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35836 Publications

A Super-SIMS for resource technology

Renno, A. D.; Akhmadaliev, S.; Belokonov, G.; Böttger, R.; von Borany, J.; Gutzmer, J.; Kaever, P.; Meyer, M.; Noga, P.; Rugel, G.; Tiessen, C. J.; Voigtländer, J.; Wagner, N.; Wiedenbeck, M.; Winter, A.; Wu, H.; Ziegenrücker, R.

The integration of an ion source with very high spatial resolution with a tandem accelerator is a long-standing concept for improving analytical selectivity and sensitivity by orders of magnitude [1-3]. Translating this design concept to reality has its challenges [e.g. 4-6]. Supporting a strong focus on natural, metallic and mineral resources the, Helmholtz Institute Freiberg for Resource Technology installed such a system at the Ion Beam Centre at HZDR. This so-called Super-SIMS will be at the core of a comprehensive pallet of micro-analytical methods devoted to the characterization of minerals and ores. Secondary ion beam from a CAMECA IMS 7f-auto are injected into the pre-existing 6MV Dresden Accelerator Mass Spectrometry facility [7,8], which quantitatively eliminates isobaric molecular species from the ion beam. Our SIMS component can function as either a stand-alone device or can be used to inject the negatively charged secondary ions at energies of up to 40 keV (to match the acceptance conditions) into the accelerator. A dedicated ion optical unit has been constructed and installed to match the SIMS ion beam to the maximum acceptance of the accelerator.
We will present measurements of the performance parameters of the instrument as well as first results of halogen (F, Cl, Br, and I) determinations in galena, sphalerite and pyrrhotite.
[1] Purser et al. Surface and Interface Analysis 1(1), 1979, 12. [2] J. M. Anthony, D. J. Donahue, A. J. T. Jull, MRS Proceedings 69 (1986) 311-316. [3] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470. [4] Ender et al. NIMB 123 (1997) 575. [5] Maden, PhD thesis, ETH Zurich 2003. [6] Fahey et al. Analytical Chemistry 88(14), 2016, 7145. [7] Akhmadaliev et al., NIMB 294 (2013) 5. [8] Rugel et al. NIMB 370 (2016) 94.

Keywords: Super-SIMS; SIMS

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

Permalink: https://www.hzdr.de/publications/Publ-27246
Publ.-Id: 27246


Box-profile implants as geochemical reference materials for EMP and SIMS

Wu, H.; Belokonov, G.; Böttger, R.; Couffignal, F.; Munnik, F.; Renno, A. D.; Wiedenbeck, M.; Ziegenrücker, R.

EMP (Electron Microprobe) and SIMS (Secondary Ion Mass Spectrometry) are widely used analytical techniques for geochemical and mineralogical applications. Nevertheless, metrologically rigorous quantification remains a major challenge for these methods. SIMS in particular is a matrix sensitive method; the use of matrix-matched reference materials (RMs) is essential in order to avoid significant analytical bias. A major problem is that the list of available reference materials for SIMS is vanishingly short compared to the needs of the analyst. A current evaluation of the GeoReM database [1] shows a strong focus on using the well-known NIST SRM 610-617 glasses for trace element analysis along with several zircons for isotope analysis, with few other matrices being readily available.
One approach for the production of matrix specific RMs is the use of ion implantation that introduces a known amount of a selected isotope into a material. This strategy is widely-used for SIMS applications in materials science, but rarely used for geochemical applications. Bumett et al. (2015) [2] demonstrated the appropriateness of this method. We choose the more elaborate way of implanting a so-called box profile to generate a homogeneous concentration of the selected isotope in three dimensions.
For proof of concept we used the mineralogically and chemically “simple” SiO2 system which addresses many interesting scientific challenges, such as the Ti-in-quartz geothermometer [3]. We implanted either 47Ti or 48Ti into synthetic, ultra-high purity silica glass. Several box profiles with concentrations between 10 and 1000 µg/g Ti and a maximum depth of homogeneous Ti distribution between 200 and 3000 nm were produced at the Ion Beam Center in Dresden-Rossendorf. Multiple implantation steps using differing ion energies and ion doses were simulated with the SRIM (Stopping and Range of Ions in Matter) software [4], optimizing for the target concentrations, implantation-depths and technical limits of the implanter. A thorough TEM assessment showed that the Ti is dispersed throughout the glass structure. We characterized several implanted test-samples by means of SIMS, EMP and other analytical techniques. The homogeneity of the Ti-concentration is within ± 5% uncertainty in all 3 dimensions.
[1] http://georem.mpch-mainz.gwdg.de, [2] D. S. Bumett, et al., Geostandards and Geoanalytical Research 39(3), 2015, 265-276., [3] J. B. Thomas, et al., Contrib. Mineral. Petr. 160(5), 2010, 743–759., [4] J. F. Ziegler, Nucl. Instrum. Meth. B 219-220, 2004, 1027-1036.

Keywords: Reference Materials; SIMS; EMP; Super-SIMS; implantation

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

Permalink: https://www.hzdr.de/publications/Publ-27245
Publ.-Id: 27245


Detecting and quantifying the relativistic Kelvin-Helmholtz instability in interstellar jets via radiation observable on Earth

Pausch, R.; Bussmann, M.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Debus, A.

We present a microscopic model of the radiation emitted during the relativistic Kelvin-Helmholtz instability (KHI) and validate our findings with particle-in-cell simulations at unprecedented spatial resolution and size that including complete far-field radiation spectra.

The KHI is expected in shear flow regions of astrophysical plasma jets, which are significant sites for particle acceleration and radiation. We demonstrate that the emitted polarized radiation can be used to identify and characterize the microscopic plasma dynamics of a KHI light-years away. We have simulated the radiation of the KHI using the particle-in-cell code PIConGPU. With this code's synthetic radiation diagnostic, based on Liénard-Wiechert potentials, quantitative predictions of the far field radiation for hundreds of observation directions and a frequency range covering 3 orders of magnitude were performed on the TITAN cluster at Oak Ridge National Laboratory. The simulation showed that the time-dependent changes in the radiation polarization and power correlate directly with the stages of the KHI. This allows identifying the linear growth phase of the KHI and quantifying its characteristic growth rate as predicted by our microscopic model.

Keywords: Kelvin Helmholtz instability; Particle-in-cell; PIConGPU; radiation

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

Permalink: https://www.hzdr.de/publications/Publ-27244
Publ.-Id: 27244


In-situ synthetic radiation diagnostics for laser wakefield acceleration

Pausch, R.; Debus, A.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Bussmann, M.

We present recent results of LWFA simulations including in-situ radiation diagnostics performed with the particle-in-cell code PIConGPU. Our results demonstrate the power provided by synthetic radiation diagnostics to determine the laser-plasma dynamics with regard to applications in experiments.

PIConGPU is currently one of the fastest 3D3V particle-in-cell codes and provides an in-situ radiation diagnostic based on Liénard-Wiechert potentials. This synthetic diagnostic is capable of quantitatively predicting the spectrally and directionally resolved far-field radiation of billions of macro-particles by an in-situ implementation in the PIC cycle. Among other things, the code enables resolving the spatial origin and temporal evolution of the radiation, determine the polarization, quantifying both coherent and incoherent radiation simultaneously and covering a frequency range from infrared to x-rays.

The talk briefly introduces the technical background of computing the radiation in-situ on GPUs. Its main focus, however, is the characteristic radiation of LWFA that allows identifying the various stages of the laser-plasma dynamics. Possible applications of these radiation signatures in laboratory experiments will be discussed.

Keywords: Laser Wakefield Accelerator; Particle-in-cell; radiation

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

Permalink: https://www.hzdr.de/publications/Publ-27243
Publ.-Id: 27243


The prognostic value of FMISO-PET-based synchronous tumor and lymph node hypoxia outperforms that of tumor hypoxia only in patients with advanced stage HNSSC – secondary analysis of Dresden FMISO trail

Bandurska-Luque, A.; Löck, S.; Haase, R.; Richter, C.; Zöphel, K.; Perrin, R.; Seidlitz, A.; Zschaeck, S.; Appold, S.; Krause, M.; Steinbach, J.; Kotzerke, J.; Zips, D.; Baumann, M.; Troost, E.

Purpose: Primary tumor (Tu) hypoxia based on hypoxia-PET is a known prognostic parameter for locally-advanced head-and-neck squamous cell carcinoma (HNSCC) patients. This secondary analysis of the prospective clinical trial [1] on repeat [18F]fluoromisonidazole (FMISO) PET/CT before and during radiochemotherapy (RCT) compared the prognostic value of synchronous Tu and lymph node metastases (LN) hypoxia with that of hypoxia only determined in Tu.

Methods: Forty-five LN-positive patients with 103 LNs were included in this analysis. FMISO-PETs were performed at baseline, week 1, 2 and 5 of RCT. Based on a qualitative scale, Tu and LN were independently categorized as hypoxic or normoxic, being FMISO uptake higher than or equal to background, respectively. Two prognostic parameters were defined: Tu-hypoxia (patients with a hypoxic Tu, independent of the LN oxygenation status) and synchronous Tu-and-LN-hypoxia. In fifteen patients with a large LN (n = 21) a quantitative analysis of FMISO PET was performed to validate hypoxia scale and to correlate with regional control (RC). Log-rank, uni- and multivariate Cox test were used to assess the parameters’ prognostic impact on locoregional control (LRC), RC and time to progression (TTP).

Results: Synchronous Tu-and-LN-hypoxia was a strong adverse prognostic factor for LRC and TTP at all time-points (p ≤ 0.005) whereas Tu-hypoxia only was significantly associated with poor LRC in week 2 and 5 (p ≤ 0.004) and with short TTP in week 1, 2 and 5 (p ≤ 0.043). The quantitative FMISO parameters correlated with RC. There was a significant correlation between the qualitative and quantitative FMISO parameters (R > 0.6–0.8).

Conclusions: FMISO-based synchronous hypoxia in the primary tumor and lymph node metastases holds strong prognostic information in HNSCC patients outperforming that based on primary tumor hypoxia only. Confirmation in ongoing prospective trials is intended before introducing in personalized radiation oncology.

  • Lecture (Conference)
    33. Deutscher Krebskongress 2018, 21.-24.02.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27241
Publ.-Id: 27241


Dose-dependent changes after proton and photon irradiation in zebrafish model

Brunner, S.; Tőkés, T.; Szabó, E. R.; Polanek, R.; Szabó, I. Z.; Reisz, Z.; Guban, B.; Szijarto, A. L.; Brand, M.; Hans, S.; Karsch, L.; Leßmann, E.; Pawelke, J.; Schürer, M.; Beyreuther, E.; Hideghety, K.

Purpose/Objective: The laser-driven ionizing (LDI) beams have unique property of ultra-high dose rate, ultra-short pulses and carry the potential toward special clinical application. Our aim was to establish an in vivo zebrafish model for radiobiological research on later LDI radiation.
Material/methods: 24 hours post-fertilization (hpf) zebrafish (Danio rerio) embryos were irradiated at the University Proton Therapy Dresden with escalated doses (5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve, at the plateau and at the middle of Spread Out Bragg Peak, and with reference 6 MV photon beams from a clinical linac (n=96 in each group). The experiment was 3 times repeated under the same conditions. On the 3th (96 hpf) and 4th (120 hpf) days after irradiation morphological malformations were documented (photo) and determined quantitatively. Two independent observers measured the length of the embryos, the degree of the yolk sac edema and the diameter of the eyes. Additionally, we have detected the DNA double-strand breaks immunohistochemically (gamma-H2AX foci) after 30 min of the irradiation at the two positions of the proton (mSOBP and plateau) and photon beams, at 5 Gy dose level.
Results: Dose-dependent organ developmental deteriorations could be detected morphologically at >10 Gy dose levels. The length of the embryo and the size of the eyes reduced, while the yolk sac edema increased significantly in dose dependent degree after 10 Gy, 15 Gy, 20 Gy and 30 Gy irradiation, at both developmental stages. At 5 Gy dose irradiation we have found significant elevation in the number of DNA double-strand breaks, as compared to the unirradiated control groups. Furthermore, data showed that after proton irradiation the degree of the DNA damage was higher, as compared to the photon irradiation.
Conclusion: We could establish a reliable quantitative morphological analysis of dose-dependent organ malformations using an in vivo vertebrate system. The zebrafish embryo model proved to be appropriate for complex evaluation of the irradiation-caused damages, molecular changes and for comparison of the biological effects of different radiation qualities. We could define the optimal parameters for future radiobiological experiments with the LDI beams.
Supported by: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund. The project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no 654148 Laserlab-Europe and by the German BMBF, grant no. 03Z1N511.

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  • Secondary publication expected from 01.11.2021

Permalink: https://www.hzdr.de/publications/Publ-27240
Publ.-Id: 27240


Development of zebrafish embryo model for radiobiology research at ELI-ALPS on laser driven hadron beams

Szabó, E. R.; Tőkés, T.; Polanek, R.; Szabó, Z.; Brunner, S.; Czifrus, S.; Fenyvesi, A.; Biró, B.; Beyreuther, E.; Pawelke, J.; Hideghéty, K.

Purpose/objective: High power lasers provide the basis of particle acceleration, but at the actual status of the development, low energy, limited size beams with special properties (ultrahigh dose rate, pulsed mode) are available under technical conditions for radiobiology experiments. Our main aim was to introduce, optimize and validate a vertebrate system for in vivo experiments to study the biological effects of novel hadron beams.
Material/methods: Series of zebrafish embryos in different ages (from 1 hour post-fertilization (hpf) to 72 hpf), in different holders varying the number/well were prepared. For irradiation we used fission neutron (0, 1.25, 1.875, 2, 2.5 Gy), cyclotron-based neutron (0, 2, 4, 6.8, 8.12, 10.28 Gy) and proton (0, 5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve (PDDC): at the plateau and at the middle of Spread Out Bragg Peak (mSOBP), furthermore, with reference linear accelerator photon (0, 5, 10, 15, 20 Gy) beam (n=96 in each group), repeated several times (≥3). Thereafter, survival, any type of organ developmental disturbance (pericardial edema, spine curvature, shortening of the body length and micro-opthalmia) were detected each days up to 7 post irradiation days (pid). Histological evaluation (size of the eye, brain necrosis, intestinal changes, liver vacuolization, hyper eosinophilic necrotic muscle-fibers) and molecular changes were evaluated with RT-PCR method at certain time points post irradiation.
Results: A higher vulnerability and radiation sensitivity could be observed at earlier stages of the embryogenesis (1-12 hpf). The LD50 was determined with the well reproducible survival curves, resulting in RBE between 10 and 4.8 for the 1MeV and 14MeV neutrons and the Relative Biological Effectivity (RBE) around 1.1-1.4 for proton sources at the two positions respectively. The morphological distortions shown close correlation to the dose delivered and their evaluation on the 4th pid exhibited a good agreement to the survival derived RBE. The gravity of the histopathological changes on the basis of semi-quantitative analysis corresponded well to the macro morphological abnormalities (eye layer disorganization, degree of brain necrosis, increased numbers of the goblet cells in the gastrointestinal tract, and muscle fibrosis).
Conclusion: Numerous features of the zebrafish embryo model makes it amenable for large scale of radiobiological investigations. On the basis of our experimental series the optimal embryonal age (hpf), radiation setup and observation time points for assessment of the different biological endpoints could be established. The defined parameters proved to be suitable for reliable RBE determination.

Acknowledgement: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund, and by the German BMBF, grant nos. 03ZIK445 and 03Z1N511. The project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no 654148 Laserlab-Europe.

  • Poster
    37. ESTRO Meeting, 20.-24.04.2018, Barcelona, Spain
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018)Suppl1, S586
    DOI: 10.1016/S0167-8140(18)31353-7

Permalink: https://www.hzdr.de/publications/Publ-27239
Publ.-Id: 27239


Hazard statements: looking for alternatives to toxicity evaluation using LCA

Rodriguez-Garcia, G.; Braun, J.; Peters, J.; Weil, M.

Life Cycle Assessment is a methodology for the evaluation of potential hazards to the environment and to human health. It can be used for decision support when selecting materials for a product. It is a detailed method that can become very labor intensive. As alternatives, we introduce here two methodologies for ranking products and materials according to their safety: Both methods are built on two pieces of European legislation. Hazard Traffic Lights is a qualitative visual way to quickly identify potential hazards. Total Hazard Points is a quantitative method for weighting the different hazards related to a product. It is based on the method developed for the German Environmental Agency (UBA), but its scope includes all materials and hazards, rather than a selection of them. As a case study, we evaluated the 9 batteries described in the UBA study and compared our results with those presented there. In our opinion, batteries are in general terms more hazardous in the UBA study. This is due to more thorough identification of hazards –including some potentially more significant – and the inclusion of all the potential hazards of a material. Since not all the materials present in the battery were quantified, both sets of results should be considered an underestimation of the possible hazard.

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Permalink: https://www.hzdr.de/publications/Publ-27237
Publ.-Id: 27237


AMS of 93 Zr: Passive absorber versus gas-filled magnet

Hain, K.; Deneva, B.; Faestermann, T.; Fimiani, L.; Gómez-Guzmán, J. M.; Koll, D.; Korschinek, G.; Ludwig, P.; Sergeyeva, V.; Thiollay, N.

Two different isobar separation techniques were tested for the detection of the long-lived fission product 93Zr (T1/2T1/2 = 1.64 ·· 106 a) using Accelerator Mass Spectrometry (AMS), i.e. a passive absorber and a gas-filled magnet, respectively. Both techniques were used in combination with a Time-of-Flight path for the identification of the stable neighboring isotopes 92Zr and 94Zr. The passive absorber was represented by a stack of silicon nitride foils for high flexibility regarding the thickness for optimal isobar separation. Ion beams with a large variety of energies, between 80 and 180 MeV, were provided for this experiment by the tandem accelerator at the Maier-Leibnitz Laboratory in Garching, Germany. With these beams, the stopping powers of 93Zr and 93Nb as a function of energy were determined experimentally and compared to the results obtained with the simulation program SRIM. Considerable discrepancies regarding the energy dependence of the two stopping power curves relative to each other were found. The lowest detection limit for 93Zr achieved with the passive absorber setup was 93Zr/Zr = 1 ·· 10−10. In comparison, by optimizing the gas-filled magnet set-up, 93Nb was suppressed by around six orders of magnitude and a detection limit of 93Zr/Zr = 5 ·· 10−11 was obtained. To our knowledge, these results represent the lowest detection limit achieved for 93Zr until now.

Keywords: 93Zr; AMS; Gas-filled magnet; Passive absorber

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Permalink: https://www.hzdr.de/publications/Publ-27236
Publ.-Id: 27236


Bubbly Flow in Stirred Tanks: Euler-Euler / RANS Modeling

Shi, P.; Rzehak, R.

Aerated stirred tanks are frequently used equipment in industries ranging from chemical engineering and biotechnology to minerals processing. In principle, CFD simulation of such equipment on industrial scales is feasible within the Euler-Euler framework of interpenetrating continua. Practical application, however, requires suitable closure models to account for phenomena on the scale of individual bubbles, which are not resolved in this approach. The present work applies a set of closure relations that was previously used with good success to describe bubbly flows in pipes and bubble columns. It turns out that model extensions are needed concerning turbulence and the drag force. To validate the model a comprehensive set of experimental data including gas fraction as well as liquid velocity and turbulence has been assembled from different literature sources. The finally proposed extended model compares reasonably well with this dataset.

Keywords: aerated stirred tanks; dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; Reynolds-stress turbulence model; CFD simulation; model validation

Permalink: https://www.hzdr.de/publications/Publ-27235
Publ.-Id: 27235


Integrating a low-field open MR scanner with a static proton therapy research beamline: proof of concept

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

Purpose
On-line image guidance using magnetic resonance (MR) imaging is expected to improve targeting precision in proton therapy (PT). However, to date no hybrid MR-PT system exists. This is partly due to unknown mutual electromagnetic interactions between the MR scanner and the PT beamline, which may compromise the quality of the proton beam or the MR image. The aim of our study was to integrate an MR scanner with a static PT research beamline and to test the feasibility of simultaneous irradiation and imaging.

Materials & methods
An open MR scanner (MrJ2200, Paramed) featuring a 0.22 T vertical permanent magnetic (B0) field was RF-shielded by a compact Faraday cage and placed at the beam exit of a horizontal static PT research beamline (IBA Proton Therapy). To account for Lorentz force-induced beam deflection in B0, the scanner had to be laterally displaced by 2 cm from the beam’s central axis, such that a proper co-alignment of the beam and the scanner’s field-of-view (FOV) could be confirmed by radiochromic film (Gafchromic EBT3, Ashland) measurements. The beam was collimated to Ø10 mm before entering the Faraday cage through a cylindrical beam guide (Fig. 1).

MR test: With the beamline magnets off, the knee, wrist and hip of a volunteer were scanned with STIR gradient echo (GE), T1-weighted GE, and T1-weighted spin echo (SE) imaging, respectively. T1-weighted SE images of a mixed-meat sausage were acquired using a knee coil without beam, with beamline magnets on and while being irradiated at 215 MeV and 5 nA for 5 minutes.

Beam test: With Faraday cage removed, beam profiles were acquired with and without MR scanner for 72, 125 and 219 MeV beams using a pixelated scintillation detector (Lynx, IBA Dosimetry) positioned 110 cm downstream of the MR scanner's isocentre. These measurements were repeated with the MR scanner in place during acquisition of three different SE and GE images (max. gradient strength up to 5.7 mT/m).

Results
MR test: MR imaging in the nearby presence of a PT beamline was feasible and showed sufficient quality for anatomical imaging of human musculoskeletal structures. MR images of the meat sausage acquired with operating beamline showed a uniform translation of <2 mm in frequency encoding direction, but no geometrical distortions.

Beam test: The scintillation detector showed a horizontal beam deflection of 22, 16 and 11 cm for 72, 125 and 219 MeV, respectively, and a vertical beam deflection <0.6 mm. Horizontal deflection was taken into account to install an in-cage beam stopper, while vertical deflection could be neglected. The beam profiles showed no influence of the gradient fields applied during image acquisition.

Conclusions
For the first time, the integration of an MR scanner and a static PT research beamline has been realized. By taking into account the scanner’s B0 field induced beam deflection, simultaneous proton beam irradiation and MR imaging of an object placed in the scanner’s FOV was feasible with acceptable beam and image quality. The beamline-induced MR image shift is subject of an ongoing performance evaluation study.

