1. A method of determining at least one parameter representative of a physical characteristic of geological formations having a borehole passing therethrough, by means of a logging tool or sonde suitable for being lowered down the borehole at the end of a cable, in which the formations are irradiated by a gamma ray source, and photons that have interacted with the formations are detected and counted in a plurality of energy windows by three detectors that are longitudinally offset relative to the source, comprising a very near detector, a near detector, and a far detector, the method being characterized by the following steps: a) creating, for each energy window, a model that is characteristic of a response of each detector; b) combining measurements coming from the three detectors to constitute a "low resolution" real measurement; c) determining a "low resolution" value of the parameter such that, when applied to the model, it gives rise to a theoretical measurement that is equal to or substantially equal to the "low resolution" real measurement; d) combining the measurements from the two detectors closest to the source to constitute a "high resolution" real measurement; and e) determining a "high resolution" value of the parameter on the basis of the "high resolution" real measurement and the "low resolution" value of the parameter, such that when the determined "high resolution" value is applied to the model, it gives rise to a theoretical value that is equal or substantially equal to the "high resolution" real measurement.