Characterization of cesium diffusion behavior into granite matrix using Rutherford backscattering spectrometry

The characterization of radionuclide diffusion behavior is necessary for performance assessment of granite as a geological barrier for high-level radioactive waste disposal. Rutherford backscattering spectrometry (RBS), a novel nuclear ion-beam technique, was selected in this study because it is suitable for analyzing the concentration gradients of heavy elements in a well-defined matrix and allows measuring diffusion coefficients on a micrometer scale. In this study Cs was selected to represent Cs-135 (a key radionuclide in high-level waste) diffusion in granite. The Cs energy spectrum and concentration deep profile were analyzed and the diffusion coefficient of Cs in granite for three different locations were determined, which were 2.06 × 10⁻¹⁹m² s⁻¹, 3.58 × 10⁻¹⁹m² s⁻¹, and 7.19 × 10⁻¹⁹m² s⁻¹-19m2 s–19m2 s⁻¹, respectively, which were of a similiar order of magnitude. Results from other studies are also compared and discussed in this paper.