Excitonic model of track registration of energetic heavy ions in insulators

The consequence of generation of dense electronic excitation along the paths of energetic heavy ions is discussed, emphasizing the fates of electron-hole pairs. It is pointed out that a substantial part of the energy imparted to electron-hole pairs in the materials in which excitons are self-trapped is converted directly to defect formation energy but do not contribute to heating. However, the thermal spike model can be an appropriate macroscopic model of the track registration of the materials in which excitons are self-trapped, because energy deposited to the material remains along the ion paths. The energy imparted to electron-hole pairs is diffused away from the ion paths in the materials in which excitons are not self-trapped. This explains the reason why the critical stopping power for track registration is higher in these materials. The difficulty for application of the thermal spike model to these materials is pointed out and it is suggested that nominal defects in densely excited region nucleate fragmental tracks. (C) 1998 Published by Elsevier Science B.V. All rights reserved.