View More View Less
  • 1 The University of Tokyo Research Center for Nuclear Science and Technology Tokai 319-11 Ibaraki (Japan)
  • 2 Hiroshima University Faculty of Engineering 1-4-1 Kagamiyama 739 Higashi Hiroshima (Japan)
  • 3 El-Minia University Egypt
Restricted access

Abstract  

PAL were measured for several low molecular organic compounds, normal and cyclic-hydrocarbons and their perfluorinated ones, from room temperature down to about 40 K, and information about the vacancies in them has been extracted from 3 andI3. Normally the size of vacancies were larger in the solids comprising larger molecules, showing thato-Ps can represent the vacancy size. In a special case of perfluorocyclohexane whose solid had to be prepared by sublimation the vacancy size was larger than expected. In all the solid molecules studied twoo-Ps states could be observed and their relative importance could easily change showing a hysteresis-like behavior. At further lower temperatures of around 40 K theo-Ps state with longer lifetime and larger intensity became overwhelming for all molecules. Also 3 andI3 were not very sensitive to most of the phase transitions, including the melting points.