Capintec CAPTUS 2000, Owner'S Manual

Page: 178 / 206

CAPINTEC, INC CAPTUS
®
2000
The voltage from the single power supply is applied concurrently to both detectors in a two
detector system. The detector switch controls the signal input to the MCA board. You can
turn the high voltage on or off by clicking on the appropriate option box with your trackball
indicator or using the
Tab key. In the event of an unexpected power surge or outage, the
software will automatically turn the high voltage off to protect the MCA board. If this occurs,
simply choose the
On option box beside the Voltage indicator to restart the system. The
voltage level may be changed to a value between 800 and 1000 Volts in 5 volt increments.
To change the voltage level, select the up arrow beside the voltage indicator to increase the
voltage. Select the down arrow to decrease the voltage level.
The gain adjustments operate in a similar manner. The coarse gain has three selections, 20,
140, and 1000. To increase the coarse gain, select the up arrow from beside the coarse gain
level, to decrease the coarse gain, select the down arrow. The fine gain adjust may be
changed from a value of .0781 to 1.000 in increments of .002 or .003. To increase the fine
gain, select the right arrow key from the arrow bar located beneath the fine gain value. To
decrease the fine gain, select the left arrow key from the arrow bar. For large incremental
changes in the fine gain, place the trackball indicator on the square located in the middle of
the arrow bar, depress the clicker. With the clicker depressed, slide the box to the desired
setting. Moving the box to the right increases the fine gain, moving the box to the left
decreases the fine gain. When the gain adjustments and voltage adjustments are correct,
select the
CLOSE button. This will cause the changes to be temporarily stored in the
software memory while in the MCA mode only, and exit the screen.
To provide a different energy calibration ratio, use the Cesium 137 rod source to provide two
peaks of known energy. Use the gain controls to adjust the location of the 662 keV peak to a
certain channel. Then use the Zero offset adjust controls to position the 32 keV peak into the
other desired channel. A description of Zero offset adjustments are provided in the following
paragraphs. 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, then adjust the voltage. Repeat this
energy calibration procedure until the peaks are positioned as required.
ADC/Zero Adjustments
To access the ADC/Zero adjustments, select ADC Threshold/Zero... , from the Setup menu
list. Figure 10-6 will appear. This screen controls the adjustment of the Zero Offset,
threshold, LLD (lower limit of detection) and ULD (upper limit of detection).
10-4 MCA July 00