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41397 Publications

Challenges in Contactless Inductive Flow Tomography for Rayleigh-Bénard Convection Cells

Sieger, M.; Mitra, R.; Schindler, F.; Vogt, T.; Stefani, F.; Eckert, S.; Wondrak, T.

Contactless inductive flow tomography (CIFT) can reconstruct the complex 3-dimensional flow structure of the large scale circulation in liquid metal filled Rayleigh-Bénard (RB) convection cells. The method relies on the precise measurement of weak magnetic fields induced by currents in the conducting liquid arising from the fluid motion in combination with primary excitation fields. The velocity distribution is reconstructed from the magnetic field measurements by solving a linear inverse problem using the Tikhonov regularization and L-curve method. A number of technical challenges have to be overcome to reach the desired accuracy of the measurement signals. In this paper we will describe our design of a new CIFT set-up for a large RB vessel with a diameter of 320 mm and a height of 640 mm. We outline the major factors perturbing the measurement signal of several tens of nanoteslas and describe solutions to decrease mechanical drifts by thermal expansion to a sub-critical level to enable CIFT measurements for high-Rayleigh number flows.

Keywords: contactless inductive flow tomography; large scale circulation; liquid metal flow; Rayleigh-Bénard convection

Related publications

  • Contribution to proceedings
    Electromagnetic processing of materials 2021, 14.-16.06.2021, Riga / virtual, Latvia
    Proceedings of the 10th international conference Electromagnetic Processing of Materials, Riga: The University of Latvia Press, 978-9934-18-686-8, 1-280
  • Lecture (Conference) (Online presentation)
    Electromagnetic processing of materials 2021, 16.06.2021, Riga / virtual, Latvia
  • Magnetohydrodynamics 58(2022)1/2, 25-32
    DOI: 10.22364/mhd.58.1-2.3
    Cited 4 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-32853
Publ.-Id: 32853


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

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

We systematically explore the stability and properties of [B₁₂X₁₁NG]⁻ adducts resulting from the binding of noble gas atoms to anionic [B₁₂X₁₁]⁻ clusters in the gas phase of mass spectrometers. [B₁₂X₁₁]⁻ can be obtained by stripping one X⁻ off the icosahedral closo-dodecaborate dianion [B₁₂X₁₂]²⁻. We study the binding of the noble gas atoms He, Ne, Ar, Kr and Xe to [B₁₂X₁₁]⁻ with substituents X = F, Cl, Br, I, CN. While He cannot be captured by these clusters and Ne only binds at low temperatures, the complexes with the heavier noble gas atoms Ar, Kr and Xe show appreciable complexation energies and exceed 1 eV at room temperature in the case of [B₁₂(CN)₁₁Xe]⁻. The predicted B–NG equilibrium distance in the complexes with Ar, Kr and Xe is only 0.10 to 0.25 Å longer than the sum of the covalent radii of the two corresponding atoms, and a significant charge transfer from the noble gas atom to the icosahedral B₁₂ cage is observed.

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

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Permalink: https://www.hzdr.de/publications/Publ-32852
Publ.-Id: 32852


Concept of High-Power CW IR-THz Source for the Radiation Source ELBE Upgrade

Evtushenko, P.; Lehnert, U.; Michel, P.; Cowan, T.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a user facility based on a 1 mA - 40 MeV CW SRF LINAC. Presently HZDR is considering upgrade options for the ELBE or its replace- ment with a new CW, SRF LINAC-based user facility. A part of the user requirements is the capability to generate IR and THz pulse in the frequency range from 0.1 through 30 THz, with pulse energies in the range from 100 J through a few mJ, at the repetition rate between 100 kHz and 1 MHz. This corresponds to the pulse energy in- crease, dependent on the wavelength, by a factor from 100 through 1000. In this contribution, we outline key aspects of a concept, which would allow to achieve such parameters. These aspects are: 1 - use of a beam with longitudinal density modulation and bunching factor of about 0.5 at the fundamental frequency; 2 - achieving the density modulation through the mechanism similar to the one used in optical klystron (OK); 3 – generating the necessary for the modulation optical beam by an FEL oscillator, and 4 - using two electron injectors. First injec- tor would provide a beam for the FEL oscillator. Second high charge injector would provide the beam for the high pulse energy generation for users. All-in-all the concept of the new radiation source is very similar to an OK, but operating with two beams simultaneously.

Keywords: ELBE; THz; superradiant; undulator radiation; high power; SRF linac

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Permalink: https://www.hzdr.de/publications/Publ-32851
Publ.-Id: 32851


Design of High-Power CW IR-THz Source for the Radiation Source ELBE Upgrade

Evtushenko, P.; Lehnert, U.; Michel, P.; Cowan, T.

The Radiation Source ELBE at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a user facility based on a 1 mA - 40 MeV CW SRF LINAC. Presently HZDR is considering upgrade options for the ELBE or its replace- ment with a new CW, SRF LINAC-based user facility. A part of the user requirements is the capability to generate IR and THz pulse in the frequency range from 0.1 through 30 THz, with pulse energies in the range from 100 J through a few mJ, at the repetition rate between 100 kHz and 1 MHz. This corresponds to the pulse energy in- crease, dependent on the wavelength by a factor from 100 through 1000. In this contribution, we outline key aspects of a concept, which would allow to achieve such parame- ters. Such key aspects are: 1 - use of a beam with longitu- dinal density modulation and bunching factor of about 0.5 at the fundamental frequency; 2 - achieving the density modulation through the mechanism similar to the one used in optical klystron (OK) and HGHG FEL; 3 - gener- ating necessary for the modulation optical beam by an FEL oscillator, and 4 - using two electron injectors, where one injector provides beam for the FEL oscillator while second high charge injector provides beam for the high energy per pulse generation for user experiments. All-in- all the concept of the new radiation source is very similar to an OK, but operating with two beams simultaneously.

Keywords: Superradiant Undulator; THz; SRF LINAC; Undulator radiation; modulated beam

Related publications

  • Open Access Logo Contribution to proceedings
    10th International Particle Accelerator Conference - IPAC 19, 19.-24.05.2019, Melbourne, Australia
    IAPC2019 Proceedings, 1702-1704
    DOI: 10.18429/JACoW-IPAC2019-TUPRB012

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Permalink: https://www.hzdr.de/publications/Publ-32850
Publ.-Id: 32850


Probing the local coordination of hexavalent uranium and the splitting of 5f orbitals induced by chemical bonding.

Amidani, L.; Retegan, M.; Volkova, A.; Popa, K.; Martin, P. M.; Kvashnina, K.

We report here the first detailed experimental and theoretical investigation of hexavalent uranium in various local configurations with high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the M4 edge. We demonstrate the pronounced sensitivity of the technique to the arrangement of atoms around the absorber and provide a detailed theoretical interpretation revealing the nature of spectral features. We show that for all local configuration analyzed, the main peak corresponds to non-bonding 5f orbitals, and the highest energy peak corresponds to anti-bonding 5f orbitals. Our findings are in agreement with the accepted interpretation of uranyl spectral features and embed the latter in the broader field of view where the spectra of a larger variety of U6+-containing samples are interpreted on the same theoretical ground.

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Permalink: https://www.hzdr.de/publications/Publ-32849
Publ.-Id: 32849


To form or not to form: PuO2 nanoparticles at acidic pH

Gerber, E.; Romanchuk, A. Y.; Weiss, S.; Kuzenkova, A.; Hynault, M.; Bauters, S.; Egorov, A.; Butorin, S. M.; Kalmykov, S. N.; Kvashnina, K. O.

Properties of the PuO2 nanoparticles (NPs) formed under acidic conditions (pH 1-4) are explored in this study at the atomic scale. High-resolution transmission electron microscopy (HRTEM) was applied to characterize the crystallinity, morphology and size of the precipitates. It was found that 2 nm crystalline NPs are formed with a crystal structure similar to bulk PuO2. High energy resolution fluorescence detected (HERFD) X-ray absorption spectroscopy at the Pu M4 edge has been used to identify the Pu oxidation states and recorded data are analyzed using the theory based on the Anderson Impurity Model (AIM). The experimental data obtained on NPs show that Pu(IV) oxidation state dominates in all NPs formed at pH 1-4. However, the suspension at pH 1 demonstrate the presence of Pu(III) in addition to the Pu(IV), which is associated with redox dissolution of PuO2 NPs under acidic conditions. As shown by UV-Vis the contribution of Pu(III) in the HERFD spectrum for the sample at pH 1 originates from the solution rather than from NPs themselves. We discuss in detail the mechanism that affects the PuO2 NP synthesis under acidic conditions and compare it with one in neutral and alkaline conditions. Future investigations of plutonium chemistry will fundamentally benefit from the insights this work provides and further applied to various environmental and technological applications

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Permalink: https://www.hzdr.de/publications/Publ-32848
Publ.-Id: 32848


Emergence of cobalt oxide nano-assemblies: X-ray in situ studies bridging the molecular- and macro- length scales

Grote, L.; Zito, C. A.; Frank, K.; Dippel, A.-C.; Reisbeck, P.; Pitala, K.; Kvashnina, K. O.; Bauters, S.; Detlefs, B.; Ivashko, O.; Pandit, P.; Rebber, M.; Harouna-Mayer, S. Y.; Nickel, B.; Koziej, D.

The key to fabricate complex, hierarchical materials is the control of chemical reactions at various length scales. The classical model of nucleation and growth fails to provide sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for an assembly of CoO polyhedral shape nanocrystals. By combining high energy-resolution fluorescence-detected X-ray absorption near edge structure (HERFD-XANES) measurements and FEFF simulation, we directly access the molecular level of the reaction. We reveal that initially Co(acac)3 rapidly reduces to Co(acac)2 and coordinates to oxygen atoms of two solvent molecules, forming a bis-adduct of the square-planar Co(acac)2 with octahedral coordination. Unlike a classical nucleation and growth mechanism, we observe that nuclie as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final assemblies are smaller than 100 nm and maintain their spherical shape, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution

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Permalink: https://www.hzdr.de/publications/Publ-32847
Publ.-Id: 32847


HERFD-XANES and RIXS study on the electronic structure of trivalent lanthanides across a series of isostructural compounds

Zasimov, P. V.; Amidani, L.; Retegan, M.; Walter, O.; Caciuffo, R.; Kvashnina, K. O.

We performed a systematic study of the complexes of trivalent lanthanide cations with the hydridotris(1-pyrazolyl)borato (Tp) ligand (LnTp3; Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu) using both high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and resonant inelastic X-ray scattering (RIXS) at the lanthanide L3 absorption edge. Here, we report the results obtained and we discuss them against simulations performed with the density functional theory and atomic multiplet theory computational approaches. The spectral shape and the elemental trends observed in the experimental HERFD-XANES spectra are well reproduced by density functional theory calculations, whilst the pre-edge energy interval is well better described by atomic multiplet theory. The RIXS data show a generally rather complex pattern that originates from the intra-atomic electron-electron interactions in the intermediate and final states, as demonstrated by the good agreement obtained with simulations considering exclusively the atomic configuration. Guided by theoretical predictions, we discuss possible origins of the observed spectral features and the trends in energy splitting across the series. The insight in the electronic structure of trivalent lanthanides compounds demonstrated here and obtained with advanced X-ray spectroscopies coupled with theoretical simulations can be applied to any lanthanide-bearing compound and be of great interest for all research fields involving lanthanides

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Permalink: https://www.hzdr.de/publications/Publ-32846
Publ.-Id: 32846


Valence fluctuations in the 3D+3 modulated Yb3Co4Ge13 Remeika Phase

Feig, M.; Akselrud, L.; Motylenko, M.; Bobnar, M.; Wagler, J.; Kvashnina, K. O.; Rafaja, D.; Leithe-Jasper, A.; Gumeniuk, R.

Yb3Co4Ge13 is the first example of a Remeika phase with a 3D + 3 [space group
P43n(a,0,0)000(0,a,0)000(0,0,a)000; a = 8:72328(1) Å, Q1 = Q2 = Q3 = 0:4974(2)]
modulated crystal structure. A slight shift of the composition towards higher Ybcontent
(i:e: Yb3:2Co4Ge12:8) leads to the disappearance of the satellite reflections and
stabilization of the disordered primitive cubic [space group Pm3n, a = 8:74072(2) Å]
Remeika prototype structure. The stoichiometric structurally modulated germanide is
a metal with hole-like charge carriers, where Yb-ions are in a temperature dependent
intermediate valence state of +2:60+2:66 for the temperature range 85-293 K. The
valence fluctuations have been investigated by means of temperature dependent X-ray
absorption spectroscopy, magnetic susceptibility and thermopower measurements

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Permalink: https://www.hzdr.de/publications/Publ-32845
Publ.-Id: 32845


Towards The Bottom of The Periodic Table

Kvashnina, K.

Towards the Bottom of the Periodic Table

Related publications

  • Invited lecture (Conferences) (Online presentation)
    Monday Meetings, 22.03.2021, Washington State University, USA

Permalink: https://www.hzdr.de/publications/Publ-32844
Publ.-Id: 32844


XAS Towards the Bottom of the Periodic Table

Kvashnina, K.

Understanding the mechanisms of different chemical reactions with actinides (An) at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode at the An M4,5 edges is now a common technique to probe the electronic structure and the An 5f states. I will provide an overview of the recently performed studies on Uranium, Thorium and Plutonium-containing materials at the European Synchrotron (ESRF) in Grenoble (France). I will show how the detailed information about the An oxidation state, electron-electron interactions, hybridization between molecular orbitals can be obtained by a combination of experimental data and electronic structure calculations. It might be of interest for fundamental research in chemistry and physics of actinides as well as for applied science.

Reading:

[1] K. O. Kvashnina, S. M. Butorin, P. Martin, and P. Glatzel, “Chemical State of Complex Uranium Oxides,” Phys. Rev. Lett., vol. 111, no. 25, p. 253002, Dec. 2013, doi: 10.1103/PhysRevLett.111.253002.

[2] K. O. Kvashnina, Y. O. Kvashnin, and S. M. Butorin, “Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials,” J. Electron Spectros. Relat. Phenomena, vol. 194, pp. 27–36, Jun. 2014, doi: 10.1016/j.elspec.2014.01.016.

[3] S. M. Butorin, K. O. Kvashnina, J. R. Vegelius, D. Meyer, and D. K. Shuh, “High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds,” Proc. Natl. Acad. Sci., vol. 113, no. 29, pp. 8093–8097, Jul. 2016, doi: 10.1073/pnas.1601741113.

[4] K. O. Kvashnina et al., “A Novel Metastable Pentavalent Plutonium Solid Phase on the Pathway from Aqueous Plutonium(VI) to PuO 2 Nanoparticles,” Angew. Chemie Int. Ed., vol. 58, no. 49, pp. 17558–17562, Dec. 2019, doi: 10.1002/anie.201911637.

[5] E. Gerber et al., “The missing pieces of the PuO 2 nanoparticle puzzle,” Nanoscale, vol. 12, no. 35, pp. 18039–18048, 2020, doi: 10.1039/D0NR03767B.

[6] I. Pidchenko, J. März, M. O. J. Y. Hunault, S. Bauters, S. M. Butorin, and K. O. Kvashnina, “Synthesis, Structural, and Electronic Properties of K 4 Pu VI O 2 (CO 3 ) 3(cr) : An Environmentally Relevant Plutonium Carbonate Complex,” Inorg. Chem., vol. 59, no. 17, pp. 11889–11893, Sep. 2020, doi: 10.1021/acs.inorgchem.0c01335.

[7] L. Amidani et al., “The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO 2,” Chem. – A Eur. J., vol. 27, no. 1, pp. 252–263, Jan. 2021, doi: 10.1002/chem.202003360.

[8] E. Gerber et al., “Insight into the structure–property relationship of UO 2 nanoparticles,” Inorg. Chem. Front., p. accepted, 2021, doi: 10.1039/D0QI01140A.

Related publications

  • Open Access Logo Invited lecture (Conferences) (Online presentation)
    GlobalXAS, 04.02.2021, Washington, USA

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Permalink: https://www.hzdr.de/publications/Publ-32843
Publ.-Id: 32843


Bubble coalescence and breakup mechanism in a vertical pipe with an obstacle

Liao, Y.; Sibel, T.-K.; Martin, N.-K.; Lucas, D.

One of the major issues in numerical study of bubbly flows is the prediction of bubble size. Among other physical processes coalescence and breakup represents a huge challenge. A variety of investigations on bubble coalescence and breakup in turbulent flows has been motivated, and a remarkable diversity of mechanisms has been observed. However, knowledge on the superposition of multiple mechanisms remains insufficient. The purpose of this work is to investigate the effect of a sudden change of flow fields on coalescence and breakup events. Turbulent bubbly flows in a vertical pipe with a ring obstacle are analyzed with ultrafast x-ray computed tomography and a generalized population balance model. The results show that coalescence and breakup are in equilibrium before the obstacle leading to a nearly unchanged bubble size distribution (BSD) and quasi fully-developed flow, which is destroyed by the presence of the obstacle. Immediately behind it, both the coalescence and breakup rates are enhanced due to intensified turbulence and recirculation, and as a result, the BSD becomes broader. At first, the increase in coalescence exceeds that in breakup such that the mean bubble size increases. After about ten millimeters downstream from the obstacle (L/D≈0.2), breakup overtakes coalescence and the BSD shifts to the direction of small bubble size. At L/D≈0.4, the bubble size before the obstacle is almost recovered, but it decreases further downstream. The predicted and measured BSDs agree well with each other upstream and downstream, where the bubble coalescence and breakup is majorly controlled by turbulence. Difficulties are encountered in capturing the drastic change in the region directly downstream of the obstacle in particular the rapid increase in coalescence rate. The test of turbulence single-phase flow through a sudden expansion reveals that it is difficult for a RANS model to reproduce the turbulence structure in the recirculation zone reliably, which directly affects the performance of coalescence and breakup models. Furthermore, coalescence resulting from other mechanisms such as wake entrainment or laminar shear is shown to have a minor contribution, and turbulence is dominant. Further investigations concerning bubble coalescence and breakup, turbulence as well as its effect on interfacial momentum transfer are necessary for the obstructed flow.

Keywords: bubble coalescence and breakup; computational fluid dynamics; obstacle; turbulence; vertical pipe flow

  • Contribution to proceedings
    The 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.-11.03.2022, Brussels, Belgium
  • Lecture (Conference)
    The 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.-11.03.2022, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-32842
Publ.-Id: 32842


X-ray Spectroscopy for Actinide Science

Kvashnina, K.

X-ray spectroscopy is a widely used technique at synchrotron radiation sources for analyses of the electronic and structural parameters of materials. This includes the determination of the oxidation state and local symmetry of the absorbing atom. This lecture aimed at PhD students and postdocs who are interested in learning about the principles and practicalities of X-ray spectroscopy, as applied to actinide science. Experimental measurements can be performed on materials in a variety of states, including liquids and solids. The high intensity and tunability of X-rays allow the investigation of a wide range of materials, including thin films, nanoparticles, amorphous materials, solutions, disordered minerals and soils. Moreover, I will provide an overview of the advanced spectroscopic techniques, such as resonant inelastic X-ray scattering (RIXS) and high-energy-resolution fluorescence detected (HERFD) absorption spectroscopy (XAS) that are available at the synchrotrons for studies of actinide systems. I will cover basic principles of X-ray spectroscopy theory and instrumental setups and I will show several examples of the studies performed on the uranium, thorium and plutonium containing materials in the hard and tender X-ray range

Related publications

  • Invited lecture (Conferences) (Online presentation)
    JDA-2021: 13th School on the Physics and Chemistry of Actinides, 22.-25.03.2021, Rennes, France

Permalink: https://www.hzdr.de/publications/Publ-32841
Publ.-Id: 32841


High energy resolution X-ray spectroscopy on uranium compounds

Kvashnina, K.

Understanding the mechanisms of different chemical reactions with uranium at the atomic level is a key step towards safe disposal of nuclear wastes and towards the identification of physical-chemical processes of radionuclides in the environment. X-ray absorption spectroscopy in high energy resolution fluorescence detection (HERFD) mode at the U L3 and M4,5 edges together with resonant inelastic X-ray scattering (RIXS) are now common techniques for probing the uranium electronic structure and for studying the physics and chemistry of uranium-containing compounds[1], [2]. I will provide an overview of the recently performed studies[3]–[5] on uranium-containing materials at the European Synchrotron (ESRF) in Grenoble (France). I will show how the detailed information about the U oxidation state and electron-electron interactions can be obtained by a combination of experimental data and electronic structure calculations. In connection with latest results, the capabilities and limitations of the HERFD and RIXS experimental methods will be discussed in details. It might be of interest for fundamental research in chemistry and physics of actinides as well as for applied science

References:

[1] K. O. Kvashnina, S. M. Butorin, P. Martin, and P. Glatzel, “Chemical State of Complex Uranium Oxides,” Phys. Rev. Lett., vol. 111, no. 25, p. 253002, Dec. 2013, doi: 10.1103/PhysRevLett.111.253002.
[2] K. O. Kvashnina, Y. O. Kvashnin, and S. M. Butorin, “Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials,” J. Electron Spectros. Relat. Phenomena, vol. 194, pp. 27–36, Jun. 2014, doi: 10.1016/j.elspec.2014.01.016.
[3] N. Boulanger et al., “Enhanced Sorption of Radionuclides by Defect-Rich Graphene Oxide,” ACS Appl. Mater. Interfaces, vol. 12, no. 40, pp. 45122–45135, Oct. 2020, doi: 10.1021/acsami.0c11122.
[4] E. Gerber et al., “Insight into the structure–property relationship of UO 2 nanoparticles,” Inorg. Chem. Front., vol. 8, no. 4, pp. 1102–1110, 2021, doi: 10.1039/D0QI01140A.
[5] A. S. Kuzenkova et al., “New insights into the mechanism of graphene oxide and radionuclide interaction,” Carbon N. Y., vol. 158, pp. 291–302, Mar. 2020, doi: 10.1016/j.carbon.2019.10.003.

