DSPEC 50
®
and DSPEC 502
®
Digital Gamma-Ray Spectrometer User’s Manual
932502G / 0618
symmetrically.
Use the up/down arrows to set the
Rise Time
from 0.8 ìs to 23.0 ìs. Once the unit has been
optimized according to Section 4.1.1, you can use any
Rise Time
without having to re-
optimize.
The value of the rise time parameter in the DSPEC 50 is roughly equivalent to twice the
integration time set on a conventional analog spectroscopy amplifier. Thus, a DSPEC 50 value
of 12 ìs corresponds to 6 ìs in a conventional amplifier. Starting with the nominal value of
12.0, you should increase values of the rise time for better resolution for expected lower count
rates, or when unusually high count rates are anticipated, reduce the rise time for higher
throughput with somewhat worse resolution.
The
Flattop
controls adjust the top of the quasi-trapezoid. The
Width
adjusts the extent of the
flattop (from 0.3 to 2.4 ìs). The
Tilt
adjustment varies the “flatness” of this section slightly.
The
Tilt
can be positive or negative. Choosing a positive value results in a flattop that slopes
downward; choosing a negative value gives an upward slope. Alternatively, the optimize
feature on the Amplifier tab can set the tilt value automatically. This automatic value is
normally the best for resolution, but it can be changed on this dialog and in the InSight mode to
accommodate particular throughput/resolution tradeoffs. The optimize feature also
automatically adjusts the pole zero setting.
The dead time per pulse is approximately
In the
Pole Zero
section, the
Start
button performs a pole zero at the specified rise time and
other shaping values. Unlike the optimize feature, it performs a pole zero for only the one rise
time. The pole zero
Stop
button aborts the pole zero, and is normally not used.
For the more advanced user, the InSight mode allows you to directly view all the parameters
and adjust them interactively while collecting live data. To access InSight mode, click the
Start
button. The InSight mode is discussed in more detail in the following section. Once data
acquisition is underway, you may wish to start the Insight mode to adjust the shaping
parameters interactively with a “live” waveform showing the actual pulse shape, or just to
verify that all is well.
4.2.1. InSight Mode
The
InSight
display (Fig. 34) shows the actual sampled waveform in the digital processing
units on a reference graticule. The Properties dialog remains active and can be used to change
settings while viewing the pulses.
As none of the traditional analog signals are available in the DSPEC 50, this mode is the only
42
