ORTEC
®
EASY-MCA™ Digital Gamma-Ray Spectrometer User’s Manual
931044C / 1014
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widely varying activity and do not know the general activity before counting. For example, the
Live Time preset can be set so that sufficient counts can be obtained for proper calculation of
the activity in the sample with the least activity. But if the sample contains a large amount of this
or another nuclide, the dead time could be high, resulting in a long counting time for the sample.
If you set the ROI Peak preset in addition to the Live Time preset, the low-level samples will
be counted to the desired fixed live time while the very active samples will be counted for the
ROI peak count. In this circumstance, the ROI Peak preset can be viewed as a “safety valve.”
Enter the Real Time and Live Time presets in units of seconds and fractions of a second. These
values are stored internally with a resolution of 20 milliseconds (ms) since the MCB clock incre-
ments by 20 ms. Real time means elapsed time or clock time. Live time refers to the amount of
time that the MCB is available to accept another pulse (i.e., is not busy), and is equal to the real
time minus the dead time (the time the MCB is not available).
Enter the ROI Peak count preset value in counts. With this preset condition, the MCB stops
counting when any ROI channel reaches this value unless there are no ROIs marked in the MCB,
in which case that MCB continues counting until the count is manually stopped.
Enter the ROI Integral preset value in counts. With this preset condition, the MCB stops count-
ing when the sum of all counts in all channels for this MCB marked with an ROI reaches this
value. This has no function if no ROIs are marked in the MCB.
The Uncertainty preset stops acquisition when the statistical or counting uncertainty of a user-
selected net peak reaches the value you have entered. Enter the Preset in % value as percent
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 MAESTRO 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 calcu-
lation. If the marker is not positioned in an ROI, the start channel is 1.5 times the FWHM below
the marker channel and the width is 3 times the FWHM.
The net peak area and statistical uncertainty are calculated in the same way as the MAESTRO
Peak Info command.
