Trial Fabrication of Practical High-Jc Superconductors by Neutron Irradiation Method

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This study aimed to increase the critical current density Jc of high-Tc conductors to the level for practical application with fast-neutron irradiation or thermal-neutron irradiation after uranium doping. We irradiated Bi-2212 single crystal specimens and Y-123 bulk specimens fabricated by melt-growth process with fast neutrons in YAYOI reactor, University of Tokyo, JMTR & JRR-3, JAERI and measured the change in superconducting properties due to irradiation. Very large enhancement in Jc and pinning potential for the specimens irradiated with the order of 10^<17> n/cm^2 were observed. Thermal annealing also much increased Jc and pinning potential for heavily irradiated specimens at 673K.We also evaluated the induced radioactivities of the materials and uranium-doped Y-123. Most of the radioactivity came from the impurities in the materials. It is concluded that decrease of radioactivity is possible by decreasing some impurities including Zn, Co, etc, and kg level of the materials can be improved in superconducting properties for practical use in spite of the radioactivity.