1. A system comprising: a downhole tool comprising: a source of neutrons; a first gamma detector at a first elevation on the downhole tool, the first gamma detector positioned to favorably receive gammas from a borehole side of the downhole tool; a second gamma detector at the first elevation, the second gamma detector positioned to favorably receive gammas from the formation; a third gamma detector at a second elevation more distant from source of neutrons than the first elevation; and a fourth gamma detector at a third elevation more distant from the source of neutrons than the second elevation; each gamma detector counts gamma arrivals to create a gamma count rate decay curve for the respective gamma detector, each gamma count rate decay curve comprising a plurality of time bins with respective count values; a computer system comprising a processor and a memory, the computer system communicatively coupled to recorded gamma count rate decay curves; the memory stores a program that, when executed by the processor, causes the processor to: apply the count value of each time bin one each to input nodes of a neural network of the program; and predict, by the neural network of the program, a geophysical parameter of the formation surrounding the borehole for each of a plurality of depths within a borehole.