783620H / 1013 5. MENU COMMANDS
The longest rise time shown in the table is 12
μs, even though some digital instruments can be set for rise times as long as 23
μs. If throughput is not an issue because all samples are low rate, increasing the rise time beyond 12
μs might achieve a small improvement in resolution. For planar detectors, such as ORTEC’s GLP, Si(Li), IGLET, and IGLET-X Series, operating at longer rise times frequently gives improved resolution.
5.3. Calibrate
Figure 91 shows the Calibrate menu. GammaVision’s calibration features now include a Calibration Wizard that assists you in performing the energy and efficiency calibrations as well as a fully implemented true-coincidence correction (TCC) calibration. This menu also allows you to access the energy and efficiency calibration features directly from the menu rather than stepping through the wizard.
The energy and efficiency calibrations of the spectrum in the
Detector, and the calibration wizard are only available if the
Detector is not acquiring data. If there is no energy calibration, then all choices except Energy..., Recall Calibration..., and
Fig. 91. Calibration
Menu.
Calibration Wizard... are inactive (gray). If the efficiency calibration exists, there will be a checkmark by the menu item.
5.3.1. General Information, Cautions, and Tips
The calibration of the system defines four relations:
! Spectrum channel numbers and energy
! FWHM of the peak and energy
! Spectrum count rate and activity in becquerels or other units
! True coincidence summing factor and energy
The data collected are in counts/unit time/channel; however, to be most useful, these data need to be converted to activities (i.e., decays/unit time at a given energy). The calibration parameters do this conversion.
These relationships are calculated from spectra, user inputs, and inputs from libraries and tables.
The calibration data are merged with the spectrum when it is saved as an
.SPC
file. The information is used in the analysis section to perform the desired analysis. Spectra saved in the
.CHN
format are compatible with older software, however the
.CHN
format does not contain the efficiency or TCC calibration data.
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