The M4,5spectrum of58Ce and the γ-α phase transition

Abstract
Absolute absorption coefficients in the region of the M4 and M5 edges are presented for cerium in CeF3, CeO2 and in the metal. Strong line absorptions (3d to 4f) occur to the low energy side of weak M4 and M5 'edges'. At each 'edge' the absorption passes through a weak broad peak attributed to transitions into a band of higher f states. The spectra of CeF3 and the metal at room temperature are structurally similar but differ clearly from the quadrivalent oxide. A shift to higher energy is found for both absorption lines and edges in the sequence fluoride-oxide-metal at room temperature. On cooling the evaporated metal absorption foil ( gamma phase) to 77 K both M4 and M5 line profiles change into forms accurately resolvable into a combination of trivalent (CeF3 like) and quadrivalent (CeO2 like) curves, suitably displaced in energy, in the proportion 59% to 43% respectively.

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