The Key

After acquiring a spectrum, identify the elements in it. If a line is identified as a β or γ line in a series then the α line from that series must be present. The height of each peak from a single element will be present in approximately the ratios listed in Table 2.1. If the beam energy is sufficient, look for K lines in addition to the lower energy L lines, or L lines in addition to the M lines. As an example, the gold Mα peak at 2.123 keV is difficult to distinguish from the lead Mα peak at 2.345 keV, particularly as M peaks are rather broad. However, the gold Lα peak at 9.712 keV is easily differentiated from the lead Lα peak at 10.550 keV. If necessary increase the accelerating voltage to generate the higher energy lines. Use automatic peak identification for suggestions, but make sure that the elements make geologic sense. After identifying the characteristic peaks, determine which elements are spurious and eliminate them from further consideration.

Determine if there are likely to be any elements not detected by the EDS. In particular, when using a detector with a beryllium window, carbon and oxygen will not be detected, leading to similar spectra from different minerals. Methods such as X-ray diffraction or examination of crystal morphology (see Welton, 1984) may be needed if these minerals must be precisely differentiated.