Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34121 Publications

CFD Studies on the gas-liquid flow in the swirl generating device

Putra, R. A.; Schäfer, T.; Neumann, M.; Lucas, D.

In this work, CFD simulations using the Euler-Euler approach were performed to model the gas-liquid flow in a swirl-generating device. The computational work was based on experiments, which are conducted in a vertical pipe packed with a static swirl element. Measurements of gas volume fractions at several planes within the swirl element were taken using high-resolution gamma-ray computed tomography (HireCT).
The simulations were carried out for the experimental conditions with defined inlet gas volumetric flow rates of 5 and 10 %. The profile of several key parameters (e.g pressure, liquid and gas velocities and gas fraction) are used to understand the flow behavior inside the device. The radial gas phase distribution obtained from the simulations assuming different mono-disperse and bi-modal bubble sizes is compared against the experimental results. The significant influence of the selected bubble sizes on the profile is shown and discussed within this paper. In general, the radial profile of gas fraction is well captured by the CFD simulations except in the transition zone where a significant discrepancy to the experiment is observed.

Keywords: Swirling flow; Multiphase flow; Swirl-vane separator; CFD simulation; Euler-Euler model

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Permalink: https://www.hzdr.de/publications/Publ-26254
Publ.-Id: 26254


Beam operation with ELBE SRF gun using Mg photo cathodes

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

In this presentation the latest results of SRF gun-II with Mg photocathode is overviewed. The stable beam from SRF gun was guided into ELBE linac for a whole week of neutron beam time and THz beam time without unexperted breakdown.

  • Lecture (Conference)
    The 3rd annual meeting of Matter and Technologies, 31.01.-02.02.2017, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-26253
Publ.-Id: 26253


Status of SRF-gun-II and Photocathodes at HZDR

Xiang, R.

In this presentation the latest results of ELBE SRF gun-II with Mg photocathodes are overviewed. And the status of Cs2Te photocathode for SRF gun is also summaried.

  • Invited lecture (Conferences)
    HOPE-II annual meeting, 11.10.2017, Rostock, Germany

Permalink: https://www.hzdr.de/publications/Publ-26252
Publ.-Id: 26252


Cs2Te and metallic photocathodes for SRF gun at HZDR

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

Quality of photocathode is one of the critical issues for the stability and reliability of the photoinjector system. SRF Gun II with Mg photocathode has successfully provided stable electron beams for ELBE users at HZDR. In this work, we present the various cleaning processes (activation) for Mg photocathodes, e.g. high intensity laser cleaning and thermal treatment. Furthermore, we show the first result of the photoemission study on the alternative metallic cathode, for instance MgY alloy.

To generate higher bunch charge up to 0.5nC, Cs2Te photocathode is planned for SRF gun II. Up to now three Cs2Te photocathodes have been used in SRF gun II, however, they show abnormal phenomena and unwanted contamination for the superconducting cavity.

  • Poster
    European Workshop on Photocathodes for Particle Accelerator Applications (EWPAA 2017), 20.-22.09.2017, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-26251
Publ.-Id: 26251


Compatibility of SC cavity and "foreigner" photocathodes in SRF gun

Xiang, R.

More and more electron accelerator projects ask for “super” electron beams with high brightness, low emittance, and high average current. Under this background, much attention is paid on the research and development of new electron sources potentially providing electron beams with better quality. Superconducting RF photoinjectors allow CW operation and meanwhile provide high E-field on cathode to generator high bunch charge and low emittance beam, thus it is a promising candidate for such kind of high current and high brightness electron source.

However, because Nb itself has too low quantum efficiency, the normal conducting photocathodes, such as alkali photocathodes, are the best photoemitter with high quantum efficiency for SRF gun. The compatibility of photocathodes made of ‘foreigner materials’ inside the sensitive Nb cavity is of the biggest difficulty for the designer of SRF gun. One has to solve a lot of unwanted problems like compatibility, particle contamination, multipacting, dark current etc.

In this presentation we collect the running results of SRF guns with normal conducting photocathodes at HZDR and BNL, share the experience gained during the long term development experiments, and discuss the relative problems in the future development.

  • Invited lecture (Conferences)
    Workshop "Operating SRF in a "dirty" machine", 14.-15.09.2017, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-26250
Publ.-Id: 26250


Simulation of bubbly flows with special numerical treatments of the semi-conservative and fully conservative two-fluid model

Dongyue, L.; Hasse, C.

Bubbly flows are found in a large number of chemical engineering applications. For the computational fluid dynamics (CFD) simulations of such multi-phase flows, both physical models and numerical treatment are crucial to obtain robust and accurate results. In this numerical study, we investigate the twofluid model (TFM) under challenging conditions such as phase segregation and inversion. For the phase segregation, a singular problem arises in the phase momentum and the two-phase k-e equations when one phase fraction approaches zero. Another numerical issue is the accurate calculation of the drag coefficient, e.g., during the phase inversion. To address the singular problem, previous studies used a nonconservative formulation after dividing by the phase fraction; in our approach, we present a robust methodology for semi-conservative and fully conservative formulations. A special numerical treatment is introduced to the phase momentum equations and the turbulence equations, which avoids the singular problem in case of phase segregation. Concerning the drag force, two novel methods, the linear and the hyperbolic blending method, respectively, are presented to obtain accurate results. For testing the new numerical treatment, the analytical solution of a two-dimensional test case is first compared with the results predicted using a semi-conservative and a fully conservative formulation. The second test case investigated is a bubble column with different superficial velocities. The results from threedimensional simulations using the novel formulations show good agreement with the literature data.
Especially when phase segregation occurs, the semi-conservative and the fully conservative formulations using the two-phase k-e model formulation converge.

Keywords: Bubble column; Two-fluid model; CFD; Drag force; OpenFOAM

Permalink: https://www.hzdr.de/publications/Publ-26249
Publ.-Id: 26249


Multiphase CFD with OpenFOAM at HZDR

Schlegel, F.

Presentation of the activities at HZDR in the field of simulation of multiphase flows with OpenFOAM.

Keywords: OpenFOAM; Multiphase; CFD; Simulation

  • Lecture (Conference)
    OpenFuelCell Workshop, 24.-25.10.2017, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26248
Publ.-Id: 26248


Hyperdoping of silicon: A last niche of defect engineering?

Berencen, Y.; Liu, F.; Wang, M.; Prucnal, S.; Rebohle, L.; Zhou, S.; Helm, M.; Skorupa, W.

Hyperdoping of silicon using ion implantation and short time annealing of chalcogen atoms and transition metals (e.g. S, Se, Te, Au and Ti) appears as a challenging and promising research topic for developing Si-based infrared photodetectors and intermediate band solar cells [i.e.1-3].
The specific physical properties, such as a near-unity broadband absorption (particularly below the Si bandgap), a large enhancement of sub-band-gap photocurrent generation, and the insulator-to-metal transition, are based on this type of doping much above the solid solubility limit of dopants in Si. We have recently been demonstrated that both, laser annealing via the liquid phase and flash lamp annealing via the solid phase can be used to process such high-dose chalcogen-implanted layers [2]. Such kind of non-equilibrium processing needs a careful adjustment of the processing parameters, especially in regard to the “thermal engineering” with processing times at or below the millisecond range, to optimize the defect engineering of this specific type of hyperdoped material. We will report on the microstructural, optical and electrical properties of this new type of silicon material as well as first applications for room-temperature extended infrared Si p-n photodiodes.
[1] J. P. Mailoa, A. J. Akey, C. B. Simmons, D. Hutchinson, J. Mathews, J. T. Sullivan, D. Recht, M. T. Winkler, J. S. Williams, J. M. Warrender, P. D. Persans, M. J. Aziz, and T. Buonassisi, Nat. Commun. 5, 3011 (2014).
[2] S. Zhou, F. Liu, S. Prucnal, K. Gao, M. Khalid, C. Baehtz, M. Posselt, W. Skorupa, and M. Helm, Sci. Rep. 5, 8329 (2015).
[3] F. Liu, S Prucnal, R. Hübner, Ye Yuan, W Skorupa, M Helm, and S. Zhou, J.Phys.D: Appl.Phys. 49 (2016) 245104.

Keywords: hyperdoping; silicon; ion implantation; flash lamp annealing; chalcogen atoms; transition metals

  • Lecture (Conference)
    17th Conference on Gettering and Defect Engineering in Semiconductor Technology (GADEST 2017), 01.-06.10.2017, Tbilisi, Georgia

Permalink: https://www.hzdr.de/publications/Publ-26247
Publ.-Id: 26247


Toward higher precision in radiooncology: Tackling the range problem in particle therapy

Pausch, G.

The promise of particle therapy at ultimate precision can only be fulfilled once the particle range can be controlled and verified with millimeter precision. In spite of considerable efforts made by research groups and commercial enterprises throughout the world means or devices for routinely measuring the particle range during treatments are still missing. On the one hand prompt gamma-ray imaging, proposed almost 15 years ago, has become widely accepted as the most promising strategy for online range verification. On the other hand none of the Compton camera concepts pursued by several groups, including our group at HZDR/OncoRay, could prove to be applicable under treatment conditions so far. The only prototype system ever used in a clinical trial is the passively collimated knife-edge slit camera by IBA. This “camera” cannot provide 3D images but measures one-dimensional prompt gamma-ray intensity profiles that allow quantifying possible shifts of the distal edge of high-weighted single pencil beam spots. Alternative, potentially less expensive approaches have been proposed by MGH (prompt gamma spectroscopy) and OncoRay (prompt gamma timing). Efforts to translate these ideas in applicable technologies and instruments are underway.
The talk will review the state-of-the art in prompt-gamma based range verification, with a focus on previous and present activities at OncoRay: (1) the lessons learned from the Compton camera project, (2) the first-in-man application of a passively collimated prompt gamma camera, and (3) the exploration and stepwise development of an alternative approach, the prompt gamma-ray timing technique.

Keywords: Particle therapy; proton therapy; treatment verification; range verification; prompt gamma rays; prompt gamma imaging; prompt gamma timing; gamma spectroscopy; Compton camera

  • Lecture (others)
    Physikalisches Kolloquium (eingeladener Vortrag), 14.12.2017, Siegen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26246
Publ.-Id: 26246


IAEA CRP benchmark of ROCOM PTS test case for the use of CFD in reactor design using the CFD-codes ANSYS CFX and TRIOCFD

Höhne, T.; Kliem, S.; Bieder, U.

Over the last 15 years, considerable effort has been expended in assembling the available information on the use of CFD in the nuclear reactor safety field. Typical application areas here are heterogeneous mixing and heat transfer in complex geometries, buoyancy-induced natural and mixed convection, etc., with specific reference to Nuclear Reactor Safety (NRS) accident scenarios such as Pressurized Thermal Shock (PTS), boron dilution, hydrogen build-up in containments, thermal fatigue and thermal striping issues, etc. The development, verification and validation of CFD codes in respect to Nuclear Power Plant (NPP) design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. Therefore, a set of ROCOM CFD-grade test data were made available to set up an International Atomic Energy Agency (IAEA) benchmark, relating to PTS scenarios. The benchmark deals with the injection of the relatively cold Emergency Core Cooling (ECC) water which can induce buoyancy-driven stratification. Data obtained from the PTS experiment were compared in the study presented here with predictions obtained from the CFD software ANSYS CFX and TrioCFD. In addition a test case without buoyancy forces was selected to show the influence of density differences.

The results of the two test cases and the numerical calculations show that mixing efficiency is strongly influenced by buoyancy effects. At higher mass flow rates without density differences the injected slug propagates in the circumferential direction around the core barrel. Buoyancy forces reduce this azimuthal propagation. The ECC water falls in an almost vertical path and reaches the lower down¬comer sen¬sor below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWRs. Both CFD codes were able to predict the observed flow patterns and mixing phenomena.

Keywords: ROCOM; PTS; PWR; RDB; Mixing; CFD

Permalink: https://www.hzdr.de/publications/Publ-26245
Publ.-Id: 26245


Ge/Si core/shell quantum dots in alumina: Tuning the optical absorption by the core and shell size(Article)

Nekić, N.; Sancho-Parramon, J.; Bogdanović-Radović, I.; Grenzer, J.; Hübner, R.; Bernstorff, S.; Ivanda, M.; Buljan, M.

Ge/Si core/shell quantum dots (QDs) recently received extensive attention due to their specific properties induced by the confinement effects of the core and shell structure. They have a type II confinement resulting in spatially separated charge carriers, the electronic structure strongly dependent on the core and shell size. Herein, the experimental realization of Ge/Si core/shell QDs with strongly tunable optical properties is demonstrated. QDs embedded in an amorphous alumina glass matrix are produced by simple magnetron sputtering deposition. In addition, they are regularly arranged within the matrix due to their self-assembled growth regime. QDs with different Ge core and Si shell sizes are made. These core/shell structures have a significantly stronger absorption compared to pure Ge QDs and a highly tunable absorption peak dependent on the size of the core and shell. The optical properties are in agreement with recent theoretical predictions showing the dramatic influence of the shell size on optical gap, resulting in 0.7 eV blue shift for only 0.4 nm decrease at the shell thickness. Therefore, these materials are very promising for light-harvesting applications.

Keywords: absorption; Ge/Si core/shell quantum dots; quantum confinement; self-assembly

Permalink: https://www.hzdr.de/publications/Publ-26244
Publ.-Id: 26244


Effect of broken axial symmetry on the electric dipole strength and the collective enhancement of level densities in heavy nuclei

Grosse, E.; Junghans, A. R.; Wilson, J. N.

The basic parameters for calculations of radiative neutron capture, photon strength functions and nuclear level densities near the neutron separation energy are determined based on experimental data without an ad hoc assumption about axial symmetry—at variance to previous analysis. Surprisingly few global fit parameters are needed in addition to information on nuclear deformation, taken from Hartree Fock Bogolyubov calculations with the Gogny force, and the generator coordinator method assures properly defined angular momentum. For a large number of nuclei the GDR shapes and the photon strength are described by the sum of three Lorentzians, extrapolated to low energies and normalised in accordance to the dipole sum rule. Level densities are influenced strongly by the significant collective enhancement based on the breaking of shape symmetry. The replacement of axial symmetry by the less stringent requirement of invariance against rotation by 180° leads to a novel prediction for radiative neutron capture. It compares well to recent compilations of average radiative widths and Maxwellian average cross sections for neutron capture by even target nuclei. An extension to higher spin promises a reliable prediction for various compound nuclear reactions also outside the valley of stability. Such predictions are of high importance for future nuclear energy systems and waste transmutation as well as for the understanding of the cosmic synthesis of heavy elements.

Keywords: nuclear structure; nuclear level density; giant resonances; nuclear astrophysics; nuclear waste transmutation

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Permalink: https://www.hzdr.de/publications/Publ-26243
Publ.-Id: 26243


Trapping of hydrogen and helium at dislocations in tungsten: an ab initio study

Bakaev, A.; Grigorev, P.; Terentyev, D.; Bakaeva, A.; Zhurkin, E. E.; Mastrikov, Y. A.

The interaction of H or He atoms with a core of edge and screw dislocations (SDs), with Burgers vector a0/2 < 111 > s are stronger traps for H and He compared to the SDs, while the H/He affinity to both types of dislocation is significantly weaker than to a single vacancy. The lowest energy atomic configurations are rationalized on the basis of the charge density distribution and elasticity theory considerations. The results obtained contribute to the rationalization of the thermal desorption spectroscopy analysis by attributing certain peaks of the release of plasma components to the detrapping from dislocations. Complementary molecular statics (MS) calculations are performed to validate the accuracy of the recently developed W-H-He embedded atom method (EAM) and bond-order potentials. It is revealed that the EAM potential can reproduce correctly the magnitude of the interaction of H with both dislocations as compared to the ab initio results. All the potentials underestimate significantly the He-dislocation interaction and cannot describe correctly the lowest energy positions for H and He around the dislocation core. The reason for the discrepancy between ab initio and the MS results is rationalized by the analysis of the fully relaxed atomic configurations.

Keywords: tungsten; plasma; hydrogen; helium; dislocations; ab initio; molecular statics

Permalink: https://www.hzdr.de/publications/Publ-26241
Publ.-Id: 26241


Magnetic excitations and continuum of a possibly field-induced quantum spin liquid in α-RuCl3

Wang, Z.; Reschke, S.; Hüvonen, D.; Do, S.-H.; Choi, K.-Y.; Gensch, M.; Nagel, U.; Rõõm, T.; Loidl, A.

We report on terahertz spectroscopy of quantum spin dynamics in α-RuCl3, a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. An extended magnetic continuum develops below the structural phase transition at Ts2=62K. With the onset of a long-range magnetic order at TN=6.5K, spectral weight is transferred to a well-defined magnetic excitation at ℏω1=2.48meV, which is accompanied by a higher-energy band at ℏω2=6.48meV. Both excitations soften in magnetic field, signaling a quantum phase transition at Bc=7T where we find a broad continuum dominating the dynamical response. Above Bc, the long-range order is suppressed, and on top of the continuum, various emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of a possibly field-induced quantum spin liquid.

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Permalink: https://www.hzdr.de/publications/Publ-26240
Publ.-Id: 26240


Excitations and relaxation dynamics in multiferroic GeV4S8 studied by terahertz and dielectric spectroscopy

Reschke, S.; Wang, Z.; Mayr, F.; Ruff, E.; Lunkenheimer, P.; Tsurkan, V.; Loidl, A.

We report on THz time-domain spectroscopy on multiferroic GeV4S8, which undergoes orbital ordering at a Jahn-Teller transition at 30.5 K and exhibits antiferromagnetic order below 14.6 K. The THz experiments are complemented by dielectric experiments at audio and radio frequencies. We identify a low-lying excitation close to 0.5 THz, which is only weakly temperature dependent and probably corresponds to a molecular excitation within the electronic level scheme of the V4 clusters. In addition, we detect complex temperature-dependent behavior of a low-lying phononic excitation, closely linked to the onset of orbitally driven ferroelectricity. In the high-temperature cubic phase, which is paramagnetic and orbitally disordered, this excitation is of relaxational character becomes an overdamped Lorentzian mode in the orbitally ordered phase below the Jahn-Teller transition, and finally appears as well-defined phonon excitation in the antiferromagnetic state. Abrupt changes in the real and imaginary parts of the complex dielectric permittivity show that orbital ordering appears via a structural phase transition with strong first-order character and that the onset of antiferromagnetic order is accompanied by significant structural changes, which are of first-order character, too. Dielectric spectroscopy documents that at low frequencies, significant dipolar relaxations are present in the orbitally ordered, paramagnetic phase only. In contrast to the closely related GaV4S8, this relaxation dynamics that most likely mirrors coupled orbital and polar fluctuations does not seem to be related to the dynamic processes detected in the THz regime.

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Permalink: https://www.hzdr.de/publications/Publ-26239
Publ.-Id: 26239


Electronic and phonon excitations in α−RuCl3

Reschke, S.; Mayr, F.; Wang, Z.; Do, S.-H.; Choi, K.-Y.; Loidl, A.

We report on terahertz (THz), infrared reflectivity, and transmission experiments for wavenumbers from 10 to 8000cm−1 (∼1meV−1eV) and for temperatures from 5 to 295 K on the Kitaev candidate material α−RuCl3. As reported earlier, the compound under investigation passes through a first-order structural phase transition, from a monoclinic high-temperature to a rhombohedral low-temperature phase. The phase transition shows an extreme and unusual hysteretic behavior, which extends from 60 to 166 K. In passing this phase transition, in the complete frequency range investigated, we found a significant reflectance change, which amounts to almost a factor of two. We provide a broadband spectrum of dielectric constant, dielectric loss, and optical conductivity from the THz to the mid-infrared regime and study in detail the phonon response and the low-lying electronic density of states. We provide evidence for the onset of an optical energy gap, which is on the order of 200 meV, in good agreement with the gap derived from measurements of the dc electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue shift on increasing temperatures.

Permalink: https://www.hzdr.de/publications/Publ-26238
Publ.-Id: 26238


Serpent solution of X2 benchmark: fresh core at HZP conditions

Bilodid, Y.; Fridman, E.

The X2 benchmark, published in AER conference proceedings, describes first 4 fuel cycles of the Khmelnitsky NPP 2nd unit (KhNPP-2) with VVER-1000 reactor. The benchmark specifications contain description of the reactor core and operational history supplemented by measured operational data. In this work, the HZP experiments conducted in the KhNPP-2 fresh core are modelled with the Serpent-2 Monte Carlo code. The numerical results are validated against the available measured core data.

Keywords: Serpent; VVER-1000; X2 benchmark

  • Contribution to proceedings
    The 27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, Munich, Germany
    Proceedings of the 27th Symposium of AER on VVER Reactor Physics and Reactor Safety
  • Lecture (Conference)
    The 27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, Munich, Germany

Permalink: https://www.hzdr.de/publications/Publ-26237
Publ.-Id: 26237


Optical conductivity in multiferroic GaV4S8 and GeV4S8: Phonons and electronic transitions

Reschke, S.; Mayr, F.; Wang, Z.; Lunkenheimer, P.; Li, W.; Szaller, D.; Bordács, S.; Kézsmárki, I.; Tsurkan, V.; Loidl, A.

