In order to probe the possibility of simulating irradiation effects with swift ions and obtaining some insight about the production rate of freely migrating defects in iron, we studied the kinetics of copper precipitation in FeCu1.34at% irradiated at 300°C with 202 MeV O- ions and 2.5 MeV electrons. The precipitation kinetics are studied in situ (GANIL for O- ions and Van de Graaff for electrons) by measuring the electrical resistivity at 30°C to reduce the phonon component. We found that, in both cases, the resistivity versus fluence (in dpa) curves are identical. This would imply either that the relatively small cascades induced by 202 MeV O- ions (compared with those produced by neutrons) are very efficient in producing freely migrating point defects or that the energy deposition by electronic excitations plays an important role. We show that this latter possibility is not relevant for 202 MeV O18 ions.