THE RELATIONSHIP BETWEEN COLLISIONAL PHASE DEFECT DISTRIBUTION AND CASCADE COLLAPSE EFFICIENCY

Defect distributions after the collisional phase of cascade damage pro cesses were calculated using the computer simulation code MARLOWE, whi ch is based on the binary collision approximation. The densities of va cant sites were evaluated in defect-dense regions at the end of the co llisional phase in simulated ion irradiations of several pure metals ( Au, Ag, Cu, Ni, Fe, Mo and W). The vacancy density distributions were compared to the measured cascade collapse efficiencies obtained from l ow-dose ion irradiations of thin foils reported in the literature to i dentify the minimum or ''critical'' values of the vacancy densities du ring the collisional phase corresponding to cascade collapse. The crit ical densities are generally independent of the cascade energy in the same metal. The relationships between physical properties of the targe t elements and the critical densities are discussed within the framewo rk of the cascade thermal spike model.