Irradiation effects on superconductors

Past studies on the effect of neutron irradiation on superconducting alloys and compounds have shown that neutron irradiation causes major changes in their superconducting characteristics such as an increase in the critical current density and a decrease in the critical temperature for superconducting transition. The present report summarizes these study results on the changes in the superconductivity and structure caused by neutron irradiation. Some problems encountered in the course of the study and still remaining to be solved are pointed out and discussed. Some recent topics on the effect of irradiation on high Tc superconducting oxides are also addressed. The increase in critical current density is attributed to the magnetic flux pinning effect due to irradiation damage. In the A15-type superconducting compounds, deterioration in the regular structure due to irradiation leads to a decrease in the critical temperature. Observations on Nb3Sn show that irradiation defects are removed during annealing up to a certain temperature, followed by recovery of the regular structure above that temperature to increase the critical temperature. (N.K.)