Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35175 Publications

Agile Software Development using GitLab and GitLab CI

Juckeland, G.; Frust, T.

This talk presents how the GitLab Community Edition installation at HZDR is used to map components of agile programming and also motivates why most scientific programming is agile.

  • Lecture (Conference)
    SEI-Tagung 2018, 16.-18.04.2018, Dresden, Deutschland

Publ.-Id: 27373

Compositional analysis in the HIM

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Serralta, E.; Facsko, S.

The helium ion microscope is well known for its imaging with spot sizes below 0.5 nm, its nano-fabrication capabilities, the small energy spread of less than 1 eV and the extremely high brightness. This is not only possible for conducting but also insulating samples without the need for a conductive coating.
This relatively new device still suffers from the lack of a well integrated material analysis. Past and ongoing activities of various labs for in situ analysis will be summarized. Recently we implemented time-of-flight spectrometry to measure the energy of backscattered helium, the mass of sputtered ions and in future the energy loss of transmitted particles [1].
The focus will be on the technical realization of the significantly improved time-of-flight secondary ion mass spectrometry setup. New results, drawbacks and derive conclusions for the practical use of this promising technique will be presented [2]. Similarities and differences to the also recently developed system using a magnetic sector will be shown [3].
For m/q ≤ 80 u a mass resolution delta m ≤ 0.3 u has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g.: C14, N15). The lateral resolution of 8 nm has been evaluated using the knife edge method and represents a world record for spatially resolved secondary ion mass spectrometry.
[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J.A. Notte, J. Huang, S. Facsko. Ultramicroscopy 162 (2016), pp 91-97
[2] N. Klingner, R. Heller, G. Hlawacek, et al. (2018), in preparation
[3] D. Dowsett, T. Wirtz. Analytical Chemistry, 2017, 89 (17), pp 8957–8965

  • Poster
    Ionenstrahlworkshop 2018, 24.04.2018, Darmstadt, Germany

Publ.-Id: 27372

Recovery of critical and strategic metals from secondary resources: Solvent extraction using the radiotracer technique

O'Toole, N.; Mansel, A.; Kelly, N.; Scharf, C.

Securing economically and ecologically viable sources of certain strategic elements, such as chromium and vanadium, represents an important challenge facing Europe currently.[1] The CHROMIC project seeks to address this issue by developing novel processes for the procurement of such metals from secondary resources. Solvent extraction (SX) is a well-known method which can separate and concentrate such chemical species, and which can provide numerous advantages over more established pyrometallurgical processes for metal purification.[2] This present work aims to construct a solvent extraction process applicable to highly alkaline slag-leach-solutions for the selective recovery of chromium, vanadium, and eventually niobium.
The extractant used in this study is Aliquat 336, an ionic liquid composed of quaternary ammonium salt, dissolved in diluents such as kerosene and methyl isobutyl ketone.[3] Model feed solutions have been created based on the most probable leach solutions for this process, with pH in the range of 12 – 13 and chromate as the major species with an approximate chromium concentration of 1 g/L. Radiolabelling samples with the isotopes chromium-51 (half-life 27.7 days) and vanadium-48 (half-life 16.0 days) allows determination of the metal content in each phase, without the need for any sample preparation of the sort which is required for other analytical techniques such as ICP-OES or ICP-MS. To the best of our knowledge, this work represents the first use of 48V radiotracer individually (and the first use of 51Cr radiotracer in combination) analysis for a solvent extraction study.[4]
Thus far experiments have principally been carried out on single-element solutions containing only one of the desired target elements. In this way we have elucidated the influence of various factors on the efficiency of extraction. The pH of extraction medium plays an important role, not just on the extractability where increasing pH causes a decrease in metal extraction, but also on the stability of the extracted solution. Similarly, the concentration of competing anions such as chloride, sulphate, or nitrate has a strong negative influence on the amount of metal extracted. For example, addition of 0.5 M sodium sulphate will in general reduce extraction of chromium to half the salt-free value. Kinetics of mass transport were determined to be rapid, a significant factor when it comes to scaling up the process from laboratory to industrial scale (mixer-settler unit). Extraction isotherms have been constructed for different possible sets of extraction conditions, and used to guide our continuing research into these systems. Preliminary experiments on mixed-element solutions seem to show coextraction of chromium and vanadium together; in future experiments a suitable scrubbing technique will be employed to attempt to fully separate and purify these elements.
The results obtained thus far indicate the viability of Aliquat 336 as extractant for these key strategic metals from expected leach solutions of industrial slags. The continuation of the project will focus on optimising the process under realistic industrial conditions.
1. Communication from the European commission to the European Parliament on Critical Raw Materials, 13.09.2017
2. Weinhardt et al, Industrial and Engineering Chemistry,43(7), 1676-1684, (1951)
3. Wionczyk et al, Hydrometallurgy, 78, 116-128, (2005)
4. Katsuta et al, Journal of Radioanalytical and Nuclear Chemistry, 222(1-2), 45-50, (1997)

Keywords: Solvent Extraction; Circular Economy; Chromium; Vanadium; Aliquat 336

  • Poster
    7th European Chemical Science (EuCheMS) Congress 2018, 26.-30.08.2018, Liverpool, United Kingdom

Publ.-Id: 27371

Superior electrical conduction of a water repelling 3D interconnected nano-network

Dhal, S.; Das, P.; Rajbhar, M. K.; Chatterjee, S.; Möller, W.; Chatterjee, S.; Ramgir, N.

A three-dimensional (3D) network of interconnected nanowires of functional materials possesses huge potential for device fabrication since it hinders sluggish interfacial charge carrier transport owing to reduced contact resistance. In the present work, the formation of a highly porous 3D interconnected nano-network by Na+ ion irradiation is demonstrated. The mechanism of solid junction formation at very low energy is established using the results obtained from TRI3DYN computer simulation studies. The formation of a 3D interconnected network resulted in a significant improvement in the electrical conduction as compared to that observed for the pristine nanotube mesh. Further, contact angle measurement shows a transition from "superhydrophilic" nature, as observed for pristine nanotubes, to "superhydrophobic" nature for the 3D nano-network. The superhydrophobicity of the 3D nano-network is expected to find application in miniaturized electronic devices, wherein water condensation and related effects such as short-circuits and erroneous signal output can be significantly minimized.

Publ.-Id: 27370

Nanofabrication activities at HZDR

Georgiev, Y. M.

During this talk I will first briefly introduce the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Institute of Ion Beam Physics and Materials Research as well as the Ion Beam Centre as a user facility run by the Institute.

Next, I will present some of the equipment available at the nanofabrication facility in Rossendorf (NanoFaRo), in particular electron beam lithography (EBL) systems as well as tools for thin film deposition and reactive ion etching (RIE), paying special attention on their capabilities.

I will then go through the most important nanofabrication projects, both internal and external, run lately at NanoFaRo, including top-down fabrication and electrical characterisation of silicon (Si) nanowire (NW) reconfigurable field effect transistors (RFETs) together with detailed study of nickel (Ni) silicidation of Si NWs; top-down fabrication of a large number of gratings with different periodicity on 2 µm thick Si membranes for laser targets; electrical contacting of randomly distributed nanostructures (bottom-up grown VO2 and hyperdoped Si NWs, DNA origami, flakes of 2D materials, etc.); top-down fabrication of four-terminal Si NW test devices for modulation doping experiments; nanopatterning of polymer brushes by reactive writing with EBL; bevel formation by EBL and RIE for dopant/conductance profiling of thin films and NWs by conductive atomic force microscopy (C-AFM); top-down fabrication of Si NWs hyperdoped with selenium (Se) as well as of plasmonic antennas on Si hyperdoped with tellurium (Te); fabrication and electrical characterisation of FETs on 2D materials, etc. Concluding this part of my talk, I will draw your attention to some highlights of our activities, focussing mostly on processes for high-resolution patterning as well as on high-precision electrical contacting of randomly distributed nanostructures.

Finally, I will discuss possibilities for collaboration between HZDR and UCC/Tyndall in the field of our activities.

Keywords: nanofabrication; electron beam lithography; reactive ion etching; silicon nanowires; reconfigurable field effect transistors; nickel silicidation; silicon gratings; silicon membranes; laser targets; DNA origami; 2D materials; conductive atomic force microscopy; hyper doped silicon nanowires; plasmonic antennas

  • Lecture (others)
    Seminar of the School of Chemistry, University College Cork, 22.03.2018, Cork, Ireland

Publ.-Id: 27368

Group IV Semiconductor Nanowires for Sensing and Nanoelectronic Applications

Georgiev, Y. M.

During the last decade, semiconductor nanowires (NWs) have received significant academic and commercial attention due to their attractive electrical and mechanical properties and large surface area to volume ratios. They have a variety of possible applications including nanoelectronics, nanophotonics, photovoltaics, sensorics, etc. Among all semiconductor NWs the ones based on group IV materials have the added value of being the most silicon (Si) compatible. This would allow their relatively easy integration into the existing semiconductor technology platform.

In my talk I will first present the NWs that we are working with. These include top-down fabricated Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up grown alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1, diameters of 50-70 nm and lengths of 1 to 3 µm. In the future we plan to work also with alloyed SiGe and SiGeSn NWs with varying content of the different materials.

I will next discuss the innovative devices that we are targeting, namely junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we are interested in Si JNTs for sensing application as well as in Ge and GeSn JNTs for digital logic. Concerning RFETs, we are currently working on Si RFETs and commencing activities on Ge RFETs. In the future we are planning to work also on GeSn RFETs.

Finally, I will pay a special attention to a novel device that we recently invented: group IV heterostructure band-to-band tunnel FET (TFET). We are planning to fabricate this device with a scalable and fully CMOS compatible process and expect it to demonstrate high Ion together with low Ioff and hence steep subthreshold slopes.

Keywords: semiconductor nanowires; nanoelectronics; silicon; germanium; germanium-tin; junctionless nanowire transistors; reconfigurable field effect transistors; heterostructure band-to-band tunnel field effect transistors

  • Lecture (others)
    Science Meets Industry, 08.03.2018, Dresden, Germany

Publ.-Id: 27367

Formation of a new type of {U38} cluster based on a controlled release of water via esterification reaction

Martin, N. P.; Volkringer, C.; Henry, N.; Trivelli, X.; Stoclet, G.; Ikeda-Ohno, A.; Loiseau, T.

A new strategy for the synthesis of large poly-oxo cluster bearing 38 tetravalent uranium atoms {U38} has been developed by controlling the water release from the esterification reaction between carboxylic acid and alcohol. The molecular entity [U38O56Cl40(H2O)2(ipa)20]·(ipa)x (ipa = isopropanol) was crystallized from the solvothermal reaction of the mixture of UCl4 and benzoic acid in isopropanol at temperature ranging from 70 to 130°C. Its crystal structure reveals the molecular assembly of the UO2 fluorite-like inner core {U14} with oxo groups bridging the uranium centers. The {U14} core is further surrounded by six tetrameric sub-units of {U4} to form the {U38} cluster. Its surface is decorated by either bridging- and terminal chloride anions or terminal isopropanol molecules. Another synthesis using the same reactant mixture at a room temperature resulted in the crystallization of discrete dinuclear complex [U2Cl4(bz)4(ipa)4] (bz = benzoate), in which each uranium center is coordinated by two chlorine atoms, four oxygen atoms from carboxylate groups and two additional oxygen atoms from isopropanol. The slow production of water released from the esterification of isopropanol allows the formation of the giant cluster with oxo bridges linking the uranium atoms at a temperature above 70°C, whereas no such oxo groups are present in the dinuclear complex formed at a room temperature. The kinetic of {U38} crystallization as well as the ester formation are analyzed and discussed. SAXS experiments indicate that the {U38} species are not dominant in the supernatant, but hexanuclear entities which are closely related to the [U6O8] type are formed.

Keywords: Actinides; uranium; cluster; polymer; coordination; solid-state chemistry; structure characterisation; solution speciation

Publ.-Id: 27366

Towards the development of chitosan nanoparticles for plutonium pulmonary decorporation

Léost, L.; Roques, J.; van de Meeren, A.; Vincent, L.; Sbirrazzuoli, N.; Hennig, C.; Rossberg, A.; Aupiais, J.; Pagnotta, S.; Den Auwer, C.; Di Giorgio, C.

Since the 1940s, great amounts of Plutonium (Pu) have been produced for both military and civil purposes. Until now, the standard therapy for decorporation following inhalation has been the intravenous injection of diethylenetriaminepentaacetic acid ligand (Ca-DTPA form). This method offers a strong complexing constant for Pu(iv) but has poor chemical specificity, therefore its efficacy is limited to actinides present in the blood. Consequently, there is no decorporation treatment currently available which efficiently removes the intracellular Pu(iv) trapped in the pulmonary macrophages. Our research shows that a nanoparticle approach could be of particular interest due to large contact area and ability to target the retention compartments of the lungs. In this study, we have focused on the inhalation process involving forms of Pu(iv) with poor solubility. We explored the design of biocompatible nanoparticles able to target the macrophages in the lung alveoli and to chelate the forms of Pu(iv) with poor solubility. Nanoparticle formation was achieved through an ionic cross-linking concept using a polycationic polymer and an anionic chelate linker. We chose N-trimethyl chitosan, for its biocompatibility, as the polycationic polymer base of the nanoparticle and the phosphonic analogue of DTPA, diethylenetriamine-pentamethylenephosphonic acid (DTPMP) as the anionic chelating linker in forming NPs TMC-DTPMP. The synthesis and physico-chemical characterization of these NPs are presented. Secondly, the complexation mechanisms of TMC-DTPMP NPs with Thorium (Th(iv)) are discussed in terms of efficiency and structure. The Extended X-Ray Absorption Fine Structure (EXAFS) of the TMC-DTPMP complex with Th(iv) as well as Pu(iv) are defined and completed with DFT calculations to further delineate the plutonium coordination sphere after complexation. Finally, preliminary cytotoxicity tests onto macrophages were assayed.

Keywords: Th(IV); Pu(IV); TMC-DTPMP NPs; EXAFS; DFT

Publ.-Id: 27365

DNA-encircled lipid bilayers

Iric, K.; Subramanian, M.; Oertel, J.; Agarwal, N. P.; Matthies, M.; Periole, X.; Sakmar, T. P.; Huber, T.; Fahmy, K.; Schmidt, T.-L.

Lipid bilayers and lipid-associated proteins play crucial roles in biology. As in vivo studies and manipulation are inherently difficult, membrane-mimetic systems are useful for the investigation of lipidic phases, lipid-protein interactions, membrane protein function and membrane structure in vitro. In this work, we describe a route to leverage the programmability of DNA nanotechnology and create DNA-encircled bilayers (DEBs). DEBs are made of multiple copies of an alkylated oligonucleotide hybridized to a single-stranded minicircle, in which up to two alkyl chains per helical turn point to the inside of the toroidal DNA ring. When phospholipids are added, a bilayer is observed to self-assemble within the ring such that the alkyl chains of the oligonucleotides stabilize the hydrophobic rim of the bilayer to
prevent formation of vesicles and support thermotropic lipid phase transitions. The DEBs are completely free of protein and can be synthesized from commercially available components using routine equipment. The diameter of DEBs can be varied in a predictable manner. The well-established toolbox from structural DNA nanotechnology, will ultimately enable the rational design of DEBs so that their size, shape or functionalization can be adapted to the specific needs of biophysical investigations of lipidic phases and the properties of membrane proteins embedded into DEB nanoparticle bilayers.

Keywords: lipid; membrane protein; DNA; nanotechnology

  • Poster
    Jahrestagung Deutsche Gesellschaft für Biophysik, 16.-19.09.2018, Düsseldorf, Deutschland
  • Nanoscale 10(2018), 18463-18467
    DOI: 10.1039/C8NR06505E

Publ.-Id: 27364

DNA-encircled lipid bilayer: a nano-scaled membrane-mimetic system

Iric, K.; Subramanian, M.; Oertel, J.; Agarwal, N. P.; Matthies, M.; Periole, X.; Sakmar, T. P.; Huber, T.; Fahmy, K.; Schmidt, T.-L.

Lipid bilayers and lipid-associated proteins play a crucial role in biology. Since studies and manipulation in vivo are inherently challenging, several in vitro membrane-mimetic systems have been developed to enable the study of lipidic phases, lipid-protein interactions and membrane protein function. Controlling the size and shape or introducing functional elements in a programmable way is, however, difficult to achieve with common systems based on polymers, peptides or membrane scaffolding proteins. In this work we describe a route leveraging the unique programmability of DNA nanotechnology to create DNA-encircled bilayers (DEBs) as a novel nano-scaled membrane-mimetic. For this, alkylated oligonucleotides are hybridized to a single-stranded minicircle (ssMC) such that all alkyl chains point to the inside stabilizing the lipid bilayer. Atomic force microscopy (AFM), transmission electron microscopy (TEM) and coarse grain molecular dynamics (CGMD) simulations confirm the formation of discoidal lipid bilayer structures. Fluorescence spectroscopy was used to monitor lipid phase transitions and revealed head group-dependent lipid-DNA interactions at the bilayer rim. The DEB technology described herein provides unprecedented control of size, shape, stability and functionalization of engineered membrane nanoparticles and will become a valuable tool for biophysical investigation of lipid phases and lipid-associated proteins and complexes.

Keywords: Nanotechnology; membrane protein; DNA; lipids

  • Poster
    FNANO2018, 15th Annual Conference Foundations of Nanoscience, 16.-19.04.2018, Durham, USA

Publ.-Id: 27363

Bentonite – a natural source for sulfate-reducing bacteria

Matschiavelli, N.; Kluge, S.; Cherkouk, A.

In order to analyze the potential influence of natural occuring microorganisms within the bentonite on the properties of the bentonite barrier, we set up microcosm-experiments. Two different Bavarian bentonites (a natural and an industrial one) were supplied with an anaerobic, synthetic Opalinus-clay pore water solution under an N2/CO2-atmosphere and were incubated for one year at 30 °C and 60 °C. To some set ups organics (acetate or lactate) or H2 were supplemented. During the incubation time samples were analyzed for several biogeochemical parameters and the evolution of microbial community.
Our results clearly demonstrate, that natural occuring microbes affect geochemical parameters. Set ups containing the industrial bentonite supplemented with lactate or H2 show the most striking effects. The respective batches were dominated (up to 81 %) by Desulfosporosinus spp. after 6 months – spore-forming, strictly anaerobic, sulfate-reducing organisms, able to survive under very harsh conditions. Concomitantly, an increase of ferrous iron and a simoultaneous decrease of ferric iron was observed as well as a decrease in sulfate – alterations that could effect different properties of and reactions within the barrier system of an HLW.

Keywords: Bentonite; sulfate-reduction; Desulfosporosinus spp

  • Lecture (Conference)
    MIND-Project Annual Meeting 2018, 07.-09.05.2018, Lausanne, Switzerland

Publ.-Id: 27362

Analyzing the large scale flow in a precessing cylinder and its ability for dynamo action

Gundrum, T.; Vogt, T.; Gao, Y.; Giesecke, A.; Stefani, F.; Eckert, S.

We carried out ultrasonic Doppler measurements of a precession driven flow in a cylindrical cavity. The experimental studies were conducted in a downscaled water experiment to analyze the possibility of hydrodynamic dynamo action in a planned large-scale liquid sodium experiment. The azimuthal and axial mode decomposition close to the outer rim reveals a significant peak for the axi-symmetric flow component with axial wavenumber k=2 in a narrow region of the precession ratio. At this peak, dynamo action is predicted for the DRESDYN sodium experiment. Specifically we analyze the ultrasonic measurement data which were transferred via slip rings from the vessel rotating about two axes. By post-processing the azimuthal dependence of the flow was extracted from the ultrasonic data. The utilized workflow eliminates the slight variations over time of the operating conditions and of the frame rate of the data acquisition. The downscaled water experiment was operated in a wide range from Re=10000 to 1.6·106, showing a very good agreement with direct numerical simulations at their upper limit of Re=10000.

Keywords: Magnetohydrodynamics; Geophysics; Precession; hydrodynamic Dynamo; UDV

  • Contribution to proceedings
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering ( ISUD 11 ), 05.-7.9.2018, Berlin, Deutschland

Publ.-Id: 27361

Shibboleth-Authenticator for Invenio

Frust, T.

The shibboleth-authenticator module for Invenio provides web browser single sign-on via the SAML protocol. It is based on the python3-saml module and supports the usage of multiple identity providers at the same time.

