K-Shell-Fluorescence Yield for Carbon and Other Light Elements

By recording the absolute number of K x-ray quanta emitted from a thin graphite target bombarded with electrons of energy E between 2 and 30 keV, the quantity ω_K^∘QK(E) for carbon has been measured, where ωK is the K-shell-fluorescence yield and QK(E) the ionization cross section for the K shell. QK(E) was calculated with the formula of Gryzinski, and the fluorescence yield of carbon was obtained as ωK=0.0035. This value is much higher than the two other experimental values, but in agreement with a semiempirical formula of Byrne and Howarth and in near agreement with a recent calculation of McGuire. It is shown that this formula and this calculation seem to be valid for elements with atomic numbers down to Z≈6.