The M emission spectra of the heavy rare earth elements 67 ≤ Z ≤ 71

The M emission spectra of the heavy rare earth elements (67)Ho, (68)Er, (69)Tm, (70)Yb, and (71)Lu were reinvestigated using wavelength dispersive spectrometry with a TAP crystal as the dispersing element. In order to resolve weak lines, which are near to the strong alpha and beta lines/bands, the regions around these lines were additionally measured using the second order reflection. In this manner in total 54 M lines were observed of which only 19 are contained in Bearden's compilation. A difference between the line positions of metals and oxides was observed only for the M alpha line of (70)Yb. This observation agrees with an earlier report of Fischer and Baun. The observed dependencies of the intensity ratios M beta/M alpha and M zeta/M alpha on the atomic number Z reflect the increasing filling of the N7 subshell with increasing Z.