Related publications

  • Software in the HZDR data repository RODARE
    Publication date: 2018-04-18
    DOI: 10.14278/rodare.13
    License: GPL-3.0


Publ.-Id: 27360

Interaction of Uranium(VI) with α‑Amylase and Its Implication for Enzyme Activity

Barkleit, A.; Hennig, C.; Ikeda-Ohno, A.

Because of its chemo- and radiotoxicity, the incorporation of uranium into human body via ingestion potentially poses a
serious health risk. When ingested, the gastrointestinal fluids are the primary media to interact with uranium, eventually influencing and even determining its biochemical behavior in the gastrointestinal tract and thereafter. The chemical interactions between uranium and the components of gastrointestinal fluids are, however, poorly understood to date. In this study, the complexation of uranium(VI) (as the uranyl ion, UO22+) with the protein α-amylase, one of the major enzymes in saliva and pancreatic juices, was investigated over a wide range of pH or uranium/α-amylase concentrations covering physiological conditions. Macroscopic sorption experiments suggested a strong and fast complexation of UO22+ to α-amylase between pH 5 and 7. Potentiometric titration was employed to determine the complex stability constants for the relevant UO22+ α-amylase complexes, which is crucial for reliable thermochemical modeling to assess the potential health risk of uranium. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that α-amylase is interacting with UO22+ primarily via its carboxylate groups presumably from the aspartic acid and glutamic acid side chains. The effect of UO22+ on the enzyme activity was also investigated to understand the potential implication of uranium for the in vivo functions of the digestive fluids, indicating that the presence of uranium inhibits the enzyme activity. This inhibitory effect can be, however, suppressed by an excess of calcium.


Publ.-Id: 27359

Monitoring scanner calibration using the image derived arterial blood SUV in whole-body FDG-PET

Maus, J.; Hofheinz, F.; Apostolova, I.; Kreissl, M. C.; Kotzerke, J.; van den Hoff, J.

The current de facto standard for quantification of tumor metabolism in oncological whole-body PET is the standardized uptake value (SUV) approach. SUV determination requires accurate scanner calibration. Residual inaccuracies of the calibration lead to biased SUV values. Especially, this can adversely affect multicenter trials where it is difficult to ensure reliable cross-calibration across participating sites. The goal of the present work was the evaluation of a new method for monitoring scanner calibration utilizing the image-derived arterial blood SUV (BSUV) averaged over a sufficiently large number of whole-body FDG-PET investigations.

Data of 681 patients from three sites which underwent routine 18F-FDG PET/CT or PET/MR were retrospectively analyzed. BSUV was determined in the descending aorta using a three-dimensional ROI concentric to the aorta’s centerline. The ROI was delineated in the CT or MRI images and transferred to the PET images. A minimum ROI volume of 5 mL and a concentric safety margin to the aortic wall was observed. Mean BSUV, standard deviation (SD), and standard error of the mean (SE) were computed for three groups of patients at each site, investigated 2 years apart, respectively, with group sizes between 53 and 100 patients. Differences of mean BSUV between the individual groups and sites were determined.

Results: SD (SE) of BSUV in the different groups ranged from 14.3 to 20.7% (1.7 to 2.8%). Differences of mean BSUV between intra-site groups were small (1.1–6.3%). Only one out of nine of these differences reached statistical significance. Inter-site differences were distinctly larger (12.6–25.1%) and highly significant (P<0.001).

Conclusions: Image-based determination of the group-averaged blood SUV in modestly large groups of whole-body FDG-PET investigations is a viable approach for ensuring consistent scanner calibration over time and across different sites. We propose this approach as a quality control and cross-calibration tool augmenting established phantom-based procedures.

Keywords: PET; Quantification; Blood SUV; Standardization; Multicenter; In vivo

Related publications

Publ.-Id: 27358

Massive Parallel Computing on GPU Architectures

Frust, T.

Graphics processing units (GPU) have evolved to massively parallel processors for general-purpose computing during the last couple of years. They are now available in small and energy-efficient embedded systems, too. This talk gives a brief overview about GPU computing and introduces the NVIDIA Jetson platform as an example for a GPU powered embedded system.

Keywords: GPU; Embedded systems; Parallel computing

  • Lecture (others)
    TOMOCON Kick-Off Meeting, 18.04.2018, Technische Universtität Dresden, Deutschland

Publ.-Id: 27357

Research Data Management

Frust, T.

The importance of research data and research data management (RDM) in the research lifecycle is growing. This talk provides an overview about data management in research projects. The goal is to make research data FAIR (Findable, Accessible, Interoperable and Retrievable) by starting early with a Data Management Plan (DMP) and making research data available in appropriate data repositories.

Keywords: Data Management; Data Management Plan; FAIR; RODARE; Zenodo

  • Lecture (others)
    TOMOCON Kick-Off Meeting, 18.04.2018, Technische Universität Dresden, Deutschland

Publ.-Id: 27356

Cyclopentadienyl Tricarbonyl 99mTc/Re Complexes Containing Spirocyclic Piperidine Moiety as Nonselective Sigma Receptor Ligands for Tumor Imaging and Therapy

Wang, X.; He, Y.; Deuther-Conrad, W.; Ye, J.; Chen, J.; Steinbach, J.; Brust, P.; Jia, H.

We have designed and synthesized a series of cyclopentadienyl tricarbonyl 99mTc/Re complexes containing a spirocyclic piperidine moiety as sigma receptor ligands. Rhenium compound 3a (4-(3H-spiro(2-benzofuran-1,4’-piperidin)-1’-yl)butylcarbonylcyclopentadienyl tricarbonyl rhenium) showed high affinity for both sigma-1 (Ki = 13.8 ± 0.7 nM) and sigma-2 (Ki = 15.1 ± 3.5 nM) receptors. In the MTT assay, 3a displayed significant and comparable antiproliferative activity in DU145, MCF7 and MCF7/Adr tumor cells to siramesine, indicating 3a is an agonist of sigma-2 receptors and a potential antitumor agent. The corresponding radiolabeled compound [99mTc]3b was prepared via double-ligand-transfer reaction from the corresponding ferrocene precursor with a radiochemical yield of 48% and a radiochemical purity of more than 99%. Studies of the cellular accumulation of [99mTc]3b in C6 and DU145 tumor cells indicated that the total binding and the intracellular association is notably high.
Incubation with haloperidol significantly reduced the radiotracer accumulation dose-dependently. The biodistribution of [99mTc]3b in nude mice bearing DU145 tumor xenografts showed high tumor uptake (4.27%ID/g) and high tumor-to-blood (12) and tumor-to-muscle (5) ratios at 2 h postinjection. Pretreatment with haloperidol resulted in a remarkable reduction of tumor accumulation, indicating the specific binding of [99mTc]3b to sigma receptors in the tumor. These findings highlight the further evaluation of cyclopentadienyl tricarbonyl 99mTc/Re complexes and prospectively the 188Re-labeled analogs containing a spirocyclic piperidine moiety as sigma ligands for tumor imaging and therapy.

  • Lecture (Conference)
    TERACHEM2018, 26.-29.09.2018, Bressanone, Italien

Publ.-Id: 27355

Liquid metal batteries - activities at the Helmholtz-Zentrum Dresden - Rossendorf

Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Stefani, F.; Weber, N.

The talk will provide an overview of the liquid metal battery (LMB) related activities at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) with a focus on magnetohydrodynamic aspects of future large scale LMBs. High current densities in the range of 4 up to 130 kA/m-2, as typical for LMBs, together with cells of large cross section will result in substantial currents accompanied by considerable magnetic fields. Thus electromagnetically driven flows and instabilities should be of concern for large enough installations, especially when the thin electrolyte layers necessitated by the limited open circuit voltages are taken into account. Beneficial effects of mild electromagnetically driven flows are to be expected for the cathodes were mixing should improve cell performance.

Keywords: liquid metal batteries; magnetohydrodynamics; Tayler instability; sloshing

  • Lecture (others)
    Seminar, 12.04.2018, Cambridge, United Kingdom

Publ.-Id: 27354

Liquid metal batteries - stationary storage for fluctuating renewable energy sources

Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Stefani, F.; Weber, N.

Liquid metal batteries are introduced as a potential means to future economic large-scale electricity storage indispensable for energy systems with high penetration of fluctuating sources. The talk will concentrate on the role of electrodynamics and fluid mechanics in the design of large single cells, discussing a few instability mechanisms that should be taken into account.

Keywords: liquid metal batteries; magnetohydrodynamics; instabilities

  • Invited lecture (Conferences)
    Battery Application and Energy Storage, 11.04.2018, London, United Kingdom

Publ.-Id: 27353

Layer-by-Layer assembly of heparin and peptide-polyethylene glycol conjugates to form hybrid nanothin films of biomatrices

Thomas, A. K.; Wieduwild, R.; Zimmermann, R.; Lin, W.; Friedrichs, J.; Bickle, M.; Fahmy, K.; Werner, C.; Zhang, Y.

We investigated the utility of a heparin/peptide-polyethylene glycol conjugate system to build Layer-by-Layer (LbL) structures, to assemble tailored multilayer-biomatrices for cell culture. The LbL assembly balances the advantages of polyelectrolyte systems and protein-based systems. Human umbilical vein endothelial cells showed distinct responses to: the film thickness and structure; the presence, density and spatial arrangement of a cell adhesion ligand within the nanothin film; and the pretreatment of the film with morphogens. The LbL technique presents a versatile tool for modifying cell culture substrates with defined and diverse biochemical and structural features, for investigating cell-material interactions.

Keywords: extracellular matrix; layer-by-layer; nano thin; heparin; biomimetic; Fourier transform infrared

Publ.-Id: 27352

Comparison of flow measurements in a cold liquid metal model for continuous casting of steel carried out by an arrangement of individual US transducers and a linear US array

Schurmann, D.; Franke, S.; Willers, B.; Eckert, S.

Flow measurements by means of the Ultrasound Doppler Velocimetry (UDV) have been carried out in a cold liquid metal mockup experiment to model the continuous casting process of steel. The setup was realized in the mini-LIMMCAST facility and represents a 1:3 scale model of a typical industrial bloom caster. An arrangement of ten individual ultrasonic sensors attached to a commercial system and an academic UDV system with linear ultrasound array was mounted along the mold to capture the velocity distribution near the meniscus and the submerged entry nozzle (SEN). The results obtained by the two measurement systems are compared and show the superiority of the academic system due to its higher spatial resolution.

Keywords: Model Experiments in Liquid Metal; Continuous Casting; UDV

  • Contribution to proceedings
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 11), 05.-07.09.2018, Berlin, Deutschland
  • Lecture (Conference)
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 11), 05.-07.09.2018, Berlin, Deutschland

Publ.-Id: 27351

ICA cleanup for improved SNR in arterial spin labeling perfusion MRI

Hao, X.; Petr, J.; Nederveen, A. J.; Wood, J.; Wang, D. J. J.; Mutsaerts, H. J. M. M.; Jann, K.

Arterial spin labeling (ASL) is a non-invasive MRI modality that can provide insight in brain hemodynamics. One main limiting factor of ASL is its relatively low signal-to-noise ratio (SNR). New technical developments like 3D readouts and background suppression have improved SNR [1] and additional post processing steps including noise regression methods can further improve temporal SNR (tSNR) [2]. We hypothesize that Independent Component Analysis (ICA) should provide separation of physiological noise from signal and thus improving SNR and cerebral blood flow (CBF) quantification as has been shown for BOLD fMRI. Therefore, in this study, we evaluated the use of ICA to separate perfusion signal from noise in ASL data.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France, 2330
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France

Publ.-Id: 27350

Late-delayed perfusion decrease following radiochemotherapy in glioblastoma patients

Petr, J.; Mutsaerts, H. J. M. M.; Platzek, I.; Keil, V. C.; Hofheinz, F.; Asllani, I.; Seidlitz, A.; Petrova, M.; Troost, E. G. C.; Krause, M.; van den Hoff, J.

Temozolomide-based radiochemotherapy (RCT) is a treatment standard for glioblastoma patients. However, RCT is associated with risks of neurocognitive decline. Perfusion is a possible early marker of tissue damage and has been shown to correlate with cognitive changes in many diseases. Perfusion decrease at 3 to 6 months after RT was recently reported in glioblastoma patients. However, it remains unclear whether the decrease is reversible and thus possibly a precursor of the late-delayed cognitive changes. In this study, we have measured perfusion changes up to 18 months following RCT. No further progress of perfusion deficits was found indicating that the early perfusion decrease is predictive of late perfusion decrease and might thus be connected with cognitive decline.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France, 4863
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France

Publ.-Id: 27349

Rethinking vascular artifacts: testing the sensitivity of ASL vascular signal as a biomarker of disease

Mulhollan, Z.; Mutsaerts, H. J. M. M.; Petr, J.; Liao, J.; Lazar, R. M.; Marshall, R. S.; Asllani, I.

It was recognized early on in the development of ASL that the contribution of the vascular signal was a confound in measuring tissue perfusion. To this end, Alsop et al. proposed introducing a post-label delay (PLD) to allow for the blood to arrive at the microvasculature level and preferably wash-out from the macro-vasculature1. Considering, however, that the ASL signal decays during the PLD, a compromise is typically made between the need to minimize the effect of the vascular signal and optimum SNR. The choice of PLD becomes more complex in clinical applications where the arterial transit time (ATT) is expected to vary considerable across patients as well as within a patient, such as in carotid occlusive disease. In such applications, a concomitant measurement of both CBF and ATT would be ideal. However, ATT acquisition leads to longer scanning time, lower SNR, and higher motion sensitivity. To this end, Mutsaerts et al. have recently shown that spatial coefficient of variation (sCoV) of the ASL signal can be used as a proxy for the ATT measurement2. In this study, we tested whether an asymmetry in sCoV in carotid occlusive patients could predict the side of the occlusion with higher sensitivity than the CBF asymmetry. We also investigated the temporal variance of the ASL signal and tested its feasibility to detect the vascular signal in the ASL data from this patient population.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France, 548
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France

Publ.-Id: 27348

Comparing pCASL measurement of CBF between 3D GRASE and 2D EPI on 1.5T and 3T systems

Baas, K. P. A.; Mutsaerts, H. J. M. M.; Petr, J.; Kuijer, J. P. A.; van de Ven, K. C. C.

We have compared CBF value agreement in healthy subjects across two readouts, 3D-GraSE and 2D-EPI, and two field strength, 1.5 and 3T, and investigated for which acquisition parameters we can reach the best agreement. Significantly higher GM CBF was observed with a 2D-EPI readout compared to a 3D-GraSE readout with equivalent acquisition resolution (p < 0.005 for 1.5T and p < 0.05 for 3T). A better agreement was observed between 3D-GraSE and 2D-EPI on 3T systems when the resolution of the 3D-GraSE readout was increased to match the effective resolution to the 2D-EPI scan (ICC = 0.772 and ICC = 0.932 respectively).

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France, 2158
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France

Publ.-Id: 27347

ASL parameters as MR biomarkers of successful cerebrovascular compensation in prolonged breath-hold: A combined pCASL and 31P/1H-MRS study

Keil, V. C.; Mutsaerts, H. J. M. M.; Eichhorn, L.; Träber, F.; Block, W.; Mädler, B.; van de Ven, K.; Siero, J. C.; Macintosh, B. J.; Petr, J.; Schild, H. H.; Hattingen, E.

This pCASL and 31P/1H-MRS study explored the cerebrovascular reactivity (CVR) and its efficacy on brain metabolic stability during a five-minute breathhold in fifteen experienced freedivers. Cerebral blood flow (CBF) increase occurred later than the decrease of the recently discovered arterial transit time correlate, spatial CoV. The latter may thus be an early CVR biomarker. CBF varied between vessel territories, gray and white matter and usually lowered with more experience. MRS showed near stable physiological cerebral ATP and pH concentrations despite peripheral lactate acidosis. In conclusion, this trial revealed that CVR sufficiently compensates the metabolic challenge of a five minute breath-hold.
In conclusion, this trial revealed that cerebral perfusion increase sufficiently compensates the metabolic challenge of a five-minute breath-hold.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France, 371
  • Lecture (Conference)
    Joint Annual Meeting ISMRM-ESMRMB 2018, 16.06.2018, Paris, France

Publ.-Id: 27346

Comparing pCASL measurement of CBF between 3D GRASE and 2D EPI on 1.5T and 3T systems

Baas, K. P. A.; Mutsaerts, H. J. M. M.; Petr, J.; Kuijer, J. P. A.; van de Ven, K. C. C.

We have compared CBF value agreement in healthy subjects across two readouts, 3D-GraSE and 2D-EPI, and two field strength, 1.5 and 3T, and investigated for which acquisition parameters we can reach the best agreement. Significantly higher GM CBF was observed with a 2D-EPI readout compared to a 3D-GraSE readout with equivalent acquisition resolution (p < 0.005 for 1.5T and p < 0.05 for 3T). A better agreement was observed between 3D-GraSE and 2D-EPI on 3T systems when the resolution of the 3D-GraSE readout was increased to match the effective resolution to the 2D-EPI scan (ICC = 0.772 and ICC = 0.932 respectively).

  • Contribution to proceedings
    10th Annual meeting of ISMRM Benelux Chapter, 26.01.2018, Antwerp, Belgium
  • Lecture (Conference)
    10th Annual meeting of ISMRM Benelux chapter, 26.01.2018, Antwerp, Belgium

Publ.-Id: 27345

Investigating Arterial Spin Labeling As Large Vessel Correlate of Svd, AD, and PD

Ingala, S.; Petr, J.; Pålhaugen, L.; Gajdos, M.; Fladby, T.; Selnes, P.; Barkhof, F.; Bjornerud, A.; Rektorova, I.; Mutsaerts, H. J. M. M.

Background: In elderly populations, cerebral blood perfusion (CBF) measurements with arterial spin labelling (ASL) are affected by macro-vascular artefacts as a result of prolonged arterial transit time (ATT) [Figure 1]. The spatial coefficient of variance (CoV) provides a robust indirect estimate of ATT, hence it might be used as a proxy of the vascular health of the subject2, alone or in conjunction with other measures such as white matter hyperintensities (WMH) volume. The goal of this study was to compare spatial CoV between healthy controls (HCs) and subjects with Alzheimer’s (AD) or Parkinson’s (PD) disease. Methods: We analysed the scans of 143 participants from the APGeM study, in which a 3D GRASE pulsed ASL protocol was added to the Siemens 3T MRI protocol for degenerative diseases. Healthy controls (HC, n=56) and participants with AD- or PD-related mild cognitive impairment or dementia (AD, n=41; PD, n=46) were included [Table 1]. We calculated grey matter (GM) CBF, spatial CoV, and WMH volume using ExploreASL [ref]. Pearson’s correlation was used to calculate the correlation of spatial CoV with age and WMH volume. Student’s-test was performed to check differences in spatial CoV between sexes. A linear regression model was built to investigate whether spatial CoV could discriminate between HC vs. AD, HC vs. PD, and AD vs. PD after correction for age and sex. WMH and spatial CoV were logtransformed.
Results: Spatial CoV showed a positive correlation with age (cor=0.35, p<0.001) and with WMH volume (cor=0.38, p <0.001) [Figure 2]. A difference in spatial CoV of 0.12 was reported (p<0.001). Spatial CoV differences were detected between HC and AD (ß=0.08, p=0.004) and between HC and PD (ß=0.09, p=0.0002) subjects [Figure 3]. However, spatial CoV was not able to discriminate between AD and PD. Conclusions: The relatively strong correlation between spatial CoV and WMH volume make ASL a promising marker to investigate the interplay between large and small vessel disease. These results suggest that cerebrovascular health is reduced in AD and PD patients. Validation studies in larger cohorts and across a wider range of disorders could provide further insight in the relation between vascular disorders and neurodegeneration.

  • Open Access Logo Contribution to proceedings
    Alzheimer's Association International Conference, 22.07.2018, Chicago, USA
    DOI: 10.1016/j.jalz.2018.06.410
  • Poster
    Alzheimer's Association International Conference, 22.07.2018, Chicago, USA

Publ.-Id: 27344

Protocol Harmonisation and in-vivo Comparison of Arterial Spin Labelling MRI for Multicenter Clinical Trials

Abaei, M.; Baas, K.; Petr, J.; Hill, D. L.; Wolz, R.; Kuijer, J.; Sokolska, M.; Barkhof, F.; Ourselin, S.; Duncan, J.; Vos, S.; Mutsaerts, H. J. M. M.; Thomas, D. L.

