Abstract
Strip samples of a dilute Ta-Nb alloy exhibit superconductivity up to a maximum field which is in close agreement with the critical field of the surface sheath, providing that the surface is carefully prepared. In other surfaces much larger critical fields are observed, which appear to be associated with a decrease in mean free path due to lattice defects. The magnitude of these effects suggests that the degree of damage near to the surface may be very much greater than that induced in the bulk by any normal deformation process.