The radiation damage during XANES experiments on alkanethiols capped gold nanoparticles has been investigated. Different carbon length chains and nanoparticle sizes have been studied. Changes in the spectra after 45 minutes of irradiation, using a bend magnet, were observed for chains with more than 6 carbon atoms and are associated with the cleavage of S-C bonds and formation of atomic sulphur on the nanoparticle surface.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas