How does the V11 firmware autocalibration work?
Auto calibration is performed by a very small activity DOT exempt radioactive source positioned near the NaI scintillator. This is usually Co60 although Cs137, K40 and Th232 can be used. A region of interest (ROI) is established to track changes in temperature that would result in up to +/- 10% shifts in energy calibration. The ROI is established such that the isotopic peak of the calibration source is in the center of this ROI. As an example Co60 uses 32 channels with the 1332 keV peak centered in the ROI. At the beginning of calibration a buffer receives counts in the ROI and when reaching 1000 counts makes a correction to the fine gain. This places the Co60 peak in the appropriate channel for calibration. As long as the SAM is operated in any one of the 3-search modes calibration will continue to take place in the background (as described above).
