783620H / 1013 5. MENU COMMANDS
If the input points are not well separated, the best fit to the data points might not be an accurate representation of the efficiency outside the fitted region.
The efficiency/energy formula is:
(13)
where:
ε = efficiency at energy E
a i
= fitting coefficients
E = energy
5.3.3.5. Polynomial Fit
The polynomial fit uses a 6-term polynomial to fit the natural logarithm of efficiency to the energy. At least five well-separated peaks are required. The function is optimized for p-type detectors. For n-type detectors, the low-energy region (below 60 keV) is not well modeled by this function, and GammaVision performs an interpolative fit instead.
This option is only on the Above knee list, and selecting it disables the knee value and the
Below knee fit.
The polynomial efficiency/energy formula is:
(14)
where:
ε = efficiency at energy E
a i
= fitting coefficients
E = energy in MeV
The result of the efficiency calibration calculation is one or two sets of coefficients (one for the fit above the knee and one for below the knee, or just one for the polynomial fit), and a set of energy-efficiency pairs. The energy-efficiency pairs are used for the interpolative fit. The pairs might also be used to recalculate the efficiency and to display the efficiency plot.
119