Arterial Spin Labelling (ASL) is a technique for measuring cerebral blood flow (CBF)1,2 and has shown promising results for discriminating Alzheimer’s disease patients from mild cognitive impairment and controls1. ASL is commercially available on all major MRI vendors; however, it has been shown that CBF values are sequence and scanner-dependent, due to variability of the acquisition methods used by each vendor. In this study, we compare the latest generation of pseudo-continuous ASL (pCASL) vendor-provided sequences to quantify between-vendor variability of whole-brain and regional CBF estimation.
Eight healthy volunteers (4/4 M/F; mean/SD/median age=47/12/48 years) were scanned on three 3T MR systems with pCASL matched acquisition parameters (Table 1) and ADNI-2 3D-T1weighted (MPRAGE). CBF quantification and post-processing was performed using ExploreASL3 in conjunction with SPM124. Post-processing included registration of the T1-MPRAGE and ASL to MNI space, parcellation of the T1-MPRAGE to grey matter (GM), white matter (WM), and regions affected in dementia (ROI_dem). Quantification was performed according to the ASL consensus paper5. Mean-CBF was calculated in ROI_dem and in the whole-brain within a standard (GM+WM>70%) and expanded (GM+WM>5%) mask. Spatial coefficient of variation (sCoV)6 was calculated for GM(>70%) and whole-brain (GM+WM>70%). Statistical significances were calculated using repeated measure ANOVA (P<0.05).
Whole-brain CBF values using the expanded mask showed better agreement between three vendors than the standard mask (Figure 1). There was no significant difference in mean-CBF of ROI_dem for Philips and Siemens, while GE showed significantly lower mean-CBF in these regions (Figure 2). sCoV also showed a similar trend, with GE having the lowest sCoV relative to Philips and Siemens for both whole-brain and GM (Figure 3).
Whole-brain CBF was similar across vendors when an expanded mask was applied. However, there was a difference between GE and Philips/Siemens in CBF and sCoV in grey matter regions. We hypothesize that the differences are related to between-scanner differences in effective spatial resolution, in particular the lower effective resolution of GE’s spiral readout7. Future work will investigate whether smoothness equalization8 can account for this. We anticipate that this work will increase the utility of ASL as a perfusion biomarker in multi-center dementia studies.

  • Open Access Logo Contribution to proceedings
    Alzheimer's Association International Conference, 22.07.2018, Chicago, USA
    DOI: 10.1016/j.jalz.2018.06.1785
  • Poster
    Alzheimer's Association International Conference, 22.07.2018, Chicago, USA

Publ.-Id: 27343

Kinetische Untersuchungen zur Laugung von Erzen und Konzentraten angereichert mit Seltenen Erden

Erben, J.; Balinski, A.

Rare earth elements are an essential part of high-tech devices in the entertainment, automotive and aerospace industry, which is why there is a growing demand for these elements. However, benefication and processing of rare earths is difficult. Thus, there are several studies concerning with the reaction chemistry and the finding of more economical extraction methods for rare earth metals. This study concerns with the liberation and reaction chemistry of a silicate rare earth ore, from the mine Strange Lake, in Canada. The chemical kinetics are focused in order to investigate the chemical behavior of rare earth elements. Therefore, a kinetic model, suggested frequently in literature, is applied and the study’s objective is the examination of the practicality of this model for this specific material. The concentrate was therefore leached for four hours at elevated temperature (50 to 90°C) and with concentrated sulfuric acid (1M to 3M H2SO4). The influence of temperature, acid concentration and pulp density was studied.
It was found that the recovery of the measured rare earth elements could be optimized from around 50 to about 80 Wt% by a temperature increase of 40°C. Hence, it is considered that leaching of rare earth elements is an endothermic process. The highest recovery could be determined for europium and yttrium with around 80 Wt% (90°C, 3M H2SO4). Besides that, a raise in sulfuric acid concentration of 2 mol/l resulted in an increase of recovery of 20 Wt% for the totality of the measured rare earth elements. Aside from agitation and particle size, also the pulp density has important impacts on the leaching process concerning retention time and throughput. In this study pulp density was raised from 5 to 25% (w/v), thereby enhancing the recovery from about 80 Wt% to about 95 Wt%. The kinetic mechanisms are described by the shrinking core model. The rate of reaction versus time and the Arrhenius plots were determined for the measured elements. It was observed that leaching of rare earth elements is controlled by transport mechanisms, which occur by inner diffusion through a porous ash layer. The activation energy EA for the measured rare earth species was respectively determined and it was found that most of these EA values are in the range of 25 kJ/mol to 50 kJ/mol. This order of magnitude allows the assumption, that the rate limiting step of leaching rare earths is inner diffusion.

Keywords: Rare Earth Elements; Leaching

  • Other
    Helmholtz-Institut Freiberg für Ressourcentechnologie, 2018
    Mentor: Balinski, Adam; Scharf, Chrisitane
    53 Seiten

Publ.-Id: 27342

Positron Studies with a Superconducting Electron Accelerator

Wagner, A.; Butterling, M.; Hirschmann, E.; Krause-Rehberg, R.; Liedke, M. O.; Potzger, K.

The Helmholtz-Center at Dresden-Rossendorf operates several user beamlines for materials research using positron annihilation energy and lifetime spectroscopy. A superconducting electron LINAC [1] serves as a driver for hard X-ray production from electron-bremsstrahlung which in turn generates positrons through pair production. GiPS, the Gamma-induced Positron Source directly generates electron-positron pairs inside the sample under investigation [2]. The source is especially suited for materials which are not qualified for vacuum conditions or because they are imposing hazardous conditions or intrinsic radioactivity. Some exemplary defect studies [3] will be presented. MePS, the Monoenergetic Positron Source utilizes positrons with discrete energies ranging from 500 eV to 16 keV [4] for thin film studies. A magnetic beam transport system guides positrons to the sample under investigation. Applications of porosimetry studies in low-k dielectrics [5] and polymer brushes [6] will be presented. The MePS facility is currently complemented by the AIDA-II - Apparatus for in-situ Defect Analysis - where defect studies can be performed in a wide temperature range during thin film growth and ion irradiation. The precedent setup AIDA-I is in operation at a 22Na-based mono-energetic continuous positron beam [7] used for Doppler-broadening spectroscopy experiments [8,9].
The MePS facility has partly been funded by the Federal Ministry of Education and Research (BMBF) with the grant PosiAnalyse (05K2013). AIDA-I was funded by the Impulse- und Networking fund of the Helmholtz-Association (FKZ VH-VI-442 Memriox). The AIDA-II facility was funded through the Helmholtz Energy Materials Characterization Platform.

[1] F. Gabriel, et al., Nucl. Instr. Meth. B 161, 1143 (2000).
[2] M. Butterling, et al., Nucl. Instr. Meth. B 269, 2623 (2011).
[3] M. Reiner, et al., Scientific Reports 6, 29109 (2016).
[4] A. Wagner, et al., Journal of Physics: Conference Series 791, 012004 (2017).
[5] A. Uedono, et al., Applied Surface Science 368, 272 (2016).
[6] G. Panzarasa, et al., Macromolecules 50, 5574 (2017).
[7] W. Anwand, et al., Defect and Diffusion Forum Vl. 331, 25 (2012).
[8] M. O. Liedke, et al., Journal of Applied Physics 117 163908 (2015).
[9] T. Kosub, et al., Nature Communications 8, 13985 (2017).

  • Invited lecture (Conferences)
    18th International Conference on Positron Annihilation, 18.-24.08.2018, Orlando, FL, USA

Publ.-Id: 27341

Optimierung eines alternativen Laugungsverfahrens zur Gewinnung von Seltenen Erden aus Erzen/Konzentraten mit hohem Anteil an säurelöslichen Silikaten mit gleichzeitiger Vorreinigung der Laugungslösung

Burisch, F.; Balinski, A.

Seltene Erdelemente (SEE), eine Gruppe aus 17 chemisch sehr ähnlichen Metallen, sind in der heutigen Zeit ein wichtiger Bestandteil unserer technologischen Entwicklung. Wichtige Anwendungen stellen beispielsweise die Herstellung von starken Dauermagneten (Neodym-Eisen-Bor, Samarium-Kobalt), Katalysatoren und Elektronik (LCD, Laser, optische Temperatursensoren) dar. Die verwendeten Mengen in den einzelnen Applikationen sind meist gering, dennoch ist die Nachfrage an diesen Metallen hoch. Dies ist darauf zurückzuführen, dass der Einsatz der SEE in manchen Anwendungsgebieten alternativlos ist.
Die Lage auf dem Weltmarkt ist problematisch, denn China besitzt derzeit das Monopol der Seltenen-Erden-Produktion. Um auch in Zukunft die Industrie mit diesen begehrten Metallen versorgen und das Chinamonopol umgehen zu können, ist es wichtig neue Ressourcen ausfindig zu machen und Technologien zur Verarbeitung zu entwickeln. Einer dieser möglichen neuen Ressourcen ist die Eudialyt-Lagerstätte Norra Kärr.
Diese Studienarbeit soll mögliche Verarbeitungsmethoden des Eudiaylt-Erzes untersuchen. Ein Teil dieser Arbeit befasst sich mit der Laugung des Erzes durch Schwefelsäure bei unterschiedlichen Laugungstemperaturen sowie Säurekonzentrationen. In der Auswertung wurde dabei auf den Laugungsverlauf und Laugungsausbeuten eingegangen. Des Weiteren sind die Säureverbräuche bestimmt und die Laugungsrückstände mittels Mineral Liberation Analysis (MLA) untersucht worden, um die mineralogische Zusammensetzung nach der Laugung beurteilen zu können. Problematisch bei der Verarbeitung des silikatischen Eudialyts ist die Entstehung von Kieselsäure in der Laugungslösung. Diese bedingt eine schlechte Filtrierbarkeit, wodurch sich der 2. Teil der Studienarbeit mit einem Verfahren zur Unterdrückung des Kieselgels befasst. Hierfür wurde ein 2-stufiger Aufschluss verwendet. Der 1. Schritt besteht aus einem Aufschluss des Erz-Säure-Gemisches bei 105 °C, der 2. Schritt aus einer Laugung mit Wasser. Die durch die Kieselgelbildung beeinflussbare Filtrationsgeschwindigkeit wurde anhand der unterschiedlichen Aufschlusszeiten verglichen. Außerdem konnte ein Vergleich der Laugungsausbeuten zwischen konventioneller und dem 2-stufigen Verfahren erfolgen. Ebenfalls geht diese Arbeit auf das Silizium als Störelement sowie Zirkonium, Hafnium und Mangan als weitere Wertelemente ein.

Keywords: Eudialyt; Seltene Erden; Laugung

  • Other
    Helmholtz-Institut Freiberg für Ressourcentechnologie, 2018
    Mentor: Balinski, Adam; Scharf, Chrisitane
    62 Seiten

Publ.-Id: 27340

Dose-guided patient positioning in proton radiotherapy using multicriteria-optimization

Kurz, C.; Süss, P.; Arnsmeyer, C.; Haehnle, J.; Teichert, K.; Landry, G.; Hofmaier, J.; Exner, F.; Hille, L.; Kamp, F.; Thieke, C.; Ganswindt, U.; Valentini, C.; Hölscher, T.; Troost, E.; Krause, M.; Belka, C.; Küfer, K.; Parodi, K.; Richter, C.

Proton radiotherapy (PT) requires accurate target alignment before each treatment fraction, ideally utilizing 3D in-room X-ray computed tomography imaging (CT). Typically, the optimal patient position is determined on the basis of anatomical landmarks or implanted markers. In the presence of non-rigid anatomical changes, however, the planning scenario cannot be exactly reproduced and positioning should rather aim at finding the optimal position in terms of the actually applied dose.
In this work, dose-guided patient alignment, implemented as multicriterial optimization (MCO) problem, has been investigated in the scope of intensity modulated and double scattered proton therapy (IMPT and DSPT) for the first time. A method for automatically determining the optimal patient position with respect to pre-defined clinical goals was implemented. Linear dose interpolation was used to access a continuous space of potential patient shifts. Fourteen head and neck (H&N) and eight prostate cancer patients with repeated CT data (up to 5 control CTs) were included in this study. Dose interpolation accuracy was evaluated and the potential dosimetric advantages of dose-guided over anatomy-based patient alignment investigated by comparison of clinically relevant target and organ-at-risk (OAR) dose-volume histogram (DVH) parameters.
Dose interpolation was found sufficiently accurate with average pass-rates of 90% and 99% for an exemplary H&N and prostate patient, respectively, using a 2% dose-difference criterion. Compared to anatomy-based alignment, the main impact of automated MCO-based dose-guided positioning was a reduced dose to the serial OARs (spinal cord and brain stem) for the H&N cohort. For the prostate cohort, under-dosage of the target structures could also be efficiently diminished. Limitations of dose-guided positioning were mainly found in reducing target over-dosage due to weight loss for H&N patients, which might require adaptation of the treatment plan.
Since labor-intense online quality-assurance is not required for dose-guided patient positioning, it might, nevertheless, be considered an interesting alternative to full online re-planning.


Publ.-Id: 27339

Influence of thin film morphology and stacking sequence on Ni-catalyzed graphitization of thin amorphous carbon films

Janke, D.; Wenisch, R.; Munnik, F.; Julin, J.; Hübner, R.; Gemming, S.; Rafaja, D.; Krause, M.

Metal-induced crystallization with layer exchange (MIC w LE) reduces the crystallization temperature of group 14 elements significantly. This is especially interesting for device fabrication on substrates with limited thermal stability. In this contribution, MIC w LE is applied on Ni and C thin film stacks with different stacking sequences. The influence of the thin film morphology and stacking on the layer exchange degree αLE and the graphitic ordering is studied comprehensively in situ and ex situ.
During annealing of the thin films at up to 700 °C, film morphology and stacking sequence had a significant impact on αLE, showing an incomplete LE for the C/Ni stack. The highest αLE of 96%, determined by RBS and ERDA, was achieved for the smoothest samples and Ni/C stacking sequence. Raman spectroscopy and TEM demonstrated the formation of 2D crystalline carbon structures independently of the stacking sequence, while the degree of graphitic ordering increased with decreasing surface roughness. The simultaneous occurrence of LE and graphitization has been demonstrated in situ by RBS and Raman, giving insights into mechanism responsible for carbon crystallization in this system.

Keywords: metal-induced crystallization; layer exchange; amorphous carbon; Rutherford backscattering spectrometry; Raman spectroscopy; elastic recoil detection

  • Poster
    International Winterschool on Electronic Properties of Novel Materials, 17.-24.03.2018, Kirchberg in Tirol, Österreich

Publ.-Id: 27337

Interactions of extremely halophilic Halobacterium species with uranium

Hilpmann, S.; Bader, M.; Bachran, M.; Steudtner, R.; Drobot, B.; Schmidt, M.; Stumpf, T.; Cherkouk, A.

Rock salt formations are considered as potential host rocks for the long-term storage of highly radioactive waste in a deep geological repository. A combination of culture-dependent and culture-independent methods was used to investigate the microbial diversity in rock salt. Extremely halophilic archaea, e.g. Halobacterium species, dominate this habitat. For long-term risk assessment it is of high interest to study how these microorganisms can interact with radionuclides if released from the waste repository. Therefore, the interactions of different extremely halophilic Halobacterium species with uranium, one of the major radionuclides of concern in the geological repository, were investigated in detail in batch experiments. A multi-spectroscopic and microscopic approach was used to decipher the interaction mechanisms on a molecular level. Depending on the used initial uranium concentration the different Halobacterium species showed a different bioassociation behaviour of uranium. By using time-resolved laser-induced fluorescence spectroscopy the formation of U(VI) phosphate minerals, such as meta-autunite, as well as the complexation with carboxylate groups was observed as a function of the uranium concentration and the Halobacterium species. Furthermore, the presence of U(VI)-phosphate minerals could be visualized by scanning electron microscopy. These findings highlight the potential significance of the microbial life in deep geological hypersaline environments and offer new insights into the microbe-actinide interactions at highly saline conditions relevant to the disposal of highly radioactive waste as well as bioremediation.

  • Poster
    8. RCA workshop, 12.-14.06.2018, Dresden, Deutschland

Publ.-Id: 27336

Data set to illustrate advanced process-synchronized computed tomography for the investigation of periodic processes

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

This data set contains raw data and data read-in routines used for the publication:
"Advanced process-synchronized computed tomography for the investigation of periodic processes"

Object of investigation: A centrifugal pump that impeller rotates at 1480 rpm and that is operated in gas-liquid two phase flow.
Used CT imaging system: HireCT (high resolution gamma-ray computed tomography) scanner of the HZDR

Keywords: Tomographic imaging; synchronized data acquisition; multiphase flow; centrifugal pump

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-04-12
    DOI: 10.14278/rodare.7
    License: CC-BY-4.0


Publ.-Id: 27335

Fabrication of Y128-and Y36-cut lithium niobate single-crystalline thin films by crystal-ion-slicing technique

Shuai, Y.; Gong, C.; Bai, X.; Wu, C.; Luo, W.; Böttger, R.; Zhou, S.; Tian, B.; Zhang, W.

Y128- and Y36-cut single-crystalline lithium niobate (LN) thin films are fabricated by the crystal-ion-slicing (CIS) technique onto LN substrates. The conditions for the successful exfoliation of submicron-thick LN thin films are independent of the wafer orientation used in the present work. Wafer bonding using benzocyclobutene (BCB) is adopted to transfer LN thin films onto substrates, instead of the generally used hydrophilic bonding, which does not need a strict surface polishing process before the bonding. A noncontact polishing method involving low-energy Ar+ irradiation is adopted to treat the sliced LN thin films. The atomic force microscopy result shows that the surface roughness of the LN thin film is reduced from 10.6 to 6.4nm.

Keywords: Lithium niobate; Crystal-ion-slicing; ion implantation

Publ.-Id: 27334

Heavy doping of CdTe single crystals by Cr ion implantation

Popovych, V. D.; Böttger, R.; Heller, R.; Zhou, S.; Bester, M.; Cieniek, B.; Mroczka, R.; Lopucki, R.; Sagan, P.; Kuzma, M.

Implantation of bulk CdTe single crystals with high fluences of 500 keV Cr+ ions was performed to achieve Cr concentration above the equilibrium solubility limit of this element in CdTe lattice. The structure and composition of the implanted samples were studied using secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) to characterize the incorporation of chromium into the host lattice and to investigate irradiation-induced damage build-up. It was found that out-diffusion of Cr atoms and sputtering of the targets alter the depth distribution and limit concentration of the projectile ions in the as-implanted samples. Appearance of crystallographically oriented, metallic α-Cr nanoparticles inside CdTe matrix was found after implantation, as well as a strong disorder at the depth far beyond the projected range of the implanted ions.

Keywords: CdTe; Ion implantation; Doping; Irradiation-induced damage; Rutherford backscattering spectrometry; Secondary ion mass spectrometry

Publ.-Id: 27333

Advanced process-synchronized computed tomography for the investigation of periodic processes

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

Computed tomography (CT) is known for giving cross-sectional images of a body. As tomographic scans require mechanical movement of components, data acquisition is commonly too slow to capture dynamic processes, which are faster than the acquisition time for a single image. Time-averaged angle-resolved CT imaging is a more recent method, which has demonstrated a capability to sharply image fast rotating machinery components by synchronizing data acquisition with rotation. However, in this modality all information on static parts disappear. In this paper, a novel data acquisition approach is introduced that combines both CT imaging methods. Eventually, the developed method is exemplarily applied to the study of gas-liquid flow in an industrial centrifugal pump using high-resolution gamma-ray tomography imaging.

Keywords: Tomographic imaging; synchronized data acquisition; multiphase flow; centrifugal pump


Publ.-Id: 27330

Ion Microscopy

Hlawacek, G.

Helium Ion Microscopy is a relatively young imaging and nanofabrication technique which is based on a gas field ionization source.
It rasters a narrow beam of helium ions as across the surface of the specimen to obtain high resolution surface sensitive images.
Usually secondary particles such as electrons are collected for image formation but also photons, backscattered atoms or sputtered sample atoms can be used for image formation.
Thanks to the very high brightness of the source a lateral resolution as small as 0.5\,nm can be achieved.
The method is in particular suitable for obtaining high resolution images of insulating samples (such as ceramic materials and biological samples) as the built in charge compensation allows to observe such specimen with out any additional conductive coatings.
In this contribution I will introduce the method and briefly introduce the underlying physics.
In the rest of the chapter a number of imaging modes will be discussed and selected examples will be presented.
Finally, an outlook is presented on the ongoing efforts to add analytical capabilities to the method.

