Effect of Thermal-Neutron Irradiation on the Superconducting Properties of Nb3Al and V3Si Doped with Fissionable Impurities

Abstract

The superconducting critical temperatures and current carrying capacities of Nb₃Al and V₃Si doped with small amounts of uranium and boron and subsequently irradiated with thermal neutrons are reported. While the critical temperatures are substantially unaffected, the critical current densities are dramatically increased by the internal fission of uranium in both materials. Samples of Nb₃Al containing 0.321 at.% uranium and V₃Si containing 0.19 at.% uranium irradiated with 1.7×10¹⁸ neutrons/cm² give superconducting critical current densities over 10⁶ A/cm² at 30 kOe. The boron‐doped samples, however, showed no effects arising from fission of boron. Two new experimental techniques have been used in this investigation. First, uranium and boron analyses as well as information on homogeneity were determined by use of the Price‐Walker nuclear track detectors. Secondly, the critical current measurements were made on 50‐mg samples of 70‐μ powders by a technique that measures the generation of odd‐harmonic voltages caused by small alternating magnetic fields applied to the sample.