Abstract : Oxide films thermally grown on titanium in a weakly oxidizing environment (5 × 10−3 Pa of dry air) under irradiation with 2, 4 and 9 MeV argon have been studied. The AFM study reveals a cratering effect of 2, 4 and 9 MeV argon and a significant surface roughening effect of 2 MeV argon, both effects being largely unexpected in this energy range. The XPS analysis shows that the TiO2 stoichiometry of the superficial oxide film is fairly well maintained under argon irradiation. The Spectroscopic Ellipsometry analysis reveals an oxide film thickness multiplied by a factor of three under irradiation with 2 MeV argon by comparison with 9 MeV argon, the irradiation effect on oxide growth remaining very limited for 4 or 9 MeV argon. The possible role of the electronic but most certainly of the nuclear energy losses on the surface damage mechanism are discussed. It is suggested that the oxidizing environment is necessary to freeze the instantaneous surface damage and permits the post-mortem observation.