Abstract
Pyrolytic graphite irradiated by neutrons at a low temperature was studied by esr. The presence of localized spin centers was confirmed from the esr intensity ratio between room temperature and liquid nitrogen temperature. The concentration ratios of localized spin centers to conduction carriers were obtained from g-values for various irradiation doses. The dose dependence of g-values and widths was explained by the rapid exchange interaction between the two spin systems, i.e. localized spin centers and conduction carriers. An increase of the width was observed around 160 K by pulse annealing experiments. The mechanism of the broadening was discussed and the spin-flip cross section was estimated in order of magnitude. The annealing behavior of the line-width above 300 K was explained as due to the annihilation of localized spin centers.
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