ESR Study of Neutron-Irradiated LiF Crystals

Abstract

The paramagnetic centers produced in LiF crystals by neutron-irradiation at different temperatures have been studied by ESR. The F-like centers, including F-centers, clustered F-centers and electrons trapped in vacancy clusters, are observed in the crystal irradiated at about 0°C. By irradiation at 80 K, however, the concentration of F-like centers is small, and the molecular ion centers predominate. The two types of interstitial centers, stable even at room temperature, are also observed in this irradiation; models are proposed for the two types. Neutral hydrogen (H°) and tritium (T°) atoms are observed in the irradiations at both room temperature and 80 K. These atoms are trapped in vacancy clusters in the crystals. It is suggested from the results of irradiations between 0°C and 80 K that vacancies evaporated from the zone play an important role in formation of the F-centers. The effects of fast neutrons at liquid helium temperature are described.