Defect-Clusters in Electron and in Neutron Irradiated Lithium Fluoride

The defect-clusters in LiF irradiated by thermal neutrons and by 100 KeV electrons have been studied by transmission electron microscopy. The defect-clusters in the electron-irradiated crystals are formed after exposure to about 1014 electrons/cm2 and they are some 30 Å in diameter having no crystallographic orientation relationship to the matrix. They grow larger under subsequent electron irradiation and stop growing when they are about 500 Å in diameter. The defect-clusters in the crystals exposed to 1013∼1018 nvt of neutrons are platelets parallel to one of the {100} planes. They are less than 200 Å in diameter and less than 50 Å in thickness. Their density, about 5×1015/cm3, is almost independent of exposure. It is probable that the defect-clusters in electron- and neutron-irradiated crystals are of same nature, since the defect-clusters in neutron irradiated crystals grow as a result of electron irradiation during observation in the electron microscope. No inhomogeneous line defects have been observed.