Europium migration in Argilaceous Rocks : on the use of Micro Laser-Induced Breakdown Spectroscopy (micro LIBS) as a Microanalysis Tool Denis Menut 1 , Michael Descostes 2 , Patrick Meier 2 , Jean Radwan 2 , Patrick Mauchien 1 and Christophe Poinssot 2 1CEA Saclay, Nuclear Energy Division, DPC/SCP/LRSI, Bâtiment 391, 91 191 Gif sur Yvette, France 2CEA Saclay, Nuclear Energy Division, DPC/SECR/L3MR, Bâtiment 450, 91 191 Gif sur Yvette, France ABSTRACT Eu migration in a Callovo-Oxfordian argilite sample was studied using the micro LIBS technique. Quantitative elemental mapping were made by micro LIBS that showed the actual distribution of the various micro areas observed on the Callovo-Oxfordian sample’s surface. Calcite, dolomite, alumino-silicates, quartz, pyrite and iron oxides were identified and their statistical distribution was determined. Experimental Eu profiles observed are consistent with diffusion process accompanied by heterogeneous sorption on alumino-silicate surface INTRODUCTION As a potential host rock candidate for a high-level radioactive repository, the argillite is under investigation in the Andra Underground Rock Laboratory in Meuse/Haute-Marne (France). Diffusion is assumed to be the main transport mechanism governing radionuclides migration through the Callovo-Oxfordian argillite formation. Most of our knowledge of the transport parameters in this medium is obtained using through diffusion techniques [1] on samples at a centimetric scale assuming homogeneous soil properties. More realistic models should consider the physical and geochemical heterogeneities at a variety of spatial scales. Micro analytical techniques demonstrated their ability to probe down to finer details such as patchwise geochemical micro areas The ability, of micro LIBS to perform localized spectrochemical analysis of nonconductive sample is of fundamental importance for numerous tasks in environmental technology. Diffusion is assumed to be the main transport mechanism governing radionucleides migration through the argillite formation. The aim of this work was to propose an alternative technique to confirm, with a microanalytical technique, the observations obtained by through diffusion technique [1]. The Laser-Induced Breakdown Spectroscopy (LIBS) technique has recently been developed as a versatile and sensitive probe for spectrochemical analysis of various materials [2]. The study of elemental composition of material surfaces by LIBS is based on analyzing the optical emission from the plasma created by a focused laser beam. The distribution of elements can be obtained by scanning the laser beam over the surface area to be investigated. This laser-based technique Mat. Res. Soc. Symp. Proc. Vol. 932 © 2006 Materials Research Society