ON THE EXPERIMENTAL-DETERMINATION OF THE MIGRATING DEFECT FRACTION UNDER CASCADE DAMAGE CONDITIONS

Information on the fraction of defects surviving intracascade recombin ation, escaping the cascade volume and migrating until their annihilat ion (''migrating defect fraction'', MDF) can be obtained from the anal ysis of radiation enhanced diffusion (RED) or radiation induced segreg ation (RIS) and maximum swelling rates. RED and RIS yield the ratio of the MDF over the effective sink strength whereas maximum swelling rat es give lower bound estimates of the MDF. The basic assumptions made i n the previous analysis of RED (RIS) and swelling are critically exami ned in the light of the present understanding of defect production in displacement cascades. MDF values deduced previously from RED are foun d to be clearly below the lower bound estimates obtained from maximum swelling rates. The discrepancy becomes even larger if the conventiona l monodefect dislocation bias is used in the analysis of swelling. Pos sible reasons for this discrepancy are discussed: (1) differences in t he contribution of mobile defect clusters produced in cascades to RED and swelling, and (2) an underestimation of both the sink strength evo lving during cascade damage conditions and the driving force for the s welling. We argue that the conventional method to deduce the sink stre ngth from sink densities observed in TEM and the application of the co nventional monodefect dislocation bias indeed yield only lower bound e stimates for the sink strength and for the swelling rate, respectively . If the MDF were established by some other method RED (or RIS) could be used to measure the sink strength.