Keywords: Helium Ion Microscopy; HIM; SIMS; RBS; imaging; Ionoluminescence

  • Book chapter
    Peter Hawkes, John C.H. Spence: Springer Handbook of Microscopy, Heidelberg: Springer, 2019, 978-3-030-00068-4, 677-714
    DOI: 10.1007/978-3-030-00069-1_14

Publ.-Id: 27329

Improving depth resolutions in positron beam spectroscopy by concurrent ion-beam sputtering

John, M.; Dalla, A.; Ibrahim, A. M.; Anwand, W.; Wagner, A.; Böttger, R.; Krause-Rehberg, R.

The depth resolution of mono-energetic positron annihilation spectroscopy using a positron beam is shown to improve by concurrently removing the sample surface layer during positron beam spectroscopy. During ion beam sputtering with argon ions, Doppler-broadening spectroscopy is performed with energies ranging from 3 keV to 5 keV allowing for high-resolution defect studies just below the sputtered surface. With this technique, significantly improved depth resolutions could be obtained even at larger depths when compared to standard positron beam experiments which suffer from extended positron implantation profiles at higher positron energies. Our results show that it is possible to investigate layered structures with a thickness of about 4 microns with significantly improved depth resolution. We demonstrated that a purposely generated ion-beam induced defect profile in a silicon sample could be resolved employing the new technique. A depth resolution of less than 100 nm could be reached.

Keywords: positron annihilation spectroscopy ion-beam sputtering

Publ.-Id: 27328

Magnetic properties of Co/Ni grain boundaries after annealing

Coutts, C.; Arora, M.; Hübner, R.; Heinrich, B.; Girt, E.

Magnetic and microstructural properties of <111> textured Cu/Nx[Co/Ni] films are studied as a function of the number of bilayer repeats N and annealing temperature. M(H) loop measurements show that coercivity, Hc, increases with annealing temperature and that the slope of the saturation curve at Hc has a larger reduction for smaller N. An increase of the magnetic anisotropy (Ku) to saturation magnetization (Ms) ratio after annealing Nx[Co/Ni] with N < 15 only partially describes the increase to Hc. Energy-dispersive X-ray spectroscopy analyses performed in scanning transmission electron microscopy mode across cross-sections of as-deposited and annealed Cu/16x[Co/Ni] films show that Cu diffuses from the seed layer into grain boundaries of Co/Ni. Diffusion of Cu reduces exchange coupling (Hex) between the magnetic grains and explains the increase in Hc. Additionally, the difference in the slope of the M(H) curves at Hc between the thick (N = 16) and thin (N = 4) magnetic multilayers is due to Cu diffusion more effectively decoupling magnetic grains in the thinner multilayer.

Publ.-Id: 27327

Prognostic value of SUR in patients with trimodality treatment of locally advanced esophageal carcinoma

Bütof, R.; Hofheinz, F.; Zöphel, K.; Schmollack, J.; Jentsch, C.; Zschaeck, S.; Kotzerke, J.; van den Hoff, J.; Michael Baumann, M.

The prognosis of patients with esophageal carcinoma remains dismal despite ongoing efforts to improve treatment options. For locally advanced tumors, several randomized trials have shown the benefit of neoadjuvant chemoradiation followed by surgery compared to surgery alone. The aim of this exploratory study was to evaluate the prognostic value of different baseline positron emission tomography (PET) parameters and their potentially additional prognostic impact at the end of neoadjuvant radiochemotherapy. Furthermore, the standard uptake ratio (SUR) as a new parameter for quantification of tumor metabolism was compared to the conventional PET parameters metabolic active volume (MTV), total lesion glycolysis (TLG), and standardized uptake value (SUV) taking into account known basic parameters.

Methods: 18F-FDG-PET/CT was performed in 76 consecutive patients ((60±10) years, 71 males) with newly diagnosed esophageal cancer before and during the last week of neoadjuvant radiochemotherapy. MTV of the primary tumor was delineated with an adaptive threshold method. The blood SUV was determined by manually delineating the aorta in the low dose CT. SUR values were computed as scan time corrected ratio of tumor SUVmax and mean blood SUV. Univariate Cox regression and Kaplan-Meier analysis with respect to locoregional control (LRC), freedom from distant metastases (FFDM), and overall survival (OS) was performed. Additionally, independence of PET parameters from standard clinical factors was analyzed with multivariate Cox regression.

Results: In multivariate analysis two parameters showed a significant correlation with all endpoints: restaging MTV and restaging SUR. Furthermore, restaging TLG was prognostic for LCR and FFDM. For all endpoints the largest effect size was found for restaging SUR. The only basic factors remaining significant in multivariate analyses were histology for OS and FFDM and age for LRC.

Conclusion: PET provides independent prognostic information for OS, LRC, and FFDM in addition to standard clinical parameters in this patient cohort. Our results suggest that the prognostic value of tracer uptake can be improved when characterized by SUR rather than by SUV. Overall, our investigation revealed a higher prognostic value of restaging parameters compared to baseline PET; therapy-adjustments would still be possible at this point of time. Further investigations are required to confirm these hypothesis-generating results.

Keywords: FDG-PET; SUV; SUR; MTV; prognostic value; esophageal cancer

Publ.-Id: 27326

Increased evidence for the prognostic value of late-treatment FDG-PET uptake in non-tumor affected oesophagus in irradiated patients with oesophageal carcinomas

Li, Y.; Hofheinz, F.; Furth, C.; Lili, C.; Hua, W.; Ghadjar, P.; Zschaeck, S.

Purpose: 18F-fluorodeoxyglucose (FDG) uptake within irradiated non-tumor affected oesophagus (NTO) at re-staging positron emission tomography (PET) is a potential surrogate to measure radiation induced inflammation (RIF). RIF itself was shown to be of high prognostic relevance in patients undergoing preoperative radiochemotherapy (RCT) for locally advanced oesophageal cancer. We assessed the prognostic relevance of NTO uptake in an independent cohort of patients treated with definitive RCT.

Methods: Seventy-two patients with oesophageal squamous cell carcinomas treated with curative intent definitive RCT were retrospectively evaluated. All patients underwent pre-treatment and re-staging FDG-PET after 40-50 Gray radiation dose. Standardized uptake values (SUVmax/SUVmean), metabolic tumor volume (MTV) and relative changes between pre-treatment and re-staging PET (∆SUVmax/∆SUVmean) were determined within tumor and NTO. Univariate Cox regression with respect to overall survival (OS), local control (LC), distant metastases (DM) and treatment failure (TF) was performed. Independence of parameters was tested in multivariate Cox regression.

Results: ∆SUVmax NTO and MTV were prognostic factors for all investigated clinical endpoints (OS, LC, DM, TF). Inclusion of clinical and PET tumor parameters in multivariate analysis showed ∆SUVmax NTO as an independent prognostic factor. Furthermore, multivariate analysis of ∆SUVmax NTO with previously published cutoffs from the preoperatively treated patients revealed ∆SUVmax NTO as independent prognostic factor for OS (HR=1.88, p=0.038), TF (HR=2.11, p=0.048) and DM (HR=3.02, p=0.047).

Conclusions: NTO-related tracer uptake during course of treatment in patients suffering from esophageal carcinoma was proven to be of high prognostic relevance. Thus, metabolically activity of NTO measured by ∆SUVmax NTO is a potential candidate for future treatment individualization (i.e. organ preservation).

Keywords: oesophageal cancer; definitive radiochemotherapy; re-staging; response assessment; normal tissue; side effects; inflammation; FDG PET

Publ.-Id: 27325

Effects of systematic partial volume errors on the computation of mean gray matter cerebral blood flow with Arterial Spin Labeling MRI

Petr, J.; Mutsaerts, H. J. M. M.; de Vita, E.; Steketee, R. M. E.; Smits, M.; Nederveen, A. J.; Hofheinz, F.; van den Hoff, J.; Asllani, I.

Objectives: Partial volume (PV) correction is an important step in arterial spin labeling (ASL) MRI used to separate perfusion effects from structural, and to calculate the mean gray-matter (GM) perfusion. There are currently three main methods to perform that: (1) including only voxels with GM volume above a preset threshold (GM-Threshold); (2) using weighted voxel contribution combined with thresholding (GM-Weighted); or (3) applying a spatial linear regression algorithm (PVEc). In all cases, GM volume is obtained from PV maps extracted from T1w images. As such, PV maps contain errors due to the difference in readout-type (a major source of geometric distortions) and spatial resolution between ASL and T1w images. Here, we estimated these errors and evaluated their effect on the performance of each PV-correction method.
Materials and Methods: Twenty-two volunteers were scanned using 2D EPI and 3D spiral ASL. For each PV-correction method, GM CBF was computed using PV maps simulated to contain estimated errors due to geometric distortions and resolution mismatch. Results were analyzed to assess the effect of each error on extraction of GM CBF from ASL data.
Results: Geometric distortion had the largest effect on the 2D EPI data whereas resolution mismatch on the 3D spiral. The PVEc method outperformed the GM-Threshold even in the presence of combined errors. The quantitative advantage of PVEc was 16% without and 10% with the combined errors for both readouts. Consistent with theoretical expectations, for error-free PV maps, PVEc method extracted the true GM CBF. In contrast, GM-Weighted overestimated GM CBF by 5% whereas GM-Threshold underestimated it by 16%. The presence of PV-map errors decreased the calculated GM CBF for all methods.
Conclusion: The quality of PV maps presents no argument for preferring the GM-Threshold method to PVEc in clinical applications of ASL.


Publ.-Id: 27324

Enhanced optical-to-THz conversion efficiency of photoconductive antenna using dielectric nano-layer encapsulation

Gupta, A.; Rana, G.; Bhattacharya, A.; Singh, A.; Jain, R.; Bapat, R. D.; Duttagupta, S. P.; Prabhu, S. S.

Photoconductive antennas (PCAs) are among the most conventional devices used for emission as well as detection of terahertz (THz) radiation. However, due to their low optical-to-THz conversion efficiencies, applications of these devices in out-of-laboratory conditions are limited. In this paper, we report several factors of enhancement in THz emission efficiency from conventional PCAs by coating a nano-layer of dielectric (TiO2) on the active area between the electrodes of a semi-insulating GaAs-based device. Extensive experiments were done to show the effect of thicknesses of the TiO2layer on the THz power enhancement with different applied optical power and bias voltages. Multiphysics simulations were performed to elucidate the under-lying physics behind the enhancement of efficiency of the PCA. Additionally, this layer increases the robustness of the electrode gaps of the PCAs with high electrical insulation as well as protect it from external dust particles.

Keywords: Terahertz emitter; GaAs; Photoconductivity; TiO2; Antireflection coating

Publ.-Id: 27323

Gapless broadband terahertz emission from a germanium photoconductive emitter

Singh, A.; Pashkin, A.; Winnerl, S.; Helm, M.; Schneider, H.

Photoconductive terahertz (THz) emitters have been fulfilling many demands required for table-top THz time-domain spectroscopy up to 3-4 THz. In contrast to the widely used photoconductive materials such as GaAs and InGaAs, Ge is a non-polar semiconductor characterized by a gapless transmission in the THz region due to absence of one-phonon absorption. We present here the realization of a Ge-based photoconductive THz emitter with a smooth broadband spectrum extending up to 13 THz and compare its performance with a GaAs-based analogue. We show that the spectral bandwidth of the Ge emitter is limited mainly by the laser pulse width (65 fs) and, thus, can be potentially extended to even much higher THz frequencies.

Keywords: Terahertz emitter; photoconductive emitter; broadband terahertz; germanium photoconductor


Publ.-Id: 27321

Untersuchung von Strahlenschäden an Plasmid-DNA durch 64Cu-markierte Pyrene unterschiedlicher Kettenlänge

Reissig, F.; Wunderlich, G.; Mamat, C.; Jentschel, C.; Pietzsch, H.-J.; Steinbach, J.; Kotzerke, J.

64Cu wird für die nuklearmedizinische Anwendung diskutiert. Neben der Kernumwandlung über Elektroneneinfang werden auch Positronen und Auger-Elektronen (AE) emittiert. Um deren Wirkungspotential an DNA zu untersuchen, wurden zunächst zwei Pyrenderivate mit unterschiedlicher Spacerlänge zwischen Pyreneinheit und DOTA-Chelator mit [64Cu]CuCl2 radiomarkiert. Die induzierten Strahlenschäden an pUC19 Plasmid-DNA wurden in Abhängigkeit von der Dosis untersucht.

Keywords: Kupfer-64; Pyrene; DNA; Auger-Elektron

  • Poster
    DGN Jahrestagung 2018, 18.-21.04.2018, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 57(2018)2, A69-A69

Publ.-Id: 27320

Bubble column with internals: Comparative hydrodynamic analysis of narrow and pilot-scale columns

Möller, F.; Kipping, R.; Hampel, U.; Schubert, M.

Bubble columns are widely applied reactors in the chemical process industry due to their excellent heat and mass transfer properties as well as their simple design and easy manufacturing without any moving part. Fischer-Tropsch and methanol syntheses are typical processes carried out in such columns. Most of the involved reactions are highly exothermic and require an efficient heat removal, for example, via internal tube bundle heat exchangers. Heat exchangers, with up to 60 m2 m-3 surface area, can be installed as dense tube bundles covering up to 60 % of the cross-sectional area, which accordingly, alter hydrodynamics, flow patterns, mixing and mass transfer significantly.
Therefore, this study aims at revealing the influence of common tube bundle layouts, i.e. triangular and square pitches, at various tube diameters at approx. 25 % cross-sectional area coverage. The studies were carried out using narrow and pilot-scale bubble columns with 100 and 400 mm diameter, respectively, operated with air and water. Ultrafast X-ray tomography as well as wire-mesh sensors were applied to study the columns’ hydrodynamics as well as the flow in individual sub-channels. In particular, holdup and bubble size distributions were measured and compared for both columns. Furthermore, it is discussed to which extend hydrodynamic parameters, such as radial holdup profiles and gas velocity profiles etc., can be utilized for scale-up purposes based on hydrodynamic similarity at both reactor scales.

  • Poster
    Jahrestreffen der ProcessNet Fachgruppen MPH, WSUE, CFD, HTT, AuW, KRI, PMT, 06.-09.03.2018, Bremen, Deutschland

Publ.-Id: 27319

Quantification: there is more to worry about than good scanner hardware and reliable calibration

Kotzerke, J.; van den Hoff, J.

Positron emission tomography (PET) is "an analytical imaging technology developed to use compounds labelled with positron-emitting radioisotopes as molecular probes to image and measure biochemical processes of mammalian biology in vivo" [1]. One outstanding feature of the PET technology is the ability to perform absolute quantification of regional perfusion, metabolism, and function [2]. There are clinical demands for quantification regarding description of biodistribution, dosimetry, intra- and inter-individual comparisons, and setup of age- and gender-specific (normal) databases. Notably, FDG PET allows diagnosis, differential diagnosis, assessment of prognosis, and patient stratification in malignant disease. Moreover, image guided therapy has been proven to improve tumour delineation and irradiation field definition regarding protection of normal tissue and dose escalation on tumour tissue [3]. After initial assessment, follow-up investigations describe the effect of therapy and influence therapeutic management regarding continuation or change of modality and intensification or de-escalation of therapy. In addition to qualitative description and quantification of tracer uptake or uptake changes during follow-up, more sophisticated kinetic modelling and analysis may be applied. However, reliability and significance of all derived numbers is influenced by technical factors and biological processes.

Publ.-Id: 27318

Dosimetry of Highly Pulsed Radiation Fields

Gotz, M.

Synchrocyclotrons and laser based particle accelerators, developed with the goal to enable more compact particle therapy facilities, may bring highly pulsed radiation field to external beam radiation therapy. In addition, such highly pulsed fields may be desirable due to their potential clinical benefits regarding better healthy tissue sparing or improved gating for moving tumors. However, they pose new challenges for dosimetry, the corner stone of any application of ionizing radiation.
These challenges affect both clinical and radiation protection dosimetry. Air-filled ionization chambers, which dominate clinical dosimetry, face the problem of increased signal loss due to volume recombination when a highly pulsed field liberates a large amount of charge in a short time in the chamber. While well established descriptions exist for this volume recombination for the moderately pulsed fields in current use (Boag's formulas), the assumptions on which those descriptions are based will most likely not hold in the prospective, highly pulsed fields of future accelerators. Furthermore, ambient dose rate meters used in radiation protection dosimetry as survey meters or fixed installations are generally only tested for continuous fields, casting doubt on their suitability to measure pulsed fields.
This thesis investigated both these aspects of dosimetry - clinical as well as radiation protection - to enable the medical application of highly pulsed radiation fields. For a comprehensive understanding, experimental investigations were coupled with theoretical considerations and developments.
Pulsed fields, varying in both dose-per-pulse and pulse duration over a wide range, were generated with the ELBE research accelerator, providing a 20 MeV pulsed electron beam. Ionization chambers for clinical dosimetry were investigated using this electron beam directly, with an aluminium Faraday cup providing the reference measurement. Whereas the dose rate meters were irradiated in the photon field generated from stopping the electron beam in the Faraday cup. In those measurements, the reference was calculated from the ionization chamber, then serving a an electron beam monitor, cross-calibrated to the photon field with thermoluminescent dosimeters.
Three dose rate meters based on different operating principles were investigated, covering a large portion of the operating principles used in radiation protection: the ionization chamber based RamION, the proportional counter LB 1236-H10 and the scintillation detector AD-b. Regarding clinical dosimetry, measurements of two prominent ionization chamber geometries, plane-parallel (Advanced Markus chamber) and thimble type (PinPoint chamber), were performed. In addition to common air-filled chambers, chambers filled with pure nitrogen and two non-polar liquids, tetramethylsilane and isooctane, were investigated.
In conjunction with the experiments, a numerical solution of the charge liberation, transport, and recombination processes in the ionization chamber was developed to calculate the volume recombination independent of the assumptions necessary to derive Boag's formulas. Most importantly, the influence of the liberated charges in the ionization chamber on the electric field, which is neglected in Boag's formulas, is included in the developed calculation.
Out of the three investigated dose rate meters only the RamION could be identified as an instrument truly capable of measuring a pulsed field. The AD-b performed below expectations (principally, a scintillator is not limited in detecting pulsed radiation), which was attributed to the signal processing, emphasizing the problem of a typical black-box signal processing in commercial instruments. The LB 1236-H10, on the other hand, performed as expected of a counting detector. While this supports the recent effort to formalize these expectations and standardize testing for counting dosimeters in DIN IEC/TS 62743, it also highlights the insufficiency of counting detectors for highly pulsed fields in general and shows the need for additional normative work to establish requirements for dose rate meters not based on a counting signal (such as the RamION), for which no framework currently exists. With these results recognized by the German radiation protection commission (SSK) the first steps towards such a framework are taken.
The investigation of the ionization chambers used in radiation therapy showed severe discrepancies between Boag's formulas and the experimentally observed volume recombination. Boag's formulas describe volume recombination truly correctly only in the two liquid-filled chambers. All the gas-filled chambers required the use of effective parameters, resulting in values for those parameters with little to no relation to their original meaning. Even this approach, however, failed in the case of the Advanced Markus chamber for collection voltages ≥ 300 V and beyond a dose-per-pulse of about 100 mGy.
The developed numerical model enabled a much better calculation of volume recombination and allowed the identification of the root of the differences to Boag's formulas as the influence of the liberated charges on the electric field. Increased positive space charge due to increased dose-per-pulse slows the collection and reduces the fraction of fast, free electrons, which are unaffected by volume recombination. The resultant increase in the fraction of charge undergoing volume recombination, in addition to the increase in the total amount of charge, results in an increase in volume recombination with dose-per-pulse that is impossible to describe with Boag's formulas. It is particularly relevant in the case of high electric fields and small electrode distances, where the free electron fraction is large. In addition, the numerical calculation allows for arbitrary pulse durations, while Boag's formulas apply only to very short pulses.
In general, the numerical calculation worked well for plane-parallel chambers, including those filled with the very diverse media of liquids, nitrogen and air. Despite its increased complexity, the thimble geometry could be implemented as well, although, in the case of the PinPoint chamber, some discrepancies to the experimental data remained, probably due to the required geometrical approximations.
A possible future development of the numerical calculation would be an improved description of the voltage dependence of the volume recombination. At the moment it requires characterizing a chamber at each desired collection voltage, which could be eliminated by an improved modeling of the volume recombination's dependence on collection voltage. Nevertheless, the developed numerical calculation presents a marked improvement over Boag's formulas to describe the dose-per-pulse dependence and pulse duration dependence of volume recombination in ionization chambers, in principle enabling the application of ionization chambers in the absolute dosimetry of highly pulsed fields.

