Leave the remaining functions as previously setup. Verify that the LTC mode is
set ON; the function is located on the Gain Device Adjust screen.
Note:
The pile up rejector (PUR) and Live time corrector (LTC) operate as an inte-
gral system. The function LTC ON, OFF, LFC controls both the PUR and
LTC functions.
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 follow the directions
“Detector Matching” on page 38.
4.
Adjust the 9660 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 OFF. If the MCA is equipped, use
the compare function to overlap the two spectra. See Figure 24:
The spectra shown in the comparison are for an ICR of 50 kcps and 4
µ
s Gaussian
Equivalent Processing Time (Rise Time: 5.6
µ
s and Flat Top: 0.8
µ
s). Note the
reduction in magnitude of both the sum peaks and background counts. Also note the
improved resolution of the sum peaks. The background reduction and improved
resolution are directly indicative of the Pileup Rejector’s capabilities, since only sum
peak pulses which are indeed 100% in coincidence are processed.
Chapter 7 - PUR/LTC Operation
48
Model 9660-9660A ICB Digital Signal Processor
