X-Ray K Absorption in Elements W(74) to U(92), and K Screening Numbers

Values are recorded for the $K$ absorption edges of elements 74, 76 to 83 inclusive, 90, and 92. Absorption is noted due apparently to the material of the slit but not to the passage of rays through the wedges formed by the jaws of the slit. An attempt is made to determine Sommerfeld's screening numbers for the $K$ shell from empirical data, on the assumption that the first term screening number is a linear function of the atomic number. Since this assumption leads to negative values for the "relativistic" screening number, it is conluded that Sommerfeld's term formula does not account for all the curvature of the lines in the Moseley diagram.