Lattice parameter and residual resistivity measurements were performed on high-purity copper samples irradiated simultaneously with 2.6 MeV electrons a t 6 K up to defect concentrations of about O.lY/,. Lattice parameter changes could be measured with a resolution of Aa/a = 5 X I n six irradiations the ratio 7 = (Aa/a)/A@ was determined as a function of defect concentration and thermal recovery. During defect production the ratio 7 amounts t o (1.75 + 0.10) X lo3 (Rcm)-l and is independent of the defect concentration.Furthermore, the ratio 7 stays constant throughout the recovery stages I, 11, and 111.Hochreine Kupferfolien wurden bei 6 K mit 2,6 MeV Elektronen bis zu Defektkonzen-