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X-ray Spectroscopic Studies of Materials for Nuclear Technology
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

X-ray spectroscopic experiments, including X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS), were performed in a large energy range (60-9000 eV) on a variety of systems, probing different elements and orbitals. The systems can preferably be divided into three groups: Actinides, copper systems and amorphous materials. We studied oxidation states of Pu in PuO2 using a closed-source experimental setup, developed by us, to lower the safety restrictions associated with such experiments. The presence of Pu with higher oxidation state than Pu(IV) was found in polycrystalline PuO2. This is an important finding since Pu with higher oxidation states has higher solubility affecting the safety of a proposed undeground repository of spent nuclear fuel which can eventually be infiltrated by groundwater. In the proposed underground repository the molecular oxygen will vanish at some point due to microbial activity and mineral oxidation. At this stage sulfur is the most important candidate for causing copper corrosion. We studied Cu films and foils exposed to sulfide solutions at both Cu L2,3, Cu K and S L2,3 edges and found for example that S L2,3 XES is useful for distinguishing between different copper sulfides and Cu Kβ XES can be used to identify monovalent Cu compounds. Amorphous, zirconium containing alloys are potentially useful materials for future nuclear reactors. The electronic structure of such materials was also investigated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , p. 56
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 874
Keyword [en]
XAS, XES, RIXS, amorphous, DOS, spectroscopy, actinides, copper, uranium, plutonium
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:uu:diva-160362ISBN: 978-91-554-8205-3 (print)OAI: oai:DiVA.org:uu-160362DiVA, id: diva2:451251
Public defence
2011-12-09, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-11-17 Created: 2011-10-21 Last updated: 2011-11-17Bibliographically approved
List of papers
1. Resonant inelastic X-ray scattering of uranium compounds at U 5d edge
Open this publication in new window or tab >>Resonant inelastic X-ray scattering of uranium compounds at U 5d edge
(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-160353 (URN)
Available from: 2011-10-21 Created: 2011-10-21
2. Closed source experimental system for soft x-ray spectroscopy of radioactive materials
Open this publication in new window or tab >>Closed source experimental system for soft x-ray spectroscopy of radioactive materials
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2008 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 79, no 9, p. 093103-Article in journal (Refereed) Published
Abstract [en]

An instrumental and experimental setup for soft x-ray spectroscopy meeting the requirements of a closed source for radioactivity is described. The system consists of a vacuum sealed cell containing the sample, mounted on a tubing system to ensure compatibility with most standard manipulators. The soft x rays penetrate a thin x-ray window separating the interior of the cell from the vacuum in the experimental chamber. Our first results for single crystal PuO2 confirm the feasibility of experiments using the setup. The results are consistent with results of first principles calculations and previously recorded spectra obtained using a standard open source setup. The results show that the closed source experimental system can be used to collect valuable experimental data from radioactive materials.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-107107 (URN)10.1063/1.2991109 (DOI)000260291800004 ()
Available from: 2009-07-16 Created: 2009-07-16 Last updated: 2017-12-13
3. Indication of single-crystal PuO2 oxidation from O 1s x-ray absorption spectra
Open this publication in new window or tab >>Indication of single-crystal PuO2 oxidation from O 1s x-ray absorption spectra
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2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 7, p. 075113-Article in journal (Refereed) Published
Abstract [en]

The electronic structure of single-crystal PuO2 is studied using O 1s x-ray absorption (XA) and x-ray emission. Interpretation of the experimental data is supported by extensive first-principles calculations on the basis of the density functional theory + U approach. The measured XA spectra show a significant difference in intensity for the first two peaks between different spots or areas on the single crystal. Our theoretical simulations show that the first peak, at similar to 531 eV, can be attributed to O 2p-Pu 5f hybridization, while the second peak, at similar to 533.4 eV, is due to hybridization of O 2p with Pu d states. The reasons for the observed differences in the O 1s XA spectra are explored by calculating a number of defect structures PuO2+x as well as by simulating the existence of Pu(V) sites. Our results indicate the presence of oxidation states higher than Pu(IV) in some areas of the single crystal. The findings also suggest that plutonium oxide with a Pu fraction in an oxidation state higher than Pu(IV) consists of inequivalent Pu sites with (PuO2)-O-(IV) and (PuO2)-O-(V) rather than representing a system where the Pu oxidation state is constantly fluctuating between Pu(IV) and Pu(V).

