Single crystal copper was irradiated with 590 MeV protons to a dose of 0.01 dpa at room temperature. Irradiated and unirradiated tensile samples were deformed and relaxation tests were performed at temperatures between 77 and 293 K. The tests show a strong temperature dependence of the flow stress of irradiated samples as compared to the unirradiated case. Deformed microstructures in the unirradiated and irradiated samples were investigated by transmission electron microscopy. The plastic deformation mechanism of the irradiated samples is dislocation slip, while in the unirradiated sample at large strains and at 77 K, twinning is observed. In the irradiated case, strain localization in the form of defect-free channel takes place, over the temperature range from 77 to 293 K. Deformation processes are analyzed through the determination of the activation volumes and energies of the deformation mechanisms, as deduced from relaxation tests. The activation energy in unirradiated Cu has an approximate value of 1.6 eV. In the irradiated samples it is suggested that more than one deformation process is operative, in the temperature range from 77 to 293 K. (C) 2004 Elsevier B.V. All rights reserved.