Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41645 Publications

Deterministic Shallow Dopant Implantation in Silicon with Detection Confidence Upper-Bound to 99.85% by Ion–Solid Interactions

Jakob, A. M.; Robson, S. G.; Schmitt, V.; Mourik, V.; Posselt, M.; Spemann, D.; Johnson, B. C.; Firgau, H. R.; Mayes, E.; McCallum, J. C.; Morello, A.; Jamieson, D. N.

Abstract

Silicon chips containing arrays of single dopant atoms can be the material of choice for classical and quantum devices that exploit single donor spins. For example, group-V donors implanted in isotopically purified 28Si crystals are attractive for large-scale quantum computers. Useful attributes include long nuclear and electron spin lifetimes of 31P, hyperfine clock transitions in 209Bi or electrically controllable 123Sb nuclear spins. Promising architectures require the ability to fabricate arrays of individual near-surface dopant atoms with high yield. Here, an on-chip detector electrode system with 70 eV root-mean-square noise (≈20 electrons) is employed to demonstrate near-room-temperature implantation of single 14 keV 31P+ ions. The physics model for the ion–solid interaction shows an unprecedented upper-bound single-ion-detection confidence of 99.85 ± 0.02% for near-surface implants. As a result, the practical controlled silicon doping yield is limited by materials engineering factors including surface gate oxides in which detected ions may stop. For a device with 6 nm gate oxide and 14 keV 31P+ implants, a yield limit of 98.1% is demonstrated. Thinner gate oxides allow this limit to converge to the upper-bound. Deterministic single-ion implantation can therefore be a viable materials engineering strategy for scalable dopant architectures in silicon devices.

Keywords: Deterministic single-ion implantation; Near-surface dopant location; Quantum computers; Ion Beam Induced Charge Collection

Permalink: https://www.hzdr.de/publications/Publ-33439


Investigation of a buoyancy-driven instability during horizontal miscible displacement*

Stergiou, G.; Dezso, H.; Eckert, K.; Schwarzenberger, K.

Abstract

Hydrodynamic instabilities in miscible reactive systems have significant impact on applications such as: CO2 sequestration, soil reparation, or particle formation in precipitation systems. A buoyancy-induced instability has been observed when a fluid horizontally displaces another miscible fluid of different density, resulting in a complex flow field. With this study, we intended to characterize the flow patterns in such systems and to investigate their dependence on parameters such as the injection flow rate and the fluids density difference. We performed reactive and non-reactive experiments in a microscale geometry and explored the intricate 3D flow conditions of the system, using micro-Particle Image Velocimetry. The results evidence the existence of flow structures present in equivalent numerical studies and reveal the dependency of the instability on the direction of the displacement.

*Funded by the German Aerospace Center (DLR) provided by BMWi, Grant No. 50WM2061.

  • Lecture (Conference)
    74th APS Division of Fluid Dynamics Meeting, 21.-23.11.2021, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-33438


Atomic layer etching of SiGe nanowires

Khan, M. B.; Shakeel, S.; Richter, K.; Ghosh, S.; Deb, D.; Hübner, R.; Mikolajick, T.; Erbe, A.; Georgiev, Y.

Abstract

Developments in the fabrication techniques like lithography, etching, thin-film deposition, and metallization, etc. have enhanced device the performance of the complementary metal-oxide-semiconductor (CMOS) transistors mainly by the scaling-down. Innovative concepts need to be incorporated to further improve the device performance as the scaling limits are being reached.
We report on the development of the atomic layer etching (ALE) process to fabricate smooth SiGe-on-insulator (SiGeOI) nanowire using the conventional dry etching tool. First, nano-patterns were made on SiGeOI samples using electron beam lithography. Then these patterns were transferred into the SiGeOI layer using an inductively coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, the ALE process was developed to smoothen the nanowire and to reduce their widths. For the surface modification step, SF6 was used, while Ar+ was used for the subsequent modified layer removal step. The ALE cycle sequence was: modification with 60 sccm SF6 for 20 s, 60 sccm Ar purge for 15 s, layer removal with 60 sccm Ar for 10 s using 25 W platen power, and 40 sccm Ar purge for 10 s.
Various ALE cycles were performed to investigate the effect of ALE on the nanowire roughness and width. The surface of etched features was studied using the atomic force microscopy (AFM) (figure 1 (a)). A reduction in the width of the wire was seen with the increasing number of the ALE cycles. Figure 1 (b) shows the root mean square (r.m.s) surface roughness of the buried oxide after certain numbers of the ALE cycles. The roughness went down from ca. 6 nm to 1 nm or below (exact value could not be calculated due to limitation of the AFM tip) as the number of ALE cycles was increased from 78 to 102.
Figure 2 shows sub-12 nm nanowires with smooth sidewalls fabricated after performing 63 ALE cycles. An etch per cycle of 1.1 Å was attained. This process, developed on a conventional ICP-RIE tool, can be used to further scale down the nanowires.

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  • Poster (Online presentation)
    Micro and Nano Engineering Conference, 2021, 20.-23.09.2021, Turin, Italy

Permalink: https://www.hzdr.de/publications/Publ-33437


Controlled Silicidation of Silicon Nanowires using Flash Lamp Annealing

Khan, M. B.; Prucnal, S.; Ghosh, S.; Deb, D.; Hübner, R.; Pohl, D.; Rebohle, L.; Mikolajick, T.; Erbe, A.; Georgiev, Y.

Abstract

Among other new device concepts, nickel silicide (NiSix)-based Schottky barrier nanowire transistors are projected to supplement down-scaling of the complementary metal-oxide-semiconductor (CMOS) technology as its physical limits are reached. Control over the NiSix phase and its intrusions into the nanowire are essential for superior performance and down-scaling of these devices. Several works have shown control over the phase, but control over the intrusion lengths has remained a challenge. To overcome this, we report a novel millisecond-range flash-lamp-annealing (FLA)-based silicidation process. Nanowires are fabricated on silicon-on-insulator substrates using a top-down approach. Subsequently, Ni silicidation experiments are carried out using FLA. It is demonstrated that this silicidation process gives unprecedented control over the silicide intrusions. Scanning electron microscopy and high-resolution transmission electron microscopy are performed for structural characterization of the silicide. FLA temperatures are estimated with the help of simulations.

Involved research facilities

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Permalink: https://www.hzdr.de/publications/Publ-33436


Stable acceleration of intense proton beams to energies beyond 80 MeV at rep-rated laser systems

Ziegler, T.; Bernert, C.; Bock, S.; Brack, F.-E.; Cowan, T.; Dover, N. P.; Garten, M.; Gaus, L.; Göthel, I.; Kiriyama, H.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Nishiuchi, M.; Püschel, T.; Rehwald, M.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

Abstract

We report on experimental investigations of proton acceleration from laser-irradiated solid foils with the Draco-PW laser, where highest proton cut-off energies were achieved for temporal pulse parameters that varied significantlyfrom those of an ideally Fourier transform limited (FTL) pulse. Controlled spectral phase modulation of the driver laser by means of an acousto-optic programmable dispersive filter enabled us to manipulate the temporal shape ofthe last picoseconds around the main pulse and to study the effect on proton acceleration from thin foil targets. The results show that short and asymmetric pulses generated by positive third order dispersion values are favourable for proton acceleration and can lead to maximum energies above 60 MeV at 18 J laser energy for thin plastic foils, effectively doubling the maximum energy compared to ideally compressed FTL pulses. This performance optimization was the key to perform worlds first dose-controlled in-vivo studies with laser accelerated protons.

The talk will further report on experiments we have carried out in the relativistically induced transparancy regime where the target turns transparent during the laser pulse interaction. We show recent data how the experimental signatures of the accelerated protons in this regime change compared to standard TNSA conditions and how we could reproduce those results at another similar laser laser system.

  • Invited lecture (Conferences)
    5th European Advanced Accelerator Concepts Workshop, 20.-23.09.2021, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-33435


Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows

Bragg, A.; Liao, Y.; Fröhlich, J.; Ma, T.

Abstract

There has been considerable discussion in recent years concerning whether a log-law exists for wall-bounded,
turbulent bubbly flows. Previous studies have argued for the existence of such a log-law, with a modified von
K´arm´an constant, and this is used in various modelling studies. We provide a critique of this idea, and present
several theoretical reasons why a log-law need not be expected in general for wall-bounded, turbulent bubbly
flows. We then demonstrate using recent data from interface-resolving Direct Numerical Simulations that when
the bubbles make a significant contribution to the channel flow dynamics, the mean flow profile of the fluid can
deviate significantly from the log-law behaviour that approximately holds for the single-phase case. The departures
are not surprising and the basic reason for them is simple, namely that for bubbly flows, the mean flow is
affected by a number of additional dynamical parameters, such as the void fraction, that do not play a role for the
single-phase case. As a result, the inner/outer asymptotic regimes that form the basis of the derivation of the loglaw
for single-phase flow do not exist in general for bubbly turbulent flows. Nevertheless, we do find that for
some cases, the bubbles do not cause significant departures from the unladen log-law behaviour. Moreover, we
show that if departures occur these cannot be understood simply in terms of the averaged void fraction, but that
more subtle effects such as the bubble Reynolds number and the competition between the wall-induced turbulence
and the bubble-induced turbulence must play a role.

Keywords: Bubbly flow; Log-law; Wall-bounded turbulent flows

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Permalink: https://www.hzdr.de/publications/Publ-33434


Origin and avoidance of double peaks in the induced voltage of a thermomagnetic generator for harvesting low-grade waste heat

Dzekan, D.; Kischnik, T. D.; Diestel, A.; Kornelius, N.; Fähler, S.

Abstract

Thermomagnetic harvesting is an emerging approach to convert low-grade
waste heat to electricity, which recently obtained a boost due to the development of both,
more efficient functional materials and innovative device concepts. Here we examine a
thermomagnetic generator which utilizes Gadolinium as thermomagnetic material and report
on double peaks of the induced voltage. By a combination of experiments and theory we
show that these double peaks originate from the interaction of an asymmetric magnetization
curve and a pretzel like magnetic field topology. Double peaks are detrimental for the output
power and can be avoided by matching the magnetization change by adjusting cold and hot
fluid flow.

Keywords: Thermomagnetic Energy Harvesting; Thermomagnetic Generator; Magnetocaloric Refrigeration; Magnetic Materials

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Permalink: https://www.hzdr.de/publications/Publ-33433


A Machine-Learning Surrogate Model for ab initio Electronic Correlations at Extreme Conditions

Dornheim, T.; Moldabekov, Z.; Cangi, A.

Abstract

The electronic structure in matter under extreme conditions is a challenging complex system prevalent in astrophysical objects and highly relevant for technological applications. We show how machine-learning surrogates in terms of neural networks have a profound impact on the efficient modeling of matter under extreme conditions. We demonstrate the utility of a surrogate model that is trained on \emph{ab initio} quantum Monte Carlo data for various applications in the emerging field of warm dense matter research.

Keywords: Machine Learning; Surrogate model; warm dense matter

Permalink: https://www.hzdr.de/publications/Publ-33432


Fermion Sign Problem in Path Integral Monte Carlo Simulations: Grand-canonical ensemble

Dornheim, T.

Abstract

We present a practical analysis of the fermion sign problem in fermionic path integral Monte Carlo (PIMC) simulations in the grand-canonical ensemble (GCE). As a representative model system, we consider electrons in a harmonic trap. We find that the sign problem in the GCE is even more severe than in the canonical ensemble at the same conditions, which, in general, makes the latter the preferred option. Despite these difficulties, we show that fermionic PIMC simulations in the GCE are still feasible in many cases, which potentially gives access to important quantities like the compressiblity or the Matsubara Greens function. This has important implications for contemporary fields of research such as warm dense matter, ultracold atoms, and electrons in quantum dots.

Keywords: path integral Monte Carlo; Fermion sign problem

Permalink: https://www.hzdr.de/publications/Publ-33431


Ab initio path integral Monte Carlo approach to the momentum distribution of the uniform electron gas at finite temperature without fixed nodes

Dornheim, T.; Böhme, M.; Militzer, B.; Vorberger, J.

Abstract

We present extensive new ab initio path integral Monte Carlo results for the momentum distribution function n(k) of the uniform electron gas in the warm dense matter regime over a broad range of densities and temperatures. This allows us to study the nontrivial exchange-correlation-induced increase of low-momentum states around the Fermi temperature, and to investigate its connection to the related lowering of the kinetic energy compared to the ideal Fermi gas. In addition, we investigate the impact of quantum statistics on both n(k) and the off-diagonal density matrix in coordinate space, and find that it cannot be neglected even in the strongly coupled electron liquid regime. Our results were derived without any nodal constraints, and thus constitute a benchmark for other methods and approximations.

Keywords: path integral Monte Carlo; uniform electron gas; momentum distribution; warm dense matter

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Permalink: https://www.hzdr.de/publications/Publ-33430


Momentum distribution of the Uniform Electron Gas at finite temperature: Effects of spin-polarization

Dornheim, T.; Vorberger, J.; Militzer, B.; Moldabekov, Z.

Abstract

We carry out extensive direct path integral Monte Carlo (PIMC) simulations of the uniform electron gas (UEG) at finite temperature for different values of the spin-polarization ξ. This allows us to unambiguously quantify the impact of spin-effects on the momentum distribution function n(k) and related properties. We find that interesting physical effects like the interaction-induced increase in the occupation of the zero-momentum state n(0) substantially depend on ξ. Our results further advance the current understanding of the UEG as a fundamental model system, and are of practical relevance for the description of transport properties of warm dense matter in an external magnetic field.
All PIMC results are freely available online and can be used as a benchmark for the development of new methods and applications.

Keywords: path integral Monte Carlo; uniform electron gas; momentum distribution; spin-effects; warm dense matter

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Permalink: https://www.hzdr.de/publications/Publ-33429


Nonlinear density response from imaginary-time correlation functions: Ab initio path integral Monte Carlo simulations of the warm dense electron gas

Dornheim, T.; Moldabekov, Z.; Vorberger, J.

Abstract

The \emph{ab initio} path integral Monte Carlo (PIMC) approach is one of the most successful methods in quantum many-body theory. A particular strength of this method is its straightforward access to imaginary-time correlation functions (ITCF). For example, the well-known density-density ITCF F(q,τ) allows one to estimate the linear response of a given system for all wave vectors q from a single simulation of the unperturbed system. Moreover, it constitutes the basis for the reconstruction of the dynamic structure factor S(q,ω) -- a key quantity in state-of-the-art scattering experiments. In this work, we present analogous relations between the nonlinear density response in quadratic and cubic order of the perturbation strength and generalized ITCFs measuring correlations between up to four imaginary-time arguments. As a practical demonstration of our new approach, we carry out simulations of the warm dense electron gas and find excellent agreement with previous PIMC results that had been obtained with substantially larger computational effort. In addition, we give a relation between a cubic ITCF and the triple dynamic structure factor S(q1,ω1;q2,ω2), which evokes the enticing possibility to study dynamic three-body effects on an \emph{ab initio} level.

Keywords: Nonlinear response; path integral Monte Carlo; imaginary-time correlation functions

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Permalink: https://www.hzdr.de/publications/Publ-33428


Nonlinear electronic density response of the ferromagnetic uniform electron gas at warm dense matter conditions

Dornheim, T.; Moldabekov, Z.; Vorberger, J.

Abstract

In a recent Letter [T.~Dornheim \emph{et al.}, Phys.~Rev.~Lett.~\textbf{125}, 085001 (2020)], we have presented the first \emph{ab initio} results for the nonlinear density response of electrons in the warm dense matter regime. In the present work, we extend these efforts by carrying out extensive new path integral Monte Carlo (PIMC) simulations of a \emph{ferromagnetic} electron gas that is subject to an external harmonic perturbation. This allows us to unambiguously quantify the impact of spin-effects on the nonlinear density response of the warm dense electron gas. In addition to their utility for the description of warm dense matter in an external magnetic field, our results further advance our current understanding of the uniform electron gas as a fundamental model system, which is important in its own right.

Keywords: Nonlinear response; path integral Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-33427


Classical bridge functions in classical and quantum plasma liquids

Lucco Castello, F.; Tolias, P.; Dornheim, T.

Abstract

Bridge functions, the missing link in the exact description of strong correlations, are indirectly extracted from specially designed molecular dynamics simulations of classical one-component plasma liquids and accurately parameterized. Their incorporation into an advanced integral equation theory description of Yukawa one-component plasma liquids and a novel dielectric formalism scheme for quantum one-component plasma liquids leads to an unprecedented agreement with available molecular dynamics simulations and new ab initio path integral Monte Carlo simulations, respectively.

Keywords: Dielectric theory; Bridge functions; path integral Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-33426


Path integral Monte Carlo approach to the structural properties and collective excitations of liquid 3He without fixed nodes

Dornheim, T.; Moldabekov, Z.; Vorberger, J.; Militzer, B.

Abstract

Due to its nature as a strongly correlated quantum liquid, ultracold helium is characterized by the nontrivial interplay of different physical effects. Bosonic 4He exhibits superfluidity and Bose-Einstein condensation. Its physical properties have been accurately determined on the basis of ab initio path integral Monte Carlo (PIMC) simulations. In contrast, the corresponding theoretical description of fermionic 3He is severely hampered by the notorious fermion sign problem, and previous PIMC results have been derived by introducing the uncontrolled fixed-node approximation. In this work, we present extensive new PIMC simulations of normal liquid 3He without any nodal constraints. This allows us to to unambiguously quantify the impact of Fermi statistics and to study the effects of temperature on different physical properties like the static structure factor S(q) , the momentum distribution n(q) , and the static density response function χ(q). In addition, the dynamic structure factor S(q, ω) is rigorously reconstructed from imaginary-time PIMC data. From simulations of 3He , we derived the familiar phonon–maxon–roton dispersion function that is well-known for 4He and has been reported previously for two-dimensional 3He films (Nature 483:576–579 (2012)). The comparison of our new results for both S(q) and S(q, ω) with neutron scattering measurements reveals an excellent agreement between theory and experiment.

Keywords: path integral Monte Carlo; Helium; ultracold atoms

Permalink: https://www.hzdr.de/publications/Publ-33425


Nonlinear interaction of external perturbations in Warm Dense Matter

Dornheim, T.; Vorberger, J.; Moldabekov, Z.; Bonitz, M.

Abstract

We present extensive new ab initio path integral Monte Carlo (PIMC) results for an electron gas at warm dense matter conditions that is subject to multiple harmonic perturbations. In addition to the previously investigated nonlinear effects at the original wave number [Dornheim \emph{et al.}, PRL \textbf{125}, 085001 (2020)] and the excitation of higher harmonics [Dornheim \emph{et al.}, PRR \textbf{3}, 033231 (2021)], the presence of multiple external potentials leads to mode-coupling effects, which constitute the dominant nonlinear effect and lead to a substantially more complicated density response compared to linear response theory. One possibility to estimate mode-coupling effects from a PIMC simulation of the unperturbed system is given in terms of generalized imaginary-time correlation functions that have been recently introduced by Dornheim \emph{et al.}~[JCP \textbf{155}, 054110 (2021)]. In addition, we extend our previous analytical theory of the nonlinear density response of the electron gas in terms of the static local field correction [Dornheim \emph{et al.}, PRL \textbf{125}, 235001 (2020)], which allows for a highly accurate description of the PIMC results with negligible computational cost.

Keywords: Nonlinear response; warm dense matter; path integral Monte Carlo; mode coupling

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Permalink: https://www.hzdr.de/publications/Publ-33424


Nonlinear Density Response and Higher Order Correlation Functions in Warm Dense Matter

Dornheim, T.; Vorberger, J.; Moldabekov, Z.

Abstract

In a recent letter [Phys. Rev. Lett. 125, 085001 (2020)], Dornheim et al. have presented the first ab initio path integral Monte Carlo (PIMC) results for the nonlinear electronic density response at warm dense matter (WDM) conditions. In the present work, we extend these considerations by exploring the relation between the nonlinear response and three-/four-body correlation functions from many-body theory. In particular, this connection directly implies a comparably increased sensitivity of the nonlinear response to electronic exchange–correlation (XC) effects, which is indeed confirmed by our analysis over the entire relevant range of densities (rs=0.5,…,10) and temperatures (θ=0.01,…,4). Finally, our work suggests the possibility of deliberately probing the nonlinear regime to experimentally probe three- and potentially even four-body correlation functions in WDM.

Keywords: Nonlinear response; warm dense matter; path integral Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-33423


Integral equation theory based dielectric scheme for strongly coupled electron liquids

Tolias, P.; Lucco Castello, F.; Dornheim, T.

Abstract

In a recent paper, Lucco Castello et al. (arXiv:2107.03537) provided an accurate parameterization of classical one-component plasma bridge functions that was embedded in a novel dielectric scheme for strongly coupled electron liquids. Here, this approach is rigorously formulated, its set of equations is formally derived, and its numerical algorithm is scrutinized. A systematic comparison with available and new path integral Monte Carlo simulations reveals a rather unprecedented agreement especially in terms of the interaction energy and the long wavelength limit of the static local field correction.

Keywords: Dielectric theory; linear response theory; path integral Monte Carlo

Permalink: https://www.hzdr.de/publications/Publ-33422


Density response of the warm dense electron gas beyond linear response theory: Excitation of harmonics

Dornheim, T.; Böhme, M.; Moldabekov, Z.; Vorberger, J.; Bonitz, M.

Abstract

In a recent letter, Dornheim et al. [Phys. Rev. Lett. 125, 085001 (2020)] have investigated the nonlinear density response of the uniform electron gas in the warm dense matter regime. More specifically, they have studied the cubic response function at the first harmonic, which cannot be neglected in many situations of experimental relevance. In this paper, we go one step further and study the full spectrum of excitations at the higher harmonics of the original perturbation based on extensive new ab initio path integral Monte Carlo (PIMC) simulations. We find that the dominant contribution to the density response beyond linear response theory is given by the quadratic response function at the second harmonic in the moderately nonlinear regime. Furthermore, we show that the nonlinear density response is highly sensitive to exchange-correlation effects, which makes it a potentially valuable tool of diagnostics. To this end, we present a theoretical description of the nonlinear electronic density response based on the recent effective static approximation to the local field correction [T. Dornheim et al., Phys. Rev. Lett. 125, 235001 (2020)], which accurately reproduces our PIMC data with negligible computational cost.

