Selecting different X-ray lines for mapping?

X-ray mapping using EDS is used for imaging the spatial variation of elements in a sample. This technique provides rapid information on element distribution, but can yield misleading results in some cases, for example when using data from overlapping peaks.

The following example shows a mineral sample, which contains both Pb and As. The maps displayed show the Pb Lα and As Kα, which are overlapped at 10.5517eV and 10.5320eV respectively. Therefore, these maps display the superimposed distribution of Pb and As.

Pb Lα	As Kα

One way to resolve this issue is to choose different X-ray lines to display the data. Using INCAEnergy it is easy to configure the system to get the most accurate results:

1.

The X-ray line used to create the map can be selected in the Element Set-up window and using the Configure button.

2.

This displays a screen where the X-ray line can be selected.

Default setting will select the X-ray line automatically, and any potential overlaps are listed. To manually select the lines to use the 'Auto line selection' box must be unchecked.

3.

The preferred line can then be selected from a drop-down list.

X-ray line selection can be changed during or after data acquisition and the line selection can be saved. Typically, Pb M would be used to detect and measure Pb. However, as this sample also contains sulphur, and S K overlaps with the Pb M line, the Pb Lβ is used to display an accurate Pb map.

4.

The selected lines will then be used to display the maps automatically in the Element Maps window. The maps now show the correct distribution of As and Pb.