Linear and nonlinear calibration
In most cases, a simple linear channel – energy function is not acceptable for post-processing, as this would lead to two adverse effects:
This picture shows the case when only a linear energy calibration is used for a typical mea­sure­ment system. This is a measurement of a 152Eu source, in the 121 keV – 1408 keV range.
The green squares depict the difference (the residual) of the calibration points' position from the linear calibration (red line).
Despite multiple calibration points, a clear tendency shows that the system has a significant nonlinear response, which reaches 0.35 keV at in the vicinity of 1408 keV.
If these discrepancies are not acceptable, the purely linear energy calibration is not enough: a correction is needed to eliminate the nonlinearity of the measurement system.
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