  • Lecture (Conference)
    MR in RT symposium, 30.06.-03.07.2018, Utrecht, Nederland

Permalink: https://www.hzdr.de/publications/Publ-27234
Publ.-Id: 27234


Commissioning of a 4D dynamic MRI motion phantom on a 3T MR scanner: motion validation study

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

Purpose:
Systems for integrated magnetic resonance guided radiation therapy (MRgRT) provide real-time and on-line MRI guidance for unequalled targeting performance of moving tumours and organs at risk. The clinical introduction of such systems requires dedicated methods for commissioning, routine machine quality assurance (QA) and verification of gated and adaptive treatment plans. The aim of the study was to develop a commissioning protocol and method for automatic quantification of target motion and geometrical fidelity using a 4D dynamic MRI motion phantom.

Materials & Methods:
The CIRS MRI-LINAC Dynamic Phantom (Model 008M) was positioned on a flat tabletop overlay (Medibord Ltd) in a 3.0T MR scanner (Ingenuity TF PET/MR, Philips) using an in-house constructed base plate for a quick and reproducible setup. The torso-shaped phantom body, which was filled with mineral oil (Marcol Blend, Philips), includes a 3D grid structure for image distortion analysis and a cylindrical thru-hole in which a software-controlled moving rod with a hypo-intense background gel and a decentralized hyper-intense target simulates 3D organ motion patterns. The geometric image distortion was determined as the mean and maximum Euclidean distance (∆mean, ∆max) between grid points in 3D spoiled gradient echo (THRIVE) MRI- and CT scans (Siemens Somatom Definition AS) after registration by means of the central fiducial. Sinusoidal 1D/2D/3D and a volunteer navigator scan-based 1D target motion pattern were evaluated using 2D cine MRI balanced turbo field echo sequences at a temporal resolution of 1.5-2 Hz. The motion tracking was performed with different pre-set frequencies (0.1-0.2 Hz) and amplitudes (up to 40/10/10 mm in IS/AP/LR direction). The target’s centre-of-mass motion pattern was reconstructed by an in-house developed automated image tracking algorithm implemented in MATLAB.

Results:
The base plate enabled a reproducible setup with a deviation of <1 mm in all directions. The geometric distortion increased with distance from the phantom’s centre predominantly in anterior direction, with ∆mean=0.56+/-0.28 mm and ∆max=1.5 mm in the THRIVE sequence relative to the CT scan. The frequencies of the reconstructed motion patterns from 2D cine MRI agree to the pre-set values within 2%; the reconstructed amplitudes showed a maximum deviation to the pre-set amplitudes of <0.8 mm in AP/LR direction and <0.4 mm in IS direction.

Conclusions:
A method and protocol for commissioning a 4D MRI dynamic motion phantom on a 3.0T MR scanner for MRgRT was developed. High-contrast and geometrically reliable 2D cine MR images of the phantom’s moving target could be obtained. The pre-set motion parameters could be extracted with sufficient spatio-temporal accuracy from 2D cine MRI in all motion directions. The method developed can be used for routine QA tests of spatio-temporally resolved MRI data in MRgRT.

Keywords: Phantom; Motion; MRI

  • Lecture (Conference)
    6th MR in RT Symposium 2018, 30.06.-03.07.2018, Utrecht, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-27233
Publ.-Id: 27233


„Radiobiology of Proton Therapy“: results of an international expert workshop

Lühr, A.; von Neubeck, C.; Pawelke, J.; Seidlitz, A.; Peitzsch, C.; Bentzen, S.; Bortfeld, T.; Debus, J.; Deutsch, E.; Langendijk, J.; Löffler, J.; Mohan, R.; Scholz, M.; Sørensen, B.; Weber, D.; Baumann, M.; Krause, M.

The physical properties of proton beams offer the potential to reduce toxicity in tumor-adjacent normal tissues. Towards this end, the number of proton radiotherapy facilities has steeply increased over the last 10-15 years to currently around 70 operational centers worldwide. However, taking full advantage of the opportunities offered by proton radiation for clinical radiotherapy requires a better understanding of the radiobiological effects of protons alone or combined with drugs or immunotherapy on normal tissues and tumors. This report summarizes the main results of the international expert workshop “Radiobiology of Proton Therapy” that was held in November 2016 in Dresden.
It addresses the major topics (1) relative biological effectiveness (RBE) in proton beam therapy, (2) interaction of proton radiobiology with radiation physics in current treatment planning, (3) biological effects in proton therapy combined with systemic treatments, and (4) testing biological effects of protons in clinical trials.
Finally, important research avenues for improvement of proton radiotherapy based on radiobiological knowledge are identified. The clinical distribution of radiobiological effectiveness of protons alone or in combination with systemic chemo- or immunotherapies as well as patient stratification based on biomarker expressions are key to reach the full potential of proton beam therapy. Dedicated preclinical experiments, innovative clinical trial designs, and large high-quality data repositories will be most important to achieve this goal.

Keywords: proton therapy; relative biological effectiveness; RBE; LET; radiobiology; clinical trials

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Permalink: https://www.hzdr.de/publications/Publ-27232
Publ.-Id: 27232


Integrating a low-field open MR scanner with a static proton therapy research beamline: Characterisation of in-beam imaging performance

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

Purpose
For the successful integration of MRI and proton therapy (PT), the mutual electromagnetic interaction between both systems needs to be investigated. So far, no combined system existed to investigate the MR imaging performance in the presence of a proton beam. Here, the aim is to characterize the imaging performance of a first in-beam MRI scanner during simultaneous proton irradiation and imaging.

Materials & methods
A 0.22 T open MRI scanner (MrJ2200, Paramed) has been installed at the horizontal static research beamline of our PT facility. The imaging performance characterization included both magnetic field homogeneity (MFH) measurements and ACR phantom tests for image quality. The MFH was mapped over a 22 cm diameter spherical volume by a magnetic field camera (MFC3045/48, Metrolab) being placed in the centre of the scanner’s field-of-view (FOV). To assess the effect of magnetic fringe fields of the nearby beamline magnets, the MFH was measured without and with magnets energized for beam energies between 70220 MeV. Phantom imaging tests were performed with the ACR small phantom being centrally positioned in the scanner FOV inside a knee coil (Fig. 1). Images were acquired by performing T1- and T2-weighted spin echo (SE) sequences with parameter settings according to the ACR phantom test protocol. Additionally, T1 and T2*- weighted gradient echo (GES and GEL, respectively) scans were performed. The phantom was irradiated by a 125 MeV pencil beam (Ø=10 mm) at dose rates of 1 and 80 Gy/min. Images were acquired for six different scenarios, starting from a reference scan with beamline magnets and beam off, followed by sequentially switching on first the beamline magnets and then the beam during both radiofrequency calibration and image acquisition or during image acquisition alone. A validated software tool (MATLAB) was used to extract the ACR imaging parameters and to estimate geometric transformations from image pairs acquired for the different scenarios.

Results
The peak-to-peak MFH was 88 ppm, which is within the scanner’s operating specifications. The MFH measurements with and without energized beamline magnets showed no significant differences (<3 ppm), but the mean baseline resonance frequency was increased by 70110 Hz depending on beam energy. The SE and GEL image quality was sufficient for analysis. GES images showed a low SNR (<15) and suffered from banding artefacts, which prevented automated evaluation of ACR parameters. For all six scenarios, differences in ACR parameters were within measurement uncertainties. A sequence-dependent uniform image translation of 0.53.0 mm in frequency encoding direction was observed due to operating the beamline. These image translations were in accordance with the baseline resonance frequency shift and showed to be inversely proportional to the gradient strengths of the sequences used (0.75.7 mT/m).

Conclusion
The imaging performance of a first low-field in-beam MRI scanner integrated with a static PT research beamline meets vendor and ACR image quality specifications. No degradation of the imaging performance was observed during simultaneous operation of the MRI and PT systems. Beamline induced off-resonance image translations need to be compensated for in the different imaging sequences.

  • Lecture (Conference)
    MR in RT Symposium, 30.06.2018, Utrecht, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-27231
Publ.-Id: 27231


Marangoni convection at electrogenerated hydrogen bubbles

Yang, X.; Baczyzmalski, D.; Cierpk, C.; Mutschke, G.; Eckert, K.

Electrolytic gas evolution is a fundamental phenomenon occurring in a large number of industrial applications. In these processes gas bubbles are formed at the electrode from a supersaturated solution. Since dissolved gases can change the surface tension, a gas concentration gradient may cause the surface tension to vary locally at the gas bubble. Surface tension gradients may also form due to temperature gradients generated by ohmic heating of the electrolyte. In both cases, the resulting shear stress can impose a convection in the electrolyte and the gas bubble (Marangoni effect). This phenomenon may influence the entire electrolytic gas evolution process, e.g., by an enhanced mass transfer. In this study, the first evidence of the Marangoni convection near growing hydrogen bubbles, generated by water electrolysis, is provided. Microscopic high speed imaging was applied to study the evolution of single hydrogen bubbles at a microelectrode.
The convection near the interface of the growing bubble was measured by using a time-resolved Particle Tracking Velocimetry (PTV) technique. The results indicate a clear correlation between the magnitude of the Marangoni convection and the electric current.

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Permalink: https://www.hzdr.de/publications/Publ-27230
Publ.-Id: 27230


Noncovalently Assembled Electroconductive Hydrogel

Xu, Y.; Yang, X.; Thomas, A. K.; Patsis, P. A.; Kurth, T.; Kräter, M.; Eckert, K.; Bornhäuser, M.; Zhang, Y.

Crosslinking biomolecules with electroconductive nanostructures through noncovalent interaction can result in modular networks with defined biological functions and physical properties such as electric conductivity and viscoelasticity. Moreover, the resulting matrices can exhibit interesting features caused by the dynamic assembly process, such as self-healing and molecular ordering. In this paper, we present a physical hydrogel system formed by mixing peptide-polyethylene glycol and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). This combinatorial approach, which uses different modular building blocks, could lead to high tunability on aspects of rheology and electrical impedance. The proposed physical hydrogel system is characterized by both a self-healing ability and injectability. Interestingly, the formation of hydrogels at relatively low concentrations led to a network of closer molecular packing of PEDOT nanoparticles, reflected by the enhanced conductivity. The biopolymer system can be used to develop 3D cell cultures with incorporated electric stimuli, as evidenced by its contribution to the survival and proliferation of encapsulated mesenchymal stromal cells and their differentiation upon electrical stimulation.

Keywords: self-assembling; PEDOT:PSS; peptide; electroconductive hydrogel; 3D cell

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Permalink: https://www.hzdr.de/publications/Publ-27229
Publ.-Id: 27229


Results of the stationary measurements at COSMEA-I facility - CT part

Bieberle, A.; Boden, S.; Beyer, M.; Hampel, U.
ContactPerson: Beyer, Matthias; DataCollector: Szalinski, Lutz; DataManager: Bieberle, André; Sponsor: Ehrlich, Alexander; Editor: Boden, Stephan

At the COSMEA-I facility cross-sectional distributions of the condensated steam is measured at five different positions along a slightly inclined condensator-tube using adapted conventional CT imaging technique based on X-ray. This data set contains the reconstructed raw data of the CT imaging scans.

Keywords: Passive heat transfer; Conventional CT imaging; Reconstructed raw data of the CT imaging scan

Related publications

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-03-20
    DOI: 10.14278/rodare.3

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Permalink: https://www.hzdr.de/publications/Publ-27228
Publ.-Id: 27228


Molekulare Bildgebung in der Onkologie mittels Positronen-Emissions-Tomographie

Derlin, T.; Grünwald, V.; Steinbach, J.; Wester, H.-J.; Ross, T. L.

Hintergrund: Mit der Positronenemissionstomographie (PET) steht ein Verfahren in der klinischen Bildgebung zur Verfügung, dass bei Durchführung als Hybridverfahren mit Computertomographie (CT) oder Magnetresonanztomographie (MRT) die simultane Erfassung anatomischer und molekularer Informationen ermöglicht. Die PET besitzt eine hohe Sensitivität zur Detektion von Tumormanifestationen. Unterschiedliche Radiopharmaka dienen der Charakterisierung verschiedener Stoffwechselprozesse oder der Analyse der Expression von Rezeptoren, Enzymen und weiteren molekularen Zielstrukturen.
Methode: Selektive Literaturrecherche in PubMed unter Bezug auf nationale und internationale Leitlinien sowie systematische Übersichtsarbeiten und Metaanalysen.
Ergebnisse: Etablierte PET Radiopharmaka wie 2-[18F]Fluor-2-desoxyglukose ([18F]FDG) erlauben die Darstellung physiologischer Prozesse auf molekularer Ebene und können entscheidende Informationen für die klinische Versorgung liefern. Für die PET stehen in zunehmendem Umfang neben gut erforschten und evaluierten auch neuere Radiopharmaka zur nicht-invasiven Phänotypisierung von Tumorerkrankungen zur Verfügung, beispielsweise zur Analyse der Expression des prostataspezifischen Membranantigens (PSMA) oder von Chemokinrezeptoren (z.B. CXCR4) auf Tumorzellen.
Schlussfolgerung: Die PET stellt einen wichtigen Bestandteil diagnostischer Algorithmen in der Onkologie dar, kann die Präzision der Diagnostik verbessern und helfen, die Therapie zu individualisieren. Eine zunehmende Anzahl an PET Radiopharmaka erweitert die verfügbaren Bildgebungsoptionen. Viele Radiopharmaka erlauben neben der nicht-invasiven Analyse der Expression therapeutisch relevanter
Zielstrukturen auch eine nachfolgende zielgerichtete Radionuklidtherapie.

Permalink: https://www.hzdr.de/publications/Publ-27227
Publ.-Id: 27227


Experimental Signals for Broken Axial Symmetry in Excited Heavy Nuclei From The Valley of Stability

Grosse, E.; Junghans, A.

An increasing number of experimental data indicates the breaking of axial symmetry in many heavy nuclei already in the valley of stability:
Multiple Coulomb excitation analysed in a rotation invariant way, gamma transition rates and energies in odd nuclei, mass predictions, the splitting of Giant Resonances (GR), the collective enhancement of nuclear level densities and Maxwellian averaged neutron capture cross sections. For the interpretation of these experimental observations, the axial symmetry breaking shows up in nearly all heavy nuclei as predicted by Hartree–Fock–Bogoliubov (HFB) calculations; this indicates a nuclear Jahn–Teller effect.
We show that nearly no parameters remain free to be adjusted by separate fitting to level density or giant resonance data, if advance information on nuclear deformations, radii etc. are taken from such calculations with the force parameters already fixed. The data analysis and interpretation have to include the quantum mechanical requirement of zero point oscillations and the distinction between static vs. dynamic symmetry breaking has to be regarded.

  • Open Access Logo Contribution to proceedings
    XXIV Nuclear Physics Workshop “Marie and Pierre Curie”, Kazimierz Dolny, Poland, September 20–24, 2017., 20.-24.09.2017, Kazimierz Dolny, Polen
    Acta Physica Polonica B, Vol. 11, No. 1-37
    DOI: 10.5506/APhysPolBSupp.11.37

Permalink: https://www.hzdr.de/publications/Publ-27226
Publ.-Id: 27226


Diffusion of oxygen in bcc Fe under the influence of other foreign atoms

Wang, X.; Posselt, M.; Faßbender, J.

First-principle calculations and kinetic Monte Carlo simulations are applied to investigate the diffusion of oxygen in bcc Fe under the influence of other foreign atoms, such as Al, Si, P, S, Ti,, Cr, Mn, Ni, Y, and Mo. In the first part of this work jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites were investigated by DFT. It is found that a second-neighbor jump consists of two consecutive first-neighbor jumps and that the barrier of the third-neighbor jump is too high to be relevant. In the second part DFT was applied to determine the modified migration barriers, i.e. for the oxygen jump between the first and the second neighbor of a foreign atom, etc. It is found that Si, P, Ni and Mo influence the migration barriers of oxygen only slightly. Al and Cr cause moderate changes, while S, Ti, and Y lead to strong modifications. With the exception of Y the migration paths are first-neighbor jumps between (modified) octahedral sites with (modified) tetrahedral sites as saddle points. Y changes some migration paths considerably. Using the migration barriers calculated by DFT the diffusion coefficient of oxygen was determined by kinetic Monte Carlo simulations considering a dilute iron alloy. In general the foreign atoms cause a reduction of the mobility of oxygen compared to that in pure bcc Fe. The strongest decrease is obtained for the foreign atoms S, Ti, and Y.

Keywords: Diffusion; oxygen; bcc Fe; Density Functional Theory; Kinetic Monte Carlo simulations

  • Poster
    DPG-Frühjahrstagung und EPS-CMD27, 11.-16.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27225
Publ.-Id: 27225


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe

Vallinayagam, M.; Posselt, M.; Faßbender, J.

In this research project the nature of yttria-based oxide nanoclusters in a bcc Fe matrix is investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the clusters.
In the first part of the work three types of structures are considered: (i) clusters consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe, (ii) clusters with Y, Ti, and O on substitutional sites, and (iii) clusters with of Y, Ti, on substitutional sites and O on octahedral interstitial sites of the bcc lattice. Simulation cells containing different structures but the same composition of atoms (Fe, Y, Ti, O) are compared. It is found that the energetics of three different structure types, i.e. their total binding energy, is very similar. This modifies the statement of Barnard et al. [1] who only considered the first type of structure and concluded that this is the most favorable. Further, more stable cluster structures are constructed using another model with the nanocluster core similar to the metal monoxide structure. Also the binding energy of monomers like O, Y, Ti, and the vacancy to the cluster are studied. O and the vacancy are strongly attracted by the nanoclusters, while the interaction with metal atoms is weaker.
[1] L. Barnard et al. Acta Mater. 60 935 (2012)

Keywords: Density Functional Theory; Y-Ti-O nanoclusters; bcc Fe

  • Poster
    DPG-Frühjahrstagung und EPS-CMD27, 11.-16.03.2018, Berlin, Deustchland

Permalink: https://www.hzdr.de/publications/Publ-27224
Publ.-Id: 27224


The role of radiative de-excitation in the neutralization process of highly charged ions interacting with a single layer of graphene

Schwestka, J.; Wilhelm, R. A.; Gruber, E.; Heller, R.; Kozubek, R.; Schleberger, M.; Facsko, S.; Aumayr, F.

X-ray emission of slow (<1 a.u.) highly charged Argon and Xenon ions is measured for transmission through a freestanding single layer of graphene. To discriminate against X-ray emission originating from the graphene's support grid a coincidence technique is used. X-ray emission of 75 keV Ar17+ and Ar18+ ions with either one or two K-shell vacancies is recorded. Using a windowless Bruker XFlash detector allows us to measure additionally Ar KLL and KLM Auger electrons and determine the branching ratio of radiative vs. non-radiative decay of Ar K-shell holes. Furthermore, X-ray spectra for 100 keV Xe22+-Xe35+ ions are compared, showing a broad M-line peak for all cases, where M-shell vacancies are present. All these peaks are accompanied by emission lines at still higher energies indicating the presence of a hollow atom during X-ray decay. We report a linear shift of the main M-line peak to higher energies for increasing incident charge state, i.e. increasing number of M-shell holes.

Keywords: Slow highly charged ions; Graphene; X-ray emission

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Permalink: https://www.hzdr.de/publications/Publ-27223
Publ.-Id: 27223


Structural incorporation of the minor actinide Cm(III) in La1-xGdxPO4 rhabdophane and monazite solid solutions

Huittinen, N.; Scheinost, A. C.; Ji, Y.; Kowalski, P. M.; Arinicheva, Y.; Wilden, A.; Neumeier, S.

Monazites (LnPO4) are envisioned as potential immobilization matrices for high-level radioactive wastes produced e.g. during the nuclear fuel cycle [1–2]. Hydrated rhabdophane (LnPO4×0.67H2O) is a precursor phase during monazite synthesis and a potential solubility-limiting solid phase under nuclear waste storage conditions [3–4]. Thus, for a reliable long-term safety assessment of nuclear waste repositories for conditioned radioactive waste, a fundamental understanding of the radionuclide incorporation process in both the pristine monazite ceramics and their alteration products is required.

In the present study we have combined time-resolved laser fluorescence spectroscopy (TRLFS), X-ray Absorption Fine Structure (XAFS) spectroscopy and ab initio atomistic simulations to investigate the structural incorporation of the minor actinide curium in synthetic La1-xGdxPO4 monazite and rhabdophane solid solutions. The solid phase was synthesized by addition of phosphoric acid to a solution containing La3+ and Gd3+ in desired relative concentrations and a small amount of the actinide (248Cm), until a white precipitate of La1-xGdxPO4 rhabdophane doped with approximately 50 ppm Cm3+ was obtained. An aliquot of the obtained solid phase was thereafter sintered at 1450°C to acquire the crystalline monazite ceramic. Structural refinement of collected XRD data for both rhabdophane and monazite solids show a linear dependency of lattice parameters as a function of Gd3+ substitution according to Vegard’s law.
Our combined spectroscopic results show that Cm3+ is incorporated in the monazite end-members (LaPO4 and GdPO4) on one specific, highly ordered lattice site. In the intermediate solid solution compositions, an increasing disorder around the Cm3+ dopant can be seen as a result of a broader distribution of possible Cm∙∙∙O bond-lengths in comparison to the end-member compositions with very well-defined nearest neighbour distances. Despite this local structural disordering, homogenous solid solutions were obtained for all synthesized monazite compositions without the formation of dopant clusters that could potentially hamper the performance of the monazite ceramics for the immobilization of minor actinide containing wastes.
The hydrated rhabdophane lattice comprises two different site types that could accommodate the actinide dopant: a 9-coordinated “hydrated” site amounting to two thirds (2/3) of the total number of lanthanide sites in the solid structure, where one coordinating oxygen atom originates from a water molecule, and an 8-fold coordinated “non-hydrated” site (1/3 of available Ln sites) where all oxygen atoms are provided by phosphate groups [4]. Based on our laser spectroscopic investigation, curium incorporation on both site types can be confirmed, however, the site occupancy is not in concordance with the hydrated rhabdophane structure. In contrast, a preferential incorporation of curium on non-hydrated lattice sites can be seen, especially for the La-rich rhabdophane compositions, implying that structural substitution reactions cannot be predicted based on the structure of the host matrix only.

