Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

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

Permalink: https://www.hzdr.de/publications/Publ-27354
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

Permalink: https://www.hzdr.de/publications/Publ-27353
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

Permalink: https://www.hzdr.de/publications/Publ-27352
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

Permalink: https://www.hzdr.de/publications/Publ-27351
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

Permalink: https://www.hzdr.de/publications/Publ-27350
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

Permalink: https://www.hzdr.de/publications/Publ-27349
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

Permalink: https://www.hzdr.de/publications/Publ-27348
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

Permalink: https://www.hzdr.de/publications/Publ-27347
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

Permalink: https://www.hzdr.de/publications/Publ-27346
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

Permalink: https://www.hzdr.de/publications/Publ-27345
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

Permalink: https://www.hzdr.de/publications/Publ-27344
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.

Background:
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.
Methods:
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).
Results:
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).
Conclusions:
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

Permalink: https://www.hzdr.de/publications/Publ-27343
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

Permalink: https://www.hzdr.de/publications/Publ-27342
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

Permalink: https://www.hzdr.de/publications/Publ-27341
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

Permalink: https://www.hzdr.de/publications/Publ-27340
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.

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Permalink: https://www.hzdr.de/publications/Publ-27339
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

Permalink: https://www.hzdr.de/publications/Publ-27337
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

Permalink: https://www.hzdr.de/publications/Publ-27336
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

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Permalink: https://www.hzdr.de/publications/Publ-27335
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

Permalink: https://www.hzdr.de/publications/Publ-27334
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

Permalink: https://www.hzdr.de/publications/Publ-27333
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

  • Open Access Logo Review of Scientific Instruments 89(2018), 073111
    Online First (2018) DOI: 10.1063/1.5038423

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Permalink: https://www.hzdr.de/publications/Publ-27330
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

Permalink: https://www.hzdr.de/publications/Publ-27329
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

Permalink: https://www.hzdr.de/publications/Publ-27328
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.

Permalink: https://www.hzdr.de/publications/Publ-27327
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

Permalink: https://www.hzdr.de/publications/Publ-27326
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

  • European Journal of Nuclear Medicine and Molecular Imaging 45(2018)10, 1752-1761
    Online First (2018) DOI: 10.1007/s00259-018-3996-1

Permalink: https://www.hzdr.de/publications/Publ-27325
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.

  • Open Access Logo Magnetic Resonance Materials in Physics, Biology and Medicine 31(2018)6, 725-734
    Online First (2018) DOI: 10.1007/s10334-018-0691-y

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Permalink: https://www.hzdr.de/publications/Publ-27324
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

Permalink: https://www.hzdr.de/publications/Publ-27323
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

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Permalink: https://www.hzdr.de/publications/Publ-27321
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

Permalink: https://www.hzdr.de/publications/Publ-27320
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

Permalink: https://www.hzdr.de/publications/Publ-27319
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.

  • European Journal of Nuclear Medicine and Molecular Imaging 44(2017)12, 1955-1957
    Online First (2017) DOI: 10.1007/s00259-017-3808-z

Permalink: https://www.hzdr.de/publications/Publ-27318
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

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Permalink: https://www.hzdr.de/publications/Publ-27317
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.

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Permalink: https://www.hzdr.de/publications/Publ-27316
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

Permalink: https://www.hzdr.de/publications/Publ-27315
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

Permalink: https://www.hzdr.de/publications/Publ-27314
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

Permalink: https://www.hzdr.de/publications/Publ-27313
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

Permalink: https://www.hzdr.de/publications/Publ-27312
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

Permalink: https://www.hzdr.de/publications/Publ-27311
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

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-27309
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.

Permalink: https://www.hzdr.de/publications/Publ-27308
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

Permalink: https://www.hzdr.de/publications/Publ-27307
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.

Einleitung
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.

Ergebnisse
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.

Zusammenfassung
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

Permalink: https://www.hzdr.de/publications/Publ-27306
Publ.-Id: 27306


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

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

Einleitung:
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.

Ergebnisse:
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).

Zusammenfassung:
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

Permalink: https://www.hzdr.de/publications/Publ-27305
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.

Purpose/Objective:
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.

Material/Methods:
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.

Results:
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.

Conclusion:
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

Permalink: https://www.hzdr.de/publications/Publ-27304
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.

Purpose/Objective
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.

Materials/Methods
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.

Results
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.

Conclusion
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

Permalink: https://www.hzdr.de/publications/Publ-27303
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

Permalink: https://www.hzdr.de/publications/Publ-27302
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

Permalink: https://www.hzdr.de/publications/Publ-27301
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

Permalink: https://www.hzdr.de/publications/Publ-27300
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

Permalink: https://www.hzdr.de/publications/Publ-27299
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

Permalink: https://www.hzdr.de/publications/Publ-27298
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.

Introduction
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.
Methods
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.
Results
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).
Conclusion
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

Permalink: https://www.hzdr.de/publications/Publ-27296
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.

Permalink: https://www.hzdr.de/publications/Publ-27295
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.

Permalink: https://www.hzdr.de/publications/Publ-27294
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.

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Permalink: https://www.hzdr.de/publications/Publ-27293
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

Permalink: https://www.hzdr.de/publications/Publ-27292
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.

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Permalink: https://www.hzdr.de/publications/Publ-27291
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

Permalink: https://www.hzdr.de/publications/Publ-27289
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

Permalink: https://www.hzdr.de/publications/Publ-27288
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

Permalink: https://www.hzdr.de/publications/Publ-27286
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

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Permalink: https://www.hzdr.de/publications/Publ-27285
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

Permalink: https://www.hzdr.de/publications/Publ-27284
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

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Permalink: https://www.hzdr.de/publications/Publ-27283
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

Permalink: https://www.hzdr.de/publications/Publ-27282
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] www.my-standards.com; see also paper by D. Savard et al., this conference

Keywords: reference materials

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

Permalink: https://www.hzdr.de/publications/Publ-27281
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.

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Permalink: https://www.hzdr.de/publications/Publ-27280
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

Permalink: https://www.hzdr.de/publications/Publ-27279
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

Permalink: https://www.hzdr.de/publications/Publ-27278
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

Permalink: https://www.hzdr.de/publications/Publ-27277
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

Permalink: https://www.hzdr.de/publications/Publ-27276
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

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Permalink: https://www.hzdr.de/publications/Publ-27275
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

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Permalink: https://www.hzdr.de/publications/Publ-27274
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

Permalink: https://www.hzdr.de/publications/Publ-27273
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.

Introduction
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.

Methods
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.

Results
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.
Conclusion
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)

Permalink: https://www.hzdr.de/publications/Publ-27272
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

Permalink: https://www.hzdr.de/publications/Publ-27271
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.

Permalink: https://www.hzdr.de/publications/Publ-27270
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.

Einleitung
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.

Ergebnisse
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.

Zusammenfassung
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

Permalink: https://www.hzdr.de/publications/Publ-27269
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

Permalink: https://www.hzdr.de/publications/Publ-27268
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

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Permalink: https://www.hzdr.de/publications/Publ-27267
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

Permalink: https://www.hzdr.de/publications/Publ-27266
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

Permalink: https://www.hzdr.de/publications/Publ-27265
Publ.-Id: 27265


Variation in PGM and BMS assemblages in the LG-6 and LG-6A chromitites of the western Bushveld Complex, South Africa

Bachmann, K.; Osbahr, I.; Tolosana-Delgado, R.; Chetty, D.; Gutzmer, J.

This study focuses on the LG-6 and LG-6A chromitite seams at the Thaba mine located on the western limb of the Bushveld Complex. Platinum group minerals and base-metal sulfides are studied by mineral liberation analysis and electron microprobe analysis to define distinct assemblages and to evaluate the potential for beneficiation. Two distinct major mineral assemblages are defined: The first assemblage is rich in PGE-sulfides and alloys of Fe and Sn as well as chalcopyrite, pentlandite while second assemblage is rich in PGE-sulfarsenides and -arsenides and -alloys of Sb and Bi, pentlandite and Co-rich pentlandite.

  • Contribution to proceedings
    International Platinum Symposium, 30.06.-06.07.2018, Polokwane, South Africa

Permalink: https://www.hzdr.de/publications/Publ-27264
Publ.-Id: 27264


PGE Distribution and Mineralogy in the LG-6 and Middle Group Chromitite Layers, Thaba Mine, Bushveld Complex

Kaufmann, F.; Hecht, L.; Bachmann, K.; Trumbull, R.; Veksler, I.; CRONIMET Chrome Mining (Pty.) Ltd.

Here we present information about concentrations, distribution and mineralogy of platinum group elements (PGE) in the sequence of chromitite layers from LG-6 to MG-4 at the Thaba mine in the north-western sector of the Bushveld Complex in South Africa. The information is based on assay analyses of drill core samples and studies of platinum group minerals and base-metal sulfides by mineral liberation analysis. Total concentrations of PGE gradually increase with the stratigraphic height from the LG-6 layer to MG-4. Detailed sampling of the LG-6, LG-6A, MG-1 and MG-2 layers revealed uneven vertical distribution of PGE with the highest concentrations at the footwall contacts. Pt-Pd ratios vary broadly from one layer to another and tend to increase from top to bottom within the individual layers. The assemblage of platinum group minerals in the LG-6 and LG-6A layers comprises equal proportions of (Pt,Pd)S, malanite and laurite, and minor amounts of Fe-Sn alloys sperrylite. PGE tellurides and bismuthotellurides are largely absent. In contrast, the PGE mineralogy of the MG-1 and MG-2 layers is dominated by laurite.

  • Contribution to proceedings
    International Platinum Symposium, 30.06.-06.07.2018, Polokwane, South Africa

Permalink: https://www.hzdr.de/publications/Publ-27263
Publ.-Id: 27263


Spatially-resolved characterization of Eu(III) interaction with granitic rock (Eibenstock, Germany)

Schmidt, M.; Molodtsov, K.

