Measurements and calculations of M-shell X-ray production in Er, Yb and Lu by 0.75-6Â MeV He ions

M-shell X-ray production cross sections for the light rare-earth elements of 68Er, 70Yb and 71Lu have been measured for incident 4He+ ions in the energy range from 0.75 to 6 MeV. The measured X-ray production cross sections are compared to the predictions of the First Born approximation, the ECPSSR theory and the ECUSAR theory. A comparison of the ytterbium M-shell X-ray production cross sections with these theories is made for two different sets of fluorescence yields and Coster-Kronig factors that are further modified for multiple ionization.