Search

Your search keyword '"Marquardt, Christian M."' showing total 30 results
Start Over Author "Marquardt, Christian M."
30 results on '"Marquardt, Christian M."'

2. Investigation of 252Cf sources with a Ge gamma-ray detector.

Author

Becker, Frank B E, Dagan, Ron, and Marquardt, Christian M

Subjects
NEUTRON emission, NUCLEAR science, DETECTORS, GAMMA ray spectrometry, SPECTROMETRY
Abstract

This study investigated the feasibility of combining high-resolution gamma-ray spectroscopy with the simulation capabilities of the Nucleonica Nuclear Science Portal with the aim to determine the properties of Cf sources. In this contribution, we present the results for a 20-month-old and a 49-year-old Cf source. In particular, the question arises whether the neutron emission rate can be determined using gamma-ray spectroscopy. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

6. Separation of plutonium and neptunium species by capillary electrophoresis--inductively coupled plasma-mass spectrometry and application to natural groundwater samples

Author

Kuczewski, Bernhard, Marquardt, Christian M., Seibert, Alice, Geckeis, Horst, Kratz, Jens Volker, and Trautmann, Norbert

Subjects
Electrophoresis -- Research, Chemistry
Abstract

Capillary electrophoresis (CE) was coupled to ICPMS in order to combine the good performance of this separation technique with the high sensitivity of the ICPMS for the analysis of plutonium and neptunium oxidation states. The combination of a fused-silica capillary with a Micro-Mist AR 30-I-FM02 nebulizer and a Cinnabar small-volume cyclonic spray chamber yielded the best separation results. With this setup, it was possible to separate a model element mixture containing neptunium (Np[O.sub.2.sup.+]), uranium (U[O.sub.2.sup.2+]), lanthanum ([La.sup.3+]), and thorium ([Th.sup.4+]) in 1 M acetic acid. The same conditions were also suitable for the separation of various oxidation states of plutonium and neptunium in different aqueous samples. All separations were obtained within less than 15 min. A detection limit of 50 ppb [equivalent to] 2 x [10.sup.-7] M (3-fold standard deviation of a blank) was achieved. To prove the negligible disturbance of the plutonium and neptunium redox equilibria during the CE separations, plutonium and neptunium speciation by CE--ICPMS in acidic solutions was compared with the results of UV/visible absorption spectroscopy and was found to be in good agreement. The CE-ICPMS system was also applied to study the reduction of Pu(VI) in a humic acid-containing groundwater at different pH values.

Published
2003

10. First structural characterization of Pa(iv) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(IV): the evidence of a curium break

Author

Banik, Nidhu lal, Vallet, Valerie, Real, Florent, Belmecheri, Reda Mohamed, Schimmelpfennig, Bernd, Rothe, Jorg, Marsac, Remi, Lindqvist-Reis, Patric, Walther, Clemens, Denecke, Melissa A., Marquardt, Christian M., Banik, Nidhu lal, Vallet, Valerie, Real, Florent, Belmecheri, Reda Mohamed, Schimmelpfennig, Bernd, Rothe, Jorg, Marsac, Remi, Lindqvist-Reis, Patric, Walther, Clemens, Denecke, Melissa A., and Marquardt, Christian M.

Abstract

More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 A. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.

Published
2016

11. First structural characterization of Pa(iv) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(iv): the evidence of a curium break

Author

Banik, Nidhu lal, primary, Vallet, Valérie, additional, Réal, Florent, additional, Belmecheri, Réda Mohamed, additional, Schimmelpfennig, Bernd, additional, Rothe, Jörg, additional, Marsac, Rémi, additional, Lindqvist-Reis, Patric, additional, Walther, Clemens, additional, Denecke, Melissa A., additional, and Marquardt, Christian M., additional

Published
2016
Full Text
View/download PDF

12. Interaction and Transport of Actinides in Natural Clay Rock with Consideration of Humic Substances and Clay Organic Compounds. (KIT Scientific Reports ; 7633)

Author

Marquardt, Christian M. [Hrsg.]

Subjects
sorption and diffusion, actinides, clay rock, humic substances, Chemistry & allied sciences, ddc:540, disposal of high-level nuclear waste
Abstract

The present report summarizes the progress and the results obtained within the BMWi financed Joint Research Project Interaction and Transport of Actinides in Natural Clay Rock with Consideration of Humic Substances and Clay Organic Compounds. The basic approach of the work was to obtain a fundamental process understanding on the molecular level of complexation and sorption reactions as well as diffusion processes. The experimental findings are supported by quantum mechanical modeling.

Published
2013

16. New insights in the formation processes of Pu(IV) colloids

Author

Walther, Clemens, primary, Rothe, Jörg, additional, Brendebach, Boris, additional, Fuss, Markus, additional, Altmaier, Marcus, additional, Marquardt, Christian M., additional, Büchner, Sebastian, additional, Cho, Hye-Ryun, additional, Yun, J.-I., additional, and Seibert, Alice, additional

Published
2009
Full Text
View/download PDF

29. First structural characterization of Pa(iv) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(IV): the evidence of a curium break

Author

Banik, Nidhu Lal, Vallet, Valerie, Real, Florent, Belmecheri, Reda Mohamed, Schimmelpfennig, Bernd, Rothe, Jorg, Marsac, Remi, Lindqvist-Reis, Patric, Walther, Clemens, Denecke, Melissa A., and Marquardt, Christian M.

Subjects
EXAFS, Dewey Decimal Classification::500 | Naturwissenschaften::540 | Chemie, Protactinium, Pa4+ ion, curium break, 3. Good health
Abstract

More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 A. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.

30. Np(IV)/Np(V) valence determinations from Np L3 edge XANES/EXAFS

Author

Denecke, Melissa A., Dardenne, Kathy, and Marquardt, Christian M.

Subjects
*X-ray absorption near edge structure, *EXTENDED X-ray absorption fine structure, *ABSORPTION, *X-ray spectroscopy, *OXIDATION
Abstract

Abstract: X-ray absorption near edge structure (XANES) spectroscopy for in situ metal valence determination has become a powerful analytical tool in heterogeneous systems. This is in part because it is applicable without prior separation procedures. For some systems, however, determining the oxidation state from XANES spectra is not straightforward and caution must be used. We show that the analysis of L3,2 edge EXAFS (extended X-ray absorption fine structure) spectra is better suited to distinguish between Np(IV) and Np(V) than from their XANES spectra. Whereas evidence for the oxidation of Np(IV) in solution samples from their Np L3 XANES is unclear, their EXAFS data unequivocally reveals Np(V) formation in the solutions. [Copyright &y& Elsevier]

Published
2005
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results