Related publications

  • Invited lecture (Conferences) (Online presentation)
    Uranium Science, 28.06.-01.07.2021, Bristol, UK

Permalink: https://www.hzdr.de/publications/Publ-32840
Publ.-Id: 32840


Thermoelectricity and electronic properties of Y1-xCexCrB4

Flipo, S.; Rosner, H.; Bobnar, M.; Kvashnina, K.; Leithe-Jasper, A.; Gumeniuk, R.

Boron-rich materials combine chemical stability with refractory properties and, consequently, are interestingfor high-temperature thermoelectric applications. Therefore, the magnetic, electrical, and thermal transportproperties of the Y1−xCexCrB4series have been investigated here to employ the concept of correlation-enhancedthermoelectric properties. Combining x-ray diffraction and energy- or wavelength-dispersive spectrometry,we find a rather narrow stability range of Y1−xCexCrB4, only samples on the Y- and Ce-rich substitutionlimits (x=0,0.05,0.95,and 1) were obtained. Electrical resistivity data show a change from semiconducting(x=0) to metallic behavior upon Ce substitution (x0.95). From magnetic susceptibility measurements andx-ray absorption spectroscopy, we find a temperature-dependent intermediate valence state of Ce of about+3.5.However, a fit of the magnetic susceptibility data to the Coqblin-Schrieffer model yields a surprisingly highKondo temperature of about 1100 K. Together with the good thermal conductivity for the studied substitutionseries this impedes a suitable thermoelectric performance. Electronic structure calculations for YCrB4supportits narrow gap semiconducting nature in contrast to previous studies. Surprisingly, its electronic structure ischaracterized by pronounced van Hove singularities very close to the Fermi-levelEF. They originate fromnearly dispersionless Cr 3dz2−r2-derived bands in a large part of the Brillouin zone, suggesting the appearance ofelectronic instabilities upon rather small electron doping into these states

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Permalink: https://www.hzdr.de/publications/Publ-32839
Publ.-Id: 32839


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

Cevirim-Papaioannou, N.; Jo, Y.; Franke, K.; Fuss, M.; de Blochouse, B.; Altmaier, M.; Gaona, X.

The isotope 94 of niobium (t1/2= 2.04·104 a) is produced during the operation of nuclear reactors due to the neutron activation of 93Nb, which is present in some structural components in nuclear reactor vessels. Related waste streams will be disposed of in repositories for low and intermediate level wastes (L/ILW), where cement is widely used for the stabilization of the waste and for construction purposes.
The retention of niobium by young cement was investigated in a series of sorption experiments using a combination of active (95Nb + 91mNb) and inactive (93Nb) niobium isotopes. Sorption experiments assessed also the impact of iso-saccharinic acid (ISA, main degradation product of cellulose) and chloride on Nb retention, both expected in specific L/ILW.
A pyrochlore-structure Ca-Nb(V) oxide was found to control the solubility of Nb(V) in cement pore water at pH= 13.5, defining [Nb(V)]aq = 2∙10-6 - 7·10–8 M. Sorption experiments revealed a strong uptake of Nb(V) by cement (5 ≤ log Rd ≤ 7, Rd in L·kg–1), in spite of the predominance of anionic hydrolysis species in the cement pore water. Sorption isotherms were found to be linear within 10–14 M ≤ [Nb(V)]aq ≤ 10–9 M. Calcium silicate hydrate (C-S-H) phases are defined as main sink of Nb(V) in cement, with Ca2+ playing a key role in bridging the negatively charged Nb(V) species to C-S-H. ISA significantly decreases the uptake of Nb(V) at [ISA]aq ≥ 10–4 M, reflecting the formation of stable (Ca-)Nb(V)-ISA complexes in the aqueous phase. Sorption is not affected by chloride within the investigated concentration range (10–5 M ≤ [Cl] ≤ 1.0 M).
This work represents the first experimental evidence on the uptake of niobium by young cement in the absence and presence of ISA and Cl, thus providing key inputs for the assessment of 94Nb retention in the context of the Safety Case for repositories for nuclear waste.

Keywords: niobium; cement; ISA; chloride; sorption

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Permalink: https://www.hzdr.de/publications/Publ-32838
Publ.-Id: 32838


Novel Radionuclides - Don’t Forget the Regulatory Side

Neels, O.

Recent years have seen many efforts to investigate several novel radionuclides, currently neither commercially available nor clinically used. Especially with the advent of theranostics aims are to improve therapeutic efficacy, to adapt the physical half live to the target under investigation or to improve the “matched pair” concept, i.e. eliminating differences in chemistry between a diagnostic and therapeutic radionuclides. This pre-Congress symposium will discuss, which candidates are promising, how technical and organisational advances may lead to better availability, where are major challenges, what is clinically required and desired, where are regulatory hurdles and where we currently stand in the development. The views from the producers, preclinical radiopharmaceutical researchers and the clinician will be included to provide an up to date status.

Keywords: Radionuclides; Theranostics; Accelerators; Mass separation; Radiopharmaceutical development

Permalink: https://www.hzdr.de/publications/Publ-32837
Publ.-Id: 32837


Regulatory Aspects of Cold Kit-Based Radiopharmaceuticals in the EU

Neels, O.

The cold kit approach is a fast and easy method for labeling tracers with radiometals used in Nuclear Medicine for 99mTc-radiopharmaceuticals since decades. The clinical success of some radiopharmaceutical labelled with Ga-68, a generator-based PET isotope, followed by the availability of registered generators and the development of new chelators, boosted the interest in development of cold kit-based 68Ga- radiopharmaceuticals as for 99mTc. The aluminium fluoride-18 (Al[18F]F) radiolabelling is an interesting “one-pot” method which involves the formation of 18F-metal complex trapped by a suitable chelator. This approach simplifies the 18F-labeling methodology along with the possibility to obtain a kit-based radiofluorination. In this session, the recent developments in kit-based labeling of 68Ga- radiopharmaceuticals and in Al[18F]F labeling will be discussed. Finally, since the regulatory aspect is an important issue for using cold kit preparations in clinical practice, an overview of the different regulations in European countries will be showed and discussed.

Keywords: Cold kit; radiolabeling; 68Ga-radiopharmaceuticals; Al[18F]F; regulatory aspects; PET

Permalink: https://www.hzdr.de/publications/Publ-32836
Publ.-Id: 32836


Optimization and automation of radiolabeling FAPI-74 using [18F]AlF chemistry

Laube, M.; Pietzsch, J.; Knieß, T.; Kopka, K.; Neels, O.

Aim/Introduction:

In recent years quinoline-based small molecules targeting the fibroblast activation protein alpha (FAP) have gained interest for imaging a variety of tumor entities (1). A number of radiotracers for SPECT and PET have been developed, but so far only three FAP inhibitor (FAPI) radioligands have been reported to be radiolabeled with fluorine-18 (2,3,4). This study shows the optimization and automation of the radiofluorination of FAPI-74.

Materials and Methods:

(S)-(4-Carboxymethyl-7-{2-[4-(3-{4-[2-(2-cyano-pyrrolidin-1-yl)-2-oxoethylcarbamoyl]-quinolin-6-yloxy}-propyl)-piperazin-1-yl]-2-oxo-ethyl}-[1,4,7]triazonan-1-yl)-acetic acid, commonly referred to as FAPI-74, was radiolabeled using the [18F]AlF chelation method. Starting from [18F]fluoride, the reaction with AlCl3, chelate formation and subsequent purification was initially optimized by manual syntheses. Optimization included the examination of different anion exchangers (QMA light, PSHCO3) and elution solutions (NaOAc buffer pH4, 0.9% NaCl) as well as careful adjustment of the reaction parameters time (0-20 min), temperature (r.t. to 100°C), amount of AlCl3 and NaOAc buffer pH4, solvents (DMSO, EtOH), and precursor concentration (1-350 µM). Radiochemical conversion (RCC) was determined by radio-UPLC of the crude reaction mixtures. Selected reaction mixtures were analyzed after decay using UPLC-MS to identify non-radioactive byproducts. The optimized radiosynthetic procedure was transferred to a fully automated radiosynthesizer (TRACERlab FXFN) and the final product was purified and formulated using semi-preparative HPLC and SPE.

Results:

Under optimized conditions, RCC of [18F]AlF-FAPI-74 of > 99% was still observed at precursor concentrations as low as 12 µM FAPI-74 after reaction in a 1:1 molar ratio with AlCl3 in DMSO/sodium acetate buffer at pH 4 at 80°C for 15 minutes. Transfer of optimized conditions and upscaling was successfully achieved and delivered radiochemical pure [18F]AlF-FAPI-74 formulated in EtOH suitable for further preclinical experiments. Work on a more rapid SPE-purification and full characterization according to GMP guidelines is in progress.

Conclusion:

The radiosynthesis of [18F]AlF-FAPI-74 was optimized and automated, which in the future will allow the production of large quantities and the distribution of this promising radiotracer to other (clinical) centers.
References:
(1) Altmann A et al. The latest developments in imaging fibroblast activation protein (FAP). J. Nucl. Med. 2021, 62(2) 160-167.
(2) Giesel FL et al. FAPI-74 PET/CT Using Either 18F-AlF or Cold-Kit 68Ga Labeling: Biodistribution, Radiation Dosimetry, and Tumor Delineation in Lung Cancer Patients. J. Nucl. Med. 2021, 62(2) 201-207.
(3) Jiang X et al. FAPI-04 PET/CT using [18F]AlF Labeling Strategy: Automatic Synthesis, Quality Control, and in vivo Assessment in Patient. Front. Oncol. 2021, 11:649148.

Permalink: https://www.hzdr.de/publications/Publ-32835
Publ.-Id: 32835


Resonance behavior of embedded and freestanding microscale ferromagnets

Cansever, H.; Anwar, M. S.; Stienen, S.; Lenz, K.; Narkovic, R.; Hlawacek, G.; Potzger, K.; Hellwig, O.; Faßbender, J.; Lindner, J.; Bali, R.

The ferromagnetic resonance of a disordered A2 Fe60Al40 of ferromagnetic strip, of dimensions 5 µm × 1 µm x 32 nm, has been observed in two vastly differing surroundings: in the first case, the ferromagnetic region was circumferenced by ordered B2 Fe60Al40, and in the second case it was free standing, adhering only to the oxide substrate. The embedded ferromagnet possesses a periodic magnetic domain structure, which transforms to a single domain structure in the freestanding case. The two cases differ in their dynamic response, for instance, the resonance field for the uniform (k = 0) mode at ~ 14 GHz excitation displays a shift from 209 to 194 mT, respectively for the embedded and freestanding cases, with the external magnetic field applied along the long axis. The resonant behavior of a microscopic ferromagnet can thus be finely tailored via control of its near-interfacial surrounding.

Keywords: Embedded nanomagnets; microresonator; ferromagnetic resonance; ion irradiation

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Permalink: https://www.hzdr.de/publications/Publ-32834
Publ.-Id: 32834


Two-dimensional magneto-photoconductivity in non-van der Waals manganese selenide

Hu, L.; Cao, L.; Li, L.; Duan, J.; Liao, X.; Long, F.; Zhou, J.; Xiao, Y.; Zeng, Y.-J.; Zhou, S.

Deficient intrinsic species and suppressed Curie temperatures (Tc) in two-dimensional (2D) magnets are major barriers for future spintronic applications. As an alternative, delaminating non-van der Waals (vdW) magnets can offset these shortcomings and involve robust bandgaps to explore 2D magneto-photoconductivity at ambient temperature. Herein, non-vdW a-MnSe2 is first delaminated as quasi-2D nanosheets for the study of emerging semiconductor, ferromagnetism and magneto-photoconductivity behaviors. Abundant nonstoichiometric surfaces induce the renormalization of the band structure and open a bandgap of 1.2 eV. The structural optimization strengthens ferromagnetic super–exchange interactions between the nearest-neighbor Mn2+, which enables us to achieve a high Tc of 320 K well above room temperature. The critical fitting of magnetization and transport measurements both verify that it is of quasi-2D nature. The above observations are evidenced bymultiplemicroscopic andmacroscopic characterization tools, in line with the prediction of firstprinciples calculations. Profiting from the negative magnetoresistance effect, the self-powered infrared magneto-photoconductivity performance including a responsivity of 330.4 mA W-1 and a millisecondlevel response speed are further demonstrated. Such merits stem from the synergistic modulation of magnetic and light fields on photogenerated carriers. This provides a new strategy to manipulate both charge and spin in 2D non-vdW systems and displays their alluring prospects in magneto-photodetection.

Keywords: Manganese selenide; two dimensional non van der Waals

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Permalink: https://www.hzdr.de/publications/Publ-32833
Publ.-Id: 32833


How to study nonlinear dynamics in semiconductors by terahertz wave free electron laser

Schneider, H.

This tutorial talk covers the study of nonlinear dynamics in semiconductor nanostructures in strong terahertz and mid-infrared fields involving a free-electron laser.

Related publications

  • Invited lecture (Conferences) (Online presentation)
    International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPT2021), 16.-19.06.2021, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-32832
Publ.-Id: 32832


Interfacial behavior of particle-laden bubbles under asymmetric shear flow

Eftekhari, M.; Schwarzenberger, K.; Heitkam, S.; Javadi, A.; Bashkatov, A.; Ata, S.; Eckert, K.

The interfacial properties of air bubbles have mostly been studied in quiescent fluids or in an axisymmetric flow field. To extend the knowledge to technologically relevant conditions, we investigate the behavior of surfactant- and particle-laden bubbles under asymmetric shear forces. Experiments are performed with a buoyant bubble at the tip of a capillary placed in a defined flow field. The response of the interface to the surrounding asymmetric flow is measured under successive reduction of the surface area. Profile analysis tensiometry is utilized to investigate the dynamic surface tension and the surface rheology of the surfactant- and particle-laden interfaces. The bulk flow and the interfacial mobility of the buoyant bubble are studied using microscopic particle image and tracking velocimetry. According to our findings, under asymmetric shear flow, surfactant-laden interfaces remain mobile regardless of the surfactant concentration. In contrast, particle-laden interfaces adopt a solid-like state and resist the interfacial flow at certain surface coverages. Elasticity measurements during successive reduction of the surface area indicate a significant change in the structure of the interface that changes its mobility. The immobilization of the interface is characterized by the ratio of the interfacial elasticity to shear forces. This dimensionless number provides an estimate the interfacial forces required to initiates interfacial immobility at defined flow field. Our findings can serve as a basis to model the boundary conditions and to modulate the hydrodynamics of bubbles and droplets with different adsorbed material.

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Permalink: https://www.hzdr.de/publications/Publ-32831
Publ.-Id: 32831


Enhanced trion emission in monolayer MoSe2 by constructing a type-I van der Waals heterostructure

Duan, J.; Chava, P.; Ghorbani Asl, M.; Krasheninnikov, A.; Erb, D.; Hu, L.; Schneider, H.; Rebohle, L.; Erbe, A.; Helm, M.; Zeng, Y.-J.; Zhou, S.; Prucnal, S.

Trions, quasi-particles consisting of two electrons combined with one hole or of two holes with one electron, have recently been observed in transition metal dichalcogenides (TMDCs) and drawn increasing attention due to potential applications of these materials in light-emitting diodes, valleytronic devices as well as for being a testbed for understanding many-body phenomena. Therefore, it is important to enhance the trion emission and its stability. In this study, we construct a MoSe2/FePS3 van der Waals heterostructure (vdWH) with type-I band alignment, which allows for carriers injection from FePS3 to MoSe2. At low temperatures, the neutral exciton (X0) emission in this vdWH is almost completely suppressed. The ITrion/Ix0 intensity ratio increases from 0.44 in a single MoSe2 monolayer to 20 in this heterostructure with the trion charging state changing from negative in the monolayer to positive in the heterostructure. The optical pumping with circularly polarized light shows a 14% polarization for the trion emission in MoSe2/FePS3. Moreover, forming such type-I vdWH also gives rise to a 20-fold enhancement of the room temperature photoluminescence from monolayer MoSe2. Our results demonstrate a novel approach to convert excitons to trions in monolayer 2D TMDCs via interlayer doping effect using type-I band alignment in vdWH

Keywords: type-I; van der Waals heterosturcture; photoluminescence enhancement; trion/exciton intensity ratio; polarization

Related publications

  • Open Access Logo Advanced Functional Materials 31(2021)40, 2104960
    Online First (2021) DOI: 10.1002/adfm.202104960
    Cited 20 times in Scopus
  • Lecture (Conference) (Online presentation)
    2021 Fall Meeting of the European Materials Research Society (E-MRS), 20.-23.09.2021, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-32827
Publ.-Id: 32827


Log file-based 4D proton dose reconstruction for interplay assessment in clinical routine and simulation studies

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

We have implemented the reconstruction of interplay-affected dose distributions from the log files of the dynamic PBS proton beam delivery and of the breathing-induced intra-fractional motion. For the first time, such an algorithm is capable to consider amplitude-sorted 4DCT phases. We have validated the reconstruction accuracy by phantom experiments for several motion patterns and magnitudes. The module is applied in combination with weekly repeat 4DCTs to routinely monitor the PBS treatments of NSCLC patients in our clinic department. Further use cases are occasional pre-treatment interplay estimations and the interplay effect evaluations within a plan comparison study investigating the benefit of 4D robustly optimized proton plans for NSCLC patients with large breathing motion (>5mm).

  • Lecture (others) (Online presentation)
    European RayStation user meeting 2021, 30.11.-01.12.2021, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-32826
Publ.-Id: 32826


Attention based deep 3d multiple instance survival models for oropharyngeal carcinoma patients

Starke, S.; Leger, S.; Zwanenburg, A.; Löck, S.

Introduction
Attention-based convolutional neural networks (CNNs) have the capability to use multiple parts of the same image to predict outcomes of interest. Especially in the domain of medical image analysis, where whole images are typically described by a single label but the identification of important image regions is unclear, this approach allows to combine competitively performing CNNs with enhanced interpretability of the decision-making process.

Materials & Methods
We developed risk models for the prediction of overall survival (OS) for 518 patients of a publicly available oropharyngeal carcinoma (OPC) cohort. Patients were randomly split into training, validation, and test cohorts (388/30/100 patients). A baseline Cox model using clinical information only and three attention-based CNNs using different likelihood functions were trained on multiple 3D instances of the pre-treatment computed tomography (CT) images. Subsequently, patients were stratified into groups at low and high risk of death using median cutoff values based on predictions determined on the training cohort. Model performance was measured using the concordance index (C-index) and differences between Kaplan-Meier curves were assessed by the log-rank test.

Results
The baseline Cox model achieved a C-Index of 0.22 and the CNN models based on the Cox, Weibull and Lognormal likelihood functions achieved C-indices of 0.34, 0.35 and 0.35, respectively, on the test cohort. All models stratified the patients into two risk groups with a statistically significant difference in OS. Attention scores between the multiple instances of a patient were similar, suggesting that all CT instances were equally important for the network decision.

Summary
We investigated the potential of attention-based multiple-instance learning for prediction of OS on an OPC cohort. Since all attention-based CNNs generated risk groups with significantly different OS based on imaging data alone, we consider this approach promising for future validation studies.

Keywords: Deep learning; Survival analysis; Oropharyngeal carcinoma; Attention

  • Lecture (Conference) (Online presentation)
    Dreiländertagung der Medizinischen Physik, 19.-21.09.2021, digital, digital

Permalink: https://www.hzdr.de/publications/Publ-32825
Publ.-Id: 32825


THEREDA - Thermodynamic Reference Database

Moog, H. C.; Bok, F.; Freyer, D.; Gaona, X.; Thoenen, T.

Part of the process to ensure the safety of radioactive waste disposal is the predictive modeling of the solubility of all relevant toxic components in a complex aqueous solution. To ensure the reliability of thermodynamic equilibrium modeling as well as to facilitate the comparison of such calculations done by different institutions it is necessary to create a mutually accepted thermodynamic reference database. To meet this demand several institutions in Germany joined efforts and created THEREDA [1].

THEREDA is a suite of programs at the base of which resides a relational databank. Special emphasis is put on thermodynamic data along with suitable Pitzer coefficients which allow for the calculation of solubilities in high-saline solutions. Registered users may either download single thermodynamic data or ready-to-use parameter files for the geochemical speciation codes PHREEQC, Geochemist’s Workbench, CHEMAPP, or TOUGHREACT. Data can also be downloaded in a generic JSON-format to allow for the import into other codes. The database can be accessed via the world wide web: www.thereda.de

Prior to release, the released part of the database is subjected to many tests. Results are compared to results from earlier releases and among the different codes. This is to ensure that by additions of new and modification of existing data no adverse side effects on calculations are caused. Furthermore, our website offers an increasing number of examples for applications, including graphical representation, which can be filtered by components of the calculated system.

[1] H. C. Moog, F. Bok, C. M. Marquardt, V. Brendler (2015): Disposal of Nuclear Waste in Host Rock formations featuring high-saline solutions - Implementation of a Thermodynamic Reference Database (THEREDA). Appl. Geochem. (55) 72-84. http://dx.doi.org/10.1016/j.apgeochem.2014.12.016

Keywords: THEREDA; Thermodynamic Reference Database; Datenbasis; Datenbank; Pitzer; Löslichkeiten; Modellierung

  • Poster (Online presentation)
    Goldschmidt2021, 04.-09.07.2021, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-32824
Publ.-Id: 32824


Uranium carbonates removal by Layered Double Hydroxides

Padberg, G.

