Charge Distribution and Local Structure of Americium-Bearing Thorium Oxide Solid Solutions

Abstract

The electronical and structural properties of Th(0.80)Am(0.20)O(2-x) materials have been studied by the coupling of X-ray diffraction and X-ray absorption spectroscopy techniques. A substoichiometric fluorite Th(IV)(0.80)Am(III)(0.20)O(1.90) solid solution is found following sintering in moisturized Ar-H(2). In contrast, heating of this sample in air leads to a nondefective fluorite Th(IV)(0.80)Am(IV)(0.20)O(2.00) solid solution. The structures of these solid solution compounds were fully characterized by assessing the interatomic distances, the coordination numbers, and the structural disorder. The effect of the sintering atmosphere on these crystallographical parameters and on the cation valences has been determined and the capability of ThO(2) to accommodate tri- and tetravalent actinides in the fluorite structure assessed.

Melting behaviour of americium-doped uranium dioxide

“…Fits were performed between 1.6 and 6 Å at both the U L II and Am L III edges, with a k-weight value of 3. As often employed for An L III /L II [18,[38][39][40], the amplitude factor (S 0 2 ) was set at 0.90 for U and Am shells. The shift in the threshold energy (DE 0 ) was varied as a global parameter.…”

XAS and XRF investigation of an actual HAWC glass fragment obtained from the Karlsruhe vitrification plant (VEK)

“…11 (Am L3). Reference spectra for the crystalline actinide(IV) dioxides UO 2 , NpO 2 , PuO 2 and AmO 2 were obtained from [37][38][39], recorded in transmission mode at the same experimental station. Data for the Am(III) aqua ion was taken from [40] and displayed in Fig.…”

Comparative XRPD and XAS study of the impact of the synthesis process on the electronic and structural environments of uranium–americium mixed oxides

“…In addition to the three single scattering paths (Me-O, Me-Me and Me-O), one multiple-scattering path (Me-OMe-O-Me) was also considered in the FEFF calculations. As often employed for An L III /L II [19][20][21][22][23][24][25], the amplitude factor (S 0 2 ) was set at 0.90 for U and Am shells. The shift in the threshold energy (ΔE 0 ) was varied as a global parameter.…”