Changes in the superconducting critical temperature after fast-neutron irradiation

Abstract

The decrease in the superconducting transition temperature T_c 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 T_c 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 T_c depression with irradiation. The total decrease in T_c of V₂Hf was 5%, while ΔT_c(Nb₃Al) =23%, ΔT_c(PbMo₆S₇) =61%, and ΔT_c(SnMo₅S₈) =51%. Log(ΔT_c) 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 T_c 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.