Phonon soft modes and damage production by high electronic excitations in pure metals

It is now well known that during high-energy heavy-ion irradiation, the very high-energy deposition in electronic excitation induces a spectacular damage creation in some types of metallic targets. A selected number of pure metals has been irradiated by GeV ions in order to test some possible criteria which might be pertinent to explain such effects: electron-phonon interaction, electrical conductivity, existence of various allotropic phases,... The present results show that the latter criterion or more precisely that the existence of a displacive transformation associated with a soft mode in the phonon spectrum seems to favour efficient energy transfers between highly excited electrons and target atoms. For titanium targets, electron microscopy observations show striations which are parallel to the incident ion beam direction