To characterize putative interactions between freely migrating defects (FMD) and remnants of energetic displacement cascades, radiation‐induced segregation (RIS) in Cu‐1 at. % Au was measured by Rutherford backscattering during separate and simultaneous irradiation at 400 °C with 1.5 MeV He and 800 keV Cu ions. The strong RIS observed during only He irradiation was greatly reduced under simultaneous Cu irradiation at approximately the same displacements per atom rate; increasing the Cu flux by a factor of 5 suppressed the RIS from the He beam almost completely. The suppression of RIS at 400 °C disappeared quickly when the Cu irradiation ceased. These results demonstrate that a transient population of interstitial and/or vacancy clusters from the Cu irradiation greatly reduces the survival rate of FMD produced by the He. ©1995 American Institute of Physics.