Analysis of the Escape Behavior of Xenon Captured in Graphite by Nuclear Recoil, (II)

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Abstract
The escape of 133Xe introduced into natural graphite by recoil from UO2 particle was studied at temperatures ranging from 200° to 1,450°C and the resulting data correlated with the duration of isothermal post-irradiation heating. The escape data were used to verify the proposed escape mechanism, which postulates three successive processes—release from trapping site, diffusion of the released xenon, and desorption from surface. The concept of initial activation energy spectrum, which determines the trapping states of xenon atoms before any annealing begins in terms of the activation energy for the release, was introduced to express the release behavior mathematically. The mathematical treatment for both the release and the diffusion processes permits expression of the whole escape process with a single equation, assuming no resistance to xenon transport in the desorption process. The validity of this equation was substantiated by observed data. It was made clear that rapid sweep of the spectrum is the cause of the initial burst stage in which the escape rate is dependent upon diffusion of the released xenon, and that the slow sweep of the spectrum causes the ensuing slackened process in which the release from the trapping sites constitutes the limiting factor for the rate of escape.

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