A Raman spectroscopic study of high-uranium zircon from the Chernobyl "lava"

Srongly zoned, high-uranium zircon which crystallized from melt formed during the accident at the Chernobyl nuclear power plant in 1986 has been studied by confocal Raman spectroscopy, EPMA and BSE imaging. The correlation between the Raman and EPMA data allowed the mode behaviour to be studied as a function of the U content. The crystals have a USiO (sub 4) content of 0.6-11.6 mol%, corresponding with 0.8-15.8 wt% UO (sub 3) . The frequency of the symmetrical and anti-symmetrical stretching mode decreases by 0.67 and 0.75 cm (super -1) per mol USiO (sub 4) , respectively, which is a result of increasing Si-O bond length with increasing U content. The line broadening, reflecting the range of local distortions (microscopic strain) is most pronounced for the lattice modes, in agreement with the large size difference of both cations. The E (sub g) lattice modes, involving the movement of the SiO (sub 4) tetrahedron and the cation within the a(b) plane, shows significantly larger line broadening with increasing U content than the B (sub 1g) modes, involving lattice vibrations along c, suggesting that the microscopic strain is significantly larger in the a(b) plane than along the c axis, which can be explained by the structural properties of zircon.