Preliminary results on positron annihilation in carbon fibers produced
from polyacrylonitrile precursor are presented. An analysis of the Do
ppler broadening of annihilation line and positron lifetime is made. T
o characterize the fibers, X-ray diffraction, electrical resistivity m
easurements, 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 t
emperature of heat treatment of carbon fibers. Chemical surface treatm
ent of carbon fibers results in a decrease of the positron lifetime in
dicating 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. Annihilat
ion parameters are discussed from the point of view of the structural
parameters of carbon fibers.