GammaVision
®
v7 (A66-BW) 783620H / 1013
Fig. 20. Display Analysis Results.
Exit this analysis session by clicking on the Analysis Sidebar’s Close button ( ) to close the
Analysis Sidebar and Analysis Results List window. Also close the Library List window.
3.2.5. Energy Calibration
For this example, we will use the spectrum files supplied with GammaVision to recalibrate the buffer. The same procedure is used to calibrate the Detector spectrum. The buffer window containing
GVDEMO.SPC
should still be displayed.
From the Calibrate menu (Fig. 21), select Energy.... The Energy Calibration Sidebar, shown in
Fig. 22, will open to the right of the spectrum area. You can move the sidebar by clicking on the titlebar and dragging as you would in any Windows application.
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783620H / 1013 3. GETTING STARTED — A GAMMAVISION TUTORIAL
Fig. 21. Start Energy
Calibration from
Menu.
Fig. 22. Energy Calibration Sidebar.
This time, so that we start from the very beginning, clear the current energy calibration by clicking on the icon to the left of the “Energy Calibration” title. This will open the control menu shown in Fig. 23. Click on Destroy. The Marker Information
Line now shows the legend uncal.
Move the cursor to channel 8226, the location of the upper
60
Co peak, at 1332.5 keV. Do this directly in the full window or by using the buttons until you get there. Click once in the E= field at the top of the Energy Calibration Sidebar, enter the correct energy for this peak (1332.5 keV), and click Enter.
The system will automatically perform a simple calibration based on this peak and the assumption that channel zero is energy zero.
The graphs of the calibration and the table of values will be shown on the display, as in Fig. 24.
Fig. 23. Energy
Calibration Sidebar
Control Menu.
If the screen becomes too visually crowded, you can either move one or more windows until they are nearly “stacked” atop each other (leave at least an edge or corner of each window showing); or close one or more windows by clicking on their Close box ( ). However, do not close the Energy Calibration Sidebar or you’ll end the calibration session. Rearrange and/or resize the windows as needed.
Now we can use the library; click Library/Select Peak to reopen the Library List window.
Double-click the 122.07 keV peak of
57
Co in the library list. The marker will move close to, but not precisely on, that peak in the spectrum based on our current “one-point calibration.”
27
GammaVision
®
v7 (A66-BW) 783620H / 1013
Fig. 24. Energy Calibration Display.
Use the buttons to put the cursor on the peak, then click once on the 122 keV entry in the library list. Note that the E= 122.07 keV in the Energy Calibration Sidebar already has the appropriate energy from the library, and you need only accept it by clicking on Enter. The refitted calibration curve is automatically displayed.
Proceed through the library list in Table 1 adding the peaks (in any order) into the calibration.
To do this, double-click within 2 channels of the peak center, then click Enter.
If you decide that you don’t want one of the peaks, you can delete it at will by clicking on the
Delete Energy button on the Calibration Sidebar.
Now examine the Energy Table and note that the Deltas (the differences between data points and the fit to the data points) are small. Next, bring the Energy plot window to the front and
28
783620H / 1013 3. GETTING STARTED — A GAMMAVISION TUTORIAL
visually inspect the calibration curve, resizing the windows as needed to allow a closer examination of the graphical fit.
Click the FWHM (full width at half maximum) radio button on the lower section of the Calibration Sidebar to display the table of FWHM results and the FWHM graph (which is shown in
Fig. 25). The FWHM fit uses the peaks specified in the energy fit. If FWHM of any peak has a deviation of more than 25% between the actual and fitted values, a warning message is displayed.
Table 1. Source Energies.
Nuclide Energy (keV)
88
Y 1836.01
57
Co
60
Co
60
Co
88
Y
122.07
1173.2
1332.51
898.02
137
Cs
113
Sn
203
Hg
109
Cd
241
Am
661.66
391.69
279.17
88.03
59.54
Fig. 25. FWHM Fit Selection.
Save the energy table for later use: click the Calibration Sidebar’s Save button, enter a name such as
GVDEMO
for the table filename, and click Save. GammaVision will append the extension
.ENT
to the filename.
To examine the Energy Table, open the Calibration Sidebar’s control menu and select Edit File.
This table is a list of peak energies and the associated channel and FWHM values used for the calibration.
The energy calibration is complete; we shall consider this to be a “good” energy calibration for the purposes of this demonstration. Close the calibration session by selecting the system menu in the calibration and selecting the Close option. This new energy calibration is now held in memory but is not yet stored on disk.
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