Field ion microscope observations of voids in neutron irradiated molybdenum

Abstract

The voids forming a three-dimensional lattice in a molybdenum specimen irradiated at 550°C to a fast neutron fluence of approximately 1 × 10²² n cm⁻² have been investigated for the fist time by the field ion microscope (FIM) technique. The numerical values obtained for the mean void diameter, the number density, and mean spacing are in approximate agreement with transmission electron microscope observations. Controlled field evaporation sequences through sixteen voids revealed complex atomic displacements around each void much of which is a result of the void intersecting the surface. The advantages of the FIM technique for the study of high number densities (< 5 × 10¹⁷ cm⁻³) of voids are discussed and the potentialities of the FIM atom probe for the solution of problems concerning the nucleation and stabilization of voids is also considered.