We report on optical spectroscopy on the lacunar spinels GaV4S8 and GeV4S8 in the spectral range from 100 to 23 000 cm−1 and for temperatures from 5 to 300 K. These multiferroic spinel systems reveal Jahn-Teller driven ferroelectricity and complex magnetic order at low temperatures. We study the infrared-active phonon modes and the low-lying electronic excitations in the cubic high-temperature phase, as well as in the orbitally and in the magnetically ordered low-temperature phases. We compare the phonon modes in these two compounds, which undergo different symmetry-lowering Jahn-Teller transitions into ferroelectric and orbitally ordered phases, and exhibit different magnetic ground states. We follow the splitting of the phonon modes at the structural phase transition and detect additional splittings at the onset of antiferromagnetic order in GeV4S8. We observe electronic transitions within the d-derived bands of the V4 clusters and document a significant influence of the structural and magnetic phase transitions on the narrow electronic band gaps.

Permalink: https://www.hzdr.de/publications/Publ-26236
Publ.-Id: 26236


Study the effect of channel oscillation on the mass transfer rate of bubbles in small channels

Haghnegahdar, M.; Boden, S.; Hampel, U.

In many industrial processes involving disperse gas and liquid, the mass transfer rate between the contacting phases is an essential parameter for the efficient design, optimization and control of the processes.
In the present study, we investigate the influence of channel oscillation on the shape, rise velocity and dissolution rate of single elongated Taylor bubbles in millimetre-sized channels. Using videoscopic observation, the position of the rising air bubble’s front tip in stagnant liquid (deionized water) in a vertical channel with circular cross section was subsequently tracked which gives the instantaneous bubble front tip rise velocity. The glass channel is vibrated using a calibrated vibration generator in horizontal direction. The amplitude (0-1.4 mm) and frequency (0-44 Hz) of vibration are adjusted by a wave generator and measured using the high precision Laser confocal displacement meter. The mass transfer rate was calculated by measuring the changes in the size of the CO2 rising bubbles. The method which was used to measure the variation of the bubble volume is X-ray radiography technique. This technique was qualified to disclose the volume of Taylor bubbles in capillaries and enabled the acquisition of a series of bubble size images of Taylor bubbles. The processed images which give volume of the bubble with high accuracy as a function of time, are used to evaluate the liquid-side mass transfer coefficient between bubble and liquid using the mass conservation equation.
The videoscopic observation of air bubbles shows that horizontal channel oscillation induces surface waves on the left and right-hand side of the Taylor bubble, which travels downward on the bubble interface. In addition, it was shown that the free rise velocity of bubbles increases as the amplitude and frequency of horizontal channel motion enlarge. Furthermore, the results for the short term dissolution of single CO2 bubbles reveal the intensification effect of channel oscillation on the mass transfer rate of Taylor bubbles.

Keywords: Vibration; Mass transfer; Small channels; CO2

  • Poster
    10th World Congress of Chemical Engineering, 01.-05.10.2017, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-26235
Publ.-Id: 26235


Improving CT calibration for proton range prediction by dual-energy CT based patient-cohort analysis

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

Purpose/Objective:
Recent studies demonstrate the clinical reliability and improved accuracy of dual-energy CT (DECT) in proton therapy. Still, a generic heuristic conversion (HLUT) of CT number to stopping-power ratio (SPR) is used in clinical routine, since a medical device for patient-specific DECT-based SPR prediction is not yet available. Here, we propose an applicable method for HLUT optimization using information from patient-specific DECT-based SPR prediction on a broad patient cohort.

Material/methods:
Clinical DECT scans of 102 brain-, 25 prostate- and 3 lung-tumor patients were evaluated in total. Each scan was acquired with a single-source DECT scanner (Definition AS) and processed in syngo.via (both Siemens Healthineers) to generate 79keV pseudo-monoenergetic CT (MonoCTs) and SPR datasets (derived from electron density and photon cross section). Voxelwise correlations of CT number and SPR were determined within the irradiated volume (20% isodose) and expressed as frequency distribution including patient information of all 3 cohorts. A piece-wise linear function was defined minimizing the deviation from the median SPR distribution for each CT number (DECT-based adapted HLUT). The intra- and inter-patient variability was also obtained from the frequency distribution. To assess dose differences and range shifts, proton treatment plans were recalculated in XiO (Elekta) on MonoCT using (A) clinical or (B) adapted HLUT, and (C) patient-specific DECT-based SPR datasets.

Results:
Mean range shifts (±1SD) of 1.2(±0.7)% for brain-, 1.7(±0.5)% for prostate- and 2.3(±0.8)% for lung- tumor patients were determined using the clinical HLUT instead of the patient-specific DECT-based SPR prediction. On average the clinical HLUT predicted larger SPR for brain, muscle and trabecular bone leading to this systematic range deviation. This effect is partially compensated in brain-tumor patients, since the clinical HLUT provides a smaller SPR for cortical bone. Using the DECT-based adapted HLUT (Fig. 1), mean range shifts were significantly reduced (p<<0.001, two-sample t-test) below 0.3% (Fig. 2). Hence, the adapted HLUT achieves a reduction of systematic deviations for all 3 tumor sites while standard deviations remained almost unchanged. Still, range shifts larger than 1% arise owing to the large intra-patient soft tissue diversity of approx. 6% (95% CI) and age-dependent inter-patient bone variation of 5%.

Conclusion:
DECT provides patient-specific information on tissue diversity and its respective proportion, which is applicable to HLUT refinement reducing systematic deviations of a standard clinical CT calibration. In principal, this can also be transferred to particle-therapy centers not using DECT. The HLUT adaptation was clinically implemented in our institution and represents a further step toward full integration of DECT for proton treatment planning. A future clinical implementation of patient-specific DECT-based SPR prediction would also individually consider intra- and inter-patient tissue variability.

Keywords: dual-energy CT; proton therapy; range uncertainty

Permalink: https://www.hzdr.de/publications/Publ-26234
Publ.-Id: 26234


Dual-energy CT enables dose calculation on scans with iodinated contrast agent

Möhler, C.; Wohlfahrt, P.; Nicolay, N. H.; Richter, C.; Greilich, S.

Purpose / Objective
Radiotherapy planning commonly requires an additional, ‘native’ CT scan for dose calculation if a contrast agent is used for tumor diagnostics and contouring. Iodinated contrast agents increase CT numbers (Hounsfield units) due to the large atomic number of iodine (Z=53), while electron density remains almost unchanged owing to its low concentration (Figure 1). With dual-energy CT (DECT), the impact of atomic number on CT image contrast can be removed, enabling the direct calculation of relative electron density (RED) for photon therapy and stopping-power ratio (SPR) for ion therapy, respectively. In this study, we are investigating the magnitude of the remaining impact of an iodinated contrast agent on DECT-derived RED/SPR and subsequent clinical treatment planning for both photon and ion therapy.

Material / Methods
As a first step, the effect of the CT contrast medium Imeron® 300 (Bracco Imaging Deutschland GmbH, Germany) on RED/SPR determination was investigated in a dilution series over a range of iodine concentrations between 0.3 and 300 mg/ml. CT images were acquired on a Somatom Definition Flash dual-source CT scanner (Siemens Healthineers, Forchheim, Germany) in single-energy (SECT, 120 kVp) and dual-energy (DECT, 80/140Sn kVp) scan mode. RED and SPR images were obtained (a) from SECT datasets by applying the respective calibrated Hounsfield look-up table and (b) from DECT datasets using the software application syngo.CT Rho/Z (Siemens) and an SPR calculation scheme previously validated by the authors in phantoms, biological material and patients.

Results
Calculating RED/SPR from a DECT dataset with typical contrast enhancement (max. 160 HU at 120 kVp corresponding to 6 mg iodine per milliliter) could limit the impact on both RED and SPR to 1% compared to 5-10% when using a contrast-enhanced SECT image (Figure 2). Consequently, dose calculation could be performed directly on DECT-derived RED/SPR images.

Conclusion
Dose calculation on a RED/SPR dataset derived from a contrast-enhanced dual-source DECT scan is conceivable. This can make additional native scans obsolete, thereby simplifying the treatment planning workflow and lowering the patient dose by 50% (one instead of two scans). A clinical trial is currently underway to investigate the role of contrast-enhanced DECT for patient radiotherapy planning.

Keywords: dual-energy CT; contrast-enhanced CT; particle therapy; range uncertainty

Permalink: https://www.hzdr.de/publications/Publ-26233
Publ.-Id: 26233


Clinical feasibility of 4D single-source dual-energy CT for proton therapy of lung-cancer patients

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

Purpose/Objective:
Dual-energy CT (DECT) provides additional patient information to potentially improve delineation and range accuracy in proton therapy. Motion during sequentially acquired DECT scans might hamper its reliability. Here, we analysed the clinical feasibility of sequential 4D DECT scans (2 consecutive respiratory correlated 4D CT scans) for non-small cell lung cancer (NSCLC) patients and its applicability for proton dose calculation.

Material/methods:
For 3 advanced stage NSCLC patients with maximal tumor motion of 1mm in cranio-caudal direction, 4D DECT scans were sequentially acquired during the course of treatment with a Siemens single-source DECT scanner. 80/140kVp average CT datasets and 4 breathing phases (relative amplitude sorting) were reconstructed and compared visually. These DECT datasets were further processed in syngo.via (Siemens Healthineers) to calculate 79keV pseudo-monoenergetic CT (MonoCTs) and stopping-power- ratio datasets (SPR, derived from electron density and photon cross section), Fig.1a. Passively scattered proton treatment plans were recalculated on MonoCT and 140kVp datasets using the clinical heuristic CT-number-to-SPR conversion (HLUT). Furthermore, worst-case scenarios using a single proton beam covering artificial target volumes encompassing the diaphragm (13-23mm motion) were generated. Dose distributions derived from MonoCT and 140kVp datasets were compared with 2D gamma analyses (0.1% dose and 1mm geometrical difference) to validate DECT image post processing. Finally, a patient- specific DECT-based SPR prediction was applied on 4D DECT datasets and followed by dose calculation to assess proton range shifts compared to the MonoCT-based HLUT approach.

Results:
Visually, no differences between the two sequential 4D DECT scans were found. Breathing patterns did not change more between the 2 scans than within a single scan. Clinical dose distributions on MonoCT and 140kVp datasets were similar with an average gamma passing rate of 99.9% (99.2%-100%). The maximal dose difference was 0.8%, Fig.1b. The worst-case scenario plans had a minimal passing rate of 92.4% (average 99.3%) with maximal dose difference of 3.3%. Using the MonoCT dataset with clinical HLUT instead of the DECT-based SPR dataset for dose calculation led to clinically relevant mean range shifts (±1SD) of 2.3(±0.8)%, Fig.2.

Conclusion:
For this challenging patient cohort, sequentially acquired 4D DECT scans showed similar patient anatomy and stable breathing pattern allowing a consistent generation of DECT-based 79keV MonoCT datasets applicable for proton dose calculation. Patient-specific DECT-based SPR prediction on average CT datasets and breathing phases performed appropriately and can potentially reduce current range uncertainty in proton therapy. Even if large motion differences occur during the 2 sequential 4D DECT scans, dose distributions can still be reliably calculated using only the 140kVp dataset and beyond that important information on motion variability and robustness is gathered.

Keywords: dual-energy CT; proton range; range uncertainty

Permalink: https://www.hzdr.de/publications/Publ-26232
Publ.-Id: 26232


Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

Kluge, T.; Rödel, C.; Rödel, M.; Pelka, A.; Mcbride, E. E.; Fletcher, L. B.; Harmand, M.; Krygier, A.; Higginbotham, A.; Bussmann, M.; Galtier, E.; Gamboa, E.; Garcia, A. L.; Garten, M.; Glenzer, S. H.; Granados, E.; Gutt, C.; Lee, H. J.; Nagler, B.; Schumaker, W.; Tavella, F.; Zacharias, M.; Schramm, U.; Cowan, T. E.

We study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibility of the method. We present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.

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Permalink: https://www.hzdr.de/publications/Publ-26231
Publ.-Id: 26231


Identification of tumour sub-volumes for improved radiomic risk modelling in locally advanced HNSCC

Leger, S.; Zwanenburg, A.; Pilz, K.; Lohaus, F.; Linge, A.; Zöphel, K.; Kotzerke, J.; Schreiber, A.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S.; Mönnich, D.; Zips, D.; Krause, M.; Baumann, M.; Richter, C.; Troost, E.; Löck, S.

Purpose/Objective: Radiomics aims to characterise the tumour phenotype using advanced image features to predict patient-specific outcome. Commonly, image features are calculated from the entire gross tumour volume (GTVe). However, tumours are biologically complex, e.g., expressing necrosis merely in the core and tumour cell proliferation at the periphery. The identification of sub-volumes to incorporate regional tumour variation into the risk models may lead to an improved outcome prediction. Therefore, we investigated different sub-volumes of the GTVe using CT imaging, developed radiomic signatures, and compared prognostic power and stratification performance of the signatures.
Material/Methods: A multicentre cohort consisting of 302 patients with advanced stage head and neck squamous cell carcinoma (HNSCC) was collected and divided into an exploratory and a validation cohort (208 and 94 patients, respectively). All patients received primary radio-chemotherapy at one of the six DKTK partner sites and underwent a non-contrast-enhanced CT scan for treatment-planning purposes. The analysis was divided into two subsequent steps (Fig. 1): (a) two distinct sub-regions were extracted from GTVe: the tumour boundary of different widths (3,5,10 mm) and the corresponding remaining core volumes. (b) extension of the highest prognostic tumour-boundary sub-volume by different widths (1,2,3,5 mm) beyond the GTVe. 1555 image features were extracted from each sub-volume. Different machine-learning algorithms were used to build radiomic models for the prediction of loco-regional tumour control (LRC). The prognostic performance was measured by the concordance index (C-Index). Finally, patients were stratified into groups of low and high risk of recurrence using the median risk value. Differences in LRC were evaluated by log-rank tests.
Results: The validation C-Index averaged over all learning algorithms and feature selection methods using the GTVe revealed a high prognostic performance for LRC (C-Index: 0.63±0.03 (mean±std)). The boundary sub-volumes GTV5mm and GTV10mm showed a slightly improved accuracy (C-Index: 0.64±0.03 and 0.64±0.02, respectively), while models based on the corresponding core volumes had a lower accuracy (C-Index: 0.59±0.03 and 0.60±0.03, respectively, (Fig. 2A)). Also the risk groups could be better separated using the GTV5mm (p<0.001), compared to the GTVe (p=0.005) and the corresponding core volume (p=0.16, (Fig. 2B)). The extension of the GTV5mm sub-region by 2mm led to a similar prognostic performance (C-Index: 0.65±0.03).
Conclusions: In our investigation, radiomic models based on the boundary of the tumour showed a higher prognostic performance for LRC compared to models based on the tumour core. This indicates that the tumour boundary may contain more prognostic information than other parts of the tumour. The identification of tumour sub-volumes associated with treatment outcome may further improve the performance of radiomic risk models.

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S263-S264
    DOI: 10.1016/S0167-8140(18)30818-1

Permalink: https://www.hzdr.de/publications/Publ-26230
Publ.-Id: 26230


Analysis of a Hypothetical LOCA in an Open Pool Type Research Reactor

Rachamin, R.; Galperin, A.; Elias, E.

An analysis of a hypothetical loss of coolant accident (LOCA) in a pool-type research reactor is presented. The study was implemented for the Israel Research Reactor 1 (IRR-1), which is a 5MW reactor using highly enriched MTR-type fuel plates reflected by Graphite elements. The reactor core is cooled by downward forced flow of light water during normal operation and by upward natural convection flow through a safety flapper valve during shutdown. LOCA in pool-type research reactors may be initiated by various incidents such as ruptures and leakages from pipes and valves in the primary cooling system, ruptures of beam tubes or cracking of the pool wall caused by, e.g., strong earthquakes. Each one of these scenarios results in a rapid drop of the pool water level after reactor SCRAM. If water flow through the break persists, the core could eventually uncover completely and be exposed to the ambient air. The present study analyzes the possibility of passively cooling an exposed reactor core by thermal radiation and natural convection to air. The core uncover time is estimated by conservatively assuming that the LOCA was initiated by a guillotine break of a 10 inch outlet cooling pipe at the bottom of the pool, causing the core to uncover about 20 min after reactor SCRAM. Longer uncover times were used for parametric comparison. Since the Graphite reflector elements surrounded the core are typically solid that do not generate heat, they have the potential to act as a heat sink. The effect of the reflector on the core cooling was studied by comparing the total heat transfer from the core with and without considering the thermal contact between the core and the Graphite reflector elements. It is shown that for an uncover time of 20 min the core could reach its melting point if thermal contact with the Graphite is neglected. On the other hand, considering perfect thermal contact between the core and the Graphite reflector, the core temperature is predicted to remain indefinitely below the clad melting point (580 oC). The decay heat generation rate after reactor shutdown plays an important role in the analysis of LOCA. Several empirical correlations and theoretical models are available for predicting the decay heat after shutdown of a continuously operating power reactor. These correlations could not be simply applied for research reactors that work intermittently. A conservative decay heat generation curve was, therefore, estimated by comparing numerical results obtained by the BGCore computer code with available semi-empirical fitting functions and the ANS 5.1 standard curves. It has been shown that the BGCore computer code predict the decay heat generation rate with a small deviation from the corresponding semi-empirical functions results and the ANS 5.1 standard curves.

  • Open Access Logo Contribution to proceedings
    The 18th IGORR conference, 03.-07.12.2017, Sydney, Australia
  • Lecture (Conference)
    The 18th IGORR conference, 03.-07.12.2017, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-26228
Publ.-Id: 26228


Alles Test mit ö ü ä ß Γ Ω Σ д und O₂-Production

Rücker, C.; Müller, F.

Description mit ö ü ä ß mit ö ü ä ß Γ Ω Σ д und O₂-Production
Hochstellung Hoch
Tiefstellung Tief

Keywords: Keyword1 und Keyword2; Keyword3; Keyword4; Keyword5, Keyword6; Keyword7

Permalink: https://www.hzdr.de/publications/Publ-26227
Publ.-Id: 26227


Mechanistic models for uranium sorption on iron minerals: Comparing their parametrization and surface species

Bok, F.; Richter, A.; März, J.; Brendler, V.

The migration of contaminants though the environment can be retarded by various processes – one of them being sorption onto mineral phases along the flow paths. This process is itself a variable combination of surface complexation, ion exchange, surface precipitation, diffusion and others. However, the data accuracy is currently still limited due to a restricted understanding of molecular events decisive for the binding onto and incorporation into solid phases. In particular, underlying surface speciation is often inconsistent and range from assumed unrealistic postulations up to spectroscopically evident species with great impact on the corresponding thermodynamic data. Respective mechanistic models required for prognostics based on reactive transport are often lacking an evaluated, consistent set of species and thermodynamic parameters. This work provides answers to these problems.
Recently, surface-sensitive spectroscopic methods developed significantly, permitting the derivation of thermodynamically consistent sorption data sets. In combination with binding site densities (including ones from crystallographic measurements), surface complexation models are deduced that describe the sorption of radionuclides accurately and with less surface species then assumed in a vast number of literature references published in the past. Due to the realistic surface speciation and the internal consistency, these models are more robust to varying chemical and environmental conditions (pH, pe, composition of the aqueous phase).
This work aims on a re-evaluation of already published protolysis and sorption raw data. As examples, the sorption of uranium(VI) onto various iron(III) and iron (II) containing mineral phases (ferrihydrite, goethite, hematite, magnetite), ubiquitous in nature and also being corrosion products of waste containers, will be presented. There, the use of the spectroscopically verified, bidentate bound uranyl surface complex is sufficient to fully describe the radionuclides sorption. Even with simple models like the diffuse double-layer model only one surface species is necessary for the sorption calculation. In most cases also the CO₂ containing ternary system does not call for additional species. Eventually, a full integration with the thermodynamic reference database THEREDA (http://www.thereda.de) is envisaged to provide a comprehensive database for a holistic geochemical modeling.

Keywords: Sorption; Surface Complexation Modeling; Iron minerals; Uranium

  • Lecture (Conference)
    255th ACS National Meeting & Exposition, 18.-22.03.2018, New Orleans, LA, USA

Permalink: https://www.hzdr.de/publications/Publ-26224
Publ.-Id: 26224


In situ ohmic contact formation for n-type Ge via non-equilibrium processing

Prucnal, S.; Frigerio, J.; Napolitani, E.; Ballabio, A.; Berencén, Y.; Rebohle, L.; Wang, M.; Böttger, R.; Voelskow, M.; Isella, G.; Hübner, R.; Helm, M.; Zhou, S.; Skorupa, W.

