FRAM’s Performance as a Function of the Energy Calibration Gain

The Fixed-Energy Response-Function Analysis with Multiple Efficiency (FRAM) code was developed at Los Alamos National Laboratory to measure by gamma-ray spectrometry the isotopic composition of plutonium, uranium, and other actinides. It is capable of analyzing gamma ray peaks obtained with germanium detectors in the energy range from 30 keV to greater than 1 MeV, including the x-ray region. The energy calibration gain of the detector system can be of almost any value. However, we normally set the energy calibration gain for a detector system so that the full-width at half-maximum (FWHM) of the gamma-ray peaks of interest would be in the range of 6-10 channels. How would a different energy calibration gain affect the measurement results? Common sense would tell us that if the peaks are very narrow so that FRAM would have a hard time extracting the peak areas accurately, then the results from those spectra may not be very good or they may have large errors. However, if the peaks are only somewhat narrower than those specified above, then how badly are the results affected? This study is to investigate how the energy calibration of a system affects the analysis.