Keywords: Cm(III); spectroscopy; incorporation; rhadbophane; monazite

  • Lecture (Conference)
    International Symposium on Solubility Phenomena and Related Equilibrium Processes (ISSP), 15.-20.07.2018, Tours, France

Permalink: https://www.hzdr.de/publications/Publ-27222
Publ.-Id: 27222


Unusual Coulomb effects in graphene

Winnerl, S.

In many semiconductors Coulomb scattering plays an essential role in the thermalization process of a non-equilibrium carrier distribution. Here we discuss three surprising and fascinating manifestations of Coulomb scattering in graphene. All phenomena are explored both experimentally and by manybody theory. The first observation concerns a double-bended saturation behavior of bleaching induced by near-infrared radiation. The second phenomenon is the optically induced anisotropy in k-space for excitation with linearly polarized radiation and its relaxation to a Fermi-Dirac distribution. The third set of experiments tackles the dynamics of graphene in a magnetic field perpendicular to the graphene layer. Here evidence for strong Auger scattering is found. We discuss the possibility to apply Landau quantized graphene as a gain medium in a tunable laser and as a tunable nonlinear optical material.

Keywords: Graphene; ultrafast dynamics; Coulomb interaction

  • Lecture (others)
    Theory seminar, Charles University in Prague, 12.04.2018, Prague, Czech Repzblic

Permalink: https://www.hzdr.de/publications/Publ-27221
Publ.-Id: 27221


Intrinsic magnetic properties of hydrided and non-hydrided Nd5Fe17 single crystals

Karpenkov, D. Y.; Skokov, K. P.; Lyakhova, M. B.; Radulov, I. A.; Faske, T.; Skourski, Y.; Gutfleisch, O.

We report on the spontaneous magnetization Ms, the exchange stiffness constant A and the magneto-crystalline anisotropy constants K1, K2, K3 and K4 of Nd5Fe17 and Nd5Fe17H16 single crystals. Field dependencies of magnetization M(H) were measured along a, b' and c principal crystallographic directions within the temperature range of 10-600 K and magnetic fields up to 40 T. Large anisotropies of spontaneous magnetization and high-field susceptibility were revealed for both compounds. The exchange stiffness parameter A was determined using Bloch's T3/2 law. In order to provide high accuracy detection of K1(T), K2(T), K3(T) and K4(T), we used two different approaches: the modified Sucksmith-Thompson technique and the Néel's phase method.

Permalink: https://www.hzdr.de/publications/Publ-27220
Publ.-Id: 27220


Electrically pumped graphene-based Landau-level laser

Brem, S.; Wendler, F.; Winnerl, S.; Malic, E.

Graphene exhibits a nonequidistant Landau quantization with tunable Landau-level (LL) transitions in the technologically desired terahertz spectral range. Here, we present a strategy for an electrically driven terahertz laser based on Landau-quantized graphene as the gain medium. Performing microscopic modeling of the coupled electron, phonon, and photon dynamics in such a laser, we reveal that an inter-LL population inversion can be achieved resulting in the emission of coherent terahertz radiation. The presented paper provides a concrete recipe for the experimental realization of tunable graphene-based terahertz laser systems.

Keywords: graphene; Landau quantization; laser; Landau-level laser

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Permalink: https://www.hzdr.de/publications/Publ-27219
Publ.-Id: 27219


ThMn12-type phases for magnets with low rare-earth content: Crystal-field analysis of the full magnetization process

Tereshina, I. S.; Kostyuchenko, N. V.; Tereshina-Chitrova, E. A.; Skourski, Y.; Doerr, M.; Pelevin, I. A.; Zvezdin, A. K.; Paukov, M.; Havela, L.; Drulis, H.

Rare-earth (R)-iron alloys are a backbone of permanent magnets. Recent increase in price of rare earths has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. For this reason strong magnets with the ThMn12 type of structure came into focus. Functional properties of R(Fe,T)12 (T-element stabilizes the structure) compounds or their interstitially modified derivatives, R(Fe,T)12-X (X is an atom of hydrogen or nitrogen) are determined by the crystal-electric-field (CEF) and exchange interaction (EI) parameters. We have calculated the parameters using high-field magnetization data. We choose the ferrimagnetic Tm-containing compounds, which are most sensitive to magnetic field and demonstrate that TmFe11Ti-H reaches the ferromagnetic state in the magnetic field of 52 T. Knowledge of exact CEF and EI parameters and their variation in the compounds modified by the interstitial atoms is a cornerstone of the quest for hard magnetic materials with low rare-earth content.

Permalink: https://www.hzdr.de/publications/Publ-27218
Publ.-Id: 27218


Field-effect transistors as electrically controllable nonlinear rectifiers for the characterization of terahertz pulses

Lisauskas, A.; Ikamas, K.; Massabeau, S.; Bauer, M.; Cibiraité, D.; Matukas, J.; Mangeney, J.; Mittendorff, M.; Winnerl, S.; Krozer, V.; Roskos, H. G.

We propose to exploit rectification in field-effect transistors as an electrically controllable higher-order nonlinear phenomenon for the convenient monitoring of the temporal characteristics of THz pulses, for example, by autocorrelation measurements. This option arises because of the existence of a gate-bias-controlled super-linear response at sub-threshold operation conditions when the devices are subjected to THz radiation. We present measurements for different antenna-coupled transistor-based THz detectors (TeraFETs) employing (i) AlGaN/GaN high-electron-mobility and (ii) silicon CMOS field-effect transistors and show that the super-linear behavior in the sub-threshold bias regime is a universal phenomenon to be expected if the amplitude of the high-frequency voltage oscillations exceeds the thermal voltage. The effect is also employed as a tool for the direct determination of the speed of the intrinsic TeraFET response which allows us to avoid limitations set by the read-out circuitry. In particular, we show that the build-up time of the intrinsic rectification signal of a patch-antenna-coupled CMOS detector changes from 20 ps in the deep sub-threshold voltage regime to below12 ps in the vicinity of the threshold voltage.

Keywords: Terahertz detection; field-effect transistor; nonlinear response; autocorrelation

Permalink: https://www.hzdr.de/publications/Publ-27217
Publ.-Id: 27217


Infrared/Terahertz Spectra of the Photogalvanic Effect in (Bi,Sb)Te based Three Dimensional Topological Insulators

Plank, H.; Pernul, J.; Gebert, S.; Danilov, S. N.; König-Otto, J.; Winnerl, S.; Lanius, M.; Kampmeier, J.; Mussler, G.; Aguilera, I.; Grützmacher, D.; Ganichev, S. D.

We report on the systematic study of infrared/terahertz spectra of photocurrents in (Bi,Sb)Te based three dimensional topological insulators. We demonstrate that in a wide range of frequencies, ranging from fractions up to tens of terahertz, the photocurrent is caused by the linear photogalvanic effect (LPGE) excited in the surface states. The photocurrent spectra reveal that at low frequencies the LPGE emerges due to free carrier Drude-like absorption. The spectra allow to determine the room temperature carrier mobilities in the surface states despite the presence of thermally activated residual impurities in the material bulk. In a number of samples we observed an enhancement of the linear photogalvanic effect at frequencies between 30 and 60 THz, which is attributed to the excitation of electrons from helical surface to bulk conduction band states. Under this condition and applying oblique incidence we also observed the circular photogalvanic effect driven by the radiation helicity.

Keywords: Topological insulators; terahertz spectroscopy; photocurrents; photogalvanic effect

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Permalink: https://www.hzdr.de/publications/Publ-27216
Publ.-Id: 27216


Shielding and source calculations for the new cyclotron and possible activation in the soil

Konheiser, J.; Ferrari, A.; Naumann, B.; Müller, S.

This presentation summarizes the results of the Monte Carlo simulation of the shielding calculations and estimates of the soil activation for the new cyclotron of the HZDR (Helmholtz-Zentrum Dresden-Rossendorf). The dose values were determined on base of the resulting neutron flux at the 18F production and were carried out with the Monte Carlo code MCNP6. The calculation of the soil activations was performed with FLUKA. The neutron source term was provided by manufacturer. A source check with MCNP6 and FLUKA codes, significant discrepancies were found to the manufacturer supplied data for the neutron source term. For this reason, experiments were carried out on a cyclotron in operation. The comparison confirmed the results of the MCNP/FLUKA calculations.
The estimated dose rate in the public area is about 0.035 μSv/h (28 MeV protons) and thus significantly below the reference value of 0.5 μSv/h(3). After 5 years of continuous beam operation and a subsequent decay time of 30 days, the activity concentration of the soil is about 0.34 Bq/g.

Keywords: shielding calculation; neutron source calculation; cyclotron; MCNP6; FLUKA

  • Lecture (others)
    88. Sitzung des Arbeitskreises Dosimetrie, 20.-21.03.2018, TU Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27215
Publ.-Id: 27215


Transglutaminase 2 as potential target for functional tumour imaging – development of assay methods and inhibitors for this enzyme

Wodtke, R.

Transglutaminase 2 (TGase 2) is a unique multifunctional enzyme whose best-characterised function is the crosslinking of proteins, which has implications not only in physiological but also in a variety of pathological conditions including fibrotic and neoplastic processes. In this context, it becomes more and more apparent that TGase 2 is a key player for the progression of several kinds of cancer and elevated levels of TGase 2 expression are directly correlated with poor prognostic indicators for survival, e.g. metastatic phenotype and drug resistance of the cancer cells. Consequently, this enzyme is considered as a promising target for the diagnosis and therapy of these diseases. According to the motivation to develop radiotracers for TGase 2 imaging by positron emission tomography (PET), which will provide insight into the importance of the crosslinking function as well as the targeting of that enzyme in vivo, the PhD project was focused on two different goals.
Within the first part, a reliable fluorimetric assay method was established as prerequisite for the identification and characterisation of TGase 2-reactive molecules. The assay is based on the measurement of an increase in fluorescence due to the release of a coumarine derivative upon TGase 2-catalysed hydrolysis or aminolysis of the fluorogenic acyl donor. However, the fluorogenic acyl donors known from the literature are characterised by a low solubility in water, which limits their applicability (1). Therefore, a series of water-soluble small peptidic acyl donors were synthesised and kinetically characterised towards TGase 2. Finally, Z-Glu(HMC)-Gly-OH turned out to have the most favourable substrate properties (2). Additionally, this compound is also a suitable substrate for other TGases, which facilitates selectivity studies.
The second part was focused on irreversible inhibitors for TGase 2 as appropriate starting point for the development of radiotracers. Based on the Nε-acryloyllysine piperazides chemotype of TGase 2 inhibitors, a library of >50 inhibitors were synthesised and their inhibitory capacity towards TGase 2 and other TGases were determined on the basis of their inactivation constants kinact/KI. Structural modifications were focused on the introduction of fluorine but also other chemical groups were considered. Kinetic investigations have uncovered important structure-activity relationships, which in combination with in silico molecular docking shed light on the binding mode for this class of inhibitors. Evaluation of selected compounds at other TGases highlighted a favourable selectivity profile towards TGase 2. Regarding an initial pharmacokinetic profiling, the potential membrane permeability of the inhibitors were determined using the PAMPA method. Considering the determined inhibitory potencies in combination with these pharmacokinetic in vitro data will provide valuable hints for the development of radiotracers for TGase 2 imaging.

(1) Gillet, S. M.; Pelletier, J. N.; Keillor, J. W. Anal. Biochem. 2005, 347, 221.
(2) Wodtke et al. ChemBioChem 2016, 17, 1263.

  • Invited lecture (Conferences)
    Frontiers in Medicinal Chemistry, Verleihung Promotionspreis der GDCh-Fachgruppe Medizinische Chemie, 11.-14.03.2018, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27213
Publ.-Id: 27213


Anwendung von Anstaupackungen bei der CO2-Absorption in wässrigen Aminlösungen

Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Kolonneneinbauten stellen einen wichtigen Bestandteil fluider Trennprozesse dar und haben einen erheblichen Einfluss auf die Prozessleistung. Anzustrebende Eigenschaften von Einbauten sind eine hohe Trenneffizienz bei gleichzeitig geringem Druckverlust sowie eine hohe Kapazität. In den vergangenen Jahrzehnten konnten erhebliche Fortschritte zur Verbesserung von Einbauten erzielt werden. In diesem Bereich zeigt die Entwicklung von Anstaupackungen (AP) ein wesentliches Potenzial zur Prozessintensivierung auf. Diese bestehen aus zwei alternierenden Lagen strukturierter Packungen mit unterschiedlicher spezifischer Oberfläche. Die untere Anstaulage weist eine geringere Lastgrenze als die darüber angeordnete Abscheidelage auf. AP werden üblicherweise zwischen den Flutpunkten der beiden Lagen betrieben, weshalb ein heterogenes Strömungsmuster entsteht. Dabei bildet sich oberhalb der gefluteten Anstaulage eine Sprudelschicht, die durch eine intensive Vermischung der Phasen geprägt ist und eine hohe Trennleistung erzielt.
Im Rahmen eines DFG-geförderten Forschungsprojekts gilt es nun, die Auswirkungen der einzelnen Strömungsregime von AP auf Fluiddynamik und Stofftransport separat zu untersuchen. Für diesen Zweck werden erstmalig Experimente an einer Absorptions-/ Desorptionsanlage durch bildgebende Messungen der Strömung in AP ergänzt. An der Universität Paderborn werden für verschiedene Design- und Betriebsparameter Technikumsversuche zur CO2-Absorption in einer wässrigen Monethanolamin-Lösung durchgeführt. Die Anlage ermöglicht die Aufnahme von Temperaturprofilen der Gasphase sowie von Konzentrationsprofilen beider Phasen. In Kooperation mit der Technischen Universität Dresden wird mittels ultraschneller Röntgentomographie ein detaillierter Einblick in die Phasenverteilung der verschiedenen Strömungszustände ermöglicht. Die bei beiden Untersuchungen anfallenden Messdaten sollen zur Erarbeitung von Korrelationen für Stoffübergang, Phasengrenzfläche, Holdup und Druckverlust genutzt werden, welche in einem rate-based-Model Verwendung finden. In dieser Arbeit werden neben einer Vorstellung des Vorhabens erste experimentelle Daten zur Absorption mit AP präsentiert.

  • Poster
    Jahrestreffen der ProcessNet Fachgruppen Mechanische Flüssigkeitsabtrennung, Kristallisation, Phytoextrakte, Adsorption, Extraktion, Fluidverfahrenstechnik und Membrantechnik, 08.-10.03.2017, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27212
Publ.-Id: 27212


Experimentelle Untersuchungen zum Einfluss von Betriebs- und Designparameter auf das Absorptionsverhalten von Anstaupackungen

Flechsig, S.; Utchenko, Y.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Aufgrund des hohen Energiebedarfs thermischer Trennverfahren besteht ein hoher Forschungsbedarf für die Entwicklung effizienter und ressourcenschonender Prozesse. Bei Trennkolonnen weisen Einbauten ein erhebliches Entwicklungspotential auf, welche die Fluiddynamik und den Stofftransport entscheidend beeinflussen.
Die Anstaupackung stellt eine Entwicklung im Bereich der Packungskolonnen dar, die eine Intensivierung des Stofftransports und eine Kapazitätserweiterung ermöglicht. Die Anstaupackung besteht aus einer Kombination von zwei Lagen typischer strukturierter Packungen mit unterschiedlicher spezifischer Oberfläche, welche alternierend angeordnet werden. Die untere Anstaulage weist dabei eine geringere Lastgrenze als die darüber angeordnete Abscheidelage auf. Anstaupackungen werden üblicherweise zwischen den Flutpunkten der beiden Lagen betrieben, wodurch ein axial heterogenes Strömungsmuster entsteht. Dabei bildet sich oberhalb der gezielt gefluteten Anstaulage eine Sprudelschicht, die durch eine intensive Vermischung und ein hohes Maß an Turbulenz der beteiligten Phasen geprägt ist und zu deutlich höheren Trennleistungen führen kann. Oberhalb der Sprudelschicht in der Abscheidelage dominiert die für Packungen typische Rieselfilmströmung in der die aus der Sprudelschicht mitgerissenen Tropfen abgeschieden werden [1].
Da bislang das Trennverhalten von Anstaupackung fast ausschließlich theoretisch analysiert wurde [2], werden im Rahmen eines von der DFG geförderten Kooperationsprojekts die Auswirkungen der einzelnen Strömungsregime auf Fluiddynamik und Stofftransport komplementär sowohl experimentell als auch theoretisch untersucht. Für diesen Zweck werden erstmalig Experimente an einer Absorptions-/ Desorptionsanlage durch bildgebende Messungen der Strömung in Anstaupackungen ergänzt. An der Universität Paderborn werden für verschiedene Design- und Betriebsparameter Technikumsversuche zur CO2-Absorption in einer wässrigen Monoethanolamin-Lösung durchgeführt. Die Anlage ermöglicht die Aufnahme von Temperaturprofilen der Gasphase sowie von Konzentrationsprofilen beider Phasen. Am Helmholtz-Zentrum Dresden-Rossendorf wird mittels ultraschneller Röntgentomographie ein detaillierter Einblick in die Phasenverteilung der verschiedenen Strömungszustände ermöglicht. Die Messdaten beider Projektpartner werden zur Erarbeitung von Korrelationen für Stoffübergang, Phasengrenzfläche, Holdup und Druckverlust genutzt, welche in einem rate-based-Model Verwendung finden.
Im Rahmen dieser Arbeit wird der Einfluss wichtiger Betriebs- und Designparameter auf das Absorptionsverhalten in Anstaupackungen experimentell untersucht, um einerseits effizienzsteigernde Betriebsbedingungen zu identifizieren und anderseits eine Basis für die experimentelle Validierung von neuen Simulationsmodellen zu schaffen. Zusätzlich wird eine empirische Korrelationsgleichung zur Bestimmung des integralen Stoffdurchgangskoeffizienten entwickelt, die den Einfluss der Temperatur des Lösungsmittels, der Gas- und Flüssigkeitsbelastung, der CO2-Konzentration im Rohgas sowie der MEA-Konzentration in der Lösung berücksichtigt. Die vorgeschlagene Korrelation ermöglicht damit eine überschlägige Auslegung von Absorptionskolonnen mit Anstaupackungen.

[1] U. Brinkmann, B. Kaibel, M. Jödecke, J. Mackowiak, E.Y. Kenig: Beschreibung der Fluiddynamik von Anstaupackungen, Chemie Ingenieur Technik 84: 36-45 (2012).
[2] Ö. Yildirim, E.Y. Kenig: Rate-based modelling and simulation of distillation columns with sandwich packings, Chemical Engineering and Processing: Process Intensification 98, 147-154 (2015).

  • Lecture (Conference)
    Jahrestreffen der Fachgemeinschaft Prozess-, Apparate- und Anlagentechnik, 20.-21.11.2017, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27211
Publ.-Id: 27211


Rate-based-Modellierung von CO2-Absorptionskolonnen mit Anstaupackungen

Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Eines der am häufigsten eingesetzten Trennverfahren zur Abscheidung von Kohlenstoffdioxid (CO2) aus Kraftwerksabgasen ist die Reaktivabsorption mit wässrigen Aminlösungen. Neben der Entwicklung effektiverer Lösungsmittel weisen die Kolonneneinbauten hinsichtlich Druckverlust, Kapazität und Trennleistung ein wesentliches Potenzial für die Prozessintensivierung und damit die Reduzierung des hohen Ressourcenbedarfs auf.
Eine Verbesserung der Trennleistung kann durch den Einsatz von Anstaupackungen erzielt werden. Diese bestehen aus zwei abwechselnden Lagen von Standardpackungen mit unterschiedlichen spezifischen Oberflächen. Die untere Packungslage (die sogenannte Anstaulage) hat eine geringere Belastungsgrenze im Vergleich zur darüberliegenden Abscheidelage. Anstaupackungen werden typischerweise bei Betriebsbedingungen zwischen den Flutpunkten beider Lagen betrieben. Durch das gezielte Fluten der Anstaulage bildet sich eine in die Abscheidelage hineinreichende Sprudelschicht, in der eine hohe Trennleistung mit intensiver Phasenvermischung erzielt wird. Im oberen Bereich der Abscheidelage können filmähnliche Strömungsmuster, Rinnsale und aus der Sprudelschicht mitgerissene Tropfen beobachtet werden [1]. Obwohl der für Trennverfahren vorteilhafte intensive Phasenkontakts bei dem integrierten Packungstyps bereits nachgewiesen wurde, fehlend validierte Auslegungsgrundlagen für eine breitere Anwendung [2].
Eine genaue Vorhersage der Leistungscharakteristik ist für die Auslegung von Anstaupackungen unerlässlich. In einem von der DFG geförderten Kooperationsprojekt zwischen Universität Paderborn und TU Dresden werden die Auswirkungen der einzelnen Strömungsregime auf die Fluiddynamik und den Stoffaustausch komplementär mit experimentellen und theoretischen Methoden untersucht. Um die Auswirkungen jedes einzelnen Strömungsregimes zu bestimmen, werden Experimente an einer Absorptions-/ Desorptionsanlage durch bildgebende Messungen in Anstaupackungen ergänzt. An der Universität Paderborn wird die CO2-Absorption in einer Pilotanlage für verschiedene Design- und Betriebsparameter untersucht. Die Anlage ermöglicht die Messung von Temperaturprofilen der Gasphase sowie von Konzentrationsprofilen beider Phasen. Mithilfe der ultraschnellen Röntgentomographie wird am Helmholtz-Zentrum Dresden-Rosendorf die Phasenverteilung innerhalb der Anstaupackung untersucht. Die Messdaten aus beiden experimentellen Methoden werden verwendet, um Korrelationen für Stofftransportkoeffizienten, Phasengrenzfläche, Holdup und Druckverlust zu entwickeln, die in einem rate-based-Modell für CO2-Absorptionsverfahren mit wässrigen Aminlösungen eingesetzt werden.
Der rate-based-Ansatz kann die Besonderheiten diverser Kolonneneinbauten durch einbautenspezifische Korrelationen berücksichtigen. Da die verschiedenen Fluiddynamikregime in Anstaupackungen unterschiedliche Auswirkungen auf den Stofftransport aufweisen, werden Absorptionskolonnen mit Anstaupackungen als eine Folge von abwechselnden Segmenten dargestellt und jedes Segment wird durch einen der Fluiddynamik entsprechenden Satz von Korrelationen beschrieben. Im Rahmen dieser Arbeit erfolgt eine Validierung des Modells mit experimentellen Daten zur CO2-Absorption.

