BNC 970 Portable Multi-Channel Analyzer (MCA) - Manual (Page 42)

Model 970 Instruction Manual 39
Procedure
1. Click on the Hardware button on the 970 Button Panel. This will open the Hardware Settings
Panel along the bottom of the Spectrum Display.
2. Check the Allow Edit check box to enable the Hardware Settings.
3. Ensure that the HV is set to a reasonable value. For relatively new 970 users, Coarse Gain
should be at x2 (the lowest setting) and the Fine Gain should be at x0.500 for an overall Gain
of x1; the Threshold should be at 50 mV.
4. Click the Start Acquisition button to begin counting the source. Allow the source to count long
enough to see the relative locations of the two
137
Cs peaks. NOTE: If excessive noise is
clearly visible in the lowest portion of the spectrum, increase the Threshold, clear the
spectrum, then restart the Acquisition. Repeat this process as needed.
5. If no peaks are visible, increase the HV and go back to step 4.
6. If both
137
Cs peaks are not visible:
7. If there are very few counts to the right of the visible peak but many to the left (i.e., only the
662 keV peak is visible) and it is towards the right of the Spectrum Display, increase the HV
and go back to step 4.
8. If there are many counts to the right of the visible peak (i.e., only the 32 keV peak is visible
and the 662 keV peak is out of view to the right), decrease the HV and go back to step 4.
9. If there are very few counts to the right of the visible peak but many to the left (i.e., only the
662 keV peak is visible) but the peak is in close to the desired location on the spectrum,
adjust the Threshold closer to zero and go back to step 4.
10. If both
137
Cs peaks are visible, but are farther apart than wanted, decrease the HV and go
back to step 4.
11. If both
137
Cs peaks are visible, but are closer together than wanted, increase the HV and go
back to step 4.
12. If the HV is at the highest HV recommended by the detector manufacturer (or if it is higher
than you are comfortable with, or is obviously distorting the spectrum), leave the HV where it
is, increase the overall Gain and go back to step 4.
13. When the two peaks are in their optimal locations, uncheck the Allow Edit box.
14. Click the Full Screen button on the Button Panel to close the Hardware Settings Panel and
restore the spectrum to the largest possible viewable area.
Once all the Hardware Settings are finalized, an Energy Calibration can be performed.
6.3 Perform Energy Calibration
Prerequisites
This procedure assumes that the detector is attached to the Model 970, the 970 is switched on,
SNAP-MCA software has been successfully started, a radioactive source of known isotopic
composition is on the detector, and the 970 Hardware Settings have been set appropriately.
Note
: The Energy Calibration is unique to each 970/detector combination. The specific Energy
Calibration settings are loaded when a specific detector is selected. If you intend to use the same
detector with different Energy Calibration values (e.g., to account for differing source geometries),
you can define separate detectors with different descriptions.