FWHM calibration concept in HyperLab
In pre-2009 versions of HyperLab, the FWHM (Full Width at Half Maximum) was described with the following formula:
and the resulting FWHM value was in channels. This expression depicts a linear dependence between the peaks' channel position (or energy) and their squared width.
This is proper for usual energy ranges (up to about 2MeV) and usual number of channels, but if you are utilizing broader energy ranges and/or many more channels, then significant differences start to emerge between the measured and predicted peak widths. Thus a more powerful FWHM function was introduced:
The meaning of this finer FWHM function remained the same: describes the FWHM in channels for any given channel value.
To create an FWHM calibration, users first specify several calibration points (channel values with belonging peak widths), and direct HyperLab to perform a least-squares fit to these data points, and determine the offset and slope parameters of the linear function, or the further polynomial parameters in case of the polynomial FWHM function. The linear function requires at least 2 calibration points, while the polynomial version requires n+1 points (n is the degree of the requested polynomial).
The FWHM calibration points as well as the fitted parameters are stored in HyperLab databases for each measurement entry. More than one FWHM calibrations may exist in the database for the same measurement, but only the last non-tentative one is treated as the current, valid FWHM calibration, and this will be automatically loaded by the peak evaluator.
The FWHM calibration editor is used to modify the values of the data points, to add or remove points, or to replace the current calibration with another from the database.
 
 
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