Abstract: Disclosed are a method and a system for well logging in which gamma radiation detected in five energy windows is converted into logs of formation thorium, uranium and potassium (Th,U,K), and of borehole barite and potassium chloride (KCl), in a process which makes use of an adaptive filter which accounts for changes in the detected gamma radiation with borehole depth, for the nature of the logging process, and for the composition of the borehole fluid. In a first, simpler embodiment, the filter is based on changes with borehole depth in the total amount of detected gamma radiation in the vicinity of the depth level of interest. In a second, more exacting embodiment, the filter is based on both the vertical variations in the Th,U,K concentrations, and the statistical variations in the measurements. In both embodiments a log of Th,U,K is produced.