Ti diffusion in MgO(100) has been studied for MgO that was prebombarded with the inert ions Ne+, Ar+, and Kr+ in the keV energy range using various ion doses, energies, momenta, and penetration ranges. Diffusion was induced by annealing to 1000 degreesC for 6 min following the prebombardment and Ti evaporation. This type of radiation enhanced diffusion (RED) is called non-steady-state RED, or NSRED. The diffusion penetration profiles were analyzed by using secondary ion mass spectrometry depth profiling techniques and TRIM ion trajectory simulations. The observed diffusion behaviors were treated with our previously developed model for NSRED. A figure of merit, Sigma, has been introduced to assess the density of extended vacancy defects (EVDs) responsible for NSRED and to compare NSRED effects for the different ion bombardment parameters. The trends observed in Sigma are in agreement with the experimentally observed RED effects and provide a quantitative measure of their magnitudes. The results show that the NSRED effects and vacancy densities responsible for NSRED correlate with the degree of vacancy production from TRIM simulations. It is found that NSRED of Ti in MgO and the density of EVDs responsible for NSRED reach a saturation level after a dose of similar to10(16) ions/cm(2) for 7 keV Ar+ prebombardment. A threshold value of the vacancy production for the formation of EVDs for NSRED at this dose is in the range of 94-111 vacancies/ion from TRIM simulations.