Keywords: Nonlinear response; warm dense matter; path integral Monte Carlo

Permalink: https://www.hzdr.de/publications/Publ-33421


Robust formation of nanoscale magnetic skyrmions in easy-plane anisotropy thin film multilayers with low damping

Flacke, L.; Ahrens, V.; Mendisch, S.; Körber, L.; Böttcher, T.; Meidinger, E.; Yaqoob, M.; Müller, M.; Liensberger, L.; Kakay, A.; Becherer, M.; Pirro, P.; Althammer, M.; Geprägs, S.; Huebl, H.; Gross, R.; Weiler, M.

Abstract

We experimentally demonstrate the formation of room-temperature skyrmions with radii of about 25 nm in easy-plane anisotropy multilayers with an interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of individual magnetic skyrmions by magnetic force microscopy and find that the skyrmions are stable in out-of-plane fields up to about 200 mT. We determine the interlayer exchange coupling as well as the strength of the interfacial DMI. Additionally, we investigate the dynamic microwave spin excitations by broadband
magnetic resonance spectroscopy. From the uniform Kittel mode we determine the magnetic anisotropy and lowdamping α < 0.04. We also find clear magnetic resonance signatures in the nonuniform (skyrmion) state. Our findings demonstrate that skyrmions in easy-plane multilayers are promising for spin-dynamical applications.

Keywords: skyrmion; ferromagnetic resonance; DMI; low damping

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Permalink: https://www.hzdr.de/publications/Publ-33420


Leptin counteracts hypothermia in hypothyroidism through its pyrexic effects and by stabilizing serum thyroid hormone levels

Weiner, J.; Roth, L.; Kranz, M.; Brust, P.; Boelen, A.; Klöting, N.; Heiker, J. T.; Blüher, M.; Tönjes, A.; Pfluger, P. T.; Stumvoll, M.; Mittag, J.; Krause, K.

Abstract

Objective: Thyroid hormones (TH) are essential for the homeostatic control of energy metabolism and the regulation of bodytemperature. The hypothalamic–pituitary–thyroid (HPT) axis is regulated by negative feedback mechanisms, ensuring that TH levels are maintained at a constant level. However, the feedback mechanisms underlying the resetting of the HPT axis regulation in the control of body temperature are still not fully understood. Here, we aimed to determine the thermoregulatory response in hypothyroid mice to different environmental temperatures and the underlying mechanisms. Methods: Distinct
thermogenic challenges were induced in hypothyroid female C57BL/6N and leptin-deficient ob/ob mice through housing at either room temperature or thermoneutrality. The thermogenic and metabolic effects were analyzed through metabolic chambers, 18F-FDG-PET/MRI, infrared thermography, metabolic profiling, histology, gene expression and Western blot analysis. Results: In hypothyroid mice maintained at room temperature, high leptin serum levels induce a pyrexic effect leading to the stabilization of body temperature through brown adipose tissue thermogenesis and white adipose tissue browning. Housing at thermoneutrality leads to the normalization of leptin levels and a reduction of the central temperature set point, resulting in decreased thermogenesis in brown and white adipose tissue and skeletal muscle and a significant decline in body temperature. Furthermore, anapyrexia in hypothyroid leptin-deficient ob/ob mice indicates that besides its pyrexic actions, leptin exerts a stimulatory effect on the HPT axis to stabilize the remaining TH serum levels in hypothyroid mice. Conclusion: This study led to the identification of a previously unknown endocrine loop in which leptin acts in concert with the HPT axis to stabilize body temperature in hypothyroid mice.

Keywords: Beige adipose tissue; Brown adipose tissue; Leptin; Thermogenesis; Thyroid hormone; White adipose tissue browning

Permalink: https://www.hzdr.de/publications/Publ-33417


Data publication: Uptake of niobium by cement systems relevant for nuclear waste disposal: impact of ISA and chloride

Franke, K.

Abstract

Daten zur Bestrahlung und Gammaspektroskopiemessung des Targets

Keywords: niobium; cyclotron; gamma spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-33416


High-gain quantum free-electron laser: Long-time dynamics and requirements

Kling, P.; Giese, E.; Carmesin, C. M.; Sauerbrey, R.; Schleich, W. P.

Abstract

We solve the long-time dynamics of a high-gain free-electron laser in the quantum regime. In this regime each electron emits at most one photon on average, independently of the initial field. In contrast, the variance of the photon statistics shows a qualitatively different behavior for different initial states of the field. We find that the realization of a seeded quantum free-electron laser is more feasible than self-amplified spontaneous emission.

Permalink: https://www.hzdr.de/publications/Publ-33415


Zr-PAPER

Mansel, A.

Abstract

Rohdaten Zr-PAPER

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Permalink: https://www.hzdr.de/publications/Publ-33414


Ghost and Gluon Propagators at Finite Temperatures within a Rainbow Truncation of Dyson–Schwinger Equations

Kaptari, L. P.; Kämpfer, B.

Abstract

The finite-temperature behaviour of ghost and gluon propagators is investigated within an approach based on the rainbow truncated Dyson–Schwinger equations in Landau gauge. In Euclidean space, within the Matsubara imaginary-time formalism, the gluon propagator is not longer a O(4) symmetric function and possesses a discrete spectrum of the fourth momentum component. This leads to a different treatment of the transversal and longitudinal (with respect to the heat bath) parts of the propagator. Correspondingly, the gluon Dyson–Schwinger equation splits also into two parts. The resulting system of coupled equations is considered within the rainbow approximation and solved numerically. The solutions for the ghost and gluon propagators are obtained as a function of temperature T, Matsubara frequency Ωn and three-momentum squared k2. The effective parameters of the approach are taken from our previous fit of the corresponding Dyson–Schwinger solution to the lattice QCD data at zero temperature. It is found that, for zero Matsubara frequency, the dependence of the ghost and gluon dressing functions on k2 are not sensitive to the temperature T, while at k2 = 0 their dependence on T is quite strong. Dependence on the Matsubara frequency Ωn is investigated as well.

Permalink: https://www.hzdr.de/publications/Publ-33413


Therapy-naïve and radioresistant 3D pancreatic cancer cell cultures are effectively radiosensitized by β1 integrin targeting

Görte, J.; Danen, E.; Cordes, N.

Abstract

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is one of the cancers with unmet need. The role of highly conformal radiotherapy is still under debate for PDAC. Owing to its desmoplastic nature, integrin-mediated interactions between PDAC cells and extracellular matrix (ECM) profoundly contribute to PDAC resistance. In this study, we investigated the radiochemosensitizing potential of β1 integrin targeting in therapy-naïve and radioresistant PDAC cell cultures grown in three-dimensional (3D) extracellular matrix (ECM).
Materials and Methods: In a panel of 3D, ECM based PDAC cell cultures, β1 integrin was inhibited by antibodies or siRNA-mediated knockdown. Together with X-ray irradiation and specific chemotherapies, we determined 3D colony formation capacity in therapy-naïve and radioresistant PDAC cultures. Kinome profiling, Western blotting and immunofluorescence stainings were employed to characterize these cell lines. Various siRNA screens were conducted to identify novel therapeutic targets.
Results: A significant radiosensitizing potential of β1 integrin inhibition was found both in therapy-naïve and radioresistant PDAC cell cultures. Kinome profiling upon β1 integrin targeting identified a generally declined tyrosine and serine/threonine kinase activity, which presented less prominent in radioresistant than in therapy-naïve PDAC cells. siRNA screens employing the top 34 deregulated kinases in combination with β1 integrin inhibition revealed less efficacy and less radiosensitization in radioresistant relative to therapy-naïve PDAC cell cultures. Triple inhibition of β1 integrin, protein kinase D1 (PDK1) and rearranged during transfection (RET) turned out to be most effective in reducing 3D colony formation of radioresistant PDAC cells.
Conclusion: Our study clearly shows that β1 integrins are robust targets for overcoming radioresistance in PDAC. This seems to apply equally to therapy-sensitive and radioresistant cells. Concerning tumor heterogeneity, this dual therapy-sensitizing potential might be exploitable for a significant improvement of patient survival.

Keywords: Radiotherapy; Integrins; Resistance; PDAC

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Permalink: https://www.hzdr.de/publications/Publ-33412


Control of Stripe-Domain-Wall Magnetization in Multilayers Featuring Perpendicular Magnetic Anisotropy

Salikhov, R.; Samad, F.; Böhm, B.; Schneider, S.; Pohl, D.; Rellinghaus, B.; Ullrich, A.; Albrecht, M.; Lindner, J.; Kiselev, N. S.; Hellwig, O.

Abstract

We report on the controlled switching of domain-wall (DW) magnetization in aligned stripe-domain
structures, stabilized in [Co(0.44 nm)/Pt(0.7 nm)]X (X = 48, 100, 150) multilayers with perpendicular
magnetic anisotropy. The switching process, induced by an external magnetic field, is monitored by measuring the evolution of the in-plane magnetization. We show that the remanent in-plane magnetization originates from the polarization of the Bloch-type DWs. With micromagnetic simulations, we reveal that
the reversal of the DW polarization is the result of the emergence and collapse of horizontal Bloch lines
within the DWs at particular strengths of the external magnetic field, applied opposite to the DW polarization. Our findings are relevant for DW-based magnonics and bubble-skyrmion applications in magnetic multilayers.

Keywords: Magnetic domains; Domain walls; Magnetization switching; Skyrmions; Spintronics; Micromagnetism

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Microscopic and spectroscopic investigations of uranium(VI) reduction by Desulfosporosinus hippei DSM 8344

Hilpmann, S.; Drobot, B.; Steudtner, R.; Hübner, R.; Bok, F.; Stumpf, T.; Cherkouk, A.

Abstract

Clay formations are potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository. Bentonites are supposed to serve as backfill material, not only for a final disposal site in clay formations but also in crystalline rock. For a long-term safety assessment, various aspects must be taken into account. Besides geological, geochemical, and geophysical considerations, also naturally occurring microorganisms play a crucial part in the environment of such a repository. In the event of a worst-case scenario, if water enters the disposal site, they can interact with the radionuclides and change for example the chemical speciation or the oxidation state (Lloyd et al., 2002).
Desulfosporosinus spp. are an important representative of anaerobic, sulfate-reducing microorganisms, which are present in clay formations as well as in bentonites. Various studies show that they are playing a major role in the microbial communities of these surroundings (Bagnoud et al., 2016; Matschiavelli et al., 2019). A closely related microorganism to the isolated species is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soil (Vatsurina et al., 2008). This bacterium was used to investigate its interactions with uranium(VI) especially regarding the reduction to the less mobile uranium(IV).
Time-dependent reduction experiments in artificial Opalinus Clay pore water (Wersin et al., 2011) (100 µM uranium(VI), pH 5.5) showed the removal of about 80% of the uranium(VI) from the supernatants within 48 h. Corresponding UV/Vis measurements of the dissolved cell pellets exhibit an increasing proportion of uranium(IV) in the cell-bound uranium. Calculations with the inclusion of extinction coefficients lead to a ratio of 39% uranium(IV) after one week. Therefore, a combined sorption-reduction process is a possible interaction mechanism.
Time-resolved laser-induced luminescence spectroscopy verifies the presence of two uranium(VI) species in the supernatant. A comparison with reference spectra leads to an assignment to a uranyl(VI) lactate and a uranyl(VI) carbonate complex. The species distribution shows a decrease of the proportion of the lactate species with time, whereas the proportion of the carbonate species remains almost constant.
Uranium aggregates are formed on the cell surface during the process, as determined by transmission electron microscopy (TEM). Furthermore, uranium occurs inside and outside the cells as well as uranium-containing vesicles.
These findings help to close existing gaps in a comprehensive safeguards concept for a repository for high-level radioactive waste in clay rock. Moreover, this study provides new insights into the interactions of sulfate-reducing microorganisms with uranium(VI).

References
Bagnoud, A., Chourey, K., Hettich, R. L., De Bruijn, I., Andersson, A. F., Leupin, O. X., Schwyn, B., and Bernier-Latmani, R.: Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock, Nat. Commun., 7, 1-10, 2016.
Lloyd, J. R. and Macaskie, L. E.: Biochemical basis of microbe-radionuclide interactions, in: Interactions of Microorganisms with Radionuclides, edited by: Keith-Roach, M. J. and Livens, F. R., Elsevier, 313-381, 2002.
Matschiavelli, N., Kluge, S., Podlech, C., Standhaft, D., Grathoff, G., Ikeda-Ohno, A., Warr, L. N., Chukharkina, A., Arnold, T., and Cherkouk, A.: The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C, Environ. Sci. Technol., 53, 10514-10524, 2019.
Vatsurina, A., Badrutdinova, D., Schumann, P., Spring, S., Vainshtein, M.: Desulfosporosinus hippei sp. nov., a mesophilic sulfate-reducing bacterium isolated from permafrost, Int. J. Syst. Evol. Microbiol., 58, 1228-1232, 2008.
Wersin, P., Leupin, O. X., Mettler, S., Gaucher, E. C., Mäder, U., De Cannière, P., Vinsot, A., Gäbler, H. E., Kunimaro, T., Kiho, K., Eichinger, L.: Biogeochemical processes in a clay formation in situ experiment: Part A - Overview, experimental design and water data of an experiment in the Opalinus Clay at the Mont Terri Underground Research Laboratory, Switzerland, Appl. Geochemistry, 26, 931-953, 2011.

Keywords: uranium(VI) reduction; sulfate-reducing microorganisms; Opalinus Clay

  • Poster
    Interdisziplinäres Forschungssymposium für die Sicherheit der nuklearen Entsorgung, 10.-12.11.2021, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33410


Microscopic and spectroscopic study of the uranium(VI) reduction by a sulfate-reducing microorganism

Hilpmann, S.; Steudtner, R.; Hübner, R.; Roßberg, A.; Prieur, D.; Bauters, S.; Kvashnina, K.; Stumpf, T.; Cherkouk, A.

Abstract

INTRODUCTION

Clay rock is a possible host rock for the long-term storage of high-level radioactive waste and bentonites are a suitable backfill material for a final repository in clay rock and crystalline rock. For a comprehensive safety assessment of such a repository over a long period, different aspects must be taken into account. Besides intensive research regarding geological, geochemical and geophysical properties, these surroundings represent a habitat for naturally occurring microorganisms. In the event of a worst-case scenario, water can enter the repository. It is possible that microorganisms can interact with the radionuclides and thereby change the chemical speciation or the oxidation state by various processes.
Desulfosporosinus spp. play an important role as a representative of anaerobic, sulfate-reducing and spore-forming microorganisms. These bacteria occur in different clay formations as well as in bentonites.1,2 A very closely related bacterium to an isolated species from bentonite is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soils.3 Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers by different microscopic and spectroscopic techniques.

DESCRIPTION OF THE WORK

For the time-dependent experiments in artificial Opalinus Clay pore water4 (100/500 µM uranium(VI), pH 5.5) the cells were cultivated in specific media and harvested in the late exponential growing phase. After washing, suspensions containing cells, uranium(VI) and lactate, were incubated at room temperature and samples were taken between zero hours and one week.

RESULTS AND DISCUSSION

The experiments showed the removal of about 80% of the uranium(VI) from the supernatants within 48 h at a concentration of 100 µM. Corresponding UV/Vis measurements of the dissolved cell pellets revealed an increasing proportion of uranium(IV) in the samples with time. After one week round about 40% of the uranium in the cell pellets was reduced. Therefore, the interaction mechanisms can be assigned to a combined sorption-reduction process.
TEM images of the uranium-incubated cells reveal the formation of uranium aggregates on the cell surface. Uranium can be found not only outside the cell in vesicles, but also inside the cell.
HERFD-XANES measurements show the presence of three oxidation states in the cell pellets. Besides uranium(VI) and uranium(IV), also uranium(V) plays a major role in the cellular reduction process. With the help of EXAFS measurements, three cell-related uranium species were detected.
This study helps to close existing gaps in a comprehensive safeguard concept for a final repository for high-level radioactive waste in clay rock. Moreover, new insights into the interaction mechanisms of sulfate-reducing microorganisms with uranium are presented.

REFERENCES

1. A. BAGNOUD et al., “Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock” Nat. Commun., 7, 1-10 (2016).

2. N. MATSCHIVELLI et al., “The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C” Environ. Sci. Technol., 53, 10514-10524 (2019).

3. A. VATSURINA et al., “Desulfosporosinus hippei sp. nov., a mesophilic sulfate-reducing bacterium isolated from permafrost” Int. J. Syst. Evol. Microbiol., 58, 1228-1232 (2008).

4. P. WERSIN et al., “Biogeochemical processes in a clay formation in situ experiment: Part A - Overview, experimental design and water data of an experiment in the Opalinus Clay at the Mont Terri Underground Research Laboratory, Switzerland” Appl. Geochemistry, 26, 931-953 (2011).

Keywords: uranium(VI) reduction; sulfate-reducing microorganisms; Opalinus Clay

  • Poster (Online presentation)
    TransRet2020, 12.-13.10.2021, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33409


Curvature-induced drift and deformation of magnetic skyrmions: Comparison of the ferromagnetic and antiferromagnetic cases

Yershov, K.; Kakay, A.; Kravchuk, V. P.

Abstract

The influence of the geometrical curvature of chiral magnetic films on the static and dynamic properties of hosted skyrmions are studied theoretically. We predict the effects of the curvature-induced drift of skyrmions under the action of the curvature gradients without any external stimuli. The strength of the curvature-induced driving force essentially depends on the skyrmion type, N\'eel or Bloch, while the trajectory of motion is determined by the type of magnetic ordering: ferro- or antiferromagnetic. During the motion along the surface, skyrmions experience deformations which depend on the its type. In the small-curvature limit, using the collective-variable approach we show, that the driving force acting on a N{\'e}el skyrmion is linear with respect to the gradient of the mean curvature. The driving acting on a Bloch skyrmion is much smaller: it is proportional to the product of the mean curvature and its gradient. In contrast to the fast N{\'e}el skyrmions, the dynamics of the slow Bloch skyrmions is essentially affected by the skyrmion profile deformation. For the sake of simplicity we restrict ourselves to the case of zero Gaussian curvature and consider cylindrical surfaces of general type. Equations of motion for ferromagnetic and antiferromagnetic skyrmions in curved magnetic films are obtained in terms of collective variables. All analytical predictions are confirmed by numerical simulations.

Keywords: skyrmions; curvature effects; ferromagnetic; antiferromagnetic; dynamics

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Evolution of low-lying M1 modes in germanium isotopes

Frauendorf, S.; Schwengner, R.

Abstract

Magnetic dipole strength functions are determined for the series of germanium isotopes from N = Z = 32 to N = 48 on the basis of a large number of ransition strengths calculated within the shell model. The evolution of the strength with increasing neutron number in the 1g 9/2 orbital is analyzed. A bimodal structure comprising an enhancement toward low transition enery and a resonance in the region of the scissors mode is identified. The low-energy enhancement is strongest near closed shells, in particular at the almost completely filled 1g 9/2 orbital, while the scissorslike resonance is most pronounced in the middle of the open shell, which correlates with the magnitude of the also deduced electric quadrupole transition strengths. The results are consistent with previous findings for the shorter series of iron isotopes and proves the occurrence and correlation of the two low-lying magnetic dipole modes as a global structural feature.

Keywords: Nuclear Structure; Nuclear reactions; Magnetic dipole radiation; Photon strength functions; Shell model

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Tungsten (VI) speciation in hydrothermal solutions up to 400°c as revealed by in-situ Raman spectroscopy

Carocci, E.; Truche, L.; Cathelineau, M.; Bazarkina, E.

Abstract

Tungsten (VI) speciation in hydrothermal solutions is investigated through in-situ Raman spectroscopy coupled to the fused silica glass capillary technique at temperatures up to 400 °C. The effect of temperature, pH, chlorinity and carbonate speciation are evaluated in systems with highly soluble salts Na2WO4 and Na6W12O39. At all investigated temperatures, the tungstate ion WO42- (927 cm-1) is the only W species in solution at pH > 10. At a given pH, the presence of dissolved carbonates and chloride does not affect the tungsten speciation. Tungsten polymers reveal to be stable up to 400 °C under acidic to circum-neutral pH conditions and total tungsten concentration above 0.01 molkgH2O-1-. Among the three observed polymers, namely [W7O24]6- (paratungstate-A, ~ 960 cm-1), [W10O32]4- (tungstate-Y, ~ 970 cm-1), and α-[H2W12O40]6- (α-metatungstate, ~ 990 cm-1), only the hepta and dodeca-tungstate are stable at elevated temperature. Combined with revised literature data, these results allow the thermodynamic stability constants of these W polymers to be constrained, enabling quantitative predictions of their relative abundance at T up to 300 °C. These predictions suggest that W polymerization occurs under hydrothermal conditions even at low W concentration (down to 10-5 mol·kgH2O-1) under acidic conditions. These observations imply that the currently available geochemical models on W transport and deposition in deep and hot geological fluids need to be revised.

Keywords: Tungsten polymers; Polytungstates; Fused silica glass capillary technique; Ore deposits

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Towards nuclear waste confinement: solid solutions and phase stability in (Th/Ce)-Y-zirconia systems

Svitlyk, V.; Weiß, S.; Hennig, C.

Abstract

INTRODUCTION

Safe disposal of spent nuclear fuel (SNF) requires matrix materials with strong resistance against corrosion and dissolution over a period of 106 years. Derivatives of zirconium-based ceramics, in particular zirconia, ZrO2, are promising materials for these applications since these phases are known to remain stable in geological cycles of up to 109 years. Here scientific and technological goals are to obtain zirconium-based ceramic materials containing maximum possible tetravalent actinides (An) without Zr/An phase separation. In addition, structural stability of these phases under various external parameters, e.g. temperature (T), pressure (P), irradiation and leaching resistance is essential in order to exclude possible discharge of the incorporated radioactive elements over a long time scale.
Five different structural modifications of zirconia are known to exist. At ambient pressure undoped ZrO2 phase exhibits three different polymorphs as a function of temperature - low-temperature (LT) monoclinic (7-fold coordination of Zr atoms, P21/c ) and parent HT tetragonal (T > 1440 K), and cubic (T > 2640 K) forms (8-fold coordination, P42/nmc and Fm-3m, respectively) [1]. Upon application of high pressure (HP) monoclinic modification of zirconia transforms into orthorhombic-I phase (Pbca, 7-fold coordination of Zr atoms similar to that observed for the parent monoclinic P21/c phase) at pressure of ~ 4 GPa [2]. Upon further compression at P > 25 GPa orthorhombic-I modification transforms into orthorhombic-II phase (Pnma, 9-fold coordination) [3] and this phase was found to be stable up to at least 100 GPa [4].
Various properties of ZrO2 can be efficiently controlled by doping. In particular, introduction of Y3+ ions is known to significantly influence phase stability range of zirconia and to stabilize desired HT modifications. Specifically, tetragonal Y-stabilized zirconia (YSZ) phases, denoted as t′, can be obtained at ambient temperature for Y content of ~ 3 - 15 at.% and the cubic YSZ phase can be stabilized for Y content > ~15 at.% [5]. The YSZ phases are, however, much more poorly studied as a function of temperature and pressure compared to the parent ZrO2 compound and the reported results are sometimes contradictory. In this work we present synchrotron radiation diffraction studies on incorporation of Th and Ce atoms in various YSZ phases as a function of composition, temperature and pressure.