Uranium as a radionuclide and heavy metal has strong negative health effects on all living beings.
Since uranium salts display a high solubility in water, its mobility in aquifers is immense
and leads to the risk of ingestion by water consuming organisms. Sources of uranium contamination
in the environment are military and mining activities as well as leaking repositories.
The objective of this work is to analyze the uranium removal properties of two double layered
hydroxides (LDH) with different redox properties in absence and presence of carbonate. The
LDH phases selected are Ca(II)-Al(III)-Cl and Fe(II)-Al(III)-Cl, hereafter named Ca-LDH and
Fe-LDH. These LDHs play a crucial role in the geosphere, as they consist of the most abundant
elements in the earth crust. Furthermore, Ca-LDH is a product of bentonite weathering, which
is an essential process considered in repository safety management.
The first aim of this work is to synthesize and characterize Ca-LDH and Fe-LDH with respect
to their stoichiometry (inductively coupled plasma mass spectrometry, Mössbauer spectroscopy,
thermogravimetric analysis, energy-dispersive X-ray spectroscopy), their structure
(X-ray diffraction, Brunauer-Emmett-Teller theory, dynamic light scattering, scanning electron
microscopy, Raman microscopy) and their electronic state (X-ray photoelectron spectroscopy,
electrophoretic mobility).
The ultimate goal is to determine the best conditions under which uranium is removed from
solution by these LDHs. This will be achieved by analyzing the parameters that influence the
process (carbonate presence, redox processes, pH, ionic strength and uranium concentration).
In comparison to Ca-LDH, Fe(II)-LDH contains a redox active moiety, so that a different mechanism
for the interaction of these LDH phases with aqueous uranium is expected. For a comprehensive
understanding of these molecular uranium reactions occuring at the LDH phase,
various spectroscopic techniques (attenuated total reflexion Fourier-transform infrared, cryo
time-resolved laser-induced fluorescence, energy-dispersive X-ray, X-ray photelectron spectroscopy)
and microscopies (Raman microscopy, scanning electron microscopy) are applied
and combined. The synthesis of Ca-LDH and Fe-LDH was successful and structurally characterized by different
techniques (XRD, DLS, electrophoretic mobility, BET, SEM, EDXS, Raman microscopy,
XPS and Mössbauer). The stoichiometry under consideration of the corresponding oxidation
states was determined as
Ca(II)₀.₅₉Al(III)₀.₄₁Cl₀.₈₂(OH)₂ · 3.0 H2O and
Fe(II)₀.₆₀Al(III)₀.₄₀Cl₀.₈₀(OH)₂ · 1.8 H2O.
Uranium removal by Ca-LDH and Fe-LDH was evaluated as a function of pH (5.5 to 11.0),
ionic strength (H2O, 0.01 M NaCl, and 0.1 M NaCl), carbonate concentration (0, 0.013 mM,
0.2 mM, 0.24 mM and 2 mM) and U(VI) concentration (from nM to mM). As a general statement,
uranium removal was higher than 95% for pH > 6.0 for both Ca-LDH and Fe-LDH under
all studied conditions. Uranium removal decreased for pH < 6 in both LDH, as these mineral
phases are only stable under alkaline conditions. Uranium removal by Ca-LDH decreased at high ionic strength (0.1 M NaCl) and carbonate
concentration (2 mM and 20 mM). For the sorption mechanism of uranium to Ca-LDH, redox
potential measurements indicate a pH, carbonate and ionic strength dependency of the sorbed
minerals. In all studied cases, uranium associated to Ca-LDH is found as U(VI). Two different
U(VI) species are detected by ATR-IR measurements at pH 9.5 in presence of carbonate. Most
tentatively, one species is corresponding to U(VI) precipitation, which is also suggested by Raman
microscopy. The other species could be correlated to U(VI) outer-sphere complexation,
which is also supported by the lack of changes in the isoelectric point of Ca-LDH in presence
of U(VI) and the decrease of chloride content on the Ca-LDH after being in contact with U(VI).
The presence of outer-sphere complexation might be the reason of the decreased U(VI) removal
at higher ionic strengths and carbonate concentrations.
Three different species of U(VI) associated to Ca-LDH are detected by TRLFS from pH 8.0
to pH 11.0 in presence and absence of carbonate. Species 1 could be related to [UO₂(OH)₃]⁻
complexation according to uranium speciation diagrams. Species 2 identity is challenging to
hypothesize. It is assumed that U(VI) incorporation occurs due to an increased Ca concentrationin solution. Species 3 is assigned to [UO₂(CO₃)₂]²⁻ complexation. A reliable identification of
this species would need the use of additional techniques, like XAS.
In contrast, uranium removal by Fe-LDH occurs via Fe(II) promoted reduction of U(VI) to
U(IV). This is confirmed by redox potential values, the detection of Fe(III) by XPS and the
observation of Fe(III) minerals (ferrihydrite, hematite and iron aluminate) by Raman. Changes
on the Fe-LDH structure after contact with U(VI) are also observed in SEM images. The confirmation
of possible stepwise uranium removal by Fe-LDH (anion exchange followed by U(VI)
reduction) would need further verification by ATR FT-IR.
To sum up, the synthesized Ca-LDH and Fe-LDH phases are found to exhibit excellent and effective
uranium removal properties under alkaline conditions, being able to remove negatively
charged uranium species from solutions. Sorption mechanisms could be suggested in a multispectroscopic
approach as outer-sphere surface complexation and incorporaton for Ca-LDH and
as uranium reductive immobilization for Fe-LDH.
This study shows, that the examined Ca-LDH and Fe-LDH can act as a naturally occuring retention
barrier in geosphere against uranium release from repositories. Therefore, these LDH
phases can possibly be part of a technical multi-barrier system preventing uranium leaking into
the biosphere. Further experiments need to be carried out by TRLFS, ATR-IR and XAS in
order to have a comprehensive identification of the uranium sorption mechanisms on Ca-LDH
and Fe-LDH.

Keywords: uranium; Reductive immobilization; Sorption; LDH

  • Master thesis
    TU Dresden, 2021
    Mentor: Prof. Dr. Thorsten Stumpf (1. Prüfer) Dr. Natalia Mayordomo (2. Prüfer)
    65 Seiten

Permalink: https://www.hzdr.de/publications/Publ-32823
Publ.-Id: 32823


The pure paramagnetism in graphene oxide

Zhang, X.; Li, G.; Li, Q.; Shaikh, M. S.; Li, Z.

Magnetic properties of graphene and its derivatives are very fascinating because of their promising application in
spintronics. Among the graphene family materials, graphene oxide is quite typical and special for the magnetic
performance. Herein we report a systematic and detailed investigation on the magnetic properties of graphene
oxide. Compared to the previous reports on the ferromagnetism, our results show that graphene oxide is indeed
only paramagnetic. The magnetic properties can be well described by the Curie-Weiss law. This study is not only
revealing the paramagnetism in graphene oxide but also calling a revisit about the magnetic properties of graphene
oxides, graphene and the other derivatives of graphene.

Keywords: Graphene oxide; Micro-Raman; Magnetization; Paramagnetism

Related publications

Permalink: https://www.hzdr.de/publications/Publ-32822
Publ.-Id: 32822


Bonding Trends in a Series of Tetravalent Th-Pu Monosalen Complexes

März, J.

Actinides (An) play an important role in chemical engineering and environmental science related to the nuclear industry or nuclear waste repositories.[1] Coordination chemistry of An using small model ligands is a useful tool to get a profound basic knowledge about fundamental physico-chemical properties of the An binding. Observed changes in e.g. the binding situation or magnetic effects among an isostructural An series with the An in the same oxidation state may deliver insight into the unique electronic An properties mainly originating from their f-electrons.
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which are dominant particularly under anoxic environmental conditions, using the organic salen ligand as a small N,O donor.[2] All syntheses were conducted under inert, water-free atmosphere using pyridine based solvents (Pyx). SC-XRD results prove that three isostructural complex series were achieved in each case, dependent on the solvent used. In all complexes, one salen ligand coordinates to the An (An = Th, U, Np, Pu) tetradentately with both nitrogen and deprotonated oxygen donor atoms. The vacant coordination sites are occupied by two chloro ligands for charge compensation as well as two respective solvent molecules, either pyridine (Py), 4-methylpyridine (Pic) or 3,5-lutidine (Lut), resulting in an eightfold coordination environment (see [AnCl2(salen)(Pic)2] as representatives in Figure 1).
The acquired experimental SC-XRD and IR results as well as supporting QC calculations point to a different bonding situation of the individual donor atoms to the actinide. Whereas the An–Nsalen/Pyx and the An–Cl bond lengths follow the decrease of the ionic radii, the An–Osalen bonds remarkably diverge from this behavior. These rather follow the trend of decreasing covalent radii, indicating an exceptionally strong bond here. QC calculations additionally indicate a weaker binding strength in the An–NPyx bonds compared to An–Nsalen. This explains the potential solvent exchange (e.g. to the other pyridine based solvents) and opens up the possibility of further chemical modification at these positions.

Keywords: Actinides; bonding analysis; thorium; uranium; neptunium; plutonium

  • Lecture (Conference) (Online presentation)
    Journées des Actinides, 22.-25.03.2021, Rennes, France

Permalink: https://www.hzdr.de/publications/Publ-32821
Publ.-Id: 32821


Effect of Background Electrolyte Composition on the Interfacial Formation of Th(IV) Nanoparticles on the Muscovite (001) Basal Plane

Neumann, J.; Qiu, C.; Eng, P.; Skanthakumar, S.; Soderholm, L.; Stumpf, T.; Schmidt, M.

Understanding the impact of actinide nanoparticle (NP) formation is important to assess radionuclide mobility in the environment. We combined Surface X-ray Diffraction (SXRD) and in situ AFM to investigate the previously reported unusual electrolyte effects on Th uptake on mica. At low [Th] (0.1 mM), interfacial structures show a broad Th electron density (~50 Å). A linear decrease of Th uptake with decreasing hydration enthalpy of the electrolyte cation (Li⁺, K⁺, NH₄⁺, Cs⁺) indicates a competitive effect between Th and the electrolyte cation. Na⁺ is a clear outlier from this trend. In situ AFM imaging confirms the results. Particles show a vertical size of ~1 – 2 nm and larger lateral dimensions of ~10 – 20 nm, which is typical for particles formed at interfaces (heterogeneous nucleation). At high [Th] = 1 and 3 mM, all investigated electrolytes (ACl, A = Li⁺, Na⁺, K⁺) show similar Th uptake, indicating a much smaller impact of electrolyte composition. The interfacial structures are dominated by a high Th loading at a distinct distance (~6.5 Å) from the surface. Therefore, the main retention mechanism at high [Th] is suggested to be the sorption of Th NPs aggregated from Th oligomers present in solution (homogeneous nucleation).

Keywords: CTR; RAXR; SXRD; AFM; surface X-ray diffraction; nanoparticles; nucleation; thorium

Permalink: https://www.hzdr.de/publications/Publ-32820
Publ.-Id: 32820


Research data: THz harmonic generation from ultraclean graphene

Deinert, J.-C.; Kovalev, S.
Project Leader: Tielrooij, Klaas-Jan; DataCollector: Kovalev, Sergey; Project Member: Soavi, Giancarlo; Project Member: Klimmer, Sebastian

Research data from the June 2021 TELBE beamtime for scientific exchange.

Keywords: Terahrtz; graphene; encapsulated graphene; nonlinear optics; harmonic generation

Related publications

Downloads

Permalink: https://www.hzdr.de/publications/Publ-32819
Publ.-Id: 32819


Analyse eines Energiespeichersystems basierend auf geologischer Unter-grundspeicherung von CO2 und CH4

Fogel, S.; Yeates, C.; Unger, S.; Hampel, U.

Die Speicherung von überschüssiger Elektroenergie aus regenerativen Energiequellen in relevanten Größenordnungen stellt eine wesentliche technologische Hürde der Energiewende in der Bundes-republik Deutschland dar. Der nationale Strombedarf in Zeiten unzureichender regenerativer Er-zeugung kann zukünftig mit Speicherkraftwerken auf Basis von aus CO2 und Elektrolysewasser-stoff produziertem synthetischen Methan (Power-to-Gas) und methangefeuerten, hocheffizienten Kraftkreisläufen (Gas-to-Power) basierend auf dem Allam-Kreislauf gedeckt werden. Durch die Nutzung von überkritischem CO2 als Kreislaufmedium lassen sich Wirkungsgrade von bis zu 66% für den Gas-to-Power-Pfad und Gesamtwirkungsgrade des Speicherzyklus von >50% erzielen. Zur Umsetzung dieses Konzeptes sind ausreichende Speicherkapazitäten für CO2, CH4 und O2 sowie regenerative Erzeugungskapazitäten vorzuhalten. Der vorliegende Beitrag untersucht den vorge-stellten Energiespeicherzyklus unter Annahme eines geschlossenen CO2-Kreislaufs gekoppelt mit geologischer Untergrundspeicherung von CO2 und CH4 im Sinne des Carbon Capture, Utilization and Storage (CCUS). Zur technischen Bewertung des Konzeptes wurde das Potential der Speiche-rung von CO2 in Aquiferen in Deutschland analysiert und eine Studie des deutschen Energiesys-tems im Jahre 2050 für verschiedene Orientierungsszenarien durchgeführt. Mit Hilfe der erstellten Szenarien konnten die zur Erlangung einer CO2-neutralen Energiespeicherung benötigen Kapazitä-ten der regenerativen Stromerzeugung, elektrolytischen Wasserstoffbereitstellung und Rekonversi-on von CH4 sowie Speicherkapazitäten für CO2, CH4 und O2 abgeleitet werden.

  • Lecture (Conference)
    53. Kraftwerkstechnisches Kolloquium, 05.-06.10.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32818
Publ.-Id: 32818


Effects of Substituents on the Molecular Structure and Redox Behavior of Uranyl(V/VI) Complexes with N3O2‑Donating Schiff Base Ligands

Takeyama, T.; Tsushima, S.; Takao, K.

Uranyl(VI) complexes with pentadentate N3O2-donating Schiff base ligands having various substituents at the ortho (R1) and/or para (R2) positions on phenolate moieties, R1,R2-Mesaldien2−, were synthesized and thoroughly character-ized by 1H NMR, IR, elemental analysis, and single crystal X-ray diffraction. Molecular structures of UO2(R1,R2-Mesaldien) are more or less affected by electron-donating or -withdrawing nature of the substituents. The redox be-havior of all UO2(R1,R2-Mesaldien) complexes were investigated to understand how substituents introduced onto the ligand affect redox behavior of these uranyl(VI) complexes. As a result, the redox potentials of UO2(R1,R2-Mesaldien) in DMSO increased from −1.590 V to −1.213 V with an increase in the electron-withdrawing nature of the substituents at the R1 and R2 positions. The spectroelectrochemical measurements and theoretical calculation (DFT and TD-DFT calculations) revealed that the center U6+ of each UO2(R1,R2-Mesaldien) complex undergoes one-electron reduction to afford the corresponding uranyl(V) complex, [UO2(R1,R2-Mesaldien)]−, regardless of difference in the substituents. Consequently, the redox active center of uranyl(VI) complexes seems not to be governed by the HOMO/LUMO gap, but to be determined by whether the LUMO is centered on a U 5f orbital or on one π* of a surrounding ligand.

Permalink: https://www.hzdr.de/publications/Publ-32817
Publ.-Id: 32817


Describing chain-like assembly of ethoxygroup-functionalized organic molecules on Au(111) using high-throughput simulations

Lokamani, M.; Kelling, J.; Ohmann, R.; Meyer, J.; Kühne, T.; Cuniberti, G.; Wolf, J.; Juckeland, G.; Huhn, T.; Zahn, P.; Moresco, F.; Gemming, S.

Due to the low corrugation of the Au(111) surface, 1,4-bis(phenylethynyl)-2,5-bis(ethoxy)benzene (PEEB) molecules can form
quasi interlocked lateral patterns, which are observed in scanning tunneling microscopy (STM) experiments at low temperatures.
We demonstrate a multi-dimensional clustering approach to quantify the anisotropic pair-wise interaction of molecules and
explain these patterns. We perform high-throughput calculations to evaluate an energy function, which incorporates the
adsorption energy of single PEEB molecules on the metal surface and the intermolecular interaction energy of a pair of PEEB
molecules. The analysis of the energy function reveals, that, depending on coverage density, specific types of pattern are
preferred which can potentially be exploited to form one-dimensional molecular wires on Au(111).

Keywords: DFTB; 1,4-bis(phenylethynyl)-2,5-bis(ethoxy)benzene (PEEB); STM; High-Throughput; Meta-Structures

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Permalink: https://www.hzdr.de/publications/Publ-32816
Publ.-Id: 32816


Transport in tight material enlightened by process tomography

Kulenkampff, J.; Bollermann, T.; Cardenas Rivera, M. A.; Fischer, C.

The analysis of fluid transport through tight barrier materials poses two major challenges: (i) Long equilibration periods require long minimum experiment durations, and, (ii) the fluid transport frequently results in complex pattern formation. Too short measuring times may feign too small transport rates; intact homogeneous samples are often missing problematic features, e.g. fractures. Both issues are detected and analyzed by using process tomography techniques, hence providing an improved understanding of transport processes in complex materials.
We thus continuously develop and apply the positron emission tomography (PET) method for geomaterials (Kulenkampff et al., 2016). It is able to trace very low concentrations of β+-emitting radionuclides during their passage through drill cores of barrier material with reasonable resolution (1 mm) and over variable periods (hours to years). The method yields time-resolved quantitative tomographic images of the tracer concentration (e.g. https://doi.org/10.5281/zenodo.166509), in contrast to input-output experiments like common permeability measurements, diffusion cells, or break-through curves.
Our current research includes the analysis of diffusive transport in heterogeneous shales (sandy facies of the Opalinuston) (BMBF and HGF iCross project), the reactive flow in fracture-filling materials of crystalline rocks (Eurad FUTURE project), and transport in engineered barriers and the contact zone (Euratom Cebama, Eurad Magic, as well as MgO and Stroefun BMWi projects). The efforts combine flow field tomography, structural imaging and reactive transport modelling for improving process understanding and to provide a bridge from the molecular to the macroscopic scale.
The benefits include:

  • Insight into temporal stability and spatial heterogeneity of the observed transport process
  • Parameterization of local velocity distribution and effective volume, comparability with pore-scale model simulations
  • Ability to quantify multiple internal transport rates without necessity to register the delayed output signal
  • Transparent and palpable visualization of processes hidden in the opaque material
The method requires specific constraints of the experimental setup (size, fluid pressure, temperature). Nevertheless, it provides unique insight into reactive transport processes observed in potential materials for nuclear waste management.
References
Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Lippmann-Pipke, J., Solid Earth 7, 1217-1231, DOI: 10.5194/se-7-1217-2016
Kulenkampff, J.: Geophysical Research Abstracts, Vol. 20, EGU2018-8813-1, 2018.

Keywords: radioactive waste disposal; geological barrier; transport experiments; positron emission tomography

  • Open Access Logo Contribution to proceedings
    Interdisziplinäres Forschungssymposium safeND, 10.-12.11.2021, Berlin, Deutschland
    Safety of Nuclear Waste Disposal, Göttingen: Copernicus Publications
    DOI: 10.5194/sand-1-293-2021

Permalink: https://www.hzdr.de/publications/Publ-32815
Publ.-Id: 32815


Electrical control of orbital and vibrational interlayer coupling in bi- and trilayer 2H-MoS2

Klein, J.; Wierzbowski, J.; Soubelet, P.; Brumme, T.; Maschio, L.; Kuc, A. B.; Müller, K.; Stier, A. V.; Finley, J. J.

Manipulating electronic interlayer coupling in layered van der Waals (vdW) mate- rials is essential for designing opto-electronic devices. Here, we control vibrational and electronic interlayer coupling in bi- and trilayer 2H-MoS2 using large external electric fields in a micro-capacitor device. The electric field lifts Raman selection rules and activates phonon modes in excellent agreement with ab-initio calculations. Through polarization resolved photoluminescence spectroscopy in the same device, we observe a strongly tunable valley dichroism with maximum circular polarization degree of ∼ 60% in bilayer and ∼ 35% in trilayer MoS2 that are fully consistent with a rate equation model which includes input from electronic band structure calculations. We identify the highly delocalized electron wave function between the layers close to the high symmetry Q points as the origin of the tunable circular dichroism. Our results demonstrate the possibility of electric field tunable interlayer coupling for controlling emergent spin-valley physics and hybridization driven effects in vdW materials and their heterostructures.

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Permalink: https://www.hzdr.de/publications/Publ-32814
Publ.-Id: 32814


Towards harmonizing clinical linear energy transfer (LET) reporting in proton radiotherapy: A European multi-centric study

Hahn, C.; Ödén, J.; Dasu, A.; Vestergaard, A.; Fuglsang Jensen, M.; Sokol, O.; Pardi, C.; Bourhaleb, F.; Leite, A.; de Marzi, L.; Smith, E.; Aitkenhead, A.; Rose, C.; Merchant, M.; Kirkby, K.; Grzanka, L.; Pawelke, J.; Lühr, A.

Background: Clinical data suggest that the relative biological effectiveness (RBE) in proton therapy (PT) varies with linear energy transfer (LET). However, LET calculations are neither standardized nor available in clinical routine. Here, the status of LET calculations among European PT institutions and their comparability are assessed and a consensus for harmonized LET reporting is presented.
Materials and methods: Eight European PT institutions used suitable treatment planning systems with their centre-specific beam model to create treatment plans in a water phantom covering different field arrangements and fulfilling commonly agreed dose objectives. They employed their locally established LET simulation environments and procedures to determine the corresponding LET distributions. Dose distributions D1.1 and DRBE assuming constant and variable RBE, respectively, and LET were compared among the institutions. Inter-centre variability was assessed based on dose- and LET-volume-histogram parameters.
Results: Treatment plans from six institutions fulfilled all clinical goals and were eligible for common analysis. D1.1 distributions in the target volume were comparable among PT institutions with variability <2.7%. However, corresponding LET values varied substantially between institutions for all field arrangements (≤57.1%), primarily due to differences in LET averaging technique and considered secondary particle spectra. Consequently, DRBE using nonharmonized LET calculations increased inter-centre dose variations substantially compared to D1.1 and significantly in mean dose to the target volume of perpendicular and opposing field arrangements (p<0.05). Harmonizing LET reporting (dose-averaging, all protons, LET to water) reduced the inter-centre variability in LET to the order of 10-15% within and outside the target volume for all beam arrangements. Consequentially, inter-institutional variability in DRBE decreased to that observed for D1.1 (p>0.05).
Conclusion: Harmonizing the reported LET among PT centres is feasible and allows for consistent multi-centric analysis and reporting of tumour control and toxicity in view of a variable RBE. It may serve as basis for harmonized variable RBE dose prescription in PT.

