POSITRON-ANNIHILATION IN CARBON-FIBERS

Preliminary results on positron annihilation in carbon fibers produced from polyacrylonitrile precursor are presented. An analysis of the Doppler broadening of annihilation line and positron lifetime is made. To characterize the fibers, X-ray diffraction, electrical resistivity measurements, and elemental analysis are performed. Only one component is found in positron lifetime spectra ranging form 373 +/- 1 to 441 +/- 1 ps. It is observed that the positron lifetime increases with the temperature of heat treatment of carbon fibers. Chemical surface treatment of carbon fibers results in a decrease of the positron lifetime indicating positron annihilation in the near-surface region. Correlation of the Doppler broadening of annihilation line and positron lifetime indicates the possibility of trapping of positrons in pores. Annihilation parameters are discussed from the point of view of the structural parameters of carbon fibers.