DEFECT RECOVERY IN ALPHA-FE E--IRRADIATED AT 300-K

Defect annealing recovery has been studied, by measuring positron life time spectra, in high-purity alpha-iron irradiated at 300 K with 3 MeV electrons to a fluency of 7 x 10(19) cm-2. Vacancy clusters containin g 6-10 single vacancies were observed immediately after irradiation du ring which they were possibly forming (the so-called ''irradiation ann ealing''). With increasing temperature, the agglomerates continually g row in size at the expense of their concentration, giving rise to the formation of microvoids (> 15 vacancies). Also present were other type s of defects, probably immobile vacancies trapped by impurity (e.g. ca rbon) atoms and dislocation/loops generated presumably from collapse o f voids during the relatively high dose irradiation and/or the anneali ng. The immobile vacancies eventually became movable at around 350 K, supplying the growing clusters and thus leading to a stabilization in their concentration till around 500 K. Between 500 and 700 K, microvoi ds gradually evaporated, but the dislocation-associated defects were a ble to survive annealing at temperatures as high as 700 K. The void si ze and concentration and their evolution have been evaluated on the ba sis of both the to date theoretical and experimental studies. The temp erature dependence was also observed of positron trapping into vacancy agglomerates of various sizes.