Method of photon spectral analysis

A method for measuring and analyzing an x-ray and .gamma.-ray spectrum of radionuclides in a medium by a spectrometer, comprising the steps of:

• a. preparing a plurality of unknown activity samples of the medium within sample containers;
• b. preparing a set of calibration samples consisting of known activity samples of high purity radionuclides and a clean background sample;
• c. measuring response spectra of the calibration samples with the spectrometer;
• d. measuring the radionuclide activities or activity concentrations from the spectra associated with the plurality of unknown activity samples;
• e. injecting a low-energy and a high-energy pulse into a spectrometer preamplifier circuit while accumulating the above spectra thereby providing an energy calibration signal at a periodic interval during steps c. and d.;
• f. analyzing a .gamma.-ray region of the spectra from the unknown activity samples using a non-linear peak fitting function;
• g. analyzing an x-ray region of the spectra from the unknown activity samples using a linear-least-squares spectral-fitting method by fitting the spectra of the plurality of unknown activity samples with the response spectra of the calibration samples;
• h. computing and displaying a Chi-squared number and a quality-of-fit value of the x-ray region data wherein a value less than two (2) indicates a good correlation between the unknown activity samples and the known activity samples, and a value greater than two (2) indicates a poor correlation between the unknown activity samples and the known activity samples;
• i. displaying the quality-of-fit value and a calibrated channel-by-channel residual when the quality-of-fit value is greater than two (2);
• and
• j. displaying an activity value for each nuclide.