Effects of Neutron Irradiation on the Superconducting Properties of NbTi and Nb₃Sn Multifilamentary Composites

Multifilamentary composite wires of Nb Ti and Nb₃Sn have been irradiated at 60 ± 5°C with fast neutrons to fluences of 6 × 10¹⁹ n/cm². Measurements of the superconducting critical current, I_c , as a function of transverse field show that the NbTi wires are only moderately affected by neutron irradiation. At a fluence of 6 × 10¹⁹ n/cm², I_c (40 kG) is 82% of the unirradiated value. The Nb₃Sn composites undergo a catastrophic reduction in I_c with an apparent threshold at a fluence of 2 to 3 × 10¹⁸ n/cm². Between 2 to 3 × 10¹⁸ and 1.1 × 10¹⁹ n/cm², I_c (40 kG) has been reduced to 4% of the unirradiated value. At a fluence of 6×10¹⁹ n/cm², the upper critical field of Nb₃Sn has been reduced from 240 kG to 9 ± 0.5 kG. The corresponding T_c has been decreased from 16.4 to 6°K. Annealing of Nb₃Sn samples irradiated to 1.1 × 10¹⁹ n/cm² produces only 19% recovery in I_c after h at 400°C.