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

Absolute absorption coefficients in the region of the M 4 and M 5 edges are presented for cerium in CeF 3 , CeO 2 and in the metal. Strong line absorptions (3d to 4f) occur to the low energy side of weak M 4 and M 5 '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 CeF 3 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 M 4 and M 5 line profiles change into forms accurately resolvable into a combination of trivalent (CeF 3 like) and quadrivalent (CeO 2 like) curves, suitably displaced in energy, in the proportion 59% to 43% respectively.