Keywords: dosimetry; pulsed radiation; radiation protection; saturation correction; volume recombination

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-090 2018
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 27317

Intrinsic Charge Dynamics in High-Tc AFeAs (O,F) Superconductors

Charnukha, A.; Pröpper, D.; Zhigadlo, N. D.; Naito, M.; Schmidt, M.; Wang, Z.; Deisenhofer, J.; Loidl, A.; Keimer, B.; Boris, A. V.; Basov, D. N.

We report the first determination of the in-plane complex optical conductivity of 1111 high-Tc superconducting iron oxypnictide single crystals PrFeAs(O,F) and thin films SmFeAs(O,F) by means of conventional and microfocused infrared spectroscopy, ellipsometry, and time-domain THz transmission spectroscopy. A strong itinerant contribution is found to exhibit a dramatic difference in coherence between the crystal and the film. Using extensive temperature-dependent measurements of THz transmission, we identify a previously undetected 2.5-meV collective mode in the optical conductivity of SmFeAs(O,F), which is strongly suppressed at Tc and experiences an anomalous T-linear softening and narrowing below T∗≈110  K≫Tc. The suppression of the infrared absorption in the superconducting state reveals a large optical superconducting gap with a similar gap ratio 2Δ/kBTc≈7 in both materials, indicating strong pairing.


Publ.-Id: 27316

Calorimetry techniques for ultra-intense laser-plasma experiments

Molodtsova, M.; Ferrari, A.; Laso Garcia, A.; Metzkes-Ng, J.; Irman, A.; Lutz, B.; Prencipe, I.; Sobiella, M.; Stach, D.; Weinberger, D.; Cowan, T. E.

With ultra-high intensity short pulse lasers generating plasma, new extreme states of matter can be created, and new concepts for particle acceleration, material science, and fusion energy can be explored. A critical component is the characterization of relativistic electrons that are accelerated and transported in the material of the target, generating ultra-intense bremsstrahlung.
Measuring the bremsstrahlung spectrum is a crucial aspect of plasma diagnostics. In this work it is showed how calorimetric techniques, based on longitudinally resolved measurements of energy deposition, are especially suitable for the reconstruction of the photon spectra and how electron dynamics can be studied.
Multi-layered scintillator calorimeters with different readouts are under development at Helmholtz-Zentrum Dresden-Rossendorf for this purpose. Prototypes have been tested at the ELBE facility both at the gELBE beamline with a well-known bremsstrahlung spectrum and in a laser-plasma environment at DRACO.

  • Lecture (Conference)
    DPG Spring Meeting 2018 of the Section on Atomic, Molecular, Plasma Physics and Quantum Optics (SAMOP), 05.-09.03.2018, Erlangen, Germany

Publ.-Id: 27315

GeoPET data for parametrization of reactive transport codes

Schymura, S.; Karimzadeh, L.; Gründig, M.; Barthen, R.; Hildebrand, H.; Mansel, A.; Franke, K.; Kulenkampff, J.; Fischer, C.; Lippmann-Pipke, J.

GeoPET is the application of positron emission tomography (PET) for direct, non-destructive, quantitative spatiotemporal measurement and visualization of fluid transport in natural geological media on drill-core scale. Data on heterogeneous flow and diffusion can be extracted from PET experiments which can be used to parameterize reactive transport models that better reflect the heterogenous nature of geochemical transport processes.
GeoPET functions through the use of positron emitting radioactive isotopes. The emitted positron quickly annihalates with electrons inside the matrix setting the physical resolution limit of the PET technique at about 1 mm spatial resolution. Upon annihilation two gamma photons are sent out in opposite directions that are detected coincidentally and thus hold information about the location of the original decay. This can be used to keep track of solute species, particles and solids. Through the use of [F-18]KF (halflife: 1.8 h) we are able to visualize heterogenous flow in geological media on drill-core scale and to extract flow fields and porosity data from the yielded data. Using Na-22 (halflife: 250 d) longer-term diffusion experiments can be perfomed and matrix-diffusion coefficients can be extracted from the data. Furthermore, through the development of appropriate labeling strategies we have visualized the transport of [I-124]MWCNTs and the initial stages of [Cu-64]CuS leaching.
In case of the technologically interesting application of in-situ copper bioleaching we have imaged matrix diffusion and the heterogenous flow through a Kupferschiefer sandstone fractured core sample. The extracted flow velocity fields and diffusion coefficients were used to parameterize a reactive transport model in the COMSOL-PHREEQC interface (iCP) to simulate mineral dissolution/precipitation, porosity change, as well as, copper extraction in the sequential leaching process employed within the BIOMOre project including water washing, acid washing and ferric iron acid leaching.

Keywords: Positronenemissions-Tomografie; positron emission tomography; Reaktiver Transport; reactive transport

  • Poster
    Aachen International Mining Symposia (AIMS 2018), 23.-24.05.2018, Aachen, Deutschland

Publ.-Id: 27314

Effect of microbial siderophore DFOB on mobility and transport of Cu: Column experiment and reactive transport modelling

Karimzadeh, L.; Lippmann-Pipke, J.; Franke, K.; Lippold, H.; Fischer, C.

We focus on the transport behaviour of Cu under conditions related to a biohydrometallurgical leaching approach using neutrophilic microorganisms in neutral to slightly alkaline solutions. The effect of the microbial siderophore desferrioxamineB (DFOB) as a model leaching organic ligand on mobility and transport of Cu in the presence of kaolinite was investigated in column experiments. A geochemical transport model was established to describe the results. It was found that DFOB strongly enhances Cu mobility. The reactive transport model (including a surface complexation model) shows good agreement with the experimental data and is suitable to predict the transport behaviour of Cu in dependence on geochemical conditions.
The results of modeling revealed that in the absence of the ligand, a pH increase from 6.5 to 8.5 significantly retarded Cu breakthrough, whereas in the presence of DFOB, Cu breakthrough curves were nearly insensitive to pH changes and close to the breakthrough curve of a non-reactive tracer.

Keywords: Reactive transport modeling; Cu mobility; Microbial siderophore DFOB

  • Lecture (Conference)
    Computational Methods in Water Resources XXII (CMWR), 03.-07.06.2018, Saint Malo, France

Publ.-Id: 27313

In situ structural study of the surface complexation of lead(II) on the chemically mechanically polished hematite (1-102) surface

Qiu, C.; Majs, F.; Eng, P.; Stubbs, J.; Douglas, T.; Schmidt, M.; Trainor, T.

A structural study of the surface complexation of Pb(II) on the (View the MathML source) surface of hematite was undertaken using crystal truncation rod (CTR) X-ray diffraction measurements under in situ conditions. The sorbed Pb was found to form inner sphere (IS) complexes at two types of edge-sharing sites on the half layer termination of the hematite (View the MathML source) surface. The best fit model contains Pb in distorted trigonal pyramids with an average Pbsingle bondO bond length of 2.27(4) Å and two characteristic Pb-Fe distances of 3.19(1) Å and 3.59(1) Å. In addition, a site coverage model was developed to simulate coverage as a function of sorbate-sorbate distance. The simulation results suggest a plausible Pb-Pb distance of 5.42 Å, which is slightly larger than the diameter of Pb’s first hydration shell. This relates the best fit surface coverage of 0.59(4) Pb per unit cell at monolayer saturation to steric constraints as well as electrostatic repulsion imposed by the hydrated Pb complex. Based on the structural results we propose a stoichiometry of the surface complexation reaction of Pb(II) on the hematite (1-102) surface and use bond valence analysis to assign the protonation schemes of surface oxygens. Surface reaction stoichiometry suggests that the proton release in the course of surface complexation occurs from the Pb-bound surface O atoms at pH 5.5.

Keywords: Pb(II); Hematite; Crystal truncation rod

Publ.-Id: 27312

Benchmark 3D reactive transport modelling of leaching of fractured calcareous sulfide ores

Karimzadeh, L.; Kulenkampff, J.; Schymura, S.; Lippmann-Pipke, J.

In the framework of the EU Horizon 2020 research project “BIOMOre” we developed a benchmark 3D reactive transport model to evaluate and predict insitu leaching (ISL) of fractured calcareous Kupferschiefer ore deposites. A critical challenge of our tasks is the implementation of the feedback between the evolution of porosity due to mineral dissolution/precipitation and modifications of the hydrodynamics of the reacting fluid. The sequential leaching of a calcareous sulfidic sandstone core (D=6 cm, L=10 cm) sampled from Kupferschiefer ore formation (Rudna mine, Poland) was done in laborytory. Here we present simulated results of the leaching of the core sample.
Geochemical modeling was performed by means of the COMSOL-PHREEQC interface iCP. The governing equations for fluid flow and conservative tracer transport are solved within the finite element code Comsol Multiphysics®. The geochemical processes considered in the model are kinetically controlled mineral dissolution and precipitation and equilibrium aqueous complexation reactions based on mass action law simulated by means of PHREEQC using BRGM database and advective-dispersive transport in the fracture and matrix diffusion in the rock mass calculated by COMSOL Multiphysics.
Calculated solution concentration of the outflow compares fairly well with the variation in the measured concentrations. Results showed that Cl is mainly released from halite which is totally removed in the washing stages. In addition our results showed that in stages 1, 2, and 3 about 0.04, 0.21, and 8.3% of Cu was extracted from sample respectively.

Keywords: reactive transport modeling; BIOMOre; insitu leaching

  • Lecture (Conference)
    Aachen International Mining Symposia (AIMS 2018), 23.-24.05.2018, Aachen, Germany

Publ.-Id: 27311

Advanced Analysis of Liquid Dispersion and Gas-Liquid Mass Transfer in a Bubble Column with Dense Vertical Internals

Möller, F.; Macisaac, A.; Lau, Y. M.; Schleicher, E.; Hampel, U.; Schubert, M.

The influence of dense vertical tube bundles in a batch bubble column reactor of 100 mm diameter and 1100 mm clear liquid height on liquid dispersion and gas-liquid mass transfer was studied. In particular, the effects of different tube patterns (triangular and square pitch), tube diameters (8 and 13 mm) and bottom end designs (flat and U-tube) having a tube diameter-to-pitch ratio of approx. 1.3 were investigated.
Dispersion coefficients were determined based on conductive tracer experiments recorded via wire-mesh sensors (WMS) with up to 90 measurement points distributed in the column’s cross-section in between the tubes. The gas-liquid mass transfer coefficient was determined via fast-responding oxygen needle probes. Tube pitch and pattern were identified as the most crucial design parameters for the extent of liquid dispersion. We found that particularly the U-tube bottom end design induces large liquid circulation patterns, which enhance dispersion. The presence of internals decreases the k_l a value as a consequence of turbulence damping, which is also confirmed by lower k_l values (e.g. 0.6 × 10-3 m s-1 for the empty BCR and 0.25 × 10-3 m s-1 for the square pitch with 8 mm tubes at 0.05 m s-1 superficial gas velocity), whereas the pitch is the most decisive design parameter. The U-tube bottom end design was identified as the most beneficial configuration with respect to liquid mixing and gas-liquid mass transfer.

Keywords: Bubble column; Heat exchanger internals; Gas-liquid mass transfer; 2D dispersion model; Wire-mesh sensor


Publ.-Id: 27309

Evolution of the spin hall magnetoresistance in Cr2O3/Pt bilayers close to the Néel temperature

Schlitz, R.; Kosub, T.; Thomas, A.; Fabretti, S.; Nielsch, K.; Makarov, D.; Goennenwein, S. T. B.

We study the evolution of magnetoresistance with temperature in thin film bilayers consisting of platinum and antiferromagnet Cr2O3 with its easy axis out of the plane. We vary the temperature from 20 °C to 60 °C, in the vicinity of the Néel temperature of Cr2O3 of approximately 37 °C. The magnetoresistive response is recorded during rotations of the external magnetic field in three mutually orthogonal planes. A large magnetoresistance having a symmetry consistent with a positive spin Hall magnetoresistance is observed in the paramagnetic phase of Cr2O3, which however vanishes when cooling to below the Néel temperature. Compared to analogous experiments in a Gd3Ga5O12/Pt bilayer, we conclude that a paramagnetic moment in the insulator induced by an applied magnetic field is not sufficient to explain the observed magnetoresistance. We speculate that the type of magnetic moment at the interface qualitatively impacts the spin angular momentum transfer, with the 3d moments of Cr sinking angular momentum much more efficiently as compared to the more localized 4f moments of Gd.

Publ.-Id: 27308

Competition of U(VI) hydroxide and carbonate complexation in alkaline solutions − implications for U(VI) retention by Ca-bentonite

Philipp, T.; Schmeide, K.; Rossberg, A.; Stumpf, T.

Thorough understanding of the aqueous complexation of U(VI) with ubiquitous inorganic ligands, such as hydroxide and carbonate, is crucial for predicting U(VI) mobility in natural and engineered systems, since retardation processes largely depend on the metal speciation. U(VI) hydrolysis [1] and complexation with carbonate in weakly alkaline media [2] have been extensively studied. This work systematically elucidates the U(VI) speciation in (hyper)alkaline solutions, where OH- and CO32- can occur in approximately equimolar quantities and compete for the complexation with U(VI). Such (hyper)alkaline conditions can evolve within deep geological repositories for radioactive waste by degradation of concrete. The effect of pH-dependent changes on the U(VI) sorption affinity was investigated by batch sorption experiments with Ca-bentonite, which is considered as buffer and backfill material within such repositories. Spectroscopic measurements provide information on the underlying retention mechanisms on the molecular level.
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) proofs the formation of (calcium) uranyl carbonate complexes in aqueous solution in the presence of carbonate. However, these complexes only form up to a certain pH. A sudden change of the speciation to uranyl hydroxides was detected above pH 10 at low carbonate concentrations (0.5 mM) and above pH 11 at high carbonate concentrations (100 mM).
Batch sorption experiments reveal that this ligand replacement of carbonate by hydroxide correlates with an increase in U(VI) retention by Ca-bentonite. The study shows that an almost complete sorption of U(VI) can be obtained in (hyper)alkaline repository environments, even though carbonate is present in substantial amounts.
In order to clarify the mechanisms responsible for the very strong U(VI) retention, uranyl complexes on the bentonite surface were examined directly, using X-ray absorption spectroscopy (Rossendorf Beamline (ROBL), ESRF, Grenoble). Extended X-ray absorption fine structure (EXAFS) spectra did not show any indication of precipitates, implying that adsorption is the dominant retention process. In all samples with high U(VI) retention, the derived uranium coordination is identical irrespective of the amount of contained carbonate. According to atomic distances and coordination numbers, the U(VI) surface complexes shift from a 5-fold to a 4-fold coordination in the equatorial plane with increasing pH. Attachment might be facilitated by charge balancing cations (i.e. Ca2+) that mediate between the negatively charged clay surface and the anionic aqueous U(VI)-hydroxide complexes.

  • Poster
    18th Radiochemical Conference, 13.-18.05.2018, Marianske Lazne, Czech Republic

Publ.-Id: 27307

Charakterisierung der Bildqualität eines in-beam MR-Scanners an einer Protonenstrahlanlage während der Bestrahlung

Gantz, S.; Schellhammer, S. M.; Karsch, L.; Smeets, J.; Serra, A.; Pawelke, J.; Hoffmann, A. L.

Echtzeit-Magnetresonanztomographie kann die Präzision der Protonentherapie verbessern.
Ziel dieser Arbeit war die Charakterisierung der Bildqualität eines in-Beam MR-Scanners während der Bestrahlung.

Material & Methoden
Ein offener 0.22 T MR-Scanner (MrJ2200, Paramed) wurde im Isozentrum einer horizontalen Protonenstrahlanlage installiert. Die MR-Bildqualität wurde anhand zweier Komponenten beurteilt. Erstens wurde die Homogenität des Magnetfeldes des MR-Scanners innerhalb eines sphärischen Volumens von 22 cm Durchmesser mithilfe einer Magnetfeldkamera (MFC3045/48, Metrolab) vermessen. Dabei wurde der Einfluss der Strahlführungsmagnete, für Protonenenergien zwischen 70 und 220 MeV, untersucht. Zweitens wurde die Bildqualität ausgehend vom Protokoll des American College of Radiology (ACR) mittels des kleinen ACR Phantomes in einer dedizierten Kniespule untersucht. Hierzu wurden sowohl die vorgegebenen T1 und T2 Spin-Echo (SE) Sequenzen als auch zwei T1- und T2*-gewichtete Gradienten-Echo (GE) Sequenzen genutzt. Neben Referenzbildern mit ausgeschalteter Strahlanlage wurden Bilder in verschiedenen Szenarien sowohl unter dem Einfluss der Strahlführungsmagnete sowie unter direkter Bestrahlung aufgenommen. Hierfür wurde ein auf 10 mm Durchmesser kollimierter Strahl der Energie 125 MeV mit Dosisraten von 1 bzw. 80 Gy/min verwendet. ACR Bildparameter sowie Bildverschiebungen wurden mithilfe einer validierten Software (Matlab) ermittelt.

Die Magnetfeldhomogenität innerhalb des untersuchten Bereiches betrug 88 ppm (peak-to-peak). Unter dem Einfluss der Strahlführungsmagnete wurden Änderungen kleiner 3 ppm gemessen, weiterhin jedoch eine Verschiebung der mittleren Resonanzfrequenz, abhängig von der gewählten Strahlenergie, um 70 bis 110 Hz. Die T1-gewichteten GE Bilder enthalten Streifenartefakte; alle anderen SE und GE Bilder konnten ausgewertet werden. Es existieren keine signifikanten Unterschiede in den ACR Parametern zwischen den unterschiedlichen Szenarien. Bildverschiebungen in Frequenzkodierrichtung betrugen zwischen 0.5 und 3 mm und weisen eine indirekte Proportionalität zu den Gradientenstärken der einzelnen Sequenzen auf.

Die Bildqualität des in-Beam MR-Scanners erfüllt die Spezifikationen des Herstellers sowie der ACR. Es wurde keine Änderung der MR-Bildqualität unter simultaner Bildgebung und Bestrahlung festgestellt, jedoch müssen Bildverschiebungen sequenzabhängig kompensiert werden.

  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27306

Dual-Energy-Computertomographie ermöglicht Dosisberechnung auf Kontrastmittel-angereicherten CT-Aufnahmen

Möhler, C.; Wohlfahrt, P.; Greilich, S.

Falls bei der Therapieplanung CT-Kontrastmittel (KM) zur Diagnose und Konturierung eingesetzt wird, muss zur Dosisberechnung in der Regel ein weiteres, „natives“ CT-Bild ohne KM aufgenommen werden. Grund dafür ist der Einfluss der hohen Ordnungszahl des im KM enthaltenen Iods. Dieser kann durch den Einsatz von Dual-Energy-CT (DECT) korrigiert werden, was die Planung auf KM-angereicherten Bildern ermöglicht.

Material & Methoden:
Der Effekt eines gebräuchlichen KM (Imeron® 300, Bracco Imaging Deutschland GmbH) auf die ermittelte Elektronendichte wurde in CT-Bildern (a) einer Verdünnungsreihe in Wasser und (b) von 7 Hirntumorpatienten gemessen. Mit einem Somatom Definition Flash DECT-Scanner (Siemens Healthineers), ausgestattet mit zwei Röntgenröhren, wurden Bilder im 120 kVp Single-Energy-CT (SECT) Modus (nur a) und 80/140Sn kVp DECT-Modus (a und b) aufgenommen. Bei den Patienten (b) wurde jeweils ein Scan mit und ohne KM durchgeführt. Elektronendichte-Bilder wurden für SECT mit einer Hounsfield-Lookup-Tabelle und für DECT mit der Software Syngo.CT Rho/Z (Siemens Healthineers) erstellt.

Bei der Verdünnungsreihe (a) führte der Einfluss des KM in den 120 kVp Bildern zu einer Überschätzung der Elektronendichte von 5-10% bei typischer Anreicherung (maximal 6 mg Iod/ml). Diese Verfälschung konnte durch den Einsatz von DECT auf unter 1% begrenzt werden. Bei den Patienten (b) betrug die mittlere Differenz zwischen den 120 kVp-äquivalenten Nativ- und KM-Bildern im Ganzhirn 1.5-4.4%, die entsprechende Differenz in den Elektronendichte-Bildern nur 0.2-0.6% (Abb. 1).

Der Einfluss von KM auf die Elektronendichte kann mittels DECT auf unter 1% reduziert werden. Dies ermöglicht den Verzicht auf einen zusätzlichen nativen Scan und somit eine Vereinfachung des klinischen Workflows und eine Reduktion der Strahlendosis auf die Hälfte.

Keywords: dual-energy CT; contrast agent; treatment planning; Kontrastmittel; Bestrahlungsplanung

  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27305

Clinical feasibility of single-source dual-spiral 4D dual-energy computed tomography for proton treatment planning of lung-cancer patients

Wohlfahrt, P.; Hofmann, C.; Troost, E. G. C.; Richter, C.; Jakobi, A.

Dual-spiral dual-energy CT (DECT) provides additional patient information to improve range accuracy in proton therapy, but is prone to motion between the two consecutively acquired scans. Here, the clinical feasibility of dual-spiral time-resolved DECT (4D-DECT) for proton treatment planning within the thoracic region was evaluated.

4D-DECT scans of three non-small-cell lung cancer (NSCLC) patients were acquired during the course of treatment with a Siemens single-source DECT scanner (Fig.1). For temporally averaged datasets and four breathing phases, the geometrical conformity of both 4D-DECT scans before (80kVp/140kVp) and after (58keV/79keV) image post-processing including deformable image registration (DIR) was assessed by normalized cross correlation (NCC).
To evaluate the reliability of dose calculation, clinical treatment plans were recalculated on DECT-derived 79keV MonoCT and 140kVp SECT datasets as reference using a heuristic conversion (HLUT) from CT number to stopping-power ratio (SPR). Dose distributions were compared with gamma analyses (0.1% dose-difference, 1mm distance-to-agreement criterion).
Finally, range differences between HLUT and patient-specific DECT-based SPR prediction were quantified.

Respiration changes during 4D-DECT acquisition resulted in NCCs>80%, indicating geometrical deviations of (1-2)mm. This was almost completely corrected by DIR leading to a high geometrical conformity with average NCC ± SD = (99.6±0.4)% corresponding to anatomical shifts below 0.2mm (not visually distinguishable). Even the impact of coughing could be corrected by DIR (Fig.2).
Clinical dose distributions on 140kVp and 79keV datasets were similar with average gamma passing rate of 99.9% and maximal dose difference of 0.8%.
Clinically relevant mean range shifts of (2.2±1.2)% were determined between patient-specific DECT-based SPR prediction and HLUT.

Dual-spiral 4D-DECT is applicable for dose calculation on 79keV MonoCT datasets in NSCLC patients. Patient-specific DECT-based SPR prediction performed properly and revealed its potential for reducing range uncertainty. Even if large motion differences hamper 4D-DECT post-processing, only the 140kVp scan can be used and additional information on respiration variability and robustness is gathered.

Keywords: dual-energy CT; proton therapy; lung cancer; 4DCT; clinical feasibility

  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27304

Clinical application of dual-energy CT for improved proton stopping-power prediction

Peters, N.; Wohlfahrt, P.; Möhler, C.; Enghardt, W.; Krause, M.; Troost, E.; Greilich, S.; Richter, C.

The sub-percentage accuracy in proton stopping-power prediction of patient-individualized range prediction (PIRP) using dual-energy CT (DECT) was demonstrated in recent studies. Although DECT-derived pseudo-monoenergetic CT scans have been introduced into clinical routine, a heuristic conversion (HLUT) from CT number to stopping power ratio (SPR) is still necessary, Fig.1(1). We propose a method to refine the clinical HLUT by applying PIRP on a broad patient cohort as a step towards its clinical implementation.

Voxelwise correlations of CT number and SPR were obtained using DECT scans of 102 brain-tumor and 25 prostate-cancer patients treated with protons. The clinical HLUT was then refined by performing a step-wise weighted linear fit of the SPR distribution in different tissue regions, Fig.1(2). Furthermore, the intra- and inter-patient variability was quantified. To assess dose differences and range shifts, proton treatment plans were recalculated using the clinical and refined HLUT as well as PIRP.

Between clinical HLUT and PIRP, mean range differences (±1SD) of (1.2±0.7)% for brain-cancer and (1.7±0.5)% for prostate-tumor patients were determined. On average, the clinical HLUT predicted larger SPR for brain, muscle and trabecular bone, leading to the systematic range deviations. They were significantly reduced (p≪0.001, two-sample t-test) below 0.3% by using the refined HLUT. However, an observed intra-patient soft-tissue diversity of 6% as well as an inter-patient bone diversity of 5% cannot be considered by any generic HLUT-based range prediction.

Retrospective application of PIRP allows for a reduction of systematic deviations found in clinical HLUT. In principal, this can also be transferred to particle-therapy centers not using DECT routinely. The refined HLUT was implemented at our institution as a step towards the currently ongoing full integration of PIRP. This includes the calibration, an end-to-end test as well as the quantification of prospects in safety margin reduction.

  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27303

Organische Chemie XI - Chemie der Carbonylverbindungen

Mamat, C.

Nachdem wir uns sehr ausführlich über Verbindungen unterhalten haben, die Kohlenstoff-Kohlenstoff-Mehrfachbindungen enthalten (Alkene, Alkine, Aromaten), wollen wir zu Verbindungsklassen und funktionellen Gruppen kommen, bei denen Kohlenstoff-Heteroatom-Doppelbindungen existieren. Das sind insbesondere Aldehyde, Ketone, Carbonsäuren und deren Derivate. Im Gegensatz zu den nichtaktivierten C=C-Doppelbindungen sind diese Kohlenstoff-Heteroatom-Doppelbindungen bereits durch die Unterschiede in den EN-Werten aktiviert. Wir finden ein elektronegatives Zentrum am Heteroatom (Sauerstoff, Stickstoff oder Schwefel) und ein elektropositives Zentrum am Kohlenstoff. Somit ist die Regioselektivität bei nucleophilen bzw. elektrophilen Angriffen vorgegeben. Wenn beispielsweise Nucleophile an diese Doppelbindung angreifen, werden sie spezifisch an den Kohlenstoff gebunden, wohingegen die Elektrophile den Sauerstoff angreifen. Neben der Carbonylgruppe, in der der Sauerstoff über eine Doppelbindung gebunden ist gibt es auch carbonylanaloge Verbindungen mit Stickstoff oder Schwefel, wobei die Elektronegativitätsdifferenz und damit die Polarisierung der Doppelbindung in der Richtung O > N > S abnimmt.

  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0049 Seiten

Publ.-Id: 27302

Organische Chemie X - Aromatische Substitution

Mamat, C.

In den vergangenen Heften haben wir uns ausführlich über die Reaktionen an gesättigten und ungesättigten Kohlenstoffatomen unterhalten, wobei wir die aromatischen Vertreter geflissentlich ausgelassen haben. Außerdem haben wir geschaut, welche Effekte diese Aromaten bzw. aromatische Reste wie Phenylgruppen auf die Stabilität von Zwischenstufen wie Carbanionen, Carbokationen oder Radikalen ausüben und welche Konsequenzen sich aus diesem Einfluss dann auf die Reaktivität und /oder (Regio-)Selektivität der Derivate ergeben.

  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0035 Seiten

Publ.-Id: 27301

Organische Chemie IX - Additionsreaktionen

Mamat, C.

Additionen sind die mit Abstand wichtigsten Reaktionen von ungesättigten Verbindungen (Alkenen, Alkinen, aber auch Carbonylverbindungen). Formal handelt es sich dabei um die Umkehrung der Eliminierungsreaktionen. Additionsreaktionen können radikalisch oder ionisch verlaufen. Im Falle eines ionischen Verlaufs können wir noch zwischen einem elektrophilen oder einem nucleophilen ersten Angriff auf die Doppelbindung unterschieden. Der vierte Typ umfasst die große Gruppe der Cycloadditionen. Diese pericyclischen Reaktionen kommen ohne geladene Teilchen aus und verlaufen meist konzertiert. Somit sind vier Typen von Additionen an die Doppelbindung zu unterscheiden.

  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0051 Seiten

Publ.-Id: 27300

Organische Chemie VIII - Eliminierungsreaktionen

Mamat, C.

Wir haben schon aus den Studienheften der Organischen Chemie I erfahren, dass Eliminierungsreaktionen am sp3- oder sp2-hybridisierten Kohlenstoff die Umkehrung von Additionsreaktionen sind. Sie treten damit als Konkurrenzreaktion zu den nucleophilen Substitutionen auf und führen generell zu ungesättigten Verbindungen (Alkenen oder Alkinen). Dabei müssen zwei σ-Bindungen gebrochen werden. Aus den beteiligten sp3-hybridisierten Kohlenstoffatomen werden sp2-hybridisierte gebildet und als Konsequenz daraus bilden sich nach Abspaltung aus sp2-hybridisierten Kohlenstoffatomen sp-hybridisierte, die an der jeweiligen Mehrfachbindung beteiligt sind. Neben der σ-Bindung zwischen den beteiligten Kohlenstoffatomen wird nun eine oder zwei π-Bindungen ausgebildet. Dabei entstehen kleine, stabile Moleküle wie z. B. Halogenwasserstoff (HCl, HBr), Wasser, CO2 und andere als eliminierte Nebenprodukte.

  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0030 Seiten

Publ.-Id: 27299

Organische Chemie VII - Radikalische und nucleophile aliphatische Substitution

Mamat, C.

Nachdem wir uns ausführlich mit den wichtigsten Stoffklassen und funktionellen Gruppen in der organischen Chemie beschäftigt haben, wollen wir nun im zweiten Teil noch einmal auf die Reaktionen und ihre Mechanismen schauen. Diese Mechanismen sind wichtige Werkzeuge, um zu verstehen, warum Reaktionen funktionieren oder auch nicht. Oder warum das eine Produkt gebildet wird und das andere nicht. Oftmals haben wir auch Konkurrenzsituationen, wie die Eliminierung bei der nucleophilen Substitution oder auch zwei (oder mehrere) reaktive Zentren, an denen die Reaktion prinzipiell ablaufen könnte. In solchen Situationen werden wir sehen, dass eine Steuerung möglich ist, je nachdem wie die Reaktionsbedingungen gewählt werden. Ein weiterer wichtiger Faktor wird durch die Kinetik der Reaktionen beschrieben. Sie gibt ebenfalls Auskunft darüber, ob und wie Reaktionen ablaufen. Wenn das alles nicht hilft, gibt es die Möglichkeit, funktionelle Gruppen, die nicht reagieren sollen, mit Schutzgruppen vor der Reaktion zu blockieren. Damit wird ebenfalls eine regioselektive Reaktion erreicht.

  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0040 Seiten

Publ.-Id: 27298

Assessment of RBE variability in proton therapy using a Monte-Carlo method

Eulitz, J.; Dutz, A.; Lutz, B.; Wüstemann, J.; Wohlfahrt, P.; Oesten, H.; Hahn, C.; Permatasari, F.; Löck, S.; Krause, M.; Enghardt, W.; Troost, E. G. C.; Lühr, A.

Routinely, a constant relative biological effectiveness (RBE) is used in proton therapy. However, experimental evidence indicates that RBE can vary with dose and linear energy transfer (LET). Here, we introduce a Monte-Carlo simulation method to assess RBE variations from follow-up magnetic resonance (MR) scans and illustrate its applicability for an exemplary brain-tumor patient.
A proton therapy Monte-Carlo model was setup to simulate dose and dose-averaged LET distributions of treatment fields on computed tomography (CT) scans and also in a water phantom for comparison with quality assurance measurements. A follow-up T1-weighted contrast-enhanced (T1w-CE) MR scan of an astrocytoma (grade 2) patient, acquired 18 months after radiochemotherapy (DRBE=1.1=60Gy), was used to delineate post-treatment image-change regions and rigidly co-registered to the planning CT. A multivariable logistic normal tissue complication model (NTCP) was built by voxel-wise correlating image changes with simulated dose and LET distributions. Tolerance doses TD10 (resulting in 10% probability of image change in a voxel) as function of LET were obtained from the NTCP model.
Measured and Monte-Carlo-predicted dose agreed within 2%. Changes on follow-up T1w-CE-MR images correlated with increasing simulated dose and LET (Fig.1). The NTCP model revealed a significant LET effect (p<0.0001) on the image change probability resulting in a decrease of modeled TD10 values from 70.3Gy to 50.6Gy for 1keV/μm and 6keV/μm, respectively, indicating a varying RBE (Fig.2).
The correlation of post-treatment MR image changes with Monte-Carlo simulations allows for testing the hypothesis of a variable proton RBE. Currently, this method is systematically evaluated and may, after validation in independent patient cohorts, reduce biological uncertainty in proton therapy.

  • Lecture (Conference)
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27296

Charge Carrier Dynamic in Ga1-xMnxAs Studied by Resistance Noise Spectroscopy

Lonsky, M.; Teschabai–Oglu, J.; Pierz, K.; Sievers, S.; Schumacher, H. W.; Yuan, Y.; Böttger, R.; Zhou, S.; Müller, J.

We report on electronic transport measurements of the magnetic semiconductor Ga1-xMnxAs, whereby the defect landscape in various metallic thin films (x = 6%) was tuned by He-ion irradiation. Changes in the distribution of activation energies, which strongly determine the low-frequency 1/f-type resistance noise characteristics, were observed after irradiation and can be explained by deep-level traps residing in the As sublattice. Various other kinds of crystalline defects such as, for instance, Mn interstitials, which possibly form nanoscale magnetic clusters with a fluctuating spin orientation, also contribute to the 1/f noise and can give rise to random telegraph signals, which were observed in films with x = 7%. In addition, we neither find evidence for a magnetic polaron percolation nor any features in the noise near the Curie temperature.

Publ.-Id: 27295

Absolute Hugoniot measurements from a spherically-convergent shock using x-ray radiography

Swift, D. C.; Kritcher, A.; Hawreliak, J.; Lazicki, A.; Macphee, A.; Bachmann, B.; Döppner, T.; Nilsen, J.; Collins, G. W.; Glenzer, S.; Rothman, S. D.; Kraus, D.; Falcone, R. W.

The canonical high pressure equation of state measurement is to induce a shock wave in the sample material and measure two mechanical properties of the shocked material or shock wave. For accurate measurements, the experiment is normally designed to generate a planar shock which is as steady as possible in space and time, and a single state is measured. A converging shock strengthens as it propagates, so a range of shock pressures is induced in a single experiment. However, equation of state measurements must then account for spatial and temporal gradients. We have used x-ray radiography of spherically-converging shocks to determine states along the shock Hugoniot. The radius-time history of the shock, and thus its speed, was measured by radiographing the position of the shock front as a function of time using an x-ray streak camera. The density profile of the shock was then inferred from the x-ray transmission at each instant of time. Simultaneous measurement of the density at the shock front and the shock speed determines an absolute mechanical Hugoniot state. The density profile was reconstructed using the known, unshocked density which strongly constrains the density jump at the shock front. The radiographic configuration and streak camera behavior were treated in detail to reduce systematic errors. Measurements were performed on the Omega and National Ignition Facility lasers, using a hohlraum to induce a spatially uniform drive over the outside of a solid, spherical sample, and a laser-heated thermal plasma as an x-ray source for radiography. Absolute shock Hugoniot measurements were demonstrated for carboncontaining samples of different composition and initial density, up to temperatures at which K-shell ionization reduced the opacity behind the shock. Here we present the experimental method, using measurements of polystyrene as an example.

Publ.-Id: 27294

Using time-resolved penumbral imaging to measure low x-ray emission signals from capsule implosions at the NIF

Bishel, D. T.; Bachmann, B.; Yi, A.; Kraus, D.; Divol, L.; Falcone, R. W.; Fletcher, L. B.; Glenzer, S. H.; Landen, O. L.; Macdonald, M. J.; Masters, N.; Neumayer, P.; Redmer, R.; Saunders, A. M.; Witte, B.; Döoppner, T.

We have developed an experimental platform at the National Ignition Facility to measure x-ray Thomson scattering (XRTS) spectra from indirectly-driven capsule implosions that create extreme density conditions near stagnation [D. Kraus et al, J. Phys. Conf. Series 717, 012067 (2016).]. In order to account for shot-to-shot variations of the stagnation time and to benchmark the achieved plasma conditions between shots and against radiation hydrodynamics simulations, we need to know the relative timing between the scattering measurement and the peak x-ray emission, which occurs at stagnation. Due to lower implosion velocity, use of a low gas fill capsule, and hot spot symmetry perturbations, the hot spot emission is 100 - 1000x weaker than that of standard ICF implosions. To address this challenge, we have developed and fielded a new pinhole-imaging snout that exploits time-resolved penumbral imaging. Using 150 µm diameter penumbral-imaging pinholes, a time series of 2D images can be reconstructed through analysis of the penumbras. The reconstructions allow us to extract the spatially and temporally resolved evolution and timing of the implosion through stagnation. We use differential filtering to extract plasma temperatures, additionally constraining the thermophysical plasma conditions. Despite fluctuations of the x-ray flash intensity of up to 5x, the emission time history is similar from shot to shot, and slightly asymmetric with respect to peak x-ray emission. Peak emission times vary by up to 250 ps and can be determined with an accuracy of 50 ps.


Publ.-Id: 27293

Hybrid plasma wakefield acceleration: Concept & preliminary results

Kurz, T.; Heinemann, T.; Knetsch, A.; Couperus, J. P.; Köhler, A.; Zarini, O.; Hidding, B.; Assmann, R.; Bussmann, M.; Osterhoff, J.; Schramm, U.; Martinez De La Ossa, A.; Irman, A.

Plasma wakefield accelerators can be driven by either a powerful laser pulse (LWFA) or a high-current charged particle beam (PWFA). We combine both acceleration methods in a staged setup to efficiently exploit the advantages of each scheme. We present preliminary results of a proof of concept-experiment at the DRACO laser facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The LWFA stage (1st stage) generates ultra relativistic electron beams with peak currents exceeding 20kA via self truncated inonization injection (STII) out of a 3mm super sonic dopant (He+N) gas jet. These beams are sent into the second 3mm dopant (H+He) gas jet, driving plasma wakefields in the non-linear bubble regime. Thereby, injected electrons induced by the field ionization form a second electron beam (witness) that ideally exeeds the driving bunch (driver) quality in terms of energy and brightness.

  • Lecture (Conference)
    DPG - Frühjahrstagung, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 27292

Calibration and cross-laboratory implementation of scintillating screens for electron bunch charge determination

Kurz, T.; Couperus, J. P.; Krämer, J. M.; Ding, H.; Kuschel, S.; Köhler, A.; Zarini, O.; Hollatz, D.; Schinkel, D.; D'Arcy, R.; Schwinkendorf, J. P.; Irman, A.; Schramm, U.; Karsch, S.

In this article we revise the calibration measurements of different scintillation screens commonly used for the detection of relativistic electrons, extending previous reference work towards higher charge density and new types of screens. Electron peak charge densities up to 10 nC/mm² were provided by focused picosecond-long electron beams delivered by the ELBE linear accelerator at the Helmholtz-Zentrum Dresden-Rossendorf.
At low charge densities, a linear scintillation response was found, followed by the onset of saturation in the range of nC/mm². The absolute calibration factor (photons/sr/pC) in this linear regime was measured to be almost a factor of 2 lower than reported by Buck et al. retrospectively implying a higher charge in charge measurements performed with the old calibration. A good agreement was found with the results by Glinec et al.. Furthermore long-term irradiation tests with an integrated dose of approximately 50 nC/mm² indicate a significant decrease of the scintillation efficiency over time.
Finally, in order to enable the transfer of the absolute calibration between laboratories, a new constant reference has been developed.


Publ.-Id: 27291

Interdisciplinary round-robin test on molecular spectroscopy of the U(VI) acetate system

Müller, K.; Foerstendorf, H.; Steudtner, R.; Tsushima, S.; Kumke, M. U.; Lefèvre, G.; Rothe, J.; Mason, H.; Szabó, Z.; Yang, P.; Adam, C.; André, R.; Brennenstuhl, K.; Cho, H.; Creff, G.; Coppin, F.; Dardenne, K.; Den Auwer, C.; Drobot, B.; Eidner, S.; Hess, N. J.; Kaden, P.; Kremleva, A.; Kretzschmar, J.; Krüger, S.; Platts, J. A.; Panak, P. J.; Polly, R.; Powell, B. A.; Rabung, T.; Redon, R.; Reiller, P. E.; Rösch, N.; Rossberg, A.; Scheinost, A. C.; Schimmelpfennig, B.; Schreckenbach, G.; Skerencak-Frech, A.; Sladkov, V.; Solari, P. L.; Wang, Z.; Washton, N. M.; Zhang, X.

In the advent of the 2nd International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS 2014), an inter-laboratory round-robin test (RRT) was initiated. The main goal of this RRT was the comprehensive molecular analysis of a simple aqueous com-plexing system – U(VI) acetate – which was selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods applied by leading laboratories in actinide or geochemical research. Ultimately, more than 40 scientists hosted at twenty insti-tutions in seven countries participated.
The outcome of this RRT can be considered on two levels: First, conformities as well as discrepancies in the results of each spectroscopic technique and their sources are evaluated. The raw data from the experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was surprisingly high. By contrast, the data obtained using luminescence spectroscopy turned out to be strongly related to the chosen acquisition pa-rameters. Second, the potentials and limitations of coupling various spectroscopic and, in particular, theoretical approaches for the comprehensive study of actinide molecule com-plexes are assessed. The additional benefits of the combined approach with regard to the exploration of the aqueous speciation of the U(VI) acetate system are elaborated.

Keywords: Uranium; acetic acid; actinides; spectroscopy; infrared; Raman; vibrational; luminescence; fluorescence; magnetic resonance; X-ray absorption; Quantum chemistry; ATR FT-IR; TRLFS; NMR; EXAFS; density functional theory; DFT; wave function theory; MP2

Publ.-Id: 27289

Production and Characterization of the 163Ho Source for the ECHo Project

Wendt, K.; Düllmann, C. E.; Kieck, T.; Dorrer, H.; Mokry, C.; Rugel, G.; Wiescher, F.; Merchel, S.; Forstner, O.

The ECHo (Electron Capture in Holmium Experiment) collaboration aims at measuring the electron neutrino mass by recording the spectrum following electron capture of 163Ho using metallic magnetic calorimeters. The radioisotope 163Ho (t1/2 = 4570 a) is produced by neutron capture from enriched 162Er in the Institute Laue-Langevin high-flux nuclear reactor. After chemical separation the important step of embedding the sample into the 180x180 𝜇m2 Au-absorbers of the ECHo detectors is carried out by laser mass spectrometric techniques. The application of multi-step resonance ionization at the 60 kV RISIKO mass separator of Mainz University ensures highest efficiency and unrivalled elemental and isotopic selectivity for ultra-pure 163Ho ion implantation with sub-millimeter beam spot. The efficiency and stability of the laser ion source and the implantation process is permanently monitored and improved to minimize any losses of the precious sample material, while an in-situ deposition of gold by parallel pulsed laser deposition (PLD) ensures a homogeneous 163Ho/Au layer production and prevents disturbing sputter effects. To screen the purity of the source from production up to use besides a number of more conventional analytical techniques accelerator mass spectrometry (AMS) of Ho at the AMS-facility of the Helmholtz-Zentrum Dresden-Rossendorf is under development to address the very low content in the 10 or lower region of the radiocontaminating isotope 166mHo (t1/2 = 1200 a).

Keywords: AMS; Holmium; electron capture; mass separator

  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.03.2018, Darmstadt, Deutschland

Publ.-Id: 27288

High Speed, High Resolution Imaging Spectrometers Based on pnCCDs for XRF and XRD Applications

Strüder, L.; Hartmann, R.; Holl, P.; Ihle, S.; Huth, M.; Schmidt, J.; Thamm, C.; Kanngießer, B.; Baumann, J.; Renno, A. D.; Grenzer, J.; Radtke, M.; Abhoud, A.; Pietsch, U.; Soltau, H.

For many years pnCCDs have been well known as X-ray detectors for spectroscopic imaging in many fields of science: X-Ray Fluorescence analysis (XRF), X-ray Diffraction (XRD) with light sources in large accelerator facilities as well as with laboratory light sources or with X -rays from celestial sources in X-ray astronomy. A brief introduction in GEXRF (Grazing Emission XRF) measurements with a laboratory laser produced plasma source will be given, PIXE (Particle Induced X-ray Emission) measurements and D2XRF (Double Dispersive X -Ray Fluorescence) and Slicing experiments with pnCCDs coupled to polycapillary optics performed at the BESSY synchrotron will be shown. Energy - dispersive Laue diffraction with ultra - hard X-rays for the analysis of defects in metals will conclude the overview of spectroscopic X-ray imaging measurements in the field of structure and dynamics of matter. pnCCDs are radiation detectors on high resistivity 450 μm thick fully sensitive silicon [1]. They are back-illuminated devices with an ultra-thin, homogeneous radiation entrance window, enabling the proper detection of X-rays up to 30 keV with high quantum efficiency. As all pnCCDs are equipped with a fully column parallel readout, frame rates on more than 1200 frames per second are achieved, keeping the read noise level at 3 electrons (rms). Some of the key performance figures are (1) a quantum efficiency above 90% from 1 keV up to 10 keV, (2) single photon counting capability starting at only 30 eV, (3) extreme radiation hardness due to the avoidance of active MOS structures, and (4) energy resolution of 130eV (FWHM) at 6 keV and 37 eV (FWHM) at 90 eV. These properties have enabled a variety of spectacular measurements. (a) GEXRF: By combining a highly brilliant laser produced plasma (LPP) source with a scanning - free setup, grazing emission X-ray fluorescence (GEXRF) measurements in the soft X - ray range were realized [2]. The detector, a pnCCD, was operated in a single photon counting mode in order to utilize its energy dispersive properties. GEXRF profiles of the Ni - Lα line of a carbon - nickel multilayer sample, which displays a lateral (bi-)layer thickness gradient, were recorded at several positions. Simulations of theoretical profiles predicted a prominent intensity dip at emission angles between 5° and 12°, depending strongly on the bi-layer thickness of the sample (see Fig.1). This information was used to retrieve the bi - layer thickness gradient. The results are in good agreement with values obtained by X-ray reflectometry, conventional X-ray fluorescence and transmission electron microscopy measurements and serve as proof of principle for the suggested GEXRF setup. (b) PIXE: The unique properties pnCCDs, coupled to polycapillary X-ray optics, allows a fast position resolved overview over a large detection area with first results visible in real time. The maximum field of view exceeds 1 cm2 and the spatial resolution approaches a few microns when using sub-pixel algorithms by centroiding the signal charge cloud in the pixel structure [3] .
The device has been used as an X-ray detector at the PIXE beamline at the Helmholtz-Zentrum Dresden Rossendorf (see Fig. 2). In addition to the above measurements (c) D2XRF and Slicing experiments performed at the BESSY synchrotron will be presented (see Fig. 3) as well as (d) Energy Dispersive Hard X-ray Laue Diffraction measurements at the ESRF.

Keywords: pnCCD; High-Speed PIXE

  • Contribution to proceedings
    Microscopy and Microanalysis 2016, 24.07.2016, Columbus, USA
    Proceedings of Microscopy and Microanalysis 2016, 100-101
    DOI: 10.1017/S1431927616001355

Publ.-Id: 27286

Neptunium(V) transport in granitic rock: A laboratory scale study on the influence of bentonite colloids

Elo, O.; Hölttä, P.; Kekäläinen, P.; Voutilainen, M.; Huittinen, N.

In the present study neptunium(V) uptake by crystalline granitic rock (Kuru Grey granite) and bentonite colloids (MX-80) under stagnant conditions in batch-type experiments and the role of stable and mobile bentonite colloids on the migration of neptunium(V) through intact granite columns under flowing water conditions was investigated. The uptake of 10-6 M neptunium(V) by 40 g/L crushed granite in 10 mM NaClO4 was found to be pH-dependent, whereas neptunium(V) uptake by MX-80 bentonite colloids (0.08-0.8 g/L) was pH-independent up to a pH-value of approximately 11. Column experiments were conducted in the presence and absence of colloids at two pH values (pH = 8 and 10) and two flow rates (0.3 mL/h and 0.8 mL/h) in 10 mM NaClO4. The neptunium(V) concentration was 2×10-4 M and the colloid concentration ranged from 0.1-1 g/L. The properties of the flow field in the columns were investigated with a conservative chloride tracer, at the same two flow rates of 0.8 and 0.3 mL/h. The resulting breakthrough curves were modeled using the analytical solution of advection–matrix diffusion equation. Based on the column experiments, neptunium(V) association with the colloids was found to occur directly in the injection phase. At slow flow rate, no influence of the bentonite colloids could be seen, implying that the non-sorbed and colloid-borne neptunium(V) are eluted from the columns at pH = 8 and that an exchange from colloid-borne to granite-sorbed neptunium(V) occurred at pH = 10. For the higher flow rate at pH = 8, clogging of flow channels, resulting in an enhanced retention of colloid-associated neptunium(V) was found. At pH = 10, adsorption of neptunium(V) on the granite reduced the clogging effect.

Keywords: Neptunium(V); Bentonite colloids; Granitic rock; Sorption; Column experiments


Publ.-Id: 27285

Model-driven parameter reconstructions from Small Angle X-ray Scattering images

Zacharias, M.

The diagnostic of plasma dynamical processes at solid densities and at the time and length scales involved in the formation of instabilities has become accessible in experiments by coherent X-ray scattering techniques through the advent of X-ray free-electron lasers. In this thesis, models for the density of structured targets under the influence of plasma expansion are studied. A general analytical derivation of the scattering signal of such targets is given and it is investigated what kind of statements regarding the expansion profile can be made based on data analyses that comprise various parametrical density models. To enable numerical investigations of experimental X-ray intensities with reduced parametrical density models, a framework has been designed in Python. The operability of the framework is demonstrated with data from experiments. Based on the results, statistically robust multi-model reconstructions of the plasma density that use the presented framework are envisioned.

Keywords: SAXS; small angle X-ray scattering; XFEL; reconstruction; plasma; numerical; Python

  • Master thesis
    TU Dresden, 2017
    Mentor: Dr. Thomas Kluge, Dr. Michael Bussmann, Prof. Dr. Ulrich Schramm, Prof. Dr. Thomas E. Cowan
    0090 Seiten
    DOI: 10.5281/zenodo.1208410

Publ.-Id: 27284

Ultrafast response of photoexcited carriers in VO₂ at high-pressure

Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund Jr., R. F.; Pashkin, A.

We utilize near-infrared pump — mid-infrared probe spectroscopy to investigate the ultrafast electronic response of pressurized VO₂. A clear anomaly in the linear mid-infrared response as well as in the fluence dependence of the pump-probe signal is observed around 8 GPa indicating a pressure-induced phase transition. Distinct pump-probe signals and a pumping threshold behavior typical for the insulating VO₂ phase persist also in the high-pressure phase. Thus, in contrast to the temperature-induced rutile metallic state of VO₂, the pressure-induced monoclinic phase preserves the energy gap. However, our results indicate the appearance and a gradual growth of additional intragap states upon increasing pressure above 8 GPa. These observations can be interpreted in terms of a bandwidth-controlled Mott – Hubbard transition.

Keywords: metal-insulator transition; vanadium dioxide; ultrafast spectroscopy; high-pressure

Related publications

Publ.-Id: 27283

Development of an efficient high-current ion source for Accelerator Mass Spectrometry

Hofsäss, H.; Bregolin, F.; Yordanov, D.; Rugel, G.; Akhmadaliev, S.; Merchel, S.; Feige, J.

A new efficient negative ion source for Accelerator Mass Spectrometry (AMS) is being built to quantify the ratios of long-lived cosmogenic radionuclides in micrometeorites. Measuring these extremely small ratios is at the technological limits of present AMS systems. The new source is designed specifically to provide a higher AMS detection sensitivity by having an optimal ion-optics design, incorporating new concepts for the construction and operation of the Cs ionizer, optimized Cs ion beam currents and Cs vapor transport, as well as the operation with higher cathode voltages than usual. Moreover, its design is modular providing ease of access and simplifying maintenance while providing better mechanical stability. Several source parameters can be controlled and measured during operation to achieve a better source performance. The new source will consist of a auto-aligning modular ionizer, a Cesium supply with active temperature control of the supply tubes, a novel shroud for the Cs supply and a cathode operated at up to -20 kV cathode bias. The design is optimized using COMSOL ion optics simulations, including space charge effects, thermal transport simulations as well as detailed sputter simulations. The authors would like to thank the Federal Ministry of Education and Research of Germany for its financial support (project 05K2016), and the HZDR's Ion Beam Center for its essential contribution to the realization of this project.

Keywords: AMS; micrometeorite

  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.03.2018, Darmstadt, Deutschland

Publ.-Id: 27282

Homogeneous pressed powder pellets as new MRMs for in situ microanalytical techniques

Garbe-Schönberg, D.; Müller, S.; Nordstad, S.; Wiedenbeck, M.; Renno, A. D.

While in-situ analytical instrumentation for the direct elemental and isotopic analysis of solid materials has undergone continuous and significant improvement over recent years, development of well-characterized and homogeneous microanalytical reference materials (MRM) for calibration and validation of analytical data has been delayed. Ideally, MRM must be homogeneous down to the single micrometer scale for major, minor, trace, and ultra-trace elements and isotopes, withstand high-vacuum and impact of high-energy electron, ion, and photon beams, stable in its physical and chemical properties over time and under various environmental conditions, certified following ISO guidelines, and available for a wide variety of materials.
We developed a method for manufacturing undiluted, binder-free pressed powder pellets[1] with particle grain size down to the nanometer range (D50 <170 nm), extremely low roughness of pellet surface (RA <50 nm), and excellent within and between pellet homogeneity. This technique has been applied so far to a wide range of very different sample types: biogenic carbonates (foraminifera, clam shells, red algae, corals), speleothem, silicate rocks, iron ores and banded iron formation, manganese nodules, sulphides UQAC-FeS, refractory minerals, plutonic and volcanic rocks, fly ash, bone-apatite, minerals for Rb/Sr age-dating[2] etc.. We successfully blended different materials opening new ways for producing e.g., series of elemental and isotopic calibration standards. These “nanopellets” have been successfully used with LA-ICP-MS, LIBS, µ-XRF, handheld-XRF instruments, and with EPMA, PIXE, SIMS. Hence, nanopellets proved to be a new and, possibly, universal matrix-matched MRM for many custom solid materials to be used with many in situ analytical techniques.
In addition, this way of sample preparation bears the potential of completely replacing conventional tedious and time-consuming wet-chemistry procedures for bulk analysis, and this holds true in particular for refractory samples like ceramics, granites, ultramafic rocks, and samples with volatile or easy-to-contaminate components (e.g., B). Here we give an overview of the present state of development of new MRM[3] and their characterization in terms of grain size distribution, surface topography, porosity, homogeneity, and accuracy of analytical results for both elemental (major, minor, trace and ultra-trace elements) and isotopic (Sr, Li, B, O) composition.

[1 ] Garbe-Schönberg D & Müller S, JAAS, 29, 990 (2014); [2] Hogmalm KJ, et al., JAAS, 32, 305 (2017); [3]; see also paper by D. Savard et al., this conference

Keywords: reference materials

  • Lecture (Conference)
    Geoanalysis 2018, 08.-13.07.2018, Sydney, Australia

Publ.-Id: 27281

Theoretical Modelling of High-Resolution X-Ray Absorption Spectra at Uranium M4 Edge

Kolorenc, J.; Kvashnina, K.

We investigate the origin of satellite features that appear in the high-resolution x-ray absorption spectra measured at the uranium M4 edge in compounds where the uranium atoms are in the U6+ oxidation state. We employ a material-specific Anderson impurity model derived from the electronic structure obtained by the density-functional theory.


Publ.-Id: 27280

Experimental investigation of three-dimensional bubbly two-phase pipe flows

Neumann, M.; Bieberle, A.; Krepper, E.; Hampel, U.

Modelling gas-liquid two-phase flow is a topic of constant relevance in nuclear thermal hydraulics. Gas-disperse two-phase flows occur in e.g. fuel elements in the reactor core, in pipes and components during pressure loss, sudden reflooding or other events. Due to the deformable gas-liquid interface and the complexity of heat, mass and momentum transfer across the interface, gas-liquid two-phase flow is very difficult to model and simulate. On the device scale it is common to use Euler/Euler multi-fluid approaches for CFD simulations, which require a good number of empirical correlations as closure models. Such models are commonly derived from experiments. Validation of the correctness of predictive simulations then also requires experiments, which must be simplified to a degree to allow provision of CFD-grade experimental data but complex enough to resemble real flow situations. The latter calls especially for investigations on flow fields in more complex three-dimensional domains, which are prototypical for e.g. bends, valves, T-junctions and rod bundles.
In this contribution the experimental investigation of generic three-dimensional two-phase flows will be presented. Experiments were performed at a vertical test section at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The test section is a pipe with an inner diameter of 54 mm and a length of 5000 mm with a flow constriction at half lengths. For the latter a ring shaped diaphragm and a half-moon shaped diaphragm have been investigated. Experiments were performed for a wide range of superficial gas and liquid velocities in the bubbly flow regime. Besides conventional measurement techniques for mass flow rates, temperatures and pressure, the ultrafast X-ray tomography scanner ROFEX for the determination of bubble dynamics, as well as a specifically adapted thermal anemometer probe for determination of liquid velocities is employed. The two-phase flow in such geometry exhibits certain important structures. In the narrow obstacle passage the flow accelerates with accordingly high shear stress being visible in large bubble deformation and break-up. Downstream a dead zone with recirculation develops and bubbles are being captured, which is associated with increased gas hold-up and bubble coalescence. The high resolution measurements allow for the first time to study the two-phase dynamics in detail and disclose velocity distributions along with gas phase and bubble size data as a function of time and space.

Keywords: two-phase flow; three-dimensional flow field; ultrafast X-ray tomography; thermal anemometry

  • Contribution to proceedings
    17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17), 03.-08.09.2017, Xi'an, China
  • Lecture (Conference)
    17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17), 03.-08.09.2017, Xi'an, China

Publ.-Id: 27279

Two-Phase Flow Studies in Complex Geometries

Neumann, M.; Hampel, U.

This contribution describes an experimental study on generic three-dimensional two-phase flows. The experiments are conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) and are a continuation of earlier studies, which were performed using a moveable flow obstacle and the wire-mesh sensor technique [1]–[3]. Although these investigations already provided very new data from a complex two-phase flow, the required minimal intrusiveness of both sensor and obstacle motion unit lead to some non-idealities with respect to the fully undisturbed flow. With a new imaging technique, ultrafast electron beam X-ray tomography, we are now able to perform investigations fully non-intrusively and to study the gas phase dynamics with high temporal and spatial resolution in two planes simultaneously. First results of the experimental study are presented here.

  • Contribution to proceedings
    48th Annual Meeting on Nuclear Technology, 16.-17.05.2017, Berlin, Deutschland
    Proceedings of the 48th Annual Meeting on Nuclear Technology

Publ.-Id: 27278

Experimental investigation of three-dimensional disperse two-phase flow

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

In vielen industriellen Prozessen und Apparaten treten Mehrphasenströmungen auf. Dies sind häufig Flüssigkeits-Gas-Strömungen, beispielsweise in der Kraftwerkstechnik, in Wärmetauschern, chemischen Reaktoren und Trennapparaten oder in Ölfördersystemen. Die Berechnung solcher Strömungen mittels computergestützter Simulationswerkzeuge (CFD-Codes), etwa zur Unterstützung der Auslegung, Optimierung und Sicherheitsbewertung, ist ein großes Ziel, welches aber schwierig zu erreichen ist, da die Physik von Zweiphasenströmungen im Vergleich zu einphasigen Strömungen um ein Vielfaches komplexer ist. Grund dafür ist die Komplexität der Transportprozesse über stark verformbare und sich verändernde Phasengrenzflächen in mehreren Zeit- und Längenskalen. Zudem werden durch anlagentechnische Komponenten, wie beispielsweise Krümmer, Ventile, T-Stücke oder querschnittsverändernde Einbauten, ausgeprägte dreidimensionale Strömungsfelder erzeugt, welche von aktuellen CFD-Codes nur sehr stark eingeschränkt berechnet werden können.
Der Beitrag beschäftigt sich mit der experimentellen Untersuchung von generischen dreidimensionalen Zweiphasenströmungen. Mit Hilfe neuartiger experimenteller Methoden soll dabei eine Datenbasis für die nachhaltige Validierung und Weiterentwicklung von CFD-Codes, speziell für dreidimensionale Strömungseffekte, erzeugt werden.

