Appendix C PUR/LTC Operation
166 Lynx II DSA User's Manual - 7096089
C. PUR/LTC Operation
The Lynx II includes a pileup rejector and a live time corrector. The pileup rejector
inspects for pulse pileup and allows only non-piled-up events to be processed and stored in
the spectrum. A result is a reduced number of counts in the pileup region and reduced
spectral interference for improved quantitative measurement and analysis.
To compensate for dead times associated with rejected pulses and amplifier processing
times, the Lynx II generates a dead time (DT) signal which extends the collection time by
the appropriate amount.
Pileup Rejection With a Live Source
The pileup rejector monitors the signal processing activities of the fast discriminator (fast
channel) and digitally filtered signal (slow channel) and allows only signals resulting from
a single detector event to be processed and stored in the spectrum. The fast discriminator
detects the arrival of input events and is capable of discriminating between multiple events
separated by less than 500 ns. If the fast discriminator detects two or more events within
the processing time of the slow channel, the event is contaminated by pileup and is
discarded.
The fast discriminator threshold is automatically adjusted just above the system noise level
for accurate operation. However, for the discriminating researcher or under special
circumstances, the threshold can be optimized manually. For instructions on adjusting the
threshold manually, see Manual Fast Discriminator Threshold.
The following steps will demonstrate the operation of the Pileup Rejector and its ability to
reduce spectral interference.
1. Connect the Lynx II and set it up as described in System Connections for a
Detector.
2. For the following demonstration of the Pileup Rejector, a
57
Co source will be used.
Due to the lower energy of this source, the system gain will need to be increased;
set the gain as follows:
Coarse Gain: x40
Fine Gain: x1.6001
Leave the remaining functions as previously set up. Verify that the LTC mode is set
on; the function is located on the Gain Device Adjust screen.
Note: The pileup rejector (PUR) and Live time corrector (LTC) operate as an integral
system. The LTC On/Off function controls both the PUR and the LTC.
To Next Page
Loading...
Need help?
General
