Canberra Lynx DSA, Руководство пользователя

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PUR Guard
Lynx DSA User's Manual - 9240227J 193
With the LTC OFF, large changes will be observed in the reference net peak
are as a function of count rate. With the LTC set ON, changes in the
reference peak net area will be significantly reduced. The Live Time
corrector extends the collection time compensating for signal processing time
and events rejected due to pileup.
Note: Performance may vary and is dependent on factors such as spectrum
energy distribution, detector characteristics such as geometry, size,
and detector ballistic deficit.
PUR Guard
The PUR Guard Time (GT) function is provided to optimize the performance of the
Pileup Rejector. The pile up reject interval is defined as GT x T
R
+T
Flat Top
where:
GT = PUR Guard Time selection; 8 selections ranging from 1.1 to 2.5 are
provided
T
R
= Filter Rise Time selection
T
Flat Top
= Filter Flat Top selection
With the default (minimum) PUR GT setting (1.1x) the pile up reject interval and the
Peaking Time are the same; as shown in the figure below.
Figure 104: PUR Reject Interval
Subsequent events arriving within the PUR reject interval are rejected, events
occurring afterwards are accepted. Increasing the Guard Time extends the pile up
rejection interval to protect subsequent events from being corrupted by anomalies
associated with the tail of the previous event. As expected, throughput is reduced as
the Guard Time and pile up rejection interval are increased. The maximum Guard
Time setting (2.5x) requires the previous event to fully return to the baseline before
subsequent events are accepted. The default Guard Time (1.1x) is minimum and
provides optimum performance and maximum throughput for most detector
applications.