The Miv and Mv x-ray absorption spectra of caesium, barium, lanthanum, and cerium.

A high- resolution curved crystal x-ray spectrometer of the Johann type and employing a proportional counter detection system, has been constructed and its design is described. An original high-intensity narrow focus x-ray source, capable of operation under conditions of ultra-high vacuum, has been designed and its performance characteristics are discussed. A preliminary investigation has been performed into the effect of the x-ray take-off angle, and the effect of variations in the tube voltage and emission current, on the intensity received at the detector. The descriptions of the experimental equipment include a method by which the metallic absorption foils could be evaporated, and subsequently cooled, under ultra-high vacuum conditions. Also described is an improved method of producing pinhole free, self-supporting aluminium windows of the order of 1000A thick. The Mv and Miv x-ray absorption spectra of CAESIUM FLUORIDE, BARIUM METAL, BARIUM FLUORIDE, BARIUM OXIDE, LANTHANUM METAL, LANTHANUM FLUORIDE, LANTHANUM OXIDE, CERIUM METAL, CEROUS FLUORIDE, and CERIC OXIDE have been examined and the existence of true edge type absorption has been established in each of the absorbers. A suggestion is made to account for the difference between the energy positions of the observed absorptions edges and those predicted from the L-spectra data, (the L-M discrepancy). A difference has been detected between the energy positions of the Miv,v absorption edges observed in the metallic and the corresponding non-metallic absorbers. The Mv and Miv absorption lines of the lanthanide absorbers have been quantitatively measured, and as a result a model has been proposed for the electronic coupling between the 3d and the 4f level. The Mv and Miv absorption spectra of the metallic absorbers have been measured at low temperatures, and only that of cerium was found to change significantly upon cooling. This change in the absorption structure has been attributed to the a = y phase transformation, and as a result it has been possible to propose a model for the crystalline structure of the a-phase of cerium.