Measurements of absolute cross sections for K-shell ionization of Fe and Mn by electron impact

K-shell ionization cross sections of iron and manganese have been measured for incident electrons with energies varying in the interval from 6.5 to 40 keV, in 1 keV steps. Cross sections were obtained by measuring characteristic x-rays emitted from thin films of the elements studied deposited on carbon self-supporting backing films. Relative cross sections were obtained with uncertainties ∼3%. Transformation to absolute units increases the uncertainties to about 11%. The results are compared with those from experiments done by other groups, from various calculations based on the first Born approximation (with corrections for exchange, Coulomb and relativistic effects) and from applying a widely used semi-empirical formula.