The Miv,v X-ray absorption spectra of ytterbium and some heavier elements.

A new curved crystal Xray spectrometer, with a spot focus Xray source and proportional counter detector, has been constructed and its design is described. The results of a preliminary investigation into the variation of the intensity received at the detector, with movement of the source, are discussed. A study of the Mv absorption line of ytterbium has been made and the Miv and Mv absorption edges of ytterbium, lutecium and hafnium together with the Miii edge of ytterbium are reported for the first time. The discrepancy between the observed positions of the Miv and Mv edges and those calculated from data on the L spectra of these elements is discussed. A comparison has been made between the absorption of ytterbium in the pure metal and in compound, and the absence of the Mv absorption line for the metal clearly indicated. The Miv and Mv edges of the metal have been found to occur at energies some 14 ev lower than those of ytterbium fluoride (or oxide) and the cause of this shift is indicated. To facilitate the preparation of pure metal foils an evaporation chamber attached to the spectrometer tank has been designed and constructed. By this means the foils could be prepared and transfered into the Xray beam without exposure to air. The measurement of the Miv and Mv edges of tantalum (oxide) is described and a suggestion made to account for the difference between their previously reported positions.