Measurements of the effects of60Co &ggr;‐ray irradiation have been made upon the dislocation internal friction and modulus defect in copper single crystals from 333° to 393°K. It is found that the number of pinning points which are nucleated on the in‐grown dislocations by the lattice defects produced by the irradiation depends upon the &ggr;‐ray flux, or more directly, upon the concentration of defects in the dislocation core. At the smallest flux level available (1.3×109photons/cm2/sec), it is found that the dislocation‐defect trapping curves are essentially linear, and that the slopes of the linear curves vary exponentially with temperature. These results form the basis of the analyses given in Parts II and III of this series.