1. adj. [Formation Evaluation]
Referring to a log of the yields of different elements in the formation, as measured by capture gamma ray spectroscopy using a pulsed neutron generator. The log is a type of pulsed neutron spectroscopy log that uses only the capture spectrum. The capture spectrum is formed by many elements, but since the main purpose of the log is to determine lithology, the principal outputs are the relative yields of silicon, calcium, iron, sulfur, titanium and gadolinium. The yields give information only on the relative concentration of these elements. To get absolute elemental concentrations, it is necessary to calibrate to cores, or, more often, use a model such as the oxide-closure model. The depth of investigation of the measurement is several inches into the formation. It can be run in open or cased hole. The absolute elemental concentrations are insensitive to fluids in the borehole and formation.