Effect of Point Defects in Copper on the Anomalous Transmission of X Rays

Anomalous x-ray transmission (Borrmann) measurements were made at 4.2 ^∘{}K on nearly perfect copper single crystals before and after irradiation at 20 ^∘{}K with 3-MeV electrons (total integrated flux 0.87 ×{} 10¹⁸ electrons/cm²). The intensity in the diffracted direction was measured for the (111), (222), (333), and (220) reflecting planes. The measured intensity changes were (1.2 ±{} 0.4)%, (4.5 ±{} 0.6)%, (8.9 ±{} 0.8)%, and (4.1 ±{} 0.8)%, respectively. The observed intensity changes are consistent with predictions if it is assumed that the damage consists of isolated interstitials and vacancies. Possible configurations of the interstitial are discussed. Measurements after annealing at 80 and 300 ^∘{}K were made. The measurements are consistent with small defect clusters forming when the irradiated crystals was heated to 80 ^∘{}K, and some clusters remaining after annealing at room temperature.