The production of extended defects by a high density of electron excitation has been described in many materials for ion irradiation and high-energy cluster irradiation. The parameter used to characterize these irradiations is generally the electronic stopping power or linear energy transfer (LET). We have studied the damage production at the surface of mica by near-field microscopy for irradiations by ions at different velocities and by high-energy clusters. At a given LET, the damage yield depends on the velocity of the ions. To describe this velocity effect, we der ne a reduced LET in which only the ionizations close to the ion path are taken into account. With this reduced LET, there is no difference between high- and low-velocity ion irradiations. However, in this description, we observe a deviation for the cluster irradiation which comes from the lower charge of the clusters. The mean charge of the clusters below the surface can be extracted from this deviation.