The mobility of (radio-)contaminants in the geosphere is controlled by their interaction with the surfaces of surrounding minerals. Typically these interactions are studied either with single mineral phases, or in field studies in natural rock formations consisting of multiple mineral phases. In the former case, the involved reactions can be characterized at the molecular level with appropriate spectroscopic tools, but the complexity of the natural rock is lost, while the latter case often only allows a quantitative approach due to the inherent complexity of the natural system.
Here we present a novel approach to bridge this gap in the understanding of sorption processes. Time-resolved laser-induced fluroescence spectroscopy (TRLFS) is a well established technique to characterize the speciation of luminescent metal ions, e.g Eu(III)[1] or Cm(III).[2] We have adapted the technique to allow scanning a rock sample consisting of a variety of mineral grains, through a focused laser beam with a spatial resolution ~ 20 µm (µTRLFS). This way we are able to obtain full emission spectra and lifetimes in each spot. Through this improvement, it is possible to not only map the distribution of a fluorescent probe on the rock, but also to determine its speciation in each location, with respect to its coordination strength and hydration state.
The interaction of Eu(III) with granitic rock thick sections from the former uranium mine Eibenstock, Germany, were investigated by µTRLFS. The investigation is complemented by mineral characterization using µXRF, EMPA, and thin section microscopy. The results clearly show the differing sorption capacity and sorption strength of the minerals contained in the granite, with the highest sorption capacity found for feldspars. In addition, grain boundaries often show a reactivity distinct from both bordering mineral grains, e.g. a quartz/biotite grain boundary showing higher adsorption than both, quartz and biotite.
In summary, the results highlight the necessity to complement studies of model systems with more realistic whole system investigations. The technical improvement to a well-established spectroscopic tool also offers opportunities for other fields of (bio)geochemistry.

(1) Binnemans, K., Coord. Chem. Rev. 2015, 295, 1-45.
(2) Edelstein, N.M., Coord. Chem. Rev. 2006, 250, 948-973.

Keywords: TRLFS; europium; sorption; granite; microscopy; µTRLFS

  • Lecture (Conference)
    Goldschmidt 2018, 12.-17.08.2018, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-27262
Publ.-Id: 27262


Regge Trajectories of Radial Meson Excitations: Exploring the Dyson-Schwinger-- Bethe-Salpeter Approach

Greifenhagen, R.; Kämpfer, B.; Kaptari, L. P.

The combined Dyson-Schwinger and Bethe-Salpeter equations in rainbow-ladder approximation are used to search for Regge trajectories of mesons in the pseudo-scalar and vector channels. We focus on the often employed Alkofer-Watson-Weigel kernel which is known to deliver good results for the ground state meson spectra; it provides linear Regge trajectories in the JP=0− channel.

Permalink: https://www.hzdr.de/publications/Publ-27261
Publ.-Id: 27261


Impact of Dipolar Interaction on Superfluid Spin Transport

Schneider, T.; Barsukov, I.; Smith, A.; Upadhyaya, P.; Liu, Y.; Fan, Y.; Wang, K.; Macdonald, A.; Tserkovnyak, Y.; Krivorotov, I. N.

Ferromagnetic easy-plane system are theoretically excepted to support a long-range coherent transport flow, normally referred as spin superfluid. However, the influence of local dipole-dipole interaction on these states are not fully investigated. Here, the present a detailed micromagnetic study of the superfluid flow in a easy-plane ferromagnetic in the presence of local dipole-dipole interactions.

  • Lecture (others)
    Spintronics group seminar, 15.03.2018, Irvine, CA, USA
  • Lecture (others)
    Group seminar Prof. Tserkovnyak, 19.03.2018, Los Angeles, USA

Permalink: https://www.hzdr.de/publications/Publ-27260
Publ.-Id: 27260


Charakterisierung der MR-Relaxations- und Bewegungseigenschaften eines 4D MRT Phantoms im Rahmen der Kommissionierung an einem 3T MR Scanner

Schneider, S.; Dolde, K.; Engler, J.; Hoffmann, A. L.; Pfaffenberger, A.

