This dual-purpose specimen determines detector efficiency, generating two well separated K lines to check the calibration of the X-ray detector. The aluminium generates a low energy line at 1.49 keV and the copper K-alpha peak occurs at 8.04 keV. The copper film is a very uniform thickness of about 60nm, carbon coated on each side.
The ratio of the Cu K/Cu L X- ray intensities is measured. This will provide a measure of detector efficiency. The detector efficiency is normally assumed to be a constant, but in fact a contaminant layer on the beryllium window can significantly affect its efficiency. It is most important to check for such variation if any reliance is to be placed on quantitative results obtained.