Anelastic Relaxation due to the Tunneling of Trapped D in Tantalum

Internal friction measurements in the kHz range have been performed on Ta containing D, O, and N at liquid-helium temperature. A relaxation process is observed below 60 K showing a sharp discontinuity in the slope at the normal-superconductor transition temperature. The process is interpreted as relaxation of a two-level system consisting of O (N)-D complexes interacting mainly with the conduction electrons.