Einleitung
Für die klinische Etablierung von Magnetresonanztomographen (MRT) in der bildgestützten Strahlentherapie, allen voran der hybriden MR-Linacs, bedarf es der Analyse und regelmäßiger Qualitätssicherung der Bewegungscharakterisierung auf Basis der MRT Bilder. Ziel dieser Studie war die Kommissionierung eines programmierbaren 4D MRT-Bewegungsphantoms bezüglich seiner bildgebenden MR-Relaxations- und Bewegungseigenschaften an einem 3T MRT und die Entwicklung einer Methode zur automatisierten Qualitätssicherung von MRT-Sequenzen zur Bewegungsanalyse.
Material & Methoden
Das MRI-LINAC Dynamic Phantom (Model 008M, CIRS) wurde mit Mineralöl (Marcol Blend, Philips) gefüllt und mit einer Hilfskonstruktion auf einer flachen Tischauflage (Medibord Ltd) positioniert. Messungen wurden an einem 3.0T MRT (Ingenuity TF PET/MR, Philips) durchgeführt. Mittels MR-Relaxometrie wurden die Relaxationszeiten des Gel-gefüllten beweglichen Zylinders und des Targets bestimmt. Die T1-Relaxationszeit wurde durch eine Inversion-Recovery Spin-Echo (IR-SE) Methode , die T2-Relaxationszeit durch eine Multi-Echo Gradient-and-Spin-Echo (GraSE) berechnet. Sinusförmige 1D, 2D und 3D Target-Trajektorien mit patiententypischen Organauslenkungen (5-40mm) und Frequenzen (0.1-0.2Hz) sowie eine 1D Patientennavigator Atemkurve wurden im Phantom generiert und mittels 2D-cine MR Sequenzen (Zeitauflösung von <0.5s) aufgenommen. Mit einer selbst entwickelten MATLAB-basierten Tracking-Software wurden die 2D-cine Bilder automatisiert analysiert.
Ergebnisse
Die Relaxationsparameter für Zylinder (T1=871±36ms / T2=13.4±1.3ms) und Target (T1=208±2.8ms / T2=30.5±0.7ms) wurden bestimmt. Die extrahierten Amplituden der Sinustrajektorien zeigen Abweichungen zu den eingestellten Werten von <0.4mm in AP/LR und <0.2mm in IS Richtung, während die Frequenzen mit Abweichungen von <0.001Hz bestimmt wurden. Die Navigatorkurve konnte mit einer mittleren Amplitudenabweichung von 0.3mm bestimmt werden, bei einer maximalen Abweichung von <1.0mm.
Zusammenfassung
Das 4D-Phantom wurde an einem klinischen 3T MRT bezüglich seiner Relaxationseigenschaften und der Möglichkeit einer 3D Bewegungsanalyse kommissioniert. Der entwickelte Aufbau und die Methodik erlauben regelmäßige Qualitätskontrollen der Bewegungscharakterisierung auf MR-Basis.

Keywords: MRT; Bewegungs-Phantom; Kommissionierung

  • Poster
    49. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik und 21. Jahrestagung der Deutschen Sektion der ISMRM, 19.-22.09.2018, Nürnberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27259
Publ.-Id: 27259


Interaction of fluid flow with heat and mass transfer in Liquid Metal Batteries

Personnettaz, P.; Landgraf, S.; Nimtz, M.; Weber, N.; Weier, T.

Liquid metal batteries (LMBs) are suggested as a possible solution of the energy storage problem. An LMB consists of three stably stratified layers, two liquid metals are separated by a molten salt electrolyte.
Operation was so far demonstrated for small prototypes only. In order to upscale cells to a viable commercial scale a deep knowledge of the physics involved is required.
The relatively simple chemistry and geometry, the presence of multiple and multi-physics phenomena and the completely fluid nature of the active materials have made the LMB an intriguing candidate for continuum mechanics studies.
The cell is in fact subject to a coexistent transport of mass, heat, charge and momentum together with chemical and electrochemical reactions.
The fluid flow that naturally occur can be beneficial if it is able to improve the mass transport, delaying the formation of solid intermetallic phases.
In our work the attention is focused on heat and mass transfer. The continuum balances are defined in general terms, taking into account the electrochemical nature of the system. The corresponding scalar fields (e.g. temperature and solute concentration) are then computed with pure diffusive models. In a second step the interaction with the induced fluid flow is taken into account. Thermal convection in Li||Bi LMBs is studied with an improved version of the multiphase VOF solver multiphaseInterFOAM. Advection-diffusion mass transfer is investigated in the positive electrode with single-phase CFD solvers.
The first results of thermo-solutal convection are presented, the modeling limits and the future development are discussed.

Keywords: LMB; Heat Transfer; Mass Transfer

  • Lecture (Conference)
    12th European Fluid Mechanics Conference, 09.-13.09.2018, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-27258
Publ.-Id: 27258


Machbarkeitsstudie zur Integration eines offenen MR-Scanners in die horizontale Strahlführung einer Protonentherapie-Anlage

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

Einleitung
Aufgrund der steilen Dosisgradienten kann die Treffgenauigkeit in der Protonentherapie (PT) durch Bewegungen und anatomische Veränderungen stark kompromittiert werden. Eine gleichzeitige Bildgebung mittels Echtzeit-Magnetresonanztomographie (MRT) könnte die Treffgenauigkeit erhöhen. Bis heute existieren jedoch keine kombinierten Systeme aus MRT und PT. Ziele dieser Studie waren deshalb die erste Integration eines MR-Scanners in eine PT-Strahlführung, die Überprüfung der Machbarkeit einer gleichzeitigen MR-Bildgebung und Bestrahlung, und die Kontrolle der MR-Bildqualität mit und ohne Strahleinfluss.