Highly scaled nanoelectronics requires effective channel doping above 5×10^19 /cm3 together with ohmic contacts with extremely low specific contact resistivity. Nowadays, Ge becomes very attractive for modern optoelectronics due to the high carrier mobility and the quasi-direct bandgap, but n-type Ge doped above 5×10^19 /cm3 is metastable and thus difficult to be achieved. In this letter, we report on the formation of low-resistivity ohmic contacts in highly n-type doped Ge via non-equilibrium thermal processing consisting of millisecond-range flash lamp annealing. This is a single-step process that allows for the formation of a 90 nm thick NiGe layer with a very sharp interface between NiGe and Ge. The measured carrier concentration in Ge is above 9×10^19 /cm3 with a specific contact resistivity of 1.2×10^(−6) Ω cm2.
Simultaneously, both the diffusion and the electrical deactivation of P are fully suppressed.

Keywords: germanium; flash lamp annealing; ion implantation; NiGe; ohmic contact

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Permalink: https://www.hzdr.de/publications/Publ-26223
Publ.-Id: 26223


Fiducial markers and daily kV imaging improve patient setup during proton RT of esophageal cancer

Apolle, R.; Rehm, M.; Thiele, J.; Brückner, S.; Hampe, J.; Troost, E. G. C.

Purpose or Objectives
The success of light ion radiotherapy is crucially sensitive to daily setup variation and anatomic changes. Irradiation of the esophagus, in particular, suffers from significant target mobility [1].

Since its commissioning, the proton facility at our institute has been using daily kV imaging for patient setup based on bony anatomy, supplemented with in-room dual-energy CT scans as needed.

We assessed target positioning with the aid of kV-visible fiducial markers placed around esophageal tumors by tracking their displacement from the planned location throughout treatment.

Materials and Methods
Five patients with esophageal cancer scheduled for neoadjuvant (4) or definite (1) radiochemotherapy using protons (all male; age 52-64 years; tumor of the middle or lower third of the esophagus; mean GTV: 24 ml) underwent endoscopic ultrasound-guided trans-esophageal placement of gold fiducial markers (VisiCoilTM, IBA Dosimetry, Belgium; diameter 0.35 mm, lengths 5 or 10 mm) demarcating the proximal and distal tumor borders.
Pairs of orthogonal kV images taken in treatment position were retrieved for 104/110 fractions. Markers were manually located in the images and their position in 3D determined by triangulation [2]. Vertebral landmarks were similarly reconstructed and used to register kV imaging to the planning CTs. Triangulation errors were estimated per marker from the geometrical compatibility of image point pairs with single 3D points. All calculations were carried out in custom software based on SciPy [3].

Results
Marker implantation proceeded without complications and placement of the distal marker was hindered by an obstructing tumor in one case only. All but one marker remained stable throughout treatment, and their visibility in kV images was generally limited, but sufficient. Marker-induced dose perturbations were not clinically relevant.
Figure 1 shows example triangulation results for one patient. Overall the standard deviation [inter-quartile range] of the distributions of marker excursions was 2.6 [2.1], 1.8 [2.0], and 3.1 [3.6] mm in the lateral, sagittal, and longitudinal directions, respectively. A Friedman test failed to reveal significant differences between the directions (p>0.7). Inter-marker distances varied by a few mm during treatment with no discernible trend. Triangulation errors ranged from 0.9 to 7.1 mm.
One notable instance of marker-indicated target displacement by 26 mm was observed (Fig. 2). This prompted the acquisition of a control CT in treatment position, which revealed an overlap of the planned and actual GTVs of merely 4% (Jaccard index 0.02). The dosimetric impact would have been a reduction of the mean and near-min (D98%) doses by 6% and 47%, respectively.

Conclusion
Exclusive reliance on bony anatomy for positioning of esophageal cancer patients cannot prevent occasional target misalignments. Gold fiducials (e.g., VisiCoilTM) and daily kV imaging are valuable tools for target-centric setup verification.

Keywords: Inter-fraction motion management; Particle therapy

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, Spain
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S521-S522
    DOI: 10.1016/S0167-8140(18)31264-7

Permalink: https://www.hzdr.de/publications/Publ-26222
Publ.-Id: 26222


Perturbing single images as a surrogate for radiomic feature robustness test-retest experiments

Zwanenburg, A.; Leger, S.; Troost, E.; Richter, C.; Löck, S.

Purpose/Objective: Radiomics is the high-throughput, machine-learning based analysis of medical images for model-based treatment decisions. It relies on image characteristics (features), which quantify aspects of a volume of interest, such as its mean intensity, volume and texture heterogeneity. Features used for modelling should be robust against perturbations, induced e.g. by patient positioning, image acquisition and contouring; otherwise resulting radiomics models may not be generalisable. Test-retest imaging is the recommended method for assessing feature robustness, but is tumour phenotype-specific. A test-retest experiment would thus be required for each radiomics study, incurring additional costs in terms of patient preparation, imaging and additional imaging dose. Therefore we asses feature robustness using single images as a surrogate and compare these with test-retest results.

Methods: Two patient cohorts with test-retest CT imaging were used: a public NSCLC cohort of 31 patients [1] and an HNSCC cohort of 19 patients. For the NSCLC cohort, two separate images were acquired within 15 minutes of each other using the same scanner and protocol. Images in the HNSCC cohort were acquired within 4 days of each other with different scanners and protocols. The gross tumour volume (GTV) was contoured and 5571 features were extracted from the GTV of each image. Image perturbation was used to assess robustness from single images. Images were perturbed by adding image noise, performing sub-voxel translation, rotation, and contour randomisation, where contour boundaries are altered based on overlap of supervoxels with the GTV. Feature robustness between test-retest images and between perturbations of a single image was measured using the intraclass correlation coefficient (ICC). Features with ICC ≥ 0.85 were considered to be robust.

Results: We identified 3831 and 1123 robust features for test-retest imaging for the NSCLC and HNSCC cohorts, respectively. Features in the HNSCC cohort were generally less reproducible compared to the NSCLC cohort. The largest overlap between non-robust features identified by test-retest imaging and single image perturbation existed for rotation with randomised contours with 96% and 86% for NSCLC and HNSCC cohorts, respectively.

Conclusion: An essential step in radiomic analyses is the selection of features that are insensitive to different imaging protocols and equipment, and inter-observer variability. We demonstrated that perturbing single images by rotations combined with random contour alteration provides a suitable alternative to test-retest imaging that is easily available in clinical routine.

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S1151-S1152
    DOI: 10.1016/S0167-8140(18)32404-6

Permalink: https://www.hzdr.de/publications/Publ-26221
Publ.-Id: 26221


Results from the Image Biomarker Standardisation Initiative

Zwanenburg, A.; Abdalah, M.; Ashrafinia, S.; Beukinga, J.; Bogowicz, M.; Dinh, C. V.; Götz, M.; Hatt, M.; Leijenaar, R.; Lenkowicz, J.; Morin, O.; Rao, A.; Socarras Fernandez, J.; Vallieres, M.; van Dijk, L.; van Griethuysen, J.; van Velden, F. H. P.; Whybra, P.; Troost, E.; Richter, C.; Löck, S.

Purpose: Radiomics is the high-throughput analysis of medical images for treatment individualisation. It conventionally relies on the quantification of different characteristics of a region of interest (ROI) delineated in the image, such as the mean intensity, volume and textural heterogeneity. The lack of standardisation of image features is one of the major limitations for reproducing and validating radiomic studies, and thus a major hurdle for further developments in the field and for clinical translation. To overcome this challenge, a large international collaboration of 19 teams from 8 countries was initiated to establish an image feature ontology, and to provide definitions of commonly used features, benchmarks for testing feature extraction and image processing software, and reporting guidelines.

Methods: The initiative consisted of two phases. In phase 1, 351 commonly used features were specified and benchmarked against a simple digital phantom, without any requirement for image pre-processing steps. The feature set consisted of commonly used radiomic features and encompasses statistical, morphological and texture characteristics of the ROI, both slice-by-slice (2D) and as a volume (3D). In phase 2, image pre-processing steps were introduced, and features were benchmarked by evaluating five pre-processing configurations on a lung cancer patient CT image. The configurations differ in treatment of the image stack (2D: A-B; 3D: C-E), the interpolation method (none: A; bi/trilinear: B-D, tricubic: E) and the grey-level discretisation method (fixed bin size: A, C; fixed number of bins: B, D-E).

Both phases were iterative, and participants had the opportunity to compare results and update their workflow implementation. We set the most frequently contributed value of each feature as its benchmark value, and subsequently determined its reliability based on the number of contributing groups and the consensus level.

Results: 19 different software implementations were tested. In both phases, only a small number of features were found to be reliable initially. The number of reliable features increased over time as problems were identified and resolved, see Figure 1 and Table 1. Remaining features for which no agreement was reached were not commonly implemented (< 3 agreeing teams), and could therefore not be reliably assessed.

Conclusion: We addressed the lack of standardised feature definitions, implementation and image pre-processing steps for radiomics by providing reliable benchmark values for commonly used features. During the initiative, the 19 teams demonstrated large initial differences, yet nevertheless managed to converge to common reference values by increasing adherence to standardised definitions. Therefore, the use of our standardised definitions and benchmarks to test and update radiomics software is imperative to increase reproducibility of future radiomics studies.

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S543-S544
    DOI: 10.1016/S0167-8140(18)31291-X

Permalink: https://www.hzdr.de/publications/Publ-26220
Publ.-Id: 26220


Dosimetric comparison of two planning target volume margin recipes for prostate radiotherapy

Ahmad, A.; Troost, E. G. C.; Löck, S.; Agolli, L.; Valentini, C.; Enghardt, W.; Geyer, P.

Background and Purpose: Planning target volume (PTV) margins are applied around the clinical target volume (CTV) to cover organ motion and patient set-up related random and systematic uncertainties that occur during the course of fractionated radiation treatment. In this study two PTV margin recipes were compared retrospectively on the basis of a prospectively acquired data to investigate the effectiveness of positioning protocol for the prostate cancer patients.
Material/Methods: In total 12 patients with prostate cancer were registered for a prospective imaging and positioning study that was approved by the local ethics committee (EK272072014). All patients received 74 Gy(RBE) in 37 treatment fractions. Overall, 379 daily in-room cCTs with the patient aligned in treatment position were available for analysis. All cCTs of a patient were registered with the planning CT (pCT) in 6 degrees of freedom using bony landmarks. The prostate, bladder and rectum were contoured on all CTs and transferred from the cCTs to the pCT. The union of overlaid prostate contours of all cCTs resulted in the composite prostate contour. First, PTV margins were determined such that 95% of composite prostate was covered for 90% of the patient population by an anisotropic expansion of the pCT prostate contour (Fig. 1). Interfractional prostate motion and related systematic and random uncertainties were assessed. Second, PTV margins were calculated using van Herk’s [1] formula. Finally, volumetric modulated arc therapy plans were generated and recalculated on the cCTs using both PTV margins recipes, and coverage (D98%) and hotspots (D2%) in the CTV as well as dose volume constraints for bladder (V65Gy, V70Gy and V75Gy) and rectum (V50Gy, V70Gy) were compared (Fig. 2).
Results: PTV margins along left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions were 4.3, 5.3 and 4.8 mm using the first approach, and 1.4, 4.8 and 3.5 mm for the second approach, respectively. Target coverage was fulfilled for all but one cCT using the first approach, but it was not fulfilled for 6/379 cCTs for the second approach. Dose-volume constraints for bladder and rectum were fulfilled for the second margin approach but for the first margin approach V70Gy for the rectum was not met sometimes (Fig. 2).
Conclusions: Using the composite prostate coverage approach, robust PTV margins were derived since they also took rotation and deformation into account and thereby ensuring CTV coverage over the course of treatment.

Keywords: Planning target volume; Endorectal balloon; Interfractional prostate motion; Control CT; Radiotherapy

Permalink: https://www.hzdr.de/publications/Publ-26219
Publ.-Id: 26219


Thermal convection in liquid metal batteries

Personnettaz, P.; Weber, N.; Koellner, T.; Nimtz, M.; Weier, T.

Liquid Metal Batteries ( LMBs ) are a promising electrochemical energy storage technology, built as a stable density stratification of two liquid metals separated by a molten salt. In this work, we focus our attention on thermal convection that appear inside Li||Bi LMBs. The chemistry of the cell is first presented. Then all possible thermal phenomena are discussed, with a continuum mechanics approach. The temperature profile is first defined in the hypothesis of pure conduction. Moreover, in order to take into account thermal convection inside the cell, the multiphase solver multiphaseInterFOAM is extended. The results of this solver are compared to the one of a pseudo-spectral code. Finally the first result of thermal convection in Li||Bi LMB is presented. The future work on transport phenomena in LMBs is also briefly summarized.

Keywords: thermal convection; transport phenomena; liquid metal battery; numerical model; OpenFOAM

  • Lecture (Conference)
    openFuelCell workshop, 24.10.2017, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26218
Publ.-Id: 26218


NTCP modelling and external validation of early side effects for proton therapy of brain tumours

Dutz, A.; Agolli, L.; Troost, E. G. C.; Krause, M.; Baumann, M.; Lühr, A.; Vermeren, X.; Geismar, D.; Timmermann, B.; Löck, S.

Purpose: To identify patients who are likely to benefit most from proton beam therapy (PBT), based on the potential reduction in normal tissue complication probability (NTCP) compared to photon therapy. The NTCP models required for this decision were developed using clinical data on early side effects for patients with brain tumours who underwent PBT.

Material and methods: Two cohorts of adult patients with brain tumours who received PBT were included in this study: 113 patients treated at University Proton Therapy Dresden were used for model training and 71 cases from West German Proton Therapy Centre Essen were used for external validation. Moreover, volumetric modulated arc therapy (VMAT) plans were retrospectively created for all patients to predict the potential reduction in NTCP when applying PBT. The radiation-induced early side effects alopecia, erythema, pain and fatigue were investigated. The occurrence of these side effects was correlated with different DVH parameters of associated organs at risk (OAR), such as skin and remaining brain. NTCP models were created using logistic regression and the area under the receiver operating characteristic curve (AUC) was used to assess their prognostic ability.

Results: The NTCP models revealed significant correlations between the incidence of alopecia grade 2 (figure a) as well as erythema grade≥1 and the DVH parameters D1%, D2%, V15Gy and V20Gy of the skin. The V20Gy models showed a very good discrimination on external validation for both endpoints (AUC≥0.75, figure b). No correlations between DVH parameters of the remaining brain and the incidence of fatigue or pain were found. Dose comparison between PBT and VMAT showed large differences in both training and validation cohort, especially in the remaining brain. The mean brain dose of the PBT plans was significantly lower compared to VMAT (median training: 6.9Gy vs 18.6Gy, median validation: 8.5Gy vs 16.0Gy; p<0.001). For alopecia grade 2, plan comparison between PBT and VMAT predicted a potential median NTCP reduction for PBT of approx. 5% (range: -39% – 32%) in the training and 1% (range: -25% – 37%) in the validation cohort. A reduction of NTCP for alopecia grade 2 for PBT by more than 10% was observed for 12/113 patients in training and for 9/71 patients in validation.

Conclusion: Plan comparison showed a large reduction in dose to the brain using PBT instead of VMAT. We found significant correlations between the occurrence of early side effects and DVH parameters of associated OARs for patients with brain tumours receiving PBT. A relevant reduction of NTCP (>10%) for PBT was calculated for approx. 10 % of the patients. However, due to the large range of NTCP reduction, patient individual calculations are mandatory. After inclusion of more relevant late side effects and neurocognitive changes, these models may be used to identify patients who are likely to benefit most from PBT [1].

[1] Langendijk JA et al. (2013) Radiother Oncol 107, 267-273.

Keywords: NTCP modelling; early side effects; proton therapy

  • Lecture (Conference)
    ESTRO37, 20.-24.04.2018, Barcelona, Spanien
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S266-S267
    DOI: 10.1016/S0167-8140(18)30821-1

Permalink: https://www.hzdr.de/publications/Publ-26217
Publ.-Id: 26217


Evaluation of fluorine-18-labelled alpha1(I)-N-telopeptide analogues as substrate-based radiotracers for PET imaging of melanoma-associated lysyl oxidase

Kuchar, M.; Neuber, C.; Belter, B.; Bergmann, R.; Lenk, J.; Wodtke, R.; Kniess, T.; Steinbach, J.; Pietzsch, J.; Löser, R.

Accumulating evidence suggests an unequivocal role of lysyl oxidases as key players of tumour progression and metastasis, which renders this enzyme family highly attractive for targeted non-invasive functional imaging of tumours. Considering their function in matrix remodelling, malignant melanoma appears as particularly interesting neoplasia in this respect. For the development of radiotracers that enable PET imaging of the melanoma-associated lysyl oxidase activity, substrates derived from the type I collagen alpha1 N-telopeptide were labelled with fluorine-18 using succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) as prosthetic reagent. With regards to potential crosslinking to tumour-associated collagen in vivo, their interaction with triple-helical type I collagen was studied by SPR. A mouse model of human melanoma was established on the basis of the A375 cell line, for which the expression of the oncologically relevant lysyl oxidase isoforms LOX and LOXL2 was demonstrated in Western blot and immunohistochemical experiments. The radiopharmacological profiles of the peptidic radiotracers were evaluated in normal rats and A375 melanoma-bearing mice by ex vivo metabolite analysis, whole-body biodistribution studies and dynamic PET imaging. Out of three 18F-labelled telopeptide analogues, the one with the most favourable substrate properties has shown favourable tumour uptake and tumour-to-muscle ratio. Lysyl oxidase-mediated tumour uptake was proven by pharmacological inhibition using β-aminopropionitrile and by employing negative-control analogues of impeded or abolished targeting capability. The latter were obtained by substituting the lysine residue by ornithine and norleucine, respectively. Comparing the tumour uptake of the lysine-containing peptide with that of the non-functional analogues indicate the feasibility of lysyl oxidase imaging in melanoma using substrate-based radiotracers.

Permalink: https://www.hzdr.de/publications/Publ-26215
Publ.-Id: 26215


Multiscaled experimental investigations of corrosion and precipitation processes after loss-of-coolant accidents in pressurized water reactors

Renger, S.; Alt, S.; Gocht, U.; Kästner, W.; Seeliger, A.; Kryk, H.; Harm, U.

In a joint research project of the Zittau/Goerlitz University of Applied Sciences (HSZG), the Technische Universitaet Dresden (TUD) and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the main emphasis is the time-related assignment of simultaneous and interacting mechanisms at zinc sources and zinc sinks at boundary conditions of a loss-of-coolant accident (LOCA) in German pressurized water reactors (PWR). The according experiments are carried out at semi-technical as well as at laboratory scale.
Zinc is used as a protective coating, e.g. for gratings in the containment, showing high corrosion resistance due to a gradual formation of passivating layers. In contrast, its long-term behaviour during LOCA changes significantly under the influence of the coolant chemistry of German PWR. As a consequence, according installations in the containment act as zinc sources due to corrosion. Released zinc ions change the chemical properties of the coolant and could e.g. lead to layer-forming depositions of zinc borates in the core, which increase the possibility of a hindered heat dissipation. For experimental and methodical investigations of these phenomena, the test rig “Zittau Flow Tray” (ZFT), a scaled sump model of a German PWR, was equipped with a full-length 3×3 fuel assembly (FA) dummy acting as core model, a preheater and a cooler component. Nine 4.4 m long fuel rod dummies simulate the decay heat by internal heating cartridges. This rig design enables experimental investigation of physico-chemical mechanisms considering coolant containing boric acid and zinc and their influence on the thermo-hydraulic processes in the reactor core at post-LOCA boundary conditions.
The time depending zinc release at hot-dip galvanized gratings (HGG) was investigated regarding their position (e.g. inside or near the leaking jet, freely suspended or submerged in the coolant) and their surface area as well as temperature and flow rate of the coolant. The experimental database allows the approximation of corrosion rates in dependence of HGG position and the accident-specific coolant leakage rate as well as the development of first mathematical approaches for the modelling of zinc sources.

Keywords: pressurized water reactor; PWR; corrosion; LOCA; loss-of-coolant accident; experiment; zinc; zinc borate; debris; deposition; precipitation; particle formation; chemical effects

  • Lecture (Conference)
    17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17), 03.-08.09.2017, Xi'an, China
  • Contribution to proceedings
    17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17), 03.-08.09.2017, Xi'an, China
    17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17)
  • Open Access Logo Nuclear Technology 205(2019)1-2, 248-261
    DOI: 10.1080/00295450.2018.1499324

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26214
Publ.-Id: 26214


Speziation trivalenter Actinide/Lanthanide im Verdauungssystem

Barkleit, A.; Wilke, C.

