Effect of Neutron Irradiation on High-Temperature Superconductors

In recent years, rapid improvements have been made to the quality of high-temperature superconductors (HTSs). We carried out a feasibility study on the application of HTS coils in medical accelerators, which are used for particle cancer therapy. In this application, HTSs are exposed to radiation. As a result, the HTS conductors become radioactive, thereby making the operation and maintenance of the reactors or accelerators difficult. Further, radiation affects the superconducting characteristics and causes an increase in the amount of nuclear waste generated. Therefore, it is necessary to investigate the effect of radiation on HTSs. In this study, we carried out irradiation experiments on Bi-2223 and YBCO tapes at room temperature by using 14-MeV neutrons (dose: 77 kGy). We also performed radioactive analyses on HTS tapes and carried out current-voltage (I-V) measurements on the tapes immersed in a liquid-nitrogen (LN₂) bath, before and after irradiation. The irradiation to YBCO had been conducted in the past. We irradiated neutrons to YBCO and Bi-2223 tapes on the assumption that they will be applied by the medical accelerator.