The effects of cascade remnants upon freely migrating defects were studied by measuring bombardment-induced segregation at 400C during simultaneous bombardment with 1.5MeV He and 400 to 800keV Ne, Ar or Cu. Radiation-induced segregation during single-ion bombardment with He, Ne, Ar and Cu, and the effects of pre-irradiation with the same ions, were also investigated. The marked segregation which was observed during bombardment with 1.5MeV He alone was greatly suppressed by simultaneous Cu bombardment. Such suppression disappeared as soon as the Cu bombardment was stopped. This indicated that it was caused by a transient population of cascade remnants, such as vacancy and/or interstitial clusters. In the case of simultaneous inert gas (He, Ne, Ar) bombardment, a similar suppression of bombardment-induced segregation was observed. However, the suppression persisted after Ne or Ar bombardment was stopped. The results demonstrated that the energetic displacement cascades, which were created by heavy ions, introduced additional point-defect annihilation sites which reduced the steady-state concentration of freely migrating defects. This implied that recombination predominated over defect annihilation under the bombardment conditions which were studied. Because the cascade remnants which were produced by the Cu ions were thermally unstable at 400C, the suppression of bombardment-induced segregation occurred only during simultaneous bombardment. During Ne and Ar bombardment, inert gas atoms which accumulated in the specimens appeared to stabilize the cascade remnants. This caused the suppression to persist during subsequent bombardment with He alone.

A.Iwase, L.E.Rehn, P.M.Baldo, L.Funk: Journal of Nuclear Materials, 1996, 238[2-3], 224-36