Dimensional and X‐Ray Diffraction Changes in Irradiated Single Crystal BeO

Single crystals of BeO were irradiated by high energy (≧ 1 MeV) neutrons to doses of 1020 to 6 × 1020 nvt at low temperature (< 100 °C). The crystal structure effects of irradiation were examined by X‐ray diffraction and measurement of interfacial angles between crystallographic faces. The diffraction patterns are characterized by duplex reflections each composed of a sharp and a broad component. The sharp component is attributed to the matrix crystal volume, which is expanded by a random distribution of point defects. The broad component is attributed to the presence of interplanar clusters lying parallel to the basal plane. This structure showed little change below 800 °C with short‐term anneal. Between 800 and 1600 °C there was nearly complete recovering of line breadth and lattice constants. The annealing data indicate (1) removal of the point defects, and (2) some growth of cluster size, during thermal annealing.