CESIUM DIFFUSION IN SODIUM BOROSILICATE GLASS STUDIED BY LOW-ENERGY ION-SCATTERING

A new, time-saving method to determine the diffusion coefficient of ca esium in sodium borosilicate glass is presented. With low-energy ion s cattering (LEIS) the diffusion coefficient of caesium in this glass, w here the main components are the same as those in nuclear waste glass, is determined in a wide temperature range (723-849 K). Compared to th e conventional concentration couple method where the diffusion has to be studied over large distances (10(5) nm), it is shown that by using LEIS accurate measurements can be performed when diffusion takes place over distances of the order of 10 nm. Diffusion coefficients for caes ium as low as 2.6 x 10(-22) m(2) s(-1) are extracted from the measurem ents. This is a factor of 10(6) smaller than that measured with the co ncentration couple method for the same system and more than a factor o f 10 smaller than diffusion coefficients for caesium determined in nuc lear waste glasses by other techniques. At high temperatures the resul ts of the different methods are in absolute agreement.