Competing Mechanism of the γ-Rays in the Grain Boundaries of High Temperature Superconductors

The behavior of the critical current density, J_c under several γ-irradiation doses have been investigated in a Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ superconducting polycrystal and in superconducting tapes of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ and T_l2Ba₂Ca₂Cu₃O₁₀. This study was conducted under several values of applied magnetic field and at high temperatures using I-V measurements. All samples in this study were irradiated at room temperature by a ⁶⁰Co γ-ray source at a dose rate of 0.5 MR/h. In the three samples used, small γ-irradiation doses were found to enhance J_c at all applied fields. The enhancement of J_c values is more significant for small values of megnetic field. Large γ-irradiation doses were found to have slight effect on enhancing J_c in the two superconducting tapes while it was found to suppress J_c values in the Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ polycrystal at small applied fields. At high temperatures and large applied fields. At high temperatures and large applied fields, large γ-irradiation doses were found to have insignificant effect on Jc in the Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ polycrystal. These results are discussed and explained in terms of the roles of conflicting mechanisms of defects created by γ-rays in the regions of the grain boundaries.