Material & Methoden
Ein offener MR-Scanner für muskuloskelettale Bildgebung mit einem vertikalen Magnetfeld von 0.22 T (MRJ2200, Paramed) wurde an einer strahldüsenlosen horizontalen Strahlführung (IBA Proton Therapy) installiert, und durch einen kompakten Faraday-Käfig von Hochfrequenz-Interferenzen abgeschirmt. Um den Protonenstrahl trotz der Strahlablenkung im Magnetfeld des Scanners zentral auf dessen Field-of-View zu richten, wurde das Magnetfeld mit einer Hall-Sonde (HHP-VU, Arepoc) vermessen. Auf dieser Grundlage wurde die mittlere Strahlablenkung für Energien zwischen 70−230 MeV mittels Monte-Carlo-Simulationen (Geant4) berechnet und der Scanner daraufhin um 2 cm versetzt zum Strahlaustritt platziert. Der Strahl wurde kollimiert (Ø=10 mm) und durch ein Strahlrohr in den Faraday-Käfig geführt. Die Strahllage im Field-of-View wurde mittels radiochromischer Filme (EBT3, Ashland) verifiziert. Zur Überprüfung der MR-Bildgebung wurden anatomische MR-Bilder eines Probanden bei deaktivierter Strahlführung sowie MR-Bilder eines Gewebephantoms mit und ohne Strahleinfluss (215 MeV, 5 nA) aufgenommen.

Ergebnisse
Die MR-Aufnahmen (Abb. 1) des Probanden zeigten die für den verwendeten Scanner übliche Bildqualität. Relevante anatomische Strukturen waren klar unterscheidbar. Am Gewebephantom wurde keine Bildverzerrung durch die Strahlführungsmagneten und den Protonenstrahl beobachtet, jedoch eine gleichförmige Bildverschiebung (< 1 mm) in Frequenzkodierrichtung, die vermutlich entweder auf statistische Schwankungen in der scannereigenen Frequenzkalibrierung oder auf das Randfeld der Strahlführungsmagnete zurückzuführen ist.

Zusammenfassung
Die Integration eines offenen MR-Scanners in den experimentellen Strahlengang einer Protonentherapie-Anlage war erfolgreich. Eine gleichzeitige MR-Bildgebung und Bestrahlung ohne Bildverzerrung ist möglich. Eine geringe und potentiell korrigierbare MR-Bildverschiebung wurde festgestellt.

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

Permalink: https://www.hzdr.de/publications/Publ-27257
Publ.-Id: 27257


THEREDA, the thermodynamic reference database for a nuclear waste disposal in Germany

Bok, F.; Moog, H. C.; Altmaier, M.; Voigt, W.; Thoenen, T.

The disposal of nuclear waste including the assessment of long-term safety is still an open question in Germany. In addition to the still pending decision about the repository host rock (salt, granite, or clay) the basic necessity of a consistent and obligatory thermodynamic reference database persists. Specific challenges are comprehensive datasets covering high temperatures and salinities. In response to deficiencies of other databases THEREDA, a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany and Switzerland, was started in 2006.
The core of THEREDA consists of a relational databank whose structure has been designed in a way that promotes the internal consistency of thermodynamic data. Data considered cover the needs of Gibbs Energy Minimizers and Law-of-Mass-Action programs alike. Pitzer coefficients to describe solute activity coefficients in high-saline solutions are considered. Both thermodynamic data and interaction coefficients can be described by temperature functions.
Ready-to-use parameter files are created from the databank in a variety of formats. Supported target codes are ChemApp, PHREEQC, EQ3/6, and Geochemist’s Work-bench. Data can alos be downloaded in a generic JSON-type format to promote conversion for other geochemical codes Prior to their release all parameter files are submitted to internal test calculations – one essential element of the quality assurance scheme. The results are documented and provided to the users and accessible via internet through http://www.thereda.de/.
Data are currently available to describe the solubility of the following radionuclides or fission elements: U(IV/VI), Th(IV), Np(IV/V), Pu(IV) Am(III), Nd(III), Cm(III), Tc(IV/ VII), Sr, Cs and the matrix elements (oceanic salt system, cement phases).
Future develpoments are thermodynamic data sets for Selenium and Oxygen in high saline solutions as well as the inclusion of low saline sorption data.

Keywords: THEREDA; Database; Thermodynamic Modelling; Radionuclides

  • Poster
    Goldschmidt2018, 12.-17.08.2018, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-27256
Publ.-Id: 27256


Thermodynamic modelling of Selenium in environmental conditions: traps, pitfalls and perspectives

Bok, F.; Jordan, N.; Brendler, V.

