Scanning Transmission X-ray Spectromicroscopy of Actinide Complexes
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1104-NN06-06
Scanning Transmission X-ray Spectromicroscopy of Actinide Complexes Markus Janousch1,2, Roy Copping1, Tolek Tyliszczak1, Ingrid Castro-Rodriguez1, and David K. Shuh1 1 Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA, 94720 2 Laboratory for Synchrotron Radiation 1, Paul Scherrer Institute, Villigen, 5232, Switzerland ABSTRACT The fundamental characterization and understanding of 5f electron behavior in actinide complexes is imperative to provide an enhanced basis for the rational and accelerated development of improved processes relevant to nuclear energy. Soft x-ray absorption spectroscopy utilizing the scanning transmission x-ray microscope (STXM) at the Advanced Light Source-Molecular Environmental Science (ALS-MES) Beamline 11.0.2 has been used to probe the electronic characteristics of a nitrogen donor ligand 2,6-Bis(2-benzimidazyl)pyridine (BBP) and its resulting U(IV) complex. The nitrogen K- and carbon K-edges have been collected from both ligand and uranium complex, as well as the uranium 4d-edge from the complex. Upon complexation, the light element absorption spectra change markedly and the uranium spectra from the complex is compared to the reference spectrum obtained from U(IV)Cl4. The evolution of the spectral features are described and interpreted within a simple conceptual framework. Based on spectral evidence alone, the uranium is bound through the pyridine-like nitrogens and the oxidation state of the uranium is consistent with a U(IV) species. INTRODUCTION Several Advanced Light Source (ALS) beamlines (BLs) are being used to investigate the chemical bonding in a range of actinide materials with soft x-ray synchroton radiation (SR) [1]. An important characteristic of the soft x-ray region is the capability to directly probe light element K-edges by near-edge x-ray absorption fine structure (NEXAFS), such as the nitrogen and oxygen K-edges, that are frequently key constituents of actinide materials. In particular, the scanning transmission x-ray microscope (STXM) at the ALS-Molecular Environmental Sciences (ALS-MES) BL 11.0.2 is being utilized for NEXAFS at the light element thresholds and at the actinide NIV,V (4d3/2,5/2) core level edges (700 eV to 940 eV) downstream of an elliptical polarization undulator (EPU) [2]. The ALS-MES STXM can image and collect NEXAFS spectra from particles with a spatial resolution better than 30 nm from 110 eV to 2160 eV [3]. Safety precautions for radioactive STXM investigations require encapsulation of the actinide materials between two thin silicon nitride windows. The ALS-MES STXM has performed spectromicroscopy studies of light actinide oxides, actinide colloids, actinide complexes through curium, and several other actinide materials systems [4-7]. The results of these initial studies have yielded information to compare to theory and have clearly shown the utility of coupling theory to soft x-ray experiments especially for actinide materials.
The rational development of new soft-donor ligands for the separation of actinide(I
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