When measuring high Z elements, which lines are typically used within the standard energy range?

• A. L lines
• B. K lines
• C. M lines
• D. N lines

Answer: (A)

In XRF, the energy of the emitted characteristic lines depends on the shell the electron drops to. For heavy (high-Z) elements, the K-shell lines are very high in energy—often exceeding the typical detector energy range of many instruments. Within the standard energy window (roughly 5–40 keV), those K-lines for heavy elements can lie outside reach, so the lines that do fit inside are the transitions to the L-shell. These L-lines (such as Lα, Lβ, etc.) sit at lower energies and are detectable with common XRF setups. While M and N lines are even lower in energy and more easily absorbed by air or filters, they’re less practical for routine high-Z analyses. Thus, L lines are typically used for measuring high-Z elements within the standard energy range.