Changes in the superconducting critical temperature after fast-neutron irradiation

The decrease in the superconducting transition temperature Tc after fast-neutron irradiation has been measured in V2Hf (C-15 Laves phase), Nb3Al (A-15 phase), PbMo6S7 (Chevrel phase), and SnMo5S8 (Chevrel phase). The samples were irradiated at 6 K and warmed to 300 K during transfer to the measuring cryostat. The Tc of the samples was measured as a function of dose up to 3.0×1019 n/cm2 (E≳0.1 MeV). The different crystal structures showed a marked difference in the sensitivity of the Tc depression with irradiation. The total decrease in Tc of V2Hf was 5%, while ΔTc(Nb3Al) =23%, ΔTc(PbMo6S7) =61%, and ΔTc(SnMo5S8) =51%. Log(ΔTc) was linear with dose for all samples as expected for radiation saturation, i.e., the damage rate was proportional to the undamaged fraction. The recovery of Tc after a series of 5-min isochronal anneals up to 1200 °C has been measured, and the annealing stages observed are discussed in terms of the radiation-induced defects.