K-Shell Fluorescence Yields for Light Elements

The $K$-shell fluorescence yield ${\omega }_K$ has been measured for the low-atomic-number elements beryllium, boron, carbon, fluorine, and magnesium. The primary vacancies in the $K$ shell were produced by an intense beam of $K$ x rays generated by electron bombardment of aluminum and carbon targets. The measured values of ${\omega }_K$ agree quite well with values calculated from a theoretical prediction of Wenzel. They exhibit only fair agreement with semiempirical formulas which include screening and relativistic effects, and with a recent calculation by McGuire based on the $K$-shell Auger transition rate.