Positrons as probes in ${\mathrm{C}}_{60}$ fullerites

The single-component positron lifetime of 402 ps measured in ${\mathrm{C}}_{60}$/15-mole % ${\mathrm{C}}_{70}$ is compared to that in the other carbon allotropic forms graphite and diamond. From the decrease of the positron lifetime in the fullerite specimen with quasihydrostatic pressure it is concluded that the positron is anninhilated on interstitial sites and not in the interior of the fullerene molecules.