Patent ID: 7482578

Claim:
A gamma ray logging system comprising: (a) a gamma ray detector for detecting gamma radiation at a plurality of actual energy levels and for generating detector output signals each representing a detected count of gamma radiation, wherein each of the detector output signals has a parameter value which is dependent upon the actual energy level of its associated detected count of gamma radiation; (b) an analyzer for sorting the detector output signals into a plurality of channels according to their parameter values in order to generate a detected gamma radiation spectrum, wherein the detected gamma radiation spectrum provides an indication of a frequency of the parameter values as a function of the parameter values; and (c) a processor which is configured to perform a calibration of the detected gamma radiation spectrum, wherein the calibration performed by the processor comprises: (i) selecting at least two data points from the detected gamma radiation spectrum, wherein each of the selected data points is comprised of a known actual energy level and its associated parameter value; (ii) determining a mathematical relationship for the selected data points; and (iii) adjusting the parameter values in the detected gamma radiation spectrum in accordance with the mathematical relationship, thereby generating a calibrated gamma radiation spectrum comprising adjusted parameter values.