Abstract: A means and method for distinguishing full energy absorption peaks from background energy in a gamma ray prospecting system. Photopeaks in the received energy spectrum are determined, and boundaries to the peaks are located. The energy within the boundaries assuming a predetermined curve between the boundaries is integrated. The filtered energy within the actual photopeak curve is also integrated, and the two integrated signals are subtracted to provide a signal representative of the net photopeak area or amplitude. This peak area (or amplitude) is directly proportional to intensity of gamma radiation due to uranium, thorium and potassium in the ground. This signal is displayed and continuously updated on a cathode ray tube as a function of time.