Abstract
Positron annihilation lifetime measurement has been performed for various kinds of unirradiated and irradiated graphites. Of the unirradiated speciemens, HOPG-type graphites showed the shortest lifetime component ( ~ 220 ps) and isotropic graphites showed a longer one ( ~ 350 ps). The longest lifetime was observed in glassy carbons ( ~ 400 ps). The electron or neutron irradiation-induced change of the positron annihilation lifetime depended on the type of graphite namely, in HOPG an increase of the positron lifetime was observed, but in isotropic graphites a decrease of the lifetime was observed. Positron annihilation angular correlation measurements have also been performed. In HOPG, for the case of P z ∥ c-axis, an angular correlation curve with a minimum at θ = 0 was observed, but the irradiation made this minimum obscure.
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