Extended Data Fig. 1: Overlap of X-ray fluorescent emissions.

a, Upper: X-ray (red) displacement of a core shell electron creates a vacancy; high energy X-rays are able to displace electrons from central shells. If the vacancy is filled by an electron from a surrounding shell, the replacement electron can lose energy as a photon emission (yellow). K-shell fluorescence is generally brighter than L-shell fluorescence as non-fluorescent core shell stabilisation phenomena such as Auger electron loss are less prevalent for innermost shells. An element has multiple emissions (for example, Kα₁, Lα₁) that depend on the shell that loses the electron and the shell that supplies the replacement electron. Lower: Emission lines that arise from different subshells. b and c, The energy gap between the major b) K-line or c) L-line emissions for an element (element 1) and a neighboring element (element 2) at multiple Z-number element steps (indicated by color above element 1). Subplots are the emission line of element 1 against which the energy difference for an emission line of element 2 is calculated. The black horizontal line at 360 eV and blue horizontal line at 355 eV are the Vortex SDD and Mirion GeCMOS detector full-width half-maximum spectral resolutions, respectively, calculated for the La Kα1 emission line (calibration spectra are shown in Extended Data Fig. 2). The red horizontal line at 200 eV is a best-case spectral resolution for current energy dispersive detectors. The dark grey vertical bar indicates the lanthanides. Note that there are fewer K-line emission overlaps than L-line emission overlaps beneath the spectral resolution limit of each detector in the lanthanide region. Emission line energies from the X-ray data booklet⁴³.