GammaVision
®
v7 (A66-BW) 783620H / 1013 a
2 a
3
= energy calibration slope defined in Eq. 8
= energy calibration quadratic coefficient defined in Eq. 8
C
= channel number
When the FWHM fit is made, the fit is automatically checked for validity. If the FWHM curve is negative at any part of the spectrum or the curve bends over (has a maximum and then goes down), a warning message, Non-physical FWHM fit, is displayed. Click OK, then display the
FWHM curve to see why the fit is incorrect. Also, if the delta between the data points and the
FWHM fit is greater than 25%, a message is displayed. The curve can be accepted if the warning is due to the fit outside the energy of interest, or some of the data points might need to be deleted. The calibration spectrum should have good peaks with many counts, so counting longer might remedy the poor fit.
The same methods used to calculate the peak centroid and width in the Calibrate section are used in the Analyze section. This ensures consistency of results.
The energy calibration is done using the spectrum in the buffer or the Detector. The calibration is linked to the spectrum used and is transferred with it when the spectrum is transferred
(e.g., from Detector to buffer or disk file).
The first step in the calibration is to collect a spectrum of a known source with isolated peaks.
The spectrum peaks must be well-defined with a small statistical uncertainty. When the Detector has finished collection (i.e., stopped), select
Calibrate from the menu bar, then Energy....
The Energy Calibration Sidebar (Fig. 92) will
Fig. 92. Energy Calibration Sidebar.
automatically open, placed over the Status Sidebar. The Calibration Sidebar can be moved by its title bar to another position. It is usually helpful to zoom in on the spectrum so the peaks are clearly displayed.
5.3.2.2. Auto Calibration
19
The Auto Calibrate button will perform a complete energy and FWHM calibration on the displayed spectrum using the working library. There are no requirements on the spectrum or the library other than there must be at least three peaks (five preferred) in the spectrum that are in the library. There can be a different number of peaks in the spectrum than in the library, that is, there can be peaks in the spectrum that are not in the library and peaks in the library that are not
19
U.S. Patent 6,006,162.
106
