Essentially all X-ray measurements are made by @[email protected] techniques but the results are seldom converted to @[email protected] or @[email protected] or @[email protected] The term @[email protected] would be appropriate if the measurements were corrected for detector efficiency but this is seldom done for X-ray chemical analysis. Therefore the term X-ray intensity, \(I\), is commonly used and expressed as photons/unit time detected. Likewise the term relative X-ray intensity, \(I_{\text{r}}\), is used to mean the intensity for the analyte in an unknown specimen divided by the intensity for a known concentration of the analyte element.