Effect of irradiation spectrum on the microstructural evolution in ceramic insulators

Abstract

Cross section transmission electron microscopy has been used to investigate the microstructure of MgAl 2O 4 (spinel) and Al 2O 3 (alumina) following irradiation with ions of varying mass and energy at room temperature and 650°C. Dislocation loop formation was suppressed in specimens irradiated with light ions, particularly in the case of spinel. An evaluation of the data showed that dislocation loop formation during irradiation at 650°C was suppressed when the ratio of the electronic- to nuclear -stopping power was greater than ∼ 10 and ∼ 1000 for spinel and alumina, respectively. These results clearly indicate that light ion and electron irradiations produce microstructures which are not representative of the microstructure that would form in these ceramics during fission or fusion neutron irradiation. The absence of observable dislocation loops following energetic light ion irradiation is believed to be due to ionization-enhanced diffusion effects, which promote point defect recombination. The effect of uniform background levels of ionizing radiation on the microstructural evolution in spinel was investigated by performing simultaneous dual-beam (He + and heavy ion) irradiations. The uniform ionizing radiation source did not affect the microstructural evolution of spinel unless the ionization was very intense (average electronic- to nuclear-stopping power ratio > 100).