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If you have a transistor-reset preamplifier (Plus Series), select it from the Preamplifier Type droplist.
Click Close to apply the new
MCB hardware settings.
3. GETTING STARTED — A GAMMAVISION TUTORIAL
Automatic Optimization
Select Acquire, then Start, to start the Detector counting.
Next, position a source such as
60
Co such that the detector’s input count rate (1) satisfies the count rate guidance instruc-
Fig. 39. The DSPEC-50 Amplifier Tab.
tions on the bottom-left corner of the Amplifier tab or (2) is ~5000 CPS. During data collection, the Dead time will be displayed at the top of the Status Sidebar to the right of the spectrum window (Fig. 40).
Return to Acquire/MCB Properties... and click the Amplifier tab. Go to the Optimize section of the dialog and click Start Auto.
This will tell the Detector to automatically adjust the amplifier’s shaping constants. While optimization is in progress, you will hear a periodic beep and see the message “Optimize in progress....”
This process typically takes about 5 minutes. Remember that if you change the shaping time, you must pole zero the Detector again.
Click Close to apply the new MCB hardware settings.
Fig. 40.
Dead Time.
Adjusting Amplifier Gain
Now adjust the amplifier gain to achieve the desired energy range across the Detector display.
Most commonly, a range of 0–3 MeV is used. If you have a
60
Co source, the 1332 keV peak should be set at approximately channel 1816 for conversion gain of 4096, and channel 3632 or
7264, respectively, for 8192 or 16384 (see Fig. 41). A source with only one or two lines (e.g.,
137
Cs or
60
Co) should be used for the initial test spectrum so you’ll be able to easily see the correct pattern of the peaks.
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Fig. 41. Spectrum with
60
Co.
To set the gain for the DSPEC-50 (and all other software-controlled ORTEC MCBs):
1) Start data collection by clicking on the Start toolbar button or by selecting Acquire/Start from the menu bar.
2) Select Acquire/MCB Properties... and click the Amplifier tab (Fig. 39).
3) Select the Coarse Gain setting from the droplist (if present), then move the slider to the fine gain desired. The spectrum display updates continuously, even while the Properties dialog is open.
4) Once the gain is approximately correct, click Close to close the control dialog, then use
<Alt + +> and <Alt + -> to make fine gain adjustments until the peak is in the desired channel. To make coarser gain adjustments, use <Alt + Shift + +> and <Alt + Shift + ->.
(These keyboard commands are discussed in Chapter 9.)
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783620H / 1013 3. GETTING STARTED — A GAMMAVISION TUTORIAL
GammaVision will retain all of these settings and adjustments on exit, and will reload them from the MCB on restart.
*** You are now ready to acquire spectral data, calibrate, and analyze your own sample data. ***
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