PNNL

Abstract

We report the synthesis of pure alkali pertechnetates and analysis of these compounds by Raman spectroscopy, X-ray spectroscopy (XANES and EXAFS), solid-state nuclear magnetic resonance (static and MAS), and neutron diffraction. The structures and spectral signatures of these compounds will aid in refining the understanding of 99Tc incorporation into and release from nuclear waste glasses. This work provides much needed data to improve performance assessment models of Tc release in waste repositories. NaTcO4 shows aspects of the high electronegativity of the Na atom, resulting in large distortions of the pertechnetate tetrahedron and deshielding of the 99Tc nucleus relative to the aqueous TcO4-. At the other extreme, the large Cs and Rb atoms interact only weakly with the pertechnetate, have closer to perfect tetrahedral symmetry at the Tc atom, and have very similar vibrational spectra, even though the crystal structure of CsTcO4 is orthorhombic while that of RbTcO4 is tetragonal. Further trends are observed in cell volume and quadrupolar coupling constant.