Electron Microscope Observation of a Radiation-Nucleated Phase Transformation in Mica

Abstract

Synthetic fluor‐phlogopite mica samples were irradiated with fission fragments, stripped into thin sheets (≲3000 Å), and annealed in air at various temperatures to study the behavior of the tracks which were formed along the paths of the fission fragments. Transmission electron microscope observations showed that the appearance of the tracks was unaltered below 775°C. At ∼800°C tracks began to thicken at their intersections with the mica surfaces and to thin in the region between the surfaces. The thickened ends grew into plate‐like particles whose selected area diffraction patterns were consistent with that of forsterite. This compound is known to be formed during the high‐temperature decomposition of unirradiated mica. The experiments thus demonstrate that individual fission fragment tracks can serve as nucleation sites for a phase transformation in mica.