Any safety assessment of nuclear waste disposal concepts requires comprehensive and consistent thermodynamic data for the respective reactive transport modelling. This includes sorption, ion exchange or surface precipitation as major retardation processes, as well as a correct description of the aqueous chemistry including redox processes.
Selenium (with the isotope Se-79 being an important fission product) can occur in oxidation states varying between +VI and –II, the latter also including several polynuclear species. Most often negatively charged species are formed rendering them extraordinarily mobile in groundwater systems. Namely for Se solubility in highly saline solutions and for Se sorption onto minerals several competing thermodynamic datasets are published to predict the behavior of selenium under environmental conditions. However, there are still critical data gaps. For example, recent findings like the selenite dimerization have to be parameterized and included into thermodynamic data collections. In addition, for the selenide chemistry, solubility data are missing as well as ion-ion interaction parameters for the calculation in brines.
Another aspect of the reactive transport of selenium is the retardation of mainly selenate and selenite via sorption onto mineral phases. For these processes, recent spectroscopic investigations in combination with batch experiments have enabled deeper insights into the sorption chemistry of selenium. Here, the various data received must be processed into consistent data sets.
Several approaches to close critical selenium data gaps will be presented. These are essential steps towards a consistent and quality approved thermodynamic data set that can be included into databases needed for the geochemical and reactive transport calculations, namely THEREDA (http://www.thereda.de) and RES³T (http://www.hzdr.de/res3t).

Keywords: Radionuclides; Selenium; Thermodynamic Modelling; Databases

  • Lecture (Conference)
    256th ACS National Meeting & Exposition, 19.-23.08.2018, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-27255
Publ.-Id: 27255


Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings

Li, Z.; Klopf, J. M.; Wang, L.; Yang, K.; Lukaszew, R. A.

Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD) and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.

Permalink: https://www.hzdr.de/publications/Publ-27254
Publ.-Id: 27254


U(VI) sorption by Ca-bentonite at pH 8-13: Spectroscopic investigation of retention mechanisms

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

Bentonite is considered as buffer and backfill material in deep geological repositories for radioactive waste. Therefore, profound understanding of radionuclide retention processes at the bentonite surface under environmentally relevant conditions is essential for a long-term safety assessment. Such conditions can involve high pH, as hyperalkaline cement pore waters evolve from corroding concrete within a repository. Since the U(VI) sorption behavior at alkaline conditions is still poorly understood, batch experiments were combined with spectroscopic investigations in order to gain insight into the underlying retention processes on the molecular level.
pH-dependent batch sorption experiments (pH 8-13) in a diluted Gipshut solution (2.5 M NaCl, 0.02 M CaCl2, 0.02 M Na2SO4, 0.0051 M KCl) at different carbonate concentrations (absence, 0.5 and 100 mM) showed a decreased U(VI) retention in the presence of carbonate up until a certain pH (pH 9.5 or pH 11, depending on [CO32-]) due to the formation of weakly sorbing (calcium) uranyl carbonate complexes in aqueous solution, confirmed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This is in accordance with previous studies [1]. However, also in the presence of carbonate, U(VI) retention is increased in even stronger alkaline solutions, which is attributed to the preferred formation of hydrolyzed U(VI) species at these conditions.
In order to clarify the mechanisms responsible for the very strong U(VI) retention in the pH range 10-12 (absence and 0.5 mM CO32-), uranyl complexes on the bentonite surface were examined directly, using site-selective TRLFS and EXAFS (ESRF, Grenoble). Selective excitation of different sorption species by varying laser energy allowed the identification of both, surface complexation and, to a smaller degree, surface precipitation. EXAFS spectra did not show any indication of precipitates, verifying that adsorption is the dominant retention process and precipitates form only as small fractions, below the EXAFS detection limit. According to atomic distances and coordination numbers for U-Oeq, U(VI) surface complexes shift from a 5-fold to a 4-fold coordination in the equatorial plane with increasing pH.

  • Lecture (Conference)
    Goldschmidt2018, 12.-17.08.2018, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-27253
Publ.-Id: 27253


Data for "Complexation of trivalent lanthanides (Eu) and actinides (Cm) with aqueous phosphates at elevated temperatures"

Jordan, N.; Starke, S.; Huittinen, N.

At the Institute of Resource Ecology, the complexation of Eu(III) and Cm(III) with aqueous phosphate was studied using laser-induced luminescence spectroscopy at low pH ([H+] = 0.1 M), different ionic strengths (0.6 to 3.1 M) and different temperatures (25 to 80 °C). The data set contains the species distribution, slope analysis and the extrapolation to zero ionic strength using R.

Keywords: Curium; Europium; phosphate complexation; linear regression

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-05-22
    DOI: 10.14278/rodare.5
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-27252
Publ.-Id: 27252


CMOS‐compatible controlled hyperdoping of silicon nanowires

Berencén, Y.; Prucnal, S.; Möller, W.; Hübner, R.; Rebohle, L.; Böttger, R.; Glaser, M.; Schönherr, T.; Yuan, Y.; Wang, M.; Georgiev, Y. M.; Erbe, A.; Lugstein, A.; Helm, M.; Zhou, S.; Skorupa, W.

