K-Shell Ionization of Intermediate- and High-ZElements by Alpha Particles

$K$ x-ray yields have been measured for ten elements ranging from Fe ($Z=26\mathrm{}$) to Au ($Z=79\mathrm{}$) using 30-100-MeV $\alpha$ particles. The new data were combined with some earlier measurements and a smooth-curve fit was performed on the x-ray production cross sections plotted as a function of target atomic number. These "smoothed" cross sections were used in comparisons with the predictions of plane-wave-Born-approximation (PWBA) and binary-encounter-approximation (BEA) calculations and resulted in the observation of a systematic atomic-number-dependent deviation between experiment and theory. By comparing the measured cross-section data to the universal BEA curve at velocity ratios in which the mean electron velocity was calculated "semi-"relativistically, over-all agreement within ± 16% was attained for all elements studied.