Radiation damage in crystals which had been bombarded with various ion species, ranging from Ni to U, was studied by means of optical absorption spectroscopy, small-angle X-ray scattering, chemical etching and annealing experiments. The results revealed a complex track structure and defect morphology. Single defects such as F and F2 centers were produced in a large halo, with a radius of several tens of nm, around the ion trajectory. Above a critical energy loss of about 10keV/nm, new effects occurred within a core region that was 2 to 4nm in diameter. This resulted in strongly anisotropic X-ray scattering and in the etchability of tracks. It was concluded that, in the core region, the defects were complex aggregates such as small Li colloids, and F and vacancy clusters. By using Monte Carlo calculations, the spatial distribution of energy deposited around the ion trajectory was compared with the track radius as deduced from small-angle X-ray scattering data. For all of the ion species, this radius corresponded to a critical dose that was regarded as being a threshold for the creation of defect aggregates in the core region.

Damage and Track Morphology in LiF Crystals Irradiated with GeV Ions. K.Schwartz, C.Trautmann, T.Steckenreiter, O.Geiss, M.Krämer: Physical Review B, 1998, 58[17], 11232-40