DESCRIPTION OF THE WORK

Five series of samples have been synthesized for the current study: ZrxY0.11ThyO2-z (y = 1 – 7%, ~ 1% step), ZrxY0.14ThyO2-z (y = 4, 7, 10, 12%), ZrxY0.21ThyO2-z (y = 0 – 11%, ~ 3% step), ZrxY0.10CeyO2-z (y = 0 – 8%, ~ 1.5% step) and ZrxY0.16CeyO2-z (y = 0 – 8%, ~ 1.5% step). All samples have been obtained via precipitation of the corresponding metal salts by increasing the pH (pH equal 8 for Th- and 11 for Ce-containing samples, correspondingly). Obtained suspensions were subsequently centrifuged and the residues were dried at 350 K. Final oxide phases were formed by annealing at 1673 K for two hours with further quenching.
Ambient, T- and P-dependent in situ synchrotron radiation diffraction experiments were performed at the ROBL BM20 beamline [6] at ESRF, Grenoble. HT was obtained with hot gas blower and HP was generated using diamond anvil cells (DAC). Diffraction data were collected on high resolution XRD1 (Pilatus 100k) and multipurpose XRD2 (Pilatus3 X 2M, HT and HP experiments) diffractometers of ROBL [6].

RESULTS AND DISCUSSION

For the tetragonal ZrxY0.11ThyO2-z and ZrxY0.14ThyO2-z series maximum Th intake was found to be ~ 10 at.%, as concluded from the corresponding expansion of the unit cell volume as a function of % Th (Fig. 1, left). In addition, appearance of ThO2 in the sample with 12 at. % Th also confirms this solubility limit. Introduction of Th atoms into the YSZ system induces flattening of the ZrO8 polyhedra (Fig. 2). This behaviour is explained by the larger ionic radius of Th4+ compared to Ce4+ (1.19 vs. 0.98 Å, respectively, in 8-fold coordination [7]). Thus, insertion of Th atoms introduces additional volume in the unit cell allowing for the coordinating oxygen atoms to arrange in a more symmetrical way with more equilibrated Zr-O distances. Accordingly, the higher Th at. % content may be expected to be favoured by higher (cubic) symmetry. Indeed, cubic ZrxY0.21ThyO2-z system featured intake of Th up to at least 11 at.%, as concluded from the corresponding expansion of the unit cell volume (Fig. 1, right). Investigations in the cubic YSZ system for higher Th content are in progress.
Structural stability of An-containing compounds is one of key requirements for introduction of these materials in the underground nuclear waste repositories (NWR) for long-term storage. This includes resistance against corrosion and internal irradiation. While the underground T-P conditions at the NWR level (typically 500 m below the ground) are rather mild (T ~ 310 K, P ~ 100 bars (or 0.01 GPa)), partial subduction of NWR over a period of million years can not be excluded. This would expose An-containing phases to more extreme temperatures and pressures. In addition, elevated T can be produced in case of a fire outbreak. Therefore, studies of structural stabilities of the corresponding matrix materials under extreme T-P conditions allow to simulate and accelerate processes which can possibly occur during the storage period.
For the corresponding studies we have synthesized Ce-containing YSZ series. Ce is widely used as surrogate atom to simulate tetravalent radioactive elements like Th, U or Pu. In situ T-dependent diffraction studies on tetragonal ZrxY0.10CeyO2-z and cubic ZrxY0.16CeyO2-z series in a RT-1150 K range revealed excellent structural stability for all the studied compounds. In particular, occupancy of Ce4+ atoms as a function of temperature does not decrease in these systems (Fig. 3, Ce0.05Y0.10Zr0.85O1.95 phase is shown as an example) indicating that the mobility of these ions does not increase with temperature. Within the error range unit cell volume increases linearly for all the phases. The corresponding coefficients of thermal expansion, defined as α = 1/V0*((V-V0)/(T-T0)), with V0(V) and T0(T) being the initial (final) unit cell volume and the sample temperature, are listed in Table 1. Cubic Ce-YSZ samples are slightly stiffer than the corresponding tetragonal phases.
Application of external pressure on the Ce0.05Y0.10Zr0.85O1.95 phase induced a structural transformation to a higher cubic symmetry around the P ~ 8.5 GPa. Interesting, occupancy of Ce4+ remains stable throughout the transition. This together with T-dependent data indicates excellent affinity of Ce atoms with the host YSZ matrices. The parent YSZ phases are, therefore, promising candidates as host matrices for radiotoxic tetravalent elements like U, Th or Pu.

ACKNOWLEDGEMENTS

We acknowledge the Federal Ministry of Education and Research (Germany) for the support of this project (BMBF grant 02NUK060).

REFERENCES

1. M. Bocanegra-Bernal et al., “Phase transitions in zirconium dioxide and related materials for high performance engineering ceramics,” J. Mater. Sci., 37, 4947, 2002. 2. O. Ohtaka et al., “Structural Analysis of Orthorhombic ZrO2 by High Resolution Neutron Powder Diffraction,” Proc. Jpn. Acad. Ser. B, 66, 193, 1990. 3. J. Haines et al., “Crystal Structure and Equation of State of Cotunnite-Type Zirconia,” J. Am. Ceram. Soc., 78, 2, 445, 1995. 4. O. Ohtaka et al., “Phase relations and equation of state of ZrO2 to 100GPa,” J. Appl. Crystallogr., 38, 5, 727–733, 2005. 5. H. G. Scott, “Phase relationships in the zirconia-yttria system,” J. Mater. Sci., 10, 9, 1527, 1975. 6. A. C. Scheinost et al., “ROBL-II at ESRF: a synchrotron toolbox for actinide research,” J. Synchr. Rad., 28, 1, 333, 2021. 7. R. D. Shannon, “Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides,” Acta Crystallogr. Sect. A, 32, 5, 751, 1976.

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  • Contribution to proceedings
    TransRet2020 - Workshop on Processes Influencing Radionuclide Transport and Retention, 12.-13.10.2021, Karlsruhe, Online, Germany

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Smart Kd-concept as efficient approach to improve geochemistry in reactive transport modelling

Stockmann, M.; Lu, R.; Gehrke, A.; Montoya, V.; Noseck, U.; Brendler, V.

Abstract

A key component of risk assessment for radioactive waste repositories in deep geological formations is the prediction of potential radionuclide (RN) transport through the geosphere. One big challenge for such large-scale heterogeneous transport simulations is the integration of realistic geochemical models and their parameters at affordable computational costs. Sorption on minerals is an important retardation process and typically applying constant distribution coefficients (Kd) that can be easily included in reactive transport codes. One of the advantage of this approach is the computational efficiency, but it cannot reflect changes in geochemical conditions. On the other hand, mechanistic surface complexation models used for process understanding can be directly coupled to transport codes with geochemical solvers, but usually only at high computational costs. An alternative is provided by the smart Kd concept (www.smartkd-concept.de) [1], specifically developed to describe variable RN sorption in transport models as consequence of changing geochemical conditions over space and time. The philosophy behind this concept is to compute multidimensional look-up tables storing distribution coefficients - but here referred to as smart Kd as they are based on mechanistic sorption models. These tables can cover wide ranges of important geochemical parameters, e.g. pH, ionic strength, and concentrations of dissolved ions. The information stored in such a look-up table can be accessed by reactive transport codes at each simulation step. This approach was already implemented in the code d3f++ [2]. Here, an additional implementation and validation of the smart Kd-approach in the code OpenGeoSys OGS6 [3, 4] is presented. The application case selected is sorption of repository-relevant RNs and possible migration scenarios through a typical sedimentary rock system covering potential host rock formations in Northern Germany. This serves as a comprehensive proof-of-concept and demonstrates the capability to describe the sorption behaviour in dependence of changing geochemical conditions quite well. As a side-effect, the large Kd-matrices that were computed can be further analysed by sensitivity and uncertainty analysis (SA/UA). Results of this case study showed that the smart Kd-approach goes considerably beyond the conventional concepts. We can illustrate that constant Kd values previously used in transport simulations are rough approximations (and not necessarily conservative ones), as in reality they rather range over several orders of magnitude. Moreover, with the results from the SA, those input parameters influencing strongest the radionuclide retardation can be identified. The results of the transport simulations with the newly implemented smart Kd-approach showed a good agreement to full reactive transport simulations using PHAST [5] or a direct coupling OGS6#PhreeqC and reflect a radionuclide-specific retardation effect. This real application case serves as a benchmark for field-scale transport simulations.

  • Lecture (Conference) (Online presentation)
    Tagung der Fachsektion Hydrogeologie der Deutschen Geologischen Gesellschaft (FH-DGGV-Tagung), 23.-26.03.2022, Jena, Deutschland

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Ein „Wireless Sensor Network“ zur Prozesscharakterisierung in Biogasfermentern

Buntkiel, L.; Budelmann, C.; Heller, A.; Annas, S.; Reinecke, S.; Hampel, U.

Abstract

Kenntnisse über die Durchmischung und die Strömungsvorgänge in Biogasfermentern ermöglichen Optimierungspotenziale bezogen auf die Vermischung, aber auch auf die Biogasausbeute und Energieeinsparung. Aufgrund der Beschaffenheit der Fermenter (große Abmessungen, Stahlbeton) und des Biosubstrats (nicht opakes Fluid) gibt es derzeit kein Messsystem, um Strömungen und räumlich verteilte Prozessparameter zu vermessen. In dem Projekt „NeoBio“ wurde dazu eine Wireless Sensor Network (WSN) entwickelt.

Keywords: Wireless Sensor Network; Sensorpartikel; Biogas; Abwasser

  • Open Access Logo Contribution to proceedings
    Biogas in der Landwirtschaft, 29.-30.09.2021, Online, Deutschland
    Biogas in der Landwirtschft - Stand und Perspektiven, Darmstadt: KTBL, 978-3-945088-83-8
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    Biogas in der Landwirtschaft, 29.-30.09.2021, Online, Deutschland
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    Biogas in der Landwirtschaft, 29.-30.09.2021, Online, Deutschland

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Radiolabeled Silicon-Rhodamines as Bimodal PET/SPECT-NIR Imaging Agents

Kanagasundaram, T.; Laube, M.; Wodtke, J.; Kramer, S. C.; Stadlbauer, S.; Pietzsch, J.; Kopka, K.

Abstract

Radiolabeled fluorescent dyes are decisive for bimodal imaging as well as highly in demand for nuclear- and optical imaging. Silicon-rhodamines (SiRs) show unique near-infrared (NIR) optical properties, large quantum yields and extinction coefficients as well as high photostability. Here, we describe the synthesis, characterization and radiolabeling of novel NIR absorbing and emitting fluorophores from the silicon-rhodamine family for use in optical imaging (OI) combined with positron emission tomography (PET) or single photon emission computed tomography (SPECT), respectively. The presented photostable SiRs were characterized using NMR-, UV-Vis-NIR-spectroscopy and mass spectrometry. Moreover, the radiolabeling conditions using fluorine-18 or iodine-123 were extensively explored. After optimization, the radiofluorinated NIR imaging agents were obtained with radiochemical conversions (RCC) up to 70% and isolated radiochemical yields (RCY) up to 54% at molar activities of g.t. 70 GBq/µmol. Radioiodination delivered RCCs over 92% and allowed to isolate the 123I-labeled product in RCY of 54% at a molar activity of g.t. 7.6 TBq/µmol. The radiofluorinated SiRs exhibit in vitro stabilities g.t. 70% after two hours in human serum. The first described radiolabeled SiRs are a promising step toward their further development as multimodal PET/SPECT-NIR imaging agents for planning and subsequent imaging-guided oncological surgery.

Keywords: multimodal imaging; PET imaging; SPECT imaging; optical imaging; organic chemistry; near-infrared fluorophores; silicon-rhodamines; radiochemistry; radiofluorination; radioiodination

Permalink: https://www.hzdr.de/publications/Publ-33401


4D log file-based proton dose reconstruction: Fraction-wise interplay analysis in clinical practice

Spautz, S.; Thiele, J.; Tschiche, M.; Troost, E. G. C.; Richter, C.; Stützer, K.

Abstract

Purpose/Objective
Pencil beam scanning (PBS) proton therapy (PT) in patients with intra-fraction, breathing-induced tumour motion might result in unrecognized deviations from the planned dose distribution. Our work pursued the clinical roll-out of a 4D log file-based proton dose reconstruction (4DlogReco). By that, we monitor the interplay effect and study its relevancy in an ongoing clinical study at the University Proton Therapy Dresden (UPTD).

Material/Methods
We had developed and experimentally validated a 4DlogReco (in RayStation v.8) based on amplitude-sorted 4DCTs, PBS machine log files and synchronized motion log files. The workflow and data handling was verified in the clinical treatment planning system by a retrospective analysis of four complete PBS-PT treatment series (incl. lung, oesophageal and pancreatic carcinoma; mean motion ≤5mm; 20-33 fractions) of patients who received weekly in-room 4DCTs for monitoring interfraction changes. For the final 4DlogReco translation into clinical practice, we initiated the MOBIL study (Monitoring Of Breathing for Interplay study with Logfiles).
Available patient data were analysed fraction-wise (Fig1). We considered individual critical organs at risk (OAR; lung, heart, spinal cord, kidneys, oesophagus), the clinical target volume (CTV) coverage, mean dose, near-maximum dose and homogeneity index [D98, Dmean, D1, HI=(D1-D98)/Dprescribed] and the deviations from the plan in the fraction-wise worst case (Δwc) and in the accumulated dose (Δacc).

Results
The 4DlogReco was successfully translated into clinical application. So far, two patients (oesophageal and pancreatic carcinoma; mean motion ≤5mm; 19 and 30 fractions) had been treated within the MOBIL study. Daily 4DlogReco took about 15min incl. data processing and dose calculation, and should speed up by an automatic log file retrieval and GPU-based dose calculation after TPS upgrade.
For the six investigated patients (incl. the four workflow test patients), intra-fraction motion led to CTV parameter differences in the worst-case fractions of Δwc(D98)=( 15.5 – 3.4)pp, Δwc(D1)=( 0.1 – 3.5)pp and Δwc(HI)=0.04 – 0.17, while there were smaller changes in the accumulated dose of Δacc(D98)=( 2.6 – -0.6)pp, Δacc(D1)=(-1.3 – 0.4)pp and Δacc(HI)=0.00 – 0.03 (Fig2). The individually relevant OAR dose parameters remained uncritical in line with the so far investigated minor motion amplitudes.

Conclusion
The first 4DlogReco workflow capable to deal correctly with amplitude-sorted 4DCTs provides a fraction-wise verification of the interplay-affected delivered and accumulated dose to moving targets. The clinical implementation of this QA module at UPTD had a direct influence on our institutional treatment protocols, as PBS-PT of lung cancer patients is now admissible for motions up to 15mm. The monitoring of such patients will provide valuable insights on the necessity of further motion compensation and of considering the accumulated 4DlogReco doses during treatment adaptation.

Keywords: PBS proton therapy; Interplay assessment; Log file-based dose reconstruction

  • Open Access Logo Lecture (Conference)
    ESTRO 2022, 06.-10.05.2022, Kopenhagen, Denmark

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Dynamically assisted tunneling in the impulse regime

Kohlfürst, C.; Queißer, F.; Schützhold, R.

Abstract

We study the enhancement of tunneling through a potential barrier V(x) by a time-dependent electric field with special emphasis on pulse-shaped vector potentials such as A(t)=A0/cosh^2(ωt). In addition to the known effects of pre-acceleration and potential deformation already present in the adiabatic regime, as well as energy mixing in analogy to the Franz-Keldysh effect in the non-adiabatic (impulse) regime, the pulse A(t) can enhance tunneling by ``pushing'' part of the wave-function out of the rear end of the barrier. Besides the natural applications in condensed matter and atomic physics, these findings could be relevant for nuclear fusion, where pulses A(t) with ω=1 keV and peak field strengths of 10^16 V/m might enhance tunneling rates significantly.

Keywords: Tunneling & traversal time; Nuclear fusion; Schroedinger equation

Permalink: https://www.hzdr.de/publications/Publ-33399


On the correlation of angular distributions of keV ions and trajectory-dependent electronic excitations in transmission channelling geometry

Holeňák, R.; Lohmann, S.; Komander, K.; Primetzhofer, D.

Abstract

We use energy discrimination of keV ions transmitted through a thin, single-crystalline silicon membrane to correlate specific angular distribution patterns formed in channelling geometry with trajectory-dependent electronic energy loss. The integral energy and intensity distribution of transmitted ions can thus be dissected into on one side axially channelled projectiles travelling along rather straight trajectories and on the other side dechannelled projectiles predominantly experiencing blocking. Angular distributions of transmitted ions are further simulated with two different Monte-Carlo codes.

Keywords: Channelling; keV ions; Monte-Carlo; Time-of-flight

  • Open Access Logo Contribution to proceedings
    25th International Conference on Ion Beam Analysis & 17th International Conference on Particle Induce X-ray Emission & International Conference on Secondary Ion Mass Spectrometry, 11.10.2021, Online, Online
    Journal of Physics: Conference Series, Volume 2326, 012008
    DOI: 10.1088/1742-6596/2326/1/012008
    arXiv: arXiv:2111.06809
    Cited 1 times in Scopus

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Towards Optimized Bioavailability of 99mTc‑Labeled Barbiturates for Non‑invasive Imaging of Matrix Metalloproteinase Activity

Honold, L.; Austrup, M.; Faust, A.; Konken, C.; Schwegmann, K.; Zinnhardt, B.; Daniliuc, C.; Haufe, G.; Schäfers, M.; Kopka, K.; Hermann, S.

Abstract

Introduction: Dysregulated activity of matrix metalloproteinases (MMPs) drives a variety of pathophysiological conditions. Non-invasive imaging of MMP activity in vivo promises diagnostic and prognostic value. However, current targeting strategies by small molecules are typically limited with respect to the bioavailability of the labeled MMP binders in vivo. To this end, we here introduce and compare three chemical modifications of a recently developed barbiturate-based radiotracer with respect to bioavailability and potential to image MMP activity in vivo.
Methods: Barbiturate-based MMP inhibitors with an identical targeting unit but varying hydrophilicity were synthesized, labeled with technetium-99m, and evaluated in vitro and in vivo. Biodistribution and radiotracer elimination were determined in C57/BL6 mice by serial SPECT imaging. MMP activity was imaged in a MMP-positive subcutaneous xenograft model of human K1 papillary thyroid tumors. In vivo data were validated by scintillation counting, autoradiography, and MMP immunohistochemistry.
Results: We prepared three new 99mTc-labeled MMP inhibitors, bearing either a glycine ([99mTc]MEA39), lysine ([99mTc]MEA61), or the ligand HYNIC with the ionic co-ligand TPPTS ([99mTc]MEA223) yielding gradually increasing hydrophilicity. [99mTc]MEA39 and [99mTc]MEA61 were rapidly eliminated via hepatobiliary pathways. In contrast, [99mTc]MEA223 showed delayed in vivo clearance and primary renal elimination. In a thyroid tumor xenograft model, only [99mTc]MEA223 exhibited a high tumor-to-blood ratio that could easily be delineated in SPECT images.
Conclusion: Introduction of HYNIC/TPPTS into the barbiturate lead structure ([99mTc]MEA223) results in delayed renal elimination and allows non-invasive MMP imaging with high signal-to-noise ratios in a papillary thyroid tumor xenograft model.

Keywords: Barbiturates; Matrix metalloproteinase inhibitors; Pyrimidine-2,4,6-triones Single photon emission; Single photon emission computed tomography; Tumor imaging

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Impact of Ion-Ion Correlations on the Adsorption of M(III) (M = Am, Eu, Y) onto Muscovite (001) in the Presence of Sulfate

Neumann, J.; Lee, S. S.; Brinkmann, H.; Eng, P.; Stubbs, J.; Stumpf, T.; Schmidt, M.

Abstract

The environmental fate of metal ions is influenced by their interactions with natural organic and inorganic ligands, which modify the ions’ structure and charge and thus influence their interactions with mineral phases. We investigate the impact of ubiquitous sulfate on the retention of trivalent f-element cations (M(III) = Am, Eu, Y) by muscovite. We combine ex situ alpha spectrometry and in situ surface X-ray diffraction (i.e., crystal truncation rod and resonant anomalous X-ray reflectivity) to determine M(III) coverages and interfacial structures at the molecular level. M(III) cations adsorb as two distinct outer-sphere (OS) complexes (i.e., adsorbed and extended OS complexes) whose coverages vary with increasing sulfate concentration, [SO42-]. When [SO42-] ≤ 0.4 mM, coverages increase and exceed the amounts needed for surface charge compensation of muscovite by a factor of ~3. This overcompensation is likely controlled by ion-ion correlations at the mineral/water interface rather than adsorption of MSO4+, which has a lower thermodynamic stability in the solutions and weaker electrostatic attraction to the mica surface than M3+. For higher [SO42-], MSO4+ and M(SO4)2- dominate solution speciation, leading to a strong decrease of the M(III) coverage due to their lower sorption affinity and weaker ion-ion correlations compared to M3+.

Keywords: Surface X-ray diffraction; Solid liquid interface; electrolyte effect; overcompensation; rare earth elements; actinides

Permalink: https://www.hzdr.de/publications/Publ-33395


Impact of background electrolyte composition on the interfacial formation of Th(IV) NPs on mica (001)

Neumann, J.; Qiu, C.; Eng, P.; Stumpf, T.; Schmidt, M.

