Pileup Rejection With a Live Source
Lynx II DSA User's Manual – 7096089 167
3. Pole/Zero Compensation
The Pole/Zero was previously adjusted and it is not necessary to do it again. If for
some reason readjustment is necessary, please refer to Methods of Detector
Matching.
4. Adjust the Lynx II Gain to locate the 122 keV
57
Co peak in channel 3500. This is to
allow the Pileup region and sum peaks to be viewed in the upper half of the
spectrum.
5. Readjust the
57
Co incoming count rate (ICR) for 50 kcps.
6. Set the MCA preset to 60 seconds Live Time.
7. Set the MCA acquire to OFF, clear the memory, and set acquire to ON.
Accumulate a spectrum with the LTC ON.
8. Save the spectral file or print the spectrum or make note of the background counts
and sum peaks for comparison with the LTC set OFF.
9. Set the LTC to OFF, clear the memory, and set acquire to ON. Accumulate a
spectrum with the LTC OFF.
10. Compare the two spectra, LTC On and LTC Off, overlapping them with the
compare function, as seen in Figure 105.
The spectra in Figure 75 show a comparison for an ICR of 50 and 4 µs Gaussian
Equivalent Processing Time (Rise Time: 5.6 µs and Flat Top: 0.8 µs). Note the reduction
in the magnitude of both the sum peaks and background counts. Also, note the improved
resolution of the sum peaks. The background reduction and improved sum peak resolution
are directly indicative of the Pileup Rejector’s capabilities since only sum peak pulses
which are indeed 100% in coincidence are processed.
Figure 75: Comparing Co-57 Spectra w/ PUR On and Off
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