Transmission electron microscopy investigation of unetched fission tracks in fluorapatite—physical process of annealing

Abstract

Light-microscope examination of neutron-bombarded and chemically etched fluorapatite samples that have been annealed at 450°C for 5 h indicate that the etchable fission damage is zero. However, transmission electron microscopy (TEM) observations of material that has not been chemically etched confirm that unetchable crystalline damage remains prominent such that the track population is not eliminated. Using TEM to examine a suite of furnace-annealed samples, it is possible to reconstruct the physical process by which fission damage is repaired. Annealing is characterized by initial development of an irregular track boundary followed by segmentation of tre track length. As the extent of annealing progress,s, the spacing between segments increases and the segment's shape approaches a spherical morphology. Finally, the spheroidal segments may be annealed.