Im Falle einer Inkorporation radioaktiver Stoffe entstehen ernsthafte gesundheitliche Risiken durch deren Chemo- und Radiotoxizität. Um die möglichen toxischen Effekte besser abschätzen und letztendlich verhindern zu können, ist es notwendig, die Speziation dieser Elemente im menschlichen Organismus auf molekularer Ebene zu verstehen. Die Speziation beeinflusst die Aufnahme, den Transport, den Metabolismus, die Einlagerung und die Ausscheidung der Elemente.
Die Gefahr einer oralen Aufnahme von Radionukliden besteht durch kontaminierte Lebensmittel oder Trinkwasser. Deshalb haben wir die Speziation von ausgewählten dreiwertigen Actiniden und Lanthaniden (Cm(III) und Eu(III)) in den Biofluiden des Verdauungstraktes näher untersucht [1]. Die Biofluide wurden nach einer international anerkannten Methode (Unified Bioaccessibility Method, UBM) der Bioaccessibility Research Group of Europe (BARGE) synthetisch hergestellt [2]. Parallel dazu wurden natürliche menschliche Speichelproben zum Vergleich in die Untersuchungen einbezogen [3].
Die Speziatonsuntersuchungen von Cm(III) und Eu(III) in den Verdauungsfluiden wurden mit Hilfe der zeitaufgelösten laserinduzierten Fluoreszenzspektroskopie (Time-Resolved Laser-induced Fluorescence Spectroscopy, TRLFS) durchgeführt. Für Speichel wurde ermittelt, dass sich zum größten Teil (60-90%) anorganische Komplexe bilden, darunter dominiert ein ternärer Komplex mit Phosphat und Carbonat als Liganden und Calcium als weiterem Kation zum Ladungsausgleich. Organische Komplexe, hauptsächlich mit dem Verdauungsenzym α-Amylase, wurden ebenfalls nachgewiesen. Wenn die Speichelmischung den Magen erreicht, findet aufgrund des niedrigen pH-Wertes im Magen (pH<2) eine Dissoziation der Komplexe statt, Cm(III) und Eu(III) liegen dann hauptsächlich in Form ihrer Aquo-Komplexe vor. Aber ein kleiner Teil der Metallionen (ca. 20%) bildet trotz des niedrigen pH-Wertes Komplexe mit dem Verdauungsenzym Pepsin. Im Dünndarm, wo die eigentliche Verdauung und die Absorption der (Nähr-, aber auch Gift-)Stoffe in den Blutkreislauf stattfindet, werden die Metallionen hauptsächlich (ca. 65%) von dem Protein Muzin komplexiert, welches Hauptbestandteil der schützenden Schleimhaut (Mucosa) ist, und ca. 35% liegen als anorganische Spezies mit Phosphat und Carbonat als Liganden vor.

[1] C. Wilke et al., J. Inorg. Biochem. 175, 2017, 248-258
[2] J. Wragg et al., British Geological Survey Open Report OR/07/027, Keyworth, Nottingham, 2009, 90 pp.
[3] A. Barkleit et al., Dalton Trans. 46, 2017, 1593-1605.

Keywords: digestive media; speciation; europium; curium

  • Invited lecture (Conferences)
    2. Workshop - Helmholtz Cross Program Activity, Querschnittsthema Strahlenforschung "Transportprozesse in Mensch und Umwelt", 24.-25.10.2017, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26213
Publ.-Id: 26213


Liquid metal batteries

Weber, N.; Ashour, R.; Galindo, V.; Herreman, W.; Horstmann, G.; Kelley, D.; Köllner, T.; Landgraf, S.; Nimtz, M.; Nore, C.; Personnettaz, P.; Salas, A.; Starace, M.; Stefani, F.; Weier, T.

The talk will give an overview on fluid dynamics in liquid metal batteries.

  • Invited lecture (Conferences)
    GDRI dynamo, 27.11.2017, Paris, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26212
Publ.-Id: 26212


Simulation and experimental verification of magnetic field induced proton dose enhancement effects

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

Purpose/Objective
Proton therapy (PT) is expected to benefit greatly from integration with magnetic resonance (MR) imaging due to its sensitivity to anatomical variations. Consequently, the concept of MR-guided PT (MRPT) receives increased interest. Previous studies on MR-guided photon therapy (MRXT) have reported local dose enhancement of up to 40% at tissue-air interfaces caused by the electron return effect (ERE) in transverse magnetic fields. For MRPT, however, no consensus on the magnitude and hence the clinical effect of the ERE can be found in the scarcely available literature. The objectives of this study were 1) to confirm the ERE for PT by measurements and 2) to determine its magnitude for clinically relevant proton energies and MR field strengths by simulation.
Material/methods
Measurements were performed with a collimated 200 MeV proton beam traversing a PMMA phantom made of one or two 10 mm vertical slabs. Dose was measured with GafChromic EBT3 films (PMMA equivalent thickness 0.312 mm) using two experimental setups: (A) as reference, one film sandwiched between two slabs and (B) two films attached to the distal end of one slab, resulting in effective measurement depths of 10.156, 0.467, and 0.156 mm from the air interface. Film irradiations were performed under the same conditions without and within a transversal field (0.92 ± 0.02 T) of a permanent magnet. All measurements were repeated 4 to 8 times and the entire experiment was performed twice.
Monte Carlo simulations were performed using Geant4 (V 10.3). The proton beam shaping devices, magnetic field and PMMA slabs were modelled in detail. The EBT3 films were simulated as PMMA slabs and dose was scored in PMMA from 25 to 1000 μm distance to the air interface. Additionally, field strengths were varied between 0.35 and 1.5 T for a 210 MeV proton beam as well as proton energy between 90 and 210 MeV at 1 T. The dose enhancement ratio was defined as dose with divided by dose without magnetic field: DB/D.
Results
Significant dose enhancement was measured at the PMMA-air interface with magnetic field compared to no field (p<0.01) and confirmed by repeated experiments. The dose enhancement decreased with increasing distance from the interface (Fig. 1). Good agreement was achieved between measured and simulated dose both with and without magnetic field.
The dose enhancement ratio was largest in simulations with strong magnetic fields increasing from 2.0% in the presence of a 0.35 T field up to 7.4% for a 1.5 T field near the interface (Fig. 2). A decrease of the proton energy resulted in a decreasing dose enhancement ratio.
Conclusion
For the first time, the ERE for proton beams in a transverse magnetic field was demonstrated experimentally. The significant dose enhancement is predictable and limited to within 1 mm from the air interface for clinically relevant proton energies and magnetic field strengths.
Although smaller than for MRXT, the ERE may affect the clinical treatment of e.g. lung tumors.

  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S317-S318

Permalink: https://www.hzdr.de/publications/Publ-26211
Publ.-Id: 26211


Robust optimization is not sufficient to account for anatomical changes in bilateral head and neck intensity-modulated proton therapy

Cubillos Mesias, M.; Troost, E.; Lohaus, F.; Agolli, L.; Rehm, M.; Richter, C.; Stützer, K.

Purpose/Objective
Robust optimization in proton therapy considers uncertainties in patient setup and particle range during the plan optimization. In general, however, anatomical changes occurring during the treatment course, potentially causing a degradation of the plan quality, are neglected. The aim of this study was to quantify the influence of these changes on the dose distribution for patients with bilateral head and neck cancer (HNC).

Material/Methods
Datasets from 20 HNC patients, consisting of a planning CT and weekly control CTs (cCT), were analyzed. Intensity-modulated proton therapy (IMPT) plans with minimax robust optimization were calculated, accounting 3 mm and 3.5% for setup and range uncertainty, respectively. Prescribed doses to the low- and high-risk clinical target volume (CTV) were 57 and 70 Gy(RBE), respectively, delivered in 33 fractions. The organs at risk (OAR) spinal cord, brainstem, parotid glands, larynx, pharyngeal constrictor and esophageal inlet muscle were considered for plan optimization. Weekly cumulative doses, taking the anatomical variations of the cCTs into account, were compared with the nominal plan.
When a reduction in target coverage and/or increased dose to OARs was detected, a plan adaptation was performed on the cCT where the dose degradation was observed. Furthermore, for these patients an additional robust plan was calculated, taking also anatomical changes from the first two cCTs into account in the robust optimization. It was evaluated if a subsequent plan adaptation would still be necessary.

Results
Nominal plans fulfilled the clinical specifications of D98% ≥ 95% of the prescribed dose to the CTVs (range 96.58-98.81% for low-risk CTV and 96.83-98.76% for high-risk CTV). During the treatment course, anatomical changes lead to reduced weekly cumulative D98% values in five patients (25%; minimum 90.17% for low-risk CTV and 89.19% for high-risk CTV). Doses in OARs remained below the clinical constrains during the treatment course. One treatment adaptation was performed for each of these five patients, which allowed a target coverage improvement (range 97.68-99.72% for low-risk CTV and 95.89-98.46% for high-risk CTV). Total cumulative doses including adaptation were acceptable (range 96.67-98.37% for low-risk CTV and 95.11-97.39% for high-risk CTV, see Figure 1a).
The results for the more sophisticated robust plan, considering the first two cCTs, were diverse: whereas plan adaption became obsolete in one patient, the total cumulative dose would, without adaptation, still have been below clinical constraints in another (Figure 1b and 2).

Conclusion
In a substantial number of patients, robust optimization only is not sufficient to account for anatomical changes occurring during the treatment course, resulting in severe target coverage degradation. Assessment of the cumulative weekly doses allowed detection of target coverage loss. The importance of frequent in-treatment imaging is underlined.

Keywords: robust optimization; treatment adaptation; proton therapy

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S271-S272
    DOI: 10.1016/S0167-8140(18)30827-2

Permalink: https://www.hzdr.de/publications/Publ-26210
Publ.-Id: 26210


First in-beam MR scanner for image-guided proton therapy: beam alignment and magnetic field effects

Schellhammer, S. M.; Karsch, L.; Smeets, J.; L'Abbate, C.; Henrotin, S.; van der Kraaij, E.; Lühr, A.; Quets, S.; Pawelke, J.; Hoffmann, A.

Purpose/Objective
Although proton therapy is expected to greatly benefit from integration with magnetic resonance (MR) imaging for on-line image guidance, to date such integration has not been realized. Both the MR scanner’s static (B0) and gradient magnetic fields may compromise beam quality. The aim of our study was 1) to align the field-of-view (FOV) of an MR scanner with a horizontal fixed proton beam line and 2) to assess the effects of the scanner’s B0 and gradient fields on the beam.

Material/methods
Beam alignment: An open MR scanner (MRJ2200, Paramed) featuring a 0.22 T vertical magnetic field was mounted on a trolley and RF-shielded by a compact Faraday cage (Fig. 1). To ensure that the beam traverses the scanner’s magnetic isocentre for beam energies between 70 and 230 MeV, the Lorentz-force induced beam deflection was predicted by Monte Carlo (Geant4) simulations based on Hall probe (HHP-VU, Arepoc) based mapping of the scanner's B0 field. The magnetic isocentre of the scanner was marked by the overlapping gradient fields being visible as dark crosses in 3 orthogonal slices using an MR imaging phantom (ACR Small Phantom). The proton beam was collimated to Ø10 mm and localized in the FOV by radiochromic film (Gafchromic EBT3, Ashland) affixed vertically to the phantom’s front.
Beam quality assessment: 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 at 220 cm from the beam exit window. These measurements were repeated while performing spin echo and gradient echo sequences (gradient up to 5.7 mT/m). Planar dose distributions of 72 and 125 MeV beams were measured at the scanner’s FOV with films placed horizontally between two PMMA slabs.

Results
Beam alignment: As a mean lateral deflection of 2 cm was predicted at the magnetic isocenter, the scanner was laterally displaced by 2 cm from the beam’s central axis. The dose distribution on the vertically oriented film confirmed a proper alignment of the beam and the FOV. Thus, the scanner's position was fixed and a cylindrical beam guide was installed into the Faraday cage at beam entrance.
Beam quality assessment: On the scintillation detector, the beam showed a horizontal deflection of 22, 16 and 11 cm for 72, 125 and 219 MeV, respectively, and a vertical deflection below 0.6 mm. The horizontal deflection was taken into account for installing a beam stopper, while vertical deflection was considered negligible. The beam profiles were not affected by the gradient fields of the sequences. Planar film measurements showed curved beam paths with a lateral Bragg peak displacement of 2 and 5 mm for 72 and 125 MeV, respectively (Fig. 2).

Conclusion
Alignment of an open MR scanner’s FOV with a horizontal fixed proton beam has been realized taking into account the scanner’s B0 field induced beam deflection. Sequence-dependent gradient fields do not affect the beam profile.

  • Lecture (Conference)
    ESTRO 37 - Annual Meeting of the European Society for Radiotherapy & Oncology, 20.-24.04.2018, Barcelona, Espana
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S318-S319
    DOI: 10.1016/S0167-8140(18)30915-0

Permalink: https://www.hzdr.de/publications/Publ-26209
Publ.-Id: 26209


Chemische Effekte bei Kühlmittelverluststörfällen in Druckwasserreaktoren - Arbeiten des Kompetenzzentrums Ost für Kerntechnik

Kryk, H.; Kästner, W.; Hampel, U.; Seeliger, A.

Zur Abfuhr der Nachzerfallswärme in der Spätphase eines Kühlmittelverluststörfalles in Druckwasserreaktoren wird das aus den Leck im Primärkreislauf austretende Kühlwasser aus dem Reaktorsumpf im sog. Sumpfumwälzbetrieb mittels der Niederdruckeinspeisepumpen in den Reaktorkern rezirkuliert. Im Containment kommt das Kühlmittel dabei in Kontakt mit Fremdstoffen, wie z.B. Isoliermaterialfasern, Staub und korrosiven Materialien, welche einerseits die Kühlmittelchemie und andererseits die Performance der den Pumpen vorgeschalteten Sumpfsiebe beeinflussen können. Weiterhin haben Studien gezeigt, dass feuerverzinkte Containment-Einbauten (z.B. Lichtgitterroste, Stützgitter von Sumpfsieben, Kanäle) einer beschleunigten Korrosion durch das borsäurehaltige Kühlmittel unterliegen. Die daraus resultierenden thermohydraulischen Effekte hängen in hohem Maße vom Löslichkeitsverhalten der Korrosionsprodukte ab. So können unlösliche Korrosionspartikel zu einem erhöhten Differenzdruck an den bereits mit Isoliermaterialfasern beladenen Sumpfsieben führen, während lösliche Korrosionsprodukte nicht zurückgehalten werden und somit in den Kern gelangen, was unter Umständen in Ausfällungsprozessen durch Temperaturänderungen resultiert.
Da ein Einfluss dieser Effekte auf die Kernkühlung nicht ausgeschlossen werden kann, ist die Untersuchung der zugrundeliegenden physikochemischen Korrosions-, Ausfällungs- und Ablagerungsprozesse sowie deren thermohydraulischen Folgen Gegenstand von gemeinsamen Forschungsvorhaben des Helmholtz-Zentrums Dresden-Rossendorf, der TU Dresden sowie der Hochschule Zittau-Görlitz. Der Vortrag gibt einen Überblick über die bisherigen Forschungsarbeiten der o.g. Institutionen sowie die wesentlichen Ergebnisse der entsprechenden BMWi-Forschungsvorhaben im Kontext der Reaktorsicherheitsforschung.

Keywords: Kühlmittelverluststörfall; KMV; Druckwasserreaktor; DWR; Korrosion; Zink; Zinkborat; Reaktorsicherheitsforschung; Loss-of-coolant Accident; LOCA; Pressurized Water Reactor; PWR; Corrosion; Zinc; Zinc Borate; Nuclear Safety Research; Chemical Effects

  • Invited lecture (Conferences)
    49. Kraftwerkstechnisches Kolloquium 2017, 17.-18.10.2017, Dresden, Deutschland
  • Contribution to proceedings
    49. Kraftwerkstechnisches Kolloquium 2017, 17.-18.10.2017, Dresden, Deutschland
    Kraftwerkstechnik 2017 - Strategien, Anlagentechnik und Betrieb, Freiberg: SAXONIA, 978-3-934409-79-8, 101-115

Permalink: https://www.hzdr.de/publications/Publ-26208
Publ.-Id: 26208


Combining different genomic signatures to improve the predictive power for LRC after PORT-C in HNSCC

Schmidt, S.; Linge, A.; Zwanenburg, A.; Leger, S.; Großer, M.; Lohaus, F.; Gudziol, V.; Nowak, A.; Tinhofer, I.; Budach, V.; Stuschke, M.; Balermpas, P.; Rödel, C.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Belka, C.; Combs, S. E.; Mönnich, D.; Zips, D.; Baretton, G. B.; Buchholz, F.; Baumann, M.; Krause, M.; Löck, S.

Purpose: To improve compare and improve the performance of a hypothesis-driven 7-gene signature by with a signature based on whole transcriptome analysis for the prognosis of loco-regional tumour control (LRC) in patients with HPV-negative locally advanced head and neck squamous cell carcinoma (HNSCC) after postoperative radiochemotherapy (PORT-C).

Material and methods: Gene expression analyses were performed on a multicentre retrospective cohort of 125 patients with HPV16 DNA negative HNSCC using the GeneChip® Human Transcriptome Array 2.0 (Affymetrix) for whole transcriptome analysis. To identify a gene signature prognostic for LRC from the whole transcriptome data, 3085 genes were considered, which previously have been related to radioresistance or response to radiotherapy [1-4]. The final gene signature was based on the comparison of different signature sizes, feature selection algorithms and prognostic models. The performance of the whole transcriptome-based signature was compared to a previously identified 7-gene signature based on nanoString analysis of a hypothesis-driven gene set containing 171 genes, using the concordance index (ci). The signatures were applied independently and combined to stratify patients into groups of low (LR) and high (HR) risk of recurrence.

Results: The identified gene signatures based on whole transcriptome data showed improved performance (ci 0.79-0.87) compared to the signatures based on the hypothesis-driven gene set (0.72-0.78). The model with the best performing gene signature contained genes related to tumourigenesis, invasion, cell cycle regulation and immune response. Patient stratification into low and high risk groups was performed for both signatures, see figures (A) and (B). The difference in LRC between both groups was highly significant (p<0.001). Compared to the 7-gene nanoString signature, the LR group showed a slightly improved LRC for the Affymetrix signature, similar to that of HPV positive tumours. Finally, a combined high risk group was defined, including patients who were classified as high risk patients by both gene signatures. This patient group showed a poor LRC of only about 45% compared to the individual signatures, see figure (C).

Conclusion: We determined a gene signature predicting LRC in a cohort of 125 HPV16 DNA negative HNSCC patients after PORT-C based on whole transcriptome analysis.
This signature showed improved performance compared to the 7-gene signature identified on a limited hypothesis-driven gene set, indicating that the inclusion of additional genes during feature selection may lead to a better performing signature.s may further enhance this signature.
The combination of both models allowed for the identification of a patient group with HPV-negative HNSCC who are on a particularly high risk of developing a recurrence, and may be considered for future dose-escalation trials.

Keywords: Head and neck squamous cell carcinoma; Genomics; Machine Learning; HNSCC; Cancer; Radiotherapy

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, Spanien
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S140-S141
    DOI: 10.1016/S0167-8140(18)30586-3

Permalink: https://www.hzdr.de/publications/Publ-26207
Publ.-Id: 26207


Research Data Management to increase research quality

Konrad, U.

The publication is an invited plenary lecture at the national workshop on documentation and information in Jakarta, Indonesia.
Research data play a fundamental role in todays open science driven research. In addition the software used to generate, process or analyse the data has to be considered for the whole research and publication process to ensure, that results are findable, accessible, interoperable, re-usable and re-producible. The lecture describes the challenges, tasks, solutions and organization structures to meet the challenges for the library and data center at the Helmholtz-Center Dresden-Rossendorf and beyond.

Keywords: Open Science; Research Data Management; Software Management; Data Center; Library

  • Invited lecture (Conferences)
    National Workshop on Documentation and Information Data, Information and Knowledge, 25.-26.10.2017, Jakarta, Indonesia
    DOI: 10.5281/zenodo.1040289

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26206
Publ.-Id: 26206


Characterization of in-beam MR imaging performance during proton beam irradiation

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

Purpose/Objective
Given the sensitivity of proton therapy (PT) to anatomical changes, it could greatly benefit from integration with magnetic resonance (MR) imaging. Hence, there is growing interest to investigate the technical feasibility of MR-integrated proton therapy (MRiPT). The aim was to operate an MRI system in the beam of a PT facility and to characterize the MR imaging performance during simultaneous irradiation.