Abstract

A mechanistic understanding of the formation of actinide nanoparticles (NPs) and its impact on the mobility of radionuclides in the environment is important for a reliable risk assessment of repositories for radioactive waste. Previous studies using surface x-ray diffraction (SXD) reported an unexpected impact of electrolyte composition on the sorption of Th(IV) on the muscovite (001) basal plane. Th uptake decreased following an unexpected trend: LiClO4 > KClO4 > NaClO4. A significantly higher coverage than needed for surface charge compensation (0.25 Th/AUC, AUC = 46.72 Ų, area of mica (001) unit cell) was observed for LiClO4 (4.9 Th/AUC), suggesting the formation of Th-NPs [1]. It remained unclear, if the electrolyte affects a reaction at the mineral surface or in solution.
We combined SXD and in situ AFM to address this question. At low [Th] (0.1 mM), the investigated electrolytes include LiCl and KCl, in comparison with the reported Th uptakes for the respective perchlorate electrolytes, and the series is extended to NH4Cl and CsCl. The results are compared to reported value for NaCl [2]. The interfacial structures show an extremely broad distribution of Th electron density up to 50 Å from the surface for LiCl and KCl. A decrease of Th uptake within the alkali series is found (Figure 1). A strong linear correlation (R2 = 0.9962) between Th uptake and ionic radius of the alkali metal ion is found, indicating that sorption competition between Th4+ and the electrolyte cation is the origin of the observed effect. The value for NaCl is a clear outlier in this series, showing a much lower uptake of Th than expected according to the trend.
Perfect agreement between the number of formed particles per area, obtained by in situ AFM, and Th uptake, observed by SXD, is found. Particles show a vertical size of ~1 – 2 nm and lateral dimensions of ~10 – 20 nm, indicating that retention occurs by the formation of NPs at the mineral-solution interface (heterogeneous nucleation), which is strongly influenced by the electrolyte.
Additionally, SXD was performed at higher [Th] = 3 mM, where the formation of Th oligomers in solution is expected. Under these conditions, LiCl (2.0 Th/AUC), NaCl (1.4 Th/AUC), and KCl (1.7 Th/AUC) show similar Th uptake, indicating a much smaller impact of electrolyte composition. The obtained interfacial structures are dominated by a high Th loading at a distinct distance (~ 6.5 Å) from the muscovite surface. Therefore, the main retention mechanism at high [Th] is suggested to be the (electrolyte-independent) formation of Th oligomers in solution and their subsequent sorption on the mineral surface.

References
[1] - M. Schmidt et al., Geochim. Cosmochim. Acta. 165, 280–293 (2015).
[2] - M. Schmidt et al., Geochim. Cosmochim. Acta. 88, 66–76 (2012).

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  • Poster (Online presentation)
    ESRF User Meeting 1-2021, 08.-10.02.2021, Grenoble, Frankreich
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    APS/CNM User Meeting 2021, 10.-14.05.2021, Lemont, USA

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Structural Investigation of the Adsorption von Y(III) on Orthoclase (001) Single Crystals using Resonant Surface X ray Diffraction

Neumann, J.; Lessing, J.; Demnitz, M.; Eng, P.; Stubbs, J.; Stumpf, T.; Schmidt, M.

Abstract

INTRODUCTION

Transport of radionuclides (RNs), from deep geological repositories for radioactive waste, such as the highly toxic trivalent minor actinides (An(III)) Am and Cm, will be controlled by their interactions with charged mineral phases. Many countries such as Finland, Sweden, and Germany consider a repository in crystalline rock, which contains large amounts of feldspars, e.g. orthoclase (K-feldspar). Hence, reliable risk assessments of potential repository sites depend on a fundamental understanding of sorption quantity and structure of An(III) on feldspars. Typically, those interactions are investigated using mineral powder samples [1], which depict an idealization of the natural system due to the small grain size of the mineral. In those studies, information about macroscopic effects on sorption processes, like crystal orientation or surface roughness, are not accessible. Therefore, in this work we study the adsorption of Y(III), as an inactive rare earth analogue for An(III), on natural single crystal orthoclase samples of the (001) crystal orientation using the modern synchrotron-based, surface X-ray diffraction technique.

DESCRIPTION OF THE WORK

Natural single crystal orthoclase samples were freshly cleaved along their (001) orientation and reacted overnight in a solution of [Y3+] = 0.01 M at pH = 5.0 or 6.9. After the reaction was finished, surface X-ray diffraction (SXRD) was measured in situ at beamline 13 ID-C (GeoSoilEnviroCARS) of the Advanced Photon Source at Argonne National Laboratory. SXRD yields the total electron density profile of the mineral/water interface by measuring crystal truncation rods (CTR). For the first time, resonant anomalous X-ray reflectivity (RAXR) is applied on orthoclase for identification and quantification of sorption species, in our case Y3+. Coverage of adsorbed Y3+ is given in units of Y/AUC (area of the orthoclase (001) unit cell = 55.57 Å2).

RESULTS AND DISCUSSION

The study investigates the adsorption of Y3+ on orthoclase (001) at two different pH values. RAXR spectra of both samples show strong modulations at the Y X-ray absorption edge (17.038 keV), indicating that Y3+ has been adsorbed to the orthoclase surface. Analysis of amplitudes and phases of the RAXR spectra yield information about coverage and distance of the adsorbed species from the surface.
At pH 5.0, two sorption species at a distance of 2.47 (Species A) and 8.35 Å (Species B1) from the uppermost oxygen-atoms (Osurf) of the mineral surface are identified. At higher pH (6.9), the adsorbed Y is located at a distance of 1.50 (Species C) and 4.38 Å (B2) from Osurf. The Y3+ aquo ion has hydration shells in a distance of 2.36 and 4.40 Å. Therefore, Species A can be attributed to an outer-sphere (OS) and species B1 and B2 to extended outer-sphere (EOS) sorption complexes. In contrast, Species C is closer to the surface than any other sorption species observed in this study. At the investigated pH of 6.9, more sites of the orthoclase surface are deprotonated, obviously leading to the release of parts of the hydration shell of Y. Therefore, Species C is interpreted as an inner-sphere (IS) sorption complex. A plausible, bidentate binding motif for Species C is suggested based on the obtained results, where Y3+ is bound to two nearest Osurf resulting in a Y-O bond length of 2.46 Å in an angle of 39.0°.
While the interfacial speciation between the two samples is different, the total Y coverage is found to be similar for both samples (~0.6 Y/AUC). At pH 6.9 more than 70 % of the adsorbed Y3+ is bound as IS complex (Species C, 0.43 Y/AUC). The obtained coverage of the IS complex corresponds to ~2/3 of an adsorbed Y3+ monolayer, assuming bidentate coordination to two Osurf. Overall, the obtained sorption quantity and interfacial speciation are in good agreement with the powder studies, supporting the applicability of the previously developed SCMs to simulate retention of An(III) by K-feldspar for macroscopic systems.
However, we also identify reasonable amounts of adsorbed EOS complexes that are typically not found in studies using mineral powders and therefore not considered thermodynamic models. This result points out the need of studies working on macroscopic mineral samples to assess the impact of those species, and more general the controlling parameters relevant for natural systems, such as crystal orientation, surface roughness, and a realistic solid-liquid ratio. In conclusion, the results of this study contribute to a more realistic and reliable prediction of the mobility of trivalent actinides in the environment, and will enable a better risk assessment for deep geological repositories for radioactive waste.

  • Lecture (Conference)
    TransRet Workshop: Processes Influencing Radionuclide Transport and Retention, 12.-13.10.2021, Karlsruhe, Deutschland

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f-element sorption onto K-feldspar – A comprehensive characterization of mechanism and thermodynamics

Neumann, J.; Brinkmann, H.; Britz, S.; Lützenkirchen, J.; Bok, F.; Stockmann, M.; Brendler, V.; Stumpf, T.; Schmidt, M.

Abstract

The mobility of radionuclides in the environment, in particular in the context of a deep geological repository for radioactive waste, is heavily influenced by their interactions with charged mineral surfaces. This study investigates the retention potential of feldspars, a main component of granite as one potential host rock for a repository. The focus is on the sorption of trivalent actinides (Am, Cm) and their rare earth analogues (Eu, La, Lu, Nd, Y) as a main source of radiotoxicity in spent nuclear fuel.
A multi-method approach was used, consisting of traditional batch sorption experiments over a broad range of experimental conditions to determine uptake. Generally, retention increases with increasing pH and reaches quantitative retention at near neutral conditions. Furthermore, a spectroscopic study of the sorption structure on the molecular level was conducted. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) using the actinide Cm as a luminescent probe, shows that four surface complexes are formed, an inner sphere sorption complex and its two hydrolysis forms, as well as a ternary feldspar/Cm/silicate complex at alkaline conditions (pH > 10).
Based on the observed comprehensive batch sorption dataset a generic surface complexation model (SCM-A) was developed that describes sorption of trivalent actinides and their rare earth analogues as a function of a variety of geochemical parameters (pH, ionic strength, metal concentration, solid-liquid ratio,…). In a second step, the dataset for the model was further increased by taking the quantitative spectroscopic results into consideration (SCM-B).
The developed SCMs deliver surface complexation parameters of the formed sorption species, which are included in thermodynamic databases. This data is essential for the subsequent calculation of distribution coefficients in modern approaches like the Smart KD-concept[1] as well as reactive transport modeling. Therefore, this study provides a contribution to a more reliable safety assessment of repositories for radioactive waste.[2]
[1] Stockmann, M. et al., "Smart Kd-values, their uncertainties and sensitivities - Applying a new approach for realistic distribution coefficients in geochemical modeling of complex systems", Chemosphere., 187, 277–285 (2017).
[2] Neumann, J. et al., "A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar", J. Colloid Interface Sci. (2020). https://doi.org/10.1016/j.jcis.2020.11.041.

  • Lecture (Conference) (Online presentation)
    Goldschmidt Konferenz, 04.-09.07.2021, Lyon, Frankreich

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Umfassende Untersuchung und Bestimmung thermodynamischer Daten der Sorption von dreiwertigen Metallionen an K-Feldspat

Neumann, J.; Brinkmann, H.; Britz, S.; Lützenkirchen, J.; Bok, F.; Stockmann, M.; Brendler, V.; Stumpf, T.; Schmidt, M.

Abstract

1 Introduction
Transport of contaminants, e.g. radionuclides, in the environment depends strongly on their interactions with mineral phases. In a repository for radioactive waste, crystalline rock (e.g. granite) as one potential host rock in Germany and many other countries, may affect the mobility of radionuclides. Main constituents of granite are feldspars. In spent nuclear fuel, trivalent actinides (Am, Cm, but also Pu) contribute strongly to the radiotoxicity. Therefore, this work studies the retention of Am and Cm, as well as their rare earths element analogues (Eu, La, Lu, Nd, Y) on K-feldspar. By combining batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS), a generic surface complexation model (SCM) was obtained that is valid for all investigated M3+. Thermodynamic sorption data were obtained and an understanding of sorption mechanisms on the molecular level was achieved.
2 Results
Batch sorption experiments were performed over a broad range of environmental conditions (pH 4 – 10, [M3+] = 52 nM – 10 µM, 3 – 50 g/L K-feldspar (dp < 21 µm; 63 – 200 µm))[1]. Sorption is weak for pH < 5, strongly increases between pH 5 – 7 and reaches complete uptake at higher pH. By deconvolution of Cm emission spectra, an inner-sphere complex and its first two hydrolysis forms were found to be responsible for retention in this pH range.
For determination of the deprotonation constant pKa of K-feldspar, as one important input parameter of the model, column titration experiments were conducted. Batch sorption results of all studied M3+ were used to develop two alternative SCMs. The experimental sorption data were used to determine surface complexation parameters by coupling the parameter estimation code UCODE with PHREEQC (SCM-A). In a second approach, spectroscopic data were also considered (SCM-B). A generic approach was used to develop the geochemical models that satisfactorily describe all of the derived M3+/K feldspar sorption edges as well as TRLFS-derived speciation. The model delivered respective stability constants of the sorption complexes, which were added to the data base of the Smart Kd-concept[2]. Therefore, this work improves the risk assessment of repositories for radioactive waste.

Figure 1: Experimental batch sorption data (symbols) and calculation results using the two developed SCMs for different experimental conditions.[1]
References
[1] Neumann, J. et al., "A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar", J. Colloid Interface Sci. (2020). https://doi.org/10.1016/j.jcis.2020.11.041.
[2] Stockmann, M. et al., "Smart Kd-values, their uncertainties and sensitivities - Applying a new approach for realistic distribution coefficients in geochemical modeling of complex systems", Chemosphere., 187, 277–285 (2017).

Keywords: sorption; trivalent; lanthanides; actinides; K-feldspar; TRLFS; SCM

  • Lecture (Conference) (Online presentation)
    Tage der Standortauswahl, 11.-12.02.2021, Freiberg, Deutschland

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Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-based Two-Dimensional Conjugated Covalent Organic Frameworks

Zhong, H.; Wang, M.; Ghorbani Asl, M.; Zhang, J.; Hoang Ly, K.; Liao, Z.-Q.; Chen, G.; Wei, Y.; Biswal, B. P.; Zschech, E.; Weidinger, I. M.; Krasheninnikov, A.; Dong, R.; Feng, X.

Abstract

Electrochemical N₂ reduction reaction (NRR) under ambient conditions is attractive for the great potential in replacing the current Haber-Bosch process towards sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising electrocatalysts for NRR. However, simultaneously boosting their activity and selectivity toward NRR remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M-N₄-C centers as novel, defined and effective catalysts, and achieve a simultaneous enhancement in the activity and selectivity towards electrochemical NRR to yield ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn and Cu) and pyrene building blocks bonded by pyrazine linkages. Significantly, the 2D c-COF catalysts with Fe-N₄-C center exhibit higher ammonia yield rate (33.6 μg h⁻¹mg⁻¹cat) and Faradaic efficiency (FE, 31.9 %) at -0.1 V vs. reversible hydrogen electrode than those with other M-N₄-C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h⁻¹mg⁻¹cat and FE >30 %). In-situ X-ray absorption spectroscopy, Raman spectroelectrochemistry and theoretical calculations unveil that the Fe-N₄-C center acts as a catalytic site. It shows a unique electronic structure with localized electronic states at the Fermi level, allowing for higher N₂ affinity and stronger binding energy of N₂, enabling faster N₂ activation and NRR kinetics than other M-N₄-C centers. Our work opens the possibility of developing metal-nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalysts and provides an atomic understanding of the NRR process on M-Nx-C based electrocatalysts for the design of high-performance NRR catalysts

Keywords: Covalent Organic Frameworks; Two-dimensional; Electrocatalyst; Nitrogen reduction reaction

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Data Publication: Development of [18F]LU14 for PET Imaging of Cannabinoid Receptor Type 2 in the Brain

Moldovan, R.-P.

Abstract

Cannabinoid receptors type 2 (CB2R) represent an attractive therapeutic target for neurodegenerative diseases and cancer. Aiming at a positron emission tomography (PET) radiotracer to monitor receptor density and/or occupancy during a CB2R-tailored therapy, we developed here cis-[18F]1-(4-fluorobutyl-N-((1s,4s)-4-methylcyclohexyl)-2-oxo-1,2-dihydro-1,8-naphthyridine-3-carboxamide ([18F]LU14) starting from the corresponding mesylate precursor. First biological evaluation revealed that [18F]LU14 is a highly affine CB2R radioligand with >80% intact tracer in brain at 30 min p.i. Its further evaluation in a well-established rat model of CB2R overexpression by PET demonstrated its ability to selectively image the CB2R in the brain and its potential as tracer to further investigate diseased related CB2R changes in expression.

Keywords: Cannabinoid receptor type 2; naphtyrid-2-one; binding affinity; radiochemistry; fluorine-18 labeling; brain; positron emission tomography

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An AMS-world without any chemistry? – Untypical measurements of ²⁶Al, ⁴¹Ca and ⁵⁵Fe

Merchel, S.; Golser, R.; Lachner, J.; Marchhart, O.; Martschini, M.; Rugel, G.; Wallner, A.; Walther, D.; Wieser, A.

Abstract

AMS measurements typically are lasting minutes to hours, but are usually preceded by time-consuming (typically days to weeks of) chemical preparation. Both, physicists and chemists are dreaming of an AMS-world without any chemistry.

Some of our earlier studies have already proven AMS being reasonable, fast and easily accessible for ⁷Be [1] and ⁴¹Ca [2] analysis if largely reducing radiochemical separation. However, to our knowledge there are only a few cases completely omitting wet chemical separation, e.g., ¹⁰Be/⁹Be in a Be mineral (phenakite) [3] and ¹⁴C/¹²C by laser-ablation AMS of stalagmites and corals [4]. Here, we focus on two new examples for “Instrumental” AMS (IAMS) at the DREsden AMS (DREAMS) facility and the Vienna Environmental Research Accelerator (VERA):

First, a pilot study to quantify ⁵⁵Fe (t₁/₂=2.76 a) in steel from a reactor vessel of a nuclear power plant by IAMS was validated (after radiochemical separation) by liquid scintillation counting (LSC) and AMS [5]. DREAMS reaches an uncertainty <10% at the 1 kBq g(Fe)⁻¹ level within 10 min measuring unprocessed steel chips. The background (<3 Bq g(Fe)⁻¹) is limited by the short measurement time. IAMS for analysing ⁵⁵Fe from neutron-capture production is reasonable and fast compared to other analytical methods.

Secondly, the ILIAMS set-up at VERA (Martschini et al., this meeting) allows to determine ratios of ²⁶Al (t₁/₂=0.7 Ma) to ²⁷Al and ⁴¹Ca (t₁/₂=0.104 Ma) to ⁴⁰Ca in stony meteorites by IAMS. The nearly complete suppression of isobars, i.e., ²⁶MgO⁻, when extracting AlO⁻, and ⁴¹KF₃⁻ when extracting CaF₃⁻, make pressure digestion (HF/HNO₃), ion exchange and precipitations unnecessary. Most stony meteorites contain ~1% Al, mainly in the form of Na-rich-Ca-poor plagioclase ((Na,Ca)(Si,Al)₄O₈)). Additional sources for >1% Ca are pyroxene (CaMgSi₂O₆) and phosphates (mainly apatite: Ca₅(PO₄)₃Cl)) [6]. IAMS has been performed using 1-2 mg representative powder of the previously-investigated chondrite Dhurmsala [7], either pure, mixed with Fe or PbF₂ powder.

For IAMS of ²⁶Al, AlO⁻ currents from Dhurmsala were - independent of mixing with Fe or pure - about 2% of Al₂O₃(Fe) ones. At ²⁶Al/²⁷Al of ~1.3x10⁻¹⁰ statistical uncertainties of 3% are reached within 15 min sputtering while cathodes last several hours. IAMS data at VERA - in the presence of about 15% Mg - are comparable to earlier (chemical processing) AMS results at DREAMS and ETH Zurich.

For IAMS of ⁴¹Ca, very stable CaF₃⁻ currents from Dhurmsala are ~5% of chemically-processed CaF₂ ones (each mixed with PbF₂). At ~1x10⁻¹¹ ⁴¹Ca/Ca, count rates of 1 min⁻¹ sputtering time are reached. IAMS data measured in the presence of about 1‰ K at VERA are comparable to earlier (chemical processing) AMS results at ANU, DREAMS and ETH Zurich.

The major uncertainty for both nuclides, originating from the current differences of standards and samples, will be addressed soon.

References: [1] Tiessen et al., JRNCh 319 (2017) 965. [2] Hampe et al., JRNCh 296 (2013) 617. [3] Merchel et al., JRNCh 298 (2013) 1871. [4] Welte et al., Anal.Chem. 88 (2016) 8570. [5] Merchel et al., JRNCh, submitted. [6] A. Bischoff, pers.comm. (2021.) [7] Merchel, PhD thesis, (1998).

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    The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australien, 14.-19.11.2021, Sydney, Australien

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¹⁰Be from commercial ⁹Be and ²⁷Al carrier solution – Some measurements

Merchel, S.; Braucher, R.; Lachner, J.; Rugel, G.

Abstract

In the DREsden Acclerator Mass Spectrometry (DREAMS) chemistry laboratory, we see elevated but constant ¹⁰Be/⁹Be levels (1.2-2.0x10⁻¹⁵) when using a customised ⁹Be carrier [1]. In satellite and DREAMS laboratories unexperienced researchers and students are performing their own chemical separation, but the “human influence” is unlikely the sole explanation. Different levels of processing blanks as a function of the preparation laboratory are well-known also at other AMS facilities [2]. In our constant approach lowering processing blank levels for ¹⁰Be/⁹Be we have investigated two potential ¹⁰Be sources: ⁹Be and ²⁷Al carrier solutions.

Beryllium-9 carrier solutions are obvious ¹⁰Be sources and commercial and customised ones from minerals were already investigated earlier [3]. Inspired by numerous users asking for ⁹Be carrier analysis, we have compiled all (new) results from different AMS facilities. Remarkably, ¹⁰Be/⁹Be varies in the range of 1-10x10⁻¹⁵ from batch to batch (LOT) of the same company, very likely related to production date [4]. Currently, Australian Chemical Reagents and LGC provide carriers with the lowest intrinsic ¹⁰Be/⁹Be. For AMS users not affording a customised ⁹Be carrier, we advise buying larger quantities of commercial carriers to guarantee long-time low ¹⁰Be/⁹Be and saving precious AMS time from analysing new batches.

Another potential source for elevated and varying ¹⁰Be/⁹Be in processing blanks are Al carrier solutions (added to processing blanks) when performing ¹⁰Be/²⁶Al projects. According to [5] commercial aluminium contained ¹⁰Be in the range of 4-10x10⁷ ¹⁰Be atoms/g(Al). Nowadays, laboratories use 0.5-3.0 mg Al for processing blanks, which would yield into 4-10x10⁵ ¹⁰Be atoms/blank increasing the ¹⁰Be/⁹Be ratio to 6-10x10⁻¹⁵.

We asked in-situ dating researchers to provide their Al solutions. To differentiate between ¹⁰Be from Al and other sources (contamination in the chemistry laboratory or the ion source) we used a “basic standard-addition approach”: For each Al solution, two AMS targets containing ~300 µg ⁹Be and either 1 mg ²⁷Al or 3 mg ²⁷Al were prepared. After minimal chemistry (hydroxide precipitation, cation exchange, Be(OH)₂ precipitation, washing, drying, ignition, mixing with Nb) samples were measured at DREAMS.

Todays’ Al solutions are lower in ¹⁰Be compared to the Al investigated by [5]. None of our results is higher than 3.55x10⁻¹⁵, however, the two processing blanks without any Al have ¹⁰Be/⁹Be ratios of 1.2-1.7x10⁻¹⁵, which is in the same range as 12 out of 14 samples from ACROS, MERCK, ROTH and Traceselect, but 2-3 times higher than the machine blank. This means ~5x10⁴ ¹⁰Be atoms/sample are added from chemicals-consumables-materials or laboratory air-dust.
For more quantitative results about the ¹⁰Be concentration of Al carriers and to identify the main sources of the ¹⁰Be contribution for the processing blanks, additional experiments with larger amounts of Al (10-50 mg) and chemicals are needed.

