MEASUREMENTS OF POINT-DEFECT CREATION RELATED TO HIGH-DENSITIES OF ELECTRONIC EXCITATIONS PRODUCED BY ENERGETIC CARBON CLUSTER BOMBARDMENTS

LiF single crystals have been bombarded at room temperature with C3 and C5 clusters with energies of 1.74 MeV/carbon atom and fluences ranging from 10(12) to 10(14) carbon atoms/cm2. Point defects (color centers: F, F2, ...) resulting from electronic excitation processes were measured by optical absorption spectroscopy. The defect concentrations were compared to those produced by irradiations with single C-12 ions with the same respective energy and dose. Using a differential optical absorption technique, it was possible to determine the defect concentrations close to the sample surface, when the tracks associated to each carbon atom of the cluster overlap. In this zone, where the ''cluster effect'' is maximum due to the very high density of electronic excitations, enhanced defect production is observed. Defect concentrations as large as those obtained previously by Kr and Xe irradiations at GANIL have been measured. In addition to the high defect production rates observed, aggregation laws (i.e. F --> F2) characteristic of cluster irradiations are also deduced.