[1] U. Brinkmann, B. Kaibel, M. Jödecke, J. Mackowiak, E.Y. Kenig: Beschreibung der Fluiddynamik von Anstaupackungen, Chemie Ingenieur Technik 84: 36-45 (2012).
[2] Ö. Yildirim, E.Y. Kenig: Rate-based modelling and simulation of distillation columns with sandwich packings, Chemical Engineering and Processing: Process Intensification 98, 147-154 (2015).

  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrentechnik, 27.-28.02.2018, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27210
Publ.-Id: 27210


New Phenomena in Gamma-Ray Strength Functions

Schwengner, R.

The excitation and deexcitation of atomic nuclei by electromagnetic radiation are fundamental processes in reactions of this many-body quantum system. At high excitation energy and high level density, statistical models are applied to describe reaction rates, which use $\gamma$-ray strength functions (γSF) to describe the average transition probabilities in a certain range of excitation energy. The experimental determination and the theoretical understanding of the properties of γSF are important for the accurate description of photonuclear reactions and radiative-capture reactions, which play a central role in the synthesis of the elements in various stellar environments.
We report photon-scattering experiments using bremsstrahlung at the γELBE facility (HZDR) and quasi-monoenergetic, polarized γ beams at the HIγS facility (TUNL, Duke Univ., Durham, USA). Systematic studies of the dipole strength revealed new phenomena that are not described by the analytical approximations currently used in reaction codes. The (γ,γ') experiments at high energy show considerable contributions to the γSF from the quasicontinuum of states. Combined with (γ,n) cross sections, the (γ,γ') data provide experimental input γSF for statistical reaction codes.

Keywords: Photonuclear reactions; Nuclear resonance fluorescence; Bremsstrahlung; Monoenergetic gamma rays; Shell Model

  • Invited lecture (Conferences)
    Frühjahrstagung 2018, 26.02.-02.03.2018, Bochum, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27208
Publ.-Id: 27208


Damage accumulation and structural modification in c-plane and a-plane GaN implanted with 400 keV Kr and Gd ions

Mackova, A.; Malinsky, P.; Jágerova, A.; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Mikulics, M.; Böttger, R.; Akhmadaliev, S.

GaN is the most actively studied wide-bandgap material, applicable e.g. in short-wavelength optoelectronic devices, high-electron-mobility transistors, and semiconductor lasers. The crystallographic orientation of an implanted crystal can significantly influence the optical properties of the implanted layer, reflecting the rearrangement of the crystal matrix after annealing. The annealing procedure, influencing dynamic recovery, point defect diffusion and large defect stabilisation, depending on the GaN crystal orientation and the used ion implantation parameters, is still an important issue to be studied. We have studied the structural and compositional changes of the GaN-epitaxial-layers of c-plane and a-plane orientations grown by MOVPE and implanted with Gd and Kr ions using the ion energy of 400 keV and ion fluences of 5 × 1014 cm-2, 1 × 1015 cm-2 and 5 × 1015 cm-2 with subsequent annealing at 800 °C in ammonia. Dopant depth profiling was accomplished by Rutherford backscattering spectrometry (RBS). Induced structure disorder and its recovery during subsequent annealing were characterised by RBS channelling and Raman spectroscopy. Ion-implanted c-plane and a-plane GaN exhibit significant differences in damage accumulation simultaneously with post-implantation annealing, inducing a different structural reorganization of the GaN structure in the buried layer depending on the introduced disorder level, i.e. depending on the ion-implantation fluence and ion mass.

Keywords: GaN damage accumulation; RBS channelling studies of implanted GaN; Structure modification in c-plane and a-plane GaN

Permalink: https://www.hzdr.de/publications/Publ-27207
Publ.-Id: 27207


Damage accumulation and structural modification in a- and c-plane GaN implanted with 400-keV and 5-MeV Au+ ions

Mackova, A.; Malinsky, P.; Jágerova, A.; Sofer, Z.; Sedmidubský, D.; Klímová, K.; Böttger, R.; Akhmadaliev, S.

c-plane (0001) and a-plane (11-20) gallium nitride (GaN) epitaxial layers were grown by Metal organic Vapour Phase epitaxy (MOVPE) on sapphire and subsequently implanted with 400-keV and 5-MeV Au+ ions using fluences 5 × 1014 to 5 × 1015 cm-2. The shallow Au depth profiling was accomplished by Rutherford backscattering spectrometry. The structural changes during implantation and subsequent annealing were characterised by Rutherford backscattering spectrometry channelling and Raman spectroscopy. The interplay between nuclear and electronic stopping, influencing defect accumulation, was monitored and discussed depending on GaN orientation. Post-implantation annealing induced a structural reorganisation of the GaN structure depending on the ion-implantation fluence, ion energy, and on the crystallographic orientation.

Keywords: damage accumulation in GaN; RBS channelling in ion-modified GaN; structure modification in c-plane and a-plane GaN

Permalink: https://www.hzdr.de/publications/Publ-27206
Publ.-Id: 27206


Adsorption of selenium(VI) onto nano transition alumina

Jordan, N.; Franzen, C.; Lützenkirchen, J.; Foerstendorf, H.; Hering, D.; Weiss, S.; Heim, K.; Brendler, V.

The adsorption of selenium(VI) onto nano transition alumina (γ/δ-Al2O3) was investigated at both macroscopic and molecular levels. The uptake of selenium(VI) was found to decrease upon increasing pH (5-10) and ionic strength (0.01-0.1 mol∙L−1). At the molecular level, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy established the predominant formation of a bidentate outer-sphere surface complex throughout the investigated pH range. The acid-base surface properties of transition alumina (surface charge) together with the Se(VI) adsorption edges were successfully described using a 1-pK with charge distribution surface complexation model and one outer-sphere surface species, namely {(≡AlOH2+0.5)2SeO42−}, according to the IR studies. These new spectroscopic results can be implemented in reactive transport models to enable a more consistent and trustworthy prognostic modeling of the environmental fate of selenium(VI).

Keywords: Selenium(VI); transition alumina; sorption; in situ ATR FT-IR spectroscopy; surface complexation modeling

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Permalink: https://www.hzdr.de/publications/Publ-27204
Publ.-Id: 27204


Parallelisierung des Wellenfrontrekonstruktionsalgorithmus auf Multicore-Prozessoren

Schenke, J.

Kurzfassung
Ziel dieser Arbeit war die Beschleunigung des von Elena-Ruxandra Cojocaru und Sébastien Bérujon in Python implementierten Wellenfrontrekonstruktionsalgorithmus. Dieser berechnet aus zwei Bildern einer Probe pixelweise die Fronten der elektromagnetischen Welle eines Röntgenlasers. Die Bilder werden hierbei von zwei hochempfindlichen Röntgen-CCD-Sensoren aufgenommen, welche in einem festen Abstand zueinander und zur Probe positioniert sind. Treffen Strahlen des Röntgenlasers auf diese, so lässt sich aus den so aufgenommenen Streubildern die Wellenfront rekonstruieren, was Rückschlüsse auf die Struktur der Probe zulässt. Auf Basis von Performance-Analysen der Python-Implementierung wurden Optimierungen und Parallelisierungsmöglichkeiten für die kritischen Programmabschnitte ermittelt, implementiert und evaluiert. Die schnellste vorgestellte Lösung basiert auf der Verteilung der Bildpaare auf mehrere Rechenkerngruppen und der Parallelisierung der Berechnung der Bildpaare auf diesen, was eine Skalierung über mehrere Knoten erlaubt. Kombiniert mit der Nutzung optimierter Bibliotheken und dem Übersetzen des Python-Codes wurde eine Beschleunigung von bis zu vier gegenüber der Referenzimplementierung mit gleicher Kernanzahl erreicht. Wurden 120 Kerne verwendet, so war eine Beschleunigung auf das bis zu 133-fache gegenüber der Referenz auf einem Kern möglich. Die Referenzdaten hierfür wurden an der Beamline BM05 der European Synchrotron Radiation Facility aufgenommen.

Abstract
The goal of this thesis was the acceleration of the wavefront reconstruction algorithm which was developed in Python by Elena-Ruxandra Cojocaru and Sébastien Bérujon. This algorithms calculates the electromagnetic wavefront of an X-ray laser from two images of a target pixelwise. The images were captured by two highly sensitive X-ray CCD sensors, which were positioned in a fixed distance to each other and the target. When the refracted X-ray beam hits these detectors a distortion image is generated from which the wavefront can be reconstructed. The result can be used to draw conclusions about the structure of the target. On the basis of performance measurements of the Python implementation optimization and parallelization possibilities for critical sections were determined, implemented and evaluated. The fastest proposed solution is based on the distribution of the image pairs onto CPU core groups and the parallelization of the calculation of the image pairs on these which allows scaling the problem over multiple nodes. This combined with the use of optimized libraries and the compilation of the Python code resulted in a speedup of up to four towards the reference implementation without the use of more cores. When using 120 cores a speedup of up to 133 towards the reference implementation running on a single core could be achieved. The here used datasets were recorded at Beamline BM05 of the European Synchrotron Radiation Facility.

Keywords: Wellenfrontrekonstruktionsalgorithmus; Python; HPC; High Performance Computing; Parallel; Multi-Core

  • Bachelor thesis
    TU Dresden, 2018
    Mentor: Dr. Michael Bussmann, Dr. Elena-Ruxandra Cojocaru, Matthias Werner
    58 Seiten

Permalink: https://www.hzdr.de/publications/Publ-27203
Publ.-Id: 27203


Bentonite - a natural habitat for sulfate-reducers

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

Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite plays a crucial role by using it as a barrier und buffer material in between the steel-canister, containg the HLW, and the surrounding host rock. In order to analyze the potential influence of natural occuring microorganisms within the bentonite on the bentonite barrier, we set up microcosm-experiments. Therefor, two different Bavarian bentonites (a natural and an industrial one) were supplied with an anaerobic, synthetic Opalinus-clay pore water solution under an N2/CO2-atmosphere and were incubated for one year at 30 °C and 60 °C. To some set ups organics (acetate or lactate) or H2 were supplemented. During the incubation time samples were taken and analyzed for several bio-geochemical parameters and the evolution of microbial diversity.
Our results clearly demonstrate, that natural accuring microbes affect geochemical parameters. Set ups containing the industrial bentonite supplemented with lactate show the most striking effects. The microbial diversity changed completely within 6 month. The respective batches were dominated (up to 81 %) by Desulfosporosinus spp. – spore-forming, strictly anaerobic, sulfate-reducing organisms, able to survive under very harsh conditions. Concomitantly, an increase of ferrous iron and a simoultaneous decrease of ferric iron was observed. Furthermore, the lactate and sulfate concentration decreased, whereas pyruvate and acetate were formed. Similar observations were also made in setups containg H2. Desulfosporosinus spp. also dominated the microbial population in the respective batches. Desulfosporosinus spp. are known to metabolize a brought range of substrates including H2 and organic acids, thereby reducing sulfate or iron to form H2S, acetate or ferric iron – metabolites that could effect different properties of the barrier system of an HLW.

Keywords: Bentonite; High-Level-Waste repository; sulfate-reduction

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

Permalink: https://www.hzdr.de/publications/Publ-27202
Publ.-Id: 27202


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

Jordan, N.; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.; Huittinen, N.

In this study, the complexation of Eu(III) and Cm(III) with aqueous phosphates was investigated using laser-induced luminescence spectroscopy. Experiments at 25 °C and different ionic strengths (0.6 to 3.1 mol∙L−1 NaClO4) established the formation of EuH2PO42+ and CmH2PO42+. From the conditional stability constants, the respective values at infinite dilution as well as the ε(Me(H2PO4)2+;ClO4−) (Me = Eu or Cm) ion interaction coefficients (using the specific ion interaction theory - SIT) were derived. Further experiments (at constant ionic strength of 1.1 mol∙L−1) showed, that upon increasing the temperature (25-80 °C), the formation of both EuH2PO42+ and CmH2PO42+ was favored. Using the van’t Hoff equation, the enthalpy ∆_R H_m^0 and entropy ∆_R S_m^0 of these reactions were derived, corroborating an endothermic and entropy driven complexation process. This work contributes to a better understanding of the coordination chemistry of both trivalent actinides and lanthanides with phosphate ions.

Keywords: complexation; europium; curium; aqueous phosphate; temperature; luminescence spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-27200
Publ.-Id: 27200


Effect of U(VI) aqueous speciation on the binding of uranium by the cell surface of Rhodotorula mucilaginosa, a natural yeast isolate from bentonites

Lopez-Fernandez, M.; Romero-Gonzalez, M.; Günther, A.; Solari, P. L.; Merroun, M. L.

This study presents the effect of aqueous uranium speciation (U-hydroxides and U-hydroxo-carbonates) on the interaction of this radionuclide with the cells of the yeast Rhodotorula mucigilanosa BII-R8. This strain was isolated from Spanish bentonites considered as reference materials for the engineered barrier components of the future deep geological repository of radioactive waste. X-ray absorption and infrared spectroscopy showed that the aqueous uranium speciation has no effect on the uranium binding process by this yeast strain. The cells bind mobile uranium species (U-hydroxides and U-hydroxo-carbonates) from solution via a time-dependent process initiated by the adsorption of uranium species to carboxyl groups. This leads to the subsequent involvement of organic phosphate groups forming uranium complexes with a local coordination similar to that of the uranyl mineral phase meta-autunite. Scanning transmission electron microscopy with high angle annular dark field analysis showed uranium accumulations at the cell surface associated with phosphorus containing ligands. Moreover, the effect of uranium mobile species on the cell viability and metabolic activity was examined by means of flow cytometry techniques, revealing that the cell metabolism is more affected by higher concentrations of uranium than the cell viability.The results obtained in this work provide new insights on the interaction of uranium with bentonite natural yeast from genus Rhodotorula under deep geological repository relevant conditions.

Keywords: Uranium biosorption; cell surface; speciation

Permalink: https://www.hzdr.de/publications/Publ-27199
Publ.-Id: 27199


Laser-Rewriteable Ferromagnetism at Thin Film Surfaces

Ehrler, J.; He, M.; Shugaev, M. V.; Polushkin, N. I.; Wintz, S.; Liersch, V.; Cornelius, S.; Hübner, R.; Potzger, K.; Lindner, J.; Fassbender, J.; Ünal, A. A.; Valencia, S.; Kronast, F.; Zhigilei, L. V.; Bali, R.

Manipulation of magnetism using laser light is considered a key to the advancement of data storage technologies. Until now, most approaches seek to optically switch the direction of magnetization rather than to reversibly manipulate the ferromagnetism itself. Here we use ~100 fs laser pulses to reversibly switch ferromagnetic ordering on and off by exploiting a chemical order-disorder phase transition in Fe60Al40, from the B2 to the A2 structure and vice versa. A single laser pulse above a threshold fluence causes non-ferromagnetic B2 Fe60Al40 to disorder and form the ferromagnetic A2 structure. Subsequent pulsing below the threshold reverses the surface to B2 Fe60Al40, erasing the laser induced ferromagnetism. Simulations reveal that the order-disorder transition is regulated by the extent of surface supercooling; above threshold the film melts-through and the consequent stability of the supercooled liquid phase suppresses vacancy diffusion, freezing the material into the disordered state. Pulsing below threshold forms a limited supercooled surface phase that solidifies at sufficiently high temperatures, enabling diffusion assisted reordering. This demonstrates that ultrafast lasers can achieve subtle atomic rearrangements in bimetallic alloys in a reversible and non-volatile fashion.

Keywords: magneto-optical devices; data storage; phase transitions; fs laser modifications; supercooling; order-disorder

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Permalink: https://www.hzdr.de/publications/Publ-27198
Publ.-Id: 27198


Application of Gas Field Ion Source to Patterning Nanoscale Magnetic Structures

Bali, R.; Schmeink, A.; Hlawacek, G.; Lindner, J.; Faßbender, J.

Magnetic nanostructures are necessary components in a variety of sensors and devices, and in prototypes of spin-transport and spin-wave devices. In the past, broad beam ion-irradiation has been used to modify the magnetic properties via a variety of mechanisms, such as alloying, intermixing and structural disordering. In this contribution, we describe the application of the highly focused noble gas ion beam of a gas field ion source (GFIS), to the nanoscale modification of magnetic properties in alloy thin films. Materials in which the saturation magnetization (Ms) can be drastically enhanced via small changes to the atomic arrangement are ideal for the GFIS approach.
In B2 alloys such as Fe60Al40, Fe50Rh50 and Fe60V40, light noble gas ion-irradiation leads to the formation of anti-site defects, which increases the Fe – Fe nearest neighbor interactions and generates an associated increase of the Ms. The disorder induced by the GFIS beam is highly localized, with the extent of the magnetized region determined by lateral scattering of ions. These B2 alloys can be used as non-ferromagnetic templates, on to which the highly focused ion-beam acts as a magnetic writing stylus. Here we examine the conditions necessary and experimentally achievable limits for producing magnetic nanostructures using GFIS.

  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27197
Publ.-Id: 27197


Strong neutron pairing in core+4n nuclei

Revel, A.; Marqués, F. M.; Sorlin, O.; Aumann, T.; Caesar, C.; Holl, M.; Panin, V.; Vandebrouck, M.; Wamers, F.; Alvarez-Pol, H.; Atar, L.; Avdeichikov, V.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boillos, J. M.; Boretzky, K.; Borge, M. J. G.; Caamano, M.; Casarejos, E.; Catford, W. N.; Cederkäll, J.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Cravo, E.; Crespo, R.; Datta Pramanik, U.; Diaz Fernandez, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L. M.; Freer, M.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Golubev, P.; Göbel, K.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Hufnagel, A.; Ignatov, A.; Johansson, H. T.; Jonson, B.; Kahlbow, J.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knyazev, A.; Kröll, T.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lindberg, S.; Machado, J.; Marganiec, J.; Movsesyan, A.; Nacher, E.; Naja, M.; Nikolskii, E.; Nilsson, T.; Nociforo, C.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Reifarth, R.; Ribeiro, G.; Rigollet, C.; Röder, M.; Rossi, D.; Savran, D.; Scheit, H.; Simon, H.; Syndikus, I.; Taylor, J. T.; Tengblad, O.; Thies, R.; Togano, Y.; Velho, P.; Volkov, V.; Wagner, A.; Weick, H.; Wheldon, C.; Wilson, G.; Winfield, J. S.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.

The emission of neutron pairs from the neutron-rich N =12 isotones 18-C and 20-O has been studied by high-energy nucleon knockout from 19-N and 21-O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay 19N(-1p)18C* -> 16-C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a 14-C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay 21-O(-1n)20-O* -> 18-O+n+n, attributed to its formation through the knockout of a deeply-bound neutron that breaks the 16-O core and reduces the number of pairs.

Keywords: R3B radioactive beams nuclear structure neutron-rich Coulomb dissociation

Permalink: https://www.hzdr.de/publications/Publ-27196
Publ.-Id: 27196


Large scale arrays of Co/Pd and Fe60Al40 nanomagnets with tunable magnetic properties for recording and magnonic applications

Krupinski, M.; Mitin, D.; Sobieszczyk, P.; Bali, R.; Zarzycki, A.; Potzger, K.; Albrecht, M.; Marszalek, M.

The fabrication and characterization of nanopatterned magnetic thin films is an important topic for magnetic recording media, sensors, information processing, and magnonic crystals. This broad spectrum of applications results from the possibility of controlling the magnetic properties of such systems in wide range by introducing artificial defects to ferromagnetic material and arranged them in ordered or disordered arrays.
This presentation will focus on the magnetic properties and switching behaviour of magnetic Co(0,3 nm)/Pd(0,9 nm) and Fe60Al40 (40 nm) films composed of arrays of dots, antidots and triangles. Such arrays of nanostructures were created by colloidal lithography complemented by RF-plasma etching and ion irradiation with 20 keV Ne+ ions, which resulted in nanomagnets with sizes down to 30 nm [1].
Using SQUID magnetometry, changes in coercive field, saturation magnetization, loop squareness, and magnetic anisotropy constant have been determined in a temperature range of 5 K – 350 K and compared with non-patterned films. The domain shapes and sizes together with the switching behaviour were studied by scanning magnetoresistive microscopy utilizing commercial reading-writing head from HDD. We have shown that the coercivity reach a maximum values for the arrays with a separation length between nanomagnets close to the domain wall width, which is caused by strong domain wall pinning. The impact of the patterning on the magnetic anisotropy is also clearly seen. The observed influence of surface morphology on magnetic properties and magnetization switching characteristics was confirmed by the micromagnetic modelling using mumax3 software. The results demonstrated that the proposed approach can be effectively used to produce large scale magnetic arrays with properties widely tuneable by temperature and patterning period.

This work was supported by Polish National Science Centre grant No 2017/01/X/ST8/01409.

  • Lecture (Conference)
    XIV International Conference on Nanostructured Materials (Nano 2018), 24.-29.06.2018, Hong Kong, Hong Kong

Permalink: https://www.hzdr.de/publications/Publ-27195
Publ.-Id: 27195


Imaging Structure and Magnetisation in New Ways Using 4D STEM

Maclaren, I.; Nord, M.; Conner, S.; Mcgrouther, D.; Allen, C. S.; Danaie, M.; Kirkland, A. I.; Bali, R.; Hlawacek, G.; Lindner, J.; Faßbender, J.

The Materials and Condensed Matter group at the University of Glasgow has long been experimenting with direct electron detectors, together with the Particle Physics Experimental group. A Medipix2 detector was integrated onto our Philips CM20FEG electron microscope in a bottom mount position in 2010 and used in initial studies [1,2]. More recently, a Medipix3 detector was installed onto our JEOL ARM200F in a fixed mount at the 35mm camera port, and together with a Merlin readout system (Quantum Detectors Ltd., Harwell, UK) it was possible to run 4D STEM imaging at >1000 frames per second, under the control of Gatan Digital Micrograph. A similar system has been installed in a bottom mount on the JEOL Grand ARM at ePSIC. Most recently, a retractable mount for the Medipix3 detector has been produced at Glasgow, and is now installed on our JEOL ARM200F in the 35mm port.

