Quantification of the impact of defect density
on dissolution rate and nanotopography on
 alpha particle irradiated biotite crystals

Alpha particles emitted from actinides can cause lattice defects in crystalline solids. These affect surface reactivity of various reactions such as dissolution, growth or sorption1. Biotite is an important rock-forming mineral in a variety of igneous and metamorphic rocks that are considered for use as deep geological repositories. The frequent occurrence of biotite in host-rocks can quantitatively influence the retention of migrating radionuclides in the far field2. Therefore, understanding and quantifying the effects exposure to radionuclides can have on the sorbing capabilities of a crystal, will lead to an improved predictability of the far-field natural barriers upon which safe waste disposal relies. In this study, we investigate the formation of crystal defects in biotite and their influence on surface reactivity. For this, two pristine biotite samples were irradiated with and 4He3+ focused ion beam in order to induce crystal structural damage. This is an analogue to the situation of radionuclide release in the repository. The irradiation parameters were chosen to avoid amorphization and to focus on crystal defect development. The samples are them surface-controlled dissolved to finally quantify the defect density by using vertical scanning interferometry (VSI). Subsequently, the surface-modified biotite samples are used for sorption experiments witch actinide analogues such as 152EU3+. Comparison of the anticipated results will provide conclusions about the quantitative changes in reactive transport processes of actinide migration in sheet-bearing host rocks.