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367 results on '"Denecke, Melissa"'

5. Structural characterization of Nd-doped calcium aluminosilicate glasses designed for the preparation of zirconolite (CaZrTi2O7) -based glass-ceramic

Author

Loiseau, Pascal, Caurant, Daniel, Baffier, Noël, Dardenne, Kathy, Rothe, Jörg, Denecke, Melissa A., and Mangold, Stefan

Subjects
Condensed Matter - Materials Science
Abstract

This work concerns glasses belonging to SiO2-Al2O3-CaO-ZrO2-TiO2-Nd2O3 system that lead to zirconolite crystallization in their bulk after nucleation + crystal growth thermal treatments and that could find application as nuclear waste form. The understanding of crystallization processes in glasses implied to investigate their structure. The environment around Ti, Zr (nucleating agents) and Nd was characterized for various Nd2O3 loadings. Electron spin resonance study of the small amount of Ti3+ occurring in glasses enabled to identify two types of sites for titanium. EXAFS showed that Zr occupied a quite well defined 6-7-fold site coordinated by oxygen at 2.20 {\AA}, with second neighbors that could correspond to Ca/Ti and Zr around 3.5 {\AA}. This short range order presents some similarities with zirconolite, which could predispose glass to zirconolite nucleation. Nd environment was probed by optical spectroscopies, ESR and EXAFS. Results showed that the environment around Nd was very constrained by the glassy network and significantly differed from the one in zirconolite. Nd occupied a highly distorted 8-9-fold coordinated site in glass with oxygen atoms at 2.53 {\AA}. No second neighbors were clearly identified by EXAFS around Nd, but the study of Nd optical fluorescence decays suggested a strong interaction between Nd ions., Comment: 5 pages; XXIst International Congress on Glass (ICG 2007), Strasbourg : France (2007)

Published
2011

13. Physics and IAEA: Atoms for Peace and Development.

Author

Koning, Arjan, Swainson, Ian, Kanaki, Kalliopi, de Vicente, Sehila M. Gonzalez, Ridikas, Danas, and Denecke, Melissa A.

Subjects
PHYSICS, NUCLEAR counters, RADIOACTIVITY measurements, ATOMIC nucleus, NUCLEAR energy, FUSION reactors, NUCLIDES, RADIOISOTOPES
Abstract

Another example is IAEA CRPs, where the IAEA brings together scientists from all over the world to collaborate on focused research topics of shared interest, important to the agency's mission. 5 IAEA Research Reactor database, https://nucleus.iaea.org/rrdb 6 International Atomic Energy Agency, I Compact Accelerator based Neutron Sources i , TECDOC-1981 (2021). The International Atomic Energy Agency (IAEA) is the world center for cooperation in the nuclear field to help accelerate and enlarge the safe, secure, and peaceful use of nuclear technologies. IAEA Nuclear Science and Instrumentation Laboratory - Training Remit NSIL is one of the eight nuclear application laboratories the IAEA operates in Seibersdorf, 40 km south of Vienna. [Extracted from the article]

Published
2023
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33. The role of the 5f valence orbitals of early actinides in chemical bonding

Author

Vitova, T, Pidchenko, I, Fellhauer, D, Bagus, P.S., Joly, Y, Pruessmann, T, Bahl, S, Gonzalez-Robles, E, Rothe, J, Altmaier, M., Denecke, Melissa Anne, Geckeis, H., Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT), Department of Chemistry, University of North Texas (UNT), Surfaces, Interfaces et Nanostructures (SIN ), Institut Néel (NEEL), and Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])

Subjects
[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute, [PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other], Chemistry & allied sciences, Science, ddc:540, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], Dalton Nuclear Institute, Actinides XANES RIXS, Article
Abstract

One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/ϕ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements., Understanding the chemistry of heavy radioactive elements is crucial to harnessing them for fuel and medicine. Here, the authors combine advanced X-ray spectroscopy and modelling to the study the chemical bonding of the 5f valence orbitals of uranium, neptunium and plutonium.

Published
2017

37. A laser ablation resonance ionisation mass spectrometer (LA-RIMS) for the detection of isotope ratios of uranium at ultra-trace concentrations from solid particles and solutions

Author

Strashnov, Ilya, primary, Izosimov, Igor, additional, Gilmour, Jamie D., additional, Denecke, Melissa Anne, additional, Almiral, Jose, additional, Cannavan, Andrew, additional, Chen, Gang, additional, Dissanayake, Champa, additional, Doroshenko, Iryna, additional, Elghali, Tibari, additional, Enston, Emma, additional, Fernando, Biyagamage Ruchika, additional, Kasozi, Gabriel, additional, Kelly, Simon, additional, Maqsood, Mohammed, additional, Muhammad, Syahidah Akmal, additional, Muryn, Christopher, additional, Pomerantsev, Alexey L., additional, Singh, Dileep Kumar, additional, Smith, Gareth, additional, Taous, Fouad, additional, Webb, Carole, additional, Williamson, David, additional, Xu, Zhenzhen, additional, Yang, Shuming, additional, and Zitek, Andreas, additional

Published
2019
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40. Quantification of common aminopolycarboxylic acids in trench leachate from the Low Level Waste Repository.

Author

O'Hanlon, James A., Chapman, Robert D., Taylor, Frank, and Denecke, Melissa A.

