BEHAVIORS OF CASCADE DAMAGE STRUCTURE UNDER ELECTRON IRRADIATION AND ANNEALING

Abstract

When the crystalline materials are neutron irradiated under fission and fusion conditions, a large number of point defects and cascade damage are introduced. These defects behaviors affect the microsturctural evolution and mechanical and chemical properties. Especially the initial damage structures influence on the micro-structural development during further irradiation but it is impossible to observe the initial stage of the irradiation damage under neutron irradiation conditions. For these study transmission electron microscopy and ion-accelerator are useful because of the possibility of direct observation under irradiation by connecting high voltage electron microscope (HVEM) with ion accelerator to simulate the neutron irradiation. Namely it is possible to study due to in-situ experiment the behaviors of cascade damage and point defects. It has been already studied on the cascade damage behaviors under ion-irradiation, and it has been pointed out that cascade collapse affect the microsturctural evolution under the irradiation. According to several researches vacancy loops were formed and also were nucleated from cascade depleted zones. However the more detailed behaviors of cascade damage have been not clarified yet. Especially the role of cascade on the segregation or nucleation of precipitate induced by irradiation, and dislocation evolution during further irradiation. In the present study, direct TEM observation and chemical compositional change have been carried out after introducing cascade by means of ion accelerator and electron-irradiation by HVEM.