Neutron scattering probes interstitials

Sensitive probes of radiation‐induced damage in metals have been hard to come by. For ionic crystals or insulators, various magnetic‐resonance and optical techniques can give detailed structural information even at very low defect concentrations. But the best tools available for studying defects in metals have been the relatively insensitive ones of neutron and x‐ray scattering. Recently two groups of theorists—Richard F. Wood and Mark Mostoller at Holifield National Laboratory, Oak Ridge, Tennessee¹ and H. R. Schober, V. K. Tewary and P. H. Dederichs at the Institut für Festkörperforschung of the Kernforschungsanlage in Jülich, West Germany²—independently predicted that the librational modes of the so‐called “dumbbell” interstitials in copper are such that the defect structure should reveal itself to neutron scattering. Experimenters at Oak Ridge rapidly followed up on their theorists' predictions and have now shown—at least tentatively—that the theorists were correct. These experiments, which were described at the International Conference on Fundamental Aspects of Radiation Damage in Metals that took place in October in Gatlinburg, Tennessee, are being hailed as a “tour de force” because they were done at exceedingly low defect concentrations.