[en] This work first deals with problems concerning accurate measurements on SQUID magnetometers and offers solutions relevant to a quick and reproducible orientation method of tiny single crystals that might be done even under liquid nitrogen. Given models to obtain the critical current density J_c(B) from magnetization measurements had to be reconstructed due to the sample shape and anisotropy effects. Taking into account the average induction B inside the sample a new evaluation procedure has been developed. Fast neutron irradiation of YBa₂Cu₃O_7-δ single crystals has proved to result in large increases of critical current densities and pinning forces. In addition the very anisotropic shift of the irreversibility line and the dependence of the critical temperature T_c on the neutron fluence have been observed. One single crystal was exposed to fast neutrons at low temperatures and its magnetization measured without warming up to more than 95 K. The increase of critical currents in this crystal was significantly larger than in those irradiated at ambient reactor temperature (ca. 50 deg C). Only part of this difference was removed during annealing at room temperature. This experiment referred to possible applications in future fusion reactors. The flux pinning mechanism in neutron-irradiated YBa₂Cu₃O_7-δ is deduced to depend on an interaction between the pre-irradiation defect structure and the intrinsic pinning mechanism on one side, and the neutron-induced cascades and point defect clusters on the other side