As previously mentioned, the shaping times recommended for highest throughput pro
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duce a trapezoidal pulse response which has approximately one-half the processing
time when compared with traditional analog Gaussian shaping amplifiers. These set
-
tings result in almost twice the throughput compared to traditional analog pulse pro
-
cessing, with little or no resolution degradation in most high-energy Ge detector
applications.
The shaping times recommended for highest Resolution produce a trapezoidal pulse
response with a processing time that is equivalent to traditional analog signal process
-
ing. Longer rise time and flat top settings provide better noise filtering and reduced
ballistic deficit. However, as the system count rate increases, resolution and through
-
put may degrade as a result of increased processing time and the effects of pulse
pile-up.
Table B.2 lists Lynx DSA rise time and flat top settings for other common detectors.
Table B.2 Settings for Other Common Detectors
Detector Rise Time/Flat Top (ms)
Scintillation [NaI(Tl)] 0.8/0.2 or 1.2/0.6
Planar Implanted Passivated Silicon (PIPS)
(Silicon Charged Particle)
0.8 / 0.2, 1.2/0.6 or 2.8/0.6
Proportional Counter 0.8/0.2, 1.2/0.6 or 2.8/0.6
Lithium Drifted Silicon [Si(Li)] 8.8/1.2 or 16.8/2.4
Coaxial Germanium 2.8/0.6 or 5.6/0.8
Low Energy Germanium 5.6/0.8, 8.8/1.2 or 16.8/2.4
Refer to the specific Detector Operator’s Manual for the recommended shaping time.
A good starting point is the Gaussian equivalent processing time selections listed in
the table on page 191. The Rise Time and Flat Top setting can be optimized further
through experimentation.
Collect spectra using rise time and flat top settings above and below the recommended
settings, to optimize resolution performance for your particular detector and applica
-
tion.
Appendix C - Shaping Adjustments
192 Lynx™ Digital Signal Analyzer
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