Hyperdoping consists of the intentional introduction of deep‐level dopants into a semiconductor in excess of equilibrium concentrations. This causes a broadening of dopant energy levels into an intermediate band between the valence and the conduction bands. Recently, bulk Si hyperdoped with chalcogens or transition metals is demonstrated to be an appropriate intermediate‐band material for Si‐based short‐wavelength infrared photodetectors. Intermediate‐band nanowires can potentially be used instead of bulk materials to overcome the Shockley–Queisser limit and to improve efficiency in solar cells, but fundamental scientific questions in hyperdoping Si nanowires require experimental verification. The development of a method for obtaining controlled hyperdoping levels at the nanoscale concomitant with the electrical activation of dopants is, therefore, vital to understanding these issues. Here, this paper shows a complementary metal‐oxide‐semiconductor (CMOS)‐compatible technique based on nonequilibrium processing for the controlled doping of Si at the nanoscale with dopant concentrations several orders of magnitude greater than the equilibrium solid solubility. Through the nanoscale spatially controlled implantation of dopants, and a bottom‐up template‐assisted solid phase recrystallization of the nanowires with the use of millisecond‐flash lamp annealing, Se‐hyperdoped Si/SiO2 core/shell nanowires are formed that have a room‐temperature sub‐bandgap optoelectronic photoresponse when configured as a photoconductor device.

Keywords: Flash lamp annealing; hyperdoping; intermediate band; ion implantation; nanowires

Permalink: https://www.hzdr.de/publications/Publ-27251
Publ.-Id: 27251


Interaction of U(VI) with α-isosaccharinic acid under acidic conditions: characterization of the formed complexes

Brinkmann, H.; Patzschke, M.; Roßberg, A.; Moll, H.; Stumpf, T.

Cellulose is a very common organic polymer and also present in considerable amounts in low and intermediate level wastes (LILW). Since it is considered to stabilize LILW with cementitious materials and to use cement-based materials as construction and backfilling material, the alkaline degradation of cellulosic material has to be taken into account. This process will lead to the formation of water-soluble carboxylates and hydroxycarboxylates, with isosaccharinic acid (isa) being the main degradation product. It was shown that the α-form of the polyhydroxy-carboxylic acid is a stronger complexant compared to the β-form and that the interaction with radionuclides affects the solubility and the sorption behavior adversely [1]. Only a limited number of studies focused on the interaction of isa with UO22+. Hence, there are gaps in thermodynamic databases for this system. The basis for reliable thermodynamic data is a detailed structural knowledge about the formed species in the system of interest.

This issue prompted us to characterize the formed complexes in the UO22+-isa system on a molecular level. Our approach to elucidate the mechanisms in aqueous solution combines different spectroscopic techniques (UV-vis, ATR-FTIR, EXAFS, and luminescence) with DFT-calculations. The mutual influence of UO22+ and isa on their speciation as well as the three detected complexes will be discussed. The outcomes are on the one hand the basis for thermodynamic investigations as well as for studies under neutral and alkaline conditions. They provide on the other hand also important information concerning the behavior of α-isa as ligand, including dominant binding motifs.

[1] Van Loon, L. R., et al., Radiochimica Acta, 1999, Vol. 86, https://doi.org/10.1524/ract.1999.86.34.183.

This project has received funding from the Euratom research and training programme 2014-2018 under Grant Agreement no. 61880.

Keywords: uranium; isosaccharinic acid; spectroscopy; speciation

  • Lecture (Conference)
    18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-27250
Publ.-Id: 27250


Binding of Antimony to Natural Organic Matter in a Finish Mine-Water Influenced Peatland

Besold, J.; Eberle, A.; Kujala, K.; Kumar, N.; Scheinost, A. C.; Pacheco, L.; Fendorf, S.; Planer-Friedrich, B.

Antimony (Sb) is a toxic element typically of low natural abundance but human activities have led to highly elevated concentrations in many soils and sediments. Recently, natural organic matter (NOM) has been discussed as effective sink for arsenic [1] and first spectroscopic studies [2,3] indicated that sulfhydryl moieties of NOM also play an important role in controlling Sb mobility in wetland sediments. However, Sb speciation in NOM-rich wetlands has not yet been studied comprehensively and direct spectroscopic evidence for this sequestration mechanism is still lacking. In order to investigate the role of NOM for Sb sequestration, we used bulk Sb K-edge X-ray absorption fine structure spectroscopy (EXAFS) from a peatland in northern Finland which receives high Sb loads from an adjacent gold mine. Sampled peat cores were kept under argon atmosphere at cool and dark conditions until freeze-drying to prevent Sb speciation changes. The peat contained up to 52 % carbon and 265 mg/kg Sb (dry weight basis). Sulfur and iron contents ranged between 4 to 8 and 2 to 10 g/kg, respectively. Aqueous Sb concentrations decreased with lateral distance from the inflow from 190 µg/L in surface waters to 8 µg/L in 80 cm depth. Based on linear combination fitting of EXAFS spectra, we found Sb to be mainly coordinated to NOM moieties in all peat samples. At 10-20 cm depth, Sb was sorbed up to 47% to iron (hydr)oxides and with increasing depth, up to 50% of trivalent Sb was complexed tri-fold to sulfhydryl moieties of NOM. At these deep peat layers, Sb was up to 100% complexed to NOM. Our results show that sorption of Sb to particulate NOM can act as an important sequestration mechanism under sulfate reducing conditions and therefore strongly influences Sb mobility in the environment.