Material and Methods
A 0.22 T open MR scanner (MrJ2200, Paramed Medical Systems) was installed in a compact Faraday cage at the fixed horizontal beamline of our PT facility. A beam guide in the wall of the cage allows beam transmission to the field-of-view (FOV) of the scanner. The scanner’s magnetic isocenter was aligned, such that a 10 mm diameter collimated proton beam of 125 MeV was stopped in the most distal image slice of the ACR Small Phantom, which was centrally positioned in the FOV inside a dedicated knee coil. Prior to irradiation, the magnet was shimmed and the magnetic field homogeneity (MFH) was mapped over a 22 cm diameter spherical volume by a magnetic field camera (MFC3045, Metrolab). To assess the effect of magnetic fringe fields of the nearby beam line magnets, the MFH measurements were repeated while these magnets were energized for beam energies between 70-220 MeV. During irradiation, the phantom was imaged using T1 and T2-weighted spin echo (SE) sequences with parameter settings according to the phantom test guidance from the ACR. Additionally, two gradient echo (GRES and GREL) scans were performed with a short repetition time (TR) and long echo time (TE): TR = 30 and 80 ms, and TE = of 8 and 30 ms, respectively, a flip angle of 20 deg and acquired voxel size of 0.63x0.79x5.00 mm3. A validated software tool (MATLAB) was used to extract the ACR imaging parameters and to estimate a geometric transformation from image pairs with and without beam.

Results
After shimming, the peak-to-peak MFH was 88 ppm, which is within the scanner’s operating specifications. The MFH measurements with and without energized beam line magnets show no significant differences, but the baseline resonance frequency was increased by 70-110 Hz depending on beam energy. The SE and GRE image quality was sufficient for analysis. Differences in ACR parameters due to operating the beam line magnets or the beam were within measurement uncertainties. A sequence-dependent translation of 0.5-3 mm in frequency encoding direction was observed in the images due to empowering of the beam line magnets, with GREL being the most sensitive sequence.

Conclusion
No degradation of the performance of the in-beam MR system was found during simultaneous operation with the PT system. Although MR imaging during irradiation does not deteriorate the ACR parameters, there is a sequence-dependent off-resonance image displacement when the beam line magnets are energized. This proof-of-concept justifies further research towards the development of a first prototype for MRiPT.

Keywords: MR imaging; proton therapy; image quality

Permalink: https://www.hzdr.de/publications/Publ-26205
Publ.-Id: 26205


Novel concept to personalize radiation oncology: Predicting cell-specific survival prior to treatment

Oesten, H.; von Neubeck, C.; Jakob, A.; Loeck, S.; Enghardt, W.; Krause, M.; Mcmahon, S. J.; Grassberger, C.; Paganetti, H.; Lühr, A.

(1) Purpose/Objective
To enhance tumor response and thus treatment outcome in radiation therapy, a dose prescription strategy prior to treatment is necessary to individualize radiation oncology.
However, prediction of cell-specific survival prior to treatment is currently unavailable. Thus, we developed an approach to stratify patients prior to therapy by predicting individual radiation response based on cell survival.

(2) Material/methods
Based on a previously developed mechanistic radiation response model of DNA repair and cell survival (S_cell) prediction for normal tissue cells, we simulated measured ∝- and β-values of 19 in vitro cancer cell lines (skin, lung, brain). The radiation model incorporates four cell-specific parameters: number of chromosomes, p53-mutation-status, cell-cycle distribution and the effective genome size (eGS). The first three are only experimentally available; the latter was obtained through minimizing the difference between the simulated and measured ∝- and β-values. A parametrization of eGS as a function of the cells’ chromosome number was proposed. The correct choice of all parameters was validated by an independent dataset of time-dependent γ-H2AX data over 24h.

(3) Results
Overall good agreement between simulated and measured in vitro cancer S_cell curves was achieved (Fig. 1). The measured β values were found to increase quadratically with the obtained eGS (R^2=0.81) irrespectively of other cell-specific parameters (Fig. 2b). The measured ∝ values increased linearly with the eGS manifesting different slopes distinguishable into the cells’ p53-mutation-status (Fig. 2a). Measured ∝ and β were predictable based on eGS with an uncertainty of one sigma: σ=0.04Gy^(-1) for ∝ and σ=0.01Gy^(-2) for β. The eGS was found to correlate (R^2=0.70) with the number of chromosomes for all but four cell lines. The detailed cell-specific cell cycle distributions were found to have a negligible impact on the radiobiological parameters. Measured time-dependent γ-H2AX data was predictable through repair kinetics simulations.

(4) Conclusion
A mechanistic model for radiation response of normal human cells was successfully modified to allow for simulations of measured in vitro S_cell of 19 cancer cell lines. Independent of cancer entity, the radiobiological value β was predictable only by the eGS while the prediction of ∝ required in addition at least knowledge of the p53-mutation-status. An enhanced correlation of the eGS with a clinically accessible parameter, as suggested, may facilitate a stratification strategy based on cell-specific survival prediction for individualized patient treatment in radiotherapy.

  • Lecture (Conference)
    ESTRO 37 - Innovation for Value and Access, 20.-24.04.2018, Barcelona, Spanien

Permalink: https://www.hzdr.de/publications/Publ-26204
Publ.-Id: 26204


Population balance modeling using class and quadrature-based moment methods with application to bubbly flows

Oertel, R.; Li, D.; Pollack, M.; Saalenbauch, S.; Schlegel, F.; Hasse, C.; Lucas, D.

Multi-phase flows with a continuous and a distinct disperse phase are essential in a variety of industrial applications, e.g., in chemical engineering or in nuclear safety research. These flows are usually polydisperse, i.e., the disperse phase exhibits a size distribution. In case of bubbly flows, the size distribution and its statistical moments are highly influenced by the overall heat- and mass transfer rates as well as the flow structure, e.g., during the transition from the homogeneous to the heterogeneous regime in bubble columns. Temporal and spatial changes of the size distribution can be described with a transport equation for the number density function (NDF), i.e., the population balance equation (PBE). Two popular Eulerian methods to solve the PBE are the method of classes and the family of Quadrature Based Methods of Moments (QBMM). Both approaches have been applied in CFD before, e.g., for simulations of stirred tanks, spray behavior or soot formation. However, OpenFOAM offers no capabilities in this regard. While the Quadrature Method of Moments (QMOM) - the basic QBMM approach - tracks only the moments of the NDF, class methods track the shape of the NDF directly by means of discretization. An extended version of QMOM, called EQMOM, allows reconstructing the NDF using a set of kernel density functions. All three approaches are implemented into the OpenFOAM library and validated against analytical solutions. A comparison for pipe flow and bubble column cases using appropriate coalescence and breakup models shows the accuracy and performance of each method. Furthermore, it is known for bubbly flows that the velocity of the disperse phase is generally size dependent and the bubbles may separate spatially. An extreme case is the lift force, which governs the lateral migration of bubbles in a liquid shear field and changes its sign at a critical diameter. This effect is not covered by the general two-fluid or Euler-Euler approach. Partially, this can be taken into account using a multi-fluid solver, by splitting the disperse phase into velocity groups with fixed boundaries. An alternative approach is to include the velocity as an internal coordinate into the PBE, which gives the generalized PBE (GBPE). Using a size-conditioned velocity approach, the GBPE can be solved within the QBMM framework. Thereby, a continuous information about the dependency of velocity on size can be obtained. The work presents first results and comparisons between the two approaches.

  • Invited lecture (Conferences)
    5th OpenFOAM User Conference, 17.-18.10.2017, Wiesbaden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26203
Publ.-Id: 26203


Markers from Australia’s nuclear legacy in marine wildlife

Hotchkis, M.; Child, D.; Johansen, M. P.; Collins, R. N.; Howell, N.; Howard, D. L.; Ikeda-Ohno, A.

Accelerator Mass Spectrometry (AMS) provides a high-sensitivity method for detection of long-lived radioisotopes. New facilities at ANSTO’s Centre for Accelerator Science are enabling us to detect plutonium by AMS with unprecedented level of sensitivity. We can now detect traces of the isotope 244Pu (half-life 80 million years) which arrive on earth on interstellar dust. However, the predominant source of plutonium on earth’s surface is from human activities, in particular from atmospheric nuclear testing of the 1950-1960’s. In Australia, the radiological residues originating from the British tests at the Montebello Islands, WA, occur in distinct isotopic and morphologic forms. The three tests had slightly different Pu isotopic signatures. Today, aided by the high sensitivity of AMS, their distinct 240/239Pu atom ratios can be differentiated in biological samples, such as failed sea turtles eggs gathered from beaches. Local fish tend to reflect a mixture of all three tests due to the movement of the fish and transport of Pu by water currents. On a larger scale, the 240/239Pu atom ratios in all samples (median ratio 0.04) are distinct from worldwide fallout (0.17-0.18) and can be used as a tracer for migrating species. The Pu exists in the environment in the form of ‘hot’ particles; the mobility of these particles and their availability for uptake into living organisms depends on their physical and chemical characteristics, which we are currently studying using a range of methods including synchrotron-based X-ray fluorescence microscopy (XFM).

Keywords: Nuclear tests; radioactive contamination; environment; plutonium; AMS; synchrotron; XFM

  • Lecture (Conference)
    ANSTO User Meeting, 22.-24.11.2017, National Centre for Synchrotron Science, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-26202
Publ.-Id: 26202


Sb-related defects in Sb-doped ZnO thin film grown by pulsed laser deposition

Luo, C.; Ping, H. L.; Azad, F.; Anwand, W.; Butterling, M.; Wagner, A.; Kuznetsov, A.; Zhu, H.; Su, S. C.; Ling, F. C. C.

Sb-doped ZnO films were fabricated on c-plane sapphire using the pulsed laser deposition method and characterized by the Hall effect measurement, X-ray photoelectron spectroscopy, X-ray diffraction, photoluminescence and positron annihilation spectroscopy. Systematic studies on the growth conditions with different Sb composition, oxygen pressure and post-growth annealing were conducted. If the Sb doping concentration is lower than the threshold ~8×E20 cm-3, the as-grown films grown with appropriate oxygen pressure could be n~4×E20 cm-3. The shallow donor was attributed to the SbZn related defect. Annealing these samples lead to the formation of the SbZn-2VZn shallow acceptor which subsequently compensated the free carrier. For samples with Sb concentration exceeding the threshold, the yielded as-grown samples were highly resistive. X-ray diffraction results showed that the Sb dopant occupied the O site rather than the Zn site as the Sb doping exceeded the threshold, whereas the SbO related deep acceptor was responsible for the high resistivity of the samples.

Keywords: ZnO; Sb-doping; shallow donors; shallow acceptors; compensating defects

Permalink: https://www.hzdr.de/publications/Publ-26200
Publ.-Id: 26200


Magnetohydrodynamic flow simulation in liquid metal batteries

Weber, N.; Personnettaz, P.; Stefani, F.; Weier, T.

Overview about numerical simulation of liquid metal batteries at HZDR

  • Lecture (Conference)
    OpenFuelCell Workshop, 24.10.2017, Forschungszentrum Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26199
Publ.-Id: 26199


Radionuklide in der Biosphäre - molekulare Wechselwirkung mit Mikroorganismen

Raff, J.

Im Rahmen des Vortrags wird anhand von verschiedenden Organismen wie Algen, Bakterien und Pilzen erläutert, wie Mikroorganismen mit Radionukliden interagieren und welche Konsequenzen diese Wechselwirkung für das Migrationsverhalten von Radionukliden in der Umwelt hat.

Keywords: Mikroorganismen; Radionuklide; Wechselwirkungen; Migration

  • Invited lecture (Conferences)
    2. Workshop – Helmholtz Cross Program Activity Querschnittsthema Strahlenforschung „Transportprozesse in Mensch und Umwelt", 24.-25.10.2017, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26198
Publ.-Id: 26198


Radionuclides in living organisms – Calorimetric determination of the radionuclide toxicity

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

Quantification of radionuclide transfer within the environment and to the food chain is required for the reliable human risk assessment. The uptake of radionuclides by plants is typically described phenomenologically by transfer factors. However, investigations on a molecular level are necessary to understand the underlying processes. We studied the interaction of U(VI) with canola cells (Brassica napus) focusing on the concentration-dependent impact of U(VI) on the cell metabolism. Isothermal microcalorimetry was used to monitor the metabolic heat flow of the cells, which was compared to the cell viability. The speciation of U(VI) in the medium was determined by time-resolved laser-induced fluorescence spectroscopy and thermodynamic modeling. The data reveal the correlation of U(VI) hydroxo species with metabolic heat release and general oxidoreductase on a quantitative toxicity scale [1].

[1] Sachs, S., Geipel, G., Bok, F., Oertel, J., Fahmy, K., Calorimetrically determined U(VI) toxicity in Brassica napus correlates with oxidoreductase activity and U(VI) speciation. Env. Sci. Technol. 51 (2017) 10843.

Keywords: plant cells; uranium; cell metabolisms; isothermal microcalorimetry; cell viability; speciation; TRLFS; thermodynamic modeling; speciation

  • Invited lecture (Conferences)
    2. Workshop - Helmholtz Cross Program Activity, Querschnittsthema Strahlenforschung "Transportprozesse in Mensch und Umwelt", 24.-25.10.2017, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26197
Publ.-Id: 26197


Ultra-high-speed X-ray imaging of laser-driven shock compression using synchrotron light

Olbinado, M. P.; Cantelli, V.; Mathon, O.; Pascarelli, O.; Rack, A.; Grenzer, J.; Pelka, A.; Roedel, M.; Prencipe, I.; Garcia, A. L.; Helbig, U.; Kraus, D.; Schramm, U.; Cowan, T.; Scheel, M.; Pradel, P.; de Resseguier, T.

A high-power, nanosecond-pulsed laser impacting the surface of a material can generate an ablation plasma that drives a shock wave into it; while in situ X-ray imaging can provide a time-resolved probe of the shock-induced material behaviour on macroscopic lengths scales. Here, we report on an investigation into laser-driven shock compression of a polyurethane foam and a graphite rod by means of single-pulse synchrotron X-ray phase-contrast imaging with a MHz frame rate. A 6-J, 10-ns-pulsed laser was used to generate shock compression. Physical processes governing the laser-induced dynamic response such as elastic compression, compaction, pore collapse, fracture, and fragmentation have been imaged; and the advantage of exploiting the partial spatial coherence of a synchrotron source for studying low-density, carbon-based materials is emphasized. The successful combination of a high-energy laser and ultra-high-speed X-ray imaging using synchrotron light demonstrates the potentiality of accessing complementary information from scientific studies of laser-driven shock compression.

Keywords: laser shock; ultra-high-speed imaging; synchrotron radiation; X-ray phase contrast; time-resolved studies; foam; graphite; shock

Permalink: https://www.hzdr.de/publications/Publ-26196
Publ.-Id: 26196


Enzymatic Decolourization of Water Using Loofa Sponge as Cellular Carrier: Immobilization and Dye Degradation Performance

Mohammed, I.; Werner, A.; Schubert, M.; Hampel, U.

In recent years, strong efforts have been made to develop sustainable biocatalytic decolorization processes for dye-polluted water. In particular, dye-oxidizing laccase enzymes immobilized on suitable carriers are promising candidates, which can be reused as long as the activity is sufficiently high.
In this work, we propose, for the first time, a new methodology to immobilize laccase from Trametes hirsute on natural-grown and decomposable cellular loofa sponge carrier and assess the capability to degrade dye-polluted water. High immobilization activity is achieved and about 70 % residual activity remains after 8 cycles. Additionally, we determined homogenous and heterogeneous kinetic parameters for free and immobilized enzymes. Results reveal four times higher Michaelis-Menten constant of the laccase immobilized on loofa due to mass transfer and mixing limitations in packed bed bio-reactor.
Eventually, the response surface methodology was applied to identify favorable operation condition in terms of dye concentration, treatment time and mixing velocity. Here, the results demonstrated a remarkable dye removal capability with shorter treatment time compared to the previous studies on immobilized laccase reported in the literature.

Keywords: Laccase; Enzymatic decolorization; Loofa sponge; Immobilization; activity analysis; Response surface methodology

Permalink: https://www.hzdr.de/publications/Publ-26195
Publ.-Id: 26195


Observation of ultrafast solid-density plasma dynamics using femtosecond X-ray pulses from a free-electron laser

Kluge, T.; Rödel, M.; Metzkes, J.; Bussmann, M.; Erbe, A.; Galtier, E.; Garcia, A. L.; Garten, M.; Georgiev, Y. M.; Gutt, C.; Hartley, N.; Huebner, U.; Lee, H. J.; Mcbride, E. E.; Nakatsutsumi, M.; Nam, I.; Pelka, A.; Prencipe, I.; Rehwald, M.; Christian, R.; Schönherr, T.; Zacharias, M.; Zeil, K.; Glenzer, S.; Schramm, U.; Cowan, T. E.

The complex physics of the interaction between short pulse high intensity lasers and solids is so far hardly accessible by experiments. As a result of missing experimental capabilities to probe the complex electron dynamics and competing instabilities, this impedes the development of compact laser-based next generation secondary radiation sources, e.g. for tumor therapy, laboratory-astrophysics, and fusion. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that Small Angle X-ray Scattering (SAXS) of femtosecond X-ray free-electron laser (XFEL) pulses facilitates new capabilities for direct in-situ characterization of intense short-pulse laser plasma interaction at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short pulse high intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the pre-inscribed grating, due to plasma expansion, which is an hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.

  • Open Access Logo Physical Review X 8(2018), 031068
    DOI: 10.1103/PhysRevX.8.031068
  • Lecture (Conference)
    59th Annual Meeting of the APS Division of Plasma Physics, 23.-27.10.2017, Milwaukee, USA
  • Lecture (Conference)
    10th International Conference on Inertial Fusion Sciences and Applications, 11.-12.09.2017, Saint Malo, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26194
Publ.-Id: 26194


Competing forces in liquid metal electrodes and batteries

Ashour, R.; Kelley, D.; Salas, A.; Starace, M.; Weber, N.; Weier, T.

Liquid metal batteries have been proposed for low-cost grid scale energy storage. During their operation, solid intermetallic phases often form in the cathode and are known to limit the efficiency of the cell. Fluid flow in the liquid electrodes can enhance mass transfer and reduce or avoid the formation of intermetallics, and fluid flow can be promoted by careful choice of the locations and topology of a battery’s electrical connections, which affect the thermal buoyant forces and electromagnetic forces acting on the electrodes. In this context we study four phenomena that drive flow: Rayleigh-Bénard convection, internally heated convection, electro-vortex flow, and swirl flow, in both experiment and simulation. In experiments, we use ultrasound Doppler velocimetry (UDV) to measure the flow of an electrode made of liquid eutectic PbBI at 160 ◦ C and subject to all four phenomena. In numerical simulations, we isolate the phenomena and simulate each separately using OpenFOAM. Comparing simulated velocities to experiments via a UDV beam model, we find that all four phenomena can enhance mass transfer in LMBs. We explain the flow direction and structure, and give estimates for the magnitude of the mean velocity depending on the cell current. We describe how the phenomena interact and propose dimensionless numbers for estimating their mutual relevance. A brief discussion of electrical connections summarizes the engineering implications of our work.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26193
Publ.-Id: 26193


In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Tokel, O.; Turnalı, A.; Makey, G.; Elahi, P.; Çolakoğlu, T.; Ergeçen, E.; Yavuz, Ö.; Hübner, R.; Zolfaghari Borra, M.; Pavlov, I.; Bek, A.; Turan, R.; Koray Kesim, D.; Tozburun, S.; Ilday, S.; Ilday, F. Ö.

Silicon is an excellent material for microelectronics and integrated photonics, with untapped potential for mid-infrared optics. Despite broad recognition of the importance of the third dimension, current lithography methods do not allow the fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements, electronic devices and better electronic–photonic integration are lacking. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1-μm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has an optical index different to that in unmodified parts, enabling the creation of numerous photonic devices. Optionally, these parts can be chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface - that is, ‘in-chip’ - microstructures for microfluidic cooling of chips, vias, micro-electromechanical systems, photovoltaic applications and photonic devices that match or surpass corresponding state-of-the-art device performances.

Permalink: https://www.hzdr.de/publications/Publ-26192
Publ.-Id: 26192


Nanomagnet fabrication by ion beams

Fassbender, J.

In recent years the tailoring of magnetic properties by means of ion irradiation and implantation techniques has become fashionable. Early investigations relied on the fact that the perpendicular magnetic anisotropy of Co/Pt multilayers depend sensitively on the interface sharpness [1]. Subsequently also the ion induced modification of exchange bias phenomena as well as interlayer exchange coupling have been investigated [2]. For single magnetic films ion implantation has been used to reduce the Curie temperature and hence the saturation magnetization [3]. Nowadays also the reverse process, i.e. the creation of nanomagnets within special binary alloys is employed [4,5]. In combination with lithography or with focused ion beams a pure magnetic patterning becomes possible [6] leading to hybrid magnetic materials [7] with properties different from both, the ion irradiated as well as the untreated material. Even ion induced chemical reduction can be employed to create a nanomagnetic pattern [8,9].
An overview of the present status in this research field will be given.
[1] C. Chappert et al., Science, 280 (1998) 1919.
[2] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D, 37 (2004) R179. [3] J. Fassbender, J. McCord, Appl. Phys. Lett., 88 (2006) 252501.
[4] E. Menendez et al., Small, 5 (2009) 229.
[5] R. Bali et al., Nano Lett., 14 (2014) 435.
[6] J. Fassbender and J. McCord, J. Magn. Magn. Mater., 320 (2008) 579. [7] J. McCord, L. Schultz, J. Fassbender, Adv. Mater., 20 (2008) 2090.
[8] S. Kim et al., Nature Nanotechnology, 7 (2012) 567.
[9] J. Fassbender, Nature Nanotechnology, 7 (2012) 554.

