Most considerations of excitation conditions either have ignored the target material of the X-ray tube and the resulting spectrum of the primary X-ray beam or have dealt with it in very general terms, making a few broad assumptions regarding its effect on the final result. This is quite understandable since any attempt to handle the quantitative relationship between the primary spectrum and the resulting fluorescent spectrum results in extremely complex and unwieldy mathematical expressions. However, with the number of different primary sources now available, it is possible to evaluate these complex expressions in terms of actual data and permit more reliable values to be placed on the relative contributions of the components in the primary spectrum.

A discussion is included of results obtained with X-ray tubes with chromium, molybdenum, tungsten, and platinum targets together with a few typical applications to actual X-ray spectrochemical procedures. Also discussed are the other variables which play a part in the excitation of fluorescent X-ray spectra, such as the primary X-ray tube voltage and the window of the X-ray tube.