[1] Langner et al. (2012) Nat. Geosci. 5, 66-73. [2] Benett et al. (2017) Environ. Chem. 2017, 14, 345–349. [3] Arsic et al. (2018) Environ. Sci. Technol. 52, 1118-1127.

Keywords: antimony; arsenic; peat; organic matter; EXAFS; XANES

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

Permalink: https://www.hzdr.de/publications/Publ-27249
Publ.-Id: 27249


Core-Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction - Kern-Schale-Strukturierung rein metallischer Aerogele für eine hocheffiziente Nutzung von Platin für die Sauerstoffreduktion

Cai, B.; Hübner, R.; Sasaki, K.; Zhang, Y.; Su, D.; Ziegler, C.; Vukmirovic, M. B.; Rellinghaus, B.; Adzic, R. R.; Eychmüller, A.

The development of core-shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of PdxAu-Pt core-shell aerogels composed of an ultrathin Pt shell and a composition-tunable PdxAu alloy core. The universality of this strategy ensures the extension of core compositions to Pd transition-metal alloys. The core-shell aerogels exhibited largely improved Pt utilization efficiencies for the oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mgPt -1 and 2.53 mA cm-2, which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core-shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core-shell electrocatalysts.
Die Entwicklung von rein metallischen Aerogelen mit Kern-Schale-Strukturen ist nach wie vor eine grundlegende Herausforderung. Hier stellen wir die Synthese von PdxAu-Pt-Kern-Schale-Aerogelen vor, welche aus einer ultradünnen Pt-Schale und einem Kern aus einer PdxAu-Legierung mit einstellbarer Zusammensetzung bestehen. Die universelle Synthesestrategie ermöglicht eine Erweiterung der Kern-Zusammensetzung hin zu Pd-Übergangsmetall-Legierungen. Die Kern-Schale-Aerogele zeigen eine stark verbesserte Nutzungseffizienz von Pt in der Sauerstoffreduktion und ihre Aktivitäten folgen einem vulkanförmigen Verlauf bezüglich der Gitterparameter des Kern-Substrats. Mit einer maximalen massenbezogenen bzw. spezifischen Aktivität von 5.25 A mgPt -1 und 2.53 mA cm-2, welche 18.7- bzw. 4.1-mal höher sind als die für Pt/C, zeigt sich die Überlegenheit dieser metallischen Kern-Schale-Aerogele. Die vorgeschlagene kernbasierte Aktivitätsabhängigkeit liefert eine neue mögliche Strategie für den Entwurf zukünftiger Kern-Schale-Elektrokatalysatoren.

Keywords: aerogels; electrocatalysis; core-shell structures; oxygen reduction reaction; sol-gel processes; Aerogele; Elektrokatalyse; Kern-Schale-Strukturen; Nanostrukturen; Sol-Gel-Prozess

Permalink: https://www.hzdr.de/publications/Publ-27248
Publ.-Id: 27248


The analysis of nothing and nearly nothing – concepts for reference materials for the Super-SIMS

Renno, A. D.

The Super-SIMS idea goes back to the year 1979 [1]. Since then several attempts have been made to install such instruments [2-5], although with varied success.
Most of the published data were either analysis of semiconductor materials or isotope ratios of natural materials. Having a strong focus on natural, metal, and mineral resources the Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This new Super-SIMS will be embedded into a system of consecutive micro-analytical methods devoted to the characterization of minerals and ores. Therefore, our focus will lie on the analysis of ultra-trace elements in these natural matrices.
Despite the high precision, the accuracy of SIMS analysis can be problematic. The sensitivity factor as well as the instrumental mass fractionation vary with the chemical composition. This so-called matrix effect demands that the sample and the reference material (RM) should have exactly the same chemical composition and structure, this is difficult to achieve. Even trace elements and in the case of the Super-SIMS ultra-trace elements may affect the sensitivity factor. The compromise is the usage of matrix matched RMs.
The combination of good lateral and depth resolution of the SIMS instrument with the resulting small sample volumes / masses (sub ng-range) and the aspired detection limits in the pg/g range yield to the fact that the probability to meet one atom of the analyte in the sample volume will be < 1.
This contribution will stimulate the discussion about the concepts of detection limit, homogeneity and heterogeneity in RMs and present considerations about the design of future RMs for ultra-trace element analysis with the Super-SIMS.

[1] Purser et al. Surface and Interface Analysis 1(1), 1979, 12.; [2] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470.; [3] Ender et al. NIMB 123 (1997) 575.; [4] Maden, PhD thesis, ETH Zurich 2003.; [5] Fahey et al. Analytical Chemistry 88(14), 2016, 7145

Keywords: Reference Materials; SIMS; Super-SIMS

  • Poster
    Geoanalysis 2018, 08.-13.07.2018, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-27247
Publ.-Id: 27247


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