillar MTJ with circular cross-section, under a constant perpendicular applied current and field. Since for realistic current range, the field-like torque is negligible compared to effective field acting along z axis, we take into account only the in-plane spin-torque term. To sustain steady-state precession, the energy supplied by the in-plane spin-torque term and energy dissipated through damping must compensate over a full precession period. In an MgO-MTJ, the magnitude of the STT is determined not by the current, but by the corresponding voltage across the barrier. As the magnetization of the free layer precesses around the z axis, the angle between the magnetic moments of the two layers changes and through the magnetoresistance effect the voltage changes if the Experiment is conducted at constant applied current. This cosine-like angular dependence of the MTJ resistance effectively introduces a spin-torque angle dependence asymmetry. In addition, even for a given angle, the resistance exhibits a specific bias dependence, with the resistance of the AP state decreasing approximately linearly with the bias, while remaining mostly constant in the P configuration. In this work, we demonstrate that the spin-torque angular asymmetry exhibited in such systems is sufficient to sustain STT-driven dynamics.

Keywords: spin-torque oscillators; spin-transfer torque; magnetic tunnel junctions; tunnel magnetoresistance

  • Lecture (Conference)
    The IEEE International Magnetics Conference (INTERMAG) 2015, 11.-15.05.2015, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-21887
Publ.-Id: 21887


Experimental investigation of interfacial structures within churn flow using a dual wire-mesh sensor

Parsi, M.; Vieira, R. E.; Torres, C. F.; Kesana, N. R.; Mclaury, B. S.; Shirazi, S. A.; Schleicher, E.; Hampel, U.

A challenging area in the field of multiphase flow is the study of churn flow. According to the multiphase flow community, churn flow has not been widely investigated in intermediate and large diameter pipes at high gas and liquid flow rates. The present work deals with an experimental study of upward vertical air–water flow in a 76.2 mm I.D. pipe. Superficial gas velocities ranging from 10 to 38 m/s and four superficial liquid velocities (0.30, 0.46, 0.61 and 0.76 m/s) were employed. The experimental data points are mostly located in churn flow and at the transition between churn and annular flow. A dual 16x16 Wire Mesh Sensor (WMS) was used to obtain the temporal/spatial variations of phase distributions over the pipe cross-section at one specific axial location (L/D = 236).
Sequences of phase distributions, axially sliced images, virtual 3-D images as well as void fraction timeseries were used to distinguish between different interfacial structures such as slugs and huge waves.
Results showed that huge waves occur with either a continuous gas core with a distinct boundary between two phases or a core with a gas–liquid mixture. Furthermore, velocities and frequencies of interfacial structures were obtained. Results are qualitatively and quantitatively consistent with the previous findings available in literature.

Keywords: churn flow; huge wave; wire mesh sensor; multiphase flow; interfacial structures

Permalink: https://www.hzdr.de/publications/Publ-21886
Publ.-Id: 21886


Control of intra-excitonic scattering in semiconductor quantum wells by an external magnetic field

Schneider, H.; Bhattacharyya, J.; Zybell, S.; Eßer, F.; Helm, M.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.

We report on the internal dynamics of excitons in high-quality GaAs quantum wells and on the control of intra-excitonic transitions by an external magnetic field. The free-electron laser FELBE in Dresden is ideally suited for selective excitation of intra-excitonic transitions, since it provides intense, spectrally narrow transform-limited terahertz pulses in a unique continuous pulse train, which also allows us to use a synchroscan streak camera system [1]. Subsequent to the production of excitons by pulsed interband excitation, we resonantly pump the 1s-2p intra-excitonic transition which is located at around 2 THz. Coulomb-mediated transfer from the optically "dark" 2p to the radiative 2s state and relaxation into the fundamental 1s state is investigated by time-resolved photoluminescence involving the 1s and 2s excitonic levels [2]. In particular, applying an external magnetic field strongly affects the observed behavior. Detailed analysis of the experimental behavior based on a newly developed microscopic theory allows us to demonstrate the remarkable impact of magnetic fields on the Coulomb and terahertz interactions in the excitonic system, which occurs as a consequence of magnetically induced changes of excitonic orbitals and energetic detuning of excitonic levels [3]. As an interesting application, we also discuss the possibility of observing terahertz gain induced by intra-excitonic transitions.
[1] J. Bhattacharyya et al., Rev. Sci. Instrum. 82, 103107 (2011)
[2] W. D. Rice et al., Phys. Rev. Lett. 110, 137404 (2013)
[3] J. Bhattacharyya et al., Phys. Rev. B 89, 125313 (2014)

Keywords: intra-exciton transitions; GaAs quantum well; terahertz excitation; free-electron laser

  • Lecture (Conference)
    SPIE Photonics West 2015, 07.-12.02.2015, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-21885
Publ.-Id: 21885


Evolution of the interfacial magnetic anisotropy in MgO/CoFeB/Ta/Ru based multilayers as a function of annealing temperature

Aleksandrov, Y.; Fowley, C.; Kowalska, E.; Sluka, V.; Yildirim, O.; Lindner, J.; Ocker, B.; Fassbender, J.; Deac, A. M.

We report effect of the annealing temperature on the dynamic and static magnetic properties of MgO/CoFeB/Ta/Ru multilayers. The angular resolved ferromagnetic resonance measurements results show that the as-deposited film exhibits in-plane magnetic anisotropy, whereas in the annealed films the magnetic easy-axis is almost along the direction perpendicular to the plane of the layers. The extracted interfacial anisotropy energy, Ki, is maximized at an annealing temperature 225 °C, in agreement with the vibrating sample magnetometry results. Although the magnetization is not fully out-of-plane, controlling the degree of the magnetization obliquity may be advantageous for specific applications such as spin-transfer oscillators.

Keywords: FMR; PMA; CoFeB

  • Lecture (Conference)
    IEEE International Magnetics Conference (INTERMAG 2015), 11.-15.05.2015, Beijing, the People's Republic of China
  • Open Access Logo AIP Advances 6(2016)6, 065321
    DOI: 10.1063/1.4954809

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Permalink: https://www.hzdr.de/publications/Publ-21884
Publ.-Id: 21884


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