GammaVision
®
v7 (A66-BW) 783620H / 1013
The energy calibration and the efficiency calibration are separated to make it easier to do these calibrations. The efficiency and TCC calibrations are linked because the TCC depends on the detector/source geometry. If properly chosen sources and libraries are used, the calibration process is simple, quick and accurate. The input values can be saved so that repeated calibrations with the same source are easy and simple.
The energy calibration can be changed without affecting the efficiency calibration. By using the
Recall Calibration... command, the previously calculated efficiency calibration can be inserted into the new calibration data.
5.3.1.1. For Best Calibration Results
It is important that the energy, efficiency, and TCC calibrations be done correctly because the calibration results will affect all analyses employing them. The energy calibration data is used to define the energies of the peaks in the spectrum. If incorrect, the calculated energies will not correspond to the correct library entry and the peak might be incorrectly identified. The shape parameters are used to define the expected shape for a singlet peak. If incorrect, peaks will be labeled as having a bad shape when they do not, and bad peaks will not be marked. Peaks marked with poor shape might not be included in the activity calculation, resulting in loss of accuracy even for singlet peaks. For deconvolutions, these parameters define the Gaussian shape used for the components of the total peak area. Incorrect peak shapes can result in poor deconvolution results and even incorrect peak height ratios in multiplets.
An incorrect efficiency calibration can cause the nuclide activity to be incorrectly reported. The knee value, if incorrectly chosen, can cause poor results near the knee, especially below the knee.
A poorly done TCC calibration will cause incorrect activity reports due to a miscorrection for cascade summing.
Using many data points near the knee aids in selecting the correct knee energy. A poor choice of type of fit can result in a good fit to poor data, which will yield a poor efficiency calibration.
NOTES
During efficiency calibration, the net peak area calculation can be affected by the library Match Width setting in effect at the time the calibration is performed. Before starting an efficiency calibration, go to the System tab under Analyze/Settings/
Sample Type... (page 152) and make sure the Match Width is set to the same value you will be using during analysis. Most users will keep the default setting, 0.5. If using a different setting, we recommend a value between 0.4 and 0.75.
For TCC calibrations, the library and TCC table should include only the nuclides present in the spectrum. In addition, note that when recalling the TCC calibration from a
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