783620H / 1013 5. MENU COMMANDS
1) Interpolative fit.
2) Linear fit of the natural logarithm of the efficiency to the natural logarithm of the energy.
3) Quadratic fit of the natural logarithm of the efficiency to the natural logarithm of the energy.
4) Polynomial fit of the natural logarithm of the efficiency to the energy.
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Fig. 103.
5) TCC Polynomial, a different six-order polynomial fit of the natural logarithm of the efficiency to the natural logarithm of the energy.
Options 1, 2, and 3 can be selected separately for two separate energy regions. Either of the two regions might be left uncalibrated by not including any points in the region, but the analysis will report zero activity (in the library peak output) for peaks in the uncalibrated region. If both regions are calibrated, the above-the-knee energy region is fitted first, and the calculated efficiency at the knee is included as a data point in the below-the-knee fit. This means that only one point need be below the knee, but two points are the minimum above the knee for a calibration to be done. Option 4 fits the entire energy range with one function and is best suited to p-type detectors. Option 5 fits the entire energy range with different functions over three energy regions and can be used for p- or n-type detectors. The combination of fit methods above and below the knee that best fit the measured efficiency data points should normally be used.
If you select None for the Above and/or Below energy range, no peak activities are calculated for that range.
5.3.3.2. Interpolative Fit
The interpolative fit uses straight lines between the data points and does a linear interpolation between two points (one above and one below) to obtain the efficiency at the selected energy.
For energies below the minimum energy data point or above the maximum data point, the efficiency is the straight-line projection of the last two data points at the appropriate end. The interpolative fit is used where the efficiency is recognized to be a complex function of energy that cannot be fit using the other functions.
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“Définition de Criteres de Qualité Pour l’Essai des Logiciels Utilisés en Spectrométrie Gamma,” Rapport
CAE-R-5347, 1986.
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