Acknowledgments: Thanks to ASTER, DREAMS, Trondheim, VERA colleagues for ¹⁰Be data, and ANU, AWI, BOKU, CENIEH, CSFK, U Bratislava, U Jerusalem, U Potsdam colleagues for carrier solutions.

References: [1] Merchel et al., JRNCh (2013). [2] Wilcken et al., NIMB (2019). [3] Merchel et al., NIMB (2008). [4] Merchel et al., MethodsX (2021). [5] Middleton et al., NIMB (1994).

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    The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australien, 14.-19.11.2021, Sydney, Australien

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Using in-situ cosmogenic 36Cl exposure dating of glacial erratics to establish a retreat chronology of the Iller Piedmont Glacier (Southern Germany)

Hildebrandt, D.; Hofmann, F.; Merchel, S.; Rugel, G.; Lachner, J.; Martschini, M.; Friedrich, A.

Abstract

The dynamic behavior of glacial retreat following the globally diachronous Last Glacial Maximum (LGM) is poorly understood. In the Northern Alpine Foreland, multiple lobes of foreland glaciers produced a complex morpho-sedimentary record. While the reconstructed LGM ice extent is laterally constant in the west, it shows significant variations in the central and eastern parts. We explore how these geological differences relate to local climatic variability and global paleoclimate during a period of rapid climate change in the late Pleistocene.

In this study, we employ cosmogenic ³⁶Cl in limestone to constrain the in-situ exposure age of glacial erratics situated on moraine walls of the Iller Piedmont Glacier. We sampled erratic boulders from three moraine crests previously interpreted to represent the LGM and two post-LGM retreat stands. We measured ³⁶Cl/Cl and Cl-nat of seven samples from all three locations by applying routine chemistry protocols (Merchel et al., 2013) and isotope-dilution AMS measurements using a dedicated ion source for halogenides (Pavetich et al., 2014) at the DREsden AMS facility.

Preliminary results show that the sampled boulder surfaces provide internally consistent, reproducible, and geologically meaningful dates. Field investigations indicate that some of the erratic boulders were affected by chemical weathering, slope processes or human activities after their glacial deposition, thereby influencing the measured in-situ ³⁶Cl concentrations. In order to account for these complexities, we apply appropriate correction factors to obtain more accurate ages and discuss the related uncertainties.

Sample preparation of 14 additional samples was performed at the Laboratory for cosmogenic nuclide extraction at the University of Natural Resources and Life Sciences (BOKU) in Vienna. We will likely present ³⁶Cl/Cl and Cl-nat data of these additional samples measured at the Vienna Environmental Research Accelerator (VERA) at the time of the meeting. The exposure age data elucidate the spatio-temporal patterns of receding glaciers in the Northern Alpine Foreland, and place constraints on climate reconstructions for Central Europe during the late Pleistocene.

Acknowledgements:

We are grateful to Stephanie Neuhuber (BOKU Vienna) for providing access to her CN laboratory. Kathrin Strößner, Hagen Hoemann, Paul Herwegh, Kaja Schulz and Sami Akber (all LMU Munich) are thanked for assistance with sample preparation. This work was funded by DFG (German Science Foundation) grant FR 1673/15-1. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden–Rossendorf (HZDR) e. V., a member of the Helmholtz Association, supported by the HZDR Beamtime Proposal 20002195-ST. AMS measurements and sample preparation in Vienna are supported by the RADIATE project under the Grant Agreement 824096319 from the EU Research and Innovation programme HORIZON 2020 trough the Transnational Access grant 21002431-ST.

References:

Merchel et al., Quat. Geochron. 18 (2013) 54.
Pavetich et al., NIMB 329 (2014) 22.

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  • Poster (Online presentation)
    The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), 14.-19.11.2021, Sydney, Australien

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Relative cerebral blood volume reduction in hyperintense brain regions of glioma patients treated with proton radio(chemo)therapy

Witzmann, K.; Raschke, F.; Wesemann, T.; Appold, S.; Krause, M.; Linn, J.; Troost, E. G. C.

Abstract

Introduction:

Adjuvant radio(chemo)therapy (RT) is part of the treatment of patients with primary brain tumors. A major challenge following radiotherapy is to distinguish between tumor recurrence and radiation-induced effects. Hyperintensities in T2-weighted (T2w) MRI are commonly observed after radiotherapy but are not specific to the underlying tissue changes. The value of advanced methods, such as perfusion MRI, has already been shown for differentiating between tumor and treatment effect [1,2]. The aim of this study was to evaluate changes of relative cerebral blood volume (rCBV) in areas of T2w-hyperintensities in order to establish an imaging biomarker differentiating between tumor and treatment effect.

Methods:

In a longitudinal study, anatomical and functional MRI data of glioma patients undergoing gross tumor resection followed by RT were collected. We analyzed a subset of this cohort, which consisted of 14 glioma patients (3 grade II, 8 grade III, 3 grade IV, average age 48.1y ± 13.5y) with tissue hyperintensities on T2w FLAIR images after proton beam irradiation. All MRI data were collected on a 3T Philips Ingenuity PET/MR scanner (Philips, Eindhoven, The Netherlands) using an 8 channel head coil and included anatomical T1w images [3D-GRE, TR/TE=10/3.7ms, FA=20°, voxel size 1×1×1mm3], contrast enhanced T1w images (CET1w) [3D Turbo Field Echo (TFE), TR/TE=8.2/3.7ms, FA=8°, voxel size 1×1×1mm3], 3D FLAIR images [TR/TE = 4800/293ms, TI = 1650ms, 2 averages, voxel size 0.49×0.49×0.5mm3, 360 slices], and dynamic susceptibility contrast (DSC) images using a PRESTO sequence [TR/TE=15/21ms, FA=7°, 60 dynamics, dynamic scan time=1.7s, voxel size 1.8×1.8×3.5mm3] with intravenous gadolinium contrast agent (0.1mol/kg, 4ml/s, 7s delay) followed by a saline flush (20ml, 4ml/s). The same dose of contrast agent was given as a pre-bolus for leakage correction of the DSC perfusion images. MRI scans were acquired prior to RT and post RT in three monthly intervals. In this analysis only the baseline data and the measurement of the latest follow-up time point (18.9 ± 8.2 months after RT) were considered.
To determine cerebral blood volume (CBV) with DSC, the signal time curves of the dynamic PRESTO measurements were converted to concentration time curves. CBV was calculated by the division of the area under the time curve determined by a gamma variate fit function with the arterial input function. CBV-maps were normalized to a normal appearing WM ROI receiving a radiation dose less than 1Gy resulting in the rCBV. The hyperintensity mask indicated on T2w images was determined by the ratio of follow-up and baseline FLAIR images which were registered non-linearly to each other with ANTs [3]. The area showing contrast enhancements in the follow-up measurement was identified by comparing CET1w and T1w images. Hyperintensity mask (HI), contrast enhancement mask (CE), planning computed tomography images (CTs), radiation dose, clinical target volume (CTV) and gross tumor volume (GTV) resp. tumor bed volume (TBV) contour were rigidly registered first to the T1w image and then to the CBV image using ANTs [3] . The region of interest (ROI) was defined based on the hyperintensity mask in the follow-up measurement excluding the GTV resp. TBV and the CE. Four patients did not show any contrast enhancement. The ROI was transferred to the baseline images to evaluate the same region in baseline and follow-up measurement. The rCBV distributions were evaluated comparing the histograms of follow-up and baseline measurement and the Kolmogorow-Smirnow (KS)-test was used to examine the similarity of the histograms. Additionally, the rCBV alterations were analyzed visually.

Results:

The KS-test revealed a significant inequality between follow-up and baseline histograms for all patients, which was expressed by a shift to lower rCBV values in the follow-up measurement (figure 2). Visual examination confirmed the impression of decreasing perfusion in the hyperintense areas, as shown for one patient in figure 1.

Discussion:

We found decreasing perfusion in the hyperintense areas which can be interpreted as treatment effect appearing after RT according to previous studies [4-6]. The baseline evaluation is more distorted by the vascular influence due to inaccuracies in registration and tissue deformation to the transmitted ROI. This can potentially lead to higher baseline perfusion values in some areas caused by grey matter (GM) or vessels. The baseline maps (figure 1B-D) show this effect of blood vessels to the rCBV in the ROI. Due to these factors, comparing mean rCBV values within the ROIs or voxel-based evaluation of the perfusion changes is compromised. Further work is now needed to correlate the observed perfusion changes with histological data.

Conclusion:

The combination of visual impression and histogram analysis showed a decreasing perfusion in the hyperintense areas. Quantitative evaluation requires the exclusion of the influence of the vessels as well as the consideration of tissue displacements. For further studies, the appearance of rCBV changes in areas depending on proximity to CE would be of high interest [7,8] as well as a dose-dependent evaluation.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB & SMRT 31st Annual Meeting, 07.-12.05.2022, London, United Kingdom
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB & SMRT 31st Annual Meeting, 07.-12.05.2022, London, United Kingdom

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Domain wall damping in ultrathin nanostripes with Dzyaloshinskii-Moriya interaction

Volkov, O.; Pylypovskyi, O.; Kronast, F.; Abert, C.; Oliveros Mata, E. S.; Makushko, P.; Mawass, M.-A.; Kravchuk, V.; Sheka, D.; Faßbender, J.; Makarov, D.

Abstract

Structural inversion symmetry breaking in low-dimensional magnetic systems determines their electronic and magnetic properties at interfaces [1,2]. Asymmetrically sandwiched magnetic films can provide strong perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interactions (DMI), which is necessary for prospective memory and logic devices based on chiral non-collinear magnetic textures, e.g. skyrmions [3,4], skyrmion bubbles and chiral domain walls (DWs) [5]. The device performance is determined by the static and dynamic micromagnetic parameters [6,7]. In particular, the speed of a DW-based racetrack memory is defined by both the strength of the external driving, e.g. magnetic field or spin-polarized current, and internal magnetic parameters, e.g. the DMI constant and damping parameter [6,7]. The necessity of having a strong DMI in asymmetrically sandwiched magnetic structures requires the utilization of ultrathin (in the range of 1 nm) magnetic films, which implies the polycrystalinity and compromized structural quality of the layer stack. Structural imperfections in addition to the spin-pumping mechanism [8,9], that arises due to the proximity of a ferromagnetic material with a heavy-metal, lead to a substantial enhancement of the magnetic damping parameter of ultrathin films compared to bulk. Accessing this parameter typically requires dynamic experiments on the motion of DWs in confined geometries, which are usually done in the creep regime due to the pronounced pinning.

Here, we demonstrate both experimentally and theoretically the presence of tilted DWs in statics in perpendicularly magnetized asymmetric //CrOx/Co/Pt layer stacks with surface-induced DMI, Fig. 1. We show that in such systems there are two possible theoretical mechanism for the appearance of titled DWs: (I) A unidirectional tilt could appear in equilibrium as a result of the competition between the DMI and additional in-plane easy-axis anisotropy, which breaks the symmetry of the magnetic texture and introduce tilts [10]. (II) A static DW tilt could appear due to the spatial variation of magnetic parameters, which introduce pinning centers for DWs. A moving DW can be trapped in a tilted state after the external driving field is off. Based on these theoretical approaches, we perform a statistical analysis of the DW tilt angles obtained in staticts after the external magnetic field used for the sample demagnetization was off. We found that the second approach corresponds better to the experimental observations and allows to determine self-consistently the range of DW damping parameters and DMI constants for the particular layer stack. Using two reference fields, which provide two characteristic tilt angles, allow us to retrieve the range of DMI strength mJ/m2 and DW damping parameters . The upper limit for the DMI constant agrees with an independent transport-based measurement giving mJ/m2, which further refines our estimate of the damping parameter . This value lies in a typical DW damping range for the Co-based asymmetrical layer stacks, that are obtained from dynamic experiments [11,12]. Thus, the combination of the proposed method with standard metrological techniques opens up opportunities for the quantification of both static and dynamic micromagnetic parameters based on static measurements of the DW morphology.
[1] A. Fert, N. Reyren, and V. Cros, Nature Reviews Materials 2, 17031 (2017).
[2] R. Wiesendanger, Nature Reviews Materials 1, 16044 (2016).
[3] A. N. Bogdanov and D. A. Yablonskiı̆, Zh. Eksp. Teor. Fiz. 95, 178 (1989).
[4] S. Woo, K. Litzius, B. Krüger, et al., Nature Materials 15, 501 (2016).
[5] S. Emori, U. Bauer, S.-M. Ahn, et al., Nature Materials 12, 611 (2013).
[6] C. Garg, S.-H. Yang, T. Phung, et al., Science Advances 3, e1602804 (2017).
[7] S. Parkin and S.-H. Yang, Nature Nanotechnology 10, 195 (2015).
[8] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, et al., Reviews of Modern Physics 77, 1375 (2005).
[9] A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, Physical Review Letters 101, 037207 (2008).
[10] O. V. Pylypovskyi, V. P. Kravchuk, O. M. Volkov, et al., Journal of Physics D: Applied Physics 53, 395003 (2020).
[11] J.-M. L. Beaujour, J. H. Lee, A. D. Kent, et al., Physical Review B 74 (2006).
[12] A. J. Schellekens, L. Deen, D. Wang, et al., Applied Physics Letters 102, 082405 (2013).

Keywords: Nanomagnetism; Dzyaloshinskii-Moriya interaction

  • Open Access Logo Lecture (Conference) (Online presentation)
    INTERMAG 2021, 26.-30.04.2021, Online, France

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OpenSource im Spannungsfeld akademischer und wirtschaftlicher Interessen

Schlegel, F.; Huste, T.; Juckeland, G.; Konrad, U.

Abstract

Quelloffene Software ist aus der heutigen Wissenschaft nicht mehr wegzudenken und insbesondere im Hinblick auf die Sicherstellung der FAIR Prinzipien stellt sie eine hinreichende Bedingung dar. Die Verwendung von quelloffener Software ist jedoch durch eine Vielzahl von Besonderheiten geprägt, beispielsweise gibt es kein eindeutiges Finanzierungsmodel, wie es für kommerzielle Software in Form von Lizenzgebühren normalerweise der Fall ist. Die freie Verfügbarkeit der Software ermöglicht zudem völlig neue Konzepte in der Ausgestaltung der Beziehung zwischen den Anbietern und den Nutzern, sowie für die Organisation der Community. Hierdurch eröffnet sich ein Gestaltungsspielraum, welcher bisher nur bedingt durch die Forschungseinrichtungen genutzt wird, aber in sich ein enormes Potential für die Zukunft birgt.

Eine im Ingenieurwesen sehr erfolgreiche quelleoffene Software ist die C++-Bibliothek OpenFOAM1 zur Lösung partieller, nichtlinearer Differenzialgleichungen. OpenFOAM wird für eine Vielzahl von unterschiedlichen Anwendungen, wie beispielsweise in der Aerodynamik, in der Hydrodynamik oder in der Chemie- und Verfahrenstechnik eingesetzt. Die Anwender finden sich dabei nicht nur im akademischen Umfeld, sondern auch in der Industrie bei unterschiedlicher Firmen. In den letzten Jahrzehnten hat sich um OpenFOAM eine sehr aktive Community gebildet, mit zum Teil sehr unterschiedlichen Interessen und einem großen Konfliktpotential. Eine der wichtigsten Fragen beim Einsatz von OpenFOAM ist die langfristige und nachhaltige Softwareentwicklung, einerseits bei den Hauptentwicklern, aber vor allem auch bei den Wissenschaftlern. In einem typischen Arbeitsablauf wird zu Beginn einer Promotion ein Fork von OpenFOAM erstellt, in welchem der Doktorand seine Entwicklungen umsetzt. Häufig wird dieser Fork nach Abschluss der Promotion weder langfristig gepflegt, noch ins Release überführt und die Forschungsergebnisse gehen teilweise verloren. Die Ursachen hierfür sind vielfältig, u. a. mangelnde Finanzierung des notwendigen Re-Factorings und des langwierigen Diskussionsprozesses mit den Hauptentwicklern durch den Fördermittelgeber oder eine unzureichende Abbildung solcher Arbeiten in den Kennzahlen der wissenschaftlichen Arbeit und den Beschäftigungsmodellen des öffentlichen Dienstes.

Das Helmholtz-Zentrum Dresden-Rossendorf hat es sich zum Ziel gesetzt eine nachhaltige Softwareentwicklung für OpenFOAM gemeinsam mit der OpenFOAM Foundation anzustreben. Der geplante Beitrag soll die bisher gesammelten Erfahrungen des Helmholtz-Zentrum Dresden-Rossendorf im Umgang mit quelloffener Software am Beispiel von OpenFOAM präsentieren, welche aus dem intensiven Engagement als OpenFOAM Community Mitglied resultieren. Hierbei profitieren die Entwickler u. a. von den Möglichkeiten der Helmholtz-Gemeinschaft, insbesondere von den Helmholtz Federated IT Services (HIFIS)2. Der Vortrag zeigt einen möglichen Weg für eine wissenschaftliche Einrichtung mit einem guten Beispiel vorangehen und vernünftige Konzepte zu entwickeln quelloffene Software adäquat einzusetzen, nachhaltig weiterzuentwickeln, langfristig zu unterstützen und zu fördern. Ziel des Beitrages ist es Erfahrungen zu teilen, Probleme anzusprechen und eine Diskussion zur Beschreibung weiterer Wege anzuregen.

  • Lecture (Conference) (Online presentation)
    Software Engineering 2022, 21.-25.02.2022, Potsdam, Deutschland

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Experimental confirmation of curvature-induced effects in magnetic nanosystems

Volkov, O.; Kakay, A.; Kronast, F.; Mawass, M.-A.; van den Brink, J.; Kravchuk, V.; Sheka, D.; Faßbender, J.; Makarov, D.

Abstract

Curvilinear magnetism is the emerging field in micromagnetism which studies influences of external geometry and its topology on magnetic vector fields [1]. Much attention was paid to fundamental theoretical investigations of curvature-induced effects for local [2,3] and non-local magnetic interactions [4], which results in the prediction of various magnetochiral effects [2,5], topologically-induced magnetic patterns [5,6], stabilization of individual skyrmions [7,8] and skyrmion lattices [9] on curvilinear defects. Recently, we provided the very first experimental confirmation and quantitative assessment of the existence of the curvature-induced chiral interaction of exchange origin in a conventional soft ferromagnetic material [10]. In its turn, the interplay between the intrinsic and exchange-induced Dzyaloshinskii-Moriya interaction (DMI) paves the way to a mesoscale DMI [3], whose symmetry and strength depends both on the geometrical and material parameters of the magnetic system. Extending this concept we proposed a novel approach towards artificial magnetoelectric materials with helimagnetic nanohelices embedded in a piezoelectric matrix [11], where electric field could control magnetic states through the utilization of curvature-induced effects.

[1] R. Streubel et. al., J. Phys. D: Appl. Phys. 49,363001 (2016).
[2] Y. Gaididei et al., Phys. Rev. Lett. 112, 257203 (2014).
[3] O. Volkov et al., Sci. Rep. 8, 866 (2018).
[4] D. D. Sheka et al., Commun. Phys. 3, 128 (2020).
[5] V. P. Kravchuk et al., Phys. Rev. B 85, 144433 (2012).
[6] O. V. Pylypovskyi et al., Phys. Rev. Lett. 114, 197204 (2015).
[7] V. P. Kravchuk et al., Phys. Rev. B 94, 144402 (2016).
[8] O. V. Pylypovskyi et al., Physical Review Applied 10, 064057 (2018).
[9] V. P. Kravchuk et al., Phys. Rev. Lett. 120, 067201 (2018).
[10] O. M. Volkov et al., Phys. Rev. Lett. 123, 077201 (2019).
[11] O. M. Volkov et al., J. Phys. D: Appl. Phys. 52, 345001 (2019).

Keywords: Nanomagnetism; Curvilinear magnetism

  • Poster (Online presentation)
    717. WE-Heraeus-Seminar — Curvilinear Condensed Matter: Fundamentals and Applications, 24.-26.06.2021, Online, Germany

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RevCAR platform as a combinatorial approach for targeting acute myeloid leukemia

Loureiro, L. R.; González Soto, K. E.; Kittel-Boselli, E.; Hoffmann, A.; Bergmann, R.; Arndt, C.; Mitwasi, N.; Kegler, A.; Bartsch, T.; Berndt, N.; Altmann, H.; Fasslrinner, F.; Bornhäuser, M.; Bachmann, M.; Feldmann, A.

Abstract

Background:

In the past years, the treatment of acute myeloid leukemia (AML) has been significantly shifted towards the development of targeted approaches. Nonetheless, clinical translation of novel immunotherapeutic strategies such as chimeric antigen receptor (CAR) T-cells in AML is still at an early stage. Given the heterogeneity of such disease, major challenges include immune escape and disease relapse, which demand for further improvements in the CAR design. To overcome such hurdles, we have invented the switchable, flexible and programmable adaptor RevCAR platform. This consists of T-cells engineered with RevCARs that are primarily inactive as they express an extracellular short peptide epitope incapable of recognizing surface antigens. RevCAR T-cells can be redirected to tumor antigens and controlled by bispecific antibodies cross-linking RevCAR T- and tumor cells resulting in tumor lysis. Remarkably, the RevCAR platform enables combinatorial tumor targeting following Boolean logic gates in which two separate RevCARs with different specificities can be simultaneously expressed and used to accomplish dual gated targeting of prominent AML antigens such as CD33 and CD123. We herein show for the first time the applicability of the RevCAR platform to target myeloid malignancies such as AML.

Methods:

Binding, functionality and proof-of-concept for combinatorial tumor targeting using the RevCAR system was assessed using both in vitro and in vivo models in different settings. For that, flow cytometry-based, cytokine release and cytotoxicity assays were performed using established AML cell lines or patient-derived material.

Results:

We have proven that AML cell lines as well as patient-derived AML blasts could be efficiently killed by redirected RevCAR T-cells targeting CD33 and CD123 in a flexible manner. Furthermore, by targeting both antigens, an AND gate logic targeting could be achieved using the RevCAR platform. This is a particular important approach to overcome existing or treatment related tumor escape variants and to tackle AML cancer heterogeneity.

Conclusions:

These accomplishments validate the preclinical versatility and controllability of the RevCAR platform embedded in one single system thereby paving the way for an improved and personalized immunotherapy of AML patients.

