CAPINTEC, INC. CAPTUS
®
3000
Click the button or press Alt+C to discard the changes and return to Figure 13-
16.
Zero Offset
The Zero Offset sets the channel location of zero keV. It is defined as percentage full-scale
with a range dependent on the installed MCA board (Zero Offset range is -20.00 to
+20.00%).
Use the scroll bar below the % Zero Offset indicator to adjust the value. Either click the right
(+) and left (-) arrows, or drag the scroll bar.
Threshold
The Threshold is set to eliminate any extraneous electronic noise while allowing counts of
the lowest possible energy to be detected. It is equivalent to a Lower Level Discriminator
(LLD). It is defined as percentage full-scale with a range dependent on the installed MCA
board (Threshold range is 0.0 to 25.0%).
Use the scroll bar below the % Threshold indicator to adjust the value. Either click the right
(+) and left (-) arrows, or drag the scroll bar.
Note: The CAPTUS
®
3000 does not have a setting for ULD. The ULD is defined as
displayed spectrum full-scale (i.e., channel 1024, or 2MeV).
• To provide a different energy calibration ratio, use the Cesium 137 rod
source to provide two peaks of known energy. Use the Gain control to adjust
the location of the 662 keV peak to a desired channel. Then use the Zero offset
adjust controls to position the 32 keV peak into a second desired channel. For
example, to manually calibrate the MCA for 3 keV/channel, place the 662 keV
peak of Cs137 in channel 221, and the 32 keV peak in channel 11. If the gain
and Zero adjustments are unable to position the peaks correctly, adjust the
voltage. Repeat this energy calibration procedure until the peaks are positioned
as required.
• To restore calibration settings, exit the MCA mode, and re-enter from the
®
13-16 MCA November 13
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