BNC 970 Portable Multi-Channel Analyzer (MCA) - Manual (Page 50)

Model 970 Instruction Manual 47
Discussion
Efficiency Calibrations are attached to specific ROI Sets. Known activities of known isotopes are
assigned to specific energies in the spectrum. SNAP-MCA uses a linear interpolation between
Efficiency Calibration points to allow Quantification of isotopes for which no specific calibration
source is available. The same Efficiency Calibration is used when performing ROI, peak, or
library-based Quantification.
Note that the ROI Set can contain isotopes that are not included in the Efficiency Calibration
source. These must be designated as “unknowns,” however, so that SNAP-MCA knows to
calculate efficiencies for these ROIs from interpolated data.
The perfect Efficiency Calibration source matches exactly the type of samples you will be
quantifying in isotopic composition, activity, and physical makeup. A good Efficiency Calibration
source contains isotopes with energies similar to or at least bracketing those you are interested
in.
Isotopes and specific peaks must be assigned to all ROIs including “unknowns.” The selections
for these are limited to those enabled in the library currently being used.
Procedure
1. Acquire a spectrum of your Efficiency Calibration source. A Background Spectrum should
also be subtracted from the display if that is how your samples will be analyzed.
2. Click on Efficiency on the SNAP-MCA Button Panel. This will open the Efficiency Calibration
Panel along the bottom of the Spectrum Display.
3. To calibrate, click on the Allow Edit box.
4. Select a specific ROI using the ROI # arrows.