Subjects
DIETHYLENETRIAMINEPENTAACETIC acid, NITRILOTRIACETIC acid, LEACHATE, ETHYLENEDIAMINETETRAACETIC acid, HIGH performance liquid chromatography, CHEMICAL preconcentration, NUCLEAR industry
Abstract

The aminopolycarboxylic acids (APCAs), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NTA), are used as decontamination agents throughout the nuclear industry; therefore, APCAs are often found in radioactive waste. Limits of acceptance on APCAs are imposed on wastes consigned to the Low Level Waste Repository (LLWR) because, when present in the waste, the ligands have the potential to mobilise otherwise surface-bound or solid radionuclides, making them available for transport to groundwater and ultimately to the bio-sphere. A selective and sensitive methodology to detect and quantify these ligands in a range of complex matrices is advantageous in supporting waste acceptance processes. A reversed-phase high-performance liquid chromatography (HPLC) procedure has been applied for quantification of EDTA, DTPA and NTA in their Fe(III)-complex form. Method validation results show linearity (r2 > 0.999), precision (intra/inter-day %RSD ≤ 10%), accuracy (recovery = 100 ± 3%), sensitivity (minimum limits of detection = 0.31, 0.38 and 4.3 μM for EDTA, DTPA and NTA, respectively) and selectivity (simultaneous determination of the three APCA complexes achieved with baseline resolution) for Fe(III)-APCAs in aqueous solution. Chromatographic peak overlap is observed for samples containing Fe(III)- and Co(III)-EDTA; two deconvolution methods (2D least-squares fitting vs. PARAFAC) were applied to resolve the peaks and the performances compared. The optimised HPLC method was applied to trench leachate samples from the LLWR site. EDTA was detected with 0.4 μM < concentrations < 1 μM in samples from four of the six sampling locations tested. The levels are not considered sufficient to increase the risk of radionuclide mobilisation. The technique is considered to be robust and will be considered further in informing limits of acceptance on APCAs. [ABSTRACT FROM AUTHOR]

Published
2019
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42. Exploring the electronic structure and speciation of aqueous and colloidal Pu with high energy resolution XANES and computations

Author

Vitova, Tonya, primary, Pidchenko, Ivan, additional, Fellhauer, David, additional, Pruessmann, Tim, additional, Bahl, Sebastian, additional, Dardenne, Kathy, additional, Yokosawa, Tadahiro, additional, Schimmelpfennig, Bernd, additional, Altmaier, Marcus, additional, Denecke, Melissa, additional, Rothe, Jörg, additional, and Geckeis, Horst, additional

Published
2018
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44. 6-(3,5-Dimethyl-1H-pyrazol-1-yl)-2,2'-bipyridine as ligand for actinide(III)/lanthanide(III) separation

Author

Girnt, Denise, Roesky, Peter W., Geist, Andreas, Ruff, Christian M., Panak, Petra J., and Denecke, Melissa A.

Subjects
Gibbs' free energy -- Evaluation, Laser spectroscopy -- Usage, Methyl groups -- Structure, Methyl groups -- Chemical properties, Pyridine -- Chemical properties, Pyridine -- Structure, Pyridine -- Thermal properties, Rare earth metals -- Chemical properties, Rare earth metals -- Thermal properties, X-rays -- Diffraction, X-rays -- Usage, Chemistry
Published
2010

45. Characterization and comparison of Cm(III) and Eu(III) complexed with 2,6-Di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine using EXAFS, TRFLS, and quantum-chemical methods

Author

Denecke, Melissa A., Geist, Andreas, Rossberg, Andre, Panak, Petra J., Weigl, Michael, and Schimmelpfennig, Bernd

Subjects
Quantum chemistry -- Research, X-ray spectroscopy -- Analysis, Europium -- Structure, Europium -- Chemical properties, Curium -- Structure, Curium -- Chemical properties, Chemistry
Abstract

The complexation of Cm(III) and Eu(III) with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-C(sub 3)H(sub 7)-BTP) in nonaqueous organic solution is studied with extended X-ray absorption spectroscopy, quantum-chemical calculations, and TRLFS. The results reveal that the n-C(sub 3)H(sub 7)-BTP selectivity for Cm(III) over Eu(III) is associated with a higher thermodynamic stability of Cm.(n-C(sub 3)H(sub 7)-BTP)(sub 3) and is not related to simple structural differences between Cm.(n-C(sub 3)H(sub 7)-BTP)(sub 3) and Eu.(n-C(sub 3)H(sub 7)-BTP)(sub 3).

Published
2005

46. Europium(II) and its halides in anhydrous room-temperature imidazolium-based ionic liquids: A combined TRES, EXAFS, and molecular dynamics study

Author

Gaillard, Clotilde, Billard, Isabelle, Chaumont, Alain, Mekki, Soufiane, Wipff, Georges, Ouadi, Ali, Denecke, Melissa A., and Moutiers, Gilles

Subjects
Absorption spectra -- Research, Europium -- Structure, Europium -- Properties, Europium -- Spectra, Molecular dynamics -- Research, Chemistry
Abstract

The state of trivalent europium dissolved in room-temperature ionic liquids (RTIL) is investigated, as a function of the RTIL anion and in the presence of added chloride using combination of spectroscopic techniques (TRES and EXAFS) and molecular dynamics simulations. The results show strong influence of the RTIL nature on the first solvation shell of europium and on its complexation with chloride.

Published
2005

47. Confinement of Iodine Molecules into Triple-Helical Chains within Robust Metal–Organic Frameworks

Author

Zhang, Xinran, primary, da Silva, Ivan, additional, Godfrey, Harry G. W., additional, Callear, Samantha K., additional, Sapchenko, Sergey A., additional, Cheng, Yongqiang, additional, Vitórica-Yrezábal, Inigo, additional, Frogley, Mark D., additional, Cinque, Gianfelice, additional, Tang, Chiu C., additional, Giacobbe, Carlotta, additional, Dejoie, Catherine, additional, Rudić, Svemir, additional, Ramirez-Cuesta, Anibal J., additional, Denecke, Melissa A., additional, Yang, Sihai, additional, and Schröder, Martin, additional

Published
2017
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