Superlattice of voids in neutron-irradiated tungsten

Abstract
Transmission electron microscopy of tungsten irradiated at about 550°C to a fast neutron fluence of approximately 1×1022 neutrons cm−2 reveal the formation of a superlattice of voids. The void lattice parameter is 195 Å and the lattice parameter to average void size is about six. Both the formation of the superlattice and the temperature dependence of the lattice parameter in tungsten, a material considered to have isotropic elastic properties, is in contradiction to present theories based on the elastic anisotropy of the host metal.