Electron spin resonance in neutron-bombarded graphite

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Abstract
An investigation has been made of the electron spin resonance (E.S.R.) of neutron-bombarded graphite. The variations of signal intensity, produced by progressive irradiation or by progressive annealing, were roughly parallel to changes of the interlayer spacing; this supports the idea that the irradiation-induced unpaired electrons are associated mainly with interstitial defects as contended by Hennig and Hove and by Mrozowski, rather than new charge carriers as believed by Müller. Further evidence is discussed which leads to the conclusion that the free spins may be situated on small interstitial-groups rather than the large clusters visible in the electron microscope. However, they do not appear to be confined to single interstitials as Hennig and Hove originally suggested, otherwise simpler kinetics of annealing would have been encountered. The contribution that vacancies make to the E.S.R. signal is surprisingly small.