One area of use of pixelated detection is for the improved differential phase contrast (DPC) mapping of magnetization in materials. Traditional DPC-STEM uses split detectors to determine the deflection of the bright field disc but suffers from additional diffraction contrast redistributing contrast within the disc thus creating image speckle on the length-scale of the grains. This can be overcome using a pixelated detector, and processing the discs using edge detection and cross correlation to give a pure disc deflection without the diffraction contrast [3]. This has been used in studying the magnetic structures arising from the patterning of B2 Fe60Al40 – this structure is ordered and paramagnetic after deposition and annealing, but after exposure to a (suitably low dose) Ne+ beam it is disordered to a BCC structure, which is strongly ferromagnetic and has a larger the parameter. We recorded diffraction patterns (Fig 1a) at a camera length to show both the central bright field disc and the inner rings of crystal diffraction spots. Fig 1b shows the plotted magnetization in one of these stripes. Fig 1c shows the lattice parameters determined from the diffraction ring radii in the directions parallel to and perpendicular to the long stripe axis. It is clear that parallel to the length, the parameter is constrained by the surrounding film, whereas there is a larger expansion perpendicular to the interface, across the width of the patterned magnetic stripe. This suggests that strain can be used to bias the magnetization in films.

Another novel use for pixelated detectors is to use high angle scattering into higher order Laue zones to reveal ordering along the beam direction, B [4]. Datasets containing such high angle information have now been recorded at atomic resolution, such as Fig 2 from a perovskite oxide heterostructure. Fig 2a shows HAADF contrast for this dataset, and both La-containing layers are much brighter than the SrTiO3 layer, as expected. Fig 2b shows the integrated intensity in the inner Laue zone ring, which only appears for the LaFeO3 layer. This arises from the doubling of the unit cell along B, and the intensity roughly corresponds to the magnitude of atomic shuffles parallel to B, showing that these only reach a maximum at the layer midpoint. Careful inspection also shows that the signal is strongest on the La columns, demonstrating that they are the primary source of the period doubling. This allows detailed investigation of the local “crystal structure”, which differs from the bulk LaFeO3 structure. The plots in Fig 2c show these trends for lines drawn from left to right, together with the outer Laue zone radius, which reveals subtle changes in lattice parameter along the beam direction across this heterostructure.

This demonstrates two exciting areas for application of such fast pixelated detectors for 4D STEM imaging, and shows that it enables new kinds of investigations, not possible with traditional detectors.

References:

[1] A MacRaighne et al., Journal of Instrumentation 6, (2011) C01047.
[2] R Beacham et al., Journal of Instrumentation 6 (2011) C12052.
[3] M Krajnak et al., Ultramicroscopy 165 (2016) 42
[4] M Nord et al., Microscopy and Microanalysis, 22 [S3] (2016) p. 476.
[5] This work was funded by the EPSRC (Fast Pixel Detectors: a paradigm shift in STEM imaging, EP/M009963/1). We thank Diamond Light Source for access and support in use of the electron Physical Science Imaging Centre (EM16952) that contributed to the results presented here.

  • Invited lecture (Conferences)
    Microscopy & Microanalysis 2018 Meeting, 05.-09.08.2018, Baltimore MD, USA

Permalink: https://www.hzdr.de/publications/Publ-27194
Publ.-Id: 27194


Nanoscale magnetic and structural characterization of Ne+ irradiated FeAl thin films using pixelated STEM

Nord, M.; Bali, R.; Hlawacek, G.; Lindner, J.; Fassbender, J.; Maclaren, I.; Mcgrouther, D.

Recent advances in 2-dimensional pixelated direct electron detectors have enabled the development of high acquisition rate imaging of the diffraction pattern in the scanning transmission electron microscope (STEM), resulting in the acquisition of a 4D STEM dataset of a full diffraction pattern for every scan position. One use for this is STEM differential phase contrast (DPC) imaging [1], which allows for quantitative measurements of the in-plane magnetic induction when operating the microscope with the objective lens turned off. This imaging mode is essentially convergent beam low angle diffraction, allowing for structural information to also be extracted from the diffraction patterns (Fig. 1b). This novel technique enables both strain and magnetic information to be extracted from a single dataset.

In this work we have simultaneously characterized both magnetic and physical (crystal) structure of patterned ferromagnetic stripes in Fe60Al40. As-deposited Fe60Al40 has an ordered B2 structure and is paramagnetic, but irradiation with Ne+ ions causes transformation to a disordered A2 ferromagnetic BCC structure with a larger lattice parameter [2]. This allows for arbitrarily shaped ferromagnetic regions to be written using a focused ion beam (FIB) with a Ne+ source. By using a JEOL ARM200cF probe aberration corrected STEM equipped with a MERLIN 1R (Medipix3) fast pixelated detector [Quantum Detectors Ltd], we are able to acquire datasets at 1 nm spatial resolution in aberration-corrected field-free Lorentz (objective-off) mode from patterned stripe structures with lateral dimensions from 0.02 – 4 µm and lengths of 10 µm (Fig. 1a). These possess unexpected domain structures in which large fraction of the magnetization deviates away from the long-axis, against shape anisotropy. To uncover the origin of the induced magnetic anisotropy we determined the strain profile in the nanowires from the diffraction patterns, which was also found to be very anisotropic, with the lattice parameter along the long axis clamped to something close to that of the surrounding film (orange trace in Fig. 1c) whereas the lattice parameter along the short axis is significantly larger (blue trace in Fig. 1c), as expected from the irradiation. Our data shows that the resulting shape-dependent anisotropic strain fields exert a strong influence on observed magnetic domain structure.

[1] Matus Krajnak, et al., Ultramicroscopy, 165 (2016) 42–50, doi:10.1016/j.ultramic.2016.03.006

[2] Rantej Bali, et al., Nano Letters, 14 (2014) 435-441, doi:10.1021/nl404521c

The authors are indebted to the EPSRC for the funding of this work via the project “Fast Pixel Detectors: a paradigm shift in STEM imaging” (Grant reference EP/M009963/1).

  • Lecture (Conference)
    19th International Microscopy Congress (IMC19), 09.-14.09.2018, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-27193
Publ.-Id: 27193


Beryllium-7 at DREsden Accelerator Mass Spectrometry

Rugel, G.; Merchel, S.; Scharf, A.; Querfeld, R.; Steinhauser, G.; Tiessen, C.

Half-lives of routine accelerator mass spectrometry (AMS) nuclides typically range from thousands to millions of years. We measured short-lived 7Be (T1/2 = 53.2 d) at the DREsden AMS-facility (DREAMS) [1] as low as 90 mBq, which can be challenging for rapid γ-counting. Simultaneous determination of 7Be and 10 Be (T1/2= 1.387 Ma) via AMS is advantageous for improved understanding of production, transport, and deposition of atmospherically produced 7,9,10Be [2].
Data was normalized to a 7 Be sample produced via 7Li(p,n)7Be, measured by γ-counting and chemically processed to BeO after adding low-level 9Be carrier (7Be/9Be ≈ 10-12). The isobar 7Li is completely eliminated by chemistry and the degrader foil technique (at detector 7Be4+, 10.2 MeV, no 7Li4+ possible). The blank ratio of 5 × 10-16 7Be/9Be (0.8 mBq) and simple and fast chemistry allows for the measurement of rainwater samples, collected in Germany, as small as 10 mL corresponding to a few times 10-14 7Be/9Be [3,4].
Thanks to D. Bemmerer (HZDR) and G. György (ATOMKI, Hungary) for help with the 7Be normalization material.
[1] G. Rugel et al., NIMB 370 (2016) 94.
[2] A.M. Smith et al., NIMB 294 (2013) 59.
[3] R. Querfeld et al., JRNC 314 (2017) 521.
[4] C. Tiessen et al. JRNC (to be submitted).

Keywords: Be-7; AMS

  • Lecture (Conference)
    MAT Science Week (Ionenstrahlworkshop), 24.-25.04.2018, Darmstadt, Deuschland

Permalink: https://www.hzdr.de/publications/Publ-27192
Publ.-Id: 27192


Doping beyond the solid solubility limit: from bulk to nanostructured semiconductors

Berencen, Y.

Hyperdoping has recently emerged as a potential powerful technique to explore new functionalities of semiconductor materials with unique electrical and optical properties [1-3]. Hyperdoping facilitates to introduce dopants into a semiconductor material at concentrations far above those obtained at equilibrium conditions, viz. doping far beyond the solubility limit. Hyperdoped Si with chalcogens or transition metals like Au or Ti has been postulated to be a promising material for many applications, especially for Si-based infrared photodetectors and intermediate band solar cells ([3] and references therein).

Most of the relevant published papers [1-3] have been limited to the study of hyperdoped bulk Si with chalcogens. Particularly, S and Se have primarily been used for this kind of purpose since they can introduce a variety of deep donor states in the upper half of the band gap of Si, which give rise to the formation of an impurity band that allows a strong sub-band gap optical absorption at wavelengths larger than 1 µm [2]. To create such an impurity band in a semiconductor like Si, whose equilibrium solubility limit for the aforementioned dopants is around 1016 cm-3 [1], high dopant concentrations exceeding the so-called Mott limit are required [1]. Therefore, non-equilibrium thermal processing to obtain hyperdoped semiconductor materials is sound.

Chalcogens are commonly introduced by pulsed-laser irradiation of the material under study, which is simultaneously immersed in an atmosphere containing chalcogen atoms [2]. Another singular approach is to use ion implantation followed by either nanosecond (ns)-range pulsed-laser melting (PLM) [1] or millisecond (ms)-range flash lamp annealing (FLA) [3]. Both PLM and FLA are advantageous if compared with conventional annealing techniques. For instance, these techniques offer high crystal quality after recrystallization, high dopant solubility and low heating of the substrate [3]. Moreover, depending on the energy density and the timescale of annealing after implantation (typically, from few ns to dozens of ms), liquid-phase or solid-phase epitaxy can be induced on the implanted material surface, which accounts for the epitaxial recrystallization atop the crystalline substrate [3]. In particular, solid-phase epitaxy via ms-range FLA was reported to be superior to liquid-phase epitaxy through ns-range PLM in terms of less dopant redistribution and high electrical activation of dopants [3].

In the last years, semiconductor nanowires (NWs) have gained increasing importance as building blocks for nanodevices like field-effect transistors, light emitting devices, photovoltaic cells and integrated photodetectors ([4] and references therein). Indeed, their reduced sizes and the physical confinement along two directions allow the tuning of electro-optical properties such as conductivity, optical absorption and photoluminescence, among others. Recently, traditional dopants such as B and P have been introduced into Si NWs by ion implantation followed by conventional annealing [5]. Recrystallization and reactivation of dopants were successfully achieved at low doses. However, both phenomena were not successful at high doses since it resulted in the formation of polycrystals and a low ratio of dopant activation. To date, there are only theoretical examinations of the properties of Si NWs hyperdoped with chalcogens [4]. These results have shown that donor defects give rise to a strong hyperfine interaction in the hyperdoped Si NWs, which can be exploited to develop a Si-based nuclear spin quantum computer [4].

Therefore, the new approach to combine Si NWs and hyperdoping with chalcogens proposed here can provide important contributions to the state-of-the-art and will help to answer important fundamental and practical scientific issues.

Reference
[1] Ertekin E., Winkler M. T., Recht D., Said A. J., Aziz M. J., Buonassisi T., Grossman J. C. (2012): Insulator-to-Metal Transition in Selenium-Hyperdoped Silicon: Observation and Origin. Published in: Physical Review Letters 108, 026401.
[2] Sher M. J., Mazur E. (2014): Intermediate band conduction in femtosecond-laser hyperdoped silicon. Published in: Applied Physics Letters 105, 032103.
[3] Zhou S., Liu F., Prucnal S., Gao K., Khalid M., Baehtz C., Posselt M., Skorupa W., Helm M. (2015): Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy. Published in: Scientific Reports 5, 8329.
[4] Petretto G., Massé A., Fanciulli M., Debernardi A. (2015): Analysis of hyperfine structure in chalcogen-doped silicon and germanium nanowires. Published in: Physical Review B 91, 125430.
[5] Fukata N., Takiguchi R., Ishida S., Yokono S., Hishita S., Murakami K., (2012): Recrystallization and reactivation of dopant atoms in ion-implanted silicon nanowires. Published in: ACS NANO 6, 3278.

Keywords: Chalcogens; silicon; hyperdoping; ion implantation; flash lamp annealing; insulator to metal transition; sub-band gap photoresponse; infrared plasmonics; nanowires

  • Lecture (others)
    Leibniz institute seminar, 22.02.2018, Leibniz Institute of Polymer Research Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-27187
Publ.-Id: 27187


A high-efficiency gas target setup for underground experiments, and redetermination of the branching ratio of the 189.5 keV 22Ne(p,γ)23Na resonance

Ferraro, F.; Takács, M. P.; Piatti, D.; Mossa, V.; Aliotta, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Depalo, R.; D'Erasmo, G.; Di Leva, A.; Elekes, Z.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marcucci, L. E.; Marigo, P.; Menegazzo, R.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Szücs, T.; Trezzi, D.; Zavatarelli, S.

The experimental study of nuclear reactions of astrophysical interest is greatly facilitated by a low-background, high-luminosity setup. The Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator offers ultra-low cosmic-ray induced background due to its location deep underground in the Gran Sasso National Laboratory (INFN-LNGS), Italy, and high intensity, 250-500 μA, proton and α ion beams. In order to fully exploit these features, a high-purity, recirculating gas target system for isotopically enriched gases is coupled to a high-efficiency, six-fold optically segmented bismuth germanate (BGO) γ-ray detector. The beam intensity is measured with a beam calorimeter with constant temperature gradient. Pressure and temperature measurements have been carried out at several positions along the beam path, and the resultant gas density profile has been determined. Calibrated γ-intensity standards and the well-known Ep = 278 keV 14N(p,γ)15O resonance were used to determine the γ-ray detection efficiency and to validate the simulation of the target and detector setup. As an example, the recently measured resonance at Ep = 189.5 keV in the 22Ne(p,γ)23Na reaction has been investigated with high statistics, and the γ-decay branching ratios of the resonance have been determined.

Permalink: https://www.hzdr.de/publications/Publ-27186
Publ.-Id: 27186


Experimental investigation of fluid dynamics in sandwich packings with ultrafast X-ray tomography

Sohr, J.; Schubert, M.; Flechsig, S.; Kenig, E. Y.; Hampel, U.

Sandwich packings consist of two layers of corrugated sheet structured packings with higher (holdup layer) and lower (de-entrainment layer) specific surface area alternatingly placed in the column. They are preferentially operated between the flooding points of both layers, which results in zones of bubbly flow, froth regime and liquid film flow in each sandwich element. Compared to conventional packed columns, sandwich packings can reach higher capacity and also higher separation efficiency as a result of intensive phase interactions. In the scope of a collaborative project, sandwich packings are experimentally and theoretically investigated. To provide detailed information on the heterogeneous flow patterns to derive reliable process models, ultrafast X-ray tomography is applied as a non-invasive measurement technique with high temporal and spatial resolution. In addition to local liquid holdup in the different layers of the packing, cross-sectional liquid distribution and axial transitions between the flow regimes are estimated. Furthermore, a method for the detection of the gas-liquid interfacial area is proposed.

  • Open Access Logo Chemical Engineering Transactions 69(2018), 727
    DOI: 10.3303/CET1869122
  • Lecture (Conference)
    11th International Conference on Distillation & Absorption, 16.-19.09.2018, Florence, Italy

Permalink: https://www.hzdr.de/publications/Publ-27185
Publ.-Id: 27185


Rate-based modelling of CO2 absorption with sandwich packings

Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.

The efficiency of fluid separation processes can be enhanced by the application of sandwich packings (SPs). They consist of two alternating layers of industrially available standard packings with different specific surface areas, one with lower (the so-called holdup layer, HL) and another with higher (the so-called de-entrainment layer, DL) capacity. SPs are typically used at operating conditions between the flooding points of HL and DL. Above the HL, a froth sub-layer is formed, which reveals high separation efficiency due to intensified phase contact. In a collaborative project, the effects of the individual flow regimes on fluid dynamics and mass transfer are being investigated, both experimentally and theoretically. In order to identify the impact of the individual flow regimes, experiments in an absorption/desorption plant are supplemented by flow imaging measurements. This paper focuses on a rate-based model, in which the heterogeneous flow patterns in SPs are considered via appropriate correlations. In order to validate this model, we measured CO2 absorption characteristics under the influence of different operating and design parameters and compared them with the simulation results.

  • Open Access Logo Chemical Engineering Transactions 69(2018), 169
    DOI: 10.3303/CET1869029
  • Poster
    11th International Conference on Distillation & Absorption, 16.-19.09.2018, Florence, Italy

Permalink: https://www.hzdr.de/publications/Publ-27184
Publ.-Id: 27184


Peptides as Biosorbents - Promising tools for resource recovery

Braun, R.; Bachmann, S.; Schönberger, N.; Matys, S.; Lederer, F.; Pollmann, K.

Despite many innovations, meeting both economic and ecological requirements remains challenging for conventional resource recovery technology. The development of highly selective peptides puts a new competitor on the market. We present an approach to identify peptides for resource recovery using Phage Surface Display. Here, we describe the development of peptides for binding of rare earth element terbium containing solids and for removal and enrichment of the heavy metal ions of cobalt and nickel out of waste waters and leaching solutions.

Keywords: phage display; biosorption; peptide; biohydrometallurgy

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Permalink: https://www.hzdr.de/publications/Publ-27183
Publ.-Id: 27183


Fluiddynamische Untersuchung von Anstaupackungen mittels ultraschneller Röntgentomographie

Sohr, J.; Schubert, M.; Flechsig, S.; Kenig, E. Y.; Hampel, U.

In Anstaupackungen bilden sich durch die Kombination von Packungslagen unterschiedlicher geometrischer Oberfläche abhängig von den Betriebsbedingungen Filmströmung und Sprudelschicht gleichzeitig aus. Durch die axial stark heterogene Strömungsmorphologie lassen integrale Holdup-Messungen keine Rückschlüsse auf lokale Flüssigkeitsinhalte in einzelnen Packungslagen zu.
Die ultraschnelle Röntgentomographie bietet dank einer Bildrate von bis zu 8000 Schnittbildern pro Sekunde die Möglichkeit, bei den hochdynamischen Zweiphasenströmungen relevante fluiddynamische Parameter in einzelnen Abschnitten der Anstaupackung nichtinvasiv zu bestimmen [1]. Neben der Ermittlung von Phasenanteilen und deren radialer sowie axialer Verteilung werden auch Methoden zur Ermittlung der Gas-Flüssigkeits-Grenzfläche angewandt. Ein weiterer entscheidender Parameter für die hydrodynamische Modellierung von Anstaupackungen ist die Höhe der Sprudelschicht [2]. Deren Bestimmung erfolgt zum einen mithilfe der ultraschnellen Röntgentomographie sowie ergänzend durch eine verteilte Druckverlustmessung mit einer axialen Auflösung von 10 mm. Im Rahmen dieses Beitrags werden sowohl die Messmethoden als auch Messergebnisse der experimentellen Untersuchungen vorgestellt.
Wir danken der DFG für die finanzielle Unterstützung des Kooperationsprojekts "Experimentelle und theoretische Untersuchung der Fluiddynamik und des Stofftrennverhaltens von Anstaupackungen" (KE 837/26-1, HA 3088/10-1).
[1] A. Janzen, M. Schubert, F. Barthel, U. Hampel, E.Y. Kenig, Chemical Engineering and Processing: Process Intensification 66, 20-26 (2013).
[2] U. Brinkmann, B. Kaibel, M. Jödecke, J. Maćkowiak, E.Y. Kenig, Chemie Ingenieur Technik 84: 36-45 (2012).

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrentechnik, 27.-28.02.2018, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27182
Publ.-Id: 27182


Cluster Formation in the Superconducting Complex Intermetallic Compound Be21Pt5

Amon, A.; Ormeci, A.; Bobnar, M.; Akselrud, L. G.; Avdeev, M.; Gumeniuk, R.; Burkhardt, U.; Prots, Y.; Hennig, C.; Leithe-Jasper, A.; Grin, Y.

Materials with the crystal structure of γ-brass type (Cu5Zn8 type) are typical representatives of intermetallic compounds. From the electronic point of view, they are often interpreted using the valence electron concentration approach of Hume−Rothery, developed previously for transition metals. The γ-brass-type phases of the main-group elements are rather rare. The intermetallic compound Be21Pt5, a new member of this family, was synthesized, and its crystal structure, chemical bonding, and physical properties were characterized. Be21Pt5 crystallizes in the cubic space group F4̅3m with lattice parameter a = 15.90417(3) Å and 416 atoms per unit cell. From the crystallographic point of view, the binary substance represents a special family of intermetallic compounds called complex metallic alloys (CMA). The crystal structure was solved by a combination of synchrotron and neutron powder diffraction data. Besides the large difference in the scattering power of the components, the structure solution was hampered by the systematic presence of very weak reflections mimicking wrong symmetry. The structural motif of Be21Pt5 is described as a 2 × 2 × 2 superstructure of the γ-brass structure (Cu5Zn8 type) or 6 × 6 × 6 superstructure of the simple bcc structural pattern with distinct distribution of defects. The main building elements of the crystal structure are four types of nested polyhedral units (clusters) with the compositions Be22Pt4 and Be20Pt6. Each cluster contains four shells (4 + 4 + 6 + 12 atoms). Clusters with different compositions reveal various occupation of the shells by platinum and beryllium. Polyhedral nested units with the same composition differ by the distance of the shell atoms to the cluster center. Analysis of chemical bonding was made applying the electron localizability approach, a quantum chemical technique operating in real space that is proven to be especially efficient for intermetallic compounds. Evaluations of the calculated electron density and electron localizability indicator (ELI-D) revealed multicenter bonding, being in accordance with the low valence electron count per atom in Be21Pt5. A new type of atomic interactions in intermetallic compounds, cluster bonds involving 8 or even 14 atoms, is found in the clusters with shorter distances between the shell atoms and the cluster centers. In the remaining clusters, four- and five-center bonds characterize the atomic interactions. Multicluster interactions within the polyhedral nested units and threecenter polar intercluster bonds result in a three-dimensional framework resembling the structural pattern of NaCl. Be21Pt5 is a diamagnetic metal and one of rather rare CMA compounds revealing superconductivity (Tc = 2.06 K).

Permalink: https://www.hzdr.de/publications/Publ-27181
Publ.-Id: 27181


Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study

Phuyala, D.; Safdari, M.; Pazoki, M.; Liu, P.; Philippe, B.; Kvashnina, K. O.; Karis, O.; Butorin, S. M.; Rensmo, H.; Edvinsson, T.; Kloob, L.; Gardner, J. M.

