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Generally speaking, most adjustments to expand the separation between peaks should be performed using
the HV adjust. Start increasing the gain only if the peak separation remains too small even at the maximum
HV recommended for the particular detector; increase the gain until the peak separation is slightly wider than
wanted, then reduce the HV as needed. If the peaks are in a good location but appear distorted, try lowering
the HV and increasing the gain.
Adjust the threshold lower if too much of the low energy portion of the spectrum is being cut off. Adjust the
threshold higher if noise is apparent in the lowest regions of the spectrum.
In using the hardware setting adjustments, the associated “Set” button will become enabled, indicating that
the value has been changed from those at which URSA-II is currently set. For example, if you change the HV
the “Set HV” becomes enabled. Clicking the associated “Set” button will (1) pause the current acquisition if
one is occurring, (2) set all hardware settings that have been changed, not just the one the particular button
is associated with, and (3) restart the acquisition using the new settings if one had been occurring without
clearing the previous spectrum.
Although it is completely up to the user (and subject to the characteristics of the detector being used), it has
been generally found that adjusting the hardware settings such that the 662 keV peak is at about channel 1200
will give an overall energy range coverage to about 2,300 keV.
Hardware settings are automatically saved and applied to a specific URSA-II/detector combination any time a
“Set” button is pressed. If different sets of hardware settings are desired for the same detector, create a “new”
detector based on that detector, changing the description to reflect the different purpose.
Procedure
4. Click on the “Hardware” button on the URSA-II button panel. This will open the hardware settings panel
along thebottom of the spectrum display.
5. Check the “Allow Edit” check box to enable the hardware settings.
6. Ensure that the HV is set to a reasonable value. For relatively new URSA-II users, coarse gain should be at x2
(thelowest setting) and the fine gain should be at x0.500 for an overall gain of x1; the threshold should be at 50
mV.
7. Click the “Start Acquisition” button to begin counting the source. Allow the source to count long enough to
see therelative locations of the two 137Cs peaks. NOTE: If excessive noise is clearly visible in the lowest portion
of thespectrum, increase the threshold, clear the spectrum, then restart acquisition. Repeat this process as
needed.
8. If no peaks are visible, increase the HV and go back to step 4.
9. If both 137Cs peaks are not visible:
10. 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.
11. 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.
12. 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.
13. If both 137Cs peaks are visible, but are farther apart than wanted, decrease the HV and go back to step 4.