Keywords: proton therapy; multi-centric study; linear energy transfer (LET); relative biological effectiveness (RBE)

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Permalink: https://www.hzdr.de/publications/Publ-32813
Publ.-Id: 32813


Comprehensive microstructural and optical characterization of the thermal stability of aluminum-titanium oxynitride thin films after high temperature annealing in air

Escobar Galindo, R.; Heras, I.; Guillén, E.; Munnik, F.; Azkona, I.; Krause, M.

The thermal stability of two AlyTi1-y(OxN1-x) layers prepared by cathodic vacuum arc deposition with different oxygen content was studied after high temperature annealing of the samples in air. These layers were designed to be part of solar-selective coating (SSC) stacks. Compositional and microstructural characterization of the thin films was performed before and after the thermal treatment by elastic recoil detection (ERD), transmission electron microscopy and Raman spectroscopy.
AlyTi1-yN sample was stable after 2 hours of annealing at 450ºC. Initial stages of the formation of a surface oxide layer after annealing at 650 ºC were observed both by ERD and Raman analysis. Contrarily, no changes were found after 2 hours annealing treatment either at 450 and 650ºC in the composition and microstructure of AlyTi1-y(OxN1-x) sample. In both samples the formation of a surface anatase TiO2 film was reported after 2 hours annealing at 800°C. These compositional and microstructural changes were correlated with the optical properties determined by spectroscopic ellipsometry. A transition from metallic to dielectric behaviour with increasing annealing temperature was observed. These results complete the durability studies on the designed SSCs based on AlyTi1-y(OxN1-x) materials, confirming that these stacks withstand breakdown at 600ºC in air.

Keywords: Solar energy; Concentrated solar power; Solar selective coatings; Temperature stability

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Permalink: https://www.hzdr.de/publications/Publ-32812
Publ.-Id: 32812


Effects of surface roughness and mineralogy on the sorption of Cm(III) on crystalline rock

Demnitz, M.; Molodtsov, K.; Schymura, S.; Schierz, A.; Müller, K.; Jankovsky, F.; Havlova, V.; Stumpf, T.; Schmidt, M.

Crystalline rock is one of the considered host rocks for a future deep geological repository for highly active radiotoxic nuclear waste. The safety assessment requires reliable information on the retention behavior of minor actinides. In this work, we applied various spatially resolved techniques to investigate the sorption of Curium onto crystalline rock (granite, gneiss) thin sections from Eibenstock, Germany and Bukov, Czech Republic. We combined Raman-microscopy, calibrated autoradiography and µTRLFS (micro-focus time-resolved fluorescence spectroscopy) with vertical scanning interferometry to study in situ the impact of mineralogy and surface roughness on Cm(III) uptake and molecular speciation on the surface. Heterogeneous sorption of Cm(III) on the surface depends primarily on the mineralogy. However, for the same mineral class sorption uptake and strength of Cm(III) increases with growing surface roughness around surface holes or grain boundaries. When competitive sorption between multiple mineral phases occurs, surface roughness becomes the major retention parameter on low sorption uptake minerals. In high surface roughness areas primarily Cm(III) inner-sphere sorption complexation and surface incorporation are prominent and in select sites formation of stable Cm(III) ternary complexes is observed. Our molecular findings confirm that predictive radionuclide modelling should implement surface roughness as a key parameter in their simulations.

Keywords: curium; luminescence; crystalline rock; granite; sorption; correlative spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-32811
Publ.-Id: 32811


Solar-selective coatings for high-temperature solar applications based on a selective transmitter on top of a black body absorber

Krause, M.; Lungwitz, F.; Mendez, A.; Hoppe, M.; Sonnenberg, J.; Garcia Valenzuela, A.; Munnik, F.; Grenzer, J.; Hübner, R.; Escobar Galindo, R.

An alternative concept to achieve solar selectivity for solar thermal materials and applications consists in the use of spectrally selective transmitter coatings.[1] These are characterized by a high transmittance in the solar range and a high reflectance in the thermal range of the electromagnetic spectrum. Suitable materials for selective transmitters are dielectric/metal/dielectric multilayers and transparent conductive oxides (TCOs).[2] The concept has a series of advantages compared to multilayer- or cermet-based solar-selective coatings (SSCs) like the easiness of manufacturing, the possibility to use standard materials as transmitter (e.g., indium tin oxide (ITO)) and absorber (e.g. Pyromark or black chrome), and the adaptability to specific requirements with respect to receiver temperature and solar concentration factor.
After a conceptual introduction, an analysis of solar plant parameters, i.e., operation temperature and solar concentration, for which this concept provides a better solar efficiency than state-of-the-art bare black body absorber, will be given.[3] We will then review the recent developments in the field, which include an excellent high-temperature in-air stability of such type of solar coatings.[4] In the second part of the talk, we will report own results toward a new TCO on black body absorber coating. Vacuum and in-air stability of the TCO SnO2:Ta at 800 °C and its structural properties before and after heat exposure are demonstrated. As potential absorber, the formation, structure, and optical properties of dense, PVD-grown CuCr2O4 thin films are studied. They are obtained in high purity from as-deposited samples by a simple in-air annealing step at 800 °C and absorb light in the whole solar range from 300 nm to 2500 nm.

[1] C.E. Kennedy, Review of Mid- to High-Temperature Solar Selective Absorber Materials, NREL Technical Reports, NREL - National Renewable Energy Laboratory, Golden, Colorado, USA, 2002.
[2] J.C.C. Fan, F.J. Bachner, Transparent heat mirrors for solar-energy applications, Applied Optics 15(4) (1976) 1012-1017.
[3] F. Lungwitz, R. Escobar-Galindo, D. Janke, E. Schumann, R. Wenisch, S. Gemming, M. Krause, Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Materials and Solar Cells 196 (2019) 84-93.
[4] H. Wang, I. Haechler, S. Kaur, J. Freedman, R. Prasher, Spectrally selective solar absorber stable up to 900 degrees C for 120 h under ambient conditions, Solar Energy 174 (2018) 305-311.

Keywords: Solar energy; Concentrated solar power; Solar selective coatings; Transparent conductive oxides; Spinel type absorber

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  • Invited lecture (Conferences) (Online presentation)
    Virtual MRS Spring Meeting 2021, Symposium EN05: Materials Challenges and Opportunities in Concentrated Solar Power Technologies, 19.-23.04.2021, Virtuell, USA

Permalink: https://www.hzdr.de/publications/Publ-32810
Publ.-Id: 32810


Formation, structure, and optical properties of copper chromite thin films for high-temperature solar absorbers

Krause, M.; Sonnenberg, J.; Munnik, F.; Grenzer, J.; Hübner, R.; Garcia Valenzuela, A.; Gemming, S.

CuCr2O4 thin films grown by physical vapour deposition were studied in order to evaluate their potential as absorber material for the next generation of concentrated solar power plants. A series of Cu-Cr-O thin films was deposited by reactive ion beam sputtering. The Cr/Cu ratio in the sputter target is demonstrated as the most important parameter to achieve the intended film stoichiometry. In-air annealing at 800 °C leads to structural transformations of the as-deposited films and results in phase compositions according to those expected from the ternary Cu-Cr-O phase diagram. Tetragonal CuCr2O4 with 98.6 at.% phase purity regarding the solid film constituents is obtained for the appropriate Cr/Cu ratio in the sputter target. CuCr2O4 thin films absorb light in the entire solar spectral range from 300 nm to 2500 nm. Their energy gap is found to be < 0.5 eV, and their solar absorptance is estimated to be (0.85 +/- 0.03). The dense microstructure with good thermal conductivity, full adhesion to the substrate, and a relatively low surface roughness are discussed as technological advantages of CuCr2O4 thin films grown by physical vapour deposition.

Keywords: solar absorber; spinels; sputtering; phase transformations; optical materials

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Permalink: https://www.hzdr.de/publications/Publ-32809
Publ.-Id: 32809


Environmental drivers of body size in North American bats

Alston, J.

Bergmann’s Rule—which posits that larger animals live in colder areas—is thought to influence variation in body size within species across space and time, but evidence for this claim is mixed. We tested four competing hypotheses for spatio-temporal variation in body size within bat species during the past two decades across North America. Bayesian hierarchical models revealed that spatial variation in body mass was most strongly correlated with mean annual temperature, supporting the heat conservation hypothesis (the mechanism historically believed to underlie Bergmann’s Rule). Across time, variation in body mass was most strongly correlated with net primary productivity, supporting the resource availability hypothesis. Climate change may influence body size in animals but will likely do so through both changes in mean annual temperature and in resource availability. Rapid reductions in body size alongside climate change have occurred in short-lived, fecund species, but such reductions may transpire more slowly in longer-lived species.

  • Invited lecture (Conferences) (Online presentation)
    Annual Meeting of the American Society of Mammalogists, 14.-18.06.2021, Virtual, USA

Permalink: https://www.hzdr.de/publications/Publ-32808
Publ.-Id: 32808


Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species’ traits

Wells, H. B. M.; Crego, R. D.; Opedal, Ø. H.; Khasoha, L. M.; Alston, J.; Reed, C. G.; Weiner, S.; Kurukura, S.; Hassan, A. A.; Namoni, M.; Ekadeli, J.; Kimuyu, D. M.; Young, T. P.; Kartzinel, T. R.; Palmer, T. M.; Pringle, R. M.; Goheen, J. R.

1. The extinction of 80% of megaherbivore (>1,000 kg) species towards the end of the Pleistocene altered vegetation structure, fire dynamics, and nutrient cycling worldwide. Ecologists have proposed (re)introducing megaherbivores or their ecological analogues to restore lost ecosystem functions and reinforce extant but declining megaherbivore populations. However, the effects of megaherbivores on smaller herbivores are poorly understood.

2. We used long-term exclusion experiments and multispecies hierarchical models fitted to dung counts to test 1) the effect of megaherbivore (elephant and giraffe) presence-absence on the occurrence (dung presence) and use intensity (dung-pile density) of mesoherbivores (2–1,000 kg), and 2) the extent to which the responses of each mesoherbivore species was predictable based on their traits (diet and shoulder height) and phylogenetic relatedness.

3. Megaherbivores increased the predicted occurrence and use intensity of zebras but reduced the occurrence and use intensity of several other mesoherbivore species. The negative effect of megaherbivores on mesoherbivore occurrence was stronger for shorter species, regardless of diet or relatedness.

4. Megaherbivores substantially reduced the expected total use intensity (i.e., cumulative dung density of all species) of mesoherbivores, but only minimally reduced the expected species richness (i.e., cumulative predicted occurrence probabilities of all species) of mesoherbivores (by <1 species).

5. Simulated extirpation of megaherbivores altered use intensity by mesoherbivores, which should be considered during (re)introductions of megaherbivores or their ecological proxies. Species’ traits (in this case shoulder height) may be more reliable predictors of mesoherbivores’ responses to megaherbivores than phylogenetic relatedness, and may be useful for predicting responses of data-limited species.

Keywords: African savanna; biotic interactions; competition; elephant; facilitation; giraffe; megafauna; trophic rewilding

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Permalink: https://www.hzdr.de/publications/Publ-32807
Publ.-Id: 32807


Daily torpor reduces the energetic consequences of habitat selection for a widespread bat

Alston, J.; Dillon, M. E.; Keinath, D. A.; Abernethy, I. M.; Goheen, J. R.

Homeothermy requires increased metabolic rates as temperatures decline below the thermoneutral zone, so homeotherms typically select microhabitats within or near their thermoneutral zones during periods of inactivity. However, many mammals and birds are heterotherms that relax internal controls on body temperature when maintaining a high, stable body temperature is energetically costly. Such heterotherms should be less tied to microhabitats near their thermoneutral zones, and because heterotherms spend more time in torpor and expend less energy at colder temperatures, heterotherms may even select microhabitats in which temperatures are well below their thermoneutral zones. We studied how temperature and daily torpor influence selection of diurnal roosts by a heterothermic bat (Myotis thysanodes). We (1) quantified the relationship between ambient temperature and daily duration of torpor, (2) simulated daily energy expenditure over a range of microhabitat (roost) temperatures, and (3) quantified the influence of roost temperature on roost selection. While warm roosts substantially reduced energy expenditure of simulated homeothermic bats, heterothermic bats modulated their use of torpor to maintain a constant level of energy expenditure over the course of a day. Daily torpor expanded the range of energetically economical microhabitats, such that roost selection was independent of roost temperature. Our work adds to a growing literature documenting functions of torpor beyond its historical conceptualization as a last-resort measure to save energy during extended or acute energetic stress.

Keywords: Bayesian hierarchical models; climate change; daily torpor; fringed myotis (Myotis thysanodes); temporal heterothermy; thermal ecology; VHF telemetry

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Permalink: https://www.hzdr.de/publications/Publ-32806
Publ.-Id: 32806


Dimeric and Trimeric Uranyl(VI)–Citrate Complexes: ¹⁷O-, ²³Na-, and ¹³⁹La-NMR – Helpful Probes for (Super-)Structure Determination

Kretzschmar, J.; Tsushima, S.; Drobot, B.; Steudtner, R.; Schmeide, K.; Brendler, V.; Stumpf, T.

Although being investigated for more than 70 years by various methods, the uranyl(VI)–citrate (U(VI)–Cit) system still reveals interesting structural and spectroscopic features. The aqueous chemistry of the system is complex, as evidenced by the still controversial discussions on speciation and structures.

Upon complexation, a chiral center is induced in Cit’s central carbon, yielding two diastereomeric pairs of enantiomers, whereupon the 2:2 complexes exhibit syn- and anti-configured isomers. In fact, the combination of ¹⁷O-NMR (at natural abundance) and DFT calculations allowed an unambiguous discrimination. Hereby symmetry and especially deviation from regular pentagonal bipyramidal coordination geometry affect the O=U=O entities’ (Oyl) chemical shifts. In aqueous solution, the syn-isomer is favored, in contrast to the preferably crystallizing anti-isomer. Both isomers interconvert mutually with exchange rates of about 30 s¹ at −6 °C and 249 s¹ at 60 °C in acidic solution, corresponding to an activation barrier of about 24 kJ mol¹.[1]

At circumneutral conditions, above 3 mM uranyl(VI) citrate concentrations, two trimeric 3:3 U(VI)–Cit complex molecules associate upon sandwiching a metal ion (Mn+) as a O=U=O→Mn+ Lewis acid–base adduct. The coordination shell formed by the six (inner) Oyl restricts the size of the enclosed Lewis acid. Among the studied metal ions, only Na+, Ca²+, and La³+ with ionic radii close to 1.0 Å match the formed cavity, while Li+ is too small, and K+ and Rb+ are too large. This cavity constitutes an anhydrous environment that shields the Mn+ from the aqueous phase, causing the sandwiched Na+ and La³+ to resonate 25 ppm and 430 ppm up-field relative to their corresponding aquo ions, respectively.
Upon increasing Mn+ charge/radius ratio, the sandwiched Lewis acids more and more withdraw electron density from those Oyl acting as Lewis base, and thus the latter sense a remarkable de-shielding. Increasing the charge of the sandwiched cation from +1 to +3, ΔδO between signals of the coordinating Oyl and the outer Oyl increases remarkably (12, 69, and 93 ppm, respectively), as the O=U=O units become progressively polarized.[2]

Literature:

[1] J. Kretzschmar et al., Inorg. Chem. 2021, 60, 7998.
[2] J. Kretzschmar et al., Chem. Commun. 2020, 56, 13133.

Keywords: NMR spectroscopy; Uranium; U(VI); Uranyl(VI); Citrate; Complex; Chirality; Diastereomers; Sandwich complex; Lewis acid-base adduct

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  • Lecture (Conference) (Online presentation)
    GDCh Jahrestagung der Fachgruppe Magnetische Resonanz (FGMR), 27.09.-01.10.2021, online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32805
Publ.-Id: 32805


Bentonite alteration in batch reactor experiments with and without fertilizing agents: implications for the disposal of radioactive waste

Podlech, C.; Matschiavelli, N.; Peltz, M.; Kluge, S.; Arnold, T.; Cherkouk, A.; Meleshyn, A.; Grathoff, G.; Warr, L. N.

Bentonite is currently proposed as a potential backfill material for sealing high-level-radioactive waste in underground repositories due to its low hydraulic conductivity, self-sealing ability and high adsorption capability. High saline pore waters, high temperatures and the influence of microbes may cause mineralogical changes and affect the long-term performance of the bentonite barrier system. In this study, long-term diffusion batch experiments were carried out at 25°C and 90°C for one and two years using two different industrial bentonites (SD80 from Greece, B36 from Slovakia) and two types of aqueous solutions, which simulated a) Opalinus clay pore water with a salinity of 19 g·L-1 and b) saline cap rock solution with a salinity of 155 g·L-1. The bentonites were supplemented with and without organic substrates to study the microbial community and their potential influence on the bentonite mineralogy. Smectite alteration was dominated by metal ion substitutions, changes in layer charge and delamination during water-clay interaction. The degree of smectite alteration and changes in the microbial diversity depended largely on the respective bentonite and the experimental condition. Thus, the low charged SD80 with 17% tetrahedral charge showed nearly no structural change, whereas B36 as a medium charged smectite with 56% tetrahedral charge became more beidellitic with increasing temperature reacted in saline cap rock solution. Based on these experiments, the alteration of the smectite is mainly attributed to the nature of the bentonite, pore water chemistry and temperature. A significant microbial influence on the here analyzed parameters was not observed within the two years of experimentation, but should not be excluded, as the detected genera are known to potentially influence geochemical processes.

Permalink: https://www.hzdr.de/publications/Publ-32803
Publ.-Id: 32803


Tailoring crystalline structure of titanium oxide films for optical applications using non-biased filtered cathodic vacuum arc deposition at room temperature

Guillén, E.; Krause, M.; Heras, I.; Rincón-Llorente, G.; Escobar-Galindo, R.

Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the O2 partial pressure (pO2), is described in detail. The composition, morphological features, crystalline structure, and optical properties of the deposited films were systematically studied by Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Raman Spectroscopy, UV-vis spectroscopy, and spectroscopic ellipsometry. This systematic investigation allowed the identification of three different groups or growth regimes according to the stoichiometry and to the phase structure of the titanium oxide films. RBS analysis revealed that a wide range of TiOx stoichiometries (0.6 < x < 2.2) were obtained, including oxygen-deficient, stoichiometric TiO2 and oxygen-rich films. TiO, Ti2O3, rutile-type TiO2, and amorphous TiO2 phase structures could be achieved, as confirmed both by Raman and XRD. Therefore the results showed a highly versatile approach, in which different titanium oxide stoichiometries and crystalline phases especially suited for diverse optical applications can be obtained by changing only two process parameters, in a process at room temperature and without applied bias. Of particular interest are crystalline rutile films with high density to be used in ultra-high reflectance metal-dielectric multilayered mirrors, and reduced-TiO2 rutile samples with absorption in the visible range as a very promising photocatalyst material.

Keywords: titanium oxide films; filtered cathodic vacuum arc; rutile; optical coatings

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Permalink: https://www.hzdr.de/publications/Publ-32800
Publ.-Id: 32800


Data publication: Detecting bacterial cell viability in few μl solutions from impedance measurements on silicon‐based biochips

Bhat, V. J.; Vegesna, S. V.; Kiani, M.; Zhao, X.; Blaschke, D.; Du, N.; Vogel, M.; Kluge, S.; Raff, J.; Hubner, U.; Skorupa, I.; Rebohle, L.; Schmidt, H.

Der Datensatz umfasst mikroskopische Bilder und Fotos zur Bestimmung der Zelldichte sowie lebender und toter Zellen inklusive Berechnungen, Protokolle und Auswertungen dazu.

Keywords: Cell viability; Dead bacterial cells; Dead bacterial cells; Impedance biochips; Live bacterial cells; Lysinibacillus sphaericus; Membrane potential

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Permalink: https://www.hzdr.de/publications/Publ-32799
Publ.-Id: 32799


Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation

Huang, L.; Li, L.; Shang, Z.; Wang, M.; Kang, J.; Luo, W.; Liang, Z.; Prucnal, S.; Kentsch, U.; Ji, Y.; Zhang, F.; Wang, Q.; Yuan, Y.; Sun, Q.; Zhou, S.; Wang, X.

We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5*10¹³ /cm² to 5*10¹⁵ /cm², the n-type dopant concentration gradually increases from 4.6*10¹⁸ /cm² to 4.5*10²⁰ /cm², while the generated vacancy density accordingly raises from 3.7*10¹³ /cm² to 3.8*10¹⁵ /cm². Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1*10¹⁵ /cm², which ceases at the overdose of 5*10¹⁵ /cm² due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.

Keywords: ion implantation; GaN; defects

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Permalink: https://www.hzdr.de/publications/Publ-32797
Publ.-Id: 32797


New insights into U(VI) sorption onto montmorillonite from batch sorption and spectroscopic studies at increased ionic strength

Stockmann, M.; Fritsch, K.; Bok, F.; Marques Fernandes, M.; Baeyens, B.; Steudtner, R.; Müller, K.; Nebelung, C.; Brendler, V.; Stumpf, T.; Schmeide, K.

The influence of ionic strength up to 3 mol/kg (background electrolytes NaCl or CaCl2) on U(VI) sorption onto montmorillonite was investigated as function of pHc in absence and presence of CO2. A multi-method approach combined batch sorption experiments with spectroscopic methods (time-resolved laser-induced fluorescence spectroscopy (TRLFS) and in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy). In the absence of atmospheric carbonate, U(VI) sorption was nearly 99% above pHc 6 in both NaCl and CaCl2 and no significant effect of ionic strength was found. At lower pH, cation exchange was strongly reduced with increasing ionic strength. In the presence of carbonate, U(VI) sorption was reduced above pHc 7.5 in NaCl and pHc 6 in CaCl2 system due to formation of aqueous UO2(CO3)x (2-2x) and Ca2UO2(CO3)3 complexes, respectively, as verified by TRLFS. A significant ionic strength effect was observed due to the formation of Ca2UO2(CO3)3 (aq), which strongly decreases U(VI) sorption with increasing ionic strength.
The joint analysis of determined sorption data together with literature data (giving a total of 213 experimental data points) allowed to derive a consistent set of surface complexation reactions and constants based on the 2SPNE SC/CE approach, yielding log K⁰ = 2.42 ± 0.04 (≡SSOUO2 +), log K⁰ = −4.49 ± 0.7 (≡SSOUO2OH), and log K⁰ = −20.5 ± 0.4 (≡SSOUO2(OH)3 2-). Ternary uranyl carbonate surface complexes were not required to describe the data. With this reduced set of surface complexes, an improved robust sorption model was obtained covering a broad variety of geochemical settings over wide ranges of ionic strengths and groundwater compositions, which subsequently was validated by an independent original dataset. This model improves the understanding of U(VI) retention by clay minerals and enables now predictive modeling of U(VI) sorption processes in complex clay rich natural environments.

