[en] EDX analysis and selective electropolishing were used to study two specimens of Fe-35Ni irradiated with neutrons at 420 degree and 520 degree C and one specimen of Fe-35Ni-15Cr irradiated at 510 degree C. Each was shown to be spinodally decomposed with the period of compositional oscillation appearing to decrease with decreasing irradiation temperature. When polishing conditions are used which promote etching, the low nickel micro-volumes are selectively attacked. The level of chromium appears to play no role in either the selective attack or the period of oscillation. The scale of surface irregularity and that of compositional oscillation appear to be identical but not related to the presence of currently existing microstructural components. 9 refs., 6 figs