Amplitude of peak
Position of the centroid
Peak width parameter, so that FWHM = 2·Width·√log(2) or Width = FWHM/1.66
The picture shows a Gaussian with Position=0, Width=3 and Amplitude=100. In this case FWHM is 6*√log(2).
The X axis depicts channel positions in a spectrum region (zero selected for the peak centroid just for convenient display), while the Y axis shows count values.
The first is the Common peak width method, which is based on gamma spectroscopy heuristics, as it fits one common peak width for each peak within a region. This model is able to describe the majority of the spectrum regions.
There are cases, however, when the Variable peak width method is required: this fits peak width for each Gaussian individually. A typical example for this case is the extremely broadening 511keV annihilation peak, where valuable peaks of various radioisotopes should be separated automatically from the annihilation peak. See “Peak evaluation algorithm settings window” for further details.