Keywords: argillaceous rock; surface complexation modeling; uranium; specific ion interaction theory (SIT); ATR FT-IR; TRLFS; 2SPNE SC/CE

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Publ.-Id: 32796


Pharmacokinetic studies of [⁶⁸Ga]Ga‑PSMA‑11 in patients with biochemical recurrence of prostate cancer: detection, differences in temporal distribution and kinetic modelling by tissue type

Strauss, D. S.; Sachpekidis, C.; Kopka, K.; Pan, L.; Haberkorn, U.; Dimitrakopoulou‑Strauss, A.

Purpose: [⁶⁸Ga]Ga-PSMA-11 is a promising radiopharmaceutical for detecting tumour lesions in prostate cancer, but knowledge of the pharmacokinetics is limited. Dynamic PET-CT was performed to investigate the tumour detection and differences in temporal distribution, as well as in kinetic modelling of [⁶⁸Ga]Ga-PSMA-11 by tissue type.
Methods: Dynamic PET-CT over the lower abdomen and static whole-body PET-CT 80–90 min p.i. from 142 patients with biochemical recurrence were retrospectively analysed. Detection rates were compared to PSA levels. Average time-activity curves were calculated from tumour lesions and normal tissue. A three-compartment model and non-compartment model
were used to calculate tumour kinetics.
Results: Overall detection rate was 70.42%, and in patients with PSA > 0.4 ng/mL 76.67%. All tumour lesions presented the steepest standardised uptake value (SUV) incline in the first 7–8 min before decreasing to different degrees. Normal tissue presented with a low uptake, except for the bladder, which accumulated activity the steepest 15–16 min. p.i.. While all tumour
lesions continuously increased, bone metastases showed the steepest decline, resulting in a significantly lower SUV than lymph node metastases (60 and 80–90 min). Transport rate from the blood and tracer binding and internalisation rate were lower in bone metastases. Heterogeneity (fractal dimension) and vascular density were significantly lower in bone metastases.
Conclusion: Even at low PSA between 0.51 and 0.99 ng/mL, detection rate was 57%. Dynamic imaging showed a time window in the first 10 min where tumour uptake is high, but no bladder activity is measured, aiding accuracy in distinction of local recurrence. Kinetic modelling provided additional information for tumour characterisation by tissue type.

Keywords: Ga-PSMA; PSMA; PSMA Kinetic; Recurrent prostate cancer

Permalink: https://www.hzdr.de/publications/Publ-32794
Publ.-Id: 32794


Cation non-stoichiometry in Fe:SrTiO3 thin films and its effect on the electrical conductivity

Morgenbesser, M.; Taibl, S.; Kubicek, M.; Schmid, A.; Viernstein, A.; Bodenmüller, N.; Herzig, C.; Baiutti, F.; de Dios Sirvent, J.; Liedke, M. O.; Butterling, M.; Wagner, A.; Artner, W.; Limbeck, A.; Tarancon, A.; Fleig, J.

The interplay of structure, composition and electrical conductivity was investigated for Fe-doped SrTiO3 thin films prepared by pulsed laser deposition. Structural information was obtained by reciprocal space mapping while solution-based inductively-coupled plasma optical emission spectroscopy and positron annihilation lifetime spectroscopy were employed to reveal the cation composition and the predominant point defects of the thin films, respectively. A severe cation non-stoichiometry with Sr vacancies was found in films deposited from stoichiometric targets. The across plane electrical conductivity of such epitaxial films was studied in the temperature range of 250 - 720 °C by impedance spectroscopy. This revealed a pseudo-intrinsic electronic conductivity despite the substantial Fe acceptor doping, i.e. conductivities being several orders of magnitude lower than expected. Variation of PLD deposition parameters causes some changes of the cation stoichiometry, but the films still have conductivities much lower than expected. Targets with significant Sr excess (in the range of several percent) were employed to improve the cation stoichiometry in the films. The use of 7 % Sr-excess targets resulted in near-stoichiometric films with conductivities close to the stoichiometric bulk counterpart. The measurements show that a fine-tuning of the film stoichiometry is required in order to obtain acceptor doped SrTiO3 thin films with bulk-like properties. One can conclude that, although RSM experiments give a first hint whether or not cation non-stoichiometry is present, conductivity measurements are more appropriate for assessing SrTiO3 film quality in terms of cation stoichiometry.

Keywords: SrTiO3 thin films; pulsed laser deposition; structure-property relations; cationic non-stoichiometry; positron annihilation spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-32792
Publ.-Id: 32792


Automated mineralogy as a novel approach for the compositional and textural characterization of spent lithium-ion batteries

Vanderbruggen, A.; Gugala, E.; Blannin, R.; Bachmann, K.; Serna-Guerrero, R.; Rudolph, M.

Mechanical recycling processes aim to separate particles based on their physical properties, such as size, shape and density, and physico-chemical surface properties, such as wettability. Secondary materials, including electronic waste, are highly complex and heterogeneous, which complicates recycling processes. In order to improve recycling efficiency, characterization of both recycling process feed materials and intermediate products is crucial. Textural characteristics of particles in waste mixtures cannot be determined by conventional characterization techniques, such as X-ray fluorescence and X-ray diffraction spectroscopy. This paper presents the application of automated mineralogy as an analytical tool, capable of describing discrete particle characteristics for monitoring and diagnosis of lithium ion battery (LIB) recycling approaches. Automated mineralogy, which is well established for the analysis of primary raw materials but has not yet been tested on battery waste, enables the acquisition of textural and chemical information, such as elemental and phase composition, morphology, association and degree of liberation. For this study, a thermo-mechanically processed black mass (<1 mm fraction) from spent LIBs was characterized with automated mineralogy. Each particle was categorized based on which LIB component it comprised: Al foil, Cu foil, graphite, lithium metal oxides and alloys from casing. A more selective liberation of the anode components was achieved by thermo-mechanical treatment, in comparison to the cathode components. Therefore, automated mineralogy can provide vital information for understanding the properties of black mass particles, which determine the success of mechanical recycling processes. The introduced methodology is not limited to the presented case study and is applicable for the optimization of differentseparation unit operations in recycling of waste electronics and batteries.

Keywords: Automated mineralogy; Black mass; Characterization; Liberation; Lithium-ion batteries; Mineral processing; Recycling

Permalink: https://www.hzdr.de/publications/Publ-32791
Publ.-Id: 32791


Understanding the M₄ edge HERFD XANES of U⁶⁺

Amidani, L.; Volkova, A.; Retegan, M.; Martin, P.; Kvashnina, K.

Hexavalent uranium is of considerable importance in the actinide field, and its characterization, consequently, of fundamental concern. The application of High-Energy-Resolution Fluorescence-Detected X-ray Absorption Near-Edge Structure (HERFD XANES) at the M4 edge of actinides is gaining great popularity, as it allows to probe the 5f electronic structure with augmented resolution compared to conventional XANES, for which M4 spectra are broad and featureless. If, from one side, the extreme sensitivity of M4 HERFD XANES to actinides’ oxidation state is well-established [1], its sensitivity to the local environment has been less extensively explored [2,3]. The partially filled 5f subshell makes intra-atomic electron interactions the primary force shaping the spectrum, and simulations treating multi-electronic effects can only approximately account for the local environment.
In these regards, U6+, with its empty 5f shell, is a fortunate exceptional case. Simulation approaches based on the one-electron approximation can then be applied, and the dependence on the local environment be carefully investigated. We report here the first investigation where experimental and simulated M4 HERFD XANES are obtained on a set of U6+ compounds with different local environment. The coordination of U6+ represented by the set of samples comprises an almost perfect UO6 octahedral bipyramid (Sr3UO6), two UO6 featuring the uranyl ion (Cs2UO2Cl4 and SrUO4), and a UO8 distorted hexagonal bipyramid (CaUO4).
Experimental M4 HERFD are shown in Figure 1. The spectral shape has a similar structure, made of three or four peaks of decreasing intensity. At the same time, it presents significant differences indicating the substantial impact on the spectral shape of the local environment. We simulated the set of U6+ compounds with the DFT-based code FDMNES [4]. The good agreement between theory and experiment, see Fig. 1, makes it reasonable to have a closer look at the underlying f-density of states and to assign spectral features to specific f-orbitals.
Simulations allow to rationalize how the local coordination of U6+ affects the M4 HERFD XANES and demonstrate its high sensitivity to the local environment. Simulations based on crystal field theory were also performed. Their comparison to FDMNES results will be discussed during the conference.

  • Lecture (Conference) (Online presentation)
    Uranium Science, 29.06.-01.07.2021, University of Bristol, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-32790
Publ.-Id: 32790


Exploring the anti-site disorder and oxygen vacancies in Sr₂FeMoO₆ thin films

Saloaro, M.; Liedke, M. O.; Angervoa, I.; Butterling, M.; Hirschmann, E.; Wagner, A.; Huhtinen, H.; Paturi, P.

To address the importance of nanoscale defects in complex magnetic oxides, we present an effective tool, variable energy positron annihilation spectroscopy, for probing the relatively small changes in anti-site disorder and oxygen vacancies of the in situ annealed double perovskite Sr₂FeMoO₆ thin films. By controlling the annealing conditions in wide pressure and temperature ranges and thus affecting the amount of nanoscale defects, we show that the magnetic properties of Sr₂FeMoO₆ thin films can be modified, particularly with the oxygen nonstoichiometry, and hence their spintronic functionality can be improved. On the basis of our findings together with proposed mechanism, we suggest that the annealing treatments can also be scaled to other complex magnetic perovskites to engineer nanoscale defects and thus improve their usability in future spintronic applications.

Keywords: spintronics; SFMO; defect engineering; oxygen vacancy; positron annihilation spectroscopy; magnetic properties; anti-site disorder

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Permalink: https://www.hzdr.de/publications/Publ-32789
Publ.-Id: 32789


An Introduction to the Materials Learning Algorithms Package (MALA)

Fiedler, L.; Cangi, A.; Ellis, J. A.; Rajamanickam, S.

Density Functional Theory (DFT) is one of the most popular quantum mechanical simulation methods, since it balances sufficient accuracy with reasonable computational cost. It is often used in material science applications at ambient and extreme conditions. Nonetheless, DFT approaches its limits in terms of computational feasbility when faced with simulation problems at larger time and length scales, especially at temperatures >> 0K. Surrogate models based on neural networks can circumvent these limitations. By training a neural network to predict properties of interest (total energy, atomic forces) based on atomic configurations, predictions with DFT-like accuracy can be done at a fraction of the computational cost.
To facilitate the creation and usage of these surrogate models, the Materials Learning Algorithms package (MALA) provides modular open-source toolbox that allows users to preprocess of DFT data, train models and postprocess model predictions using only a few lines of code. MALA is jointly developed by the Center for Advanced Systems Understanding (CASUS), Sandia National Laboratories (SNL) and Oak Ridge National Laboratory (ORNL).

Keywords: Density Functional Theory; Machine Learning

Permalink: https://www.hzdr.de/publications/Publ-32788
Publ.-Id: 32788


Imaging neutron capture cross sections: i-TED proof-of-concept and future prospects based on Machine-Learning techniques.

Babiano-Suárez, V.; Lerendegui-Marco, J.; Balibrea-Correa, J.; Caballero, L.; Calvo, D.; Ladarescu, I.; Real, D.; Domingo-Pardo, C.; Calviño, F.; Casanovas, A.; Tarifeño-Saldivia, A.; Alcayne, V.; Guerrero, C.; Millán-Callado, M. A.; Rodriguez-González, T.; Barbagallo, M.; Aberle, O.; Amaducci, S.; Andrzejewski, J.; Audouin, L.; Bacak, M.; Bennett, S.; Berthoumieux, E.; Billowes, J.; Bosnar, D.; Brown, A.; Busso, M.; Caamaño, M.; Calviani, M.; Cano-Ott, D.; Cerutti, F.; Chiaveri, E.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Cosentino, L.; Cristallo, S.; Damone, L. A.; Davies, P. J.; Diakaki, M.; Dietz, M.; Dressler, R.; Ducasse, Q.; Dupont, E.; Durán, I.; Eleme, Z.; Fernández-Dominguez, B.; Ferrari, A.; Finocchiaro, P.; Furman, V.; Göbel, K.; Garg, R.; Gawlik, A.; Gilardoni, S.; Gonçalves, I. F.; González-Romero, E.; Gunsing, F.; Harada, H.; Heinitz, S.; Heyse, J.; Jenkins, D. G.; Junghans, A.; Käppeler, F.; Kadi, Y.; Kimura, A.; Knapova, I.; Kokkoris, M.; Kopatch, Y.; Krtička, M.; Kurtulgil, D.; Lederer-Woods, C.; Leeb, H.; Lonsdale, S. J.; Macina, D.; Manna, A.; Martinez, T.; Masi, A.; Massimi, C.; Mastinu, P.; Mastromarco, M.; Maugeri, E. A.; Mazzone, A.; Mendoza, E.; Mengoni, A.; Michalopoulou, V.; Milazzo, P. M.; Mingrone, F.; Moreno-Soto, J.; Musumarra, A.; Negret, A.; Ogállar, F.; Oprea, A.; Patronis, N.; Pavlik, A.; Perkowski, J.; Persanti, L.; Petrone, C.; Pirovano, E.; Porras, I.; Praena, J.; Quesada, J. M.; Ramos-Doval, D.; Rauscher, T.; Reifarth, R.; Rochman, D.; Rubbia, C.; Sabaté-Gilarte, M.; Saxena, A.; Schillebeeckx, P.; Schumann, D.; Sekhar, A.; Smith, A. G.; Sosnin, N. V.; Sprung, P.; Stamatopoulos, A.; Tagliente, G.; Tain, J. L.; Tassan-Got, L.; Thomas, T.; Torres-Sánchez, P.; Tsinganis, A.; Ulrich, J.; Urlaß, S.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vescovi, D.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Woods, P. J.; Wright, T.; Žugec, P.

i-TED is an innovative detection system which exploits Compton imaging techniques to achieve a superior signal-to-background ratio in (n, γ ) cross-section measurements using time-of-flight technique. This work presents the first experimental validation of the i-TED apparatus for highresolution time-of-flight experiments and demonstrates for the first time the concept proposed for background rejection. To this aim, the 197 Au(n, γ ) and 56 Fe(n, γ ) reactions were studied at CERN n_TOF using an i-TED demonstrator based on three position-sensitive detectors. Two C6 D6 detectors were also used to benchmark the performance of i-TED. The i-TED prototype built for this study shows a factor of ∼3 higher detection sensitivity than state-of-the-art C6 D6 detectors in the 10 keV neutron-energy region of astrophysical interest. This paper explores also the perspectives of further enhancement in performance attainable with the final i-TED array consisting of twenty position-sensitive detectors and new analysis methodologies based on Machine-Learning techniques.

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Publ.-Id: 32787


First Results of the 140Ce(n,gamma)141Ce Cross-Section Measurement at n_TOF

Amaducci, S.; Colonna, N.; Cosentino, L.; Cristallo, S.; Finocchiaro, P.; Krtička, M.; Massimi, C.; Mastromarco, M.; Mazzone, A.; Mengoni, A.; Valenta, S.; Aberle, O.; Alcayne, V.; Andrzejewski, J.; Audouin, L.; Babiano-Suarez, V.; Bacak, M.; Barbagallo, M.; Bennett, S.; Berthoumieux, E.; Billowes, J.; Bosnar, D.; Brown, A.; Busso, M.; Caamaño, M.; Caballero-Ontanaya, L.; Calviño, F.; Calviani, M.; Cano-Ott, D.; Casanovas, A.; Cerutti, F.; Chiaveri, E.; Cortés, G.; Cortés-Giraldo, M.; Damone, L.-A.; Davies, P.-J.; Diakaki, M.; Dietz, M.; Domingo-Pardo, C.; Dressler, R.; Ducasse, Q.; Dupont, E.; Durán, I.; Eleme, Z.; Fernández-Dominguez, B.; Ferrari, A.; Furman, V.; Göbel, K.; Garg, R.; Gawlik, A.; Gilardoni, S.; Gonçalves, I.; González-Romero, E.; Guerrero, C.; Gunsing, F.; Harada, H.; Heinitz, S.; Heyse, J.; Jenkins, D.; Junghans, A.; Käppeler, F.; Kadi, Y.; Kimura, A.; Knapova, I.; Kokkoris, M.; Kopatch, Y.; Kurtulgil, D.; Ladarescu, I.; Lederer-Woods, C.; Leeb, H.; Lerendegui-Marco, J.; Lonsdale, S.-J.; Macina, D.; Manna, A.; Martinez, T.; Masi, A.; Mastinu, P.; Maugeri, E.-A.; Mendoza, E.; Michalopoulou, V.; Milazzo, P.; Mingrone, F.; Moreno-Soto, J.; Musumarra, A.; Negret, A.; Ogállar, F.; Oprea, A.; Patronis, N.; Pavlik, A.; Perkowski, J.; Piersanti, L.; Petrone, C.; Pirovano, E.; Porras, I.; Praena, J.; Quesada, J.-M.; Ramos-Doval, D.; Rauscher, T.; Reifarth, R.; Rochman, D.; Rubbia, C.; Sabaté-Gilarte, M.; Saxena, A.; Schillebeeckx, P.; Schumann, D.; Sekhar, A.; Smith, G.; Sosnin, N.; Sprung, P.; Stamatopoulos, A.; Tagliente, G.; Tain, J.; Tarifeño-Saldivia, A.; Tassan-Got, L.; Thomas, B.; Torres-Sánchez, P.; Tsinganis, A.; Ulrich, J.; Urlaß, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vescovi, D.; Vlachoudis, V.; Vlastou, R.; Wallner, A.; Woods, P.; Wright, T.; Žugec, P.

An accurate measurement of the 140Ce(n,g) energy-dependent cross-section was performed
at the n_TOF facility at CERN. This cross-section is of great importance because it represents a
bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in
stars. The measurement was motivated by the significant difference between the cerium abundance
measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy
can be ascribed to an overestimation of the 140Ce capture cross-section due to a lack of accurate
nuclear data. For this measurement, we used a sample of cerium oxide enriched in 140Ce to 99.4%.
The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which
allowed us to overcome the difficulties present in the previous measurements, thanks to their very
low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their
average parameters are fundamental to improve the evaluation of the 140Ce Maxwellian-averaged
cross-section.

Keywords: cerium; 140Ce; neutron capture; cross-section; n_TOF; MACS; nucleosynthesis

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Permalink: https://www.hzdr.de/publications/Publ-32785
Publ.-Id: 32785


Time evolution of Molecular Binding in Mechanically controlled Break-Junctions

Lokamani, M.; Günther, F.; Kilibarda, F.; Kelling, J.; Gemming, S.; Erbe, A.

Mechanically controllable break junctions (MCBJs) are devices, in which the electrical properties of single molecules can be investigated with extreme precision using atomically structured metallic electrodes. The current-voltage (IV) characteristics in such junctions are considerably affected by the binding positions of the anchoring groups on the tip-facets and the configuration of the molecule. Hence, characterizing the electronic transport properties during a single tip-tip opening provides interesting insights in to the tip-molecule interaction.
In this contribution/poster, we present a novel, high-throughput approach to reproduce the time evolution of the electronic transport characteristics. For this, we performed transport calculations using the self-consistent charge scheme of the density-functional-based tight binding (SCC-DFTB)[1] approach and the Green’s function formalism. In particular, we evaluated the energy level E0 and the coupling Γ of the dominating transport channel using the single level model[2]. In contrast to standard approaches, we consider not just one molecule orientation but many thermodynamically relevant configurations. The obtained parameters were averaged using statistical weights obtained from Metropolis simulation considering up to 80.000 different configurations for selected tip-tip distances. The dependence of the averaged quantities with respect to the tip-tip separation reveals characteristic features also observed in experiments for similar molecular systems.
Our approach allows us to relate these features to binding-site and molecule-curvature effects and therefore provides a better interpretation of the experimental results.

1. M. Elstner, D. Porezag, G. Jungnickel, J. Elsner, M. Haugk, T. Frauenheim, S. Suhai, and G. Seifert, Self-consistent-charge density-functional tight-binding method for simulations of complex materials properties, Phys. Rev. B 58, 7260 (1998)
2. Cuevas, J. C.; Scheer, E. In Molecular Electronics: An Introduction to Theory and Experiment; Reed, M., Ed.; World Scientific Series in Nanoscience and Nanotechnology, Vol. 1; World Scientific: Singapore,Hackensack, NJ, 201

Keywords: mechanically controlled break junctions; high-throughput simulations; density-functional-based tight binding; Salen; PEEB; single-level-model

  • Open Access Logo Poster (Online presentation)
    Nanotech France 2021 The 6th ed. of Nanotech France 2021 Int. Conference and Exhibition, 23.-25.06.2021, Paris, France

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Permalink: https://www.hzdr.de/publications/Publ-32783
Publ.-Id: 32783


Detecting bacterial cell viability in few μl solutions from impedance measurements on silicon‐based biochips

Bhat, V. J.; Vegesna, S. V.; Kiani, M.; Zhao, X.; Blaschke, D.; Du, N.; Vogel, M.; Kluge, S.; Raff, J.; Hubner, U.; Skorupa, I.; Rebohle, L.; Schmidt, H.

