Neutron-Inelastic-Scattering Measurements of Phonon Perturbations by Defects in Irradiated Copper

Neutron-scattering measurements have been made at 10 $K$ of phonons in a copper crystal neutron-irradiated at 4 $K$. The results, though clearly showing $q$-dependent defect-phonon perturbation effects, could not be explained entirely by simplified calculations for the $〈100〉$ split interstitial. A 300-K anneal removed the irradiation-induced line broadening and frequency shifts but only ∼ 50% of the additional peak structure, which was completely removed only after an 800-K anneal.