Elements measured sequentially
A sequential XRF spectrometer enables any number and combination of elements to be measured sequentially - from Be (atomic number 4) to U (atomic number 92) and beyond.
A sequential spectrometer employs an optical assembly called a 'goniometer', which is equipped with two concentric, rotatable shafts. These enable the analyzing crystal to turn through angular increments (theta degrees), while the detector rotates through 2-theta degrees to intercept the diffracted beam. Spectral peaks are detected at various wavelengths, according to the conditions described by Bragg's law.
The results of continuous scanning over an angular range can be plotted as a spectral pattern, from which the elements present in a sample may be identified. Individual peak intensities are measured to determine element concentrations.
Measurement times as short as 2 seconds suffice for many elements - although longer times are required for the lightest elements, which produce relatively small numbers of characteristic fluorescent photons.