Keywords: magnetism; ion irradiation; magnetic patterning

  • Invited lecture (Conferences)
    Moscow International Symposium on Magnetism, 01.-05.07.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-26191
Publ.-Id: 26191


Gefüge und Eigenschaften des warmfesten Chromstahls P91

Kohlar, S.

Aufgabenstellung:
Aus einem Rohrstück des Materials P91 soll nach der Erarbeitung eines Probenplans zunächst das Gefüge in allen 3 Orientierungen metallographisch charakterisiert werden. Anschließend wird das Material mechanisch - technologisch sowie bruchmechanisch und fraktographisch untersucht. Die daraus erhaltenen Werkstoffkennwerte sollen mit dem Gefüge und dem fraktographischen Befund in Beziehung gesetzt werden.
Großer Beleg, angefertigt 2009

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-082 2017
    ISSN: 2191-8708, eISSN: 2191-8716

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-26190
Publ.-Id: 26190


Beschleunigertechnologie und Forschung am ELBE - Zentrum für Hochleistungsstrahlenquellen

Justus, M.

Das ELBE - Zentrum für Hochleistungsstrahlenquellen ist die größte Nutzer-Forschungsanlage des Helmholtz-Zentrums Dresden-Rossendorf (HZDR). Mit dem 40 MeV -Elektronenbeschleuniger werden Wissenschaftlern mit Hilfe von Freie-Elektronen-Lasern, Terahertz-Quellen und Festkörper-Targets verschiedenen Arten von Sekundärstrahlung für interdisziplinäre Grundlagenforschung angeboten. Im Vortrag werden Grundlagen zur Beschleunigerphysik vermittelt und die Bedeutung von Teilchenbeschleunigern für die Forschung aufgezeigt. Anhand von supraleitender Beschleunigertechnik, Freie-Elektronen-Laser, Strahldiagnostik und Kontrollsystemen werden technologischen Herausforderungen und Lösungen für den Betrieb des Elektronenbeschleunigers erläutert. Außerdem werden einige Forschungsergebnisse aus ELBE-Nutzerexperimenten vorgestellt.

  • Lecture (others)
    Wissenschaftliches Seminar, 12.12.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26189
Publ.-Id: 26189


3D motion validation with clinically used cine-MRI and a MR-LINAC phantom

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

Purpose/Objective:
Magnetic resonance (MR)-guided radiotherapy shows high potential to improve the precision and accuracy of radiation therapy. Especially hybrid MR-LINAC devices provide the possibility to perform on-line MR imaging during dose delivery and offer efficient tumour tracking or gating techniques for high-precision treatment of moving tumours. For the commissioning of such systems, the accuracy and reliability of real-time motion tracking through MR-imaging needs to be assessed. In this study we evaluate the dynamic target localization accuracy of a programmable MRI-compatible motion phantom using clinical cine-MRI sequences in all three spatial dimensions.
Material/Methods:
The phantom (CIRS Model 008M MRI-LINAC Dynamic Phantom) has a body representing a human thorax in shape and proportion that was filled with a 6,61g/l NaCl water solution. It incorporates an off-centric cylindrical rod with embedded gel-based target that can be moved and rotated through a programmable actuator. Sinusoidal motion trajectories with patient-oriented breathing frequencies (0.1-0.2 Hz) and motion amplitudes (5 mm – 20 mm) in all three spatial dimensions were programmed in the phantom’s Motion Control Software. Balanced steady-state free procession sequences (TE/TR=2.3/4.6 ms; FOV=300×300×150 mm³; Res=1.34х1.34 mm², SliceThickness=7 mm, FA=30°) were acquired in cine mode on a 3T MR scanner (Philips Achieva) with a time resolution of 489 ms. The center-of-mass motion of the target was extracted from the cine images using a manual segmentation-based procedure. Both the measured frequency and amplitude were compared to the programmed motion parameters. The frequencies were determined with a Fast Fourier Transform (FFT). The phantom was also fed with a real patient’s 1D-navigator-based breathing pattern to evaluate the accuracy of non-regular target motion detection.
Results:
The frequencies (f) and amplitudes (A) extracted from the cine-MRI are in good agreement to the pre-set values. For the sinusoidal motion patterns, we observed 2% deviations between the measured and pre-set frequencies in IS direction for f=0.1 Hz and f=0.2 Hz with A=20 mm. In AP and LR direction the frequency deviation is 3% for f=0.2 Hz and A=5 mm. The amplitudes were determined with a precision of 99% in IS, and 92% in AP/LR direction with deviations smaller than 0.4 mm. For the real patient’s navigator breathing-pattern with main frequency components between 0.14-0.2 Hz and amplitudes between 5-20 mm we observed an amplitude accuracy of 98% with a maximum deviation of 1.2 mm in IS direction. The uncertainties in frequency and amplitude are dominated by the spatial and time resolution.
Conclusion:
The study shows motion parameters of the MRI-LINAC Phantom to be extracted from cine-MRI with high accuracy. Dynamic target localization through cine-MRI is feasible and accurate for the management of respiratory motion in radiation oncology.

Keywords: Intrafractional Motion Management - Tracking

  • Poster
    Estro 37, 20.04.2018, Barcelona, Spain
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S511-S512
    DOI: 10.1016/S0167-8140(18)31251-9

Permalink: https://www.hzdr.de/publications/Publ-26188
Publ.-Id: 26188


S-layer protein-AuNP systems for the colorimetric detection of metal and metalloid ions in water

Jung, J.; Lakatos, M.; Bengs, S.; Matys, S.; Raff, J.; Blüher, A.; Cuniberti, G.

Bacterial surface layer proteins (S-layer) possess unique binding properties for metal ions. By combining the binding capability of S-layer proteins with the optical properties of gold nanoparticles (AuNP), namely plasmonic resonance, a colorimetric detection system for metal and metalloid ions in water was developed. Eight S-layer proteins from different bacteria species were used for the functionalization of AuNP. The thus developed biohybrid systems, AuNP functionalized with S-layer proteins, were tested with different metal salt solutions, e.g. Indium(III)-chloride, Yttrium(III)-chloride or Nickel(II)-chloride, to determine their selective and sensitive binding to ionic analytes. All tested S-layer proteins displayed unique binding affinities for the different metal ions. For each S-layer and metal ion combination markedly different reaction patterns and differences in concentration range and absorption spectra were detected by UV/Vis spectroscopy. In this way, the selective detection of tested metal ions was achieved by differentiated analysis of a colorimetric screening assay of these biohybrid systems. A highly selective and sensitive detection of yttrium ions down to a concentration of 1.67×10-5 mol/l was achieved with S-layer protein SslA functionalized AuNP. The presented biohybrid systems can thus be used as a sensitive and fast sensor system for metal and metalloid ions in aqueous systems.

Keywords: S- layer; gold nanoparticles; colorimetric assay; Rare Earth Elements

Permalink: https://www.hzdr.de/publications/Publ-26187
Publ.-Id: 26187


Nanoscale imaging and compositional analysis in the helium ion microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Möller, W.; Facsko, S.

Ongoing miniaturization in semiconductor industry, nanotechnology and life science demands further improvements for high-resolution imaging, fabrication and analysis of the produced nanostructures. Continuously shrinking object dimensions led to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques.
Ion beam analysis performed on nanometer scale may comply with this challenge. Therefore a minimal probe size is required which can be achieved using a Gas Field Ionization Source (GFIS) in a Helium Ion Microscope (HIM). Due to the high brightness of up to 5•109 A•cm-2•sr-1 and the sharp primary ion energy of 30000 ± 1 eV spot sizes of 0.5 nm can be achieved.
Besides the probe size, the nanoscale analysis is limited by the extremely small amount of sample material and the resulting severe ion beam damage. Only the combination of the techniques with highest degree of information could reveal the composition of nanoscale objects.
Secondary Ion Mass Spectrometry (SIMS), as one of the most powerful techniques for surface analysis directly provides information about elemental, molecular and even isotopic composition. However, quantification in mixed layers cannot be done from pure SIMS measurements without comparison to standards. This drawback is partly compensated by Rutherford Backscattering Spectrometry (RBS) but at a loss of sensitivity. In order to combine this compositional information with the high resolution Secondary Electron (SE) imaging correlative microscopy represents the best way.
Recently, we implemented minimal invasive Time of Flight (TOF) spectrometry into the HIM to enable SIMS as well as RBS [1, 2]. The TOF measurements are triggered by blanking the primary ion beam into an existing Faraday cup and release the beam for short time windows to ensure minimal applied fluencies and obtaining a maximum of information from the region of interest.
In the present contribution we intent to present the technical realization of our approach and show results, drawbacks and derive conclusions for the practical use of this promising technique.
[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J.A. Notte, J. Huang, S. Facsko. Ultramicroscopy 162 (2016), 91-97
[2] R. Heller, N. Klingner, G. Hlawacek. Helium Ion Microscopy, Chapter 12, Springer (2016)

Keywords: HIM SIMS Nano TOF

  • Invited lecture (Conferences)
    23rd International Conference on Ion Beam Analysis IBA-2017, 11.10.2017, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-26186
Publ.-Id: 26186


Interaction between Double Diffusive Convection and Solidification in Ammonium-Chloride Solutions

Anders, S.; Eckert, S.

This paper presents an experimental investigation of thermally and chemically driven convection with simultaneous crystallisation in a concentrated aqueous ammonium-chloride solution. Measurements were performed in a transparent Hele-Shaw cell (200·100·10mm3) between two massive copper blocks equipped with internal water channels controlling the thermal boundary conditions at the upper and lower horizontal boundaries. The temperatures were regulated by thermostats in a range between -20°C and +40°C giving Rayleigh numbers up to around 0.2·10 9 . A double-wall construction with climatisation was implemented in order to avoid thermal losses through the side walls. Temperatures were monitored by thermocouples calibrated to an accuracy better than 0.05K.
Various flow regimes were studied by choosing different temperature boundary conditions.
The focus was on configurations with negative vertical temperature gradients where thermal convection occurs once a critical temperature difference is exceeded. At sufficient supercooling free crystals nucleate in the upper part of the cell, grow and descend due to their higher density compared to the ambient fluid.
The flow field in the liquid was measured by PIV using fluorescent tracer-particles and laser illumination. PTV with LED-background lighting was used to determine the size-evolution and the trajectories of the free-moving crystals. The application of alternating lighting methods and advanced digital image filtering allows for simultaneous operation of PIV and PTV. This approach enables a quantitative study of the interplay of different convection regimes and the solidification process. For example the relation between drag-coefficient, crystal size and crystal growth was investigated.
As a reference case a stable stratification resulting from parallel cooling of the top and bottom walls was investigated. The following solidification phenomena were observed during the experiments: columnar growth at the walls, nucleation and growth of equiaxed crystals in the bulk, chimney-formation in the mushy layer as well as the remelting of columnar and equiaxed dendrites.

Keywords: equiaxed solidification; double diffusive convection; dual phase velocimetry; PTV; PIV

  • Lecture (Conference)
    SP17, Solidification Processing 2017, 25.-28.07.2017, Beaumont Estate, Old Windsor, United Kingdom
  • Contribution to proceedings
    SP17, Solidification Processing 2017, 25.-28.07.2017, Beaumont Estate, Old Windsor, United Kingdom
    Proceedings of the 6th Decennial International Conference on Solidification Processing, London: BCAST, Brunel University London, 978-1-908549-29-7, 350-353

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Permalink: https://www.hzdr.de/publications/Publ-26185
Publ.-Id: 26185


Combined experimental and numerical analysis of a bubbly liquid metal flow

Krull, B.; Strumpf, E.; Keplinger, O.; Shevchenko, N.; Fröhlich, J.; Eckert, S.; Gerbeth, G.

The paper proposes a combined experimental and numerical procedure for the investigation of bubbly liquid-metal flows. It describes the application to a model configuration consisting of a recirculating GaInSn flow driven by an argon bubble chain. The experimental methods involve X-ray measurements to detect the bubbles and UDV measurements to gain velocity information about the liquid metal. The chosen numerical method is an immersed boundary method extended to deformable bubbles. The model configuration includes typical phenomena occurring in industrial applications and allows insight into the physics of bubbly liquid-metal flows. It constitutes an attractive test case for assessing further experimental and numerical methods.

Keywords: Bubbly liquid-metal flows; Xray radiography; UDV; GaInSn

Permalink: https://www.hzdr.de/publications/Publ-26184
Publ.-Id: 26184


Development of an 18F-radioligand for in vivo monocarboxylate transporter 1 (MCT1) tumor imaging with PET

Sadeghzadeh, M.; Brust, P.; Fischer, S.; Moldovan, R.-P.

Impressive developments in the areas of imaging technology and imaging tracers have strengthened preclinical imaging studies on the “hallmarks of cancer” to provide fundamentals for translation to the clinic. Until today, many positron emission tomography (PET) based molecular biomarkers have been used with that regard [1]. Particularly, significant effort has been dedicated to the development and validation of PET biomarkers for tumor cell proliferation and metabolism. Monocarboxylate transporter 1 (MCT1) is an integral plasma membrane protein which bidirectionally transports lactate and ketone bodies along a concentration gradient and is highly expressed in non-hypoxic regions of human colon, breast, head and neck, lung and other tumors. Accordingly, MCT1 inhibitors are regarded to be of potential clinical use [2]. Since there is no selective PET tracer available based on this class of compounds the aim of this project is the development an 18F-labelled radioligand for in vivo imaging of MCT1-overexpressing brain tumors.

Keywords: Fluorine-18 radioligand; Positron Emission Tomography (PET) imaging; Monocarboxylate transporter 1 (MCT1); Brain Tumor

  • Poster
    Network Meeting of the Alexander von Humboldt Foundation, 18.-20.10.2017, Bielefeld, Germany

Permalink: https://www.hzdr.de/publications/Publ-26183
Publ.-Id: 26183


Comparison of robust optimized proton planning strategies for dose escalation in pancreatic cancer

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

Purpose or Objective
In patients with locally advanced unresectable pancreatic cancer, neoadjuvant or primary radiochemotherapy (RCT) are alternative treatment options. Today, treatment outcome after RCT is poor, in part due to radiosensitive organs at risk (OARs) limiting the prescribed dose to the target volume. Proton beam techniques enable delivering high radiation doses to the target volume while sparing OARs. In this in-silico feasibility study, we assessed different strategies for dose escalation to 66Gy(RBE) using a simultaneous integrated boost technique and robust multi-field optimized intensity modulated (rMFO-IMPT) pencil beam scanned protons and evaluated their robustness.

Material and Methods
For each of six pancreatic cancer patients, four different rMFO-IMPT plans were optimized on free-breathing treatment planning CTs using the RayStation treatment planning system (V5.99, RaySearch Laboratories AB, Sweden). These planning strategies consisted of equally-weighted beams: (S1) two posterior oblique (PO) beams, (S2) lateral right beam and left PO beam, (S3) two PO beams plus right non-coplanar beam, and (S4) three non-coplanar beams. At least 95% of 66Gy(RBE) in 30 fractions was prescribed to 95% of the boost volume (GTV), and 51Gy(RBE) was prescribed to 95% of the CTV (GTV with margin and elective volume). A dose fall-off range of 10 mm around the GTV was preset, and setup and range uncertainty parameters of 3 mm and of 3.5% for GTV and CTV coverage were chosen, respectively. The OAR dose constraints adhered to local guidelines and QUANTEC. For each patient and planning strategy, conformity and homogeneity index (CI, HI) of target doses as well as doses to GTV, CTV, and OARs were calculated. Together with additional robustness evaluations of the worst-case scenarios (±3 mm, ±3.5%) the best planning strategy for dose escalation was sought for.

Results
All nominal plans reached the prescribed dose to the GTV and CTV (Fig. 1a). The CI of all planning strategies was similar (mean CI: 0.6-0.7) even though S3 and S4 were more homogeneous. In some patients, S1 was associated with excess dose to the kidneys (Fig. 1b). Radiation doses (D2%, V45Gy) to the duodenum exceeded the constraints since that OAR was next to or within the target volume, while for the remaining gastrointestinal organs radiation doses were similar for the different strategies and within preset limits (Fig. 1c, d). Overall, S3 and S4 showed the best dose distribution for all OARs. Robustness evaluation of all plans revealed that in total only 38% of the D95% values (S1: 31%, S2: 31%, S3: 39%, S4: 51%) in the worst-case scenarios fulfilled the dose requirement for the GTV leading to an insufficient robustness. Conversely, more than 90% of the D95% values to the CTV were robust against uncertainties, with S3 being most robust (97%).

Conclusion
Disregarding the inter- and intra-fractional organ motion, dose escalation is possible using robust MFO-IMPT plans with three beams, of which at least one non-conformal.

Keywords: Robust planning

Permalink: https://www.hzdr.de/publications/Publ-26182
Publ.-Id: 26182


Aliovalent cation substitution in UO2: Electronic and local struc-tures of U1-yLayO2±x solid solutions

Prieur, D.; Martel, L.; Vigier, J.-F.; Scheinost, A. C.; Kvashnina, K. O.; Somers, J.; Martin, P. M.

For nuclear fuel related applications, the oxygen stoichiometry of mixed oxides U1-yMyO2±x is an essential property as it af-fects the fuel properties and may endanger the safe operation of nuclear reactors. A careful review of the open literature indicates that this parameter is difficult to assess properly and that the nature of the defects, i.e. oxygen vacancies or UV, in aliovalent cation – doped UO2 is still subject to controversy. To confirm the formation of UV, we have investigated the room temperature stable U1-yLayO2±x phase using several experimental methods (e.g. XRD, XANES and NMR) confirmed by theo-retical calculations. This paper presents the experimental proof of UV and its effect we identified in both electronic and local structure. We observe that UV is formed in quasi equimolar proportion as LaIII in U1-yLayO2±x (y=0.06; 0.11; 0.22) solid solu-tions. The fluorite structure is maintained despite the cationic substitution but the local structure is affected as variations of the interatomic distances are found. Therefore, we provide here the definitive proof that the substitution of UIV with LaIII is not accommodated by the creation of O vacancies as has often been assumed. The UO2 fluorite structure compensates the incorporation of an aliovalent cation by the formation of UV in quasi equimolar proportions

Keywords: UO2; Lanthanum; XANES; EXAFS; NMS

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Permalink: https://www.hzdr.de/publications/Publ-26181
Publ.-Id: 26181


Inter-center variability in CT-to-SPR conversion in particle therapy: Survey-based evaluation

Taasti, V.; Bäumer, C.; Dahlgren, C.; Deisher, A.; Ellerbrock, M.; Free, J.; Gora, J.; Kozera, A.; Lomax, T.; de Marzi, L.; Molinelli, S.; Teo, K.; Wohlfahrt, P.; Peetersen, J.; Muren, L.; Hansen, D.; Richter, C.

Purpose/Objective
To assess the inter-center variability of the conversion between CT number and particle stopping power ratio (SPR), a survey-based evaluation was carried out in the framework of the European Particle Therapy Network (EPTN). The conversion is applied to treatment planning CTs to finally derive the proton range in patients. Currently, CT scan protocols for treatment planning are not standardized in image acquisition and reconstruction parameters. Hence, the CT-to-SPR conversion (Hounsfield look-up table, HLUT), depending on the former parameters, has to be defined by each center individually. Aiming to access the current status of inter-center differences, this investigation is a first step towards better standardization of CT-based SPR derivation.
Material/methods
A questionnaire was sent out to particle therapy centers involved in the EPTN and a few centers in the United States. The questionnaire asked for details on CT scanners, acquisition and reconstruction parameters, the calibration and definition of the HLUT, as well as body-region specific HLUT selection. It was also assessed whether the influence of beam hardening (BH) on the HLUT was investigated and if an experimental validation of the HLUT was performed. Furthermore, different future techniques were rated regarding their potential to improve range prediction accuracy.
Results
Twelve centers completed the survey (10 in Europe, 2 in the US). Scan parameters, especially reconstruction kernel and beam hardening correction, as well as the HLUT generation varied widely between centers. Eight of the twelve centers applied a stoichiometric calibration method, while three defined the HLUT entirely based on tissue substitutes, and one center used a combination of both. All facilities performed a piecewise linear fit to convert CT numbers into SPRs, but the number of line segments used varied from 2 to 11 (Table 1). Nine centers had investigated the influence of BH, and seven of them had evaluated the size dependence of their conversion. All except one center had validated their HLUT experimentally, but the validation schemes varied widely. A few things were though found to be common for most centers: 1) CT scans were most commonly acquired at 120 kVp, 2) all centers individually customized their CT-to-SPR conversion, and 3) dual energy CT was seen as a promising technique to reduce CT-related uncertainties (Figure 1).
Conclusion
In general, a large inter-center variability in implementation of CT scans, image reconstruction and especially in CT-to-SPR conversion was found. The benefit of a future standardization is obvious: It would reduce the time-intensive site-specific efforts as well as variations in treatment quality. Due to the interdependency of multiple parameters, no conclusion can be drawn on the derived SPR accuracy and its inter-center variability. As a next step within the EPTN, an inter-center comparison of CT-based SPR prediction accuracy will be performed with a ground-truth phantom.