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-148485 (URN)10.1103/PhysRevB.83.075113 (DOI)000287484500002 ()
Available from: 2011-03-07 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
4. Electron transfer during selenium reduction by iron surfaces in aqueous solution: high resolution X-ray absorption study
Open this publication in new window or tab >>Electron transfer during selenium reduction by iron surfaces in aqueous solution: high resolution X-ray absorption study
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2009 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 190, no 1, p. 012191-Article in journal (Refereed) Published
Abstract [en]

We present a study of selenate (SeO42-) on an iron surface in ground water solution by X-ray absorption near-edge spectroscopy. Spectral sharpening is obtained by using the high energy resolution fluorescence detection technique that also efficiently suppresses the strong fluorescence signal from the Fe surface in the highly dilute samples (Se concentration < 3 ppm). We observe fully reduced Se on polished Fe surfaces while no changes are found for Se on oxidized Fe surface.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-147302 (URN)10.1088/1742-6596/190/1/012191 (DOI)
Note

Times Cited: 2 DiCicco, A Filipponi, A 14th International Conference on X-Ray Absorption Fine Structure (XAFS14) Jul 26-31, 2009 Camerino, ITALY

Available from: 2011-02-24 Created: 2011-02-24 Last updated: 2017-12-11
5.
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6. Cu Kβ2,5 X-ray emission spectroscopy as a tool for characterization of monovalent copper compounds
Open this publication in new window or tab >>Cu Kβ2,5 X-ray emission spectroscopy as a tool for characterization of monovalent copper compounds
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2012 (English)In: Journal of Analytical Atomic Spectrometry, ISSN 0267-9477, E-ISSN 1364-5544, Vol. 27, no 11, p. 1882-1888Article in journal (Refereed) Published
Abstract [en]

Cu Kβ 2,5 X-ray emission and resonant inelastic X-ray scattering measurements were performed on monovalent and divalent copper compounds. The data were compared with the results of local-density- approximation calculations. The methods were found to be efficient tools for studies of Cu 4p states in the valence band and for distinguishing between different monovalent copper compounds. This is of particular importance for the debate concerning copper corrosion in oxygen-free water.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-160355 (URN)10.1039/C2JA30095H (DOI)000310479900006 ()
Available from: 2011-10-21 Created: 2011-10-21 Last updated: 2017-12-08Bibliographically approved
7. Exposure of Oxidized Copper Surfaces to Aqueous Na2S Solution Studied with Soft X-Ray Spectroscopy
Open this publication in new window or tab >>Exposure of Oxidized Copper Surfaces to Aqueous Na2S Solution Studied with Soft X-Ray Spectroscopy
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2011 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 158, no 1, p. C1-C5Article in journal (Refereed) Published
Abstract [en]

We present results from X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) of oxidized polycrystalline copper surfaces [Cu(I) and Cu(II), respectively] exposed to a 1.0 mM aqueous solution of Na2S (sodium sulfide) for several hours. Scanning electron microscopy reveals that the Cu oxide surfaces attain a much rougher texture upon sodium sulfide exposure, and that the exposed Cu(II) oxide sample exhibits areas with crystallites. The XAS spectra show that sodium sulfide effectively reduces Cu(II) oxide to Cu(I) compounds. The RIXS spectra of the exposed surfaces closely resemble those of the Cu2O reference sample with the notable exception of their Cu LIII,II-RIXS spectra. We conclude that copper evidently forms a Cu(I) compound with oxygen but with a Cu 3d-band of much reduced width, pointing to the possibility of a more complex compound containing both oxygen and sulfur.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-139392 (URN)10.1149/1.3504891 (DOI)000284697900020 ()
Available from: 2010-12-27 Created: 2010-12-23 Last updated: 2017-12-11Bibliographically approved
8. Structural stability and oxidation resistance of amorphous Zr-Al alloys
Open this publication in new window or tab >>Structural stability and oxidation resistance of amorphous Zr-Al alloys
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2010 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 401, no 1-3, p. 38-45Article in journal (Refereed) Published
Abstract [en]

