Crystals which had been bombarded with Au, Pb and Bi ions, having energies of MeV to GeV, were studied by means of micro-indentation measurements and dislocation etching. At fluences which were above a critical value of 109/cm2, the bulk microhardness could be improved by a factor of 2, and the surface microhardness could be improved by a factor of more than 3. The radiation-induced hardening followed the evolution of the energy loss along the ion path. Annealing experiments indicated that the complex defect aggregates which were created in the tracks played a major role in the hardness changes. Evidence of severe structural modification was found upon etching indentation impressions in highly-irradiated crystals. This led to patterns which were similar to those found for amorphous and micro-grained materials. Dislocation etching also revealed the existence of long-range stress fields which extended deeply into the non-irradiated material.

Hardening and Formation of Dislocation Structures in LiF Crystals Irradiated with MeV–GeV Ions. I.Manika, J.Maniks, K.Schwartz, C.Trautmann: Nuclear Instruments and Methods in Physics Research B, 2002, 196[3-4], 299-307