Using two different types of impedance biochips (PS5 and BS5) with ring top electrodes, a distinct change of measured impedance has been detected after adding 1–5 μL (with dead or live Gram‐positive Lysinibacillus sphaericus JG‐A12 cells to 20 μL DI water inside the ring top electrode. We relate observed change of measured impedance to change of membrane potential of L. sphaericus JG‐A12 cells. In contrast to impedance measurements, optical density (OD) measurements cannot be used to distinguish between dead and live cells. Dead L. sphaericus JG‐A12 cells have been obtained by adding 0.02 mg/mL of the antibiotics tetracycline and 0.1 mg/mL chloramphenicol to a batch with OD0.5 and by incubation for 24 h, 30 °C, 120 rpm in the dark. For impedance measurements, we have used batches with a cell density of 25.5 × 10⁸ cells/mL (OD8.5) and 270.0 × 10⁸ cells/mL (OD90.0). The impedance biochip PS5 can be used to detect the more resistive and less capacitive live L. sphaericus JG‐A12 cells. Also, the impedance biochip BS5 can be used to detect the less resistive and more capacitive dead L. sphaericus JG‐A12 cells. An outlook on the application of the impedance biochips for high‐throughput drug screening, e.g., against multi‐drug‐resistant Gram‐positive bacteria, is given.

Keywords: Cell viability; Dead bacterial cells; Dead bacterial cells; Impedance biochips; Live bacterial cells; Lysinibacillus sphaericus; Membrane potential

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Permalink: https://www.hzdr.de/publications/Publ-32782
Publ.-Id: 32782


Data publication: Creep Properties of 9Cr and 14Cr ODS Tubes Tested by Inner Gas Pressure

Sornin, D.; Ehrnsten, U.; Mozzani, N.; Rantala, J.; Walter, M.; Hobt, A.; Aktaa, J.; Onorbe, E.; Hernandez-Mayoral, M.; Ulbricht, A.; Gicquel, S.; Frank, L.; de Carlan, Y.

Skript Messdata Online ILL data’’ https://doi.ill.fr/10.5291/ILL-DATA.1-01-146. 2015.

Keywords: ODS steel; Tube creep test; Inner gas pressure

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Permalink: https://www.hzdr.de/publications/Publ-32780
Publ.-Id: 32780


Creep Properties of 9Cr and 14Cr ODS Tubes Tested by Inner Gas Pressure

Sornin, D.; Ehrnsten, U.; Mozzani, N.; Rantala, J.; Walter, M.; Hobt, A.; Aktaa, J.; Onorbe, E.; Hernandez-Mayoral, M.; Ulbricht, A.; Gicquel, S.; Frank, L.; de Carlan, Y.

Oxide-dispersion strengthened steels are promising materials for extreme service conditions including nuclear reactors core. In service conditions, nuclear fuel claddings are exposed to the fission gas pressure at temperatures about 700°C. This paper presents novel results on ODS creep properties from a round robin of inner gas pressure creep test. A gas pressure creep test, simulating fission gas loading, was designed and achieved by four different European teams. Lifetime and specific behavior of ODS steel tube are prospected. Based on a mechanical clamping achieving gas tightness, short length tubes samples are tested by different laboratories. In situ laser measurements exhibit the radial expansion of ODS steel tubes before failure. Post-mortem, geometrical characterizations are performed to determine hoop strains at failure. A consistent creep lifetime is observed by all the teams even with slightly different testing apparatus and clamping systems. Under inner gas pressure, ODS steels exhibit a typical failure by leakage associated to a very small radial expansion. This behavior results from a brutal failure (burst) without evidence of tertiary creep stage. This failure mode of ODS cladding in creep conditions is consistently observed on all samples of the study. Inner gas pressure creep tests were compared, for the first time, by four European laboratories on ODS steel tube. This technique, simulating the fission gas pressure loading, is applied on small and mechanically clamped samples. This technique shows a remarkable consistency between the different laboratories results and demonstrates to be efficient for ODS steel cladding tube qualification. The results show a correlation between the creep properties and the microstructure.

Keywords: ODS steel; Tube creep test; Inner gas pressure

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Permalink: https://www.hzdr.de/publications/Publ-32777
Publ.-Id: 32777


Mechanically flexible magnetoelectronics for human-machine interfaces and soft robotics

Makarov, D.

In this presentation I review our activities on flexible, printable and stretchable functional elements for human-machine interfaces, interactive electronics, soft robotics and cancer research.

Keywords: flexible magnetic field sensors; printable magentic field sensors; flexible heater

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  • Invited lecture (Conferences) (Online presentation)
    International School on Programmable Smart Sensors based on Bio-compatible Nanocomposite Materials (NanoSens), 17.-24.06.2021, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-32775
Publ.-Id: 32775


Does the uncertainty in relative biological effectiveness affect patient treatment in proton therapy?

Sørensen, B. S.; Pawelke, J.; Bauer, J.; Burnet, N. G.; Dasu, A.; Høyer, M.; Karger, C. P.; Krause, M.; Schwarz, M.; Underwood, T. S. A.; Wagenaar, D.; Whitfield, G.; Lühr, A.

Clinical treatment with protons relies on the concept of relative biological effectiveness (RBE) to convert the absorbed dose into an RBE-weighted dose that equals the dose for radiotherapy with photons causing the same biological effect. Currently, in proton therapy a constant RBE of 1.1 is generically used. However, empirical data indicate that the RBE is not constant, but increases at the distal edge of the proton beam. This increase in RBE is of concern, as the clinical impact is still unresolved, and clinical studies demonstrating a clinical effect of an increased RBE are emerging.
Within the European Particle Therapy Network (EPTN) work package 6 on radiobiology and RBE, a workshop was held in February 2020 in Manchester with one day of discussion dedicated to the impact of proton RBE in a clinical context. Current data on RBE effects, patient outcome and modelling from experimental as well as clinical studies were presented and discussed. Furthermore, representatives from European clinical proton therapy centres, who were involved in patient treatment, laid out their current clinical practice on how to consider the risk of a variable RBE in their centres. In line with the workshop, this work considers the actual impact of RBE issues on patient care in proton therapy by reviewing preclinical data on the relation between linear energy transfer (LET) and RBE, current clinical data sets on RBE effects in patients, and applied clinical strategies to manage RBE uncertainties. A better understanding of the variability in RBE would allow development of proton treatments which are safer and more effective.

Keywords: proton therapy; relative biological effectiveness (RBE)

Permalink: https://www.hzdr.de/publications/Publ-32773
Publ.-Id: 32773


Self-discharge mitigation in a liquid metal displacement battery

Mushtaq, K.; Zhao, J.; Weber, N.; Mendes, A.; Sadoway, D. R.

Recently, a disruptive idea was reported about the discovery of a new type of battery named Liquid Displacement Battery (LDB) comprising liquid metal electrodes and molten salt electrolyte. This cell featured a novel concept of a porous electronically conductive faradaic membrane instead of the traditional ion-selective ceramic membrane. LDBs are attractive for stationary storage applications but need mitigation against self-discharge. In the instant battery chemistry, Li|LiCl-PbCl2|Pb, reducing the diffusion coefficient of lead ions can be a way forward and a solution can be the addition of PbO to the electrolyte. The latter acts as a supplementary barrier and complements the function of the faradaic membrane. The remedial actions improved the cell’s coulombic efficiency from 92% to 97% without affecting the voltage efficiency. In addition, the limiting current density of a 500 mAh cell increased from 575 to 831 mA/cm² and the limiting power from 2.53 to 3.66 W. Finally, the effect of PbO on the impedance and polarization of the cell was also studied.

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Permalink: https://www.hzdr.de/publications/Publ-32771
Publ.-Id: 32771


First direct limit on the 334 keV resonance strength in 22Ne(α,γ)26Mg reaction

Piatti, D.; Masha, E.; Aliotta, M.; Balibrea-Correa, J.; Barile, F.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Compagnucci, A.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Prati, P.; Rapagnani, D.; Schiavulli, L.; Skowronski, J.; Stöckel, K.; Straniero, O.; Szücs, T.; Takacs, M. P.; Zavatarelli, S.

In stars, the fusion of 22Ne and 4He may produce either 25Mg, with the emission of a neutron, or 26Mg and a γ ray. At high temperature, the (α,n) channel dominates, while at low temperature, it is energetically hampered. The rate of its competitor, the 22Ne(α,γ)26Mg reaction, and, hence, the minimum temperature for the (α,n) dominance, are controlled by many nuclear resonances. The strengths of these resonances have hitherto been studied only indirectly. The present work aims to directly measure the total strength of the resonance at E_{r}=334keV (corresponding to E_{x}=10949keV in 26Mg). The data reported here have been obtained using high intensity 4He+ beam from the INFN LUNA 400 kV underground accelerator, a windowless, recirculating, 99.9% isotopically enriched 22Ne gas target, and a 4π bismuth germanate summing γ-ray detector. The ultra-low background rate of less than 0.5 counts/day was determined using 67 days of no-beam data and 7 days of 4He+ beam on an inert argon target. The new high-sensitivity setup allowed to determine the first direct upper limit of 4.0×10−11 eV (at 90% confidence level) for the resonance strength. Finally, the sensitivity of this setup paves the way to study further 22Ne(α,γ)26Mg resonances at higher energy.

Keywords: Nuclear reactions; Nucleosynthesis; abundances – Stars: AGB and post-AGB

Permalink: https://www.hzdr.de/publications/Publ-32770
Publ.-Id: 32770


Nachhaltiges Bauen in der Praxis: Bestandserhalt und ökologische Sanierung

Dirlich, S.; Schweiker, K.

Nachhaltiges Bauen ist immer noch eine Nische im Baubereich, obwohl es zahlreiche Vorteile bietet. Mittlerweile wünscht sich auch die Präsidentin der EU-Kommission zur Umsetzung des „Green Deals“ einen Aufbruch auch im Baubereich, der als „New European Bauhaus“ bezeichnet wird in Anlehnung an die Ideen des Bauhauses im 20. Jahrhundert. Auch der Bund Deutscher Architekten (BDA) fordert in seinem Manifest zum klimagerechten Bauen aus dem Jahr 2020 eine Abkehr vom konventionellen Bauen und schlägt eine Reihe von Maßnahmen zu dessen Umsetzung vor, so u. a. „Achtung des Bestands“, „einfach intelligent“ oder „vollständige Entkarbonisierung“.
Beim nachhaltigen Bauen geht es u. a. darum, den gesamten genutzten Wohnraum zu reduzieren, möglichst natürliche und regionale Baustoffe mit geringem Energieinhalt zu nutzen, eine zukunftsfähige Medienversorgung einzusetzen und klimaangepasst zu bauen, also den Bedingungen, die das Klima vorgibt, mit architektonischen statt ingenieurtechnischen Lösungen zu begegnen. Eine Möglichkeit, auf diese Anforderungen einzugehen, besteht im traditionellen Bauen und der Übertragung auf zukunftsfähiges Bauen. Traditionelles Bauen kann als ein Vorbild dienen, um nachhaltig und klimagerecht zu bauen. In früheren Zeiten wurde so gebaut, wie es die regionalen Baustoffe hergaben und die klimatischen Verhältnisse erforderten. Einerseits können in den tropischen Klimazonen Häuser errichtet werden, die den lokal vorhandenen Gegebenheiten gerecht werden und den Menschen trotz der oftmals großen Hitze einigermaßen angenehme Wohnverhältnisse ermöglichen. Andererseits können in den arktischen Gebieten Menschen durch die geschickte Ausnutzung von Bauprinzipien bei eisigen Temperaturen für akzeptable Wärme in den eigenen Wänden zu sorgen. Dabei kann gerade Holz als sehr variabler und in vielfältigen Bereichen einsetzbarer Baustoff dienen, der mittlerweile auch in den Bauordnungen der Länder stärker anerkannt wird. Holz ist zudem noch eine Kohlenstoffsenke und hat insbesondere im Gegensatz zu sehr CO2-intensiven Bauprodukten auf Zementbasis wie Beton große Vorteile bezüglich der Klimarelevanz. In Verbindung mit dem ebenfalls traditionellen Baumaterial Lehm können regionale Rohstoffe genutzt werden, die sich darüber hinaus gut ergänzen und nicht zuletzt auch hohen ästhetischen Ansprüchen genügen.
In der Praxis setzt die Umsetzung nachhaltiger Bauprinzipien oftmals den Willen der Bauherren ebenso voraus wie die Erfahrungen der Bauplanerin/des Bauplaners mit nachhaltigem Bauen. Wenn beides gegeben ist, wie bei der Sanierung einer Doppelhaushälfte in einer Siedlung in Dresden-Reick, kann Wohnraum entstehen, der sowohl aus architektonischer als auch ökologischer Sicht überzeugend ist. Im Verlauf des Bauprozesses mussten teilweise auch die Handwerker überzeugt werden, da die bauseitigen Lösungen beim Einsatz ökologischer Materialien und Bauprinzipien nicht immer mit der konventionellen Herangehensweise zu erzielen sind. Durch entsprechende intensive Absprachen mit den betreffenden Handwerkern konnte aber immer eine überzeugende Lösung erreicht werden und dadurch konnten zudem beide Seiten voneinander lernen.

Keywords: Nachhaltiges Bauen; sustainable building; Bestandserhalt; preservation of existing buildings

  • Book chapter
    Leal Filho, Walter: Theorie und Praxis der Nachhaltigkeit, Berlin: Springer Spektrum, 2022, 9783631871645

Permalink: https://www.hzdr.de/publications/Publ-32769
Publ.-Id: 32769


Nachhaltige Ressourcengewinnung aus Haldenmaterial

Dirlich, S.; Büttner, P.

Die Bergbauindustrie verursacht beim Abbau von Rohstoffen große Umweltauswirkungen. Allerdings sind moderne Industriegesellschaften ohne die Gewinnung von Rohstoffen nicht denkbar. Hochtechnologie und insbesondere auch Umwelttechnologien benötigen in der Herstellung in nicht unerheblichem Maße Metalle und Minerale wie Kupfer, Indium, Lithium, Gallium, Germanium aber auch Seltene Erden und viele weitere Elemente. Die Hinterlassenschaften des Bergbaus in Form von Halden, die fortwährend bei der Rohstoffgewinnung entstehen, sorgen aber für extreme Umweltbelastungen und enthalten zudem noch immer zahlreiche Wertminerale in oft recht hohen Konzentrationen. Diese können durch verschiedene physikalische, chemische und/oder biotechnologische Aufbereitungsverfahren rückgewonnen werden. Solche Technologien sind aus den folgenden Gründen als nachhaltig zu bezeichnen.
Durch die (erneute) Aufbereitung des Haldenmaterials, bei der eine bessere Ressourcennutzung erzielt wird, lässt sich die Ressourceneffizienz erhöhen. Insbesondere Halden, die vor längerer Zeit entstanden sind, enthalten noch beträchtliche Konzentrationen an wertvollen Stoffen mit wirtschaftlicher Bedeutung. Diese aus den Halden zu gewinnen bedeutet damit, dass insgesamt weniger primärer Rohstoffe aus dem Boden gewonnen werden müssen.
Neben der Rohstoffgewinnung hat die Behandlung des Haldenmaterials auch noch zum Ziel, die potenziellen Schadstoffemissionen und anderen Umweltwirkungen zu vermindern. Teilweise kommen dabei die gleichen Verfahren zum Zuge wie bei der Gewinnung der Wertminerale. Die Sanierung solcher Bergbauhinterlassenschaften ist in vielen Fällen gesetzlich vorgeschrieben und zudem sind in den vergangenen Jahrzehnten weltweit zahlreiche katastrophale Unfälle mit Halden vorgefallen, so dass eine Haldensanierung in vielen Fällen sowieso betrieben werden muss.
Aus wirtschaftlicher Sicht ist dabei aber zu beachten, dass die Rohstoffgewinnung in aller Regel nur als eine zusätzliche Einnahmequelle dienen kann, um einen Teil der Kosten für die Haldensanierung zu decken. Theoretische Annahmen zeigen regelmäßig, dass die in den Haldenvolumina enthaltenen Wertstoffkonzentrationen zwar durchaus relevante Größenordnungen erreichen, diese aber bei genauerer Betrachtung insbesondere der Gegenrechnung der Kosten für die erforderlichen Verfahrensschritte standhalten müssen, so dass in vielen Fällen letztendlich – wenn überhaupt – ein Nullsummenspiel gegeben ist.
Am Helmholtz-Institut Freiberg wurde und wird in zahlreichen Projekten an entsprechenden Verfahren geforscht. Darüber hinaus koordiniert das HIF ein großes regionales Netzwerk (recomine), das sich den Bergbaualtlasten an der Schnittstelle von Umwelttechnologie, Ressourcentechnologie und Digitalisierung widmet und unter dessen Schirm Lösungen entwickelt werden, die regional getestet und weiterentwickelt, letztlich auf dem Weltmarkt angeboten werden sollen.

Keywords: remining; Ressourcentechnologie; Nachhaltigkeit; Haldensanierung

  • Book chapter
    Leal Filho, Walter: Theorie und Praxis der Nachhaltigkeit, Berlin: Springer Spektrum, 2022, 9783631871645

Permalink: https://www.hzdr.de/publications/Publ-32768
Publ.-Id: 32768


Nonreciprocity of spin waves in magnetic nanotubes with helical equilibrium magnetization

Salazar-Cardona, M. M.; Körber, L.; Schultheiß, H.; Lenz, K.; Thomas, A.; Nielsch, K.; Kakay, A.; Otálora, J. A.

Spin waves (SWs) in magnetic nanotubes have shown interesting nonreciprocal properties in their dispersion relation, group velocity, frequency linewidth, and attenuation lengths. The reported chiral effects are similar to those induced by the Dzyaloshinskii–Moriya interaction but originating from the dipole–dipole interaction. Here, we show that the isotropic-exchange interaction can also induce chiral effects in the SW transport; the so-called Berry phase of SWs. We demonstrate that with the application of magnetic fields, the nonreciprocity of the different SW modes can be tuned between the fully dipolar governed and the fully exchange governed cases, as they are directly related to the underlying equilibrium state. In the helical state, due to the combined action of the two effects, every single sign combination of the azimuthal and axial wave vectors leads to different dispersions, allowing for a very sophisticated tuning of the SW transport. A disentangle- ment of the dipole–dipole and exchange contributions so far was not reported for the SW transport in nanotubes. Furthermore, we propose a device based on coplanar waveguides that would allow to selectively measure the exchange or dipole induced SW nonreciprocities. In the context of magnonic applications, our results might encourage further developments in the emerging field of 3D magnonic devices using curved magnetic membranes.

Keywords: spin wave; nanotube; nonreciprocity; transducer

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Permalink: https://www.hzdr.de/publications/Publ-32767
Publ.-Id: 32767


Structured membrane formation via biopolymer-surfactant coacervation

Schwarzenberger, K.; Keshavarzi, B.; Stergiou, Y.; Javadi, A.; Eckert, K.

Coacervation can yield membranes with different permeabilities, making it attractive for technological applications in encapsulation or separation processes. During coacervation, oppositely charged species like polymers and surfactants form complexes due to coulombic attraction. These polymer-surfactant complexes are insoluble in the aqueous phase leading to phase separation. As a result, a structured membrane can form in the contact zone between a polymer and a surfactant solution. However, the details of the structure formation processes are only poorly understood.
In this study, we use a combination of the anionic biopolymer xanthan gum and cationic CnTAB surfactants. The quasi 2D-geometry of the Hele-Shaw cell allows us to observe the membrane formation and the growth dynamics in-situ. By this, we can link the membrane properties for different surfactant types and concentrations to the underlying mass transfer and structure formation processes.
The results show that the density and permeability of the formed membrane significantly depend on surfactant chain length and concentration. In a wide range of experiments, the formation of a porous structure is observed whose characteristics depend on the process parameters. The pore formation can be explained as instability of the growing membrane surface in interaction with the supply of polymer across the depleted zone in the vicinity of the membrane front. Our insights provide the basis to control membrane thickness, density, porosity and pore structure. These properties are essential for technological applications since they determine the selectivity, permeability and mechanical stability of the membrane.

  • Lecture (Conference)
    ECIS 2021, 06.-10.09.2021, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-32766
Publ.-Id: 32766


Comparative therapeutic exploitability of acute adaptation mechanisms to photon and proton irradiation in 3d head and neck squamous cell carcinoma cell cultures

Meerz, A.; Deville, S. S.; Muller, J.; Cordes, N.

For better tumor control, high-precision proton beam radiation therapy is currently being intensively discussed relative to conventional photon therapy. Here, we assumed that radiation type-specific molecular response profiles in more physiological 3D, matrix-based head and neck squamous cell carcinoma (HNSCC) cell cultures can be identified and therapeutically exploited. While proton irradiation revealed superimposable clonogenic survival and residual DNA double strand breaks (DSB) relative to photon irradiation, kinome profiles showed quantitative differences between both irradiation types. Pharmacological inhibition of a subset of radiation-induced kinases, predominantly belonging to the mitogen-activated protein kinase (MAPK) family, failed to sensitize HNSCC cells to either proton or photon irradiation. Likewise, inhibitors for ATM, DNA-PK and PARP did not discriminate between proton and photon irradiation but generally elicited a radio-sensitization. Conclusively, our results suggest marginal cell line-specific differences in the radio-sensitivity and DSB repair without a superiority of one radiation type over the other in 3D grown HNSCC cell cultures. Importantly, radiation-induced activity changes of cytoplasmic kinases induced during the first, acute phase of the cellular radiation response could neither be exploited for sensitization of HNSCC cells to photon nor proton irradiation.

Keywords: 3D cell culture; HNSCC; Molecular targeting; Photon irradiation; Proton beam irradiation

Permalink: https://www.hzdr.de/publications/Publ-32765
Publ.-Id: 32765


An introduction to Automatic Differentiation with theory and code examples.

Schmerler, S.

An introduction to Automatic Differentiation with theory and code examples.

Permalink: https://www.hzdr.de/publications/Publ-32764
Publ.-Id: 32764


Solubility of thorium in 14%Y-stabilized zirconia

Svitlyk, V.; Weiß, S.; Hennig, C.