  • Lecture (Conference) (Online presentation)
    World Immunotherapy Council´s 4th Young Investigator Symposium (WIC), 10.11.2021, Washington, USA

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Influence of surface activation on the microporosity of PE-CVD and PE-ALD SiOx thin films on PDMS

Hoppe, C.; Mitschker, F.; Mai, L.; Liedke, M. O.; de Los Arcos, T.; Awakowicz, P.; Devi, A.; Elsherif, A. G. A.; Butterling, M.; Wagner, A.; Grundmeier, G.

Abstract

The microporosity, structure and permeability of SiOx thin films deposited by microwave plasma enhanced chemical vapour deposition and by plasma-enhanced atomic layer deposition on PDMS substrates were investigated by positron annihilation spectroscopy and complementary techniques. The chemical composition and morphology were analysed by X-ray photoelectron spectroscopy, polarization modulated-infrared reflection-absorption spectroscopy, time of flight spectroscopy and atomic force microscopy. The SiOx films were deposited onto spin-coated PDMS substrates, which were exposed to an oxygen plasma prior to thin film deposition. A correlation between the oxygen fluence during the oxygen plasma treatment and the microporosity of bth PE-CVD and PE-ALD SiOx films could be established. It was observed that a longer exposure to the oxygen plasma treatment resulted in formation of a SiOx-like surface near region of the PDMS film. In comparison to the as spin-coated PDMS surface, the oxidised surface near region led to an overall decrease in micropore density and to a shift towards smaller pore sizes within the deposited SiOx films.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; porosity; SiOx; plasma enhanced chemical vapour deposition; plasma-enhanced atomic layer deposition

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Curvature-induced effects in magnetic nanosystems

Volkov, O.; Sheka, D.; Kravchuk, V.; Rößler, U.; Faßbender, J.; Makarov, D.

Abstract

Curvilinear magnetic objects are in focus of intensive research due to the possibility to obtain new
fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. In
geometrically-broken magnetic objects all energy functionals, that contains spatial derivatives, e.g.
exchange, magnetostatic and intrinsic Dzyaloshinskii-Moriya (DMI) interactions, are reshaping in a
way of appearance additional curvature-induced chiral and anisotropy terms. These novel chiral
magnetic responses arise in the physical space, by introducing bends and twists to magnetic
architectures even of conventional materials. We address both experimentally and theoretically the
appearance of curvature-induced exchange effects in parabolic nanostripes with different
geometrical parameters [2]. We show that a pinning of transversal domain wall at the parabolic apex
is originated due to the presence of local curvature-induced DMI that creates a subsequent pinning
potential. Measuring the depinning field enables to quantify the effective exchange-driven DMI
interaction constant. In its turn, the interplay between the intrinsic and exchange-induced DMI
paves the way to a mesoscale DMI, whose symmetry and strength depend both on the geometrical
and material parameters [3]. Developing this concept we propose a novel approach towards
artificial ME materials with helimagnetic nanohelices embedded in a piezoelectric matrix [4]. By
applying an electric field, small geometrical changes of pitch and radius could lead to the phase
transition from a homogeneously magnetized state (full average magnetic moment) to a periodical
one (zero average magnetic moment).

[1] R. Streubel et. al., J. Phys. D: Appl. Phys. 49,363001 (2016).
[2] O. Volkov et al.. Phys. Rev. Lett. 123, 077201 (2019).
[3] O. Volkov et al., Sci. Rep. 8, 866 (2018).
[4] O. Volkov et al., J. Phys. D: Appl. Phys. 52, 345001 (2019).

Keywords: Nanomagnetism; Curvilinear magnetism

  • Lecture (Conference) (Online presentation)
    APS March Meeting 2021, 15.-19.03.2021, Online, USA

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KupferDigital Digital – Datenökosystem für die digitale Material- entwicklung auf Basis Ontologie-basierter digitaler Repräsentationen von Kupfer und Kupferlegierungen

Eisenbart, M.; Weber, M.; Wenige, L.; van den Boogaart, K. G.; Klengel, S.; Skrotzki, B.; Tikana, L.; Hupperz, M.; Füting, M.

Abstract

Mit der Initiative MaterialDigital fördert das BMBF die Digitalisierung der Materialwissen-
schaft und Werkstoff technik in Deutschland. In diesem Rahmen fungiert die Plattform
MaterialDigital als Anlaufstelle für alle Interessenten und koordiniert die Aktivitäten zu
Digitalisierung in der Werkstoff welt. Mit dem im März 2021 gestarteten Projekt KupferDigital
ist nun auch der Werkstoff Kupfer ist bei der Initiative Plattform MaterialDigital vertreten. Das
Ziel des Projektes ist es, den Kupferlebenszyklus von der Erzgewinnung über die Material-
entwicklung und Herstellung sowie des Produktlebens bis hin zum Recycling digital zu
repräsentieren. Als Basis der Digitalisierung dienen hierzu Ontologien, die die digitale Material-
und Prozessbeschreibung einheitlich ermöglichen sollen und auch im größeren Zusammenhang
der Plattform MaterialDigital als gemeinsamer Standard entwickelt werden sollen.
Entstehen soll ein Datenökosystem, in dem der Datenaustausch über die verschiedenen
Instanzen des Lebenszyklus hinweg ermöglicht werden soll. Damit kann die Material- und
Produktentwicklung im eigenen Unternehmen Aspekte aus den anderen Stationen des
Lebenszyklus berücksichtigen und zum Beispiel Aspekte der Nachhaltigkeit berücksichtigen.

Keywords: Ontology; Copper Life Cycle

  • Poster
    Kupfer-Symposium 2021, 24.-25.11.2021, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33374


Fundamentals of curvilinear ferromagnetism: statics and dynamics of geometrically curved wires and narrow ribbons

Sheka, D.; Pylypovskyi, O.; Volkov, O.; Yershov, K.; Kravchuk, V. P.; Makarov, D.

Abstract

Low-dimensional magnetic architectures including wires and thin films are key enablers of prospective ultrafast and energy efficient memory, logic and sensor devices relying on spin-orbitronic and magnonic concepts. Curvilinear magnetism emerged as a novel approach in material science, which allows tailoring of the fundamental anisotropic and chiral responses relying on the geometrical curvature of magnetic architectures. Much attention is dedicated to magnetic wires of Möbius, helical or DNA-like double helical shapes, which act as prototypical objects for the exploration of the fundamentals of curvilinear magnetism. Although there is a bulk number of original publications covering fabrication, characterization and theory of magnetic wires, there is no comprehensive review of the theoretical framework of how to describe these architectures. Here, we summarize theoretical activities on the topic of curvilinear magnetic wires and narrow nanoribbons, providing a systematic review of the emergent interactions and novel physical effects caused by the curvature. We discuss prospective research directions of curvilinear spintronics and spin-orbitronics, outline the fundamental framework for curvilinear magnonics and introduce mechanically flexible curvilinear architectures for soft robotics.

Keywords: curvilinear magnetism; nanowires; ribbons

Permalink: https://www.hzdr.de/publications/Publ-33373


Metal Oxides

Scheinost, A.; Singh, B.

Abstract

Oxide minerals (include oxides, hydroxides, oxyhydroxides and hydrated oxides) are primary and secondary minerals of Si, Fe, Mn, Al and Ti. Secondary oxides, particularly of Fe, Al and Mn, are perhaps the most reactive and important components in many soils due to their high specific surface area and strong sorption capacity for many essential and potentially toxic elements. Iron and Mn oxides also play key roles in many redox reactions and have major influence on the transformation and availability of organic and inorganic contaminants in soils. This chapter provides an overview of the oxide minerals in soils, with an emphasis on their structure and composition, environmental conditions for their formation and their properties.

Keywords: Goethite; Hematite; ferrihydrite; gibbsite; quartz; redox; adsorption; secondary minerals

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Permalink: https://www.hzdr.de/publications/Publ-33372


Measurement of magnetic fringe fields from a proton pencil beam scanning nozzle causing MR image ghosting artefacts during in-beam MR imaging

Semioshkina, E.; Oborn, B.; Hoffmann, A. L.

Abstract

INTRODUCTION:

Proton therapy (PT) produces highly conformal dose distributions with steep gradients at the target boundaries due to the finite range of protons. This reduces normal-tissue doses, particularly at the distal side of the tumor where the Bragg peak is located. However, the targeting precision of PT is compromised by a lack of image guidance: imaging modalities in treatment rooms of PT facilities are often limited to X-ray based on-board 2D kV or 3D cone-beam CT imaging. The integration of fast real-time MR imaging could significantly improve on-board imaging and therefore increase the targeting accuracy of PT, especially for moving tumors [1].
However, a full integration of MRI and PT at the treatment isocenter is technically challenging due to the electromagnetic interaction between both systems. Although a first proof-of-concept for in-beam MRI has proven successful in combination with a static proton research beamline [2], the combination of a research prototype in-beam MRI system with a beamline featuring an actively scanned proton beam (figure 1) has proven problematic. MR images acquired during proton pencil beam scanning (PBS) dose delivery were blurred by coherent ghosting artefacts due to dynamic magnetic fringe fields produced by nearby beam steering magnets overlapping with the B0 field of the MR scanner (figure 2) [3]. One way to eliminate these artifacts could be passive magnetic shielding of the beam steering magnets. This would lead to decoupling the magnetic fields of the MR scanner and the PBS nozzle. To be able to design an optimal shielding solution, a detailed understanding of the magnitude of the magnetic fringe fields produced by the PBS nozzle is mandatory. The aim of this study was to measure the magnetic fringe fields produced by the PBS nozzle. The experimental data will be used to help optimize and validate a finite element model (FEM) of the PBS nozzle that is under development.
METHODS:
A proton beam of therapeutic quality was generated by an isochronous cyclotron (C230, IBA SA, Louvain-la-Neuve, Belgium). The proton PBS nozzle of a horizontal research beamline included two sets of dipole magnets to scan the beam in horizontal (X) and vertical (Y) direction across a target volume during dose delivery. A fluxgate magnetometer (Mag649-200, Metrolab Technology SA, Geneva, Switzerland) was used to measure the magnitude of the magnetic fringe fields produced by the beam scanning magnets. It was positioned on a mobile tripod in front of the PBS nozzle at 13 locations as demonstrated in figure 3 at the height of the central beam axis (i.e. 126 cm above floor level). The delivery of two dose spot maps was emulated by energizing the magnets of the PBS beamline for a proton beam of 220 MeV, but no beam was released from the cyclotron in order to prevent radiation damage to the magnetometer. A beam energy of 220 MeV was chosen to achieve the maximum magnitude of magnetic fringe fields produced by the beamline magnets, and thus represent the worst-case scenario. Each dose spot map included a single dose point of 4500 monitor units (MUs) irradiated at a dose rate of approximately 155.2 MU/s. The X scanning magnets were energized to emulate the delivery of two dose spots to extreme positions at (X = -20 cm, Y = 0 cm) and (X = 20 cm, Y = 0 cm) relative to the beam isocenter. This experiment was repeated three times. The Y scanning magnets were not energized, as their fringe fields were previously shown not to affect the MR image quality [3].
RESULTS:
The maximum magnitude of the magnetic fringe field of scanning magnets was measured on the central beam axis at PBS isocenter (Figure 4). The fringe field magnitude varied from 2 µT to 6 µT over the volume where the in-beam MR scanner will be placed. A slight asymmetry in the measured values along the lateral direction (i.e. perpendicular to the central beam axis) was observed (see figure 4a).

DISCUSSION:

The resolution and the measuring range of the magnetometer are well suited to perform the measurements in the volume of high interest, i.e. the volume where the in-beam MR scanner is positioned. Even the 1 µT changes in the magnetic field, e.g., the asymmetry along the lateral direction, were detected. The asymmetric measurement results from the asymmetric design of the PBS nozzle. However, the resolution of 0.5 µT did not allow measurements in lower magnetic fields and the magnetometer became oversaturated in the regions of higher magnetic field strengths. Further measurements outside the volume in which the MR scanner is positioned, e.g., in the immediate proximity of the PBS nozzle where the magnetic field strength is largest, require a magnetometer with an extended measuring range and resolution.

CONCLUSION:

The magnitude of the magnetic fringe field produced by the PBS nozzle was successfully measured experimentally for two dose spot maps at extreme spot scanning positions. The valuable measurement data will be used to optimize and validate the FEM model of the PBS nozzle. More measurements using different beam energies, dose spot positions and measurement positions of the magnetometer are needed to complete the validation of the FEM.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-33371


Application of multi-edge HERFD-XAS to assess the uranium valence electronic structure in potassium uranate (KUO3)

Bes, R.; Leinders, G.; Kvashnina, K.

Abstract

The uranium valence electronic structure in the prototypical undistorted perovskite
KUO3 is reported on the basis of a comprehensive experimental study using multi-
edge HERFD-XAS and relativistic quantum chemistry calculations based on DFT.
Very good agreement is obtained between theory and experiments, including the con-
firmation of previously reported Laporte forbidden f-f transitions and X-ray photo-
electron spectroscopic measurements. Many spectral features are clearly identified in
the probed U-f, U-p and U-d states and the contribution of the O-p states in those fea-
tures could be assessed. The octahedral crystal field strength, 10Dq, was found to be 6.6(1.5) eV and 6.9(4) eV from experiment and calculations respectively. Calculated
electron binding energies down to U-4f states are also reported.

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Permalink: https://www.hzdr.de/publications/Publ-33370


Effective coordination numbers from EXAFS: General approaches for dioxides

Romanchuk, A.; Trigub, A.; Plakhova, T.; Kuzenkova, A.; Svetogorov, R.; Kvashnina, K.; Kalmykov, S.

Abstract

EXAFS is one of the comprehensive usable method to characterize structures of various
materials including radioactive and nuclear materials. Unceasing discussions about the interpretation of
EXAFS results for actinides nanoparticles (NPs) or colloids remain during the last decates. In this paper,
the new experimental data for PuO2 and CeO2 NPs with different average sizes are compared with
published data on AnO2 NPs that shed the light on the best fit and interpretation of the structural data.
Structurally PuO2, CeO2, ThO2, and UO2 NPs demonstrate similar behavior. Only ThO2 NPs have a
more disordered and even partly amorphous structure that results in EXAFS characteristics. The
proposed new core-shell model for NPs with calculated effective coordination number perfectly fits the
results on variations in Me-Me shell with the decrease of NPs size.

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Geographical data analysis in the historical research

Mertel, A.

Abstract

Část interdisciplinárních studií v sociálních vědách se v posledních letech zastřešuje termíny jako "Cultural Analytics", "Cliodynamics" nebo "Digital (Geo) Humanities". Soustřeďují pozornost na otázky digitalizace, sdílení a popisu (metadata) zdrojů, datové analýzy a vizualizace ve vědeckých oblastech, kterým jsou tradičně vlastní spíše kvalitativní metody, což platí v neposlední řadě i pro historický výzkum. Úkolem (geografické) datové analýzy je obecně snaha transformovat data do podoby, ze které je možné získat novou vědomost. Přestože je dnes proces datové analýzy relativně standardizovaný, prostředí historického výzkumu má několik specifik, k nimž je třeba přihlížet. Prezentace se soustředí na tyto specifika v kontextu geografické datové analýzy, jež jsou přítomna v procesu sběru a zpracování dat, volby a implementace metodologie a také interpretace a validace výstupů.

Keywords: spatial data analysis; historical science; data uncertainty; geocoding; source modeling; least cost analysis; environmental modeling

  • Invited lecture (Conferences)
    LINDAT CLARIAH-CZ Talk, 12.11.2021, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-33368


Symmetry and curvature effects on spin waves in vortex-state hexagonal nanotubes

Körber, L.; Zimmermann, M.; Wintz, S.; Finizio, S.; Kronseder, M.; Bougeard, D.; Dirnberger, F.; Weigand, M.; Raabe, J.; Otálora, J. A.; Schultheiß, H.; Josten, E.; Lindner, J.; Kézsmárki, I.; Back, C. H.; Kakay, A.

Abstract

Analytic and numerical studies on curved magnetic nano-objects predict numerous exciting effects that can be referred to as magneto-chiral effects, which do not originate from intrinsic Dzyaloshinskii–Moriya interaction or interface-induced anisotropies. In constrast, these chiral effects stem from isotropic exchange or dipole-dipole interaction, present in all magnetic materials, which acquire asymmetric contributions in case of curved geometry of the specimen. As a result, for example, the spin-wave dispersion in round magnetic nanotubes becomes asymmetric, namely spin waves of the same frequency propagating in opposite directions along the nanotube exhibit different wavelenghts. Here, using time-resolved scanning transmission X-ray microscopy experiments, standard micromagntic simulations and a dynamic-matrix approach, we show that the spin-wave spectrum undergoes additional drastic changes when transitioning from a continuous to a discrete rotational symmetry, i.e. from round to hexagonal nanotubes, which are much easier to fabricate. The polygonal shape introduces localization of the modes both to the sharp, highly curved corners and flat edges. Moreover, due to the discrete rotational symmetry, the degenerate nature of the modes with azimuthal wave vectors known from round tubes is partly lifted, resulting in singlet and duplet modes. For comparison with our experiments, we calculate the microwave absorption from the numerically obtained mode profiles which shows that a dedicated antenna design is paramount for magnonic applications in 3D nano-structures. To our knowledge these are the first experiments directly showing real space spin-wave propagation in 3D nano objects.

Keywords: spin wave; dispersion; curvature; micromagnetic modeling; hexagonal; symmetry; STXM

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Permalink: https://www.hzdr.de/publications/Publ-33367


Numerical reverse engineering of general spin-wave dispersions: Bridge between numerics and analytics using a dynamic-matrix approach

Körber, L.; Kakay, A.

Abstract

Modern problems in magnetization dynamics require more and more the numerical determination of the spin-wave spectra and -dispersion in magnetic systems where analytic theories are not yet available. Micromagnetic simulations can be used to compute the spatial mode profiles and oscillation frequencies of spin-waves in magnetic system with almost arbitrary geometry and different magnetic interactions. Although numerical approaches are very versatile, they often do not give the same insight and physical understanding as analytical theories. For example, it is not always possible to decide whether a certain feature (such as dispersion asymmetry, for example) is governed by one magnetic interaction or the other. Moreover, since numerical approaches typically yield the normal modes of the system, it is not always feasible to disentangle hybridized modes. In this manuscript, we build a bridge between numerics and analytics by presenting a methodology to calculate the individual contributions to general spin-wave dispersions in a fully numerical manner. We discuss the general form of any spin-wave dispersion in terms of the effective (stiffness) fields produced by the modes. Based on a special type of micromagnetic simulation, the numerical dynamic-matrix approach, we show how to calculate each stiffness field in the respective dispersion law, separately for each magnetic interaction. In particular, it becomes possible to disentangle contributions of different magnetic interactions to the dispersion asymmetry in systems where non-reciprocity is present. At the same time, dipolar-hybridized modes can be easily disentangled. Since this methodology is independent of the geometry or the involved magnetic interactions at hand, we believe it is attractive for experimental and theoretical studies of magnetic systems where there are no analytics available yet, but also to aid the development of new analytical theories.

Keywords: spin wave; Micromagnetic simulations; theory; dispersion; dynamic-matrix approach; normal modes; hybridization; numerics

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Permalink: https://www.hzdr.de/publications/Publ-33366


Data for: Heterogeneous sorption of radionuclides predicted by crystal surface nanoroughness

Yuan, T.; Schymura, S.; Bollermann, T.; Molodtsov, K.; Chekhonin, P.; Schmidt, M.; Stumpf, T.; Fischer, C.

Abstract

Reactive transport modeling (RTM) is an essential tool for the prediction of contaminants’ behavior in the bio- and geosphere. However, RTM of sorption reactions is constrained by the reactive surface site assessment. The reactive site density variability of the crystal surface nanotopography provides an “energetic landscape”, responsible for heterogeneous sorption efficiency, not covered in current RTM approaches.  Here, we study the spatially heterogeneous sorption behavior of Eu(III), as an analogue to trivalent actinides, on a polycrystalline nanotopographic calcite surface and quantify the sorption efficiency as a function of surface nanoroughness. Based on experimental data from micro-focus time-resolved laser-induced luminescence spectroscopy (µTRLFS), vertical scanning interferometry, and electron back-scattering diffraction (EBSD), we parameterize a surface complexation model (SCM) using surface nanotopography data. The validation of the quantitatively predicted spatial sorption heterogeneity suggests that retention reactions can be considerably influenced by nanotopographic surface features. Our study presents a way to implement heterogeneous surface reactivity into a predictive SCM for enhanced prediction of radionuclide retention.

Keywords: Sorption reactions; Crystal surface reactivity; µTRLFS; Surface complexation modeling; Radionuclide migration

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Permalink: https://www.hzdr.de/publications/Publ-33364


Data publication: Nanoindentation response of ion-irradiated Fe, Fe-Cr alloys and ferritic-martensitic steel Eurofer 97: The effect of ion energy

Das, A.; Altstadt, E.; Kaden, C.; Kapoor, G.; Akhmadaliev, S.; Bergner, F.

Abstract

The dataset consists of inputs from ion irradiation experiments, nanoindentation and empirical modeling results for Fe (G379), ferrritic Fe-9Cr (G385), martensitic Fe-9Cr (L252) and Eurofer 97 steel. The dataset also includes the basic characterization of microstructure.

Keywords: iron; Fe-Cr alloy; ferritic-martensitic steel; ion irradiation; displacement damage; nanoindentation; irradiation hardeníng; indentation size effect

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Permalink: https://www.hzdr.de/publications/Publ-33362


A Small Step, a Giant Leap: Somatic Hypermutation of a Single Amino Acid Leads to Anti-La Autoreactivity

Bartsch, T.; Arndt, C.; Loureiro, L. R.; Kegler, A.; Puentes-Cala, E.; Soto, J. A.; Kurien, B. T.; Feldmann, A.; Berndt, N.; Bachmann, M.

Abstract

The anti-La mab 312B, which was established by hybridoma technology from human-La transgenic mice after adoptive transfer of anti-human La T cells, immunoprecipitates both native eukaryotic human and murine La protein. Therefore, it represents a true anti-La autoantibody. During maturation, the anti-La mab 312B acquired somatic hypermutations (SHMs) which resulted in the replacement of four aa in the complementarity determining regions (CDR) and seven aa in the framework regions. The recombinant derivative of the anti-La mab 312B in which all the SHMs were corrected to the germline sequence failed to recognize the La antigen. We therefore wanted to learn which SHM(s) is (are) responsible for anti-La autoreactivity. Humanization of the 312B ab by grafting its CDR regions to a human Ig backbone confirms that the CDR sequences are mainly responsible for anti-La autoreactivity. Finally, we identified that a single amino acid replacement (D > Y) in the germline sequence of the CDR3 region of the heavy chain of the anti-La mab 312B is sufficient for anti-La autoreactivity.

