A study of the modification of the 5f states in phase α and delta-plutonium by X-ray absorption spectroscopy

An analysis of the M(IV-V) absorption spectra of Pu has shown an electronic structure modification between the α and delta phases: this is due to an increase of the 5f atomic states number in Pu delta. These results are in agreement with a suggestion emitted by J. Friedel according to whom the 5f electrons are much more localized around each ion in the high temperature plutonium phases than in Pu α. They experimentally corroborate that the atomic volume expansion between α and delta phases is connected to an increase in the number of localized electrons, the latter screening the nuclear charge. Conversely, any atomic volume contraction must be followed by the opposite electronic modification, therefore by a 5f electrons delocalization towards the 6d or 7s states. The experiment allows them to check indirectly that a 5f-6d promotion must occur that the delta→epsilon and epsilon→liquid transformations since they take place with volume contraction. It confirms the actived self interstitial model which has been proposed to explain the anomalous self-diffusion observed for epsilon plutonium and for cerium