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Deutschland

Publ.-Id: 27277

Developing a Single Plane Compton Camera for Radionuclide Imaging

Deneva, B.; Roemer, K.; Wagner, A.; Enghardt, W.; Pausch, G.; Koegler, T.

Anger cameras are still the primary technology for radionuclide imaging in nuclear medicine [1]. Despite the achieved advances in improving the image quality over the past 60 years since its invention [2], there are physical limits to the camera performance (limited detection efficiency, decreasing spatial resolution of high energetic gamma rays, fixed dependency of the spatial resolution and detection efficiency from the used collimator). In order to overcome these limitations, the concept of the “Single Plane Compton Camera” (SPCC, see also Ref. [3]) was developed. The SPCC is based on the idea of the “Directional Gamma Radiation Detector” published in Ref. [4] and [5].
A setup for the investigation of the SPCC concept was developed recently at the Helmholtz-Zentrum Dresden - Rossendorf. Based on a GAGG:Ce (Gadolinium Aluminum Gallium Garnet, Gd3Al2Ga3O12) scintillator array and read out by digital silicon photomultipliers the setup is intend to deliver spatial information of activity distributions. The authors will present first experimental results acquired with the new setup and will compare them to predictions obtained from particle transport calculations performed with GEANT 4 [6].
[1] S. R. Cherry, J. A. Sorenson and M. E. Phelps, Physics in Nuclear Medicine, 4th ed., Elsevier, 2013.
[2] H. Anger, "A new instrument for mapping gamma ray emitters," Biology and Medicine Quaterly Report, 1957.
[3] G. Pausch et al., Paper N60-1 presented at the 2016 IEEE NSS/MIC in Strasbourg, France, Conference Record
[4] G. Kraft et al., U.S. patent no. 8030617 B2, granted in Oct. 2011
[5] A. Gueorguiev et al. U.S. patent no. 8299441 B2, granted in Oct. 2012
[6] A. Allison, "Geant 4 - a simulation toolkit", Nucl. Instr. and Meth. A. 506, (2003) 250-303

Keywords: Radionuclide imaging; Single Plane Compton Imaging; SPCI; radiation detector

  • Open Access Logo Contribution to proceedings
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.-22.09.2018, Nürnberg, Deutschland

Publ.-Id: 27276

Preyssler-Pope-Jeannin Polyanions [NaP5W30O110]14- and [AgP5W30O110]14-: Synthesis, Structural Characterization, Electrochemistry, Antiproliferative and Antibacterial Activity

Haider, A.; Zarschler, K.; Joshi, S. A.; Smith, R.; Lin, Z.; Mougharbel, A.; Herzog, U.; Müller, C. E.; Stephan, H.; Kortz, U.

The Preyssler-Pope-Jeannin polyanion [NaP5W30O110]14- (1) has been prepared by microwave-assisted synthesis in only 2 h with a yield comparable to the reported hydrothermal procedure. The purity of 1 was confirmed by FT-IR and multinuclear NMR (31P, 183W) analysis. The silver(I)-containing analogue [AgP5W30O110]14- (2) has also been prepared by hydrothermal (6 d) as well as microwave-based (2 h) procedures. Polyanion 2 was characterized in the solid state by FT-IR, single-crystal XRD, TGA, and elemental analysis and in solution by 31P and 183W NMR, electrochemistry and ESI-MS. The antiproliferative activities against human cells as well as the antimicrobial properties towards Gram-positive and Gram-negative bacteria were comparatively evaluated for 1 and 2.

Keywords: Polyoxoxmetalates; Microwave-Assisted Synthesis; Nuclear Magenetic Resonance (NMR); Bioactivity


Publ.-Id: 27275

Performance demonstration of the PEnELOPE main amplifier HEPA I using broadband nanosecond pulses

Albach, D.; Loeser, M.; Siebold, M.; Schramm, U.

We report on the energetic and beam quality performance of the second to the last main amplifier section HEPA I of the PEnELOPE laser project. A polarization coupled double-12-pass scheme to verify the full amplification capacity of the last two amplifiers HEPA~I and II was used. The small signal gain for a narrow band cw laser was 900 and 527 for a broadband nanosecond pulse, demonstrating 12.6 J of output pulse energy. Those pulses, being spectrally wide enough to support equivalent 150 fs long ultrashort pulses, are shown with an excellent spatial beam quality. A first active correction of the wavefront using a deformable mirror resulted in a Strehl ratio of 76 % in the single-12-pass configuration for HEPA I.

Keywords: Diode-pumped lasers; ytterbium; laser amplifiers; laser diagnostics; pulse energy


Publ.-Id: 27274

Reactive transport modeling using heterogeneous flow field data based on positron emission tomography

Lippold, H.; Kulenkampff, J.; Karimzadeh, L.; Stuhlfauth, C.; Lippmann-Pipke, J.; Fischer, C.

Discrepancies between experimental and RTM results are often attributed to flow field heterogeneities. Positron emission tomography (PET) provides direct and quantitative insight into flow fields in complex media, such as barrier materials or porous rocks.
Adsorption and transport of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) in a homogeneous sand-goethite system were investigated as a function of pH. Interaction of MCPA with the solid surface was geochemically modeled using the charge distribution multisite complexation (CD-MUSIC) approach. Based on this calibrated surface complexation model, retardation of MCPA in transport experiments was significantly underestimated by 1D simulations with hydrodynamic parameter values obtained from a fit to the breakthrough of HTO as a conservative tracer.
On the basis of flow field data derived from PET measurements, heterogeneous flow observed for 18F as a tracer was reproduced in 2D simulations (with flow velocities controlled by the pressure gradient field according to Darcy’s law) assuming a peripheral zone with increased porosity and permeability. Using this flow model, the predicted breakthrough of MCPA was significantly more realistic compared to 1D simulations with the same chemical parameter values. Thus, this study demonstrates quantitatively that inconsistencies between static (batch) and dynamic (column) systems can be caused by heterogeneities in fluid flow, i.e., not necessarily by non-equilibrium conditions. This in turn highlights the need to consider real flow fields in predictive transport models.

  • Lecture (Conference)
    Goldschmidt 2018, 12.-17.08.2018, Boston, United States of America

Publ.-Id: 27273

Magnetic field-induced proton dose enhancement: Experimental verification and Monte-Carlo simulation

Lühr, A.; Burigo, L. N.; Gantz, S.; Schellhammer, S.; Hoffmann, A. L.

Proton therapy (PT) is expected to benefit from integration with magnetic resonance (MR) imaging. However, the magnetic field distorts the dose distribution and induces a local dose enhancement at tissue-air interfaces by the electron return effect (ERE). For MR-integrated photon therapy, a dose enhancement ratio (DER) of 40% compared to no magnetic field has been reported. Here, measurements and calculations of DER for proton beams in transverse magnetic fields are reported.

Two measurement setups were used: EBT3 films were either attached to the distal face of one or sandwiched between two 10 mm PMMA slabs. Films were irradiated with a 200 MeV proton beam, both with and without transverse magnetic field (0.92 T). High-resolution Monte-Carlo simulations were used to reproduce the experimental findings and to calculate the DER for proton energies between 50−200 MeV and magnetic field strengths between 0.35−3 T within the first 0.05 mm (DERmax) and as function of distance from the air interface.

A DER of (2.2±0.4)% and (0.5±0.6)% was measured at 0.156 and 0.467 mm from the interface, respectively (Fig.1). Measurements and simulations agreed within 0.15%. Simulations using a 200 MeV beam showed a DERmax of 2.6% and 8.2% for 0.35 and 1.5 T, respectively (Fig.2). At 1 T, DERmax increased from 3.2% to 7.6% between 50 and 200 MeV.
For proton beams, the ERE in transverse magnetic fields is measurable. The dose enhancement is well predictable, decreases with distance from the interface, and is negligible after 1 mm. Although small, the impact of the ERE cannot be ignored for dosimetry with air-filled ionization chambers and in porous media (e.g. lung treatment).

Keywords: proton therapy; magnetic resonance imaging; MRI; MR; radiotherapy; dosimetry; electron return effect

  • Abstract in refereed journal
    TBD (2018)

Publ.-Id: 27272

Synthesis and radiofluorination of novel fluoren-9-one based derivatives for the imaging of α7 nicotinic acetylcholine receptor with PET

Teodoro, R.; Scheunemann, M.; Wenzel, B.; Peters, D.; Deuther-Conrad, W.; Brust, P.

By structure-activity relationship studies on the tilorone scaffold, the ‘one armed’ substituted dibenzothiophenes and the fluoren-9-ones were identified as the most potential α7 nAChR ligands. While the suitability of dibenzothiophene derivatives as PET tracers is recognized, the potential of fluoren-9-ones is insufficiently investigated. We herein report on a series of fluoren-9-one based derivatives targeting α7 nAChR with compounds 8a and 8c possessing the highest affinity and selectivity. Accordingly, with [18F]8a and [18F]8c we designed and initially evaluated the first fluoren-9-one derived α7 nAChR selective PET ligands. A future application of these radioligands is facilitated by the herein presented successful implementation of fully automated radiosynthesis.

Keywords: α7 nAChR; PET; Radiofluorination; Fluoren-9-one; Dibenzothiophenes

Publ.-Id: 27271

Consolidation of surface speciations by a combined spectroscopic and modeling approach

Foerstendorf, H.; Jordan, N.; Heim, K.; Mayordomo, N.; Steudtner, R.; Stockmann, M.

A reliable risk assessment of a deep geological waste disposal site for spent nuclear fuel refers to thermodynamic data bases which must contain resilient data sets. This information can be obtained from Surface Complexation Modeling (SCM) of batch sorption data, which is in turn consolidated by molecular information of relevant, prevailing species at mineral surfaces derived from spectroscopic investigations.
A combined approach of optical spectroscopic techniques, such as vibrational and luminescence spectroscopy, classical batch sorption studies and SCM was applied for the study of the surface speciation of actinide- and selenium oxyanions on mineral phases. In this study, spectroscopic findings of the surface speciation of uranium(VI) and selenium(IV) and (VI) on different mineral oxide phases, serving as models for complex naturally occurring minerals in a host rock of a nuclear waste repository, are presented.
From the ternary sorption system U(VI)/phosphate/SiO2, the formation of two binary uranyl surface species and of a precipitate was found to be sufficient to satisfactorily fit the respective batch results by SCM. For the selenium(IV) and selenium(VI) binary sorption systems, a single predominant inner-sphere selenite and outer-sphere selenate surface species on alumina phases were identified by vibrational spectroscopy, respectively. With respect to the bidentate binding mode observed for both oxyanionic surface species, SCM provided excellent fitting results of the batch sorption data.
The results of this study demonstrated that the combined approach of in situ spectroscopy and batch sorption studies contributes to an improved performance of future assessments for the migration of radionuclides an fission products in the environment of a repository site.

  • Lecture (Conference)
    Goldschmidt 2018, 12.-17.08.2018, Boston, U.S.A.

Publ.-Id: 27270

Einfluss der Bildgebung eines in beam MR-Scanners auf die Dosisprofile eines Protonenstrahls

Karsch, L.; Gantz, S.; Pawelke, J.; Schellhammer, S.; Smeets, J.; Hoffmann, A.

Eine in Echtzeit ausgeführte Magnetresonanztomografie (MRT) könnte die geometrische Präzision der Protonentherapie künftig verbessern. Zur MR-Bildgebung werden jedoch magnetische Gradientenfelder in Pulssequenzen auf- und abgebaut, die mit den Protonen wechselwirken. Aufgrund der geringen Stärke der Gradientenfelder wird theoretisch keine Änderung der Dosisverteilung des Protonenstrahls durch diese magnetischen Felder erwartet. Ziel dieser Arbeit war einerseits die Entwicklung eines Aufbaus zur gleichzeitigen Strahldetektion und MR-Bildaufnahme und andererseits die experimentelle Untersuchung der Beeinflussung des Protonenstrahls durch die gleichzeitige MR-Bildgebung.

Material & Methoden
Ein offener 0.22 T MR-Scanner (MrJ2200, Paramed) wurde an einer horizontalen Protonenstrahlführung installiert, so dass der Protonenstrahl auf das magnetische Isozentrum des MR-Scanners gerichtet ist. Um den Einfluss der MR-Bildgebung auf den Protonenstrahl zu untersuchen wurden zwei Experimente mit unterschiedlichen Aufbauten und MR-Pulssequenzen durchgeführt.
Im Absorptionsexperiment wurde im Isozentrum des MR-Scanners ein mit Flüssigszintillator (BC517H, Saint Gobain) gefülltes Phantom aus PMMA platziert. Das vom bestrahlten Szintillator emittierte Licht wurde mittels einer Kamera aufgezeichnet. Aus den Kamerabildern wurde auf die statistische Genauigkeit des Verfahrens geschlossen und diese mit der Differenz der über mehrere Aufnahmen gemittelten Dosisprofile verglichen.
Beim Transmissionsexperiment wurde auf ein bildgebendes Phantom verzichtet und die Dosisprofile ca. 1 m hinter dem Isozentrum des MR-Scanners mit einem Festkörper-Szintillator basierten 2D-Detektor (Lynx, IBA) aufgezeichnet. Die gemessenen Dosisprofile wurden durch eine gedrehte zweidimensionale Normalverteilung angenähert.

Im Absorptionsexperiment liegen die Unterschiede in den Pixelwerten der Kamerabilder zwischen laufender und ausgeschalteter MR-Bildgebung innerhalb der statistischen Schwankungen. Auch im Transmissionsexperiment zeigen die fünf Anpassungsparameter der Normalverteilung keine Änderung in den Dosisprofilen durch die Bildaufnahme des MR-Scanners.

Gleichzeitige Detektion des Protonenstrahles während einer MR-Bildaufnahme ist mit Hilfe von Phantomen, die mit Flüssigszintillator gefüllt sind, möglich. Die einzelnen MR-Pulssequenzen zeigen keinen Einfluss auf den Protonenstrahl, so dass in der Bestrahlungsplanung einer MR-integrierten Protonentherapie nur das statische Magnetfeld des MR-Scanners berücksichtigt werden muss.

Keywords: MR; Radiation Therapy; Proton Therapy

  • Poster
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 19.09.2018, Nürnberg, Deutschland

Publ.-Id: 27269

Quantitative Measurement of Interaction between Solidification and Convection in Ammonium-Chloride Solutions

Anders, S.; Noto, D.; Eckert, S.

An experimental investigation of double-diffusive convection with simultaneous crystallisation in ammonium-chloride solutions will be presented. Measurements were performed in a transparent Hele-Shaw with controlled thermal boundary conditions. The flow field of the liquid was measured by PIV. Using thermochromic liquid crystals, the temperature field inside the fluid was established. PTV was used to determine the size-evolution and the trajectories of the salt crystals. Alternating lighting methods and digital image filtering allow for simultaneous operation of PIV, PTV and temperature field measurement. This enables a quantitative study of the interplay of convection regimes and solidification processes like columnar and equiaxed crystallization, chimney-formation and remelting.

Keywords: Iron Snow; PTV; PIV; TLC; Multiphase Flow; Solidification; Double-diffusive Convection

  • Lecture (Conference)
    Symposium zur Simulation Metallurgischer Prozesse 2018, 30.01.-02.02.2018, Feuerkogel, Österreich

Publ.-Id: 27268

The mineralogy of weathering products of Bi-bearing tennantite – clues for the process and the mobilisation of heavy metals and toxic elements

Keim, M.; Staude, S.; Marquardt, K.; Bachmann, K.; Opitz, J.; Markl, G.

Since the complex sulfosalts of the tennantite-tetrahedrite solid-solution series [(Cu,Ag)6Cu4(Fe,Zn,Cu,Hg,Cd)2(Sb,As,Bi,Te)4(S,Se)13] are widespread in many geological environments and accommodate heavy metals and toxic elements, a better understanding of the general weathering process and mobility of elements are important to evaluate environmental risks. In this study, the weathering of Bi-rich members of this mineral group were investigated in detail using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, µXRD and MLA. Observation reveal a subdivision in four temporally distinguishable weathering stages, spatially attributed to weathering environments of different chemical potentials. During the first stage, weathering occurs as tubes within the fahlore producing a phase assemblage of nm-sized roméite group minerals, tripuhyite, a crystalline Cu-oxide phase and crystalline Cu-sulfides. The textural appearance and the occurrence of these secondary sulfide indicates a low oxidation potential during this stage, typical for cementation zones. Mass balance calculations show that during this stage As, Zn and partially S are released to the weathering fluids. In contrast, Sb, Bi, Fe, S and Cu are stored in the roméite group minerals, tripuhyite, the copper oxide phase, and sulfides. During weathering stage 2, amorphous and nano-crystalline arsenates were formed replacing fahlore in most cases as weathering fronts. Their textures indicate a fluid with higher oxidation potential than in stage 1, typical for oxidation zones. The occurrence of arsenates shows that arsenic in contrast to stage 1 behaves immobile during this stage. Bismuth behaves immobile and is stored in the amorphous nano-crystalline phase. Mass balance calculations reveal that Zn, Sb, and S and partially Cu are lost, whereas Fe is added. Weathering stage 3 occurs only locally and reflects processes in micro compartments that are different for each locality and not characteristic for the general weathering process including the dissolution of former phases but also precipitation of new ones such as amorphous Cu-silicates. Stage 4 is characterized by the formation of crystalline Cu-Ba-Ca-Al-arsenates and Cu-carbonates mostly along cracks and in voids, spatially independent of the precursor fahlore. This stage reflects the increasing importance of the local geology, host rock and gangue mineralogy on weathering, typical in near surface environments of oxidation zones, where elements are highly mobile and a high fluid rock ratio is realized.

Keywords: Tennantite-tetrahedrite; weathering; bismuth; cementation zone; oxidation zone; Schwarzwald


Publ.-Id: 27267

Applied Mineralogy for Resource Efficiency of Platinum Metals - Towards a Geometallurgical Model

Bachmann, K.; Menzel, P.; Tolosana-Delgado, R.; Gutzmer, J.

A geometallurgical model allows to predict parameters relevant for mineral beneficiation in a spatial domain. Therefore, we need a basic understanding of the geolocial architecture which can be provided by 3D geological models. Additionally, a tailored sample selection and characterization is crucial. This may include drill core logging data, whole rock geochemistry, modal mineralogies, micro-textures and mineral association as well as mineral chemistry data. In a next step, it is necessary to integrate the data into a spatial context and to derive process-relevant paramters. Finally, the development of domains with similar mineral beneficiation characteristics as well as geostatistical interpolation of relevant parameters onto a 3D geometry is possible.

  • Invited lecture (Conferences)
    Joint AMREP & DST-CIMERA Symposium, 14.-15.03.2018, Johannesburg, South Africa

Publ.-Id: 27266

Microbial diversity and activity in rock salt formations

Cherkouk, A.; Bader, M.; Bachran, M.; Swanson, J. S.; Steudtner, R.; Drobot, B.; Schmidt, M.; Musat, N.; Rossberg, A.; Ikeda-Ohno, A.; Stumpf, T.

Rock salt formations are considered as potential host rocks for the long-term storage of highly radioactive waste in a deep geological repository. A combination of culture-dependent and culture-independent methods was used to investigate the microbial diversity in rock salt. Extremely halophilic archaea, e.g. Halobacterium species, dominate this habitat. For long-term risk assessment it is of high interest to study how these microorganisms can interact with radionuclides if released from the waste repository. Therefore, the interactions of the extremely halophilic archaeon Halobacterium noricense DSM 15987T with uranium, one of the major radionuclides of concern in the geological repository, were investigated in detail in batch experiments. A multi-spectroscopic and microscopic approach was used to decipher the interaction mechanisms on a molecular level. H. noricense DSM 15987T showed a multistage bioassociation of uranium. By using time-resolved laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy the formation of U(VI) phosphate minerals, such as meta-autunite, was observed. Furthermore, the presence of U(VI)-phosphate mineral could be visualized by scanning electron microscopy. These findings highlight the potential significance of the microbial life in deep geological hypersaline environments and offer new insights into the microbe-actinide interactions at highly saline conditions relevant to the disposal of highly radioactive waste as well as bioremediation.

  • Poster
    ISME17 - 17th International Symposium on Microbial Ecology, 12.-17.08.2018, Leipzig, Deutschland

Publ.-Id: 27265

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