Effect of uranium doping and thermal neutron irradiation on the flux-pinning of silver-clad Bi-Sr-Ca-Cu-O tapes

Ag/Bi-2223 tapes doped with small quantities of ²³⁵UO ₄ powder were prepared by the powder-in-tube process and irradiated in a thermal neutron environment. Substantial improvements in critical current density (J_c)-applied field (H) performance and anisotropy have been previously reported. However, the radioactivity of the silver sheath is a limiting factor for commercial and industrial applications of this technique. Here we report the performance of the technique using various doping levels (from 0.15 to 2 percent by weight (wt.%) UO₄) and thermal neutron fluences (Φ_n), in order to further reduce the silver radioactivity. Optimum fluence levels are identified and an optimum combination in terms of J_c - H performance is discussed. At a doping level of 2% ²³⁵ UO₄, a normalised J_c enhancement of 250 times is observed for an 0.8 T field aligned along the c-axis, and 25 times at 3 T along the ab-plane at 77 K, compared to pre-irradiation values. At 0.6%, these figures are 500 and 10 times, respectively. The effects of the uranium doping and thermal neutron irradiation on the flux pinning strengths are also directly probed using dynamic relaxation techniques. The results show an increase in the effective pinning potential after doping and irradiation