Fission Fragment Damage in Semiconductors and Ionic Crystals

抄録

Electron microscopic observation is carried out on fission fragment irradiated germanium, silicon and magnesium oxide which have different grain size and thickness. Tracks of fission fragments are observed in evaporated films of germanium with about 10 Å grain size and of magnesium oxide with about 50 Å grain size, while no track is observed in other materials. A number of small spots are found to appear in large crystal films of germanium and silicon after the irradiation. It is found by electron diffraction study that there are a number of small disturbed or recrystalized regions in highly irradiated large crystals of germanium and silicon. The mechanism of thermal spike is discussed in some detail based on a estimate of the energy distribution of excited electrons and relaxation times for various collision processes of these electrons, and a new model which is applicable to non-metallic crystals is presented. Calculations of the temperature distribution in a spike region based on this model is found to give a good result consistent with the present experiment.