We investigated the structural stability and oxidation resistance of Zr-Al films upon annealing in air. The concentration of Zr was varied from 0 to 100 at.%, with a step of 10 at.%. The films were fabricated using ultra-high vacuum based magnetron sputtering. The as-deposited films with Zr content from 17.3 at.% to 70.7 at.% were found to be X-ray amorphous at room temperature. When exposed to air a thin oxide layer, typically less than 6 nm, is formed. The thickness of the oxide layers increases when the samples are annealed in air and most of these are found to be fully oxidized at 700 degrees C with the formation of crystalline and amorphous oxides on the top of crystalline and amorphous metal films, respectively. The amorphous oxide layers are found to be dense, with well defined thicknesses. An experimental non-equilibrium phase diagram is provided, covering the whole concentration range of the Zr-Al system. (C) 2010 Elsevier B.V. All rights reserved.

National Category
Physical Sciences Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-136147 (URN)10.1016/j.jnucmat.2010.03.016 (DOI)000279194300005 ()
Available from: 2010-12-10 Created: 2010-12-10 Last updated: 2017-12-11Bibliographically approved
9. Atomic and electronic structure of amorphous Al-Zr alloy films
Open this publication in new window or tab >>Atomic and electronic structure of amorphous Al-Zr alloy films
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2011 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 26, p. 265503-Article in journal (Refereed) Published
Abstract [en]

Amorphous Al73Zr27 alloy film, grown and then subjected to heat treatments at 400 and 700 degrees C, was studied using a combination of x-ray diffraction and soft x-ray spectroscopic techniques. The Al L-2,L-3 and Al K x-ray absorption spectroscopy (XAS) and Al L-2,L-3 x-ray emission spectroscopy (XES) used allowed probing the unoccupied and occupied Al 3s, d states and unoccupied Al 3p states in the sample studied. An irreversible transition from amorphous alloy to a mixture of polycrystalline alloy and amorphous alloy, and then to an amorphous oxide phase was observed. After the annealing at 400 degrees C the Al L-2,L-3 spectra obtained by XAS could be explained as sums of spectra from amorphous Al73Zr27 alloy and (poly) crystalline Al. This indicates that the sample consists of a mixture of Al-rich crystalline and Zr-enhanced amorphous alloys, as compared to the stoichiometry of the as-deposited Al73Zr27 sample, and that the electronic wavefunctions in the crystalline and amorphous regions can be considered to be confined within the respective regions. The relative amounts of Al atoms were found to be around 1: 3 in the crystalline and amorphous phases, respectively, as deduced from the analysis of changes in the electronic structure using Al L-2,L-3 XAS data. The interpretation was confirmed by the Al K XAS and Al L-2,L-3 XES. Upon further annealing at 700 degrees C the polycrystalline phase transformed into amorphous oxide, while the amorphous alloy phase underwent gradual oxidation. The important finding was that the greater part of the sample remained in the amorphous state throughout the temperature regimes described.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-155925 (URN)10.1088/0953-8984/23/26/265503 (DOI)000291658700018 ()
Available from: 2011-07-05 Created: 2011-07-04 Last updated: 2017-12-11Bibliographically approved
10. Temperature dependence of the electrical resistivity of highly amorphous Fe-Zr films and multilayers
Open this publication in new window or tab >>Temperature dependence of the electrical resistivity of highly amorphous Fe-Zr films and multilayers
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(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-160356 (URN)
Available from: 2011-10-21 Created: 2011-10-21 Last updated: 2012-03-07

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