Abstract
Among the wide range of spent nuclear fuel alteration products, uranophane-type uranyl silicates have attracted particular attention due to their ability to incorporate additional ions into their crystal structures, including other radionuclides. Two such mineral phases, uranophane (s.s.) (Ca(UO2)2(SiO3OH)2.5(H2O)) and boltwoodite ((K, Na)(UO2)(SiO3OH).1.5H(2)O), have been characterised by Raman, luminescence and laser-induced breakdown spectroscopy. Well-defined Raman features were observed in each case with the two minerals being differentiated by detection of the nu(3)(SiO4)(2-)and delta(SiOH) modes for uranophane but not boltwoodite. Some distinction between uranophane-alpha and -beta was observed by Raman, but the phase sensitivity was more apparent in the luminescence emission peak positions. The luminescence signal emitted for boltwoodite was much weaker than with uranophane, suggesting that the associated K+ and Na+ cations in the former are more efficient at chemical quenching than Ca2+. This study also reports the first luminescence excitation data for uranophane and boltwoodite.