The free defect survival ratio is calculated by “cascade-annealing” computer simulation using MARLOWE and modified DAIQUIRI codes in various cases of PKA spectra. The number of subcascades is calculated by “cut-off” calculation using MARLOWE. The adequacy of these methods is checked by comparing the results with experiments (surface segregation measurements and TEM cascade defect observations). The correlation using the weighted average recoil energy as a parameter shows that the saturation of the free defect survival ratio at high PKA energies has a close relation to the cascade splitting into subcascades.