Permalink: https://www.hzdr.de/publications/Publ-33361


Characterizing material liberation of multi-material lightweight structures from shredding experiments and finite element simulations

Heibeck, M.; Rudolph, M.; Modler, N.; Reuter, M.; Filippatos, A.

Abstract

Most products in automotive, aerospace, and household appliance industry are multi-material structures. Materials are connected through a variety of joining techniques with the aim of optimizing performance during production and operation phase. However, during recycling in the end-of-life phase, different materials combined in multi-material structures need to be liberated, e.g. disconnected, and separated again to enable high material recoveries. Typical recycling approaches use shredding technologies to liberate materials. Efficient material liberation contributes to achieving high recycling rates for end-of-life products set by the European Union, thereby reducing the need for primary resource extraction and leading to a more sustainable development.

To characterize material liberation, we conducted an experimental shredding study with multi-material lightweight structures typical for automotive A-frames consisting of steel and composite materials, which were shredded in two sequences in a pilot rotary shear. We characterized feed and resulting progeny particles through a set of quantitative and qualitative metrics, thereby tracking changes in joint characteristics, material composition and particle sizes over the course of two processing steps. We found that material liberation is dependent on many design and shredding parameters. Our characterization approach for feed and progeny particles allows for linking design parameters to liberation behaviour. Due to high variability of design and shredding parameters experimental data acquisition is effortful. Therefore, we present an outlook on first results of our physics-based, numerical simulation model using Finite Element Method. Once validated, shredding simulations of many design configurations shall inform the designer about the liberation behaviour of a multi-material structure, such as the A-frame specimens.

Keywords: Recycling; Shredding; Multi-material design; Material liberation; Joint characterization; Composites; Finite Element Method

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Two-dimensional materials under ion irradiation: from defect production to structure and property engineering

Ghorbani Asl, M.; Kretschmer, S.; Krasheninnikov, A.

Abstract

Similar to their bulk 3D counterparts, the properties of two-dimensional
(2D) materials can be tuned by controllable introduction of impurities
and defects using beams of energetic ions, which requires
complete microscopic understanding of their response to ion irradiation.
The behavior of 2D materials under ion beam is also interesting in the context of their applications in radiation-hostile environments such as cosmic space. While irradiation effects in 3D systems are well understood, a growing body of experimental facts indicate that many concepts of energetic particle-solid interaction developed for 3D materials are not applicable to 2D systems due to their very geometry, or require substantial modifications. In this Chapter, we discuss at length the response of 2D materials to ion irradiation in different regimes with the main focus on the role of reduced dimensionality. We illustrate the differences between the impact of ions on 3D and 2D materials by examples taken from the recent theoretical and experimental studies on the response of 2D materials to ion irradiation and outline general trends in their behavior under irradiation. Finally, we discuss how ion beams can be used to engineer the structure and properties of 2D materials.

Keywords: Two-dimensional materials; ion irradiation; defect; engineering

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Chelators for treatment of iron and copper overload: Shift from low-molecular-weight compounds to polymers

Hruby, M.; Santana Martinez, I. I.; Stephan, H.; Pouckova, P.; Benes, J.; Stepanek, P.

Abstract

Iron and copper are essential micronutrients needed for the proper function of every cell. However, in excessive amounts these elements are toxic as they may cause oxidative stress resulting in damage of liver and other organs. This may happen due to poisoning, as side effect of thalassemia infusion thera-py or due to hereditary diseases hemochromatosis or Wilson´s disease. The current golden standard of therapy of iron and copper overload is the use of low-molecular-weight chelators of these elements. However, these agents suffer from severe side effects, are often expensive and possess unfavourable pharmacokinetics, which is all limiting useability of such therapy. The emerging concept are poly-mer-supported iron- and copper-chelating therapeutics, either for parenteral or oral use, which show vivid potential to keep therapeutic efficacy of low-molecular-weight agents while avoiding their draw-backs and especially side effects. Critical evaluation of this new perspective polymer approach is the purpose of this review article.

Keywords: iron; copper; polymer; chelator; Wilson's disease; hemochromatosis

Permalink: https://www.hzdr.de/publications/Publ-33358


SOLSTICE - Na-Zn molten salt batteries

Duczek, C.; Lee, J.; Monrrabal Marquez, G.; Weber, N.; Weier, T.

Abstract

The first results of the EU project SOLSTICE will be presented.

  • Communication & Media Relations
    Battery Innovation Days (online Messestand) 23.11.2021

Permalink: https://www.hzdr.de/publications/Publ-33357


SOLSTICE - Na-Zn molten salt batteries

Weber, N.; Heinz, M.; Lee, J.; Weier, T.

Abstract

The talk gives a very short overview on the EU project SOLSTICE.

  • Invited lecture (Conferences) (Online presentation)
    Horizon 2020 Batteries Projects clustering event, 17.-18.11.2021, Brüssel, Belgien

Permalink: https://www.hzdr.de/publications/Publ-33356


Liberation and separation of valuable components from LED modules: presentation of two innovative approaches

Balinski, A.; Recksiek, V.; Stoll, M.; Christesen, C. S.; Stelter, M.

Abstract

The rapid development of light-emitting-diode (LED) technology is attributed to its superiority over light sources of earlier generations. Although LED lamps, compared to compact fluorescent lamps, are considered less harmful to the environment, there is still no efficient solution to deal with them at the end of their lifecycle. The first part of the study provides a detailed characterisation of LED lamps, focusing on their most interesting component: the LED module. LED packages attached to the module are highly enriched with Ga, In, Pd, Ag, Au, Sr, Y, Ce, Eu, Gd, and Lu, with the content of each element varying greatly depending on the LED technology. In the second part of this research, two new approaches for liberation and concentration of valuable components from LED modules are presented and compared: a chemical route and a thermal route. The chemical treatment leads to a highly selective separation of LED chips and encapsulation. Enrichment factors up to about 125 are achieved, and a concentrate is obtained containing approximately 14 wt% of the aforementioned valuable components. However, the process requires aromatic solvents, which are viewed as toxic. The thermal treatment results in separation of the aluminium heat sink from all other components of the LED module. Enrichment is approximately ten times lower, but the approach is technically feasible.

Keywords: LED lamps; recycling; waste electrical and electronic equipment; gallium; precious metals; rare earth elements

Permalink: https://www.hzdr.de/publications/Publ-33355


Germanium as an ultrabroadband THz material

Helm, M.; Singh, A.; Pashkin, O.; Winnerl, S.; Beckh, C.; Sulzer, P.; Leitenstorfer, A.; Schneider, H.

Abstract

Germanium, as an elemental semiconductor, has no Reststrahlen band and is thus suited as a broadband THz material, even for THz generation. The drawback of its long carrier lifetime due to the indirect band gap can be remedied through ion implantation, and the relatively small size of the gap allows excitation with fiber lasers in the telecom range. We demonstrate THz emission from Ge photoconductive antennas reaching as far as 70 THz.

Keywords: germanium; THz; photoconductive antenna; braodband

  • Invited lecture (Conferences) (Online presentation)
    RJUSE TeraTech 2021, 01.-04.11.2021, Sendai, Japan
  • Contribution to proceedings
    RJUSE TeraTech 2021, 01.-04.11.2021, Sendai, Japan
    RJUSE TeraTech 2021 Conference Digest

Permalink: https://www.hzdr.de/publications/Publ-33354


Data publication: How 5f electron polarizability drives covalency and selectivity in actinide N-donor complexes

Köhler, L.; Patzschke, M.; Schmidt, M.; Stumpf, T.; März, J.

Abstract

Diese Daten beinhalten die Synthese und Charakterisierung neuartiger Actinid (Th, U, Np, Pu) Komplexe mit pyrrolbasierten Liganden, sowie ebenfalls die Ligandsynthese. Darunter fallen SC-XRD, NMR, IR, UV-VIS und EA Daten. Des weiteren quantenchemische Berechnungen zu den Systemen, sowie der Vergleich zum bereits bekannten Salen System.

Keywords: actinides; N donor ligands; bonding analysis; f electrons; pyrrole

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Computational Science at HZDR: Tools, Services, and Consulting to Empower Your Research

Pape, D.; Lokamani, M.; Knodel, O.; Müller, S.; Huste, T.; Steinbach, P.; Juckeland, G.; Fiedler, M.

Abstract

The Computational Science Department FWCC and its sister departments offer various tools and services to empower scientists at HZDR in their research. This presentation held at the 2021 PhD seminar aims at introducing the working groups DMS and MT-DMA as well as the Helmholtz Incubator Platforms HIFIS and Helmholtz AI, all hosted by FWCC, and the library FWCB. It presents a selection of said services and shows options of contact for receiving help in the topics presented.

Keywords: Computational Science; Research Software Engineering; High Performance Computing; Data Management; Machine Learning; Artificial Intelligence; Data Science

  • Lecture (others)
    PhD Seminar 2021, 18.10.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33351


Modelling electrochemistry and mass transfer in sodium-zinc liquid metal batteries - an overview

Duczek, C.

Abstract

The presented poster was prepared for the doctoral seminar 2021 at HZDR. It gives a short overview about numerical modelling of sodium-zinc liquid metal batteries, which are investigated in the European Union's Horizon 2020 project "SOLSTICE".

  • Poster
    Doctoral Seminar 2021, 18.10.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33350


Data publication: Strong Binding of Noble Gases to [B₁₂X₁₁]⁻: a theoretical study

Wöhner, K.; Wulf, T.; Vankova, N.; Heine, T.

Abstract

This dataset contains output files of DFT and DLPNO calculations of the investigated species. At the DFT level of theory full geometry optimizations and frequency analysis where done. At DLPNO level of theory single point calculations were done.

Keywords: Boron; Anions; Complexation; Cluster chemistry; Group 17 compounds

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Data publication: Development of fluorinated and methoxylated benzothiazole derivatives as highly potent and selective cannabinoid CB2 receptor ligands

Aly, M. W.; Ludwig, F.-A.; Deuther-Conrad, W.; Brust, P.; Abadi, A. H.; Moldovan, R.-P.; Osman, N. A.

Abstract

Numerous studies have indicated the upregulation of the cannabinoid type 2 receptors (CB2 receptors) in neuroinflammation and cancer, and that their visualization with PET (Positron emission tomography) could provide a valuable diagnostic and/or therapy-monitoring tool in such disorders. However, the availability of reliable CB2-selective imaging probes is still lacking in clinical practice. Encouraged by promising CB2 affinity results obtained for a benzothiazole lead compound, 6a, further structural optimizations led to the development of a series of fluorinated and methoxylated benzothiazole derivatives, endowed with extremely high CB2 binding affinity and an exclusive selectivity to the CB2 receptor, along with structural sites suitable for radiolabeling. Compounds 20, 21, 24, 25, 29, 32 and 33 displayed subnanomolar CB2 Ki values (ranging from 0.16 nM to 0.68 nM) while lacked affinity to the CB1 receptor subtype. The fluorinated analogs, 21 and 29, were evaluated for their in vitro metabolic stability in mouse and human liver microsomes (MLM and HLM). Both 21 and 29 displayed an exceptionally high stability (98% and 91% intact compounds, respectively) after 60 min incubation with MLM. Contrastingly, compound 29 revealed an almost 2-fold greater metabolic stability after incubation with HLM for 60 min. Taken together, our data represent remarkably potent and selective CB2 ligands as credible leads that can be further exploited for 18F- or 11C-radiolabeling and utilization as PET tracers.

Keywords: Benzothiazole; Cannabinoid receptor type 2; CB2 ligands; Fluorine; Metabolic studies; PET

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Permalink: https://www.hzdr.de/publications/Publ-33347


Data publication: Design, radiosynthesis and preliminary biological evaluation in mice of a brain-penetrant 18F-labelled σ2 receptor ligand

Moldovan, R.-P.; Gündel, D.; Teodoro, R.; Ludwig, F.-A.; Fischer, S.; Toussaint, M.; Schepmann, D.; Wünsch, B.; Brust, P.; Deuther-Conrad, W.

Abstract

The σ2 receptor (transmembrane protein 97), which is involved in cholesterol homeostasis, is of high relevance for neoplastic processes. The upregulated expression of σ2 receptors in cancer cells and tissue in combination with the antiproliferative potency of σ2 receptor ligands motivates the research in the field of 2 receptors for the diagnosis and therapy of different types of cancer. Starting from the well described 2-(4-(1H-indol-1-yl)butyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline class of compounds, we synthesized a novel series of fluorinated derivatives, bearing the F-atom at the aromatic indole/azaindole subunit. RM273 (2-[4-(6-fluoro-1H-pyrrolo[2,3-b]pyridin-1-yl)butyl]-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline) was selected for labelling with 18F and evaluation regarding detection of σ2 receptors in the brain by positron emission tomography. Initial metabolism and biodistribution studies of [18F]RM273 in healthy mice revealed promising penetration of the radioligand into the brain. Preliminary in vitro autoradiography on brain cryosections of an orthotopic rat glioblastoma model proved the potential of the radioligand to detect the upregulation of σ2 receptor in glioblastoma cells compared to healthy brain. The results indicate that the herein developed σ2 receptor ligand [18F]RM273 has potential to assess by non-invasive molecular imaging the correlation between the availability of σ2 receptors with properties of brain tumors such as tumor proliferation or resistance towards particular therapies

Keywords: σ2 receptor; transmembrane protein 97; azaindoles; binding affinity; radiochemistry; fluorine-18 labeling; positron emission tomography (PET); brain-penetration; glioblastoma; orthotopic

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Permalink: https://www.hzdr.de/publications/Publ-33346


Effect of temperature and cell viability on uranium biomineralization by the uranium mine isolate Penicillium simplicissimum

Schaefer, S.; Steudtner, R.; Hübner, R.; Krawczyk-Bärsch, E.; Merroun, M. L.

Abstract

Remediation of heavy-metal-contaminated sites represents a serious environmental problem worldwide. Currently, cost- and time-intensive chemical treatments are mainly performed. Bioremediation by heavy-metal-tolerant microorganisms is considered a more eco-friendly and comparatively cheap alternative. The fungus KS1 (Penicillium simplicissimum), isolated from the flooding water of a former uranium (U) mine in Germany, shows promising U bioremediation potential mainly through biomineralization. The adaption of KS1 to heavy-metal-contaminated sites is indicated by an increased U removal capacity of up to 550 mg U per g dry biomass compared to the non-heavy-metal-exposed P. simplicissimum reference strain DSM 62867 (200 mg U per g dry biomass). In addition, the effect of temperature and cell viability of KS1 on U biomineralization was investigated. While viable KS1 cells at 30 °C removed U mainly extracellularly via metabolism-dependent biomineralization, a decrease in temperature to 4 °C or implementation of dead-autoclaved KS1 cells at 30 °C revealed increased occurrence of passive biosorption and bioaccumulation, as observed by scanning transmission electron microscopy. The precipitated U species were assigned to uranyl phosphates with a structure similar to that of autunite via cryo-time-resolved laser fluorescence spectroscopy. The major involvement of phosphorus in U precipitation by the fungus KS1 was additionally supported by the observation of increased phosphatase activity for viable cells at 30 °C. Furthermore, viable KS1 cells actively secreted small molecules, most likely phosphorylated amino acids, which interacted with U in the supernatant and were not detected in experiments with dead-autoclaved cells. Our studies provide new insights into the influence of temperature and cell viability on U phosphate biomineralization by fungi and highlight the potential use of KS1 particularly for U bioremediation purposes.

Keywords: Biomineralization; Bioremediation; Fungal biomass; Uranium; Wastewater

Permalink: https://www.hzdr.de/publications/Publ-33342


Continuous-time movement modeling

Alston, J.; Simoes Silva, I. M.; Fleming, C. F.; Noonan, M. J.

Abstract

In this workshop, we presented an introduction to continuous-time movement models for modeling animal movement

  • Lecture (Conference) (Online presentation)
    2021 The Wildlife Society Annual Meeting, 01.11.2021, virtual, virtual

Permalink: https://www.hzdr.de/publications/Publ-33341


Movement ecology research at CASUS

Alston, J.; Calabrese, J.

Abstract

In this presentation, we provided an introduction to the animal movement research we conduct at CASUS.

  • Open Access Logo Lecture (Conference) (Online presentation)
    2021 EuroBoar Annual Meeting, 25.10.2021, virtual, virtual

Permalink: https://www.hzdr.de/publications/Publ-33340


State with spontaneously broken time-reversal symmetry above the superconducting phase transition

Grinenko, V.; Weston, D.; Caglieris, F.; Wuttke, C.; Hess, C.; Gottschall, T.; Maccari, I.; Gorbunov, D.; Zherlitsyn, S.; Wosnitza, J.; Rydh, A.; Kihou, K.; Lee, C.-H.; Sarkar, R.; Dengre, S.; Garaud, J.; Charnukha, A.; Hühne, R.; Nielsch, K.; Büchner, B.; Klauss, H.-H.; Babaev, E.

Abstract

The most well-known example of an ordered quantum state—superconductivity—is caused by the formation and condensation of pairs of electrons. Fundamentally, what distinguishes a superconducting state from a normal state is a spontaneously broken symmetry corresponding to the long-range coherence of pairs of electrons, leading to zero resistivity and diamagnetism. Here we report a set of experimental observations in hole-doped Ba1−xKxFe2As2. Our specific-heat measurements indicate the formation of fermionic bound states when the temperature is lowered from the normal state. However, when the doping level is x ≈ 0.8, instead of the characteristic onset of diamagnetic screening and zero resistance expected below the superconducting phase transition, we observe the opposite effect: the generation of self-induced magnetic fields in the resistive state, measured by spontaneous Nernst effect and muon spin rotation experiments. This combined evidence indicates the existence of a bosonic metal state in which Cooper pairs of electrons lack coherence, but the system spontaneously breaks time-reversal symmetry. The observations are consistent with the theory of a state with fermionic quadrupling, in which long-range order exists not between Cooper pairs but only between pairs of pairs.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

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A two-sublattice model for extracting rare-earth anisotropy constants from measurements on (Nd,Ce)2(Fe,Co)14B single crystals

Gomez Eslava, G.; Fayyazi, B.; Skokov, K.; Scurschii, I.; Gorbunov, D.; Gutfleisch, O.; Dempsey, N. M.; Givord, D.

Abstract

Anisotropy constants are obtained from an analysis of single crystal magnetization curves measured up to high fields. The anisotropy of the 3d transition metal sublattice is considered, as well as molecular exchange field coupling between the rare-earth (R) and transition metal sublattices (M). This procedure allows for non colinear R and M magnetic moments, meaning that their angles with respect to the easy axis are independent variables. With this approach we obtain anisotropy constants that are larger than those reported in the literature, which reflects the anisotropy of the isolated R sublattice. Results for Co and/or Ce doped Nd2Fe14B single crystals are presented, showing the influence of such substitutions on the magnetocrystalline anisotropy. These results indicate that the enhanced performance of NdFeB-based magnets co-doped with Ce and Co can be ascribed to an improvement in intrinsic properties.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

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Permalink: https://www.hzdr.de/publications/Publ-33338


Data publication: Inverse-Dirichlet Weighting Enables Reliable Training of Physics Informed Neural Networks

Maddu, S.; Sturm, D.; Müller, C. L.; Sbalzarini, I. F.

Abstract

Scripts and notebooks to reproduce the results presented in the paper "Inverse-Dirichlet Weighting Enables Reliable Training of Physics Informed Neural
Networks", Maddu et al., 2021

Keywords: physics informed neural networks; sobolev training; computational physics; deep learning; data-driven modeling; multi-objective optimization; catastrophic forgetting; active turbulence

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  • Software in external data repository
    Publication year 2021
    Programming language: Python
    System requirements: python, numpy, scipy, sklearn, torch, matplotlib, seaborn, pandas
    License: MIT
    Hosted on GitHub: Link to location

Permalink: https://www.hzdr.de/publications/Publ-33337


Antiferromagnetic resonance in the cubic iridium hexahalides (NH4)2IrCl6 and K2IrCl6

Bhaskaran, L.; Ponomaryov, O.; Wosnitza, J.; Khan, N.; Tsirlin, A. A.; Zhitomirsky, M. E.; Zvyagin, S.

Abstract

We report on high-field electron spin resonance studies of two iridium hexahalide compounds (NH4)2IrCl6 and K2IrCl6. In the paramagnetic state, our measurements reveal isotropic g factors g = 1.79(1) for the Ir4+ ions, in agreement with their cubic symmetries. Most importantly, in the magnetically ordered state, we observe two magnon modes with zero-field gaps of 11.3 and 14.2 K for (NH4)2IrCl6 and K2IrCl6, respectively. Based on that and using linear spin-wave theory, we estimate the nearest-neighbor exchange couplings and anisotropic Kitaev interactions J1/kB = 10.3 K, K/kB = 0.7 K for (NH4)2IrCl6, and J1/kB = 13.8 K, K/k = 0.9 K for K2IrCl6, revealing the nearest-neighbor Heisenberg coupling as the leading interaction term, with only a weak Kitaev anisotropy.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

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Permalink: https://www.hzdr.de/publications/Publ-33336


Inverse Dirichlet Weighting Enables Reliable Training of Physics Informed Neural Networks

Maddu, S.; Sturm, D.; Müller, C. L.; Sbalzarini, I. F.

Abstract

We characterize and remedy a failure mode that may arise from multi-scale dynamics with scale imbalances during training of deep neural networks, such as Physics Informed Neural Networks (PINNs). PINNs are popular machine-learning templates that allow for seamless integration of physical equation models with data. Their training amounts to solving an optimization problem over a weighted sum of data-fidelity and equation-fidelity objectives. Conflicts between objectives can arise from scale imbalances, heteroscedasticity in the data, stiffness of the physical equation, or from catastrophic interference during sequential training. We explain the training pathology arising from this and propose a simple yet effective inverse-Dirichlet weighting strategy to alleviate the issue. We compare with Sobolev training of neural networks, providing the baseline of analytically epsilon-optimal training. We demonstrate the effectiveness of inverse-Dirichlet weighting in various applications, including a multi-scale model of active turbulence, where we show orders of magnitude improvement in accuracy and convergence over conventional PINN training. For inverse modeling using sequential training, we find that inverse-Dirichlet weighting protects a PINN against catastrophic forgetting.

