FLUX PINNING IN NEUTRON-IRRADIATED HIGH-TC SINGLE-CRYSTALS

Neutron irradiation effects on high-T(c) single crystals will be reviewed. Since the transition temperature initially decreases only slowly with fluence, the radiation-induced changes in the magnetization can be attributed to radiation-induced defects rather than to changes in the primary superconductive parameters. Detailed investigations of the fluence dependence show that J(c) is enhanced considerably (up to 1- 2 x 10(22) m-2, E > 0.1 MeV), that the irreversibility lines are shifted to higher fields and temperatures, and that the rate of magnetization relaxation is strongly reduced. Based on recent information on the size and volume concentration of the radiation-induced collision cascades, the experimental data will be discussed in terms of (weak) flux pinning by the pre-irradiation defects, intrinsic pinning for H//a,b as well as strong pinning by cascades. Considerable interaction between the newly introduced pinning sites and the pre-irradiation defect structures has to be invoked.