Layered two-dimensional (2D) hybrid organic-inorganic perovskites (HOP) are promising materials for light harvesting applications due to their chemical stability, wide flexibility in composition, and recent increases in photovoltaic power conversion efficiencies. Three 2D lead iodide perovskites were studied through various X-ray spectroscopic techniques to derive detailed electronic structures and band energetics profiles at a titania interface. Core-level and valence band photoelectron spectra of HOP were analyzed to resolve the electronic structure changes due to the reduced-dimensionality of inorganic layers. The results show orbital narrowing when comparing the HOP, the layered precursor PbI2, and the conventional 3D (CH3NH3)PbI3 such that different localizations of band edge states and narrow band states are unambiguously due to the decrease in dimensionality of the layered HOPs. Support from density functional theory (DFT) calculations provide further details on the interaction and bandgap variations of the electronic structure. We observed an interlayer distance dependent dispersion in the near band edge electronic states. The results show how tuning the interlayer distance between the inorganic layers affects the electronic properties and provides important design principles for control of the interlayer charge transport properties, such as the change in effective charge masses as a function of the organic cation length. The results of these findings can aid in establishing design principles for new, layered

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Publ.-Id: 27180


Evidence for a dynamical ground state in the frustrated pyrohafnate Tb2Hf2O7

Anand, V. K.; Opherden, L.; Xu, J.; Adroja, D. T.; Hillier, A. D.; Biswas, P. K.; Herrmannsdörfer, T.; Uhlarz, M.; Hornung, J.; Wosnitza, J.

We report the physical properties of Tb2Hf2O7 based on ac magnetic susceptibility χac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M(H), and heat capacity C(T ) measurements combined with muon spin relaxation (μSR) and neutron powder diffraction measurements. No evidence for long-range magnetic order is found down to 0.1 K. However, χac(T ) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz) indicating slow spin dynamics. The slow spin dynamics is further evidenced from the μSR data (characterized by a stretched exponential behavior) which show persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering) but no magnetic Bragg peaks. The analysis of the diffuse scattering data reveals a dominant antiferromagnetic interaction in agreement with the negative Weiss temperature. The absence of long-range magnetic order and the presence of slow spin dynamics and persistent spin fluctuations together reflect a dynamical ground state in Tb2Hf2O7.

Permalink: https://www.hzdr.de/publications/Publ-27179
Publ.-Id: 27179


Increasing stripe-type fluctuations in AFe2As2 (A = K, Rb, Cs) superconductors probed by 75As NMR spectroscopy

Zhang, Z. T.; Dmytriieva, D.; Molatta, S.; Wosnitza, J.; Khim, S.; Gass, S.; Wolter, A. U. B.; Wurmehl, S.; Grafe, H.-J.; Kühne, H.

We report 75As nuclear magnetic resonance measurements on single crystals of RbFe2As2 and CsFe2As2. Taking previously reported results for KFe2As2 into account, we find that the anisotropic electronic correlations evolve towards a magnetic instability in the AFe2As2 series (with A = K, Rb, Cs). Upon isovalent substitution with larger alkali-metal ions, a drastic enhancement of the anisotropic nuclear spin-lattice relaxation rate and decreasing Knight shift reveal the formation of pronounced spin fluctuations with stripe-type modulation. Furthermore, a decreasing power-law exponent of the nuclear spin-lattice relaxation rate (1/T1)HIIab, probing the in-plane spin fluctuations, evidences an emergent deviation from Fermi-liquid behavior. All these findings clearly indicate that the expansion of the lattice in the AFe2As2 series tunes the electronic correlations towards a quantum critical point at the transition to a yet unobserved ordered phase.

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Publ.-Id: 27178


Defect induced magnetism in SiC

Zhou, S.

Defect induced magnetism, which can be controllably generated by ion or neutron irradiation, is attracting intensive research interest. It not only challenges the traditional opinions about magnetism, but also has some potential applications in spin-electronics. SiC is a new candidate for the investigation of defect-induced ferromagnetism after graphitic materials and oxides due to its high material purity and crystalline quality [1, 2]. In this contribution, we present a comprehensive investigation on the structural and magnetic properties of ion implanted and neutron irradiated SiC samples. In combination with X-ray absorption spectroscopy, high-resolution transmission electron microscopy and first-principles calculations, we try to understand the mechanism in a microscopic picture.
For neon or xenon ion implanted SiC, we identify a multi-magnetic-phase nature [3]. The magnetization of SiC can be decomposed into paramagnetic, superparamagnetic and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. By combining X-ray magnetic circular dichroism and first-principles calculations, we clarify that p-electrons of the nearest-neighbor carbon atoms around divacancies are mainly responsible for the long-range ferromagnetic coupling [4]. Thus, we provide a correlation between the collective magnetic phenomena and the specific electrons/orbitals. Moreover, a negative magnetoresistance has been observed in ferromagnetic an conducting SiC, indicating the interplay between magnetism and free carriers [5].
With the aim to verify if a sample containing defects through its bulk volume can persist ferromagnetic coupling, we applied neutron irradiation to introduce defects into SiC [6]. Besides a weak ferromagnetic contribution, we observe a strong paramagnetism, scaling up with the neutron fluence. The ferromagnetic contribution only occurs in a narrow fluence window or after annealing. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: Defects favor spin polarization at the expense of magnetic interaction. Moreover, the interaction between the nuclear spin and the paramagnetic defect can effectively tune the spin-lattice relaxation time (T1) as well as the nuclear spin coherent time (T2) [7].

[1] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).
[2] Y. Wang, et al., Phys. Rev. B 90, 214435 (2014).
[3] Y. Wang, et al., Phys. Rev. B 89, 014417 (2014).
[4] Y. Wang, et al., Scientific Reports, 5, 8999 (2015).
[5] Y. Liu, et al., Phys. Rev. B 95, 195309 (2017).
[6] Y. Wang, et al., Phys. Rev. B 92, 174409 (2015).
[7] Z. Zhang, et al., Phys. Rev. B 95, 085203 (2017).

  • Invited lecture (Conferences)
    International Workshop: Functionality of Oxide Interfaces, 26.02.-02.03.2018, Benedictine Abbey of Frauenwörth, Germany

Permalink: https://www.hzdr.de/publications/Publ-27177
Publ.-Id: 27177


Interplay between localization and magnetism in (III,Mn)V dilute ferromagnetic semiconductors

Zhou, S.; Yuan, Y.; Sawicki, M.; Rushforth, A. W.; Zhao, J.; Dietl, T.; Helm, M.

Although the interplay between hole-mediated ferromagnetism and hole localization has long been recognized as the central issue in dilute ferromagnetic semiconductors (DFSs), its understanding remains in a nascent stage and contradicting approaches are under consideration [1, 2]. Some of the difficulties lie in the sample preparation: the dual role of Mn in III-V compounds providing local spins and holes, the poor control over donor defects (Mn interstitials and As antisites) etc. In this contribution, we examine the influence of localization on the hole-mediated ferromagnetism in (III,Mn)V DFSs by utilizing the well-developed ion-beam technology for microelectronics which can overcome the aforementioned difficulties [3].
First, we have used ion implantation of Mn combined with pulsed laser melting to prepare Ga1−xMnxAs and In1−xMnxAs with Mn concentration from 0.3% to 1.8% covering both sides of the insulator-metal transition [4-8]. The system evolves with x from a paramagnetic phase (probed down to 1.8 K), to a superparamagnetic material, to reach, via a mixed phase consisting of percolating ferromagnetic clusters and superparamagnetic grains, a global ferromagnetism without any superparamagnetism. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1−xMnxAs compared to Ga1−xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Second, we use inert Helium ions to precisely compensate holes by donor defects, thereafter to shift the Fermi energy in DFSs while keeping the Mn concentration constant [9-12]. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a monotonous decrease of Curie temperature TC down to zero and a spin-reorientation transition with hole compensation while the conduction is changed from metallic to insulating. The previously questioned existence of TC below 10 K is also confirmed in heavily compensated samples. Our comprehensive results support strongly the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions even on the insulator side of the metal-insulator transition.

[1] M. Sawicki et al., Nat. Phys. 6, 22 (2010).
[2] M. Kobayashi et al., Phys. Rev. B 89, 205204 (2014).
[3] S. Zhou, J. Phys. D: Appl. Phys. 48, 263001 (2015).
[4] S. Zhou et al., Appl. Phys. Express 5, 093007 (2012).
[5] Y. Yuan…, S. Zhou, J. Phys. D: Appl. Phys. 48, 235002 (2015).
[6] S. Prucnal…, S. Zhou, Phys. Rev. B 92, 224407 (2015).
[7] Y. Yuan…, S. Zhou, Phys. Rev. Mater. 1, 054401 (2017).
[8] Y. Yuan…, S. Zhou, J. Phys.: Condens. Matter 30, 095801 (2018).
[9] L. Li…, S. Zhou, J. Phys. D: Appl. Phys. 44 099501 (2011).
[10] S. Zhou et al., Phys. Rev. B 95, 075205 (2016).
[11] M. Lonsky…, S. Zhou, J. Müller, Phys. Rev. B 97, 054413 (2018).
[12] Y. Yuan..., S. Zhou, J. Phys. D: Appl. Phys., in press (2018).

  • Poster
    34th International conference on the physics of semiconductors, 29.07.-03.08.2018, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-27176
Publ.-Id: 27176


Hydrogen-assisted Post-growth Doping of Tellurium into Molybdenum Disulfide Monolayers with Tunable Compositions

Yin, G.; Zhu, D.; Lv, D.; Zhang, Z.; Hashemi, A.; Krasheninnikov, A. V.; Komsa, H.-P.; Jin, C.

Herein we report the successful doping of tellurium (Te) into molybdenum disulfide (MoS2) monolayers to form MoS2xTe2(1−x) alloy with variable compositions via a hydrogen-assisted post-growth chemical vapor deposition process. It is confirmed that H2 plays an indispensable role in the Te substitution into as-grown MoS2 monolayers. Atomic-resolution transmission electron microscopy allows us to determine the lattice sites and the concentration of introduced Te atoms. At a relatively low concentration, tellurium is only substituted in the sulfur sublattice to form monolayer MoS2(1−x)Te2x alloy, while with increasing Te concentration (up to ∼27.6% achieved in this study), local regions with enriched tellurium, large structural distortions, and obvious sulfur deficiency are observed. Statistical analysis of the Te distribution indicates the random substitution. Density functional theory calculations are used to investigate the stability of the alloy structures and their electronic properties. Comparison with experimental results indicate that the samples are unstrained and the Te atoms are predominantly substituted in the top S sublattice. Importantly, such ultimately thin Janus structure of MoS2(1−x)Te2x exhibits properties that are distinct from their constituents. We believe our results will inspire further exploration of the versatile properties of asymmetric 2D TMD alloys.

Keywords: 2D materials; post-growth; tellurium; TMDC; MoS2

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Publ.-Id: 27175


Big Bang Cosmology in the Lab: The 2H(p,γ)3He reaction studied at LUNA

Stöckel, K. For The Luna Collaboration

Recent high-precision measurements of the primordial 2H abundance have opened the path to use Big Bang nucleosynthesis to constrain the primordial baryon to photon ratio with similar precision as the cosmic microwave background. This would provide an independent cross-check on current Big Bang models. However, the interpretation of the abundance is limited by the lack of precise nuclear data, in particular on the main 2H destruction channel, the 2H(p,γ)3He reaction. A new experiment to study the 2H(p,γ)3He cross section directly in the Big Bang energy window is underway at the LUNA 400 kV accelerator, deep underground in the Gran Sasso laboratory, Italy. The progress of experiment and analysis will be summarized. – Supported by DFG (BE 4100/4-1).

  • Lecture (Conference)
    DPG-Frühjahrstagung Bochum 2018, 26.02.-02.03.2018, Bochum, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27174
Publ.-Id: 27174


Monothioarsenate transformation kinetics determines arsenic sequestration by sulfhydryl groups of peat

Besold, J.; Biswas, A.; Suess, E.; Scheinost, A. C.; Rossberg, A.; Mikutta, C.; Kretzschmar, R.; Gustafsson, J. P.; Planer-Friedrich, B.

In peatlands, arsenite was reported to be effectively sequestered by sulfhydryl groups of organic matter. To which extent porewater arsenite can react with reduced sulfur to form thioarsenates and how this affects arsenic sequestration in peatlands, is unknown. Here, we show that in the arsenic-rich peatland Gola di Lago, Switzerland, up to 93% of all arsenic species in surface and porewaters were thioarsenates. The dominant species, monothioarsenate, likely formed from arsenite and surface-associated zero-valent sulfur (S(0)). Laboratory incubations with sulfide-reacted peat showed for both, monothioarsenate and arsenite, increasing total arsenic sorption with decreasing pH from 8.5 to 4.5. However, X-ray absorption spectroscopy revealed no binding of monothioarsenate via sulfhydryl groups. The sorption observed at pH 4.5 was acid-catalyzed dissociation of monothioarsenate, forming arsenite. The lower the pH and the more sulfhydryl sites, the more arsenite sorbed which in turn shifted equilibrium towards further dissociation of monothioarsenate. At pH 8.5, monothioarsenate was stable over 41 days. In conclusion, arsenic is effectively sequestered in anoxic, acidic environments where arsenite is the only arsenic species. Where fluctuating redox conditions enable sulfide oxidation to S(0), monothioarsenate forms and at neutral to alkaline pH, slow transformation kinetics make this species highly mobile.

Keywords: arsenic; speciation; wetland; ground water; xafs

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Publ.-Id: 27173


Analysis of the Electric-Double-Layer formation by in-situ Rutherford Backscattering Spectrometry

Baghban Khojasteh Mohammadi, N.; Heller, R.; Bergmann, U.; Apelt, S.

A setup for in-situ Rutherford Backscattering Spectrometry (RBS) has been installed at the 2 MV Van-de-Graaff accelerator at the Ion Beam Center (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Online analysis of solid-liquid interfaces as well as electro-chemistry experiments are conducted by this technique. A Si3N4 window separates the liquid from the vacuum in the RBS chamber. A He+ beam (E = 1.7 MeV) is utilized for the RBS measurements. RBS as well as Particle Induced X-Ray Emission Spectroscopy (PIXE) spectra are recorded simultaneously to increase the sensitivity for trace elements. The technique was employed for direct measurements of the Electric-Double-Layer (EDL) formation on Si3N4. Investigations of the EDL formation at solid-liquid interfaces are of great significance due to the various valuable applications such as super-capacitors that can be utilized to provide a backup power supply or applied in various other fields [1-3]. In our preliminary experiments, the specific adsorption of Barium ions from a 1mM BaCl2 solution with various pH values was observed in a direct and quantitative manner. Sensitivity of the technique reaches the ppm range and areal densities can be measured down to 0.1 atomic monolayer.
[1]Kötz et al., (2002). The 12th International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Dec, USA.
[2]Faggioli et al., (1999). J. Power Sources, 84(2): 261.
[3]Simon et al., (2008). Nature materials, 7(11): 845.

Keywords: in-situ RBS; Electric-Double-Layer

  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.04.2018, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-27172
Publ.-Id: 27172


An experimental approach to reactive transport in geomaterials: GeoPET

Kulenkampff, J.; Franke, K.; Gründig, M.; Hildebrand, H.; Karimzadeh, L.; Schymura, S.; Fischer, C.

Detailed understanding of reactive transport in geomaterials of chemical species, including radionuclides, is required for the utilization of the subsoil, e.g. for designing ore production by in-situ leaching, or for radioactive waste disposal. To complement the well-established conventional approach, i.e. computer model simulations based upon bulk material parameters and geochemical data bases, we apply process tomography with positron emission tomography (GeoPET) for direct observation and parameterization of the reactive transport processes. This enables to consider heterogeneity as pervasive feature of processes in complex media. One example is localized flow meandering along fractures, where preferential flow may jeopardize leaching efficiency. On the other hand, fissure networks through otherwise tight material could provide fast transport pathways through geological barriers.
Our workflow consist of 1) production of appropriate PET-nuclides and labelling, 2) transport experiment on samples of drill core size with the labelled species, 3) recording of PET-data (list-mode-files) during the course of tracer propagation, 4) computation of PET-frames with appropriate frame rate and correction for material effects, 5) parameterization of the spatiotemporal data set with the target parameters effective volume distribution and velocity distribution.
The choice of PET-nuclides is broader than in common biomedical PET applications, because longevity and toxicity of the tracers are inconsiderable, but spatial resolution and efficient corrections for attenuation and scatter require attention. The development of the GeoPET method during the past decade is described in Kulenkampff et al. (2016).
As illustration, we present an example from ore leaching, where the leaching solution is flown through an artificial fracture. During leaching we experimentally determined the macroscopic flow field with GeoPET. With these hydrodynamic data we are able to establish a realistic and light-weight reactive transport model which can directly serve for efficient design of leaching.
The procedure is one good example for the benefit of radiotracers for unravelling complex processes by non-destructive molecular imaging. We strongly suggest utilizing this distinguished tool, in particular for .parameterization and upscaling of heterogeneous reactive transport models.

Kulenkampff, J., Gründig, M., Zakhnini, A., Lippmann-Pipke, J. 2016. Geoscientific process monitoring with positron emission tomography (GeoPET), Solid Earth, 7, 1217-1231, 10.5194/se-7-1217-2016.

  • Lecture (Conference)
    RadChem 2018, 13.-18.05.2018, Mariánské Lázně, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-27171
Publ.-Id: 27171


Comparison of different treatment planning approaches for intensity-modulated proton therapy with simultaneous integrated boost for pancreatic cancer

Stefanowicz, S.; Stützer, K.; Zschaeck, S.; Jakobi, A.; Troost, E. G. C.

Background
Neoadjuvant radio(chemo)therapy of non-metastasized, borderline resectable or unresectable locally advanced pancreatic cancer is complex and prone to cause side-effects, e.g., in gastrointestinal organs. Intensity-modulated proton therapy (IMPT) enables a high conformity to the targets while simultaneously sparing the normal tissue such that dose-escalation strategies come within reach. In this in silico study, we compared four IMPT planning strategies including robust multi-field optimization (rMFO) and a simultaneous integrated boost (SIB) for dose-escalation in pancreatic cancer patients.

Methods
For six pancreatic cancer patients referred for adjuvant or primary radiochemotherapy four rMFO-IMPT-SIB treatment strategies of two or three (non-)coplanar beam arrangements were calculated. Dose values for both targets, the elective clinical target volume (CTV) and the SIB, and the organs at risk as well as target conformity and homogeneity indexes, derived from the dose volume histograms, were statistically compared.

Results
All treatment plans of each strategy fulfilled the prescribed doses to the targets (D95%≥95%, D2%≤107%). No significant differences for the conformity index were found (p>0.05), however, treatment plans with a three non-coplanar beam approach were most homogenous to both targets (p<0.045). Dose constraints for large and small bowel as well as for the liver and the spinal cord were met with all beam arrangements. Irrespective of the planning strategies, the dose constraint for the duodenum and stomach were not met. Using the three-beam arrangements, the dose to the left kidney could be significant decreased when compared to a two-beam strategy (p<0.045).

Conclusion
Based on our findings we recommend a three-beam configuration with at least one non-coplanar beam for rMFO-IMPT-SIB in advanced pancreatic cancer patients achieving a homogeneous dose distribution in the target while simultaneously minimizing the dose to the organs at risk.

Keywords: pancreatic cancer; intensity modulated proton therapy; simultaneous integrated boost; dose escalation

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Publ.-Id: 27170


High-Yield Optical Undulators Scalable to Optical Free-Electron Laser Operation by Traveling-Wave Thomson-Scattering

Steiniger, K.

All across physics research, incoherent and coherent light sources are extensively utilized.
Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources.
But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays.

This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources.
The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems.

TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources.
Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized.

Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods.

This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems.
The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range.
These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis.
It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser.

Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed.
The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups.
An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, too.

Keywords: Traveling-Wave; Thomson scattering; X-ray; free-electron laser; pulse-front tilt

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-089 2018
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-27169
Publ.-Id: 27169


Thick Permalloy films for the imaging of spin texture dynamics in perpendicularly magnetized systems

Finizio, S.; Wintz, S.; Bracher, D.; Kirk, E.; Semisalova, A. S.; Förster, J.; Zeissler, K.; Weßels, T.; Weigand, M.; Lenz, K.; Kleibert, A.; Raabe, J.

Performance combined with simplicity: we demonstrate that thick Permalloy films exhibiting a weak growth-induced perpendicular magnetic anisotropy can be employed as an ideal test system for the study of magnetodynamical processes in perpendicularly magnetized systems exhibiting magnetic textures ranging from isolated magnetic bubbles to more complex n"pi" states.

Keywords: Skyrmion; STXM; PMA

Permalink: https://www.hzdr.de/publications/Publ-27168
Publ.-Id: 27168


Magnetic small-angle neutron scattering

Mühlbauer, S.; Honecker, D.; Perigo, E. A.; Bergner, F.; Disch, S.; Heinemann, A.; Erokhin, S.; Berkov, D.; Leighton, C.; Eskildsen, M. R.; Michels, A.

Small-angle neutron scattering (SANS) is one of the most important techniques for microstructure determination, being utilized in a wide range of scientific disciplines, such as materials science, physics, chemistry, and biology. The reason for its great significance is that conventional SANS is probably the only method capable of probing structural inhomogeneities in the bulk of materials on a mesoscopic real-space length scale, from roughly 1 − 300 nm. Moreover, the exploitation of the spin degree of freedom of the neutron provides SANS with a unique sensitivity to study magnetism and magnetic materials at the nanoscale. As such, magnetic SANS ideally complements more real-space and surface-sensitive magnetic imaging techniques, e.g., Lorentz transmission electron microscopy, electron holography, magnetic force microscopy, Kerr microscopy, or spin-polarized scanning tunneling microscopy. In this review article we summarize the recent applications of the SANS method to study magnetism and magnetic materials. This includes a wide range of materials classes, from nanomagnetic systems such as soft magnetic Fe-based nanocomposites, hard magnetic Nd−Fe−B-based permanent magnets, magnetic steels, ferrofluids, nanoparticles, and magnetic oxides, to more fundamental open issues in contemporary condensed matter physics such as skyrmion crystals, noncollinar magnetic structures in noncentrosymmetric compounds, magnetic/electronic phase separation, and vortex lattices in type-II superconductors. Special attention is paid not only to the vast variety of magnetic materials and problems where SANS has provided direct insight, but also to the enormous progress made regarding the micromagnetic simulation of magnetic neutron scattering.

