Positron annihilation in C60 and C70 fullerenes and other carbon phases

A positron-annihilation study was applied to C-60 and C-70 fullerenes and other carbon phases such as nanotubes and graphite. Positrons in C-60 and C-70 fullerenes and nanotubes display a single-component time-annihilation spectrum. The results of the lifetimes were 389+/-2 psec for the C-60 fullerene, 384+/-2 psec for the C-70 fullerene, and 387+/-1 psec for the nanotube. In addition to the lifetime spectra, we measured the Doppler-broadened line shape of the 511-keV annihilation gamma ray, which reflects the density distribution in momentum space of the annihilation electrons sampled by the positron. The annihilation gamma-ray line shapes show a remarkable difference between the C-60 and C-70 fullerenes and graphite on one hand and nanotube phases on the other hand. The full width at half maximum of the distribution of the annihilation electron momentum decomposed from the obtained spectra are 2.36x10(-3)m(0)c for C-60, 2.38x10(-3)m(0)c for C-70, and 2.51x10(-3) m(0)c for nanotube and graphite phases. [S0163-1829(99)14447-3].