Keywords: proton therapy; Stopping power ratio; CT; HLUT

  • Lecture (Conference)
    ESTRO 37, 20.-24.04.2018, Barcelona, España
  • Poster
    57th Annual Meeting of the Particle Therapy Co-Operative Group (PTCOG), 21.-26.05.2018, Cincinnati, USA
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 127(2018), S533-S534
    DOI: 10.1016/S0167-8140(18)31279-9

Permalink: https://www.hzdr.de/publications/Publ-26180
Publ.-Id: 26180


Spin-wave reciprocity in the presence of Néel walls

Körber, L.; Wagner, K.; Kákay, A.; Schultheiß, H.

The reciprocity of spin-wave propagation in 180° Néel walls and surrounding domains is studied. For this, the dispersion relation, phase fronts and spin-wave intensities are analyzed via micromagnetic simulations. Despite the in-plane curling of the magnetization, the domain wall itself acts as a reciprocal channel, whereas non-reciprocal spin-wave propagation is found within the domains. Since the spin-wave localization depends on the selected frequency, this may allow to control the degree of propagation asymmetry.

Keywords: Nanomagnetics; spin waves; domain wall; reciprocity; micromagnetics

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Permalink: https://www.hzdr.de/publications/Publ-26179
Publ.-Id: 26179


Laboratory-scale X-ray absorption spectroscopy approach for actinide research: Experiment at the uranium L3-edge

Bes, R.; Ahopelto, T.; Honkanen, A.-P.; Huotari, S.; Leinders, G.; Pakarinen, J.; Kvashnina, K. O.

We report the first proof of principle of an efficient and cost-effective bentchtop alternatives to synchrotron radiation beamlines to perform at laboratory scale Xray Absorption Spectroscopy (XAS) at the U L3-edge in transmission mode. We find excellent agreement with synchrotron-based studies for concentrated samples, in reasonable acquisition time, for UO2, KUO3 and b-UO3 samples. The approach described here already constitutes an inexpensive answer to the XAS beamline over-subscription in the field of actinide’s research for state of the art experiments.
Moreover, our results opens the door to many future applications in the field of actinide’s research, including f-electron chemistry, environmental chemistry and nuclear energy physico-chemistry such as advanced nuclear fuel and long term
nuclear waste disposal.

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Permalink: https://www.hzdr.de/publications/Publ-26178
Publ.-Id: 26178


New insight in the uranium valence state determination in UyNd1-yO2-x

Bes, R.; Kvashnina, K.; Rossberg, A.; Dotavio, G.; Desgranges, L.; Pontillon, Y.; Solari, P. L.; Butorin, S. M.; Martin, P.

The charge compensation mechanisms in UyNd1-yO2-x and its consequence on the overall O stoichiometry (or O/M ratio where M=Nd+U) have been studied through the uranium valence state mixture evolution as a function of Nd content up to y=0.62 by means of high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS) at the U M4-edge. Our results clearly demonstrate the formation of U5+ at low Nd content (y < 0.15). Upon increasing the Nd content, oxygen vacancies and the formation of U6+ appear as competing mechanisms for intermediate Nd concentrations, leading to the co-existence of U4+/U5+/U6+ mixed valence and an overall hypostoichiometry (O/M < 2.00). Finally, the formation of U6+ associated with strongly distorted U local environment is observed for high Nd concentrations (y=0.62), leading to an overall hyperstoichiometry (O/M < 2.00)

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Permalink: https://www.hzdr.de/publications/Publ-26177
Publ.-Id: 26177


Electronic structure studies of bismuth compounds by high energy resolution X-ray spectroscopy and ab-initio calculations

Mistonov, A. A.; Chumakov, A. P.; Ermakov, R. P.; Iskhakova, L. D.; Zakharova, A. V.; Chumakova, A. V.; Kvashnina, K. O.

Bismuth-based compounds are widely used as superconductors, catalysts and material for optical devices. Its properties and possibilities to control it are determined by the electronic structure and local environment of Bi-centres. Although x-ray spectroscopy is a powerful method to reveal the crystal and electronic structures, the results obtained so far were limited by the energy resolution of the experimental data. Here we report, for the first time, x-ray absorption near edge structure (XANES) data, recorded in high energy resolution uorescence detection (HERFD) mode at the Bi LIII and LI edges for the number of bismuth compounds. Experimental data are analyzed by ab initio calculations, using finite difference method (FDMNES) code for metallic Bi, Bi2O3, BiPO4, Bi4(GeO4)3 and NaBiO3 compounds. It is shown, that oxidation state as well as Bi-ligand bonds length determines the exact position of the absorption edge. Additionally, the strong Bi p-d orbital mixing is observed. The obtained results can be used as an input for the further electronic structure investigations of the bismuth compounds, in different chemical states.

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Permalink: https://www.hzdr.de/publications/Publ-26176
Publ.-Id: 26176


Investigating spin-transfer torques induced by thermal gradients on magnetic tunnel junctions using microcavity ferromagnetic resonance

Cansever, H.; Fowley, C.; Narkovic, R.; Lenz, K.; Kowalska, E.; Yildirim, O.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Deac, A. M.

Similar to electrical currents flowing through magnetic multilayers [1], it has been predicted that thermal gradients applied across the spacer of a spin-valve or a magnetic tunnel junction may induce pure spin currents and generate ‘thermal’ spin-transfer torques (T-STTs) large enough to induce magnetization dynamics [2-3]. Nevertheless, providing detailed experimental studies in this direction has so far proved elusive, due to difficulties in generating sufficiently large thermal gradients for such effects to be observed. Here, we describe a different approach, which focuses on observing and quantifying spin-transfer torques induced by thermal gradients in magnetic multilayers by means of ferromagnetic resonance (FMR) response under open circuit conditions. The FMR response is measured using specially designed planar microresonators, which generate ac fields perpendicular to the plane of the layers [4]. Such microresonators, with loop diameters of 10 and 20 μm were optimized at a fixed frequency of 14 GHz. Magnetic multilayers with different compositions were patterned using electron-beam lithography into micron-sized pillars with different cross-sections. Microresonators were fabricated using UV lithography such that the magnetic device lies in the center of the loop. An example is shown in Fig 1. For laser heating, we used a diode laser with 51 mW power (5-10 μm focus in diameter). Fig 2 shows a set of FMR measurements performed on an 8x10 μm elliptical shape Py/Cu/Py magnetic multilayer under laser heating, with different laser powers. A clear change is observed at higher than 30 mW laser power, with the FMR line exhibiting changes in resonance field and linewidth. These changes likely arise from a combination of the induced TSTT and the heating of the whole device. The results are analyzed by means of conventional FMR modeling and the thermal gradients are estimated from COMSOL simulations.This project is funded by DFG Priority Programme SPP 1538 Spincaloritronics (SpinCat) and supported by the Nanofabrication Facilities at Ion Beam Center.

Keywords: thermal spin transfer torque; microresonator; ferromagnetic resonance; magnetic tunnel junction

  • Lecture (Conference)
    Magnetism and Magnetic Materials MMM 2017, 06.-10.11.2017, Pittsburgh, PA, USA

Permalink: https://www.hzdr.de/publications/Publ-26175
Publ.-Id: 26175


Decoupling the two roles of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates

Tauchnitz, T.; Nurmamytov, T.; Hübner, R.; Engler, M.; Facsko, S.; Schneider, H.; Helm, M.; Dimakis, E.

Liquid Ga droplets play a double role in the self-catalyzed growth of GaAs nanowires on Si(111) substrates covered with a native SiOx layer: they induce the formation of nano-sized holes in SiOx and then drive the uniaxial nanowire growth directly onto the underlying Si. The independent control of the two mechanisms is a prerequisite for mastering the growth of nanowires, but it is challenging in a conventional growth procedure where they both take place under the same droplets. To that end, we have developed an in situ procedure where the Ga droplets used for the formation of SiOx holes are removed before new Ga droplets drive the growth of GaAs nanowires. In that way, it was made possible to study the interaction between Ga droplets and SiOx, to create holes in SiOx with controlled number density and size and, finally, to grow GaAs nanowires only within those holes. Our results show unprecedented control of the nanowire nucleation with unique possibilities: (1) deliberate control of the number density of nanowires within three orders of magnitude (106-109 cm-2) without patterning the substrate and without changing the growth conditions, (2) highly synchronous nucleation events and, thus, exceptionally narrow nanowire length distributions (standard deviation < 1 % for 3 mm long nanowires), (3) high yield of vertical nanowires up to 80 % (against GaAs islands), (4) highly reproducible results, and (5) independent control of the nanowire diameter from the number density. We anticipate that our methodology could be also exploited for different materials or other types of nanostructures.

Permalink: https://www.hzdr.de/publications/Publ-26174
Publ.-Id: 26174


AER Working Group D on VVER Safety Analysis – Report of the 2017 Meeting

Kliem, S.

The AER Working Group D on VVER reactor safety analysis held its 26th meeting in Erlan-gen, Germany, during the period 10-11 May, 2017. The meeting was hosted by AREVA Germany and was held in conjunction with the 11th workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 11 participants attended the meeting of the working group D, all 11 from AER member organizations. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given presentations and the discussions can be attributed to the following topics:
• Safety analyses methods and results
• Code development and benchmarking
• Future activities
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairman.

  • Contribution to proceedings
    27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, München, Deutschland
    Proceedings of the 27th Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest, 9789637351280, 11-18
  • Lecture (Conference)
    27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26173
Publ.-Id: 26173


Production of Amphiphilic Hydroxamate Siderophores Marinobactins by Marinobacter sp. DS40M6 for Bioflotation Process

Schrader, S.; Kutschke, S.; Rudolph, M.; Pollmann, K.

Marinobacter sp. DS40M6 produces the siderophores marinobactins, which are amphiphilic and contain hydroxamate functional groups responsible for a strong complexation of iron(III). First tests about growth and production conditions showed on the one hand a high rate for both growth of bacteria and siderophore production at 25°C. The pH value, on the other hand, demonstrated a contrary effect, thus the optimal pH 7.0 for growth was not the most efficient pH value for siderophore production.

Permalink: https://www.hzdr.de/publications/Publ-26172
Publ.-Id: 26172


Bioflotation with amphiphilic siderophores

Schrader, S.; Kutschke, S.; Pollmann, K.; Rudolph, M.

Siderophores are small organic molecules with a high affinity for binding Fe(III) and the ability to form strong complexes. They are produced by microorganisms (aerobic bacteria and fungi) and some plants to equalize the low bioavailability of iron in their environment.
The biotechnological production of siderophores offers the application in very different fields. For example, they are used as medicine against iron or heavy metal poisoning. Other applications are their utilization for the extraction, recovery and treating of iron as well as other elements, that also can be bound by siderophores. In addition, their application in froth flotation processes could be an attractive novel approach. Molecules produced by the chemical industry with functional groups like hydroxamates have been already applied successfully in this processing method. It can be suggested that siderophores carrying the same functional groups should also work well as collectors. Particularly the group of amphiphilic siderophores that have both hydrophilic and hydrophobic areas are very interesting. The natural hydrophobic property of these chelating agents could avoid additional chemicals and further working steps for making the target mineral particles hydrophobic for an efficient flotation process.
The main advantage of using biotechnology for the production of siderophores is the wide natural diversity of the structures. A lot of microorganisms and their produced siderophores have already been identified and analyzed in detail. So there is an enormous variety of different molecules available. The aim of this study is to test for the first time, whether it is possible to use siderophores in flotation processes. In addition optimized processes for both the biotechnological production and the froth flotation have to be developed. This presupposes also the investigation and characterization of the binding properties during these procedures.

  • Lecture (Conference)
    Mineral Engineering Conference 2017, 20.-23.09.2017, Wisła, Poland

Permalink: https://www.hzdr.de/publications/Publ-26171
Publ.-Id: 26171


Bioflotation – Kombination der Biotechnologie mit dem klassischen Prozess der Flotation

Schrader, S.; Kutschke, S.; Pollmann, K.; Rudolph, M.

Die Idee der Verknüpfung von Biotechnologie mit der Aufbereitung von Mineralien wurde auf den Gebieten Bioleaching von Metallen und Bioremediation mineralischer Abfälle bereits eingehend untersucht. Ein neues Interessensgebiet ist nun die Kombination von Biotechnologie mit dem klassischen Prozess der Flotation.

  • Poster
    Tagung Aufbereitung und Recycling, 08.-09.11.2017, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26170
Publ.-Id: 26170


Production of amphiphilic hydroxamate siderophore marinobactin by Marinobacter sp. DS40M6 for bioflotation process

Schrader, S.; Kutschke, S.; Rudolph, M.; Pollmann, K.

Siderophores are small biomolecules (400-1500 Da) with the ability to form strong complexes with Fe(III) and other metals. A wide range of siderophore structures are already well-known.
The biotechnological production of these organic compounds with bacteria enables them to be used for extracting and recycling metals.
The application of siderophores in traditional froth flotation process enables the development of a sustained bioflotation.

Keywords: siderophores; marinobactin; bioflotation

  • Poster
    22. International Biohydrometallurgy Symposium 2017, 24.-27.09.2017, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-26169
Publ.-Id: 26169


Variability in crystal surface reactivity: A critical constraint for reactive transport modeling

Fischer, C.

Reactive transport modeling of fluid-solid interactions relies on (i) contrasts in fluid flow velocity and (ii) variability of surface reactivity. The first point is based on data from, e.g., PET and µCT techniques. The second point, however, is usually addressed by simple kinetic data only. Thus, it neglects information about the intrinsic variability of crystal surface reactivity that often results in a rate range of 2-3 orders of magnitude (1). Such variability is however an important constraint for the evolution of surface roughness and porosity pattern in crystalline matter (2). Here, we highlight important sources of the intrinsic variability of crystal surface reactivity and their impact on surface reaction rates. Rate maps (3) and rate spectra (4) provide critical information about the spatial and temporal variability of surface reactivity that is required to predict the evolution of porosity pattern in crystalline matter (5).

1. Luttge A, Arvidson RS, & Fischer C (2013) A Stochastic Treatment of Crystal Dissolution Kinetics. Elements 9(3):183-188.
2. Fischer C, Kurganskaya I, Schäfer T, & Luttge A (2014) Variability of Crystal Surface Reactivity: What do we know? (Review Article). Applied Geochemistry 43:132-157.
3. Fischer C & Luttge A (2017) Beyond the conventional understanding of water–rock reactivity. Earth and Planetary Science Letters 457:100-105.
4. Fischer C, Arvidson RS, & Luttge A (2012) How predictable are dissolution rates of crystalline material? Geochimica et Cosmochimica Acta 98:177-185.
5. Michaelis M, Fischer C, Colombi Ciacchi L, & Luttge A (2017) Variability of Zinc Oxide Dissolution Rates. Environmental Science & Technology 51(8):4297-4305.

  • Poster
    Reactive Transport in the Earth and Environmental Sciences in the 21st Century, 02.-05.10.2017, Amboise, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-26168
Publ.-Id: 26168


Manipulation of antiferromagnetic domain distribution in Mn2Au by ultrahigh magnetic fields and by strain

Sapozhnik, A. A.; Abrudan, R.; Skourski, Y.; Jourdan, M.; Zabel, H.; Kläui, M.; Elmers, H. J.

Evidence for a spin reorientation in antiferromagnetic (AFM) Mn2Au thin films induced by high magnetic fields as well as by the application of in-plane mechanical stress is provided. The AFM domain population in the samples was investigated by resonant X-ray Magnetic Linear Dichroism (XMLD) measurements at the L3 edge of Mn using a variable linear polarization of the incident photon beam. As grown samples show no XMLD signal due to averaging over a random AFM domain distribution. After the exposure to a 70 T in-plane magnetic field a clear XMLD signal indicating the generation of a preferential AFM domain orientation is obtained. The same type of XMLD signal is observed when the thin films are strained, demonstrating the feasibility of AFM Domain manipulation by magnetic fields and stress in Mn2Au.

Permalink: https://www.hzdr.de/publications/Publ-26167
Publ.-Id: 26167


Magnetic structure in a U(Ru0.92Rh0.08)2Si2 single crystal studied by neutron diffraction in static magnetic fields up to 24 T

Prokes, K.; Bartkowiak, M.; Rivin, O.; Prokhnenko, O.; Förster, T.; Gerischer, S.; Wahle, R.; Huang, Y.-K.; Mydosh, J. A.

We report a high-field-induced magnetic phase in a single crystal of U(Ru0.92Rh0.08)2Si2. Our neutron study, combined with high-field magnetization, shows that the magnetic phase above the first metamagnetic transition at μ0H = 21.6 T has an uncompensated commensurate antiferromagnetic structure with a propagation vector Q2 = (2/3 0 0) possessing two single-Q domains. U moments of 1.45(9)μB directed along the c axis are arranged in an up-up-down sequence propagating along the a axis, in agreement with bulk measurements. The U magnetic form factor at high fields is consistent with both the U3+ and U4+ types. The low-field short-range order that emerges from pure URu2Si2 due to Rh doping is initially strengthened by the field but disappears in the field-induced phase. The tetragonal symmetry is preserved across the transition, but the a-axis lattice parameter increases already at low fields. Our results are in agreement with an itinerant electron model with 5f states forming bands pinned in the vicinity of the Fermi surface that is significantly reconstructed by the applied magnetic field.

Permalink: https://www.hzdr.de/publications/Publ-26166
Publ.-Id: 26166


Magnetic field induced tunneling and relaxation between orthogonal configurations in solids and molecular systems

Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Baryshnikov, K. A.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y. V.

We report the effect of magnetic field induced quantum tunneling and relaxation transitions between orthogonal configurations in polyatomic systems where no tunneling is expected. Typical situations of this kind occur in molecular systems and local centers in crystals in ground and excited electronic T states, subject to the T⊗e problem of the Jahn-Teller effect, where the wave functions of the three tetragonally distorted configurations are orthogonal. A detailed microscopic theory of this effect shows how the magnetic field violates the orthogonality between the latter allowing for tunneling and relaxations, which decrease in strong fields due to the induced decoherence. The novel effect is demonstrated experimentally as a big, sharp peak in ultrasound attenuation by Cr2+ centers in ZnSe:Cr2+ in the magnetic field B = 0.15 T at the temperature below 8 K. It may influence a variety of magnetic, electronic, and photonic properties of any system in an electronic T state.

Permalink: https://www.hzdr.de/publications/Publ-26165
Publ.-Id: 26165


Neutron imaging of froth structure and particle motion

Heitkam, S.; Rudolph, M.; Lappan, T.; Sarma, M.; Eckert, S.; Trtik, P.; Lehmann, E.; Vontobel, P.; Eckert, K.

This article reports on the simultaneous measurement of foam structure and attached particles employing neutron imaging. An aqueous foam sample is placed in the NEUTRA beamline at PSI, enabling a spatial resolution of less than 200 micron to be achieved at a frame rate of more than 1 Hz. A forced drainage setup allows the liquid content of the foam to be controlled. The averaged attenuation of the neutrons is demonstrated to yield the liquid fraction of the foam. Hydrophobized gadolinium particles with a diameter of 200 microns are added to the foam. Using two surfactants, different levels of hydrophobicity are achieved. Depending on the drainage flow and the hydrophobicity, the particles are washed out of the foam at different rates. An avalanche-like motion of particle clusters is observed. Neutron radiography is demonstrated to yield unique insights into the unsteady froth flotation process.

Keywords: Neutron imaging; Flotation; Froth; Particle Tracking

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Permalink: https://www.hzdr.de/publications/Publ-26164
Publ.-Id: 26164


Coarsening evolution of dendritic sidearms: from synchrotron experiments to quantitative modeling

Neumann-Heyme, H.; Shevchenko, N.; Lei, Z.; Eckert, K.; Keplinger, O.; Grenzer, J.; Beckermann, C.; Eckert, S.

