Abstract
Induced fission tracks have been imaged in fluorapatite with a JEOL JEM-2000FX analytical transmission electron microscope that is equipped with a cold stage and anticontamination device. Near the atomic level, fission tracks are not perfectly linear, continuous features but are composed of segments of extended damage that are separated by gaps of undamaged microstructure. From dark-field TEM images, it appears that the damage around tracks is not extensive. Track width is crystallographically controlled. Parallel to the c axis, tracks display widths of 5–13 nm and hexagonal faceting parallel to [0001]. Tracks perpendicular to the c axis display widths of 3–9 nm. Track annealing can be observed in situ by adjusting the heating current to the cold stage. The annealing of induced fission tracks in fluorapatite in the microscope is dependent on the current density of the specimen (i.e., radiolytic annealing) and the temperature of the specimen (i.e., thermal annealing). Track annealing is characleized by initial shortening from the track ends, followed by the development of gaps 4–100 nm wide along the track length that appear to represent restored microstructure. The rate at which individual tracks anneal is variable and may reflect differences in track orientation, grain composition, and degree of initial partial annealing.