Y-stabilized zirconia (YSZ) is one of the reference materials for immobilization of actinide elements for long-term and secure storage of radioactive waste. YSZ adapts different structural modifications, namely monoclinic, tetragonal (unstable) and cubic. Changes in relative Y content and synthesis temperature can be used to obtained specific structural form. However, for an intermediate Y content of ~5-17 at. % a mixture of cubic and unstable tetragonal modifications can form thus compromising corresponding long-term structural integrity. Nevertheless, for this Y concentration range a stabilized tetragonal (t′) phase can be obtained through a rapid quenching of the parent cubic modification. In this work we report studies of solubility of Th in 14%Y- stabilized (t′) zirconia phase.
Series of 14%Y-ZrO2 compounds with Th at. % content of 3, 6, 9 and 12 were synthesized by sol-gel method using salts of Zr(IV), Y(III) and Th(IV) as starting materials with a final sintering temperature of 1400 K. Subsequent powder X-ray diffraction measurements were performed in order to study underlying phase and structural evolutions. It was found that the cell parameters increase nearly linearly for the Th content from 3 to 9% and no cell increase is observed for the end-member with 12%Th. Additionally, ThO2 was found to precipitate in this sample. This may indicate that Th solubility limit in the 14%Y-ZrO2 system lies within the 9-12% range. Interestingly, Th content was reported to exceed 15% for the 25%Y-ZrO2 system, as concluded from electron microscopy data. This sample, however, was found to be 25%Y-ZrO2–ThO2 phase separated. Considering that in the current study traces of ThO2 have been found already in the 9%Th sample, conditions of thermal treatment with the resulting phase equilibria may impact the Th solubility. Further details on structural and phase properties in the Th-14%Y-ZrO2 system will be presented.

Related publications

  • Poster (Online presentation)
    MRS 2021 – 45th Scientific Basis for Nuclear Waste Management (SBNWM), 25.-28.10.2021, Juelich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32763
Publ.-Id: 32763


Electrostatic and (electro-)steric stabilization of colloidal particles by natural organic matter

Uygan, S. S. S.; Lippold, H.; Schymura, S.

Natural organic matter, such as humic and fulvic acids play a major role in the mobility of contaminants in the environment including radionuclides and nanoparticles formed by them. Humic and fulvic acids may act as stabilizers, i.e. natural surfactants, for colloids, thereby increasing their stability and mobility in the Geo- and Biosphere. This stabilization of colloidal matter is caused by three basic mechanisms: (1) electrostatic stabilization, (2) electrosteric stabilization and (3) steric stabilization. These mechanisms can contribute to different degrees to the stabilization of particulate contaminants by natural organic matter in colloidal dispersion and also influence their interactions with mineral surfaces. In order to understand the different contributions controlled homoaggregation studies on monodisperse nanoparticles have been performed using model stabilizers, such as ionic surfactants and polymers. These model scenarios allowed us to isolate electrostatic and steric components in aggregation studies using dynamic light scattering. By comparing these results to systems with different humic and fulvic acids we can elucidate which components control the stabilization of colloidal contaminants by natural organic matter.

Keywords: nanoparticles; natural organic matter; colloidal stability

  • Lecture (Conference) (Online presentation)
    Goldschmidt 2021, 04.-09.07.2021, Lyon, France

Permalink: https://www.hzdr.de/publications/Publ-32762
Publ.-Id: 32762


Taxonomic and Metabolic Profiling for Microbial Communities in Opalinus Clay Rocks from Deep Subsurface Biosphere

Wei, T.-S.; Kluge, S.; Schleicher, A.; Des Los Rios, A.; Cherkouk, A.

Background: Microorganisms in deep terrestrial subsurface harbor unique metabolic traits due to insufficient sunlight, oxygen and organic carbons. Previous studies reported that in the porewaters from boreholes of Opalinus clay rocks under a deep geological repository (DGR), autotrophoic H2-oxidizing sulfate-reducing bacteria (SRB)—Peptococcaceae, Desulfatialea and Desulfobulbaceae—together with other heterotrophic and fermentative bacteria were able to alleviate the H2 pressure accumulated from the process during anoxic corrosion of steel containers for nuclear wastes. Objective and Method: What remains elusive is whether these microorganisms are porewater- or rock-origin. Thus, we re-analyzed the above-mentioned porewater communities based on the amplicon sequence variant (ASV) instead of operational taxonomic unit clustering. In addition, two cores of Opalinus rocks were collected in November of 2019. The extracted DNA/RNA from these rock samples will be subjected to 16S amplicon sequencing, metagenome and metatransctriptome to investigate microbial diversity and metabolisms; microbial colonization will also be examined via scanning electron microscopy. Result: Our principal coordinates analysis indicated that the community structure of original porewaters between different boreholes were significantly distinct in the same DGR site. Moreover, the chao1 diversity index suggested that some rare biosphere may thrive in the H2-spiked communities. The differential analysis further showed that up to 213 ASVs were significantly enriched in the H2-injected porewater communities, mainly belonging to Proteobacteria, Firmicutes, Desulfobacterota, and Bacteroidota. This ASV-resolute analysis indicated that bacteria involved in this microbial loop is more complex than previously appreciated. Besides, the preliminary results showed the DNA content of newly collected Opalinus rocks was extremely low based on Qubit quantification (0.57 ± 0.07 to 0.61 ± 0.04 ng/g of clay), whereas the total RNA was not quantifiable via Qubit. Despite this, the V4 region of 16S rRNA gene was able to be amplified, indicating the presence of microorganisms with low biomass. In future, 16S amplicon sequences from rocks will be analyzed together with porewater communities. The DNA will be applied to multiple displacement amplification prior to metagenome sequencing. The understanding of microbial ecology in deep subsurface not only benefits nuclear wastes management but also underpins the notion of evolutionary and astrobiology.

Keywords: microbial ecology; metagenome; nuclear waste management; deep subsurface biosphere

  • Poster (Online presentation)
    World Microbe Forum 2021, 20.-24.06.2021, Online, USA

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Permalink: https://www.hzdr.de/publications/Publ-32761
Publ.-Id: 32761


Interplay Of Flow Conditions, Cell Properties And Surface Structures In Attachment Of Bacterial Cells

Rybkin, I.; Schymura, S.; Strok, M.; Rijavec, T.; Fischer, C.; Lapanje, A.

Attachment of bacteria in natural conditions enable them a sustainable development, resulting in biofilm formation. Staying within biofilms, bacteria areprotected from colonization by other microbes, and they form mutualistic communities that allow to trade off inevitable compounds. The presence of thebiofilms is also a key process in biotechnological setups since microbes are protected from abiotic conditions (e.g. temperature, flushing, product separation),which enables a long term processing without continuous replacement of biomass. However, not all bacteria tend to attach very well and form biofilms sincethey lack surface receptors, do not produce extracellular matrices or do not have other appendages (e.g. pili, flagella) that facilitate the attachment. Therefore,we propose an alternative solution by micro-structuring the surface with different sizes of holes, which would enable cells to attach. Accordingly, we aimed todetermine interplay between (i) topography, (ii) fluid flow as well as salt concentration and (iii) the cell geometry and cell wall structure to the process ofattachmentt of cells. Our results showed that the structured surfaces with the depth, close to the size of bacteria are the most suitable to induce cellularattachment. We observed that specific features as biofilm formation or cell wall structure significantly differentiate the cells in the ability to colonize the surface.Since we tested attachment under flow conditions, the amount of deposited cells was dependent on the particular conditions of flow, while salinity of mediasignificantly improved the attachment.

Keywords: attachment of bacteria; biofilm; silicon wafers

  • Poster (Online presentation)
    World Microbe Forum, 20.-24.06.2021, online, online

Permalink: https://www.hzdr.de/publications/Publ-32760
Publ.-Id: 32760


Increased mobility of tetravalent actinides through silicate colloid formation – An analog study using 89Zr radiotracer

Schymura, S.; Mansel, A.; Weiß, S.; Zänker, H.; Franke, K.

Tetravalent actinides form colloids at near neutral pH in the presence of silicic acid. This may have significant impact on actinide mobility in the far field of a nuclear waste repository or the case of accidental release of actinides into the environment as silicate is ubiquitous in natural waters and is of special importance in the case of nuclear waste repositories in crystalline rock formations. We investigated the formation, stability and mobility of such colloids employing the tetravalent actinide analog zirconium and the radiotracer Zr-89. The radiotracer was produced at the in-house IBA Cyclone 18/9 cyclotron at the HZDR Research Site Leipzig. A foil of metallic yttrium was irradiated with 14.5 MeV protons to trigger the nuclear reaction Y-89(p,n)Zr-89. The target was subsequently dissolved and the radiotracer was isolated via ion chromatography methods using UTEVA resin.
The radiotracer was employed to synthesize zirconium oxyhydroxy silicate colloids that form spontaneously at near neutral pH at Si concentrations between 0.5 – 2 mM. In contrast to the Zr(O)(OH)2 particles that precipitate without silicates these colloids remain in stable dispersion. Column experiments in model porous media reveal a potentially massively increased mobility of these colloids due to very low affinities for the geomatrix surface.
The stability of these colloids was further investigated by producing particles from solutions containing various Zr : Si ratios. Homoaggregation affinity measurements on these systems by dynamic light scattering reveal an increasing stabilization of the colloids with increasing silica content hinting at (electro-)steric stabilization mechanisms due to polymeric silicic acid structures at the colloid surface. Consequently an increased mobility of low concentration tetravalent actinides through colloid formation may occur in environments with silicic acid presence.

Keywords: Actinides; Colloids; Stability; Transport

  • Poster (Online presentation)
    Goldschmidt 2021, 04.-09.07.2021, Lyon, France

Permalink: https://www.hzdr.de/publications/Publ-32759
Publ.-Id: 32759


The effect of UV-C irradiation and EDTA on the uptake of Co2+ by antimony oxide in the presence and absence of competing cations Ca2+ and Ni2+

Malinen, L.; Repo, E.; Harjula, R.; Huittinen, N. M.

In nuclear power plants and other nuclear facilities the removal of cobalt from radioactive liquid waste is needed to reduce the radioactivity concentration in effluents. In liquid wastes containing strong organic complexing agents such as EDTA cobalt removal can be problematic due to the high stability of the Co-EDTA complex. In this study, the removal of cobalt from NaNO3 solutions using antimony oxide (Sb2O3) synthesized from potassium hexahydroxoantimonate was investigated in the absence and presence of EDTA. The uptake studies on the ion exchange material were conducted both in the dark (absence of UV-light) and under UV-C irradiation. Ca2+ or Ni2+ were included in the experiments as competing cations to test the selectivity of the ion exchanger. Results show that UV-C irradiation noticeably enhances the cobalt sorption efficiency on the antimony oxide. It was shown that nickel decreased the sorption of cobalt to a higher extent than calcium. Finally, the sorption data collected for Co2+ on antimony oxide was modeled using six different isotherm models. The Sips model was found to be the most suitable model to describe the sorption process. The Dubinin-Radushkevich model was further used to calculate the adsorption energy, which was found to be 6.2 kJ mol-1.

Keywords: cobalt; EDTA; sorption; antimony oxide; UV-C; competing cations

Permalink: https://www.hzdr.de/publications/Publ-32756
Publ.-Id: 32756


Solubility of thorium in 14%Y-stabilized zirconia ceramics

Svitlyk, V.; Weiß, S.; Hennig, C.

Y-stabilized zirconia (YSZ) is one of the reference materials for immobilization of actinide elements for long-term and secure storage of radioactive waste. YSZ adapts different structural modifications, namely monoclinic, tetragonal (unstable) and cubic [1]. Changes in relative Y content and synthesis temperature can be used to obtain specific structural form. However, for an intermediate Y content of ~5-17 at.% a mixture of cubic and unstable tetragonal modifications can form thus compromising corresponding long-term structural integrity. Nevertheless, for this Y concentration range a stabilized tetragonal (t′) phase can be obtained through a rapid quenching of the parent cubic modification. Addition of Th was shown to influence phase composition and stability in the YSZ system as well [2]. In this work we report studies of solubility of Th in 14%Y- stabilized zirconia phase.
Series of 14%Y-ZrO2 compounds with Th at. % content of 3, 6, 9 and 12 were synthesized by sol-gel method from salts of Zr(IV), Y(III) and Th(IV). Subsequent powder synchrotron radiation diffraction measurements were performed in order to study underlying phase and structural evolutions. It was found that the cell parameters increase nearly linearly for the Th content from 3 to 9% and no cell increase is observed for the end-member with 12%Th. Additionally, ThO2 was found to precipitate in this sample. This may indicate that Th solubility limit in the 14%Y-ZrO2 system situates near 9%. Interestingly, Th content was reported to exceed 15% for the 25%Y-ZrO2 system, as concluded from electron microscopy data [3]. Studied samples, however, were found to be 25%Y-ZrO2–ThO2 phase separated. Considering that in the current study traces of ThO2 have been found already in the 9%Th sample, conditions of thermal treatment with the resulting phase equilibria may impact Th solubility. Further details on structural and phase properties in the Th-14%Y-ZrO2 system will be presented.

[1] Scott H G 1975 J. Mater. Sci. 10 1527–35
[2] Zhao M, Ren X, Yang J and Pan W 2016 Ceram. Int. 42 501–8
[3] Grover V, Sengupta P and Tyagi A K 2007 Mater. Sci. Eng. B 138 246–50

Related publications

  • Poster (Online presentation)
    Conference Association Française de Cristallographie, 29.06.-02.07.2021, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-32755
Publ.-Id: 32755


First experiments with two new diffractometers at the Rossendorf Beamline/ESRF

Hennig, C.; Svitlyk, V.

The Institute of Resource Ecology / HZDR is operating the Rossendorf Beamline (ROBL/BM20) at the ESRF for over 20 years. A second experimental hutch with two diffractometers for single crystal, powder and surface diffraction has been constructed in the last two years. As CRG beamline provides ROBL 1/3 of its beam time via the ESRF proposal system to the user community, whereas 2/3 are reserved for in-house research.
One diffractometer is a 6-circle Huber diffractometer with Eulerian cradle geometry (XRD-1). It will be used for high-resolution powder diffraction and surface diffraction. Powder diffraction measurements will be performed with a Pilatus 100k Si or an Eiger CdTe 500k detector mounted on the detector arm. The Bragg reflexes are extracted by radial integration using a modified pyFAI code.
The diffractometer for single crystal diffraction and in situ diffraction measurements (XRD-2) is equipped with a Pilatus3 X 2M detector. Diffraction measurements can be combined simultaneously with XANES and XRF spectroscopy. The setup comprises a cryo stream cooler (80-400 K) and a heater (up to 1200 K). The diffractometer is controlled with the Pylatus software and the single crystal data extraction is performed with CrysAlisPro.
We will report the first experiments performed on the two diffractometers.

Keywords: powder diffraction; single crystal diffraction; surface diffraction

Related publications

  • Poster (Online presentation)
    Conference Association Française de Cristallographie 2021, 29.06.-02.07.2021, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-32754
Publ.-Id: 32754


Quantitative nanoscale imaging using transmission He ion channelling contrast: Proof-of-concept and application to study isolated crystalline defects

Tabean, S.; Mousley, M.; Pauly, C.; de Castro, O.; Serralta Hurtado De Menezes, E.; Klingner, N.; Hlawacek, G.; Wirtz, T.; Eswara, S.

Quantitative nanoscale imaging using transmission He ion channelling contrast: Proof-of-concept and application to study isolated crystalline defects

Keywords: HIM; STIM; channeling

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Permalink: https://www.hzdr.de/publications/Publ-32753
Publ.-Id: 32753


Heat transfer assessment of the COSMEA facility cooling side

Adili, T.; Panneer Selvam, K.; Leyer, S.; Moonesi Shabestary, A.

Reliable performance of passive safety systems – which function using natural physics laws such as density difference without external interventions during an accident- is an important issue with respect to nuclear power plant (NPP) safety. Investigation of thermal behavior and the operational stability of passive safety systems in Generation III and III+ nuclear reactors is the objective of the German project PANAS (PAssive Nachzerfallswärme-AbfuhrSysteme – Passive Residual Heat Removal System) funded by the German Federal Ministry of Education and Research (BMBF). In this context, experiments are being performed in the high-pressure COSMEA test facility at HZDR (Helmholtz Zentrum Dresden Rossendorf) to assess the emergency condenser (EC) based on the KERENA boiling water reactor. The objective of the presented work is to complement previous efforts related to the primary side heat transfer coefficient with the focus on heat transfer assessment of the secondary side. The assessment of state-of-the-art heat transfer models has been presented, and it shows that they often fail to predict the heat transfer behavior of the secondary side in COSMEA test facility. Therefore, because of the system’s sensitive heat transfer behavior due to different factors such as mass flow rate, it is important to have an accurate determination of heat transfer performance in the system. In this regard, a 3D CFD simulation of the COSMEA secondary side by ANSYS CFX has been proposed to show the flow pattern, temperature gradient and heat transfer performance of the system. The COSMEA experiments serve as validation basis for the CFD simulation.

Keywords: Heat transfer model; COSMEA; ANSYS CFX

  • Contribution to proceedings
    The 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19), 06.-11.03.2022, Brussels, Belgium

Permalink: https://www.hzdr.de/publications/Publ-32752
Publ.-Id: 32752


Aufbau einer Versuchsanlage mit superkritischen Kohlenstoffdioxid (sCO2) als Arbeitsmedium in Kraftkreisläufen

Unger, S.; Fogel, S.; Rath, S.; Gampe, U.; Hampel, U.

Der Großteil elektrischer Energieerzeugung erfolgt durch thermische Kraftkreisläufe, welche durch eine Wärmequelle versorgt werden. Hierbei werden zwei Typen kommerzieller Anlagen betrieben, der offene direkt befeuerte Brayton oder Joule-Kreislauf (bsp. Gasturbinenkreisläufe) und der geschlossene indirekt befeuerte Rankine-Kreislauf (Dampfkreislauf). Neben diesen konventionellen Kraftkreisläufen existiert seit einigen Jahren, basierend auf den Brayton-Kreislauf, ein innovatives Konzept mit superkritischen Kohlenstoffdioxid (sCO2) als Arbeitsmedium. Zahlreiche Studien haben gezeigt, dass sCO2 Kreisläufe das Potential haben, höhere Wirkungsgrade zu erreichen, einen niedrigeren Brennstoff- und Wasserverbrauch zu erzielen (Subbaraman et al., 2011; Kacludis et al., 2012; Shelton et al., 2016). SCO2 kombiniert den Vorteil der hohen Dichte von Flüssigkeiten und die niedrige Viskosität von Gasen, sodass geringere Komponentengrößen, kleinere Footprints der Gesamtanlage und damit niedrigere Kapitalkosten möglich sind.
Bei der Prozessführung wird zwischen dem offenen und dem geschlossenen sCO2 Brayton-Kreislauf unterschieden. Bei einem geschlossenen Kreislauf wird sCO2 nahe des kritischen Punktes (ca. 31 °C und 74 bar) verdichtet, in einem Rekuperator vorgewärmt, in einem Erhitzer durch die Wärmequelle aufgeheizt, in einer Expansionsturbine entspannt, durch den Rekuperator auf der Gegenseite geführt und anschließend bis nahe des kritischen Punktes zurückgekühlt, um den Kreislauf erneut zu beginnen. Dieser Prozess kann für unterschiedlichste Wärmequellen, wie fossile Kraftstoffe, Kernenergie, industrielle Abwärme, Geothermie oder Solarstrahlung eingesetzt werden. Der offene Kreislauf adressiert dagegen höhere Temperaturen und wird üblicherweise für eine Sauerstoffverbrennung untersucht. Dabei wird ein Sauerstoff-Methan-Gemisch bei hohen Druck und hoher Temperatur verbrannt. Das Rauchgas wird dann, vermischt mit großen Mengen sCO2, in einer Turbine entspannt. Das sCO2-Wasserdampf-Gemisch wird ebenfalls in einem Rekuperator genutzt, um anschließend Wasser sowie kleine Mengen CO2 mittels Kondensation sowie Abtrennung aus dem Kreislauf zu entfernen. Der verbleibende sCO2-Strom wird erneut dem Verbrennungsprozess zugeführt. Dieser offene Kreislauf ist besonders attraktiv, um Erdgas, synthetisch erzeugte Gase oder vergaste Kohle zu nutzen. Verglichen mit dem geschlossenen Kreislauf können hier noch höhere Wirkungsgrade und Leistungsdichten erreicht werden.
Um diese Kraftwerkskonzepte sowie die dafür notwendigen Komponenten auf einer experimentellen Basis untersuchen zu können, wurde das Projekt CARBOSOLA in Zusammenarbeit mit der TU Dresden, dem DLR und der Siemens Energy AG initiiert. Inhalt dieses Projektes ist unter anderem der Aufbau einer Versuchsanlage am HZDR, zur Untersuchung von sCO2 bei bis zu 650 °C, bei gleichzeitig 300 bar und einem Massenstrom bis zu 3,3 kg/s. Die damit verbundenen Herausforderungen und Lösungen werden erläutert.

Keywords: superkritischen Kohlenstoffdioxid; Energieumwandlung; hohe Wirkungsgrade; CARBOSOLA

  • Lecture (Conference)
    53. Kraftwerkstechnisches Kolloquium, 05.-06.10.2021, Dresden, Deutschland
  • Contribution to proceedings
    53. Kraftwerkstechnisches Kolloquium, 05.-06.10.2021, Dresden, Deutschland
    Proceedings des 53. Kraftwerkstechnisches Kolloquium

Permalink: https://www.hzdr.de/publications/Publ-32751
Publ.-Id: 32751


Inverting the Beamline

Steinbach, P.

In many domains of modern physics, we encounter the situation that generations of scientists have created high precision simulations of the effects under study. Today, these simulations have become essential to the scientific method. However, these
(often mechanistic) simulations of high predictive power carry with them a burden of inference. Once a forward process has been simulated, an inversion of a simulation given observed data from experiments is challenging, sometimes even impossible.

