USE OF X-RAY FLUORESCENCE METHODS FOR MEASURING PLATING THICKNESSES.

As well as their more well known range of radiographic applications, X-rays generated within a sample under suitable excitation conditions can give information regarding the elements present. This X-radiation contains spectra whose energies are characteristics of the elements from which they originate. Characteristic elemental X-ray spectra, being relatively simple compared to their equivalent emissions in the optical wavelength region, are in general free from spectral interferences of radiation originating from any other elements present in the sample. It is characteristic X-ray spectral lines that are utilized for the measurement of plating thicknesses. These lines are conventionally excited by irradiating the sample with 'white' X-radiation emergent from the window of an adjacent X-ray tube. The incident 'white' spectrum must of course contain photons of sufficient energy to excite the lines of interest.