1. A method comprising: obtaining a gamma count rate decay curve one each for a plurality of gamma detectors of a nuclear logging tool, the gamma count rate decay curves recorded at a particular borehole depth; applying at least a portion of each gamma count rate decay curve to input nodes of a neural network; predicting by the neural network a value indicative of gas saturation of a formation surrounding the borehole at the particular borehole depth, the predicting by the neural network in the absence of a formation porosity value supplied to the neural network; repeating the obtaining, applying and predicting for a plurality of borehole depths; producing a plot of the value indicative of gas saturation of the formation as a function of borehole depth.