Vacancies in the solids of low molecular weight organic compounds observed by positron annihilation |
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Authors: | Y. Ito Hamdy F. M. Mohamed M. Shiotani |
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Affiliation: | (1) Research Center for Nuclear Science and Technology, The University of Tokyo, Tokai, 319-11 Ibaraki, (Japan);(2) Faculty of Engineering, Hiroshima University, 1-4-1 Kagamiyama, 739 Higashi Hiroshima, (Japan);(3) Present address: El-Minia University, Egypt |
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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. |
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