Thermal Neutron Irradiation and Large Pinning Enhancement in Superconducting Materials

Up to 25 times enhancement of magnetic critical current density has been observed at 70 K and 2500 O for 3% 6Li-doped sintered YBCO sample irradiated with thermal neutrons at a dose of 1 x 1018 n/cm2. High energy reaction product of 6Li and thermal neutron, the 2.73 MeV 3H and 2.05 MeV 4He produced uniform damage throughout the bulk sample. The strong field dependence of the Jc enhancement points to the weak center nature of the radiation defects. The upper critical field of this weak center decreases with temperature, and is about 800, 300, 150 Oe at 30, 50, 70 K respectively.