Baseline Restorer Mode
The baseline restorer in the Model 2016 is flexible in that both the symmetrical and
asymmetrical modes are offered. In the SYMmetrical mode, the restoration currents
are identical for above and below the baseline. For the asymmetrical mode, the restorer
current above the baseline (referenced to the positive output), is much less than that
below the baseline.
The symmetrical restorer mode is used on Ge systems with fast shaping and high count
rates or with low quality preamps, for scintillation and proportional counting, and with
Si systems.
The symmetrical mode should always be used for detector systems which exhibit base-
line discontinuities resulting from excessive noise and/or high voltage effects, preamp
reset pulses and preamp secondary time constants. Secondary preamp fall time con-
stants result in unipolar output undershoots making it difficult to optimize the ampli-
fier preamp matching.
The asymmetrical restorer mode offers superior high performance for high resolution
Ge spectroscopy.
Amplifier Shaping Selection
Shaping time constant selection generally is a compromise between optimizing
throughput and resolution.
For germanium detectors, 4
µ
s shaping provides optimum resolution at low count
rates, but 2
µ
s provides better performance over a wider range of count rates. For very
high count rate applications the 2016A is recommended for its high throughput. For
lower count rate and low energy applications, the 2016B is recommended for its better
resolution.
For high resolution detectors, longer shaping time constants offer better signal to noise
(S/N) ratio and reduced sensitivity to the effects of detector ballistic deficit. However,
as the system count rate increases, resolution will degrade rapidly as a result of the am-
plifier’s long processing time and the effects of pulse pile-up.
The optimum shaping time constant depends on the detector characteristics (such as
size, noise characteristics, collection characteristics), preamplifier and incoming count
rate. The 2016’s shaping-time constant ranges for other common detectors are listed in
the following table.
41
Baseline Restorer Mode
