Pileup Rejection With a Live Source
Lynx DSA User's Manual - 9240227J
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C. PUR/LTC Operation
The Lynx includes a pileup rejector and live time corrector. The pile up rejector
inspects for pulse pileup and allows only non-piled up events to be processed and
stored into the spectrum. The 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 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 digital 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 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 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 pile up rejector (PUR) and Live time corrector (LTC) operate as
an integral system. The LTC On/Off function controls both the PUR
and the LTC.
