Low-temperature—irradiation study of flux-line pinning in type-II superconductors

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Abstract
Annealed wires of Nb and Nb—20 at.% Ta were irradiated at liquid-helium temperature in two different modes. In one mode thermal neutrons produced 75% of the damage, while in the other mode fast neutrons produced 85% of the damage. The increase in critical current with fluence was measured in order to determine its dependence on pin type and density and material purity. Damage due to the fast-neutron component of the flux dominated the flux pinning in both modes. The observations were consistent with the collective statistical summation theory and inconsistent with the conventional single-particle theory. The elementary pinning interaction deduced from the data by using the collective statistical theory agreed well with a recent theoretical calculation of the interaction due to the electron scattering mechanism.