The local dynamics of dendritic sidearms during coarsening are studied by combining in-situ radiography observations with numerical and analytical models. A flat sample of a Ga-In alloy is partially solidified and then held isothermally in a vertical temperature gradient. The evolving dendritic microstructure is visualized using synchrotron X-ray imaging at the BM20 (ROBL) beamline at ESRF, France. During the coarsening stage, the temporal evolution of the geometrical features of sidebranches is captured by automated image processing. This data is used to quantify the dynamics of two basic evolution mechanisms for sidebranches: retraction and pinch-off. The universal dynamics of sidearm necks during pinch-off are exploited to determine the product of liquid diffusivity and capillarity length, Dd_0, as a parameter that is crucial in the calibration of quantitative models. By employing an idealized phase-field model for the evolution of a single sidebranch, the behavior of selected sidebranches is reproduced from the experiments in a consistent way.

Keywords: Dendritic solidification; microstructure; coarsening; sidearm detachment; X-ray radiography; phase-field model; material properties

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Permalink: https://www.hzdr.de/publications/Publ-26163
Publ.-Id: 26163


Structural and thermodynamic investigation of AnIVLI(O)HOPO(Article)

Aupiais, J.; Younes, A.; Moisy, P.; Hennig, C.; Rossberg, A.; Brunel, B.; Kerbaa, M.; Vidaud, C.; Den Auwer, C.

For the first time, capillary electrophoresis coupled with inductively coupled plasma mass spectrometry has been used to determine the stability constants of PuIV with the multidentate hydroxypyridinonate chelating agents 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO) in 0.1 M NaNO3 solution, pcH = 1.395 at 25 °C through competition with the NTA ligand. The limiting electrophoretic mobility was found to be zero for AnIV[5-LIO(Me-3,2-HOPO)] and slightly positive for AnIV[3,4,3-LI(1,2-HOPO)] (AnIV = Th, Pu). They were respectively assigned to the formation of the 1:2 neutral species An[5-LIO(Me-3,2-HOPO)]2 and a mixture of the neutral species AnIV[3,4,3-LI(1,2-HOPO)] and its protonated form AnIVH[3,4,3-LI(1,2-HOPO)]+. The corresponding stability constants of ThIV with both chelators were evaluated through the same experiments for the sake of comparison. The stability of both PuIV-HOPOs was about ten orders of magnitude better than that of the equivalent ThIV complexes. To complement these thermodynamic data, structural parameters of Pu[3,4,3-LI(1,2-HOPO)] and Th[3,4,3-LI(1,2-HOPO)] complexes in solution have been derived from EXAFS experiments and compared to previously reported crystallographic structures.

Permalink: https://www.hzdr.de/publications/Publ-26162
Publ.-Id: 26162


Calibration of scintillation screens for ultrashort electron bunch detection

Kurz, T.; Couperus, J. P.; Krämer, J. M.; Ding, H.; Kuschel, S.; Köhler, A.; Zarini, O.; Hollatz, D.; Schinkel, D.; D‘Arcy, R.; Schwinkendorf, J. P.; Irman, A.; Schramm, U.; Karsch, S.

This work reports on the calibration of scintillating screens for diagnoses of high-charge density electron beams origination from laser plasma accelerators (LPA). Our setup at the conventional ELBE accelerator is cross-calibrated with an integrating current transformer (ICT) and allows for calibration over a large charge density range, thus enabling the study both the linear and non-linear scintillating screen response, as well as long-term stability tests of the screens. In contrast to previous works, the calibration presented here is performed under conditions with a close mimic to real experimental LPA conditions.
A linear response of the scintillator to the applied electron charge was found, followed by a saturation process starting in the range of nC/mm^2. Mimicking a 1-Hz LPA, long–term stability tests showed a significant decrease of the scintillation efficiency over time.
Finally, we present a method where a LED-based constant light source provides an easy method for absolute calibration of charge diagnostic systems at LPAs. This method eliminates many potential error sources existing in currently used methods and enables the transfer of absolute charge calibrations between laboratories.

  • Poster
    3rd European Advanced Accelerator Concepts Workshop, 24.-30.09.2017, Isola d'Elba, Italy
  • Invited lecture (Conferences)
    Joint ARIES-ADA Workshop on 'Scintillation Screens and Optical Technology for transverse Profile Measurements', 01.-03.04.2019, Kraków, Polska

Permalink: https://www.hzdr.de/publications/Publ-26161
Publ.-Id: 26161


Demonstration of a beam loaded nanocoulomb-class laser wakefield accelerator

Couperus, J. P.; Pausch, R.; Köhler, A.; Zarini, O.; Krämer, J. M.; Kurz, T.; Garten, M.; Huebl, A.; Gebhardt, R.; Helbig, U.; Bock, S.; Zeil, K.; Debus, A.; Bussmann, M.; Schramm, U.; Irman, A.

Laser-plasma wakefield acceleration is capable of producing quasi-monoenergetic electron beams reaching into the GeV range with few-femtoseconds bunch duration. Scaling the charge to the nanocoulomb range would yield hundreds of kiloamperes peak-current and stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and γ-ray sources, compact FELs and laboratory-size beam-driven plasma accelerators. Laser-plasma accelerators generating such high currents operate in the beam loading regime where the accelerating field is strongly modified by the self-fields of the injected bunch, improving the final beam quality if appropriately controlled. Here we experimentally investigate the effects of beam loading at the theoretically predicted limit by loading unprecedented charges of about 0.5 nC within a mono-energetic peak into the first plasma cavity. As the energy balance is reached, the final energy spread is minimized. We show that the beam quality is maintained up to an estimated peak-current of 50 kA, an order of magnitude larger than in state-of-the-art conventional and laser-plasma accelerators.

  • Lecture (Conference)
    3rd European Advanced Accelerator Concepts Workshop, 24.-30.09.2017, Isola d'Elba, Italy
  • Lecture (Conference)
    Conference on High Intensity Laser and attosecond science in Israel (CHILI), 11.-13.12.2017, Tel-Aviv, Israel

Permalink: https://www.hzdr.de/publications/Publ-26160
Publ.-Id: 26160


Research on the chemistry of f-elements at HZDR - A general overview of the division Chemistry of the f-Elements

Ikeda-Ohno, A.

Established in June 2014, the division Chemistry of the f-Elements at the Institute of Resource Ecology (IRE) is conducting research on the fundamental physics/chemistry of f-elements, i.e. actinides and lanthanides. This presentation intends to provide a general overview of the recent research activities in the division, in order to possible research overlapping between HZDR-IRE and CEA-Marcoule for future collaborations.

Keywords: actinides; f-elements; coordination; chemistry

  • Lecture (others)
    Internal colloquium, 05.10.2017, CEA-Marcoule, France

Permalink: https://www.hzdr.de/publications/Publ-26159
Publ.-Id: 26159


Drone-borne hyperspectral monitoring of acid mine drainage. An example from the Sokolov lignite district.

Jackisch, R.; Lorenz, S.; Zimmermann, R.; Möckel, R.; Gloaguen, R.

This contributions aims to demonstrate the potential of unmanned aerial systems (UAS) to monitor areas affected by Acid mine drainage (AMD). The investigated area covers a recultivated tailing, which is and part of the Sokolov coalmine district in the Czech Republic. A high abundance of AMD minerals occurs in a confined space of the selected test site, which AMD minerals in high abundances can signal potential environmental predicament. The deposited mine waste material contains pyrite and itsthe consecutive weathering products, mainly iron hydroxides and oxides, which affect the natural pH values of the Earth’s surface. While previous research done in this area relies on satellite and air-borne data, our approach focuses on lightweight drone systems providing ground readiness within hours and, thus,, enabling rapid field campaigns. High spatial image resolutions and and precise target determination are additional advantages of UAS-based mapping. During April to September 2016, in total four field and flight campaigns were conducted. For validation, the waste heap was probed in-situ for pH, X-ray fluorescence (XRF) and, reflectance spectrometry. and sSampling points were surveyed by a differential GNSS global navigation satellite systems. Ground truth was achieved by collecting samples that were characterized for pH, X-ray diffraction and XRF in laboratory conditions. Sampling points were surveyed by a differential GNSS global navigation satellite systems. Hyperspectral data were processed and corrected for atmospheric, topographic and illumination effects. High-resolution point clouds and digital elevation models were built from drone-borne RGB data using Structure-from-Motion. The supervised classification of hyperspectral image (HSI) data suggests the presence of jarosite and goethite -, minerals associated with the acidic environmental conditions (pH range = 2.3 – 2.8 in situ). We identified specific iron absorption bands in the UAS-HS data, and was confirmed with ground-truth spectroscopy. The distribution of in-situ pH data supports the UAS-based mineral classification results. Evaluation of the applied methods highlights the drone surveying as a fast, non-invasive, inexpensive technique for multi-temporal environmental monitoring of the post-mining landscape.

Keywords: Hyperspectral; Remote sensing; unmanned aerial system; Acid mine drainage; Iron minerals; Image classification, Sokolov, post-mining

Permalink: https://www.hzdr.de/publications/Publ-26158
Publ.-Id: 26158


Ion Beam Induced Surface Modification of ta-C Thin Films

Berova, M.; Sandulov, M.; Tsvetkova, T.; Kitova, S.; Bischoff, L.; Boettger, R.

Thin film samples (d ~ 40 nm) of tetrahedral amorphous carbon (ta-C), deposited by filtered cathodic vacuum arc, were implanted with Ga+ at ion energy E = 20 keV and ion fluences D = 3E14 - 3E15 cm-2 and N+ with the same energy and ion fluence D = 3 E14 cm-2. The Ga+ ion beam induced surface structural modification of the implanted material, displayed by formation of new phase at non-equilibrium condition, which could be accompanied by considerable changes in the optical properties of the ta-C films. The N+ implantation also results in modification of the surface structure. The induced structural modification of the implanted material results in a considerable change of its topography and optical properties. Nanoscale topography and structural properties characterisation of the Ga+ and N+ implanted films were performed using atomic spectroscopy analysis. The observed considerable surface structural properties modification in the case of the higher fluence Ga+ implanted samples results from the relatively high concentration of introduced Ga+ atoms, which is of the order of those for the host element.

Keywords: carbon; ion implantation; atomic force microscopy

Permalink: https://www.hzdr.de/publications/Publ-26157
Publ.-Id: 26157


Visualization of gas-liquid multiphase pseudo-slug flow using Wire-Mesh Sensor

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

Intermittent two-phase flows are commonly encountered in the petroleum industry. Much attention has been focused by several researchers on intermittent flows existing at low superficial gas velocities (<10 m/s). There is limited work performed on intermittent structures persisting at higher superficial gas velocities (pseudo-slug flows). In the present experimental study, a conductivity-based Wire-Mesh Sensor (WMS) was used to visualize and characterize pseudo-slug flow. Experiments were performed in a 76.2 mm horizontal pipe with air and water as the working fluids at atmospheric conditions. The superficial gas and liquid velocities ranged from 9 m/s to 35 m/s and 0.45 m/s to 0.76 m/s, respectively. A 16 × 16 WMS was placed 17 m away from the pipe inlet to measure spatio-temporal void-fraction distribution. The WMS data acquisition frequency was set to 10 kHz. From the void-fraction time series data, the periodic pseudo-slug structures were visualized. The visualization suggested that unlike slug flow where the liquid structures fill the pipe cross-section, the pseudo-slugs were extremely aerated structures (high gas-liquid mixing) formed due to the gas penetration into the liquid slug body. This paper also presents the measurements of important hydrodynamic characteristics such as cross-sectional averaged void-fraction time series and mean void fraction. The effect of liquid viscosity on the visualized structures is also presented.

Keywords: Flow visualization; Intermittent multiphase flows; Pseudo-slug flow; Slug flow; Wire-mesh sensor

Permalink: https://www.hzdr.de/publications/Publ-26156
Publ.-Id: 26156


Fission and other fast neutron induced reactions investigated at nELBE

Beyer, R.; Junghans, A. R.; Dietz, M.; Kögler, T.; Schwengner, R.; Urlaß, S.; Wagner, A.

The nELBE neutron time-of-flight facility provides neutrons in the energy range from about 10 keV up to 10 MeV with an intensity of about 10⁴ n/s/cm². The combination of the superconducting electron accelerator ELBE and a compact liquid lead neutron production target delivers neutron bunches within a time spread of a few picoseconds and a repetition rate of 100 to 400 kHz (cw) enabling high resolution time-of-flight measurement even with flight paths of only 5 to 11 meters. At nELBE different types of fast neutron induced nuclear reactions can be and have been investigated, ranging from total neutron cross section measurement over elastic and inelastic scattering to neutron induced fission. E.g. the neutron induced fission cross section of Pu-242 has been measured in the range from 0.5 to 10 MeV relative to U-235(n,fis) using two fission ionization chambers. A statistical uncertainty down to 1.1 % and systematic uncertainty of about 2.7 % was reached.

Keywords: nELBE; neutron time-of-flight; transmission; inelastic scattering; fission

  • Poster
    LANL FIESTA Fission School & Workshop, 17.-22.09.2017, Santa Fe, New Mexico, USA

Permalink: https://www.hzdr.de/publications/Publ-26155
Publ.-Id: 26155


Fission measurements at nELBE

Beyer, R.; Dietz, M.; Junghans, A. R.; Kögler, T.; Schwengner, R.; Urlaß, S.

The nELBE neutron time-of-flight facility provides neutrons in the energy range from about 10 keV up to 10 MeV with an intensity of about 104 n/s/cm2. The combination of the superconducting electron accelerator ELBE and a compact liquid lead neutron productiontarget delivers neutron bunches within a time spread of a few picoseconds and a repetition rate of 100 to 400 kHz (cw) enabling high resolution time-of-flight measurement even with flight paths of only 5 to 11 meters. At nELBE different types of fast neutron induced nuclear reactions can be and have been investigated, ranging from total neutron cross section measurement over elastic and inelastic scattering to neutron induced fission. E.g. the neutron induced fission cross section of 242Pu has been measured in the range from 0.5 to 10 MeV relative to 235U(n,f) using two fission ionization chambers. A statistical uncertainty down to 1.1% and systematic uncertainty of about 2.7% was reached.

Keywords: nELBE; neutron time-of-flight; fission

  • Invited lecture (Conferences)
    LANL FIESTA Fission School & Workshop, 17.-22.09.2017, Santa Fe, New Mexico, USA

Permalink: https://www.hzdr.de/publications/Publ-26154
Publ.-Id: 26154


Magnetic field induced strong valley polarization in the three-dimensional topological semimetal LaBi

Kumar, N.; Shekhar, C.; Klotz, J.; Wosnitza, J.; Felser, C.

LaBi is a three-dimensional rocksalt-type material with a surprisingly quasi-two-dimensional electronic structure. It exhibits excellent electronic properties such as the existence of nontrivial Dirac cones, extremely large magnetoresistance, and high charge-carrier mobility. The cigar-shaped electron valleys make the charge transport highly anisotropic when the magnetic field is varied from one crystallographic axis to another. We show that the electrons can be polarized effectively in these electron valleys under a rotating magnetic field. We achieved a polarization of 60% at 2 K despite the coexistence of three-dimensional hole pockets. The valley polarization in LaBi is compared to the sister compound LaSb where it is found to be smaller. The performance of LaBi is comparable to the highly efficient bismuth.

Permalink: https://www.hzdr.de/publications/Publ-26153
Publ.-Id: 26153


Charge Density Waves in Graphite: Towards the Magnetic Ultraquantum Limit

Arnold, F.; Isidori, A.; Kampert, E.; Yager, B.; Eschrig, M.; Saunders, J.

Graphite is a model system for the study of three-dimensional electrons and holes in the magnetic quantum limit, in which the charges are confined to the lowest Landau levels.We report magneto-transport measurements in pulsed magnetic fields up to 60 T, which resolve the collapse of two charge density wave states in two, electron and hole, Landau levels at 52.3 and 54.2 T, respectively. We report evidence for a commensurate charge density wave at 47.1 T in the electron Landau level, and discuss the likely nature of the density wave instabilities over the full field range. The theoretical modeling of our results predicts that the ultraquantum limit is entered above 73.5 T. This state is an insulator, and we discuss its correspondence to the “metallic” state reported earlier.We propose that this (interaction-induced) insulating phase supports surface states that carry no charge or spin within the planes, but does, however, support charge transport out of plane.

Permalink: https://www.hzdr.de/publications/Publ-26152
Publ.-Id: 26152


Magnetic field induced phase transitions and phase diagrams of multiferroic Mn0.95Co0.05WO4 with cycloidal spin structure

Urcelay-Olabarria, I.; Ressouche, E.; Wang, Z.; Skourski, Y.; Ivanov, V. Y.; Popov, Y. F.; Vorobev, G. P.; Balbashov, A. M.; Qureshi, N.; Garcia-Munoz, J. L.; Skumryev, V.; Mukhin, A. A.

Slightly Co-doped MnWO4 at the lowest 5% Co concentration, for which the multiferroic cycloidal phase becomes a ground state, has been studied in magnetic fields up to 60 T by bulk magnetic and electric polarization measurements along different crystallographic directions. The field induced magnetic transitions up to 12 T and the ways they proceed were tracked also by single-crystal neutron diffraction, and the relevant field induced magnetic structures were identified and refined. The complete magnetoelectric phase diagrams for magnetic fields along distinct directions in relation to the cycloidal spin structure have been constructed for magnetic field values exceeding those necessary to induce a spin-flip transition into the paramagnetic state. Their common feature is the existence of nonpolar sinusoidal phases identified by the disappearance of the electric polarization in a field regime slightly below the spin-flip transition. At lower magnetic fields either continuous or abrupt field induced reorientations of the cycloidal magnetic structures were observed, respectively, for a field direction along the crystallographic b axis or along the easy magnetic axis, and the different character of those transitions has been attributed to specific features in the magnetic anisotropy.

Permalink: https://www.hzdr.de/publications/Publ-26151
Publ.-Id: 26151


Influence of MOCVD Growth Pressure on Magnetoresistance of Nanostructured La-Ca-Mn-O Films Used for Magnetic Field Sensors

Zurauskiene, N.; Pavilonis, D.; Klimantavicius, J.; Balevicius, S.; Stankevic, V.; Kersulis, S.; Plausinaitiene, V.; Abrutis, A.; Lukose, R.; Skapas, M.; Juskenas, R.; Knasiene, B.; Naujalis, E.; Law, J. M.

The results of structure and magnetoresistance (MR) of nanostructured La1−xCaxMnyO3 (LCMO) films, grown at different gas pressure (from 3 to 7 Torr) by pulse injection metal–organic chemical vapor deposition (MOCVD) technique, are presented. The MR was investigated in pulsed magnetic fields up to 60 T in the temperature range 1.5–294 K. The results were analyzed from the perspective of using these films for magnetic field sensors operating at low temperatures. It was demonstrated that with the increase of Ar + O2 gas pressure, the surface morphology of the films becomes rougher and grain size increases. Also, the ratio of Mn/(La + Ca) increases with the increase of the pressure. Large MR of the films was observed in a wide temperature range below the ferromagnetic–paramagnetic phase transition. It was shown that at cryogenic temperatures, the films grown at gas pressure of 3 Torr have higher sensitivity in lower magnetic field range (<10 T), while in high magnetic fields (20–60 T), the properties of films grown at higher gas pressure 5–7 Torr are favored. The obtained results allow evaluating the influence of MOCVD growth pressure on MR and sensitivity to the magnetic field of LCMO manganites used for pulsed magnetic field sensors.

Permalink: https://www.hzdr.de/publications/Publ-26150
Publ.-Id: 26150


Structural and Magnetic Properties of the Trirutile-type 1D-Heisenberg Anti-Ferromagnet CuTa2O6

Golubev, A.; Dinnebier, R. E.; Schulz, A.; Kremer, R. K.; Langbein, H.; Senyshyn, A.; Law, J. M.; Hansen, T. C.; Koo, H.-J.; Whangbo, M.-H.

We prepared trirutile-type polycrystalline samples of CuTa2O6 by low-temperature decomposition of a Cu−Ta−oxalate precursor. Diffraction studies at room temperature identified a slight monoclinic distortion of the hitherto surmised tetragonal trirutile crystal structure. Detailed high-temperature X-ray and neutron powder diffraction investigations as well as Raman scattering spectroscopy revealed a structural phase transition at 503(3) K from the monoclinic structure to the tetragonal trirutile structure. GGA+U density functional calculations of the spin-exchange parameters as well as magnetic susceptibility and isothermal magnetization measurements reveal that CuTa2O6 is a new 1D Heisenberg magnet with predominant anti-ferromagnetic nearest-neighbor intrachain spin-exchange interaction of ∼50 K. Interchain exchange is a factor of ∼5 smaller. Heat capacity and low-temperature high-intensity neutron powder diffraction studies could not detect long-range order down to 0.45 K.

Permalink: https://www.hzdr.de/publications/Publ-26149
Publ.-Id: 26149


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