Interstitial Dislocation Loops in Beryllium Oxide irradiated at High Temperatures

Abstract

THE presence of large numbers of prismatic dislocation loops parallel to the hexagonal {0001} basal planes of beryllium oxide after neutron irradiation at high temperatures (greater than 700° C) has been well established by transmission electron microscopy^1–3. In addition, relatively low concentrations of loops lying on {11&2macr;0} prism planes have also been observed³. However, the nature of the defects comprising these loops has not previously been determined, primarily for two reasons: (a) Beryllium oxide does not lend itself to controlled chemical thinning, and specimens have therefore been prepared by crushing or fracture techniques. Prominent {10&1macr;0} cleavage in beryllium oxide causes nearly all chips suitable for study to be cleavage fragments perpendicular to the basal plane, and the abundant basal loops are therefore usually viewed edge-on and appear as lines perpendicular to the c-axis. (b) Most specimens so far available for investigation have received rather high neutron dosages (∼10²¹ nvt, E_n ≥ 1 MeV), and have usually contained such high densities of basal loops that overlap prevented the investigation of individual images.