THE ROLE OF ELECTRON-PHONON COUPLING IN THE FORMATION OF CLUSTERED VACANCY DEFECTS IN ELEMENTAL METALS FROM HEAVY-ION IRRADIATION

The role of electron-phonon coupling in reducing the lifetime of the t hermal spike of a collision cascade has been examined by calculating t he power absorbed by the electronic system of the lattice and comparin g the data with published results for the defect yield in a wide varie ty of elemental metals. A modified version of TRIM has been used to ca lculate the cascade energy density for all the irradiation conditions and materials considered. A strong dependence of the efficiency of dis location loop production (defect yield) on the cascade energy density was determined, and only at constant cascade energy density were varia tions in the defect yield for different materials compared. Good corre lation was found between the strength of electron-phonon coupling and the defect yield data for those materials that exhibit strong electron -phonon coupling. As the strength of this coupling decreased, other fa ctors which influence the molten zone lifetime, such as the melting te mperature, were found to become more significant. However, from the da ta examined, it was not possible to determine which parameters control led the thermal spike lifetime in those metals for which the power abs orbed by the electronic system was negligible; a correlation between a long thermal spike lifetime and low melting temperature was noted.