Permalink: https://www.hzdr.de/publications/Publ-27167
Publ.-Id: 27167


Detecting Beryllium-10 from exotic decays by Accelerator Mass Spectrometry (AMS)

Forstner, O.; Merchel, S.; Lachner, J.; Rugel, G.; Is541 Kollaboration

The one-neutron halo-nucleus 11Be decays via beta-minus to the stable nucleus 11B (t1/2=13.76 s). In rare cases a subsequent emission of a proton leads to the unstable nucleus 10Be. Theoretical calculations predict a branching ratio of this rare decay channel of below 10-7. With the capability of AMS in measuring ultra-low isotopic ratios (10Be/9Be < 10-15) the branching ratio of beta-delayed proton decay to 10Be could be measured for the first time.
A beam of 11Be ions was produced at the radioactive ion beam facility ISOLDE at CERN. After mass separation the ions were implanted in Cu targets. These targets containing the produced 10Be were spiked with low-level 9Be and in the form of BeO chemically prepared as AMS targets at HZDR. The resulting 10Be/9Be ratios were determined via AMS at the VERA laboratory of the University of Vienna. With the known quantity of added 9Be the amount of implanted 10Be was calculated. Due to the low expected branching ratio and the resulting low number of implanted 10Be atoms a high efficiency paired with a low background of the 9Be carrier material was necessary.
To further widen the spectrum of radionuclides measureable by AMS and lowering the detection limits for similar nuclear physics research, we are planning to implement an optical filtering method for selective suppression of isobars by laser photodetachment (LISEL) at the 6 MV tandem accelerator at HZDR.

Keywords: AMS

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

Permalink: https://www.hzdr.de/publications/Publ-27166
Publ.-Id: 27166


Plasmonic nanoparticles embedded in single crystals synthesized by gold ion implantation for enhanced optical nonlinearity and efficient Q-switched lasing

Nie, W. J.; Zhang, Y. X.; Yu, H. H.; Li, R.; He, R. Y.; Dong, N. N.; Wang, J.; Hübner, R.; Böttger, R.; Zhou, S. Q.; Amekura, H.; Chen, F.

We report on the synthesis of embedded gold (Au) nanoparticles (NPs) in Nd:YAG single crystals using ion implantation and subsequent thermal annealing. Both linear and nonlinear absorption of the Nd:YAG crystals have been enhanced significantly due to the embedded Au NPs, which is induced by the surface plasmon resonance (SPR) effect in the visible light wavelength band. Particularly, through a typical Z-scan system excited by a femtosecond laser at 515 nm within the SPR band, the nonlinear absorption coefficients of crystals with Au NPs have been observed to be nearly 5 orders of magnitude larger than that without Au NPs. This giant enhancement of nonlinear absorption properties is correlated with the saturable absorption (SA) effect, which is the basis of passive Q-switching or mode-locking for pulsed laser generation. In addition, the linear and nonlinear absorption enhancement could be tailored by varying the fluence of implanted Au+ ions, corresponding to the NP size and concentration modulation. Finally, the Nd:YAG wafer with embedded Au NPs has been applied as a saturable absorber in a Pr:LuLiF4 crystal laser cavity, and efficient pulsed laser generation at 639 nm has been realized, which presents superior performance to the MoS2 saturable absorber based system. This work opens an avenue to enhance and modulate the nonlinearities of dielectrics by embedding plasmonic Au NPs for efficient pulsed laser operation.

Permalink: https://www.hzdr.de/publications/Publ-27165
Publ.-Id: 27165


OpenFOAM – a contributer‘s point of view

Schlegel, F.; Liao, Y.; Oertel, R.; Meller, R.

Der Vortrag behinhaltet einen Überblick über die Arbeiten im Bereich Mehrphasen-Simulation der Abteilung FWDC mit Hilfe der C++-Bibliothek OpenFOAM.

  • Lecture (Conference)
    German CFD Meeting, 06.03.2018, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27164
Publ.-Id: 27164


Magnetic Properties of Coupled Co/Mo/Co Structures Tailored by Ion Irradiation

Wawro, A.; Kurant, Z.; Jakubowski, M.; Tekielak, M.; Pietruczik, A.; Böttger, R.; Maziewski, A.

Modifications of the magnetic properties of Co=Mo=Co films activated by irradiation with 30-keV Ar and 17-keV Ne ion beams are investigated and compared with the influence of 35-keV Ga ions. This system is magnetized in the sample plane and exhibits a twofold anisotropy. The interlayer coupling of magnetization in as-deposited structures is parallel except for the Mo spacer thickness range between 0.5 and 1.0 nm, where the magnetization of the Co layers is antiparallel oriented. The coupling changes and gradually reduced strength of the ferromagnetic properties are compared for all ion types and discussed as a function of the Mo spacer thickness and the ion fluence. The structural evolution of the studied films with increasing fluence determined from TRIDYN simulations is discussed in relation to the observed magnetic changes.We also propose various types of magnonic crystals that can be fabricated by exploiting the results presented in this work.

Keywords: Ion Irradiation; layered magnetic structures; interlayer coupling; magnetism

Permalink: https://www.hzdr.de/publications/Publ-27163
Publ.-Id: 27163


Localized ion beam mixing using a focused Neon beam for future SET applicatons

Xu, X.; Hlawacek, G.; Wolf, D.; Engelmann, H.-J.; Prüfer, T.; Hübner, R.; Bischof, L.; von Borany, J.; Facsko, S.; Heinig, K.-H.

The increased use of personal computing devices and the Internet of Things (IoT) is accompanied by a demand for a computation unit with extra low energy dissipation. The Single Electron Transistor (SET), which uses a Coulomb island to manipulate the movement of single electrons, is a candidate device for future low-power electronics. However, so far its development is hindered by low-temperature requirements and the absence of CMOS compatibility. By combining advanced top-down lithography with botom-up self-assembly of Si nano dots (NDs) we will overcome this barrier.
In this work, Si NDs—suitable as RT Coulomb islands—are formed via ion beam mixing followed by thermally stimulated phase separation. Spatial control over the ND formation is achieved by using the highly focused Neon beam with a diameter of only 2 nm available in the helium ion microscope (HIM).
The impinging energetic ions will locally mix excess Si from a top Si-layer and into a buried SiO 2 layer which is grown on a Si wafer. This results in a mixing volume small enough for restricted Ostwald ripening and successful single ND formation. The formation of spatially controlled single NDs with a diameter of only 2.2 nm is confrmed by comparing the energy fltered transmission electron microscopy (EFTEM) Si plasmon-loss intensity with simulated plasmon loss images. The conditions for ND formation, namely the dependence on primary energy, irradiation fuence, layer thickness and thermal budget during rapid thermal annealing (RTA), are optimized based on an extensive survey of this multidimensional parameter space. The investigation is guided by TRIDYN simulations of the Si excess in an SiO 2 layer due to ion beam mixing and 3D Kinetic Monte-Carlo (3DkMC) simulation for the phase separation during the thermal treatment. To achieve a CMOS compatible mass fabrication of individual NDs the results are than transferred to Si + broad beam irradiation and cross checked by EFTEM. In this case localization will be achieved by pre-structuring the sample into narrow pillars using lithography.
This work has been funded by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement No. 688072 “IONS SET”.

Keywords: HIM

  • Lecture (Conference)
    picoFIB, 31.01.2018, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-27162
Publ.-Id: 27162


External validation of an NTCP model for acute esophageal toxicity in locally advanced NSCLC patients treated with intensity-modulated 5 (chemo-)radiotherapy

Dankers, F.; Wijsman, R.; Troost, E.; Tissing-Tan, C.; Kwint, M.; Belderbos, J.; de Ruysscher, D.; Hendriks, L.; de S.-Oei, L.-F.; Rodwell, L.; Dekker, A.; Monshouwer, R.; Hoffmann, A.; Bussink, J.

Purpose: We externally validated a previously established multivariable normal-tissue complication probability (NTCP) model for Grade ≥2 acute esophageal toxicity (AET) after intensity-modulated (chemo-)radiotherapy or volumetric-modulated arc therapy for locally advanced non-small cell lung cancer.
Experimental design: A total of 603 patients from five cohorts within four different Dutch institutes were included. Using the NTCP model, containing predictors concurrent chemoradiotherapy, mean esophageal dose, gender and clinical tumor stage, the risk of Grade ≥2 AET was estimated per patient and model discrimination and (re)calibration performance was evaluated for all cohorts.
Results: Five validation cohorts experienced higher incidence of Grade ≥2 AET compared to the training cohort (49.3%-70.2% vs 35.6%; borderline significant for one cohort, highly significant for four cohorts). For three cohorts, discriminative performance was similar to the training cohort (area under the curve (AUC) 0.81-0.89 vs 0.84). In the two remaining cohorts the model showed poor discriminative power (AUC 0.64 and 0.63). Reasonable calibration performance was observed in two cohorts, and recalibration further improved performance in all three cohorts with good discrimination. Recalibration for the two poorly discriminating cohorts did not improve performance.
Conclusions: The NTCP model for AET prediction was successfully validated in three out of five patient cohorts. The model did not perform well in two cohorts, which included patients receiving substantially 105 different treatment.
Before applying the model in clinical practice validation of discrimination and calibration performance on a local cohort is recommended. Recalibration of the model is advised to match predicted probabilities to locally observed frequencies of AET.

Permalink: https://www.hzdr.de/publications/Publ-27161
Publ.-Id: 27161


Charge exchange and energy loss of slow highly charged ions transmitted through 2D materials

Wilhelm, R. A.; Creutzburg, S.; Schwestka, J.; Gruber, E.; Kozubek, R.; Lehnert, T.; Leiter, R.; Heller, R.; Krasheninnikov, A.; Facsko, S.; Kaiser, U.; Kotakoski, J.; Schleberger, M.; Aumayr, F.

Slow highly charged ions carry a large amount (several 10 keV) of potential energy, which gets released by target excitation and secondary particle emission upon impact on a solid surface. The energy release can trigger permanent material modifications on semi-conducting and insulating materials [1]. To understand the energy release mechanism and get information on it’s time scale, we use freestanding 2D materials, limiting the interaction time of the ions upon transmission to a few femtoseconds. We detect the ions after the interaction by means of charge state, energy, and angle resolved detection techniques. Further, we detect emitted secondary electrons in coincidence with a particular charge exchange.
Using freestanding single layer graphene, our experimental findings revealed an ultrafast charge exchange and projectile de-excitation mechanism [2,3]. We also determined the in-plane current density in the material, which is transiently active to supply electrons to the ion, to be in the order of 1012A/cm2. Still, graphene is able to sustain these large current densities for a fs-time-scale without rupture. Here we go one step further and present results of ion transmission spectroscopy of single layer hBN and MoS2, which are insulating and semi-conducting, respectively.

  • Invited lecture (Conferences)
    IBMM 2018 - International Conference on Ion Beam Modification of Materials, 24.-29.06.2018, San Antonio, TX, USA

Permalink: https://www.hzdr.de/publications/Publ-27160
Publ.-Id: 27160


From the creation of carbon nanomembranes in a low energy electron microscope to perforation with highly charged ions

Wilhelm, R. A.; Neumann, C.; Küllmer, M.; Winter, A.; Turchanin, A.

Carbon nanomembranes are materials with only nm thickness, which can be used as freestanding membranes in filtration applications. They exhibit interesting properties as they can be e.g. transformed into (semi-)metallic graphene, but are insulating in their pristine phase. Using a Low Energy Electron Microscope allowed us to follow the formation of a carbon nanomembrane by electron-induced cross-linking of a self-assembled monolayer in-situ and in real-time. Releasing the membrane from the substrate and irradiating it with highly chared ions leads finally to regularely sized nanopores.

  • Lecture (others)
    Seminar AG Turchanin, 11.01.2018, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27159
Publ.-Id: 27159


Synemin is a novel co-regulator of non-homologous end joining in head and neck cancer cells

Deville, S. S.; Förster, S.; Cordes, N.

Introduction:
Cancer therapy resistance is one of the major obstacles for higher cure rates. Novel key players of the resistome are focal adhesion proteins (FAPs). As FAPs are critically involved in DNA repair, we here characterize the yet unknown function of the FAP and intermediate filament protein Synemin (SYN) as a novel DNA repair regulator and potential cancer drug target in head and neck squamous cell carcinoma (HNSCC).

Methods and materials:
Our novel 3D High Throughput esiRNA Screen (3DHTesiRNAs) using laminin-rich extracellular matrix (lrECM) was conducted to measure radiation-induced residual DNA double strand breaks (DSBs; foci assay) and clonogenic radiation survival in UTSCC15-pEGFP-53BP1 cells. Validations were performed in 10 additional HNSCC cell lines in 3D lrECM. Upon SYN depletion, DSB repair reporter assays for non-homologous end joining (NHEJ) and homologous recombination (HR) as well as Western Blotting for protein expression and phosphorylation were carried out. SYN depleted cells with and without irradiation were analyzed for kinase activity profiling (PamGene) and protein interactome determination using a sequential immunoprecipitation/mass spectrometry approach.

Results and Discussion:
Among the targets found in the 3DHTesiRNAs, SYN turned out as one of the top FAP candidate determinants of HNSCC cell survival. SYN silencing radiosensitized HNSCC cells, while its exogenous overexpression induced radioprotection. We found an increased SYN/chromatin interaction and a marked perinuclear SYN accumulation post irradiation. Intriguingly, SYN depletion elicited a 40% reduction in NHEJ activity without affecting HR or alt-EJ. In line, ATM, DNA-PKcs and c-Abl phosphorylation as well as Ku70 expression strongly declined in SYN depleted and irradiated cells relative to controls and, in contrast, to the rescue of these protein modifications by SYN overexpression. Single, double and triple depletion of SYN, DNA-PKcs and c-Abl resulted in similar radiosensitization and DSB levels as observed for SYN only, suggesting its upstream role. In the kinome analysis we observed variable changes in the serine/threonine kinases, in contrast to the tyrosine kinases with a pronounce reduced kinase activity after SYN silencing.

Conclusion:
Our data suggest the intermediate filament SYN as a new important determinant of DNA repair, tyrosine kinome and radioresistance of HNSCC cells. These observations further support the notion that DNA repair is controlled by cooperative interactions between nuclear and cytoplasmic proteins.

Keywords: synemin; radiobiology

  • Poster
    EACR 2018 - 25th Biennial Congress of the European Association for Cancer Research, 30.06.-03.07.2018, Amsterdam, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-27158
Publ.-Id: 27158


beta8 integrin critically contributes to pancreatic cancer cell radiochemoresistance and intracellular vesicle trafficking under stress conditions

Lee, W.-C.; Jin, S.; Cordes, N.

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies in the world and has a 5-year relative overall survival rate of less than 5%. Thus, there is a great need for functional targeting d strategies. As cell-matrix adhesion is essential for the survival, invasion and therapy resistance, we sought to identify the function of 117 focal adhesion proteins (FAP) in PDAC cell radiochemoresistance. Intriguingly, 8 integrin turned out to be one of the most potential novel targets in PDAC.
Material and methods: We performed a 3D endoribonuclease-prepared siRNA (esiRNA)-based high throughput screening (3DHTesiS) in PDAC cell cultures (established and patient-derived (PDC)) grown in laminin-rich extracellular matrix (IrECM). In addition to characterizing 8 integrin expression, distribution and co-localization with other cellular organelles such as golgi apparatus, clonogenic survival assays were performed upon esiRNA-mediated knockdown, X-ray irradiation (6 Gy single dose) and gemcitabine. Fiji software was used to determine Peason’s correlation coefficient, vesicle distribution and expression patterns upon irradiation or gemcitabine. An inhibitor screen was conducted to identify pathway involved in changes of 8 integrin localization upon treatment.
Results: We identified a series of novel targets including 8 integrin. Without cytotoxicity, 8 integrin depletion elicited radiochemosensitization in PDAC, PDCs cell lines and reduced sphere formation and 3D invasion into collagen-I. Intriguingly, we found 8 integrin located in perinuclear area where it colocalized with the cis-Golgi matrix protein GM130. Upon irradiation and gemcitabine, 8 integrin dissociated from the perinuclear region and spread throughput the cytosol without enhanced localization to exosomes; a process abrogated by antimycin A or oligomycin pre-treatment.
Summary: Our findings, generated in 3D lrECM PDAC cell ccultures, suggest 8 integrin as a novel determinant of PDAC radiochemoresistance. Moreover, 8 integrin may, although not found in the cell membrane to facilitate cell adhesion, a critical role in intracellular vesicle trafficking under stress conditions. Ongoing work will unravel the underlying mechanisms how 8 integrin is controlling cytoplasmic and nuclear survival pathways.

Keywords: beta8 integrin; radiotherapy

  • Poster
    EACR 2018 - European Association for Cancer Research, 30.06.-03.07.2018, Amsterdam, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-27157
Publ.-Id: 27157


Switching the uniaxial magnetic anisotropy by ion irradiation induced compensation

Yuan, Y.; Amarouche, T.; Xu, C.; Rushforth, A.; Boettger, R.; Edmonds, K.; Campion, R.; Gallagher, B.; Helm, M.; von Bardeleben, H.; Zhou, S. Q.

In the present work, the uniaxial magnetic anisotropy of GaMnAsP is modified by helium ion irradiation. According to the micro-magnetic parameters, e.g. resonance fields and anisotropy constants deduced from ferromagnetic resonance measurements, a rotation of the magnetic easy axis from out-of-plane [001] to in-plane [100] direction is achieved. From the application point of view, our work presents a novel avenue in modifying the uniaxial magnetic anisotropy in GaMnAsP with the possibility of lateral patterning by using lithography or focused ion beam.

Permalink: https://www.hzdr.de/publications/Publ-27156
Publ.-Id: 27156


Electronic phase separation in insulating (Ga, Mn) As with low compensation: super-paramagnetism and hopping conduction

Yuan, Y.; Wang, M.; Xu, C.; Hübner, R.; Böttger, R.; Jakiela, R.; Helm, M.; Sawicki, M.; Zhou, S.

In the present work, low compensated insulating (Ga,Mn)As with 0.7% Mn is obtained by ion implantation combined with pulsed laser melting. The sample shows variable-range hopping transport behavior with a Coulomb gap in the vicinity of the Fermi energy, and the activation energy is reduced by an external magnetic field. A blocking super-paramagnetism is observed rather than ferromagnetism. Below the blocking temperature, the sample exhibits a colossal negative magnetoresistance. Our studies confirm that the disorder-induced electronic phase separation occurs in (Ga,Mn)As samples with a Mn concentration in the insulator–metal transition regime, and it can account for the observed superparamagnetism and the colossal magnetoresistance.

Permalink: https://www.hzdr.de/publications/Publ-27155
Publ.-Id: 27155


Investigation of a possible electronic phase separation in the magnetic semiconductors Ga1−xMnxAs and Ga1−xMnxP by means of fluctuation spectroscopy

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

We present systematic temperature-dependent resistance noise measurements on a series of ferromagnetic Ga1−xMnxAs epitaxial thin films covering a large parameter space in terms of the Mn content x and other variations regarding sample fabrication. We infer that the electronic noise is dominated by switching processes related to impurities in the entire temperature range. While metallic compounds with x>2% do not exhibit any significant change in the low-frequency resistance noise around the Curie temperature TC, we find indications for an electronic phase separation in films with x<2% in the vicinity of TC, manifesting itself in a maximum in the noise power spectral density. These results are compared with noise measurements on an insulating Ga1−xMnxP reference sample, for which the evidence for an electronic phase separation is even stronger and a possible percolation of bound magnetic polarons is discussed. Another aspect addressed in this work is the effect of ion-irradiation-induced disorder on the electronic properties of Ga1−xMnxAs films and, in particular, whether any electronic inhomogeneities can be observed in this case. Finally, we put our findings into the context of the ongoing debate on the electronic structure and the development of spontaneous magnetization in these materials.

Permalink: https://www.hzdr.de/publications/Publ-27154
Publ.-Id: 27154


Time of Flight Backscatter and Secondary Ion Spectrometry in a Helium Ion Microscope

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

Helium Ion Microscopy (HIM) utilizes a Gas Field Ion Source (GFIS) to create a Helium or Neon ion beam with a diameter better than 0.5 nm and 1.8 nm, respectively. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating. The latter specimens are typically found in the fields of biosciences, MEMS/NEMS technology, catalyst research and many others. The availability of He and Ne ions with either low or moderate sputter yields, allow direct write nano-structuring with a precision below 10 nm in the HIM [1, 2].
However, the existing GFIS based focused ion beam (FIB) tools suffer from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. While HIM technology is relatively young several efforts have been made to add such an analytic capability to the technique. So far, ionoluminescence [1, 3], backscattering spectrometry (BS) [1, 4, 5], and secondary ion mass spectrometry (SIMS) using a magnetic sector [6] or time of flight (TOF) setup have been demonstrated [4].
After a brief introduction to HIM itself and a summary of the existing approaches I will focus on our own time of flight based analytic approaches. TOF-HIM is enabled by using a fast blanking electronics to chop the primary beam into pulses with a minimal length of only 20 ns. In combination with an multichannel-plate based stop detector this enables TOF backscatter spectrometry (TOF-BS) using He ions at an energy of only 30 keV. The achieved lateral resolution is 54 nm and represents a world record for spatially resolved backscattering spectrometry. The energy resolution has been measured to be 1.5 keV (5%). This is sufficient to separate most of the elements (see fig. 1) and allows the detection of thin surface layers formed from heavy elements. The results will be compared to the theoretical reachable lateral and energy resolution and the limiting experimental and physical constraints of this approach will be reviewed.
Finally first TOF-SIMS results obtained with a very simple experimental configuration will be presented. Based on the findings obtained with this poor man’s version of TOF-SIMS setup a dedicated extraction optics for secondary ions has been designed and tested. This revised setup can be operated in point and shoot mode to obtain high resolution SIMS data or in imaging mode to obtain element maps of the specimen surface. First experiments revealed a very high relative transmission of up to 76% which is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. For m/q ≤ 80 u a Dm ≤ 0.3 u has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g.: C, N). The lateral resolution of 8 nm has been evaluated using the knife edge method and a 75%/25% criterion which represents a world record for spatially resolved secondary ion mass spectrometry.

