783620H / 1013 5. MENU COMMANDS
uncertainty at 1 sigma of the net peak area. The range is from 99% to 0.1% in 0.1% steps. You have complete control over the selected peak region. The region must be at least 7 channels wide with 3 channels of background on each side of the peak. Note that GammaVision calculates this preset once per 40 seconds. Therefore, the software will continue data acquisition up to
40 seconds after the preset has been reached, and the uncertainty achieved for a high count-rate sample may be lower than the preset value.
Use the Start Channel and Width fields to enter the channel limits directly, or click on Suggest
Region. If the marker is positioned in an ROI around the peak of interest, Suggest Region reads the limits of the ROI with the marker and display those limits in the Start Chan and Width fields. The ROI can be cleared after the preset is entered without affecting the uncertainty calculation. If the marker is not in positioned in an ROI: for calibrated spectra, the start channel is
1.5 times the FWHM below the marker channel, and the width is 3 times the FWHM; for uncalibrated spectra, the region is centered on the peak located within two channels of the marker and as wide as the peak.
The net peak area and statistical uncertainty are calculated in the same manner as for the Peak
Info command.
MDA Preset
The MDA preset (Fig. 86) can monitor up to 20 nuclides at one time, and stops data collection when the values of the minimum detectable activity (MDA) for all of the user-specified MDA nuclides reach the needed value. Presets are expressed in Bq, and are evaluated every
40 seconds. The detector must be calibrated for energy in all spectroscopy applications, and for efficiency in all applications but MAESTRO.
The MDA presets are implemented in the MCB (i.e., the entries you make on this screen are saved in the MCB memory), and have no direct link to MDA methods selected in the analysis options for applications such as ScintiVision™, ISOTOPIC, etc. The MDA preset calculation uses the following formula: where:
a, b, and c are determined by the MDA criteria you choose.
Counts is the gross counts in an ROI that is 2.5×FWHM around the target peak energy.
Live time is evaluated in 40 second intervals for the MDA presets.
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