EFFECTS OF CONCURRENT IRRADIATION WITH IONS AND ELECTRONS ON THE FORMATION PROCESS OF DEFECT CLUSTERS IN COVALENT AND IONIC-CRYSTALS

In order to understand concurrent effects of damage cascades, isolated point defects and ionization on the formation process of defect clusters in covelent and ionic crystals, in-situ observations of Ge, Si and MgAl2O4 crystals have been performed under dual-beam irradiation with ions and electrons in the HVEM accelerator facility at Kyushu University. Damage cascades in the covalent crystals show up their contrast through overlap or help from other damage cascades. Simultaneous electron irradiation eliminates damage cascades in the covalent crystals through the irradiation-induced and -enhanced migration of point defects. In the ionic crystal, on the other hand, no damage cascades show up their contrast, but interstitial loops are formed through the nucleation and growth process. Effects of concurrent irradiation with ions and electrons on this process are based on defect reactions among damage cascades and isolated point defects. Homogeneous ionizing radiation plays no significant role on the nucleation and growth process of defect clusters.