EXAFS with grazing incidence: application to leached nuclear waste glasses

Measurements have been made of the effects of water corrosion on the fluorescence EXAFS emission above the Lsub(III) edge of U from a flat borosilicate glass containing simulated nuclear waste with a cation concentration of about 3 wt%. The x-rays were incident at grazing angles below the critical angle for total external reflection, limiting the penetration depth to about 3 nm. The observed changes may thus be associated with the surface region formed during corrosion. The magnitude of the U Lsub(III) threshold increases with leaching, indicating that there is an increase in the concentration of U in the surface region. There is a corresponding modification of the form of the EXAFS signal suggesting an increase of the U-U structural correlations. This EXAFS technique of limiting x-ray penetration into a sample by use of grazing incidence does not require vacuum conditions, and should be applicable to other surface effects. (author)