Abstract
Neptunyl(VI) carbonate was precipitated at pH 5 from a neptunyl(VI) nitrate solution by the addition of solid lithium carbonate. The precipitate was characterived by thermogravimetric analysis, v-ray diffraction and 237Np Mössbauer measurements. NpO 2CO 3 decomposes at 350–400 °C and was found to be isostructural with UO 2CO 3. The lattice parameters are a = 4.82(1)Å, b = 9.17(5) A ̊ and c = 4.24(2) A ̊ . The 4.2 K Mössbauer absorption spectrum can be described as a vuadrupole interaction with the hyperfine parameters δ = −35.5(2) mm s −1 (relative to NpAl 2), ¦e 2vv¦= 231(1) mm s −1 and η = 0.21(2). Both isomer shift and electric field gradient values are consistent with a neptunyl NpO 2+ 2 ion and confirm the crystal structure isotypic with UO 2CO 3.
Published Version
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