Magnetic field dependence of the relative critical current density in γ-irradiated polycrystalline YBa₂Cu₃O₇

The effect of different doses of γ-rays on the behavior of the critical current density, J_c in an YBa₂Cu ₃O₇ polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a ⁶⁰Co γ-ray source at a dose rate of 0.5 MR/h. J_c was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J_c above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non-monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ-rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms.