Rutherford back-scattering spectrometry was used to measure diffusion constants of bromide in NaCl crystals at 20 to 600C. For crystals grown from the melt at 500C and above, the data agreed well with literature data measured using other techniques. At about 450C, the activation energy fell markedly; leading to a knee in the Arrhenius plot and surprisingly high diffusion constants, at room temperature, of some 2 x 10-16cm2/s (table 117). In crystals grown from aqueous solution, cleavage led to a significant surface enrichment of Br on the newly formed surface, compared to the bulk composition. In such porous crystals, Br could move by several microns within minutes. Pre-annealing (500C, 3h) prevented this surface enrichment. The diffusion constants in such pre-annealed crystals were approximately the same as in melt-grown crystals.

Diffusion Constants of Br in NaCl Measured by Rutherford Backscattering Spectroscopy. M.Hess, U.K.Krieger, C.Marcolli, T.Peter, R.H.Doremus, W.A.Lanford: Journal of Applied Physics, 2009, 105[12], 124910