Calibration chart tab
The energy calibration chart allows you to overview the quality of the calibration.
This sheet contains the chart itself at the top, and a peak list at the bottom.
The chart shows the calibration points' difference from the energy calibration line as filled green rectangles; the calibration line with red, and the standard uncertainty of the calculated energy values.
The peak list may be used to add new points quickly to the calibration. The peak list is filtered to display the significant peaks only: only the peaks with less than 0.5% peak area uncertainty will be displayed – however, this value can be edited under the list. If you find too few peaks in the list, change this value to, say, 5%, and all the peaks above this limit will be listed immediately. To add a peak to the calibration, select it by clicking on its row, then click the Add button beside the list.
On the chart, gray triangles depict the positions of the fitted peaks, which are listed in the peak list table. When you click on a peak, its point will be shown with bolder line, and the corresponding data row will be selected. The difference of the fitted peaks are zero from the calibration curve, as the peak energies are computed from their channel value. When a peak is used for calibration, a matching library peak is selected for its fitted position, so a real difference may be computed.
The gray triangles may help you to notify if you are using dangerous extrapolation: if the last green calibration point is too far from the last fitted peak – that is, from the last gray triangle –, its energy value may be rather uncertain. In this case, it is advisable to use another, closer peak as an additional calibration point.
If you see a strong non-random tendency among the linear calibration points, and the difference exceeds, say, 0.1keV, this may indicate significant nonlinearity of your measurement system. In this case, it is advisable to create a nonlinearity calibration, and use it together with the two-point linear energy calibration as a nonlinearity compensation. See details in section “System nonlinearity analysis