STRUCTURE AND KINETICS OF CASCADES IN COPPER UNDER ION AND OR ELECTRON-IRRADIATION

An in-situ observation system of radiation damage under ion and/or electron irradiation, which consists of a 1250 keV transmission electron microscope, an ion accelerator and an imaging system, is outlined. The microstructural evolution of cascades during dual beam irradiation with 30 keV Xe+ ions and 250 keV or 1000 keV electrons has been examined in copper at room temperature using the system. The density of cascades shows a linear increase followed by a square root dependence on irradiation time under irradiation with ions and 250 keV electrons. On the contrary, dual beam irradiation with 30 keV Xe+ ions and 1000 keV electrons gives a linear nucleation rate followed by a much slower nucleation rate eventually leading to saturation. The saturation value is lower at the higher 1000 keV electron flux. A kinetic equation for describing the microstructural evolution of cascades, which includes the effect of free interstitials produced by 1000 keV electrons, is proposed.