In this presentation, I'd like to provide an introduction to simulation based inference for inverting a beamline simulation at BESSY in Berlin. In this project, I studied the inversion of a beamline simulation using state-of-the-art machine learning. We will start our journey with normalizing flows, walk by conditional invertible neural networks and finish with Automatic Posterior Transformation for Likelihood-Free Inference. To stay with the metaphor: please bring your mathematical boots, wear a hat of Bayes Law and bring your best compass of statistics - otherwise you likely get lost in about a quarter of the presentation.

Keywords: beamline; simulation; normalizing flows; posterior; inverse problem; machine learning

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Permalink: https://www.hzdr.de/publications/Publ-32750
Publ.-Id: 32750


Methods for the non-invasive analysis of the inventory status for containers during extended interim storage (DCS-Monitor II)

Wagner, M.; Kobelt, S.; Stephan, M.; Reinicke, S.; Hampel, U.

In the completed project DCS-MONITOR, feasibility studies for non-invasive monitoring of the container contents were carried out by the applicants using numerical and laboratory experimental tools. Radiation-based measurement techniques, thermography, acoustic spectroscopy and technical vibration analysis were investigated for their suitability. The previous analyses showed that the photon and neutron field around the vessel, muon imaging and passive acoustic spectroscopy are in principle suitable for monitoring the vessel inventory, but also differ in their informative value. For thermography, a lack of informative value was found for physical reasons. For active vibration diagnostics, technical hurdles and informative value were assessed negatively. With regard to passive acoustic spectroscopy, experts also dispute whether embrittled cladding tubes burst at all, with a corresponding sound emission in the container. On the basis of these results, the approaches of radiation field-based diagnostics with gamma radiation, neutrons and muons are investigated in more detail within the project DCS-MONITOR II in order to qualify them as an applicable monitoring procedure especially for CASTOR casks. For the first time, this includes studies on large scale geometries and containers.

  • Lecture (Conference) (Online presentation)
    5th Workshop on the Safety of the Extended Dry Storage of Spent Nuclear Fuel, 09.-10.06.2021, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-32749
Publ.-Id: 32749


Indikatoren für Open Science: Report des Helmholtz Open Science Forum

Ferguson, L. M.; Pampel, H.; Bertelmann, R.; Dirnagl, U.; Zohbi, J.; Kapitza, D.; Keup-Thiel, E.; Konrad, U.; Lorenz, S.; Mittermaier, B.; Rechid, D.; Schuck-Zöller, S.

Open Access, Open Research Data und Open Research Software: Diese Themen prägen die aktuellen Diskussionen zu Open Science in der Helmholtz-Gemeinschaft. Doch an welchen Indikatoren lässt sich der Kulturwandel hin zu Open Science festmachen? Und welche Anreize setzen Indikatoren für die Entwicklung von Open Access? Diesen und weiteren Fragen widmete sich das virtuelle Helmholtz Open Science Forum unter dem Motto „Indikatoren für Open Science“ am 20. Januar 2021. Im Zuge der Veranstaltung wurden anhand von Impuls- und Praxisvorträgen Indikatoren für Open Science vorgestellt, untersucht und mit einem breiten Publikum aus der Helmholtz-Gemeinschaft diskutiert. Dieser Report fasst die Vorträge und Diskussionen des Forums zusammen und bietet eine Basis für weitere Entwicklungen des Themenfeldes in der Gemeinschaft.

Keywords: Open Access; Softwareentwicklung; Software Development; Indikatoren; Indicators; Helmholtz Gemeinschaft; Open Science

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Permalink: https://www.hzdr.de/publications/Publ-32748
Publ.-Id: 32748


Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light

Kanj, A. B.; Bürck, J.; Vankova, N.; Li, C.; Mutruc, D.; Chandresh, A.; Hecht, S.; Heine, T.; Heinke, L.

The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal–organic framework (MOF). The azobenzene undergoes trans-to-cis-photoisomerization upon irradiation with green light and reverts back to trans upon violet light. While each moiety in cis conformation is chiral, we show the trans isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, R- and S-cis as well as R- and S-trans, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites R-cis and R-trans enantiomers, producing a MOF with enriched S-enantiomers, and vice versa. The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, trans and cis, are stabilized in nonplanar, chiral conformations in the MOF, the trans isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.

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Permalink: https://www.hzdr.de/publications/Publ-32747
Publ.-Id: 32747


Hermes Project Poster

Druskat, S.; Schlauch, T.; Bertuch, O.; Juckeland, G.; Knodel, O.

The goal of this project is to support researchers in publishing their research software, in a way that makes it findable, comprehensible, citable and reusable. The key to this is the creation, curation and deposit of rich metadata with software publications. To this end, the project will conceptualize, produce and provide well-documented, adoption-ready workflows with automation interfaces and reference implementations for InvenioRDM and Dataverse.

Keywords: research software; FAIR; software publication; metadata; workflows

  • Open Access Logo Poster (Online presentation)
    Info event for the second project call of the Helmholtz Incubator Platform Helmholtz Metadata Collaboration (HMC), 15.06.2021, Berlin, Germany
  • Open Access Logo Poster (Online presentation)
    Helmholtz Metadata Collaboration | Conference 2022, 05.-06.10.2022, online, online
    DOI: 10.5281/zenodo.7092347

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Permalink: https://www.hzdr.de/publications/Publ-32746
Publ.-Id: 32746


Heliport Project Poster

Knodel, O.; Voigt, M.; Ufer, R.; Pape, D.; Lokamani, M.; Müller, S.; Gruber, T.; Juckeland, G.; Kaluza, M. C.; Hein, J.; Kessler, A.; Eckner, E.; Schuller, B.

The HELIPORT project aims at developing a platform which accommodates the complete life cycle of a scientific project and links all corresponding programs, systems and workflows to create a more FAIR and comprehensible project description.

Keywords: Data Management; Heliport; Metadata; Data provenance; FAIR

  • Open Access Logo Poster (Online presentation)
    Info event for the second project call of the Helmholtz Incubator Platform Helmholtz Metadata Collaboration (HMC), 15.06.2021, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-32745
Publ.-Id: 32745


Superradiant many-qubit absorption refrigerator

Kloc, M.; Meier, K.; Hadjikyriakos, K.; Schaller, G.

We show that the lower levels of a large-spin network with a collective anti-ferromagnetic interaction and collective couplings to three reservoirs may function as a quantum absorption refrigerator. In appropriate regimes, the steady-state cooling current of this refrigerator scales quadratically with the size of the working medium, i.e., the number of spins. The same scaling is observed for the noise and the entropy production rate.

Keywords: open quantum systems; collective interactions; quantum heat engine; quantum absorbtion refrigerator; Dicke superradiance

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Permalink: https://www.hzdr.de/publications/Publ-32744
Publ.-Id: 32744


Non-equilibrium boundary driven quantum systems: models, methods and properties

Gabriel, T. L.; Dario, P.; Gernot, S.

Recent years have seen tremendous progress in the theoretical understanding of quantum systems driven dissipatively by coupling them to different baths at their edges. This was possible because of the concurrent advances in the models used to represent these systems, the methods employed, and the analysis of the emerging phenomenology. Here we aim to give a comprehensive review of these three integrated research directions. We first provide an overarching view of the models of boundary driven open quantum systems, both in the weak and strong coupling regimes. This is followed by a review of state-of-the-art analytical and numerical methods, both exact, perturbative and approximate. Finally, we discuss the transport properties of some paradigmatic one-dimensional chains, with an emphasis on disordered and quasiperiodic systems, the emergence of rectification and negative differential conductance, and the role of phase transitions.

Keywords: open quantum systems; quantum transport; phase transitions; local and global master equations; chain models

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Permalink: https://www.hzdr.de/publications/Publ-32743
Publ.-Id: 32743


Validation of Serpent-SUBCHANFLOW-TRANSURANUS pin-by-pin burnup calculations using experimental data from the Temelín II VVER-1000 reactor

Garcia, M.; Vocka, R.; Tuominen, R.; Gommlich, A.; Leppanen, J.; Valtavirta, V.; Imke, U.; Ferraro, D.; van Uffelen, P.; Milisdorfer, L.; Sanchez-Espinoza, V.

This work deals with the validation of a high-fidelity multiphysics system coupling the Serpent 2 Monte Carlo neutron transport code with SUBCHANFLOW, a subchannel thermalhydraulics code, and TRANSURANUS, a fuel-performance analysis code. The results for a full-core pin-by-pin burnup calculation for the ninth operating cycle of the Temelín II VVER-1000 plant, which starts from a fresh core, are presented and assessed using experimental data. A good agreement is found comparing the critical boron concentration and a set of pin-level neutron flux profiles against measurements. In addition, the calculated axial and radial power distributions match closely the values reported by the core monitoring system. To demonstrate the modeling capabilities of the three-code coupling, pin-level neutronic, thermalhydraulic and thermomechanic results are shown as well. These studies are encompassed in the final phase of the EU Horizon 2020 McSAFE project, during which the Serpent-SUBCHANFLOW-TRANSURANUS system was developed. © 2021

Keywords: Fuel-performance analysis; High-fidelity multiphysics; Monte Carlo neutron transport; Pin-level burnup; Subchannel thermalhydraulics; VVER-1000

Permalink: https://www.hzdr.de/publications/Publ-32740
Publ.-Id: 32740


Morphology-Tunable Synthesis of Intrinsic Room-Temperature Ferromagnetic γ-Fe2O3 Nanoflakes

Jia, Z.; Wang, W.; Li, Z.; Sun, R.; Zhou, S.; Leonard Deepak, F.; Su, C.; Li, Y.; Wang, Z.

Intrinsic two-dimensional (2D) magnetic materials with room-temperature ferromagnetism and air stability are highly desirable for spintronic applications. However, the experimental observations of such 2D or ultrathin ferromagnetic materials are rarely reported owing to the scarcity of these materials in nature and for the intricacy in their synthesis. Here, we report a successful controllable growth of ultrathin γ-Fe2O3 nanoflakes with a variety of morphologies tunable by the growth temperature alone using a facile chemical vapor deposition method and demonstrate that all ultrathin nanoflakes still show intrinsic room-temperature ferromagnetism and a semiconducting nature. The γ-Fe2O3 nanoflakes epitaxially grown on α-Al2O3 substrates take a triangular shape at low temperature and develop gradually in lateral size, forming eventually a large-scale γ-Fe2O3 thin film as the growth time increases due to a thermodynamic control process. The morphology of the nanoflakes could be tuned from triangular to stellated, petaloid, and dendritic crystalloids in sequence with the rise of precursor temperature, revealing a growth process from thermodynamically to kinetically dominated control. Moreover, the petaloid and dendritic nanoflakes exhibit enhanced coercivity compared with the triangular and stellated nanoflakes, and all the nanoflakes with diverse shapes possess differing electrical conductivity. The findings of such ultrathin, air-stable, and room-temperature ferromagnetic γ-Fe2O3 nanoflakes with tunable shape and multifunctionality may offer guidance in synthesizing other non-layered magnetic materials for next-generation electronic and spintronic devices.

Keywords: γ-Fe2O3 nanoflakes; morphology tunable synthesis; room-temperature ferromagnetism; coercivity; resistivity

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Permalink: https://www.hzdr.de/publications/Publ-32739
Publ.-Id: 32739


The response of the accumulator plants Noccaea caerulescens, Noccaea goesingense and Plantago major towards the uranium

Burger, A.; Weidinger, M.; Baumann, N.; Vesely, A.; Lichtscheidl, I.

Uranium (U) is a naturally occurring metal; its environmental levels can be increased due to processes in the nuclear industry and fertilizer production. The transfer of U in the food chain from plants is associated with deleterious chemical and radiation effects. To date, limited information is available about U toxicity on plant physiology. This study investigates the responses of metal-accumulating plants to different concentrations of U. The plants Noccaea caerulescens and Noccaea goesingense are known as metal hyperaccumulators and therefore could serve as candidates for the phytoremediation of radioactive hotspots; Plantago major is a widely used pharmaceutical plant that pioneers polluted grounds and therefore should not contain high concentrations of toxic elements. The experimental plants were grown hydroponically at U concentrations between 1 μM and 10 mM. The content of U and essential elements was analyzed in roots and leaves by ICP-MS. The amount of accumulated U was influenced by its concentration in the hydroponics. Roots contained most of the metal, whereas less was transported up to the leaves, with the exception of N. goesingense in a medium concentration of U. U also influenced the nutrient profile of the plants. We localized the U in plant tissues using EDX in the SEM. U was evenly distributed in roots and leaves of Noccaea species, with one exception in the roots of N. goesingense, where the central cylinder contained more U than the cortex. The toxicity of U was assessed by measuring growth and photosynthetic parameters. While root biomass of N. caerulescens was not affected by U, root biomass of N. goesingense decreased significantly at high U concentrations of 0.1 and 10 mM and root biomass of P. major decreased at 10 mM U. Dry weight of leaves was decreased at different U concentrations in the three plant species; a promotive effect was observed in N. caerulescens at lowest concentration offered. Chlorophyll a fluorescence was not affected or negatively affected by U in both Noccaea species, whereas in Plantago also positive effects were observed. Our results show that the impact of U on Plantago and Noccaea relates to its external concentration and to the plant species. When growing in contaminated areas, P. major should not be used for medicinal purpose. Noccaea species and P. major could immobilize U in their rhizosphere in hotspots contaminated by U, and they could extract limited amounts of U into their leaves.

Keywords: Accumulation; Chemotoxicity; Distribution; Localization; Uptake; Uranium

Permalink: https://www.hzdr.de/publications/Publ-32738
Publ.-Id: 32738


Influence of plants on speciation and mobility of U(VI) and Eu(III)

Jessat, J.; Moll, H.; John, W.; Steudtner, R.; Hübner, R.; Drobot, B.; Vogel, M.; Bok, F.; Stumpf, T.; Sachs, S.

For a safety assessment of repositories, possible accident scenarios must be considered. If radionuclides (RNs) are released from a repository into the groundwater, they can migrate and interact with the biosphere. In addition to microorganisms, higher organisms such as plants also play a role in this context. For this reason, it is necessary that a process understanding on RN plant interactions on the molecular level is elucidated by suitable biochemical and spectroscopic methods to improve biogeochemical models for a reliable modeling of the transfer behavior of RNs in the environment up to the food chain. Interaction with plant cells can lead to immobilization and speciation changes of the RNs. Uranium as the main component (by mass) of spent nuclear fuel rods is of interest for our investigations. Furthermore, we studied europium as a non-radioactive analogue for the trivalent actinides Am(III) and Cm(III), whereby the former in particular will dominate the radiotoxicity in a potential repository. We investigated the time and concentration-dependent immobilization of these two metals to the biomass of different plant cell cultures. Biochemical methods were accompanied by spectroscopic (time-resolved laser-induced fluorescence spectroscopy, TRLFS) and microscopic techniques for determination of speciation and localization of the metals within the plant cells, respectively. In addition, the combination of luminescence spectroscopy with microscopy in the form of chemical microscopy revealed for the first time the spatially resolved localization of different Eu(III) species in plant root tissues. We observed bioassociation (immobilization) of U(VI)/Eu(III), but in some cases also re-mobilization of U(VI), which temporally coincided with a change in the metal speciation in solution. Moreover, we successfully identified metabolites released by the plant cells that can complex with U(VI)/Eu(III) and influence their mobility and thus bioavailability in the environment. Our studies can help to integrate RN plant interactions in assessment strategies of nuclear waste repositories.

Keywords: plants; TRLFS; uranium; europium; speciation; immobilization

  • Lecture (Conference) (Online presentation)
    45th Scientific Basis for Nuclear Waste Management Symposium, 25.-28.10.2021, Jülich, Germany

Permalink: https://www.hzdr.de/publications/Publ-32737
Publ.-Id: 32737


High-field spin-flop state in green dioptase

Prokhnenko, O.; Marmorini, G.; Nikitin, S. E.; Yamamoto, D.; Gazizulina, A.; Bartkowiak, M.; Ponomaryov, O.; Zvyagin, S.; Nojiri, H.; Diaz-Ortega, I. F.; Anovitz, L. M.; Kolesnikov, A. I.; Podlesnyak, A.

The high-field magnetic properties and magnetic order of the gem mineral green dioptase Cu6[Si6O18] · 6H2O have been studied by means of single-crystal neutron diffraction in magnetic fields up to 21 T and magnetization measurements up to 30 T. In zero field, the Cu2+ moments in the antiferromagnetic chains are oriented along the c axis with a small off-axis tilt. For a field applied parallel to the c axis, the magnetization shows a spin-flop-like transition at B = 12.2 T at 1.5 K. Neutron diffraction experiments show a smooth behavior in the intensities of the magnetic reflections without any change in the periodicity of the magnetic structure. Bulk and microscopic observations are well described by a model of ferromagnetically coupled antiferromagnetic XXZ spin- 1/2 chains, taking into account a change of the local easy-axis direction.We demonstrate that the magnetic structure evolves smoothly from a deformed Néel state at low fields to a deformed spin-flop state in a high field via a strong crossover around B. The results are generalized for different values of interchain coupling and spin anisotropy.

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Permalink: https://www.hzdr.de/publications/Publ-32736
Publ.-Id: 32736


Joint project: Geochemical retention of radionuclides on cement alteration phases (GRaZ) - Subproject B

Schmeide, K.; Philipp, T.; Wolter, J.-M.; Kretzschmar, J.; Dullies, P.; Lippold, H.; Schymura, S.; Stumpf, T.

The report summarizes the results obtained by the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf within the BMWi-financed Joint Research Project “Geochemical retention of radionuclides on cement alteration phases (GRaZ)”. The project focused on the retention behavior of Ca-bentonite and cementitious material, both constituents of the geo-engineered barrier of deep geological repositories for high-level radioactive waste, towards radionuclides. Specifically, the influence of increased salinities and of hyperalkaline conditions on interaction processes in the system radionuclides – organics – clay/cementitious materials – aquifer was studied. For this purpose, complexation, sorption and desorption studies were performed at alkaline to hyperalkaline pH conditions (pH 8-13) and under variation of the ionic strength (0.1 to 4 M) applying complex solution compositions. For the U(VI) citrate system molecular structures dominating in the pH range 2-9 were studied spectroscopically (NMR, UV-Vis, FT-IR). As dominating species 2:2, 3:3, 3:2 and, above critical concentrations also 6:6 and 9:6 U(VI) citrate complexes were identified or confirmed and complex formation constants were determined. U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions in mixed electrolyte solutions was studied by means of batch sorption experiments. The U(VI) retention on Ca-bentonite was shown to be very effective at pH>10, even in the presence of carbonate and despite the prevalence of anionic aqueous uranyl species. The presence of two independent U(VI) surface complexes on Ca-bentonite at pH 8-13 was shown by site-selective TRLFS and EXAFS spectroscopy. The sorption of anionic uranyl hydroxide complexes to the mineral surface was shown to be mediated by calcium cations. In further experiments, the effect of isosaccharinic acid (ISA) and polycarboxylate ether (PCE) on U(VI) and Eu(III) sorption, respectively, on Ca-bentonite was studied. An effect of ISA on U(VI) sorption on Ca-bentonite only occurs when ISA is present in very high excess to U(VI). The effect of PCE, as a commercial cement superplasticizer, on Eu(III) sorption onto Ca-bentonite was negligible already at moderate ionic strengths. The retention of U(VI) and Cm(III) by various C-(A-)S-H phases, representing different alteration stages of concrete, was studied by batch sorption experiments. Sorbed or incorporated actinide species were identified by TRLFS. The stability of U(VI) and Cm(III) doped C-(A-)S-H phases at high ionic strengths conditions was studied in solutions simulating the contact with North German claystone formation water. Potential changes of actinide speciation as well as formation of secondary phases due to leaching effects were followed spectroscopically. The results of this project show that both bentonite and cementitious material constitute an important retention barrier for actinides under hyperalkaline conditions and increased ionic strength.

Keywords: uranium; curium; europium; Ca-bentonite; site-selective TRLFS; EXAFS; speciation; C-S-H; cement; ionic strength; citric acid; complexation; NMR; surface complexation; TRLFS

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  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-114 2021
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-32735
Publ.-Id: 32735


ALFERROCK Heat Storage Systems in the Chemical Process Industry

Hampel, U.; Unger, S.; Vishwakarma, V.; Bangalore Mohankumar, M.

Energy storage is a central element of future energy systems. In the process industry, the storage of heat is of particular importance. The talk discusses possible applications of high-temperature heat storage in thermal separation processes using the example of a new heat storage material produced from bauxite residues by the company Alferrock GmbH.

Keywords: heat storage; sensible heat storage; high-temperature heat storage; chemical industry; distillation

  • Invited lecture (Conferences) (Online presentation)
    72. BHT - Freiberger Universitätsforum, 09.-11.06.2021, Freiberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-32734
Publ.-Id: 32734


Value of functional in-vivo endpoints in preclinical radiation research

Kummer, B.; Lock, S.; Gurtner, K.; Hermann, N.; Yaromina, A.; Eicheler, W.; Baumann, M.; Krause, M.; Jentsch, C.

Background: Cancer research faces the problem of high rates of clinical failure of new treatment approaches after positive preclinical data. We hypothesize that a major confounding factor to this problem in radiooncology is the choice of the preclinical endpoint. Methods: We present a comprehensive re-evaluation of large-scale preclinical in-vivo data on fractionated irradiation alone or simultaneously with Epidermal Growth Factor Receptor inhibition. Taking the permanent local tumour control assay as a gold standard, we evaluated different tumour volume dependent endpoints that are widely used for preclinical experiments. Results: The analysis showed the highest correlations between volume related and local tumour control endpoints after irradiation alone. For combined treatments, wide inter-tumoural variations were observed with reduced correlation between the endpoints. Evaluation of growth delay per Gray (GD/Gy) based on two or more dose levels showed closest correlation with local tumour control dose 50% (TCD50). Conclusions: GD/Gy with at least two dose groups correlates with TCD50, but cannot replace the latter as the goldstandard.

Keywords: Combined modality therapy; EGFR; Irradiation; Neoplasms; Preclinical research; Xenografts

Permalink: https://www.hzdr.de/publications/Publ-32733
Publ.-Id: 32733


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