GBS Elektronik MCA 166 - Manual (Page 29)

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photomultiplier voltage and temperature. This drift can be
compensated by regulating the fine gain of the amplifier on the position of a reference
peak. The reference peak has to be marked as a ROI. Usual is to use the 60 keV - Peak
of an Am241 - source. Some detectors have for this purpose a built-in Am241 source. In
enrichment measurements, it is also possible to stabilize on the 186 keV peak of U235.
To activate stabilization, turn on stabilization by toggling the stabilization on/off setting
with the spacebar.
With “Do visual Stab.” you can adjust the values for Stabilization ROI begin, Stabilization
ROI end and Stabilization Centroid (target channel where the peak should be).
When stabilization is enabled; in the acquisition screen can be found Stab: / x% / y . Here
x is the change in gain in percent of the regulation range. As the regulation range is +/-
20%, an indicated change of 100% means a change of gain by a factor 1.2.
y represents the current number of the stabilization cycles. Every 25000 counts in the
peak area the centroid of this period is recalculated, the gain adjusted and the
stabilization counter is advanced by one unit.
3.3.2.7 Setup Summary
This feature provides an overview on the setup parameters. It does not allow any editing
and is meant to give an overview on the current setup parameters.
3.3.3 Data acquisition menu
The acquire menu provides a start function to start data collection. The data gathering is
controlled from the graphic screen. It further provides an energy calibration menu.
3.3.3.1 Measurement
The first graphic screen is the ACQUIRE screen, which contains operative information like
count rate, stabilization status, presets for the measurement and which provides a quickly
updated live display of the spectrum. To start a measurement, press F4. During a
measurement only 256 channels (the width of the spectral display) are transferred
automatically every 2 sec. from the Mini MCA to the (Palmtop-) PC.
Figure 9. Acquire Screen that will appear after selecting START from the Acquire menu
If an intermediate evaluation is needed, a full spectrum (snap shot, not updated unless
requested) is presented on a second graphical screen (EVALUATION screen) showing