Probing plutonium dioxide nanoparticles with synchrotron methods

INTRODUCTION

Plutonium is a chemical element of significant environmental and toxicological concern. At nuclear legacy sites, previous research has demonstrated that plutonium can migrate in colloidal form in the subsurface environment across several kilometers [1-2]. Recent spectroscopic and microscopic investigations showed that so called “colloidal Pu(IV) polymers” are in fact aggregates of PuO2 nanoparticles with diameters ~ 2 nm [3-4]. The exact stoichiometry and structure of such nanoparticles remain, however, still questionable, especially with respect to surface hydration and hydroxylation, as well as the purity of the tetravalent oxidation state considering the existence of four different oxidation states (with relatively small energy barriers III, IV, V, and VI) under environmental conditions.

RESULTS

This contribution will show first results of plutonium oxide nanoparticle studies at the large-scale facility – The European Synchrotron (ESRF) by X-ray spectroscopy and X-ray diffraction methods. Pu oxide nanoparticles were prepared by rapid chemical precipitation using precursors in the different oxidation states (Pu(III), Pu(IV), Pu(V) and Pu(VI)). These precursors were obtained by chemical reduction or oxidation of Pu stock solution. The obtained nanoparticles were characterized at the Rossendorf Beamline (ROBL) at the ESRF, dedicated to actinide science. The recently upgraded ROBL beamline provides unique opportunities to study actinide materials by several experimental techniques: high energy resolution fluorescence detection (HERFD) [5], X-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS) [6], extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) simultaneously.
We will show how the detailed information about local and electronic structure and plutonium oxidation state in different nanoparticles can be obtained using the variety of methods.