Keywords: HIM

  • Invited lecture (Conferences)
    Microscopy and Microanalysis, 05.-09.08.2018, Baltimore, USA
    DOI: 10.1017/S1431927618004506
  • Lecture (Conference)
    CAARI - 25th Conference on Application of Accelerators in Research and Industry, 13.-17.08.2018, Fort Worth, USA
  • Lecture (Conference)
    AVS International Symposium & Exhibition, 21.-26.10.2018, Long Beach, USA

Permalink: https://www.hzdr.de/publications/Publ-27153
Publ.-Id: 27153


Harnessing the Coordination Chemistry of 1,4,7-Triazacyclononane for Biomimicry and Radiopharmaceutical Applications

Joshi, T.; Kubeil, M.; Nsubuga, A.; Singh, G.; Gasser, G.; Stephan, H.

TACN-based mono- and poly-nuclear metal complexes have found extensive use as biological mimics for understanding the structural and operational aspects of complex natural systems. Their coordination flexibility has also provided researchers access to a vast library of radiometal binding motifs that display excellent thermodynamic stability and kinetic inertness upon metal complexation. Synthetic modification on the TACN backbone has yielded ligands that can form metal complexes with coordination geometries well-suited for these applications. In particular, Leone Spiccia’s research has played a significant role in accelerating the progress in these two fields. With a focus on providing an overview of his contributions to the biomimicry and radiopharmaceutical disciplines, this minireview uses relevant examples to put in perspective the utility of macrocyclic coordination chemistry for biological inorganic chemistry applications.

Keywords: 1; 4; 7-Triazacyclononane; Coordination Chemistry; Metal complexes; Metallobiosites; Radiopharmaceuticals

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-27152
Publ.-Id: 27152


RODARE Logos

Frust, T.

RODARE (Rossendorf Data Repository) is the institutional data repository at Helmholtz-Zentrum Dresden-Rossendorf. The initial logos of the platform are collected in this upload and are available as Open Access.

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-02-28
    DOI: 10.14278/rodare.1
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-27151
Publ.-Id: 27151


Exploration targeting by multivariate compositional extrema

van den Boogaart, K. G.; Tolosana Delgado, R.; Mckinley, J.

Many different exploration targeting methods exist, like weights of evidence; inferring the probability of a deposit based on a local geology; genetic models identifying favourable conditions; and fractal based methods trying to identify regions of high value of certain fractal measures. This contribution proposes an approach potentially useful for deposits under cover: to find locations which are locally extrema on a certain spatial scale.

While surface features typically dominate the absolute values of measurements, covered objects can still produce large halos of much smaller absolute value. Our method thus looks for halos at a certain spatial scale. It does so by estimating a band filtered negative of the second derivative of the random field from spatial data, either from regular data or from a geostatistical analysis. In a certain sense this is looking for local peakiness, but filters the high frequency noise from surface effects by means of signal processing methods. The local maxima and their surrounding are then taken as the potential targets.

In a multivariate surface dataset, as provided by a geochemical exploration campaign, such a filter can be applied to the complete vector (i.e. the clr or ilr transformed compositions). This results is a nought mean compositional random field. Furthermore the bandwidth of the filter can be varied and considered as a third dimension. In this 3D map, we can again find various types of extremal points. The location on the 2D geographic space of the extreme value of the signal depends on the location of the deposit. Furthermore, the location on the third dimension relates to the deposit size or depth, and its compositional value describes its geochemical properties.

We demonstrate the effects of the method with a regional geochemical exploration dataset.

Keywords: Potential Mapping; Geostatistics; Signal Analysis

  • Lecture (Conference)
    IAMG 2018 - 19th Annual Conference of the International Association for Mathematical Geosciences, 02.-09.09.2018, Olomouc, Česká republika
  • Contribution to proceedings
    IAMG 2018 - 19th Annual Conference of the International Association for Mathematical Geosciences, 02.-09.09.2018, Oulomoc, Česká republika
    Short Abstracts of IAMG2018 – The 19th Annual Conference of the International Association for Mathematical Geosciences, Olomouc, Czech Republic: IAMG, 978-80-270-4612-6

Permalink: https://www.hzdr.de/publications/Publ-27150
Publ.-Id: 27150


Analyse der Bildrekonstruktion auf Basis von irregulären Gittern für die Untersuchung von Mehrphasenströmungen mittels ultraschneller Röntgen-Computertomographie

Pfahl, A.

Hauptbestandteil dieser Arbeit ist die ausführliche Evaluation der computertomographischen Bildgebung auf diversen irregulären Gitterstrukturen. Obwohl das derzeitige Standardverfahren der Bildrekonstruktion, die gefilterte Rückprojektion auf regulären Pixelgittern, sich im Besonderen für einen schnellen Bildgebungsprozess und die Verarbeitung großer Datenmengen eignet, so verfügen die resultierenden Bilder aufgrund der dabei notwendigen Interpolationsschritte über eine Bildqualität, die den Anforderungen in einigen Anwendungsgebieten nicht genügt. Aus diesem Grund rückt zur Vermeidung bzw. Reduzierung der Interpolationsfehler ein alternativer Lösungsansatz, basierend auf algebraischen Rekonstruktionstechniken, unter Einbezug der realen Geometrie des bildgebenden Systems, der dadurch bedingten maximal erreichbaren
Ortsauflösung sowie Vorwissen über das Untersuchungsobjekt mithilfe irregulärer Rekonstruktionsgitter in den Fokus.
Da die Erzeugung irregulärer Gitterstrukturen zumeist mit einem hohen Rechen- und Speicheraufwand verbunden ist, müssen effiziente Algorithmen erarbeitet und implementiert werden. Auch die aus den Gittern resultierenden stark unterbestimmten Gleichungssysteme, für die die üblicherweise zum Einsatz kommenden algebraischen Verfahren keine respektablen Lösungen hervorbringen, stellen eine Herausforderung dar. Daher müssen alternative Algorithmen betrachtet werden. Die Beurteilung der irregulären Gitter und somit des vom Standard abweichenden Konzeptes erfolgt schließlich anhand globaler und lokaler Bildgütekriterien und stets im Vergleich zur Rekonstruktion auf regulären Pixelgittern in der Hoffnung, eine signifikante Qualitätssteigerung in den rekonstruierten Bildern verzeichnen zu können.

Keywords: ultraschnell; Röntgen; Computertomographie; Bildrekonstruktion

  • Master thesis
    Universität zu Lübeck, 2018
    Mentor: Martina Bieberle, Thorsten M. Buzug
    73 Seiten

Permalink: https://www.hzdr.de/publications/Publ-27149
Publ.-Id: 27149


Virtual mineral processing simulation in software MLALookUP

Krupko, N.; Kern, M.; van den Boogaart, K. G.

Designing a more effective and productive mineral processing plant is a major objective for engineers and researchers. An optimized flowsheet produces one or more concentrates with high recovery and grade of the target mineral(s) and low impurities of minerals that reduce the value of the concentrate. In the initial stages of flowsheet development, lab-scale experiments are prepared and meticulously reviewed. This process is very time-consuming and cost-intensive. Furthermore, the results of these experiments can be inconclusive.
To overcome these problems, a virtual mineral processing simulation software called MLALookUP was developed. The simulation model helps to predict the performance of a processing plant and to find the optimal order of processing techniques to reach the targeted concentrate composition. MLALookUP uses data from mineral liberation analysis (MLA), a tool that generates and analyses high-resolution images with compositional particle information by combining scanning electron microscopy and energy-dispersive X-ray spectroscopy.
The software uses geometallurgical properties of the material that was analyzed with MLA. Depending on these properties, MLALookUP runs virtual separation machines, which are prepared and analyzed by the user on the basis of threshold parameters. Starting with the feed material, a sequence of virtual separation machines simulates all processing steps until the final concentrate. In this way, the values of grade, recovery and mass proportion are predicted in each stream. The software gives the possibility to vary processing threshold parameters and to define the optimal order of processing experiments in a flowsheet.

  • Contribution to proceedings
    IAMG2018 - 19th Annual Conference of the International Association for Mathematical Geosciences, 02.-08.09.2018, Olomouc, Česká republika
    Short Abstracts of IAMG2018 – The 19th Annual Conference of the International Association for Mathematical Geosciences, Olomouc, Czech Republic: IAMG, 978-80-270-4612-6

Permalink: https://www.hzdr.de/publications/Publ-27147
Publ.-Id: 27147


The metrics of calorimetry in radionuclide-dependent plant metabolism

Fahmy, K.; Sachs, S.; Bok, F.; Geipel, G.; Oertel, J.

Radioecological studies depend on the quantitative toxicity assessment of environmental radionuclides. At low dose exposure, the life span of affected organisms is barely shortened enabling the transfer of radionuclides through an almost intact food chain. Lethality-based toxicity estimates are not adequate in this regime because they require higher concentrations. However, increased radionuclide concentration alters its speciation, rendering the extrapolation to the low dose exposure chemically inconsistent. Here, we demonstrate that microcalorimetry provides a sensitive real-time monitor of toxicity of uranium (in the U(VI) oxidation state) in a plant cell model of Brassica napus. We introduce the calorimetric descriptor “metabolic capacity” and show that it correlates with enzymatically determined cell viability. It is independent of physiological models and robust against the naturally occurring fluctuations in the metabolic response to U(VI) of plant cell cultures. In combination with time-resolved laser-induced fluorescence spectroscopy and thermodynamic modeling, we show that the plant cell metabolism is affected predominantly by hydroxo-species of U(VI) with an IC50 threshold of ~90 µM. The data emphasize the yet little exploited potential of microcalorimetry for the speciation-sensitive ecotoxicology of radionuclides.

Keywords: microcalorimetry; time-resolved laser fluorescence; metabolism; uranium; ecology

  • Lecture (Conference)
    XX Conference of International Society for Biological Calorimetry (ISBC 2018), 13.-15.06.2018, Krakow, Polen

Permalink: https://www.hzdr.de/publications/Publ-27146
Publ.-Id: 27146


Probing charged lepton flavor violation with the Mu2e experiment

Mueller, S. E.

The Mu2e experiment, currently under construction at the Fermi National Accelerator Laboratory near Chicago, will search for the neutrinoless conversion of muons to electrons in the field of an aluminum nucleus. This charged lepton flavor-changing process is highly suppressed in the Standard Model and therefore undetectable. There exist however scenarios for physics beyond the Standard Model that predict small but observable rates.The Mu2e experiment aims at a sensitivity four orders of magnitude better than existing experiments. This is achieved by a rigorous control of all backgrounds that could mimic the monoenergetic signal electron.

The design and status of the Mu2e experiment will be presented. In addition, I will highlight the results from several test runs carried out at HZDR's ELBE facility to study the radiation hardness and performance of components for the Mu2e calorimeter and for the detector that monitors the rate of stopped muons in the aluminum target.

Keywords: charged lepton flavor violation; muon to electron conversion; MU2E; ELBE

  • Lecture (Conference)
    DPG Spring Meeting 2018, 26.02.-02.03.2018, Bochum, Germany

Permalink: https://www.hzdr.de/publications/Publ-27145
Publ.-Id: 27145


Cost-competitiveness of siderophores in recovering of critical metals from waste streams

Jain, R.; Pollmann, K.

Siderophores are known for their specificity and sensitivity towards the critical metals whose supply is at risk in future. Thus, the use of these siderophores for the recovery of these critical metals from their low concentrated wastewater is very attractive options. However, there is no detailed cost estimation for their application in wastewater. This study detailed the economic feasibility of application of desferrioxamines for the recovery of gallium from industrial wastewater. The study looked into the factors such as regeneration recycles, downstream processing, cost of gallium, operational cost of the technology and cost & grade of desferrioxamine production. The calculations showed that minimum 10 regeneration cycles are required for the cost-effectiveness of the technology. Further, siderophores, at the present level of technology, are easily economically feasible for metals costing 300 € per Kg (indium and dysprosium).

  • Lecture (Conference)
    Sustainable mineral 2018, 14.-15.06.2018, Windhoek, Namibia

Permalink: https://www.hzdr.de/publications/Publ-27144
Publ.-Id: 27144


Formation and Aggregation of ZrO2 Nanoparticles on Muscovite (001)

Qiu, C.; Eng, P. J.; Hennig, C.; Schmidt, M.

The aggregation of nanoparticles is a key step in the formation of solid phases and a controlling factor for the behavior of suspended nanoparticles in solution. Using a charged mineral surface [muscovite (001)] we apply the surface X-ray diffraction techniques Crystal Truncation Rod (CTR) measurements and Resonant Anomalous X-ray reflectivity (RAXR) to investigate the aggregation process of Zr nanoparticles at the sub-nm scale. The aggregation process was studied as a function of ionic strength (0, 1, 10, and 100 mM NaCl), and the interfacial particles were characterized by CTR/RAXR and AFM. The observations are consistent with an aggregation process that follows a multi-step mechanism, which starts with the 3D aggregation of primary building units to form nanosheets. These sheets continue to grow through addition of building units to their reactive edges at higher ionic strength. Once the size and concentration of aggregates is sufficient, “face-to-face” stacking of nanosheets becomes the preferred aggregation mechanism as this minimizes the electrostatic repulsion of the charge that accumulates along nanosheet edges.

Keywords: Zr; muscovite; X-ray surface diffraction

Permalink: https://www.hzdr.de/publications/Publ-27143
Publ.-Id: 27143


Experimental Investigation on the Heat Transfer of Innovative Finned Tubes for Passive Cooling of Nuclear Spent Fuel Pools

Unger, S.; Beyer, M.; Arlit, M.; Hampel, U.

In beyond-design-basis accidents active spent fuel pool cooling by pumps may not be possible. Promising concepts to enhance the reliability of nuclear power plants are passive heat removal systems using air as an unlimited heat sink. However the major drawbacks of such systems are small heat transfer coefficients, particularly on air side. Thus finned tube bundle heat exchangers are used to extend the heat transfer surface. However, conventional heat exchangers are limited in heat transfer capacity. For this purpose an innovative fin design was developed and experimentally investigated. A significant heat transfer enhancement was found for a moderate flow disturbance.

  • Contribution to proceedings
    49th Annual Meeting on Nuclear Technology, 29.-30.05.2018, Berlin, Deutschland
    Proceedings of the 49th Annual Meeting on Nuclear Technology
  • Lecture (Conference)
    49th Annual Meeting on Nuclear Technology, 29.-30.05.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-27142
Publ.-Id: 27142


High-field magnetoelasticity of Tm2Co17 and comparison with Er2Co17

Andreev, A. V.; Zvyagin, A. A.; Skourski, Y.; Yasin, S.; Zherlitsyn, S.

Acoustic properties (ultrasound velocity and attenuation) and magnetostriction were measured in pulsed fields up to 60 T applied along the c axis of Tm2Co17 single crystal. Similar to Er2Co17, the transition in Tm2Co17 is accompanied by clear anomalies in the sound velocity. The observed 0.3% jump of the sound velocity at the transition is negative in Tm2Co17, whereas it is positive in Er2Co17. The magnetostriction at the transition also differs very much from that in Er2Co17. In Tm2Co17, the transition is accompanied by a smooth minimum of 0.15×10-4 in longitudinal magnetostriction whereas in Er2Co17 by a very sharp expansion of much larger magnitude (1.2×10-4). In the transverse mode, the effect in Tm2Co17 looks as very broad minimum of low amplitude (<0.1×10-4) whereas in Er2Co17 as very sharp and large shrinkage (2.6×10-4). Thus, both the magnetoacoustics and magnetostriction are rather different in Tm2Co17 and Er2Co17. This supports different nature of the field-induced transitions in these compounds.

Permalink: https://www.hzdr.de/publications/Publ-27141
Publ.-Id: 27141


Unconventional field induced phases in a quantum magnet formed by free radical tetramers

Saúl, A.; Gauthier, N.; Askari, R. M.; Coté, M.; Maris, T.; Reber, C.; Lannes, A.; Luneau, D.; Nicklas, M.; Law, J. M.; Green, E. L.; Wosnitza, J.; Bianchi, A. D.; Feiguin, A.

We report experimental and theoretical studies on themagnetic and thermodynamic properties ofNIT-2Py, a free radical based organic magnet. From magnetization and specific-heat measurements we establish the temperature versus magnetic field phase diagram which includes two Bose-Einstein condensates (BEC) and an infrequent half-magnetization plateau. Calculations based on density functional theory demonstrate that magnetically this system can be mapped to a quasi-two-dimensional structure of weakly coupled tetramers. Density matrix renormalization group calculations show the unusual characteristics of the BECs where the spins forming the low-field condensate are different than those participating in the high-field one.

Permalink: https://www.hzdr.de/publications/Publ-27140
Publ.-Id: 27140


Multiplet of skyrmion states on a curvilinear defect: Reconfigurable skyrmion lattices

Kravchuk, V. P.; Sheka, D. D.; Kákay, A.; Volkov, O. M.; Rößler, U. K.; van den Brink, J.; Makarov, D.; Gaididei, Y.

Typically, the chiral magnetic Skyrmion is a single-state excitation. Here we propose a system, where multiplet of Skyrmion states appears and one of these states can be the ground one. We show that the presence of a localized curvilinear defect drastically changes the magnetic properties of a thin perpendicularly magnetized ferromagnetic film. For a large enough defect amplitude a discrete set of equilibrium magnetization states appears forming a ladder of energy levels. Each equilibrium state has either a zero or a unit topological charge; i.e., topologically trivial and Skyrmion multiplets generally appear. Transitions between the levels with the same topological charge are allowed and can be utilized to encode and switch a bit of information. There is a wide range of geometrical and material parameters, where the Skyrmion level has the lowest energy. Thus, periodically arranged curvilinear defects can result in a Skyrmion lattice as the ground state.

Keywords: Skyrmions; curvilinear defects

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Permalink: https://www.hzdr.de/publications/Publ-27139
Publ.-Id: 27139


Clinical translation and regulatory aspects of CAR/TCR-based adoptive cell therapies-the German Cancer Consortium approach.

Krackhardt, A. M.; Anliker, B.; Hildebrandt, M.; Bachmann, M.; Eichmüller, S. B.; Nettelbeck, D. M.; Renner, M.; Uharek, L.; Willimsky, G.; Schmitt, M.; Wels, W. S.; Schüssler-Lenz, M.

Adoptive transfer of T cells genetically modified by TCRs or CARs represents a highly attractive novel therapeutic strategy to treat malignant diseases. Various approaches for the development of such gene therapy medicinal products (GTMPs) have been initiated by scientists in recent years. To date, however, the number of clinical trials commenced in Germany and Europe is still low. Several hurdles may contribute to the delay in clinical translation of these therapeutic innovations including the significant complexity of manufacture and non-clinical testing of these novel medicinal products, the limited knowledge about the intricate regulatory requirements of the academic developers as well as limitations of funds for clinical testing. A suitable good manufacturing practice (GMP) environment is a key prerequisite and platform for the development, validation, and manufacture of such cell-based therapies, but may also represent a bottleneck for clinical translation. The German Cancer Consortium (DKTK) and the Paul-Ehrlich-Institut (PEI) have initiated joint efforts of researchers and regulators to facilitate and advance early phase, academia-driven clinical trials. Starting with a workshop held in 2016, stakeholders from academia and regulatory authorities in Germany have entered into continuing discussions on a diversity of scientific, manufacturing, and regulatory aspects, as well as the benefits and risks of clinical application of CAR/TCR-based cell therapies. This review summarizes the current state of discussions of this cooperative approach providing a basis for further policy-making and suitable modification of processes.

Keywords: CAR/TCR-transgenic T cells; Cellular therapy; Clinical translation; Regulatory aspects

Permalink: https://www.hzdr.de/publications/Publ-27138
Publ.-Id: 27138


On the insulator-to-metal transition in titanium-implanted silicon

Liu, F.; Wang, M.; Berencén, Y.; Prucnal, S.; Engler, M.; Hübner, R.; Yuan, Y.; Heller, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Hyperdoped silicon with deep level impurities has attracted much research interest due to its promising optical and electrical properties. In this work, single crystalline silicon supersaturated with titanium is fabricated by ion implantation followed by both pulsed laser melting and flash lamp annealing. The decrease of sheet resistance with increasing Ti concentration is attributed to a surface morphology effect due to the formation of cellular breakdown at the surface and the percolation conduction at high Ti concentration is responsible for the metallic-like conductivity. The insulator-to-metal transition does not happen. However, the doping effect of Ti incorporation at low concentration is not excluded, which might be responsible for the sub-bandgap optical absorption reported in literature.

Keywords: Hyperdoped silicon; deep level impurities; flash lamp annealing; insulator-to-metal transition

Permalink: https://www.hzdr.de/publications/Publ-27136
Publ.-Id: 27136


Intensity-modulated proton therapy decreases dose to organs at risk in low-grade glioma patients: results of a multicentric in silico ROCOCO trial

Eekers, D.; Roelofs, E.; Cubillos-Mesias, M.; Niel, C.; Smeenk, R.; Minken, A.; Granzier, M.; Janssens, G.; Kaanders, J.; Lambin, P.; Troost, E. G. C.

Background and Purpose
Patients with low-grade glioma (LGG) have a prolonged survival expectancy due to better discriminative tumor classification and multimodal treatment. Consequently, longterm treatment toxicity, e.g., neurocognitive function, gains importance. Contemporary radiotherapy techniques such as intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), Tomotherapy (TOMO) and intensity-modulated proton therapy (IMPT) enable high-dose irradiation of the target but they differ regarding delivered dose to organs at risk (OARs). The aim of this comparative in silico study was to determine the dosimetric differences in delivered doses to the OARs.
Material and Methods
Imaging datasets of twenty-five LGG patients having undergone postoperative radiotherapy were included. For each of these patients, in silico treatment plans to a total dose of 50.4Gy to the target volume were generated for the four treatment modalities investigated (i.e., IMRT, VMAT, TOMO, IMPT). Resulting treatment plans were analyzed regarding dose to target and surrounding OARs comparing IMRT, TOMO and IMPT to VMAT (reference technique).
Results
In total, 100 treatment plans for the twenty-five patients were analyzed. Compared to VMAT the IMPT mean dose (Dmean) for 9 out of 10 (90%) OARs was statistically significantly (p<0.02) reduced, for TOMO 3/10 (30%) and 1/10 (10%) for IMRT. IMPT was the prime modality reducing dose to the OARs followed by TOMO. The pituitary gland was best spared by TOMO (Table 2).
Conclusions
The low dose volume to the majority of OARs was significantly reduced when using IMPT compared to VMAT. Whether this will lead to a significant reduction in neurocognitive decline is to be determined in carefully designed future clinical trials.

Keywords: In silico planning study; Low Grade Glioma; Photon and proton irradiation; IMPT; VMAT; IMRT; TOMO

Permalink: https://www.hzdr.de/publications/Publ-27134
Publ.-Id: 27134


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