RADIATION-INDUCED PEAK EFFECT IN SUPERCONDUCTING NbZr

Abstract
A peak in the critical current vs magnetic field characteristic of Nb−25% Zr has been produced during a low‐temperature (∼30°K), 15‐MeV deuteron irradiation (1017 deuterons/cm2). The peak occurs at fields near the upper critical field, Hc2; essentially no changes were observed at lower fields. Annealing at 77°K produced almost no change in the peak whereas it nearly disappeared after annealing at 300°K. It is concluded that this peak is a bulk effect associated with radiation‐induced defects of intermediate size and complexity which are effective pinning centers near Hc2, but are too ``weak'' to affect the critical current at lower fields. A number of possible mechanisms are briefly discussed.