The effects of irradiation at cyrogenic temperatures and electron irradiation on Tsub(c) and the transport properties of A-15 superconductors

The electrical resistivity rho and Tsub(c) have been measured on vapor deposited films of Nb3Ge and Nb3Sn subjected to α-particle and electron irradiation. Both Nb3Sn and Nb3Ge films held at 30 K were irradiated with 2.5 MeV α-particles. Tsub(c) and rho0, the electrical resistivity at 25 K, were measured in situ as a function of fluence without warming up the samples. In addition, Nb3Sn films held at 500C were irradiated with 2.0 MeV electrons. Tsub(c) was found to correlate with rho0, which implies that Tsub(c) is affected by the total defect concentration. Of particular interest is the shape of the Tsub(c) vs. rho0 curve for low fluences. A discussion is given of why this low fluence region is important in distinguishing between different models of Tsub(c) depressions. It is believed that the strong depression in Tsub(c) with increasing rho0 (until saturation of Tsub(c)) is due to smearing of the density of states. The density of states in the damaged films was estimated from critical field data, along with measurement of rho0. (Auth.)