Revisiting M -shell binding energies for elements with 72 ≤ Z ≤ 83

Abstract

Experimental M4 and M5 cross-section curves of some sixth-period elements were observed to exhibit an abnormal crossover above 20 keV, when the M5 binding energy is taken from the most commonly used databases available in the literature for the assessment of absorption effects [Aguilar, Castellano, Segui, Trincavelli, and Carreras, J. Anal. At. Spectrom. 38, 751 (2023)]. This clearly suggests the need for a revision of the published binding-energy values [Bearden and Burr, Rev. Mod. Phys. 39, 125 (1967); Larkins, At. Data Nucl. Data Tables 20, 311 (1977)]. The self-absorption effects of the Mβ line and of bremsstrahlung in an energy region close to the M5 binding energy were analyzed by using energy and wavelength dispersive spectroscopy, respectively. An important inconsistency in the x-ray absorption was found when assessed accordingly with the literature, which led to shift the M5-edge positions of Re, Os, Ir, and Pt. In the particular case of rhenium, theoretical calculations have been performed to assess M binding energies. To this end, the many-electron Dirac equation was numerically solved to estimate the configuration energies associated with M5 one-vacancy states. The binding energies obtained are consistent with the present experimental results, and with the most widely accepted characteristic-energy values.