CORRELATION OF VACANCIES IN ALPHA-IRON AND COPPER AFTER LOW-TEMPERATURE NEUTRON-IRRADIATION OBSERVED BY SMALL-ANGLE SCATTERING OF SYNCHROTRON-RADIATION

The correlation of vacancies in Fe and Cu, irradiated with fast neutrons at low temperature, was examined by small-angle scattering (SAS) of synchrotron radiation. The scattering curves were analysed in terms of a distribution of depleted zones (DZ) according to the appropriate recoil spectrum, After irradiation and annealing at 90 K single vacancies and small agglomerates were found in Fe. 70% of them were correlated in DZ with an average radius of 12.6 Angstrom,and a mean vacancy concentration of 1.1%. In Cu we observed larger agglomerates-<n> = 11-15 vacancies-in DZ with an average radius of 8.2 Angstrom and a mean vacancy concentration of 5.2%. A strong scattering signal at very low scattering angles is attributed to correlations between the individual cascade zones, During recovery we observed agglomeration of the vacancies in both metals. While in Cu the correlation between individual DZ survived annealing at 430 K, the correlation vanished in Fe samples during annealing in stage m. A computer code was developed to simulate the correlation between the individual cascades in Fe. It was found that the observed negative curvature of the resistivity damage rate can be explained by this correlation effect.