Keywords: physics informed neural networks; sobolev training; computational physics; deep learning; data-driven modeling; multi-objective optimization; catastrophic forgetting; active turbulence

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Permalink: https://www.hzdr.de/publications/Publ-33335


Electric-field manipulation of the magnetocaloric effect in a Fe49Rh51/PZT composite

Amirov, A. A.; Gottschall, T.; Chirkova, A. M.; Aliev, A. M.; Baranov, N. V.; Skokov, K. P.; Gutfleisch, O.

Abstract

By simultaneous measurements in a purpose-built setup, an electric-field manipulation of the magnetocaloric effect and strain in a Fe49Rh51/PZT composite with a sandwich-type connection was demonstrated. Using the strain measurements from two gauges attached to the opposite sides of the composite, as well as finite element modeling (FEM) simulations, it was shown that the deformation in the composite is of a bending type. Mechanical strain induced by the electric field does not exceed ∼500 ppm, which is four times smaller than the expansion of FeRh during the transition ∼2000 ppm. Applying an electric voltage to the PZT favors the transition, but the further expansion of FeRh is hindered and thus blocks the antiferromagnetic-ferromagnetic transition. Obtained experimental results and FEM simulations can be used in the design of new multicaloric composites with optimal ratio between PZT and multicaloric material.

Involved research facilities

  • High Magnetic Field Laboratory (HLD)

Permalink: https://www.hzdr.de/publications/Publ-33334


Convection triggers local MR signal loss during proton beam irradiation of liquid water phantoms

Peter, J.; Gantz, S.; Karsch, L.; Pawelke, J.; Hoffmann, A. L.

Abstract

MRI-based proton beam visualisation in water has proven feasible in exploratory irradiation experiments performed on a first research prototype in-beam MRI system. Beam-induced convection was hypothesised to be implicated into MR signal loss observed within the beam volume. In this study, this hypothesis was tested in liquid water-filled phantoms by suppression of convection-induced motion using mechanical barriers and temperature control of water expansivity. In absence of convection-induced motion, no beam-induced signal changes occurred, supporting the hypothesis that convection triggers local MR signal loss during proton beam irradiation. The elucidation of the exact mechanism of convection-induced signal loss requires further investigation.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB 2022, 07.-12.05.2022, London/online, United Kingdom
    Proceedings of the joint annual meeting ISMRM-ESMRMB 2022 & ISMRT Annual Meeting
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB & ISMRT 31st Annual Meeting, 07.-12.05.2022, London, Vereinigtes Königreich

Permalink: https://www.hzdr.de/publications/Publ-33333


ILIAMS assisted AMS of ⁹⁰Sr at VERA

Marchhart, O.; Hanstorp, D.; Honda, M.; Lachner, J.; Martschini, M.; Priller, A.; Steier, P.; Wieser, A.; Golser, R.

Abstract

The long-lived fission product ⁹⁰Sr is produced in the nuclear fuel cycle or in nuclear weapon tests with a high yield of 4%. It is very mobile in the environment and due to its chemical similarities to calcium is easily incorporated in the body, e.g. in bones or in teeth, following ingestion or inhalation. With a half-life of T1⁄2=28.90 years [1] its uptake and retention in the human body poses potential health risks. ⁹⁰Sr also has significant potential as an environmental tracer.

The established method to measure ⁹⁰Sr is decay counting. However, this is time consuming, as the ingrowth of ⁹⁰Y over a period of two weeks is needed due to ⁹⁰Sr being a pure and low-energy beta emitter. The main challenge in ⁹⁰Sr detection with mass spectrometric methods is the interference of isobars, i.e. ⁹⁰Zr and ⁹⁰Y. Limits of detection of mass spectrometric methods such as ICP-MS, RIMS and conventional AMS are all above or close to the radiometric detection limit of 3 mBq.

The new Ion Laser InterAction Mass Spectrometry (ILIAMS) technique [2,3] at the Vienna Environmental Research Accelerator (VERA) overcomes the isobaric problem. ILIAMS achieves near complete suppression of isobars via element selective laser photodetachment in a gas-filled radio frequency quadrupole ion guide. The technique exploits differences in the electron affinities (EA) between the isotope of interest and its isobars by neutralizing anions with EAs below the photon energy while leaving anions with EAs above the photon energy unaffected. Additionally, chemical reactions with the buffer gas may enhance separation.

The Sr samples are produced as SrF₂ and mixed with PbF₂, which allows the extraction of an intense SrF₃⁻ ion beam [4]. Using a 532 nm continuous wave laser at 10 W and a He+O₂ mixture, with an oxygen content of 3%, as buffer gas, ILIAMS achieves a suppression of ZrF₃⁻ and YF₃⁻ vs. SrF₃⁻ of >10⁷ at 35% ⁹⁰Sr transmission through ILIAMS. Extraction of SrF₃⁻ from the ion source and elemental separation in an ionization chamber leads to an additional ⁹⁰Zr suppression of 10⁵. The overall ⁹⁰Sr detection efficiency is 0.4‰; a blank level of ⁹⁰Sr/Sr = (4.5±3.2)×10⁻¹⁵ is reached. This corresponds to a more than tenfold improved detection limit of <0.1 mBq, i.e. 10⁵ atoms of ⁹⁰Sr in a 1 mg Sr sample. Measurements of samples from an in-house dilution series with ⁹⁰Sr/Sr ratios ranging from 10⁻¹¹ to 10⁻¹⁴ prove the linearity of this technique. First tests on different environmental samples – from bone to soils – were successful, showing no influence on the detection limit on “real” samples.

[1] R.R. Kinsey et.al., The NUDAT/PCNUDAT Program for Nuclear Data, Data extracted from the NUDAT database, version 2.8
[2] M. Martschini et.al., The ILIAMS project – An RFQ ion beam cooler for selective laser photodetachment at VERA, Nucl. Instrum. Methods. Phys. Res. B, 456 (2019) 213-217
[3] M.Martschini, this meeting
[4] X.-L. Zhao. et. al., Studies of anions from sputtering I: Survey of MFn⁻, Nucl. Instrum. Methods. Phys. Res. B, 268 (2010) 807-811

  • Poster (Online presentation)
    15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-33332


135Cs and 137Cs detection in environmental samples by AMS

Wieser, A.; Lachner, J.; Zok, D.; Martschini, M.; Steier, P.; Priller, A.; Golser, R.

Abstract

The isotopic ratio ¹³⁵Cs/¹³⁷Cs can be used to assign sources of anthropogenic cesium input, as a geochemical tracer, or for modifying anthropogenic radionuclide dispersion models. The long-lived ¹³⁵Cs is also of interest in stellar nucleosynthesis models, where ¹³⁴Cs is an important s-process branching point, defining the ¹³⁴Ba/¹³⁶Ba ratio as both those nuclides are shielded from the r-process. ¹³⁵Cs is a pure beta-emitter with a low end-point energy and a long but not very well known half-life around 2.3 Ma. Therefore, ¹³⁵Cs is hard to detect via radiometric methods. Mass spectrometry on the other side has to deal with the isobaric interferences ¹³⁵Ba and ¹³⁷Ba for Cs detection.
The new method of Ion Laser InterAction Mass Spectrometry (ILIAMS) at the Vienna Environmental Research Accelerator (VERA) overcomes this problem by exploiting differences in the electron affinities of CsF₂⁻ and BaF₂⁻. There, the ion beam is cooled and overlapped with a 532 nm laser beam of 10W power in a He buffer gas filled radiofrequency quadrupole. Ions like BaF₂⁻ with a detachment energy lower than the photon energy of 2.33 eV are efficiently suppressed by photodetachment, while CsF₂⁻ ions with a detachment energy higher than the photon energy remain unaffected. With this approach an isobar suppression of more than 10⁶ was achieved for BaF₂⁻, while reaching a CsF₂⁻ transmission of 40% through the RFQ ion cooler. A ¹³³CsF₂⁻ current on the order of 50 nA from a mixed Cs₂SO₄ and PbF₂ – matrix is extracted from the MC-SNICS ion source and measured in the 3+ charge state on the high-energy side with an accelerator transmission of 30%. In order to improve the yield for CsF₂⁻ and keep cross-contamination in the ion source between samples low, we investigated and present the results of two sputtering processes: Rubidium sputtering and negative ion production without external sputter agent.
We achieved reproducible detection of ¹³⁵Cs and ¹³⁷Cs in an in-house reference material with an isotopic ratio of ¹³⁵Cs/¹³⁷Cs ≈ 2.5. Further, first environmental samples showing the ¹³⁵Cs/¹³⁷Cs signature of the nuclear accidents in Chernobyl and Fukushima were measured at VERA and compared to values obtained by ICP-QQQ-MS by Zok et al. [1] at the Leibniz University of Hannover. The ILIAMS assisted AMS measurements at VERA reach blank levels of ¹³⁵Cs/¹³³Cs ≈ 6∙10⁻¹² and ¹³⁷Cs/¹³³Cs ≈ 3∙10⁻¹² .
Monitoring mass 136 throughout a measurement, where only stable barium and cerium are present, shows that at these levels there is no contribution to the background from insufficient isobar suppression so that the limitation for the AMS blank level is cross contamination in the ion source. We aim to reduce this blank value by at least two orders of magnitude to perform measurements of environmental samples also far from directly contaminated sites.

[1] Zok et al., Determination of Characteristic vs Anomalous ¹³⁵Cs/¹³⁷Cs Isotopic Ratios in Radioactively Contaminated Environmental Samples, Environ. Sci. Technol. 2021, 55, 8, 4984–4991

  • Poster (Online presentation)
    15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-33331


From the U-233/U-236 fingerprint towards an environmental tracer: Tracking down the sources of anthropogenic U-233

Hain, K.; Golser, R.; Hou, X.; Lachner, J.; Lin, M.; Meszar, M.; Qiao, J.; Sakaguchi, A.; Steier, P.; Wagreich, M.; Wallner, G.; Wiederin, A.; Wolf, J.

Abstract

Recently, the atomic ²³³U/²³⁶U ratio was proposed as a superior oceanographic tracer as the ²³³U/²³⁶U signature allows to distinguish environmental emissions of civil nuclear industry from weapons fallout [1] and uranium (U) behaves conservatively in sea water. In this previous work, the ratios detected in representative compartments of the environment affected either by releases of nuclear power production or by weapons fallout differ by one order of magnitude and varied between 0.1·10-²and 3.7·10-². Significant amounts of ²³³U were only released in nuclear weapons fallout, either produced by fast neutron capture on ²³⁵U or directly by ²³³U fuelled devices. For tracer applications, a careful characterization of the principal sources of ²³³U including the contribution from natural production is required.

The ²³³U/²³⁶U ratios were analysed in samples from different locations, partly time-resolved or of well-known age to be able to narrow down the time span of the maximum ²³³U release. Samples comprised air filters from 1961-1965 collected in Austria, i.e. the period of maximum deposition of global fallout, two time-resolved sediment cores from the Baltic Sea and sediment from the urban layered archaeosphere in the underground of Vienna (Austria). In addition, a depth profile of ²³³U/²³⁶U in a water column located in the Northeast Pacific Ocean was also analysed. This sampling station is assumed to be less affected by tropospheric fallout from a suspected ²³³U fuelled device (Nevada Test Site, 1955). Whenever possible, the ²³³U/²³⁶U data were directly compared to other isotopic signatures and/or mono-isotopic makers, such as ²⁴⁰Pu/²³⁹Pu or ²⁴¹Am, respectively.

The Baltic Sea sediment core confirms a maximum deposition of ²³³U around 1954/1955 [2]. This finding is supported by the rather low ²³³U/²³⁶U ratios (below 0.5·10-²) on the air filters from Vienna indicating a comparatively low ²³³U deposition during global fallout maximum. Values of around 0.1 were measured for the maximum of the ²³³U/²³⁶U ratio in the Baltic Sea sediment. The isotope ratios including ²³³U/²³⁶U found in a layer of the Vienna underground material which was assigned to the 1960s, clearly point to atmospheric atomic bomb fallout. The ²³³U/²³⁶U ratios in the upper part of the Pacific water column showed very stable values of (1.33±0.13) ·10-² which are in good agreement with the published value for global fallout [1].

The new data confirms the previous result that the maximum releases of ²³³U happened before the global fallout maximum in 1963. The consistently high ratios found in the Pacific Ocean indicate at least a contribution from thermonuclear explosions to the global inventory of ²³³U. The unexpectedly high ²³³U/²³⁶U values in the Baltic Sea show the necessity to systematically identify the global and local ²³³U input sources. Nevertheless, our preliminary data indicate that the ²³³U/²³⁶U ratio serves as a potential marker for the on-set of the Anthropocene, even in the rather demanding urban environment.

References
[1] K. Hain, et al. Nat Commun 11(2020), 1275.
[2] M. Lin, et al. Environ. Sci. Technol. 55(2021), 13, 8918–8927

  • Invited lecture (Conferences) (Online presentation)
    15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-33330


Data - CST Studio files used for "Modeling of the effective permittivity of open-cell ceramic foams inspired by Platonic solids"

Camacho Hernandez, J. N.

Abstract

CST Studio files with the geometry of sintered and Platinic foams used for calculating their effective permittivity. The permittivity of the continuous medium and the skeleton can be changed in materials. To change the porosity of platinum foams, the diameter of the struts in the parameter list must be changed. These files were used for preparing the article "Modeling of the effective permittivity of open-cell ceramic foams inspired by Platonic solids"

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Permalink: https://www.hzdr.de/publications/Publ-33329


Ion Laser InterAction Mass Spectrometry – prospects for AMS without chemistry

Martschini, M.; Lachner, J.; Marchhart, O.; Merchel, S.; Priller, A.; Steier, P.; Wieser, A.; Golser, R.

Abstract

Laser photodetachment and molecular dissociation processes of anions provide unprecedented isobar suppression factors of >10¹⁰ for several established AMS isotopes like ³⁶Cl [1] or ²⁶Al [2] and give access to new AMS isotopes like ⁹⁰Sr [3], ¹³⁵Cs [4] or ¹⁸²Hf [5] at environmental levels. Five years ago, a setup for Ion-Laser InterAction Mass Spectrometry (ILIAMS) was coupled to the Vienna Environmental Research Accelerator (VERA) five years ago. Its potential and applicability as a new means of isobar suppression in AMS has since been explored at this state-of-the-art 3 MV tandem facility [6]. Over this time, ILIAMS has been proven to meet AMS requirements regarding efficiency, reliability and robustness with a typical reproducibility of results of 3%.

The benefits of the ILIAMS technique are in principle helpful for any AMS machine, irrespective of attainable ion beam energy. ILIAMS exploits differences in electron affinities (EA) within elemental or molecular isobaric systems neutralizing anions with EAs smaller than the photon energy. Alternatively, these differences in EA can also facilitate anion separation via chemical reactions with the buffer gas, although the possibility of reverse reactions may cause some plateau effect not observed with laser photodetachment. In order to achieve the required ion-laser interaction times or ion-gas collision energies, the anion beam is decelerated to almost thermal energies within a gas-filled radiofrequency quadrupole.

Since isobar suppression via ILIAMS is so efficient, there is often no need for any further element separation in the detection setup. Hence, highly-populated charge states can be selected after the accelerator, which in combination with 100% efficient ion detection in an ionization chamber more than compensates for transmission losses in ILIAMS, which are on the order of 20-50%. Thus, counting statistics with ILIAMS are typically similar or better than with conventional AMS means, e.g. 500 cts of ²⁶Al in a 10 min run on a sample with 26Al/Al = 10−¹².

Recent test measurements also demonstrated that, owing to the virtually complete suppression of isobars, ²⁶Al (extraction of AlO−) and ⁴¹Ca (extraction of CaF₃−), can be measured directly from stony meteorite samples as little as 1-2 mg without doing any chemical sample preparation [7]. There is also potential for ILIAMS measurements of terrestrial cosmogenic ²⁶Al in in-situ-dating quartz originating from high altitudes. Last but not least, ³⁶Cl may even become accessible without the need for sulfur reduction by chemical treatment and, maybe, without accelerator at all.

[1] Lachner et al., NIMB 92 (2019) 146.
[2] Lachner et al., IJMS 465 (2021) 116576.
[3] Marchhart et al., this meeting
[4] Wieser et al., this meeting
[5] Martschini et al., EPJ Web of Conferences 232 (2020) 02003.
[6] Martschini et al., NIMB 456 (2019) 213.
[7] Merchel et al., this meeting

  • Invited lecture (Conferences) (Online presentation)
    15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-33328


Optimization of 10Be beam transport at DREAMS ( DREsden AMS)

Lachner, J.; Rugel, G.; Stübner, K.; Vivo Vilches, C.; Winkler, S.; Wallner, A.

Abstract

¹⁰Be measurements at DREAMS take up a large fraction of the AMS beam times at the 6MV accelerator at the ion beam center of HZDR. Currently, they are undertaken at a terminal voltage of 4.5 MV [Rugel et al., NIMB 2016]. Here, we investigated potential benefits from a change in accelerator terminal voltage in order to increase the efficiency of ¹⁰Be counting.
Presently, after the stripping in Ar gas in the accelerator, Be2+ ions are directed towards a 1 μm thin SiN foil placed after the analysing magnet on the high-energy side that helps to suppress the ¹⁰B interference by differential energy loss and separation in an electrostatic analyser. After passage through the absorber foil the mean charge state of Be ions is increased and the 4+ charge state is selected and transported to the detector. In this mode of operation, losses of ¹⁰Be ion beam intensity on the way from the low-energy side of the system to the detector are dominated by these two charge exchange processes [Arnold et al., NIMB 2010].
However, there is only limited data for the recharge behaviour of Be in a stripper gas at energies relevant for the measurements at DREAMS [Hofmann et al., NIMB 1987; Niklaus et al., NIMB 1994]. For an argon gas stripper, Niklaus et al. [NIMB 1994], suggest lower terminal voltages for optimal transmission of ¹⁰Be2+. On the other hand, an increase of the overall energy of the Be2+ beam after the accelerator will certainly allow for a higher Be4+ yield after the passage through the absorber foil.
In contrast to the original data by Niklaus et al. [NIMB 1994], we found that increasing the terminal voltage to ≥ 5MV does not reduce the yield of the Be2+ charge state after the accelerator.

As a further recharge to the 4+ charge state is conducted in a foil after the analysing magnet it is desirable to hit the foil with the highest available energy/velocity to have optimal stripping of Be2+ to the naked ion. Thus, the efficiency of ¹⁰Be measurements can indeed be improved by increasing the terminal voltage, both at DREAMS and at other AMS facilities of a similar size that are using the absorber method with a charge exchange from 2+ to 4+ for isobar suppression.
We present data on the performance of the system at higher beam energies documenting an increase in overall detection efficiency by 25%. Under these conditions the interfering isobar ¹⁰B is still well separated, and no additional interferences (e.g. from nuclear reactions) appear in our spectra.

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  • Poster (Online presentation)
    15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australia

Permalink: https://www.hzdr.de/publications/Publ-33327


The performance of ²¹⁰Pb AMS for the radioassay of materials considered for the construction of ultra-low background experiments in Astroparticle Physics

Vivo Vilches, C.; Gornea, R.; Weiser, B.; Zhao, X.; Francisco, B. B. A.; Kieser, W. E.

Abstract

One of the most important tasks in the design and construction of ultra-low background experiments is the radioassay of the materials used. This requires the selection of the materials and enables the calculation of expected detector background. The ASTREA project (Accelerator mass spectrometry Survey of Trace Radionuclides for Experiments in Astroparticle physics) addresses AMS radioassay challenges for a few rare event experiments. Some examples are nEXO, which is searching for neutrinoless double beta decay; and NEWS-G and DarkSide, which are attempting to directly detect dark matter. This project, led by the André E. Lalonde AMS Laboratory (AEL-AMS) at the University of Ottawa, is performed in collaboration with Carleton University, Queens University and University of Alberta.

The main focus of the project is screening Pb-210 in various detector construction materials, with emphasis on low background copper and high-performance polymers. We have studied the possibility of using 2 different materials for the AMS measurements: lead fluoride (PbF2) and lead oxide (PbO) targets, producing respectively (PbF3)- and (PbO2)- ions on the LE side. In both cases, the 210Pb/206Pb blank ratio is in the 1e-14–1e-13 range. Measurements on 1-2 g Kapton films have established upper limits in the range 850-2500 mBq/kg at 90% C.L.

Future ASTREA activities will focus on the Pb-210 assay in acrylic, which is considered for future low background dark matter detectors. Previous best results, obtained in 2014 by γ-counting 2 kg of acrylic, have established an upper limit for the Pb-210 concentration of 0.3 mBq/kg. Our proposed method, using AMS, should provide a limit of detection in the 0.01-0.1 mBq/kg range.

Other important study looks at the Pb-210 contamination in the electroformation process of the copper for the NEWS-G and nEXO detectors. For the Pb-210 concentration in the copper, we estimate a limit of detection in the 0.3-1.0 mBq/kg range.

Keywords: ²¹⁰Pb contamination; Accelerator mass spectrometry; Rare event searches; Astroparticle physics; Radiopurity

  • Lecture (Conference) (Online presentation)
    The 15th International Conference on Accelerator Mass Spectrometry, 19.11.2021, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-33325


Nanoindentation response of ion-irradiated Fe, Fe-Cr alloys and ferritic-martensitic steel Eurofer 97: The effect of ion energy

Das, A.; Altstadt, E.; Kaden, C.; Kapoor, G.; Akhmadaliev, S.; Bergner, F.

Abstract

Nanoindentation of ion-irradiated nuclear structural materials and model alloys has received considerable interest in the published literature. In the reported studies, the materials were typically exposed to irradiations using a single ion energy varying from study to study from below 1 MeV to above 10 MeV. However, systematic investigations into the effect of ion energy are still missing, meaning that the possibilities to gain insight from systematic energy variations are not yet exhausted. We have exposed pure Fe, ferritic Fe-9Cr, martensitic Fe-9Cr and the ferritic-martensitic reduced-activation steel Eurofer 97 to ion irradiations at 300 °C using 1 MeV, 2 MeV and 5 MeV Fe2+ ions as well as 8 MeV Fe3+ ions and applied nanoindentation, using a Berkovich diamond indenter, to characterize as-irradiated samples and unirradiated references. The effect of the ion energy on the measured nanoindentation response is discussed for each material. Two versions of a primary-damage-informed model are applied to fit the measured irradiation-induced hardening. The models are critically compared with the experimental results also taking into account reported microstructural evidence. Related ion-neutron transferability issues are addressed.

Keywords: iron; Fe-Cr alloy; ferritic-martensitic steel; ion irradiation; displacement damage; nanoindentation; irradiation hardeníng; indentation size effect

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Permalink: https://www.hzdr.de/publications/Publ-33324


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