ORTEC DSPEC Pro, Руководство пользователя по оборудованию

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DSPEC Pro
®
Digital Gamma-Ray Spectrometer User’s Manual 794380D / 0914
42
Figure 25. An Example of the Tradeoff Between
Throughput and Count Rate.
To add an MDA preset, enter the preset value in the MDA or Correction field; select the
Nuclide and Energy; enter the desired values for coefficients a, b, and c; then click Add New.
To edit an existing preset, click to highlight it in the table. This will load its Nuclide, Energy,
and coefficients in the lower sections of the dialog. Change as needed, then click Update.
To remove a preset, click to highlight it in the table, then click Delete.
IMPORTANT
These MDA presets are not dynamically calculated. Each time you add an
MDA preset to this table, its CorrectionFactor value is calculated and stored in
the MCB’s memory. If you then load a different library, change the efficiency
calibration, or change the system geometry, the spectroscopy application will
not update the existing CorrectionFactors, and your MDA presets may no
longer be applicable.
When using spectrum analysis applications such as GammaVision and Scinti-
Vision, you can create an analysis options file (
.SDF
or
.SVD
file) for each
system geometry that you use; and include in it a set of MDA presets specific to
that geometry, efficiency calibration, and nuclide library. You can then recall
this tailored analysis options file as needed.
2.4. Setting the Rise Time in Digital MCBs
To achieve the best results when using a digital spectrometer, such as the DSPEC Pro, we
recommend that you set the rise time of the pulses being processed by the digital filter to the
minimum value for the resolution needed.
The pulse rise time (and also fall time) is
based on the time required for each pulse
to reach its peak value. This “peaking time”
is about twice that indicated by the conven-
tional time constants displayed on the front
panel of commercial analog amplifiers. For
example, germanium detectors are often
specified at a 6-
µ
s time constant; this set-
ting is equivalent to 12-
µ
s peaking (rise)
time in our digital spectrometers.
Up to some value of rise time, one
can expect improved resolution with increasing rise time; there will, however, be a tradeoff in
maximum throughput to memory. Figure 25 illustrates an example of this tradeoff. ORTEC